Endogenous apelin is protective against retinal dysfunction in type 1 diabetic Akita mice

Retinal neurodegeneration occurs in the early stages of diabetic retinopathy and contributes to the development of vascular lesions, which lead to macular edema and traction retinal detachment. Apelin is an endogenous peptide ligand of the G protein-coupled receptor APJ, and the apelin/APJ system has recently been reported to play a crucial role in maintenance of homeostasis in various tissues, including retina. In the present study, we investigated the protective effect of endogenous apelin against retinal dysfunction in type 1 diabetic Akita mice. Retinal function was evaluated by electroretinography. mRNA expression levels were measured by real-time RT-PCR. Electroretinogram responses in Akita mice were declined with age and significantly decreased at 4 months of age. Apelin and APJ mRNA expression levels in the retina of 4-months-old Akita mice were lower than those in the age-matched wild type mice. The electroretinogram reductions in apelin deficient Akita mice were marked compared with Akita mice. Apelin deficiency did not affect transitions in the blood glucose levels in Akita mice. These results indicate that endogenous apelin is protective against retinal dysfunction in Akita mice, suggesting that apelin prevents retinal neurodegeneration in the early diabetic retinopathy.