ISBN 9783843941242

978-3-8439-4124-2, Reihe Biochemie

Bahar Najafi
Novel functions of the ESCRT-I protein VPS37a in liver metabolism

110 Seiten, Dissertation Technische Universität München (2019), Softcover, A5

Zusammenfassung / Abstract

Hepatocytes are highly complex and multifunctional cells in the liver, which are able to adapt their metabolic activities depending on the environmental stimuli, such as fasting and refeeding. This is generally obtained by the action of the hormones glucagon and insulin that control hepatic glucose production and fatty acid metabolism. A possible mechanism for the metabolic regulation of endocytosis could be the recruitment of endosomal proteins in response to the fasting-refeeding transition. To identify these proteins organelles were isolated from mouse livers of 12h fasted and 2h refed mice and analyzed via proteomics. Upon refeeding we observed a relocalization and reorganization of endosomal proteins, e.g. members of the endosomal sorting complexes required for transport-I (ESCRT-I) machinery especially VPS37a. Many studies have indicated that VPS37a might change liver metabolism. In this study we show that a downregulation of VPS37a leads to an insulin independent increase in hepatic glucose production in vitro and in vivo. Interestingly VPS37a was downregulated in human liver samples of diabetic, obese and nonalcoholic fatty liver disease (NAFLD) patients. Furthermore, VPS37a was also downregulated in livers of db/db and ob/ob mice pointing towards a potential function in diabetes and obesity. An in vitro KD of VPS37a increased the gene expression levels of G6pase and PCK1 and the protein levels of the glucagon receptor indicating a role of VPS37a in glucagon signalling pathway and gluconeogenesis. To further investigate the effects of an in vivo KD of VPS37a a pyruvate tolerance test (PTT) was performed, which showed an increase in hepatic glucose production in the VPS37a KD mice. Intriguingly, the gene expression levels of the glucagon receptor and many genes downstream of the glucagon signalling pathway were upregulated upon in vivo KD of VPS37a. In addition to that, the protein levels of the glucagon receptor were also increased in the livers of VPS37a KD mice. The increase in gluconeogenesis through upregulation of the glucagon signalling pathway was further supported by the elevated fasted blood glucose levels of the VPS37a KD mice after 6h fasting. Since an excess in hepatic glucose production and fasted blood glucose levels are key pathologies of type 2 diabetes our data suggests a possible role of VPS37a in diabetes.