Fight Aging! Newsletter, June 1st 2020

Androgenetic alopecia (AGA) - commonly known as male-pattern baldness (female-pattern baldness in women) -- is a condition caused by genetic, hormonal, and environmental factors. It affects an estimated 50 percent of all men and almost as many women older than 50. Adipose tissue-derived stem cells (ADSCs) secrete several growth hormones that help cells develop and proliferate. According to laboratory and experimental studies, growth factors such as hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF) and platelet-derived growth factor (PDGF) increase the size of the hair follicle during hair development.

The team recruited 38 patients (29 men and nine women) with AGA and assigned half to an intervention group that received the stem cell constituent extract (ADSC-CE) topical solution and half as a control group that received a placebo. Twice daily, each patient applied the ADSC-CE topical solution or placebo to their scalp using their fingers. "At the end of 16 weeks, the group that received the ADSC-CEs had a significant increase in both hair count and follicle diameter. Our findings suggest that the application of the ADSC-CE topical solution has enormous potential as an alternative therapeutic strategy for hair regrowth in patients with AGA, by increasing both hair density and thickness while maintaining adequate treatment safety. The next step should be to conduct similar studies with large and diverse populations in order to confirm the beneficial effects of ADSC-CE on hair growth and elucidate the mechanisms responsible for the action of ADSC-CE in humans."

Accumulating evidence suggests that adipose-derived stem cell constituent extract (ADSC-CE) helps hair regrowth in patients with androgenetic alopecia (AGA). However, the effects of ADSC-CE have not been demonstrated in a randomized, double-blind, vehicle-controlled clinical trial. In this randomized, double-blind, vehicle-controlled clinical trial, 38 patients (29 men) with AGA were assigned to an intervention group (IG), with twice-daily self-application of the ADSC-CE topical solution over the scalp with fingers, or to a control group (CG). Changes in hair count and thickness from the baseline at 16 weeks were evaluated using a phototrichogram.

Overall, 34 (89%) patients (mean age, 45.3 years) completed the study. The phototrichogram at week 8 showed more increase in hair count in the IG than in the CG, and intergroup differences in the change of hair count remained significant until week 16 with overall changes of 28.1% vs 7.1%, respectively. Similarly, a significant improvement in hair diameter was observed in the IG (14.2%) after 16 weeks when compared with hair diameter in the CG (6.3%). Our findings suggest that the application of the ADSC-CE topical solution has enormous potential as an alternative therapeutic strategy for hair regrowth in patients with AGA, by increasing both hair density and thickness while maintaining adequate treatment safety.

Senescent cells produce proinflammatory and matrix-degrading molecules, which harm their surrounding nonsenescent cells. Senotherapy targeting for senescent cells is designed to attenuate age-related dysfunction and promote healthy aging and the removal of senescent cells by direct killing, either by apoptotic (senoptosis) or nonapoptotic (senolysis) methods, is an effective serotherapeutic approach. In the genetic model, INK-ATTAC mice, to undergo the inducible elimination of p16Ink4a-expressing cells, these mice in which p16Ink4a-positive senescent cells were eliminated exhibited a long life span and the attenuation of several aging phenotypes in white adipose tissue, the heart, and the kidney.

Senescent cells accumulate in fat in aging, and exercise-mediated reduction as well as genetic clearance improved glucose metabolism or lipotoxicity, respectively. Senescent T cells (referred to as senescence-associated T cells; SA-T cells), defined as CD4+ CD44high CD62Llow PD-1+ CD153+ cells, accumulate in visceral adipose tissues (VAT) in obese individuals and produce proinflammatory cytokines, causing chronic inflammation, metabolic disorders, and cardiovascular diseases. However, it is still unknown whether the selective depletion of senescent T cells can attenuate the age-related pathological changes.

Here, we show the long-lasting effect of using CD153 vaccination to remove senescent T cells from high-fat diet (HFD)-induced obese C57BL/6J mice. We administered a CD153 peptide-KLH (keyhole limpet hemocyanin) conjugate vaccine with and confirmed an increase in anti-CD153 antibody levels that was sustained for several months. After being fed a HFD for 10-11 weeks, adipose senescent T cell accumulation was significantly reduced in the VAT of vaccinated mice, accompanied by improved glucose tolerance and insulin resistance. A complement-dependent cytotoxicity (CDC) assay indicated that the mouse IgG2 antibody produced in the vaccinated mice successfully reduced the number of senescent T cells.

Throughout the lifespan, microglia, the primary innate immune cells of the brain, fulfill a plethora of homeostatic as well as active immune defense functions, and their aging-induced dysfunctionality is now considered as a key trigger of aging-related brain disorders. Recent evidence suggests that both organism's sex and age critically impact the functional state of microglia but in vivo determinants of such states remain unclear. Therefore, we analyzed in vivo the sex-specific functional states of microglia in young adult, middle aged and old wild type mice by means of multicolor two-photon imaging, using the microglial Ca2+ signaling and directed process motility as main readouts.

Our data revealed the sex-specific differences in microglial Ca2+ signaling at all ages tested, beginning with young adults. Furthermore, for both sexes it showed that during the lifespan the functional state of microglia changes at least twice. Already at middle age the cells are found in the reactive or immune alerted state, characterized by heightened Ca2+ signaling but normal process motility whereas old mice harbor senescent microglia with decreased Ca2+ signaling, and faster but disorganized directed movement of microglial processes.

The 6-12 months long caloric restriction (70% of ad libitum food intake) counteracted these aging-induced changes shifting many but not all functional properties of microglia toward a younger phenotype. The improvement of Ca2+ signaling was more pronounced in males. Importantly, even short-term (6-week-long) caloric restriction beginning at old age strongly improved microglial process motility and induced a significant albeit weaker improvement of microglial Ca2+ signaling. Together, these data provide first sex-specific in vivo characterization of functional properties of microglia along the lifespan and identify caloric restriction as a potent, cost-effective, and clinically relevant tool for rejuvenation of microglia.

When a cell reaches the end of its life or becomes damaged beyond repair it normally either kills itself or signals the immune system to remove it. Unfortunately, every so often this mechanism fails. The cell stays around indefinitely and starts poisoning its environment. Over time, more and more of these harmful, death resistant, senescent cells accumulate. Senescent cells are thought to be one of the main drivers of aging and age-related diseases.

Senolytics are drugs that selectively remove senescent cells by disabling the mechanisms that allow them to survive. Dasatinib (D), a well-established medication used in the treatment of cancer and quercetin (Q), a flavonoid common in plants were among the first senolytics to be discovered. As they have been shown to affect different types of senescent cells, they are often employed in combination.

Studies in rodents have shown that clearing senescent cells can prevent, delay, or alleviate multiple age-related diseases and extend the healthy lifespan by up to 35%. Based on the promising results in animal testing, it is supposed that intermittent dosing of D+Q also leads to the elimination of senescent cells in humans with the accompanying health and rejuvenation benefits. As the first clinical trials in humans have been completed and interest in the practical application of D+Q is increasing, Forever Healthy seeks to assess the risks, benefits, and therapeutic protocols of using D+Q as a senolytic therapy.

Currently, there are only results from 3 trials in humans in which D+Q was evaluated as a senolytic therapy. The majority of human studies used D or Q in cancer therapy and provided information on side effects and safety. The benefits shown in animals were significant and were observed in many organ systems. However, several of the benefits only occurred in diseased animals (i.e. diabetic mice), while the healthy control group did not benefit from the treatment.

The benefits reported in human studies are mainly focussed on senescent cell markers. So far, these markers are only hypothesized to translate to clinically meaningful effects. Few benefits had direct clinical relevance, and those were not really convincing. Additionally, 2 out of the 3 clinical studies were in patients with pre-existing disease so there is very limited information on the effect in healthy individuals. The potential risks of D are extensive and well-known through its use in the treatment of cancer. While the clinical trials that used D+Q as a senolytic therapy reported only mild to moderate adverse events, it is of note that the low number of participants in these studies might not deliver a representative result.

Furthermore, the human studies all used different treatment protocols and there is no consensus on the measurement of efficacy in clinical practice. Therefore, until there are more studies showing benefits in humans, a clearer picture of the senolytic-use specific risk profile, and a consensus on a treatment protocol, it seems prudent to avoid the use of D+Q as a senolytic therapy.

Our T cells let us down as we age, becoming weaker pathogen fighters. This decline helps explain why elderly people are more susceptible to infections and less responsive to vaccines. One reason T cells falter as we get older is that mitochondria, the structures that serve as power plants inside cells, begin to malfunction. But T cells might not just reflect aging. They could also promote it. Older people have chronic inflammation throughout the body, known as inflammaging, and researchers have proposed it spurs aging. T cells may stoke this process because they release inflammation-stimulating molecules.

To test that hypothesis, researchers genetically modified mice to lack the TFAM protein in the mitochondria of their T cells. This alteration forces the cells to switch to a less efficient metabolic mechanism for obtaining energy. By the time the rodents were 7 months old, typically the prime of life for a mouse, they already appeared to be in their dotage. Compared with typical mice, the modified rodents were slow and sluggish. They had shrunken, weak muscles, and were less resistant to infections. Like many elderly people, they suffered from weakened hearts and shed much of their body fat. T cells from the altered mice poured out molecules that trigger inflammation, the team found, suggesting the cells could be partially responsible for the animals' physical deterioration.

The scientists also tested whether they could slow the aging clock. First they dosed the mice with a drug that blocks tumour necrosis factor alpha (TNF-alpha), one of the inflammation-inducing molecules that T cells unleash; the treatment increased the animals' grip strength, improved their performance in a maze, and boosted the heart's pumping power. The researchers also gave the animals a compound that raises levels of nicotinamide adenine dinucleotide (NAD), a molecule that's vital for metabolic reactions that enable cells to extract energy from food. NAD's cellular concentrations typically decline with age, and the researchers found that ramping it up in the mice made them more active and strengthened their hearts.

The impact of immunometabolism on age-associated diseases remains uncertain. Here, we show that T cells with dysfunctional mitochondria due to mitochondrial transcription factor A (TFAM) deficiency act as accelerators of senescence. In mice, these cells instigate multiple aging-related features, including metabolic, cognitive, physical, and cardiovascular alterations, which together result in premature death. T cell metabolic failure induces the accumulation of circulating cytokines, which resembles chronic inflammation characteristic of aging ("inflammaging"). This cytokine storm itself acts as a systemic inducer of senescence. Blocking TNF-α signaling or preventing senescence with NAD+ precursors partially rescues premature aging in mice with Tfam-deficient T cells. Thus, T cells can regulate organismal fitness and lifespan, highlighting the importance of tight immunometabolic control in both aging and the onset of age-associated diseases.

There are several members of the HDAC family of enzymes, and their primary function is to modify histones - proteins around which DNA is spooled. These modifications control gene expression by blocking genes in certain stretches of DNA from being copied into RNA. In 2013, researchers linked HDAC1 to DNA repair in neurons. In the current paper, the researchers explored what happens when HDAC1-mediated repair fails to occur. To do that, they engineered mice in which they could knock out HDAC1 specifically in neurons and another type of brain cells called astrocytes.

For the first several months of the mice's lives, there were no discernable differences in their DNA damage levels or behavior, compared to normal mice. However, as the mice aged, differences became more apparent. DNA damage began to accumulate in the HDAC1-deficient mice, and they also lost some of their ability to modulate synaptic plasticity - changes in the strength of the connections between neurons. The older mice lacking HCAC1 also showed impairments in tests of memory and spatial navigation.

The researchers found that HDAC1 loss led to a specific type of DNA damage called 8-oxo-guanine lesions, which are a signature of oxidative DNA damage. Studies of Alzheimer's patients have also shown high levels of this type of DNA damage, which is often caused by accumulation of harmful metabolic byproducts. The brain's ability to clear these byproducts often diminishes with age. An enzyme called OGG1 is responsible for repairing this type of oxidative DNA damage, and the researchers found that HDAC1 is needed to activate OGG1. When HDAC1 is missing, OGG1 fails to turn on and DNA damage goes unrepaired. Many of the genes that the researchers found to be most susceptible to this type of damage encode ion channels, which are critical for the function of synapses.

Several years ago, researchers screened libraries of small molecules in search of potential drug compounds that activate or inhibit members of the HDAC family. In the new paper, researchers used one of these drugs, called exifone, to see if they could reverse the age-related DNA damage they saw in mice lacking HDAC1. The researchers used exifone to treat two different mouse models of Alzheimer's, as well as healthy older mice. In all cases, they found that the drug reduced the levels of oxidative DNA damage in the brain and improved the mice's cognitive functions, including memory. Exifone was approved in the 1980s in Europe to treat dementia but was later taken off the market because it caused liver damage in some patients. Researchers are optimistic that other, safer HDAC1-activating drugs could be worth pursuing as potential treatments for both age-related cognitive decline and Alzheimer's disease.

Ageism is a reality in western societies and current views of older people are too often tinged with false beliefs and prejudices. Public authorities often consider older adults to be a burden rather than an integral segment of the population whose members must be supported. Older adults are rarely given a voice and are seldom considered when making decisions. The media has a considerable role in the propagation of ageist stereotypes and negative attitudes towards older adults, particularly in times of crisis when age is not a relevant factor. The COVID-19 pandemic has accentuated the exclusion of and prejudice against older adults. The current crisis highlights a disturbing public discourse about aging that questions the value of older adults' lives and disregards their valuable contributions to society.

Even though COVID-19 mortality rates are higher in older adults compared to other age groups, our concern is that age is being conflated with frailty and co-morbidity, which are likely to be the more important factors associated with mortality. Social media highlights older adults who sacrifice their own lives so that ventilators can be used for someone younger. When medical equipment, and hospital capacity becomes scarce, care providers may be faced with the ethical decisions about whose life takes priority and age may become a deciding factor. The United States have formally adopted the Ventilator Allocation Guidelines whereby "age may be considered as a tie-breaking criterion in limited circumstances". This may lead people to believe that an older person's life may be less valuable than that of someone younger. What will be the cost to society of the sacrificed lives of older adults?

As concerned advocates and researchers interested in aging, it is our opinion that we should be aware of and try to reduce the ageist views being propagated during COVID-19. Higher mortality rates for any group, including older adults, have devastating consequences. It's not just the preventable loss of human lives or strain being placed on our healthcare and social systems, older adults are invaluable members of society. They are a source of generational knowledge and wisdom, they contribute to the workforce in increasing numbers, they volunteer and they are key to the strength of our economies and our families. We cannot afford to be careless about these lost lives because of ageist attitudes. We need to consider what we stand to lose if we let ageism influence how we discuss and treat older adults during and after the COVID-19 pandemic.

One important question in aging research is how differences in genomics and transcriptomics determine the maximum lifespan in various species. Despite recent progress, much is still unclear on the topic, partly due to the lack of samples in non-model organisms and due to challenges in direct comparisons of transcriptomes from different species. The novel ranking-based method that we employ here is used to analyze gene expression in the gray whale and compare its de novo assembled transcriptome with that of other long- and short-lived mammals.

Gray whales are among the top 1% longest-lived mammals. Despite the extreme environment, or maybe due to a remarkable adaptation to its habitat (intermittent hypoxia, Arctic water, and high pressure), gray whales reach at least the age of 77 years. In this work, we show that long-lived mammals share common gene expression patterns between themselves, including high expression of DNA maintenance and repair, ubiquitination, apoptosis, and immune responses. Additionally, the level of expression for gray whale orthologs of pro- and anti-longevity genes found in model organisms is in support of their alleged role and direction in lifespan determination. Remarkably, among highly expressed pro-longevity genes many are stress-related, reflecting an adaptation to extreme environmental conditions.

The conducted analysis suggests that the gray whale potentially possesses high resistance to cancer and stress, at least in part ensuring its longevity. This new transcriptome assembly also provides important resources to support the efforts of maintaining the endangered population of gray whales.

The aging organism develops a chronic state of initially smoldering and then progressively overt inflammation that contributes to the aging process and thus has been nicknamed "inflammaging". A recent paper reveals that purified CD4+ T lymphocytes from healthy, lean, older (57-68 years) donors produce more TH17-associated/supportive cytokines (IL-6, IL-17A, IL-17F, IL-21, and IL-23) than cells from younger (28-38 years) subjects - a TH17-linked cytokine hyperproducer phenotype (TH17-CHP).

The overarching cause of TH17-CHP appears to be reduced autophagy of mitochondria, which compromises mitochondrial turnover and quality control, as indicated by an increase in mitochondrial mass, an increase in the proton leak, and a reduction in the mitochondrial inner transmembrane potential. In addition, mitochondria contained in CD4+ T cells from older donors exhibited an enhanced basic and maximal oxygen consumption, correlating with reduced glycolytic lactate production, enhanced production of reactive oxygen species (ROS). Conversely, knockdown of the essential autophagy gene ATG3 (but not that of PINK1, a gene specifically involved in mitophagy) inhibited autophagy in CD4+ T cells from younger subjects, inducing TH17-CHP similar to the one spontaneously found in CD4+ T cells from older donors.

Altogether, these results have important conceptual and clinical implications at several levels. They suggest yet another causal link between "normal" aging and deficient autophagy involving a vicious cycle in which aging causes an autophagy defect that then aggravates the aging phenotype. Here, it appears that aging compromises autophagy in CD4+ T lymphocytes to stimulate the secretion of several pro-inflammatory interleukins, thus contributing to inflammaging. However, it remains to be determined in preclinical experiments, in mouse models, whether a selective autophagy (or mitophagy) defect solely affecting CD4+ cells would be sufficient to cause TH17-CHP in vivo and accelerate the aging process. As it stands, it appears that autophagy has rather broad anti-inflammatory effects, notably by avoiding the spill of mitochondrial or nuclear DNA into the cytoplasm (to avoid activation of the cGAS/STING pathway) or by inhibiting excessive activation of the NLRP3 inflammasome.

With advancing age, osteoclast-induced bone resorption outpaces osteoblast-induced bone deposition, leading to a gradual loss of bone mass. The use of therapeutic agents that inhibit osteoclast activity and differentiation has been proposed as a strategy to prevent osteoporosis and other bone-related diseases. Osteoclast differentiation is induced by macrophage-colony stimulating factor (M-CSF), receptor activator of nuclear factor (NF)-κB ligand (RANKL), and osteoprotegerin. These cytokines are involved in signaling pathways that balance the activities of osteoblasts and osteoclasts to maintain bone mass homeostasis. The monoclonal antibody denosumab is the only RANKL inhibitor currently approved by the FDA, and has been reported to reduce bone turnover and increase bone mineral density (BMD).

Given that plasma proteins include aging-related factors, we hypothesized that aging would dynamically alter the plasma levels of proteins involved in age-related bone loss. We used a proteomic approach to identify plasma proteins that were differentially expressed between young and old mice, and investigated their effects on osteoclasts and osteoblasts. We focused on Cadherin-13 (CDH-13), examining its impact on osteoclast differentiation and bone resorption. Finally, we tested whether intraperitoneal administration of CDH-13 could prevent age-related bone loss in mice.

Our results demonstrated that CDH-13 inhibits osteoclast differentiation by blocking RANKL signaling. Although the underlying molecular mechanisms remain to be elucidated, we speculate that plasma CDH-13 may function as a decoy receptor of RANKL or as a RANK receptor antagonist. We also found that CDH-13 was enriched in the blood of young mice and helped to preserve bone mass by inhibiting RANKL-induced osteoclast differentiation. Multiple circulating factors regulate bone mass. Our results suggested that CDH-13 is an age-related bone factor, and that lower levels of CDH-13 disrupt the balance of bone remodeling and promote age-related bone loss. Since the inhibition of RANKL has long been recognized as a therapeutic strategy for osteoporosis, our findings suggest that CDH-13 could be used as a novel therapeutic molecule to inhibit bone loss.

Somatic chromosomal mosaicism is the presence of cell populations differing with respect to the chromosome complements (e.g. normal and abnormal) in an individual. Chromosomal mosaicism is associated with a wide spectrum of disease conditions and aging. This type of intercellular genomic variations is commonly associated with a wide spectrum of genetic diseases ranging from chromosomal syndromes to complex disorders, but dynamic changes of mosaicism rates produced by the accumulation of somatic mutations (i.e. aneuploidy) seem to be an important cytogenetic mechanism for human aging.

Cytogenetic and cytogenomic studies of normal and pathological aging consistently demonstrate an increase in rates of chromosomal mosaicism and instability in relation to age. After age 60, older ages have been associated with higher rates of chromosomal mosaicism and instability. Thus, this data allows us to hypothesize that external inhibition of age-dependent chromosome instability and a decrease of somatic chromosomal mosaicism rates might be an opportunity for anti-aging therapeutic interventions.

Furthermore, somatic cancer-associated mutations commonly occur in aged human tissues of presumably healthy individuals. It is not surprising inasmuch as chromosomal mosaicism and instabilities are risk factors for cancers. In general, aging-related diseases are commonly mediated by chromosomal instability and/or mosaic aneuploidy. The results of molecular genetic studies of aging correlate with observations on mutation load contribution to limiting or shortening the lifespan. Additionally, there is evidence that inhibiting chromosome instability might underlie successful anti-aging strategies. Thus, genetic instability at chromosomal level involved in human aging and/or lifespan shortening is an intriguing target for lifespan-extension and anti-aging interventions.

Although various studies have identified physical activity as a possible primary preventive protective factor for brain health, the mechanisms by which physical activity affect cognitive function are not fully understood. Until recently, it was thought that physical activity was beneficial to brain health by means of reducing the impact of known risk factors, such as cardiovascular and cerebrovascular disease, stroke, or diabetes. However, there is a growing body of literature from human and animal studies that indicates that the benefits may be more direct, involving the promotion of synaptogenesis, neuroplasticity, and growth and survival of neurons, as well as the reduction of inflammation and stress.

The field of cognitive aging is constantly seeking more reliable biomarkers that accurately reflect the brain's functioning. Functional connectivity (FC) is one factor that has been reported to be affected by the aging process. It is thought to reflect typical cognitive changes in aging. Previous literature has documented disruptions in major large-scale networks during aging in the absence of disease; however, these findings have focused mostly on the default mode network (DMN) and its connections to other regions.

In the present study, we examined the longitudinal relationship between FC and self-reported changes in physical activity in community-dwelling older adults. Given that the DMN, the frontal-parietal network (FPN, also known as the central executive network), and the subcortical network (SN) are widely-examined networks that are associated with abilities such as introspection, executive function, and motor function, respectively, we focused our preliminary investigations on connectivity within these three networks.

We found that specific within-person increases in physical activity may track closely with FC. Importantly, there appears to be specificity regarding the regionality of this effect. Our findings suggest that within-person increases in physical activity are specifically associated with greater frontal-subcortical and within-subcortical network synchrony. Increased FC in these networks may further support the positive effect of physical activity on brain health markers.

Scientists have collected plenty of evidence linking exercise to brain health, with some research suggesting fitness may even improve memory. But what happens during exercise to trigger these benefits? New research that mapped brain changes after one year of aerobic workouts has uncovered a potentially critical process: Exercise boosts blood flow into two key regions of the brain associated with memory. Notably, the study showed this blood flow can help even older people with memory issues improve cognition, a finding that scientists say could guide future Alzheimer's disease research.

The study documented changes in long-term memory and cerebral blood flow in 30 participants, each of them 60 or older with memory problems. Half of them underwent 12 months of aerobic exercise training; the rest did only stretching. The exercise group showed a 47 percent improvement in some memory scores after one year compared with minimal change in the stretch participants. Brain imaging of the exercise group, taken while they were at rest at the beginning and end of the study, showed increased blood flow into the anterior cingulate cortex and the hippocampus - neural regions that play important roles in memory function.

Evidence is mounting that exercise could at least play a small role in delaying or reducing the risk of Alzheimer's disease. For example, a 2018 study showed that people with lower fitness levels experienced faster deterioration of vital nerve fibers in the brain called white matter. A study published last year showed exercise correlated with slower deterioration of the hippocampus. "Cerebral blood flow is a part of the puzzle, and we need to continue piecing it together. But we've seen enough data to know that starting a fitness program can have lifelong benefits for our brains as well as our hearts."

Dwarf mice were found to have functionally altered adipose tissues. Generally, three types of adipose tissue are found in mammals: white, brown, and beige. White adipose tissue (WAT) is considered the body's energy storage for times of energy scarcity while brown adipose tissue (BAT) is a unique, major energy consuming, heat producing organ. This highly thermogenic BAT, found commonly in small sized mammals and juveniles of larger-bodied mammals including humans, is very important for physiology in general and metabolic homeostasis in particular. It not only maintains endothermy but also is crucial for many physiological processes relating to decreased metabolic rate. Lastly, beige adipose is originally derived from WAT precursors but has properties more similar to BAT.

For decades, both WAT and BAT were largely excluded from evolutionary and developmental research in cell and tissue biology. Due to the common notion that adipose tissue was mainly assigned a passive role for lipid storage, insulation, and mechanical buffering it was considered a large source of unwanted biological variance due to individual feeding status and other environmental factors driving the extent and composition of WAT and BAT. More recently, WAT has been recognized as a major endocrine organ, and as such, the interest in adipose tissues has increased dramatically.

Interestingly, there seem to be peculiarities in WAT localization in homozygous long-lived Ames dwarf (AD) mice compared to normal sized, heterozygous controls. The potential differences in WAT depots compared to other laboratory mice became most visible when AD were exposed to a high fat diet containing 60% fat. Diet-induced obesity in AD seemingly did not lead to expected metabolic derangements which clearly developed in littermate controls, despite significant increases in the amount of their subcutaneous and visceral depots. Instead, "obese" AD mice remained insulin sensitive and showed normal levels of adiponectin. The adipokine adiponectin, acts as an important anti-inflammatory factor and usually correlates positively with the retention of insulin sensitivity.

We thus hypothesize here that growth hormone deficient, genetically dwarf mice, such as Ames dwarf and Snell dwarf, have a metabolic advantage when kept on high-fat diets through the storing of triglycerides preferentially in subcutaneous depots as opposed to evoking depots around the visceral organs like many common laboratory mouse models. This is important as visceral WAT is primarily associated with metabolic complications such as insulin resistance, increased inflammation, and even cancer, which have detrimental effects on tissue health and metabolism. To date, no adverse metabolic effects are described from expansion of subcutaneous WAT. Rather subcutaneous WAT has been assigned metabolic beneficial roles through its browning ability.

Nicotinamide adenine dinucleotide (NAD) is a vital metabolic redox co-enzyme found in eukaryotic cells and is necessary for over 500 enzymatic reactions. It plays a crucial role in various biological processes, including metabolism, aging, cell death, DNA repair, and gene expression. The deficiency of NAD+ is closely associated with diverse pathophysiologies, including type 2 diabetes (T2D), obesity, heart failure, Alzheimer's disease (AD), and cerebral ischemia. The NAD+ levels decline in multiple organs with age, and this contributes to the development of various age-related diseases. Therefore, NAD+ supplementation could be an effective therapy for the treatment of the conditions mentioned above.

Nicotinamide mononucleotide (NMN) is one of the intermediates in NAD+ biosynthesis. In mammalian cells, NAD+ is synthetized, predominantly through NMN, to replenish the consumption by NADase participating in physiologic processes including DNA repair, metabolism, and cell death. Recent preclinical studies have demonstrated that the administration of NMN could compensate for the deficiency of NAD+, and NMN supplementation was able to effect diverse pharmacological activities in various diseases.

Given that NMN has shown high efficacy and benefits in various mouse models of human disease, several clinical trials of NMN have been conducted to investigate its clinical applicability. This has led to some capsule formulations of NMN being approved and put on the market as health supplements. The first phase I human clinical study for NMN is to examine the safety and bioavailability of NMN in human bodies. Recently, it was reported that a single oral administration of NMN up to 500 mg was safe and effectively metabolized in healthy subjects without causing severe adverse events. The major final metabolites of NMN were significantly increased in a dose-dependent manner by NMN administration.

A phase II study is also underway to assess the safety of long-term NMN in healthy subjects, the kinetics of NMN and metabolites of NAM, and the effect of daily administration of NMN on glucose metabolism. Other clinical trials of NMN are ongoing to examine the effect of NMN on insulin sensitivity, endothelial function, blood lipids, body fat and liver fat, and fat tissue and muscle tissue markers of cardiovascular and metabolic health. Additionally, a study has been initiated to evaluate the effect of long-term oral administration of NMN on various hormones in healthy volunteers. Recently, a new clinical study was initiated to evaluate the effect of NMN oral administration on the body composition in elderly persons.

In summary, despite the tremendous research efforts aimed at exploiting the therapeutic potential of NMN to treat metabolic and aging-related diseases, the clinical and toxicological evidence to support its utility is currently insufficient. Thus, further research is needed to increase the prospects of developing drugs based on NMN.