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Insulin and IGF-I action on insulin receptors, IGF-I receptors, and hybrid insulin/IGF-I receptors in vascular smooth muscle cells
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences. (Hans Arnqvist)
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Medicine, Department of Endocrinology and Gastroenterology UHL.
2006 (English)In: American Journal of Physiology. Endocrinology and Metabolism, ISSN 0193-1849, E-ISSN 1522-1555, Vol. 291, no 5, 1124-1130 p.Article in journal (Refereed) Published
Abstract [en]

Insulin and insulin-like growth factor I (IGF-I) are known to affect cardiovascular disease. We have investigated ligand binding and the dose-response relationship for insulin and IGF-I on vascular smooth muscle cells (VSMCs) at the receptor level. VSMCs from rat thoracic aorta were serum starved, stimulated with IGF-I or insulin, lysed, immunoprecipitated, and analyzed by Western blot. D-[U-14C]Glucose accumulation and [6-3H]thymidine incorporation into DNA were also measured. Specific binding of both insulin and IGF-I was demonstrated, being higher for IGF-I. Both IGF-I receptor (IGF-IR) and insulin receptor (IR) β-subunits were detected and coprecipitated after immunoprecipitation (IP) against either of the two. No coprecipitation was found after reduction of disulphide bonds with dithiotreitol before IP. After stimulation with 10–10–10–9 M IGF-I, IP of the IGF-IR, or IR β-subunit and immunoblot with anti-phosphotyrosine antibody, we found two distinct bands indicating phosphorylation of both the IGF-IR and the IR β-subunit. Stimulation with 10–10–10–9 M insulin and IP against the IGF-IR did not show phosphorylation of either β-subunit, whereas after IP of the IR we found phosphorylation of the IR β-subunit. [14C]Glucose accumulation and [3H]thymidine incorporation were elevated in cells stimulated with IGF-I at 10–10–10–7 M, reaching maximum by 10–9 M. Insulin stimulation showed measurable effects only at supraphysiological concentrations, 10–8–10–7 M. In conclusion, coprecipitation of both the IGF-IR and the IR β-subunit indicates the presence of hybrid insulin/IGF-I receptors in VSMC. At a physiological concentration, insulin activates the IR but does not affect either glucose metabolism or DNA synthesis, whereas IGF-I both activates the receptor and elicits biological effect.

Place, publisher, year, edition, pages
Rockville Pike: American Physiological Society , 2006. Vol. 291, no 5, 1124-1130 p.
Keyword [en]
insulin-like growth factor I, ligand binding, receptor phosphorylation, immunoprecipitation, deoxyribonucleic acid synthesis, glucose metabolism
National Category
Cell and Molecular Biology
Identifiers
URN: urn:nbn:se:liu:diva-18629DOI: 10.1152/ajpendo.00565.2005OAI: oai:DiVA.org:liu-18629DiVA: diva2:220823
Available from: 2009-06-08 Created: 2009-06-02 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Insulin resistance and IGF-I sensitivity in vascular cells - impact of hybrid receptors: With special regard to diabetes
Open this publication in new window or tab >>Insulin resistance and IGF-I sensitivity in vascular cells - impact of hybrid receptors: With special regard to diabetes
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diabetic complications largely affect the circulation and are associated with resistance to insulin and altered levels of insulin-like growth factor-I (IGF-I). Insulin resistance and altered IGF-I levels are also associated with vascular disease. Insulin and IGF-I are highly homologous peptides and can cross react with each others respective receptors, insulin receptors (IR) and IGF-I receptors (IGFIR), which also share homology to a large extent and can form hybrid IR/IGF-IR. Cultured endothelial and vascular smooth muscle cells from different vascular beds express considerably more IGF-IR than IR. Since the direct action of insulin and IGFs on the vasculature remains poorly understood, our aim was to study mechanisms behind insulin resistance and IGF-I sensitivity and the possible impact of hybrid IR/IGF-IR in vascular cells.

This thesis is based on four papers investigating the presence of IR and IGF-IR in cultured endothelial and vascular smooth muscle cells, and in tissue specimens from human left internal mammary artery (LIMA). We examined, in cultured vascular smooth muscle cells and endothelial cells, the phosphorylation of IR and IGF-IR, and IR and IGF-IR mediated actions, i e subsequent downstream signalling and biological effects, in response to physiologic and supraphysiologic concentrations of insulin, IGF-I and IGF-II. We also examined the presence of insulin/IGF-I hybrid receptors in these cell types. To compare our results in vitro with the in vivo situation we investigated the relative gene expression of IGF-IR to IR in LIMA.

We conclude that: 1) the relative abundance of IGF-IR is considerably higher than IR in vascular cells in vitro and in vivo; 2) in addition to IR and IGF-IR, hybrid IR/IGF-IR are present in vascular cells; 3) IR activation at physiological concentrations (≤10-9M) does not propagate downstream signalling and biological effects in endothelial and vascular smooth muscle cells; 4) low concentrations of IGF-I activate IGF-IR, as well as IR due to the presence of hybrid IR/IGF-IR, and propagate downstream signalling and biological effects in endothelial and vascular smooth muscle cells; and 5) the biological effects mediated by IGF-II suggests a role for IGF-II in vascular smooth muscle cells.

The papers included in this thesis provide new insight on how IGFs and insulin act in the vasculature. The preponderance of IGF-IR relative to IR in addition to sequestration of IR into hybrid IR/IGF-IR contributes to an insulin resistance located at the receptor level in endothelial and vascular smooth muscle cells.

Hence, our results suggest that IGFs rather than insulin have an impact on vascular function.

Abstract [sv]

Diabeteskomplikationer drabbar till stor del cirkulationen och är associerade med resistans för insulin samt ändrade nivåer av insulin-liknande tillväxtfaktor typ I (IGF-I). Insulinresistans och ändrade IGF-I nivåer är också associerade med hjärt-kärlsjukdom. Insulin och IGF-I är mycket lika och kan vid höga koncentrationer korsreagera med varandras respektive receptorer, insulinreceptorer(IR) och IGF-I-receptorer(IGF-IR), som också är mycket lika och kan bilda hybridreceptorer (hybrid IR/IGF-IR). Odlade endotelceller och glatta muskelceller från olika kärlbäddar uttrycker betydligt fler IGF-IR jämfört med IR. Eftersom direkt verkan av insulin och IGF-I i kärlvägg är dåligt utredd, var vårt mål att studera mekanismer bakom insulinresistans och IGF-I känslighet samt möjlig betydelse av hybrid IR/IGF-IR i kärlväggens celler.

Den här avhandlingen baseras på fyra arbeten som undersökt förekomst av IR och IGF-IR i odlade endotelceller och glatta muskelceller från kärl, samt i vävnad från human vänster inre bröstartär (LIMA). I odlade endotelceller och glatta muskelceller från kärl har vi undersökt fosforylering av IR och IGF-IR, samt IR -och IGF-IR medierade svar, dvs vidare signalering nedströms och biologiska effekter, till följd av stimulering med insulin, IGF-I och IGF-II vid fysiologiska och suprafysiologiska koncentrationer. Vi har också undersökt förekomst av hybrid IR/IGF-IR i dessa celltyper. För att relatera våra in vitro försök till situationen in vivo, undersökte vi även det relativa genuttrycket av IGF-IR jämfört med IR i LIMA.

Vi drar följande slutsatser: 1) den relativa förekomsten av IGF-IR är betydligt högre än IR i kärlceller in vitro och in vivo; 2) förutom IR och IGF-IR förekommer i celler från kärlvägg även hybrid IR/IGF-IR; 3) IR aktiverad vid fysiologiska koncentrationer (≤10-9 M) propagerar inte vidare intracellulär signalering eller biologiska effekter, i endotelceller och glatta muskelceller från kärl; 4) låga koncentrationer av IGF-I aktiverar IGF-IR, och även IR tack vare förekomsten av hybrid IR/IGF-IR, samt propagerar vidare intracellulär signalering och biologiska effekter i endotelceller och glatta muskelceller från kärl; och 5) de biologiska effekterna till följd av IGF-II-stimulering föreslår en roll för IGF-II i glatta muskelceller från kärl.

Arbetena inkluderade i den här avhandlingen bidrar med nya insikter i hur IGFs och insulin verkar i kärlvägg. Det övervägande antalet IGF-IR relativt IR samt inkorporeringen av IR in i hybrid IR/IGFIR orsakar en insulinresistens lokaliserad på receptornivå i endotelceller och glatta muskelceller från kärl. Sammantaget talar våra resultat för att IGFs snarare än insulin är av vikt för kärlväggens funktion.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 45 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1136
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-19288 (URN)978-91-7393-597-5 (ISBN)
Public defence
2009-06-03, Berzeliussalen, Campus US, Linköpings Universitet, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2009-06-16 Created: 2009-06-16 Last updated: 2009-08-21Bibliographically approved

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Johansson, Git SArnqvist, Hans J

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