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 β (TGF-β) plays an important role in diabetic retinopathy. βIG-H3 is a downstream target molecule of TGF-β 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-β and βIG-H3 induced by high concentrations of glucose in the cell culture media. An anti-TGF-β antibody was used to block glucose-induced retinal pericytes apoptosis. Retinal pericytes were also transfected with cDNA encodings either wild-type or mutant βIG-H3 lacking Arg-Gly-Asp (RGD) sequences in order to validate the effects of βIG-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-β levels as compared with 5.5 mM glucose after 5 days, and βIG-H3 levels after 3, 5 and 7 days of exposure (P < 0.01). TGF-β increased cell death and βIG-H3 levels in a dose-dependent manner, with a maximal effect observed at 1 ng/mL. An anti-TGF-β antibody nearly completely blocked high glucose-induced cell death. Wild-type βIG-H3-transfected cells showed a significant increase in cell death as compared with mutant βIG-H3-transfected (Mycb-c) cells, untransfected or mock-transfected cells. Conclusion: These results suggest that hyperglycaemia-induced expression of TGF-β and βIG-H3 contributes to accelerated retinal pericytes apoptosis. βIG-H3 induces pericytes apoptosis through its RGD motif, which may constitute an important pathogenic mechanism leading to pericytes loss in diabetic retinopathy.