Activation of fibroblasts is essential for physiological tissue repair. Uncontrolled activation of fibroblasts, however, may lead to tissue fibrosis with organ dysfunction. Although several pathways capable of promoting fibroblast activation and tissue repair have been identified, their interplay in the context of chronic fibrotic diseases remains incompletely understood. Here, we provide evidence that transforming growth factor-β (TGFβ) activates autophagy by an epigenetic mechanism to amplify its profibrotic effects. TGFβ induces autophagy in fibrotic diseases by SMAD3-dependent downregulation of the H4K16 histone acetyltransferase MYST1, which regulates the expression of core components of the autophagy machinery such as ATG7 and BECLIN1. Activation of autophagy in fibroblasts promotes collagen release and is both, sufficient and required, to induce tissue fibrosis. Forced expression of MYST1 abrogates the stimulatory effects of TGFβ on autophagy and re-establishes the epigenetic control of autophagy in fibrotic conditions. Interference with the aberrant activation of autophagy inhibits TGFβ-induced fibroblast activation and ameliorates experimental dermal and pulmonary fibrosis. These findings link uncontrolled TGFβ signaling to aberrant autophagy and deregulated epigenetics in fibrotic diseases and may contribute to the development of therapeutic interventions in fibrotic diseases.
BackgroundAutophagy is catabolic process allowing cells to degrade unnecessary or dysfunctional cellular organelles. Aberrant activation of autophagy has been also implicated into the pathogenesis of fibrotic diseases. Several stimuli present in fibrosis such as pro-fibrotic cytokines are known to activate autophagy.ObjectivesThe objective of this work is characterise the regulation of autophagy by TGFβ and analyse whether targeting of autophagy in fibroblasts may prevent their aberrant activation in fibrotic diseases.MethodsTo selectively disable autophagy in fibroblasts we generate Atg7fl/flx Col1a2;CreER mice. The role of the autophagy was investigated in the model of bleomycin- and TβRIact-induced dermal and pulmonary fibrosis. Overexpression of Myst1 was achieved by adenovirus encoding for Myst1. Collagen release and protein expression were measure by Western blot. Target genes were analysed by RT-PCR. Co-immunoprecipitation and reporter assay were performed to study physical and functional interactions between MYST1 and SMAD3. To monitor the autophagic flux in vitro and in vivo we generate an adenovirus encoding for tandem fluorescent-tagged LC3 (mRFP-EGFP-LC3), defined as reliable autophagy maker.ResultsWe provide evidence that transforming growth factor-β (TGFβ) activates autophagy by an epigenetic mechanism to amplify its profibrotic effects. TGFβ induces autophagy in fibrotic diseases by SMAD3-dependent downregulation of the H4K16-histoneacetlytransferase MYST1, which controls the expression of core components of the autophagy machinery such as ATG7 and BECLIN1. Activation of autophagy in fibroblasts promotes collagen release and is both, sufficient and required, to induce tissue fibrosis. Forced expression of MYST1 abrogates the stimulatory effects of TGFβ on autophagy and re-establishes the epigenetic control of autophagy in fibrotic conditions. Interference with the aberrant activation of autophagy inhibits TGFβ-induced fibroblast activation and ameliorates experimental dermal and pulmonary fibrosis. These findings link uncontrolled TGFβ signalling to aberrant autophagy and altered epigenetics in fibrotic diseases and may open new avenues for therapeutic intervention in fibrotic diseases.ConclusionsWe demonstrate that the epigenetic control of autophagy is disturbed by a TGFβ-dependent downregulation of MYST1. The increased activation of autophagy induces fibroblast-to-myofibroblast transition and promotes fibrotic tissue remodelling. Re-expression of MYST1 prevents aberrant autophagy, limits the profibrotic effects of TGFβ and ameliorates experimental fibrosis. Restoration of the epigenetic control of autophagy might thus be a novel approach to ameliorate fibrotic tissue remodelling.Disclosure of InterestA. Zehender: None declared, N.-Y. Lin: None declared, A. Stefanica: None declared, C.-W. Chen: None declared, A. Soare: None declared, T. Wohlfahrt: None declared, S. Rauber: None declared, C. Bergmann: None declared, A. Ramming: None declared, O. Distler Grant/research support from: Actelion, Pfizer...
Background Autophagy is an essential, homeostatic process by which cells digest unnecessary or damaged organelles. Atg7 is essentially required for formation of theautophagosome. The DMARD chloroquine (CQ) has been identified to arrest autophagy function by blocking the fusion between autophagosomes and lysosomes. Accumulating evidence demonstrates that autophagy is involved in the pathology of varies diseases including infections, cancer and neurodegeneration and recent reports also linked autophagy to osteoclastogenesis and rheumatoid arthritis. Objectives Osteoporosis is a disease associated with aging and hormones imbalance that causes bone fragility and susceptibility to fractures result from increased osteoclastogenesis and insufficient osteoblastogenesis. The underlying mechanisms are incompletely understood. Here, we investigated the role of autophagy in the murine model of osteoporosis. Methods Systemic bone loss was induced by ovariectomy (OVX). Autophagy was modulated by genetic as well as pharmacologic approaches. For genetic inhibition of autophagy, we crossbred Atg7fl/fl mice with LysM Cre+ mice to generate Atg7fl/fl x LysM Cre+ mice with selective inactivation of autophagy function in the monocyte lineage. For pharmacological inhibition, eight-week-old mice underwent daily intraperitoneal injection of 20mg kg-1 CQ for a total of 50 days. We applied Microcomputed tomography to analyze bone density in vivo. TRAP staining and bone histomorphometry were used to confirm osteoclast number in tissue. To assess osteoclast formation and activity in vitro, Atg7fl/fl x LysM Cre+ BMCs and CQ treated BMCs were cultured on bone slices and analysed by the TRAP staining and Toluidine blue staining (n=6, for each group). Results To investigate the effect of CQ on OVX-induced systemic bone loss, we analyzed the bone density (bone volume/trabecular volume; Bv/Tv) and the trabecular number (Tb. N.) at the proximal tibias. Bv/Tv and Tb. N. were strongly reduced in sham-treated OVX mice. The decreases in Bv/Tv and in Tb. N. were reduced by 76 % and 60% in CQ treated OVX mice (n=6, p<0.05 for both). Inhibition of autophagy by selective knockdown of Atg7 in monocytic cells (Atg7fl/fl x LysM Cre-mice) also prevented OVX-induced osteoporosis and prevented OVX-induced decreases in Bv/Tv and in Tb. N.. Histomorphometric analyses demonstrated decreased osteoclast counts in CQ-treated mice and Atg7fl/fl x LysM Cre-mice, respectively, compared to controls. Consistent with these in vivo results, inhibition of autophagy, either by treatment with CQ or by knockdown of Atg7, also prevented osteoclast differentiation and osteoclast mediated bone resorption in vitro. Conclusions We demonstrate that inhibition of autophagy either by genetic or by pharmacological approachessignificantly reduced OVX-induced osteoporosis in mice. These findings identify the autophagy machinery as a potential target for the treatment of osteoporoses. Considering the potent anti-osteoporotic effects and the availability of approved inhibitors such ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.