Hypoxia-inducible factor 1α/IL-6 axis in activated hepatic stellate cells aggravates liver fibrosis

Hepatic stellate cells (HSCs) upregulate hypoxia inducible factor 1 alpha (HIF-1α) expression in response to fibrosis-induced hypoxia. The mechanism by which HIF-1α promotes liver fibrosis in HSCs is not fully understood. In this study, we found that increased expression of α-SMA, HIF-1α and IL-6, as well as colocalization of α-SMA and HIF-1α, and HIF-1α and IL-6, were observed in liver fibrotic tissues of patients and a mouse model. HIF-1α expression induced IL-6 secretion in activated HSCs and the increase could be abolished by HIF-1α suppression or HIF1A gene knockdown. HIF-1α directly bound to the hypoxia response element (HRE) region in HSC IL6/Il6 promoters. Additionally, culturing naïve CD4 T cells with supernatant from HSCs in which HIF-1α is highly expressed increased IL-17A expression, and the expression could be abolished by HIF1A knockdown in LX2. In turn, the IL-17A-enriched supernatant induced IL-6 secretion in HSCs. Together, these results show that HIF-1α upregulates IL-6 expression in HSCs and induces IL-17A secretion through directly binding to the HRE of IL6 promoter.