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TBC1D8B Mutations Implicate RAB11-Dependent Vesicular Trafficking in the Pathogenesis of Nephrotic Syndrome.

ABSTRACT: BACKGROUND:Mutations in about 50 genes have been identified as monogenic causes of nephrotic syndrome, a frequent cause of CKD. These genes delineated the pathogenetic pathways and rendered significant insight into podocyte biology. METHODS:We used whole-exome sequencing to identify novel monogenic causes of steroid-resistant nephrotic syndrome (SRNS). We analyzed the functional significance of an SRNS-associated gene in vitro and in podocyte-like Drosophila nephrocytes. RESULTS:We identified hemizygous missense mutations in the gene TBC1D8B in five families with nephrotic syndrome. Coimmunoprecipitation assays indicated interactions between TBC1D8B and active forms of RAB11. Silencing TBC1D8B in HEK293T cells increased basal autophagy and exocytosis, two cellular functions that are independently regulated by RAB11. This suggests that TBC1D8B plays a regulatory role by inhibiting endogenous RAB11. Coimmunoprecipitation assays showed TBC1D8B also interacts with the slit diaphragm protein nephrin, and colocalizes with it in immortalized cell lines. Overexpressed murine Tbc1d8b with patient-derived mutations had lower affinity for endogenous RAB11 and nephrin compared with wild-type Tbc1d8b protein. Knockdown of Tbc1d8b in Drosophila impaired function of the podocyte-like nephrocytes, and caused mistrafficking of Sns, the Drosophila ortholog of nephrin. Expression of Rab11 RNAi in nephrocytes entailed defective delivery of slit diaphragm protein to the membrane, whereas RAB11 overexpression revealed a partial phenotypic overlap to Tbc1d8b loss of function. CONCLUSIONS:Novel mutations in TBC1D8B are monogenic causes of SRNS. This gene inhibits RAB11. Our findings suggest that RAB11-dependent vesicular nephrin trafficking plays a role in the pathogenesis of nephrotic syndrome.

SUBMITTER: Kampf LL

PROVIDER: S-EPMC6900796 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Publications

<i>TBC1D8B</i> Mutations Implicate RAB11-Dependent Vesicular Trafficking in the Pathogenesis of Nephrotic Syndrome.

Kampf Lina L LL Schneider Ronen R Gerstner Lea L Thünauer Roland R Chen Mengmeng M Helmstädter Martin M Amar Ali A Onuchic-Whitford Ana C AC Loza Munarriz Reyner R Berdeli Afig A Müller Dominik D Schrezenmeier Eva E Budde Klemens K Mane Shrikant S Laricchia Kristen M KM Rehm Heidi L HL MacArthur Daniel G DG Lifton Richard P RP Walz Gerd G Römer Winfried W Bergmann Carsten C Hildebrandt Friedhelm F Hermle Tobias T

Journal of the American Society of Nephrology : JASN 20191115 12

<h4>Background</h4>Mutations in about 50 genes have been identified as monogenic causes of nephrotic syndrome, a frequent cause of CKD. These genes delineated the pathogenetic pathways and rendered significant insight into podocyte biology.<h4>Methods</h4>We used whole-exome sequencing to identify novel monogenic causes of steroid-resistant nephrotic syndrome (SRNS). We analyzed the functional significance of an SRNS-associated gene <i>in vitro</i> and in podocyte-like <i>Drosophila</i> nephrocy ...[more]

PMID: 31732614

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Project description:BACKGROUND: Nephrotic syndrome is traditionally classified on the basis of the response to standard steroid treatment. Mutations in more than 24 genes have been associated with nephrotic syndrome in children, although the great majority of steroid-resistant cases have been attributed to mutations in three main genes: NPHS1, NPHS2 and WT1. The aims of this study were to identify mutations in these genes more frequently reported as mutated and to characterize each variation using different in silico prediction algorithms in order to understand their biological functions. METHODS: We performed direct sequence analysis of exons 8 and 9 of WT1, 8 exons of NPHS2 and 29 exons of NPHS1, including NPHS2 and NPHS1 intron-exon boundary sequences, as well as 700 bp of the 5' UTR from both genes in 27 steroid-resistant patients aged between 3 months and 18 years. RESULTS: Analysis of the NPHS2 gene revealed four missense mutations, one frameshift mutation and three variations in the 5' UTR. Four patients presented compound heterozygosis, and four other patients presented one heterozygous alteration only. WT1 and NPHS1 gene analysis did not reveal any mutations. DISCUSSION: This is the first study focusing on genetics of SRNS in Brazilian children. Identification of mutations is important because it could influence physicians' decision on patient treatment, as patients carrying mutations can be spared the side effects of immunosuppressive therapy and ultimately could be considered for kidney transplantation from a living donor. CONCLUSIONS: After molecular analysis of the genes more frequently reported as mutated in 27 steroid-resistant nephrotic syndrome patients, we identified NPHS2 mutations confirming the hereditary character of the kidney disease in only 14.8% of patients. Therefore, the next step is to perform a next generation sequencing based analysis of glomeluropathy-related panel of genes for the remaining patients in order to search for mutations in other genes related to steroid-resistant nephrotic syndrome.

Dataset Information

TBC1D8B Mutations Implicate RAB11-Dependent Vesicular Trafficking in the Pathogenesis of Nephrotic Syndrome.

Publications

<i>TBC1D8B</i> Mutations Implicate RAB11-Dependent Vesicular Trafficking in the Pathogenesis of Nephrotic Syndrome.

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