Abstract
Purpose :
Traumatic optic neuropathy (TON) is an injury to optic nerve (ON) leading to visual loss. Autophagy is vital in central nervous system injury for cell survival and for cell death, but the role of autophagy in TON is still uncertain. We chose two different autophagy activators, p62 siRNA and rapamycin, to test their protections for retinal ganglion cells (RGCs) in an animal model of ON crush injury.
Methods :
Adult male Wistar rats were received an intravitreal injection of autophagy inducers, p62 siRNA or rapamycin, after ON crush experiments. The level of autophagy-related markers was examined by immunoblotting analysis and immunostaining analysis. Two weeks after ON crush, the neuroprotective effects were evaluated by measuring Flash-VEP as well as RGC survival rate. The RGC apoptosis was measured by TUNEL assay. The macrophage infiltration in the ON was determined by counting the number of ED1-positive cells. Macrophage polarization was determined by q-PCR analysis. Blood –optic nerve barrier (BOB) disruption was evaluated by TEM. The role of mTORC2 activation in RGC protection was evaluated by counting viable RGCs.
Results :
Both P62 siRNA and rapamycin treatments induced autophagy, but only p62 siRNA treatment provided protective effects in visual function and RGCs survival by Flash-VEP and RGC morphometry respectively. Also, the number of macrophages infiltration at the ON lesion site was lower in the p62 siRNA-treated group. Moreover, the p62 siRNA treatment induced more M2 macrophage polarization than rapamycin. Rapamycin inhibited both mTORC1 and mTORC2 activation whereas p62 siRNA only inhibited mTORC1 activation and maintained the mTORC2 and Akt activation. Further, Inhibition of mTORC2-induced Akt activation resulted in BOB disruption by TEM. Interestingly, combined treatment with rapamycin and an mTORC2 activator, SC79, improved the RGCs survival.
Conclusions :
Our findings suggest that keeping mTORC2-Akt activation after autophagy induction is crucial for protecting RGCs from death as well as stabilization of BOB at ON in the traumatic optic nerve injury model.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.