局灶性脑缺血再灌注大鼠过氧化物酶体增殖物激活受体亚型表达的改变

Altered peroxisome proliferator-activated receptor isotypes expression after focal cerebral ischemiareperfusion in rats

目的观察局灶性脑缺血再灌注大鼠过氧化物酶体增殖物激活受体（peroxisome proliferator-activated receptor, PPAR）各亚型（PPARα、PPARδ／β和PPARγ）表达的改变，并初步探讨PPAR改变的意义。方法健康雄性SD大鼠分为假手术组、模型组、治疗组。制作大鼠大脑中动脉阻塞2h再灌注22h模型（MCAO／R），治疗组于MCAO／R前1h给予PPAR全激动剂苯扎贝特。分别采用3％氯化三苯四唑（2,3,5-triphenyhetrazolium, TFC）染色法观察脑梗死体积；Western blot法和免疫组织化学法观察PPAR各亚型蛋白表达和分布的变化。结果与假手术组相比，脑缺血再灌注（1）引起梗死的平均体积为44．30％；（2）使脑组织PPAR各亚型表达均增加，分别增加了1．47、3．52和2．25倍，差别具有统计学意义（免疫组织化学检测t值分别为8．63、9．29和13．62，Western blot检测t值分别为8．16、9．24和6．43，均P=0．000）；（3）PPAR各亚型免疫阳性细胞增加主要表现在缺血侧半暗带区域，而非缺血侧（对侧）表达没有明显改变。与模型组相比，苯扎贝特能够：（1）显著降低脑梗死体积，平均减少54．36％，差异具有统计学意义（t=7．69，P=0．000）；（2）进一步增加PPAR各亚型表达，分别增加了95．45％、183．47％、224．61％，差异具有统计学意义（免疫组织化学检测t值分别为7．36、5．64和10．50，Western blot检测t值分别为13．02、17．52和13．64，均P=0．000）；（3）不但使缺血侧PPAR免疫阳性细胞增加，而且使非缺血侧增加。结论局灶性脑缺血再灌注损伤大鼠脑组织PPARα、PPARδ／β和PPARγ表达增加，可能是脑组织的一种代偿性神经保护反应。

Objective To examine peroxisome proliferator-activated receptor （PPAR） isotypes （PPARα, PPARδ/β and PPARγ） expression in rats after cerebral ischemia-repeffusion （I/R） and I/R in combination with pan-PPAR co-agonist, and to explore the effect of altered PPAR expressions in brain injury. Methods Adult male SD rats underwent 2-hour middle cerebral artery occlusion followed by a 22- hour repcrfusion （MCAO/R）. One hour before the operation, the mice received either vehicle （I/R-group） or bezafibrate （6 mg/kg） treatment （Beza-group）. TTC （2,3,5-triphenyltetrazolium） staining was adopted to determine the volume of cerebral infarction. The expressions of PPAR isotypes were characterized by immunohistochemical staining （IHC） and Western blot. Furthermore, the spatial localizations of PPAR isotypes were analyzed with respect to ipsilateral ischemic （core and penumbra） and contralateral nonischemic hemisphere. Results Compared with sham-group, 2 h ischemia and 22 h reperfusion caused （ 1 ） 44. 30% infarct volume in average in ipsilateral hemisphere ; （ 2 ） Marked increased PPAR expression in all three isotypes evaluated by IHC （ t = 8.63, 9.29, 13.62, P = 0. 000） and Western blot （ PPARα by 1.47- fold, PPARδ/βby 3.52-fold, and PPARγby 2. 25-fold ; t = 8. 16, 9. 24, 6.43 ; P = 0. 000） ; （ 3 ） Marked increase in PPAR staining in the ischemia-affeeted region of the ipsilateral MCA territory, in particular in the ischemic penumbra. No detectable increase in number and intensity was observed in the contralateral （nonisehemic） hemisphere. The pan-PPAR co-agonists bezafibrate can activate all 3 subtypes of the receptor. Compared with I/R-group, （1）Ischemic size in bezafibrate-group rats was significantly decreased than that in I/R group （20. 22 ±6. 18 versus 44. 30 ±4. 54, t =7.69, P =0. 000）. （2） Bezafibrate treatment further increased the alterations of all PPAR expression, which were induced by the exoosure of I/R. as determined by IHC （t =7. 36, 5.64, 10. 50, and P =0. 000） and Western blot （PPARa by 95. 45%, PPARδ/βby 183.47%, and PPARγ by 224.61%; t = 13.02, 17.52, 13.64, and P = 0.000）. （3） The PPAR immunoreaetive expressions were observed in not only the ipsilateral but the eontralateral hemisphere of bezafibrate-group. Conclusions Cerebral I/R injury increases the expression of all three PPAR isotypes and activation of PPAR by pan-PPAR agonist not only reduces ischemie size but further enhances the alteration of PPAR. The up-regulation of PPAR expression may represent the compensatory self-protection against brain I/R injury.