Proinsulin C-peptide increases nitric oxide production by enhancing mitogen-activated protein-kinase-dependent transcription of endothelial nitric oxide synthase in aortic endothelial cells of Wistar rats

Diabetologia. 2003 Dec;46(12):1698-705. doi: 10.1007/s00125-003-1232-3. Epub 2003 Oct 30.

Abstract

Aims/hypothesis: Recent studies have suggested that proinsulin C-peptide improves vascular functions, possibly through nitric oxide (NO) production. To clarify the molecular mechanisms of vascular NO production induced by C-peptide, we examined the effects of C-peptide on NO production and NO synthase expression in rat aortic endothelial cells in connection with mitogen-activated protein kinase (MAPK) activation.

Methods: Aortic endothelial cells were isolated from female Wistar rats, cultured to confluence, and serum-starved for 24 h before treatment with C-peptide. Nitric oxide production was measured by the DAF-2 fluorescence dye method and relative amounts of endothelial nitric oxide synthase (eNOS) protein and its mRNA were semi-quantified by western blot and RT-PCR analyses respectively. Activation of MAPK was estimated by western blot detection of activity-related phosphorylation and in vitro kinase assay.

Results: Stimulation of cells with C-peptide for 3 h doubled NO production, which was suppressed by the NO synthase inhibitor, N(G)-nitro- L-arginine methyl ester (L-NAME). Stimulation also increased mRNA and protein contents of eNOS in a manner sensitive to the transcription inhibitor actinomycin D. It did not affect inducible NO synthase mRNA. C-peptide also induced rapid phosphorylation and activation of extracellular signal-regulated kinase (ERK, also known as p44/42MAPK), but not of p38MAPK. In cells pretreated with the ERK inhibitor PD98059 the C-peptide-elicited increase of NO production and eNOS was abrogated in a dose-dependent manner; suppression of ERK phosphorylation induced by C-peptide also occurred.

Conclusions/interpretation: Our results show that C-peptide increases NO production by increasing eNOS protein contents through ERK-dependent up-regulation of eNOS gene transcription. This could explain some actions of C-peptide on the vasculature, indicating a pivotal role for C-peptide in vascular homeostasis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Aorta
  • Base Sequence
  • C-Peptide / pharmacology*
  • Cells, Cultured
  • DNA Primers
  • Endothelium, Vascular / drug effects
  • Endothelium, Vascular / enzymology
  • Endothelium, Vascular / physiology*
  • Female
  • Kinetics
  • Mitogen-Activated Protein Kinases / metabolism*
  • Nitric Oxide / biosynthesis*
  • Nitric Oxide Synthase / genetics*
  • Nitric Oxide Synthase Type III
  • RNA, Messenger / genetics
  • Rats
  • Rats, Wistar
  • Reverse Transcriptase Polymerase Chain Reaction
  • Transcription, Genetic / drug effects
  • Transcription, Genetic / genetics*

Substances

  • C-Peptide
  • DNA Primers
  • RNA, Messenger
  • Nitric Oxide
  • Nitric Oxide Synthase
  • Nitric Oxide Synthase Type III
  • Nos3 protein, rat
  • Mitogen-Activated Protein Kinases