Characterization of the Receptors for Insulin and the Insulin-Like Growth Factors on Micro- and Macrovascular Tissues*

Abstract

Insulin and insulin-like growth factors (IGFs) have been implicated in the pathogenesis of diabetic retinopathy and peripheral vascular complications. Previously, we have shown that retinal capillary endothelial cells responded to insulin and IGFs for metabolic and growth effects, whereas aortic endothelial cells were not responsive. In contrast, vascular supporting cells from both retinal capillaries (i.e. pericytes) and aorta (i.e. smooth muscle cells) responded equally to insulin, IGF-I, and IGF-II. The structure and ligand specificities of the receptor for these peptides were studied by covalently cross-linking 125I-labeled peptide hormones to their respective receptors using disuccinimidyl suberate, followed by polyacrylamide gel electrophoresis and autoradiography. The binding subunit of the insulin receptor, alpha-subunit, for all cell types was found to have a mol wt 145,000 under reduced conditions. Labeling of this band was inhibited by 10(-9) M insulin, antiinsulin receptor antibodies, and 10(-8) M IGF-I, but not by multiplication-stimulating activity (IGF-II). The beta-subunit of the insulin receptor in endothelial cells was identified by its ability to be autophosphorylated when stimulated by insulin and was found to have a mol wt of 99,000. Covalent cross-linking of IGF-I to its receptor revealed a mol wt of 145,000, similar to that of insulin receptor, except that IGF-I was 100-fold more potent than insulin in competing with [125I]IGF-I for binding. [125I]IGF-II in all cells was cross-linked to receptor with mol wt of 260,000 and 230,000 under reduced and nonreduced conditions, respectively. IGF-I competed weakly with [125I]IGF-II, whereas insulin was ineffective. [125I]IGF-II also bound to the band with alpha mol wt of 135,000, which was inhibited by insulin, IGF-I, and IGF-II. In summary, receptors for insulin, IGF-I, and IGF-II on cells from micro- and macrovessels are biochemically similar to those in other cells. Interestingly, the finding of large numbers of IGF-I and IGF-II receptors on endothelial cells suggests that these growth factors play a physiological role and are involved in vascular complications associated with diabetes.

Identification of persistent defects in insulin receptor structure and function capillary endothelial cells from diabetic rats.

“…This band corresponds to the a subunit ofthe insulin receptor observed in other endothelial or nonendothelial tissues, although the apparent molecular weight of the receptor in endothelial cells is slightly higher than that in nonendothelial tissues. In addition, the major intense band or bands at > 200 kD were found that had been reported by us previously as cross-linked a subunit of the insulin receptor (30). However, affinity labeling studies using divalent agents are not quantitative, because of uncertainty of the cross-linking efficiency in each experiment.…”

Associations between genetic variants and the severity of metabolic syndrome in subjects with type 2 diabetes

“…The binding receptors to epidermal growth factor, including IGFR2, were shown to play a role in the development of microvascular complications in T2D (Jialal et al, 1985). This gene encodes a receptor for both IGF2 and mannose 6-phosphate, which function mainly in immune-or cancer-related disorders.…”

The FoxO transcription factors and metabolic regulation

“…Insulin receptors (IRs) have been demonstrated on endothelial cells of both large and small blood vessels [119]. The findings that vascular endothelial cell-specific IR knockout mice (VENIRKO) on a low-salt diet showed significant insulin resistance suggest that insulin signaling in endothelial cells participates in the mechanism that correct whole-body insulin sensitivity and vascular function [120].…”