State Key Laboratory of Medical Neurobiology and Institute of Brain Sciences, Fudan University, Shanghai, China.
Stroke. 2012 Nov;43(11):3063-70. doi: 10.1161/STROKEAHA.112.659656. Epub 2012 Aug 28.
Mononuclear phagocytes are highly plastic cells that assume diverse phenotypes in response to microenvironmental signals. The phenotype-specific roles of microglia/macrophages in ischemic brain injury are poorly understood. A comprehensive characterization of microglia/macrophage polarization after ischemia may advance our knowledge of poststroke damage/recovery.
Focal transient cerebral ischemia was induced in mice for 60 minutes; animals were euthanized at 1 to 14 days of reperfusion. Reverse-transcriptase polymerase chain reaction and immunohistochemical staining for M1 and M2 markers were performed to characterize phenotypic changes in brain cells, including microglia and infiltrating macrophages. In vitro experiments using a transwell system, a conditioned medium transfer system, or a coculture system allowing cell-to-cell contacts were used to further elucidate the effect of neuronal ischemia on microglia/macrophage polarization and, conversely, the effect of microglia/macrophage phenotype on the fate of ischemic neurons.
Local microglia and newly recruited macrophages assume the M2 phenotype at early stages of ischemic stroke but gradually transformed into the M1 phenotype in peri-infarct regions. In vitro experiments revealed that ischemic neurons prime microglial polarization toward M1 phenotype. M1-polarized microglia or M1-conditioned media exacerbated oxygen glucose deprivation-induced neuronal death. In contrast, maintaining the M2 phenotype of microglia protected neurons against oxygen glucose deprivation.
Our results suggest that microglia/macrophages respond dynamically to ischemic injury, experiencing an early "healthy" M2 phenotype, followed by a transition to a "sick" M1 phenotype. These dual and opposing roles of microglia/macrophages suggest that stroke therapies should be shifted from simply suppressing microglia/macrophage toward adjusting the balance between beneficial and detrimental microglia/macrophage responses.
单核吞噬细胞是高度可塑性的细胞，可根据微环境信号呈现出不同的表型。小胶质细胞/巨噬细胞在缺血性脑损伤中的表型特异性作用尚不清楚。对缺血后小胶质细胞/巨噬细胞极化的全面描述可能会增进我们对卒中后损伤/恢复的认识。
在小鼠中诱导局灶性短暂性脑缺血 60 分钟；动物在再灌注的 1 至 14 天处死。通过逆转录酶聚合酶链反应和免疫组织化学染色来检测 M1 和 M2 标志物，以对包括小胶质细胞和浸润巨噬细胞在内的脑细胞表型变化进行特征描述。使用 Transwell 系统、条件培养基转移系统或允许细胞间接触的共培养系统进行的体外实验，进一步阐明神经元缺血对小胶质细胞/巨噬细胞极化的影响，以及小胶质细胞/巨噬细胞表型对缺血性神经元命运的影响。
局部小胶质细胞和新募集的巨噬细胞在缺血性中风的早期阶段呈现 M2 表型，但在梗死周边区域逐渐转化为 M1 表型。体外实验表明，缺血性神经元使小胶质细胞向 M1 表型极化。M1 极化的小胶质细胞或 M1 条件培养基加剧了氧葡萄糖剥夺诱导的神经元死亡。相反，维持小胶质细胞的 M2 表型可保护神经元免受氧葡萄糖剥夺。
我们的研究结果表明，小胶质细胞/巨噬细胞对缺血性损伤做出动态反应，经历早期的“健康”M2 表型，随后转变为“病态”M1 表型。小胶质细胞/巨噬细胞的这种双重和相反作用表明，卒中治疗应从单纯抑制小胶质细胞/巨噬细胞转向调节有益和有害的小胶质细胞/巨噬细胞反应之间的平衡。
