Fight Aging! Newsletter, January 9th 2023

Microglia are central nervous system macrophages, specialized in the phagocytosis (i.e., engulfment and degradation) of bacteria, synapses, neurons, debris, and aggregated proteins. Microglia can phagocytose synapses during development, neuropathology, and aging, and microglia can also phagocytose dendrites, axons, and intact neurons. Microglial phagocytosis of neuronal structures is mediated by eat-me signals, opsonins, and phagocytic receptors. Interestingly, it has been shown that genetic knockout of the opsonin C3 reduced aging-induced loss of hippocampal synapses, neurons, and memory; and similarly, knockout of the phagocytic receptor TREM2 reduced aging-induced hippocampal synaptic and neuronal loss in mice. Thus, one may hypothesize that the neuroinflammation accompanying aging drives microglial phagocytosis of synapses, resulting in memory impairment and brain atrophy. Microglial biology changes with age, including upregulated expression of phagocytic receptors and opsonins, potentially resulting in excessive phagocytosis of the aging brain.

The P2Y6 receptor (P2Y6R, expressed from the P2ry6 gene) is a microglial receptor that mediates microglial phagocytosis of neurons. P2Y6R is expressed by multiple cell types in the body, but within the brain is almost exclusively expressed by microglia. Damaged or stressed neurons release the nucleotide UTP, which is rapidly degraded into UDP by extracellular nucleotide-degrading enzymes, and localized UDP then activates the P2Y6R on microglia to engulf such neurons. We have shown that activating P2Y6R causes microglia to engulf live neurons, and P2Y6R deficiency prevents lipopolysaccharide (LPS)-induced microglial phagocytosis of neurons both in vitro and in vivo. Moreover, P2Y6R knockout mice were also resistant to memory loss induced by beta-amyloid and extracellular tau. These previous studies lead us to ask whether (i) P2Y6R mediates microglial phagocytosis of synapses, and (ii) the synaptic and memory loss induced by natural aging of mice was also mediated by P2Y6R.

We found that aging wild-type mice to 17 months of age resulted in synapse and memory loss, whereas P2Y6R knockout mice had preserved memory. Microglia from 17-month-old wild-type mice had an age-associated increase in the internalization of synaptic material, but no such increase was observed in microglia from 17-month-old knockout mice. Moreover, we show here that inactivation of P2Y6R decreases microglial phagocytosis of isolated synapses (synaptosomes) and synaptic loss in neuronal-glial co-cultures. These findings are significant as they support the hypothesis that microglial phagocytosis of synapses contributes to aging-induced memory loss, and, more specifically, that inhibition of the P2Y6R may prevent this memory loss.

From our earliest days, SENS Research Foundation has funded allotopic expression (AE) work in outside labs and had our in-house MitoSENS scientists laser-focused on the core biotechnology required to achieve all of that in cells. That's a sufficiently challenging and underinvested area of rejuvenation biotechnology to make it one of the best ways to get a healthy longevity bang for our donors' bucks. But once our and other scientists have developed allotopic constructs for all thirteen of the genes encoded in the mitochondrial DNA that work perfectly, we still need to get it into our cells to make it work! So your question is: how will we do that?

The first thing to point out is that the sheer scale of the problem isn't nearly as intimidating as the question assumes. Yes, there are some 30-37 trillion cells in the human body - but not all cells are high-priority targets for AE, and we can ignore a few cell types entirely. Most notably, red blood cells alone account for some 84% of all the cells in the human body, and they (uniquely) don't even contain mitochondria! With nothing there, there's nothing to break - or to fix.

But all right: every other cell in the body has mitochondria. However, although mitochondrial DNA can suffer mutations in any cell that bears mitochondria, only a tiny fraction of such mutations cause problems that meaningfully impact the rate of aging or impair our health. Where MitoSENS is badly needed is to supply a backup system in cell types that last for decades and don't divide - cells like brain neurons, heart muscle cells, and skeletal muscle fiber segments. The cells of interest are a small fraction of postmitotic cells in which the entire cell is overtaken by mitochondria that all bear the same single large deletion. This problem is even more prominent in Alzheimer's disease and Parkinson's disease, as well as in aging muscle and other particular diseases and disabilities of aging. And this takeover not only isn't constrained by the cell's mitophagy quality control machinery: perversely, it seems to be driven by it. It's for these cells that a robust mitochondrial damage-repair strategy is most clearly and most urgently needed. And to return to the question of scale: as a fraction of the body's cells, they are a tiny minority. Neurons comprise only about 0.03% of all the cells in the body, and muscle cells only 0.001%. However, that's still in the order of 100 billion neurons to engineer! So how are we going to do that?

Several potential gene therapy approaches are currently or soon to be used in human clinical trials, but none that are up to the task of delivering rejuvenation biotechnologies like AE that require it. Phage integrases would be a powerful alternative gene therapy technology for AE - if they can be made to work for humans. Phages are a kind of virus that naturally infects bacteria, not people. But there are compelling reasons to harness them for gene therapy if we can. First, they can insert gene constructs of essentially any size into their target site in the genomes of organisms they infect. Second, unlike AAVs, phage integrases will almost never insert their genetic payload anywhere but a few specific, non-disruptive, "safe" places in the genome - and for structural reasons, their genetic payload is highly unlikely to insert itself elsewhere in the genome independent of the integrase.

That sounds like exactly what we need! So the main challenge - and it's a big one! - is that phage integrases are designed to insert viral genes into bacterial genomes: the safe "docking site" that they target is not naturally present in either mice or humans. Thus first, hardwire the "docking site" into the genome of the mouse or human in whom you want to deliver therapies. Then you're free to use the more powerful phage integrase to safely deliver as large a construct as you like. For testing candidate rejuvenation biotechnologies in animal studies, you can engineer the docking site into a line of mice, which will then be born ready to receive new candidate gene therapies via phage integrases at any point in the lifespan. SENS Research Foundation began funding the development of these "Maximally-Modifiable Mice" (MMM) almost a decade ago, and our in-house MitoSENS team is now using them to test allotopic expression in living mice.

This is a critical step in proving out the engineered phage integrase system as a platform for gene therapy, and advancing AE from a technical achievement in cell biology into a working rejuvenation biotechnology that can keep our mitochondria cranking out cellular energy, even in the face of age-related mutations. But as you'll probably have noticed, there's just one problem: humans aren't born with a phage integrase docking site engineered into our genomes! Let's be frank about this: we don't yet know how exactly we will get the docking site engineered into all of the cells - or even all the high-priority cells for AE - of a person. Getting the docking site inserted into all of these cells using other gene therapy approaches will be challenging. But it's nothing compared to the alternative: delivering each and every one of the 13 mitochondrially-encoded proteins individually into all the not-previously-modified cells that need them using those same flawed tools.

Mitochondria play a fundamental role in cellular survival and growth by supplying energy in the form of ATP via oxidative phosphorylation. Isolated mitochondria can be transferred to any cell type via simple coincubation or brief centrifugation in vitro. Isolated mitochondria can also be internalized into tissues through local or systemic injection in vivo. It was suggested that mitochondrial internalization would be mediated by micropinocytosis or actin-dependent endocytosis. In animal models and patients, the injection of autologous or nonautologous mitochondria has been effective in treating injury and diseases, including ischemia/reperfusion injury, spinal cord injury, mouse fatty liver, cognitive deficits, inflammatory diseases, and Parkinson's disease.

Although the underlying mechanisms of such effects are not fully understood, it has been suggested that the transfer of healthy mitochondria (or mitochondrial transplantation) ameliorates mitochondrial defects and helps recover cellular function by increasing mitochondrial biogenesis or replacing abnormal mitochondria with healthy mitochondria. Recently, our data have demonstrated that mitochondrial transplantation attenuated the lipopolysaccharide-induced inflammation in vitro and in vivo by blockade of the activity of NFκB. Therefore, the transfer of fully functional mitochondria into defective cells or tissues could be an effective therapeutic strategy for treating mitochondrial dysfunction.

The key to successful mitochondrial transplantation therapy is the trafficking of mitochondria to the target cells, in which they can exert their biological effects. Therefore, systemically administrated mitochondria must have abilities that guide them to the sites with mitochondrial damage. Intravenously injected mitochondria might localize preferentially to damaged tissues; mitochondrial trafficking to the sites of injury is not well studied, however.

In the present study, we isolated mitochondria conjugated with green fluorescent protein (MTGFP) from stable HEK293 cells expressing TOM20 fused to an upstream green fluorescent protein (GFP). In a coculture system, MTGFP was internalized in a cell type-specific manner. We also found that selective MTGFP transplantation depended on the mitochondrial function of the receiving fibroblasts. Furthermore, compared with MTGFP injected intravenously into normal mice, MTGFP injected intravenously into bleomycin-induced idiopathic pulmonary fibrosis (IPF) mice located more abundantly in the lung tissue, suggesting that mitochondrial trafficking to damaged cells and tissues occurred.

Studies in Drosophila have identified several genetic manipulations of mitochondrial proteins that have shown some promise in increasing lifespan. For example, induction of Dynamin-related protein 1 (Drp1), which is a major regulator of mitochondrial fission, during midlife in Drosophila increases lifespan. Similarly, forced expression of the yeast alternative NADH:ubiquinone oxidoreductase, which catalyzes the transfer of electrons from NADH to ubiquinone via FAD without pumping protons across the mitochondrial inner membrane increases lifespan. Further, overexpression of the alternative NADH:ubiquinone oxidoreductase reduces reactive oxygen species (ROS) production and increases several markers of complex 1 (CI) activity.

Paradoxically, a restrained knockdown of several CI proteins also enhances longevity. While the exact mechanisms involved in triggering the increased lifespan caused by mild CI disruption are still being unraveled, compensatory mitochondrial stress signaling cascades seem to contribute prominently. However, the question of whether boosting the expression of individual CI subunits can extend lifespan remains uncharted.

The boot-shaped respiratory complex I (CI) consists of a mitochondrial matrix and membrane domain organized into N-, Q- and P-modules. The N-module is the most distal part of the matrix domain, whereas the Q-module is situated between the N-module and the membrane domain. The proton-pumping P-module is situated in the membrane domain.

We explored the effect of aging on the disintegration of CI and its constituent subcomplexes and modules in Drosophila flight muscles. We find that the fully-assembled complex remains largely intact in aged flies. And while the effect of aging on the stability of many Q- and N-module subunits in subcomplexes was stochastic, NDUFS3 was consistently down-regulated in subcomplexes with age. This was associated with an accumulation of many P-module subunits in subcomplexes. The potential significance of these studies is that genetic manipulations aimed at boosting, perhaps, a few CI subunits may suffice to restore the whole CI biosynthesis pathway during muscle aging.

Scientists are great at making mice live longer. Rapamycin, widely prescribed to prevent organ rejection after a transplant, increases the life expectancy of middle-age mice by as much as 60 percent. Drugs called senolytics help geriatric mice stay sprightly long after their peers have died. The diabetes drugs metformin and acarbose, extreme calorie restriction, and, by one biotech investor's count, about 90 other interventions keep mice skittering around lab cages well past their usual expiration date. The newest scheme is to hack the ageing process itself by reprogramming old cells to a younger state.

What about us? How far can scientists stretch our life span? And how far should they go? Between 1900 and 2020, human life expectancy more than doubled, to 73.4 years. But that remarkable gain has come at a cost: a staggering rise in chronic and degenerative illnesses. Ageing remains the biggest risk factor for cancer, heart disease, Alzheimer's, type 2 diabetes, arthritis, lung disease, and just about every other major illness. It's hard to imagine anyone wants to live much longer if it means more years of debility and dependence.

But if those mouse experiments lead to drugs that clean up the molecular and biochemical wreckage at the root of so many health problems in old age, or to therapies that slow-or, better yet, prevent-that messy buildup, then many more of us would reach our mid-80s or 90s without the aches and ailments that can make those years a mixed blessing. And more might reach what is believed to be the natural maximum human life span, 120 to 125 years. Few people get anywhere close. In industrialised nations, about one in 6,000 reaches the century mark and one in five million makes it past 110.

Human biology, it seems, can be optimised for greater longevity. Unimaginable riches await whoever cracks the code. No wonder investors are pouring billions into trying. This work is powered by artificial intelligence, big data, cellular reprogramming, and an increasingly exquisite understanding of the zillions of molecules that keep our bodies humming. Some researchers even talk about "curing" ageing.

The first indications that elephant lineage contains genetic strategies to enhance cancer protection mechanisms came from studies that found that elephants have a lower cancer rate than expected based on their body size compared with other mammalian species. This was related to multiple copies of the TP53 gene, widely known as a crucial tumor suppressor gene (TSG), preventing the growth and survival of potentially malignant cells. While most mammals have only one TP53 copy in their genome, the African bush elephant genome contains 19 extra copies of TP53, 9 to 20 copies were identified in the Asian elephant genome, and 21 to 24 copies were found in the African forest elephant genomes.

Many genomes of giant whales have been sequenced thus far but did not reveal duplications of TP53 similar to those in elephants, suggesting that they evolved different anticancer adaptations. Comparative genomics in the bowhead whale, the longest-lived whale, identified genes under positive selection and specific mutations in genes linked to cancer, aging, the cell cycle, and DNA repair, but without conclusive experiments. Researchers reported signals of positive selection in seven TSGs: CXCR2, ADAMTS8, ANXA1, DAB2, DSC3, EPHA2, and TMPRSS11A. Moreover, they revealed that the turnover rate of TSGs was almost 2.4 times faster in cetaceans than in other mammals, showing 71 duplicated genes in at least one of the Cetaceans species. Most duplication events and positively selected genes were identified in the lineage of large baleen whales, suggesting that they have evolved additional anticancer mechanisms.

As in other mammalian lineages, the maximum life span and body mass are correlated in primates, and the great apes are the largest body size and long-lived species among them. Researchers found only five genes with positive selection signals for the great ape lineage (IRF3, SCRN3, DIAPH2, GASK1B, and SELENO), all of which have functions related to cancer development and inflammatory responses. The results show that the evolution of strategies for cancer resistance in the primate lineage is quite diverse, with modifications that can be found at the coding, expression, and regulatory levels, and that although the great apes lineage provides evidence of specific changes capable of giving greater longevity to the species of the group, the understanding of the relationship with cancer resistance is still developing for nonhuman species and needs to be further investigated.

Bats have exceptional longevity given their body size, but there is still little data on how they evolved their extended lifespan and resisted cancer. Previous studies found reduced GH-IGF1 signaling associated with increased resistance to cancer. Additionally, it has been reported that long-lived bats have resilient telomeres that remain long despite advanced age. Also, bats do not show an increased level of mitochondrial damage given their metabolic rate, suggesting that this group evolved adaptations in their DNA repair and maintenance mechanisms. These molecular adaptations were underpinned by a study showing that bats exhibit a unique age-related regulation of genes associated with DNA repair, immunity, and tumor suppression that underlies extended bat longevity. Furthermore, it was reported that long-lived bats possess specific miRNAs that function as tumor suppressors. This provides a new potential molecular mechanism to decrease cancer risk not yet identified in any other lineage.

Long-lived species have evolved by reducing the rate of aging, which is an inherent consequence of oxidative metabolism. Hence, species that live longer benefit from more efficient intracellular metabolic pathways, including lipid, protein, and carbohydrate metabolism. The aim of this work is to determine whether the content of proteins' building blocks, named amino acids, are related with mammalian longevity. This was accomplished by analyzing the amino acid content in the hearts of seven mammalian species with a longevity ranging from 3.8 to 57 years.

Our findings demonstrate that the heart's content of amino acids differs between species and is globally lower in long-lived species. Moreover, long-lived species have lower content of amino acids containing sulfur, such as methionine and its related metabolites. Methionine constitutes a central hub of intracellular metabolic adaptations leading to an extended longevity. Our results support the existence of metabolic adaptations in terms of sulfur-containing amino acids. As has been described previously, our work supports the idea that the human population could benefit from reduced calorie intake, which would lead to reduced age-related diseases and healthier aging.

Aging is a natural process that an organism gradually loses its physical fitness and functionality. Great efforts have been made to understand and intervene in this deteriorating process. The gut microbiota affects host physiology, and dysbiosis of the microbial community often underlies the pathogenesis of host disorders. The commensal microbiota also changes with aging; however, the interplay between the microbiota and host aging remains largely unexplored. Here, we systematically examined the ameliorating effects of the gut microbiota derived from the young on the physiology and phenotypes of the aged.

As the fecal microbiota was transplanted from young mice at 5 weeks after birth into 12-month-old ones, the thickness of the muscle fiber and grip strength were increased, and the water retention ability of the skin was enhanced with thickened stratum corneum. Muscle thickness was also marginally increased in 25-month-old mice after transferring the gut microbiota from the young. Bacteria enriched in 12-month-old mice that received the young-derived microbiota significantly correlated with the improved host fitness and altered gene expression. In the dermis of these mice, transcription of Dbn1 was most upregulated and DBN1-expressing cells increased twice.

We revealed that the young-derived gut microbiota rejuvenates the physical fitness of the aged by altering the microbial composition of the gut and gene expression in muscle and skin. Dbn1, for the first time, was found to be induced by the young microbiota and to modulate skin hydration. Our results provide solid evidence that the gut microbiota from the young improves the vitality of the aged.

Senescence represents a unique cellular stress response characterized by a stable growth arrest, macromolecular alterations, and wide spectrum changes in gene expression. Classically, senescence is the end-product of progressive telomeric attrition resulting from the repetitive division of somatic cells. In addition, senescent cells accumulate in premalignant lesions, in part, as a product of oncogene hyperactivation, reflecting one element of the tumor suppressive function of senescence. Oncogenic processes that induce senescence include overexpression/hyperactivation of H-Ras, B-Raf, and cyclin E as well as inactivation of PTEN.

Oncogenic viruses, such as Human Papilloma Virus (HPV), have also been shown to induce senescence. High-risk strains of HPV drive the immortalization, and hence transformation, of cervical epithelial cells via several mechanisms, but primarily via deregulation of the cell cycle, and possibly, by facilitating escape from senescence. Despite the wide and successful utilization of HPV vaccines in reducing the incidence of cervical cancer, this measure is not effective in preventing cancer development in individuals already positive for HPV. Accordingly, in this commentary, we focus on the potential contribution of oncogene and HPV-induced senescence (OIS) in cervical cancer. We further consider the potential utility of senolytic agents for the elimination of HPV-harboring senescent cells as a strategy for reducing HPV-driven transformation and the risk of cervical cancer development.

The biomarker, called "brain-derived tau," or BD-tau, outperforms current blood diagnostic tests used to detect Alzheimer's-related neurodegeneration clinically. It is specific to Alzheimer's disease and correlates well with Alzheimer's neurodegeneration biomarkers in the cerebrospinal fluid (CSF). Current blood diagnostic methods can accurately detect abnormalities in plasma amyloid beta and the phosphorylated form of tau, but the biggest hurdle lies in the difficulty of detecting markers of neurodegeneration that are specific to the brain and aren't influenced by potentially misleading contaminants produced elsewhere in the body.

For example, blood levels of neurofilament light, a protein marker of nerve cell damage, become elevated in Alzheimer's disease, Parkinson's and other dementias, rendering it less useful when trying to differentiate Alzheimer's disease from other neurodegenerative conditions. On the other hand, detecting total tau in the blood proved to be less informative than monitoring its levels in CSF. Researchers have now developed a technique to selectively detect BD-tau while avoiding free-floating "big tau" proteins produced by cells outside the brain, however.

To do that, they designed a special antibody that selectively binds to BD-tau, making it easily detectible in the blood. They validated their assay across over 600 patient samples from five independent cohorts, including those from patients whose Alzheimer's disease diagnosis was confirmed after their deaths, as well as from patients with memory deficiencies indicative of early-stage Alzheimer's. The tests showed that levels of BD-tau detected in blood samples of Alzheimer's disease patients using the new assay matched with levels of tau in the CSF and reliably distinguished Alzheimer's from other neurodegenerative diseases. Levels of BD-tau also correlated with the severity of amyloid plaques and tau tangles in the brain tissue confirmed via brain autopsy analyses.

Aortic aneurysms are characterized by local inflammation with degeneration around the aorta, leading to vessel weakening and dilatation. Degenerative remodeling in the medial layer of aortic aneurysm tissue is characterized by loss of vascular smooth muscle cells (vSMC) and destruction of the extracellular matrix (ECM). This medial degeneration leads to weakening and progressive dilatation of the vascular wall, and ultimately results in aortic dissection or aneurysm rupture.

Telomere shortening is a predictor of age-related diseases, and its progression is associated with premature vascular disease. The aim of the present work was to investigate the impacts of chronic hypoxia and telomeric DNA damage on cellular homeostasis and vascular degeneration of thoracic aortic aneurysm (TAA). We analyzed healthy and aortic aneurysm specimens (215 samples) for telomere length, chronic DNA damage, and resulting changes in cellular homeostasis, focusing on senescence and apoptosis.

Compared with healthy thoracic aorta, patients with tricuspid aortic valve (TAV) showed telomere shortening with increasing aneurysm size, in contrast to genetically predisposed bicuspid aortic valve (BAV). In addition, telomere length was associated with chronic hypoxia and telomeric DNA damage and with the induction of senescence-associated secretory phenotype (SASP). Aneurysm in TAV specimens showed a significant difference in SASP-marker expression of IL-6, NF-κB, mTOR, and cell-cycle regulators (γH2AX, Rb, p53, p21), compared to healthy thoracic aorta and and aneurysm in BAV. We conclude that chronic hypoxia is associated with telomeric DNA damage and the induction of SASP in a diseased aortic wall, promising a new therapeutic target.

Neuroinflammation exists in variety of aging-related neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), major depressive disorder (MDD), ischemic stroke, spinal cord injury, and schizophrenia. Among the many critical molecules that regulate neuroinflammation, the NLRP3 inflammasome complex was found to play important roles in cellular immune response such as during stress and infection. Recent evidence demonstrates that NLRP3-medicated neuroinflammation is involved in the pathology of neurodegenerative diseases.

Misfolded protein aggregates in neurons are well-known, cellular hallmarks in a variety of neurodegenerative diseases. Misfolded proteins and damaged organelles are degraded by inflammation-related cells such as microglia in the brain. Activated-NLRP3 inflammasome in microglia plays a key role for fighting with misfolded proteins to rescue neurons. Autophagy and ubiquitin-proteasome system in neurons also take part in the degradation or recycling of these mutant aggregates proteins. However, excessive aggregates in neurons impair the autophagy and ubiquitin protein degradation system, leading to activation of NLRP3 inflammasomes in microglia and neuronal death. Microglia activates NLRP3 inflammasomes and releases cytokines in response to toxic protein aggregates in neurodegenerative diseases.

AD is a common, age-dependent neurodegenerative disease which is characterized with the accumulation of amyloid beta (Aβ) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein aggregates. The Aβ aggregates in brain are considered as a key pathological hallmark of AD. Interestingly, NLRP3 inflammasomes were found in AD patient's brain and animal models. Thus, approaches to degrading protein aggregates by the autophagy system and inhibit the neuroinflammation is a promising direction for the treatment of neurodegenerative diseases characterized by misfolded proteins.

Aging is associated with cognitive impairment, including dementia and mild cognitive impairment (MCI). Successful drug development for improving or maintaining cognition in seniors is critically important. Although many novel targets are being explored for improving cognition in the past two decades, there are only several drugs approved to improve cognition in Alzheimer's disease (AD) and no drug has been approved for cognitive protection in MCI patients.

A growing number of studies show that non-pharmacological interventions can enhance cognition in the last decade. Emerging evidence indicates exercise not only promotes physical health but also contributes to the preservation of cognition function. The mechanisms account for the neuroprotective effects of exercise on the brain include evaluated neurotrophic factor levels, increased synaptogenesis, improved vascularization, decreased systemic inflammation, and reduced abnormal protein deposition.

Various pharmacological (cholinesterase inhibitors, memantine, antidiabetic agents, probiotics, cerebrolysin) and non-pharmacological interventions (cognition-oriented treatments, non-invasive brain stimulation, physical exercise, and lifestyle-related interventions) have been proposed for cognitive impairment in older people. Although a variety of new drug targets has been identified for cognition enhancement in older adults, these new drugs are still in development. The existing potential drug targets should be further exploited, and discovering new drug targets could be a solution to the lack of effective drugs. Most non-pharmacological interventions showed a small to moderate beneficial effect on cognitive function in cognitive impairment old people. Thus, combinations of pharmacological and non-pharmacological interventions or combinations of different types of non-pharmacological interventions may be more efficient in improving or preserving cognition.

Aging is a major risk factor for common neurodegenerative diseases. Although multiple molecular, cellular, structural, and functional changes occur in the brain during aging, the involvement of caveolin-2 (Cav-2) in brain ageing remains unknown. We investigated Cav-2 expression in brains of aged mice and its effects on endothelial cells. Human umbilical vein endothelial cells (HUVECs) showed decreased THP-1 adhesion and infiltration when treated with Cav-2 siRNA compared to control siRNA. In contrast, Cav-2 overexpression increased THP-1 adhesion and infiltration in HUVECs.

Increased expression of Cav-2 and iba-1 was observed in brains of old mice. Moreover, there were fewer iba-1-positive cells in the brains of aged Cav-2 knockout (KO) mice than of wild-type aged mice. The levels of several chemokines were higher in brains of aged wild-type mice than in young wild-type mice; moreover, chemokine levels were significantly lower in brains of young mice as well as aged Cav-2 KO mice than in their wild-type counterparts. Expression of PECAM1 and VE-cadherin proteins increased in brains of old wild-type mice but was barely detected in brains of young wild-type and Cav-2 KO mice.

Collectively, our results suggest that Cav-2 expression increases in the endothelial cells of aged brain, and promotes leukocyte infiltration and age-associated neuroinflammation.

Clinical evidence of cellular senescence in cancer patients has long been underestimated, in part due to the difficult detection, since currently no specific and universal markers for senescent cells exist. Historically, cellular senescence was primarily considered as an endogenous tumor suppressor mechanism halting the proliferation of damaged cells which are at risk of malignant transformation, thereby protecting against cancer. However, during the last two decades, a more nuanced view on the involvement of cellular senescence in tumorigenesis and response to therapy has emerged.

Here, we provided a comprehensive overview on the prognostic implications of cellular senescence in cancer patients with solid tumors. Increasing clinical evidence add to the antagonistic pleiotropy of cellular senescence as differential prognostic outcomes, ranging from improved to impaired outcome, are demonstrated. In a simplified model we propose that the prognostic implications of oncogene-induced senescence (OIS) as well as therapy-induced senescence (TIS) are highly context-dependent and primarily depend on the senescence burden, the secretion and the composition of the senescence-associated secretory phenotype (SASP) and/or duration of SASP presence, thereby providing a rationale for the differential outcomes of OIS as well TIS observed within the same cancer type as well as between different types of cancer.

The detection of cellular senescence in cancer patients can be achieved by various methods and using various markers. Despite clear algorithms to accurately assess and quantify senescent cells in vitro and in vivo, a plethora of different senescence markers, single or combined with other markers, are currently used to demonstrate the presence of cellular senescence. Hence, it is difficult to compare clinical data and to draw reliable conclusions regarding the prognostic implications of cellular senescence, as well as the implementation of emerging senolytics (i.e., targeted removal of senescent cells) and senomorphics that modify/suppress the SASP, underlining the need for a uniform and consistent application of recognized and validated markers of cellular senescence.