C-peptide is internalised in human endothelial and vascular smooth muscle cells via early endosomes

P. Luppi, X. Geng, V. Cifarelli, P. Drain, M. Trucco

Research output: Contribution to journalArticlepeer-review

36 Scopus citations

Abstract

Aims/hypothesis: There is increasing evidence that C-peptide exerts intracellular effects in a variety of cells and could be beneficial in patients with type 1 diabetes. Exactly how C-peptide achieves these effects, however, is unknown. Recent reports showed that C-peptide internalised in the cytoplasm of HEK-293 and Swiss 3T3 cells, where it was not degraded for at least 1 h after uptake. In this study, we investigated the hypothesis that C-peptide is internalised via an endocytic pathway and traffics to classic endocytic organelles, such as endosomes and lysosomes. Methods: We studied the internalisation of C-peptide in vascular endothelial and smooth muscle cells, two relevant targets of C-peptide activity, by using Alexa Fluor-labelled C-peptide probes in living cells and immunohistochemistry employing confocal laser-scanning microscopy. To examine trafficking to subcellular compartments, we used fluorescent constructs tagged to RAB5A, member RAS oncogene family (RAB5A) to identify early endosomes, or to lysosomal-associated membrane protein 1 (LAMP1) to identify lysosomes. Results: C-peptide internalised in the cytoplasm of cells within punctate structures identified as early endosomes. Internalisation was clearly detectable after 10 min of incubation and was blocked at 4°C as well as with excess of unlabelled C-peptide. A minor fraction of vesicles, which increased with culture time, co-localised with lysosomes. Uptake of C-peptide was reduced by monodansylcadaverine, a pharmacological compound that blocks clathrin-mediated endocytosis, and by nocodazole, which disrupts microtubule assembly. Conclusions/interpretation: C-peptide internalises in the cytoplasm of cells by endocytosis, as demonstrated by its localisation in early endosomes. Endosomes might represent a signalling station, through which C-peptide might achieve its cellular effects.

Original languageEnglish
Pages (from-to)2218-2228
Number of pages11
JournalDiabetologia
Volume52
Issue number10
DOIs
StatePublished - Oct 2009

Keywords

  • C-peptide
  • Endocytosis
  • Endosomes
  • Endothelial cells
  • Lysosomes
  • Smooth muscle cells

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