The interaction of Cx43, IGF-I and IGFBP-5 in models of wound closure

The insulin-like growth factor I: insulin-like growth factor binding protein 5 (IGF-I:IGFBP-5) ratio is perturbed in diabetic skin and may contribute to impaired cell migration in diabetic wounds. Gap junctions, and their constituent proteins the connexins, are also raised at the wound edge in diabetes. The connexin mimetic peptide Gap27 increases scrape-wound closure in human skin models by inhibiting Cx43 function. This study examined the relative roles of IGF-I, IGFBP-5 and the gap junction protein connexin43 (Cx43) in scrape-wound cell migration.
Cells were pre-treated for 5 days with 5.5 mM glucose and 1 nM insulin (NGI), or 25 mM glucose and 10 nM insulin (HGI). HGI conditions contained levels of glucose and insulin to mimic those seen in uncontrolled type II diabetes. Migration studies examined scrape-wound closure rates in 2D human epidermal keratinocyte and 3D organotypic skin models over 48 h in the presence or absence of 100 ng/ml IGF-I, 4 µg/ml IGFBP-5 and 100 µM Gap27.
Addition of IGF-I increased scrape-wound closure in both 2D and 3D organotypic cultures (P < 0.001). Furthermore, IGFBP-5 counteracted this effect (P < 0.05). Gap27 increased wound closure in addition to that seen with IGF-I, and overrode inhibitory IGFBP-5 effects (P < 0.001). Gap27 reduced GJIC in both NGI and HGI conditions, but IGF-I and IGFBP-5 did not have a significant effect. Neither IGF-I or IGFBP-5 had effects on hemichannels as determined by ATP assays. IGF-I increased cell proliferation in NGI, and Gap27 increased proliferation in both NGI and to a less extent HGI conditions. Treatment with IGF-I did not appear to alter connexin expression in organotypic models.
Gap27 blocked connexin-mediated communication and increased cell migration rates in both NGI and HGI conditions. IGF-I increased migration of Gap27-treated cells further, while IGFBP-5 retarded them. Gap27 overcame the inhibited migration due to IGFBP-5. The effects of IGF-I and IGFBP-5 do not seem to be mediated directly by GJIC or hemichannel activity. Both cell proliferation and cell migration play a role in scrape wound closure. IGFBP-5 plays a central role in a diabetic environment and can impede IGF-I mediated effects. However, in diabetic tissue where the IGF-I:IGFBP-5 ratio is disturbed, Gap27 can be predicted to have a positive effect on chronic wound healing.