Attenuation of TORC1 signaling delays replicative and oncogenic RAS-induced senescence

Lactate-upregulated ARG2 expression induces cellular senescence in fibroblast-like synoviocytes of osteoarthritis via activating the mTOR/S6K1 signaling pathway

Cellular senescence was implicated in the pathogenesis of age-related diseases such as osteoarthritis (OA). Increasing evidence suggests that alterations in the OA joint microenvironment play a crucial role in the pathogenesis of OA. This study aims to establish a clear link between the impact of accumulated lactate on the senescence of fibroblast-like synoviocytes (FLS) within the OA microenvironment. OA models and models with intra-articular injection of lactate were established in rat models, histological analyses were performed. Human OA-FLS treated with lactate was analyzed by mRNA sequencing, senescence related experiments and underlying signaling pathway activation were comprehensively evaluated. This study confirmed that OA models and lactate-injection models exhibited higher synovitis scores. Enrichment analyses indicated dysregulated cell cycle and cellular senescence pathways in OA-FLS treated with lactate. Lactate significantly up-regulated arginase 2 (ARG2) expression and promoted OA-FLS senescence, including G1/S arrest, increased reactive oxygen species and β-galactosidase production, high expression of senescence-associated secretory phenotype factors, which could be attenuated by siRNA-Arg2. The ARG2-mTOR/S6K1 axis was identified as a potential signaling for lactate-induced OA-FLS senescence, and activated mTOR/S6K1 signaling could be reduced by siRNA-Arg2, rapamycin (mTOR inhibitor), and LY294002 (PI3K inhibitor). Our study provides novel targets and insights for OA therapies.

An expedited screening platform for the discovery of anti-ageing compounds in vitro and in vivo

BACKGROUND

Restraining or slowing ageing hallmarks at the cellular level have been proposed as a route to increased organismal lifespan and healthspan. Consequently, there is great interest in anti-ageing drug discovery. However, this currently requires laborious and lengthy longevity analysis. Here, we present a novel screening readout for the expedited discovery of compounds that restrain ageing of cell populations in vitro and enable extension of in vivo lifespan.

METHODS

Using Illumina methylation arrays, we monitored DNA methylation changes accompanying long-term passaging of adult primary human cells in culture. This enabled us to develop, test, and validate the CellPopAge Clock, an epigenetic clock with underlying algorithm, unique among existing epigenetic clocks for its design to detect anti-ageing compounds in vitro. Additionally, we measured markers of senescence and performed longevity experiments in vivo in Drosophila, to further validate our approach to discover novel anti-ageing compounds. Finally, we bench mark our epigenetic clock with other available epigenetic clocks to consolidate its usefulness and specialisation for primary cells in culture.

RESULTS

We developed a novel epigenetic clock, the CellPopAge Clock, to accurately monitor the age of a population of adult human primary cells. We find that the CellPopAge Clock can detect decelerated passage-based ageing of human primary cells treated with rapamycin or trametinib, well-established longevity drugs. We then utilise the CellPopAge Clock as a screening tool for the identification of compounds which decelerate ageing of cell populations, uncovering novel anti-ageing drugs, torin2 and dactolisib (BEZ-235). We demonstrate that delayed epigenetic ageing in human primary cells treated with anti-ageing compounds is accompanied by a reduction in senescence and ageing biomarkers. Finally, we extend our screening platform in vivo by taking advantage of a specially formulated holidic medium for increased drug bioavailability in Drosophila. We show that the novel anti-ageing drugs, torin2 and dactolisib (BEZ-235), increase longevity in vivo.

CONCLUSIONS

Our method expands the scope of CpG methylation profiling to accurately and rapidly detecting anti-ageing potential of drugs using human cells in vitro, and in vivo, providing a novel accelerated discovery platform to test sought after anti-ageing compounds and geroprotectors.

In vitro heterochronic parabiosis identifies pigment epithelium-derived factor as a systemic mediator of rejuvenation by young blood

Several decades of heterochronic parabiosis (HCPB) studies have demonstrated the restorative impact of young blood, and deleterious influence of aged blood, on physiological function and homeostasis across tissues, although few of the factors responsible for these observations have been identified. Here we develop an in vitro HCPB system to identify these circulating factors, using replicative lifespan (RLS) of primary human fibroblasts as an endpoint of cellular health. We find that RLS is inversely correlated with serum donor age and sensitive to the presence or absence of specific serum components. Through in vitro HCPB, we identify the secreted protein pigment epithelium-derived factor (PEDF) as a circulating factor that extends RLS of primary human fibroblasts and declines with age in mammals. Systemic administration of PEDF to aged mice reverses age-related functional decline and pathology across several tissues, improving cognitive function and reducing hepatic fibrosis and renal lipid accumulation. Together, our data supports PEDF as a systemic mediator of the effect of young blood on organismal health and homeostasis and establishes our in vitro HCPB system as a valuable screening platform for the identification of candidate circulating factors involved in aging and rejuvenation.

Palbociclib-Induced Cellular Senescence Is Modulated by the mTOR Complex 1 and Autophagy

Despite not dividing, senescent cells acquire the ability to synthesize and secrete a plethora of bioactive molecules, a feature known as the senescence-associated secretory phenotype (SASP). In addition, senescent cells often upregulate autophagy, a catalytic process that improves cell viability in stress-challenged cells. Notably, this "senescence-related autophagy" can provide free amino acids for the activation of mTORC1 and the synthesis of SASP components. However, little is known about the functional status of mTORC1 in models of senescence induced by CDK4/6 inhibitors (e.g., Palbociclib), or the effects that the inhibition of mTORC1 or the combined inhibition of mTORC1 and autophagy have on senescence and the SASP. Herein, we examined the effects of mTORC1 inhibition, with or without concomitant autophagy inhibition, on Palbociclib-driven senescent AGS and MCF-7 cells. We also assessed the pro-tumorigenic effects of conditioned media from Palbociclib-driven senescent cells with the inhibition of mTORC1, or with the combined inhibition of mTORC1 and autophagy. We found that Palbociclib-driven senescent cells display a partially reduced activity of mTORC1 accompanied by increased levels of autophagy. Interestingly, further mTORC1 inhibition exacerbated the senescent phenotype, a phenomenon that was reversed upon autophagy inhibition. Finally, the SASP varied upon inhibiting mTORC1, or upon the combined inhibition of mTORC1 and autophagy, generating diverse responses in cell proliferation, invasion, and migration of non-senescent tumorigenic cells. Overall, variations in the SASP of Palbociclib-driven senescent cells with the concomitant inhibition of mTORC1 seem to depend on autophagy.

Defining regorafenib as a senomorphic drug: therapeutic potential in the age-related lung disease emphysema

Senescence, a hallmark of aging, is a factor in age-related diseases (ARDs). Therefore, targeting senescence is widely regarded as a practicable method for modulating the effects of aging and ARDs. Here, we report the identification of regorafenib, an inhibitor of multiple receptor tyrosine kinases, as a senescence-attenuating drug. We identified regorafenib by screening an FDA-approved drug library. Treatment with regorafenib at a sublethal dose resulted in effective attenuation of the phenotypes of βPIX knockdown- and doxorubicin-induced senescence and replicative senescence in IMR-90 cells; cell cycle arrest, and increased SA-β-Gal staining and senescence-associated secretory phenotypes, particularly increasing the secretion of interleukin 6 (IL-6) and IL-8. Consistent with this result, slower progression of βPIX depletion-induced senescence was observed in the lungs of mice after treatment with regorafenib. Mechanistically, the results of proteomics analysis in diverse types of senescence indicated that growth differentiation factor 15 and plasminogen activator inhibitor-1 are shared targets of regorafenib. Analysis of arrays for phospho-receptors and kinases identified several receptor tyrosine kinases, including platelet-derived growth factor receptor α and discoidin domain receptor 2, as additional targets of regorafenib and revealed AKT/mTOR, ERK/RSK, and JAK/STAT3 signaling as the major effector pathways. Finally, treatment with regorafenib resulted in attenuation of senescence and amelioration of porcine pancreatic elastase-induced emphysema in mice. Based on these results, regorafenib can be defined as a novel senomorphic drug, suggesting its therapeutic potential in pulmonary emphysema.

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.

Therapeutic Antiaging Strategies

Aging constitutes progressive physiological changes in an organism. These changes alter the normal biological functions, such as the ability to manage metabolic stress, and eventually lead to cellular senescence. The process itself is characterized by nine hallmarks: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. These hallmarks are risk factors for pathologies, such as cardiovascular diseases, neurodegenerative diseases, and cancer. Emerging evidence has been focused on examining the genetic pathways and biological processes in organisms surrounding these nine hallmarks. From here, the therapeutic approaches can be addressed in hopes of slowing the progression of aging. In this review, data have been collected on the hallmarks and their relative contributions to aging and supplemented with in vitro and in vivo antiaging research experiments. It is the intention of this article to highlight the most important antiaging strategies that researchers have proposed, including preventive measures, systemic therapeutic agents, and invasive procedures, that will promote healthy aging and increase human life expectancy with decreased side effects.

Factors and Pathways Modulating Endothelial Cell Senescence in Vascular Aging

Aging causes a progressive decline in the structure and function of organs. With advancing age, an accumulation of senescent endothelial cells (ECs) contributes to the risk of developing vascular dysfunction and cardiovascular diseases, including hypertension, diabetes, atherosclerosis, and neurodegeneration. Senescent ECs undergo phenotypic changes that alter the pattern of expressed proteins, as well as their morphologies and functions, and have been linked to vascular impairments, such as aortic stiffness, enhanced inflammation, and dysregulated vascular tone. Numerous molecules and pathways, including sirtuins, Klotho, RAAS, IGFBP, NRF2, and mTOR, have been implicated in promoting EC senescence. This review summarizes the molecular players and signaling pathways driving EC senescence and identifies targets with possible therapeutic value in age-related vascular diseases.

Senescence and cancer - role and therapeutic opportunities

Cellular senescence is a state of stable, terminal cell cycle arrest associated with various macromolecular changes and a hypersecretory, pro-inflammatory phenotype. Entry of cells into senescence can act as a barrier to tumorigenesis and, thus, could in principle constitute a desired outcome for any anticancer therapy. Paradoxically, studies published in the past decade have demonstrated that, in certain conditions and contexts, malignant and non-malignant cells with lastingly persistent senescence can acquire pro-tumorigenic properties. In this Review, we first discuss the major mechanisms involved in the antitumorigenic functions of senescent cells and then consider the cell-intrinsic and cell-extrinsic factors that participate in their switch towards a tumour-promoting role, providing an overview of major translational and emerging clinical findings. Finally, we comprehensively describe various senolytic and senomorphic therapies and their potential to benefit patients with cancer.

The entry of cells into senescence can act as a barrier to tumorigenesis; however, in certain contexts senescent malignant and non-malignant cells can acquire pro-tumorigenic properties. The authors of this Review discuss the cell-intrinsic and cell-extrinsic mechanisms involved in both the antitumorigenic and tumour-promoting roles of senescent cells, and describe the potential of various senolytic and senomorphic therapeutic approaches in oncology.

Cellular senescence is a natural barrier to tumorigenesis; senescent cells are widely detected in premalignant lesions from patients with cancer.

Cellular senescence is induced by anticancer therapy and can contribute to some treatment-related adverse events (TRAEs).

Senescent cells exert both protumorigenic and antitumorigenic effects via cell-autonomous and paracrine mechanisms.

Pharmacological modulation of senescence-associated phenotypes has the potential to improve therapy efficacy and reduce the incidence of TRAEs.

Cell senescence, rapamycin and hyperfunction theory of aging

A hallmark of cellular senescence is proliferation-like activity of growth-promoting pathways (such as mTOR and MAPK) in non-proliferating cells. When the cell cycle is arrested, these pathways convert arrest to senescence (geroconversion), rendering cells hypertrophic, beta-Gal-positive and hyperfunctional. The senescence-associated secretory phenotype (SASP) is one of the numerous hyperfunctions. Figuratively, geroconversion is a continuation of growth in non-proliferating cells. Rapamycin, a reversible inhibitor of growth, slows down mTOR-driven geroconversion. Developed two decades ago, this model had accurately predicted that rapamycin must extend life span of animals. However, the notion that senescent cells directly cause organismal aging is oversimplified. Senescent cells contribute to organismal aging but are not strictly required. Cell senescence and organismal aging can be linked indirectly via the same underlying cause, namely hyperfunctional signaling pathways such as mTOR.

Senescence-associated tumor growth is promoted by 12-Lipoxygenase

Radiation therapy is a commonly used treatment modality for cancer. Although effective in providing local tumor control, radiation causes oxidative stress, inflammation, immunomodulatory and mitogenic cytokine production, extracellular matrix production, and premature senescence in lung parenchyma. The senescence associated secretory phenotype (SASP) can promote inflammation and stimulate alterations in the surrounding tissue. Therefore, we hypothesized that radiation-induced senescent parenchymal cells in irradiated lung would enhance tumor growth. Using a murine syngeneic tumor model of melanoma and non-small cell lung cancer lung metastasis, we demonstrate that radiation causes a significant increase in markers of premature senescence in lung parenchyma within 4 to 8 weeks. Further, injection of B16F0 (melanoma) or Lewis Lung carcinoma (epidermoid lung cancer) cells at these time points after radiation results in an increase in the number and size of pulmonary tumor nodules relative to unirradiated mice. Treatment of irradiated mice with a senolytic agent (ABT-737) or agents that prevent senescence (rapamycin, INK-128) was sufficient to reduce radiation-induced lung parenchymal senescence and to mitigate radiation-enhanced tumor growth. These agents abrogated radiation-induced expression of 12-Lipoxygenase (12-LOX), a molecule implicated in several deleterious effects of senescence. Deficiency of 12-LOX prevented radiation-enhanced tumor growth. Together, these data demonstrate the pro-tumorigenic role of radiation-induced senescence, introduces the dual TORC inhibitor INK-128 as an effective agent for prevention of radiation-induced normal tissue senescence, and identifies senescence-associated 12-LOX activity as an important component of the pro-tumorigenic irradiated tissue microenvironment. These studies suggest that combining senotherapeutic agents with radiotherapy may decrease post-therapy tumor growth.

Anti-aging: senolytics or gerostatics (unconventional view)

Senolytics are basically anti-cancer drugs, repurposed to kill senescent cells selectively. It is even more difficult to selectively kill senescent cells than to kill cancer cells. Based on lessons of cancer therapy, here I suggest how to exploit oncogene-addiction and to combine drugs to achieve selectivity. However, even if selective senolytic combinations will be developed, there is little evidence that a few senescent cells are responsible for organismal aging. I also discuss gerostatics, such as rapamycin and other rapalogs, pan-mTOR inhibitors, dual PI3K/mTOR inhibitors, which inhibit growth- and aging-promoting pathways. Unlike senolytics, gerostatics do not kill cells but slow down cellular geroconversion to senescence. Numerous studies demonstrated that inhibition of the mTOR pathways by any means (genetic, pharmacological and dietary) extends lifespan. Currently, only two studies demonstrated that senolytics (fisetin and a combination Dasatinib plus Quercetin) extend lifespan in mice. These senolytics slightly inhibit the mTOR pathway. Thus, life extension by these senolytics can be explained by their slight rapamycin-like (gerostatic) effects.

Effects of Siberian fir terpenes extract Abisil on antioxidant activity, autophagy, transcriptome and proteome of human fibroblasts

Background: Abisil is an extract of Siberian fir terpenes with antimicrobial and wound healing activities. Previous studies revealed that Abisil has geroprotective, anti-tumorigenic, and anti-angiogenic effects. Abisil decreased the expression of cyclin D1, E1, A2, and increased the phosphorylation rate of AMPK.

Objective: In the present study, we analyzed the effect of Abisil on autophagy, the mitochondrial potential of embryonic human lung fibroblasts. We evaluated its antioxidant activity and analyzed the transcriptomic and proteomic effects of Abisil treatment.

Results: Abisil treatment resulted in activation of autophagy, reversal of rotenone-induced elevation of reactive oxygen species (ROS) levels and several-fold decrease of mitochondrial potential. Lower doses of Abisil (25 μg/ml) showed a better oxidative effect than high doses (50 or 125 μg/ml). Estimation of metabolic changes after treatment with 50 μg/ml has not shown any changes in oxygen consumption rate, but extracellular acidification rate decreased significantly. Abisil treatment (5 and 50 μg/ml) of MRC5-SV40 cells induced a strong transcriptomic shift spanning several thousand genes (predominantly, expression decrease). Among down-regulated genes, we noticed an over-representation of genes involved in cell cycle progression, oxidative phosphorylation, and fatty acid biosynthesis. Additionally, we observed predominant downregulation of genes encoding for kinases. Proteome profiling also revealed that the content of hundreds of proteins is altered after Abisil treatment (mainly, decreased). These proteins were involved in cell cycle regulation, intracellular transport, RNA processing, translation, mitochondrial organization.

Conclusions: Abisil demonstrated antioxidant and autophagy stimulating activity. Treatment with Abisil results in the predominant downregulation of genes involved in the cell cycle and oxidative phosphorylation.

mTOR Activity and Autophagy in Senescent Cells, a Complex Partnership

Cellular senescence is a form of proliferative arrest triggered in response to a wide variety of stimuli and characterized by unique changes in cell morphology and function. Although unable to divide, senescent cells remain metabolically active and acquire the ability to produce and secrete bioactive molecules, some of which have recognized pro-inflammatory and/or pro-tumorigenic actions. As expected, this “senescence-associated secretory phenotype (SASP)” accounts for most of the non-cell-autonomous effects of senescent cells, which can be beneficial or detrimental for tissue homeostasis, depending on the context. It is now evident that many features linked to cellular senescence, including the SASP, reflect complex changes in the activities of mTOR and other metabolic pathways. Indeed, the available evidence indicates that mTOR-dependent signaling is required for the maintenance or implementation of different aspects of cellular senescence. Thus, depending on the cell type and biological context, inhibiting mTOR in cells undergoing senescence can reverse senescence, induce quiescence or cell death, or exacerbate some features of senescent cells while inhibiting others. Interestingly, autophagy—a highly regulated catabolic process—is also commonly upregulated in senescent cells. As mTOR activation leads to repression of autophagy in non-senescent cells (mTOR as an upstream regulator of autophagy), the upregulation of autophagy observed in senescent cells must take place in an mTOR-independent manner. Notably, there is evidence that autophagy provides free amino acids that feed the mTOR complex 1 (mTORC1), which in turn is required to initiate the synthesis of SASP components. Therefore, mTOR activation can follow the induction of autophagy in senescent cells (mTOR as a downstream effector of autophagy). These functional connections suggest the existence of autophagy regulatory pathways in senescent cells that differ from those activated in non-senescence contexts. We envision that untangling these functional connections will be key for the generation of combinatorial anti-cancer therapies involving pro-senescence drugs, mTOR inhibitors, and/or autophagy inhibitors.

Redd1 knockdown prevents doxorubicin-induced cardiac senescence

Regulated in development and DNA damage response-1 (Redd1) is a stress-response gene that is transcriptionally induced by diverse stressful stimuli to influence cellular growth and survival. Although evidence suggests that aging may drive Redd1 expression in skeletal muscles, the expression patterns and functions of Redd1 in senescent cardiomyocytes remain unspecified. To address this issue, in vitro and in vivo models of cardiomyocyte senescence were established by administration of doxorubicin (Dox). Redd1 overexpression and knockdown was achieved in cultured H9c2 cardiomyocytes and mouse tissues using, respectively, lentivirals and adeno-associated virus 9 (AAV9) vectors. In the hearts of both aged (24 months old) and Dox-treated mice, as well as in Dox-exposed H9c2 cardiomyocytes, high Redd1 expression accompanied the increase in both cellular senescence markers (p16INK4a and p21) and pro-inflammatory cytokine expression indicative of a stress-associated secretory phenotype (SASP). Notably, Redd1 overexpression accentuated, whereas Redd1 silencing markedly attenuated, Dox-induced cardiomyocyte senescence features both in vitro and in vivo. Notably, AAV9-shRNA-mediated Redd1 silencing significantly alleviated Dox-induced cardiac dysfunction. Moreover, through pharmacological inhibition, immunofluorescence, and western blotting, signaling pathway analyses indicated that Redd1 promotes cardiomyocyte senescence as a downstream effector of p38 MAPK to promote NF-kB signaling via p65 phosphorylation and nuclear translocation.

Translational Control during Cellular Senescence

Senescence is a state of long-term cell cycle arrest that arises in cells that have incurred sublethal damage. While senescent cells no longer replicate, they remain metabolically active and further develop unique and stable phenotypes that are not present in proliferating cells. On one hand, senescent cells increase in size, maintain an active mTORC1 complex, and produce and secrete a substantial amount of inflammatory proteins as part of the senescence-associated secretory phenotype (SASP). On the other hand, these progrowth phenotypes contrast with the p53-mediated growth arrest typical of senescent cells that is associated with nucleolar stress and an inhibition of rRNA processing and ribosome biogenesis. In sum, translation in senescent cells paradoxically comprises both a global repression of translation triggered by DNA damage and a select increase in the translation of specific proteins, including SASP factors.

Transcriptional repression of NFKBIA triggers constitutive IKK- and proteasome-independent p65/RelA activation in senescence

The IκB kinase (IKK)‐NF‐κB pathway is activated as part of the DNA damage response and controls both inflammation and resistance to apoptosis. How these distinct functions are achieved remained unknown. We demonstrate here that DNA double‐strand breaks elicit two subsequent phases of NF‐κB activation in vivo and in vitro, which are mechanistically and functionally distinct. RNA‐sequencing reveals that the first‐phase controls anti‐apoptotic gene expression, while the second drives expression of senescence‐associated secretory phenotype (SASP) genes. The rapidly activated first phase is driven by the ATM‐PARP1‐TRAF6‐IKK cascade, which triggers proteasomal destruction of inhibitory IκBα, and is terminated through IκBα re‐expression from the NFKBIA gene. The second phase, which is activated days later in senescent cells, is on the other hand independent of IKK and the proteasome. An altered phosphorylation status of NF‐κB family member p65/RelA, in part mediated by GSK3β, results in transcriptional silencing of NFKBIA and IKK‐independent, constitutive activation of NF‐κB in senescence. Collectively, our study reveals a novel physiological mechanism of NF‐κB activation with important implications for genotoxic cancer treatment.

IER2-induced senescence drives melanoma invasion through osteopontin

Expression of the immediate-early response gene IER2 has been associated with the progression of several types of cancer, but its functional role is poorly understood. We found that increased IER2 expression in human melanoma is associated with shorter overall survival, and subsequently investigated the mechanisms through which IER2 exerts this effect. In experimental melanoma models, sustained expression of IER2 induced senescence in a subset of melanoma cells in a p53/MAPK/AKT-dependent manner. The senescent cells produced a characteristic secretome that included high levels of the extracellular phosphoglycoprotein osteopontin. Nuclear localization of the IER2 protein was critical for both the induction of senescence and osteopontin secretion. Osteopontin secreted by IER2-expressing senescent cells strongly stimulated the migration and invasion of non-senescent melanoma cells. Consistently, we observed coordinate expression of IER2, p53/p21, and osteopontin in primary human melanomas and metastases, highlighting the pathophysiological relevance of IER2-mediated senescence in melanoma progression. Together, our study reveals that sustained IER2 expression drives melanoma invasion and progression through stimulating osteopontin secretion via the stochastic induction of senescence.

Sustained mTORC1 activity during palbociclib-induced growth arrest triggers senescence in ER+ breast cancer cells

Palbociclib, a selective CDK4/6 kinase inhibitor, is approved in combination with endocrine therapies for the treatment of advanced estrogen receptor positive (ER+) breast cancer. In pre-clinical cancer models, CDK4/6 inhibitors act primarily as cytostatic agents. In two commonly studied ER+ breast cancer cell lines (MCF7 and T47D), CDK4/6 inhibition drives G1-phase arrest and the acquisition of a senescent-like phenotype, both of which are reversible upon palbociclib withdrawal (incomplete senescence). Here we identify an ER+ breast cancer cell line, CAMA1, in which palbociclib treatment induces irreversible cell cycle arrest and senescence (complete senescence). In stark contrast to T47D and MCF7 cells, mTORC1 activity is not stably suppressed in CAMA1 cells during palbociclib treatment. Importantly, inhibition of mTORC1 signaling either by the mTORC1 inhibitor rapamycin or by knockdown of Raptor, a unique component of mTORC1, during palbociclib treatment of CAMA1 cells blocks the induction of complete senescence. These results indicate that sustained mTORC1 activity promotes complete senescence in ER+ breast cancer cells during CDK4/6 inhibitor-induced cell cycle arrest. Consistent with this mechanism, genetic depletion of TSC2, a negative regulator of mTORC1, in MCF7 cells resulted in sustained mTORC1 activity during palbociclib treatment and evoked a complete senescence response. These findings demonstrate that persistent mTORC1 signaling during palbociclib-induced G1 arrest is a potential liability for ER+ breast cancer cells, and suggest a strategy for novel drug combinations with palbociclib.

From causes of aging to death from COVID-19

COVID-19 is not deadly early in life, but mortality increases exponentially with age, which is the strongest predictor of mortality. Mortality is higher in men than in women, because men age faster, and it is especially high in patients with age-related diseases, such as diabetes and hypertension, because these diseases are manifestations of aging and a measure of biological age. At its deepest level, aging (a program-like continuation of developmental growth) is driven by inappropriately high cellular functioning. The hyperfunction theory of quasi-programmed aging explains why COVID-19 vulnerability (lethality) is an age-dependent syndrome, linking it to other age-related diseases. It also explains inflammaging and immunosenescence, hyperinflammation, hyperthrombosis, and cytokine storms, all of which are associated with COVID-19 vulnerability. Anti-aging interventions, such as rapamycin, may slow aging and age-related diseases, potentially decreasing COVID-19 vulnerability.

Deficiency in IκBα in the intestinal epithelium leads to spontaneous inflammation and mediates apoptosis in the gut

The IκB kinase (IKK)-NF-κB signaling pathway plays a multifaceted role in inflammatory bowel disease (IBD): on the one hand, it protects from apoptosis; on the other, it activates transcription of numerous inflammatory cytokines and chemokines. Although several murine models of IBD rely on disruption of IKK-NF-κB signaling, these involve either knockouts of a single family member of NF-κB or of upstream kinases that are known to have additional, NF-κB-independent, functions. This has made the distinct contribution of NF-κB to homeostasis in intestinal epithelium cells difficult to assess. To examine the role of constitutive NF-κB activation in intestinal epithelial cells, we generated a mouse model with a tissue-specific knockout of the direct inhibitor of NF-κB, Nfkbia/IκBα. We demonstrate that constitutive activation of NF-κB in intestinal epithelial cells induces several hallmarks of IBD including increased apoptosis, mucosal inflammation in both the small intestine and the colon, crypt hyperplasia, and depletion of Paneth cells, concomitant with aberrant Wnt signaling. To determine which NF-κB-driven phenotypes are cell-intrinsic, and which are extrinsic and thus require the immune compartment, we established a long-term organoid culture. Constitutive NF-κB promoted stem-cell proliferation, mis-localization of Paneth cells, and sensitization of intestinal epithelial cells to apoptosis in a cell-intrinsic manner. Increased number of stem cells was accompanied by a net increase in Wnt activity in organoids. Because aberrant Wnt signaling is associated with increased risk of cancer in IBD patients and because NFKBIA has recently emerged as a risk locus for IBD, our findings have critical implications for the clinic. In a context of constitutive NF-κB, our findings imply that general anti-inflammatory or immunosuppressive therapies should be supplemented with direct targeting of NF-κB within the epithelial compartment in order to attenuate apoptosis, inflammation, and hyperproliferation. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

The roles of MTOR and miRNAs in endothelial cell senescence

Accumulation of senescent cells in vascular endothelium is known to contribute to vascular aging and increases the risk of developing cardiovascular diseases. The involvement of classical pathways such as p53/p21 and p16/pRB in cellular senescence are well described but there are emerging evidence supporting the increasingly important role of mammalian target of rapamycin (MTOR) as driver of cellular senescence via these pathways or other effector molecules. MicroRNAs (miRNAs) are a highly conserved group of small non-coding RNAs (18-25 nucleotides), instrumental in modulating the expression of target genes associated with various biological and cellular processes including cellular senescence. The inhibition of MTOR activity is predominantly linked to cellular senescence blunting and prolonged lifespan in model organisms. To date, known miRNAs regulating MTOR in endothelial cell senescence remain limited. Herein, this review discusses the roles of MTOR and MTOR-associated miRNAs in regulating endothelial cell senescence, including the crosstalk between MTOR Complex 1 (MTORC1) and cell cycle pathways and the emerging role of MTORC2 in cellular senescence. New insights on how MTOR and miRNAs coordinate underlying molecular mechanisms of endothelial senescence will provide deeper understanding and clarity to the complexity of the regulation of cellular senescence.

mTORC1 and mTORC2 Differentially Regulate Cell Fate Programs to Coordinate Osteoblastic Differentiation in Mesenchymal Stromal Cells

Vascular regeneration depends on intact function of progenitors of vascular smooth muscle cells such as pericytes and their circulating counterparts, mesenchymal stromal cells (MSC). Deregulated MSC differentiation and maladaptive cell fate programs associated with age and metabolic diseases may exacerbate arteriosclerosis due to excessive transformation to osteoblast-like calcifying cells. Targeting mTOR, a central controller of differentiation and cell fates, could offer novel therapeutic perspectives. In a cell culture model for osteoblastic differentiation of pluripotent human MSC we found distinct roles for mTORC1 and mTORC2 in the regulation of differentiation towards calcifying osteoblasts via cell fate programs in a temporally-controlled sequence. Activation of mTORC1 with induction of cellular senescence and apoptosis were hallmarks of transition to a calcifying phenotype. Inhibition of mTORC1 with Rapamycin elicited reciprocal activation of mTORC2, enhanced autophagy and recruited anti-apoptotic signals, conferring protection from calcification. Pharmacologic and genetic negative interference with mTORC2 function or autophagy both abolished regenerative programs but induced cellular senescence, apoptosis, and calcification. Overexpression of the mTORC2 constituent rictor revealed that enhanced mTORC2 signaling without altered mTORC1 function was sufficient to inhibit calcification. Studies in mice reproduced the in vitro effects of mTOR modulation with Rapamycin on cell fates in vascular cells in vivo. Amplification of mTORC2 signaling promotes protective cell fates including autophagy to counteract osteoblast differentiation and calcification of MSC, representing a novel mTORC2 function. Regenerative approaches aimed at modulating mTOR network activation patterns hold promise for delaying age-related vascular diseases and treatment of accelerated arteriosclerosis in chronic metabolic conditions.

Disease or not, aging is easily treatable

Is aging a disease? It does not matter because aging is already treated using a combination of several clinically-available drugs, including rapamycin. Whether aging is a disease depends on arbitrary definitions of both disease and aging. For treatment purposes, aging is a deadly disease (or more generally, pre-disease), despite being a normal continuation of normal organismal growth. It must and, importantly, can be successfully treated, thereby delaying classic age-related diseases such as cancer, cardiovascular and metabolic diseases, and neurodegeneration.

mTOR as a central regulator of lifespan and aging

The mammalian/mechanistic target of rapamycin (mTOR) is a key component of cellular metabolism that integrates nutrient sensing with cellular processes that fuel cell growth and proliferation. Although the involvement of the mTOR pathway in regulating life span and aging has been studied extensively in the last decade, the underpinning mechanisms remain elusive. In this review, we highlight the emerging insights that link mTOR to various processes related to aging, such as nutrient sensing, maintenance of proteostasis, autophagy, mitochondrial dysfunction, cellular senescence, and decline in stem cell function.

Rapamycin, proliferation and geroconversion to senescence

Rapamycin inhibits cell proliferation, yet preserves (re)-proliferative potential (RPP). RPP is a potential of quiescent cells that is lost in senescent cells. mTOR drives conversion from quiescence to senescence (geroconversion). By suppressing geroconversion, rapamycin preserves RPP. Geroconversion is characterized by proliferation-like levels of phospho-S6K/S6/4E-BP1 in nonproliferating cells arrested by p16 and/or p21. mTOR-driven geroconversion is associated with cellular hyperfunction, which in turn leads to organismal aging manifested by age-related diseases.

Overexpression of the recently identified oncogene REDD1 correlates with tumor progression and is an independent unfavorable prognostic factor for ovarian carcinoma

Background

Regulated in development and DNA damage response (REDD1), a gene responding to hypoxia or multiple DNA damage events, was recently implicated in cancer development and progression. Previously, in vivo and in vitro experiments indicated that REDD1 functions as an oncogene in ovarian cancer cells. However, the role of REDD1 in cancer cell migration and invasion and in clinical significance of prognostic values is not examined in detail.

Methods

We detected the REDD1 protein expression by immunohistochemistry in 18 normal ovarian surface epithelium or fallopian tube epithelium specimens, 24 ovarian borderline tumors, and 229 ovarian cancers. Fisher’s exact test, logistic regression analysis, the Kaplan–Meier method, and the log-rank test were used to evaluate the association of REDD1 with clinical factors, overall survival and disease-free survival. The prognostic predictive value of REDD1 for ovarian cancer patients was evaluated using multivariate Cox proportional hazard regression models. REDD1 expression in HEY, HEY A8, SKOV3, SKOV3 ip1, OVCA429, OVCA433 and A2780 human ovarian epithelial cancer cell lines was detected by western blotting. The role of REDD1 in cell invasion and migration was assessed by transwell migration and invasion assays using SKOV3, A2780, HEY, HEYA8, and SKOV3-REDD1 with parental A2780-REDD1 HEY-REDD1i and HEY A8-REDD1i.

Results

High expression of REDD1 was observed in 35.4% of primary ovarian carcinoma samples. Overexpression of cytoplasmic REDD1 in ovarian cancer was significantly associated with serous carcinoma (P < 0.001), late-stage disease (P < 0.001), ascites (P < 0.001), and partial or non-response to chemotherapy (P < 0.001). High cytoplasmic expression of REDD1 was correlated with poorer overall survival (P < 0.001) and disease-free survival (P < 0.001). The multivariate Cox proportional hazards regression analysis indicated that patients with high cytoplasmic REDD1 expression had a high risk of death (P < 0.001) and high risk of an event (i.e., recurrence, progression, or death) (P < 0.001). REDD1 was first reported as an independent prognostic factor in ovarian cancer patients. In addition, REDD1 overexpression enhanced ovarian cancer cell migration and invasion.

Conclusion

REDD1 is an independent unfavorable prognostic factor in ovarian carcinoma and may promote ovarian cancer metastasis.

Electronic supplementary material

The online version of this article (10.1186/s13000-018-0754-4) contains supplementary material, which is available to authorized users.

mTOR kinase leads to PTEN-loss-induced cellular senescence by phosphorylating p53

Loss of PTEN, the major negative regulator of the PI3K/AKT pathway induces a cellular senescence as a failsafe mechanism to defend against tumorigenesis, which is called PTEN-loss-induced cellular senescence (PICS). Although many studies have indicated that the mTOR pathway plays a critical role in cellular senescence, the exact functions of mTORC1 and mTORC2 in PICS are not well understood. In this study, we show that mTOR acts as a critical relay molecule downstream of PI3K/AKT and upstream of p53 in PICS. We found that PTEN depletion induces cellular senescence via p53-p21 signaling without triggering DNA damage response. mTOR kinase, a major component of mTORC1 and mTORC2, directly binds p53 and phosphorylates it at serine 15. mTORC1 and mTORC2 compete with MDM2 and increase the stability of p53 to induce cellular senescence via accumulation of the cell cycle inhibitor, p21. In embryonic fibroblasts of PTEN-knockout mice, PTEN deficiency also induces mTORC1 and mTORC2 to bind to p53 instead of MDM2, leading to cellular senescence. These results collectively demonstrate for the first time that mTOR plays a critical role in switching cells from proliferation signaling to senescence signaling via a direct link between the growth-promoting activity of AKT and the growth-suppressing activity of p53.

Cellular Senescence, Neurological Function, and Redox State

SIGNIFICANCE

Cellular senescence, characterized by permanent cell cycle arrest, has been extensively studied in mitotic cells such as fibroblasts. However, senescent cells have also been observed in the brain. Even though it is recognized that cellular energetic metabolism and redox homeostasis are perturbed in the aged brain and neurodegenerative diseases (NDDs), it is still unknown which alterations in the overall physiology can stimulate cellular senescence induction and their relationship with the former events. Recent Advances: Recent findings have shown that during prolonged inflammatory and pathologic events, the blood-brain barrier could be compromised and immune cells might enter the brain; this fact along with the brain's high oxygen dependence might result in oxidative damage to macromolecules and therefore senescence induction. Thus, cellular senescence in different brain cell types is revised here.

CRITICAL ISSUES

Most information related to cellular senescence in the brain has been obtained from research in glial cells since it has been assumed that the senescent phenotype is a feature exclusive to mitotic cells. Nevertheless, neurons with senescence hallmarks have been observed in old mouse brains. Therefore, although this is a controversial topic in the field, here we summarize and integrate the observations from several studies and propose that neurons indeed senesce.

FUTURE DIRECTIONS

It is still unknown which alterations in the overall metabolism can stimulate senescence induction in the aged brain, what are the mechanisms and signaling pathways, and what is their relationship to NDD development. The understanding of these processes will expose new targets to intervene age-associated pathologies.-Antioxid. Redox Signal. 28, 1704-1723.

Nutrient sensing, growth and senescence

Cell growth is dictated by a wide range of mitogenic signals, the amplitude and relative contribution of which vary throughout development, differentiation and in a tissue-specific manner. The ability to sense and appropriately respond to changes in mitogens is fundamental to control cell growth, and reduced responsiveness of nutrient sensing pathways is widely associated with human disease and ageing. Cellular senescence is an important tumour suppressor mechanism that is characterised by an irreversible exit from the cell cycle in response to replicative exhaustion or excessive DNA damage. Despite the fact that senescent cells can no longer divide, they remain metabolically active and display a range of pro-growth phenotypes that are supported in part by the mTORC1-autophagy signalling axis. As our understanding of the basic mechanisms of controlling mTORC1-autophagy activity and cell growth continues to expand, we are able to explore how changes in nutrient sensing contribute to the acquisition and maintenance of cellular senescence. Furthermore, while the protective effect of senescence to limit cellular transformation is clear, more recently, the age-related accumulation of these pro-inflammatory senescent cells has been shown to contribute to a decline in organismal fitness. We will further discuss whether dysregulation of nutrient sensing pathways can be targeted to promote senescent cell death which would have important implications for healthy ageing.

Endothelial replicative senescence delayed by the inhibition of MTORC1 signaling involves MicroRNA-107

Accumulation of senescent endothelial cells can contribute to endothelium dysfunction. Suppression of MTOR signaling has been shown to delay senescence but the mechanism that underpins this effect, particularly one that involves miRNAs, remains to be further defined. This study sought to identify miRNAs involved in MTORC1-mediated inhibition of replicative senescence in endothelial cells. Pre-senescent HUVECs were prolonged treated with low dose rapamycin (1 nM), an MTOR inhibitor. Rapamycin treatment down-regulated the phosphorylated MTOR, RPS6 and 4EBP1 expressions, which confirmed MTORC1 suppression. Prolonged low dose rapamycin treatment has significantly reduced the percentage of senescence-associated beta galactosidase (SA-β gal) positively stained senescent cells and P16INK4A expression in these cells. On the contrary, the percentage of BrdU-labelled proliferating cells has significantly increased. RPTOR, a positive regulator of MTORC1 was knockdown using RPTOR siRNA to inhibit MTORC1 activation. RPTOR knockdown was evidenced by significant suppressions of RPTOR mRNA and protein expression levels. In these cells, the expression of miR-107 was down-regulated whereas miR-145-5p and miR-217 were up-regulated. Target gene prediction revealed PTEN as the target of miR-107 and this was confirmed by biotin pull-down assay. Over-expression of miR-107 has decreased PTEN expression, increased MTORC1 activity, induced cell cycle arrest at G0/G1 phase and up-regulated P16INK4A expression but mitigated tube formation. Collectively, our findings revealed that delayed endothelial replicative senescence caused by the inhibition of MTORC1 activation could be modulated by miR-107 via its influence on PTEN.

SALL1 functions as a tumor suppressor in breast cancer by regulating cancer cell senescence and metastasis through the NuRD complex

Background

SALL1 is a multi-zinc finger transcription factor that regulates organogenesis and stem cell development, but the role of SALL1 in tumor biology and tumorigenesis remains largely unknown.

Methods

We analyzed SALL1 expression levels in human and murine breast cancer cells as well as cancer tissues from different types of breast cancer patients. Using both in vitro co-culture system and in vivo breast tumor models, we investigated how SALL1 expression in breast cancer cells affects tumor cell growth and proliferation, metastasis, and cell fate. Using the gain-of function and loss-of-function strategies, we dissected the molecular mechanism responsible for SALL1 tumor suppressor functions.

Results

We demonstrated that SALL1 functions as a tumor suppressor in breast cancer, which is significantly down-regulated in the basal like breast cancer and in estrogen receptor (ER), progesterone receptor (PR) and epidermal growth factor receptor 2 (HER2) triple negative breast cancer patients. SALL1 expression in human and murine breast cancer cells inhibited cancer cell growth and proliferation, metastasis, and promoted cell cycle arrest. Knockdown of SALL1 in breast cancer cells promoted cancer cell growth, proliferation, and colony formation. Our studies revealed that tumor suppression was mediated by recruitment of the Nucleosome Remodeling and Deacetylase (NuRD) complex by SALL1, which promoted cancer cell senescence. We further demonstrated that the mechanism of inhibition of breast cancer cell growth and invasion by SALL1-NuRD depends on the p38 MAPK, ERK1/2, and mTOR signaling pathways.

Conclusion

Our studies indicate that the developmental control gene SALL1 plays a critical role in tumor suppression by recruiting the NuRD complex and thereby inducing cell senescence in breast cancer cells.

Electronic supplementary material

The online version of this article (10.1186/s12943-018-0824-y) contains supplementary material, which is available to authorized users.

Is there a role for placental senescence in the genesis of obstetric complications and fetal growth restriction?

The placenta ages as pregnancy advances, yet its continued function is required for a successful pregnancy outcome. Placental aging is a physiological phenomenon; however, there are some placentas that show signs of aging earlier than others. Premature placental senescence and aging are implicated in a number of adverse pregnancy outcomes, including fetal growth restriction, preeclampsia, spontaneous preterm birth, and intrauterine fetal death. Here we discuss cellular senescence, a state of terminal proliferation arrest, and how senescence is regulated. We also explore the role of physiological placental senescence and how aberrant placental senescence alters placental function, contributing to the pathophysiology of fetal growth restriction, preeclampsia, spontaneous preterm labor/birth, and unexplained fetal death.

Identification of Salvia haenkei as gerosuppressant agent by using an integrated senescence-screening assay

Cellular senescence is a stable cell cycle arrest that is the causative process of aging. The PI3K/AKT/mTOR pathway is implicated in the control of cellular senescence and inhibitors of this pathway have been successfully used for life span prolongation experiments in mammals. PTEN is the major regulator of the PI3K/AKT/mTOR pathway and loss of PTEN promotes a senescence response termed PICS. Here we report a novel-screening assay, for the identification of compounds that block different types of senescence response. By testing a library of more than 3000 natural and chemical compounds in PTEN deficient cells we have found that an extract from Salvia haenkei (SH), a native plant of Bolivia is a potent inhibitor of PICS. SH also decreases replicative and UV-mediated senescence in human primary fibroblasts and in a model of in vitro reconstructed human epidermis. Mechanistically, SH treatment affects senescence driven by UV by interfering with IL1-α signalling. Pre-clinical and clinical testing of this extract by performing toxicity and irritability evaluation in vitro also demonstrate the safety of SH extract for clinical use as anti-aging skin treatment.

Targeting metabolism in cellular senescence, a role for intervention

Cellular senescence has gained much attention as a contributor to aging and susceptibility to disease. Senescent cells undergo a stable cell cycle arrest and produce pro-inflammatory cytokines. However, an additional feature of the senescence phenotype is an altered metabolic state. Despite maintaining a non-dividing state, senescent cells display a high metabolic rate. Metabolic changes characteristic of replicative senescence include altered mitochondrial function and perturbations in growth signaling pathways, such as the mTORC1-signaling pathway. Recent evidence has raised the possibility that these metabolic changes may be essential for the induction and maintenance of the senescent state. Interventions such as rapamycin treatment and methionine restriction impact key aspects of metabolism and delay cellular senescence to extend cellular lifespan. Here, we review the metabolic changes and potential metabolic regulators of the senescence program. In addition, we will discuss how lifespan-extending regimens prevent metabolic stress that accompanies and potentially regulates the senescence program.

A progressive reduction in autophagic capacity contributes to induction of replicative senescence in Hs68 cells

Autophagy has been implicated in delayed aging and extended longevity. Here, we aimed to study the possible effects of autophagy during the progression of replicative senescence, which is one of the major features of aging. Human foreskin fibroblasts, Hs68 cells, at an initial passage of 15 were serially cultured for several months until they reached cellular senescence. A decrease in cell proliferation was observed during the progression of senescence. Induction of replicative senescence in aged cells (at passage 40) was confirmed by senescence-associated β-galactosidase (SA-β-gal) activity that represents a sensitive and reliable marker for quantifying senescent cells. We detected a significantly increased percentage (%) of SA-β-gal-positive cells at passage 40 (63%) when compared with the younger SA-β-gal-positive cells at passage 15 (0.5%). Notably, the gradual decrease in basal autophagy coincided with replicative senescence induction. However, despite decreased basal autophagic activity in senescent cells, autophagy inducers could induce autophagy in senescent cells. RT-PCR analysis of 11 autophagy-related genes revealed that the decreased basal autophagy in senescent cells might be due to the downregulation of autophagy-regulatory proteins, but not autophagy machinery components. Moreover, the senescence phenotype was not induced in the cells in which rapamycin was added to the culture to continuously induce autophagy from passage 29 until passage 40. Together, our findings suggest that reduced basal autophagy levels due to downregulation of autophagy-regulatory proteins may be the mechanism underlying replicative senescence in Hs68 cells.

mTOR Inhibition Rejuvenates the Aging Gingival Fibroblasts through Alleviating Oxidative Stress

The aging periodontium may be vulnerable to periodontal pathogens and poor response to inflammation and susceptible to tumorigenesis. Human gingival fibroblasts (hGFs) through continuously replicative culture served as an in vitro surrogate for aging. To investigate the effects of the mechanistic target of rapamycin (mTOR) inhibition on the aging gingiva, we stimulated the high-passage hGFs with rapamycin (20 nmol/L) for 3 days and 30 days. The cellular and biological changes were examined by immunofluorescence, real-time PCR, ELISA, Western blotting, and flow cytometry. The data demonstrated that the inhibition of mTOR signaling led to fewer senescence-associated beta-galactosidase- (SA-β-Gal-) positive cells, delayed the onset of senescence, preserved the capability of proliferation, and lowered the expression levels of relevant senescence-associated markers, such as p16^INK4a, p21^CIP1a, interleukin-6 (IL-6), and IL-8. In addition, when infected by prominent periodontal pathogens, Porphyromonas gingivalis (ATCC 33277), rapamycin-pretreated groups decreased the expression of inflammatory cytokines (IL-6 and IL-8) compared with the control group. mTOR inhibition upregulated the gene expression of antioxidant components (Cat, Sod2, and Prdx3; P < 0.05) and consequently neutralized the excessive reactive oxygen species (ROS). In conclusion, our results indicated that mTOR inhibition might rejuvenate the aging gingiva to some extent and relieve inflammation through eliminating oxidative stress.

Radiation-Induced Fibrosis: Mechanisms and Opportunities to Mitigate. Report of an NCI Workshop, September 19, 2016

A workshop entitled "Radiation-Induced Fibrosis: Mechanisms and Opportunities to Mitigate" (held in Rockville, MD, September 19, 2016) was organized by the Radiation Research Program and Radiation Oncology Branch of the Center for Cancer Research (CCR) of the National Cancer Institute (NCI), to identify critical research areas and directions that will advance the understanding of radiation-induced fibrosis (RIF) and accelerate the development of strategies to mitigate or treat it. Experts in radiation biology, radiation oncology and related fields met to identify and prioritize the key areas for future research and clinical translation. The consensus was that several known and newly identified targets can prevent or mitigate RIF in pre-clinical models. Further, basic and translational research and focused clinical trials are needed to identify optimal agents and strategies for therapeutic use. It was felt that optimally designed preclinical models are needed to better study biomarkers that predict for development of RIF, as well as to understand when effective therapies need to be initiated in relationship to manifestation of injury. Integrating appropriate endpoints and defining efficacy in clinical trials testing treatment of RIF were felt to be critical to demonstrating efficacy. The objective of this meeting report is to (a) highlight the significance of RIF in a global context, (b) summarize recent advances in our understanding of mechanisms of RIF,

Melanocytic nevi and melanoma: unraveling a complex relationship

Approximately 33% of melanomas are derived directly from benign, melanocytic nevi. Despite this, the vast majority of melanocytic nevi, which typically form as a result of BRAF^V600E-activating mutations, will never progress to melanoma. Herein, we synthesize basic scientific insights and data from mouse models with common observations from clinical practice to comprehensively review melanocytic nevus biology. In particular, we focus on the mechanisms by which growth arrest is established after BRAF^V600E mutation. Means by which growth arrest can be overcome and how melanocytic nevi relate to melanoma are also considered. Finally, we present a new conceptual paradigm for understanding the growth arrest of melanocytic nevi in vivo termed stable clonal expansion. This review builds upon the canonical hypothesis of oncogene-induced senescence in growth arrest and tumor suppression in melanocytic nevi and melanoma.

The Senescence-Associated Secretory Phenotype: Critical Effector in Skin Cancer and Aging

Cellular senescence, a state of stable cell cycle arrest in response to cellular stress, is an indispensable mechanism to counter tumorigenesis by halting the proliferation of damaged cells. However, through the secretion of an array of diverse cytokines, chemokines, growth factors, and proteases known as the senescence-associated secretory phenotype (SASP), senescent cells can paradoxically promote carcinogenesis. Consistent with this, removal of senescent cells delays the onset of cancer and prolongs lifespan in vivo, potentially in part through SASP reduction. In this review, we consider the evidence for the SASP and "SASP-like" inflammation in driving skin carcinogenesis, emphasizing how further understanding of both the roles and mechanisms of SASP expression may offer new targets for skin cancer prevention and therapy.

Dual mTORC1/C2 inhibitors suppress cellular geroconversion (a senescence program)

In proliferating cells, mTOR is active and promotes cell growth. When the cell cycle is arrested, then mTOR converts reversible arrest to senescence (geroconversion). Rapamycin and other rapalogs suppress geroconversion, maintaining quiescence instead. Here we showed that ATP-competitive kinase inhibitors (Torin1 and PP242), which inhibit both mTORC1 and TORC2, also suppressed geroconversion. Despite inhibition of proliferation (in proliferating cells), mTOR inhibitors preserved re-proliferative potential (RP) in arrested cells. In p21-arrested cells, Torin 1 and PP242 detectably suppressed geroconversion at concentrations as low as 1-3 nM and 10-30 nM, reaching maximal gerosuppression at 30 nM and 300 nM, respectively. Near-maximal gerosuppression coincided with inhibition of p-S6K(T389) and p-S6(S235/236). Dual mTOR inhibitors prevented senescent morphology and hypertrophy. Our study warrants investigation into whether low doses of dual mTOR inhibitors will prolong animal life span and delay age-related diseases. A new class of potential anti-aging drugs can be envisioned.

Mammalian Target of Rapamycin Inhibition With Rapamycin Mitigates Radiation-Induced Pulmonary Fibrosis in a Murine Model

PURPOSE

Radiation-induced pulmonary fibrosis (RIPF) is a late toxicity of therapeutic radiation. Signaling of the mammalian target of rapamycin drives several processes implicated in RIPF, including inflammatory cytokine production, fibroblast proliferation, and epithelial senescence. We sought to determine if mammalian target of rapamycin inhibition with rapamycin would mitigate RIPF.

METHODS AND MATERIALS

C57BL/6NCr mice received a diet formulated with rapamycin (14 mg/kg food) or a control diet 2 days before and continuing for 16 weeks after exposure to 5 daily fractions of 6 Gy of thoracic irradiation. Fibrosis was assessed with Masson trichrome staining and hydroxyproline assay. Cytokine expression was evaluated by quantitative real-time polymerase chain reaction. Senescence was assessed by staining for β-galactosidase activity.

RESULTS

Administration of rapamycin extended the median survival of irradiated mice compared with the control diet from 116 days to 156 days (P=.006, log-rank test). Treatment with rapamycin reduced hydroxyproline content compared with the control diet (irradiation plus vehicle, 45.9 ± 11.8 μg per lung; irradiation plus rapamycin, 21.4 ± 6.0 μg per lung; P=.001) and reduced visible fibrotic foci. Rapamycin treatment attenuated interleukin 1β and transforming growth factor β induction in irradiated lungs compared with the control diet. Type II pneumocyte senescence after irradiation was reduced with rapamycin treatment at 16 weeks (3-fold reduction at 16 weeks, P<.001).

CONCLUSIONS

Rapamycin protected against RIPF in a murine model. Rapamycin treatment reduced inflammatory cytokine expression, extracellular matrix production, and senescence in type II pneumocytes.

Rejuvenating immunity: "anti-aging drug today" eight years later

The 2014 year ended with celebration: Everolimus, a rapamycin analog, was shown to improve immunity in old humans, heralding ‘a turning point’ in research and new era in human quest for immortality. Yet, this turning point was predicted a decade ago. But what will cause human death, when aging will be abolished?

Ageing and the telomere connection: An intimate relationship with inflammation

Telomeres are the heterochromatic repeat regions at the ends of eukaryotic chromosomes, whose length is considered to be a determinant of biological ageing. Normal ageing itself is associated with telomere shortening. Here, critically short telomeres trigger senescence and eventually cell death. This shortening rate may be further increased by inflammation and oxidative stress and thus affect the ageing process. Apart from shortened or dysfunctional telomeres, cells undergoing senescence are also associated with hyperactivity of the transcription factor NF-κB and overexpression of inflammatory cytokines such as TNF-α, IL-6, and IFN-γ in circulating macrophages. Interestingly, telomerase, a reverse transcriptase that elongates telomeres, is involved in modulating NF-κB activity. Furthermore, inflammation and oxidative stress are implicated as pre-disease mechanisms for chronic diseases of ageing such as neurodegenerative diseases, cardiovascular disease, and cancer. To date, inflammation and telomere shortening have mostly been studied individually in terms of ageing and the associated disease phenotype. However, the interdependent nature of the two demands a more synergistic approach in understanding the ageing process itself and for developing new therapeutic approaches. In this review, we aim to summarize the intricate association between the various inflammatory molecules and telomeres that together contribute to the ageing process and related diseases.

Senescence from G2 arrest, revisited

Senescence was classically defined as an irreversible cell cycle arrest in G1 phase (G1 exit) triggered by eroded telomeres in aged primary cells. The molecular basis of this G1 arrest is thought to be due to a DNA damage response, resulting in accumulation of the cyclin dependent kinase (Cdk) inhibitors p21 and p16 that block the inactivating phosphorylation of the retinoblastoma tumor suppressor pRb, thereby preventing DNA replication. More than a decade ago, several studies showed that p21 also mediates permanent DNA damage-induced cell cycle arrest in G2 (G2 exit) by inhibiting mitotic Cdk complexes and pRb phosphorylation. The idea that the senescence program can also be launched after G2 arrest has gained support from several recent publications, including evidence for its existence in vivo.

Tumor promoter-induced cellular senescence: cell cycle arrest followed by geroconversion

Phorbol ester (PMA or TPA), a tumor promoter, can cause either proliferation or cell cycle arrest, depending on cellular context. For example, in SKBr3 breast cancer cells, PMA hyper-activates the MEK/MAPK pathway, thus inducing p21 and cell cycle arrest. Here we showed that PMA-induced arrest was followed by conversion to cellular senescence (geroconversion). Geroconversion was associated with active mTOR and S6 kinase (S6K). Rapamycin suppressed geroconversion, maintaining quiescence instead. In this model, PMA induced arrest (step one of a senescence program), whereas constitutively active mTOR drove geroconversion (step two). Without affecting Akt phosphorylation, PMA increased phosphorylation of S6K (T389) and S6 (S240/244), and that was completely prevented by rapamycin. Yet, T421/S424 and S235/236 (p-S6K and p-S6, respectively) phosphorylation became rapamycin-insensitive in the presence of PMA. Either MEK or mTOR was sufficient to phosphorylate these PMA-induced rapamycin-resistant sites because co-treatment with U0126 and rapamycin was required to abrogate them. We next tested whether activation of rapamycin-insensitive pathways would shift quiescence towards senescence. In HT-p21 cells, cell cycle arrest was caused by IPTG-inducible p21 and was spontaneously followed by mTOR-dependent geroconversion. Rapamycin suppressed geroconversion, whereas PMA partially counteracted the effect of rapamycin, revealing the involvement of rapamycin-insensitive gerogenic pathways. In normal RPE cells arrested by serum withdrawal, the mTOR/pS6 pathway was inhibited and cells remained quiescent. PMA transiently activated mTOR, enabling partial geroconversion. We conclude that PMA can initiate a senescent program by either inducing arrest or fostering geroconversion or both. Rapamycin can decrease gero-conversion by PMA, without preventing PMA-induced arrest. The tumor promoter PMA is a gero-promoter, which may be useful to study aging in mammals.

Translating the effects of mTOR on secretory senescence

Cellular senescence is often accompanied by the production of secreted proteins that mediate the diverse effects of senescence on the tissue microenvironment. The mammalian target of rapamycin (mTOR), a master regulator of protein synthesis, is now shown to control the senescence-associated secretory phenotype by modulating gene transcription and mRNA translation and stabilization.

Geroconversion: irreversible step to cellular senescence

Cellular senescence happens in 2 steps: cell cycle arrest followed, or sometimes preceded, by gerogenic conversion (geroconversion). Geroconvesrion is a form of growth, a futile growth during cell cycle arrest. It converts reversible arrest to irreversible senescence. Geroconversion is driven by growth-promoting, mitogen-/nutrient-sensing pathways such as mTOR. Geroconversion leads to hyper-secretory, hypertrophic and pro-inflammatory cellular phenotypes, hyperfunctions and malfunctions. On organismal level, geroconversion leads to age-related diseases and death. Rapamycin, a gerosuppressant, extends life span in diverse species from yeast to mammals. Stress-and oncogene-induced accelerated senescence, replicative senescence in vitro and life-long cellular aging in vivo all can be described by 2-step model.

Heparan sulfation is essential for the prevention of cellular senescence

Cellular senescence is considered as an important tumor-suppressive mechanism. Here, we demonstrated that heparan sulfate (HS) prevents cellular senescence by fine-tuning of the fibroblast growth factor receptor (FGFR) signaling pathway. We found that depletion of 3'-phosphoadenosine 5'-phosphosulfate synthetase 2 (PAPSS2), a synthetic enzyme of the sulfur donor PAPS, led to premature cell senescence in various cancer cells and in a xenograft tumor mouse model. Sodium chlorate, a metabolic inhibitor of HS sulfation also induced a cellular senescence phenotype. p53 and p21 accumulation was essential for PAPSS2-mediated cellular senescence. Such senescence phenotypes were closely correlated with cell surface HS levels in both cancer cells and human diploid fibroblasts. The determination of the activation of receptors such as FGFR1, Met, and insulin growth factor 1 receptor β indicated that the augmented FGFR1/AKT signaling was specifically involved in premature senescence in a HS-dependent manner. Thus, blockade of either FGFR1 or AKT prohibited p53 and p21 accumulation and cell fate switched from cellular senescence to apoptosis. In particular, desulfation at the 2-O position in the HS chain contributed to the premature senescence via the augmented FGFR1 signaling. Taken together, we reveal, for the first time, that the proper status of HS is essential for the prevention of cellular senescence. These observations allowed us to hypothesize that the FGF/FGFR signaling system could initiate novel tumor defenses through regulating premature senescence.