The involvement of leucine-rich α-2 glycoprotein in the progression of skin and lung fibrosis in bleomycin-induced systemic sclerosis model

Objective Systemc sclerosis (SSc) is an autoimmune disorder characterized by fibrosis of the skin and internal organs. Recently, it has been shown that leucine-rich alpha-2 glycoprotein (LRG) functions as a modulator of transforming growth factor-beta (TGF-beta) signaling in fibrosis. We aimed to characterize the effect of LRG in SSc model and SSc patients. Methods Histological analysis was performed on LRG knockout (KO) and wild type (WT) mouse in the skin and the lung after bleomycin administration. Serum LRG levels were measured during the injection period. Gene expression analysis of the skin and lung tissue from LRG KO and WT mice was performed. In addition, serum LRG levels were determined in SSc patients and healthy controls. Results LRG KO mice display an inhibition of fibrosis in the skin in association with a decrease of dermal thickness, collagen deposition, and phospho-Smad3 expression after bleomycin. Serum LRG concentration significantly increased in WT mice after bleomycin. There was also a suppression of inflammation and fibrosis in the LRG KO mouse lung indicated by a reduction of lung weight, collagen content, and phospho-Smad3 expression after bleomycin. Gene expressions of TGF-beta and Smad2/3 were significantly reduced in LRG KO mice. Serum LRG levels in SSc patients were significantly higher than those in controls. Conclusion LRG promotes fibrotic processes in SSc model through TGF-beta-Smad3 signaling, and LRG can be a biomarker for SSc in humans and also a potential therapeutic target for SSc.