Identification of Unexpected Pathomechanisms Underlying the Human Usher Syndrome.

Abstract

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.