ABSTRACT: Atherosclerosis represents an age-related disease, which remains one of the leading cause of deaths in developed countries. It begins with a local deposition of lipid in the innermost part of the artery – intima. Thereafter a number of immune cells are attracted and infiltrate into the artery wall, where, together with endothelia and smooth muscle cells, form an atherosclerotic plaque (Libby, 2008). Thus, atherosclerosis is considered as an inflammatory disease, characterized by intense immunological activity (Libby P, 2012). One of the main risk factor for atherosclerosis is aging. It was demonstrated that there is an accumulation of senescent cells within atherosclerotic plaque (..). Accordingly, vascular smooth muscle cells (VSMCs) derived from the lesion demonstrate a phenotype characteristic for senescent cells: diminished proliferative potential, shorter telomeres, increased number of DNA damage and upregulation of SA-β-gal activity (Gorenne, 2006; Matthes, 2006, Mahomoudi, 2008). Accumulation of senescent VSMCs within the area of plaque development promotes its instability due to lack of proliferation and impaired production of extracellular matrix, both leading to weakening of fibrous cap (Gorenne, 2006). This has been further confirmed by the observation, that elimination of senescent cells in the atherosclerosis-prone low-density lipoprotein receptor-deficient (Ldlr-/-) mice slowed down the disease progression (27789842). One of the most important feature of senescent cells, that has the biggest impact on tissue microenvironment, is their ability to secrete a number of cytokines, chemokines, matrix metalloproteinases and growth factors collectively known as the Senescence Associated Secretory Phenotype (SASP) (20078217, 28165648). Apart from soluble factors, senescent cells secret also an increased number of extracellular vesicles (EVs), research of which has only recently begun (32461143). EVs are small membranous vesicles that can be categorized based on their size and origin, into: exosomes, microvesicles and apoptotic bodies. EVs play crucial role as carriers of proteins, different types of RNA and DNA, lipids and metabolites that, take part in intercellular communication (23420871). They were shown to participate in many physiological but also pathological conditions. Studies performed over the last decade proved that EVs affect atherosclerosis progression at different stages by several distinct mechanisms (as reviewed by Knokhot, 2020, 33261815). The increased concentrations of EVs have been found in plasma of patients suffering from cardiovascular diseases as well as in atherosclerotic plaque itself (Yin, 2015, 26142082; Rautou, 2011, 21852557). However, the role of EVs derived from senescent cells in atherosclerosis, particularly in the context of the plaque development, remains unknown. The functioning of immune cells within atherosclerotic plaque is modulated by local milieu. Thus, senescent cells present in the lesion can influence plaque development by non-cell autonomous mechanism. Indeed, recently it was demonstrated that SASP factors secreted by senescent VSMCs promote recruitment of monocytes, induce expression of adhesion receptors on endothelial cells and activate adjacent normal VSMCs, promoting inflammation in the plaque (Gardner, 2015). However, the role of EVs in this context has not been studied. Thus, we have undertaken research aimed at investigating the role of senescent cell derived EVs on immune cells activity. To this end, we isolated and characterized the EVs secreted by human VSMCs undergoing senescence. We performed unbiased quantitative proteomic analysis of both soluble and insoluble SASP components. Moreover, we analyzed the influence of EVs derived from senescent and non-senescent cells on T lymphocytes and monocytes. Altogether our studies revealed that EVs produced by senescent VSMCs strengthen inflammatory response of the immune cells, what would have a tremendous significance in atherosclerotic plaque development.
Dominik Cysewski 