Department of Cell Biology and Physiology, University of North Carolina, Chapel Hill, United States.
Department of Pharmacology, University of North Carolina, Chapel Hill, United States.
Elife. 2019 Nov 4;8:e47789. doi: 10.7554/eLife.47789.
Alexander disease (AxD) is a fatal neurodegenerative disorder caused by mutations in glial fibrillary acidic protein (GFAP), which supports the structural integrity of astrocytes. Over 70 GFAP missense mutations cause AxD, but the mechanism linking different mutations to disease-relevant phenotypes remains unknown. We used AxD patient brain tissue and induced pluripotent stem cell (iPSC)-derived astrocytes to investigate the hypothesis that AxD-causing mutations perturb key post-translational modifications (PTMs) on GFAP. Our findings reveal selective phosphorylation of GFAP-Ser13 in patients who died young, independently of the mutation they carried. AxD iPSC-astrocytes accumulated pSer13-GFAP in cytoplasmic aggregates within deep nuclear invaginations, resembling the hallmark Rosenthal fibers observed in vivo. Ser13 phosphorylation facilitated GFAP aggregation and was associated with increased GFAP proteolysis by caspase-6. Furthermore, caspase-6 was selectively expressed in young AxD patients, and correlated with the presence of cleaved GFAP. We reveal a novel PTM signature linking different GFAP mutations in infantile AxD.
亚历山大病（AxD）是一种致命的神经退行性疾病，由神经胶质纤维酸性蛋白（GFAP）的突变引起，该蛋白支持星形胶质细胞的结构完整性。超过 70 种 GFAP 错义突变导致 AxD，但将不同突变与疾病相关表型联系起来的机制仍不清楚。我们使用 AxD 患者脑组织和诱导多能干细胞（iPSC）衍生的星形胶质细胞来研究假设，即 AxD 致病突变会破坏 GFAP 上的关键翻译后修饰（PTM）。我们的研究结果揭示了在年轻死亡的患者中，GFAP-Ser13 的选择性磷酸化，与他们携带的突变无关。AxD iPSC-星形胶质细胞在深核内陷的细胞质聚集体中积累 pSer13-GFAP，类似于体内观察到的特征性 Rosenthal 纤维。丝氨酸 13 磷酸化促进了 GFAP 的聚集，并与 caspase-6 介导的 GFAP 蛋白水解增加有关。此外，caspase-6 在年轻的 AxD 患者中选择性表达，并与 cleaved GFAP 的存在相关。我们揭示了一种新的 PTM 特征，将婴儿 AxD 中的不同 GFAP 突变联系起来。
