Targeting Apolipoprotein E4 rescues photoreceptor degeneration by inhibiting the disease-associated microglia activation in experimental retinal detachment.

Retinal detachment (RD) is a prevalent ocular disorder that leads to photoreceptor death and irreversible visual impairment. Following RD, microglia—the resident immune cells of the retina—become activated and participate in regulating inflammatory responses and tissue repair processes. A distinct microglial subtype, disease-associated microglia (DAM) emerges in stressed neuronal microenvironments. However, its specific contribution to photoreceptor degeneration remains poorly understood. Apolipoprotein E (ApoE), a major lipoprotein predominantly expressed in brain and ocular myeloid cells, has been implicated in modulating neurodegeneration within the central nervous system through influencing DAM activation. In this study, we employed an experimental mouse model of RD and observed upregulation of ApoE and DAM-related markers at three days following RD induction. Genetic deletion of ApoE significantly attenuated photoreceptor loss and suppressed neuroinflammatory responses after RD, accompanied by reduced DAM activation. Furthermore, modulation of the ApoE-Galectin-3 axis reduced TUNEL-positive cells and inhibited TLR4-dependent inflammatory cascades post-RD. Using humanized ApoE allele mice, we further elucidated that the ApoE4 isoform significantly downregulated DAM-associated markers (including Galectin-3, Spp-1 and Gpnmb), promoted photoreceptor survival, and attenuated retinal inflammation. In contrast, ApoE2 and ApoE3 conferred no protection benefit compared to wild-type mice after RD. Our findings indicate that ApoE-mediated DAM activation exacerbates photoreceptor degeneration after RD insult. Both ApoE deficiency and ApoE4 expression potentially mitigated RD-induced photoreceptor death and ameliorated neuroinflammatory pathways via suppression of DAM activation. Collectively, our study highlights ApoE4 as a promising therapeutic target for modulating microglial cells to promote neuronal survival in photoreceptor degeneration conditions.