Mansouri Bobbak, Henne William M, Oomman Sowmini K, Bliss Richard, Attridge Jennifer, Finckbone VelvetLee, Zeitouni Tarek, Hoffman Trent, Bahr Ben A, Strahlendorf Howard K, Strahlendorf Jean C
Department of Physiology, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.
Eur J Pharmacol. 2007 Feb 28;557(2-3):106-14. doi: 10.1016/j.ejphar.2006.11.032. Epub 2006 Nov 22.
AMPA receptor-elicited excitotoxicity is manifested as both a type of programmed cell death termed dark cell degeneration and edematous necrosis, both of which are linked to increased intracellular Ca2+ concentration. The appearance of marked cytoskeletal changes in response to abusive AMPA receptor activation, coupled with increased intracellular Ca2+ concentration suggests activation of various destructive enzymes such as calpains, a family of Ca2+-dependent cysteine proteases. Since calpains and AMPA have been linked to both necrotic cell death and programmed cell death, we sought to determine the role of calpains in mediating both types of AMPA-mediated toxicity in Purkinje neurons of the cerebellum. These studies employed immunohistochemistry for cytoskeletal breakdown products of calpain activity coupled with confocal microscopy and pharmacological interventions with calpain and AMPA receptor antagonists. The present study identifies an early involvement of calpains in mediating AMPA-induced dark cell degeneration, but not edematous necrosis, based upon the effectiveness of AMPA to generate calpain-derived alpha-spectrin cleavage products in cerebellar Purkinje neurons that express dark cell degeneration, and the effectiveness of calpain antagonists, PD150606 and MDL28170, to attenuate AMPA-induced dark cell degeneration. Moreover, the AMPA receptor antagonist CNQX, a proven inhibitor of AMPA-elicited dark cell degeneration, also blocked AMPA-induced increases in alpha-spectrin, further suggesting interplay between abusive AMPA receptor activation, calpain activation and dark cell degeneration. Since AMPA-induced dark cell degeneration possesses morphological changes that resemble those that occur following brain ischemia in vivo, hypoglycemia, or extended seizure episodes, the involvement of calpains as mediators of cell death is potentially far reaching and has widespread therapeutic implications in numerous CNS disorders.
AMPA 受体引发的兴奋性毒性表现为一种程序性细胞死亡，称为暗细胞变性，以及水肿性坏死，这两种情况均与细胞内 Ca2+ 浓度升高有关。对过度的 AMPA 受体激活作出反应时出现明显的细胞骨架变化，再加上细胞内 Ca2+ 浓度升高，提示各种破坏性酶如钙蛋白酶（一类 Ca2+ 依赖性半胱氨酸蛋白酶）被激活。由于钙蛋白酶和 AMPA 与坏死性细胞死亡和程序性细胞死亡均有关联，我们试图确定钙蛋白酶在介导小脑浦肯野神经元中两种类型的 AMPA 介导的毒性中的作用。这些研究采用免疫组织化学检测钙蛋白酶活性的细胞骨架分解产物，结合共聚焦显微镜以及使用钙蛋白酶和 AMPA 受体拮抗剂进行药理学干预。本研究确定，基于 AMPA 在表达暗细胞变性的小脑浦肯野神经元中产生钙蛋白酶衍生的 α-血影蛋白裂解产物的有效性，以及钙蛋白酶拮抗剂 PD150606 和 MDL28170 减轻 AMPA 诱导的暗细胞变性的有效性，钙蛋白酶在介导 AMPA 诱导的暗细胞变性而非水肿性坏死中起早期作用。此外，AMPA 受体拮抗剂 CNQX（一种已证实的 AMPA 引发的暗细胞变性抑制剂）也阻断了 AMPA 诱导的 α-血影蛋白增加，进一步表明过度的 AMPA 受体激活、钙蛋白酶激活和暗细胞变性之间存在相互作用。由于 AMPA 诱导暗细胞变性所具有的形态学变化类似于体内脑缺血、低血糖或癫痫持续发作后出现的变化，钙蛋白酶作为细胞死亡介质的参与可能影响深远，并且在众多中枢神经系统疾病中具有广泛的治疗意义。
