Hypertension affects one billion people and is a principal reversible risk factor for cardiovascular disease. A rare Mendelian syndrome, pseudohypoaldosteronism type II (PHAII), featuring hypertension, hyperkalemia, and metabolic acidosis, has revealed previously unrecognized physiology orchestrating the balance between renal salt reabsorption versus K+ and H+ excretion1. We used exome sequencing to identify mutations in Kelch-like 3 (KLHL3) or Cullin 3 (CUL3) in 41 PHAII kindreds. KLHL3 mutations are either recessive or dominant, while CUL3 mutations are dominant and predominantly de novo. CUL3 and BTB-Kelch proteins such as KLHL3 are components of Cullin/RING E3 ligase complexes (CRLs) that ubiquitinate substrates bound to Kelch propeller domains2–8. Dominant KLHL3 mutations are clustered in short segments within the Kelch propeller and BTB domains implicated in substrate9 and Cullin5 binding, respectively. Diverse CUL3 mutations all result in skipping of exon 9, producing an in-frame deletion. Because dominant KLHL3 and CUL3 mutations both phenocopy recessive loss-of-function KLHL3 mutations, they may abrogate ubiquitination of KLHL3 substrates. Disease features are reversed by thiazide diuretics, which inhibit the Na-Cl cotransporter (NCC) in the distal nephron of the kidney; KLHL3 and CUL3 are expressed in this location, suggesting a mechanistic link between KLHL3/CUL3 mutations, increased Na-Cl reabsorption, and disease pathogenesis. These findings demonstrate the utility of exome sequencing in disease gene identification despite combined complexities of locus heterogeneity, mixed models of transmission, and frequent de novo mutation, and establish a fundamental role for KLHL3/CUL3 in blood pressure, K+, and pH homeostasis.

The peroxisome proliferator-activated receptor subtype ␥ (PPAR␥) ligands, namely the synthetic insulin-sensitizing thiazolidinedione (TZD) compounds, have demonstrated great potential in the treatment of type II diabetes. However, their clinical applicability is limited by a common and serious side effect of edema. To address the mechanism of TZD-induced edema, we generated mice with collecting duct (CD)-specific disruption of the PPAR␥ gene. We found that mice with CD knockout of this receptor were resistant to the rosiglitazone-(RGZ) induced increases in body weight and plasma volume expansion found in control mice expressing PPAR␥ in the CD. RGZ reduced urinary sodium excretion in control and not in conditional knockout mice. Furthermore, RGZ stimulated sodium transport in primary cultures of CD cells expressing PPAR␥ and not in cells lacking this receptor. These findings demonstrate a PPAR␥-dependent pathway in regulation of sodium transport in the CD that underlies TZD-induced fluid retention.roziglitazone ͉ Cre recombinase ͉ Evans blue technique T hiazolidinediones (TZDs), synthetic insulin-sensitizing drugs that include troglitazone, pioglitazone, and rosiglitazone (RGZ), are highly effective in the treatment of type II diabetes. TZDs are believed to mediate their antidiabetic effect via activation of peroxisome proliferator-activated receptor ␥ (PPAR␥) (1). In addition to lowering blood glucose, these drugs also benefit cardiovascular parameters, such as blood pressure and endothelial function (2, 3). However, fluid retention, presented as rapid weight gain, and peripheral and pulmonary edema have emerged as the most common and serious side effects of TZDs (4-6). Global awareness of this side effect has increased as a result of the growing number of reported cases. In a recent issue of Circulation (7), the American Heart Association and American Diabetes Association jointly issued a Consensus Statement commenting on the safety of TZD as related to edema. The mechanisms of fluid retention in patients treated with TZDs are poorly understood and may involve a number of factors, including reduction of urinary sodium excretion (8), alteration of endothelial permeability (9), increased sympathetic nervous system activity (10), or altered interstitial ion transport (11). To evaluate the relative contributions of these individual mechanisms, tissue-or cell-type-specific approaches are needed in carefully designed studies.PPARs are a group of zinc finger-containing transcription factors, representing a family of the nuclear hormone receptor gene superfamily. To date, three subtypes of PPARs encoded by different genes have been described from several species: PPAR␣, -␤͞␦, and -␥ (12, 13). They share a high degree of similarity in their overall amino acid sequences, particularly in the DNA-binding domain (14). The three isoforms of the PPARs heterodimerize with retinoid X receptor, bind to the same peroxisome proliferatorresponsive element in the promoter regions of their target genes, and modulate gene transcripti...

The intercalated cells of the kidney collecting duct are specialized for physiologically regulated proton transport. In these cells, a vacuolar H+-ATPase is expressed at enormous levels in a polarized distribution on the plasma membrane, enabling it to serve in transepithelial H+ transport. In contrast, in most eukaryotic cells, vacuolar H+-ATPases reside principally in intracellular compartments to effect vacuolar acidification. To investigate the basis for the selective amplification of the proton pump in intercalated cells, we isolated and sequenced cDNA clones for two isoforms of the -56-kDa subunit of the H+-ATPase and examined their expression in various tissues. The predicted amino acid sequence of the isoforms was highly conserved in the internal region but diverged in the amino and carboxyl termini. mRNA hybridization to a cDNA probe for one isoform (the "kidney" isoformn) was detected only in kidney cortex and medulla, whereas mRNA hybridization to the other isoform of the -56-kDa subunit and to the H+-ATPase 31-kDa subunit was found in the kidney and other tissues. Immunocytochemistry of rat kidney with an antibody specific to the kidney isoform revealed intense staining only in the intercalated cells. Staining was absent from proximal tubule and thick ascending limb, where H+-ATPase was detected with a monoclonal antibody to the 31-kDa subunit of the H+-ATPase. This example ofspecific amplification ofan isoform of one subunit of the vacuolar H+-ATPase being limited to a specific cell type suggests that the selective expression of the kidney isoform of the -56-kDa subunit may confer the capacity for amplification and other specialized functions of the vacuolar H+-ATPase in the renal intercalated cell.Vacuolar H+-ATPases participate in a remarkably diverse variety of cellular functions. In the intracellular membrane compartments of eukaryotic cells, they acidify endosomes, lysosomes, and other components of the vacuolar system, serving in endocytosis and secretion (1). In cells specialized for H' transport, such as the renal intercalated cell (2, 3) and the osteoclast (4), vacuolar H+-ATPases reside in high densities in a polarized distribution on the plasma membrane, effecting transcellular proton transport. How the vacuolar class of H+-ATPases performs such diverse functions remains unknown. Accumulating evidence suggests that structural subsets of the vacuolar H+-ATPases exist that may have unique roles. In prior studies, we reported that a vacuolar H+-ATPase preparation isolated from bovine kidney microsomes could be resolved on an HPLC ion-exchange column as two peaks of activity that exhibited differences in the structure of their -56-kDa subunits on SDS/polyacrylamide gels (5). More recently, we found that H+-ATPase purified from different membrane compartments in the mammalian kidney varied in their structural and functional properties (6). Again, differences in the structure ofthe -56-kDa polypeptide subunit were noted. Work from several laboratories has subsequently revealed at least ...