The Kidney

Fibroblast growth factor-23 rs7955866 polymorphism and risk of chronic kidney disease

Background

A missense gain-of-function fibroblast growth factor-23 (FGF23) gene single nucleotide polymorphism (SNP) (rs7955866) has been associated with FGF23 hypersecretion, phosphaturia, and bone disease. Excess circulating FGF23 was linked with atherosclerosis, hypertension, initiation, and progression of chronic kidney disease (CKD).

Methods

The study included 72 CKD stage 2/3 Egyptian patients (27–71 years old, 37 females) and 26 healthy controls matching in age and sex. Repeated measures of blood pressure were used to quantify hypertension on a semiquantitative scale (grades 0 to 5). Fasting serum urea, creatinine, uric acid, total proteins, albumin, calcium, phosphorus, vitamin D3, intact parathyroid hormone (iPTH), and intact FGF23 (iFGF23) were measured. DNA extracted from peripheral blood leucocytes was used for genotyping of FGF23 rs7955866 SNP using the TaqMan SNP genotyping allelic discrimination method.

Results

Major causes of CKD were hypertension, diabetic kidney disease, and CKD of unknown etiology. There was no significant difference in minor allele (A) frequency between the studied groups (0.333 in GI and 0.308 in GII). Median (IQR) serum iFGF23 was significantly higher in GI [729.2 (531.9–972.3)] than in GII [126.1 (88.5–152.4)] pg/mL, P < 0.001. Within GI, the minor allele (A) frequency load, coded for codominant inheritance, had a significant positive correlation with both hypertension grade (r = 0.385, P = 0.001) and serum iFGF23 (r = 0.259, P = 0.028). Hypertension grade had a significant positive correlation with serum phosphorus and iFGF23.

Conclusions

For the first time in an Egyptian cohort, we report a relatively high frequency of the rs7955866 SNP. It may remain dormant or become upregulated in response to some environmental triggers, notably dietary phosphorus excess, leading to increased circulating iFGF23 with ensuing hypertension and/or renal impairment. Subjects with this SNP, particularly in the homozygous form, are at increased risk for CKD of presumably “unknown” etiology, with a tendency for early onset hypertension and increased circulating iFGF23 out of proportion with the degree of renal impairment. Large-scale population studies are needed to confirm these findings and explore the role of blockers of the renin–angiotensin–aldosterone system and sodium chloride cotransporters in mitigating hypertension associated with FGF23 excess.

The Key Role of Epithelial to Mesenchymal Transition (EMT) in Hypertensive Kidney Disease

Accumulating evidence indicates that epithelial-to-mesenchymal transition (EMT), originally described as a key process for organ development and metastasis budding in cancer, plays a key role in the development of renal fibrosis in several diseases, including hypertensive nephroangiosclerosis. We herein reviewed the concept of EMT and its role in renal diseases, with particular focus on hypertensive kidney disease, the second leading cause of end-stage renal disease after diabetes mellitus. After discussing the pathophysiology of hypertensive nephropathy, the 'classic' view of hypertensive nephrosclerosis entailing hyalinization, and sclerosis of interlobular and afferent arterioles, we examined the changes occurring in the glomerulus and tubulo-interstitium and the studies that investigated the role of EMT and its molecular mechanisms in hypertensive kidney disease. Finally, we examined the reasons why some studies failed to provide solid evidence for renal EMT in hypertension.

A synthetic peptide from transforming growth factor-β₁ type III receptor inhibits NADPH oxidase and prevents oxidative stress in the kidney of spontaneously hypertensive rats

AIMS

The NADPH oxidases constitute a major source of superoxide anion (·O2(-)) in hypertension. Several studies suggest an important role of NADPH oxidases in different effects mediated by transforming growth factor-β₁ (TGF-β₁). We investigated whether a chronic treatment with P144, a peptide synthesized from type III TGF-β₁ receptor, inhibited NADPH oxidases in the renal cortex of spontaneously hypertensive rats (SHR).

RESULTS

Here, we show that chronic administration of P144 significantly reduced the NADPH oxidase expression and activity as well as the oxidative stress observed in control vehicle-treated SHR (V-SHR). In addition, P144 was also able to reduce the significant increase in the renal fibrosis and in mRNA expression of different components of collagen metabolism, as well as in the levels of connective tissue growth factor observed in V-SHR. Finally, TGF-β₁-stimulated NRK52E exhibited a significant increase in NADPH oxidase expression and activity as well as a TGF-β₁-dependent intracellular pathway that were inhibited in the presence of P144.

INNOVATION

Our experimental evidence suggests that reversing oxidative stress may be therapeutically useful in preventing fibrosis-associated renal damage. We show here that (i) the TGF-β₁-NADPH oxidases axis is crucial in the development of fibrosis in an experimental hypertensive renal disease animal model, and (ii) the use of P144 reverses TGF-β₁-dependent NADPH oxidase activity; thus, P144 may be considered a novel therapeutic tool in kidney disease associated with hypertension.

CONCLUSION

We demonstrate that P144 inhibits NADPH oxidases and prevents oxidative stress in kidneys from hypertensive rats. Our data also suggest that these effects are associated with the renal antifibrotic effect of P144.

Genetic locus on MWF rat chromosome 6 affects kidney damage in response to L-NAME treatment in spontaneously hypertensive rats

A major quantitative trait locus (QTL) on rat chromosome (RNO)6 was linked to albuminuria in Munich Wistar Frömter rats (MWF). We tested whether transfer of MWF RNO6 into the background of albuminuria-resistant spontaneously hypertensive rats (SHR) induces albuminuria in consomic SHR-6(MWF) animals. Male MWF, SHR, and SHR-6(MWF) were sham operated and treated between 6 and 24 wk of age with normal water (Sham) or with water containing 20 mg/l N(G)-nitro-L-arginine methyl ester (L-NAME) or unilaterally nephrectomized (Nx). Compared with SHR albuminuria was not increased in SHR-6(MWF) in both Sham and Nx groups. All animals survived the observation period in Sham and Nx groups, while premature mortality occurred from 12-14 wk on in L-NAME-treated SHR and SHR-6(MWF) compared with MWF L-NAME animals, in which survival was not affected (P < 0.005, respectively). Subsequent further analysis of L-NAME-treated animals at 12 wk of age showed significantly increased arterial blood pressures in both SHR and SHR-6(MWF) compared with control (P < 0.05), with higher levels in SHR compared with consomics (P < 0.05). However, L-NAME-treated consomic animals demonstrated increased albuminuria compared with SHR (12.7 +/- 3.5 vs. 0.8 +/- 0.2 mg/24 h; P < 0.05) and an induction of tubulointerstitial structural injury and expression of neutrophil gelatinase-associated lipocalin mRNA (P < 0.05 vs. other strains). Our study demonstrates that isolation of the RNO6 albuminuria QTL from the MWF background and transfer into SHR fails to induce an albuminuria phenotype during normal conditions or after nephron reduction. Moreover, our data indicate that genes on RNO6 contribute to the development of L-NAME-induced renal damage in the SHR strain.