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.

Platelet Activation Is Triggered by Factors Secreted by Senescent Endothelial HMEC-1 Cells In Vitro.

Aging is one of the main risk factors for the development of chronic diseases, with both the vascular endothelium and platelets becoming functionally altered. Cellular senescence is a form of permanent cell cycle arrest initially described in primary cells propagated in vitro, although it can also be induced by anticancer drugs and other stressful stimuli. Attesting for the complexity of the senescent phenotype, senescent cells synthesize and secrete a wide variety of bioactive molecules. This "senescence-associated secretory phenotype" (SASP) endows senescent cells with the ability to modify the tissue microenvironment in ways that may be relevant to the development of various physiological and pathological processes. So far, however, the direct role of factors secreted by senescent endothelial cells on platelet function remains unknown. In the present work, we explore the effects of SASP factors derived from senescent endothelial cells on platelet function. To this end, we took advantage of a model in which immortalized endothelial cells (HMEC-1) were induced to senesce following exposure to doxorubicin, a chemotherapeutic drug widely used in the clinic. Our results indicate that (1) low concentrations of doxorubicin induce senescence in HMEC-1 cells; (2) senescent HMEC-1 cells upregulate the expression of selected components of the SASP and (3) the media conditioned by senescent endothelial cells are capable of inducing platelet activation and aggregation. These results suggest that factors secreted by senescent endothelial cells in vivo could have a relevant role in the platelet activation observed in the elderly or in patients undergoing therapeutic stress.

Study protocol for the epigenetic characterization of angor pectoris according to the affected coronary compartment: Global and comprehensive assessment of the relationship between invasive coronary physiology and microRNAs.

BACKGROUND: MicroRNAs (miRNAs) are noncoding RNAs involved in post-transcriptional genetic regulation with a proposed role in intercellular communication. miRNAs are considered promising biomarkers in ischemic heart disease. Invasive physiological evaluation allows a precise assessment of each affected coronary compartment. Although some studies have associated the expression of circulating miRNAs with invasive physiological indexes, their global relationship with coronary compartments has not been assessed. Here, we will evaluate circulating miRNAs profiles according to the coronary pattern of the vascular compartment affectation. STUDY AND DESIGN: This is an investigator-initiated, multicentre, descriptive study to be conducted at three centres in Spain (NCT05374694). The study will include one hundred consecutive patients older than 18 years with chest pain of presumed coronary cause undergoing invasive physiological evaluation, including fractional flow reserve (FFR) and index of microvascular resistance (IMR). Patients will be initially classified into four groups, according to FFR and IMR: macrovascular and microvascular affectation (FFR≤0.80 / IMR≥25), isolated macrovascular affectation (FFR≤0.80 / IMR<25), isolated microvascular affectation (FFR>0.80 / IMR ≥25) and normal coronary indexes (FFR>0.80 / IMR<25). Patients with isolated microvascular affectation or normal indexes will also undergo the acetylcholine test and may be reclassified as a fifth group in the presence of spasm. A panel of miRNAs previously associated with molecular mechanisms linked to chronic coronary syndrome will be analysed using RT-qPCR. CONCLUSIONS: The results of this study will identify miRNA profiles associated with patterns of coronary affectation and will contribute to a better understanding of the mechanistic pathways of coronary pathology.

Platelets, a Key Cell in Inflammation and Atherosclerosis Progression.

Platelets play important roles in thrombosis-dependent obstructive cardiovascular diseases. In addition, it has now become evident that platelets also participate in the earliest stages of atherosclerosis, including the genesis of the atherosclerotic lesion. Moreover, while the link between platelet activity and hemostasis has been well established, the role of platelets as modulators of inflammation has only recently been recognized. Thus, through their secretory activities, platelets can chemically attract a diverse repertoire of cells to inflammatory foci. Although monocytes and lymphocytes act as key cells in the progression of an inflammatory event and play a central role in plaque formation and progression, there is also evidence that platelets can traverse the endothelium, and therefore be a direct mediator in the progression of atherosclerotic plaque. This review provides an overview of platelet interactions and regulation in atherosclerosis.