Altered renal sodium transporter expression in an animal model of type 2 diabetes mellitus

Hemodynamic factors play an important role in the development and/or progression of diabetic nephropathy. We hypothesized that renal sodium transporter dysregulation might contribute to the hemodynamic alterations in diabetic nephropathy. Otsuka Long Evans Tokushima Fatty (OLETF) rats were used as an animal model for type 2 diabetes. Long Evans Tokushima (LETO) rats were used as controls. Renal sodium transporter regulation was investigated by semiquantitative immunoblotting and immunohistochemistry of the kidneys of 40-week-old animals. The mean serum glucose level in OLETF rats was increased to 235+/-25 mg/dL at 25 weeks, and the hyperglycemia continued up to the end of 40 weeks. Urine protein/ creatinine ratios were 10 times higher in OLETF rats than in LETO rats. At 40th week, the abundance of the epithelial sodium channel (ENaC) beta-subunit was increased in OLETF rats, but the abundance of the ENaC gamma-subunit was decreased. No significant differences were observed in the ENaC alpha-subunit or other major sodium transporters. Immunohistochemistry for the ENaC beta-subunit showed increased immunoreactivity in OLETF rats, whereas the ENaC gamma-subunit showed reduced immunoreactivity in these rats. In OLETF rats, ENaC beta-subunit upregulation and ENaC gamma-subunit downregulation after the development of diabetic nephropathy may reflect an abnormal sodium balance

Effects of Thiazide on the Expression of TRPV5, Calbindin-D28K, and Sodium Transporters in Hypercalciuric Rats

TRPV5 is believed to play an important role in the regulation of urinary calcium excretion. We assessed the effects of hydrochlorothiazide (HCTZ) on the expression of TRPV5, calbindin-D28K, and several sodium transporters in hypercalciuric rats. Sprague-Dawley rats were divided into 4 groups; control, HCTZ, high salt, and high salt with HCTZ group in experiment 1; control, HCTZ, high calcium (Ca), and high Ca with HCTZ group in experiment 2. To quantitate the expression of TRPV5, calbindin-D28K, and sodium transporters, western blotting was performed. In both experiments, HCTZ significantly decreased urinary calcium excretion. TRPV5 protein abundance decreased in all hypercalciuric rats, and restored by HCTZ in both high salt with HCTZ and high Ca with HCTZ group. Calbindin-D28K protein abundance increased in the high salt and high salt with HCTZ groups, but did not differ among groups in experiment 2. Protein abundance of NHE3 and NKCC2 decreased in all hypercalciuric rats, and were restored by HCTZ in only high Ca-induced hypercalciuric rats. In summary, protein abundance of TRPV5, NHE3, and NKCC2 decreased in all hypercalciuric rats. The hypocalciuric effect of HCTZ is associated with increased protein abundance of TRPV5 in high salt or calcium diet-induced hypercalciuric rats

Association of Angiotensin II Type 2 Receptor Gene A1818T Polymorphism with Progression of Immunoglobulin A Nephropathy in Korean Patients

We determined the relationship between the progression of immunoglobulin A nephropathy (IgAN) and the A1818T polymorphism in intron 2 of Angiotensin II type 2 receptor (AT2R) gene, which might play protective roles in the pathogenesis of IgAN. Patients with biopsy-proven IgAN were recruited from the registry of the Progressive REnal disease and Medical Informatics and gEnomics Research (PREMIER) which was sponsored by the Korean Society of Nephrology. A1818T polymorphism of AT2R gene was analyzed with PCR-RFLP method and the association with the progression of IgAN, which was defined as over 50% increase in baseline serum creatinine level, was analyzed with survival analysis. Among the 480 patients followed for more than 10 months, the group without T allele had significantly higher rates of progression of IgAN than the group with T allele (11.4% vs. 3.9%, p=0.024), although there were no significant differences in the baseline variables such as initial serum creatinine level, the degree of proteinuria, and blood pressure. In the Cox's proportional hazard model, the hazard ratio of disease progression in the patients with T allele was 0.221 (95% confidence interval for Exp(B): 0.052-0.940, p=0.041) compared to that of without T allele. In conclusion, A1818T polymorphism of AT2R gene was associated with the progression of IgAN

The heme oxygenase-1 genotype is a risk factor to renal impairment of IgA nephropathy at diagnosis, which is a strong predictor of mortality

The induction of heme oxygenase-1 (HO-1) ameliorates oxidative stress and inflammatory process, which play important roles in IgA nephropathy. We hypothesized length polymorphism in the promoter region of the HO-1 gene, which is related to the level of gene transcription, is associated with disease severity of IgA nephropathy. The subjects comprised 916 patients with IgA nephropathy and gene data. Renal impairment was defined as an estimated glomerular filtration rate less than 60 mL/min/1.73 m(2) at diagnosis. The short (S: 28) (GT) repeats in the HO-1 gene was determined. The frequencies of S/S, S/M, M/M, S/L, L/M, and L/L genotypes were 7.2%, 6.9%, 3.1%, 30.8%, 22.7%, and 29.4%, respectively. The baseline characteristics were not different. In the S/S genotypic group, the renal impairment rate was 18.2%, which was lower than 32.2% in the group with M/M, L/M, or L/L genotype. The odds ratio of renal impairment in S/S genotype, compared to that in M/M, L/M, or L/L genotype, was 0.216 (95% confidence interval, 0.060-0.774, p=0.019). The HO-1 gene promoter length polymorphism was related to the renal impairment of IgA nephropathy at diagnosis, which is an important risk factor for mortality in IgA nephropathy patients

Transcriptional activator tone-binding protein in cellular protection and differentiation

The TonE-binding protein (TonEBP) is a transcriptional activator in the Rel family that includes NF kappa B and NFAT. TonEBP is critical for the development and function of the renal medulla, which is a major regulator of water homeostasis. TonEBP is also implicated in diabetic nephropathy and inflammation. Established methods for biochemical and histochemical detection and functional analysis of TonEBP, including identification of novel TonEBP target genes, are described for those who are interested in investigating function and regulation of TonEBP.open6

Activation of rice <em>nicotianamine synthase</em> 2 (<em>OsNAS2</em>) enhances iron availability for biofortification

Because micronutrients in human diets ultimately come from plant sources, malnutrition of essential minerals is a significant public health concern. By increasing the expression of nicotianamine synthase (NAS), we fortified the level of bioavailable iron in rice seeds. Activation of iron deficiency-inducible OsNAS2 resulted in a rise in Fe content (3.0-fold) in mature seeds. Its ectopic expression also increased that content. Enhanced expression led to higher tolerance of Fe deficiency and better growth under elevated pH. Mice fed with OsNAS2-D1 seeds recovered more rapidly from anemia, indicating that bioavailable Fe contents were improved by this increase in OsNAS2 expression

Downregulation of renal sodium transporters and tonicity-responsive enhancer binding protein by long-term treatment with cyclosporin A

Tonicity-responsive enhancer binding protein (TonEBP) is a transcriptional activator that is regulated by ambient tonicity. TonEBP protects the-rental medulla from the deleterious effects of hyperosmolality and regulates the urinary concentration by stimulating aquaporin-2 and urea transporters. The therapeutic use of cyclosporin A (CsA) is limited by nephrotoxicity that is manifested by reduced GFR, fibrosis, and tubular defects, including reduced urinary concentration. It was reported recently that long-term CsA treatment was associated with decreased renal expression of TonEBP target genes, including aquaporin-2, urea transporter, and aldose reductase. This study tested the hypothesis that long-term CsA treatment reduces the salinity/tonicity of the renal medullary interstitium as a result of inhibition of active sodium transporters, leading to downregulation of TonEBP. CsA treatment for 7 d did not affect TonEBP or renal function. Whereas expression of sodium transporters was altered, the medullary tonicity seemed unchanged. Conversely, 28 d of CsA treatment led to downregulation of TonEBP and overt nephrotoxicity. The downregulation of TonEBP involved reduced expression, cytoplasmic shift, and reduced transcription of its target genes. This was associated with reduced expression of active sodium transporters-sodium/potassium/chloride transporter type 2 (NKCC2), sodium/chloride transporter, and Na+,K+-ATPase-along with increased sodium excretion and reduced urinary concentration. Infusion of vasopressin restored the expression of NKCC2 in the outer medulla as well as the expression and the activity of TonEBP. It is concluded that the downregulation of TonEBP in the setting of long-term CsA administration is secondary to the reduced tonicity of the renal medullary interstitium.close191

Secretory-defect distal renal tubular acidosis is associated with transporter defect in H(+)-ATPase and anion exchanger-1

Recent progress in molecular physiology has permitted us to understand pathophysiology of various channelopathies at a molecular level. The secretion of H(+) from alpha-intercalated cells is mediated by apical plasma membrane H(+)-ATPase and basolateral plasma membrane anion exchanger-1 (AE1). Studies have demonstrated the lack of H(+)-ATPase immunostaining in the intercalated cells in a few patients with distal renal tubular acidosis (dRTA). Mutations in H(+)-ATPase and AE1 gene have recently been reported to cause dRTA. This study extends the investigation of the role of transporter defect in dRTA by using immunohistochemical methods. Eleven patients with hyperchloremic metabolic acidosis were diagnosed functionally to have secretory-defect dRTA: urine pH >5.5 during acidemia, normokalemia or hypokalemia, and urine-to-blood pCO(2) <25 mmHg during bicarbonaturia. Renal biopsy tissue was obtained from each patient, and immunohistochemistry was carried out using antibodies to H(+)-ATPase and AE1. For comparison, renal tissues from the patients who had no evidences of distal acidification defect by functional studies were used: four with glomerulopathy or tubulointerstitial nephritis (disease controls) and three from nephrectomized kidneys for renal cell carcinoma (normal controls). The H(+)-ATPase immunoreactivity in alpha-intercalated cells was almost absent in all of the 11 patients with secretory-defect dRTA. In addition, 7 of 11 patients with secretory-defect dRTA were accompanied by negative AE1 immunoreactivity. In both disease controls and normal controls, the immunoreactivity of H(+)-ATPase and AE1 was strong in alpha-intercalated cells. In conclusion, significant defect in acid-base transporters is the major cause of secretory-defect dRTA