Nonalcoholic fatty liver disease (NAFLD) is the most prevalent liver disease, but its progression to the severe form of nonalcoholic steatohepatitis (NASH) is unpredictable. Hepatocyte steatosis alters endoplasmic reticulum (ER) calcium stores and induces mitochondrial dysfunction leading to hepatocellular inflammation and apoptosis. Moreover, obese mice have impaired sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2) function, responsible for transporting Ca2+ from the cytoplasm to ER. We thus hypothesized that restoration of SERCA2 activity may improve hepatocyte function during lipotoxicity. To test this hypothesis, 8-week-old male C57Bl/6J (wild type, WT) or melanocortin-4 receptor knockout (MC4R-/-) mice were placed on either chow or Western diet (WD) for 8 weeks. Half of the WD-fed mice were also given injections of CDN1163 once every two weeks to activate SERCA2. Sodium [13C3]lactate was infused intravenously into conscious, unrestrained mice for 2 hours and 13C-enrichments of plasma glucose and liver metabolites were measured by GC-MS, then used to regress liver metabolic fluxes using the INCA modeling platform. CDN1163 treatment significantly decreased weight and fat mass of both WT and MC4R-/- WD-fed mice without affecting food intake or lean mass. Moreover, CDN1163 improved insulin sensitivity of WT and MC4R-/- mice. CDN1163 decreased NAFLD activity score in WT, but failed to reduce histological features of NASH in MC4R-/- mice. Liver free fatty acids, diglycerides and ceramides were not affected; however, CDN1163 decreased triglyceride content in WT mice. Liver metabolic fluxes analysis revealed that CDN1163 accelerated pyruvate cycling in WT and MC4R-/- mice, which may explain how CDN1163 helped hepatocytes adapt to an excess of energy substrates. Taken together, these data suggest that SERCA2 activation had a protective effect on liver when NAFLD was less severe (WT) but was insufficient to rescue lipotoxicity after progression to NASH had occurred (MC4R-/-).
T. Bednarski: None. M. Rahim: None. J. Young: Board Member; Self; Metalytics. Consultant; Self; Pfizer Inc.
National Institutes of Health (R01DK106348)