Decod­ing the Molec­u­lar Sig­na­tures of Night Blind­ness

Congenital stationary night blindness (CSNB) is an inherited retinal disorder that severely impairs vision under low-light conditions, such as at dusk or in darkness. The disease is caused by mutations in the L-type calcium channel CaV1.4, which plays a crucial role in signal transmission within the retina. These mutations disrupt synaptic communication between photoreceptors and downstream neurons. To date, no causal treatment or cure for CSNB exists.

A research team led by Matthias Ganglberger and Alexandra Koschak from the Department of Pharmacology and Toxicology at the Institute of Pharmacy, University of Innsbruck, has now taken an important step toward a deeper understanding of congenital stationary night blindness type 2 (CSNB2). In collaboration with colleagues from the Institute of Biochemistry, the team conducted a comprehensive proteomic analysis using three different mouse models. Their results provide the first detailed molecular map of the pathophysiological changes triggered by disease-causing mutations in the CaV1.4 channel and lay the groundwork for future therapeutic strategies.

“Our proteomic analyses show that different mutations—RX and IT in our study—lead to distinct molecular consequences,” explains Matthias Ganglberger. “This is highly relevant for the development of personalized therapies that are tailored to the specific mutation carried by the patient.”

CaV1.4 channels play a key role in so-called ribbon synapses. These highly specialized chemical synapses enable photoreceptors to transmit graded light signals across a wide dynamic range to downstream bipolar cells. As a result, ribbon synapses are central to visual processing and were therefore a major focus of the study. Dysfunction of the CaV1.4 channel, as observed in CSNB2, leads to characteristic impairments in visual signal transmission.

The researchers compared three mouse strains: a wild-type strain expressing a functional CaV1.4 channel, and two clinically relevant mutant strains carrying either the RX or IT variant. Both variants have been identified in CSNB2 patients. “Interestingly, these two mutations exhibit partially opposing biophysical properties,” explains Alexandra Koschak. “They differ in their gating behavior—that is, how the channel opens and closes—which in turn alters calcium influx into the synapse.”

Using state-of-the-art proteomic techniques, the team identified more than 4,000 proteins in synapse-enriched retinal samples, allowing an exceptionally comprehensive view of mutation-specific molecular alterations.

Different mutations – different mechanisms – one disease

Pathway analyses revealed distinct molecular signatures for each mutation. In the RX variant, the researchers observed pronounced dysregulation of proteins involved in synaptic organization and function. Particularly affected were proteins associated with calcium signaling and vesicular trafficking. Proteins directly involved in visual signal transmission were markedly downregulated, reflecting the severe functional deficits caused by this mutation. Detailed analysis of the ribbon synapse demonstrated how dysfunction of the CaV1.4 channel disrupts the entire presynaptic protein network.

By contrast, the IT variant showed a different molecular profile, with extensive changes in synaptic proteins including significant alterations in metabolic pathways. These findings highlight that CSNB2 is not a uniform molecular disease but rather comprises distinct subtypes defined by the underlying channel mutation.

Evidence of degenerative and inflammatory processes

The study also uncovered signs of retinal stress and degeneration. Markers of apoptosis—programmed cell death—were detected in both mutant strains, albeit to different extents. Several stress-associated proteins were strongly upregulated. Immunohistochemical analyses further supported these findings: in the RX variant, microglial cells—the immune cells of the retina—displayed altered morphology, indicating the presence of neuroinflammatory processes.

Currently, CSNB2 can be diagnosed using genetic testing and electrophysiological methods. While genotyping can identify mutations in the CACNA1F gene encoding CaV1.4, it does not reveal how a specific mutation affects channel function or downstream molecular pathways. The RX and IT variants, for example, arise from mutations in the same gene, yet they result in fundamentally different channel dysfunctions and molecular consequences. Whereas the RX variant leads to extensive synaptic remodeling, the IT variant primarily affects cellular metabolism.

Molecular characterization therefore offers significant advantages over conventional electroretinography (ERG). While ERG typically reveals the characteristic “negative ERG” pattern associated with CSNB2, it cannot distinguish between different underlying channel mutations. In contrast, mutation-specific molecular signatures enable precise differentiation between disease mechanisms. This demonstrates that diagnosis must extend beyond the identification of a mutated gene: it is crucial to understand which specific channel variant is present and how it alters molecular function.

“This study provides the first comprehensive molecular atlas of the pathophysiological changes in CSNB2,” concludes Alexandra Koschak. “The finding that different mutations give rise to distinct molecular profiles is a decisive step toward the development of targeted, personalized therapies.”

The research team is now conducting functional follow-up studies to validate these results and plans to investigate whether the identified protein changes can also be detected in samples from human patients in the future.