Usher syndrome (USH) is the most common form of hereditary deaf-blindness. There is no effective treatment for vision loss to date. Here we aimed to evaluate AAV-mediated ocular gene therapy for USH1C in pigs. USH1CR31∗ and wild type (WT) pigs were bilaterally subretinal injected with 200 μL of 1∗1011 vg/eye Anc80 AAV vectors expressing USH1C_a1 under the control of either a rod-specific human rhodopsin kinase (GRK1) promoter, a ubiquitous promoter (CAG), or vehicle control. Retinal structure and function were assessed by optical coherence tomography and electroretinography (ERG) at baseline and every six months post-injection. Decreased ERG amplitudes and reduction of total retinal thickness were observed in all groups following surgery. At 18 months post-injection, animals were sacrificed and treated and untreated retinal regions were analyzed by qRT-PCR, Western blots, pathohistological examinations, and immunohistochemistry. Both vectors resulted in high levels of USH1C_a1 transcript expression, but only slightly increased harmonin protein expression in USH1CR31∗ pigs. Across all treatment groups, chorioretinal atrophy (CRA) was observed, accompanied by reduced retinal thickness and increased GFAP expression.In conclusion, both vectors achieved efficient retinal transgene delivery in USH1CR31∗ pigs. However, CRA developed in all groups, even in vehicle-injected controls. The extensive retinal damage associated with CRA has likely masked a potentially beneficial therapeutic effect. For future translational development, optimization of dosing, and modifications in surgical technique will be of crucial importance.

Adhesion G protein-coupled receptors (aGPCRs) constitute a structurally and functionally distinct group within the superfamily of GPCRs. In 2015, the International Union of Pharmacology invited the Adhesion GPCR Consortium to publish a comprehensive review about aGPCRs and establish a unified nomenclature. Since then, substantial progress has been made in delineating the biological roles, molecular architecture, biochemical properties, expression profiles, ligand repertoire, and activation and signaling strategies of aGPCRs. Commensurate with these advances, their relevance to human pathophysiology has become increasingly apparent. In a coordinated effort, the Adhesion GPCR Consortium has reviewed recent progress in this field and provides a comprehensive assessment of the current understanding of aGPCR biology, including a focus on human and mammalian aGPCRs, their evolutionary origins, methodological approaches, and model systems for their investigation, as well as emerging approaches for their therapeutic targeting. SIGNIFICANCE STATEMENT: Adhesion G protein-coupled receptors are versatile cell-surface proteins that integrate structural, biochemical, and physiological functions, with major roles in health and disease. This review summarizes current knowledge of their molecular features, functions in diverse model systems, and emerging opportunities for therapeutic targeting, providing a comprehensive resource that connects basic biology with translational applications across multiple scientific disciplines.

Müller glial cells maintain retinal homeostasis and provide structural and metabolic support. The pig eye closely resembles the human eye in morphology and physiology, offering strong translational potential. Here, we present a protocol for isolating and culturing primary Müller glial cells from pig retina to study their function in health and disease. We describe steps for eyeball dissection, retinal isolation, photoreceptor cell depletion, and retinal digestion. We then detail procedures for the selection, culture, and characterization of Müller glial cells.

ADGRV1 is the largest member of adhesion G protein-coupled receptor (aGPCR) family. In the cell, aGPCRs serve in two major functions, namely in cell adhesion and signal transduction. Mutations in ADGRV1 were linked not only to Usher syndrome (USH), which causes deaf-blindness, but recently, also to epilepsy. While the USH defects are attributed to the loss of fiber links between membranes formed by the extracellular domain of ADGRV1, the pathomechanisms leading to epilepsy remain elusive to date. Here, we study the specific functions of ADGRV1 in astrocytes, where it is most highly expressed in the nervous system. Affinity proteomics demonstrated the interaction of ADGRV1 with proteins enriched in astrocytes. Different transcriptomes of USH2C patient-derived cells and Adgrv1-deficient mouse hippocampi compared to controls indicated dysregulation of cellular processes important in astrocyte function. Cell counts and morphometric analysis revealed reduced numbers and altered morphology of astrocytes in the hippocampus of Adgrv1-mutant mice. Monitoring the glutamate uptake in colorimetric assay and by live cell imaging of a genetic glutamate reporter consistently showed that glutamate uptake from the extracellular environment is significantly reduced in Adgrv1-deficent astrocytes. Expression analyses of key enzymes of the glutamate glutamine cycle and the glutamate metabolism indicated imbalanced glutamate homeostasis in Adgrv1-deficient astrocytes. Finally, we provide evidence that the supportive function of astrocytes in neuronal development also relies on ADGRV1 expression in astrocytes. Our data collectively provide first insights into the molecular pathophysiology associated with ADGRV1 defects in the brain, which may relate to the development of epilepsy associated with mutations in ADGRV1.

Primary cilia are antenna-like sensory organelles present on almost all eukaryotic cells. Their sensory capacity relies on receptors, in particular G-protein-coupled receptors (GPCRs) which localize to the ciliary membrane. Here we show that ADGRV1, a member of the GPCR subfamily of adhesion GPCRs, is part of a large protein network, interacting with numerous proteins of a comprehensive ciliary proteome. ADGRV1 is localized to the base of prototypic primary cilia in cultured cells and the modified primary cilia of retinal photoreceptors, where it interacts with TRiC/CCT chaperonins and the Bardet Biedl syndrome (BBS) chaperonin-like proteins. Knockdown of ADGRV1, CCT2 and 3, and BBS6 result in common ciliogenesis phenotypes, namely reduced ciliated cells combined with shorter primary cilia. In addition, the localization of ADGRV1 to primary cilia depends on the activity of a co-complex of TRiC/CCT chaperonins and the BBS chaperonin-like proteins. In the absence of components of the TRiC/CCT-BBS chaperonin co-complex, ADGRV1 is depleted from the base of the primary cilium and degraded via the proteasome. Defects in the TRiC/CCT-BBS chaperonin may lead to an overload of proteasomal degradation processes and imbalanced proteostasis. Dysfunction or absence of ADGRV1 from primary cilia may underly the pathophysiology of human Usher syndrome type 2 and epilepsy caused by mutations in ADGRV1.

Purpose: This study aimed to evaluate early-phase safety of subretinal application of AAVanc80.CAG.USH1Ca1 (OT_USH_101) in wild-type (WT) pigs, examining the effects of a vehicle control, low dose, and high dose. Methods: Twelve WT pigs (24 eyes) were divided into three groups: four pigs each received bilateral subretinal injections of either vehicle, low dose (3.3 × 1010 vector genomes [vg] per eye), or high dose (1.0 × 1011 vg per eye). Total retinal thickness (TRT) was evaluated using optical coherence tomography and retinal function was assessed with full-field electroretinography (ff-ERG) at baseline and two months post-surgery. After necropsy, retinal changes were examined through histopathology, and human USH1C_a1/harmonin expression was assessed by quantitative PCR (qPCR) and Western blotting. Results: OT_USH_101 led to high USH1C_a1 expression in WT pig retinas without significant TRT changes two months after subretinal injection. The qPCR revealed expression of the human USH1C_a1 transgene delivered by the adeno-associated virus vector. TRT changes were minimal across groups: vehicle (256 ± 21 to 243 ± 18 µm; P = 0.108), low dose (251 ± 32 to 258 ± 30 µm; P = 0.076), and high dose (242 ± 24 to 259 ± 28 µm; P = 0.590). The ff-ERG showed no significant changes in rod or cone responses. Histopathology indicated no severe retinal adverse effects in the vehicle and low dose groups. Conclusions: Early-phase clinical imaging, electrophysiology, and histopathological assessments indicated that subretinal administration of OT_USH_101 was well tolerated in the low-dose treatment arm. OT_USH_101 treatment resulted in high expression of human USH1C_a1. Although histopathological changes were not severe, more frequent changes were observed in the high-dose group.

Purpose:Transgenic pig models are a valuable model for preclinical testing of gene and cell therapies. Subretinal injection (SRI) is a common drug delivery method but has been associated with retinal thinning and atrophy. This study examined whether SRI volume correlates with retinal thinning in the pig eye and compared the effects of balanced salt solution (BSS) and adeno-associated virus (AAV) injections. Methods:Ten eyes from five transgenic pigs were included in this study. Eight eyes received escalating subretinal injection volumes (SRVs) (50, 100, 150, and 200 µL) of either BSS or AAV [5 × 1011 vg/mL], targeting the cone-rich area centralis of the pig eye. After six months, outer retinal thickness inside versus outside the bleb area (ΔORT) was quantified using optical coherence tomography (OCT). Histology was performed to confirm OCT findings. Results:Treated eyes showed clinically relevant (-21.5 ± 2.7 µm) outer retinal thinning inside the bleb area (P = 0.0001). A strong, statistically significant, linear correlation (R² = 0.73 P = 0.0068) was found between SRV and ORT loss. There was a 1 µm loss of ORT for every 9 µL of SRV. ORT loss was similar between AAV and BSS, except at the highest volume (200 µL, 1 × 1011 vg), where greater thinning occurred with AAV over BSS (Δ11 µm). Conclusions:This study supports the notion that SRV could be an independent factor in development of outer retinal thinning in the pig eye. Modifying surgical technique to favor the placement of multiple smaller blebs of <100 µL might mitigate retinal thinning because of volumetric stress and enhance the preclinical safety profile of investigational therapies.

Human Usher syndrome (USH) is the most common form of hereditary deaf-blindness, characterized by inner ear defects and late-onset vision loss. USH is a complex genetic disorder, clinically and genetically heterogeneous. To date, there is no treatment for the ocular phenotype of any USH subtype, as the underlying pathomechanisms of the disease in the eye are far from being understood. We aim to elucidate the function of USH proteins to gain insight into the pathomechanisms leading to the retinal phenotype in USH. Here, we focus on the USH1 proteins SANS (USH1G) and harmonin (USH1C), and the USH2C protein ADGRV1. Results from affinity capture approaches revealed putative interacting proteins to these USH proteins, indicative of diverse various unexpected molecular pathways and modules. Functional studies in both cellular and animal models confirmed the roles of SANS in the pre-mRNA splicing of other retinal genes, especially USH genes and harmonin as a suppressor of the canonical Wnt signaling. Additionally, ADGRV1 showed characteristics of a metabotropic mechanoreceptor regulating cell adhesions, Ca2+ homeostasis of the cell, and autophagy. The dysfunction of these pathways and processes may contribute to the development of USH and are novel potential targets for future therapies.

Mammalian cryptochrome 1 (CRY1) is a central player in the circadian transcription-translation feedback loop, crucial for maintaining a roughly 24-h rhythm. CRY1 was suggested to also function as a blue-light photoreceptor in humans and has been found to be expressed at the mRNA level in various cell types of the inner retina. However, attempts to detect CRY1 at the protein level in the human retina have remained unsuccessful so far. Using various C-terminal specific antibodies recognizing full-length CRY1 protein, we consistently detected selective labeling in the outer segments of short wavelength-sensitive (SWS1, "blue") cone photoreceptor cells across human, bonobo, and gorilla retinae. No other retinal cell types were stained, which is in contrast to what would be expected of a ubiquitous clock protein. Subcellular fractionation experiments in transfected HEK cells using a C-terminal specific antibody located full-length CRY1 in the cytosol and membrane fractions. Our findings indicate that human CRY1 has several different functions including at least one nonclock function. Our results also raise the likely possibility that several different versions of CRY1 exist in humans. We suggest that truncation of the C-terminal tail, maybe to different degrees, may affect the localization and function of human CRY1.

Adhesion GPCRs are structurally identified on the basis of a large extracellular region, similar to the Class B GPCR, but which is linked to the 7TM region by a GPCR autoproteolysis-inducing (GAIN) domain [15] containing a GPCR proteolysis site (GPS). The N-terminal extracellular region often shares structural homology with adhesive domains (e.g. cadherins, immunolobulin, lectins) facilitating inter- and matricellular interactions and leading to the term adhesion GPCR [120, 468]. Several receptors have been suggested to function as mechanosensors [355, 322, 442, 49, 327]. Cryo-EM structures of the 7-transmembrane domain of several adhesion GPCRs have been determined recently [326, 31, 450, 241, 334, 336, 490, 327]. The nomenclature of these receptors was revised in 2015 as recommended by NC-IUPHAR and the Adhesion GPCR Consortium [145].

The USH1G protein SANS is a small multifunctional scaffold protein. It is involved in several different cellular processes, such as intracellular transport, in the cytoplasm, or splicing of pre-mRNA, in the cell nucleus. Here, we aimed to gain insight into the regulation of the subcellular localization and the nuclear–cytoplasmic shuttling of SANS and its paralog ANKS4B, not yet reported in the nucleus. We identified karyopherins mediating the nuclear import and export by screening the nuclear interactome of SANS. Sequence analyses predicted in silico evolutionarily conserved nuclear localization sequences (NLSs) and nuclear export sequences (NESs) in SANS, but only NESs in ANKS4B, which are suitable for karyopherin binding. Quantifying the nuclear–cytoplasmic localization of wild-type SANS and NLS/NES mutants, we experimentally confirmed in silico predicted NLS and NES functioning in the nuclear–cytoplasmic shuttling in situ in cells. The comparison of SANS and its paralog ANKS4B revealed substantial differences in the interaction with the nuclear splicing protein PRPF31 and in their nuclear localization. Finally, our results on pathogenic USH1G/SANS mutants suggest that the loss of NLSs and NESs and thereby the ability to control nuclear–cytoplasmic shuttling is disease-relevant.

ADGRV1 is the largest member of adhesion G protein-coupled receptor (aGPCR) family. In the cell, aGPCRs have dual roles in cell adhesion and signal transduction. Mutations in ADGRV1 have been linked not only to Usher syndrome (USH), which causes deaf-blindness, but recently also to various forms of epilepsy. While the USH defects are attributed to the loss of fiber links between membranes formed by the extracellular domain of ADGRV1, the pathomechanisms leading to epilepsy remain elusive to date. Here, we study the specific functions of ADGRV1 in astrocytes where it is highest expressed in the nervous system. Affinity proteomics showed the interaction of ADRGV1 with proteins enriched in astrocytes. Dysregulations of cellular processes important in astrocyte function were indicated by the different transcriptomes of patient-derived cells and Adgrv1-deficent mouse hippocampi compared to appropriate controls. Alteration in morphology and reduced numbers of astrocytes in the hippocampus of Adgrv1-deficent mice. Monitoring the glutamate uptake in colorimetric assay and by live cell imaging of a genetic glutamate reporter consistently showed that glutamate uptake from the extracellular environment is significantly reduced in Adgrv1-deficent astrocytes. Expression analyses of key enzymes of the glutamate-glutamine cycle in astrocytes and the glutamate metabolism indicated imbalanced glutamate homeostasis in Adgrv1-deficient astrocytes. Finally, we provide evidence that the supportive function of astrocytes in neuronal development also relies on ADGRV1 expression in astrocytes. Our data collectively provides first insights into the molecular pathophysiology underlying the development of epilepsy associated with mutations in ADGRV1 . Highlights ![Figure][1]</img> ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes

Pre-mRNA splicing is an essential process orchestrated by the spliceosome, a dynamic complex assembled stepwise on pre-mRNA. We have previously identified that USH1G protein SANS regulates pre-mRNA splicing by mediating the intranuclear transfer of the spliceosomal U4/U6.U5 tri-snRNP complex. During this process, SANS interacts with the U4/U6 and U5 snRNP-specific proteins PRPF31 and PRPF6 and regulates splicing, which is disturbed by variants of USH1G/SANS causative for human Usher syndrome (USH), the most common form of hereditary deaf–blindness. Here, we aim to gain further insights into the molecular interaction of the splicing molecules PRPF31 and PRPF6 to the CENTn domain of SANS using fluorescence resonance energy transfer assays in cells and in silico deep learning-based protein structure predictions. This demonstrates that SANS directly binds via two distinct conserved regions of its CENTn to the two PRPFs. In addition, we provide evidence that these interactions occur sequentially and a conformational change of an intrinsically disordered region to a short α-helix of SANS CENTn2 is triggered by the binding of PRPF6. Furthermore, we find that pathogenic variants of USH1G/SANS perturb the binding of SANS to both PRPFs, implying a significance for the USH1G pathophysiology.

VLGR1/ADGRV1 (very large G protein-coupled receptor-1) is the largest known adhesion G protein-coupled receptor. Mutations in VLGR1/ADGRV1 cause Usher syndrome (USH), the most common form of hereditary deaf-blindness, and have been additionally linked to epilepsy. Although VLGR1/ADGRV1 is almost ubiquitously expressed, little is known about the subcellular function and signalling of the VLGR1 protein and thus about mechanisms underlying the development of diseases. Using affinity proteomics, we identified key components of autophagosomes as putative interacting proteins of VLGR1. In addition, whole transcriptome sequencing of the retinae of the Vlgr1/del7TM mouse model revealed altered expression profiles of gene-related autophagy. Monitoring autophagy by immunoblotting and immunocytochemistry of the LC3 and p62 as autophagy marker proteins revealed evoked autophagy in VLGR1-deficient hTERT-RPE1 cells and USH2C patient-derived fibroblasts. Our data demonstrate the molecular and functional interaction of VLGR1 with key components of the autophagy process and point to an essential role of VLGR1 in the regulation of autophagy at internal membranes. The close association of VLGR1 with autophagy helps to explain the pathomechanisms underlying human USH and epilepsy related to VLGR1 defects.

VLGR1/ADGRV1 (very large G protein-coupled receptor-1) is the largest adhesion G protein-coupled receptor aGPCRs. Mutations in VLGR1/ADGRV1 are associated with human Usher syndrome (USH), the most common form of deaf-blindness, and also with epilepsy in humans and in mice. Although VLGR1 is almost ubiquitously expressed in CNS and ocular and inner ear sensory cells. Little is known about the pathogenesis of the diseases related to VLGR1. We previously identified VLGR1 as a vital component of focal adhesions (FA) serving as a metabotropic mechanoreceptor that controls cell spreading and migration. FAs are highly dynamic and turnover frequently in response to internal and external signals. Here, we aimed to elucidate how VLGR1 participates in FA turnover. Nocodazole washout assays and live-cell imaging of RFP-paxillin consistently demonstrated that FA disassembly was not altered, de novo assembly of FA was significantly delayed in Vlgr1-deficient astrocytes indicating that VLGR1 is enrolled in the assembly of FAs. In FRAP experiments recovery rates were significantly reduced in Vlgr1-deficient FAs, indicating reduced turnover kinetics in VLGR1-deficient FAs. We showed that VLGR1 regulates cell migration by controlling the FA turnover during their assembly. From this, we expect novel insights into pathomechanisms related to pathogenic dysfunctions of VLGR1.

Human Usher syndrome (USH) is the most common form of hereditary combined deaf-blindness. USH is a complex genetic disorder, and the pathomechanisms underlying the disease are far from being understood, especially in the eye and retina. The USH1C gene encodes the scaffold protein harmonin which organizes protein networks due to binary interactions with other proteins, such as all USH proteins. Interestingly, only the retina and inner ear show a disease-related phenotype, although USH1C/harmonin is almost ubiquitously expressed in the human body and upregulated in colorectal cancer. We show that harmonin binds to β-catenin, the key effector of the canonical Wnt (cWnt) signaling pathway. We also demonstrate the interaction of the scaffold protein USH1C/harmonin with the stabilized acetylated β-catenin, especially in nuclei. In HEK293T cells, overexpression of USH1C/harmonin significantly reduced cWnt signaling, but a USH1C-R31* mutated form did not. Concordantly, we observed an increase in cWnt signaling in dermal fibroblasts derived from an USH1CR31*/R80Pfs*69 patient compared with healthy donor cells. RNAseq analysis reveals that both the expression of genes related to the cWnt signaling pathway and cWnt target genes were significantly altered in USH1C patient-derived fibroblasts compared to healthy donor cells. Finally, we show that the altered cWnt signaling was reverted in USH1C patient fibroblast cells by the application of Ataluren, a small molecule suitable to induce translational read-through of nonsense mutations, hereby restoring some USH1C expression. Our results demonstrate a cWnt signaling phenotype in USH establishing USH1C/harmonin as a suppressor of the cWnt/β-catenin pathway.