Roles of endothelin receptors in astrocytic activation on brain pathologies

1.内皮素诱导的神经营养因子的产生：内皮素（ET）刺激培养的大鼠星形胶质细胞中的GDNF和BDNF（众所周知的神经营养因子）的产生。ET诱导的GDNF产生可通过清除细胞内Ca^<2+>和抑制ERK信号通路而被抑制。NFkB抑制剂和糖皮质激素预处理对ET诱导的GDNF产生无影响，但可抑制H_2O_2诱导的GDNF产生。脑室连续灌注7 d可使海马和纹状体GDNF和BDNF表达增加。免疫组化结果表明，这些神经营养因子是由星形胶质细胞产生的。提示星形胶质细胞ET受体的激活可能是神经营养药物刺激神经营养因子的靶点之一.内皮素诱导的星形胶质细胞增殖：通过聚焦粘着斑激酶（FAK）（一种与粘着斑相关的酪氨酸激酶）的作用探讨内皮素诱导的星形胶质细胞增殖的机制。ET刺激星形胶质细胞中FAK和ERK的磷酸化。细胞松弛素D抑制ET诱导的FAK磷酸化，但不抑制ERK磷酸化。细胞松弛素D可减少ET-1诱导的BrdU掺入。用野生型FAK瞬时转染后，星形胶质细胞BrdU掺入增加。ET-1对显性阴性FAK突变体转染的星形胶质细胞BrdU掺入的影响减弱。ET-1可增加星形胶质细胞cyclin D1和D3蛋白的表达。转染野生型FAK可增加星形胶质细胞中cyclin D3的表达，而cyclin D1的表达不受影响。ET诱导的细胞周期蛋白D3表达的增加，而不是D1，被显性负性FAK突变体阻止。这些结果表明FAK参与了由α-淀粉样蛋白诱导的星形胶质细胞增殖。

1. Endothelin-induced production of neurotrophic factors : Endothelin (ET) stimulated production of GDNF and BDNF, well-known neurotrophic factors, in rat cultured astorcytes. ET-induced GDNF production was inhibited by removal of intracellular Ca^<2+> and inhibition of ERK signal pathway. An inhibitor of NFkB (pyrrolidin dithiocarbamate) and pre-treatment with glucocorticoid had no effect on the ET-induced GDNF production, while GDNF production induced by H_2O_2 was prevented by them. Continuousinfusion of ETs into cerebral ventricle for 7 days increased GDNF and BDNF in hippocampus and striatum, respectively. Immunohistechemical examinations showed that these neurotrophic factors were produced by astrocytes. These findings suggest that activation of astrocytic ET receptors can be one target of neurotrophic drugs to stimulate neurotrophic factors.2. Endothelin-induced astrocytic proliferation : The mechanisms of ET-indeuced astrocytic proliferation by focusing roles of focal adhesion kinase (FAK), a tyrosine kinase associated with focal adhesions. ET stimulated phosphorylation of both FAK and ERK in astrocytes. Cytochalasin D inhibited ET-induced phosphorylation of FAK, but not that of ERK. Cytochalasin D reduced the incorporation of bromdeoxyuridine (BrdU) induced by ET-1. A transient transfection with wild-type FAK was followed byan increase in astrocytic BrdU incorporation. The effect of ET-1 on BrdU incorporation was diminished in astrocytes transfected with dominant-negative FAK mutants. ET-1 increased expression of cyclin D1 and D3 proteins in cultured astrocytes. Transfection with wild-type FAK increased expression of cyclin D3 in astrocytes, while that of cyclin D1 was not affected. The ET-induced increase in cyclin D3 expression, but not D1, was prevented by dominant-negative FAK mutants. These results suggest an involvement of FAK in astrocytic proliferation induced by ETs.