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.

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.

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.

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Introduction: The initial transition from a proliferative to a senescent state is accompanied by a reduction in the activity of the cyclin-cyclin-dependent kinase (CDK) complexes, which in turn could be explained by the activation of the p53-p21CIP1/WAF1 and/or p16INK4a-pRB signaling pathways. As overexpression of D-type cyclins is commonly observed in gastric cancer cells, the use of CDK4/6 inhibitors could represent a viable alternative for gastric cancer treatment. Nonetheless, senescent cell can synthesize and secrete a plethora of bioactive molecules (a feature known as the senescence-associated secretory phenotype, SASP) with the potential of modifying the tumor microenvironment in ways that could be therapeutically deleterious. Among processes that are upregulated in most senescent cells, autophagy has received great attention during the last years. So far, however, the role of autophagy in the modulation of SASPs has yet to be clarified. Previous work from our lab has revealed an increased autophagic flux in gastric cancer cell lines undergoing drug-induced senescence, suggesting a regulatory role in the implementation of this modality of cellular senescence. More specifically, the secretory phenotype of senescent gastric cancer cells seems to depend on the autophagy status. Materials and Methods: In order to determine the role of autophagy in the modulation of the SASP, cellular senescence was pharmacologically triggered in gastric cancer cell lines (AGS, MKN-45) through inhibition of CDK4/6 activity (0.5-1.0 μM of Palbociclib for 48 and 96 hours), with or without the concomitant inhibition of autophagy by either genetic (knocking down ATG5) or pharmacologic (treatment with 0.5 μM of Spautin-1) approaches. The expression of factors secreted by senescent cells under different experimental conditions was analyzed from conditioned media; and the same conditioned media were used in assays aimed to assess migration, invasion, and cell proliferation of non-senescent cells. Results and Discussion: Inhibition of autophagy in senescent cells led to a downregulation in the expression of proinflammatory molecules that were overexpressed in autophagy-proficient senescent cells (MIF, IL-8, IL1β). Unlike conditioned media derived from AGS cells, conditioned media derived from senescent MKN-45 cells that were rendered deficient in autophagy enhanced the invasive capabilities of non-senescent cells. Our results suggest that autophagy modulates the expression of SASP components and, by so doing, affects the behavior of neighboring non-senescent cells. Interestingly, these effects were also influenced by the genetic status of gastric cancer cells. This work was supported by Fondecyt ANID 11201182 Citation Format: Claudio A. Valenzuela, Danitza Rebolledo, Angel Cayo, Whitney Venturini, Raúl Segovia, Rodrigo Moore-Carrasco, Nelson Brown. The secretome produced by senescent gastric cancer cells can lead to different paracrine effects depending on the status of autophagy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5983.