Searching for Associations Between Biomarkers of Senescent Cells Accumulation in Different Tissues in Older and Oldest-Old Patients

Relevance. Understanding the biological mechanisms of aging is necessary to prevent and slow down the development of age-associated diseases. One of the leading causes of aging considered to be the accumulation of so-called senescent, or aging, cells (SC). Cellular aging is necessary for tissue renewal and regeneration, but excessive accumulation of SC leads to the activation of chronic aseptic inflammation, tissue dysfunction and development of age-associated diseases. Currently, approaches to selective elimination of SCs, as well as control of their activity and reversion of the senescent state are being actively developed. The assessment of stem cell involvement in aging and disease development requires the use of dependable and relevant biomarkers. A commonly used biomarker to indicate a cessation in cell growth is the expression of cell cycle inhibitors (for example, p16/INK4a) since the arrest of proliferation is one of the main attributable features of SC. However, evaluation of this marker is difficult inclinical practice. Typically, the stiffness ofthe vascular wall, some hemodynamic and biochemical parameters, as well as the content of certain cytokines and growth factors in the blood are determined as markers of age-associated diseases. In this work, we aimed to study the relationship between established clinical systemic biomarkers of aging and development of age-associated diseases and biomarkers of KS at the tissue and cellular levels.

The aim of the study is to establish the associations between various biomarkers of SC accumulation at the cellular, tissue and system levels.

Materials and methods. Study included 38 patients aged 65 to 85 years. In all patients, traditional risk factors for cardiovascular diseases, arterial wall stiffness were assessed, and samples were obtained (peripheral blood, skin, subcutaneous fat), from which various types of cells were then isolated (mononuclear blood cells (MBC), fibroblasts (FB) and mesenchymal stromal cells (MSCs), and also histological analysis of biopsy specimens to evaluate various MC markers was performed.

Results. In the obtained samples, various indicators of the accumulation of senescent cells were determined, and the relationships between the rigidity of the vascular wall, traditional risk factors for CVD, biomarkers of inflammation and the accumulation of senescent cells in tissues and cell populations were analyzed. Using correlation analysis, a strong significant association was confirmed between the key biomarker of KS — the level of p16 expression in tissues — and age (r = 0.6, p < 0.001), which corresponds to literature data [2]. At the organismal level, its relationship with the pulse wave velocity (r = 0.394, p = 0.015), in the systemic circulation — with the level of VCAM-1 (r = 0.312, p = 0.006) and with the level of p16 mRNA in the MNC (r = 0.380, p = 0.046). Statistically significant correlations were identified with the proliferation rates of PB and MSCs in culture and the acquisition of the agingassociated secretory phenotype (SASP) by cells: thus, level of p16 significantly correlated with the level of IL-6 (strong relationship) and MCP-1 (weak relationship) in cell secretome. The results of multivariate linear regression analysis confirmed that, regardless of age, p16 expression is associated with the proliferation of isolated cells and IL-6 in SASP. Using computer modeling, after normalizing the characteristics, a formula was determined that allows one to predict the level of p16 expression in tissues, relying only on non-invasively determined indicators.

Conclusion. Thus, the association between clinical parameters reflecting vascular aging and biomarkers of SC accumulation in tissues and in cells isolated from these tissues into culture has been demonstrated. The possibilities of minimally invasive determination of indicators of accumulation of senescent cells in patients over 65 years of age have also been determined, which opens up new opportunities for monitoring the effectiveness of senolytic therapy.