Cav1.4 congenital stationary night blindness is associated with an increased rate of proteasomal degradation.

Pathogenic, generally loss-of-function, variants in CACNA1F, encoding the Cav1.4α1 calcium channel, underlie congenital stationary night blindness type 2 (CSNB2), a rare inherited retinal disorder associated with visual disability. To establish the underlying pathomechanism, we investigated 10 clinically derived CACNA1F missense variants located across pore-forming domains, connecting loops, and the carboxy-tail domain of the Cav1.4α subunit. Homology modeling showed that all variants cause steric clashes; informatics analysis correctly predicted pathogenicity for 7/10 variants. In vitro analyses demonstrated that all variants cause a decrease in current, global expression, and protein stability and act through a loss-of-function mechanism and suggested that the mutant Cav1.4α proteins were degraded by the proteasome. We showed that the reduced current for these variants could be significantly increased through treatment with clinical proteasome inhibitors. In addition to facilitating clinical interpretation, these studies suggest that proteasomal inhibition represents an avenue of potential therapeutic intervention for CSNB2.

A Review of Genetic and Physiological Disease Mechanisms Associated With Cav1 Channels: Implications for Incomplete Congenital Stationary Night Blindness Treatment.

Calcium channels are crucial to a number of cellular functions. The high voltage-gated calcium channel family comprise four heteromeric channels (Cav1.1-1.4) that function in a similar manner, but that have distinct expression profiles. Three of the pore-forming α1 subunits are located on autosomes and the forth on the X chromosome, which has consequences for the type of pathogenic mutation and the disease mechanism associated with each gene. Mutations in this family of channels are associated with malignant hyperthermia (Cav1.1), various QT syndromes (Cav1.2), deafness (Cav1.3), and incomplete congenital stationary night blindness (iCSNB; Cav1.4). In this study we performed a bioinformatic analysis on reported mutations in all four Cav α1 subunits and correlated these with variant frequency in the general population, phenotype and the effect on channel conductance to produce a comprehensive composite Cav1 mutation analysis. We describe regions of mutation clustering, identify conserved residues that are mutated in multiple family members and regions likely to cause a loss- or gain-of-function in Cav1.4. Our research highlights that therapeutic treatments for each of the Cav1 channels will have to consider channel-specific mechanisms, especially for the treatment of X-linked iCSNB.

Small molecules restore the function of mutant CLC5 associated with Dent disease.

Dent disease type 1 is caused by mutations in the CLCN5 gene that encodes CLC5, a 2Cl- /H+ exchanger. The CLC5 mutants that have been functionally analysed constitute three major classes based on protein expression, cellular localization and channel function. We tested two small molecules, 4-phenylbutyrate (4PBA) and its analogue 2-naphthoxyacetic acid (2-NOAA), for their effect on mutant CLC5 function and expression by whole-cell patch-clamp and Western blot, respectively. The expression and function of non-Class I CLC5 mutants that have reduced function could be restored by either treatment. Cell viability was reduced in cells treated with 2-NOAA. 4PBA is a FDA-approved drug for the treatment of urea cycle disorders and offers a potential therapy for Dent disease.