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Proc Natl Acad Sci U S A. 2019 Feb 15. pii: 201815150. doi: 10.1073/pnas.1815150116. [Epub ahead of print]

PGC1A regulates the IRS1:IRS2 ratio during fasting to influence hepatic metabolism downstream of insulin.

Author information

1
Institut de Recherches Cliniques de Montréal (IRCM), Montreal, QC, Canada H2W 1R7.
2
Faculty of Medicine, University of Montreal, Montreal, QC, Canada H3T 1J4.
3
Division of Experimental Medicine, McGill University, Montreal, QC, Canada H4A 3J1.
4
Centre de Recherche de l'Institut Universitaire de Cardiologie et de Pneumologie de Québec, Faculté de Médecine (CRIUCPQ), Université Laval, Québec, QC, Canada G1V 4G5.
5
Centre de Recherche sur le Cancer, Université Laval, Québec, QC, Canada G1R 3S3.
6
Institut de Recherches Cliniques de Montréal (IRCM), Montreal, QC, Canada H2W 1R7; jennifer.estall@ircm.qc.ca.

Abstract

Precise modulation of hepatic glucose metabolism is crucial during the fasting and feeding cycle and is controlled by the actions of circulating insulin and glucagon. The insulin-signaling pathway requires insulin receptor substrate 1 (IRS1) and IRS2, which are found to be dysregulated in diabetes and obesity. The peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1A) is a fasting-induced transcriptional coactivator. In nonalcoholic fatty liver disease and in patients with type 2 diabetes, low hepatic PGC1A levels are associated with insulin resistance. However, how PGC1A activity impacts the hepatic insulin-signaling pathway is still unclear. We used gain- and loss-of-function models in mouse primary hepatocytes and measured hepatocyte insulin response by gene and protein expression and ex vivo glucose production. We found that the PGC1A level determines the relative ratio of IRS1 and IRS2 in hepatocytes, impacting insulin receptor signaling via protein kinase B/AKT (AKT). PGC1A drove the expression of IRS2 downstream of glucagon signaling while simultaneously reducing IRS1 expression. We illustrate that glucagon- or PGC1A-induced IRS2 expression was dependent on cAMP Response Element Binding Protein activity and that this was essential for suppression of hepatocyte gluconeogenesis in response to insulin in vitro. We also show that increased hepatic PGC1A improves glucose homeostasis in vivo, revealing a counterregulatory role for PGC1A in repressing uncontrolled glucose production in response to insulin signaling. These data highlight a mechanism by which PGC1A plays dual roles in the control of gluconeogenesis during the fasting-to-fed transition through regulated balance between IRS1 and IRS2 expression.

KEYWORDS:

PGC-1; Ppargc1a; fasting; gluconeogenesis; liver

PMID:
30770439
DOI:
10.1073/pnas.1815150116
Free PMC Article

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