HSP90α is specifically required for rod photoreceptor function and cannot be replaced by HSP90β

Abstract Heat Shock Protein 90 (HSP90) is a critical molecular chaperone that exists as two cytosolic paralogs, HSP90α and HSP90β, which share high sequence identity but may perform non-redundant functions in vivo . Loss of HSP90α in mice results in progressive rod photoreceptor degeneration despite normal retinal development and expression of HSP90β. To investigate whether HSP90β can substitute for HSP90α in photoreceptors, we generated adeno-associated virus (AAV) vectors expressing HA-tagged HSP90α or HSP90β under the control of a short rhodopsin promoter. In Hsp90α -/- mice, subretinal delivery of AAV- Hsp90aa1 (HSP90α) restored rod function and prevented photoreceptor degeneration, as measured by electroretinography (ERG). In contrast, AAV-mediated expression of HSP90β failed to rescue rod function despite comparable expression levels. Overexpression of either paralog in wild-type mice had no adverse effects on retinal function. These findings reveal a paralog-specific and intrinsic requirement for HSP90α in rod photoreceptors, demonstrating that HSP90β cannot compensate for its loss despite structural similarity.