Antagonizing the irreversible thrombomodulin-initiated proteolytic signaling alleviates age-related liver fibrosis via senescent cell killing
Cellular senescence is a stress-induced, stable cell cycle arrest phenotype which generates a pro-inflammatory microenvironment, leading to chronic inflammation and age-associated diseases. Determining the fundamental molecular pathways driving senescence instead of apoptosis could enable the identification of senolytic agents to restore tissue homeostasis. Here, we identify thrombomodulin signaling as a key molecular determinant of the senescent cell fate. Although normally restricted to endothelial cells, thrombomodulin is rapidly upregulated and maintained throughout all phases of the senescent program in aged mammalian tissues and in senescent cell models. Mechanistically, thrombomodulin activates a proteolytic feed-forward signaling pathway by stabilizing a multi-protein complex in early endosomes, thus forming a molecular basis for the irreversibility of the senescent program and ensuring senescent cell viability. Therapeutically, thrombomodulin signaling depletion or inhibition using vorapaxar, an FDA-approved drug, effectively ablates senescent cells and restores tissue homeostasis in liver fibrosis models. Collectively, these results uncover proteolytic thrombomodulin signaling as a conserved pro-survival pathway essential for senescent cell viability, thus providing a pharmacologically exploitable senolytic target for senescence-associated diseases. Overall design: To determine THBD's necessity in establishing senescence, THBD was depleted in IMR90 cells undergoing HRas-induced senescence or palbociclib-induced senescent Huh7 cells. Bulk RNA-seq are performed .