Two activation states of reactive astrocytes termed A1 and A2 subtypes emerge at the lesion sites following spinal cord injury (SCI). A1 astrocytes are known to be neurotoxic that participate in neuropathogenesis, whereas A2 astrocytes have been assigned the neuroprotective activity. Heat shock transcription factor 1 (HSF1) plays roles in protecting cells from stress-induced apoptosis and in controlling inflammatory activation. It is unknown whether HSF1 is involved in suppressing the conversion of A1 astrocytes following SCI. A contusion model of the rat spinal cord was established, and the correlations between HSF1 expression and onset of A1 and A2 astrocytes were assayed by Western blot and immunohistochemistry. 17-AAG, the agonist of HSF1, was employed to treat the primary cultured astrocytes following a challenge by an A1-astrocyte-conditioned medium (ACM) containing 3 ng/ml of IL-1α, 30 ng/ml of TNF-α, and 400 ng/ml of C1q for induction of the A1 subtype. The effects of 17-AAG on the phenotype conversion of astrocytes, as well as underlying signal pathways, were examined by Western blot or immunohistochemistry. The protein levels of HSF1 were significantly increased at 4 days and 7 days following rat SCI, showing colocalization with astrocytes. Meanwhile, C3-positive A1 astrocytes were observed to accumulate at lesion sites with a peak at 1 day and 4 days. Distinctively, the S100A10-positive A2 subtype reached its peak at 4 days and 7 days. Incubation of the primary astrocytes with ACM markedly induced the conversion of the A1 phenotype, whereas an addition of 17-AAG significantly suppressed such inducible effects without conversion of the A2 subtype. Activation of HSF1 remarkably inhibited the activities of MAPKs and NFκB, which was responsible for the regulation of C3 expression. Administration of 17-AAG at the lesion sites of rats was able to reduce the accumulation of A1 astrocytes. Collectively, these data reveal a novel mechanism of astrocyte phenotype conversion following SCI, and HSF1 plays key roles in suppressing excessive increase of neurotoxic A1 astrocytes.

中文翻译：

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HSF1参与抑制大鼠脊髓损伤后星形胶质细胞的A1表型转换

称为 A1 和 A2 亚型的反应性星形胶质细胞的两种激活状态出现在脊髓损伤 (SCI) 后的病变部位。已知 A1 星形胶质细胞具有参与神经发病机制的神经毒性，而 A2 星形胶质细胞已被赋予神经保护活性。热休克转录因子 1 (HSF1) 在保护细胞免受应激诱导的细胞凋亡和控制炎症激活方面发挥作用。尚不清楚 HSF1 是否参与抑制 SCI 后 A1 星形胶质细胞的转化。建立大鼠脊髓挫伤模型，采用Western blot和免疫组化检测HSF1表达与A1、A2星形胶质细胞发病的相关性。17-AAG，HSF1 的激动剂，用于治疗原代培养的星形胶质细胞，经过 A1 星形胶质细胞条件培养基 (ACM) 的攻击，该培养基含有 3 ng/ml IL-1α、30 ng/ml TNF-α 和 400 ng/ml C1q 用于诱导A1 亚型。通过蛋白质印迹或免疫组织化学检查 17-AAG 对星形胶质细胞表型转换以及潜在信号通路的影响。HSF1 蛋白水平在大鼠 SCI 后 4 天和 7 天显着增加，显示与星形胶质细胞共定位。同时，观察到C3阳性A1星形胶质细胞在病变部位聚集，在第1天和第4天达到高峰。不同的是，S100A10 阳性 A2 亚型在第 4 天和第 7 天达到高峰。用 ACM 孵育原代星形胶质细胞显着诱导了 A1 表型的转变，而添加 17-AAG 显着抑制了这种诱导效应，而没有转换 A2 亚型。HSF1的激活显着抑制了负责调节C3表达的MAPKs和NFκB的活性。在大鼠的病变部位施用 17-AAG 能够减少 A1 星形胶质细胞的积累。总的来说，这些数据揭示了 SCI 后星形胶质细胞表型转换的新机制，HSF1 在抑制神经毒性 A1 星形胶质细胞过度增加中起关键作用。