Functional and transport analyses of CLCN5 genetic changes identified in Dent disease patients.

Dent disease type 1, an X-linked inherited kidney disease is caused by mutations in electrogenic Cl(-)/H(+) exchanger, ClC-5. We functionally studied the most frequent mutation (S244L) and two mutations recently identified in RKSC patients, Q629X and R345W. We also studied T657S, which has a high minor-allele frequency (0.23%) in the African-American population, was published previously as pathogenic to cause Dent disease. The transport properties of CLC-5 were electrophysiologically characterized. WT and ClC-5 mutant currents were inhibited by pH 5.5, but not affected by an alkaline extracellular solution (pH 8.5). The T657S and R345W mutations showed the same anion selectivity sequence as WT ClC-5 (SCN(-)>NO3(-)≈Cl(-)>Br(-)>I(-)). However, the S244L and Q629X mutations abolished this anion conductance sequence. Cell surface CLC-5 expression was quantified using extracellular HA-tagged CLC-5 and a chemiluminescent immunoassay. Cellular localization of eGFP-tagged CLC-5 proteins was also examined in HEK293 cells with organelle-specific fluorescent probes. Functional defects of R345W and Q629X mutations were caused by the trafficking of the protein to the plasma membrane since proteins were mostly retained in the endoplasmic reticulum, and mutations showed positive correlations between surface expression and transport function. In contrast, although the S244L transport function was significantly lower than WT, cell surface, early endosome, and endoplasmic reticulum expression was equal to that of WT CLC-5. Function and trafficking of T657S was equivalent to the WT CLC-5 suggesting this is a benign variant rather than pathogenic. These studies demonstrate the useful information that can be gained by detailed functional studies of mutations predicted to be pathogenic.

Paracrine Wnt1 Drives Interstitial Fibrosis without Inflammation by Tubulointerstitial Cross-Talk.

AKI with incomplete epithelial repair is a major contributor to CKD characterized by tubulointerstitial fibrosis. Injury-induced epithelial secretion of profibrotic factors is hypothesized to underlie this link, but the identity of these factors and whether epithelial injury is required remain undefined. We previously showed that activation of the canonical Wnt signaling pathway in interstitial pericytes cell autonomously drives myofibroblast activation in vivo. Here, we show that inhibition of canonical Wnt signaling also substantially prevented TGFß-dependent myofibroblast activation in vitro. To investigate whether Wnt ligand derived from proximal tubule is sufficient for renal fibrogenesis, we generated a novel mouse strain with inducible proximal tubule Wnt1 secretion. Adult mice were treated with vehicle or tamoxifen and euthanized at 12 or 24 weeks postinjection. Compared with vehicle-treated controls, kidneys with tamoxifen-induced Wnt1 expression from proximal tubules displayed interstitial myofibroblast activation and proliferation and increased matrix protein production. PDGF receptor ß-positive myofibroblasts isolated from these kidneys exhibited increased canonical Wnt target gene expression compared with controls. Notably, fibrotic kidneys had no evidence of inflammatory cytokine expression, leukocyte infiltration, or epithelial injury, despite the close histologic correlation of each with CKD. These results provide the first example of noninflammatory renal fibrosis. The fact that epithelial-derived Wnt ligand is sufficient to drive interstitial fibrosis provides strong support for the maladaptive repair hypothesis in the AKI to CKD transition.

Sulfate but not thiosulfate reduces calculated and measured urinary ionized calcium and supersaturation: implications for the treatment of calcium renal stones.

BACKGROUND: Urinary sulfate (SO4(2-)) and thiosulfate (S2O3(2-)) can potentially bind with calcium and decrease kidney stone risk. We modeled the effects of these species on the concentration of ionized calcium (iCa) and on supersaturation (SS) of calcium oxalate (CaOx) and calcium phosphate (CaP), and measured their in vitro effects on iCa and the upper limit of stability (ULM) of these salts. METHODS: Urine data from 4 different types of stone patients were obtained from the Mayo Nephrology Clinic (Model 1). A second data set was obtained from healthy controls and hypercalciuric stone formers in the literature who had been treated with sodium thiosulfate (STS) (Model 2). The Joint Expert Speciation System (JESS) was used to calculate iCa and SS. In Model 1, these parameters were calculated as a function of sulfate and thiosulfate concentrations. In Model 2, data from pre- and post STS urines were analyzed. ULM and iCa were determined in human urine as a function of sulfate and thiosulfate concentrations. RESULTS: Calculated iCa and SS values for all calcium salts decreased with increasing sulfate concentration. Thiosulfate had no effect on these parameters. In Model 2, calculated iCa and CaOx SS increased after STS treatment, but CaP SS decreased, perhaps due to a decrease in pH after STS treatment. In confirmatory in vitro experiments supplemental sulfate, but not thiosulfate, significantly increased the calcium needed to achieve the ULM of CaP and tended to increase the oxalate needed to reach the ULM of CaOx. Sulfate also significantly decreased iCa in human urine, while thiosulfate had no effect. CONCLUSION: Increasing urinary sulfate could theoretically reduce CaOx and CaP stone risk. Although STS may reduce CaP stone risk by decreasing urinary pH, it might also paradoxically increase iCa and CaOx SS. As such, STS may not be a viable treatment option for stone disease.

PAP inhibitor with in vivo efficacy identified by Candida albicans genetic profiling of natural products.

Natural products provide an unparalleled source of chemical scaffolds with diverse biological activities and have profoundly impacted antimicrobial drug discovery. To further explore the full potential of their chemical diversity, we survey natural products for antifungal, target-specific inhibitors by using a chemical-genetic approach adapted to the human fungal pathogen Candida albicans and demonstrate that natural-product fermentation extracts can be mechanistically annotated according to heterozygote strain responses. Applying this approach, we report the discovery and characterization of a natural product, parnafungin, which we demonstrate, by both biochemical and genetic means, to inhibit poly(A) polymerase. Parnafungin displays potent and broad spectrum activity against diverse, clinically relevant fungal pathogens and reduces fungal burden in a murine model of disseminated candidiasis. Thus, mechanism-of-action determination of crude fermentation extracts by chemical-genetic profiling brings a powerful strategy to natural-product-based drug discovery.

Mechanism-of-action determination of GMP synthase inhibitors and target validation in Candida albicans and Aspergillus fumigatus.

Mechanism-of-action (MOA) studies of bioactive compounds are fundamental to drug discovery. However, in vitro studies alone may not recapitulate a compound's MOA in whole cells. Here, we apply a chemogenomics approach in Candida albicans to evaluate compounds affecting purine metabolism. They include the IMP dehydrogenase inhibitors mycophenolic acid and mizoribine and the previously reported GMP synthase inhibitors acivicin and 6-diazo-5-oxo-L-norleucine (DON). We report important aspects of their whole-cell activity, including their primary target, off-target activity, and drug metabolism. Further, we describe ECC1385, an inhibitor of GMP synthase, and provide biochemical and genetic evidence supporting its MOA to be distinct from acivicin or DON. Importantly, GMP synthase activity is conditionally essential in C. albicans and Aspergillus fumigatus and is required for virulence of both pathogens, thus constituting an unexpected antifungal target.