Flow cytometry analysis of mitochondrial apoptotic priming with BH3 profiling on senescent cells.

Cellular senescence is a stable form of cell cycle arrest triggered by diverse stressors such as telomere shortening, oncogene activation, DNA damage, and chemotherapy. While senescence acts as a tumor-suppressive mechanism, the long-term accumulation of senescent cells contributes to chronic inflammation, tissue dysfunction, and age-related diseases, largely through the senescence-associated secretory phenotype (SASP). Senescent cells are characterized by increased expression of p16INK4a and p21CIP1, enlarged morphology, and resistance to apoptosis. This apoptotic resistance is mainly driven by the upregulation of anti-apoptotic BCL-2 family of proteins, including BCL-2, BCL-xL, and MCL-1. Senolytics - drugs that selectively induce apoptosis in senescent cells - target these survival pathways to promote senescent cell clearance. BH3 profiling is a functional assay that assesses mitochondrial apoptotic priming by exposing permeabilized cells to BH3-domain peptides and measuring cytochrome c release. This technique allows the identification of anti-apoptotic dependencies in senescent cells and can be used in combination with senescence markers (p16 and p21) via flow cytometry to pinpoint populations with enhanced apoptotic resistance. Understanding the apoptotic landscape of senescent cells is critical for optimizing senolytic strategies and improving therapeutic outcomes, particularly in contexts such as cancer and therapy-induced senescence.