Haploinsufficiency of the Insulin Receptor in the Presence of a Splice-Site Mutation in Ppp2r2a Results in a Novel Digenic Mouse Model of Type 2 Diabetes

Diabetes. 2016 May;65(5):1434-46. doi: 10.2337/db15-1276. Epub 2016 Feb 11.

Abstract

Insulin resistance in mice typically does not manifest as diabetes due to multiple compensatory mechanisms. Here, we present a novel digenic model of type 2 diabetes in mice heterozygous for a null allele of the insulin receptor and an N-ethyl-N-nitrosourea-induced alternative splice mutation in the regulatory protein phosphatase 2A (PP2A) subunit PPP2R2A. Inheritance of either allele independently results in insulin resistance but not overt diabetes. Doubly heterozygous mice exhibit progressive hyperglycemia, hyperinsulinemia, and impaired glucose tolerance from 12 weeks of age without significant increase in body weight. Alternative splicing of Ppp2r2a decreased PPP2R2A protein levels. This reduction in PPP2R2A containing PP2A phosphatase holoenzyme was associated with decreased serine/threonine protein kinase AKT protein levels. Ultimately, reduced insulin-stimulated phosphorylated AKT levels were observed, a result that was confirmed in Hepa1-6, C2C12, and differentiated 3T3-L1 cells knocked down using Ppp2r2a small interfering RNAs. Altered AKT signaling and expression of gluconeogenic genes in the fed state contributed to an insulin resistance and hyperglycemia phenotype. This model demonstrates how genetic changes with individually small phenotypic effects interact to cause diabetes and how differences in expression of hypomorphic alleles of PPP2R2A and potentially other regulatory proteins have deleterious effects and may therefore be relevant in determining diabetes risk.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Alternative Splicing
  • Animals
  • Cell Line
  • Diabetes Mellitus, Type 2 / blood
  • Diabetes Mellitus, Type 2 / genetics*
  • Diabetes Mellitus, Type 2 / metabolism
  • Diabetes Mellitus, Type 2 / physiopathology
  • Disease Models, Animal*
  • Disease Progression
  • Haploinsufficiency*
  • Heterozygote
  • Insulin Resistance
  • Male
  • Mice
  • Mice, Mutant Strains
  • Mutation*
  • Protein Phosphatase 2 / antagonists & inhibitors
  • Protein Phosphatase 2 / genetics*
  • Protein Phosphatase 2 / metabolism
  • RNA Interference
  • RNA Splice Sites*
  • RNA, Small Interfering
  • Receptor, Insulin / genetics*
  • Receptor, Insulin / metabolism
  • Signal Transduction

Substances

  • RNA Splice Sites
  • RNA, Small Interfering
  • Receptor, Insulin
  • Ppp2r2a protein, mouse
  • Protein Phosphatase 2