Molecular Mechanisms Of Cellular Senescence Research Articles

The Molecular Mechanisms in Senescent Cells Induced by Natural Aging and Ionizing Radiation.

This review discusses the relationship between cellular senescence and radiation exposure. Given the wide range of ionizing radiation sources encountered by people in professional and medical spheres, as well as the influence of natural background radiation, the question of the effect of radiation on biological processes, particularly on aging processes, remains highly relevant. The parallel relationship between natural and radiation-induced cellular senescence reveals the common aspects underlying these processes. Based on recent scientific data, the key points of the effects of ionizing radiation on cellular processes associated with aging, such as genome instability, mitochondrial dysfunction, altered expression of miRNAs, epigenetic profile, and manifestation of the senescence-associated secretory phenotype (SASP), are discussed. Unraveling the molecular mechanisms of cellular senescence can make a valuable contribution to the understanding of the molecular genetic basis of age-associated diseases in the context of environmental exposure.

The key role of a basic domain of histone H2B N-terminal tail in the action of 5-bromodeoxyuridine to induce cellular senescence.

5-Bromodeoxyuridine (BrdU), a thymidine analogue, is an interesting reagent that modulates various biological phenomena. BrdU, upon incorporation into DNA, causes destabilized nucleosome positioning which leads to changes in heterochromatin organization and gene expression in cells. We have previously shown that BrdU effectively induces cellular senescence, a phenomenon of irreversible growth arrest in mammalian cells. Identification of the mechanism of action of BrdU would provide a novel insight into the molecular mechanisms of cellular senescence. Here, we showed that a basic domain in the histone H2B N-terminal tail, termed the HBR (histone H2B repression) domain, is involved in the action of BrdU. Notably, deletion of the HBR domain causes destabilized nucleosome positioning and derepression of gene expression, as does BrdU. We also showed that the genes up-regulated by BrdU significantly overlapped with those by deletion of the HBR domain, the result of which suggested that BrdU and deletion of the HBR domain act in a similar way. Furthermore, we showed that decreased HBR domain function induced cellular senescence or facilitated the induction of cellular senescence. These findings indicated that the HBR domain is crucially involved in the action of BrdU, and also suggested that disordered nucleosome organization may be involved in the induction of cellular senescence.

Senescence mechanisms and targets in the heart.

Cellular senescence is a state of irreversible cell cycle arrest associated with ageing. Senescence of different cardiac cell types can direct the pathophysiology of cardiovascular diseases (CVDs) such as atherosclerosis, myocardial infarction, and cardiac fibrosis. While age-related telomere shortening represents a major cause of replicative senescence, the senescent state can also be induced by oxidative stress, metabolic dysfunction, and epigenetic regulation, among other stressors. It is critical that we understand the molecular pathways that lead to cellular senescence and the consequences of cellular senescence in order to develop new therapeutic approaches to treat CVD. In this review, we discuss molecular mechanisms of cellular senescence, explore how cellular senescence of different cardiac cell types (including cardiomyocytes, cardiac endothelial cells, cardiac fibroblasts, vascular smooth muscle cells, and valve interstitial cells) can lead to CVD, and highlight potential therapeutic approaches that target molecular mechanisms of cellular senescence to prevent or treat CVD.

Targeting Premature Renal Aging: from Molecular Mechanisms of Cellular Senescence to Senolytic Trials.

The biological process of renal aging is characterized by progressive structural and functional deterioration of the kidney leading to end-stage renal disease, requiring renal replacement therapy. Since the discovery of pivotal mechanisms of senescence such as cell cycle arrest, apoptosis inhibition, and the development of a senescence-associated secretory phenotype (SASP), efforts in the understanding of how senescent cells participate in renal physiological and pathological aging have grown exponentially. This has been encouraged by both preclinical studies in animal models with senescent cell clearance or genetic depletion as well as due to evidence coming from the clinical oncologic experience. This review considers the molecular mechanism and pathways that trigger premature renal aging from mitochondrial dysfunction, epigenetic modifications to autophagy, DNA damage repair (DDR), and the involvement of extracellular vesicles. We also discuss the different pharmaceutical approaches to selectively target senescent cells (namely, senolytics) or the development of systemic SASP (called senomorphics) in basic models of CKD and clinical trials. Finally, an overview will be provided on the potential opportunities for their use in renal transplantation during ex vivo machine perfusion to improve the quality of the graft.

Molecular Mechanisms of Senescence and Implications for the Treatment of Myeloid Malignancies.

Simple SummarySenescence is a cellular program in response to stress and can prevent the expansion of pre-malignant and malignant cells by cell cycle arrest. However, long-term pro-tumorigenic effects have been described. This review aims to compile molecular mechanisms of cellular senescence and to discuss potential therapeutic implications in myeloid malignancies.Senescence is a cellular state that is involved in aging-associated diseases but may also prohibit the development of pre-cancerous lesions and tumor growth. Senescent cells are actively secreting chemo- and cytokines, and this senescence-associated secretory phenotype (SASP) can contribute to both early anti-tumorigenic and long-term pro-tumorigenic effects. Recently, complex mechanisms of cellular senescence and their influence on cellular processes have been defined in more detail and, therefore, facilitate translational development of targeted therapies. In this review, we aim to discuss major molecular pathways involved in cellular senescence and potential therapeutic strategies, with a specific focus on myeloid malignancies.

Similarities and interplay between senescent cells and macrophages.

Senescence is a cellular program that prevents the replication of old, damaged, or cancerous cells. Senescent cells become growth arrested and undergo changes in their morphology, chromatin organization, and metabolism, and produce a bioactive secretome. This secretome, the senescence-associated secretory phenotype (SASP), mediates many of the pathophysiological effects associated with senescent cells, for example, recruiting and activating immune cells such as macrophages. The relation between senescent cells and macrophages is intriguing: senescent cells recruit macrophages, can induce them to undergo senescence, or can influence their polarization. Senescent cells and macrophages share multiple phenotypic characteristics; both have a high secretory status, increased lysosome numbers, or the ability to activate the inflammasome. Senescent cells accumulate during aging and disease, and killing them results in widespread benefits. Here we discuss similarities between senescent cells and macrophages and interpret the latest developments in macrophage biology to understand the molecular mechanisms of cellular senescence. We describe evidence and effects of senescence in macrophages and speculate on the ontogeny of the senescent-like state in macrophages. Finally, we examine the macrophage-senescent cell interplay and its impact on macrophage effector functions during inflammatory conditions and in the tumor microenvironment.

The role of cellular senescence in diabetes mellitus and osteoporosis: molecular pathways and potential interventions.

The improving effectiveness of health care leads inevitably to a rapid increase in the elderly population worldwide. At advanced ages, however, people experience chronic disabilities, which significantly increase the social and economic burden while curtailing survival, independence, and quality of life of the aging population. As aging is a multifactorial process, apart from genetic predisposition, other environmental factors, such as chronic sterile inflammation and cellular senescence, contribute as crucial participants and have been targeted to reverse their deleterious effects on tissue homeostasis and functional integrity. Cellular senescence refers to the essentially irreversible inhibition of cellular proliferation when cells are subjected to extrinsic or endogenous stress. Although the process of cellular senescence has long been known, recent evidence demonstrated that it characterizes many aging phenotypes and that elimination of senescent cells at the tissue level can improve age-related tissue dysfunction. These observations have renewed scientific interest in possible therapeutic interventions. Two major chronic diseases associated with aging that impose an enormous burden on global health systems are type 2 diabetes and osteoporosis. This review presents current data on (i) the underlying molecular mechanisms of cellular senescence, (ii) its relationship to these two endocrine diseases that are today prevalent worldwide, and (iii) future prospects of targeted intervention with the aim of simultaneously improving the progression and prognosis of these serious problems of aging.

Cellular senescence and autophagy in the pathogenesis of chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF).

Aging is associated with impairments in homeostasis. Although aging and senescence are not equivalent, the number of senescent cells increases with aging. Cellular senescence plays important roles in tissue repair or remodeling, as well as embryonic development. Autophagy is a process of lysosomal self-degradation that maintains a homeostatic balance between the synthesis, degradation, and recycling of cellular proteins. Autophagy diminishes with aging; additionally, accelerated aging can be attributed to reduced autophagy. Cellular senescence has been widely implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD), a disease of accelerated lung aging, presumably by impairing cell repopulation and by aberrant cytokine secretion in the senescence-associated secretory phenotype. The possible participation of autophagy in the pathogenic sequence of COPD has been extensively explored. Although it has been reported that increased autophagy may induce epithelial cell death, an insufficient reserve of autophagy can induce cellular senescence in bronchial epithelial cells of COPD. Furthermore, advanced age is one of the most important risk factors for the development of idiopathic pulmonary fibrosis (IPF). Telomere shortening is found in blood leukocytes and alveolar epithelial cells from patients with IPF. Accelerated senescence of epithelial cells plays a role in IPF pathogenesis by perpetuating abnormal epithelial-mesenchymal interactions. Insufficient autophagy may be an underlying mechanism of accelerated epithelial cell senescence and myofibroblast differentiation in IPF. Herein, we review the molecular mechanisms of cellular senescence and autophagy and summarize the role of cellular senescence and autophagy in both COPD and IPF.

Epigenetics: Reprogrammable interface of the genome and environments.

Epigenetics: Reprogrammable interface of the genome and environments.

Photoaging

Photoaging

Cellular Senescence in Cardiovascular Diseases: Potential Age-Related Mechanisms and Implications for Treatment

The aging process is associated with a loss of complexity in the dynamics of physiological systems that reduce the ability to adapt to stress, causing frailty and/or age-related diseases. At the cellular level, proliferative and/or oxidative-stress induced cell senescence associated with a pro-inflammatory state may greatly contribute to age-associated impaired tissue and organ functions. Senescence of endothelial and cardiac cells observed over normal aging, appear to be accelerated in age-related diseases and in particular, in cardiovascular disease (CVD). Although the molecular mechanisms of cellular senescence have been extensively studied, a complete understanding of their role in CVD is still limited. Cardiac, endothelial (EC), vascular smooth muscle (VSMC), leukocytic and stem cells (endothelial progenitor cells (EPC), embryonic stem cells (ESC) and haematopoietic stem cells (HSC)) may play a pivotal role on the maintenance and regeneration of cardiovascular tissue. Age-associated changes of such cells may enhance the risk of developing CVD. The purpose of this review is to illustrate how cellular senescence may affect tissue repair and maintenance toward CVD, focusing on the role played by telomere length and microRNA expression. Finally, interventions aimed at improving the age-related decline in vascular cells during aging and disease, as well as strategies to harness the regenerative capacity of stem cells in CVD will be discussed.

Abstract PL06-03: Inflammation and cancer: Interweaving microRNA, free radical, innate immune, and p53 networks.

Abstract Infection and chronic inflammation contribute to the etiology and pathogenesis of about 1 in 4 of all cancer cases. Mediators of the inflammatory response, e.g., cytokines, free radicals, prostaglandins, non-coding RNAs, and growth factors, can induce genetic and epigenetic changes including point mutations in tumor suppressor genes, DNA methylation and post-translation modifications, causing alterations in critical pathways responsible for maintaining the normal cellular homeostasis and leading to the development and progression of cancer IL-6 and IL-8 cooperate with microRNA in the induction of cellular senescence in benign tumors and as autocrine growth factors in carcinoma. Cellular senescence is also a tumor suppressor mechanism of p53. We are studying the molecular mechanisms of cellular senescence in normal and malignant human cells and the role of the telomeric multiprotein complex, shelterin, that includes TRF2 and POT1. Our ongoing studies have revealed that p53 and its endogenous isoforms regulate both specific microRNAs and TRF2 expression as mechanisms of replicative senescence. In addition, POT1 isoforms are functionally diverse in both maintaining telomeric integrity and preventing p53-dependent senescence induced by telomeric shortening. A switch in the expression patterns of p53 isoforms Δ133Np53 and p53beta can cause cellular senescence in vitro and is also associated with the transition of benign to malignant human colon tumors in vivo. A positive feedback between p53 and TRF2 during telomere-damage signaling and cellular senescence has been discovered. Expression of microRNAs and inflammatory genes are biomarkers of cancer risk, diagnosis, prognosis, and therapeutic outcome. We are especially interested in the interaction of the innate immune pathway with environmental tobacco smoking in lung cancer risk and the interaction of inflammatory cytokines, p53 isoforms, and microRNAs as prognostic classifiers of early stage lung, esophageal, and colon cancer and their functional role in the development of micrometastases. Citation Format: Curtis C. Harris. Inflammation and cancer: Interweaving microRNA, free radical, innate immune, and p53 networks. [abstract]. In: Proceedings of the Fifth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2012 Oct 27-30; San Diego, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(10 Suppl):Abstract nr PL06-03.

The Role of Cellular Senescence During Vascular Calcification: A Key Paradigm in Aging Research

Vascular calcification has severe clinical consequences and is considered an accurate predictor of future adverse cardiovascular events. Vascular calcification refers to the deposition of calcium phosphate mineral, most often hydroxyapatite, in arteries. Extensive calcification of the vascular system is a key characteristic of aging. In this article, we outline the mechanisms governing vascular calcification and highlight its association with cellular senescence. This review discusses the molecular mechanisms of cellular senescence and its affect on calcification of vascular cells, the relevance of phosphate regulation and the function of FGF23 and Klotho proteins. The association of vascular calcification and cellular senescence with the rare human aging disorder Hutchison-Gilford Progeria Syndrome (HGPS) is highlighted and the mouse models used to try to determine the underlying pathways are discussed. By understanding the pathways involved in these processes novel drug targets may be elucidated in an effort to reduce the effects of cellular aging as a risk factor in cardiovascular disease.

Abstract OPS01-02: Inflammation and cancer: Interweaving microRNA, innate immune, and p53 pathways

Abstract Infection and chronic inflammation contribute to the etiology and pathogenesis of about one in four of all cancer cases. Mediators of the inflammatory response, e.g., cytokines, free radicals, prostaglandins, non-coding RNAs, and growth factors, can induce genetic and epigenetic changes including point mutations in tumor suppressor genes, DNA methylation and posttranslation modifications, causing alterations in critical pathways responsible for maintaining the normal cellular homeostasis and leading to the development and progression of cancer (1-6). IL-6 and IL-8 cooperate with microRNA in the induction of cellular senescence in benign tumors (7-9) and as autocrine growth factors in carcinoma (10-14). Cellular senescence is also a tumor suppressor mechanism of p53 (15,16). We are studying the molecular mechanisms of cellular senescence in normal and malignant human cells and the role of the telomeric multiprotein complex, shelterin, that includes TRF2 and POT1. Our ongoing studies have revealed that p53 and its endogenous isoforms regulate both specific microRNAs and TRF2 expression as mechanisms of replicative senescence. In addition, POT1 isoforms are functionally diverse in both maintaining telomeric integrity and preventing p53-dependent senescence induced by telomeric shortening (17,18). A switch in the expression patterns of p53 isoforms 133Np53 and p53 beta can cause cellular senescence in vitro and is also associated with the transition of benign to malignant human colon tumors in vivo (19). Expression of microRNAs and inflammatory genes are biomarkers of cancer risk, diagnosis, prognosis, and therapeutic outcome. We are especially interested in the interaction of the innate immune pathway with environmental tobacco smoking in lung cancer risk (20) and the interaction of inflammatory cytokines, p53 isoforms, and microRNAs as prognostic classifiers of early stage lung and colon cancer and their functional role in the development of micrometastases [reviewed in (3)] (21-25).

Inflammation, senescence and cancer: interweaving microRNA, inflammatory cytokines and p53 networks

The p53 pathway is an intrinsic monitor and response pathway of telomeric attrition involved in cellular aging and senescence. Cellular senescence is tumor suppressive that can be activated by p53 in cancer cells. We are studying the molecular mechanisms of cellular senescence in normal and malignant human cells and the role of the telometric multiprotein complex, shelterin, that includes TRF2 and POT1 [1-3]. Our ongoing studies have revealed that p53 and its endogenous isoforms regulate both specific microRNAs and TRF2 expression as mechanisms of replicative senescence. In addition, POT1 isoforms are functionally diverse in both maintaining telomeric integrity and preventing p53-dependent senescence induced by telomeric shortening. A switch in the expression patterns of p53 isoforms, Δ133Np53 and p53 beta, is also associated with the transition of benign to malignant human cancers. Chronic inflammation and deregulation of microRNAs have roles in human carcinogenesis [4-7]. In addition to our mechanistic and genetic studies, we are investigating the expression of microRNAs and inflammatory genes as cancer biomarkers of diagnosis, prognosis, and therapeutic outcome [8-11]. We are especially interested in developing prognostic classifiers of early stage cancer.

Molecular mechanisms of cellular senescence

Molecular mechanisms of cellular senescence

Molecular mechanisms of cellular senescence and immortalization of human cells

Cellular senescence was originally described as a phenomenon observed in cultured human cells. Accumulating lines of evidence now indicate that the same processes also take place in vivo, suggesting important implications for tumor development. Telomere shortening is the most well-established cause of cellular senescence that can be induced by many other intrinsic and extrinsic factors. The retinoblastoma susceptibility gene product is a convergent target that is downstream of these factors. p53, p38MAPK and cyclin-dependent kinase inhibitors p16INK4a (p16) and p21CIP1 (p21) are key mediators. As most stresses that induce cellular senescence are also known causes of cancer, a common strategy might be applied to the development of cancer chemopreventive agents and anti-ageing drugs.

Upregulation of the gene encoding a cytoplasmic dynein intermediate chain in senescent human cells

Normal human somatic cells, unlike cancer cells, stop dividing after a limited number of cell divisions through the process termed cellular senescence or replicative senescence, which functions as a tumor-suppressive mechanism and may be related to organismal aging. By means of the cDNA subtractive hybridization, we identified eight genes upregulated during normal chromosome 3-induced cellular senescence in a human renal cell carcinoma cell line. Among them is the DNCI1 gene encoding an intermediate chain 1 of the cytoplasmic dynein, a microtubule motor that plays a role in chromosome movement and organelle transport. The DNCI1 mRNA was also upregulated during in vitro aging of primary human fibroblasts. In contrast, other components of cytoplasmic dynein showed no significant change in mRNA expression during cellular aging. Cell growth arrest by serum starvation, contact inhibition, or gamma-irradiation did not induce the DNCI1 mRNA, suggesting its specific role in cellular senescence. The DNCI1 gene is on the long arm of chromosome 7 where tumor suppressor genes and a senescence-inducing gene for a group of immortal cell lines (complementation group D) are mapped. This is the first report that links a component of molecular motor complex to cellular senescence, providing a new insight into molecular mechanisms of cellular senescence.