Department of Internal Medicine, Shanghai Children's Medical Center, Shanghai Jiaotong University School of Medicine, Shanghai, China.
PLoS One. 2013 Aug 7;8(8):e71553. doi: 10.1371/journal.pone.0071553. Print 2013.
Phenylketonuria (PKU), an autosomal recessive disorder of amino acid metabolism caused by mutations in the phenylalanine hydroxylase (PAH) gene, leads to childhood mental retardation by exposing neurons to cytotoxic levels of phenylalanine (Phe). A recent study showed that the mitochondria-mediated (intrinsic) apoptotic pathway is involved in Phe-induced apoptosis in cultured cortical neurons, but it is not known if the death receptor (extrinsic) apoptotic pathway and endoplasmic reticulum (ER) stress-associated apoptosis also contribute to neurodegeneration in PKU. To answer this question, we used specific inhibitors to block each apoptotic pathway in cortical neurons under neurotoxic levels of Phe. The caspase-8 inhibitor Z-IETD-FMK strongly attenuated apoptosis in Phe-treated neurons (0.9 mM, 18 h), suggesting involvement of the Fas receptor (FasR)-mediated cell death receptor pathway in Phe toxicity. In addition, Phe significantly increased cell surface Fas expression and formation of the Fas/FasL complex. Blocking Fas/FasL signaling using an anti-Fas antibody markedly inhibited apoptosis caused by Phe. In contrast, blocking the ER stress-induced cell death pathway with salubrinal had no effect on apoptosis in Phe-treated cortical neurons. These experiments demonstrate that the Fas death receptor pathway contributes to Phe-induced apoptosis and suggest that inhibition of the death receptor pathway may be a novel target for neuroprotection in PKU patients.
苯丙酮尿症（PKU）是一种常染色体隐性遗传的氨基酸代谢紊乱疾病，由苯丙氨酸羟化酶（PAH）基因突变引起，通过使神经元暴露于细胞毒性水平的苯丙氨酸（Phe）导致儿童智力迟钝。最近的一项研究表明，线粒体介导的（内在）凋亡途径参与了培养的皮质神经元中 Phe 诱导的凋亡，但尚不清楚死亡受体（外在）凋亡途径和内质网（ER）应激相关凋亡是否也有助于 PKU 中的神经退行性变。为了回答这个问题，我们在神经毒性水平的 Phe 下使用特定的抑制剂阻断皮质神经元中的每个凋亡途径。半胱天冬酶-8 抑制剂 Z-IETD-FMK 强烈减弱了 Phe 处理神经元中的凋亡（0.9 mM，18 h），表明 Fas 受体（FasR）介导的细胞死亡受体途径参与了 Phe 毒性。此外，Phe 显著增加了细胞表面 Fas 的表达和 Fas/FasL 复合物的形成。使用抗 Fas 抗体阻断 Fas/FasL 信号显著抑制了 Phe 引起的凋亡。相比之下，用 salubrinal 阻断 ER 应激诱导的细胞死亡途径对 Phe 处理的皮质神经元中的凋亡没有影响。这些实验表明 Fas 死亡受体途径参与了 Phe 诱导的凋亡，并表明抑制死亡受体途径可能是 PKU 患者神经保护的一个新靶点。
