Insulin resistance and metabolic hepatocarcinogenesis with parent-of-origin effects in A×B mice.

Insulin resistance is a defining feature of metabolic syndrome and type 2 diabetes mellitus but also may occur independently of these conditions. Nonalcoholic fatty liver disease (NAFLD), the hepatic manifestation of these disorders, increases the risk of hepatocellular carcinoma (HCC). However, mechanisms linking hyperinsulinemia to NAFLD and HCC require clarification. We describe a novel model of primary insulin resistance and HCC with strong parent-of-origin effects. Male AB6F1 (A/JCr dam × C57BL/6 sire) but not B6AF1 (B6 dam × A/J sire) mice developed spontaneous insulin resistance, NAFLD, and HCC without obesity or diabetes. A survey of mitochondrial, imprinted, and sex-linked traits revealed modest associations with X-linked genes. However, a diet-induced obesity study, including B6.A chromosome substitution-strain (consomic) mice, showed no segregation by sex chromosome. Thus, parent-of-origin effects were specified within the autosomal genome. Next, we interrogated mechanisms of insulin-associated hepatocarcinogenesis. Steatotic hepatocytes exhibited adipogenic transition characterized by vacuolar metaplasia and up-regulation of vimentin, adipsin, fatty acid translocase (CD36), peroxisome proliferator-activated receptor-γ, and related products. This profile was largely recapitulated in insulin-supplemented primary mouse hepatocyte cultures. Importantly, pyruvate kinase M2, a fetal anabolic enzyme implicated in the Warburg effect, was activated by insulin in vivo and in vitro. Thus, our study reveals parent-of-origin effects in heritable insulin resistance, implicating adipogenic transition with acquired anabolic metabolism in the progression from NAFLD to HCC.

Sex hormone influence on hepatitis in young male A/JCr mice infected with Helicobacter hepaticus.

Hepatitis B virus (HBV), the leading cause of human hepatocellular carcinoma, is especially virulent in males infected at an early age. Likewise, the murine liver carcinogen Helicobacter hepaticus is most pathogenic in male mice infected before puberty. We used this model to investigate the influence of male sex hormone signaling on infectious hepatitis. Male A/JCr mice were infected with H. hepaticus or vehicle at 4 weeks and randomized into surgical and pharmacologic treatment groups. Interruption of androgen pathways was confirmed by hormone measurements, histopathology, and liver gene and Cyp4a protein expression. Castrated males and those receiving the competitive androgen receptor antagonist flutamide had significantly less severe hepatitis as determined by histologic activity index than intact controls at 4 months. Importantly, the powerful androgen receptor agonist dihydrotestosterone did not promote hepatitis. No effect on hepatitis was evident in males treated with the 5alpha-reductase inhibitor dutasteride, the peroxisome proliferator-activated receptor-alpha agonist bezafibrate, or the nonsteroidal anti-inflammatory drug flufenamic acid. Consistent with previous observations of hepatitis-associated liver-gender disruption, transcriptional alterations involved both feminine (cytochrome P450 4a14) and masculine (cytochrome P450 4a12 and trefoil factor 3) genes, as well gender-neutral (H19 fetal liver mRNA, lipocalin 2, and ubiquitin D) genes. Hepatitis was associated with increased unsaturated C(18) long-chain fatty acids (oleic acid and linoleic acid) relative to saturated stearic acid. Our results indicate that certain forms of androgen interruption can inhibit H. hepaticus-induced hepatitis in young male mice, whereas androgen receptor agonism does not worsen disease. This raises the possibility of targeted hormonal therapy in young male patients with childhood-acquired HBV.

Hepatocellular carcinoma associated with liver-gender disruption in male mice.

Hepatocellular carcinoma (HCC) is a male-predominant cancer associated with chronic hepatitis. Like human viral hepatitis, murine Helicobacter hepaticus infection produces inflammation and HCC with a masculine bias. We used this model to identify potential mechanisms of male HCC predisposition. Male weanling A/JCr mice (n = 67) were gavaged with H. hepaticus or vehicle. At 1 year, mice were distributed into four groups: surgical castration, chemical castration, castration followed by dihydrotestosterone supplementation, or sexually intact controls. Responses to infection were compared with IFN-gamma challenge alone. At 21 months, there was no significant difference in hepatitis between groups. Neither castration nor androgen receptor agonism altered tumor incidence. Infected mice with severe, but not mild, disease exhibited a mosaic of alterations to sexually dimorphic genes and microsomal long-chain fatty acids. By microarray, tumorigenic hepatitis was strongly associated with liver-gender disruption, defined as the loss of a gender-identifying hepatic molecular signature. IFN-gamma alone produced similar changes, demonstrating a role for proinflammatory cytokines in this process. In conclusion, hepatocarcinogenesis in male mice with chronic hepatitis is maturationally imprinted and androgen-independent. Proinflammatory cytokines may promote HCC in a male-predominant fashion due to high sensitivity of the masculinized liver to loss of sex-specific transcriptional balance. Liver-gender disruption has pleiotropic implications for hepatic enzyme activity, lipid processing, nuclear receptor activation, apoptosis, and proliferation. We propose a multistep model linking chronic hepatitis to liver cancer through cytokine-mediated derangement of gender-specific cellular metabolism. This model introduces a novel mechanism of inflammation-associated carcinogenesis consistent with male-predominant HCC risk.