Thiazide-sensitive Sodium Chloride Cotransporter Research Articles

A 48-year adult male with convulsion, collapses and generalized weakness – a rare presentation of Gitelman’s Syndrome

Hypokalaemia is a common clinical condition, very often the cause of which can be determined by the patient’s clinical history. Gitelman’s syndrome is an inherited renal tubular disorder that must be considered in some cases of hypokalaemia. We present this case of a 48-year-old male patient admitted in our nephrology department for recurrent hypokalaemia. The patient had generalized seizure followed by unconsciousness, generalized weakness, fatigue, palpitation, orthostatic hypotension and polyuria for one month. Patient was on treatment for systemic hypertension with amlodipine and olmesartan. On blood gas analysis, he had a metabolic alkalosis (pH 7.53; pCO2 40 mm Hg; HCO3 34.1mmol/l). Biochemical analysis revealed hyponatremia (105.8mmol/l), hypokalemia (2.07mmol/l), hypochloraemia (74.0mmol/l), hypomagnesaemia (1.10mmol/l) and hypocalcaemia (7.2 mg/dl). Serum creatinine (1.9 mg/dl) and blood urea (6.3mmol/l) were normal. Further investigations revealed hypocalciuria (0.5mmol/l; NR 2.5–7.5) and increased urinary excretion of sodium (210.0 mmol/l; NR 20–110), Potassium (35mmol/l) and chloride (220mmol/l; NR 55–125). Renal ultra-sonogram was normal. A diagnosis of Gitelman’s syndrome was established. We started treatment with sodium chloride, potassium chloride and magnesium sulfate supplementation. Serum potassium was stabilized around 3mmol/l and the patient had significant clinical improvement. The aim of our article is to remind Gitelman’s syndrome in the differential diagnosis of persistent hypokalemia and to highlight the need for further investigations in patients with recurrent hypokalaemic episodes. This rare, inherited, autosomal recessive renal tubulopathy is associated with several genetic mutations in the thiazide-sensitive sodium chloride co-transporter and magnesium channels in the distal convoluted tubule. Patients with Gitelman’s syndrome present during adolescence or adulthood as an inherited autosomal recessive traits with a wide range of clinical presentations from being asymptomatic to predominant muscular symptoms such as fatigue, weakness in association with hypocalciuria, hypomagnesemia with hypermagnesuria and normal prostaglandin production. Clinical suspicion should be raised in those with recurrent hypokalaemic paralysis with metabolic alkalosis associated with hypomagnesaemia. Treatment of Gitelman’s syndrome consists of long-term potassium and magnesium salt supplementation. In general, the long-term prognosis and life expectancy is excellent. CBMJ 2021 January: vol. 10 no. 01 P: 54-58

Low Salt Delivery Triggers Autocrine Release of Prostaglandin E2 From the Aldosterone-Sensitive Distal Nephron in Familial Hyperkalemic Hypertension Mice.

Aberrant activation of with-no-lysine kinase (WNK)-STE20/SPS1-related proline-alanine-rich protein kinase (SPAK) kinase signaling in the distal convoluted tubule (DCT) causes unbridled activation of the thiazide-sensitive sodium chloride cotransporter (NCC), leading to familial hyperkalemic hypertension (FHHt) in humans. Studies in FHHt mice engineered to constitutively activate SPAK specifically in the DCT (CA-SPAK mice) revealed maladaptive remodeling of the aldosterone sensitive distal nephron (ASDN), characterized by decrease in the potassium excretory channel, renal outer medullary potassium (ROMK), and epithelial sodium channel (ENaC), that contributes to the hyperkalemia. The mechanisms by which NCC activation in DCT promotes remodeling of connecting tubule (CNT) are unknown, but paracrine communication and reduced salt delivery to the ASDN have been suspected. Here, we explore the involvement of prostaglandin E2 (PGE2). We found that PGE2 and the terminal PGE2 synthase, mPGES1, are increased in kidney cortex of CA-SPAK mice, compared to control or SPAK KO mice. Hydrochlorothiazide (HCTZ) reduced PGE2 to control levels, indicating increased PGE2 synthesis is dependent on increased NCC activity. Immunolocalization studies revealed mPGES1 is selectively increased in the CNT of CA-SPAK mice, implicating low salt-delivery to ASDN as the trigger. Salt titration studies in an in vitro ASDN cell model, mouse CCD cell (mCCD-CL1), confirmed PGE2 synthesis is activated by low salt, and revealed that response is paralleled by induction of mPGES1 gene expression. Finally, inhibition of the PGE2 receptor, EP1, in CA-SPAK mice partially restored potassium homeostasis as it partially rescued ROMK protein abundance, but not ENaC. Together, these data indicate low sodium delivery to the ASDN activates PGE2 synthesis and this inhibits ROMK through autocrine activation of the EP1 receptor. These findings provide new insights into the mechanism by which activation of sodium transport in the DCT causes remodeling of the ASDN.

Potassium Effects on NCC Are Attenuated during Inhibition of Cullin E3-Ubiquitin Ligases.

The thiazide-sensitive sodium chloride cotransporter (NCC) plays a vital role in maintaining sodium (Na+) and potassium (K+) homeostasis. NCC activity is modulated by with-no-lysine kinases 1 and 4 (WNK1 and WNK4), the abundance of which is controlled by the RING-type E3 ligase Cullin 3 (Cul3) and its substrate adapter Kelch-like protein 3. Dietary K+ intake has an inverse correlation with NCC activity, but the mechanism underlying this phenomenon remains to be fully elucidated. Here, we investigated the involvement of other members of the cullin family in mediating K+ effects on NCC phosphorylation (active form) and abundance. In kidneys from mice fed diets varying in K+ content, there were negative correlations between NCC (phosphorylated and total) and active (neddylated) forms of cullins (Cul1, 3, 4, and 5). High dietary K+ effects on phosphorylated NCC were attenuated in Cul3 mutant mice (CUL3-Het/Δ9). Short-term (30 min) and long-term (24 h) alterations in the extracellular K+ concentration did not affect cullin neddylation levels in ex vivo renal tubules. In the short term, the ability of high extracellular K+ to decrease NCC phosphorylation was preserved in the presence of MLN4924 (pan-cullin inhibitor), but the response to low extracellular K+ was absent. In the long term, MLN4924 attenuated the effects of high extracellular K+ on NCC phosphorylation, and responses to low extracellular K+ were absent. Our data suggest that in addition to Cul3, other cullins are involved in mediating the effects of K+ on NCC phosphorylation and abundance.

The Pharmacological Inhibition of CaMKII Regulates Sodium Chloride Cotransporter Activity in mDCT15 Cells.

Simple SummaryThe renal sodium chloride cotransporter (NCC) plays an important role in the total body electrolyte balance and blood pressure control. The regulation of this protein by the actin cytoskeleton has not been thoroughly studied. Here, we investigate a novel association between the actin cytoskeleton protein filamin A and the NCC using a mouse cellular model and in the native kidney. Our results show for the first time that the disruption of the actin cytoskeleton reduces NCC activity and filamin A plays an essential role in NCC protein expression in cells of the distal convoluted tubule. We further show that the pharmacological inhibition of the Ca2+/calmodulin dependent protein kinase II (CAMKII) augments NCC protein expression. These results introduce a new mechanism for the regulation of the NCC.The thiazide-sensitive sodium chloride cotransporter (NCC) in the distal convoluted tubule is responsible for reabsorbing up to one-tenth of the total filtered load of sodium in the kidney. The actin cytoskeleton is thought to regulate various transport proteins in the kidney but the regulation of the NCC by the actin cytoskeleton is largely unknown. Here, we identify a direct interaction between the NCC and the cytoskeletal protein filamin A in mouse distal convoluted tubule (mDCT15) cells and in the native kidney. We show that the disruption of the actin cytoskeleton by two different mechanisms downregulates NCC activity. As filamin A is a substrate of the Ca2+/calmodulin-dependent protein kinase II (CaMKII), we investigate the physiological significance of CaMKII inhibition on NCC luminal membrane protein expression and NCC activity in mDCT15 cells. The pharmacological inhibition of CaMKII with the compound KN93 increases the active form of the NCC (phospho-NCC) at the luminal membrane and also increases NCC activity in mDCT15 cells. These data suggest that the interaction between the NCC and filamin A is dependent on CaMKII activity, which may serve as a feedback mechanism to maintain basal levels of NCC activity in the distal nephron.

Activation of the Thiazide-Sensitive Sodium-Chloride Cotransporter by Beta3-Adrenoreceptor in the Distal Convoluted Tubule.

We previously showed that the beta-3 adrenergic receptor (BAR3) is expressed in most segments of the nephron where its agonism promotes a potent antidiuretic effect. We localized BAR3 in distal convoluted tubule (DCT) cells expressing the thiazide-sensitive sodium-chloride cotransporter (NCC). Aim of this study is to investigate the possible functional role of BAR3 on NCC modulation in DCT cells. Here, we found that, in mice, the knockout of BAR3 was paralleled by a significant attenuation of NCC phosphorylation, paralleled by reduced expression and activation of STE-20/SPS1-related proline-alanine-rich kinase (SPAK) and WNKs the main kinases involved in NCC activation. Conversely, in BAR1/2 knockout mice, we found reduced NCC abundance with no changes in the phosphorylation state of NCC. Moreover, selective BAR3 agonism promotes both SPAK and NCC activation in wild-type mouse kidney slices. In conclusion, our findings suggest a novel role for BAR3 in the regulation of NCC in DCT.

High dietary potassium causes ubiquitin-dependent degradation of the kidney sodium-chloride cotransporter

The thiazide-sensitive sodium-chloride cotransporter (NCC) in the renal distal convoluted tubule (DCT) plays a critical role in regulating blood pressure (BP) and K+ homeostasis. During hyperkalemia, reduced NCC phosphorylation and total NCC abundance facilitate downstream electrogenic K+ secretion and BP reduction. However, the mechanism for the K+-dependent reduction in total NCC levels is unknown. Here, we show that NCC levels were reduced in ex vivo renal tubules incubated in a high-K+ medium for 24–48 h. This reduction was independent of NCC transcription, but was prevented using inhibitors of the proteasome (MG132) or lysosome (chloroquine). Ex vivo, high K+ increased NCC ubiquitylation, but inhibition of the ubiquitin conjugation pathway prevented the high K+-mediated reduction in NCC protein. In tubules incubated in high K+ media ex vivo or in the renal cortex of mice fed a high K+ diet for 4 days, the abundance and phosphorylation of heat shock protein 70 (Hsp70), a key regulator of ubiquitin-dependent protein degradation and protein folding, were decreased. Conversely, in similar samples the expression of PP1α, known to dephosphorylate Hsp70, was also increased. NCC coimmunoprecipitated with Hsp70 and PP1α, and inhibiting their actions prevented the high K+-mediated reduction in total NCC levels. In conclusion, we show that hyperkalemia drives NCC ubiquitylation and degradation via a PP1α-dependent process facilitated by Hsp70. This mechanism facilitates K+-dependent reductions in NCC to protect plasma K+ homeostasis and potentially reduces BP.

Aldosterone contributes to hypertension in male mice inducibly overexpressing human endothelin-1 in endothelium

Mechanisms of blood pressure (BP) regulation by endothelin (ET)-1 produced by endothelial cells are complex and remain unclear. Long-term exposure to human ET-1 (hET-1) in mice inducibly overexpressing hET-1 in the endothelium (ieET-1) caused sustained BP elevation. ET-1 has been shown to stimulate the release of aldosterone. Whether aldosterone plays a role in hET-1 overexpression-induced BP elevation and vessel injury is unknown. Nine- to 12-week-old male ieET-1 mice and control mice expressing a tamoxifen-inducible Cre recombinase (CreERT2) in the endothelial cells (ieCre) were treated with tamoxifen for 5 days and studied 3 months later. Endothelial hET-1 overexpression increased plasma aldosterone levels, which was reversed by 2-week treatment with atrasentan, an endothelin type A receptors blocker. Aldosterone synthase and cryptochrome 2 adrenal cortex mRNA expression was decreased in ieET-1 mice. Two-week treatment with eplerenone, a mineralocorticoid receptor antagonist, reduced systolic BP by 10 mmHg in ieET-1 mice during rest time. Saline challenge-induced sodium excretion and renal cortex thiazide-sensitive sodium-chloride cotransporter mRNA expression were decreased in ieET-1 mice. The sensitivity of mesenteric arteries to contraction by norepinephrine was increased in ieET-1 mice, and was abrogated by eplerenone treatment, whereas sensitivity of endothelium-independent relaxation responses to sodium nitroprusside was enhanced. Resistance artery remodeling was reduced in eplerenone-treated ieET-1 vs. ieET-1 and ieCre mice. These results demonstrate that aldosterone contributes to BP elevation and vascular norepinephrine sensitivity and remodeling caused by hET-1 overexpression in endothelium in mice.

Update on Treatment of Hypertension After Renal Transplantation.

To incorporate novel findings on pathophysiology and treatment of posttransplant hypertension. (1) The sodium retaining effects of CNIs are mediated by stimulation of the thiazide-sensitive sodium chloride co-transporter in the distal convoluted tubule and in this regard chlorthalidone was proven to be an effective antihypertensive drug in renal transplantation. (2) Local and not systemic activation of the renin-angiotensin-aldosterone system plays a crucial role in the pathogenesis of posttransplant hypertension. (3) Recent randomized controlled trials failed to prove the presumed superiority of renin-angiotensin blockers in kidney transplantation. (4) Steroid-free and mammalian target of rapamycin-based immunosuppressive drug combinations did not show favorable effects on blood pressure control. (5) In a recent report the risk of non-melanoma skin cancer was higher with thiazide diuretics. But the increased cancer risk in transplant recipients is mainly attributed to comorbidities, such as diabetes and hypertension and of course to the transplantation condition itself or the obligatory application of immunosuppression, and has little to do with the antihypertensive medication Actual recommendations about BP targets in adult renal transplant recipients are coming from a post hoc analysis of a large randomized trial with another primary endpoint. Unless convincing studies on treatment of hypertension after renal transplantation are available, the ESC/ESH Guidelines 2018 should apply for these patients.

Thiazide-Sensitive NCC (Sodium-Chloride Cotransporter) in Human Metabolic Syndrome: Sodium Sensitivity and Potassium-Induced Natriuresis.

The thiazide-sensitive sodium-chloride cotransporter (NCC;SLC12A3) is central to sodium and blood pressure regulation. Metabolic syndrome induces NCC upregulation generating sodium-sensitive hypertension in experimental animal models. We tested the role of NCC in sodium sensitivity in hypertensive humans with metabolic syndrome. Conversely, oral potassium induces NCC downregulation producing potassium-induced natriuresis. We determined the time course and magnitude of potassium-induced natriuresis compared with the natriuresis following hydrochlorothiazide (HCTZ) as a reference standard. We studied 19 obese hypertensive humans with metabolic syndrome during 13-day inpatient confinement. We determined sodium sensitivity by change in 24-hour mean systolic pressure by automated monitor from days 5 (low sodium) to 10 (high sodium). We determined NCC activity by standard 50 mg HCTZ sensitivity test (day 11). We determined potassium-induced natriuresis following 35 mmol KCl (day 13). We determined (1) whether NCC activity was greater in sodium-sensitive versus sodium-resistant participants and correlated with sodium sensitivity and (2) time course and magnitude of potassium-induced natriuresis following 35 mmol KCl directly compared with 50 mg HCTZ. NCC activity was not greater in sodium-sensitive versus sodium-resistant humans and did not correlate with sodium sensitivity. Thirty-five-millimoles KCl produced a rapid natriuresis approximately half that of 50 mg HCTZ with a greater kaliuresis. Our investigation tested a key hypothesis regarding NCC activity in human hypertension and characterized potassium-induced natriuresis following 35 mmol KCl compared with 50 mg HCTZ. In obese hypertensive adults with metabolic syndrome ingesting a high-sodium diet, 35 mmol KCl had a net natriuretic effect approximately half that of 50 mg HCTZ.

Investigation of Vestibular Function in Adult Patients with Gitelman Syndrome: Results of an Observational Study.

Gitelman syndrome (GS) is a rare salt-losing tubulopathy caused by an inactivating mutation in the SLC12A3 gene, encoding the thiazide-sensitive sodium chloride cotransporter (NCC). Patients with GS frequently complain of vertigo, usually attributed to hypovolemia. Because NCC is also located in the endolymphatic sac, we hypothesized that patients with GS might have vestibular dysfunction. Between April 2013 and September 2016, 20 (22%) out of 90 patients followed at the reference center complained of vertigo in the absence of orthostatic hypotension. Sixteen of them were referred to an otology department for investigation of vestibular function. The vertigo was of short duration and triggered in half of them by head rotation. Seven patients (44%) had a vestibular syndrome. Vestibular syndrome was defined: (1) clinically, as nystagmus triggered by the head shaking test (n = 5); and/or (2) paraclinically, as an abnormal video head impulse test (n = 0), abnormal kinetic test (n = 4) and/or abnormal bithermal caloric test (n = 3). Five patients had associated auditory signs (tinnitus, aural fullness or hearing loss). In conclusion, we found a high frequency of vestibular disorder in GS patients suffering from vertigo, suggesting a role of NCC in the inner ear. Referent physicians of these patients should be aware of this extrarenal manifestation that requires specific investigations and treatment.

Gitelman Syndrome: A Rare Cause of Persistent Hypokalemia

Gitelman syndrome is a rare autosomal recessive renal tubular disease, caused by mutations in the SLC12A3 gene, which encodes the renal thiazide-sensitive sodium-chloride cotransporter (NCCT) in the distal renal convoluted tubule. We present a 48-years-old male referred to our observation after being considered not suitable to a previous proposed surgery due to persistent hypokalemia. No valued symptoms were described. Laboratory tests showed metabolic alkalosis, hypomagnesemia, hypokalemia and secondary hyperaldosteronism. Genetic test was performed and sequence analysis of the SLC12A3 gene revealed a homozygous mutation confirming this disease. The aim of this report is to remind and increase awareness of the existence of GS, manage the condition properly and consider the risk of disease recurrence to the next generations.

Dietary potassium and the kidney: lifesaving physiology.

Potassium often has a negative connotation in Nephrology as patients with chronic kidney disease (CKD) are prone to develop hyperkalaemia. Approaches to the management of chronic hyperkalaemia include a low potassium diet or potassium binders. Yet, emerging data indicate that dietary potassium may be beneficial for patients with CKD. Epidemiological studies have shown that a higher urinary potassium excretion (as proxy for higher dietary potassium intake) is associated with lower blood pressure (BP) and lower cardiovascular risk, as well as better kidney outcomes. Considering that the composition of our current diet is characterized by a high sodium and low potassium content, increasing dietary potassium may be equally important as reducing sodium. Recent studies have revealed that dietary potassium modulates the activity of the thiazide-sensitive sodium-chloride cotransporter in the distal convoluted tubule (DCT). The DCT acts as a potassium sensor to control the delivery of sodium to the collecting duct, the potassium-secreting portion of the kidney. Physiologically, this allows immediate kaliuresis after a potassium load, and conservation of potassium during potassium deficiency. Clinically, it provides a novel explanation for the inverse relationship between dietary potassium and BP. Moreover, increasing dietary potassium intake can exert BP-independent effects on the kidney by relieving the deleterious effects of a low potassium diet (inflammation, oxidative stress and fibrosis). The aim of this comprehensive review is to link physiology with clinical medicine by proposing that the same mechanisms that allow us to excrete an acute potassium load also protect us from hypertension, cardiovascular disease and CKD.

WNK-SPAK/OSR1-NCC kinase signaling pathway as a novel target for the treatment of salt-sensitive hypertension.

Hypertension is the most prevalent health condition worldwide, affecting ~1 billion people. Gordon's syndrome is a form of secondary hypertension that can arise due to a number of possible mutations in key genes that encode proteins in a pathway containing the With No Lysine [K] (WNK) and its downstream target kinases, SPS/Ste20-related proline-alanine-rich kinase (SPAK)and oxidative stress responsivekinase1 (OSR1). This pathway regulates the activity of the thiazide-sensitive sodium chloride cotransporter (NCC), which is responsible for NaCl reabsorption in the distal nephron. Therefore, mutations in genes encoding proteins that regulate the NCC proteins disrupt ion homeostasis and cause hypertension by increasing NaCl reabsorption. Thiazide diuretics are currently the main treatment option for Gordon's syndrome. However, they have a number of side effects, and chronic usage can lead to compensatory adaptations in the nephron that counteract their action. Therefore, recent research has focused on developing novel inhibitory molecules that inhibit components of the WNK-SPAK/OSR1-NCC pathway, thereby reducing NaCl reabsorption and restoring normal blood pressure. In this review we provide an overview of the currently reported molecular inhibitors of the WNK-SPAK/OSR1-NCC pathway and discuss their potential as treatment options for Gordon's syndrome.

The hypokalemia mystery: distinguishing Gitelman and Bartter syndromes from 'pseudo-Bartter syndrome'.

The Gitelman and Bartter syndromes (GS and BS, respectively) are characterized by the constellation of hypokalemia, hypochloremia, metabolic alkalosis, hyperreninemic hyperaldosteronism, low to normal blood pressure and juxtaglomerular apparatus hypertrophy. These are due to pathogenic variants in the genes that encode the thiazide-sensitive sodium–chloride cotransporter NCC (SLC12A3) in the distal convoluted tubule or transporters involved in sodium chloride reabsorption in the loop of Henle. ‘Pseudo-Bartter syndrome’ (PBS) is caused by extrarenal or acquired renal salt losses and shares the same plasma electrolyte profile and acid–base disturbances, making the distinction from the genetic forms very challenging. PBS has various etiologies, including diuretic and laxative abuse, self-induced vomiting and the side effects of some antimicrobials. Additionally, congenital chloride diarrhea, cystic fibrosis, Pendred syndrome and chloride-deficient diet can manifest as PBS. In this review we focus on factitious PBS secondary to diuretic abuse, laxative abuse or self-induced vomiting, whereby we point out some clinical and laboratory clues to help clinicians make the correct diagnosis.

SUN-LB133 Analysis of Clinical Characteristics and Gene Mutation in Four Cases of Gitelman Syndrome

Gitelman syndrome is an autosomal recessive renal tubular disorder characterized by renal salt wasting with secondary hyperreninemia and hyperaldosteronism, chronic hypokalemia with renal K wasting and metabolic alkalosis, and hypomagnesemia, and hypocalciuria. GS was found to be caused by mutations in SLC12A3 encoding the thiazide-sensitive sodium chloride cotransporter (NCCT) on the apical membrane of distal convoluted tubule. The prevalence worldwide is estimated at approximately 1:40,000, making it one of the most frequent inherited renal tubular disorders. To date, over 400 mutations scattered throughout SLC12A3 have been identified in GS patients. The majority of patients are compound heterozygous for SLC12A3 mutations, but a significant number of GS patients are found to carry only a single SLC12A3 mutation. The type of the SLC12A3 mutation may be a determinant factor in the severity of GS. The purpose of this study is to analyze clinical characteristics and gene mutation in four cases of GS. Methods: Four patients with closely resembling Gitelman syndrome was selected. Results: Six SLCl2A3 gene mutations were found in these four patients. There were one SLCl2A3 homozygous mutation in case 1 and case 3, and two SLCl2A3 heterozygous mutations in case 2 and case 4, respectively. This six gene mutations include missense mutations, frameshift mutations, and nonsense mutations. Four patients were diagnosed with Gitelman syndrome. Case 4 is the most severe with severe hypokalemia, accompanied by ventricular arrhythmias, which may be related to the presence of two SLC12A3 gene mutations in the patient. Conclusions: Four patients in this study were diagnosed with Gitelman syndrome based on their clinical characteristics and genetic testing results. For patients with hyperreninemia and hyperaldosteronism, chronic hypokalemia with renal K wasting and metabolic alkalosis, and hypomagnesemia, and hypocalciuria need to exclude Gitelman syndrome.Key words: Gitelmen Syndrome, Mutations, SlC12A3 gene

A Novel Genetically Defined Mouse Model of Hypertensive Nephropathy

The molecular pathways that drive hypertensive nephropathy remain poorly understood. Hypertension (HTN) and chronic kidney disease are comorbid disorders with a correlation as high as 70% in African‐Americans over 65 years old. Because impaired kidney function can be the cause or consequence of HTN, identification of causal hypertensive nephropathy pathways has been especially difficult. Here, we overcome the roadblock with a new genetically‐defined mouse model of HTN that exhibit a low‐renin salt‐sensitive form of the disease, similar to HTN in individuals of sub‐Saharan African descent. The mice, created by introducing activating mutations in the Ste20p‐related proline alanine‐rich kinase (SPAK) in a distal convoluted tubule cell‐specific manner, become hypertensive solely as a consequence of constitutive activation of the thiazide‐sensitive sodium chloride cotransporter (NCC) and salt retention.For these studies, the constitutively active (CA)‐SPAK and control (C57BL/6J) mice were fed control or high salt diet (HSD), and renal function was evaluated over 40 weeks, together with telemetric measurements of blood pressure. RNA‐Seq was performed to evaluate changes in the transcriptional profile in the renal cortex, and corroborated biochemically.Renal function in CA‐SPAK mice began to deteriorate at 20 weeks as evidenced by significant elevation of BUN, creatinine, and frank albuminuria, which gradually increased over the next 20 weeks. HSD consumption exacerbated hypertension in CA‐SPAK mice, and accelerated the decline in renal function. Microscopic evaluation of trichrome‐stained specimens revealed no significant changes in the kidney parenchyma. Thus hypertension appears to drive kidney insufficiency long before the development of nephroangiosclerosis.By contrast, a significant change in the transcription profile was observed between CA‐SPAK mice and controls at an early stage when microalbuminuria begins to develop. 1905 differentially expressed (DE) genes were identified (modified TREAT method, FDR < 0.05 for genes > 10% change). Remarkably, the DE profile was enriched in 26% of the known genes associated with albuminuria in humans (Chi Square test, p = 0.00031). Significant downregulation of key components of the glomerular filtration barrier slit diaphragm genes (nephrin, podocalyxin, synaptopodin, actinin a4, phospholipase C ɛ1) and the proximal tubule protein scavenger, Cubilin, were also observed in the CA‐SPAK. Pathway analysis was especially enriched in proinflammatory responses. Signature genes associated with Major Histocompatibility Complex class II, T helper 17 lymphocytes master regulator transcription factors and B lymphocytes markers were up‐regulated in the CA‐SPAK mice.In conclusion, progression of renal insufficiency in CA‐SPAK mice indicates a causal role of hypertension in nephropathy, and incriminates an inflammatory component as a key driver of early damage to the glomerular filtration barrier and tubular protein reabsorption.Support or Funding InformationThis study was supported by NIH.

Collecting system–specific deletion of Kcnj10 predisposes for thiazide- and low-potassium diet–induced hypokalemia

The basolateral potassium channel KCNJ10 (Kir4.1), is expressed in the renal distal convoluted tubule and controls the activity of the thiazide-sensitive sodium chloride cotransporter. Loss-of-function mutations of KCNJ10 cause EAST/SeSAME syndrome with salt wasting and severe hypokalemia. KCNJ10 is also expressed in the principal cells of the collecting system. However, its pathophysiological role in this segment has not been studied in detail. To address this, we generated the mouse model AQP2cre:Kcnj10flox/flox with a deletion of Kcnj10 specifically in the collecting system (collecting system-Kcnj10-knockout). Collecting system-Kcnj10-knockout mice responded normally to standard and high potassium diet. However, this knockout exhibited a higher kaliuresis and lower plasma potassium than control mice when treated with thiazide diuretics. Likewise, collecting systemKcnj10-knockout displayed an inadequately high kaliuresis and renal sodium retention upon dietary potassium restriction. In this condition, these knockout mice became hypokalemic due to insufficient downregulation of the epithelial sodium channel (ENaC) and the renal outer medullary potassium channel (ROMK) in the collecting system. Consistently, the phenotype of collecting system-Kcnj10-knockout was fully abrogated by ENaC inhibition with amiloride and ameliorated by genetic inactivation of ROMK in the collecting system. Thus, KCNJ10 in the collecting system contributes to the renal control of potassium homeostasis by regulating ENaC and ROMK. Hence, impaired KCNJ10 function in the collecting system predisposes for thiazide and low potassium diet-induced hypokalemia and likely contributes to the pathophysiology of renal potassium loss in EAST/SeSAME syndrome.

Gitelman Syndrome: What the Clinician Needs to know

Gitelman syndrome has a prevalence of 1-10/40.000, representing the most common inherited disease of renal tubules. It is due to inactivating mutations of the SLC12A3 gene that encodes the thiazide-sensitive Sodium Chloride Cotransporter (NCC) located in the apical membrane of the distal convoluted tubules, resulting in hypokalemic metabolic alkalosis associated with hypomagnesemia and hypocalciuria. Although it is generally considered a benign tubular disease, a number of complications have been observed in some patients.

Resistance to Insulin in Patients with Gitelman Syndrome and a Subtle Intermediate Phenotype in Heterozygous Carriers: A Cross-Sectional Study.

Gitelman syndrome is a salt-losing tubulopathy caused by mutations in the SLC12A3 gene, which encodes the thiazide-sensitive sodium-chloride cotransporter. Previous studies suggested an intermediate phenotype for heterozygous carriers. To evaluate the phenotype of heterozygous carriers of pathogenic SLC12A3 mutations, we performed a cross-sectional study of patients with Gitelman syndrome, heterozygous carriers, and healthy noncarriers. Participants measured their BP at home for three consecutive days before hospital admission for blood and urine sampling and an oral glucose tolerance test. We enrolled 242 participants, aged 18-75 years, including 81 heterozygous carriers, 82 healthy noncarriers, and 79 patients with Gitelman syndrome. The three groups had similar age, sex ratio, and body mass index. Compared with healthy noncarriers, heterozygous carriers showed significantly higher serum calcium concentration (P=0.01) and a trend for higher plasma aldosterone (P=0.06), but measures of home BP, plasma and urine electrolytes, renin, parathyroid hormone, vitamin D, and response to oral glucose tolerance testing were similar. Patients with Gitelman syndrome had lower systolic BP and higher heart rate than noncarriers and heterozygote carriers; they also had significantly higher fasting serum glucose concentration, higher levels of markers of insulin resistance, and a three-fold higher sensitivity to overweight. According to oral glucose tolerance testing, approximately 14% of patients with Gitelman syndrome were prediabetic, compared with 5% of heterozygous carriers and 4% of healthy noncarriers. Heterozygous carriers had a weak intermediate phenotype, between that of healthy noncarriers and patients with Gitelman syndrome. Moreover, the latter are at risk for development of type 2 diabetes, indicating the heightened importance of body weight control in these patients.

Cholinergic Mediated Renal Sodium Retention in Young Spontaneously Hypertensive Rats

Cholinergic activation with systemic nicotine infusion induces renal inflammation and the premature development of hypertension in young pre-hypertensive spontaneously hypertensive rats (SHR), a genetic model of essential hypertension. We hypothesized that the nicotine induced inflammatory response is associated with renal sodium retention in the young SHR. Young pre-hypertensive SHR and age matched Wistar Kyoto (WKY) controls received subcutaneous infusion of either saline (n=10 for each strain) or nicotine (15mg/kg/day) (n=10 for each strain) for 14 days. Animals received normal chow for the first 7 days of infusion and were changed to either a “low-salt” (LSD, 0.01% NaCl) (n=10) or “high-salt” (HSD, 4% NaCl) (n=10) diet. Animals were maintained in metabolic cages during the LSD and HSD periods. Nicotine did not alter sodium excretion significantly in WKY fed LSD or HSD, nor SHR fed LSD. In contrast, nicotine induced a 24% increase in renal sodium retention in SHR fed HSD, compared to controls (2.0±0.1 mM/gm vs 2.6±0.7mM/gm) (p<0.01). Moreover, nicotine-induced sodium retention in young SHR fed HSD was associated with an increase in renal gene expression of serum & glucocorticoid kinase (SGK1) by 34% (p<0.033) and renal Na-K-Cl cotransporter (NKCC2) by 58% (p<0.01), compared to controls. Similarly, there was a 20% increase in the full length form (85kDa) of the alpha subunit of epithelial sodium channel (αENaC) 20% (p<0.05); however, no increase in the cleaved form (25kDa) of αENaC was observed, when compared to controls. No significant change in renal expression of the thiazide-sensitive sodium-chloride co-transporter (NCC) was noted in response to nicotine when young SHR were fed HSD. We conclude that cholinergic mediated hypertension in the young SHR may be a form of salt-sensitive hypertension, possibly related to renal inflammation and supported by renal sodium retention, and increased expression of renal sodium transporters. Support or Funding Information NIH 5K08HL119588-02; Foundation de Leduq Nicotine Induces Renal Sodium Retention in Young Pre-hypertensive Spontaneously Hypertensive Rats (SHR) on a High-Salt Diet (HSD). This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.