H 2 O 2 and mTOR control the senescence-associated secretory phenotype by coordinating Ca 2+ transients through TRPC6 expression and activation

Cellular senescence has evolved as a protective mechanism to arrest growth of cells with oncogenic potential. While senescent cells have lost the ability to divide, they remain metabolically active and adapt a deleterious senescence associated secretory phenotype (SASP) central to the progression of several age-associated disease pathologies. The SASP is mechanistically regulated by the pro-inflammatory cytokine interleukin-1 alpha (IL-1α) whose expression and activity is responsive to the senescence associated (SA) oxidant production and the accompanying disruption of calcium (Ca 2+ ) homeostasis. Using primary IMR-90 human fetal lung fibroblasts as a model of replicative senescence, we explored the molecular underpinnings facilitating increased Ca 2+ entry in senescent cells. We establish that the redox-responsive Transient Receptor Potential TRPC6 channel is compromised due to desensitization owing to SA increases in steady state hydrogen peroxide (H 2 O 2 ) production. SA dysregulation of Ca 2+ is also accompanied by loss of response to H 2 O 2 -induced Ca 2+ influx that can be rescued with catalase pre-treatments. Senescent cells are also insensitive to Ca 2+ entry induced by hyperforin, a specific activator of TRPC6 that can be restored by catalase pre-treatments, further suggesting redox regulation of TRPC6 in senescence. Inhibition of TRPC6 channel activity restores ability of senescent cells to respond to peroxide-induced Ca 2+ in addition to suppressing SASP gene expression. Furthermore, mammalian target of rapamycin (mTOR) signaling regulates SASP by means of modulating TRPC6 channel expression. Together, our findings provide compelling evidence that H 2 O 2 and mTOR-mediated regulation of TRPC6 channel modulates SASP gene expression. As TRP channels emerge as targets of pharmacologic intervention for numerous disease pathologies, it is exciting to speculate that effect of TRP interventions may be attributed in part to inhibition of senescence and the SASP.