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.