Abstract：
Together with its β-subunit OSTM1, ClC-7 performs 2Cl-/H+ exchange across lysosomal membranes. Pathogenic variants in either gene cause lysosome-related pathologies, including osteopetrosis and lysosomal storage. CLCN7 variants can cause recessive or dominant disease. Different variants entail different sets of symptoms. Loss of ClC-7 causes osteopetrosis and mostly neuronal lysosomal storage. A recently reported de novo CLCN7 mutation (p.Tyr715Cys) causes widespread severe lysosome pathology (hypopigmentation, organomegaly, and delayed myelination and development, \"HOD syndrome\"), but no osteopetrosis. We now describe two additional HOD individuals with the previously described p.Tyr715Cys and a novel p.Lys285Thr mutation, respectively. Both mutations decreased ClC-7 inhibition by PI(3,5)P2 and affected residues lining its binding pocket, and shifted voltage-dependent gating to less positive potentials, an effect partially conferred to WT subunits in WT/mutant heteromers. This shift predicts augmented pH gradient-driven Cl- uptake into vesicles. Overexpressing either mutant induced large lysosome-related vacuoles. This effect depended on Cl-/H+-exchange, as shown using mutants carrying uncoupling mutations. Fibroblasts from the p.Y715C patient also displayed giant vacuoles. This was not observed with p.K285T fibroblasts probably due to residual PI(3,5)P2 sensitivity. The gain of function caused by the shifted voltage-dependence of either mutant likely is the main pathogenic factor. Loss of PI(3,5)P2 inhibition will further increase current amplitudes, but may not be a general feature of HOD. Overactivity of ClC-7 induces pathologically enlarged vacuoles in many tissues, which is distinct from lysosomal storage observed with the loss of ClC-7 function. Osteopetrosis results from a loss of ClC-7, but osteoclasts remain resilient to increased ClC-7 activity.
摘要：
ClC-7与其β亚基OSTM1一起在溶酶体膜上进行2Cl-/H交换。任一基因的致病变异都会导致溶酶体相关病理，包括骨质疏松,溶酶体贮存,和色素缺陷。CLCN7变体可引起隐性或显性疾病。不同的变体需要不同的症状集。ClC-7的丢失导致骨硬化和主要是神经元溶酶体储存。最近报道的从头CLCN7突变（p。Tyr715Cys）引起广泛的严重溶酶体病理学和色素沉着不足（“HOD综合征”），但没有骨质疏松.我们现在描述了两个额外的HOD个体，具有先前描述的p.Tyr715Cys和一个新的p.Lys285Thr突变，分别。两种突变均降低了PI（3,5）P2对ClC-7的抑制作用，并影响了其结合袋内衬的残基，并将依赖于电压的门控转移到较小的正电势，在WT/突变体异聚体中部分赋予WT亚基的作用。这种变化预示着pH梯度驱动的Cl-摄取到囊泡中的增加。过表达任一突变体均可诱导大的溶酶体相关液泡。这种效应取决于Cl-/H+-交换，如使用携带解偶联突变的突变体所示。来自p.Y715C患者的成纤维细胞也显示出巨大的空泡。这在p.K285T成纤维细胞中未观察到,可能是由于一些ClC-7K285T保留的PI(3,5)P2敏感性。由任一突变体的电压依赖性偏移引起的功能增益可能是其致病性的主要原因。它们失去PI(3,5)P2抑制将进一步增加电流，但可能不是HOD的一般特征。ClC-7的过度活性在许多组织中引起病理上扩大的空泡，这与观察到的ClC-7功能丧失的溶酶体储存不同。石骨症是由ClC-7的损失引起的,但是破骨细胞对增加的ClC-7活性保持弹性。
