Diabetic microangiopathy: IGFBP control endothelial cell growth by a common mechanism in spite of their species specificity and tissue peculiarity.

Endothelial cells (EC) play a role in many diseases including diabetes mellitus. EC share common functions, such as angiogenesis and vascular remodeling both regulated by proliferation and apoptosis, anti-thrombotic properties, regulation of vascular tone, control in the passage of nutrients and secretion of peptides and growth factors. However, EC are characterized by site-specificity so their characteristics depend on the organs and tissues where they are. The IGF system induces important growth factors that control cell growth in different microvascular EC (mEC). This family includes IGF-I and IGF-II peptides, their receptors and regulatory proteins IGF-binding proteins (IGFBP-1 to IGFBP-6). The IGFBP modulate their interaction with the IGF membrane receptors and might be regulated at a transcriptional and post-transcriptional level, thus determining the biological IGF-dependent effects on target cells. The IGF system is also a mediator of vascular diseases, and its altered balance might contribute to endothelial dysfunction with the development and evolution of diabetic microangiopathy. We reported here the reviewed literature of IGFBP production from various sources of mEC, showing that they predominantly express IGFBP-2 through IGFBP-5 mRNA. The different pattern of IGFBP secretion depends on the anatomical district and on the species of the tissues. Nevertheless, based on our and other experimental observations, we suggested that a common mechanism of IGFBP regulation in mEC could be hypothized. In retinal and glomerular EC the IGFBP4/IGFBP5 ratio controls the response of these cells to IGF-I and high levels of glucose, in terms of cellular growth.