TBK1 Knockdown Alleviates Axonal Transport Deficits in Retinal Ganglion Cells Via mTORC1 Activation in a Retinal Damage Mouse Model

Purpose: Glaucoma is the leading cause of irreversible blindness worldwide and is characterized by progressive retinal ganglion cell (RGC) death and optic nerve degeneration. Axonal transport deficits are the earliest crucial pathophysiological changes in glaucoma. Genetic variation in the TANK-binding kinase 1 gene (TBK1) plays a role in the pathogenesis of glaucoma. This study was designed to investigate intrinsic factors underlying RGCs' damage and to explore the molecular mechanism of TBK1 involvement in glaucomatous pathogenesis.

Methods: We established a mouse model of acute ocular hypertension and used TBK1 conditional knockdown mice to investigate the role of TBK1 in glaucoma. CTB-Alexa 555 was utilized to evaluate axonal transport in mice. To observe the efficiency of gene knockdown, we performed immunofluorescence staining. Immunoblotting and immunoprecipitation assays were performed to examine protein‒protein colocalization. RT‒qPCR was performed to measure the mRNA levels of TBK1.

Results: In this study, we found that conditional TBK1 knockdown in RGCs resulted in increased axonal transport and protection against axonal degeneration. Through mechanistic studies, we found that TBK1 inhibited mTORC1 pathway activation by phosphorylating RAPTOR at Ser1189. Phosphorylation of RAPTOR at Ser1189 abrogated the interaction of RAPTOR with the Deubiquitinase USP9X, leading to an increase in RAPTOR ubiquitination and a subsequent decline in protein stabilization.

Conclusions: Our study identified a novel mechanism involving an interaction between the glaucoma risk gene TBK1 and the pivotal mTORC1 pathway, which may provide new therapeutic targets in glaucoma and other neurodegenerative diseases.