Osteopontin promotes collagen I synthesis in hepatic stellate cells by miRNA-129-5p inhibition
Introduction
Liver fibrosis is a chronic scarring process of the liver and characterized by an increased and altered deposition of extracellular matrix (ECM) components, particular collagen type I [1]. The fibrillar collagen type I, is encoded by two different genes, col1A1 and col1A2, and accounts for 36% of the total collagens in ECM of healthy liver. During liver fibrogenesis, collagen type I is the predominant isoform deposited into perisinusoidal space [2], [3].
In the fibrotic liver, activated hepatic stellate cells (HSCs) are identified as the main producers of ECM in liver and their activation represents the critical event in liver fibrosis. After liver injury, the quiescent HSCs trans-differentiate into myofibroblast-like cells that characterized by the expression of α-smooth muscle actin (α-SMA) [4]. In addition, the ECM contains a complex mix of proteins that promote cell proliferation, migration, and differentiation. One ECM component with such roles is the matricellular glycophosphoprotein, osteopontin (OPN), also known as secreted phosphoprotein 1. Recently, OPN levels have been highlighted as a potential biomarker of liver disease, levels correlating with the severity of disease. Moreover, OPN has been reported to promote the progression of fibrosis in nonalcoholic steatohepatitis [5] and liver fibrosis [6]. OPN emerges as a key cytokine within the ECM protein network, expressed in HSCs, could drive the HSC pro-fibrogenic phenotype and collagen type I protein expression, contributing to scarring and liver fibrosis [7]. However, the molecular mechanism on OPN mediating collagen type I remain elusive.
MicroRNAs (miRNAs) are short 20–22 nucleotides that regulate gene expression by binding to the 3′-untranslated region (3′-UTR) of the target mRNAs [8]. There is an increasing evidence that aberrant miRNAs are involved in liver fibrosis, and miRNAs are HSC regulators which may play roles in the regulation of antifibrotic or profibrotic genes during hepatic fibrosis [9], [10]. For example, collagen type I is predicted as miR-129-5p target gene by TARGETSCAN database in human cell lines. Recently, it was reported that miR-129-5p, one of the downregulated microRNAs in systemic sclerosis fibroblasts, mediated the collagen type I reduction [11]. However, knowledge of the function and role of miR-129-5p in liver fibrosis is still not understood.
In this study, we found that miR-129-5p was decreased in OPN-induced HSC and human liver fibrotic tissues. Upregulation of miR-129-5p decreased the expression levels of collagen type I and α-SMA and promoted HSC proliferation. It is confirmed that collagen type I is a direct target of miR-129-5p. Therefore, the major aim of this work was to determine how miR-129-5p become a antifibrogenic “switch” and to characterize whether OPN mediates collagen type I expression through miR-129-5p.
Section snippets
Human liver samples
Liver tissues were taken from 10 patients with clinically diagnosed liver cirrhosis suffered from HBV who underwent liver transplantation. Liver tissues with normal histology (n = 8) obtained from patients with various benign liver conditions or transplant donors were used as controls. All clinical samples are from the First Affiliated Hospital of the Guangdong Pharmaceutical University, Guangzhou, China. Written informed consent was obtained from each patients and volunteers, and the study was
OPN is induced in liver fibrosis
The expression of OPN was significantly increased in fibrotic liver, compared to control liver (Fig. 1A), and presented quantitatively in Fig. 1B. Furthermore, increased mRNA levels of OPN was also observed in the fibrotic liver tissues (Fig. 1C). Consistently, the expression of Col1α1 and α-SMA was also increased in fibrotic livers (Fig. 1D and E). These data suggest that OPN signaling is activated in human fibrotic livers and might be involved in the pathogenesis of liver fibrosis.
OPN regulates collagen expression in HSCs
Next, we
Discussion
Liver fibrosis is characterized by accumulation of ECM, mainly produced by activated HSCs. Our results has been for the first time demonstrated that the expression of miR-129-5p was significantly correlated with Col 1 synthesis and HSC activation, and miR-129-5p is the central mediator of induction of Col 1 induced by OPN.
It is well-known that OPN is significantly induced during liver injury, both in humans and in rodents [5], [16], [17]. In recent years, it has been demonstrated that the
Acknowledgements
This work was supported by the research grants from the National Natural Science Foundation of China (81300331); the Science and Technology Planning Project of Guangdong Province (2014A020212460), China; the Key Project of Natural Science Foundation of Guangdong Province (2016A030311014), China; Natural Science Foundation of Guangdong Province (2015A030313582), China; and Guangdong Provincial Medical Science and Technology Research Foundation (A2015092), China. We also thank the support from
Potential conflict of interest
None to report.
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- 1
These authors contributed equally to this work.