Nonsense Mutation in USH2A Exon-13 Activates the Innate Immune Response in Müller Glial Cells

Pathological USH2A mutations cause Usher Syndrome type II, characterized by progres-sive retinitis pigmentosa and hearing and balance impairment. This study aims to inves-tigate the cellular mechanisms underlying USH2A-related retinal degeneration using hu-man induced pluripotent stem cell (hiPSC)-derived retinal organoids. The introduction of a homozygous nonsense mutation in the USH2A hotspot exon-13 resulted in normal photoreceptor development, but loss of ciliary localization of usherin long form B and its interacting proteins, ADGRV1 and whirlin. Notably, single-cell RNA sequencing revealed unexpected significant changes in Müller glial cells (MGCs), with disruptions in the translation, innate immune response, and endolysosomal system. These findings suggest that, while photoreceptor cells are mildly affected by the exon-13 USH2A mutation, MGCs exhibit major dysfunction, potentially contributing to the disease progression and there-fore shedding light on potential alternative therapeutic targets.