Single-Cell RNA Sequencing Reveals Microglial Dynamics in Photoreceptor Degeneration of Retinitis Pigmentosa

Purpose
Retinitis pigmentosa (RP) is an inherited retinal disorder characterized by progressive photoreceptor degeneration and eventual blindness, with no effective treatment available. Increasing evidence implicates neuroinflammation in RP pathogenesis, but the underlying mechanisms remain unclear. Using single-cell RNA sequencing (scRNA-seq), we analyzed transcriptomic changes in retinal microglia during photoreceptor degeneration to uncover how microglia-mediated inflammation contributes to RP.

Methods
We investigated transcriptomic alterations in microglia during photoreceptor degeneration by performing scRNA-seq on microglia isolated from the retinas of the rd10 mouse model of RP at P16, P25, and P30, representing key stages of disease progression. Age-matched C57BL/6J mice at P30 were used as healthy controls. Microglial cells were isolated by fluorescence-activated cell sorting (FACS) using CD11b and CD45 surface markers. Bioinformatic analyses, including cell clustering, pseudotime trajectory inference, and differential gene expression analysis, were performed to characterize dynamic microglial responses during RP.

Results
By scRNA-seq analysis of microglia, distinct microglial subpopulations were identified. Trajectory analysis revealed a transition from homeostatic microglia to activated states of microglia like disease-associated microglia (DAM). Notably, microglia in rd10 retinas exhibited upregulation of pro-inflammatory chemokines such as Ccl2, Ccl7, Ccl12, and Cxcl2, alongside downregulation of homeostatic markers including P2ry12, Siglech, Sparc, and Tmem119. Furthermore, we identified the Ccl7–STAT1 signaling axis as a potential mediator of microglia-driven neurotoxicity and photoreceptor degeneration in RP.

Conclusions
These findings reveal stage-specific microglial activation and identify the Ccl7 signaling as a potential driver of neuroinflammation and photoreceptor degeneration in RP.