Science for all Seasons: Mitochondrial Diseases and Function

Science for all Seasons: Mitochondrial Diseases and Function Broad Institute 30.3K subscribers Subscribe 58 Share Download Clip Save 2,517 views Oct 26, 2021 Science for All Seasons: Mitochondrial Diseases and Function We all heard it in our grade-school science classes: "The mitochondrion is the powerhouse of the cell." And yes, this little organelle — likely the remnant of a bacterium absorbed by early cells millions of years ago — has the crucial job of providing the energy the cell needs. Molecular biologist Vamsi Mootha, who for years has studied mitochondrial biology, will describe how his research has led him to a new understanding of your mitochondrias' fundamental purpose, and discuss what that means for human health. Host: Tom Ulrich Speakers: Vamsi Mootha Vamsi Mootha is an institute member of the Broad Institute and founding co-director of the institute’s Metabolism Program. Mootha’s research is primarily focused on the mitochondrion, the “powerhouse of the cell,” and its role in human disease. Mootha’s group has worked with platforms at the Broad Institute to produce a near-comprehensive, mitochondrial protein inventory called MitoCarta. MitoCarta now serves as a molecular blueprint for mitochondria and has been widely used by the research community. Mootha and colleagues have used this inventory to discover the mitochondrial calcium uniporter, a major channel of communication between mitochondria and rest of the cell, as well as more than twenty disease genes that underlie severe, inborn errors of metabolism. He utilizes a multidisciplinary approach that combines computation, biochemistry, and clinical genetics. Mootha is an investigator of the Howard Hughes Medical Institute. He is also a professor of systems biology and medicine at Harvard Medical School and a professor in the Department of Molecular Biology at Massachusetts General Hospital. He has received numerous honors, including a MacArthur Foundation Fellowship, the Judson Daland Prize of the American Philosophical Society, and the 2014 Keilin Medal of the Biochemical Society. He is also an elected member of the Association of American Physicians and the National Academy of Sciences. Mootha received his undergraduate degree in mathematical and computational science at Stanford University, where he graduated Phi Beta Kappa with highest honors. He received his M.D. in 1998 from Harvard Medical School in the Harvard-MIT Division of Health Sciences and Technology, where his thesis work was focused on mitochondrial bioenergetics. He subsequently completed his internship and residency in internal medicine at Brigham and Women’s Hospital in 2001, after which he completed postdoctoral fellowship training at the Whitehead Institute/MIT Center for Genome Research. For more information visit: https://www.broadinstitute.org Copyright Broad Institute, 2021. All rights reserved. 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Show transcript Transcript Introduction 0:00 hello and welcome to this evening's science for all seasons talk the science for all seasons talk give you a chance 0:05 to explore hot topics in genomics and biology with experts from the broad institute my name is tom ulrich and i'm 0:12 the associate director for science communications at the broad and it's my pleasure to welcome all of you here this evening and to introduce our speaker bom 0:19 cimutha vomsi is an institute member here at the broad and is the co-director of our metabolism program 0:25 he also holds professorships in systems biology and medicine at harvard medical school and in molecular biology at 0:32 massachusetts general hospital vamps is going to talk about our mitochondria which we all know as the 0:37 powerhouse of the cell but in his studies of mitochondrial diseases fomsey has come to the idea 0:43 that our mitochondria have another fundamental function that also impacts our cellular and overall health which 0:49 he'll discuss tonight if you have any questions for vomsky please ask them using youtube's chat 0:55 feature and we'll do our best to discuss them during the q a portion of the evening and if you're tweeting please use the 1:01 hashtag broadsfas bomcy the microphone is yours 1:09 good evening thank you so much tom for that kind introduction and it's a real pleasure for me to be here today and 1:15 speak at signs for all seasons um over the next hours so i'm hoping to 1:20 take us all on a small voyage into our mitochondria and this is an organelle that first captured my imagination when 1:27 i was a medical student more than 25 years ago or so and the electron micrographs that you see in the 1:32 background these are electron micrographs of mitochondria from different organs in 1:38 our body's tissues and it's these beautiful images that just initially 1:43 grabbed my fancy and as i learned about their evolutionary history their roles in disease i was hooked and this is all 1:50 that i've been working on since then and i've had my own laboratory as tom said at mgh and at the broad for a little bit 1:57 over 15 years or so this is the outline of my talk today i'm Mitochondria 2:02 going to provide a brief primer on mitochondria and then i want to introduce you to what happens to mitochondria in a variety of human 2:09 diseases and then i want to share with you our approach to mitochondria and i want to go deep on one story towards the end 2:15 that i think is focused on disease but is providing new insights into the role of mitochondria 2:25 so this is what mitochondria actually look like in living cells i think most of us are accustomed to those static 2:31 electron micrographs that we've all seen in our high school biochemistry textbooks but if you actually image 2:37 mitochondria in living cells using fluorescence microscopy this is what they look like 2:42 so every single one of these red thread-like structures 2:47 is one mitochondrion and as you can see within each of our cells they're swimming around they're dividing and 2:54 they're fusing they almost look like tiny microscopic life forms and that is 2:59 of course because about two billion years ago or so they were free swimming 3:04 bacteria so our mitochondria that looked like this today about 2 billion years 3:09 ago were probably free sowing bacteria not that different than e coli 3:16 so how did this happen so there's something called the endosymbiotic event i'm sure many of you have heard about 3:21 this in your high school or college biology classes but what we think happened was that approximately 2 3:27 billion years ago or so there's a close relationship between one cell an archaeon and then another bacterium not 3:34 that different than e coli this relationship became very close and at some point it became permanent and this 3:41 cell is actually the common ancestor to humans and plants and slime mold and 3:47 baker's yeast and so clearly one of the most important events in the history of 3:52 life now this is a cartoon of a human cell 4:00 and inside of the nucleus you're going to see chromosomes and so most of our body's 4:06 dna is in the nucleus and this consists of about 3 billion bases and we receive these chromosomes 4:12 in this dna both from mom and from dad but our mitochondria are really living 4:18 fossils if you look inside of them that you still have a tiny circular genome 4:24 that looks a little bit like a bacterial genome it's much smaller than it was 2 billion years ago but it's still a 4:29 reminder of the bacterial ancestry of this organelle and this particular genome is passed 4:36 from mom to offspring from mom to offspring 4:43 now as we all know the mitochondrion is called the powerhouse of the cell so why is that well 4:50 the organelle houses a number of different machines it's super important for 4:57 metabolism but inside of these inner membranes of the mitochondrion 5:02 are the machinery called the respiratory chain this membrane this inner membrane 5:10 if if you splay it out from one individual that's basically the same surface area as an entire football field 5:16 it's the most proteinaceous membrane in the human cell and it's 5:21 chock full of these little uh protein complexes uh and what these protein complexes are 5:27 going to do it's called the respiratory chain and they're going to enable what's called oxidative phosphorylation or 5:33 oxboss so this is the process by which the food that we eat gets burned with 5:38 oxygen and then get converted to atp and just some food for thought each one 5:44 of us in a given day is breathing about 500 liters of oxygen 5:50 and we're turning over about 50 kilograms of atp per day so that's how active the inner 5:56 membrane of our mitochondria are every day now we have two pathways for making 6:02 atp we can either use glycolysis on the cytosol and that's going to yield about 2 atp per glucose molecule and that 6:08 doesn't need mitochondria or oxygen however if we choose to use our mitochondria and if we use oxygen we'll 6:16 now all of a sudden be able to get about 36 atp molecules where glucose consumed 6:22 it's a huge power boost and this is why the mitochondrion is called the powerhouse of the cell for good reason 6:29 now i want to introduce a water wheel analogy because i think this might be useful later on as we talk about what 6:35 happens in mitochondrial disease so what's happening inside of that inner membrane and i think it's 6:42 very analogous to what's happening with the water wheel and if the water wheel is actually equipped with a turbine 6:48 so as water flows from high elevation to a low elevation the water wheel turns and that 6:54 mechanical energy is going to get converted into an electrical energy by the turbine 7:00 now inside of the mitochondrion the food and the oxygen they want to react with each other and if they do there's a lot 7:06 of energy to be harnessed however there needs to be a path by which they can react the mitochondrion provides a 7:13 vehicle for those two to react with each other and there are tiny microscopic turbines the machines that i just showed 7:20 that now spin that will now effectively convert the adp to the 80 adp and this 7:26 is the cellular energy currency that powers our motors and allows me to think 7:32 right now so hopefully this waterwheel analogy makes sense and we'll get back to it a 7:37 little bit later so that's a brief primer on mitochondria 7:43 and now i want to share with you what happens in in health and in disease 7:49 it is now well appreciated that virtually all of us as we age we experience a mild 7:58 decline in mitochondrial function this is one of the strongest biomarkers of the aging process 8:04 now what's unclear is whether this is actually driving the aging process or if we have sick tissue and hence sick 8:10 mitochondria at the opposite end of the extreme are an extremely large collection of 8:16 individually rare orphan diseases these are typically children but sometimes 8:22 adults that are born with birth defects in some part of their mitochondria 8:27 this leads to a single organ or multi-systemic disease in these diseases there's little doubt that the 8:33 mitochondrial defect is causal for the pathology and then there's some common diseases 8:39 between these two where again we observe mitochondrial dysfunction because 8:44 or correlation it's unclear right now so what's happening with aging in 8:50 trounce showed a few decades ago or so that if you biopsy skeletal muscle from individuals of varying ages we can 8:57 purify their mitochondria put them in a test tube and measure rates of oxygen consumption in atp production and what 9:04 you can see is that this declines as a function of age this extends in vivo as well so it's 9:12 possible to take humans of varying ages you exercise them and measure how much 9:17 oxygen they're consuming while they're exercising as fast as they can after the age of 30 9:23 this particular metric the vo2 max declines about 10 percent per decade 9:29 in all of us and so that's the bad news but the good news is we know that 9:34 regular exercise can send this trend upwards 9:42 i want to introduce that opposite end of the extreme now these rare orphan mitochondrial diseases 9:48 because this is uh what we have been focusing on historically both because they represent our great unmet medical 9:54 need and also because studying them may provide insights into some more common conditions these are tough diseases diagnosing them 10:01 is really hard because virtually any organ system can be impacted some of these patients have one organ system 10:07 impacted others have multiple organ systems impacted and when a diagnosis is finally arrived 10:13 at the patient has gone to more than seven different specialists before the diagnosis is achieved we 10:20 don't have any simple blood tests right now that tell us whether the mitochondrial disease is getting better or worse there's more than 300 genetic 10:27 forms to date without a single fda approved medicine 10:33 so that's sort of the spectrum of mitochondrial dysfunction from the rare into the common and what's super 10:38 fascinating is that this field is now gaining uh widespread interest 10:43 a few years ago in the new yorker there's actually an article entitled silicon valley's quest to live forever 10:49 there's a lot of interest in aging and in this particular article the author takes us through a 10:56 party at a hollywood party where goldie han is sitting on a sofa 11:01 and she asks a question i have a question about the mitochondria i've been told about a molecule called 11:07 glutathione that helps the health of a cell and like i said i've been studying 11:13 mitochondria for more than 25 years uh never in my wildest imagination what i've thought that there'd be an article 11:19 in the new yorker that would have goldie han asking a question a very good question also about mitochondria Lab Approach to Mitochondria 11:30 so now i've provided a primer on mitochondria and i've introduced it what happens to mitochondria in helping in 11:35 disease and now what i want to do is i want to share with you our lab's approach to this organelle 11:43 so we're really trying to take a systematic approach to mitochondria and i'd like to use a particular analogy to 11:49 describe what we're trying to do i grew up in southeast texas where one of my brothers was a real car enthusiast he 11:55 would go and buy old cars and then we would work on fixing them up and the first thing that we would do when he 12:01 would buy a new old car is we'd go to a store called autozone and we'd buy what's 12:06 called a chilton manual that specialized for that particular make and model of the car and as you open up the pages of this 12:13 booklet the first few pages have all the parts of the car and their parts numbers the next few pages have all of the 12:20 wiring diagrams of the electrical system the air conditioner the transmission and the carburetor then the next few 12:26 chapters are about how to how to debug the car when it's not starting properly and how to fix it and to a large extent 12:33 this is what we're trying to do not for a 1965 mustang but for the mitochondrion 12:42 and so the first step in our lab's efforts was really to try to figure out what all the parts are 12:48 back in 1981 fred sanger and colleagues sequenced the mitochondrial genome from 12:54 humans and they reported that it encodes 13 proteins total 12:59 i'm sure you can appreciate that when you look at the electron micrographs of mitochondria they're so glorious they 13:04 must consist of more than just 13 proteins and by necessity all of the other proteins must be coming from the 13:10 nuclear genome this was sequenced in the year 2001 in draft form and i trained uh with eric 13:17 lander in genomics my goal subsequently has been to try to figure out what all of the components are that come from the 13:23 nuclear genome that end up in the mitochondrion and so over the course of our labs 13:29 a little bit more than 15 year history we've worked very closely with the broad institute's proteomics platform to build 13:35 a parts list for this organelle and this is really work that was initially spearheaded by 13:41 david pagliarini one of the first postdocs in my laboratory as well as sarah calvo a 13:46 computational biologist in my laboratory and using a mix of mass spectrometry imaging 13:52 and computation we've been able to put together a list of 1100 proteins 13:57 that comprises this organelle and we've continually updated this list and we've made this freely available to the 14:03 research community now a large number of these proteins have 14:08 never been studied before and we would love to know what they do and so what what's beautiful about the new 14:14 tools of genomics is that we can we can study all 1100 of those proteins get snapshots of all 1100 of those proteins 14:21 at once using new tools like rna-seq microarrays and proteomics and so we 14:26 love doing those types of genomics experiments and then we developed computer algorithms which with with 14:32 which to mine all of that data as well as what's available in the public domain and through this experimental and 14:38 computational approach we're working at the function of a lot of the circuits of the mitochondrion 14:46 we're also very interested in understanding which of those mitochondria circuits are altered in disease and to understand this what 14:53 we've been doing is we've been collecting blood from patients in close collaboration with our clinical colleagues throughout the world we 14:59 collect blood from patients and their family members that tend to be unaffected and then we use 15:04 next-generation dna sequencing to try to understand what which of those protein components 15:10 are defective and then we also use something called metabolomics to try to understand all of the biochemistry of 15:15 these disorders so in this way we are identifying the genes and the biochemical pathways that are altered in 15:23 some of these rare mitochondrial diseases and this is our long-term goal 15:29 precision mitochondrial medicine our hope is that from a single tube of blood we should be able to establish a genetic 15:35 diagnosis and from that same tube of blood by looking at the chemicals we ought to be able to stage the severity 15:41 of the disease now if we only have a therapy then what we can do is we can monitor these 15:47 chemicals to see if the patient is getting better or worse and so what's really missing right now 15:53 is a novel therapy and that's what i want to focus on in tonight's talk and the time that 15:58 remains 16:06 so back in 2014 um we completed what i think is one of the most experiment 16:12 one of the most important experiments in my laboratory with generous funding from the marriott family foundation 16:17 we used a new genomics method to screen for ways to cope with a broken 16:23 mitochondria and this was a screen that was performed by a talented graduate student isha jane 16:29 at that time now this screen gave rise to a very counter-intuitive idea it gave rise to 16:37 the idea that hypoxia so low oxygen might actually serve as a therapy 16:44 and this is a bit counter-intuitive because we usually think of oxygen as being life-giving and any of us that 16:49 have ever gone to the hospital one of the first things that will happen is that we will be given oxygen and so this screen actually told us the 16:56 exact opposite it was telling us let's dial down the oxygen when there's mitochondrial disease 17:04 i want to share with you some of the work that we did with this idea and first i need to just introduce a disease and a disease model in which we've been 17:11 exploring this idea the disease in which we've been exploring this idea is called lee syndrome this is a disease that was 17:17 first described in 1951 it's the most common pediatric mitochondrial disease 17:23 and it's associated with a subacute degeneration of the grace of the gray matter of the brain 17:29 there's more than 80 different genes either on the nuclear dna or the mitochondrial dna that have been 17:35 identified and we don't have a single fda approved medicine for lee syndrome 17:40 a bit more than 10 years ago or so richard palmeter's group in washington 17:46 described a mouse model of lee syndrome they knocked out one of those nuclear genes that's important for the 17:53 functioning of the mitochondrion and these mice are born fine but then right around at two months of age they become 17:59 very sick they stop moving properly they'll lose their body weight and then they'll develop these lesions in their brains by 18:06 mri that are resembling the lesions that we see in the humans 18:12 so we received these uh mice and we wanted to see whether this idea 18:17 of dialing down the oxygen might work and so i'm going to show you a video of 18:25 five mice all five of these mice have this neurological disease except two of them 18:32 have been breathing 11 oxygen now all of us at sea level are breathing 21 oxygen 18:38 but what we're able to do is we're able to dilute the air with nitrogen that two of these mites are breathing so now 18:45 they're breathing only 11 oxygen and they're all five of them are placed on the cage at the same time for the 18:51 purposes of the video but see if you can guess which two mice have been breathing thin 18:57 air 19:20 so i hope that was obvious the results were really really striking we were overwhelmed by just how powerful the 19:26 effects of hypoxia were in this mouse model and i want to point out that we did these mouse studies in collaboration 19:33 with warren zappol's laboratory at mass general hospital that had experience delivering hypoxia to mouse models 19:40 now this mouse model will die at two months of age from the neurological disease that i just told you about 19:46 however if they're breathing thin air this is what the survival curve looked like 19:53 at the time of publication you know there were zero mice that had 19:58 died from this disease post-publication we carried out the survival curves and the mice are not fully cured of their 20:05 disease they'll still die from their cardiovascular disease at approximately one year of age so a dramatic extension 20:11 of life spent from about two months to almost a year just by dialing down the oxygen levels 20:19 and as you can see from the video it wasn't just life spent but the health span was all to dramatically improve they're putting on body weight they're 20:25 moving around they just look a lot more robust a really natural question is if low 20:32 oxygen is good what happens with high oxygen we decided to 20:38 provide the mites with 55 oxygen this is an o2 level that's often experienced by 20:43 patients in the hospital and these mice will die within about three to five days of exposure to 55 20:51 oxygen so these mice that have mitochondrial disease are very sensitive to high oxygen 20:58 within one week of us publishing this paper i received telephone calls and emails from 21:04 clinicians around the country in the world that she shared with me vignettes of their outpatients that had 21:10 mitochondrial disease that were actually placed in hyperbaric oxygen that's a great way of flooding the system of 21:17 oxygen and they shared with me anecdotes of even outpatients that became comatose 21:22 within 24 hours of hyperbaric oxygen and never woke up again and so these are 21:28 anecdotes that suggested that hyperbaric oxygen may be detrimental but when combined with our 21:34 mouth studies strongly suggest that high oxygen can be toxic in the setting of 21:39 mitochondrial disease now we've been working with famito echinosis laboratory at mass general 21:46 hospital to understand exactly what's happening his laboratory is able to place 21:51 probes into the brains of these mice we can actually measure what the oxygen levels are 21:57 this is what the oxygen level should be in the brain of a healthy wild-type mouse 22:03 as you can see in the mouse model of mitochondrial disease there's dramatically elevated 22:08 [Music] levels of oxygen in the brain now we're interpreting this as high 22:13 unused oxygen in the brain remember all the oxygen that we're breathing a very large fraction of the o2 that we're 22:20 breathing is actually getting consumed in the mitochondrion and so our inference here is that when 22:25 the mitochondrion is broken the oxygen is still being delivered but it's not being extracted and as a consequence is 22:31 accumulating and by simply dialing down the oxygen that's we're breathing in these mice we can normalize this brain 22:38 hyperoxia and so 22:43 the canonical model of mitochondrial disease is based on the canonical idea that it's the powerhouse of the cell 22:49 when the mitochondria is broken there's less energy there's less atp and this is definitely a component of the pathology 22:56 i'm not arguing that however i think what's what's often overlooked and i think what 23:02 our work is telling us is very important is that when the mitochondria is broken there's also high unused oxygen 23:10 and that this high unused oxygen can be toxic and it can actually cause 23:15 pathology and this is why when we dial down the amount of o2 that's being breached by these mice we can actually 23:20 alleviate their disease i want to just go back briefly to this water wheel analogy 23:26 so again the the water that's flowing is turning this water wheel it's turning a turbine and 23:33 it's producing electrical energy if the water wheel is blocked for some reason sure there's not going to be 23:39 enough electricity however we're also going to see some flooding upstream and even a drought 23:45 potentially downstream and i think what our work is telling us is that this flood of oxygen 23:53 can damage uh parts of our cell and this is where a lot of our research is focused right now we're trying to 23:58 understand what parts of our body cells molecules and pathways can get oxidized by 24:06 too much oxygen and in the same way that a copper penny can turn green or 24:14 an iron nail can rust that's all because of oxidation we believe that 24:19 oxygen itself can damage certain parts by molecules of our cells and 24:25 this is also contributing to the pathology Limitations 24:30 so i've shown you that chronic continuous 11 hypoxia is promising in in 24:36 in mouse models everything that i've shown you so far requires that we place the mouse 24 7 in a box breathing 11 24:43 oxygen now translating that into a therapy might be challenging and so an important 24:49 question is whether something more practical may work we've tried intermittent hypoxia in 24:55 these mice models and that does not work so we can't do 12 hours on 12 hours off 25:00 how about something like instead of 11 which is pikes peak or mont blanc how about if we 25:06 went to denver instead so 17 unfortunately that's also not effective 25:13 there's also genetic ways and chemical ways that we can trick the cells into thinking that they're hypoxic and in the 25:20 context of a mouse model that i just showed you tricking the cell into thinking that it's hypoxic is not good enough so the 25:27 only thing that's working right now is chronic continuous 11 oxygen 25:32 i also want to emphasize that it has dramatic effects on the brain disease but it's not fixing the cardiovascular 25:37 disease so these are some of the limitations of the approach that i'm sharing with you 25:43 and i want to emphasize please do not try this at home this is pre-clinical research hypoxia can be very very 25:49 dangerous and so we have a lot of pre-clinical research that we need to do before we can try to move these ideas 25:55 into patients now a really important question is 26:03 whether we can reverse any of this disease most of these patients will 26:09 actually present um with some of these neurological deficits already present on their mris so really 26:17 important question is whether any of that is reversible an advantage of this mouse model is it has a it has a very stereotyped 26:23 trajectory and right around two months of age these mice will now fulfill our hospital's 26:29 euthanasia criteria so we can ask what if we start hypoxia at this point and 26:34 when we do we see that the mice are now regaining their body weight and it's it's quite dramatic in which you call 26:41 this affectionately uh our lab's lazarus effect on this end of s4 mouse model 26:47 if we do brain mris on this mouse model what you see is that these lesions that 26:52 we uh see by mri we can make them disappear after a few weeks of hypoxia therapy and so we find this to be very 26:59 exciting and we believe that this is also supported by human anecdotes as well and uh missy 27:05 walker and uh maria miranda in my group have recently written a review article that uh has 27:13 shared some uh uh cases of reversibility in humans we believe that the 27:18 observations we're making in mice also extend to humans as well 27:23 so we believe that we have made a really important and what i think is a super exciting discovery and that is that 27:30 hypoxia is a suppressor of mitochondrial dysfunction 27:38 what i mean by that is hypoxia allow cells and organisms to cope with broken mitochondria 27:45 we're really excited about this discovery and we have a lot of active work ongoing right now aimed at trying to understand 27:52 the full mechanism by which uh this is working both in cell culture as well as 27:57 uh in vivo we really want to know whether this will generalize to other diseases as i said earlier there's about 28:04 300 monogenic mitochondrial diseases and everything i've shown you so far is focused on one of those and then finally 28:12 i've shared with you some of the limitations of being able to translate this into the clinic so we're working on trying to identify safe practical 28:19 effective means of moving the science forward 28:24 what's really exciting is that in newer work that we've done in cell culture at least there appear to 28:30 be hundreds of mitochondrial mutants uh that show a fitness defect at 21 28:36 but can then be suppressed simply by lowering the oxygen tension so at least in cell culture uh it looks like this is 28:42 going to generalize maybe not to every one of those mitochondrial diseases but to a lot of them 28:47 there's one disease that we're really excited about and that's friedrichs ataxia this is actually the most common 28:53 monogenic mitochondrial disease and it's due to a recessive loss of a 28:59 gene called frataxin which was historically considered to be an essential gene nobody had ever knocked 29:05 it out completely but in human cells in yeast models as well as in worm 29:12 models we can completely knock out this gene and make 29:18 the cell yeast or worm survive simply by dialing down the oxygen and i 29:23 want to just highlight this one particular slide from c elegans worm models this is what worms ordinarily 29:29 look like each of those squiggly lines is one worm uh and if we knock out this gene completely in a worm 29:36 you don't see any worms because it's lethal so this is consistent with the idea that this is an essential gene now 29:42 if we just dial down the oxygen these worms not only survive but they will now complete their entire reproductive life 29:49 cycle as well and so um it's a dramatic effect uh in 29:54 worms and in yeast and human cells and now we're trying to move this uh up the preclinical uh chain if you will uh with 30:01 the goal of trying to impact uh this disease 30:09 i wanted to take a step back and just think about what the broader implications of our work is 30:15 when we think about human disease we often think about the cross product of genes 30:21 and environment and i think what our work is telling us 30:26 is that when it comes to mitochondrial disease and mitochondrial genetics the key variable is environmental oxygen 30:35 remember our genes co-evolve with the environment and by studying patients 30:41 we've uncovered what i think is a really important g by e interaction genetics by 30:47 environment interaction and this particular interaction may actually um 30:53 uh be related to an even more ancient event now 30:59 i told you earlier about the endosymbiotic event that took place about 2 billion years ago or so 31:05 and a really important question is what was the selective advantage for this archaeon and for this mitochondrion to 31:12 get together and form a permanent union one of and there's a number of theories 31:19 as to what the selective advantage was and you know one of the ones that's commonly cited amongst high school 31:24 students and college students is the atp power advantage the mitochondrion that was engulfed 31:29 provided a lot of power to the host and i would emphasize that that probably is is true but the question is could there 31:35 be other advantages as well now if we go back uh a few 100 million 31:41 years prior to this endosymbiotic event you know we have to remember that life on our planet started out in a 31:47 completely anaerobic state and then around 2.4 billion years ago or so was what's called the great oxygenation 31:54 event and so we went from no oxygen to some oxygen and again oxygen is life-giving but it can be corrosive as 32:01 well and this was it probably caused a lot of problems for anaerobic organisms 32:06 and so a possibility is that another advantage of endosymbiosis was the 32:12 ability of this mitochondrion not only to produce a lot of atp but also to 32:18 consume oxygen and detoxify it Hypoxia 32:26 i think our work has important implications for uh rare mitochondrial diseases 32:32 we will instinctively give supplemental oxygen to patients when they come to the hospital and in the vast majority of 32:39 cases this is totally fine however if somebody has rare mitochondrial disease 32:46 and they don't have any signs of hypoxia i think our work is suggesting that we may need to think twice before giving 32:52 supplemental oxygen when it's not even indicated and so our community is now beginning to 32:58 take notice about this possibility i think our work has potential 33:05 therapeutic implications as well we're doing a lot of pre-clinical work in mouse models and worm models that i 33:11 told you about earlier but we've also just recently completed a safety study of hypoxia in the hospital 33:18 so my colleagues lorenzo bera and stuart harris have created hypoxia in a tent at mass 33:24 general hospital uh and we brought in a couple of uh healthy volunteers that spend about a week or so uh as the o2 33:31 levels are dropped and so we're gaining experience delivering hypoxia in a hospitalized setting just trying to 33:36 understand what the human physiology and what metabolic responses are and so these are still in healthy humans 33:42 but hopefully the information from these types of studies or pre-clinical studies will then allow us 33:49 to develop therapies for some of these patients 33:54 now everything that i've told you about today is focused on rare mitochondrial diseases but might there be broader 34:01 benefits of hypoxia remember i told you that virtually every single common age-associated disease is associated 34:08 with a subtle decline in mitochondrial activity and so does anything that we've learned have 34:14 relevance to more common diseases and so now i'm definitely speculating uh and 34:20 what i wanted is i wanted to share with you this one paper that was actually published by the indian army now the indian army usually 34:28 is not in the business of publishing health outcomes research studies but they made a really interesting 34:33 observation that they felt compelled to share with the broader community india 34:39 in the 1960s had a lot of border disputes with china and at that time what india ended up doing 34:46 was to deploy 150 000 troops at the indochina border 34:51 now it's a vast border and out of those 150 000 individuals 20 000 of them were 34:57 at high elevation comparable to the levels of oxygen that we're talking about today 35:02 the other 130 000 were either at the plains or at sea level 35:09 and they were stationed there for about seven years and over the next seven years the 35:14 clinicians in the army were able to see uh you know how these soldiers were doing what's remarkable is that over the 35:21 seven year period the incidence of diabetes hypertension and ischemic heart disease were all much lower in the 35:28 individuals living at high altitude now of course lots of things are different between uh sea level and high 35:35 elevation the temperature is different uh uv radiation is different the clothing is different the food is 35:40 different the activity level is different but one of the things that is different is oxygen levels as well uh 35:46 and so it's tempting to speculate that chronic mild hypoxia 35:52 might actually have some health benefits again this is pure speculation but with the types of hypotheses that 35:58 are raised by our work so um in closing i've shared with you a 36:03 primer on mitochondria i've told you about mitochondria and human disease and 36:08 i've shared with you our approach to this organelle that's led to some new insights namely the idea that low oxygen 36:15 can actually buffer defects in the mitochondrion and that this has i think potential implications for understanding 36:20 the basic biology of the organelle but also for understanding uh how to alleviate mitochondrial disease Collaborators 36:28 now this is probably the most important slide i really wanted to thank the past and present members of my laboratory as 36:34 well as our wonderful collaborators that have helped us with all of the work that i've shared with you today this has been 36:39 a lot of teamwork over the more than 15 years that we've had our laboratory and i really want to do a shout out to 36:45 dave pagliarini and sarah calvo those are the two that really created that first mitocardia inventory that's so 36:51 widely used today i also want to do a special shout out to isha jane she was a graduate student 36:57 that did that initial genetic screen and gave rise to that very initial idea that low oxygen could be beneficial in the 37:04 setting of mitochondrial disease and they were all helped by a number of 37:09 other members of our laboratory and also i'm very grateful for our collaborators 37:14 uh most of whom i have mentioned throughout the course of this talk but including dr warren zapal at mass 37:20 general hospital who's been a a a really wonderful collaborator for hypoxia 37:25 studies gary robkin with whom we're doing some warm studies of hypoxia and then others that have helped us in 37:31 our proteomics work our genetics work in biomarker studies these are the generous funding agencies 37:37 that have invested in our labs i really want to thank them and finally i want to 37:42 just dedicate this lecture to dr david holtzman he was a pediatric neurologist that 37:49 actually saw patients with mitochondrial disease at mgh and he was also a mitochondriac he loved this organelle 37:57 and as it turns out he left us exactly three years ago today 38:03 and so i just want to do a shout out to him because he was a dear friend to our laboratory 38:08 so with that i'm happy to take any questions that you may have Why study mitochondria 38:18 thank you so much thompson that was a fantastic talk uh we've had a few questions come in and one of the ones 38:24 that i wanted to actually start with was how did you get interested in studying mitochondria what got you fired up about 38:30 this this organelle it's a great question and uh what i would say is that uh when i was a first 38:36 or second year medical student we were in our pathology class and quite honestly it was those electron 38:43 micrographs we had a tiny tiny uh section in our pathology book on mitochondria and maybe just 10 minutes 38:50 of an introduction to what are called mitochondrial myopathies and when i saw those images i learned that they used to be bacteria 38:56 that they still have a dna and we're just briefly introduced to their elaborate biochemistry all of those 39:02 um turbines if you will i just thought that this is the coolest organelle and 39:08 basically from that point onwards that's all that i've been uh working on both as a student as a fellow trainee and in our 39:15 own laboratory and then speaking of the the the bacterial ancestor of the How big was the bacterial ancestor 39:21 mitochondria how how think do you think how big do you think that um that ancestor's genome 39:28 might have been i mean clearly it's loss the mitochondria lost a lot of genes over time as it became part of other 39:33 cells um what kinds of genes do you think might have been lost and how many genes do you think it might have originally had 39:39 yeah no great question and so you know we think that that original bacterium probably had a genome with about one to 39:45 two thousand uh proteins that it encoded and then roughly once every million years uh one of those 39:53 proteins was either lost altogether or that dna was recoded into the nuclear 39:58 genome so this is what we call reductive evolution that original genome that encoded anywhere between 1 000 to 2000 40:05 proteins it's been whittled down tiny tiny tiny tiny so that today our mitochondrial genome only includes 13 40:11 proteins and a whole bunch of those original genes have either been lost altogether because they're just not 40:16 needed or they've been transferred to the nuclear genome and then re-imported from the nuclear genome into the 40:21 organelle and our mitochondria today have a lot of eukaryotic innovations as 40:27 well our mitochondria can do a lot of things that that original bacteria couldn't do so the proteome of the mitochondrion 40:33 really is a mosaic consisting of some ancient proteins as well as some newly derived proteins as well What genes and proteins from the nuclear genome interact with mitochondria 40:41 so that absolutely leads to another question that i wanted to put to was what kinds of genes and proteins from the cell from the from the nuclear 40:47 genome interact with mitochondria and the mitochondrial genome yeah it's a 40:52 great great question and so that mitochondrial genome it only encodes 13 proteins and all the rnas that are 41:00 required for the translation of those 13 proteins and so the 13 proteins that are encoded 41:07 by the mitochondrial genome they're all a part of that respiratory chain those turbines that i showed earlier 41:12 okay and those 13 have to work with at least 77 other proteins that are coming in from the nuclear genome in addition 41:19 the entire ribosome for the mitochondrion all the protein components are encoded by the nuclear genome 41:27 imported and all those proteins interact with the rnas coming off of the 41:32 mitochondrial genome so that you have a functioning mitochondrial ribosome which is completely distinct 41:38 from the ribosome in the cytosol wow that's that sounds quite complicated Are there any correlations between mitochondria and nuclear genomes 41:43 uh more than i can fully grasp um are there any correlations and this 41:49 is from one of our viewers are there any correlations between mitochondrial dna mutations and nuclear dna mutations do 41:55 you see certain sets of variants or certain sets of mutations that get passed along together that's a really 42:02 really good question um and this is what we call epistasis where um 42:08 a variant of the empty dna sort of segregates other variant in the nuclear genome uh we don't we believe that this 42:16 is happening in humans but there isn't any really good rigorous data to support that yet but if you look 42:21 in yeast if you look in drosophila uh there there's pretty good convincing 42:27 examples of where a genetic variant in the nuclear genome is matched to a particular empty dna and when they're 42:34 not matched with each other we have problems but when you put if you have either one of 42:39 them in isolation you have problems but when they're present together everything is okay How do you change oxygen concentrations in the laboratory 42:46 one of our what our viewers was asking about the the methods that you use to change um 42:52 oxygen concentrations in the laboratory i understand that with with mice you were saying you were telling me before 42:57 that you basically pump oxygen or pump nitrogen into into the cages so that it sort of 43:03 dilutes the air a little bit but in the laboratory so in a in an incubator in a lab what do you what method do you use 43:09 to get the oxygen concentration lower yeah actually whether it's cell culture or worms or mice or even 43:17 humans at mgh it's the same strategy we have nitrogen generators 43:23 or we have nitrogen tanks and we're basically diluting that 21 oxygen that's found at sea level we 43:30 dilute it with nitrogen to bring it down so it's actually the same strategy in all cases 43:36 okay switching a little bit to something more physiological you talked a little bit about how mitochondrial function changes How do mitochondria change with age 43:43 with age and how it gets reduced over time do the number of 43:48 do the number of mitochondria in our cells change as well or is it just the function and is do they change with age 43:54 or with environment or do this sort of stay you know somewhat level over time 43:59 yeah great great questions and so as we age both the number of mitochondria 44:05 decreases and the activity per mitochondria decreases so that initial intron slide that i showed that was 44:12 actually normalized to the amount of mitochondria you could see the downward slope but the number of mitochondria goes down as well so this actually is 44:18 one of the strongest biomarkers of the aging process itself 44:24 and then in terms of the environment when one goes to high altitude to low o2 44:29 levels for a long time we do lose some of our mitochondria at high altitude as well 44:35 interesting one of our viewers was asking about um other methods that the cell might have Boosting ATP production 44:41 besides oxfords for um boosting atp production are there 44:46 other ways that the cell is capable of doing that or that the mitochondria is capable of doing that yeah great question so um the classic example that 44:54 most students are familiar with is what's called glycolysis and so that doesn't need the mitochondrion at all 45:01 and the glucose will get converted to lactate and in that process you'll be able to generate about two 45:06 molecules of atp per glucose molecule there's a few other pathways like that they're broadly called substrate level 45:12 phosphorylation in which you have a substrate level phosphorylation pathway that's resident within our mitochondrion 45:18 that doesn't need all those turbines and it doesn't need oxygen so there are a few other backup pathways 45:23 for making atp as well okay are there any forms of Subclinical forms of mitochondrial disease 45:30 subclinical forms of mitochondrial disease that you've that you or others have come across that can be triggered 45:36 by exposure to high oxygen levels over over their lifetime yeah i know this is a great great 45:42 question and so uh there's actually a disease called um a retinopathy of prematurity 45:50 and so a few decades ago what was happening was that when 45:57 infants were being born premature they'd be placed in a small incubator to keep them nice and warm and keep their gases 46:04 controlled and those preemies would actually be given supplemental oxygen 46:10 and a fair number of them were actually developing a retinal disease because of the high 46:16 oxygen and then later on somebody named named beckman a very very 46:22 famous bioengineer developed one of the first oxygen meters and 46:28 somebody had the hypothesis that maybe the high oxygen that the infants were receiving was actually causing the 46:34 retinopathy and once they could measure it they started to decrease the o2 levels and now the retinopathy was not 46:40 forming and so there's instances like that where supplemental oxygen can cause 46:46 pathologies and if somebody receives really high oxygen for a long time they can develop 46:53 pulmonary disease as well including something called respiratory distress syndrome so 46:59 oxygen uh is a little bit like goldilocks is a lot of as a lot of people say 47:06 you definitely don't want too little but too much can be bad but you want the right amount What counts as a mitochondrial disease 47:12 a couple of our viewers have been asking more for a little bit more detail about what counts as a mitochondrial disease 47:17 and i know at the earlier in the talk you sort of list it off some things affect the brain some things affect the heart some things affect other organ 47:23 systems like what are some of the mitochondrial diseases that i know they're generally rare but which you 47:29 know are seen in the clinic in general yeah so there's debate about this i mean 47:34 this is something that um i try to depict in that slide with the entire spectrum of mitochondrial diseases uh 47:42 all the way from aging to rare mitochondrial diseases that are that are due to a single gene defect so 47:49 when i'm talking about those 300 single gene defects i'm talking about a defect 47:54 where the mutated gene is encoding a mitochondrial protein so there's 300 48:00 monogenic disorders of the mitochondrial proteome okay now you can classify diseases in a 48:07 variety of ways this is what's called mesology right you can classify diseases on the basis of the genetics or the 48:13 biochemistry or on the basis of the clinical presentations and so usually when i'm talking about a 48:19 miter disease i'm usually talking about a disease where the defect in the mitochondrion is really playing a causal 48:25 role in the pathology what i'll say is that the diseases that you may be familiar 48:30 with are diseases like parkinson's disease that's a relatively common neurodegenerative disease i think it 48:36 impacts about five percent of uh individuals over the age of six or sixty five so it's a very very common 48:41 neurodegenerative disease and it is associated with mitochondrial 48:46 dysfunction right and there's a lot of people out there that will actually argue that parkinson's is the most 48:52 common uh mitochondrial disease uh but there's a lot of active debate right now whether 48:58 or not the defects you definitely see defects in mitochondria and parkinson's disease but whether they're the drivers 49:04 of the disease or whether they're secondary that's something that's debated right now but i would say parkinson's may be the most common 49:09 condition that a fair number of the community believe is a mitochondrial disease 49:15 and out of those 300 rare mitochondrial diseases the most common is something called friedrichs ataxia and that one 49:22 impacts about 1 in 50 000 individuals in north america Local hypoxia 49:27 one of our viewers had a question about um the benefits of exercise you mentioned one of your slides how you're 49:33 aging you can sort of not reverse but ameliorate the effects of of um of aging 49:40 on your your vo2max and on your mitochondrial function with exercise and the question was that do you think 49:46 that local hypoxia might have some of the beneficial effects of physical activity on mitochondria 49:53 it's a great great question you definitely form local hypoxia with 49:59 exercise and whether that in any way is related to the dramatic effects that we're seeing of low oxygen of these rare mito 50:06 disease it's a super interesting question what i can tell you is that when i had that one text slide in our 50:13 mouse models of mitochondrial brain disease intermittent hypoxia does not appear to 50:19 be working however for that particular brain disease but there is a small thread of literature 50:25 that actually suggests that intermittent hypoxia can be very helpful for spinal cord injury as well 50:32 and so whether the benefits of intermittent hypoxia for spinal cord injury whether 50:37 the benefits of exercise which does cause localized hypoxia are related to the biology that we're focusing on it's 50:45 an open and wonderful wonderful question when it comes to the the root causes of Genetic causes 50:51 the of the mitochondrial diseases that you see in that others see do you find that their their genetic causes tend to 50:58 be more mutations in the nuclear genome or the or the mitochondrial genome because you said there's a lot of 51:03 interaction between the two or does it really depend on the individual condition 51:08 so if you take all of these genetic mitochondrial diseases the vast majority of the disease genes 51:15 are nuclear right because the nuclear genome just has an outsized genetic impact on the 51:21 organelle however if you take the number of individual patients most patients 51:26 actually have mutations in the mitochondrial genome and the age of onset tends to be very 51:32 different for the mtdna diseases for the versus the nuclear diseases so these follow a bimodal distribution uh and so 51:39 the ones that are appearing earlier in life they tend to have mutations of the nuclear genes and those that present 51:45 later in life in teens or in early adulthood those tend to be due to mutations in the mitochondrial 51:51 dna that just came in that caught my eye so Oxygen levels 51:56 essentially in your models of um in your models of your mouse models of mitochondrial disease when you put them 52:02 at different oxygen levels do you see any relationship with the changes in red blood cells or hemoglobin 52:09 yeah so uh definitely so what ends up happening is um when we place the mice at low oxygen 52:16 they will mount a polycythemic response so they will increase their red blood cell mass this is what happens to 52:22 healthy humans when they go to high altitude and this is what happens to our mouse models as well 52:28 um and so that's the normal physiologic response and so we actually think this is why 52:34 the intermittent hypoxia may not be working because when we do something like 12 hours on 12 hours off 52:40 the 12 hours when they're in hypoxia is increasing their hematocrit the 52:46 amount of oxygen carrying capacity and now they're coming into normoxia hypoxia 52:51 normoxy hypoxia and we are speculating that this is giving them a gush of a gush of of oxygen that's actually 53:00 toxic that's what we think is happening and in your mouse models especially the the Atp production 53:07 lazarus mouse model so the one that you're able to rescue by by bringing it into a hypoxic environment do you see 53:12 differences not just in their their activity in their survival but in their atp production 53:18 yeah great question um we actually uh have limited means of 53:24 measuring atp production capacity in in in brain tissues in these mouse models 53:30 what i can tell you is that we're developing these various blood tests that i told you about using that technology called metabolomics 53:37 in our mouse models of mitochondrial disease as well as in our human patients with lee syndrome or me loss 53:44 we're actually not typically seeing a biochemical or a metabolic signature of atp deficiency 53:51 okay the biochemical is actually related to 53:57 that buildup of oxygen and nadh if that makes sense and so we we don't see a strong atp deficiency 54:04 biomarker at least in the blood uh in trying to make these measurements in the brain 54:10 right now is very challenging okay just a couple more questions so one of Antioxidants 54:15 them is do do you think or have you seen any evidence of antioxidants like vitamin c or vitamin e or selenium or 54:22 things like that having an effect on on mitochondrial function i am so glad that somebody asked that 54:29 question so antioxidants have consistently uh failed efficacy studies for 54:34 friedreich's ataxia in our mouse model we and others have tried very strong antioxidants and this is a really 54:41 important point and i didn't get into in my talk but we actually do think 54:47 that high unused ox we think that a function of mitochondria is to consume oxygen 54:53 when they're not functioning properly the oxygen is accumulating and that can cause damage 55:01 however it's not the traditional superoxide and hydrogen peroxide type of a free radical type of a damage 55:07 what we think is happening is that the dioxygen itself is oxidizing things and 55:13 so as an example if i have an iron nail that if i have oxygen it's 55:19 possible to actually oxidize that iron okay and when you oxidize iron you've 55:25 oxidized the iron and you've produced a free radical and you can throw antioxidants and 55:30 vitamins on the free radical to make it go away however the damage that has happened is we have oxidized the iron 55:38 and so we actually think that a lot of the free radicals may be epiphenomenon and that the dioxygen 55:44 itself is oxidizing precious biomolecules and that's the pathology if our hypothesis is correct 55:51 uh and we're still testing it then traditional antioxidant therapies should not work 55:57 so can't necessarily reverse anything it might keep more damage from happening but whatever damage has been done has 56:03 been done kind of like you can't de-rust a nail yes uh except um you know that lazarus 56:10 model what we are seeing com is uh which you see um you know if if we 56:16 get to the point of no return if if the mouse is really dead i very much doubt that we're going to reverse that but we 56:22 at the early stages when we see the mri lesions in the brains that part and that lee syndrome mouse 56:28 model we're actually able to reverse that and what may be happening is we're preventing further damage and now 56:35 perhaps the low oxygen and the damage to tissue there may be factors that are now going to help to promote repair so we're 56:42 actually working on trying to understand whether the low oxygen is only preventing further damage or if there's 56:48 an active process of repair as well okay so last question that i wanted to throw Personalized therapies 56:54 to and which is sort of like look into your crystal ball a little bit of further down the line when 57:01 new therapies for for mitochondrial diseases start to become available do you imagine that there would be a suite 57:07 of treatments that could be used across different mitochondrial diseases or do you imagine that individual patients 57:13 would likely need truly personalized therapies based on their own 57:19 mitochondrial nuclear mutations or whatever pathway happens to be broken in that individual patient 57:26 yeah it's a great great question and something that we think about a lot and deeply and i think we're going to need 57:31 to have a mix of approaches as of today there are 300 monogenic 57:37 mitochondrial diseases and most of these are not just rare but they're ultra rare 57:43 and so i think biotech pharma may go after some of these to try to use gene 57:49 replacement technologies or gene editing technologies to fix the root genetic cause 57:54 however there's a very long tail of very rare mitochondrial diseases these literally impact 10 known patients in 58:02 the world right now trying to come up with a a gene therapy or gene repair type of a 58:08 program for that very long tail is going to be tough and so we think that we're going to need other therapies that you 58:15 know impact uh some of the downstream confidence consequences of a breakage in the 58:21 electron transport chain and from our laboratory you know what we think is happening is there's a flood upstream 58:27 and there's a drought downstream and we think that the drought and and and the flood 58:33 are contributing to some of the pathology and so the hope is that the molecules and approaches that we develop 58:38 to address those two aspects we'll actually enjoy application in a number of these 58:43 different conditions so i think we're going to need to have multiple approaches and i can't 58:49 underscore enough how important biomarkers really high quality biomarkers are going to be so that we 58:54 can make sure to provide the right therapy to the right patient and we can also see whether it's working in a 59:00 rigorous way all right and with that thank you so much francie for giving such a wonderful 59:05 talk this evening and thank you to all of you for virtually joining us for this evening science for all seasons talk 59:12 we hope you enjoyed it uh we hope you like what you heard and if you did uh and then please consider watching other 59:17 talks from this series you can find them all at broadinstitute.org fsas 59:23 uh or on the broad institute youtube channel uh our recording of tonight's talk will be posted on the channel at youtube.com 59:31 user slash broad institute uh to find out about other live streamed events and new videos from the broad 59:38 institute consider subscribing to our youtube channel and tell your friends and family to subscribe as well 59:43 thank you again for joining us this evening we hope you found the talk enjoyable and informative and have a great night 1:00:03 you Broad Institute 30.3K subscribers Videos About Facebook Twitter