title: Disruption of JAK2 in adipocytes impairs lipolysis and improves fatty liver in mice with elevated GH.
abstract: Nonalcoholic fatty liver disease (NAFLD) is considered the hepatic expression of the metabolic syndrome, and its prevalence is increasing. The factors that influence the development of fatty liver and its progression to steatohepatitis and cirrhosis are not well understood. The pleiotropic hormone, GH, has been associated with an increased risk of NAFLD in humans and mice. GH is known to have diverse effects on lipid metabolism including decreasing body fat in vivo, presumably through stimulation of lipolysis via an undefined mechanism. Previously we described mice with hepatocyte-specific deletion of the GH signaling mediator, Janus kinase 2 (JAK2L). JAK2L animals have elevated serum GH, reduced body fat, high liver triglyceride content, and increased serum markers of hepatocyte injury (alanine transaminase and aspartate transaminase). We aimed to determine whether the elevation of GH in JAK2L mice contributed to fatty liver by promoting lipolysis directly in adipocytes. We generated mice with adipocyte-specific disruption of JAK2 (JAK2A) and found that GH resistance in adipocytes reduced lipolysis and increased body fat. JAK2A mice were then crossed to JAK2L mice, and the resultant JAK2L/A animals had increased body fat and decreased lipolysis, despite elevated circulating GH. Furthermore, the increased triglyceride content, serum alanine transaminase, and serum aspartate transaminase observed in JAK2L mice were nearly normalized with the additional disruption of JAK2 in adipocytes (JAK2L/A mice). Our results offer novel mechanistic insights into the long-recognized effects of GH on lipid flux and suggest that GH signaling may play an important regulatory role in the development of NAFLD.
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, San Francisco, California 94158, USA.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Nordstrom
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Tran
authors.forename: Brandon C
authors.initials: BC
authors.lastname: Sos
authors.forename: Kay-Uwe
authors.initials: KU
authors.lastname: Wagner
authors.forename: Ethan J
authors.initials: EJ
authors.lastname: Weiss
mesh_terms: D017667:Adipocytes / Q000166:cytology; D000273:Adipose Tissue / Q000166:cytology / Q000502:physiology; D000410:Alanine Transaminase / Q000097:blood; D000818:Animals; D001219:Aspartate Aminotransferases / Q000097:blood; D001823:Body Composition; D005234:Fatty Liver / Q000235:genetics / Q000378:metabolism*; D005355:Fibrosis; D015870:Gene Expression; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism*; D053614:Janus Kinase 2 / Q000172:deficiency / Q000235:genetics*; D050356:Lipid Metabolism / Q000235:genetics*; D008066:Lipolysis / Q000235:genetics*; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D065626:Non-alcoholic Fatty Liver Disease; D011986:Receptors, Somatotropin; D015398:Signal Transduction; D014280:Triglycerides / Q000032:analysis / Q000378:metabolism
chemical_list: D011986:Receptors, Somatotropin; D014280:Triglycerides; D013006:Growth Hormone; D001219:Aspartate Aminotransferases; D000410:Alanine Transaminase; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2