Yasuyuki Nagasawa

The CXCL12 (SDF-1)/CXCR4 Axis Is Essential for the Development of Renal Vasculature

CXC chemokine ligand 12 (CXCL12; stromal cell-derived factor 1) is a unique homeostatic chemokine that signals through its cognate receptor, CXCR4. CXCL12/CXCR4 signaling is essential for the formation of blood vessels in the gastrointestinal tract during development, but its contribution to renal development remains unclear. Here, we found that CXCL12-secreting stromal cells surround CXCR4-positive epithelial components of early nephrons and blood vessels in the embryonic kidney. In glomeruli, we observed CXCL12-secreting podocytes in close proximity to CXCR4-positive endothelial cells. Both CXCL12- and CXCR4-deficient kidneys exhibited identical phenotypes; there were no apparent abnormalities in early nephrogenesis or in differentiation of podocytes and tubules, but there was defective formation of blood vessels, including ballooning of the developing glomerular tuft and disorganized patterning of the renal vasculature. To clarify the relative importance of different cellular defects resulting from ablation of CXCL12 and CXCR4, we established endothelial cell-specific CXCR4-deficient mice, which recapitulated the renal phenotypes of conventional CXCR4-deficient mice. We conclude that CXCL12 secreted from stromal cells or podocytes acts on endothelial cells to regulate vascular development in the kidney. These findings suggest new potential therapeutic targets for remodeling the injured kidney.

Identification and Characterization of Pkhd1, the Mouse Orthologue of the Human ARPKD Gene

PKHD1, the gene mutated in human autosomal recessive polycystic kidney disease has recently been identified. Its translation products are predicted to belong to a superfamily of proteins involved in the regulation of cellular adhesion and repulsion. One notable aspect of the gene is its unusually complex pattern of splicing. This study shows that mouse Pkhd1 and its translation products have very similar properties to its human orthologue. Mouse Pkhd1 extends over approximately 500 kb of genomic DNA, includes a minimum of 68 nonoverlapping exons, and exhibits a complex pattern of splicing. The longest ORF encodes a protein of 4059aa predicted to have an N-terminal signal peptide, multiple IPTs and PbH1 repeats, a single transmembrane span (TM), and a short cytoplasmic C-terminus. Although the protein sequence is generally well conserved (approximately 73% average identity), the C-termini share only 55% identity. The pattern of Pkhd1 expression by in situ hybridization was also examined in developing and adult mouse tissues over a range of ages (E12.5 to 3 mo postnatal). High levels of expression were present in renal and biliary tubular structures at all time points examined. Prominent Pkhd1 signals were also found in a number of other organs and tissues. Tissue-specific differences in transcript expression were revealed through the use of single exon probes. These data show that key features of human PKHD1 are highly conserved in the mouse and suggest that the complicated pattern of splicing is likely to be functionally important.

Fully phosphorylated fetuin-A forms a mineral complex in the serum of rats with adenine-induced renal failure

The serum glycoprotein fetuin-A is an important inhibitor of extra-osseous calcification, but correlations between serum fetuin-A levels and the extent of vascular calcification are controversial. In this study, we used a rat model of adenine-induced renal failure with secondary hyperparathyroidism that exhibits all characteristic features of patients with chronic kidney disease. These rats had medial vascular calcification along with reduced levels of both serum and hepatic fetuin-A. Treatment with an inhibitor of ectopic calcification, alendronate, decreased bone turnover and eliminated completely the vascular calcification in this rat model, but there was no change in the levels of hepatic and serum fetuin-A. Centrifugation of the serum of untreated rats with renal failure gave a small precipitate composed of fetuin-A, calcium, magnesium, and phosphate; this complex, absent from normal rat serum, was not found in the serum of alendronate-treated rats with renal failure. Rat serum contained three types of phosphorylated fetuin-A, as well as unphosphorylated forms, but only the fully phosphorylated fetuin-A was present in the mineral complex. The amount of this complex reflected the risk of mineral precipitation. Our results suggest that the measurement of serum fetuin-mineral complex rather than fetuin-A alone might provide a better indication of extra-osseous calcification propensity.

Milder Presentation of Recessive Polycystic Kidney Disease Requires Presence of Amino Acid Substitution Mutations

Autosomal recessive polycystic kidney disease (ARPKD; MIM 263200) is a hereditary and severe form of polycystic disease affecting the kidneys and biliary tract with an estimated incidence of 1 in 20,000 live births. The clinical spectrum is widely variable: up to 50% of affected neonates die shortly after birth, whereas others survive to adulthood. Mutations at a single locus, polycystic kidney and hepatic disease 1 (PKHD1), are responsible for all typical forms of ARPKD. Mutation detection was performed in PKHD1 by DHPLC in 85 affected, unrelated individuals. Seventy-four amplicons were amplified and analyzed from the PKHD1 genomic locus. Sequence variants were considered pathogenic when they were not observed in 160 control individuals (320 chromosomes). For purposes of genotype-phenotype comparisons, families were stratified by clinical presentation into two groups: the severe perinatal group, in which at least one affected child presented with perinatal disease and neonatal demise, and the less severe, nonperinatal group, in which none of the affected children died in the neonatal period. Forty-one mutations were found in 55 affected disease chromosomes; 32 of these mutations have not been reported previously. Mutations were distributed throughout the portions of gene encoding the predicted extracellular portion of the protein product. The most commonly encountered mutation, T36M, was found in 8 of 55 disease chromosomes. Amino acid substitutions were found to be more commonly associated with a nonlethal presentation, whereas chain terminating mutations were more commonly associated with neonatal demise (chi(2) = 11.54, P = 0.003). All patients who survive the neonatal period have at least one amino acid substitution mutation, suggesting that such substitutions produce milder disease through production of partially functional protein products. The nature of the germline mutations in ARPKD plays a significant role in determining clinical outcome.

Effect of Renin-Angiotensin-Aldosterone System Triple Blockade on Non-Diabetic Renal Disease: Addition of an Aldosterone Blocker, Spironolactone, to Combination Treatment with an Angiotensin-Converting Enzyme Inhibitor and Angiotensin II Receptor Blocker

Although dual blockade of the renin-angiotensin-aldosterone system (RAAS) with the combination of an angiotensin-converting enzyme inhibitor (ACE-I) and angiotensin II receptor blocker (ARB) is generally well-established as a treatment for nephropathy, this treatment is not fully effective in some patients. Based on the recent evidence implicating aldosterone in renal disease progression, this study was conducted to examine the efficacy of blockade with three different mechanisms by adding an aldosterone blocker in patients who do not respond adequately to the dual blockade. A 1-year randomized, open-label, multicenter, prospective controlled study was conducted, in which 32 non-diabetic nephropathy patients with proteinuria exceeding 0.5 g/day were enrolled after more than 12 weeks of ACE-I (5 mg enalapril) and ARB (50 mg losartan) combination treatment. These patients were allocated into two groups of 16 patients each: a triple blockade group in which 25 mg of spironolactone daily was added to the ACE-I and ARB combination treatment, and a control group in which 1 mg of trichlormethiazide or 20 mg of furosemide was added to the combination treatment instead of spironolactone depending upon the creatinine level. After 1 year of treatment, the urinary protein level decreased by 58% (p<0.05) with the triple blockade but was unchanged in the controls. Furthermore, urinary type IV collagen level decreased by 40% (p<0.05) with the triple blockade but was unchanged in the controls. The decreases in urinary protein and urinary type IV collagen were not accompanied by a decrease in blood pressure. Mean serum creatinine, potassium and blood pressure did not change significantly by either treatment. In conclusion, triple blockade of the RAAS was effective for the treatment of proteinuria in patients with non-diabetic nephropathy whose increased urinary protein had not responded sufficiently to a dual blockade. (Hypertens Res 2008; 31: 59−67)

Intact fibroblast growth factor 23 levels predict incident cardiovascular event before but not after the start of dialysis

PURPOSE Low 25-hydroxyvitamin D (25D), increased levels of fibroblast growth factor 23 (FGF23), parathyroid hormone (PTH), and alkaline phosphatase (ALP) were reported to be risk factors for mortality in chronic kidney disease (CKD). However, the independent associations of these factors with cardiovascular disease (CVD), the leading cause of death among CKD patients, remain unclear. Our purpose was to identify which of these factors predict incident CVD in CKD. METHODS In this prospective cohort study, we enrolled 738 predialysis outpatients in the two nephrology departments. We employed Cox proportional hazards analyses to elucidate predictors of the endpoint, defined as fatal or non-fatal cardiovascular event requiring hospitalization. Multiple imputation was performed for missing values. RESULTS Mean estimated glomerular filtration rate (eGFR) was 35 mL/min/1.73 m(2). During a median duration of 4.4 years, 86 patients developed the endpoint, of whom 62 patients achieved it before the initiation of dialysis. Multivariable analyses revealed that high serum intact FGF23 levels predicted the outcome preceding dialysis initiation (hazard ratio (HR) per lnFGF23 (SD), 1.64 (1.27-2.30)), while 25D, PTH, and bone-specific ALP did not. Adding FGF23 to the conventional model of age, sex, diabetes, prior CVD, pulse pressure, and eGFR, led to a net reclassification improvement of 6.87% (P=0.04). Not censoring the patients at the start of dialysis and continuing follow-up even after dialysis, FGF23 levels did not predict the outcome (HR, 1.16 (0.91-1.48)). Complete case analyses yielded similar results. CONCLUSIONS Intact FGF23 levels in predialysis CKD predicted incident cardiovascular events requiring hospitalization before starting dialysis, but did not predict events during the entire follow-up period, including post dialysis initiation.

Cigarette smoking and progression of IgA nephropathy.

BACKGROUND Multiple community-based cohort studies of mainly middle-aged and elderly populations have shown that cigarette smoking is a risk factor for chronic kidney disease. However, little information is available about an effect of cigarette smoking on progression of primary kidney diseases, including immunoglobulin A (IgA) nephropathy. STUDY DESIGN Retrospective cohort study. SETTING & PARTICIPANTS 971 of 1,001 patients with a diagnosis of IgA nephropathy in 3 major nephrology centers in Osaka, Japan, between 1992 and 2005 who enrolled in the Study of Outcome and Practice Pattern of IgA Nephropathy (STOP-IgAN). PREDICTORS Smoking status and number of cigarettes smoked at the time of diagnosis using kidney biopsy. Dose-dependent associations between cigarette smoking and outcomes were assessed in multivariate Cox proportional hazards models. Significantly different clinical characteristics between non-/past and current smokers were controlled for using propensity score-based adjustment, stratification, and matching. OUTCOMES 50% increase in serum creatinine level as primary outcome. A composite outcome of a 100% increase in serum creatinine level or end-stage renal disease (ESRD) and ESRD alone as secondary outcomes. RESULTS During the median 5.8 years (interquartile range, 2.6-10.2) of the observational period, 117 participants progressed to a 50% increase in serum creatinine level and 47 advanced to ESRD. Multivariate Cox proportional hazards models identified current smokers (HR, 2.03 [95% CI, 1.33-3.10] for primary outcome) and number of cigarettes at kidney biopsy (HR, 1.21 [95% CI, 1.06-1.39] per 10 cigarettes per day) as significant predictors of outcomes. Propensity score-based models confirmed these results. Tests for interaction showed that the association of current smoking with adverse outcomes was stronger in those with lower compared with higher estimated glomerular filtration rates. LIMITATION Baseline smoking status was not verified using biochemical tests. Smoking status during the observational period was unavailable. CONCLUSIONS Cigarette smoking, in a dose-dependent manner, was identified as a key prognostic factor in IgA nephropathy. Smoking cessation should be encouraged as part of the treatment for IgA nephropathy.

Active vitamin D and its analogue, 22-oxacalcitriol, ameliorate puromycin aminonucleoside-induced nephrosis in rats

BACKGROUND Recent studies have demonstrated that podocyte injury, which results in proteinuria, leads to tubulointerstitial fibrosis. Although some studies have revealed that vitamin D administration protects renal structure and function in mesangial cell proliferative and/or excessive matrix productive models, the effects of vitamin D on podocyte injury have remained uncertain. METHODS In this study, we examined whether administration of active vitamin D (calcitriol) or its analogue, 22-oxacalcitriol (maxacalcitol), is preventative in podocyte injury using the puromycin aminonucleoside nephrosis model with neither mesangial proliferation nor matrix accumulation. RESULTS Before the onset of proteinuria, renal 1alpha-hydroxylase and 24-hydroxylase were markedly down-regulated and up-regulated, respectively, leading to impaired vitamin D activation. Thereafter, serum 25-hydroxyvitamin D decreased along with the increased excretion of vitamin D-binding protein in urine. After confirming that podocytes express vitamin D receptor and all retinoid X receptors (RXRs) except RXR-alpha, we found that daily administration of calcitriol or its analogue 22-oxacalcitriol ameliorated the nephrotic state by protecting podocytes, as shown by the reduced staining of desmin (podocyte injury marker) and the upregulation of nephrin and podocin. These data suggest that the impairment of the vitamin D system plays a role in increasing proteinuria in podocyte injury. CONCLUSIONS We demonstrated the breakdown of the vitamin D activation system in podocyte injury, and established a preventative role for vitamin D in podocyte injury.

The impact of diabetes mellitus on vitamin D metabolism in predialysis patients

Although diabetes mellitus (DM) disturbs bone metabolism, little is known concerning its effects on laboratory abnormalities in chronic kidney disease-mineral and bone disorders (CKD-MBD). We extracted data for 602 patients from the Osaka Vitamin D Study in patients with CKD (OVIDS-CKD), an observational study enrolling predialysis outpatients. No enrolled patients received vitamin D, bisphosphonate, estrogen or raloxifene. We measured 1- 84 PTH, 25-hydroxyvitamin D (25D), calcitriol, fibroblast growth factor-23 (FGF-23), calcium (Ca), and phosphate (P). Since there were 112 DM patients (group D), we extracted 112 age-, sex-, and eGFR-matched non-DM counterparts (group N). We compared biochemical markers between groups, and then performed multiple regression analyses for all 602 subjects to confirm the results obtained. Group D had significantly higher corrected Ca and P than group N throughout all stages of CKD. In group D, 25D decreased as renal function declined, while in group N it remained constant (interaction P<0.05). Despite higher P and poorer vitamin D status in DM, there were no differences in 1- 84 PTH level between group D and group N stratified by stage of CKD, resulting in significantly lower calcitriol levels in group D in late CKD. Multiple regression analyses revealed that DM was significantly associated with low vitamin D status even with adjustment for urinary protein, and that this poorer vitamin D status in DM was responsible for lower calcitriol level associated with DM. Despite higher P, lower FGF-23 in early CKD (stages 1 + 2) and comparable level of FGF-23 in late stages of CKD (stages 3, 4, and 5) were observed in group D. We interpreted these results to indicate that inappropriate production of FGF-23 in DM might explain higher serum phosphate in DM. Multiple regression analysis with adjustment for covariates confirmed an independent relationship between DM and low FGF-23, implying the existence of dysfunction or decreased density of osteocytes in DM. Given the origin of these phosphaturic hormones, DM may thus have markedly deleterious effects on parathyroid and bone. Poorer vitamin D status and higher CaP product might be partly responsible for functional and structural changes of vasculature, respectively, in DM.

Serum Osteoprotegerin as a Screening Tool for Coronary Artery Calcification Score in Diabetic Pre-Dialysis Patients

Although cardiovascular disease is a principal cause of death in patients with chronic kidney disease (CKD), it is often asymptomatic in diabetic patients. The coronary artery calcification score (CACS) measured by multidetector computed tomography (MDCT) is useful for screening ischemic heart disease in the general population. We investigated which clinical parameters predict high CACS in predialysis diabetic nephropathy (DN). Participants were 85 patients with DN. Nobody had any history of coronary angioplasty or coronary bypass surgery. We measured blood counts, blood chemistry, bone alkaline phosphatase, intact-PTH, interleukin-6, osteoprotegerin (OPG), hemoglobin A1c, 25-hydroxyvitamin D (25(OH)D) and fetuin-A. CACS and bone mineral density (BMD) were measured by a single 16-slice MDCT and DEXA, respectively. The median value of CACS equaled 256 Agatston units (range 0–4494 units). Stepwise increase in CACS with CKD stage progression was observed (p<0.01 for trend). Simple regression analyses showed that Log (CACS+1) was positively correlated with age, systolic blood pressure, phosphorus and OPG. In addition, it was negatively correlated with nutritional parameters, such as body mass index, albumin, total-cholesterol and 25(OH)D. Fetuin-A and BMD had no impact on CACS. Multiple regression analyses showed that low albumin and high OPG were associated with high CACS. The sensitivity of OPG for detecting CACS>200 was 80%, when the cut-off value was 1.2 ng/mL. In conclusion, CACS increased with CKD stage progression in predialysis DN patients. Serum OPG was positively associated with high CACS and can be a useful screening tool for severe coronary calcification, whereas no association between fetuin-A and CACS was found.