Microglia Regulate Apoptosis Of Photoreceptors After Retinal Detachment

Purpose: Retinal detachment(RD)is a common ophthalmological disease,the reason of visual injury is the apoptosis of photoreceptor.Our previous study has found that apoptosis of photoreceptor is regulated by many factors,which need to be further studied.In recent years,it has been found that microglia play an important role in neurodegenerative diseases and are the cells firstly respond to central nervous system or retinal injury.Microglia have been found activated after retinal detachment,but the role of microglia activation in photoreceptor apoptosis remains unclear.Therefore,this study will explore whether the intervention of retinal microglia can affect the apoptosis of photoreceptor after retinal detachment and thereby affect the visual function.Method: RD model was established in Wistar rats by subretinal injection of sodium hyaluronate solution.We detected microglia activation after RD 6h,1d,3d,5d,7d,14 d by immunofluorescence staining,compared Müller cells activation between groups by immunofluorescence staining,and detected photoreceptor apoptosis after RD 6h,1d,3d,7d by TUNEL staining.We used fluorescence quantitative PCR and Western Blot to detect expression level of inflammation-related gene and neurotrophic factors.Using M-CSF to activate microglia or GW2580 to deplete microglia,the healthy male Wistar rats were randomly divided into normal group,RD group,medication group and RD+medication group.We cut the retina into slices after RD 3d and do the quantitative comparison of microglia activation and photoreceptor apoptosis by immunofluorescence staining and TUNEL staining.We measured retinal outer nuclear layer thickness to compare retinal structure and measured electroretinogram to compare retinal photosensitive function.Then we compared Müller cells’ activation and expression level of BDNF,GDNF and IL-1β.One-Way ANOVA was used to compare the results in different groups,a P value less than 0.05 was regarded as significant difference.Result: Photoreceptor apoptosis and microglia activation peaked at 3 days after retinal detachment.Müller cells’ activation was significantly increased,and the expression of IL-1β and BDNF was first increased and then decreased.When M-CSF was used to activate microglia,apoptotic photoreceptor in M-CSF+RD group were significantly reduced compared with that in RD group(P<0.01),retinal ONL/INL ratio in M-CSF+RD group was greater than that in RD group(P<0.05),and a-wave amplitude in M-CSF+RD group was higher than that in RD group(P<0.05).In addition,Müller cells in both M-CSF+RD group and M-CSF group were activated,and BDNF protein level was increased.BDNF protein level in M-CSF+RD group was significantly higher than that in RD group(P<0.001).After the depletion of microglia by GW2580+RD group,the number of apoptotic photoreceptors in GW2580+RD group was significantly higher than that in RD group(P<0.01).There was no significant change between GW2580+RD group and RD group.The amplitude of a wave and b wave in GW2580+RD group was lower than that in RD group(P<0.05).In addition,the activation of Müller cells was weakened in both GW2580+RD group and GW2580 group.The BDNF protein level of GW2580+RD group was slightly lower than that of RD group(P<0.05).Conclusion: Photoreceptor apoptosis and microglia activation occur after retinal detachment,which both peak at RD 3d.Microglia inhibit photoreceptor apoptosis by activating Müller cells and accelerating BDNF secretion,which protects retina.Microglia may be a potential therapeutic target for intervention of the apoptosis of photoreceptors after RD to restore visual function in the future.