Lowered cortistatin expression is an early event in the human diabetic retina and is associated with apoptosis and glial activation

PURPOSE Cortistatin (CST), a neuropeptide with strong structural and functional similarities to somatostatin, is abundant in the vitreous fluid, and it is decreased in patients with proliferative diabetic retinopathy. The aims of the present study were to explore whether the retina produces CST, and to compare its expression between diabetic and nondiabetic donors. Retinal neurodegeneration was assessed by measuring glial fibrilar acidic protein (GFAP) by confocal laser microscopy and counting the apoptotic TUNEL positive cells in which nuclear fragmentation as well as condensation were present. METHODS Human postmortem eyes (10) from five diabetic donors were compared with 10 eyes from five nondiabetic donors, matched by age. CST mRNA (RT-PCR) and CST (confocal laser microscopy) were measured separately in both the neuroretina and retinal pigment epithelium (RPE). Retinal neurodegeneration was assessed by measuring glial fibrillar acidic protein (GFAP) by confocal laser microscopy and counting the apoptotic cells by TUNEL. RESULTS CST was found to be produced by the human retina, and higher levels of CST mRNA were found in RPE than in the neuroretina. CST mRNA levels in diabetic donors were significantly lower in both the RPE (p=0.001) and the neuroretina (p=0.03) in comparison with nondiabetic donors. CST immunofluorescence was in agreement with mRNA expression, but the differences were only significant when comparing neuroretinas (p=0.03). Increased GFAP and a higher degree of apoptosis were observed in diabetic retinas in comparison with nondiabetic retinas. These changes were inversely related with CST levels. CONCLUSIONS CST is expressed in the human retina. There is more CST in the RPE than in the neuroretina. A lower expression of CST exists in diabetic retinas and it is associated with retinal neurodegeneration.