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Expression and function of receptors for insulin-like growth factor-I and insulin in human coronary artery smooth muscle cells
Linköping University, Department of Clinical and Experimental Medicine, Cellbiology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Cellbiology. Linköping University, Faculty of Health Sciences.
2005 (English)In: Diabetologia, ISSN 0012-186X, Vol. 48, no 10, 2155-2161 p.Article in journal (Refereed) Published
Abstract [en]

Aims/hypothesis: Hyperinsulinaemia and insulin resistance, as well as low IGF-I, have been implicated in the pathogenesis of cardiovascular disease. Little is known about direct effects of IGF-I and insulin on human coronary artery smooth muscle cells (HCASMCs). Our aim was to characterise the expression and function of IGF-I receptor (IGF-IR) and insulin receptor (IR) in HCASMCs. Materials and methods: Cultured HCASMCs were used. mRNA expression was measured by quantitative real-time RT-PCR analysis. Receptor proteins, phosphorylation of β-subunits and the presence of hybrid IR/IGF-IR were analysed by immunoprecipitation and western blotting. DNA synthesis and glucose metabolism were assessed using [3H]thymidine incorporation and D-[U-14C]glucose accumulation respectively. Results: The mRNA expression of IGF-IR was approximately eight-fold higher than that of IR in HCASMCs. The presence of IGF-IR and IR could be demonstrated by immunoprecipitation and western blot analysis. Phosphorylation of the IGF-IR β-subunit was obtained by IGF-I at 10−10–10−8 mol/l and insulin at 10−8 mol/l. Insulin and IGF-I at 10−10–10−9 mol/l phosphorylated the IR β-subunit. When immunoprecipitated with monoclonal anti-IR α-subunit or IGF-IR α-subunit antibodies, we found bands in slightly different positions, suggesting the presence of hybrid IR/IGF-IR. IGF-I at 10−9–10−8 mol/l significantly stimulated [3H]thymidine incorporation and at a concentration of 10−9–10−7 mol/l also D-[U-14C]glucose accumulation in HCASMCs. Insulin at 10−9–10−7 mol/l had no effect on DNA synthesis, but increased glucose accumulation at 10−7 mol/l. Conclusions/interpretation: Our study provides experimental evidence that IGF-IR and possibly hybrid IR/IGF-IR play a role in HCASMCs.

Place, publisher, year, edition, pages
2005. Vol. 48, no 10, 2155-2161 p.
Keyword [en]
Human coronary artery smooth muscle cells, Hybrid insulin receptor/IGF-I receptor, IGF-I receptor, Insulin receptor
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-12556DOI: 10.1007/s00125-005-1890-4OAI: oai:DiVA.org:liu-12556DiVA: diva2:1697
Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2009-02-16
In thesis
1. Expression and function of IGF-I and insulin receptors in human micro- and macrovascular cells
Open this publication in new window or tab >>Expression and function of IGF-I and insulin receptors in human micro- and macrovascular cells
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Insulin-like growth factor and insulin are phylogenetically closely related polypeptides and have large structural and biological similarities. Low circulating insulin-like growth factor-I (IGF-I), diabetes as well as insulin resistance have been implicated in the pathogenesis of cardiovascular disease, but the mechanisms involved are still not clear. Furthermore, little is known about direct effects of insulin-like growth factor-I (IGF-I) and insulin on human micro- and macrovascular cells.

In these studies we investigated the expression and function of insulin-like growth factor-I receptors (IGF-IR) and insulin receptors (IR) in human micro- and macrovascular endothelial cells and in human coronary artery smooth muscle cells.

Our results showed expression of both IGF-IR and IR in human dermal microvascular (HMVEC), aortic (HAEC) umbilical vein (HUVEC) and coronary artery (HCAEC) endothelial cells as well as in human coronary artery smooth muscle cells (HASMC). The gene expression of IGF-IR was several times more abundant than that of IR. Ligand binding studies confirmed that the IGF-IR was severalfold more abundant than the IR. It also demonstrated that insulin and glargine interacted with the IGF-IR with thousand- and hundredfold, respectively, less potency than IGF-I itself. The presence of IGF-IR and IR proteins and activation of their β-subunits was revealed by immunoprecipitation and Western blot analysis in human macrovascular endothelial cells and in coronary artery smooth muscle cells. At physiological concentrations (≤10-9 M) IGF-I and insulin activated their cognate receptors. The presence of hybrid IR/IGF-IR was shown through detection of the β-subunit for IGF-IR and IR on the same membrane by Western blot after immunoprecipitation with specific antibodies against either IGF-IR or IR, implying coprecipitation of the IGF-IR β-subunit and the IR β-subunit. The inability of physiological concentrations of insulin to phosphorylate IR β-subunit immunoprecipitated with IGF-IR antibodies and that IGF-I at physiological concentration activates the IR β-subunit is another evidence for the presence of the hybrid IR/IGF-IR. At physiological concentrations (≤10-9 M) IGF-I stimulated DNA synthesis and glucose incorporation into human coronary artery smooth muscle cells (HCASMC) and DNA synthesis in microvascular endothelial cells (HMVEC), but not in human macrovascular endothelial cells (HCAEC or HUVEC). No effect of insulin was found. Although physiological concentrations of insulin (≤10-9 M) were able to activate IR, insulin had no biological effects on the vascular cells studied. A possible explanation is that the insulin receptor signalling is too attenuated due to the presence of hybrid IR/IGF-IR and low number of IR expressed in the cells studied. Regarding the safety in the use of glargine, we show that glargine has 10-fold higher affinity for IGF-IR than human insulin. However, the glargine concentrations obtained in vivo during diabetes treatment is too low to affect the IGF-IR.

In conclusions our studies provide experimental evidence that human micro- and macrovascular endothelial and vascular smooth muscle cells express both IGF-IR and IR. Our in vitro data suggest that the cells studied are sensitive to IGF-I, but insensitive to insulin and this is due to the preponderance of IGF-IR and presence of hybrid IR/IGF-IR.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2008. 89 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1045
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-12558 (URN)978-91-7393-972-0 (ISBN)
Public defence
2008-03-14, Berzeliussalen (hus 463, ingång 65), Hälsouniversitet, Campus US, Linköpings universitet, Linköping, 09:00 (Swedish)
Opponent
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Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2009-08-21Bibliographically approved

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Chisalita, Simona I. Arnqvist, Hans J.

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