Metabolic and Cardiac Manifestations in a Mouse Model of Genetic Mitochondrial Hepatopathy Without Obesity: Evidence for a Sexual Dimorphism

In non-alcoholic fatty liver disease (NAFLD), liver mitochondrial dysfunction plays an important role in the development of cardiac abnormalities independent of obesity per se. However, the mechanisms underlying the development of these abnormalities, and whether these are affected by sex remain unclear. In the present study, we sought to address this question using a mouse model of hepatic mitochondrial deficiency caused by loss of Lrpprc (H-Lrpprc-/- ) as these mice develop microvesicular steatosis and a NAFLD lipidomic-like profile without obesity.Our working hypothesis is that metabolic defects in the liver would trigger metabolic and functional abnormalities in the heart in a sex-dependent manner.Detailed phenotyping experiments were performed in male and female H-Lrpprc-/- mice and their controls at 14 weeks of age. Glucose metabolism was monitored by blood glucose as well as insulin, and glucose tolerance tests (ITT, OGTT). Cardiac manifestations were studied using molecular (qPCR), lipidomic (mass spectrometry) and functional (oximetry on isolated mitochondria, intraventricular pressures by Millar probe) analyses.Genetic inactivation of Lrpprc resulted in an >60% reduction of LRPPRC protein content in both males and females, which resulted in comparable structural liver abnormalities. In contrast, the resulting metabolic and cardiac functional changes displayed a marked sexual dimorphism. Lrpprc deficiency in the liver was associated with fasting hypoglycemia and increased insulin sensitivity in both sexes, but more so in males. Lrpprc deficiency was also associated with a remodeling of specific markers of mitochondrial function exclusively in the female myocardium. This included 1) reduced expression of gene markers for mitochondrial biogenesis (Tfam), fusion (Mfn1-2), and fatty acid (FA) utilization and oxidation (Pparα, Cd36, Cpt1b, Cpt2, Vlcad, Lcad, Mcad), 2) impairment of FA-dependent mitochondrial respiration, and 3) increased cardiac triglyceride levels. Paradoxically, cardiac function was preserved in females, while males displayed mild diastolic dysfunction as evidenced by increased early and late diastolic pressures (0.29 and 2.39 fold vs. male wild type respectively) amongst other parameters.Collectively, these results indicate that metabolic defects in the liver can result in significant sex-dependent abnormalities that affect both the mitochondrial/metabolic phenotype and contractile function independent of obesity. This experimental model may prove useful to better understand the mechanisms underlying the sex-related variability in the progression of lean NAFLD in humans.