SASH1 S519N variant links skin hyperpigmentation and premature hair graying to dysfunction of melanocyte lineage

A better understanding of human melanocyte and melanocyte stem cell (McSC) biology is essential for treating melanocyte-related diseases. This study employed an inherited pigmentation disorder carrying the SASH1S519N variant in a Hispanic family to investigate the SASH1 function in melanocyte lineage and the underlying mechanism for this disorder. We used a multidisciplinary approach, including clinical exams, human cell assays, yeast two-hybrid screening, and biochemical techniques. Results linked early hair graying to the SASH1S519N variant, a previously unrecognized clinical phenotype in hyperpigmentation disorders. We identified SASH1 as a novel regulator in McSC maintenance and discovered that TNKS2 is crucial for SASH1's role in vitro. Additionally, the S519N variant is located in one of multiple tankyrase binding motifs and alters the binding kinetics and affinity of the interaction. In summary, this disorder showcases accelerated aging in human McSC, linking both gain and loss of pigmentation to McSC dysfunction in the same individuals. The findings offer new insights into the roles of SASH1 and TNKS2 in McSC maintenance and the molecular mechanisms of pigmentation disorders. We propose that a comprehensive clinical evaluation of patients with skin disorders should include an assessment and history of hair pigmentation loss. Overall design: We knocked down SASH1 in primary melanocyte cells using nucleofection, and cultured cells in sphere conditions. The sphere assay enriches for stem-like cells. Results showed that SASH1 is involved in mitotis in stem-like melanocyte cells.

深入解析人类黑素细胞（melanocyte）与黑素细胞干细胞（melanocyte stem cell, McSC）的生物学特性，是治疗黑素细胞相关疾病的核心前提。本研究以西班牙裔家族中携带SASH1S519N突变的遗传性色素沉着紊乱为研究对象，探究SASH1在黑素细胞谱系中的功能，以及该紊乱的潜在发病机制。本研究采用多学科研究策略，涵盖临床检查、人类细胞实验、酵母双杂交筛选与生物化学技术。研究结果显示，早发性白发与SASH1S519N突变存在关联——这是一类此前在色素沉着过度性疾病中未被报道的临床表型。本研究证实SASH1是维持McSC功能的新型调控因子，并发现TNKS2对SASH1在体外的调控作用至关重要。此外，S519N突变位于多个端锚聚合酶结合基序之一，可改变该相互作用的结合动力学与结合亲和力。综上，该遗传性紊乱揭示了人类McSC的加速衰老现象，将同一患者体内的色素沉着过多与不足均与McSC功能异常联系起来。本研究结果为阐明SASH1与TNKS2在McSC维持中的作用，以及色素沉着紊乱的分子机制提供了全新视角。我们建议，对皮肤疾病患者进行全面临床评估时，应纳入毛发色素脱失情况的评估与病史采集。实验整体设计：本研究通过核转染技术在原代黑素细胞中敲低SASH1的表达，并在球体培养条件下对细胞进行培养。球体培养实验可富集获得干细胞样细胞，结果显示SASH1参与干细胞样黑素细胞的有丝分裂过程。