Characterization of TMEM251 that causes a new type of severe lysosome storage disease

溶酶体是回收通过内吞作用递送的物质的重要细胞器， 自噬影响溶酶体的先天性遗传缺陷导致衰弱和致命的溶酶体 贮藏性疾病（LSD，人类约70）。一种严重的LSD形式，I细胞疾病，导致 骨骼发育不良，身材矮小，心脏肥大，在头十年死亡。由它造成 GlcNAc-1-磷酸转移酶（GNPT）中的突变，其在顺式- 高尔基体用分选信号甘露糖-6-磷酸（M6 P）标记溶酶体酶。M6 P缺失 导致大多数溶酶体酶的分泌和缺陷溶酶体。2021年初，A 本文报道了一种类似于I细胞病的新型严重LSD。患者会出现骨骼 发育不良、身材矮小、心脏缺陷，有些人在幼儿期就夭折了。它们的溶酶体 酶也被分泌到血浆中。它是由TMEM 251突变引起的，但 TMEM 251的细胞功能和疾病的分子机制仍有待进一步研究。 处理。 在全基因组CRISPR敲除筛选中， 在人类溶酶体膜蛋白中，我们独立地发现TMEM 251是必需的 对溶酶体功能的影响。敲除TM 251导致溶酶体功能障碍，因为分泌 未加工的溶酶体酶因此，溶酶体积累大量的 未消化的物质，如自噬体和内吞囊泡。符合人类 在病理学上，敲除斑马鱼中的TM 251导致心脏缺陷和骨骼发育不良。 我们假设TM 251在溶酶体酶的M6 P生物合成途径中起作用。 我们将追求三个具体的目标来表征TM 251在溶酶体生物发生中的作用。在 目的1，我们将表征膜拓扑结构，定位，和寡聚化的TM 251。在 目的2，我们将在两个细胞中剖析TM 251和GNPT复合物之间的关系， 有机体水平。在aim 3中，我们将研究导致溶酶体的信号级联 在敲除TM 251后上调。我们的研究结果将揭示TM 251在M6 P中的作用 并为一种新的溶酶体贮积病提供了分子机制， 严重影响儿童健康。

The lysosome is an essential organelle to recycle materials delivered by endocytosis and autophagy. Inborn genetic defects affecting the lysosome cause debilitating and fatal lysosomal storage diseases (LSDs, ~70 in humans). One severe form of LSD, the I-cell disease, leads to skeletal dysplasia, short stature, cardiomegaly, and death in the first decade. It is caused by mutations in the GlcNAc-1-phosphotransferase enzyme (GNPT), which functions at the cis- Golgi to label lysosome enzymes with sorting signal mannose-6-phosphate (M6P). Missing M6P leads to the secretion of most lysosomal enzymes and defective lysosomes. In early 2021, a new type of severe LSD similar to the I-cell disease was reported. Patients will develop skeletal dysplasia, short stature, cardiac defects, and some die in early childhood. Their lysosomal enzymes are also secreted into the plasma. It is caused by mutations in TMEM251, but the cellular function of TMEM251 and the molecular mechanism for the disease remain to be addressed. In a genome-wide CRISPR knockout screen to identify genes critical for the degradation of human lysosome membrane proteins, we independently discovered TMEM251 to be essential for lysosome function. Knocking out TM251 leads to lysosomal dysfunction due to the secretion of unprocessed lysosomal enzymes. Consequently, lysosomes accumulate numerous undigested materials such as autophagic bodies and endocytic vesicles. Consistent with human pathology, knocking out TM251 in Zebrafish leads to cardiac defects and skeletal dysplasia. We hypothesize that TM251 functions in the M6P biogenesis pathway of lysosomal enzymes. We will pursue three specific aims to characterize the role of TM251 in lysosome biogenesis. In aim 1, we will characterize membrane topology, localization, and oligomerization of TM251. In aim 2, we will dissect the relationship between TM251 and the GNPT complex at both cellular and organismal levels. In aim 3, we will study the signaling cascade that leads to lysosome upregulation after knocking out TM251. Our findings will uncover the role of TM251 in the M6P biogenesis and provide a molecular mechanism for a new lysosome storage disease that severely affects child health.