Lipoprotein lipase (LPL) plays a central role in incorporating plasma
lipids into tissues and regulates lipid metabolism and energy balance in the human body. Conversely, LPL expression is almost absent in normal adult livers. Therefore, its physiological role in the liver remains unknown. We aimed to elucidate the role of LPL in the pathophysiology of
nonalcoholic steatohepatitis (NASH), a hepatic manifestation of
obesity. Hepatic stellate cell (HSC)-specific LPL-knockout (LplHSC-KO ) mice, LPL-floxed (Lplfl/fl ) mice, or double-mutant
toll-like receptor 4-deficient (Tlr4-/- ) LplHSC-KO mice were fed a high-fat/high-
cholesterol diet for 4 weeks to establish the
nonalcoholic fatty liver model or an high-fat/high-
cholesterol diet for 24 weeks to establish the NASH model. Human samples, derived from patients with
nonalcoholic fatty liver disease, were also examined. In human and mouse NASH livers, serum
obesity-related factors, such as
free fatty acid,
leptin, and
interleukin-6, dramatically increased the expression of LPL, specifically in HSCs through
signal transducer and activator of transcription 3 signaling, as opposed to that in hepatocytes or hepatic macrophages. In the NASH mouse model,
liver fibrosis was significantly reduced in LplHSC-KO mice compared with that in Lplfl/fl mice. Nonenzymatic LPL-mediated
cholesterol uptake from serum
lipoproteins enhanced the accumulation of free
cholesterol in HSCs, which amplified TLR4 signaling, resulting in the activation of HSCs and progression of hepatic
fibrosis in NASH. Conclusion: The present study reveals the pathophysiological role of LPL in the liver, and furthermore, clarifies the pathophysiology in which
obesity, as a background factor, exacerbates NASH. The LPL-mediated HSC activation pathway could be a promising therapeutic target for treating
liver fibrosis in NASH.