Abstract 18317: Activation of Autophagy Mediates Insulin-Like Growth Factor I (igf-1)-Induced Anti-Apoptotic Effect in Vascular Smooth Muscle Cells
Introduction: We have previously shown that smooth muscle cell (SMC)-specific IGF-1 receptor (IGF1R) deficiency enhances plaque SMC apoptosis and increases atherosclerosis in Apoe-null mice, however the underlying mechanism was not identified. Autophagy is a reparative process safeguarding plaque cells against oxidative injury, by degrading the damaged intracellular material.
Hypothesis: We hypothesized that IGF-1-induced autophagy in SMC mediates IGF-1-induced anti-apoptotic effect.
Methods: We isolated aortic SMC from floxed IGF-1R mice (control, FIR) and from SMC-specific IGF1R-null mice (22KI), and confirmed cell identity by staining for SMC markers α-SMA and calponin. 22KI SMC had increased cell-doubling time (22KI, 79±6h vs. FIR, 61±5h) and decreased cell proliferation (reduced EdU labeling). We quantified autophagy by measuring LC3-II (autophagy marker) levels (immunoblotting) and assessing autophagosome puncta number (Autophagy detection kit, Abcam)
Results: Serum deprivation induced a ~2-fold increase in LC3-II and autophagosome number (4.4±0.6 vs.2.2±0.4, P<0.001) in FIR cells; however, autophagy activation was blocked in 22KI cells. IGF-1 dose-dependently (10-100 ng/mL, 4h) activated autophagy in FIR cells (100 ng/ml, LC3-II: 2.2-fold increase, autophagosome number: 1.9-fold increase, both P<0.001), however, IGF-1 did not change autophagy indices in 22KI cells. H2O2 (110uM, 12h) induced 3.2-fold stronger apoptosis of 22KI SMC compared to FIR (P<0.05) (Cell Death ELISA) indicating that IGF1R deficiency sensitizes SMC to oxidant-induced apoptosis. IGF-1 prevented H2O2-induced apoptosis in FIR, and this effect was reversed by treatment with autophagy inhibitor (3-MA, 10uM, 4h). IGF-1-induced anti-apoptotic effect was not seen in 22KI cells.
Conclusions: In summary, IGF-1R deficiency blocked serum deprivation-induced autophagy and increased cell sensitivity to apoptosis. Further, by activating autophagy, IGF-1 might have protected SMC against oxidant-induced apoptosis. These results establish a novel autophagy-dependent mechanism mediating IGF-1-induced anti-apoptotic effect in SMC, potentially contributing to the anti-atherogenic effect of IGF-1.
Author Disclosures: X. Hou: None. T. Yoshida: None. Y. Higashi: None. P. Snarski: None. Z. Li: None. P. Delafontaine: None. S. Danchuk: None. S. Sukhanov: None.
- © 2016 by American Heart Association, Inc.