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Targeted renal knockdown of Na+/H+ exchanger regulatory factor Sip1 produces uric acid nephrolithiasis in Drosophila.

ABSTRACT: Nephrolithiasis is one of the most common kidney diseases, with poorly understood pathophysiology, but experimental study has been hindered by lack of experimentally tractable models. Drosophila melanogaster is a useful model organism for renal diseases because of genetic and functional similarities of Malpighian (renal) tubules with the human kidney. Here, we demonstrated function of the sex-determining region Y protein-interacting protein-1 (Sip1) gene, an ortholog of human Na+/H+ exchanger regulatory factor (NHERF1), in Drosophila Malpighian tubules and its impact on nephrolithiasis. Abundant birefringent calculi were observed in Sip1 mutant flies, and the phenotype was also observed in renal stellate cell-specific RNA interference Sip1 knockdown in otherwise normal flies, confirming a renal etiology. This phenotype was abolished in rosy mutant flies (which model human xanthinuria) and by the xanthine oxidase inhibitor allopurinol, suggesting that the calculi were of uric acid. This was confirmed by direct biochemical assay for urate. Stones rapidly dissolved when the tubule was bathed in alkaline media, suggesting that Sip1 knockdown was acidifying the tubule. SIP1 was shown to collocate with Na+/H+ exchanger isoform 2 (NHE2) and with moesin in stellate cells. Knockdown of NHE2 specifically to the stellate cells also increased renal uric acid stone formation, and so a model was developed in which SIP1 normally regulates NHE2 activity and luminal pH, ultimately leading to uric acid stone formation. Drosophila renal tubules may thus offer a useful model for urate nephrolithiasis.

SUBMITTER: Ghimire S

PROVIDER: S-EPMC6843049 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Targeted renal knockdown of Na+/H+ exchanger regulatory factor Sip1 produces uric acid nephrolithiasis in Drosophila.

Ghimire Saurav S Terhzaz Selim S Cabrero Pablo P Romero Michael F MF Davies Shireen A SA Dow Julian A T JAT

American journal of physiology. Renal physiology 20190731 4

Nephrolithiasis is one of the most common kidney diseases, with poorly understood pathophysiology, but experimental study has been hindered by lack of experimentally tractable models. Drosophila melanogaster is a useful model organism for renal diseases because of genetic and functional similarities of Malpighian (renal) tubules with the human kidney. Here, we demonstrated function of the sex-determining region Y protein-interacting protein-1 (Sip1) gene, an ortholog of human Na<su ...[more]

PMID: 31364377

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Project description:Renal stone formation is a common multifactorial disorder, of unknown etiology, with an established genetic contribution. Lifetime risk for nephrolithiasis is approximately 10% in Western populations, and uric acid stones account for 5%-10% of all stones, depending on climatic, dietary, and ethnic differences. We studied a small, isolated founder population in Sardinia, characterized by an increased prevalence of uric acid stones, and performed a genomewide search in a deep-rooted pedigree comprising many members who formed uric acid renal stones. The pedigree was created by tracing common ancestors of affected individuals through a genealogical database based on archival records kept by the parish church since 1640. This genealogical information was used as the basis for the study strategy, involving screening for alleles shared among affected individuals, originating from common ancestors, and utilization of large pedigrees to obtain greater power for linkage detection. We performed multistep linkage and allele-sharing analyses. In the initial stage, 382 markers were typed in 14 closely related affected subjects; interesting regions were subsequently investigated in the whole sample. We identified two chromosomal regions that may harbor loci with susceptibility genes for uric acid stones. The strongest evidence was observed on 10q21-q22, where a LOD score of 3.07 was obtained for D10S1652 under an affected-only dominant model, and a LOD score of 3.90 was obtained using a dominant pseudomarker assignment. The localization was supported also by multipoint allele-sharing statistics and by haplotype analysis of familial cases and of unrelated affected subjects collected from the isolate. In the second region on 20q13.1-13.3, multipoint nonparametric scores yielded suggestive evidence in a approximately 20-cM region, and further analysis is needed to confirm and fine-map this putative locus. Replication studies are required to investigate the involvement of these regions in the genetic contribution to uric acid stone formation.

Project description:Background and objectivesIdiopathic uric acid nephrolithiasis, which is closely associated with obesity and the metabolic syndrome, is increasing in prevalence. Unduly acidic urine pH, the quintessential pathophysiologic feature of this disease, is in part explained by inadequate excretion of the principal urinary buffer ammonium. The role of net acid excretion in the pathogenesis of uric acid nephrolithiasis is incompletely understood.Design, setting, participants, & measurementsWe compared acid-base parameters of patients with idiopathic uric acid nephrolithiasis with matched control subjects under controlled diets in an inpatient metabolic unit. Measurements included fasting blood and 24-hour urine chemistries and 24-hour urine metabolomic analysis. Comparisons between groups included analysis of covariance models controlling for urine pH or body mass index.ResultsSubjects with idiopathic uric acid nephrolithiasis had lower urine pH (5.5 versus 5.9; P<0.001) and higher net acid excretion (60 versus 43 mEq/24 h; P<0.001), with the excess H+ carried by nonammonium buffers. In all subjects, there was a positive relationship of net acid excretion with higher body mass index in spite of strictly controlled equivalent dietary acid intake. This relationship was most evident among control subjects (r=0.36; P=0.03). It was attenuated in patients with idiopathic uric acid nephrolithiasis whose net acid excretion remained fixedly high and ammonium excretion remained low relative to net acid excretion, resulting in low urine pH over a wide body mass index range. Urinary metabolomics was performed to attempt to identify excess organic acids presented to the kidney in idiopathic uric acid nephrolithiasis. Among the tricarboxylic acid cycle intermediates and amino acid and lipid metabolites analyzed, 26 organic anions with acid dissociation constants values in the range of urine pH showed greater protonation. However, protons carried by the identified organic acids did not entirely account for the higher titratable acidity seen in idiopathic uric acid nephrolithiasis.ConclusionsHigher acid load to the kidney, resulting in higher urinary net acid excretion, is an important factor in the pathogenesis of idiopathic uric acid nephrolithiasis.

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Dataset Information

Targeted renal knockdown of Na+/H+ exchanger regulatory factor Sip1 produces uric acid nephrolithiasis in Drosophila.

Publications

Targeted renal knockdown of Na<sup>+</sup>/H<sup>+</sup> exchanger regulatory factor <i>Sip1</i> produces uric acid nephrolithiasis in <i>Drosophila</i>.

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