Section on Developmental Genetics, Program on Endocrinology and Molecular Genetics, Eunice Kennedy-Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland.
J Inherit Metab Dis. 2019 Sep;42(5):944-954. doi: 10.1002/jimd.12106. Epub 2019 May 14.
Mutations in at least 13 different genes (called CLNs) underlie various forms of neuronal ceroid lipofuscinoses (NCLs), a group of the most common neurodegenerative lysosomal storage diseases. While inactivating mutations in the CLN1 gene, encoding palmitoyl-protein thioesterases-1 (PPT1), cause infantile NCL (INCL), those in the CLN3 gene, encoding a protein of unknown function, underlie juvenile NCL (JNCL). PPT1 depalmitoylates S-palmitoylated proteins (constituents of ceroid) required for their degradation by lysosomal hydrolases and PPT1-deficiency causes lysosomal accumulation of autofluorescent ceroid leading to INCL. Because intracellular accumulation of ceroid is a characteristic of all NCLs, a common pathogenic link for these diseases has been suggested. It has been reported that CLN3-mutations suppress the exit of cation-independent mannose 6-phosphate receptor (CI-M6PR) from the trans Golgi network (TGN). Because CI-M6PR transports soluble proteins such as PPT1 from the TGN to the lysosome, we hypothesized that CLN3-mutations may cause lysosomal PPT1-insufficiency contributing to JNCL pathogenesis. Here, we report that the lysosomes in Cln3-mutant mice, which mimic JNCL, and those in cultured cells from JNCL patients, contain significantly reduced levels of Ppt1-protein and Ppt1-enzyme activity and progressively accumulate autofluorescent ceroid. Furthermore, in JNCL fibroblasts the V0a1 subunit of v-ATPase, which regulates lysosomal acidification, is mislocalized to the plasma membrane instead of its normal location on lysosomal membrane. This defect dysregulates lysosomal acidification, as we previously reported in Cln1 mice, which mimic INCL. Our findings uncover a previously unrecognized role of CLN3 in lysosomal homeostasis and suggest that CLN3-mutations causing lysosomal Ppt1-insuffiiciency may at least in part contribute to JNCL pathogenesis.
至少 13 种不同基因（称为 CLN）的突变导致各种形式的神经元蜡样脂褐质沉积症（NCL），这是最常见的神经退行性溶酶体贮积病之一。CLN1 基因（编码棕榈酰蛋白硫酯酶-1，PPT1）的失活突变导致婴儿型 NCL（INCL），而 CLN3 基因（编码一种未知功能的蛋白）的突变导致少年型 NCL（JNCL）。PPT1 去棕榈酰化 S-棕榈酰化蛋白（蜡样物质的组成部分），这些蛋白需要被溶酶体水解酶降解，而 PPT1 缺乏会导致溶酶体中堆积自发荧光的蜡样物质，从而导致 INCL。由于所有 NCL 都存在细胞内堆积的蜡样物质，因此这些疾病具有共同的致病联系。据报道，CLN3 突变会抑制阳离子非依赖性甘露糖 6-磷酸受体（CI-M6PR）从反高尔基网络（TGN）中输出。由于 CI-M6PR 将 PPT1 等可溶性蛋白从 TGN 运输到溶酶体，我们假设 CLN3 突变可能导致溶酶体 PPT1 不足，从而导致 JNCL 的发病机制。在这里，我们报告说，模仿 JNCL 的 Cln3 突变小鼠的溶酶体，以及来自 JNCL 患者的培养细胞中的溶酶体，其 Ppt1 蛋白和 Ppt1 酶活性水平显著降低，并逐渐积累自发荧光的蜡样物质。此外，在 JNCL 成纤维细胞中，V0a1 亚基的 v-ATPase 会错误定位到质膜而不是溶酶体膜上，这与我们之前在模仿 INCL 的 Cln1 小鼠中报道的情况相同。我们的发现揭示了 CLN3 在溶酶体平衡中的一个以前未被认识的作用，并表明导致溶酶体 Ppt1 不足的 CLN3 突变至少部分导致 JNCL 的发病机制。
