Intracellular C3 modulates senolytic responsiveness in senescent cells and aged tissues via AKT/S6K pro-survival signaling

Abstract Pathological accumulation of senescent cells (SnCs) across tissues drives aging and age-related diseases. Senolytic agents targeting senescent cell anti-apoptotic pathways (SCAPs) hold promise for treating age-related diseases, yet their efficacy is limited by the heterogeneity of SnC survival mechanisms beyond canonical BCL-2 family pathways. Here, we identify intracellular complement C3 (intC3) as a previously unrecognized determinant of senolytic responsiveness. C3 was consistently and markedly upregulated across diverse senescent cell types and aged tissues; however, its depletion via knockout (KO) or knockdown (KD) did not alter canonical senescence phenotypes. Unexpectedly, C3 KD attenuated ABT263- and bortezomib-mediated SnC apoptosis, while sustaining pro-survival AKT/S6K signaling. In aged C3-knockout (C3KO) mice, ABT263 failed to effectively eliminate SnCs, resulting in persistent senescence markers, unresolved senescence-associated secretory phenotype (SASP), and exacerbated fibrosis. Mechanistically, AKT inhibition rescued senolytic sensitivity in C3-KD SnCs, confirming AKT/S6K as the functional downstream mediator. These findings redefine intC3 as an intracellular stress sensor that sensitizes SnCs to apoptotic clearance—transcending its canonical extracellular immune role—and position the intC3–AKT axis as a potential target for overcoming senolytic resistance.