Background: Hepatic stellate cells (HSCs) activation is the principal event in the development of liver fibrosis in which succinate-G-protein coupled receptor 91 signaling has recently been shown to be a contributor. Moreover, endoplasmic reticulum (ER) stress has been reported to involve in HSC activation, but its association with succinate in pathogenesis of liver fibrosis remains scarce. In this study, we investigated the role of gemigliptin, an antidiabetic dipeptidyl peptidase-4 inhibitor, in the succinate-induced ER stress and activation of HSCs. Methods: LX-2 cells, the immortalized human HSCs, were treated with succinate and gemigliptin. For animal experiments, C57BL/6N mice were divided into 3 groups: control diet, high-fat high-cholesterol (HFHC) diet, and HFHC diet mixed with gemigliptin. Results: Succinate significantly induced HSC activation and increased expression of inflammatory markers and the increase in the migration of HSCs. The treatment of succinate also caused ER dilation and activated the unfolded protein response signaling as protein kinase RNA-like ER kinase, eIF2alpha, binding immunoglobulin protein, suggesting increasing ER stress in HSCs. All responses of HSCs to succinate were attenuated with the co-treatment of gemigliptin. Moreover, the exposure of HSCs to tunicamycin, an inducer of ER stress, promoted the expression of α-smooth muscle actin, proliferation and migration of HSCs. In vivo, the level of fibrotic and ER stress markers was increased in mice fed with HFHC diet and the administration of gemigliptin improved these changes in HFHC-induced mice. Conclusion This study showed the involvement of ER stress in the activation of succinateinduced LX-2 HSCs and gemigliptin significantly reduced ER stress in HSC activation.Therefore, gemigliptin may become an anti-fibrotic agent and targeting to succinate and ER stress may be a promising therapeutic in the management of liver fibrosis.

Background: Dipeptidyl peptidase-4 inhibitors (DPP-4Is) are used clinically as oral antidiabetic agents. Although DPP-4Is are known to ameliorate liver fibrosis, the protective mechanism of DPP-4Is in liver fibrosis remains obscure. In this study, gemigliptin was used to investigate the potential of DPP-4Is to alleviate the progression of liver fibrosis. Methods: To clarify the effects and mechanisms of gemigliptin, we conducted various experiments in LX-2 cells (immortalized human hepatic stellate cells [HSCs], the principal effectors of hepatic fibrogenesis), which were activated by succinate and exhibited elevated expression of α-smooth muscle actin, collagen type 1, and pro-inflammatory cytokines and increased cell proliferation. In vivo, we examined the effects and mechanisms of gemigliptin on a high-fat, high-cholesterol–induced mouse model of nonalcoholic steatohepatitis (NASH). Results: Gemigliptin decreased the expression of fibrogenesis markers and reduced the abnormal proliferation of HSCs. In addition, gemigliptin reduced the succinate-induced production of mitochondrial reactive oxygen species (ROS), intracellular ROS, and mitochondrial fission in HSCs. Furthermore, in the mouse model of NASH-induced liver fibrosis, gemigliptin alleviated both liver fibrosis and mitochondrial dysfunction. Conclusion Gemigliptin protected against HSC activation and liver fibrosis by alleviating mitochondrial dysfunction and ROS production, indicating its potential as a strategy for preventing the development of liver disease.

Background: Hepatic stellate cells (HSCs) are the central players interacting with multiple cell types in liver fibrosis. The crosstalk between HSCs and macrophages has recently become clearer. Irisin, an exercise-responsive myokine, was known to have a potentially protective role in liver and renal fibrosis, especially in connection with stellate cells. This study investigated the effects of irisin on the interaction between HSCs and macrophages. Methods: Tamm-Horsfall protein-1 (THP-1) human monocytes were differentiated into macrophages, polarized into the inflammatory M1 phenotype with lipopolysaccharide. Lieming Xu-2 (LX-2) cells, human HSCs, were treated with conditioned media (CM) from M1 macrophages, with or without recombinant irisin. HSCs responses to CM from M1 macrophages were evaluated regarding activation, proliferation, wound healing, trans-well migration, contractility, and related signaling pathway. Results: CM from M1 macrophages significantly promoted HSC proliferation, wound healing, transwell migration, and contractility, but not activation of HSCs. Irisin co-treatment attenuated these responses of HSCs to CM. However, CM and irisin treatment did not induce any changes in HSC activation. Further, irisin co-treatment alleviated CM-induced increase of phopho-protein kinase B (pAKT), matrix metalloproteinase-9 (MMP-9), and tissue inhibitor of metalloproteinases-1 (TIMP-1). Conclusion These findings suggested that irisin may play a protective role in the pathogenesis of liver fibrosis, especially when working in the crosstalk between HSCs and macrophages.