Department of Anatomy and Neurosciences, Neuroscience Campus Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
Neurobiol Dis. 2012 Mar;45(3):839-50. doi: 10.1016/j.nbd.2011.10.012. Epub 2011 Oct 25.
Parkinson's disease (PD) is characterized by accumulation of α-synuclein aggregates and degeneration of melanized, catecholaminergic neurons. The tissue transglutaminase (tTG) enzyme catalyzes molecular protein cross-linking. In PD, tTG levels are increased and cross-linking has been identified as an important factor in α-synuclein aggregation. In our quest to link tTGs distribution in the human brain to the hallmarks of PD pathology, we recently reported that catecholaminergic neurons in PD disease-affected brain areas display typical endoplasmic reticulum (ER) granules showing tTG immunoreactivity. In the present study, we set out to elucidate the nature of the interaction between tTG and the ER in PD pathogenesis, using retinoic-acid differentiated SH-SY5Y cells exposed to the PD-mimetic 1-methyl-4-phenylpyridinium (MPP(+)). Alike our observations in PD brain, MPP(+)-treated cells displayed typical TG-positive granules, that were also induced by other PD mimetics and by ER-stress inducing toxins. Additional immunocytochemical and biochemical investigation revealed that tTG is indeed associated to the ER, in particular at the cytoplasmic face of the ER. Upon MPP(+) exposure, additional recruitment of tTG toward the ER was found. In addition, we observed that MPP(+)-induced tTG activity results in transamidation of ER membrane proteins, like calnexin. Our data provide strong evidence for a, so far unrecognized, localization of tTG at the ER, at least in catecholaminergic neurons, and suggests that in PD activation of tTG may have a direct impact on ER function, in particular via post-translational modification of ER membrane proteins.
帕金森病（PD）的特征是α-突触核蛋白聚集和黑色素、儿茶酚胺能神经元变性。组织转谷氨酰胺酶（tTG）酶催化分子蛋白质交联。在 PD 中，tTG 水平升高，交联已被确定为α-突触核蛋白聚集的重要因素。在我们将 tTG 在人类大脑中的分布与 PD 病理学的特征联系起来的探索中，我们最近报道 PD 病变受影响的大脑区域中的儿茶酚胺能神经元显示出典型的内质网（ER）颗粒，具有 tTG 免疫反应性。在本研究中，我们着手阐明 tTG 和 ER 在 PD 发病机制中的相互作用的性质，使用视黄酸分化的 SH-SY5Y 细胞暴露于 PD 模拟物 1-甲基-4-苯基吡啶（MPP(+))。与我们在 PD 大脑中的观察结果一样，MPP(+)-处理的细胞显示出典型的 TG 阳性颗粒，这些颗粒也被其他 PD 模拟物和 ER 应激诱导毒素诱导。额外的免疫细胞化学和生化研究表明，tTG 确实与 ER 相关，特别是在 ER 的细胞质侧。在 MPP(+)暴露后，发现 tTG 向 ER 的额外募集。此外，我们观察到 MPP(+)-诱导的 tTG 活性导致 ER 膜蛋白的转酰胺化，如钙连蛋白。我们的数据为 tTG 在 ER 中的定位提供了强有力的证据，至少在儿茶酚胺能神经元中是这样，并且表明在 PD 中，tTG 的激活可能对 ER 功能具有直接影响，特别是通过 ER 膜蛋白的翻译后修饰。
