Differential TGF-β2 expression in the anterior and posterior eye segments in mice with early streptozotocin-induced diabetes

The pathogenesis of diabetic retinopathies (DRs), the main cause of blindness in the population with type 1 or type 2 diabetes, is still poorly understood. In DRs pathology, vascular endothelial growth factor VEGF and transforming growth factor beta (TGF-β) may play a role in disease progression, especially in relation to angiogenesis and inflammation in the retina, respectively. In the present study we investigated expression of TGF-β and VEGF in the anterior and posterior eye segments in streptozotocin-induced diabetic mice (STZ-mice) with an incipient (10 d) and fully developed (20 d) diabetes after injection. In previous studies we have shown that TGF-β2 induces increased formation of extracellular material (ECM) in the outer trabecular meshwork (TM) in the subendothelial region of Schlemm's canal (SC). Therefore, TM and SC as well as the morphology of the scleral and retinal capillaries were investigated using qualitative and quantitative ultrastructural methods. Surprisingly, vascular endothelial cells were morphologically unchanged, and there were no signs of edema. VEGF expression was unchanged in the anterior or posterior segment of the eye. However, we found increased TGF-β2 expression in the anterior segment of the eye, increased ECM in the TM, and thickened basement membranes of the scleral and retinal capillaries. In contrast, decreased TGF-β2 expression was observed in the posterior segment of the eye. These findings suggest that early DR-related changes occur independently of VEGF and highlight the need to further investigate the cell-specific regulation of TGF-β2 in different ocular regions.