Subretinal CD14+ monocytes, observed in geographic atrophy, induce loss of photoreceptor outer segments and lead to rod apoptosis.

Abstract

 

Purpose

 

Rod photoreceptor cell loss has been shown to be particularly prominent in geographic atrophy (GA), and residual cones and rods within the geographic lesion lack their outer segment. GA is also associated with CCR2⁺subretinal inflammatory monocyte accumulation in and around the GA lesion and inflammatory monocytes have been shown to induce RPE cell death in vitro.<br /> It is not clear if or how the chronic subretinal monocyte accumulation participates in the pathological changes of photoreceptors in GA. We here evaluate the subretinal monocyte accumulation and photoreceptor phenotype in GA patients and investigated the influence of CD14+monocytes on photoreceptors ex vivo.<br />

 

Methods

 

CD14, rhodopsin, cone arrestin, L/M opsin and S opsin were visualized using immunohistochemistry on donor eyes from control subjects and GA patients. CD14+cells, cones and rods were quantified within the GA lesion and at increasing distances from the lesion. Adherent CD14+ human blood-derived monocytes were co-cultured with an overlying mouse retinal explant and photoreceptor apoptosis (TUNEL) and cone morphology (peanut agglutinine (PNA) immunohistochemistry) was analyzed after 18h.<br />

 

Results

 

Our results show the association of subretinal CD14+ monocytes accumulation with a 90% of the rod population in donor eyes with GA lesions. Residual cones within the lesion were 50% of the extrafoveal normal cone count. However residual cones and rods within the lesion were not distributed equally and lacked their outer segments. In retinal explants co-cultured with CD14+monocytes, apoptosis of rod photoreceptors dramatically increased (1600%), but the number of PNA+ cone photoreceptors was not affected. Cones and rods invariably had lost their outer segments compared to controls.

 

Conclusions

 

Our experiments confirm the subretinal accumulation of monocytes and photoreceptor changes in GA lesions. Our results suggest that subretinal inflammatory monocytes contribute to rod cell loss and might participate in the loss of cone and rod outer segments observed in the residual photoreceptors within the lesion. Inhibition of subretinal monocyte accumulation in GA might help inhibit rod apoptosis.