Regulation of sodium balance is a critical factor in the maintenance of euvolemia, and dysregulation of renal sodium excretion results in disorders of altered intravascular volume, such as hypertension. The amiloridesensitive epithelial sodium channel (ENaC) is thought to be the only mechanism for sodium transport in the cortical collecting duct (CCD) of the kidney. However, it has been found that much of the sodium absorption in the CCD is actually amiloride insensitive and sensitive to thiazide diuretics, which also block the Na-Cl cotransporter (NCC) located in the distal convoluted tubule. In this study, we have demonstrated the presence of electroneutral, amiloride-resistant, thiazide-sensitive, transepithelial NaCl absorption in mouse CCDs, which persists even with genetic disruption of ENaC. Furthermore, hydrochlorothiazide (HCTZ) increased excretion of Na + and Cl -in mice devoid of the thiazide target NCC, suggesting that an additional mechanism might account for this effect. Studies on isolated CCDs suggested that the parallel action of the Na + -driven Cl -/HCO 3 -exchanger (NDCBE/SLC4A8) and the Na + -independent Cl -/HCO 3 -exchanger (pendrin/SLC26A4) accounted for the electroneutral thiazide-sensitive sodium transport. Furthermore, genetic ablation of SLC4A8 abolished thiazide-sensitive NaCl transport in the CCD. These studies establish what we believe to be a novel role for NDCBE in mediating substantial Na + reabsorption in the CCD and suggest a role for this transporter in the regulation of fluid homeostasis in mice.

SUMMARY The purpose of this study was to examine global epidemiological trends in human norovirus (NoV) outbreaks by transmission route and setting, and describe relationships between these characteristics, viral attack rates, and the occurrence of genogroup I (GI) or genogroup II (GII) strains in outbreaks. We analysed data from 902 RT-PCR-confirmed, human NoV outbreaks extracted from a systematic review of articles published from 1993 to 2011 and indexed under the terms “norovirus” and “outbreak.” Multivariate regression analyses demonstrated that foodservice and winter outbreaks were significantly associated with higher attack rates. Food- and waterborne outbreaks were associated with multiple strains (GI+GII). Waterborne outbreaks were significantly associated with GI strains, while healthcare-related and winter outbreaks were associated with GII strains. These results identify important trends for epidemic NoV detection, prevention, and control.

We used a systems biology-based approach to investigate the basis of cell-specific expression of the water channel aquaporin-2 (AQP2) in the renal collecting duct. Computational analysis of the 5-flanking region of the AQP2 gene (Genomatix) revealed 2 conserved clusters of putative transcriptional regulator (TR) binding elements (BEs) centered at ؊513 bp (corresponding to the SF1, NFAT, and FKHD TR families) and ؊224 bp (corresponding to the AP2, SRF, CREB, GATA, and HOX TR families). Three other conserved motifs corresponded to the ETS, EBOX, and RXR TR families. To identify TRs that potentially bind to these BEs, we carried out mRNA profiling (Affymetrix) in mouse mpkCCDc14 collecting duct cells, revealing expression of 25 TRs that are also expressed in native inner medullary collecting duct. One showed a significant positive correlation with AQP2 mRNA abundance among mpkCCD subclones (Ets1), and 2 showed a significant negative correlation (Elf1 and an orphan nuclear receptor Nr1h2). Transcriptomic profiling in native proximal tubules (PT), medullary thick ascending limbs (MTAL), and IMCDs from kidney identified 14 TRs (including Ets1 and HoxD3) expressed in the IMCD but not PT or MTAL (candidate AQP2 enhancer roles), and 5 TRs (including HoxA5, HoxA9 and HoxA10) expressed in PT and MTAL but not in IMCD (candidate AQP2 repressor roles). In luciferase reporter assays, overexpression of 3 ETS family TRs transactivated the mouse proximal AQP2 promoter. The results implicate ETS family TRs in cell-specific expression of AQP2 and point to HOX, RXR, CREB and GATA family TRs as playing likely additional roles.aquaporin 2 ͉ kidney ͉ microarrays ͉ transcription ͉ vasopressin R enal water excretion is tightly regulated chiefly through effects of vasopressin on the molecular water channel, aquaporin-2 (AQP2) (1). AQP2 gene expression in the kidney is restricted to collecting duct principal cells and connecting tubule cells (2, 3). Aside from control of trafficking of AQP2-containing vesicles (1), AQP2 is regulated through changes in the total abundance of the AQP2 protein in collecting duct cells. Vasopressin increases the renal abundance of the AQP2 protein (4) via changes in AQP2 mRNA levels (5), in part by transcriptional regulation. Studies in transgenic mice in which 14-15 kb of the 5Ј-flanking region of the AQP2 gene was coupled to reporters established that cell-specific expression of the AQP2 gene in the collecting duct is dependent on cis-elements in this region (6, 7). Altered AQP2 protein abundance in the renal collecting duct is largely responsible for water balance abnormalities associated with diverse clinical states including lithium-induced diabetes insipidus, congestive heart failure, and the syndrome of inappropriate antidiuresis (1). Understanding the roles of AQP2 in these clinical states hinges largely on understanding the mechanism of cell-specific expression of the AQP2 gene.Sequencing of the 5Ј-flanking region of the AQP2 gene revealed several putative cis-binding element (BE) motifs including a c...

The kidney, epididymis, and lungs are complex organs with considerable epithelial cell heterogeneity. This has limited the characterization of pathophysiological transport processes that are specific for each cell type in these epithelia. The purpose of the present study was to develop new tools to study cell-specific gene and protein expression in such complex tissues and organs. We report the production of a transgenic mouse that expresses enhanced green fluorescent protein (EGFP) in a subset of epithelial cells that express the B1 subunit of vacuolar H(+)-ATPase (V-ATPase) and are actively involved in proton transport. A 6.5-kb portion of the V-ATPase B1 promoter was used to drive expression of EGFP. In two founders, quantitative real-time RT-PCR demonstrated expression of EGFP in kidney, epididymis, and lung. Immunofluorescence labeling using antibodies against the B1 and E subunits of V-ATPase and against carbonic anhydrase type II (CAII) revealed specific EGFP expression in all renal type A and type B intercalated cells, some renal connecting tubule cells, all epididymal narrow and clear cells, and some nonciliated airway epithelial cells. No EGFP expression was detected in collecting duct principal cells (identified using an anti-AQP2 antibody) or epididymal principal cells (negative for V-ATPase or CAII). This EGFP-expressing mouse model should prove useful in future studies of gene and protein expression and their physiological and/or developmental regulation in distinct cell types that can now be separated using fluorescence-assisted microdissection, fluorescence-activated cell sorting, and laser capture microdissection.

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