Journal of the American Society of Nephrology current issue

This Month's Highlights

2009-06-30

On the Passing of Thomas E. Andreoli

Seldin, D. W. — 2009-06-30

How to Build a Tight but Permeable Glomerular Junction

Martini, S., Kretzler, M. — 2009-06-30

Type II Calcimimetics and Polycystic Kidney Disease: Unanswered Questions

Torres, V. E. — 2009-06-30

The Promise of Well-Being: Stay in Shape with N(i)ck

Benzing, T. — 2009-06-30

Glomerular Filtration: Still Sympathetic to Endothelin's Influence?

Hunley, T. E., Kon, V. — 2009-06-30

Do Genes Allow Inflammation to Kill or Not to Kill?

Kovesdy, C. P., Kalantar-Zadeh, K. — 2009-06-30

Why Is the Mortality of Dialysis Patients in the United States Much Higher than the Rest of the World?

Foley, R. N., Hakim, R. M. — 2009-06-30

Resolved: Targeting a Higher Hemoglobin Is Associated with Greater Risk in Patients with CKD Anemia: Pro

Singh, A. K., Himmelfarb, J., Szczech, L. A. — 2009-06-30

Some time has passed since the torrent of discussion surrounding the cardiovascular risk of pushing up hemoglobin concentrations in dialysis patients with erythropoietin. The debate here reflects a look back on the tension produced by confusing data and outcomes. Is it the target hemoglobin per se or the high doses of erythropoietin in subsets of resistant patients that is the problem? You decide.

Apical Lumen Formation in Renal Epithelia

Schluter, M. A., Margolis, B. — 2009-06-30

The ability to form epithelial lumina is a central architectural characteristic of virtually all organs and indispensable for their function. Ontogenetically, the kidney is one of the best-characterized organs, but concepts of the regulated formation of its hollow epithelial structures are still emerging. Epithelial cell lines provide the opportunity to study molecular mechanisms in simplified assays modeling cyst and tube formation. In these systems, several groups have identified molecules implicated in lumen formation, and their downregulation results in either multiple-lumen or no-lumen phenotypes. On the basis of these phenotypes, we propose a working model, assigning proteins to groups with similar functions. Defects within these specific protein groups lead to distinct epithelial phenotypes. Studies of mesenchymal-to-epithelial transition underline the importance of these protein groups, but converting these basic models of lumen formation to an understanding of the mesenchymal to tubule formation during kidney development is still challenging.

Vascular Calcification: The Killer of Patients with Chronic Kidney Disease

Mizobuchi, M., Towler, D., Slatopolsky, E. — 2009-06-30

Cardiovascular complications are the leading cause of death in patients with chronic kidney disease (CKD). Vascular calcification is a common complication in CKD, and investigators have demonstrated that the extent and histoanatomic type of vascular calcification are predictors of subsequent vascular mortality. Although research efforts in the past decade have greatly improved our knowledge of the multiple factors and mechanisms involved in vascular calcification in patients with kidney disease, many questions remain unanswered. No longer can we accept the concept that vascular calcification in CKD is a passive process resulting from an elevated calcium-phosphate product. Rather, as a result of the metabolic insults of diabetes, dyslipidemia, oxidative stress, uremia, and hyperphosphatemia, "osteoblast-like" cells form in the vessel wall. These mineralizing cells as well as the recruitment of undifferentiated progenitors to the osteochondrocyte lineage play a critical role in the calcification process. Important transcription factors such as Msx 2, osterix, and RUNX2 are crucial in the programming of osteogenesis. Thus, the simultaneous increase in arterial osteochondrocytic programs and reduction in active cellular defense mechanisms creates the "perfect storm" of vascular calcification seen in ESRD. Innovative clinical studies addressing the combined use of inhibitors that work on vascular calcification through distinct molecular mechanisms, such as fetuin-A, osteopontin, and bone morphogenic protein 7, among others, will be necessary to reduce significantly the accrual of vascular calcifications and cardiovascular mortality in kidney disease. In addition, the roles of oxidative stress and inflammation on the fate of smooth muscle vascular cells and their function deserve further translational investigation.

How Does the Ureteric Bud Branch?

Nigam, S. K., Shah, M. M. — 2009-06-30

Many genes that modulate kidney development have been identified; however, the molecular interactions that direct arborization of the ureteric bud (UB) remain incompletely understood. This article discusses how "systems" approaches may shed light on the structure of the gene network during UB branching morphogenesis and the mechanisms involved in the formation of a branched collecting system from a straight epithelial tube in the context of a stage model. In vitro and genetic studies suggest that the stages seem to be governed by a conserved network of genes that establish a "tip-stalk generator"; these genes sustain iterative UB branching tubulogenesis through minimal alterations in the network architecture as a budding system shifts to one that autocatalytically branches through budding. The differential expression of stage-specific positive and inhibitory factors in the mesenchyme, likely presented in the context of heparan sulfate proteoglycans, and effector molecules in the epithelium seems to regulate advancement between stages; similar principles may apply to other branching epithelia such as the lung, salivary gland, pancreas, mammary gland, and prostate. Active mesenchymal interactions with the UB seem to govern vectorial arborization and tapering of the collecting system and its terminal differentiation. Cessation of branching correlates with induction of mesenchyme as well as local extracellular matrix changes. Perturbations of these mechanisms and/or single-nucleotide polymorphisms in genes regulating UB branching may predispose to a variety of renal diseases (e.g., hypertension and chronic kidney disease) by altering nephron number. Decentralization of the gene–protein interaction network may explain the relative paucity of branching phenotypes in mutant mice and in human disease.

Cellular Origins of Type IV Collagen Networks in Developing Glomeruli

Abrahamson, D. R., Hudson, B. G., Stroganova, L., Borza, D.-B., St. John, P. L. — 2009-06-30

Laminin and type IV collagen composition of the glomerular basement membrane changes during glomerular development and maturation. Although it is known that both glomerular endothelial cells and podocytes produce different laminin isoforms at the appropriate stages of development, the cellular origins for the different type IV collagen heterotrimers that appear during development are unknown. Here, immunoelectron microscopy demonstrated that endothelial cells, mesangial cells, and podocytes of immature glomeruli synthesize collagen 121(IV). However, intracellular labeling revealed that podocytes, but not endothelial or mesangial cells, contain collagen 345(IV). To evaluate the origins of collagen IV further, we transplanted embryonic kidneys from Col4a3-null mutants (Alport mice) into kidneys of newborn, wildtype mice. Hybrid glomeruli within grafts containing numerous host-derived, wildtype endothelial cells never expressed collagen 345(IV). Finally, confocal microscopy of glomeruli from infant Alport mice that had been dually labeled with anti-collagen 5(IV) and the podocyte marker anti-GLEPP1 showed immunolabeling exclusively within podocytes. Together, these results indicate that collagen 345(IV) originates solely from podocytes; therefore, glomerular Alport disease is a genetic defect that manifests specifically within this cell type.

Nucleotides Downregulate Aquaporin 2 via Activation of Apical P2 Receptors

2009-06-30

Vasopressin regulates water reabsorption in the collecting duct, but extracellular nucleotides modulate this regulation through incompletely understood mechanisms. We investigated these mechanisms using immortalized mouse collecting duct (mpkCCD) cells. Basolateral exposure to dDAVP induced AQP2 localization to the apical membrane, but co-treatment with ATP internalized AQP2. Because plasma membrane-bound P2 receptors (P2R) mediate the effects of extracellular nucleotides, we examined the abundance and localization of P2R in mpkCCD cells. In the absence of dDAVP, P2Y₁ and P2Y₄ receptors localized to the apical membrane, whereas P2X₂, P2X₄, P2X₅, P2X₇, P2Y₂, P2Y₁₁, and P2Y₁₂ receptors localized to the cytoplasm. dDAVP induced gene expression of P2X₁, which localized to the apical domain, and led to translocation of P2X₂ and P2Y₂ to the apical and basolateral membranes, respectively. In co-expression experiments, P2R activation decreased membrane AQP2 and AQP2-mediated water permeability in Xenopus oocytes expressing P2X₂, P2Y_2, or P2Y₄ receptors, but not in oocytes expressing other P2R subtypes. In summary, these data suggest that AQP2-mediated water transport is downregulated not only by basolateral nucleotides, mediated by P2Y₂ receptors, but also by luminal nucleotides, mediated by P2X₂ and/or P2Y₄ receptors.

Slit Diaphragms Contain Tight Junction Proteins

Fukasawa, H., Bornheimer, S., Kudlicka, K., Farquhar, M. G. — 2009-06-30

Slit diaphragms are essential components of the glomerular filtration apparatus, as changes in these junctions are the hallmark of proteinuric diseases. Slit diaphragms, considered specialized adherens junctions, contain both unique membrane proteins (e.g., nephrin, podocin, and Neph1) and typical adherens junction proteins (e.g., P-cadherin, FAT, and catenins). Whether slit diaphragms also contain tight junction proteins is unknown. Here, immunofluorescence, immunogold labeling, and cell fractionation demonstrated that rat slit diaphragms contain the tight junction proteins JAM-A (junctional adhesion molecule A), occludin, and cingulin. We found these proteins in the same protein complexes as nephrin, podocin, CD2AP, ZO-1, and Neph1 by cosedimentation, coimmunoprecipitation, and pull-down assays. PAN nephrosis increased the protein levels of JAM-A, occludin, cingulin, and ZO-1 several-fold in glomeruli and loosened their attachment to the actin cytoskeleton. These data extend current information about the molecular composition of slit diaphragms by demonstrating the presence of tight junction proteins, although slit diaphragms lack the characteristic morphologic features of tight junctions. The contribution of these proteins to the assembly of slit diaphragms and potential signaling cascades requires further investigation.

Dietary Phosphorus Acutely Impairs Endothelial Function

2009-06-30

Excessive dietary phosphorus may increase cardiovascular risk in healthy individuals as well as in patients with chronic kidney disease, but the mechanisms underlying this risk are not completely understood. To determine whether postprandial hyperphosphatemia may promote endothelial dysfunction, we investigated the acute effect of phosphorus loading on endothelial function in vitro and in vivo. Exposing bovine aortic endothelial cells to a phosphorus load increased production of reactive oxygen species, which depended on phosphorus influx via sodium-dependent phosphate transporters, and decreased nitric oxide production via inhibitory phosphorylation of endothelial nitric oxide synthase. Phosphorus loading inhibited endothelium-dependent vasodilation of rat aortic rings. In 11 healthy men, we alternately served meals containing 400 mg or 1200 mg of phosphorus in a double-blind crossover study and measured flow-mediated dilation of the brachial artery before and 2 h after the meals. The high dietary phosphorus load increased serum phosphorus at 2 h and significantly decreased flow-mediated dilation. Flow-mediated dilation correlated inversely with serum phosphorus. Taken together, these findings suggest that endothelial dysfunction mediated by acute postprandial hyperphosphatemia may contribute to the relationship between serum phosphorus level and the risk for cardiovascular morbidity and mortality.

CTGF Promotes Inflammatory Cell Infiltration of the Renal Interstitium by Activating NF-{kappa}B

2009-06-30

Connective tissue growth factor (CTGF) is an important profibrotic factor in kidney diseases. Blockade of endogenous CTGF ameliorates experimental renal damage and inhibits synthesis of extracellular matrix in cultured renal cells. CTGF regulates several cellular responses, including adhesion, migration, proliferation, and synthesis of proinflammatory factors. Here, we investigated whether CTGF participates in the inflammatory process in the kidney by evaluating the nuclear factor-kappa B (NF-B) pathway, a key signaling system that controls inflammation and immune responses. Systemic administration of CTGF to mice for 24 h induced marked infiltration of inflammatory cells in the renal interstitium (T lymphocytes and monocytes/macrophages) and led to elevated renal NF-B activity. Administration of CTGF increased renal expression of chemokines (MCP-1 and RANTES) and cytokines (INF-, IL-6, and IL-4) that recruit immune cells and promote inflammation. Treatment with a NF-B inhibitor, parthenolide, inhibited CTGF-induced renal inflammatory responses, including the up-regulation of chemokines and cytokines. In cultured murine tubuloepithelial cells, CTGF rapidly activated the NF-B pathway and the cascade of mitogen-activated protein kinases, demonstrating crosstalk between these signaling pathways. CTGF, via mitogen-activated protein kinase and NF-B activation, increased proinflammatory gene expression. These data show that in addition to its profibrotic properties, CTGF contributes to the recruitment of inflammatory cells in the kidney by activating the NF-B pathway.

Calcimimetic Inhibits Late-Stage Cyst Growth in ADPKD

2009-06-30

In polycystic kidney disease (PKD), genetic mutations in polycystin 1 and 2 lead to defective intracellular trafficking of calcium, thereby decreasing intracellular calcium and altering cAMP signaling to favor proliferation. We hypothesized that calcimimetics, allosteric modulators of the calcium-sensing receptor, would reduce cyst growth by increasing intracellular calcium. We randomly assigned 20-wk-old male rats with a form of autosomal dominant PKD (heterozygote Cy/+) to one of four groups for 14 to 18 wk of treatment: (group 1) no treatment; (group 2) calcimimetic R-568 formulated in the diet; (group 3) R-568 plus calcium-supplemented drinking water (R-568 plus Ca); or (group 4) Ca-supplemented drinking water with a normal diet (Ca). Severity of PKD did not progress in any of the three treatment groups between 34 and 38 wk. Compared with no treatment, cyst growth was unaffected at 34 wk by all treatments, but cyst volume and fibrosis were lower at 38 wk, with both R-568-treated groups demonstrating a greater reduction than calcium alone. Between 34 and 38 wk, the total kidney weight increased by 78% in the control group (P < 0.001) and by 19% in the Ca group (P < 0.01), but did not increase in the R-568 or R-568 plus Ca groups, suggesting inhibition of disease progression despite equivalent suppression of parathyroid hormone. In summary, treatment of hyperparathyroidism halts late-stage progression of rodent cystic kidney disease. The benefit of R-568 alone suggests calcium-sensing receptor modulation may have additional inhibitory effects on late-stage cyst growth resulting from a direct modulation of intracellular calcium.

Nck Proteins Maintain the Adult Glomerular Filtration Barrier

2009-06-30

Within the glomerulus, the scaffolding protein nephrin bridges the actin-rich foot processes that extend from adjacent podocytes to form the slit diaphragm. Mutations affecting a number of slit diaphragm proteins, including nephrin, cause glomerular disease through rearrangement of the actin cytoskeleton and disruption of the filtration barrier. We recently established that the Nck family of Src homology 2 (SH2)/SH3 cytoskeletal adaptor proteins can mediate nephrin-dependent actin reorganization. Formation of foot processes requires expression of Nck in developing podocytes, but it is unknown whether Nck maintains podocyte structure and function throughout life. Here, we used an inducible transgenic strategy to delete Nck expression in adult mouse podocytes and found that loss of Nck expression rapidly led to proteinuria, glomerulosclerosis, and altered morphology of foot processes. We also found that podocyte injury reduced phosphorylation of nephrin in adult kidneys. These data suggest that Nck is required to maintain adult podocytes and that phosphotyrosine-based interactions with nephrin may occur in foot processes of resting, mature podocytes.

IRF-1 Promotes Inflammation Early after Ischemic Acute Kidney Injury

2009-06-30

Acute renal ischemia elicits an inflammatory response that may exacerbate acute kidney injury, but the regulation of the initial signals that recruit leukocytes is not well understood. Here, we found that IFN regulatory factor 1 (IRF-1) was a critical, early proinflammatory signal released during ischemic injury in vitro and in vivo. Within 15 min of reperfusion, proximal tubular cells of the S3 segment produced IRF-1, which is a transcription factor that activates proinflammatory genes. Transgenic knockout of IRF-1 ameliorated the impairment of renal function, morphologic injury, and inflammation after acute ischemia. Bone marrow chimera experiments determined that maximal ischemic injury required IRF-1 expression by both leukocytes and radioresistant renal cells, the latter identified as S3 proximal tubule cells in the outer medulla by in situ hybridization and immunohistochemistry. In vitro, reactive oxygen species, generated during ischemia/reperfusion injury, stimulated expression of IRF-1 in an S3 proximal tubular cell line. Taken together, these data suggest that IRF-1 gene activation by reactive oxygen species is an early signal that promotes inflammation after ischemic renal injury.

Bestrophin 1 Promotes Epithelial-to-mesenchymal Transition of Renal Collecting Duct Cells

2009-06-30

Bestrophin 1 (Best1) controls intracellular Ca²⁺ concentration, induces Ca²⁺-activated Cl^- conductance, and increases proliferation of colon carcinoma cells. Here, we show that expression of Best1 in mouse renal collecting duct (CD) cells causes i) an increase in cell proliferation, ii) a loss of amiloride-sensitive Na⁺ absorption, iii) induction of Ca²⁺-dependent Cl^- conductance (CaCC), and iv) epithelial-to-mesenchymal transition. During conditions of high proliferation or when we exposed CD cells to serum or TGF–β1, we observed upregulation of Best1, increased CaCC, redistribution of the epithelial-to-mesenchymal transition marker β-catenin, and upregulation of vimentin. In contrast, suppression of Best1 by RNAi inhibited proliferation, reduced CaCC, and downregulated markers of EMT. CaCC and expression of Best1 were independent of the cell cycle but clearly correlated to cell proliferation and cell density. During renal inflammation in LPS-treated mice or after unilateral ureteral obstruction, we observed transient upregulation of Best1. These data indicate that repression of cell proliferation, CaCC, and expression of Best1 occurs during mesenchymal-to-epithelial transition once CD cells polarize and terminally differentiate. These results may suggest a role for Best1 in renal fibrosis and tissue repair.

The E-Selectin Ligand Basigin/CD147 Is Responsible for Neutrophil Recruitment in Renal Ischemia/Reperfusion

2009-06-30

E-selectin and its ligands are essential for extravasation of leukocytes in inflammation. Here, we report that basigin (Bsg)/CD147 is a ligand for E-selectin that promotes renal inflammation in ischemia/reperfusion. Compared with wild-type mice, Bsg-deficient (Bsg^–/–) mice demonstrated striking suppression of neutrophil infiltration in the kidney after renal ischemia/reperfusion. Although E-selectin expression increased similarly between the two genotypes, Bsg^–/– mice exhibited less renal damage, suggesting that Bsg on neutrophils contribute to renal injury in this model. Neutrophils expressed Bsg with N-linked polylactosamine chains and Bsg^–^/^– neutrophils showed reduced binding to E-selectin. Bsg isolated from HL-60 cells bound to E-selectin, and tunicamycin treatment to abolish N-linked glycans from Bsg abrogated this binding. Furthermore, Bsg^–^/^– neutrophils exhibited reduced E-selectin-dependent adherence to human umbilical vein endothelial cells in vitro. Injection of labeled neutrophils into mice showed that Bsg^–^/^– neutrophils were less readily recruited to the kidney after renal ischemia/reperfusion than Bsg^+/+ neutrophils, regardless of the recipient's genotype. Taken together, these results indicate that Bsg is a physiologic ligand for E-selectin that plays a critical role in the renal damage induced by ischemia/reperfusion.

Connexin 40 Mediates the Tubuloglomerular Feedback Contribution to Renal Blood Flow Autoregulation

Just, A., Kurtz, L., de Wit, C., Wagner, C., Kurtz, A., Arendshorst, W. J. — 2009-06-30

Connexins are important in vascular development and function. Connexin 40 (Cx40), which plays a predominant role in the formation of gap junctions in the vasculature, participates in the autoregulation of renal blood flow (RBF), but the underlying mechanisms are unknown. Here, Cx40-deficient mice (Cx40-ko) had impaired steady-state autoregulation to a sudden step increase in renal perfusion pressure. Analysis of the mechanisms underlying this derangement suggested that a marked reduction in tubuloglomerular feedback (TGF) in Cx40-ko mice was responsible. In transgenic mice with Cx40 replaced by Cx45, steady-state autoregulation and TGF were weaker than those in wild-type mice but stronger than those in Cx40-ko mice. N-Nitro-L-arginine-methyl-ester (L-NAME) augmented the myogenic response similarly in all genotypes, leaving autoregulation impaired in transgenic animals. The responses of renovascular resistance and arterial pressure to norepinephrine and acetylcholine were similar in all groups before or after L-NAME inhibition. Systemic and renal vasoconstrictor responses to L-NAME were also similar in all genotypes. We conclude that Cx40 contributes to RBF autoregulation by transducing TGF-mediated signals to the afferent arteriole, a function that is independent of nitric oxide (NO). However, Cx40 is not required for the modulation of the renal myogenic response by NO, norepinephrine-induced renal vasoconstriction, and acetylcholine- or NO-induced vasodilation.

Amino Acid Transporter LAT3 Is Required for Podocyte Development and Function

2009-06-30

LAT3 is a Na+-independent neutral l-amino acid transporter recently isolated from a human hepatocellular carcinoma cell line. Although liver, skeletal muscle, and pancreas are known to express LAT3, the tissue distribution and physiologic function of this transporter are not completely understood. Here, we observed that glomeruli express LAT3. Immunofluorescence, confocal microscopy, and immunoelectron microscopy revealed that LAT3 localizes to the apical plasma membrane of podocyte foot processes. In mice, starvation upregulated glomerular LAT3, phosphorylated AKT1, reconstituted the actin network, and elongated foot processes. In the fetal kidney, we observed intense LAT3 expression at the capillary loops stage of renal development. Finally, zebrafish morphants lacking lat3 function showed collapsed glomeruli with thickened glomerular basement membranes. Permeability studies of the glomerular filtration barrier in these zebrafish morphants demonstrated a disruption of selective glomerular permeability. Our data suggest that LAT3 may play a crucial role in the development and maintenance of podocyte structure and function by regulating protein synthesis and the actin cytoskeleton.

Linkage Analysis of Albuminuria

2009-06-30

American Indians have a higher prevalence of albuminuria than the general population, likely resulting from a combination of environmental and genetic risk factors. To localize gene regions influencing variation in urinary albumin-to-creatinine ratio, we performed a linkage analysis and explored gene-by-diabetes, -hypertension, and -obesity interactions in a large cohort of American Indian families. We recruited >3600 individuals from 13 American Indian tribes from three centers (Arizona, North and South Dakota, and Oklahoma). We performed multipoint variance component linkage analysis in each center as well as in the entire cohort after controlling for center effects. We used two modeling strategies: Model 1 incorporated age, gender, and interaction terms; model 2 also controlled for diabetes, BP, body mass index, HDL, LDL, triglycerides, and smoking status. We evaluated interactions with diabetes, hypertension, and obesity using additive, interaction-specific linkage and stratified analyses. Loci suggestive for linkage to urinary albumin-to-creatinine ratio included 1q, 6p, 9q, 18q, and 20p. Gene-by-diabetes interaction was present with a quantitative trait locus specific to the diabetic stratum in the Dakotas isolated on 18q21.2 to 21.3 using model 1 (logarithm of odds = 3.3). Gene-by-hypertension interaction was present with quantitative trait loci specific to the hypertensive stratum in the Dakotas on 7q21.11 using model 1 (logarithm of odds = 3.4) and 10q25.1 using model 2 (logarithm of odds = 3.3). These loci replicate findings from multiple other genome scans of kidney disease phenotypes with distinct populations and are worthy of further study.

Possible Effects of the New Medicare Reimbursement Policy on African Americans with ESRD

2009-06-30

Association of Preventive Health Care with Atherosclerotic Heart Disease and Mortality in CKD

Snyder, J. J., Collins, A. J. — 2009-06-30

Chronic kidney disease (CKD, stages 1 to 4) affects approximately 13.1% of United States adults and leads to ESRD, cardiovascular disease, and premature death. Here, we assessed adherence to a subset of Kidney Disease Outcomes Quality Initiative preventive health care guidelines and identified associations between adherence and incident atherosclerotic heart disease (ASHD). Using the Medicare 5% data set, 1999 to 2005 (about 1.2 million patients per year), we created 3-yr rolling cohorts. We classified CKD and diabetes during year 1, assessed preventive care during year 2, and evaluated ASHD outcomes during year 3. We defined preventive care by the receipt of laboratory measurements (serum creatinine, lipids, calcium and phosphorus, parathyroid hormone, and, for patients with diabetes, hemoglobin A1c), influenza vaccination, and by at least one outpatient visit to a nephrologist. Among patients with CKD, 80% received ≥2 serum creatinine tests during the year, and only 11% received parathyroid hormone testing. Cumulative incidence of the combined ASHD outcome was 25% and 11% for patients with and without prevalent cardiovascular disease, respectively. Except for serum creatinine testing, preventive care associated with lower ASHD rates in the subsequent year, ranging from 10% lower for those who received influenza vaccinations and ≥2 A1c tests, to 43% lower for calcium-phosphorus assessment. Receiving ≥2 serum creatinine tests associated with a 13% higher rate of ASHD. A higher number of preventive measures associated with lower rates of ASHD. In summary, these data support an association between preventive measures and reduced cardiovascular morbidity and mortality.

Chromogranin A Regulates Renal Function by Triggering Weibel-Palade Body Exocytosis

2009-06-30

Chromogranin A (CHGA), a protein released from secretory granules of chromaffin cells and sympathetic nerves, triggers endothelin-1 release from endothelial cells. CHGA polymorphisms associate with an increased risk for ESRD, but whether altered CHGA–endothelium interactions may explain this association is unknown. Here, CHGA led to the release of endothelin-1 and Weibel–Palade body exocytosis in cultured human umbilical vein endothelial cells. In addition, CHGA triggered secretion of endothelin-1 from glomerular endothelial cells and TGF-β1 from mesangial cells cocultured with glomerular endothelial cells. In humans, plasma CHGA correlated positively with endothelin-1 and negatively with GFR. GFR was highly heritable in twin pairs, and common promoter haplotypes of CHGA predicted GFR. In patients with progressive hypertensive renal disease, a CHGA haplotype predicted rate of GFR decline. In conclusion, these data suggest that CHGA acts through the glomerular endothelium to regulate renal function.

A Recessive Gene for Primary Vesicoureteral Reflux Maps to Chromosome 12p11-q13

2009-06-30

Primary vesicoureteral reflux (pVUR) is one of the most common causes of pediatric kidney failure. Linkage scans suggest that pVUR is genetically heterogeneous with two loci on chromosomes 1p13 and 2q37 under autosomal dominant inheritance. Absence of pVUR in parents of affected individuals raises the possibility of a recessive contribution to pVUR. We performed a genome-wide linkage scan in 12 large families segregating pVUR, comprising 72 affected individuals. To avoid potential misspecification of the trait locus, we performed a parametric linkage analysis using both dominant and recessive models. Analysis under the dominant model yielded no signals across the entire genome. In contrast, we identified a unique linkage peak under the recessive model on chromosome 12p11-q13 (D12S1048), which we confirmed by fine mapping. This interval achieved a peak heterogeneity LOD score of 3.6 with 60% of families linked. This heterogeneity LOD score improved to 4.5 with exclusion of two high-density pedigrees that failed to link across the entire genome. The linkage signal on chromosome 12p11-q13 originated from pedigrees of varying ethnicity, suggesting that recessive inheritance of a high frequency risk allele occurs in pVUR kindreds from many different populations. In conclusion, this study identifies a major new locus for pVUR and suggests that in addition to genetic heterogeneity, recessive contributions should be considered in all pVUR genome scans.

CCR5 Deletion Protects Against Inflammation-Associated Mortality in Dialysis Patients

2009-06-30

The CC-chemokine receptor 5 (CCR5) is a receptor for various proinflammatory chemokines, and a deletion variant of the CCR5 gene (CCR532) leads to deficiency of the receptor. We hypothesized that CCR532 modulates inflammation-driven mortality in patients with ESRD. We studied the interaction between CCR5 genotype and levels of high-sensitivity C-reactive protein (hsCRP) in 603 incident dialysis patients from the multicenter, prospective NEtherlands COoperative Study on the Adequacy of Dialysis (NECOSAD) cohort. CCR5 genotype and hsCRP levels were both available for 413 patients. During 5 yr of follow-up, 170 patients died; 87 from cardiovascular causes. Compared with the reference group of patients who had the wild-type CCR5 genotype and hsCRP ≤ 10 mg/L (n = 225), those carrying the deletion allele with hsCRP ≤ 10 mg/L (n = 55) had similar mortality, and those carrying the wild-type genotype with hsCRP > 10 mg/L (n = 108) had an increased risk for mortality (HR: 1.82; 95% CI: 1.29 to 2.58). However, those carrying the deletion allele with hsCRP > 10 mg/L (n = 25) had a mortality rate similar to the reference group; this seemingly protective effect of the CCR5 deletion was even more pronounced for cardiovascular mortality. We replicated these findings in an independent Swedish cohort of 302 ESRD patients. In conclusion, the CCR532 polymorphism attenuates the adverse effects of inflammation on overall and cardiovascular mortality in ESRD.