Medical Faculty, Institute of Biochemistry and Molecular Biology, University of Bonn, Bonn, Germany.
Medical Faculty, Core Facility Mass Spectrometry, Institute of Biochemistry and Molecular Biology, University of Bonn, Bonn, Germany.
J Biol Chem. 2021 Sep;297(3):101064. doi: 10.1016/j.jbc.2021.101064. Epub 2021 Aug 8.
An inherited deficiency of arylsulfatase A (ASA) causes the lysosomal storage disease metachromatic leukodystrophy (MLD) characterized by massive intralysosomal storage of the acidic glycosphingolipid sulfatide and progressive demyelination. Lyso-sulfatide, which differs from sulfatide by the lack of the N-linked fatty acid, also accumulates in MLD and is considered a key driver of pathology although its concentrations are far below sulfatide levels. However, the metabolic origin of lyso-sulfatide is unknown. We show here that ASA-deficient murine macrophages and microglial cells express an endo-N-deacylase that cleaves the N-linked fatty acid from sulfatide. An ASA-deficient astrocytoma cell line devoid of this activity was used to identify the enzyme by overexpressing 13 deacylases with potentially matching substrate specificities. Hydrolysis of sulfatide was detected only in cells overexpressing the enzyme fatty acid amide hydrolase (FAAH). A cell-free assay with recombinant FAAH confirmed the novel role of this enzyme in sulfatide hydrolysis. Consistent with the in vitro data, deletion of FAAH lowered lyso-sulfatide levels in a mouse model of MLD. Regardless of the established cytotoxicity of lyso-sulfatide and the anti-inflammatory effects of FAAH inhibition seen in mouse models of several neurological diseases, genetic inactivation of FAAH did not mitigate, but rather exacerbated the disease phenotype of MLD mice. This unexpected finding was reflected by worsening of rotarod performance, increase of anxiety-related exploratory activity, aggravation of peripheral neuropathy, and reduced life expectancy. Thus, we conclude that FAAH has a protective function in MLD and may represent a novel therapeutic target for treatment of this fatal condition.
芳基硫酸酯酶 A（ASA）的遗传性缺乏会导致溶酶体贮积病异染性脑白质营养不良（MLD），其特征是大量酸性糖脂硫酸脂在溶酶体内贮积和进行性脱髓鞘。与硫酸脂不同的是，缺少 N 连接脂肪酸的溶硫酸脂也在 MLD 中积累，尽管其浓度远低于硫酸脂水平，但被认为是病理学的关键驱动因素。然而，溶硫酸脂的代谢来源尚不清楚。我们在这里表明，ASA 缺乏的鼠巨噬细胞和小神经胶质细胞表达一种内 N-脱酰酶，可从硫酸脂中切割 N 连接脂肪酸。缺乏这种活性的 ASA 缺陷星形细胞瘤细胞系被用于通过过表达 13 种具有潜在匹配底物特异性的脱酰酶来鉴定该酶。仅在过表达脂肪酸酰胺水解酶（FAAH）的细胞中检测到硫酸脂的水解。用重组 FAAH 进行的无细胞测定证实了该酶在硫酸脂水解中的新作用。与体外数据一致，FAAH 的缺失降低了 MLD 小鼠模型中的溶硫酸脂水平。无论在几种神经疾病的小鼠模型中观察到溶硫酸脂的既定细胞毒性和 FAAH 抑制的抗炎作用如何，FAAH 的遗传失活都没有减轻，而是加剧了 MLD 小鼠的疾病表型。这一意外发现反映在旋转棒性能恶化、焦虑相关探索性活动增加、周围神经病恶化和预期寿命缩短。因此，我们得出结论，FAAH 在 MLD 中具有保护作用，可能成为治疗这种致命疾病的新治疗靶点。
