Background: Autophagy is catabolic process allowing cells to degrade unnecessary or dysfunctional cellular organelles. Failure of appropriate regulation of autophagy, however, can severely perturb tissue homeostasis. Recent studies demonstrate that autophagy is activated in several fibrotic diseases such as liver fibrosis, renal interstitial fibrosis, cardiac fibrosis.

Objectives: The objective of this work was to characterize the activation of autophagy in systemic sclerosis (SSc) and to decipher its role in the pathogenesis of SSc.

Methods: Activation of autophagy in skin samples of patients and murine models of SSc was assessed by co-staining of LC3B and P62 with the lysosomal marker LAMP2. The role of the autophagy was investigated in the model of bleomycin-induced dermal fibrosis. Beclin1 was overexpressed using adenovirus encoding for Beclin1 . To knockdown Atg7 in vivo was achieved by subcutaneous injections of Atg7 siRNA or non-targeting siRNA. In vivo , 3-methyladenine (3-MA) was administered i.p. in a concentration of 15 mg/kg ones daily. Protein expression was measured by Western blot. Target genes were analyzed by qPCR. To monitor the autophagic flux, we generated adenoviral vectors encoding for tandem fluorescent-tagged LC3 (mRFP-EGFP-LC3).

Results: In the present study, we demonstrate that autophagy is activated in fibroblasts in SSc skin and also in experimental fibrosis models as compared to respective non-fibrotic control tissue with enhanced activity in in vivo and in vitro autophagy reporter studies. The aberrant activation of autophagy had profound stimulatory effects on fibroblasts. Activation of autophagy by forced expression of BECLIN1 promoted fibroblast-to-myofibroblast transition and stimulated the collagen release by cultured human fibroblasts and induced fibrosis in murine model. Nevertheless, inhibition of autophagy can deactivate myofibroblasts and induce regression of tissue fibrosis. Knockdown of ATG7 or BECLIN1 in human fibroblasts reduced the expression of αSMA and the number of stress fibers in myofibroblasts, indicating re-differentiation of myofibroblasts into resting fibroblasts upon inhibition of autophagy. Similar results were obtained with the autophagy inhibitors CQ and 3-MA. In vivo , siRNA mediated knockdown of Atg7 effectively prevented progression of fibrosis in a model of established bleomycin-induced skin fibrosis. Inactivation of autophagy decreased dermal thickness, myofibroblast counts and hydroxyproline content to below pretreatment levels, indicating regression of bleomycin-induced skin fibrosis. In addition, treatment of mice with the autophagy inhibitor 3-MA ameliorated bleomycin-induced skin fibrosis.

Conclusion: We demonstrate that autophagy activity is enhanced in fibroblasts of SSc patients and in murine models of SSc. The increased activation of autophagy induces fibroblast-to-myofibroblast transition and promotes fibrotic tissue remodeling. However, inhibition of autophagy can deactivate myofibroblasts and induce regression of tissue fibrosis.

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[4]Hernández-Gea V, Ghiassi-Nejad Z, Rozenfeld R, et al . Autophagy releases lipid that promotes fibrogenesis by activated hepatic stellate cells in mice and in human tissues. Gastroenterology 142, 938-946 (2012).

Disclosure of Interests: Ariella Zehender: None declared, Yi-Nan Li: None declared, Neng-Yu Lin: None declared, Andrea-Hermina Györfi: None declared, Alina Soare: None declared, Christina Bergmann: None declared, Andreas Ramming: None declared, Georg Schett: None declared, Jörg H.W. Distler Consultant of: Actelion, Active Biotech, Anamar, ARXX, Bayer Pharma, Boehringer Ingelheim, Celgene, Galapagos, GSK, Inventiva, JB Therapeutics, Medac, Pfizer, RuiYi and UCB., Grant/research support from: Anamar, Active Biotech, Array Biopharma, aTyr, BMS, Bayer Pharma, Boehringer Ingel-heim, Celgene, Galapagos, GSK, Inventiva, Novartis, Sanofi-Aventis, RedX, UCB., Employee of: stock owner of 4D Science and Scientific head of FibroCure