Addition of exogenous sodium palmitate increases the IAPP/insulin mRNA ratio via GPR40 in human EndoC-βH1 cells

Ups J Med Sci. 2017 Aug;122(3):149-159. doi: 10.1080/03009734.2017.1368745. Epub 2017 Oct 5.

Abstract

Background: Enhanced IAPP production may contribute to islet amyloid formation in type 2 diabetes. The objective of this study was to determine the effects of the saturated fatty acid palmitate on IAPP levels in human β-cells.

Methods: EndoC-βH1 cells and human islets were cultured in the presence of sodium palmitate. Effects on IAPP/insulin mRNA expression and secretion were determined using real-time qPCR/ELISA. Pharmacological activators and/or inhibitors and RNAi were used to determine the underlying mechanisms.

Results: We observed that EndoC-βH1 cells exposed to palmitate for 72 h displayed decreased expression of Pdx-1 and MafA and increased expression of thioredoxin-interacting protein (TXNIP), reduced insulin mRNA expression and glucose-induced insulin secretion, as well as increased IAPP mRNA expression and secretion. Further, these effects were independent of fatty acid oxidation, but abolished in response to GPR40 inhibition/downregulation. In human islets both a high glucose concentration and palmitate promoted increased IAPP mRNA levels, resulting in an augmented IAPP/insulin mRNA ratio. This was paralleled by elevated IAPP/insulin protein secretion and content ratios.

Conclusions: Addition of exogenous palmitate to human β-cells increased the IAPP/insulin expression ratio, an effect contributed to by activation of GPR40. These findings may be pertinent to our understanding of the islet amyloid formation process.

Keywords: Amyloid; fatty acids; insulin; islet amyloid polypeptide (IAPP); palmitate.

MeSH terms

  • Animals
  • Cell Line
  • Fatty Acids / metabolism
  • Glucose / metabolism
  • Humans
  • Insulin / genetics
  • Insulin / metabolism*
  • Islet Amyloid Polypeptide / genetics
  • Islet Amyloid Polypeptide / metabolism*
  • Islets of Langerhans / drug effects
  • Islets of Langerhans / metabolism
  • Mice
  • Oxidation-Reduction
  • Palmitic Acid / pharmacology*
  • Protein Kinase C / metabolism
  • RNA, Messenger / genetics*
  • Receptors, G-Protein-Coupled / metabolism*
  • Signal Transduction
  • Transcription Factors / metabolism

Substances

  • FFAR1 protein, human
  • Fatty Acids
  • Insulin
  • Islet Amyloid Polypeptide
  • RNA, Messenger
  • Receptors, G-Protein-Coupled
  • Transcription Factors
  • Palmitic Acid
  • protein kinase D
  • Protein Kinase C
  • Glucose

Grant support

This work was supported by Wesslers stiftelse, the Swedish Diabetes Foundation, the Family Ernfors Foundation, EXODIAB, Barndiabetesfonden and VR 2015-02297 (G.T.W.). Human islets were provided through the JDRF award 31-2008-416 (ECIT Islet for Basic Research program).