MAPK p38/Ulk1 pathway inhibits autophagy and induces IL-1ß expression in hepatic stellate cells.

ABSTRACT

In the past, hepatic stellate cells (HSCs) were considered to be noninflammatory cells and to contribute to liver fibrosis by producing extracellular matrix. Recently, it was found that HSCs can also secrete cytokines and chemokines and therefore participate in hepatic inflammation. Autophagy participates in many immune response processes in immune cells. It is unclear whether autophagy is involved in inflammatory cytokine induction in HSCs. MAPK p38, Ulk1 phosphorylation, and the Ulk1-Atg13 complex were analyzed in HSC-T6 cells after LPS treatment. The relationship between autophagy inhibition and inflammation was investigated in primary rat HSCs. We discovered that LPS inhibited autophagy through MAPK p38. The activation of MAPK p38 induced Ulk1 phosphorylation, which disrupted the Ulk1-Atg13 complex and therefore inhibited autophagy. Furthermore, in primary rat HSCs, we demonstrated that autophagy inhibition regulated IL-1ß induction, which depended on the MAPK p38/Ulk1 pathway. Our results reveal a continuous signaling pathway, MAPK p38-Ulk1 phosphorylation-Ulk1-Atg13 disruption, which inhibits autophagy and induces IL-1ß expression in HSCs.NEW & NOTEWORTHY LPS inhibits autophagy in a concentration- and dose-dependent manner in HSC-T6 cells. MAPK p38 induces phosphorylation of Ulk1, which disrupts the Ulk1-Atg13 complex and is therefore required for the inhibition of autophagy by LPS. LPS induces IL-1ß expression via the MAPK p38/Ulk1 pathway in HSCs.