Mount H T, Elkabes S, Dreyfus C F, Black I B
Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, USA.
J Neurochem. 1998 Mar;70(3):1045-53. doi: 10.1046/j.1471-4159.1998.70031045.x.
We have examined the role of the p75 neurotrophin receptor in survival-promoting effects of nerve growth factor (NGF) and neurotrophin-3 (NT-3) on cultured Purkinje cells. Previously, we showed that NGF promotes Purkinje cell survival in conjunction with (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD), an agonist of metabotropic excitatory amino acid receptors, whereas NT-3 by itself increases cell number. We now present evidence that p75 plays different roles in Purkinje cell responses to the two neurotrophins. A metabotropic receptor of the mGluR1 subtype may interact with p75 function, so as to regulate Purkinje cell responsiveness to neurotrophins. When cerebellar cultures were grown for 6 days in the presence of ACPD and a mutant form of NGF that does not bind to p75, no increase in Purkinje cell number was observed. Moreover, the survival-promoting effect of wild-type NGF and ACPD could be inhibited by a neutralizing antiserum to p75 or by a pyrazoloquinazolinone inhibitor of neurotrophin binding to p75. In contrast, the response to NT-3 was potentiated by anti-p75 treatment and by the quinazolinone. These data indicate the mediation of p75 in the trophic response to NGF-ACPD and a negative modulatory role of p75 in the action of NT-3. To probe the role of ACPD in the p75-dependent response to NGF, metabotropic receptor subtype-specific ligands were tested. The pattern of agonist specificity implicated the mGluR1 subtype, a receptor that is expressed at high levels by Purkinje cells and linked to activation of protein kinase C (PKC). Down-regulation or blockade of PKC abolished the response to NGF-ACPD. Consistent with the opposite roles of p75 in effects of the two neurotrophins, blockade of mGluR1 or PKC potentiated the survival response elicited by NT-3. In sum, our data suggest that afferent excitatory transmitters activate specific metabotropic receptors to elicit a p75-mediated action of NGF. NT-3 acts on Purkinje cells by a different mechanism that is not absolutely p75-dependent and that is reduced by neurotrophin access to p75 and metabotropic receptor activity.
我们研究了p75神经营养因子受体在神经生长因子（NGF）和神经营养因子-3（NT-3）对培养的浦肯野细胞的促存活作用中的作用。此前，我们发现NGF与代谢型兴奋性氨基酸受体激动剂（1S,3R）-1-氨基环戊烷-1,3-二羧酸（ACPD）协同促进浦肯野细胞存活，而NT-3自身可增加细胞数量。我们现在提供证据表明，p75在浦肯野细胞对这两种神经营养因子的反应中发挥不同作用。代谢型谷氨酸受体1（mGluR1）亚型的代谢型受体可能与p75功能相互作用，从而调节浦肯野细胞对神经营养因子的反应性。当小脑培养物在ACPD和一种不与p75结合的NGF突变体存在下培养6天时，未观察到浦肯野细胞数量增加。此外，野生型NGF和ACPD的促存活作用可被抗p75中和抗血清或神经营养因子与p75结合的吡唑并喹唑啉酮抑制剂抑制。相反，抗p75处理和喹唑啉酮可增强对NT-3的反应。这些数据表明p75介导了对NGF-ACPD的营养反应，并且p75在NT-3的作用中起负调节作用。为了探究ACPD在对NGF的p75依赖性反应中的作用，测试了代谢型受体亚型特异性配体。激动剂特异性模式表明是mGluR1亚型，该受体在浦肯野细胞中高水平表达并与蛋白激酶C（PKC）的激活相关。PKC的下调或阻断消除了对NGF-ACPD的反应。与p75在两种神经营养因子作用中的相反作用一致，mGluR1或PKC的阻断增强了NT-3引发的存活反应。总之，我们的数据表明传入兴奋性递质激活特定的代谢型受体以引发NGF的p75介导作用。NT-3通过不同机制作用于浦肯野细胞，该机制并非绝对依赖p75，并且神经营养因子与p75的结合及代谢型受体活性会降低这种作用。
