LDLR dysfunction induces LDL accumulation and promotes pulmonary fibrosis.

Treatments for pulmonary fibrosis (PF) are ineffective because its molecular pathogenesis and therapeutic targets are unclear. Here, we show that the expression of low-density lipoprotein receptor (LDLR) was significantly decreased in alveolar type II (ATII) and fibroblast cells, whereas it was increased in endothelial cells from systemic sclerosis-related PF (SSc-PF) patients and idiopathic PF (IPF) patients compared with healthy controls. However, the plasma levels of low-density lipoprotein (LDL) increased in SSc-PF and IPF patients. The disrupted LDL-LDLR metabolism was also observed in four mouse PF models. Upon bleomycin (BLM) treatment, Ldlr-deficient (Ldlr-/-) mice exhibited remarkably higher LDL levels, abundant apoptosis, increased fibroblast-like endothelial and ATII cells and significantly earlier and more severe fibrotic response compared to wild-type mice. In vitro experiments revealed that apoptosis and TGF-ß1 production were induced by LDL, while fibroblast-like cell accumulation and ET-1 expression were induced by LDLR knockdown. Treatment of fibroblasts with LDL or culture medium derived from LDL-pretreated endothelial or epithelial cells led to obvious fibrotic responses in vitro. Similar results were observed after LDLR knockdown operation. These results suggest that disturbed LDL-LDLR metabolism contributes in various ways to the malfunction of endothelial and epithelial cells, and fibroblasts during pulmonary fibrogenesis. In addition, pharmacological restoration of LDLR levels by using a combination of atorvastatin and alirocumab inhibited BLM-induced LDL elevation, apoptosis, fibroblast-like cell accumulation and mitigated PF in mice. Therefore, LDL-LDLR may serve as an important mediator in PF, and LDLR enhancing strategies may have beneficial effects on PF.

Involvement of Disabled-2 on skin fibrosis in systemic sclerosis.

BACKGROUND: Systemic sclerosis (SSc) is a connective tissue disease characterized by inflammation and fibrosis. Our previous research found Disabled-2 (DAB2) expression was significantly downregulated by salvianolic acid B, a small molecular medicine which attenuated experimental skin fibrosis of SSc. These suggest that DAB2 plays an important role in SSc skin fibrosis, but the role of DAB2 in SSc remains unclear. OBJECTIVES: To investigate the role of DAB2 in SSc. METHODS: DAB2 expression level was detected in the skin and peripheral blood mononuclear cells of SSc patients. Bleomycin (BLM)-induced SSc mice and primary SSc skin fibroblasts were used to investigate the effect of DAB2 downregulation on fibrosis. RNA-seq transcriptome analysis was performed to underlie the mechanism of DAB2 in fibroblasts. RESULTS: DAB2 expression was enhanced in SSc lesion skin and was positively correlated with fibrotic genes, such as α-SMA and PAI-1. The in vivo study revealed that DAB2 downregulation alleviated skin fibrosis, alleviating skin thickness and reducing collagen deposition, and DAB2 knockdown ameliorated the inflammatory cell infiltration. The in vitro study showed that DAB2 knockdown reduced extracellular matrix genes and proteins expression. Moreover, Transcriptome analysis revealed TGF-ß and focal adhesion signaling pathways were the main downregulated pathways involved in DAB2 siRNA treated fibroblasts. CONCLUSIONS: Taken together, our results revealed that DAB2 was increased in SSc skin, and DAB2 downregulation inhibited BLM-induced mouse skin fibrosis and SSc skin fibroblasts activation. DAB2 played an important role in the pathogenesis of SSc and DAB2 modulation may represent a potential therapeutic method for SSc.

MiR-3606-3p inhibits systemic sclerosis through targeting TGF-ß type II receptor.

Systemic sclerosis (SSc) is a multisystemic fibrotic disease characterized by excessive collagen deposition and extracellular matrix synthesis. Though transforming growth factor-ß (TGF-ß) plays a fundamental role in the pathogenesis of SSc, the mechanism by which TGF-ß signaling acts in SSc remains largely unclear. Here, we showed that TGF-ß type II receptor (TGFBR2) was significantly upregulated in both human SSc dermal tissues and primary fibroblasts. In fibroblasts, siRNA-induced knockdown of TGFBR2 resulted in a reduction of p-SMAD2/3 levels and reduced production of type I collagen. Additionally, functional experiments revealed that downregulation of TGFBR2 yielded an anti-growth effect on fibroblasts through inhibiting cell cycle progression. Further studies showed that miR-3606-3p could directly target the 3'-UTR of TGFBR2 and significantly decrease the levels of both TGFBR2 mRNA and protein. Furthermore, SSc dermal tissues and primary fibroblasts contain significantly reduced amounts of miR-3606-3p, and the overexpression of miR-3606-3p in fibroblasts replicates the phenotype of TGFBR2 downregulation. Collectively, our findings demonstrated that increased TGFBR2 could be responsible for the hyperactive TGF-ß signaling observed in SSc. Moreover, we identified a pivotal role for miR-3606-3p in SSc, which acts, at least partly, through the attenuation of TGF-ß signaling via TGFBR2 repression, suggesting that the regulation of miR-3606-3p/TGFBR2 could be a promising therapeutic target that could improve the treatment strategy for fibrosis.