缺血启动脑白质损伤新生大鼠室管膜下区和白质的胶质源性内在修复功能

摘要

目的 探讨缺血启动脑白质损伤新生大鼠室管膜下区(SVZ)和白质途径对损伤白质的内源性自我修复功能.方法 建立5日龄脑室周围白质软化(PVL)新生大鼠模型,随机分为PVL组和Sham组,光镜和电镜下评估脑白质病理和髓鞘形成,TUNEL法观察脑白质细胞凋亡,5-溴脱氧尿核苷(Brdu)示踪以及免疫荧光共标记技术观察SVZ和白质胶质源性祖细胞的激活、增殖、迁移和分化情况.结果 建模后第7和21天,PVL组大鼠脑室周围白质的凋亡细胞数较Sham组增加,差异均有统计学意义(P<0.05);PVL组的脑白质均呈现轻度或重度病变;PVL组脑白质内髓鞘形成数目以及髓鞘厚度亦低于Sham组,差异均有统计学意义(P均<0.01).PVL组在各时段的NG2+祖细胞和BrdU+(源自SVZ)以及GPR17+(源自白质)的O4+少突胶质细胞(OL)前体均较Sham组明显增多,差异均有统计学意义(P均<0.05);建模第7天,PVL组的GPR17+不成熟OL和成熟OL均未能检测到,代之为BrdU+不成熟OL和成熟OL;直至建模第21天,PVL组的不成熟OL和成熟OL-直呈低水平状态,低于Sham组(P均<0.05).结论 缺血可诱导PVL大鼠脑SVZ和白质这两条途径的胶质源性祖细胞激活和出现明显增殖,并沿OL系细胞分化和迁移至脑白质的损伤部位进行修复,但最终仅有极少量新生细胞能分化为未成熟和成熟OL.推测有限的内源性修复作用可能与不良的脑微环境密切相关.%Objective To explore an endogenous self-repair of cerebral white matter injury from both the subep-endymal ventricular zone (SVZ) and the white matter (WM) in neonatal rats with ischemic periventricular leukomalacia (PVL). Methods The five-day-old neonatal rats with PVL were randomly divided into the Sham group and the PVL group. The light and electron microscopes were used to assess the histopathological change and myelination of the WM, and the TUNEL staining was performed to detect the apoptotic cells of the WM. The proliferation, differentiation and migration of the glial progenitor cells from both SVZ and WM were respectively observed by 5-bromodeoxyuridine (Brdu) tracer and the double-label fluorescent immunoanalysis. Results At 7 and 21 days of PVL model established, it showed that the numbers of apoptostic cells in the WM in the PVL group increased significantly compared with those in the Sham group (all P<0.01). The WM of all PVL rats displayed either mild or severe histopathological changes. The number and the thickness of the my-elin sheaths in the PVL group were all obviously more reduced than those in the Sham group (all P<0.01). Furthermore, it was observed that the numbers of the NG2+ progenitor cells and the BrdLT (from SVZ) or GPR17+ (from WM) O4+ oligoden-drocytes (OL) precursor cells in the every time points in the PVL group were all significantly more than those of the Sham group (all P<0.05). At 7 days of PVL model established, the GRP17+/CNPase+ immature OLs and the GRP17+/MBP+ mature OLs had not been detected in PVL rats, which inteaded with Brdu+ immature and mature OLs. Until at 21 days of PVL model established, the numbers of immature and mature OLs were always at the low lever, which was significantly lower than those in the Sham group (all P＜0.05). Conclusions Ischemic WM injury may activate endogenous self-repair pathways, one from SVZ and other from WM. The activated SVZ- and WM-glial progenitor cells appear to proliferate markedly, differentiate along an oligodendroglial pathway, and migrate to the lesion for repair. However, only a few newly generated precursor cells can differentiate into the immature or mature OLs. It is speculated that the limited endogenous repair in WM is probably correlated to a poor cerebral micro environment.