Growth hormone resistance exacerbates cholestasis‐induced murine liver fibrosis

Abstract

Growth hormone (GH) resistance has been associated with liver cirrhosis in humans but its contribution to the disease remains controversial. In order to elucidate whether GH resistance plays a causal role in the establishment and development of liver fibrosis, or rather represents a major consequence thereof, we challenged mice lacking the GH receptor gene (Ghr–/–, a model for GH resistance) by crossing them with Mdr2 knockout mice (Mdr2–/–), a mouse model of inflammatory cholestasis and liver fibrosis. Ghr–/–;Mdr2–/– mice showed elevated serum markers associated with liver damage and cholestasis, extensive bile duct proliferation, and increased collagen deposition relative to Mdr2–/– mice, thus suggesting a more severe liver fibrosis phenotype. Additionally, Ghr–/–;Mdr2–/– mice had a pronounced down‐regulation of hepatoprotective genes Hnf6, Egfr, and Igf‐1, and significantly increased levels of reactive oxygen species (ROS) and apoptosis in hepatocytes, compared to control mice. Moreover, single knockout mice (Ghr–/–) fed with a diet containing 1% cholic acid displayed an increase in hepatocyte ROS production, hepatocyte apoptosis, and bile infarcts compared to their wild‐type littermates, indicating that loss of Ghr renders hepatocytes more susceptible to toxic bile acid accumulation. Surprisingly, and despite their severe fibrotic phenotype, Ghr–/–;Mdr2–/– mice displayed a significant decrease in tumor incidence compared to Mdr2–/– mice, indicating that loss of Ghr signaling may slow the progression from fibrosis/cirrhosis to cancer in the liver. Conclusion: GH resistance dramatically exacerbates liver fibrosis in a mouse model of inflammatory cholestasis, therefore suggesting that GH resistance plays a causal role in the disease and provides a novel target for the development of liver fibrosis treatments. (Hepatology 2015;61:613‐626)

Growth Hormone Mediates Its Protective Effect in Hepatic Apoptosis through Hnf6

“…Common features in hepatic cholestatic injury are hepatocyte cell death and hepatic fibrosis, with apoptosis driving the fibrogenesis response (19, 20). Experimental models of cholestasis in GH-resistant mice provide strong evidence for GH role in protecting against hepatocyte death [9,10,18–21]. To evaluate if Hnf6 directly regulates hepatocyte apoptosis and if Hnf6 mediates GH function in apoptosis, BDL was performed in Hnf6 -/- (referred to as KO) mice with conditional inactivation of hepatic Hnf6 in hepatocytes and biliary epithelial cells.…”

“…GH has also previously been shown to attenuate hepatocyte death. In GH receptor Ghr -deficient mice, cholic acid feeding worsens cholestasis and hepatocyte apoptosis [9]. Additionally, compared to mdr2 (multi-drug resistant transporter-2) null mutant mice, cholestasis, hepatic fibrosis and hepatocyte apoptosis were exacerbated in mdr2 / Ghr or mdr2 / Stat5 double null mice [9] [10] [11].…”

“…In GH receptor Ghr -deficient mice, cholic acid feeding worsens cholestasis and hepatocyte apoptosis [9]. Additionally, compared to mdr2 (multi-drug resistant transporter-2) null mutant mice, cholestasis, hepatic fibrosis and hepatocyte apoptosis were exacerbated in mdr2 / Ghr or mdr2 / Stat5 double null mice [9] [10] [11]. In these GH-resistant mice, Hnf6 expression was diminished, suggesting that increased susceptibility to hepatic apoptosis in the absence of GH function can be attributed to impaired Hnf6 hepatocyte-specific function, and that Hnf6 biological function is broader than the previously demonstrated Hnf6 regulation of hepatocyte proliferation and metabolic activities.…”

The characteristics of activated portal fibroblasts/myofibroblasts in liver fibrosis

“…The majority of the myofibroblasts come from aPFs/myofibroblasts (Baghdasaryan et al, 2010), but bone marrow derived fibrocytes may be involved in the pathogenesis (Strack et al, 2011). This model has been used for novel therapies for chronic cholestasis, targeting anti-cholestatic, anti-inflammatory and antifibrogenic pathways (Baghdasaryan et al, 2010; Miethke et al, 2016; Stiedl et al, 2015; Strack et al, 2011). …”

FGF2 inhibits endothelial–mesenchymal transition through microRNA-20a-mediated repression of canonical TGF-β signaling

“…In fibroproliferative diseases, the endothelium shows resistance to a number of mitogens, such as FGF2, vascular endothelial growth factor A (VEGFa) and insulin-like growth factor-1 (IGF1) (Baelde et al, 2007;Cheng et al, 2014;Stiedl et al, 2015). We therefore wondered whether these mitogens could relay some protective effects at non-affected sited versus affected sites where the response to these mitogens is lost.…”