GLIS2 Prevents Hepatic Fibrosis by Competitively Binding HDAC3 to Inhibit Hepatic Stellate Cell Activation

Abstract

Background: The role of GLIS2 in fibrotic diseases is controversial. GLIS2 deficiency has been reported to contribute to renal fibrosis in mice and has also been reported to prevent high lipid-induced mice hepatic fibrosis.

Methods: Hepatic fibrosis in mice was induced by CCl4. Hematoxylin and eosin, Masson, Sirius red, and enzyme-linked immunosorbent assay were used to detect and evaluate the stage of hepatic fibrosis in humans or mice. A study model of tetracycline-responsive GLIS2 knockout hepatic stellate cells (HSCs) was constructed and named GLIS2-SG-Dox. By adding transforming growth factor β1 to stimulate the transdifferentiation of HSCs, the activation status of HSCs was comprehensively evaluated from the aspects of cell proliferation, migration, and the amount of lipid droplets. In mechanistic studies, dual-luciferase, coimmunoprecipitation, yeast two-hybrid system, chromatin immunoprecipitation, and DNA pulldown were performed to investigate or to prove the molecular mechanism that GLIS2 was involved in regulating liver fibrosis. Throughout the study, real-time fluorescence polymerase chain reaction (quantitative reverse-transcription polymerase chain reaction) was used to detect the relative abundance of messenger RNA expression of each target gene, Western blot was used to detect the relative abundance of protein, and immunohistochemistry or immunofluorescence was used to observe the subcellular localization of the target protein.

Results: The expression of GLIS2 was significantly decreased in human liver fibrosis tissues and CCL4-induced mouse liver fibrosis tissues, especially in HSCs. In the GLIS2-SG-Dox cells, the peroxisome proliferator-activated receptor γ (PPAR-γ) pathway was inactive and cells underwent myofibroblastic transdifferentiation transformation. Overexpression of GLIS2 can increase the acetylation level of PPAR-γ and alleviate CCL4-induced liver fibrosis in mice. Mechanically, relatively abundant GLIS2 and histone deacetylase 3 (HDAC3) form chelates to avoid the deacetylation of PPAR-γ, so as to maintain the activation level of PPAR-γ signaling pathway in HSCs cells. In this process, HDAC3 acts as a medium for GLIS2 to influence PPAR-γ signaling. Nonetheless, when GLIS2 is absent, HDAC3 deacetylates PPAR-γ, activates HSCs, and leads to liver fibrosis.

Conclusions: GLIS2 deficiency promotes myofibroblastic transdifferentiation and activation of HSCs. Mechanically, GLIS2 regulates the acetylation of PPAR-γ by competitively binding to HDAC3 in HSCs.

Keywords: Acetylation; GLIS2; HDAC3; Hepatic Fibrosis; PPAR-γ.