Fight Aging! Newsletter, March 21st 2022

Aging is accompanied by changes in vascular structure and function, especially in the large arteries. Due to their elasticity and resilience capacities, the concentric elastic lamellae of the aorta play a pivotal role in reducing the high systolic pressure at the outlet the heart. In other words, elastic lamellae stretch during cardiac ejection phases allowing the radius of the aorta to increase and to convert the pulsatile flow leaving the heart into a continuous flow in arteries. With age, these elastic lamellae exhibit wear characterized by zones of rupture. This leads to loss of elasticity and progressive hardening of the aorta and release of elastin-derived peptides (EDPs) in the circulating blood.

Elastic fibers fragmentation and release of elastin degradation products, also known as elastin-derived peptides (EDPs), are typical hallmarks of aged conduit arteries. Along with the direct consequences of elastin fragmentation on the mechanical properties of arteries, the release of EDPs has been shown to modulate the development and/or progression of diverse vascular and metabolic diseases including atherosclerosis, thrombosis, type 2 diabetes, and nonalcoholic steatohepatitis.

Most of the biological effects mediated by these bioactive peptides are due to a peculiar membrane receptor called elastin receptor complex (ERC). This heterotrimeric receptor contains a peripheral protein called elastin-binding protein, the protective protein/cathepsin A, and a transmembrane sialidase, the neuraminidase-1 (NEU1). In this review, after an introductive part on the consequences of aging on the vasculature and the release of EDPs, we describe the composition of the ERC, the signaling pathways triggered by this receptor, and the current pharmacological strategies targeting ERC activation.

The MitoSENS team continue to make progress in developing rejuvenation biotechnologies to prevent, reverse, or remove mutant mitochondria from aging cells. The center of their work continues to be allotopic expression, placing "backup copies" of the mitochondrial DNA into the nucleus, which would supply the proteins that mutation-bearing mitochondria can no longer produce for themselves, and thus keep them (and our cells) functioning normally over time. The MitoSENS team's 2016 breakthrough with allotopic expression of the mitochondrial genes ATP8 and ATP6 marked an important milestone. Since then, they've continued to work to advance the field, including showing how the distinct way that mitochondria encode genetic instructions into their DNA can be better "translated" for use in the nuclear genome, resulting in robust but transient protein production for all of the 13 genes. The team is now working on creating stable expression for these proteins and in achieving functional relevance.

In a new peer-reviewed scientific paper, the MitoSENS team gives an overview of where the field is at and the obstacles that are holding us back. They first highlight some of the drugs, supplements, and stem cell treatments that have been tried and failed (or only had modest effects) to treat inherited mitochondrial diseases. But then they get to the heart of the matter: the challenges that now need to be overcome in order to move allotopic expression towards the clinic. These include mastering the targeting of allotopically-expressed proteins to the right place in the mitochondria; modifying either the protein products themselves or the way we deliver them to prevent these proteins being incorrectly assembled in places other than their intended location; and controlling the level of protein production and its regulation by the cell (since too little protein production wouldn't have a therapeutic effect, and too much might be harmful).

Mitochondria are at the interface between several critical functions in the cell, including metabolism, signaling, and immune surveillance. Advances in our understanding of mitochondrial biology and function have illuminated the role of mitochondrial dysfunction in pathology and aging. The unique properties of the organelle predispose its genome to mutations and compromised functions leading to several diseases collectively called mitochondriopathies. Researchers have exploited various technologies, including small-molecule drugs, allogeneic hematopoietic stem cell transplantation, mitochondrial replacement, as well as gene-editing tools, such as nucleic acid therapy and mitochondria-targeted restriction endonucleases, in alleviating these diseases. While modulating organelle function using small molecules is attractive at the outset and benefits from ease of administration, few leads have been identified that hold curative promise, and this treatment modality leaves the root cause of pathology unaddressed.

Recent gene editing approaches, such as targeted restriction endonucleases and base-editing enzymes show promise, though they are limited by their narrow specificity and may require patient-to-patient customization. Gene therapy in the form of allotopic expression has received the most attention for its potential as a robust method for reversing the symptoms of mitochondrial DNA (mtDNA) mutations. Synchronizing allotopic expression for the 13 mtDNA genes with the nuclear-mitochondrial transcription and translation machinery can overcome limitations in competing with pre-existing mutant proteins in the respiratory chain complexes due to heteroplasmy, a condition commonly observed in known mtDNA pathologies. Furthermore, advances in technologies capable of inserting large DNA cargos into the nuclear genome, such as safe harbor expression or mini chromosomes, will allow for testing multiple allotopic genes simultaneously. While validating the technology in vivo has its challenges due to inadequate animal models for all the protein coding genes, the ease of generating precise human iPSCs, particularly from patients with specific mtDNA mutations, may allow us to test these gene therapy approaches on a case-by-case basis in vitro.

Cellular senescence is a process that leads to a state of irreversible growth arrest in response to a variety of intrinsic and extrinsic stresses. Initially, the phenomenon was found when cultured cells were shown to undergo a limited number of cell divisions in vitro. Cellular senescence is different from cell quiescence which represents a transient and reversible cell cycle arrest. Cellular senescence can be a physiologically or pathologically relevant program depending on the specific situation. It normally functions as a vital tumor suppressive mechanism and also plays an important role in tissue damage repair. However, senescent cells (SnCs) have been implicated in various age-related diseases.

Accordingly, selective elimination of SnCs has been exploited as a novel strategy to treat the diseases. In addition, SnCs have also been implicated in infectious diseases. For example, virus infection can induce cellular senescence, which was found to be a pathogenic trigger of cytokine escalation and organ damage, and recently found to be associated with the COVID-19 severity in the elderly. Clearance of virus-induced SnCs was considered as a novel treatment option against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and perhaps other viral infections.

One of the characteristics of SnCs is their ability to resist apoptosis. Until now, small molecules that can selectively kill SnCs, termed senolytics, were developed to target the proteins in the SnC anti-apoptotic pathways (SCAPs). However, due to the high heterogeneity in gene expression and their diverse origins, SnCs may use different SCAPs to maintain their survival, making it difficult to use a single senolytic to kill all types of SnCs. Although significant progresses on the development of senolytics have been made, some proteins involved in the SCAPs have been overlooked, their potential of being senolytic targets have not been investigated. Therefore, gaining more insights into the apoptosis-resistant mechanism of SnCs may greatly help to design or screen more effective senolytics that can be used to treat SnC-associated disorders.

In this review, we discussed the latest research progresses and challenge in senolytic development, described the significance of regulation of senescence and apoptosis in aging, and systematically summarized the SCAPs involved in the apoptotic resistance in SnCs.

Somatic stem cells integrate critical environmental inputs that inform decisions on self-renewal, differentiation, and subsequent tissue turnover. Aging is a risk factor for many diseases, and recent studies are starting to uncover the molecular mechanisms of how environmental factors, such as diet, can influence stem cell behavior over time. With aging, many adult stem cell populations accumulate damage and become impaired in their function, which leads to inefficient tissue repair and may predispose to age-associated diseases such as cancer. Although numerous studies have shown that dietary restriction confers beneficial effects on overall organismal lifespan, we are just starting to uncover the complexities of metabolic dependencies in stem cells and how the availability of specific nutrients are sensed within a heterogeneous population of stem, progenitor, and niche cells and communicated between each other. The advent of new single cell technologies has already begun to enhance our ability to resolve the complex metabolic heterogeneity and interactions that exist in certain niches, such as in the gut crypt and bone marrow.

Recent studies using single cells technologies have also revealed that seemingly uniform, terminally differentiated cells in the liver and intestinal villus have specific transcriptional metabolic profiles that are driving cell function. These differences among hepatocytes and enterocytes were largely influenced by location, proximity to nutrients, and oxygen supply within their respective tissues. In the upcoming years, as multiple single cell -omic technologies advance and integrate, we will begin to see more advanced tissue maps of transcriptional, proteomic, and metabolomic signatures of stem and progenitor cells and their corresponding niches, both under homeostatic conditions as well as during aging and other pathological states. These types of studies will also likely layer dietary patterns with other environmental factors to expand our understanding of how nutrients and systemic metabolism impact tissue homeostasis. Finally, the constant improvement and engineering of primary 3D organoid cultures will allow us to more precisely examine intrinsic and extrinsic age-associated changes, as well as measure the activity of metabolic pathways, in response to defined nutrient conditions. We will be able to incorporate and study other signals in these systems, such as cytokines, hormones, and microbial metabolites. All of these advances will conceivably lead to better strategies and therapies for tissue repair with age, while carefully avoiding interventions that may accelerate age-dependent diseases such as cancer.

With only a few noted exceptions, mitochondria are the main source of cellular energy in eukaryotes. These organelles process dietary reducing equivalents and oxygen through the electron transport chain (ETC) to produce ATP via oxidative phosphorylation (OXPHOS). Mitochondria are involved in other important cellular functions. To varying extents, different cell types rely on these different functions, which, in turn, determines their intracellular localization, dynamics, number, and respiratory flux. As organisms age, these different mitochondrial processes degrade to differing extents and in tissue specific ways. A lingering question in the field of aging biology concerns the source of this dysfunction.

As a consequence of an endosymbiotic event ∼2 billion years ago that gave rise to mitochondria, these organelles have retained a small rudimentary genome that, in animals, is comprised of a circular double-stranded DNA molecule (mtDNA) present in dozens to thousands of copies per cell. The relatively small genome is extremely compact and encodes a total of 37 genes: 22 tRNAs, two mitochondrial ribosomal RNAs, and 13 peptides that comprise essential components of the ETC. As such, proper maintenance of the genetic information is essential for energy production and therefore maintaining cell homeostasis. One long-standing hypothesis in aging research is that the loss of genetic information encoded by the mtDNA is an important driver of aging.

With limited DNA repair capacity and higher replicative index, mtDNA has a substantially higher de novo mutation rate compared to nuclear DNA. The mitochondrial genome is maternally inherited, with most mtDNA within a cell and organism being an exact copy of the original maternal mtDNA pool, a phenomenon known as homoplasmy. However, mtDNA is susceptible to mutations within the germline, which can result in a number of devastating maternally inherited diseases. In addition to causing overt disease, mtDNA mutations can be present at lower levels, a condition known as heteroplasmy. The heteroplasmic allele fraction can range from very low levels to near homoplasmy and can be inherited or occur de novo within somatic tissues during aging and development.

Because of the multi-copy nature of mtDNA, it is estimated that the phenotypic threshold for pathogenic heteroplasmies is ∼60-90% of mitochondrial genomes within a cell. To add more complexity to the condition of heteroplasmy, the occurrence and frequency of mtDNA mutations may have different outcomes depending on the timing of their occurrence, the specific tissue in which they arise, and the total mtDNA content of the cell. Despite decades of study, the complex nature of mitochondrial genetics has made the exact role of somatic mtDNA mutations in aging difficult to discern.

In this review, we focus on the complicated observational and experimental evidence suggesting that, at least in some capacity, somatic mtDNA mutations are involved in the aging process with an emphasis of when, where, and how these mutations arise during aging. Additionally, we highlight current limitations in our knowledge and critically evaluate the controversies stemming from these limitations. Lastly, we highlight new and emerging possibilities that offer potential ways forward to increase our understanding of somatic mtDNA in the aging process.

Aging is a significant risk factor for the development of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Inflammation also plays a role in the development of neurodegenerative diseases. Inflammaging, a low level of chronic inflammation that occurs due to old age, is a normal part of the aging process. It has been shown that the inflammasome contributes to age-related inflammation and development of neurodegenerative diseases. Thus, the inflammasome is a potential therapeutic target to ameliorate inflammaging and to prevent and/or treat neurodegenerative diseases.

In this study, we show the anti-inflammatory effects of anti-ASC, a monoclonal antibody against ASC, in the cortex of aged mice. We found that protein levels of IL-1β, ASC, caspase-1, and NLRP1 were significantly elevated in the cortex of aged mice and that anti-ASC treatment inhibits the protein levels of these inflammasome signaling proteins. ASC speck formation was examined and protein levels of ASC specks were increased in old age and anti-ASC inhibits the formation of ASC specks. Moreover, we investigated the protein levels of the non-canonical inflammasome proteins caspase-8 and caspase-11. We found that caspase-8 was also elevated in the cortex of aged mice and that anti-ASC decreased the protein levels of this protein. However, we did not see any significant differences between young and aged mice in the protein levels of caspase-11.

Together, these results indicate that a novel NLRP1-caspase-8 non-canonical inflammasome is present in the cortex of mice and that anti-ASC is a potential therapeutic to decrease inflammasome-mediated inflammaging in the central nervous system.

In 2016, researchers reported for the first time that they could use the Yamanaka factors to counter the signs of aging and increase life span in mice with a premature aging disease. More recently, the team found that, even in young mice, the Yamanaka factors can accelerate muscle regeneration. Following these initial observations, other scientists have used the same approach to improve the function of other tissues like the heart, brain, and optic nerve, which is involved in vision.

In the new study, researchers tested variations of the cellular rejuvenation approach in healthy animals as they aged. One group of mice received regular doses of the Yamanaka factors from the time they were 15 months old until 22 months, approximately equivalent to age 50 through 70 in humans. Another group was treated from 12 through 22 months, approximately age 35 to 70 in humans. And a third group was treated for just one month at age 25 months, similar to age 80 in humans. "What we really wanted to establish was that using this approach for a longer time span is safe. Indeed, we did not see any negative effects on the health, behavior, or body weight of these animals."

When the researchers looked at normal signs of aging in the animals that had undergone the treatment, they found that the mice, in many ways, resembled younger animals. In both the kidneys and skin, the epigenetics of treated animals more closely resembled epigenetic patterns seen in younger animals. When injured, the skin cells of treated animals had a greater ability to proliferate and were less likely to form permanent scars - older animals usually show less skin cell proliferation and more scarring. Moreover, metabolic molecules in the blood of treated animals did not show normal age-related changes.

This youthfulness was observed in the animals treated for seven or 10 months with the Yamanaka factors, but not the animals treated for just one month. What's more, when the treated animals were analyzed midway through their treatment, the effects were not yet as evident. This suggests that the treatment is not simply pausing aging, but actively turning it backwards - although more research is needed to differentiate between the two.

Induced pluripotent stem cells (iPSCs) reprogrammed from replicative senescing or centennial cells had restored the telomere and mitochondrial functions with a gene expression profile similar to embryonic stem cells (ESCs). This and other avenues of research confirm that cellular age can be reversed. These seminal results led the scientific community to ask whether cellular rejuvenation due to reprogramming could take place in vivo.

To answer this question, researchers generated transgenic mouse models, expressing Yamanaka factors (OSKM) under the control of doxycycline. Strikingly, they observed the emergence of teratomas in several organs, thus demonstrating the feasibility of in vivo reprogramming. However, to prevent deterioration related to aging or to rejuvenate the organism, it is important not to generate fully dedifferentiate cells, as this leads to a deterioration of the animal's health or tumor formation. Consequently, it was judicious to think to trigger the reprogramming process and stop it before obtaining pluripotent cells, hoping that it might erase cellular aging marks instead of favoring senescence. Researchers envisioned such a strategy and proposed a protocol to induce partial reprogramming in a homozygous progeria transgenic mouse model. They induced OSKM expression for 2 days per week during the lives of the animals with doxycycline and observed a significant increase in the lifespan of these animals, as well as the improvements in age-related hallmarks.

The use of strategies based on mRNA to express the factors needed for cell reprogramming has rapidly emerged as a promising technology to achieve the goal of partial reprogramming. Hence, in this review, after a brief revisiting of the state-of-the-art various technologies, we will focus on methods based on RNA that induce the conversion of somatic cells into pluripotent cells. We will frame these technological advances in the context of recent cutting-edge approaches to reverse age-related cell and tissue phenotypes by reprogramming them towards pluripotency.

During development, mammalian stem cells readily proliferate to produce neurons throughout the brain and cells - called glia - that help support them. Glia help maintain optimal brain function by performing essential jobs like cleaning up waste and insulating nerve fibers. However, the mature brain largely loses that stem cell capacity. Only two small regenerative zones, or niches, remain in the adult brain, leaving it with extremely limited capacity to heal itself following injury or disease.

Looking for a way to spur this "multipotent" regeneration, researchers used a genetic engineering technique in adult mouse brains to induce astrocytes, a subset of glia, to produce different transcription factors, proteins pivotal for controlling cell identity. These experiments showed that a single transcription factor - a protein known as DLX2 - appeared to reprogram astrocytes into neural stem-like cells capable of producing neurons and multiple subtypes of glial cells.

The researchers confirmed these findings both using a technique called lineage tracing, in which they followed progeny of the altered astrocytes as they multiplied, as well as marker analysis that showed that these new cells had the expected identities of neurons or glia. Researchers suggest that DLX2 might someday be used as a tool to treat traumatic brain injuries, strokes, and degenerative conditions .

Determinants of length of life are not well understood, and therefore increasing lifespan is a challenge. Cardinal theories of aging suggest that oxidative stress (OxS) and mitochondrial dysfunction contribute to the aging process, but it is unclear if they could also impact lifespan. Glutathione (GSH), the most abundant intracellular antioxidant, protects cells from OxS and is necessary for maintaining mitochondrial health, but GSH levels decline with aging. Based on published human studies where we found that supplementing glycine and N-acetylcysteine (GlyNAC) improved/corrected GSH deficiency, OxS, and mitochondrial dysfunction, we hypothesized that GlyNAC supplementation could increase longevity.

We tested our hypothesis by evaluating the effect of supplementing GlyNAC vs. placebo in C57BL/6J mice on (a) length of life; and (b) age-associated GSH deficiency, OxS, mitochondrial dysfunction, abnormal mitophagy and nutrient-sensing, and genomic damage in the heart, liver, and kidneys. Results showed that mice receiving GlyNAC supplementation (1) lived 24% longer than control mice; (2) improved/corrected impaired GSH synthesis, GSH deficiency, OxS, mitochondrial dysfunction, abnormal mitophagy and nutrient-sensing, and genomic damage. These studies provide proof-of-concept that GlyNAC supplementation can increase lifespan and improve multiple age-associated defects. GlyNAC could be a novel and simple nutritional supplement to improve lifespan and healthspan, and warrants additional investigation.

Obstructive sleep apnea (OSA) affects 22 million people in the U.S. and is linked to a higher risk of hypertension, heart attacks, stroke, diabetes, and many other chronic conditions. Age acceleration testing involves a blood test that analyzes DNA and uses an algorithm to measure a person's biological age. The phenomenon of a person's biological age surpassing their chronological age is called "epigenetic age acceleration", and is linked to overall mortality and to chronic diseases.

Researchers studied 16 adult nonsmokers who were diagnosed with OSA and compared them to eight control subjects without the condition to assess the impact of OSA on epigenetic age acceleration over a one-year period. After a baseline blood test, the OSA group received continuous positive airway pressure (CPAP) treatment for one year before being tested again.

"Our results found that OSA-induced sleep disruptions and lower oxygen levels during sleep promoted faster biological age acceleration compared to the control group. However, the OSA patients who adhered to CPAP showed a deceleration of the epigenetic age, while the age acceleration trends did not change for the control group. Our results suggest that biological age acceleration is at least partially reversible when effective treatment of OSA is implemented."

Yellow-bellied marmots are able to virtually halt the aging process during the seven to eight months they spend hibernating in their underground burrows. The study, the first to analyze the rate of aging among marmots in the wild, shows that this anti-aging phenomenon kicks in once the animals reach 2 years old, their age of sexual maturity. The researchers studied marmot blood samples collected over multiple summer seasons in Colorado, when the animals are active above ground, to build statistical models that allowed them to estimate what occurred during hibernation. They assessed the biological aging of the marmots based on what are known as epigenetic changes - hundreds of chemical modifications that occur to their DNA.

This process, the researchers said, helps explain why the average life span of a yellow-bellied marmot is longer than would be expected from its body weight. Hibernation, an evolutionary adaptation that allows animals to survive in harsh seasonal environments where there is no food and temperatures are very low, is common among smaller mammals, like marmots. The marmots' hibernation alternates between periods of metabolic suppression that last a week or two and shorter periods of increased metabolism, which generally last less than a day. During metabolic suppression, their breathing slows and their body temperature drops dramatically.

All of these hibernation-related conditions - diminished food consumption, low body temperature and reduced metabolism - are known to counter the aging process and promote longevity. This delayed aging is likely to occur in other mammals that hibernate, because the molecular and physiological changes are similar.

Microglia-mediated neuroinflammation is a common feature shared by various neurodegenerative diseases. Neuroinflammatory includes microglial activation, and microglia could polarize into either M1 pro-inflammatory phenotype or M2 anti-inflammatory phenotype in response to different micro-environmental disturbances, which are called classical activation and alternative activation, respectively. M1 microglia release inflammatory cytokines and chemokines, resulting in inflammation and neuronal death. However, tissue maintenance and repair are associated with alternative activation of M2 microglia. M1 microglia induce inflammation and neurotoxicity, while M2 microglia induce anti-inflammatory and neuroprotection, both of which are involved in the pathogenesis of neurodegenerative diseases, therefore microglia act as a double-edged sword in neurodegenerative diseases.

It's impossible to repair or regenerate damaged neurons by current drugs nowadays once neurodegenerative diseases occur or even before the onset of diseases, but current drugs could alleviate disease-related symptoms by restricting the extent of neuroinflammation. Fortunately, the balance between microglia M1/M2 polarization has a promising therapeutic prospect in the pathogenesis of neurodegenerative diseases. However, previous studies have shown that several M1 inhibitive agents are unhelpful.

As inhibiting M1 microglia alone is not enough, promoting M2 microglia activation simultaneously might also be required for treating neurodegenerative diseases. Promoting microglia polarization shift from M1 to M2 phenotype may be a more prospective strategy in the therapy of neurodegenerative diseases. Activated microglia is also a double-edged sword in other central nervous system diseases such as ischemic stroke, spinal cord injury, and traumatic brain injury. There have been many studies about modulation of microglia polarization from M1 to M2 in these diseases, which may provide many interesting ideas in neurodegenerative diseases.

The study followed 51 older adults, tracking their physical activity and fitness measurements. The participants performed tests specifically designed to measure cognitive functioning and underwent MRIs to assess brain functioning. They also wore a device that measured the intensity of the wearer's physical activity, number of steps taken and distance covered. The researchers assessed fitness through a six-minute walking test, during which participants walked as quickly as they could to cover the most distance possible within the time limit.

The brain is made up of a bunch of distinct networks. Different parts of the brain are active at different times. While one of these networks is active, the other should be shut off. If it's not, that's a sign that a person's brain isn't functioning as well as it should be. These networks are the key to being able to perform basic tasks in daily life, such as remembering important information and exhibiting self-control. But as people age, these tasks often become more difficult. This study was the first to examine how these networks interact with physical activity and fitness to impact how the brain functions.

"This paper is exciting because it gives us some evidence that when people whose brain networks aren't functioning optimally engage in physical activity, we see improvement in their executive function and their independence. Maybe just take the stairs on the way to work. Stand up and walk around a little bit more. That's where you get the most bang for your buck, not crazy, high-intensity exercise."

Investigators recruited 4,066 volunteers to supply blood and stool samples and facial skin images and to undergo physical fitness examinations. The volunteers were between the ages of 20 and 45 years; 52% were female and 48% were male. "Most human aging studies have been conducted on older populations and in cohorts with a high incidence of chronic diseases. Because the aging process in young healthy adults is largely unknown and some studies have suggested that age-related changes could be detected in people as young as their 20s, we decided to focus on this age range."

In total, 403 features were measured, including 74 metabolomic features, 34 clinical biochemistry features, 36 immune repertoire features, 15 body composition features, 8 physical fitness features, 10 electroencephalography features, 16 facial skin features, and 210 gut microbiome features. These features were then classified into nine categories, including cardiovascular-related, renal-related, liver-related, sex hormone, facial skin, nutrition/metabolism, immune-related, physical fitness-related, and gut microbiome features.

Because of the difference in sex-specific effects, the groups were divided into male and female. The investigators then developed an aging-rate index that could be used to correlate different bodily systems with each other. Based on their findings, they classified the volunteers either as aging faster or aging slower than their chronological age. Overall, they discovered that biological ages of different organs and systems had diverse correlations, and not all were expected. Although healthy weight and high physical fitness levels were expected to have a positive impact, the investigators were surprised by other findings. For example, having a more diverse gut microbiota indicated a younger gut while at the same time having a negative impact on the aging of the kidneys, possibly because the diversity of species causes the kidneys to do more work.