The Study Of SIRT4’s Localization And Function In The Retina

Purpose:Sirtuin 4(SIRT4)is one of seven mammalian sirtuins that possesses ADP-ribosyltransferase,lipoamidase and deacylase activities and plays indispensable role in metabolic regulation.SIRT4 is highly expressed in retina,but the role of SIRT4 in the retina is not clearly understood.The purpose of this study was to explore the location and function of SIRT4 in the retina.Methods:The cytoplasmic,nuclear and mitochondrial proteins were extracted from retinas of C57BL/6 mice to analyze the expression of SIRT4 protein.Immunofluorescence was used to analyze the localization of SIRT4 and Müller glial cell markers in rat and mouse retinas.Western blotting was used to assess SIRT4 and glutamine synthetase(GS)protein expression at different developmental stages in mice retinas.And we further analysed the retinal structure,electrophysiological function and the expression of GS protein in SIRT4-deficient mice.Excitotoxicity was caused by intravitreal injection of glutamate(50 nmol)in mice with intraperitoneal injection of resveratrol(20 mg/Kg),and then retinas were subjected to Western blotting and paraffin section staining to analyze the effect of SIRT4 on excitotoxicity.Results:We showed that SIRT4 was highly expressed in retinal mitochondria and colocated with Müller glial cell markers(GS and Vimentin).Besides,SIRT4 was highly expressed in the lens epithelial cells and choroid at 5 days after birth,and ciliary epithelial cells at 2 months of age.The protein expression pattern of SIRT4 was similar to that of GS,and both increased with development.There were no significant retinal structure or electrophysiological function changes in SIRT4-deficient mice,while the expression of GS protein was decreased.Moreover,administration of resveratrol can upregulate the expression of SIRT4 and GS protein while reducing the retinal injury caused by excessive glutamate.Conclusions:Our results suggest that SIRT4 is highly expressed in retinal Müller glial cells and is relevant to the expression of GS.SIRT4 does not appear to be essential in retinal development,but resveratrol,as an activator of SIRT4,can upregulate GS protein expression and protect the retina from excitotoxicity.