Nox3 expression and function in retinal ganglion cells and Amacrine cells

NADPH oxidase 3 (Nox3), expressed in the endolymphatic duct and sac within the vestibule of the inner ear, is essential for otoconia formation. Mice with functionally deficient Nox3 exhibit a "head-tilt" phenotype. Recently, we reported that Nox3 expression in the cochlea is induced by aging, cisplatin treatment, and intense noise exposure, contributing to the primary source of reactive oxygen species (ROS) and causing acquired sensorineural hearing loss. However, its expression and function outside the inner ear remain poorly characterized. To explore novel Nox3 functions, we used Nox3-Cre;tdTomato mice, in which Cre recombinase (Cre) is knocked into the ATG site of Nox3, enabling visualization of Nox3 expression via tdTomato fluorescence. We identified Nox3 expression in retinal ganglion cells (RGCs) and GABAergic amacrine cells (ACs). The tdTomato-positive cells increased by 2 months of age and then plateaued in Nox3-Cre^+/-;tdTomato^+/+ (heterozygous knock-in [KI], hereafter HT Nox3-knockout [KO]) mice, while in Nox3-Cre^+/+;tdTomato^+/+ (homozygous KI, hereafter Nox3-KO) mice, the increase occurred by 12 months, suggesting that Nox3-derived ROS are toxic to RGCs and ACs. Additionally, Nox3-KO mice showed reduced a-, b-, and scotopic threshold response (STR)-waves in electroretinogram (ERG) compared to WT mice. Treatment with cisplatin, a well-known toxic agent for the retina and optic nerve, reduced tdTomato-positive cells in the retinae of 2-month-old HT Nox3-KO mice but not in Nox3-KO mice, compared to age-matched controls. Nox3-KO retinae developed normally. Thus, Nox3 is expressed in RGCs and ACs to regulate retinal function; however, excessive Nox3-derived ROS cause toxicity under pathological conditions, including aging.