Unconjugated
The mammalian target of rapamycin (mTOR) pathway is a crucial cellular signaling hub, which integrates internal and external cues to modulate the cell cycle, protein synthesis and metabolism. The present study hypothesized that inhibiting mTOR signaling may induce cells to enter lower and more stable bioenergetic states, in which neurons have greater resistance to various insults. Neurotrophin withdrawal from photoreceptor cells (661W cells) was mimicked using serum deprivation, and the neuroprotective mechanisms were studied following suppression of the mTOR pathway. Treatment with an mTOR specific inhibitor, rapamycin, reduced intracellular levels of reactive oxygen species, suppressed oxidative stress, and attenuated mitochondrial dysfunction. In addition, inhibiting mTOR signaling induced a G2/M cell cycle arrest, thus providing an opportunity to repair damaged DNA and block the cell death cascade. These results suggested that inhibition of mTOR had a neuroprotective effect on serum‑deprived 661W cells. In conclusion, the mTOR pathway is a critical molecular signal for cell cycle regulation and energy metabolism, and inhibiting the mTOR pathway may attenuate neurotrophin withdrawal‑induced damage. These observations may provide evidence for the treatment of retinal degenerative disease, since inducing neurons into a lower and more stable bioenergetic state by blocking mTOR signaling may slow the progression of neurodegenerative diseases.
The NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway plays a critical role in protecting against oxidative stress in brain ischemia and reperfusion injury. Glycogen synthase kinase 3β (GSK-3β) may play a critical role in regulating Nrf2 in a Kelch-like ECH-associated protein 1 (Keap1)-independent manner. However, the relationship between GSK-3β and Nrf2 in brain ischemia and reperfusion injury is not clear. In this study, we explored the mechanisms through which GSK-3β regulates Nrf2 and Nrf-2/ARE pathways in vitro and in vivo. We used oxygen and glucose deprivation/reoxygenation (OGD/R) in primary cultured cortical neurons and a middle cerebral artery occlusion-reperfusion (MCAO/R) rat model to mimic ischemic insult. In this study, GSK-3β siRNA and inhibitors (SB216763 and LiCl) were used to inhibit GSK-3β in vitro and in vivo. After inhibiting GSK-3β, expression of total and nuclear Nrf2, Nrf2-ARE binding activity, and expression of Nrf2/ARE pathway-driven genes HO-1 and NQO-1 increased. Overexpression of GSK-3β yielded opposite results. These results suggest that GSK-3β downregulates Nrf2 and the Nrf2/ARE pathway in brain ischemia and reperfusion injury. GSK-3β may be an endogenous antioxidant relevant protein, and may represent a new therapeutic target in treatment of ischemia and reperfusion injury.