Induction of ischemic tolerance as a promising treatment against diabetic retinopathy

Protection of retinal ganglion cells against optic nerve injury by induction of ischemic preconditioning

AIM

To explore if ischemic preconditioning (IPC) can enhance the survival of retinal ganglion cells (RGCs) after optic nerve axotomy.

METHODS

Twenty-four hours prior to retinal ischemia 60min or axotomy, IPC was applied for ten minutes in groups of (n=72) animals. The survival of RGCs, the cellular expression of heat shock protein 27 (HSP27) and heat shock protein 70 (HSP70) and the numbers of retinal microglia in the different groups were quantified at 7 and 14d post-injury. The cellular expression of HSP27 and HSP70 and changes in the numbers of retinal microglia were quantified to detect the possible mechanism of the protection of the IPC.

RESULTS

Ten minutes of IPC promoted RGC survival in both the optic nerve injury (IPC-ONT) and the retinal ischemia 60min (IPC-IR60) groups, examined at 7d and 14d post-injury. Microglial proliferation showed little correlation with the extent of benefit effects of IPC on the rescue of RGCs. The number of HSP27-positive RGCs was significantly higher in the IPC-ONT group than in the sham IPC-ONT group, although the percentage of HSP27-positive RGCs did not significantly differ between groups. For the IPC-IR60 group, neither the number nor the percentage of the HSP27-positive RGCs differed significantly between the IPC and the sham-operated groups. The number of HSP70-positive RGCs was significantly higher for both the IPC-ONT and the IPC-IR60 experimental groups, but the percentages did not differ.

CONCLUSION

The induction of IPC enhances the survival of RGCs against both axotomy and retinal ischemia.

mTOR inhibition attenuates glucose deprivation-induced death in photoreceptors via suppressing a mitochondria-dependent apoptotic pathway

Acute energy depletion contributes to ischemia-induced retinal neuronal injury, causing photoreceptor death and subsequent vision loss. The mTOR pathway is a crucial cellular signaling hub modulating RNA transcription, protein synthesis, and metabolic balance. Thus, we mimicked acute energy depletion in photoreceptor cells (661W cells) with glucose deprivation and investigated neuroprotective mechanisms of mTOR inhibition. We found that treatment with rapamycin, an mTOR-specific inhibitor, reduced intracellular ROS, maintained the mitochondrial membrane potential and restored mitochondrial dysfunction. In addition, inhibiting the mTOR signal suppressed DRP1 translocation to the mitochondria, pro-apoptotic mitochondrial protein release, and caspase 3 activation when glucose was deprived. Inhibition of mTOR offers significant neuroprotection against glucose deprivation-induced injury in 661W cells, chiefly via suppressing mitochondrial-dependent pathways. These observations may shed light on treating ischemia-related retinal diseases.