Bone Morphogenetic Protein Signal Pathway Mediates Isoflurane Postconditioning-induced Neuroprotection In Middle Cerebral Artery Occlusion Rat

Objective: To investigate the protection of different concentration isoflurane postconditioning after cerebral ischemia-reperfusion injury in rats and the role of the BMP in this neuroprotection.Methods: Adult male Sprague-Dawley rats(230- 260 g) were randomly assigned into five groups: Sham(S), Ischemia-reperfusion(I/R), Isoflurane postconditioning(1 MAC ISO, ISPOC1 group; 2 MAC ISO, ISPOC2 group; 3 MAC ISO, ISPOC3 group), Inhibitors + 1MAC ISPOC(LDN + ISO group; Noggin + ISO group; SB + ISO group), Inhibitors(LDN group; Noggin group; SB group). And subjected to right middle cerebral artery occlusion(MCAO) for 90 min expect sham group. ISPOC was induced 90 min after brain ischemia by exposing the animals to 1 MAC, 2 MAC or 3 MAC isoflurane + air for 60 min. In the Sham, I/R: animal were exposed to air 60 min after brain ischemia. Inhibitors were injected into rats’ Jugular vein at 30 min before MCAO surgery. Neurological deficit scores and cerebral infarct volumes were evaluated 24 h, respectively after reperfusion. Hematoxylin eosin stain and Nesson stain was used to observe the morphological changes of hippocampus. Apoptosis of CA1 cells in the hippocampus was detected by TUNEL method and propidium iodide(PI). Expression levels of BMP7, Smad1/5/8, and P38 MAPK were determined by Immunohistochemistry and Western bloting.Result:T he successful rate of the models was 79.2%. Postconditioning by isoflurane at 1 MAC and 2 MAC significantly decreased the neurobehavioral deficit score and infarct volume compared with the I/R group(P < 0.05), but no significantly difference in neurobehavioral deficit score and infarct volume was detected between the I/R and ISPOC3(P > 0.05). Degeneration and necrosis of neuron occurred, which exacerbated at 24 h, with hyperplasia of neuroglial cells and Nissl bodies loss in I/R group and ISPOC3 group. In ISPOC1 and ISPOC2 group, the cell damages were slighter than I/R group(P < 0.05). The numbers of TUNEL-positive cells and PI-positive cells in I/R group and ISPOC3 group were higher than those in the Sham group(P < 0.05). The 1 MAC and 2 MAC isoflurane postconditioning significantly reduced the cell apoptosis and death in the hippocampal CA1 region(P < 0.05). BMP7 protein gradually increased after I/R injury, with the highest values observed in the 1 MAC isoflurane postconditioning group(P < 0.05). After injecting the BMP7 blocker LDN193189, the expression of BMP7 and p-Smad2/3 decreased significantly, but the expression of p-P38 increased(P < 0.05). When the injection of LDN193189 was abolished, the expression of p-P38 increased, and the expression of BMP7 was decreased by the injection of SB203580 alone(P < 0.05).Conclusion:A fter MCAO 90 min, isoflurane postconditioning 60 min enhanced tolerance of cerebral ischemia and reperfusion injury, and when the 1 MAC isoflurane, the neurprotection was strongest. BMP7 signaling pathway involved in regulating the neuroprotective effect of isoflurane posttreatment. Isoflurane can upregulate the expression of BMP7 and downregulate that of p-P38 MAPK.