2.Depto. de Farmacología, Facultad de Medicina, Universidad Complutense, Avda. Complutense s/n, 28040 Madrid, Spain.
J Leukoc Biol. 2014 Apr;95(4):587-98. doi: 10.1189/jlb.0613326. Epub 2013 Dec 12.
PPARγ-achieved neuroprotection in experimental stroke has been explained by the inhibition of inflammatory genes, an action in which 5-LO, Alox5, is involved. In addition, PPARγ is known to promote the expression of CD36, a scavenger receptor that binds lipoproteins and mediates bacterial recognition and also phagocytosis. As phagocytic clearance of neutrophils is a requisite for resolution of the inflammatory response, PPARγ-induced CD36 expression might help to limit inflammatory tissue injury in stroke, an effect in which 5-LO might also be involved. Homogenates, sections, and cellular suspensions were prepared from brains of WT and Alox5(-/-) mice exposed to distal pMCAO. BMMs were obtained from Lys-M Cre(+) PPARγ(f/f) and Lys-M Cre(-) PPARγ(f/f) mice. Stereological counting of double-immunofluorescence-labeled brain sections and FACS analysis of cell suspensions was performed. In vivo and in vitro phagocytosis of neutrophils by microglia/macrophages was analyzed. PPARγ activation with RSG induced CD36 expression in resident microglia. This process was mediated by the 5-LO gene, which is induced in neurons by PPARγ activation and at least by one of its products--LXA4--which induced CD36 independently of PPARγ. Moreover, CD36 expression helped resolution of inflammation through phagocytosis, concomitantly to neuroprotection. Based on these findings, in addition to a direct modulation by PPARγ, we propose in brain a paracrine model by which products generated by neuronal 5-LO, such as LXA4, increase the microglial expression of CD36 and promote tissue repair in pathologies with an inflammatory component, such as stroke.
过氧化物酶体增殖物激活受体 γ（PPARγ）通过抑制炎症基因实现实验性中风的神经保护作用，这一作用涉及 5-脂氧合酶（5-LO）、Alox5。此外，PPARγ 已知可促进 CD36 的表达，CD36 是一种清道夫受体，可结合脂蛋白并介导细菌识别和吞噬作用。由于中性粒细胞的吞噬清除是炎症反应消退的必要条件，因此 PPARγ 诱导的 CD36 表达可能有助于限制中风中的炎症组织损伤，而 5-LO 也可能参与其中。从暴露于远端 pMCAO 的 WT 和 Alox5（-/-）小鼠的大脑中制备匀浆、切片和细胞悬浮液。从 Lys-M Cre（+）PPARγ（f/f）和 Lys-M Cre（-）PPARγ（f/f）小鼠中获得 BMM。对双免疫荧光标记的脑切片进行立体计数，并对细胞悬浮液进行 FACS 分析。分析小胶质细胞/巨噬细胞对中性粒细胞的体内和体外吞噬作用。RSG 激活 PPARγ 诱导驻留小胶质细胞中 CD36 的表达。这个过程是由 5-LO 基因介导的，PPARγ 激活诱导神经元中的 5-LO 基因表达，至少有一种其产物——LXA4——可独立于 PPARγ 诱导 CD36。此外，CD36 表达通过吞噬作用促进炎症消退，同时实现神经保护。基于这些发现，除了 PPARγ 的直接调节作用外，我们还在大脑中提出了一种旁分泌模型，即神经元 5-LO 产生的产物，如 LXA4，增加小胶质细胞中 CD36 的表达，并促进具有炎症成分的病理（如中风）中的组织修复。
