Cell senescence, rapamycin and hyperfunction theory of aging

Corticotropin-releasing hormone inhibits autophagy by suppressing PTEN to promote apoptosis in dermal papilla cells

BACKGROUND

Stress-related hair loss is on the rise, largely due to escalating levels of stress-related corticotropin-releasing hormone (CRH) through poorly defined mechanisms. CRH-mediated activation of corticotropin-releasing hormone receptors (CRHRs) on dermal papilla cells (DPCs) is a likely cause of stress-related hair loss. The aim of the study is to elucidate the key mechanisms of alopecia caused by CRH and provide potential new targets for the treatment of stress-related hair loss.

METHODS

4D label-free quantitative proteomics of DPCs and the chronic unpredictable mild stress mouse (CUMS) model were used to explore the relationship and mechanism between CRH, DPCs and hair regeneration.

RESULTS

CRH initially downregulated PTEN to suppress autophagy, leading to DPC apoptosis. Overexpression of PTEN enhanced autophagy and mitigated CRH-dependent DPC apoptosis. CRH inhibited PTEN and activated the PI3K/AKT/mTOR pathway, whereas rapamycin inhibited this pathway and activated autophagy, consequently lowering apoptosis, suggesting that increased susceptibility to apoptosis is caused by decreased autophagy. CUMS-induced hair growth disruption is accompanied by an increase in CRHRs and a decrease in PTEN levels within the dermal papilla. Intracutaneous injection of CRH impeded hair regeneration and decreased PTEN in mice, concurrent with inhibition of autophagy and increased apoptosis.

CONCLUSIONS

These findings indicate that PTEN loss coupled with PI3K/AKT/mTOR-mediated autophagy inhibition and apoptosis in DPCs is a key mechanism of stress-related hair loss induced by CRH and suggests that topical activation of PTEN or enhancement of autophagy, e.g. through rapamycin, may have a therapeutic effect on stress-induced hair loss disorders such as alopecia.

A Binary siRNA-Loaded Tetrahedral DNA Nanobox for Synergetic Anti-Aging Therapy

Extensive accumulation of senescent cells contributes to organismal aging, and slowing down the process of cellular senescence may ameliorate age-related pathologies. Targeted inhibition of the mechanistic target of rapamycin complex 1 (mTORC1) is found to suppress the conversion of cells to senescence. The regulatory-associated protein of mTOR (Raptor), a key component of mTORC1, has been implicated as important in the aging process, and its druggability deserves to be investigated. Due to high efficiency and high convenience in drug construction, siRNA shows great potential in silencing Raptor expression via RNA interfering therapy. Here, we developed a functionalized anti-aging nanoplatform based on tetrahedral DNA nanostructures (TDNs) encapsulating siRNA targeting Raptor for synergistic anti-aging therapy, named siR-TDNbox. Anti-inflammatory and antioxidant properties of TDN beneficially attenuate age-associated inflammation while serving as siRNA nanocarrier, and thus play a binary role. The results suggest that the siR-TDNbox binary therapeutic nanoplatform has demonstrated an excellent ability to delay aging, inhibit mTORC1 signaling, and extend lifespan. This anti-aging nanoplatform may provide a medium for the combined application of traditional senotherapeutic drugs and promote the upgrading of nanomaterials with anti-aging effects.

Rapamycin ameliorates senescence of periodontal ligament stem cells and promotes their osteogenesis via the PI3K/AKT pathway

Periodontal ligament stem cells (PDLSCs) have been regarded as ideal candidates for tissue regeneration due to their excellent self-renewal and multipotent differentiation ability. Rapamycin (RAPA) is reported to play an important role in the regulation of biological properties of stem cells and a variety of physiological processes. This study investigates whether RAPA could ameliorate the senescence and accelerate the osteogenic differentiation of PDLSCs, particularly the regenerative potential in a rat calvarial bone defect model, and the underlying mechanisms involved. β-galactosidase staining, quantitative real-time polymerase chain reaction, and western blot analysis were performed to assess the effects of RAPA on senescent PDLSCs. The osteogenic differentiation ability of PDLSCs was detected by alkaline phosphatase staining and activity, Alizarin Red S staining, and gene and protein levels of osteogenesis-related markers. The underlying signaling pathways were investigated via RNA transcriptome sequencing analysis and WB tests. Calvarial bone defects in rat were treated with PDLSCs pre-incubated with or without RAPA and/or H2O2. The results showed that RAPA could enhance the osteogenic potentials of PDLSCs via PI3K/AKT signaling pathway, and reversed H2O2-induced senescence and osteogenic differentiation inhibition of PDLSCs. Moreover, calvarial defects transplanted with RAPA-treated PDLSCs showed significantly greater new bone formation compared with other groups, and also improved the H2O2-induced impairment of bone formation, whether by micro-computed tomography examination or by histological analysis. Collectively, RAPA was capable of promoting osteogenic differentiation of PDLSCs via PI3K/AKT signaling pathway in vitro, facilitating calvarial bone regeneration and reversing H2O2-induced impairment of osteogenic differentiation and cell senescence in PDLSCs.

PD-1-Enhanced Treg Cell Senescence in Advanced Maternal Age

Senescence occurs earlier in the immune system than in solid organs as age increases. Regulatory T (Treg) cells are among the first cells to exhibit signs of aging. However, whether advanced-age pregnancy involves Treg cell aging remains unclear. This study demonstrated that the aging of women is accompanied by aging Treg cells and that PD-1 regulates Treg cell aging. The transfer of young Treg cells can improve the pregnancy outcomes of reproductive-aged mice by reducing the level of IFN-γ, a proinflammatory cytokine secreted by Treg cells in aged mice. Transferring α-PD-1 mAb-treated aged Treg cells increases the level of IL-10, an anti-inflammatory cytokine secreted by Treg cells in reproductive-aged mice. Collectively, these findings suggest a potential therapeutic strategy for preventing adverse pregnancy outcomes in older women.

Single-Cell Analysis Dissects the Effects of Vitamin D on Genetic Senescence Signatures Across Murine Tissues

Background/Objectives: Vitamin D (VD) plays a crucial role in age-related diseases, and its influence on cellular senescence (CS) could help clarify its function in aging. Considering VD's pleiotropic effects and the heterogeneity of CS. Methods: we utilized single-cell RNA sequencing (scRNA-seq) to explore these dynamics across multiple tissues. We analyzed three murine tissue datasets (bone, prostate, and skin) obtained from public repositories, enriching for senescence gene signatures. We then inferred gene regulatory networks (GRNs) at the tissue and cell-type levels and performed two cell communication analyses: one for senescent cells and another for interactions between senescent and non-senescent cells. Results: VD supplementation significantly decreased senescence scores in the skin (p = 3.96×10-134) and prostate (p=1.56×10-34). GRN analysis of the prostate revealed an altered macrophage-fibroblast regulatory relationship. In bone, distinct aging-related modules emerged for different bone lineages. In skin, contrary differentiation patterns between suprabasal and basal cells were observed. The main VD-modulated pathways were involved in inflammation, extracellular matrix remodeling, protein metabolism, and translation. VD reduced fibroblast-macrophage interactions in the prostate and skin but increased overall cellular crosstalk in bone. Conclusions: Our findings demonstrate that VD alleviates CS burden across tissues by modulating inflammation and metabolic processes and promoting differentiation. Key aging-related genes modulated by VD were linked to anabolism and cellular differentiation, suggesting VD's potential for therapeutic interventions targeting age-related diseases.

A loss of primary cilia by a reduction in mTOR signaling correlates with age-related deteriorations in condylar cartilage

Age-related deterioration of condylar cartilage is an etiological factor in temporomandibular joint-osteoarthritis (TMJ-OA). However, its underlying mechanism remains unknown. Therefore, we examined age-related changes and the relationship between mTOR signaling and primary cilia in condylar cartilage to determine the intrinsic mechanisms of age-related TMJ-OA. Age-related morphological changes were analyzed using micro-computed tomography and safranin O-stained histological samples of the mandibular condyle of C57BL/6J mice (up to 78 weeks old). Immunohistochemistry was used to assess the activity of mTOR signaling, primary cilia frequency, and Golgi size of condylar chondrocytes. Four-week-old mice receiving an 11-week series of intraperitoneal injections of rapamycin, a potent mTOR signaling inhibitor, were used for the histological evaluation of the condylar cartilage. The condylar cartilage demonstrated an age-related reduction in cartilage area, including chondrocyte size, cell density, and cell size distribution. The Golgi size, primary cilia frequency, and mTOR signaling also decreased with age. Rapamycin injections resulted in both diminished cartilage area and cell size, resembling the phenotypes observed in aged mice. Rapamycin-injected mice also exhibited a smaller Golgi size and lower primary cilia frequency in condylar cartilage. We demonstrated that a loss of primary cilia due to a decline in mTOR signaling was correlated with age-related deteriorations in condylar cartilage. Our findings provide new insights into the tissue homeostasis of condylar cartilage, contributing to understanding the etiology of age-related TMJ-OA.

Elucidation of anti-human melanoma and anti-aging mechanisms of compounds from green seaweed Caulerpa racemosa

Human melanoma is linked with aging-related disorders, prompting interest in the development of functional foods derived from natural ingredients to mitigate its incidence. Molecules in green seaweeds such as Caulerpa racemosa can serve this purpose due to their anti-tumor and anti-inflammatory properties. A previous work study compounds profiling has been carried out, and in this research the molecular docking studies targeting receptors associated with melanoma (GRP78, IRE1, BRAF) and aging (mTOR, AMPK, SIRT1) identified four promising compound in an extract of C. racemosa. The current study aims to the mechanism of those compounds at a cellular level using the human A375 (BRAF-V600E mutation) and A375 and B16-F10 cell lines. The MTT assay was used to evaluate the potential of GSCRE compounds against A375 and B16-F10 cell lines, with comparisons made to normal HDFa cell lines. Results indicated that compound C2, also known as Caulersin, demonstrated a significantly different ∆G affinity binding score compared to the control drug Dabrafenib. GSCRE crude extract, particularly C2, showed potential in modulating mTOR, AMPK, and SIRT1 pathways and downregulating GRP78, IRE1, and BRAF signaling (p < 0.05). Interestingly, C2 was less effective in suppressing A375 and B16-F10 cell lines (LD50 C2 < LD50 Dabrafenib/control), with its LD50 value nearly matching that of the Trametinib control in B16-F10 cell lines. Consequently, GSCRE, especially C2 or Caulersin, shows promise as a new molecule for developing functional foods to combat aging and human melanoma. However, further in vivo studies and clinical trials are necessary to confirm these findings.

Immunosenescence in digestive system cancers: Mechanisms, research advances, and therapeutic strategies

Increasing lifespans and external environmental factors have contributed to the increase of age-related diseases, particularly cancer. A decrease in immune surveillance and clearance of cancer cells is the result of immunosenescence, which involves the remodeling of immune organs, the changes and functional decline of immune cell subsets, in association with systemic low-grade chronic inflammation. Stem cells aging in bone marrow and thymic involution are the most important causes of immunosenescence. Senescent cancer cells promote the differentiation, recruitment, and functional upregulation of immune-suppressive cell subsets e.g. regulatory T cells (Tregs), myeloid-derived suppressor cell (MDSC), tumor-associated macrophages (TAMS) through senescence-associated secretory phenotype (SASP) further exacerbating the immunosuppressive microenvironment. For digestive system cancers, age-related damage to the intestinal mucosal barrier, the aging of gut-associated lymphoid tissue (GALT), exposure to xenobiotic stimuli throughout life, and dysbiosis make the local immune microenvironment more vulnerable. This article systematically reviews the research progress of immunosenescence and immune microenvironment in digestive system cancers, as well as the exploration of related therapy strategies, hoping to point out new directions for research in the digestive system cancers.

Inhibition of mTOR prevents glucotoxicity-mediated increase of SA-beta-gal, p16INK4a, and insulin hypersecretion, without restoring electrical features of mouse pancreatic islets

An over-activation of the mechanistic target of rapamycin (mTOR) pathway promotes senescence and age-related diseases like type 2 diabetes. Besides, the regenerative potential of pancreatic islets deteriorates with aging. Nevertheless, the role of mTOR on senescence promoted by metabolic stress in islet cells as well as its relevance for electrophysiological aspects is not yet known. Here, we investigated whether parameters suggested to be indicative for senescence are induced in vitro in mouse islet cells by glucotoxicity and if mTOR inhibition plays a protective role against this. Islet cells exhibit a significant increase (~ 76%) in senescence-associated beta-galactosidase (SA-beta-gal) activity after exposure to glucotoxicity for 72 h. Glucotoxicity does not markedly influence p16INK4a protein within 72 h, but p16INK4a levels increase significantly after a 7-days incubation period. mTOR inhibition with a low rapamycin concentration (1 nM) entirely prevents the glucotoxicity-mediated increase of SA-beta-gal and p16INK4a. At the functional level, reactive oxygen species, calcium homeostasis, and electrical activity are disturbed by glucotoxicity, and rapamycin fails to prevent this. In contrast, rapamycin significantly attenuates the insulin hypersecretion promoted by glucotoxicity by modifying the mRNA levels of Vamp2 and Snap25 genes, related to insulin exocytosis. Our data indicate an influence of glucotoxicity on pancreatic islet-cell senescence and a reduction of the senescence markers by mTOR inhibition, which is relevant to preserve the regenerative potential of the islets. Decreasing the influence of mTOR on islet cells exposed to glucotoxicity attenuates insulin hypersecretion, but is not sufficient to prevent electrophysiological disturbances, indicating the involvement of mTOR-independent mechanisms.

Roles of Menin in T cell differentiation and function: Current knowledge and perspectives

The commitment to specific T lymphocytes (T cell) lineages is governed by distinct transcription factors, whose expression is modulated through epigenetic mechanisms. Unravelling these epigenetic mechanisms that regulate T cell differentiation and function holds significant importance for understanding T cells. Menin, a multifunctional scaffolding protein, is implicated in various cellular processes, such as cell proliferation, cell cycle control, DNA repair and transcriptional regulation, primarily through epigenetic mechanisms. Existing research indicates Menin's impact on T cell differentiation and function, while a comprehensive and systematic review is currently lacking to consolidate these findings. In the current review, we have highlighted recent studies on the role of Menin in T cell differentiation and function, focusing mainly on its impact on the memory Th2 maintenance, Th17 differentiation and maintenance, CD4+ T cell senescence, and effector CD8+ T cell survival. Considering Menin's crucial function in maintaining effector T cell function, the potential of inhibiting Menin activity in mitigating inflammatory diseases associated with excessive T cell activation has also been emphasised.

Resveratrol inhibits pancreatic cancer proliferation and metastasis by depleting senescent tumor-associated fibroblasts

BACKGROUND

Pancreatic cancer, a formidable gastrointestinal neoplasm, is characterized by its insidious onset, rapid progression, and resistance to treatment, which often lead to a grim prognosis. While the complex pathogenesis of pancreatic cancer is well recognized, recent attention has focused on the oncogenic roles of senescent tumor-associated fibroblasts. However, their precise role in pancreatic cancer remains unknown. Resveratrol is a natural polyphenol known for its multifaceted biological actions, including antioxidative and neuroprotective properties, as well as its potential to inhibit tumor proliferation and migration. Our current investigation builds on prior research and reveals the remarkable ability of resveratrol to inhibit pancreatic cancer proliferation and metastasis.

AIM

To explore the potential of resveratrol in inhibiting pancreatic cancer by targeting senescent tumor-associated fibroblasts.

METHODS

Immunofluorescence staining of pancreatic cancer tissues revealed prominent coexpression of α-SMA and p16. HP-1 expression was determined using immunohistochemistry. Cells were treated with the senescence-inducing factors known as 3CKs. Long-term growth assays confirmed that 3CKs significantly decreased the CAF growth rate. Western blotting was conducted to assess the expression levels of p16 and p21. Immunofluorescence was performed to assess LaminB1 expression. Quantitative real-time polymerase chain reaction was used to measure the levels of several senescence-associated secretory phenotype factors, including IL-4, IL-6, IL-8, IL-13, MMP-2, MMP-9, CXCL1, and CXCL12. A scratch assay was used to assess the migratory capacity of the cells, whereas Transwell assays were used to evaluate their invasive potential.

RESULTS

Specifically, we identified the presence of senescent tumor-associated fibroblasts within pancreatic cancer tissues, linking their abundance to cancer progression. Intriguingly, Resveratrol effectively eradicated these fibroblasts and hindered their senescence, which consequently impeded pancreatic cancer progression.

CONCLUSION

This groundbreaking discovery reinforces Resveratrol's stature as a potential antitumor agent and positions senescent tumor-associated fibroblasts as pivotal contenders in future therapeutic strategies against pancreatic cancer.

Enhancing adipose tissue functionality in obesity: senotherapeutics, autophagy and cellular senescence as a target

Obesity, a global health crisis, disrupts multiple systemic processes, contributing to a cascade of metabolic dysfunctions by promoting the pathological expansion of visceral adipose tissue (VAT). This expansion is characterized by impaired differentiation of pre-adipocytes and an increase in senescent cells, leading to a pro-inflammatory state and exacerbated oxidative stress. Particularly, the senescence-associated secretory phenotype (SASP) and adipose tissue hypoxia further impair cellular function, promoting chronic disease development. This review delves into the potential of autophagy modulation and the therapeutic application of senolytics and senomorphics as novel strategies to mitigate adipose tissue senescence. By exploring the intricate mechanisms underlying adipocyte dysfunction and the emerging role of natural compounds in senescence modulation, we underscore the promising horizon of senotherapeutics in restoring adipose health. This approach not only offers a pathway to combat the metabolic complications of obesity, but also opens new avenues for enhancing life quality and managing the global burden of obesity-related conditions. Our analysis aims to bridge the gap between current scientific progress and clinical application, offering new perspectives on preventing and treating obesity-induced adipose dysfunction.

mTOR and SGLT-2 Inhibitors: Their Synergistic Effect on Age-Related Processes

The aging process contributes significantly to the onset of chronic diseases, which are the primary causes of global mortality, morbidity, and healthcare costs. Numerous studies have shown that the removal of senescent cells from tissues extends lifespan and reduces the occurrence of age-related diseases. Consequently, there is growing momentum in the development of drugs targeting these cells. Among them, mTOR and SGLT-2 inhibitors have garnered attention due to their diverse effects: mTOR inhibitors regulate cellular growth, metabolism, and immune responses, while SGLT-2 inhibitors regulate glucose reabsorption in the kidneys, resulting in various beneficial metabolic effects. Importantly, these drugs may act synergistically by influencing senescence processes and pathways. Although direct studies on the combined effects of mTOR inhibition and SGLT-2 inhibition on age-related processes are limited, this review aims to highlight the potential synergistic benefits of these drugs in targeting senescence.

A comprehensive model for the biochemistry of ageing, senescence and longevity

Various models for ageing, each focussing on different biochemical and/or cellular pathways have been proposed. This has resulted in a complex and non-coherent portrayal of ageing. Here, we describe a concise and comprehensive model for the biochemistry of ageing consisting of three interacting signalling hubs. These are the nuclear factor kappa B complex (NFκB), controlling the innate immune system, the mammalian target for rapamycin complex, controlling cell growth, and the integrated stress responses, controlling homeostasis. This model provides a framework for most other, more detailed, biochemical pathways involved in ageing, and explains why ageing involves chronic inflammation, cellular senescence, and vulnerability to environmental stress, while starting with the spontaneous formation of advanced glycation end products. The totality of data underlying this model suggest that the gradual inhibition of the AMPK-ISR probably determines the maximal lifespan. Based on this model, anti-ageing drugs in general, are expected to show hormetic dose response curves. This complicates the process of dose-optimization. Due to its specific mechanism of action, the anti-aging drug alkaline phosphatase is an exception to this rule, because it probably exhibits saturation kinetics.

Cellular Senescence and Inflammaging in the Bone: Pathways, Genetics, Anti-Aging Strategies and Interventions

Advancing age is associated with several age-related diseases (ARDs), with musculoskeletal conditions impacting millions of elderly people worldwide. With orthopedic conditions contributing towards considerable number of patients, a deeper understanding of bone aging is the need of the hour. One of the underlying factors of bone aging is cellular senescence and its associated senescence associated secretory phenotype (SASP). SASP comprises of pro-inflammatory markers, cytokines and chemokines that arrest cell growth and development. The accumulation of SASP over several years leads to chronic low-grade inflammation with advancing age, also known as inflammaging. The pathways and molecular mechanisms focused on bone senescence and inflammaging are currently limited but are increasingly being explored. Most of the genes, pathways and mechanisms involved in senescence and inflammaging coincide with those associated with cancer and other ARDs like osteoarthritis (OA). Thus, exploring these pathways using techniques like sequencing, identifying these factors and combatting them with the most suitable approach are crucial for healthy aging and the early detection of ARDs. Several approaches can be used to aid regeneration and reduce senescence in the bone. These may be pharmacological, non-pharmacological and lifestyle interventions. With increasing evidence towards the intricate relationship between aging, senescence, inflammation and ARDs, these approaches may also be used as anti-aging strategies for the aging bone marrow (BM).

NPRL2 is required for proliferation of oncogenic Ras-transformed bronchial epithelial cells

Nitrogen permease regulator-like 2 (NPRL2/TUSC4) is known to exert both tumor-suppressing and oncogenic effects in different types of cancers, suggesting that its actions are context dependent. Here, we delineated the molecular and functional effects of NPRL2 in malignantly transformed bronchial epithelial cells. To do so, we depleted NPRL2 in oncogenic HRas-transduced and malignantly transformed human bronchial epithelial (BEAS2B), Ras-AI-T2 cells. Intriguingly, depletion of NPRL2 in these cells induced activation of mTORC1 downstream signaling, inhibited autophagy, and impaired Ras-AI-T2 cell proliferation both in vitro and in vivo. These results suggest that NPRL2 is required for oncogenic HRas-induced cell transformation. Depletion of NPRL2 increased levels of the DNA damage marker γH2AX, the cell cycle inhibitors p21 and p27, and the apoptosis marker cleaved-PARP. These NPRL2-depleted cells first accumulated at G1 and G2, and later exhibited signs of mitotic catastrophe, which implied that NPRL2 depletion may be detrimental to oncogenic HRas-transformed cells. Additionally, NPRL2 depletion reduced heat shock factor 1/heat shock element- and NRF2/antioxidant response element-directed luciferase reporter activities in Ras-AI-T2 cells, indicating that NPRL2 depletion led to the suppression of two key cytoprotective processes in oncogenic HRas-transformed cells. Overall, our data suggest that oncogenic HRas-transduced and malignantly transformed cells may depend on NPRL2 for survival and proliferation, and depletion of NPRL2 also induces a stressed state in these cells.

Senescence: A new kid in the block of the metabolic response to surgical trauma

Tumor growth is associated to chronic metabolic changes which inform the clinical phenotype and the outcome of patients with cancer. Surgery further triggers a cascade of acute neuro-immune responses leading to hypermetabolic and catabolic state. The metabolic mechanisms associated to surgical stress are well described. Preventive and therapeutic strategies have been developed, yet they appear not to benefit all surgical patients with cancer, even in the presence of a similar tumor type as well surgical procedures. Recent studies show that aging is associated with enrichment of senescent cells in different organs and tissues. Senescent cells are characterized by a specific senescence-associated secretory phenotype (SASP), which limits the potential for resilience of tissues and organs. Enhancement of the metabolic and functional recovery of patients with cancer undergoing surgery may therefore require additional therapies addressing SASP and senescent cells. Preliminary results obtained in experimental models recommend to further explore the role of senescence in mediating the metabolic changes and tissue resistance to efficient recovery.

Underlying Mechanisms and Treatment of Cellular Senescence-Induced Biological Barrier Interruption and Related Diseases

Given its increasing prevalence, aging is of great concern to researchers worldwide. Cellular senescence is a physiological or pathological cellular state caused by aging and a prominent risk factor for the interruption of the integrity and functionality of human biological barriers. Health barriers play an important role in maintaining microenvironmental homeostasis within the body. The senescence of barrier cells leads to barrier dysfunction and age-related diseases. Cellular senescence has been reported to be a key target for the prevention of age-related barrier diseases, including Alzheimer's disease, Parkinson's disease, age-related macular degeneration, diabetic retinopathy, and preeclampsia. Drugs such as metformin, dasatinib, quercetin, BCL-2 inhibitors, and rapamycin have been shown to intervene in cellular senescence and age-related diseases. In this review, we conclude that cellular senescence is involved in age-related biological barrier impairment. We further outline the cellular pathways and mechanisms underlying barrier impairment caused by cellular senescence and describe age-related barrier diseases associated with senescent cells. Finally, we summarize the currently used anti-senescence pharmacological interventions and discuss their therapeutic potential for preventing age-related barrier diseases.

Rapamycin Inhibits Senescence and Improves Immunomodulatory Function of Mesenchymal Stem Cells Through IL-8 and TGF-β Signaling

Mesenchymal stromal cells (MSCs) grown in high-density monolayers (sheets) are promising vehicles for numerous bioengineering applications. When MSC sheets are maintained in prolonged cultures, they undergo rapid senescence, limiting their downstream efficacy. Although rapamycin is a potential agent that can inhibit senescence in cell cultures, no study has investigated rapamycin's effect on MSCs grown in high-density culture and its effect on downstream target gene expression. In this study, placental-derived MSCs (PMSCs) were seeded at high density to generate PMSC sheets in 24 hours and were then treated with rapamycin or vehicle for up to 7 days. Autophagy activity, cell senescence and apoptosis, cell size and granularity, and senescence-associated cytokines (IL-6 and IL-8) were analyzed. Differential response in gene expression were assessed via microarray analysis. Rapamycin significantly increased PMSC sheet autophagy activity, inhibited cellular senescence, decreased cell size and granularity at all timepoints. Rapamycin also significantly decreased the number of cells in late apoptosis at day 7 of sheet culture, as well as caspase 3/7 activity at all timepoints. Notably, while rapamycin decreased IL-6 secretion, increased IL-8 levels were observed at all timepoints. Microarray analysis further confirmed the upregulation of IL-8 transcription, as well as provided a list of 396 genes with 2-fold differential expression, where transforming growth factor-β (TGF-β) signaling were identified as important upregulated pathways. Rapamycin both decreased senescence and has an immunomodulatory action of PMSCs grown in sheet culture, which will likely improve the chemotaxis of pro-healing cells to sites of tissue repair in future bioengineering applications.

Senescence-associated ß-galactosidase staining over the lifespan differs in a short- and a long-lived fish species

During the aging process, cells can enter cellular senescence, a state in which cells leave the cell cycle but remain viable. This mechanism is thought to protect tissues from propagation of damaged cells and the number of senescent cells has been shown to increase with age. The speed of aging determines the lifespan of a species and it varies significantly in different species. To assess the progress of cellular senescence during lifetime, we performed a comparative longitudinal study using histochemical detection of the senescence-associated beta-galactosidase as senescence marker to map the staining patterns in organs of the long-lived zebrafish and the short-lived turquoise killifish using light- and electron microscopy. We compared age stages corresponding to human stages of newborn, childhood, adolescence, adult and old age. We found tissue-specific but conserved signal patterns with respect to organ distribution. However, we found dramatic differences in the onset of tissue staining. The stained zebrafish organs show little to no signal at newborn age followed by a gradual increase in signal intensity, whereas the organs of the short-lived killifish show an early onset of staining already at newborn stage, which remains conspicuous at all age stages. The most prominent signal was found in liver, intestine, kidney and heart, with the latter showing the most prominent interspecies divergence in onset of staining and in staining intensity. In addition, we found staining predominantly in epithelial cells, some of which are post-mitotic, such as the intestinal epithelial lining. We hypothesize that the association of the strong and early-onset signal pattern in the short-lived killifish is consistent with a protective mechanism in a fast growing species. Furthermore, we believe that staining in post-mitotic cells may play a role in maintaining tissue integrity, suggesting different roles for cellular senescence during life.

Oncogenic signals prime cancer cells for toxic cell overgrowth during a G1 cell cycle arrest

CDK4/6 inhibitors are remarkable anti-cancer drugs that can arrest tumor cells in G1 and induce their senescence while causing only relatively mild toxicities in healthy tissues. How they achieve this mechanistically is unclear. We show here that tumor cells are specifically vulnerable to CDK4/6 inhibition because during the G1 arrest, oncogenic signals drive toxic cell overgrowth. This overgrowth causes permanent cell cycle withdrawal by either preventing progression from G1 or inducing genotoxic damage during the subsequent S-phase and mitosis. Inhibiting or reverting oncogenic signals that converge onto mTOR can rescue this excessive growth, DNA damage, and cell cycle exit in cancer cells. Conversely, inducing oncogenic signals in non-transformed cells can drive these toxic phenotypes and sensitize the cells to CDK4/6 inhibition. Together, this demonstrates that cell cycle arrest and oncogenic cell growth is a synthetic lethal combination that is exploited by CDK4/6 inhibitors to induce tumor-specific toxicity.

GDF11 and aging biology - controversies resolved and pending

Since the exogenous administration of GDF11, a TGF-ß superfamily member, was reported to have beneficial effects in some models of human disease, there have been many research studies in GDF11 biology. However, many studies have now confirmed that exogenous administration of GDF11 can improve physiology in disease models, including cardiac fibrosis, experimental stroke, and disordered metabolism. GDF11 is similar to GDF8 (also called Myostatin), differing only by 11 amino acids in their mature signaling domains. These two proteins are now known to be biochemically different both in vitro and in vivo. GDF11 is much more potent than GDF8 and induces more strongly SMAD2 phosphorylation in the myocardium compared to GDF8. GDF8 and GDF11 prodomain are only 52% identical and are cleaved by different Tolloid proteases to liberate the mature signaling domain from inhibition of the prodomain. Here, we review the state of GDF11 biology, highlighting both resolved and remaining controversies.

Towards disease-oriented dosing of rapamycin for longevity: does aging exist or only age-related diseases?

Both individuals taking rapamycin, an anti-aging drug, and those not taking it will ultimately succumb to age-related diseases. However, the former, if administered disease-oriented dosages for a long time, may experience a delayed onset of such diseases and live longer. The goal is to delay a particular disease that is expected to be life-limiting in a particular person. Age-related diseases, quasi-programmed during development, progress at varying rates in different individuals. Rapamycin is a prophylactic anti-aging drug that decelerates early development of age-related diseases. I further discuss hyperfunction theory of quasi-programmed diseases, which challenges the need for the traditional concept of aging itself.

The meaning of adaptation in aging: insights from cellular senescence, epigenetic clocks and stem cell alterations

With recent rapid progress in research on aging, there is increasing evidence that many features commonly considered to be mechanisms or drivers of aging in fact represent adaptations. Here, we examine several such features, including cellular senescence, epigenetic aging and stem cell alterations. We draw a distinction between the causes and consequences of aging and define short-term consequences as 'responses' and long-term ones as 'adaptations'. We also discuss 'damaging adaptations', which despite having beneficial effects in the short term, lead to exacerbation of the initial insult and acceleration of aging. Features commonly recognized as 'basic mechanisms of the aging process' are critically examined for the possibility of their adaptation-driven emergence from processes such as cell competition and the wound-like features of the aging body. Finally, we speculate on the meaning of these interactions for the aging process and their relevance for the development of antiaging interventions.

Cancer prevention with rapamycin

Rapamycin (sirolimus) and other rapalogs (everolimus) are anti-cancer and anti-aging drugs, which delay cancer by directly targeting pre-cancerous cells and, indirectly, by slowing down organism aging. Cancer is an age-related disease and, figuratively, by slowing down time (and aging), rapamycin may delay cancer. In several dozen murine models, rapamycin robustly and reproducibly prevents cancer. Rapamycin slows cell proliferation and tumor progression, thus delaying the onset of cancer in carcinogen-treated, genetically cancer-prone and normal mice. Data on the use of rapamycin and everolimus in organ-transplant patients are consistent with their cancer-preventive effects. Treatment with rapamycin was proposed to prevent lung cancer in smokers and former smokers. Clinical trials in high-risk populations are warranted.

Cellular senescence: when growth stimulation meets cell cycle arrest

At the very moment of cell-cycle arrest, the cell is not senescent yet. For several days in cell culture, the arrested cell is acquiring a senescent phenotype. What is happening during this geroconversion? Cellular enlargement (hypertrophy) and hyperfunctions (lysosomal and hyper-secretory) are hallmarks of geroconversion.

Are menopause, aging and prostate cancer diseases?

There is no doubt that prostate cancer is a disease. Then, according to hyperfunction theory, menopause is also a disease. Like all age-related diseases, it is a natural process, but is also purely harmful, aimless and unintended by nature. But exactly because these diseases (menopause, prostate enlargement, obesity, atherosclerosis, hypertension, diabetes, presbyopia and thousands of others) are partially quasi-programmed, they can be delayed by slowing aging. Is aging a disease? Aging is a quasi-programmed disease that is partially treatable by rapamycin. On the other hand, aging is an abstraction, a sum of all quasi-programmed diseases and processes. In analogy, the zoo consists of animals and does not exist without animals, but the zoo is not an animal.

Mitochondrial Metabolism in X-Irradiated Cells Undergoing Irreversible Cell-Cycle Arrest

Irreversible cell-cycle-arrested cells not undergoing cell divisions have been thought to be metabolically less active because of the unnecessary consumption of energy for cell division. On the other hand, they might be actively involved in the tissue microenvironment through an inflammatory response. In this study, we examined the mitochondria-dependent metabolism in human cells irreversibly arrested in response to ionizing radiation to confirm this possibility. Human primary WI-38 fibroblast cells and the BJ-5ta fibroblast-like cell line were exposed to 20 Gy X-rays and cultured for up to 9 days after irradiation. The mitochondrial morphology and membrane potential were evaluated in the cells using the mitochondrial-specific fluorescent reagents MitoTracker Green (MTG) and 5,5',6,6'-tetraethyl-benzimidazolylcarbocyanine iodide (JC-1), respectively. The ratio of the mean MTG-stained total mitochondrial area per unit cell area decreased for up to 9 days after X-irradiation. The fraction of the high mitochondrial membrane potential area visualized by JC-1 staining reached its minimum 2 days after irradiation and then increased (particularly, WI-38 cells increased 1.8-fold the value of the control). Their chronological changes indicate that the mitochondrial volume in the irreversible cell-cycle-arrested cells showed significant increase concurrently with cellular volume expansion, indicating that the mitochondria-dependent energy metabolism was still active. These results indicate that the energy metabolism in X-ray-induced senescent-like cells is active compared to nonirradiated normal cells, even though they do not undergo cell divisions.

Classification of Signature-Based Phenotypes of Aging-Related Genes to Identify Prognostic and Immune Characteristics in HCC

Hepatocellular carcinoma (HCC), which has become one of the most significant malignancies causing cancer-related mortality, presents genetic and phenotypic heterogeneity that makes predicting prognosis challenging. Aging-related genes have been increasingly reported as significant risk factors for many kinds of malignancies, including HCC. In this study, we comprehensively dissected the features of transcriptional aging-relevant genes in HCC from multiple perspectives. We applied public databases and self-consistent clustering analysis to classify patients into C1, C2, and C3 clusters. The C1 cluster had the shortest overall survival time and advanced pathological features. Least absolute shrinkage and selection operator (LASSO) regression analysis was adopted to build the prognostic prediction model based on six aging-related genes (HMMR, S100A9, SPP1, CYP2C9, CFHR3, and RAMP3). These genes were differently expressed in HepG2 cell lines compared with LO2 cell lines measured by the mRNA expression level. The high-risk score group had significantly more immune checkpoint genes, higher tumor immune dysfunction and exclusion score, and stronger chemotherapy response. The results indicated that the age-related genes have a close correlation with HCC prognosis and immune characteristics. Overall, the model based on six aging-associated genes demonstrated great prognostic prediction ability.

Coordination of the AMPK, Akt, mTOR, and p53 Pathways under Glucose Starvation

Glucose is a direct energy source for eukaryotic cells, and its deficiency elicits complex stress responses and diverse cellular outcomes. Although several signaling pathways involved have been identified, how they coordinately dictate the cell fate remains obscure. We propose a minimal network model for the cellular response to glucose restriction, characterizing the glucose uptake and signaling of the AMPK, Akt, mTOR, and p53 pathways. We demonstrate that in the presence of sufficient growth factors and amino acids, cells may undergo proliferation, senescence, or apoptosis, depending on the extracellular glucose level. AMPK is first activated upon glucose limitation, activating p53 to induce cell-cycle arrest; possibly, cells resume proliferation after timely glucose restoration. For long-term energy stress, cell senescence is maintained by low/intermediate levels of p53 and persistent activation of mTOR and Akt, or cells commit apoptosis when the proteins undergo biphasic dynamics, e.g., p53 switches from intermediate levels to high levels while mTOR and Akt become inactivated in the later phase. The biphasic dynamics of p53 are associated with flipping of two bistable switches. Appropriate mTOR levels are required for optimal cell-fate decision. This work suggests that senescence and apoptosis occur sequentially in glucose-depleted cells, and a theoretical framework is provided for exploring the cellular response to energy stress.

Involvement of inflammatory responses in the brain to the onset of major depressive disorder due to stress exposure

Major depressive disorder (MDD) is a multifactorial disease affected by several environmental factors. Although several potential onset hypotheses have been identified, the molecular mechanisms underlying the pathogenesis of this disorder remain unclear. Several recent studies have suggested that among many environmental factors, inflammation and immune abnormalities in the brain or the peripheral tissues are associated with the onset of MDDs. Furthermore, several stress-related hypotheses have been proposed to explain the onset of MDDs. Thus, inflammation or immune abnormalities can be considered stress responses that occur within the brain or other tissues and are regarded as one of the mechanisms underlying the stress hypothesis of MDDs. Therefore, we introduce several current advances in inflammation studies in the brain that might be related to the pathophysiology of MDD due to stress exposure in this review.

Focus on the Contribution of Oxidative Stress in Skin Aging

Skin aging is one of the most evident signs of human aging. Modification of the skin during the life span is characterized by fine lines and wrinkling, loss of elasticity and volume, laxity, rough-textured appearance, and pallor. In contrast, photoaged skin is associated with uneven pigmentation (age spot) and is markedly wrinkled. At the cellular and molecular level, it consists of multiple interconnected processes based on biochemical reactions, genetic programs, and occurrence of external stimulation. The principal cellular perturbation in the skin driving senescence is the alteration of oxidative balance. In chronological aging, reactive oxygen species (ROS) are produced mainly through cellular oxidative metabolism during adenosine triphosphate (ATP) generation from glucose and mitochondrial dysfunction, whereas in extrinsic aging, loss of redox equilibrium is caused by environmental factors, such as ultraviolet radiation, pollution, cigarette smoking, and inadequate nutrition. During the aging process, oxidative stress is attributed to both augmented ROS production and reduced levels of enzymatic and non-enzymatic protectors. Apart from the evident appearance of structural change, throughout aging, the skin gradually loses its natural functional characteristics and regenerative potential. With aging, the skin immune system also undergoes functional senescence manifested as a reduced ability to counteract infections and augmented frequency of autoimmune and neoplastic diseases. This review proposes an update on the role of oxidative stress in the appearance of the clinical manifestation of skin aging, as well as of the molecular mechanisms that underline this natural phenomenon sometimes accelerated by external factors.

Atlos Labs and the quest for immortality: but can we live longer right now?

Some visionaries prefer to dream of immortality rather than to actually live longer. Here I discuss how combining rapamycin with other modalities may let us live long enough to benefit from future discoveries in cellular reprogramming and what needs to be done at Atlos Labs to make this happen.