To investigate the protective effect and optimal intervention time of remote ischemic post-conditioning (RIPostC) on ischemic penumbra of stroke rats, and preliminarily explore the brain protective mechanisms of RIPostC.

A rat middle cerebral artery occlusion (MCAO) model was constructed and reperfusion was performed after 2 hours of embolization. Thirty-six Sprague Dawley rats were divided into a sham operated group (Sham group), an ischemic/reperfusion group (I/R group), an immediate intervention after ischemia group (RIPostC-0 h group), an intervention after ischemia for 2 h group (RIPostC-2 h group), an intervention after ischemia for 6 h group (RIPostC-6 h group), and an intervention after ischemia for 12 h group (RIPostC-12 h group). RIPostC was performed 5 minutes each time with four cycles. After 24 hours of reperfusion, the neurological function was evaluated using the modified neurological severity score (mNSS), the cerebral infarction volume was evaluated by staining with 2,3,5-triphenyltetrazolium chloride (TTC), the brain water content was measured by a dry-wet weight method, the transient receptor potential mucolipin 1 (TRPML1) messenger RNA (mRNA) was detected by fluorescence quantitative PCR, and the protein expression of TRPML1, autophagy related protein Beclin1, microtubule-associated protein 1 light chain 3 (LC3), and p62 was detected by western-blotting.

Significant statistical differences were observed in the mNSS score, cerebral infarction volume, brain water content, LC3-II/LC3-I ratio, Beclin1, p62, and TRPML1 mRNA and protein of the six groups (F = 4.640, 9.968, 10.211, 83.414, 32.074, 8.234, 172.232, 27.462; all P < 0.05). Compared with the I/R group, the mNSS score, cerebral infarction volume, brain water content, and p62 protein were significantly reduced, and the LC3-II/LC3-I ratio, Beclin1, and TRPML1 mRNA and protein were significantly increased in all RIPostC groups (all P < 0.05). The RIPostC-0 h group also had a more significant increase in TRPML1 mRNA and protein than other RIPostC groups (all P < 0.05). In addition, the cerebral infarction volume in the RIPostC-0 h group, RIPostC-2 h group, and RIPostC-6 h group was decreased more significantly than that in the RIPostC-12 h group (all P < 0.05).

RIPostC can significantly reduce infarction volumes, alleviate brain edema, and improve neurological deficits, which should be implemented immediately after reperfusion. The neuroprotective effect of RIPostC may be achieved by upregulating TRPML1 to increase autophagy levels in the cerebral I/R area.