Evolution of Hepatic Steatosis to Fibrosis and Adenoma Formation in Liver-Specific Growth Hormone Receptor Knockout Mice

Abstract

Background: Non-alcoholic fatty liver disease (NAFLD) is one of the most common forms of chronic liver diseases closely associated with obesity and insulin resistance; deficient growth hormone (GH) action in liver has been implicated as a mechanism. Here, we investigated the evolution of NAFLD in aged mice with liver-specific GHR deletion.Methods: We examined glucose tolerance, insulin responsiveness, and lipid profiles in aged male mice (44–50 weeks) with GHRLD. We performed proteomics analysis, pathway-based Superarray assay, as well as quantitative RT-PCR to gain molecular insight into the mechanism(s) of GHR-deficiency-mediated NAFLD. In addition, we examined the pathological changes of livers of aged GHRLD male mice.Results: The biochemical profile was consistent with that of the metabolic syndrome: abnormal glucose tolerance, impaired insulin secretion, and hyperlipidemia. RT-qPCR analysis of key markers of inflammation revealed a three- to fivefold increase in TNFα and CCL3, confirming the presence of inflammation. Expression of fibrotic markers (e.g., Col1A2 and Col3A1) was significantly increased, together with a two- to threefold increase in TGFβ transcripts. Proteomics analyses showed a marked decrease of Mup1 and Selenbp2. In addition, pathway-analysis showed that the expression of cell cycle and growth relevant genes (i.e., Ccnd1, Socs2, Socs3, and Egfr) were markedly affected in GHRLD liver. Microscopic analyses (H&E) of GHRLD livers revealed the presence of hepatic adenomas of different stages of malignancy.Conclusion: Abrogation of GH signaling in male liver leads to metabolic syndrome, hepatic steatosis, increased inflammation and fibrosis, and development of hepatic tumor. Since obesity, a common precursor of NAFLD, is a state of deficient GH secretion and action, the GHRLD model could be used to unravel the contribution of compromised hepatic GH signaling in these pathological processes, and help to identify potential targets for intervention.

Traditional and novel aspects of the metabolic actions of growth hormone

“…This novel metabolic effect has now been demonstrated in other studies [17,18] and suggests the possibility of treating obese individuals with the metabolic syndrome and fatty liver with GH [17]. Moreover, in long-term follow up of mice with GHR deletion in the liver, about 30% go on to develop hepatic adenomas, preceded by evidence of inflammation and up-regulation of inflammatory and oncogenic pathways [13]. When GHR signaling is knocked out in muscle, mice lacking GHR develop metabolic features that were not observed in the IGF-1R knockouts including marked peripheral adiposity, insulin resistance, and .…”

“…Two different doses of glucose were used, each showing that glucose tolerance remains unaltered, whereas insulin secretion increases markedly to overcome insulin resistance. in the liver, muscle or fat [11][12][13][14][15][16][17][18]. When GHR is deleted in the liver, circulating IGF-I concentrations decline by approximately 90-95%, but in the absence of the negative feedback effect of IGF-I, GH levels increase 3-4 fold from approximately 10 to 40 ng/ml [11].…”

MECHANISMS IN ENDOCRINOLOGY: Lessons from growth hormone receptor gene-disrupted mice: are there benefits of endocrine defects?

“…The Li-GHRKO mice do not have decreased number of cancers and do not have increased lifespan, suggesting that lowered IGF-1 itself is insufficient to increase lifespan or the level of IGF-1deficiency may play an important role in extended lifespan. GHRLD mice have increased incidence of liver cancer probably due to steatosis induced by the absence of hepatic GH action (302). Also, as discussed above, improved glucose homeostasis and insulin sensitivity may be one of the keys of longevity.…”

The somatotropic axis and aging: Benefits of endocrine defects

“…In an effort to identify local and systemic effects of GH signaling in its various target organs, several laboratories generated mice with targeted deletion of the GH receptor in the liver, muscle, adipose tissue, pancreatic β-cells or macrophages [43–50]. The resulting animals with organ specific GH resistance were phenotypically very different from the GHRKO mice.…”