Acute Loss of TrkB Signaling Impairs the Survival of Mature Retinal Ganglion Cells and Retinal Function

Purpose: To determine whether acute loss of tropomyosin receptor kinase B (TrkB) signaling in mature retinal ganglion cells (RGCs) induces RGC degeneration and retinal functional impairment in the adult mouse retina. Methods: TrkB deletion was induced in adult TrkBflox/flox mice by intravitreal administration of adeno-associated virus serotype 2 (AAV2)-Cre. AAV2-Cre tropism was examined using tdTomato reporter mice and retinal cell markers. TrkB, RNA-binding protein with multiple splicing (RBPMS), calretinin, glutamine synthetase, and recoverin protein levels were assessed by western blotting. RGC survival was evaluated by RBPMS immunostaining of retinal flatmounts. Retinal function was assessed by analyzing the second-order kernel of multifocal electroretinography. Acute TrkB deletion was compared with developmental TrkB deletion in TrkBflox/flox;c-kit-Cre mice. Results: AAV2-Cre predominantly transduced RBPMS-positive RGCs, with little overlap with calretinin-positive amacrine cells, glutamine synthetase-positive Müller glia, or recoverin-positive photoreceptors. AAV2-Cre administration at 7 weeks of age reduced TrkB protein levels. RBPMS protein levels and RBPMS-positive RGC density were significantly decreased 5 weeks after AAV2-Cre administration at 12 weeks of age, whereas calretinin, glutamine synthetase, and recoverin protein levels were unchanged. Retinal responses of the second-order kernel were also significantly reduced. In contrast, RGC density was not significantly altered in TrkBflox/flox;c-kit-Cre mice at 12 weeks of age. Conclusions: Acute TrkB deletion in the adult retina induces RGC degeneration and impairs retinal function, whereas no significant reduction in RGC density was detected following developmental TrkB deletion at 12 weeks of age. These findings indicate that endogenous TrkB signaling is required for mature RGC maintenance and suggest that reduced TrkB signaling may contribute to glaucomatous RGC degeneration.