The expression of whirlin and Cav1.3α1 is mutually independent in photoreceptors

AbstractWhirlin is a gene responsible for Usher syndrome type II (USH2) and congenital deafness. In photoreceptors, it organizes a protein complex through binding to proteins encoded by other USH2 genes, usherin (USH2A) and G-protein-coupled receptor 98 (GPR98). Recently, Cav1.3α1 (α1D) has been discovered to interact with whirlin in vitro and these two proteins are localized to the same subcellular compartments in photoreceptors. Accordingly, it is proposed that Cav1.3α1 is in the USH2 protein complex and that the USH2 protein complex is involved in regulating Ca2+ in photoreceptors. To test this hypothesis, we investigated the interdependence of Cav1.3α1 and whirlin expression in photoreceptors. We found that lack of Cav1.3α1 did not change the whirlin distribution or expression level in photoreceptors. In the retina, several Cav1.3α1 splice variants were found at the RNA level. Among them, the whirlin-interacting Cav1.3α1 long variant had no change in its protein expression level in the absence of whirlin. The localization of Cav1.3α1 in photoreceptors, published previously, cannot be confirmed. Therefore, the mutual independence of whirlin and Cav1.3α1 expressions in photoreceptors suggests that Cav1.3α1 may not be a key member of the USH2 protein complex at the periciliary membrane complex

Disruption of CFAP418 interaction with lipids causes widespread abnormal membrane-associated cellular processes in retinal degenerations

Syndromic ciliopathies and retinal degenerations are large heterogeneous groups of genetic diseases. Pathogenic variants in the CFAP418 gene may cause both disorders, and its protein sequence is evolutionarily conserved. However, the disease mechanism underlying CFAP418 mutations has not been explored. Here, we apply quantitative lipidomic, proteomic, and phosphoproteomic profiling and affinity purification coupled with mass spectrometry to address the molecular function of CFAP418 in retinas. We show that CFAP418 protein binds to lipid metabolism precursor phosphatidic acid (PA) and mitochondrion-specific lipid cardiolipin but does not form a tight and static complex with proteins. Loss of Cfap418 in mice disturbs membrane lipid homeostasis and membrane-protein association, which subsequently causes mitochondrial defects and membrane remodeling abnormalities across multiple vesicular trafficking pathways in photoreceptors, especially the endosomal sorting complexes required for transport (ESCRT) pathway. Ablation of Cfap418 also increases the activity of PA-binding protein kinase Cα in the retina. Overall, our results indicate that membrane lipid imbalance is a pathological mechanism underlying syndromic ciliopathies and retinal degenerations, which is associated with other known causative genes of these diseases

Adenylyl cyclase 6 plays a minor role in the mouse inner ear and retina.

Adenylyl cyclase 6 (AC6) synthesizes second messenger cAMP in G protein-coupled receptor (GPCR) signaling. In cochlear hair cells, AC6 distribution relies on an adhesion GPCR, ADGRV1, which is associated with Usher syndrome (USH), a condition of combined hearing and vision loss. ADGRV1 is a component of the USH type 2 (USH2) protein complex in hair cells and photoreceptors. However, the role of AC6 in the inner ear and retina has not been explored. Here, we found that AC6 distribution in hair cells depends on the USH2 protein complex integrity. Several known AC6 regulators and effectors, which were previously reported to participate in ADGRV1 signaling in vitro, are localized to the stereociliary compartments that overlap with AC6 distribution in hair cells. In young AC6 knockout (Adcy6-/-) mice, the activity of cAMP-dependent protein kinase, but not Akt kinase, is altered in cochleas, while both kinases are normal in vestibular organs. Adult Adcy6-/- mice however exhibit normal hearing function. AC6 is expressed in mouse retinas but rarely in photoreceptors. Adcy6-/- mice have slightly enhanced photopic but normal scotopic vision. Therefore, AC6 may participate in the ADGRV1 signaling in hair cells but AC6 is not essential for cochlear and retinal development and maintenance

Whirlin Replacement Restores the Formation of the USH2 Protein Complex in Whirlin Knockout Photoreceptors

Usher syndrome is a genetic disorder that manifests as both vision and hearing loss. The authors show that the AAV-mediated gene replacement of whirlin, the causative gene for a subtype of Usher syndrome, can rescue the primary defect in whirlin knockout mice

Adenylyl cyclase 6 plays a minor role in the mouse inner ear and retina.

Adenylyl cyclase 6 (AC6) synthesizes second messenger cAMP in G protein-coupled receptor (GPCR) signaling. In cochlear hair cells, AC6 distribution relies on an adhesion GPCR, ADGRV1, which is associated with Usher syndrome (USH), a condition of combined hearing and vision loss. ADGRV1 is a component of the USH type 2 (USH2) protein complex in hair cells and photoreceptors. However, the role of AC6 in the inner ear and retina has not been explored. Here, we found that AC6 distribution in hair cells depends on the USH2 protein complex integrity. Several known AC6 regulators and effectors, which were previously reported to participate in ADGRV1 signaling in vitro, are localized to the stereociliary compartments that overlap with AC6 distribution in hair cells. In young AC6 knockout (Adcy6-/-) mice, the activity of cAMP-dependent protein kinase, but not Akt kinase, is altered in cochleas, while both kinases are normal in vestibular organs. Adult Adcy6-/- mice however exhibit normal hearing function. AC6 is expressed in mouse retinas but rarely in photoreceptors. Adcy6-/- mice have slightly enhanced photopic but normal scotopic vision. Therefore, AC6 may participate in the ADGRV1 signaling in hair cells but AC6 is not essential for cochlear and retinal development and maintenance