High glucose-induced apoptosis in bovine retinal pericytes is associated with transforming growth factor β and βIG-H3: βIG-H3 induces apoptosis in retinal pericytes by releasing Arg-Gly-Asp peptides

BACKGROUND Transforming growth factor beta (TGF-beta) plays an important role in diabetic retinopathy. betaIG-H3 is a downstream target molecule of TGF-beta that may participate in the pathogenesis of diabetic retinopathy and in particular in the loss of pericytes during early pathological changes. METHODS We observed bovine retinal pericytes apoptosis and the increased expression of TGF-beta and betaIG-H3 induced by high concentrations of glucose in the cell culture media. An anti-TGF-beta antibody was used to block glucose-induced retinal pericytes apoptosis. Retinal pericytes were also transfected with cDNA encodings either wild-type or mutant betaIG-H3 lacking Arg-Gly-Asp (RGD) sequences in order to validate the effects of betaIG-H3 and RGD signalling on retinal pericytes apoptosis. RESULTS A cell death-detecting enzyme-linked immunosorbent assay revealed that 25 mM glucose significantly increased cell death compared with 5.5 mM glucose after 5 or 7 days of exposure (P < 0.01). High glucose significantly increased the TGF-beta levels as compared with 5.5 mM glucose after 5 days, and betaIG-H3 levels after 3, 5 and 7 days of exposure (P < 0.01). TGF-beta increased cell death and betaIG-H3 levels in a dose-dependent manner, with a maximal effect observed at 1 ng/mL. An anti-TGF-beta antibody nearly completely blocked high glucose-induced cell death. Wild-type betaIG-H3-transfected cells showed a significant increase in cell death as compared with mutant betaIG-H3-transfected (Mycb-c) cells, untransfected or mock-transfected cells. CONCLUSION These results suggest that hyperglycaemia-induced expression of TGF-beta and betaIG-H3 contributes to accelerated retinal pericytes apoptosis. betaIG-H3 induces pericytes apoptosis through its RGD motif, which may constitute an important pathogenic mechanism leading to pericytes loss in diabetic retinopathy.