Figure 6. ASAH1 is a potential senolytic target. (A, B) Proliferating and senescent cells were either left untreated (DMSO) or treated with acid ceramidase inhibitor (ACi), with or without D+Q for 48 h, whereupon cell viability was assessed by direct cell counting (A) and the activities of caspase 3/7 were assessed (B). (C, D) Senescent cells were treated as in (A), with addition of ZVAD-FMK (a pan-caspase inhibitor) whereupon cell viability was assessed by direct cell counting (C) and caspase 3/7 activities were measured (D). (E) Proliferating or pre-senescent cells were transfected either with control or ASAH1 siRNA; two days after transfection, cells were treated with either control DMSO or D+Q for 48 h followed by assessment of cell viability by direct cell counting. (F) Proposed model: in proliferating cells, ASAH1 is rapidly degraded by machineries that include the ubiquitin-proteasome degradation system, while in senescent cells, ASAH1 is stable, in turn promoting senescent cell survival and resistance to senolytic cell death.