Molecular Characterization of A Novel Mutation In The Renal NaCl Cotransporter Causing Gitelman's Syndrome By Impairing Transporter Trafficking

Mutations affecting the sodium-chloride cotransporter (NCC) in the distal convoluted tubule of the nephron are causative of Gitelman's syndrome (GS), a rare autosomal recessive disease characterized by electrolytic alterations similar to those induced by high dose thiazide treatment. Notably, the co-existence of hypomagnesemia and hypocalciuria is a feature of GS which is a distinguish hallmark from another hypokalemic renal tubulopathy, the Bartter's syndrome (BS). Commonly GS is heterozygous compound with an estimated prevalence of 1:40000 and can be silent for years before the revealing in the early adulthood. Recognizing the genetic background is fundamental for the screening and the diagnosis of the disease, as recently studies showed that mutation affecting regulators of renal salt handling are underestimated in the general population. In a registry of BS/GS based at our University we discovered a novel point mutation (c.1204G>A which codify for an amino acid exchange G394D) in the sodium-chloride cotransporter NCC (SLC12A3) in a young woman with hypokalemia, hypomagnesemia and hypocalciuria associated to muscle pain and cramps. The present study aimed to investigate how this mutation affects NCC function by using a molecular biology approach and providing functional evidences. After a prior screening with bioinformatics tools predicting the possible pathogenicity of the mutation, were created different expression vectors with either the wild-type (wt-NCC) or the mutated G394D-NCC sequences. DNA and in-vitro transcribed RNA were afterwards transfected in a human embryonic kidney cells line (HEK293) and injected into oocytes deriving from Xenopus Laevis frog respectively. In transfected HEK 293 cells, wildtype NCC was detected by immunoblotting as two bands at approximately 130 kDa and 115 kDa corresponding to fully and core-glycosylated NCC, respectively. In contrast, G394D-NCC was seen as a single band at about 115 kDa only, suggesting an impaired maturation of the mutated protein. Similar findings were made in the oocyte expression system. Confocal microscopy on the oocytes, did also show a strong cell surface localization of wildtype NCC while mutated NCC was retained at intracellular compartments. Consistently, a decent thiazide-sensitive 22Na+ uptake into injected oocytes was only found for wildtype but not mutated NCC. Taken together all the findings in this study, a novel GS point mutation has been characterized to diminish NCC function by impairing trafficking of the protein to the cell surface. The absence of any mature glycosylation form of G394D-NCC suggests that the mutation impairs protein folding leading to a retention of NCC in the endoplasmic reticulum

Relationship between NOX4 level and angiotensin II signaling in Gitelman's syndrome. Implications with hypertension

Recent evidence showed that endogenous nicotinamide adenine dinucleotide phosphate-oxidase 4 (NOX4) may exert a protective role on the cardiovascular system inducing vasodilation, reduction of blood pressure, and anti-proliferative actions. However, the functional significance of NOX4 in the cardiovascular system in humans remains elusive. Mononuclear cell levels of NOX4 were assessed by immunoblotting in 14 Gitelman's patients (GS), a unique human model of endogenous Ang II signaling antagonism and activation of anti-atherosclerotic and anti-remodeling defenses, and compared to 11 untreated essential hypertensive patients as well as to 11 healthy normotensive subjects. The association between NOX4 and its effector heme oxygenase (HO-1) (sandwich immunoassay) was also evaluated. NOX4 protein levels were decreased in hypertensive patients as compared to both GS and healthy subjects (1.06±0.31 AU vs. 1.76±0.54, P=0.002 and vs. 1.61±0.54, P=0.018, respectively). NOX4 protein level did not differ between GS and healthy subjects. HO-1 levels were increased in GS patients as compared to both hypertensive patients and healthy subjects (8.65±3.08 ng/ml vs 3.70±1.19, P<0.0001, and vs 5.49±1.04, P=0.008, respectively. NOX4 levels correlate with HO-1 levels only in GS (r(2)=0.63; P=0.001), (r(2)=0.088; P=ns, in hypertensive patients and r(2)=0.082; P=ns, in healthy subjects). Our findings show that NOX4 and its effector HO-1 are reduced in hypertensive patients compared to GS patients, a human model opposite to hypertension. Although the functional significance of NOX4 needs further clarification, our preliminary data in a unique human model of anti-atherosclerotic and anti-remodeling defenses activation, highlight the potentially protective role of NOX4 in the human cardiovascular system

The blocking of angiotensin II type 1 receptor and RhoA/Rho kinase activity in hypertensive patients: Effect of olmesartan medoxomil and implication with cardiovascular-renal remodeling

Hypothesis/Introduction: The pathophysiological role of oxidative stress (OxSt) in hypertension and target organ damage is recognized. Angiotensin II (Ang II) induces OxSt via NAD(P)H oxidase activation and production of proinflammatory cytokines/growth factors leading to cardiovascular-renal remodeling. Ang II stimulates the RhoA/Rho kinase (ROCK) pathway, which is deeply involved in the development of cardiovascular-renal remodeling via OxSt induction. Olmesartan, an Ang II type 1 receptor blocker, possesses antioxidant and activating nitric oxide system-related effects, which we have shown in terms of p22 phox reduction, heme oxygenase-1 and calcitonin gene-related peptide increase. This study evaluates in 15 untreated hypertensive patients the effect of olmesartan treatment on p63RhoGEF, key in Ang II-induced ROCK activation, and MYPT-1 phosphorylation, a marker of ROCK activity. Materials and methods: The p63RhoGEF protein level and MYPT-1 phosphorylation (Western blot) were evaluated at baseline, and after three and six months of olmesartan treatment. Results: Olmesartan normalized systolic and diastolic BP ( p < 0.001), reduced p63RhoGEF level: 1.3±0.25 d.u. (baseline) vs 1.0±0.29 (three months), p < 0.0001 vs 1.0±0.22, (six months), p < 0.0001 and MYPT-1 phosphorylation: 1.2 ±0.14 (baseline) vs 0.9±0.19 (three months), p = 0.008, vs 0.8±0.16 (six months), p = 0.001. Conclusions: These data added to our previous results further provide a mechanistic rationale for olmesartan's antioxidant/anti-inflammatory potential translation, in the long term, toward anti-atherosclerotic/anti-remodeling effects reported by clinical trials

Pathophysiology of Post Transplant Hypertension in Kidney Transplant: Focus on Calcineurin Inhibitors Induced Oxidative Stress and Renal Sodium Retention and Implications with RhoA/Rho Kinase Pathway.

Post-transplant hypertension is a common occurrence during treatment with calcineurin inhibitors (CNIs) in kidney transplant population. The pathogenesis of vasoconstriction induced by CNIs involves vascular tone alterations and kidney sodium transport regulation. Among the factors involved a key role is played by the activation of intrarenal renin-angiotensin system with enhanced release of Angiotensin II (Ang II) and increase of oxidative stress. A common pathway between oxidative stress and hypertension induced by CNIs may be identified in the involvement of the activation of RhoA/Rho kinase pathway, key for the induction of hypertension and cardiovascular-renal remodeling, of the oxidative stress mediated increased nitric oxide (NO) metabolism and increased renal sodium retention via increased activity of thiazide-sensitive sodium chloride cotransporter (NCC) in the distal tubule. We examined literature data including those coming from our group regarding the role of oxidative stress and sodium retention in CNIs induced hypertension and their involvement in cardiovascular-renal remodeling. Based on the available data, we have provided support to the activation of RhoA/Rho kinase pathway as an important effector in the pathophysiology of CNIs induced post-transplant hypertension via activation of oxidative stress and sodium retention. Clarification of how the biochemical and molecular mechanisms that regulate the processes involved in CNIs induced post transplant hypertension work and interact, would provide further insights not only into the comprehension of the pathophysiology of CNIs induced post transplant hypertension but could also have a positive impact on the clinical ground through the identification of significant targets. Their specific pharmacologic targeting might have multiple beneficial effects on the whole cardiovascular-renal function. The demonstration that in kidney transplanted patients with CNIs induced post-transplanted hypertension, the treatment of hypertension with different antihypertensive drugs inducing a comparable blood pressure reduction but different effects for example on oxidative stress and oxidative stress related proteins and/or Rho kinase and sodium retention, could be helpful for the choice of the antihypertensive treatment in these patients which takes advantage from effects of these drugs beyond blood pressure reduction

Endothelin-1 Drives Epithelial-Mesenchymal Transition In Hypertensive Nephroangiosclerosis

BACKGROUND: Tubulointerstitial fibrosis, the final outcome of most kidney diseases, involves activation of epithelial mesenchymal transition (EMT). Endothelin‐1 (ET‐1) activates EMT in cancer cells, but it is not known whether it drives EMT in the kidney. We therefore tested the hypothesis that tubulointerstitial fibrosis involves EMT driven by ET‐1. METHODS AND RESULTS: Transgenic TG[mRen2]27 (TGRen2) rats developing fulminant angiotensin II–dependent hypertension with prominent cardiovascular and renal damage were submitted to drug treatments targeted to ET‐1 and/or angiotensin II receptor or left untreated (controls). Expressional changes of E‐cadherin and α‐smooth muscle actin (αSMA) were examined as markers of renal EMT. In human kidney HK‐2 proximal tubular cells expressing the ET(B) receptor subtype, the effects of ET‐1 with or without ET‐1 antagonists were also investigated. The occurrence of renal fibrosis was associated with EMT in control TGRen2 rats, as evidenced by decreased E‐cadherin and increased αSMA expression. Irbesartan and the mixed ET‐1 receptor antagonist bosentan prevented these changes in a blood pressure–independent fashion (P < 0.001 for both versus controls). In HK‐2 cells ET‐1 blunted E‐cadherin expression, increased αSMA expression (both P < 0.01), collagen synthesis, and metalloproteinase activity (P < 0.005, all versus untreated cells). All changes were prevented by the selective ET(B) receptor antagonist BQ‐788. Evidence for involvement of the Rho‐kinase signaling pathway and dephosphorylation of Yes‐associated protein in EMT was also found. CONCLUSIONS: In angiotensin II–dependent hypertension, ET‐1 acting via ET(B) receptors and the Rho‐kinase and Yes‐associated protein induces EMT and thereby renal fibrosis

Molecular Characterization of A Novel Mutation In The Renal NaCl Cotransporter Causing Gitelman's Syndrome By Impairing Transporter Trafficking

Mutations affecting the sodium-chloride cotransporter (NCC) in the distal convoluted tubule of the nephron are causative of Gitelman's syndrome (GS), a rare autosomal recessive disease characterized by electrolytic alterations similar to those induced by high dose thiazide treatment. Notably, the co-existence of hypomagnesemia and hypocalciuria is a feature of GS which is a distinguish hallmark from another hypokalemic renal tubulopathy, the Bartter's syndrome (BS). Commonly GS is heterozygous compound with an estimated prevalence of 1:40000 and can be silent for years before the revealing in the early adulthood. Recognizing the genetic background is fundamental for the screening and the diagnosis of the disease, as recently studies showed that mutation affecting regulators of renal salt handling are underestimated in the general population. In a registry of BS/GS based at our University we discovered a novel point mutation (c.1204G>A which codify for an amino acid exchange G394D) in the sodium-chloride cotransporter NCC (SLC12A3) in a young woman with hypokalemia, hypomagnesemia and hypocalciuria associated to muscle pain and cramps. The present study aimed to investigate how this mutation affects NCC function by using a molecular biology approach and providing functional evidences. After a prior screening with bioinformatics tools predicting the possible pathogenicity of the mutation, were created different expression vectors with either the wild-type (wt-NCC) or the mutated G394D-NCC sequences. DNA and in-vitro transcribed RNA were afterwards transfected in a human embryonic kidney cells line (HEK293) and injected into oocytes deriving from Xenopus Laevis frog respectively. In transfected HEK 293 cells, wildtype NCC was detected by immunoblotting as two bands at approximately 130 kDa and 115 kDa corresponding to fully and core-glycosylated NCC, respectively. In contrast, G394D-NCC was seen as a single band at about 115 kDa only, suggesting an impaired maturation of the mutated protein. Similar findings were made in the oocyte expression system. Confocal microscopy on the oocytes, did also show a strong cell surface localization of wildtype NCC while mutated NCC was retained at intracellular compartments. Consistently, a decent thiazide-sensitive 22Na+ uptake into injected oocytes was only found for wildtype but not mutated NCC. Taken together all the findings in this study, a novel GS point mutation has been characterized to diminish NCC function by impairing trafficking of the protein to the cell surface. The absence of any mature glycosylation form of G394D-NCC suggests that the mutation impairs protein folding leading to a retention of NCC in the endoplasmic reticulum.Le mutazioni che colpiscono il cotrasportatore per il sodio e cloro (NCC) nel tubulo contorto distale del nefrone, sono responsabili della sindrome di Gitelman (GS). Quest'ultima è una rara tubulopatia renale autosomica recessiva caratterizzata da alterazioni elettrolitiche simili a quelle indotte dal trattamento ad alte dosi con diuretici tiazidici. La co-presenza di ipomagnesemia e ipocalciuria è una delle caratteristiche di GS che la distinguono da un'altra tubulopatia renale ipokalemica, la sindrome di Bartter (BS). Generalmente, i soggetti affetti sono eterozigoti composti con una prevalenza stimata di 1 su 40000. La malattia può essere silente per anni prima di presentarsi nell'età  adulta. Riconoscerne la componente genetica è fondamentale per lo screening e la diagnosi. Recenti studi hanno di fatto dimostrato come le mutazioni a carico dei regolatori renali dell'omeostasi del sodio siano sottostimate nella popolazione generale. Nel nostro database universitario di pazienti BS/GS abbiamo riscontrato una nuova mutazione puntiforme (c.1204G>A che comporta lo scambio aminoacidico Gly394Asp) nel cotrasportatore del sodio e cloro NCC (SLC12A3) in una giovane donna con ipokaliemia, ipomagnesemia e ipocalciuria associati a dolori e crampi muscolari. Il presente studio ha lo scopo di investigare tramite un approccio biologico molecolare come questa mutazione influenzi la funzionalità  di NCC. Previo screening con softwares bioinformatici che predicono la possibile patogenicità  della mutazione, sono stati creati dei vettori di espressione contenenti le sequenze per NCC wild type e per NCC con mutazione G394D. Successivamente, le sequenze sono state trasfettate in una linea di cellule fetali umane ricombinate (HEK293) e in ovociti derivati da rane Xenopus Laevis. Nelle cellule trasfettate, l'immunoblotting di NCC wild-type ha dimostrato la presenza di due bande approssimativamente a 130 KDa e 115 KDa che corrispondono rispettivamente alla forma glicosilata e nativa della proteina. Al contrario, G394D-NCC presenta una sola banda a 115 KDa. Risultati simili sono stati ottenuti negli ovociti. In questi ultimi l'immunoistochimica ha inoltre mostrato una forte localizzazione di NCC wild-type presso la membrana, mentre NCC mutato rimane in compartimenti cellulari interni. Gli studi funzionali di uptake del sodio radioattivo (22Na+) hanno ulteriormente confermato che solo la proteina wild-type è in grado di riassorbire il sodio al contrario di G394D-NCC. I risultati di questo studio dimostrano come la nuova mutazione puntiforme inibisca la funzione di NCC a causa della diminuita capacità della proteina di raggiungere la superficie cellulare. L'assenza di una forma glicosilata matura di G394D-NCC suggerisce che la mutazione ne condizioni il folding e ne provochi la ritenzione nel reticolo endoplasmico ove vengo attivati processi di degradazione anticipata

Effetto del tè verde sullo stress ossidativo e sul rimodellamento cardiovascolare nei pazienti in dialisi.

Le malattie cardiovascolari sono la causa più comune di mortalità e di morbidità nei pazienti in fase avanzata di danno renale ed in dialisi cronica. Essendo il tè verde riconosciuto come ottimo antiossidante, in questo studio durato sei mesi, si sono valutati sui pazienti in fase avanzata di danno renale e in dialisi cronica , gli effetti del tè verde 'ex vivo' sullo stress ossidativo e sui markers di proliferazione, usando un approccio di biologia molecolare

Oxidative Stress and Cardiovascular-Renal Damage in Fabry Disease: Is There Room for a Pathophysiological Involvement?

Fabry disease is an X-linked lysosomal storage disease caused by mutations in the GLA gene that lead to a reduction or an absence of the enzyme &alpha;-galactosidase A, resulting in the progressive and multisystemic accumulation of globotriaosylceramide. Clinical manifestation varies from mild to severe, depending on the phenotype. The main clinical manifestations are cutaneous (angiokeratomas), neurological (acroparesthesias), gastrointestinal (nausea, diarrhea abdominal pain), renal (proteinuria and kidney failure), cardiovascular (cardiomyopathy and arrhythmias), and cerebrovascular (stroke). A diagnosis of Fabry disease can be made with an enzymatic assay showing absent or reduced &alpha;-galactosidase A in male patients, while in heterozygous female patients, molecular genetic testing is needed. Enzyme replacement therapy (ERT) with recombinant human &alpha;-galactosidase is nowadays the most-used disease-specific therapeutic option. Despite ERT, cardiocerebrovascular-renal irreversible organ injury occurs, therefore additional knowledge and a deeper understanding of further pathophysiological mechanisms leading to end organ damage in Fabry disease are needed. Recent data point toward oxidative stress, oxidative stress signaling, and inflammation as some such mechanisms. In this short review, the current knowledge on the involvement of oxidative stress in cardiovascular-renal remodeling is summarized and related to the most recent evidence of oxidative stress activation in Fabry disease, and clearly points toward the involvement of oxidative stress in the pathophysiology of the medium- to long-term cardiovascular-renal damage of Fabry disease