Cerebral ischemia-reperfusion-induced autophagy protects against neuronal injury by mitochondrial clearance

Abstract

Cerebral ischemia-reperfusion (I-R) is a complex pathological process. Although autophagy can be evoked by ischemia, its involvement in the reperfusion phase after ischemia and its contribution to the fate of neurons remains largely unknown. In the present investigation, we found that autophagy was activated in the reperfusion phase, as revealed in both mice with middle cerebral artery occlusion and oxygen-glucose deprived cortical neurons in culture. Interestingly, in contrast to that in permanent ischemia, inhibition of autophagy (by 3-methyladenine, bafilomycin A 1, Atg7 knockdown or in atg5(-/-) MEF cells) in the reperfusion phase reinforced, rather than reduced, the brain and cell injury induced by I-R. Inhibition of autophagy either with 3-methyladenine or Atg7 knockdown enhanced the I-R-induced release of cytochrome c and the downstream activation of apoptosis. Moreover, MitoTracker Red-labeled neuronal mitochondria increasingly overlapped with GFP-LC3-labeled autophagosomes during reperfusion, suggesting the presence of mitophagy. The mitochondrial clearance in I-R was reversed by 3-methyladenine and Atg7 silencing, further suggesting that mitophagy underlies the neuroprotection by autophagy. In support, administration of the mitophagy inhibitor mdivi-1 in the reperfusion phase aggravated the ischemia-induced neuronal injury both in vivo and in vitro. PARK2 translocated to mitochondria during reperfusion and Park2 knockdown aggravated ischemia-induced neuronal cell death. In conclusion, the results indicated that autophagy plays different roles in cerebral ischemia and subsequent reperfusion. The protective role of autophagy during reperfusion may be attributable to mitophagy-related mitochondrial clearance and inhibition of downstream apoptosis. PARK2 may be involved in the mitophagy process.

Mitophagy-dependent necroptosis contributes to the pathogenesis of COPD

“…Mild oxidative stress specifically triggers mitophagy in a Drp1-dependent manner (45). Recent studies have applied Mdivi-1, a pharmacological inhibitor of Drp1, for the study of mitophagy (28)(29)(30)(31). Here, we confirmed that CSE regulated Drp1 in pulmonary epithelial cells.…”

“…We used Mdivi-1, a known inhibitor of mitochondrial fission, as a tool to study the relationships between mitophagy and mitochondrial dysfunction. Although Mdivi-1 is characterized as a pharmacological inhibitor of Drp1, recent studies have also implicated Mdivi-1 as an inhibitor of mitophagy (28)(29)(30)(31). We first tested the efficacy of this compound as an inhibitor of mitochondrial fission in response to CSE.…”

Role of the ubiquitin–proteasome system in brain ischemia: Friend or foe?

“…However, when lysosome inhibitors were applied, LC3-II protein levels failed to elevate indicating an autophagic-flux impairment in the hippocampus ). An upregulation in LC3-II protein levels was also observed during reperfusion after 1 h of transient MCAO, but in this case no changes in the autophagic-flux were observed in the penumbra region (Zhang et al, 2013a). This discrepancy may be due to the differences in the methodology used to induce brain ischemia (global vs focal ischemia) and or to intrinsic properties of the brain region analysed, which was different in the two sets of experiments.…”

“…This discrepancy may be due to the differences in the methodology used to induce brain ischemia (global vs focal ischemia) and or to intrinsic properties of the brain region analysed, which was different in the two sets of experiments. The class III phosphoinositide 3-kinase (PI3K) inhibitor 3-methyladenine (3-MA), a wellknown inhibitor of autophagosome expansion thus inhibiting autophagy, further increased the infarct volume after transient MCAO and reinforced apoptotic cell death 24 h after OGD in cultured cerebrocortical neurons (Zhang et al, 2013a). This increase in vulnerability to OGD in the presence of 3-MA was due to the defective mitochondrial clearance by the autophagic pathway thus failing in aborting apoptosis (Adhami et al, 2007;Zhang et al, 2013a).…”

“…The class III phosphoinositide 3-kinase (PI3K) inhibitor 3-methyladenine (3-MA), a wellknown inhibitor of autophagosome expansion thus inhibiting autophagy, further increased the infarct volume after transient MCAO and reinforced apoptotic cell death 24 h after OGD in cultured cerebrocortical neurons (Zhang et al, 2013a). This increase in vulnerability to OGD in the presence of 3-MA was due to the defective mitochondrial clearance by the autophagic pathway thus failing in aborting apoptosis (Adhami et al, 2007;Zhang et al, 2013a). At this point it is still not understood how lysosomes are involved in inducing apoptosis under ischemic conditions.…”