title: Autophagy fosters myofibroblast differentiation through MTORC2 activation and downstream upregulation of CTGF.
abstract: Recent evidence suggests that autophagy may favor fibrosis through enhanced differentiation of fibroblasts in myofibroblasts. Here, we sought to characterize the mediators and signaling pathways implicated in autophagy-induced myofibroblast differentiation. Fibroblasts, serum starved for up to 4 d, showed increased LC3-II/-I ratios and decreased SQSTM1/p62 levels. Autophagy was associated with acquisition of markers of myofibroblast differentiation including increased protein levels of ACTA2/αSMA (actin, α 2, smooth muscle, aorta), enhanced gene and protein levels of COL1A1 (collagen, type I, α 1) and COL3A1, and the formation of stress fibers. Inhibiting autophagy with 3 different class I phosphoinositide 3-kinase and class III phosphatidylinositol 3-kinase (PtdIns3K) inhibitors or through ATG7 silencing prevented myofibroblast differentiation. Autophagic fibroblasts showed increased expression and secretion of CTGF (connective tissue growth factor), and CTGF silencing prevented myofibroblast differentiation. Phosphorylation of the MTORC1 target RPS6KB1/p70S6K kinase was abolished in starved fibroblasts. Phosphorylation of AKT at Ser473, a MTORC2 target, was reduced after initiation of starvation but was followed by spontaneous rephosphorylation after 2 d of starvation, suggesting the reactivation of MTORC2 with sustained autophagy. Inhibiting MTORC2 activation with long-term exposure to rapamycin or by silencing RICTOR, a central component of the MTORC2 complex abolished AKT rephosphorylation. Both RICTOR silencing and rapamycin treatment prevented CTGF and ACTA2 upregulation, demonstrating the central role of MTORC2 activation in CTGF induction and myofibroblast differentiation. Finally, inhibition of autophagy with PtdIns3K inhibitors or ATG7 silencing blocked AKT rephosphorylation. Collectively, these results identify autophagy as a novel activator of MTORC2 signaling leading to CTGF induction and myofibroblast differentiation.
authors.affiliation: a Centre de Recherche du Hospitalier de l'Université de Montréal (CRCHUM) and Université de Montréal ; Montreal , QC , Canada.
authors.forename: Monique
authors.initials: M
authors.lastname: Bernard
authors.forename: Mélanie
authors.initials: M
authors.lastname: Dieudé
authors.forename: Bing
authors.initials: B
authors.lastname: Yang
authors.forename: Katia
authors.initials: K
authors.lastname: Hamelin
authors.forename: Katy
authors.initials: K
authors.lastname: Underwood
authors.forename: Marie-Josée
authors.initials: MJ
authors.lastname: Hébert
mesh_terms: D001343:Autophagy; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D058546:Class III Phosphatidylinositol 3-Kinases / Q000378:metabolism; D055513:Connective Tissue Growth Factor / Q000378:metabolism*; D006801:Humans; D000076225:Mechanistic Target of Rapamycin Complex 2; D046912:Multiprotein Complexes / Q000378:metabolism*; D058628:Myofibroblasts / Q000166:cytology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D015533:Transcriptional Activation / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D058546:Class III Phosphatidylinositol 3-Kinases; D055513:Connective Tissue Growth Factor; D000076225:Mechanistic Target of Rapamycin Complex 2; D046912:Multiprotein Complexes; D019869:Phosphatidylinositol 3-Kinases; D058570:TOR Serine-Threonine Kinases; D016212:Transforming Growth Factor beta; C526317:CCN2 protein, human
keywords: 3-MA, 3-methyladenine; ACTA2, actin, α 2, smooth muscle, aorta; AKT; ATG7; Ctl, control; DAPI, 4′, 6-diamidino-2-phenylindole; ECM, extracellular matrix; FBS, fetal bovine serum; GF, growth factor; LC3B, MAP1LC3B (microtubule-associated protein 1 light chain 3 β); LY, LY294002; MTORC2; N, normal growth medium; R, rapamycin; SS, serum-free (starvation) medium; T, TGFB1 (transforming growth factor, β 1); TUBA, tubulin, α; V, vehicle; W, wortmannin; WB, western blotting; autophagy; connective tissue growth factor (CTGF); differentiation; fibroblast; fibrosis; iso, isotype control; myofibroblast; rapamycin