Nonalcoholic fatty liver disease (NAFLD) is a common complication of obesity that can progress to nonalcoholic steatohepatitis (NASH), a serious liver pathology that can advance to cirrhosis. The mechanisms responsible for NAFLD progression to NASH remain unclear. Lack of a suitable animal model that faithfully recapitulates the pathophysiology of human NASH is a major obstacle in delineating mechanisms responsible for progression of NAFLD to NASH and, thus, development of better treatment strategies. We identified and characterized a novel mouse model, middle-aged male low-density lipoprotein receptor (LDLR) 2/2 mice fed a high-fat diet (HFD), which developed NASH associated with four of five metabolic syndrome (MS) components. In these mice, as observed in humans, liver steatosis and oxidative stress promoted NASH development. Aging exacerbated the HFD-induced NASH such that liver steatosis, inflammation, fibrosis, oxidative stress, and liver injury markers were greatly enhanced in middle-aged versus young LDLR 2/2 mice. Although expression of genes mediating fatty acid oxidation and antioxidant responses were up-regulated in young LDLR 2/2 mice fed HFD, they were drastically reduced in MS mice. However, similar to recent human trials, NASH was partially attenuated by an insulin-sensitizing peroxisome proliferator-activated receptor-gamma (PPARc) ligand, rosiglitazone. In addition to expected improvements in MS, newly identified mechanisms of PPARc ligand effects included stimulation of antioxidant gene expression and mitochondrial b-oxidation, and suppression of inflammation and fibrosis. LDLR-deficiency promoted NASH, because middle-aged C57BL/6 mice fed HFD did not develop severe inflammation and fibrosis, despite increased steatosis. Conclusion: MS mice represent an ideal model to investigate NASH in the context of MS, as commonly occurs in human disease, and NASH development can be substantially attenuated by PPARc activation, which enhances b-oxidation. (HEPATOLOGY 2010;52:2001-2011 N onalcoholic steatohepatitis (NASH) is the most common liver disease in the Western world, affecting more than 18% of obese individuals.1 NASH is strongly associated with insulin resistance, and nearly five out of six NASH patients have metabolic syndrome (MS).2 NASH can progress to cirrhosis, but despite its severity and prevalence, there are no approved treatments for NASH. However, the recent PIVENS trial 3 demonstrated improvement in NASH histology with either vitamin E or the insulin-sensitizing peroxisome proliferator-activated receptor-gamma (PPARc) ligand, pioglitazone (PIO). The vitamin E effect underscored the critical role of oxidative stress in NASH but occurred in the absence of an Abbreviations: ALT, alanine aminotransferase; AST, aspartate aminotransferase; CPT1A, carnitine palmitoyltransferase 1a; DNL, de novo lipogenesis; HFD, high-fat diet; LCM, laser capture microdissection; LDLR, low-density lipoprotein receptor; MS, metabolic syndrome; NAFLD, nonalcoholic fatty liver disease; NASH, nonalcoholic steatohep...

Fibroblast growth factor 2 (FGF2), angiopoietin 1 (Ang1), and vascular endothelial growth factor (VEGF) are angiogenic factors implicated in the vascular development of the corpus luteum (CL). Each factor is regulated or influenced by leptin in non-ovarian tissues. Moreover, leptin and its receptor, ObRb, have been identified in luteal tissue throughout the luteal phase. Therefore, leptin is hypothesized to influence luteal vasculature through the regulation of FGF2, Ang1, and VEGF. Multiparous, cycling crossbred female goats (does) were allocated to early (n=12), mid (n=8), and late (n=11) stages of the luteal phase for CL collection. Luteal tissue was harvested and either snap frozen in liquid N2, paraffin embedded, or cultured with leptin (0, 10−12, 10−11, 10−10, 10−9, 10−8 M). Tissue was analyzed for FGF2, Ang1, VEGF, ObRb, and leptin expression. Angiopoietin 1, FGF2, VEGF expression was higher (P≤0.001) in the mid-luteal stage than the early stage. Expression decreased (P≤0.001) during the late luteal stage with the exception of VEGF, which remained elevated. In contrast, leptin and ObRb were lowest (P≤0.003) during the mid-luteal stage compared to the early and late stages. All factors were detected in and/or around vessels in early stage tissue compared to mid and late stages. Leptin stimulated (P≤0.02) Ang1, FGF2, and VEGF expression only in early stage luteal cultures. Collectively, these data provide evidence that leptin may be involved in the luteal angiogenic process during the early stage of CL formation.

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NASH, which is closely associated with metabolic syndrome (MS), is the most common cause of chronic liver disease in the Western world, but has no approved treatment. Middle‐aged (MA, 12‐month) male LDLR−/− mice fed 3 months of high‐fat diet (HFD) develop MS (obesity, elevated fasting glucose and triglycerides, and decreased HDL), and reveal a classical NASH phenotype of liver steatosis, inflammation and fibrosis. We hypothesized that treatment with the insulin‐sensitizer rosiglitazone (RSG) could prevent NASH by attenuating MS development and age‐related oxidative stress. RSG treatment dramatically reduced, but did not completely prevent, steatosis in HFD‐fed MA LDLR−/− mice. RSG reversed HFD‐mediated decreases in liver fatty acid oxidation genes (CPT1, ACADm, HADHa), and attenuated HFD‐induced decreases in antioxidant genes (DJ‐1, Nrf2, NQO1, SOD2, GPX‐1 and ‐4). But RSG had no effect on HFD‐generated increases in fibrosis genes (Coll1α2, Coll4α1 and TGF‐β1) or inflammation genes (MCP‐1, TNFα, CD68). RSG‐treatment of palmitate‐treated primary hepatocytes showed that RSG increased expression of both fatty acid oxidation and synthesis genes. RSG induced β‐oxidation in liver mitochondria, as seen by increased respiratory control ratios and ADP to ATP conversion with palmitoyl‐carnitine. RSG may thus prevent steatosis, at least partially, through direct effects to promote hepatocyte β‐oxidation.