title: Mechanistic Target of Rapamycin Complex 1 (mTORC1) and mTORC2 as Key Signaling Intermediates in Mesenchymal Cell Activation.
abstract: Fibrotic diseases display mesenchymal cell (MC) activation with pathologic deposition of matrix proteins such as collagen. Here we investigate the role of mTOR complex 1 (mTORC1) and mTORC2 in regulating MC collagen expression, a hallmark of fibrotic disease. Relative to normal MCs (non-Fib MCs), MCs derived from fibrotic human lung allografts (Fib-MCs) demonstrated increased phosphoinositide-3kinase (PI3K) dependent activation of both mTORC1 and mTORC2, as measured by increased phosphorylation of S6K1 and 4E-BP1 (mTORC1 substrates) and AKT (an mTORC2 substrate). Dual ATP-competitive TORC1/2 inhibitor AZD8055, in contrast to allosteric mTORC1-specific inhibitor rapamycin, strongly inhibited 4E-BP1 phosphorylation and collagen I expression in Fib-MCs. In non-Fib MCs, increased mTORC1 signaling was shown to augment collagen I expression. mTORC1/4E-BP1 pathway was identified as an important driver of collagen I expression in Fib-MCs in experiments utilizing raptor gene silencing and overexpression of dominant-inhibitory 4E-BP1. Furthermore, siRNA-mediated knockdown of rictor, an mTORC2 partner protein, reduced mTORC1 substrate phosphorylation and collagen expression in Fib-, but not non-Fib MCs, revealing a dependence of mTORC1 signaling on mTORC2 function in activated MCs. Together these studies suggest a novel paradigm where fibrotic activation in MCs increases PI3K dependent mTORC1 and mTORC2 signaling and leads to increased collagen I expression via the mTORC1-dependent 4E-BP1/eIF4E pathway. These data provide rationale for targeting specific components of mTORC pathways in fibrotic states and underscore the need to further delineate mTORC2 signaling in activated cell states.
authors.affiliation: From the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine.
authors.forename: Natalie M
authors.initials: NM
authors.lastname: Walker
authors.affiliation: From the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Belloli
authors.affiliation: College of Pharmacology.
authors.forename: Linda
authors.initials: L
authors.lastname: Stuckey
authors.affiliation: From the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Chan
authors.affiliation: Department of Surgery, and.
authors.forename: Jules
authors.initials: J
authors.lastname: Lin
authors.affiliation: Department of Surgery, and.
authors.forename: William
authors.initials: W
authors.lastname: Lynch
authors.affiliation: Department of Surgery, and.
authors.forename: Andrew
authors.initials: A
authors.lastname: Chang
authors.affiliation: From the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine.
authors.forename: Serina M
authors.initials: SM
authors.lastname: Mazzoni
authors.affiliation: Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109.
authors.forename: Diane C
authors.initials: DC
authors.lastname: Fingar
authors.affiliation: From the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, vlama@umich.edu.
authors.forename: Vibha N
authors.initials: VN
authors.lastname: Lama
mesh_terms: D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism; D006801:Humans; D008168:Lung / Q000473:pathology; D016040:Lung Transplantation; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D009025:Morpholines / Q000494:pharmacology; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011658:Pulmonary Fibrosis / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D024042:Collagen Type I; D009025:Morpholines; D046912:Multiprotein Complexes; C546624:(5-(2,4-bis((3S)-3-methylmorpholin-4-yl)pyrido(2,3-d)pyrimidin-7-yl)-2-methoxyphenyl)methanol; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus
keywords: Bronchiolitis obliterans syndrome; Chronic allograft rejection; collagen; extracellular matrix protein; fibrosis; mammalian target of rapamycin (mTOR); mesenchymal cell; pulmonary fibrosis