Hypoxia and gerosuppression: the mTOR saga continues

Role of hypoxia in cellular senescence

Senescent cells persist and continuously secrete proinflammatory and tissue-remodeling molecules that poison surrounding cells, leading to various age-related diseases, including diabetes, atherosclerosis, and Alzheimer's disease. The underlying mechanism of cellular senescence has not yet been fully explored. Emerging evidence indicates that hypoxia is involved in the regulation of cellular senescence. Hypoxia-inducible factor (HIF)- 1α accumulates under hypoxic conditions and regulates cellular senescence by modulating the levels of the senescence markers p16, p53, lamin B1, and cyclin D1. Hypoxia is a critical condition for maintaining tumor immune evasion, which is promoted by driving the expression of genetic factors (such as p53 and CD47) while triggering immunosenescence. Under hypoxic conditions, autophagy is activated by targeting BCL-2/adenovirus E1B 19-kDa interacting protein 3, which subsequently induces p21WAF1/CIP1 as well as p16Ink4a and increases β-galactosidase (β-gal) activity, thereby inducing cellular senescence. Deletion of the p21 gene increases the activity of the hypoxia response regulator poly (ADP-ribose) polymerase-1 (PARP-1) and the level of nonhomologous end joining (NHEJ) proteins, repairs DNA double-strand breaks, and alleviates cellular senescence. Moreover, cellular senescence is associated with intestinal dysbiosis and an accumulation of D-galactose derived from the gut microbiota. Chronic hypoxia leads to a striking reduction in the amount of Lactobacillus and D-galactose-degrading enzymes in the gut, producing excess reactive oxygen species (ROS) and inducing senescence in bone marrow mesenchymal stem cells. Exosomal microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) play important roles in cellular senescence. miR-424-5p levels are decreased under hypoxia, whereas lncRNA-MALAT1 levels are increased, both of which induce cellular senescence. The present review focuses on recent advances in understanding the role of hypoxia in cellular senescence. The effects of HIFs, immune evasion, PARP-1, gut microbiota, and exosomal mRNA in hypoxia-mediated cell senescence are specifically discussed. This review increases our understanding of the mechanism of hypoxia-mediated cellular senescence and provides new clues for anti-aging processes and the treatment of aging-related diseases.

Can Maternal Exercise Prevent High-Altitude Pulmonary Hypertension in Children?

Leslie, Eric, Ann L. Gibson, Laura V. Gonzalez Bosc, Christine Mermier, Sean M. Wilson, and Michael R. Deyhle. Review: can maternal exercise prevent high-altitude pulmonary hypertension in children? High Alt Med Biol. 24:1-6, 2023.-Chronic high-altitude exposure reduces oxygen delivery to the fetus during pregnancy and causes pathologic pulmonary artery remodeling, This increases the risk of high-altitude pulmonary hypertension (PH), which is a particularly fatal disease that is difficult to treat. Therefore, finding ways to prevent high-altitude PH, including during the neonatal period, is preferable. Cardiorespiratory exercise can improve functional capacity and quality of life in patients with high-altitude PH. However, similar to other treatments and surgical procedures, the benefits are not enough to cure the disease after a diagnosis. Cardiorespiratory exercise by mothers during pregnancy (i.e., maternal exercise) has not been previously evaluated to prevent the development of high-altitude PH in children born and living at high altitude. This focused review describes the pathophysiology of high-altitude PH and the potential benefit of maternal exercise for preventing the disease caused by high-altitude pregnancies.

Hamartin: An Endogenous Neuroprotective Molecule Induced by Hypoxic Preconditioning

Hypoxic/ischemic preconditioning (HPC/IPC) is an innate neuroprotective mechanism in which a number of endogenous molecules are known to be involved. Tuberous sclerosis complex 1 (TSC1), also known as hamartin, is thought to be one such molecule. It is also known that hamartin is involved as a target in the rapamycin (mTOR) signaling pathway, which functions to integrate a variety of environmental triggers in order to exert control over cellular metabolism and homeostasis. Understanding the role of hamartin in ischemic/hypoxic neuroprotection will provide a novel target for the treatment of hypoxic-ischemic disease. Therefore, the proposed molecular mechanisms of this neuroprotective role and its preconditions are reviewed in this paper, with emphases on the mTOR pathway and the relationship between the expression of hamartin and DNA methylation.

The effects of environmental stressors on candidate aging associated genes

BACKGROUND

Aging is defined as a biological and physical complex process that is characterized by the increase in susceptibility to diseases and eventually death. Aging may occur at different rates between and within species, especially or (it varies) among the long-lived ones. Here, we ask whether this diversity (e.g. aging phenotype) stems from genetic or environmental factors or as a combination between the two (epigenetics). Epigenetics play a central role in controlling changes in gene expression during aging. DNA methylation is the most abundant epigenetic modification among vertebrates and is essential to mammalian development.

MATERIALS AND METHODS

In this study, we utilized the HELPtag assay to identify five candidate genes that were significantly hyper- or hypo-methylated across four different age groups in mice. The candidate genes were annotated using ensemble and their expression was further tested in vitro using the murine RAW 264.7 cell line to examine the effect of three environmental stressors (UV radiation, Hypoxia and fasting) on their expression. RNA was extracted at different time points followed by cDNA synthesis. Changes in gene expression were evaluated using qRT-PCR.

RESULTS

We show that fasting and UV radiation reduced the viability of RAW264.7 cells. We also found a significant change in three candidate genes' expression levels during fasting (TOP2B, RNF13 and MRPL4). Furthermore, we found a significant change in the four candidate genes' expression levels following UVC treatment (TOP2B, RNF13, PKNOX1 and CREB5) and yet no changes were recorded in hypoxic conditions.

CONCLUSION

Our results suggest that the model we used was a fitting model for the assessment of environmental stressors on candidate gene expression. In addition, we established a cellular response to the environment via changes in gene expression.

Cell Senescence in Lupus

Purpose of Review

The concept of cellular senescence has been evolving. Although originally proposed based on studies of serum-driven replication of cell lines in vitro, it is now clear that cellular senescence occurs in vivo. It has also become clear that cellular senescence can be triggered by a number of stimuli such as radiation, chemotherapy, activation of oncogenes, metabolic derangements, and chronic inflammation.

Recent Findings

As we learn more about the mechanisms of cellular aging, it has become important to ask whether accelerated cellular senescence occurs in lupus and other systemic rheumatologic diseases.

Summary

Accelerated cellular aging may be one explanation for some of the excess morbidity and mortality seen in lupus patients. If so, drugs targeting cellular senescence may provide new options for preventing long-term complications such as organ failure in systemic lupus erythematosus patients.

Virus/Host Cell Crosstalk in Hypoxic HPV-Positive Cancer Cells

Oncogenic types of human papillomaviruses (HPVs) are major human carcinogens. The expression of the viral E6/E7 oncogenes plays a key role for HPV-linked oncogenesis. It recently has been found that low oxygen concentrations (“hypoxia”), as present in sub-regions of HPV-positive cancers, strongly affect the interplay between the HPV oncogenes and their transformed host cell. As a result, a state of dormancy is induced in hypoxic HPV-positive cancer cells, which is characterized by a shutdown of viral oncogene expression and a proliferative arrest that can be reversed by reoxygenation. In this review, these findings are put into the context of the current concepts of both HPV-linked carcinogenesis and of the effects of hypoxia on tumor biology. Moreover, we discuss the consequences for the phenotype of HPV-positive cancer cells as well as for their clinical behavior and response towards established and prospective therapeutic strategies.

Induction of dormancy in hypoxic human papillomavirus-positive cancer cells

Oncogenic human papillomaviruses (HPVs) are closely linked to major human malignancies, including cervical and head and neck cancers. It is widely assumed that HPV-positive cancer cells are under selection pressure to continuously express the viral E6/E7 oncogenes, that their intracellular p53 levels are reconstituted on E6/E7 repression, and that E6/E7 inhibition phenotypically results in cellular senescence. Here we show that hypoxic conditions, as are often found in subregions of cervical and head and neck cancers, enable HPV-positive cancer cells to escape from these regulatory principles: E6/E7 is efficiently repressed, yet, p53 levels do not increase. Moreover, E6/E7 repression under hypoxia does not result in cellular senescence, owing to hypoxia-associated impaired mechanistic target of rapamycin (mTOR) signaling via the inhibitory REDD1/TSC2 axis. Instead, a reversible growth arrest is induced that can be overcome by reoxygenation. Impairment of mTOR signaling also interfered with the senescence response of hypoxic HPV-positive cancer cells toward prosenescent chemotherapy in vitro. Collectively, these findings indicate that hypoxic HPV-positive cancer cells can induce a reversible state of dormancy, with decreased viral antigen synthesis and increased therapeutic resistance, and may serve as reservoirs for tumor recurrence on reoxygenation.

HIF-1α and rapamycin act as gerosuppressant in multiple myeloma cells upon genotoxic stress

Multiple myeloma (MM) is still an incurable hematological malignancy. Despite recent progress due to new anti-myeloma agents, the pathology is characterized by a high frequency of de novo or acquired resistance. Delineating the mechanisms of MM resistance is essential for therapeutic advances. We previously showed that long-term genotoxic stress induces the establishment of a senescence-associated secretory phenotype, a pro-inflammatory response that favors the emergence of cells with cancer stem-like properties. Here, we studied the short-term response of MM cells following treatment with various DNA damaging agents such as the energetic C-ion irradiation. MM cells are highly resistant to all treatments and do not enter apoptosis after they arrest cycling at the G2 phase. Although the DNA damage response pathway was activated, DNA breaks remained chronically in damaged MM cells. We found, using a transcriptomic approach that RAD50, a major DNA repair gene was downregulated early after genotoxic stress. In two gerosuppression situations: induction of hypoxia and inhibition of the mammalian target of rapamycin (mTOR) pathway, we observed, after the treatment with a DNA damaging agent, a normalization of RAD50 expression concomitant with the absence of cell cycle arrest. We propose that combining inhibitors of mTOR with genotoxic agents could avoid MM cells to senesce and secrete pro-inflammatory factors responsible for cancer stem-like cell emergence and, in turn, relapse of MM patients.

Nutrient-Deprived Retinal Progenitors Proliferate in Response to Hypoxia: Interaction of the HIF-1 and mTOR Pathway

At a cellular level, nutrients are sensed by the mechanistic Target of Rapamycin (mTOR). The response of cells to hypoxia is regulated via action of the oxygen sensor Hypoxia-Inducible Factor 1 (HIF-1). During development, injury and disease, tissues might face conditions of both low nutrient supply and low oxygen, yet it is not clear how cells adapt to both nutrient restriction and hypoxia, or how mTOR and HIF-1 interact in such conditions. Here we explore this question in vivo with respect to cell proliferation using the ciliary marginal zone (CMZ) of Xenopus. We found that both nutrient-deprivation and hypoxia cause retinal progenitors to decrease their proliferation, yet when nutrient-deprived progenitors are exposed to hypoxia there is an unexpected rise in cell proliferation. This increase, mediated by HIF-1 signalling, is dependent on glutaminolysis and reactivation of the mTOR pathway. We discuss how these findings in non-transformed tissue may also shed light on the ability of cancer cells in poorly vascularised solid tumours to proliferate.

Hypoxia-Inducible Histone Lysine Demethylases: Impact on the Aging Process and Age-Related Diseases

Hypoxia is an environmental stress at high altitude and underground conditions but it is also present in many chronic age-related diseases, where blood flow into tissues is impaired. The oxygen-sensing system stimulates gene expression protecting tissues against hypoxic insults. Hypoxia stabilizes the expression of hypoxia-inducible transcription factor-1α (HIF-1α), which controls the expression of hundreds of survival genes related to e.g. enhanced energy metabolism and autophagy. Moreover, many stress-related signaling mechanisms, such as oxidative stress and energy metabolic disturbances, as well as the signaling cascades via ceramide, mTOR, NF-κB, and TGF-β pathways, can also induce the expression of HIF-1α protein to facilitate cell survival in normoxia. Hypoxia is linked to prominent epigenetic changes in chromatin landscape. Screening studies have indicated that the stabilization of HIF-1α increases the expression of distinct histone lysine demethylases (KDM). HIF-1α stimulates the expression of KDM3A, KDM4B, KDM4C, and KDM6B, which enhance gene transcription by demethylating H3K9 and H3K27 sites (repressive epigenetic marks). In addition, HIF-1α induces the expression of KDM2B and KDM5B, which repress transcription by demethylating H3K4me2,3 sites (activating marks). Hypoxia-inducible KDMs support locally the gene transcription induced by HIF-1α, although they can also control genome-wide chromatin landscape, especially KDMs which demethylate H3K9 and H3K27 sites. These epigenetic marks have important role in the control of heterochromatin segments and 3D folding of chromosomes, as well as the genetic loci regulating cell type commitment, proliferation, and cellular senescence, e.g. the INK4 box. A chronic stimulation of HIF-1α can provoke tissue fibrosis and cellular senescence, which both are increasingly present with aging and age-related diseases. We will review the regulation of HIF-1α-dependent induction of KDMs and clarify their role in pathological processes emphasizing that long-term stress-related insults can impair the maintenance of chromatin landscape and provoke cellular senescence and tissue fibrosis associated with aging and age-related diseases.

Functional properties of bone marrow derived multipotent mesenchymal stromal cells are altered in heart failure patients, and could be corrected by adjustment of expansion strategies

BACKGROUND

Bone marrow multipotent mesenchymal stromal cells (BM-MMSC) considered as a prospective substrate for cell therapy applications, however adult stem cells could be affected by donor-specific factors: age, gender, medical history. Our aim was to investigate how HF affects the functional properties of BM-MMSC.

MATERIALS AND METHODS

BM-MMSC from 10 healthy donors (HD), and 16 donors with chronic HF were evaluated for proliferative activity, ability to differentiate, replicative senescence, expression of genes that affect regeneration and fibrosis. The effect of culturing conditions on efficiency of BM-MMSC expansion was determined.

RESULTS

HF-derived BM-MMSC demonstrated early decrease of proliferative activity and upregulation of genes that control both, regeneration and fibrosis: Tgf-β pathway, synthesis of ECM, remodeling enzymes, adhesion molecules. We assume that these effects were related to increase of frequency of myofibroblast-like CD146+/SMAα+ CFU-F in HF samples; (ii) low seeding density and hypoxia resulted in predominant purification and expansion of CD146+/SMAα- CFU-Fs. (iii) the activity of NPs system was downregulated in HF BM-MMSC;

CONCLUSIONS

downregulation of NP signaling in combination with upregulation of Tgf-β pathway in BM-MMSC would result in pro-fibrotic phenotype and make these cells non-effective for therapeutic applications; the corrections in culturing strategy resulted in 2(3)-2(7) increase of expansion efficiency.

Gerosuppression in confluent cells

The most physiological type of cell cycle arrest - namely, contact inhibition in dense culture - is the least densely studied. Despite cell cycle arrest, confluent cells do not become senescent. We recently described that mTOR (target of rapamycin) is inactive in contact-inhibited cells. Therefore, conversion from reversible arrest to senescence (geroconversion) is suppressed. I this Perspective, we further extended the gerosuppression model. While causing senescence in regular cell density, etoposide failed to cause senescence in contact-inhibited cells. A transient reactivation of mTOR favored geroconversion in etoposide-treated confluent cells. Like p21, p16 did not cause senescence in high cell density. We discuss that suppression of geroconversion in confluent and contact-inhibited cultures mimics gerosuppression in the organism. We confirmed that levels of p-S6 were low in murine tissues in the organism compared with mouse embryonic fibroblasts in cell culture, whereas p-Akt was reciprocally high in the organism.

A generic cycling hypoxia-derived prognostic gene signature: application to breast cancer profiling

Background

Temporal and local fluctuations in O₂ in tumors require adaptive mechanisms to support cancer cell survival and proliferation. The transcriptome associated with cycling hypoxia (CycHyp) could thus represent a prognostic biomarker of cancer progression.

Methods

We exposed 20 tumor cell lines to repeated periods of hypoxia/reoxygenation to determine a transcriptomic CycHyp signature and used clinical data sets from 2,150 breast cancer patients to estimate a prognostic Cox proportional hazard model to assess its prognostic performance.

Results

The CycHyp prognostic potential was validated in patients independently of the receptor status of the tumors. The discriminating capacity of the CycHyp signature was further increased in the ER+ HER2- patient populations including those with a node negative status under treatment (HR=3.16) or not (HR=5.54). The CycHyp prognostic signature outperformed a signature derived from continuous hypoxia and major prognostic metagenes (P<0.001). The CycHyp signature could also identify ER+HER2 node-negative breast cancer patients at high risk based on clinicopathologic criteria but who could have been spared from chemotherapy and inversely those patients classified at low risk based but who presented a negative outcome.

Conclusions

The CycHyp signature is prognostic of breast cancer and offers a unique decision making tool to complement anatomopathologic evaluation.

Contact inhibition and high cell density deactivate the mammalian target of rapamycin pathway, thus suppressing the senescence program

During cell cycle arrest caused by contact inhibition (CI), cells do not undergo senescence, thus resuming proliferation after replating. The mechanism of senescence avoidance during CI is unknown. Recently, it was demonstrated that the senescence program, namely conversion from cell cycle arrest to senescence (i.e., geroconversion), requires mammalian target of rapamycin (mTOR). Geroconversion can be suppressed by serum starvation, rapamycin, and hypoxia, which all inhibit mTOR. Here we demonstrate that CI, as evidenced by p27 induction in normal cells, was associated with inhibition of the mTOR pathway. Furthermore, CI antagonized senescence caused by CDK inhibitors. Stimulation of mTOR in contact-inhibited cells favored senescence. In cancer cells lacking p27 induction and CI, mTOR was still inhibited in confluent culture as a result of conditioning of the medium. This inhibition of mTOR suppressed p21-induced senescence. Also, trapping of malignant cells among contact-inhibited normal cells antagonized p21-induced senescence. Thus, we identified two nonmutually exclusive mechanisms of mTOR inhibition in high cell density: (i) CI associated with p27 induction in normal cells and (ii) conditioning of the medium, especially in cancer cells. Both mechanisms can coincide in various proportions in various cells. Our work explains why CI is reversible and, most importantly, why cells avoid senescence in vivo, given that cells are contact-inhibited in the organism.

Stem cells, redox signaling, and stem cell aging

SIGNIFICANCE

Functional stem cell decline has been postulated to result in loss of maintenance of tissue homeostasis leading to organismal decline and diseases of aging.

RECENT ADVANCES

Recent findings implicate redox metabolism in the control of stem cell pool and stem cell aging. Although reactive oxygen species (ROS) are better known for their damaging properties to DNA, proteins and lipids, recent findings suggest that ROS may also be an integral physiological mediator of cellular signaling in primary cells.

CRITICAL ISSUES

Here we review recent published work on major signaling pathways and transcription factors that are regulated by ROS and mediate ROS regulation of stem cell fate. We will specifically focus on how alterations in this regulation may be implicated in disease and particularly in diseases of stem cell aging. In general, based on the work described here we propose a model in which ROS function as stem cell rheostat.

FUTURE DIRECTIONS

Future work in elucidating how ROS control stem cell cycling, apoptotic machinery, and lineage determination should shed light on mechanisms whereby ROS may control stem cell aging.

Gerometabolites: the pseudohypoxic aging side of cancer oncometabolites

Oncometabolites are defined as small-molecule components (or enantiomers) of normal metabolism whose accumulation causes signaling dysregulation to establish a milieu that initiates carcinogenesis. In a similar manner, we propose the term "gerometabolites" to refer to small-molecule components of normal metabolism whose depletion causes signaling dysregulation to establish a milieu that drives aging. In an investigation of the pathogenic activities of the currently recognized oncometabolites R(-)-2-hydroxyglutarate (2-HG), fumarate, and succinate, which accumulate due to mutations in isocitrate dehydrogenases (IDH), fumarate hydratase (FH), and succinate dehydrogenase (SDH), respectively, we illustrate the fact that metabolic pseudohypoxia, the accumulation of hypoxia-inducible factor (HIFα) under normoxic conditions, and the subsequent Warburg-like reprogramming that shifts glucose metabolism from the oxidative pathway to aerobic glycolysis are the same mechanisms through which the decline of the "gerometabolite" nicotinamide adenine dinucleotide (NAD)(+) reversibly disrupts nuclear-mitochondrial communication and contributes to the decline in mitochondrial function with age. From an evolutionary perspective, it is reasonable to view NAD(+)-driven mitochondrial homeostasis as a conserved response to changes in energy supplies and oxygen levels. Similarly, the natural ability of 2-HG to significantly alter epigenetics might reflect an evolutionarily ancient role of certain metabolites to signal for elevated glutamine/glutamate metabolism and/or oxygen deficiency. However, when chronically altered, these responses become conserved causes of aging and cancer. Because HIFα-driven pseudohypoxia might drive the overproduction of 2-HG, the intriguing possibility exists that the decline of gerometabolites such as NAD(+) could promote the chronic accumulation of oncometabolites in normal cells during aging. If the sole activation of a Warburg-like metabolic reprogramming in normal tissues might be able to significantly increase the endogenous production of bona fide etiological determinants in cancer, such as oncometabolites, this undesirable trade-off between mitochondrial dysfunction and activation of oncometabolites production might then pave the way for the epigenetic initiation of carcinogenesis in a strictly metabolic-dependent manner. Perhaps it is time to definitely adopt the view that aging and aging diseases including cancer are governed by a pivotal regulatory role of metabolic reprogramming in cell fate decisions.

Rapamycin extends life- and health span because it slows aging

Making headlines, a thought-provocative paper by Neff, Ehninger and coworkers claims that rapamycin extends life span but has limited effects on aging. How is that possibly possible? And what is aging if not an increase of the probability of death with age. I discuss that the JCI paper actually shows that rapamycin slows aging and also extends lifespan regardless of its direct anti-cancer activities. Aging is, in part, MTOR-driven: a purposeless continuation of developmental growth. Rapamycin affects the same processes in young and old animals: young animals' traits and phenotypes, which continuations become hyperfunctional, harmful and lethal later in life.

S6K in geroconversion

Markers of cellular senescence depend in part on the MTOR (mechanistic target of rapamycin) pathway. MTOR participates in geroconversion, a conversion from reversible cell cycle arrest to irreversible senescence. Recently we demonstrated that hyper-induction of cyclin D1 during geroconversion was mostly dependent on MEK, whereas rapamycin only partially inhibited cyclin D1 accumulation. Here we show that, while not affecting cyclin D1, siRNA for p70S6K partially prevented loss of RP (replicative/regenerative potential) during p21-induced cell cycle arrest. Similarly, an inhibitor of p70 S6 kinase (PF-4708671) partially inhibited phosphorylation of S6 and preserved RP, while only marginally prevented cyclin D1 induction. Thus S6K and MEK play different roles in geroconversion.

Molecular dynamics of the full-length p53 monomer

The p53 protein is frequently mutated in a very large proportion of human tumors, where it seems to acquire gain-of-function activity that facilitates tumor onset and progression. A possible mechanism is the ability of mutant p53 proteins to physically interact with other proteins, including members of the same family, namely p63 and p73, inactivating their function. Assuming that this interaction might occurs at the level of the monomer, to investigate the molecular basis for this interaction, here, we sample the structural flexibility of the wild-type p53 monomeric protein. The results show a strong stability up to 850 ns in the DNA binding domain, with major flexibility in the N-terminal transactivations domains (TAD1 and TAD2) as well as in the C-terminal region (tetramerization domain). Several stable hydrogen bonds have been detected between N-terminal or C-terminal and DNA binding domain, and also between N-terminal and C-terminal. Essential dynamics analysis highlights strongly correlated movements involving TAD1 and the proline-rich region in the N-terminal domain, the tetramerization region in the C-terminal domain; Lys120 in the DNA binding region. The herein presented model is a starting point for further investigation of the whole protein tetramer as well as of its mutants.

Berberine suppresses gero-conversion from cell cycle arrest to senescence

Berberine (BRB), a natural alkaloid, has a long history of medicinal use in both Ayurvedic and old Chinese medicine. Recently, available as a dietary supplement, Berberine is reported to have application in treatment of variety diseases. Previously we observed that BRB inhibited mTOR/S6 signaling concurrently with reduction of the level of endogenous oxidants and constitutive DNA damage response. We currently tested whether Berberine can affect premature, stress-induced cellular senescence caused by mitoxantrone. The depth of senescence was quantitatively measured by morphometric parameters, senescence-associated β-galactosidase, induction of p21WAF1, replication stress (γH2AX expression), and mTOR signaling; the latter revealed by ribosomal S6 protein (rpS6) phosphorylation. All these markers of senescence were distinctly diminished, in a concentration-dependent manner, by Berberine. In view of the evidence that BRB localizes in mitochondria, inhibits respiratory electron chain and activates AMPK, the observed attenuation of the replication stress-induced cellular senescence most likely is mediated by AMPK that leads to inhibition of mTOR signaling. In support of this mechanism is the observation that rhodamine123, the cationic probe targeting mitochondrial electron chain, also suppressed rpS6 phosphorylation. The present findings reveal that: (a) in cells induced to senescence BRB exhibits gero-suppressive properties by means of mTOR/S6 inhibition; (b) in parallel, BRB reduces the level of constitutive DNA damage response, previously shown to report oxidative DNA damage by endogenous ROS; (c) there appears to a causal linkage between the (a) and (b) activities; (d) the in vitro model of premature stress-induced senescence can be used to assess effectiveness of potential gero-suppressive agents targeting mTOR/S6 and ROS signaling; (e) since most of the reported beneficial effects of BRB are in age-relate diseases, it is likely that gero-suppression is the primary activity of this traditional medicine.

MEK drives cyclin D1 hyperelevation during geroconversion

When the cell cycle becomes arrested, MTOR (mechanistic Target of Rapamycin) converts reversible arrest into senescence (geroconversion). Hyperexpression of cyclin D1 is a universal marker of senescence along with hypertrophy, beta-Gal staining and loss of replicative/regenerative potential (RP), namely, the ability to restart proliferation when the cell cycle is released. Inhibition of MTOR decelerates geroconversion, although only partially decreases cyclin D1. Here we show that in p21- and p16-induced senescence, inhibitors of mitogen-activated/extracellular signal-regulated kinase (MEK) (U0126, PD184352 and siRNA) completely prevented cyclin D1 accumulation, making it undetectable. We also used MEL10 cells in which MEK inhibitors do not inhibit MTOR. In such cells, U0126 by itself induced senescence that was remarkably cyclin D1 negative. In contrast, inhibition of cyclin-dependent kinase (CDK) 4/6 by PD0332991 caused cyclin D1-positive senescence in MEL10 cells. Both types of senescence were suppressed by rapamycin, converting it into reversible arrest. We confirmed that the inhibitor of CDK4/6 caused cyclin D1 positive senescence in normal RPE cells, whereas U0126 prevented cyclin D1 expression. Elimination of cyclin D1 by siRNA did not prevent other markers of senescence that are consistent with the lack of its effect on MTOR. Our data confirmed that a mere inhibition of the cell cycle was sufficient to cause senescence, providing MTOR was active, and inhibition of MEK partially inhibited MTOR in a cell-type-dependent manner. Second, hallmarks of senescence may be dissociated, and hyperelevated cyclin D1, a marker of hyperactivation of senescent cells, did not necessarily determine other markers of senescence. Third, inhibition of MEK was sufficient to eliminate cyclin D1, regardless of MTOR.

Xenohormetic and anti-aging activity of secoiridoid polyphenols present in extra virgin olive oil: a new family of gerosuppressant agents

Aging can be viewed as a quasi-programmed phenomenon driven by the overactivation of the nutrient-sensing mTOR gerogene. mTOR-driven aging can be triggered or accelerated by a decline or loss of responsiveness to activation of the energy-sensing protein AMPK, a critical gerosuppressor of mTOR. The occurrence of age-related diseases, therefore, reflects the synergistic interaction between our evolutionary path to sedentarism, which chronically increases a number of mTOR activating gero-promoters (e.g., food, growth factors, cytokines and insulin) and the "defective design" of central metabolic integrators such as mTOR and AMPK. Our laboratories at the Bioactive Food Component Platform in Spain have initiated a systematic approach to molecularly elucidate and clinically explore whether the "xenohormesis hypothesis," which states that stress-induced synthesis of plant polyphenols and many other phytochemicals provides an environmental chemical signature that upregulates stress-resistance pathways in plant consumers, can be explained in terms of the reactivity of the AMPK/mTOR-axis to so-called xenohormetins. Here, we explore the AMPK/mTOR-xenohormetic nature of complex polyphenols naturally present in extra virgin olive oil (EVOO), a pivotal component of the Mediterranean style diet that has been repeatedly associated with a reduction in age-related morbid conditions and longer life expectancy. Using crude EVOO phenolic extracts highly enriched in the secoiridoids oleuropein aglycon and decarboxymethyl oleuropein aglycon, we show for the first time that (1) the anticancer activity of EVOO secoiridoids is related to the activation of anti-aging/cellular stress-like gene signatures, including endoplasmic reticulum (ER) stress and the unfolded protein response, spermidine and polyamine metabolism, sirtuin-1 (SIRT1) and NRF2 signaling; (2) EVOO secoiridoids activate AMPK and suppress crucial genes involved in the Warburg effect and the self-renewal capacity of "immortal" cancer stem cells; (3) EVOO secoiridoids prevent age-related changes in the cell size, morphological heterogeneity, arrayed cell arrangement and senescence-associated β-galactosidase staining of normal diploid human fibroblasts at the end of their proliferative lifespans. EVOO secoiridoids, which provide an effective defense against plant attack by herbivores and pathogens, are bona fide xenohormetins that are able to activate the gerosuppressor AMPK and trigger numerous resveratrol-like anti-aging transcriptomic signatures. As such, EVOO secoiridoids constitute a new family of plant-produced gerosuppressant agents that molecularly "repair" the aimless (and harmful) AMPK/mTOR-driven quasi-program that leads to aging and aging-related diseases, including cancer.