Lipocalin‐2 activates hepatic stellate cells and promotes nonalcoholic steatohepatitis in high‐fat diet–fed Ob/Ob mice

In obesity and type 2 diabetes mellitus, leptin promotes insulin resistance and contributes to the progression of NASH via activation of hepatic stellate cells (HSCs). However, the pathogenic mechanisms that trigger HSC activation in leptin‐deficient obesity are still unknown. This study aimed to determine how HSC‐targeting lipocalin‐2 (LCN2) mediates the transition from simple steatosis to NASH. APPROACH AND RESULTS: Male wild‐type (WT) and ob/ob mice were fed a high‐fat diet (HFD) for 20 weeks to establish an animal model of NASH with fibrosis. Ob/ob mice were subject to caloric restriction or recombinant leptin treatment. Double knockout (DKO) mice lacking both leptin and lcn2 were also fed an HFD for 20 weeks. In addition, HFD‐fed ob/ob mice were treated with gadolinium trichloride to deplete Kupffer cells. The LX‐2 human HSCs and primary HSCs from ob/ob mice were used to investigate the effects of LCN2 on HSC activation. Serum and hepatic LCN2 expression levels were prominently increased in HFD‐fed ob/ob mice compared with normal diet‐fed ob/ob mice or HFD‐fed WT mice, and these changes were closely linked to liver fibrosis and increased hepatic α‐SMA/matrix metalloproteinase 9 (MMP9)/signal transducer and activator of transcription 3 (STAT3) protein levels. HFD‐fed DKO mice showed a marked reduction of α‐SMA protein compared with HFD‐fed ob/ob mice. In particular, the colocalization of LCN2 and α‐SMA was increased in HSCs from HFD‐fed ob/ob mice. In primary HSCs from ob/ob mice, exogenous LCN2 treatment induced HSC activation and MMP9 secretion. By contrast, LCN2 receptor 24p3R deficiency or a STAT3 inhibitor reduced the activation and migration of primary HSCs. CONCLUSIONS: LCN2 acts as a key mediator of HSC activation in leptin‐deficient obesity via α‐SMA/MMP9/STAT3 signaling, thereby exacerbating NASH.