CRISPR-Cas3 gene editing system restores dystrophin function in stem cells derived from patients with Duchenne

Duchenne muscular dystrophy (DMD) is a muscle degeneration disorder caused by mutations affecting the dystrophin gene. On August 24th in the journal Stem Cell Reports, researchers show how a dual CRISPR RNA method restored dystrophin protein function in induced pluripotent stem cells derived from DMD patients. The approach worked by removing large sections of the dystrophin gene, allowing the cells to skip faulty or misaligned sections of the genetic code. This yields truncated but still functional proteins for a wide variety of mutation patterns associated with DMD.

"Dual CRISPR-Cas3 is a promising tool to induce a gigantic genomic deletion and restore dystrophin protein via multi-exon skipping induction," says senior author Akitsu Hotta of Kyoto University. "We expect this study to enlighten new ways to treat DMD patients and other genetic disorders that require extensive deletions."

Due to significant variations in the mutation patterns affecting the dystrophin gene, deleting a small section of the gene can only be used for a limited number of DMD patients. For example, the most common mono-exon skipping of exons 51, 53, and 45 can be applied to 13%, 8%, and 8% of DMD patients, respectively.

Multi-exon skipping (MES) has broad applicability to various DMD mutation patterns. By targeting the mutation hotspots in the dystrophin gene, MES from exon 45 to 55 was estimated to benefit more than 60% of DMD patients. Unfortunately, few techniques are available to induce a large deletion to cover the target exons spread over several hundred kilobases.

To overcome this hurdle, Hotta and his team used CRISPR-Cas3 to induce a deletion of up to 340 kilobases at the dystrophin exon 45-55 region in various DMD mutation patterns. Because it was rare to observe a deletion of more than a hundred kilobases using a single CRISPR RNA -- which helps to locate the correct segment of DNA -- the researchers used a pair of CRISPR RNAs inwardly sandwiching the target genomic region.

The authors note potential limitations of the dual CRISPR RNA system. First, there is variation in the deletion pattern, and the precise start and end points of the deletion cannot be fully controlled. This could be a drawback when a large but precise deletion is required. Second, the study did not demonstrate the functionality of the recovered dystrophin protein. Third, other methods should be developed to improve the overall genome editing efficiency of the Cas3 system.

"Our dual-Cas3 system might apply to future gene therapies once we're able to deliver the dual-Cas3 components in vivo to skeletal muscle tissues safely and efficiently," says Hotta. "The ability to induce several hundred kilobases of DNA deletion itself also has broad applicability for basic research when a large deletion is needed."

This study was partly supported by the Japan Agency for Medical Research and Development, the Japan Society for the Promotion of Science, the iPS Cell Research Fund, and the National Center of Neurology and Psychiatry. Akitsu Hotta is a scientific adviser of C4U, and several co-authors have submitted a patent regarding this study.

Journal Reference:

1. Yuto Kita, Yuya Okuzaki, Youichi Naoe, Joseph Lee, Uikyu Bang, Natsumi Okawa, Akane Ichiki, Tatsuya Jonouchi, Hidetoshi Sakurai, Yusuke Kojima, Akitsu Hotta. Dual CRISPR-Cas3 system for inducing multi-exon skipping in DMD patient-derived iPSCs. Stem Cell Reports, 2023; DOI: 10.1016/j.stemcr.2023.07.007

https://www.sciencedaily.com/releases/2023/08/230824111922.htm

 

Rebuilding, regenerating lung cells

 Researchers from the Center for Regenerative Medicine (CReM), a joint venture between Boston University and Boston Medical Center, have discovered a novel approach for engrafting engineered cells into injured lung tissue. These findings may lead to new ways for treating lung diseases, such as emphysema, pulmonary fibrosis and COVID-19. The two studies describing the methodologies for engineering lung stem cells and transplanting them into injured experimental lungs without immunosuppression appear online in Cell Stem Cell.

For more than 20 years, the scientists leading this work have pursued a way to engraft cells into injured lung tissues with the goal of regenerating lung airways or alveoli. They suspected that for engraftment to be long-lived and functional it would be important to reconstitute the stem or progenitor "compartments" of the lung, also sometimes known as stem cell niches. They concentrated on first developing methods for engineering each of the lung's stem or progenitor cells in the laboratory using pluripotent stem cells, and then developed methods for transplanting these cells into experimental mouse models with injured lungs.

In their study "Airway Stem Cell Reconstitution by Transplantation of Primary or Pluripotent Stem Cell-Derived Basal Cells," the CReM researchers focus on the lung airways. These airways are lined by an epithelium that has well described stem cells called "basal cells," which are responsible for maintaining these airways throughout life.

"By differentiating experimental model and human pluripotent stem cells into airway basal cells in the laboratory dish, we were then able to use these cells to reconstitute the stem cell compartment of the injured model airways in vivo (in living tissue). This resulted in life-long engraftment of the engineered basal cells in an immunocompetent model. Because the cells engrafted as basal cells, the normal stem cell of the airways, they were able to self-renew or make copies of themselves by dividing and also giving rise to other cell types that together make a functional airway epithelium," explained corresponding author Darrell Kotton, MD, the David C. Seldin Professor of Medicine at Boston University Chobanian & Avedisian School of Medicine and director of the CReM.

In their second paper, "Durable alveolar engraftment of PSC-derived lung epithelial cells into immunocompetent mice," CReM researchers targeted the lung air sacks, known as alveoli. Kotton and his team developed methods for engrafting engineered cells into the alveoli, the region of the lung responsible for gas exchange. The engrafted cells formed both types of alveolar cells, called type 1 and type 2 pneumocytes. Since type 2 pneumocytes act as progenitors of lung alveoli throughout life, forming new type 2 pneumocytes out of their transplanted engineered cells ensured the cells would self-renew and differentiate to maintain lung alveoli for a long time.

The researchers believe the reconstitution of lung stem and progenitor cells in the airways and alveoli using cells engineered from pluripotent stem cells is an important finding with many implications for the future treatment of lung diseases that involve injury, degeneration or mutations. "Since induced pluripotent stem cells (iPSCs) can be generated from the blood or skin of any individual through a technology called reprogramming, we hope this work will help to pave the way towards developing new therapeutic approaches where iPSCs can be made from any patient with lung disease, differentiated into lung stem cells in the laboratory, and used for transplantation to reconstitute the healthy airway and alveolar epithelial tissues in a way that is durable and functional," said Martin Ma, first author of the first paper and a BU MD/PhD student in the Kotton lab.

For those suffering from genetic lung diseases, like cystic fibrosis and primary ciliary dyskinesia, it is possible to gene-edit the iPSCs in the laboratory prior to transplantation, meaning the newly engrafted cells will have had their gene mutation corrected and should be free of disease. "Since these cells will be the patient's own cells, differing only in the corrected gene, in theory they should not be rejected after transplantation back into that patient, thus avoiding any need for immunosuppression, as we have demonstrated in our two proof-of-concept syngeneic transplantation studies in immunocompetent experimental models" added Michael Herriges, PhD, first author of the second paper and a postdoctoral fellow in the Kotton lab.

According to Kotton, these papers represent the culmination of 20 years of research. "While treatment of lung diseases like emphysema, pulmonary fibrosis and COVID-19 will take a lot more research, we are hopeful that those with gene mutations that cause damage to lung airways or alveoli, such as children or adults with familial forms of lung disease, might be treatable in the future with this type of approach."

Journal References:

1. Liang Ma, Bibek R. Thapa, Jake A. Le Suer, Andrew Tilston-Lünel, Michael J. Herriges, Andrew Berical, Mary Lou Beermann, Feiya Wang, Pushpinder S. Bawa, Anat Kohn, Alexandra B. Ysasi, Hirofumi Kiyokawa, Taylor M. Matte, Scott H. Randell, Xaralabos Varelas, Finn J. Hawkins, Darrell N. Kotton. Airway stem cell reconstitution by the transplantation of primary or pluripotent stem cell-derived basal cells. Cell Stem Cell, 2023; DOI: 10.1016/j.stem.2023.07.014
2. Michael J. Herriges, Maria Yampolskaya, Bibek R. Thapa, Jonathan Lindstrom-Vautrin, Feiya Wang, Jessie Huang, Cheng-Lun Na, Liang Ma, McKenna M. Montminy, Pushpinder Bawa, Carlos Villacorta-Martin, Pankaj Mehta, Darrell N. Kotton. Durable alveolar engraftment of PSC-derived lung epithelial cells into immunocompetent mice. Cell Stem Cell, 2023; DOI: 10.1016/j.stem.2023.07.016

https://www.sciencedaily.com/releases/2023/08/230824111925.htm

Epigenetic mechanism that causes bitter taste distortion discovered

 A bitter taste in the mouth is often a symptom or side effect of illness, which may be the result of how the body reacts to pathogens. A new study published in iScience, by Hong Wang, PhD, an Associate Member at the Monell Chemical Sense Center, and colleagues sheds light on the mechanisms involved in the complex interplay between taste perception and immune function. Their work also highlights the potential of a sequencing tool for investigating epigenetic mechanisms that affect taste-cell gene expression. Epigenetics is the study of how and when genes are expressed rather than alteration of the genetic code itself.

In addition to being unpleasant, a bitter taste in the mouth or from food can contribute to a loss of appetite, an effect associated with ailments from the common cold to cancer. Bitter taste can also affect patients' willingness to take certain medications, especially when they are young children. Bitter receptors are encoded by Tas2r genes, which also provide an important defense against bacteria and parasites in the mouth and gut. However, this process is not well understood.

For this study, the team explored how inducing inflammation would affect gene regulation of these taste receptors. Using lipopolysaccharide (LPS), a compound that induces inflammation similar to that caused by bacterial infections, they found that mice showed a distinct elevated aversion to bitter tastes. The team used nerve-recording experiments to confirm that this aversion originates in the taste buds of mice, rather than in their brains.

"Our study had very clear data showing this is actually a change at the peripheral level, not deep in the brain," said Wang, confirming that genes in taste cells govern bitter taste distortion to this type of inflammation.

This finding has interesting clinical implications for the study of behavioral aspects of illness, such as a loss of appetite. When people are sick they often do not feel like eating. This can affect even humans' love for sugary treats, as other studies have noted. Mice also have a decreased preference for sweet tastes during illness and forced intake of sugar can make them sicker. These results potentially indicate a protective behavior with a biological or evolutionary basis.

To investigate the underlying gene expression mechanisms of the bitterness response, the team used several methods of analysis. Real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) revealed a significantly increased response across the majority of the Tas2r taste-receptor genes, with peak gene expression ranging from three to five days during the sickness period.

The researchers also used single-cell sequencing assay for transposase-accessible chromatin (scATAC-seq) to explore the expression of Tas2r genes in response to LPS -- the first reported instance of this method to study taste receptor gene expression. LPS markedly increased the accessibility of many Tas2r genes, indicating that the bitter taste distortion in this experiment is caused by an epigenetic mechanism, similar to how disease-causing bacteria can affect those genes.

Finally, the study showed that LPS-induced inflammation globally affected gene expression in taste stem cells, suggesting a "remodeling" of the cells' genome. This may leave an epigenetic memory, enabling the cells to respond faster to future infections, but may also contribute to long-lasting effects on taste responses. This finding sheds light on why cancer treatment and certain chronic illnesses can cause a lingering bitter taste in the mouth or alter the taste perception of certain foods.

This diverse response across taste receptors has potential implications for research on how to make more effective bitter blockers for medications and other edible health and wellness products. "The spectrum of the bitter taste receptor expression is not uniform," Wang said. "If we want to look at a bitter blocker for an individual taste receptor, we may want to take these factors into consideration, such as whether it's for after a sickness, during a sickness, or which of the taste receptor genes is most prominently expressed."

Journal Reference:

1. Ha Nguyen, Javier Albayay, Richard Höchenberger, Surabhi Bhutani, Sanne Boesveldt, Niko A Busch, Ilja Croijmans, Keiland W Cooper, Jasper H B de Groot, Michael C Farruggia, Alexander W Fjaeldstad, John E Hayes, Thomas Hummel, Paule V Joseph, Tatiana K Laktionova, Thierry Thomas-Danguin, Maria G Veldhuizen, Vera V Voznessenskaya, Valentina Parma, M Yanina Pepino, Kathrin Ohla. Covid-19 affects taste independent of taste–smell confusions: results from a combined chemosensory home test and online survey from a large global cohort. Chemical Senses, 2023; 48 DOI: 10.1093/chemse/bjad020

https://www.sciencedaily.com/releases/2023/08/230824120153.htm

Half as many AF patients dying of heart attacks and strokes in the UK now

 Patients living with one of the UK's most common heart rhythm conditions are 50% less likely to die from a heart attack or stroke than they were at the start of the millennium, new research has found.

Analysis of the health records of more than 70,000 patients newly diagnosed with atrial fibrillation (AF) showed that mortality from related cardiovascular and cerebrovascular diseases more than halved over the 16-year study period.

AF is associated with an increased risk of stroke.

The research showed that dementia now accounts for more deaths within one year of an AF diagnosis than acute stroke, heart attack and heart failure combined, demonstrating the need for more research into the link between dementia and AF.

The study team believe the lower mortality rate can be attributed to better detection and treatment for AF, which, according to the British Heart Foundation, affects more than 1.5 million people in the UK.

But the findings reveal significant health inequalities, showing that the most socioeconomically deprived patients were 22% more likely to die from AF-related conditions than people from the most affluent group.

Additionally, patients are now more likely to be diagnosed with coexisting health conditions such as diabetes, cancer and chronic kidney disease, which have greater health implications for them than AF.

Senior author Chris Gale, Professor of Cardiovascular Medicine, Honorary Consultant Cardiologist, and Co-Director of the Leeds Institute for Data Analytics at the University of Leeds said: "Atrial fibrillation is a common and often undetected heart rhythm disorder that increases the risk of stroke. Advances in health care have now reduced the chance of having a stroke related to AF, and from dying as result of it, if AF is detected and treated.

"However, our study also reveals important disparities in care associated with deprivation and the co-existence of other illnesses. Proactively diagnosing and treating AF in these groups will likely further reduce death and disability from cardiovascular disease. Equally, for many people, AF is a marker of co-existent disease -- identifying and treating these additional disease states could further improve outcome for people with AF."

The team is now calling for randomised clinical trials to determine whether the earlier identification and treatment of AF and associated co-morbidities could effectively improve cardiovascular health.

Data analysis

The research examined data from electronic health records of 72,412 patients from a representative sample of the UK population, who had been diagnosed with AF between 2001 and 2017. The team assessed the health outcomes in patients in the first year after their AF diagnosis, and analysed changes in cause-specific mortality and hospitalisation over time and by sex, age, socioeconomic status and diagnostic care setting.

The average patient was aged 75.6. Some 48.2% of patients were women, and 61.8% had three or more comorbidities.

Over the study period, coexisting health concerns became more common, with almost 70% of newly diagnosed AF patients also having at least three comorbidities.

Mortality rates at one year post diagnosis were investigated, as well as the number of hospital admissions with an overnight stay within 1 year of diagnosis.

Over the study period, 20% of patients died from any cause within a year of being diagnosed with AF -- but this declined over time.

However the researchers found that deaths due to cardiovascular and cerebrovascular events (strokes) more than halved over the study period. Cardiovascular deaths declined from 7.3% in 2001/02 to 3% in 2016/2017, while cerebrovascular deaths declined from 2.6% to 1.1%.

The researchers say that the lower rates of cardiovascular deaths among AF patients in the study may be partly explained by improvements in strategies to prevent heart disease, and by changes in clinical practice that could lead to people being diagnosed earlier.

By contrast, there was an increase in mortality rates from mental and neurological disorders, from 2.5% in 2001/02 to 10.1% in 2016/17. Of these deaths, 87.2% were caused by dementia, Alzheimer's disease and Parkinson's disease. The research team say that while this could be partly due to greater awareness

of dementia, it also strengthens the evidence that the relationship between AF and dementia is a pressing research priority.

Other findings include:

• Hospitalisation is common within a year of AF diagnosis, with almost two further admissions experienced by patients

• Hospitalisation rates have increased by 17% due to increasing admissions from non-cardio/cerebrovascular causes, especially in older patients

• Hospitalisation for cardiovascular and cerebrovascular causes have decreased by 38% and 28%, respectively, but for non-cardio/cerebrovascular causes hospitalisation has increased by 42%

• Older people have experienced the greatest rise in hospitalisation, with those aged 80 years or more experiencing a 39% rise in hospitalisation within a year of AF diagnosis

Health inequalities

Professor Gale said: "Patients diagnosed in hospital or from the most deprived group had worse outcomes compared with those diagnosed in the community or from the most affluent group.

"Although increased burden of comorbidities might partly explain the increased frequency of death in these groups, the persisting difference after full adjustment for these factors suggests other social and health-care factors might also contribute.

"Our previous research showed that the most deprived individuals in the UK experience an AF diagnosis at a younger age than the most affluent individuals. This discrepancy in outcomes warrants targeted strategies and healthcare resource planning."

Lead author Jianhua Wu, Professor of Biostatistics and Health Data Science in the Queen Mary University of London's Wolfson Institute of Population Health said: "AF is one of the most prevalent heart conditions in the UK and as such it is crucial that we understand whether or not the current management of the condition is successful. Our findings provide vital evidence about the effectiveness of treatments for this condition, while also showing that other conditions are becoming more prevalent among AF patients -- potentially providing avenues for exploration of more targeted treatments."

Journal Reference:

1. Jianhua Wu, Ramesh Nadarajah, Yoko M Nakao, Kazuhiro Nakao, Chris Wilkinson, J Campbell Cowan, A John Camm, Chris P Gale. Temporal trends of cause-specific mortality after diagnosis of atrial fibrillation. European Heart Journal, 2023; DOI: 10.1093/eurheartj/ehad571

https://www.sciencedaily.com/releases/2023/08/230825122031.htm

Platelets can replicate the benefits of exercise in the brain

 Pre-clinical trials by University of Queensland researchers have found an injection of a specific blood factor can replicate the benefits of exercise in the brain.

Dr Odette Leiter and Dr Tara Walker from UQ's Queensland Brain Institute led a team which discovered platelets, the tiny blood cells critical for blood clotting, secrete a protein that rejuvenates neurons in aged mice in a similar way to physical exercise.

"We know exercise increases production of new neurons in the hippocampus, the part of the brain important for learning and memory, but the mechanism hasn't been clear," Dr Leiter said.

"Our previous research has shown platelets are involved, but this study shows platelets are actually required for this effect in the aged mice."

The researchers focused on exerkines, the biological compounds released into the bloodstream during exercise, which are believed to stimulate the exercise-induced response in the brain.

"We discovered that the exerkine CXCL4/Platelet factor 4 or PF4, which is released from platelets after exercise, results in regenerative and cognitive improvements when injected into aged mice," Dr Leiter said.

Dr Walker said the findings have significant implications for the development of drug interventions.

"For a lot of people with health conditions, mobility issues or of advanced age, exercise isn't possible, so pharmacological intervention is an important area of research," she said.

"We can now target platelets to promote neurogenesis, enhance cognition and counteract age-related cognitive decline."

The researchers said the next step is to test the response in Alzheimer diseased mice, before moving towards human trials.

"It's important to note this is not a replacement for exercise," Dr Walker said.

"But it could help the very elderly or someone who has had a brain injury or stroke to improve cognition."

Journal Reference:

1. Odette Leiter, David Brici, Stephen J. Fletcher, Xuan Ling Hilary Yong, Jocelyn Widagdo, Nicholas Matigian, Adam B. Schroer, Gregor Bieri, Daniel G. Blackmore, Perry F. Bartlett, Victor Anggono, Saul A. Villeda, Tara L. Walker. Platelet-derived exerkine CXCL4/platelet factor 4 rejuvenates hippocampal neurogenesis and restores cognitive function in aged mice. Nature Communications, 2023; 14 (1) DOI: 10.1038/s41467-023-39873-9

https://www.sciencedaily.com/releases/2023/08/230817164030.htm

The Long-Running Nitrosamine Problem

 BY DEREK LOWE

I wrote a few years ago here about the then-current problem with nitrosamine contamination in several commercial drug substances. But that story has never really gone away, as this new paper details.. At the time, the immediate problem was the switch that some manufacturers had made to dimethylformamine (DMF) in a particular synthetic step, and followed that with different conditions for the formation of a tetrazole ring. These produced small amount of nitrous acid in the workup, which reacted with small amounts of dimethylamine left over from the earlier step.

N-nitrosoamines are not something that you want to get exposed to a lot of; that's something that everyone agrees on. At the same time, we are often exposed to small amounts - for example, by consuming meats that have been cured by sodium nitrite/nitrate. As a side note, don't be fooled by the products in that category (sausage, bacon) that advertise as "no added nitrites" or even as "uncured". In the US, anyway, such products are taking advantage of a labeling loophole: they're adding celery extract (or other vegetable extracts) which are high in nitrate, which is reduced to nitrite in situ. You are getting the same nitrite-cured meat you would otherwise (that's why it's red and not gray), and this is providing the same protection against botulism and other bacterial growth that you would get otherwise (which is a big reason nitrite is added to cure meats in the first place), but you're just paying more for it while being given the impression that you're not getting any nitrites at all.

Nitrite in foods can react with endogenous amines to make the N-nitroso species, just as it did in that chemistry process mentioned above. But you don't have to be eating bacon to get exposed: nitrosamines are also produce by fermentation, in foods that have been dried through heating  by reaction of nitrogen oxides from combustion, an example being malted barley used to make beer, and in the process of cooking itself. Some of these can produce notably higher nitrosamine levels than are found in cured meat. Tobacco products are particularly high routes of exposure. The arguing starts, as it generally does in toxicology and has since at least the time of Paracelsus, about what doses are harmful. On a molecular level, the problem is that monoalkyl N-nitrosamines (which are produced from dialkylnitrosamines through oxidative dealkylation) get transformed into reactive diazonium salts. These are undisputed DNA alkylating agents, and a great deal of evidence links high or prolonged exposure to these to several types of cancer in humans and many other animal species.

Dietary sources aside, it seems reasonable to ask that the drug industry not add still more sources of N-nitroso exposure to the list. As it stands, acceptable regulatory limits on exposure through pharmaceutical intake are set about tenfold lower than what people get through their food - that new paper mentioned in the first paragraph goes into a great deal of detail on the various ways to measure exposure, but all of them come down to pretty stringent limits in drug manufacture. The authors are at pains to make clear that pharmaceuticals cannot be made "nitroso-free", any more than the food supply can be. If you have amines and oxygen, you are going to see some level of these things.

And that means that the original problem of things like N,N-dimethyl- or N,N-diethylnitrosamine, which were the contaminants that made the news back in 2018-2019, is nowhere near the end of the story. If you look more closely in the parts-per-billion range, you can find all sorts of N-nitroso things that are produce by oxidation of pharmaceutical ingredients and excipients (and the same goes for food, of course). We definitely want to look out for contamination introduced by chemical processes, but some of these things are just going to form on their own. Right now there's a big push to standardize and validate analytical methods for such things, and another big effort to come up with a standard way to measure how worried we should be about their carcinogenenic potential. The Ames test, for example, is commonly used as a front-line read on mutagenicity, so we need to figure out how well it picks up on these compounds. That's a post here from July of 2002. My writing style does not seem to have changed much! The "to be continued" at the end of it is the link in the next paragraph.

It would be very easy to say "Hey, I know what limit I want for carcinogens in my prescription drugs and in my food: zero. How about that?" But that is not going to happen. It's not possible. And by that I don't mean "It's too expensive" or "We don't wanna"; I literally mean that it's not possible. I also don't mean "It's not possible in our dirty, contaminated, industrial civilization under the conditions of late capitalism", either, in case you might be thinking in that direction. Uncontacted hunter-gatherer tribes foraging for fresh berries in the middle of the jungle are constantly exposed to carcinogens, too. I am sounding a note here that I first did in the early days of this blog, and here's link back to a post from 2002 on these issues.

The potential problem is that if we make the testing regime for N-nitrosos too onerous that some low-margin producers of generic drugs might just decide that some products aren't worth the trouble and cease production. We'll need to do some more risk/reward calculations, to try to understand the harm done in each direction. Eventually, as the new paper linked in the first paragraph says, the industry will have a "new normal" for nitrosamine testing and mitigation - but we're not there yet.

https://www.science.org/content/blog-post/long-running-nitrosamine-problem

The Aging Brain: Is Misplaced DNA to Blame?

 BY DEREL LOWE

What is "aging", anyway? Everyone immediately knows what you mean when you refer to a person's body getting old, but what's really happening? That question has occupied a lot of researchers over the years, and things are slowly starting to become a bit more clear. And as we learn the details, there's a key shift in attitude that tends to come over you. Without thinking about it much, aging seems like it's inevitable, just something that happens, all the time to everyone, always has and always will. As the narrator of the late Martin Amis' The Information puts it, "Meanwhile, time goes about its immemorial work of making everyone look, and feel, like shit".

Hard to argue with that! But does it have to? Thermodynamically you can blame entropy, creeping disorder spreading through the system, and that really does seem to be what happens (see below). But living systems are not thermodynamically closed - we can in theory put energy into them and repair things, the same way that you can clean your kitchen when things start to pile up in the sink and on the counters. In theory. We actually do have plenty of repair mechanisms on a cellular level, and one of the features of aging is that the repair mechanisms themselves start to fail.

This new paper is a good illustration of what could be going on. The cGAS-STING pathway (which I wrote about here in the context of innate immunity) is constantly checking for the presence of double-stranded DNA out in the cytosol, because it really shouldn't be there. That would normally be the sign of a viral infection (viral DNA floating around), and that's how the body reacts to it (that STING name is short for "stimulator of interferon genes"). There are autoimmune diseases such as lupus where dsDNA gets spread around to the point that it sets off this inflammatory pathway. A lot of cGAS-STING research comes from that direction, and since immunotherapy is such a huge field in cancer treatment these days, this mechanism gets a lot of attention there, too.

Well, another condition that is characterized by a constant inflammatory response (apparently in the absence of infection as well) is. . .aging. It's a clear source of trouble in a number of different tissues - this has been recognized for some time now, and a great deal of work has gone into figuring out why this happens and what might be done about it. Several years ago it was recognized that the cGAS-STING system was a key part of the inflammation seen in microglial cells in the aging brain (and in the brains of people with neurodegenerative diseases). And this new paper has tracked down further details: the reason this inflammatory pathway has been set off is the leakage of DNA from damaged mitochondria in those microglial cells.

This same team had earlier reported small-molecule STING inhibitors, and they found that administering one of these compounds actually did interrupt the inflammatory cascade in a number of different tissues in mice, and specifically seemed to lead to improved cognitive function in aged mice across several different measurements. It's quite a striking effect, and naturally this immediately makes you wonder about using this as a therapy. STING, as mentioned, also seems to be involved in a number of specific neurodegenerative diseases (Alzheimer's, Parkinson's, ALS, frontotemporal dementia and more), and there are certainly possibilities there as well.

As the authors note, there are some broad connections to be made here, and some thing things that have to be differentiated. The biggest connection is between mitochondrial dysfunction (long investigated in the context of aging) and inflammation (likewise!) There really does seem to be a direct link between these two now because of this leakage of mitochondrial DNA into the cytosol. That's a big insight, not least because it places the mitochondrial trouble upstream of the inflammation. But that may not be universal - there are other situations where it could be genomic DNA that is setting off this response, and it doesn't have to be just in microglia, either (but rather in neurons, etc.) But a common theme is cGAS-STING, responding to aging cells as if they were under viral attack and never letting up on the response to it.

As this overview of the work notes, though, we're going to have to take these insights step by step. Mouse cells simply don't live as long as human cells, because mice don't, and insights into aging from a shorter-lived species may or may not translate to human effects (or at least the human effects that we'd like to see!) There's also the potential problem that when you dial down cGAS-STING, you are inevitably dialing down the response to viral infections. It may be that just in the same way that there appear to be tradeoffs between aging and cancer, there may be others between aging and the ability to deal with viruses. But let's find out!

https://www.science.org/content/blog-post/aging-brain-misplaced-dna-blame