Differential alterations in the GHRH-GH-GHR-STAT5-IGF-1 axis reveals unique sexual dimorphic hepatic signatures of the male-dominant, metabolic genes Asns and Lcn13

JOSE CORDOBA-CHACON; BELEN BRIE; RHONDA D. KINEMAN; ANDRE SARMENTO-CABRAL; DAMASIA BECU-VILLALOBOS

Congreso; The Growth Hormone and Prolactin Family in Biology & Disease; 2019

FASEB

Growth hormone (GH) is a pituitary protein which stimulates insulin-like growth factor-1 (Igf-1) production and together GH/IGF1 control postnatal growth, and metabolism. GH binds to its receptor (GHR) and phosphorylates STAT5 (p-STAT5), a transcription factor. The pattern of GH secretion is sex dependent where pulsatile GH release in males results in intermittent binding of p-STAT5 to DNA, while continuous GH release in females leads to persistent p-STAT5 binding, establishing sex-dependent hepatic gene transcription. Here we contrast the sexually dimorphic hepatic gene expression in mouse models with alterations in GH output or hepatocyte GH signaling to further define the steps in the regulatory cascade that influence GH-dependent hepatic sexual dimorphism, in particular genes related to metabolic regulation.We selected male predominant GH-dependent hepatic genes known to regulate metabolic function: asparagine synthetase (Asns) and lipocalin 13 (Lcn13). ASNS participates in the synthesis of asparagine, is involved in the regulation of glucose levels and a potential target in hepatocellular carcinoma. LCN13 suppresses gluconeogenesis and lipogenesis, and increases fatty acid β oxidation. Initial screening by gene array showed these genes were reduced in livers of male aHepGHRkd, compared to controls, consistent with previous reports indicating these genes are downregulated in hypophysectomized males and have predicted sites for STAT5b binding in their promoters. In addition, we compared the relative expression levels of these metabolic genes to the well-known GH-mediated, male-dominant, STAT5-dependent gene, Cyp7b1.qPCR showed high hepatic expression of Asns, Lcn13 and Cyp7b1 in male mice was reduced under conditions of low GHRH/GH/IGF1 (neuroDrd2KO [1]) and after adult-onset loss of hepatocyte GHR expression (aHepGHRkd [2]). Hepatocyte expression of a constitutively active STAT5 (STAT5bCA) did not restore expression in male aHepGHRkd mice, consistent with the predicted persistent (feminized) pattern of STAT5bCA:DNA binding. In this same vein, elevated GH/IGF1 levels due to somatotrope-specific loss of Igf1 and insulin receptors (HiGH [3]) feminized the expression of Asns, Lcn13 and Cyp7b1, in males. Hepatocyte-specific loss of Igf1 (aHepIGF1kd), dramatically lowered IGF1, leading to elevated GH levels, and reduced Lcn13 in male livers. Curiously, the expression of Asns and Cyp7b1 was increased in both male and female aHepIGF1kd livers. Similarly, when STAT5bCA was introduced into wildtype mice, Lcn13 was reduced in male livers, while the expression of Asns and Cyp7b1 was increased in male and female livers. We hypothesize that the differences observed in the STAT5CA and aHepIGF1kd models are mediated by differential activity of cofactors or epigenetic regulation. We found that methylation of gene promoter was not involved in the sexual differences observed for Cp7b1 or Asns, while miR-155-5p may be involved in Cyp7b1 sex differences.