Cell Type-specific Post-transcriptional Regulation of Production of the Potent Antiangiogenic and Proatherogenic Protein Thrombospondin-1 by High Glucose

Sanghamitra Bhattacharyya,Tina E Marinic,Irene Krukovets,George Hoppe,Olga I Stenina

doi:10.1074/jbc.m706435200

Abstract

Hyperglycemia is an independent risk factor for development of vascular diabetic complications. Vascular dysfunction in diabetics manifests in a tissue-specific manner; macrovasculature is affected by atherosclerotic lesions, and microvascular complications are described as "aberrant angiogenesis": in the same patient angiogenesis is increased in some tissues (e.g. retinal neovascularization) and decreased in others (e.g. in skin). Molecular cell- and tissue-specific mechanisms regulating the response of vasculature to hyperglycemia remain unclear. Thrombospondin-1 (TSP-1), a potent antiangiogenic and proatherogenic protein, has been implicated in the development of several vascular diabetic complications (atherosclerosis, nephropathy, and cardiomyopathy). This study examines cell type-specific regulation of production of thrombospondin-1 by high glucose. We previously reported the increased expression of TSP-1 in the large arteries of diabetic animals. mRNA and protein levels were up-regulated in response to high glucose. Unlike in macrovascular cells, TSP-1 protein levels are dramatically decreased in response to high glucose in microvascular endothelial cells and retinal pigment epithelial cells (RPE). This down-regulation is post-transcriptional; mRNA levels are increased. In situ mRNA hybridization and immunohistochemistry revealed that the level of mRNA is up-regulated in RPE of diabetic rats, whereas the protein level is decreased. This cell type-specific posttranscriptional suppression of TSP-1 production in response to high glucose in microvascular endothelial cells and RPE is controlled by untranslated regions of TSP-1 mRNA that regulate coupling of TSP-1 mRNA to polysomes and its translation. The cell-specific regulation of TSP-1 suggests a potential mechanism for the aberrant angiogenesis in diabetics and TSP-1 involvement in development of various vascular diabetic complications.

Highlights

The precise regulation of these levels remains a problem
Increased TSP-1 Production in Macrovascular endothelial cells (EC)—We recently reported that the expression of TSP-1 is increased in the aorta and carotid artery of diabetic Zucker rats at the protein and mRNA levels [26].This increase in production of the potent antiangiogenic protein TSP-1 in macrovessels was associated with the decreased number of vasa vasorum, or small blood vessels, growing through the vascular wall and feeding the inner layers of vascular cells
Cell lines derived from microvascular endothelial cells (MVEC) and retinal pigment epithelial (RPE) (MVEC, CDC.EU/HMEC1 and RF/6A; RPE, ARPE19 and D407) retained this ability to suppress TSP-1 production upon incubation with high glucose (Fig. 2), suggesting that the differential regulation of TSP-1 in MVEC and RPE versus macrovascular EC and other cells from large blood vessels is an inherited property that is preserved in cell culture and in transformed cell lines

Summary

Introduction

The precise regulation of these levels remains a problem. Vascular diabetic complications remain most prevalent and dangerous and account for the greatest numbers of deaths and hospitalizations in diabetic patients. We report a finding of a cell type- and cell origin-specific post-transcriptional mechanism of down-regulation of TSP-1 expression by glucose This mechanism is not present in endothelial cells (EC) from large blood vessels, vascular smooth muscle cells (SMC), and fibroblasts, where the transcriptional increase in TSP-1 mRNA upon acute glucose stimulation of cells leads to the increased expression of TSP-1 protein [26]. The mechanism controlling TSP-1 production is activated by high glucose, operates at the level of mRNA translation and is controlled by untranslated regions of mRNA The finding of such a cell type- and cell origin-specific mechanism of suppression of the protein production may provide a molecular basis for aberrant angiogenesis in diabetic individuals. Cell- and tissue-specific regulation of TSP-1 production may represent an important link between diabetes, hyperglycemia, and a variety of vascular complications of diabetes

Methods

Results

Conclusion