Unbalanced Regulation of Sec22b and Ykt6 Blocks Autophagosome Axonal Retrograde Flux in Neuronal Ischemia--Reperfusion Injury.

Cerebral ischemia--reperfusion (I/R) injury in ischemic penumbra is accountable for poor outcome of ischemic stroke patients receiving recanalization therapy. Compelling evidence previously demonstrated a dual role of autophagy in stroke. This study aimed to understand the traits of autophagy in the ischemic penumbra and the potential mechanism that switches the dual role of autophagy. We found that autophagy induction by rapamycin and lithium carbonate performed before ischemia reduced neurologic deficits and infarction, while autophagy induction after reperfusion had the opposite effect in the male murine middle cerebral artery occlusion/reperfusion (MCAO/R) model, both of which were eliminated in mice lacking autophagy (Atg7^flox/flox; Nestin-Cre). Autophagic flux determination showed that reperfusion led to a blockage of axonal autophagosome retrograde transport in neurons, which then led to autophagic flux damage. Then, we found that I/R induced changes in the protein levels of Sec22b and Ykt6 in neurons, two autophagosome transport-related factors, in which Sec22b significantly increased and Ykt6 significantly decreased. In the absence of exogenous autophagy induction, Sec22b knock-down and Ykt6 overexpression significantly alleviated autophagic flux damage, infarction, and neurologic deficits in neurons or murine exposed to cerebral I/R in an autophagy-dependent manner. Furthermore, Sec22b knock-down and Ykt6 overexpression switched the outcome of rapamycin posttreatment from deterioration to neuroprotection. Thus, Sec22b and Ykt6 play key roles in neuronal autophagic flux, and modest regulation of Sec22b and Ykt6 may help to reverse the failure of targeting autophagy induction to improve the prognosis of ischemic stroke. [ABSTRACT FROM AUTHOR]