Plasma Membrane Calcium ATPases Drive Cytoplasmic Acidification and Photoreceptor Degeneration in Retinitis Pigmentosa

Purpose: RP is the most common inherited retinal dystrophy. Limited understanding of how diverse genetic defects converge to cause photoreceptor degeneration hinders the development of mutation-agnostic therapies. Although intracellular Ca²⁺ dysregulation is an early hallmark across genetic variants, its mechanistic link to photoreceptor degeneration remains unclear. This study investigated whether plasma membrane calcium ATPases (PMCA)–mediated Ca²⁺ extrusion induces cytoplasmic acidification that contributes to photoreceptor death in two mouse models of RP. Methods: PMCA expression (immunofluorescence, RT-qPCR), cytoplasmic acidification (LysoTracker Red [LTR] staining), ultrastructural changes (electron microscopy), calpain-2 activity (in situ zymography) and cell death (TUNEL) were assessed in RP mouse retinas. PMCA-mediated acidification was validated in wild-type (WT) retinal explants under ionophore-induced Ca²⁺ overload. Neuroprotection by PMCA inhibition was evaluated ex vivo (retinal explants) and in vivo (intravitreal injection) by histological photoreceptor preservation. Results: Retinas from rd10 and homozygous P23H mice exhibited cytoplasmic acidification respect to WT. During the early stages of degeneration, the proportion of acidified photoreceptors (LTR-positive) exceeded that of TUNEL-positive photoreceptors, with LTR staining appearing before the onset of TUNEL labeling. Acidification correlated with PMCA upregulation. Ionophore-induced Ca²⁺ overload recapitulated cytoplasmic acidification ex vivo in WT retinas, which was prevented by PMCA inhibition. In rd10 mice, PMCA inhibition preserved photoreceptors ex and in vivo at different stages. Conclusions: Our findings identify PMCA as a key mediator of pathological cytoplasmic acidification in RP and improve understanding of mechanisms underlying photoreceptor degeneration, which may facilitate the development of mutation-independent therapies and stage-specific interventions for RP progression.