The post-transcriptional regulatory RNA-binding protein PTBP1 functions as an inhibitor in hepatic stellate cell activation and liver fibrosis

BACKGROUND: Hepatic stellate cell (HSC) activation is the key step in liver fibrogenesis characterized by excessive extracellular matrix (ECM) accumulation, which is based on fibrogenic factors-induced changes in gene expression in HSCs. The post-transcriptional gene-expression regulation plays a crucial role in regulation of gene expression by controlling mRNA fate through RNA binding proteins (RBPs), RBPs are essentially involved in the process of HSC activation and liver fibrogenesis. Since the activated HSCs possess the characteristics of neuron and the roles of multifunctional polypyrimidine tract binding protein 1 (PTBP1), a key RBP in inhibiting neuron differentiation, in HSC activation and liver fibrosis are elusive, this research aimed to investigate the effects of PTBP1 on HSC activation and liver fibrosis. METHODS: The study employed RNA sequencing, targeted over-expression of Ptbp1, Ptbp1 gene-knockdown mice, different mouse model of liver fibrosis, and liver samples from clinical patients. RESULTS: Ptbp1 silencing in HSCs in vitro led to an increase in the expression of many pro-fibrotic genes, including at least the most potent fibrogenic factors, fibrogenic factor receptors, signal transducer, and ECM, but caused a decrease in the expression of pro-apoptotic genes and transcriptional factor Srebp1c, a key one to inhibiting HSC activation. Ptbp1 knockdown in mouse upregulated the expression of pro-fibrotic genes and enhanced HSC activation as well as liver fibrosis. Targeted over-expression of Ptbp1 in HSCs in the model of liver fibrosis further confirmed the effects of PTBP1 on the pro- and anti-fibrotic gene expression in HSCs, HSC activation, and liver fibrosis. Ptbp1 could bind to Srebp1c mRNA, thus inhibiting its degradation. PTBP1 also blocked PI3K/Akt pathway in HSCs. Its levels were reduced in the activated HSCs in livers from mice and clinical patients. CONCLUSION: This research demonstrated a previously unrecognized inhibitory effect of the multifunctional PTBP1 on HSC activation and liver fibrogenesis and the underlying mechanisms were involved in PTBP1 regulation of the important pro- or anti-fibrotic genes. Given that PTBP1 targeted lots of important pro- and anti-fibrotic genes, PTBP1 may serve as a potential therapeutic strategy for treatment of liver fibrosis.