Variants in TBC1D8B cause nephrotic syndrome. TBC1D8B is a GTPase-activating protein for Rab11 (RAB11-GAP) that interacts with nephrin, but how it controls nephrin trafficking or other podocyte functions remains unclear.

We generated a stable deletion in Tbc1d8b and used microhomology-mediated end-joining for genome editing. Ex vivo functional assays utilized slit diaphragms in podocyte-like Drosophila nephrocytes. Manipulation of endocytic regulators and transgenesis of murine Tbc1d8b provided a comprehensive functional analysis of Tbc1d8b.

A null allele of Drosophila TBC1D8B exhibited a nephrocyte-restricted phenotype of nephrin mislocalization, similar to patients with isolated nephrotic syndrome who have variants in the gene. The protein was required for rapid nephrin turnover in nephrocytes and for endocytosis of nephrin induced by excessive Rab5 activity. The protein expressed from the Tbc1d8b locus bearing the edited tag predominantly localized to mature early and late endosomes. Tbc1d8b was required for endocytic cargo processing and degradation. Silencing Hrs, a regulator of endosomal maturation, phenocopied loss of Tbc1d8b. Low-level expression of murine TBC1D8B rescued loss of the Drosophila gene, indicating evolutionary conservation. Excessive murine TBC1D8B selectively disturbed nephrin dynamics. Finally, we discovered four novel TBC1D8B variants within a cohort of 363 patients with FSGS and validated a functional effect of two variants in Drosophila, suggesting a personalized platform for TBC1D8B-associated FSGS.

Variants in TBC1D8B are not infrequent among patients with FSGS. TBC1D8B, functioning in endosomal maturation and degradation, is essential for nephrin trafficking.

TBC1D8B的变异会导致肾病综合征。 TBC1D8B 是 Rab11 (RAB11-GAP) 的 GTP 酶激活蛋白，可与去氧肾上腺素相互作用，但其如何控制去氧肾上腺素运输或其他足细胞功能仍不清楚。

我们在Tbc1d8b中生成了稳定的缺失，并使用微同源介导的末端连接进行基因组编辑。离体功能测定利用足细胞样果蝇肾细胞中的狭缝隔膜。内吞调节因子的操作和小鼠Tbc1d8b的转基因提供了 Tbc1d8b 的全面功能分析。

果蝇 TBC1D8B的无效等位基因表现出去氧肾上腺素错误定位的肾细胞限制表型，类似于具有该基因变异的孤立性肾病综合征患者。该蛋白是肾细胞中去氧肾上腺素快速周转以及过度 Rab5 活性诱导的去氧肾上腺素内吞作用所必需的。从带有编辑标签的Tbc1d8b基因座表达的蛋白质主要定位于成熟的早期和晚期内体。 Tbc1d8b 是内吞货物加工和降解所必需的。沉默Hrs （内体成熟的调节因子）， Tbc1d8b的表型缺失。小鼠TBC1D8B的低水平表达挽救了果蝇基因的丢失，表明进化保守。过量的小鼠 TBC1D8B 选择性干扰去氧肾上腺素动力学。最后，我们在 363 名 FSGS 患者的队列中发现了四种新的TBC1D8B变异，并在果蝇中验证了两种变异的功能作用，这为TBC1D8B相关 FSGS 提供了一个个性化平台。

TBC1D8B变异在 FSGS 患者中并不罕见。 TBC1D8B 在内体成熟和降解中发挥作用，对于去氧肾上腺素运输至关重要。