Abstract Body (Do not enter title and authors here): Background: IGF-1 is a major growth factor, which promotes cell proliferation, and survival. IGF-1 reduced atherosclerosis in aortas in Apoe-/- mice and in coronaries in hypercholesterolemic pigs (FH pigs). Cell senescence is an irreversible cell proliferation arrest associated with the progression of atherosclerosis, however specific mechanisms linking senescence with atherogenesis remain to be identified.
Hypothesis: We hypothesized that IGF1 receptor (IGF1R) downregulation would induce SMC senescence in vitro and that activation of IGF1R signaling would suppress SMC senescence in the atherosclerotic plaque.
Methods: Bleomycin (10ug/ml, 5d)-treated aortic SMC were used as in vitro senescence model. Cell proliferation was assessed with Incucyte live-cell system, senescence markers (γ-H2AX histone and p21) - by IHC, β-galactosidase (βGal) activity – X-gal assay, IGF-1-induced signaling – immunoblotting for pSer473-AKT.
Results: Bleomycin-treated SMC have downregulated IGF1R levels (4.1-fold decrease) and inhibited IGF-1 signaling (8.3-fold reduction) (all are P<0.05 vs. control) indicating that cell senescence inhibits IGF-1 signaling. SMC treatment with 3uM picropodophyllin (IGF1R inhibitor) or with 100nM ganitumab (IGF1R antibody) decreased IGF-1-induced signaling, arrested SMC proliferation and upregulated senescence markers (βGal activity and γ-H2AX expression) showing that specific inhibition of IGF-1 signaling induces cell senescence. To test whether activation of IGF-1 signaling inhibits senescence in plaque cells we used coronary sections obtained from IGF-1 (100μg/kg/d, 180d)-treated or control FH pigs. IGF-1 downregulated senescence markers in the plaque fibrous cap: βGal: 62% decrease, p21: 68% decrease (all are P<0.05 vs. control) and depleted SMC-like senescent cells (βGal⁺/aSMA⁺ cells) (19% decrease vs. control). Spatial transcriptomics indicated that coronary plaques from IGF-1-treated pigs have a significantly decreased senescence module score (the average expression of 63 senescence genes relative to random gene list controls) in the plaque fibrous cap.
Conclusions: IGF1R downregulation induced SMC senescence in vitro and activation of IGF1R signaling downregulated senescence markers, and decreased levels of SMC-like senescent cells in the porcine coronary plaque. Our results identified a novel mechanism linking reduced IGF-1 signaling with cell senescence and progression of atherosclerosis and provide a potential novel therapeutic target.