CELL-TYPE-SPECIFIC MOLECULAR CHANGES IN PHOTORECEPTORS BY A CAV1.4 C-TERMINAL TRUNCATION VARIANT CAUSING CSNB2

Pathogenic variants in the CACNA1F gene, encoding the Cav1.4 L-type calcium channel, cause congenital stationary night blindness type 2 (CSNB2) in humans. Our lab recently published a mouse model carrying the R1827X (RX) truncation variant, which lacks the C-terminal modulatory domain. In these mice, the rod pathway is functionally and morphologically disrupted, as evidenced by altered synaptic ribbon architecture and pronounced sprouting primarily in rod bipolar cells. The rod pathway impairment is corroborated by electroretinography showing specific deficits in rod-mediated responses while cone pathways remained unaffected. However, electron microscopy revealed ultrastructural deficits in both rod and cone photoreceptors, including floating ribbons causing ribbon-less active zones. Despite these synaptic alterations in cones, no functional phenotype was observed, prompting the hypothesis that cones possess compensatory mechanisms at the molecular level to maintain function.
To investigate this differential molecular response, we established a low-cell-input proteomics pipeline optimized for FACS-sorted rods and cones from RX mutant and control retinas. This platform enabled robust detection of low-abundance synaptic proteins, including the Cav1.4 channel complex and associated interactors. Proteomic analysis uncovered decreased Cav1.4 protein levels in both cell types. Interestingly, rods showed additional altered protein involved in the vesicle release machinery, such as vGlut1 and SV2a.
These initial findings point to divergent molecular changes in rods versus cones to Cav1.4 RX dysfunction, suggesting at potential compensatory mechanisms in cones that warrant further validation. Future studies will focus on validating these mechanisms and exploring their therapeutic potential for CSNB2.