高钾饮食对大鼠肾脏WNK1不同转录本表达的作用及其意义

背景 WNK1是新近发现的肾脏多个离子转运体及通道的调控蛋白,与醛固酮离子转运途径有关.目的 探讨高钾饮食致体内醛固酮增高对大鼠肾脏WNK1不同转录本表达的作用及其意义.方法 采用高钾饮水饲养Wistar大鼠8只,检测血清、24 h尿液离子质量浓度及血清醛固酮质量浓度.半定量RT-PCR方法 检测大鼠肾脏WNK1-L和WNK1-KS基因表达情况.结果 与正常对照组(n=8)比较,高钾组(n=8)血清醛固酮水平显著升高[(1.86±0.66)比对照组:(0.25±0.04)μg/L,P<0.01],为对照的7.4倍.血清及尿液钾离子和尿液氯离子质量浓度升高(P<0.05),尿液钠离子质量浓度下降(P<0.05),血清钠离子和氯离子无差异(P>0.05).高钾组WNK1-L表达量无差异(0.27±0.07比0.26±0.07,P>0.05),WNK1-KS表达量显著上升(1.60±0.22比0.38±0.08,P<0.01).结论 高钾饮食导致大鼠醛固酮质量浓度升高,醛固酮可通过调控WNK1-KS表达起到排钾保钠的生理作用.     

大鼠急性缺血性肾功能衰竭血管内皮生长因子水平的变化

目的 探讨大鼠肾脏缺血/再灌注损伤(IRI)后不同时段血管内皮生长因子(VEGF)浓度的变化在急性肾衰竭(ARF)中的发病机制.方法 建立大鼠肾脏IRI模型,采用ELISA法检测IRI术后不同时间段血、尿VEGF水平,并与肾功能做相关分析.结果 手术组术后6 h血清尿素氮(BUN)、肌酐(SCr)、血钾显著升高,至术后48 h达高峰,从术后72 h开始回落(P<0.05).手术组术后6 h血清VEGF显著升高,术后12 h达高峰,从术后24 h开始下降至正常;手术组术后6 h尿液VEGF显著升高(P<0.01),至术后24 h降至低于假手术组,从术后48 h开始回升.血VEGF水平与尿VEGF水平呈正相关,与血钾、BUN、SCr水平无显著相关(P>0.05).结论 血、尿VEGF升高水平可以作为ARF大鼠肾脏IRI早期肾脏缺血缺氧的监测指标.     

高脂高糖饮食对自发性高血压大鼠水通道蛋白1mRNA表达及对尿钠排泄的影响

目的探讨高脂高糖饮食对自发性高血压大鼠(SHR)水通道蛋白1(AQP-1)mRNA与NO表达的影响,及其在加重尿钠排泄中的作用。方法 6周龄雄性SHR 24只随机分为高脂高糖组12只和普通饲料组12只,第8、12周末观察高脂高糖饮食对其NO、尿钠排泄等的影响,并计算肾质量指数。12周末RT-PCR检测肾脏AQP-1mRNA表达。结果与普通饲料组比较,高脂高糖组第8、12周末血压、血浆NO、肾脏尿钠排泄量明显降低(P<0.05),12周末肾组织AQP-1mRNA表达明显降低[(0.54±0.07)vs(1.28±0.39),P<0.01],第12周末肾质量指数明显升高[(3.40±2.00)mg/g vs(2.30±1.00)mg/g,P<0.05]。结论长期高脂高糖饮食可加重SHR肾脏损害,其机制可能与内源性NO合成降低、肾脏AQP-1mRNA表达降低相关。     

雌二醇对大鼠血管紧张素Ⅱ及其1型受体表达的影响

目的雌二醇对去卵巢SD大鼠血管紧张素Ⅱ及其1型受体表达的影响。方法24只12周龄雌性SD大鼠随机分为3组:去卵巢组、去卵巢加雌二醇(简称雌二醇)组和假手术组。测量术前和术后大鼠体重、血压,检测血清雌二醇、血浆血管紧张素Ⅱ、心脏、肾皮质、主动脉血管紧张素Ⅱ1型受体mRNA的表达水平。并用离体培养血管平滑肌细胞,检测雌二醇对血管平滑肌血管紧张素Ⅱ1型受体mRNA表达的影响。结果1.三组大鼠在手术前体重没有明显差别,三个月后,与假手术组比较,去卵巢组大鼠体重显著增加(475.8±23.0比372.1±13.1,P<0.05),雌二醇组与假手术组比较无明显差别(387.3±15.9比372.1±13.1,P>0.05)。2.术前三组大鼠血压没有明显的差别。三个月后,去卵巢组大鼠血压明显升高(117.5±7.6比104.4±6.2mmHg,P<0.05),雌二醇组血压不升高,与假手术组没有差别。3.与假手术组比较,去卵巢组血浆血管紧张素Ⅱ浓度明显升高(617.7±80.1比215.0±26.7,P<0.05)。雌二醇组血浆血管紧张素Ⅱ浓度与假手术组没有区别。4.与假手术组比较,去卵巢组心脏、肾脏、主动脉血管mRNA表达明显增加,雌二醇组无显著差异。5.体外培养血管平滑肌细胞,在0.2%小牛血清培养基的条件下,加入10-6mol/L雌二醇,从4h开始抑制血管平滑肌细胞血管紧张素Ⅱ1型受体mRNA的表达,12h血管紧张素Ⅱ1型受体mRNA的表达明显降低(0.65±0.06比0.85±0.07,P<0.05)。在0.2%小牛血清培养基的条件下,10-5、10-6和10-7mol/L雌二醇呈浓度依赖性的抑制血管紧张素Ⅱ1型受体mRNA的表达,当雌二醇10-6mol/L血管紧张素Ⅱ1型受体mRNA的表达显著降低(0.67±0.06比0.85±0.07,P<0.05)。结论1.雌二醇可抑制血管紧张素Ⅱ1型受体的表达及降低血管紧张素Ⅱ水平。2.雌二醇对心血管系统作用可能通过降低血管紧张素Ⅱ及其1型受体的表达     

中性粒细胞趋化因子在急性胰腺炎相关急性肺损害中的作用

目的:探讨中性粒细胞趋化因子(CINC)在急性胰腺炎相关的急性肺损害(ALI)中的作用.方法:分别采用ip雨蛙肽和胰胆管逆行注射50g/L牛磺胆酸钠建立大鼠轻症、重症急性胰腺炎模型.84只SD大鼠随机分为雨蛙肽组、生理盐水组、牛磺胆酸钠组和手术对照组.分别检测各组不同时间点血清淀粉酶、肺干湿重比和肺组织病理学改变,用免疫组织化学法和半定量逆转录聚合酶链反应(RT-PCR)法检测肺组织中CINC蛋白和CINCmRNA表达的变化情况.结果:雨蛙肽组各时间点CINC蛋白和CINCmRNA的表达与生理盐水组无明显差异(P>0.05);牛磺胆酸钠组与手术对照组相比,血清淀粉酶、肺干湿重比显著升高(P<0.05),术后1h肺组织CINCmRNA的表达开始升高(1h:0.23±0.07vs0.07±0.04,P<0.05;3h:0.36±0.07vs0.06±0.04,P<0.05;6h:0.56±0.07vs0.09±0.05,P<0.01;12h:0.49±0.09vs0.11±0.03,P<0.01),术后3h开始有CINC蛋白的表达,随着时间的延长表达逐渐增强,且与肺组织的病理改变呈正相关.结论:CINC可能在胰腺炎相关的急性肺损害中起了重要的作用.     

NF-κB对急性坏死性胰腺炎大鼠甲状旁腺激素受体表达和低钙血症的影响

目的 探讨NF-κB对ANP大鼠甲状旁腺激素受体(PTH1R)表达及低钙血症的影响.方法 将雄性SD大鼠24只按完全随机法分为对照组、ANP组和四氢化吡咯二硫代氨基甲酸脂预处理组(PDTC组),各8只.以5%牛磺脱氧胆酸钠逆行胰胆管注射建立ANP模型.观察6 h后各组血清钙浓度以及胰腺组织病理改变,蛋白免疫印渍法检测肾脏和骨组织NF-κB、PTH1R蛋白表达,RT-PCR检测肾脏和骨组织FTH1R mRNA表达.结果 对照组、ANP组和PDTC组血钙浓度分别为(2.31±0.03)mmol/L、(2.01±0.03)mmol/L和(2.12±0.05)mmol/L,3组间差异显著(P<0.05).ANP组肾脏和骨组织的NF-κB蛋白表达量分别为1.53±0.08和0.47±0.19;PDTC组分别为0.61±0.13和0.36±0.06,两组差异显著(P<0.05).ANP组肾脏和骨组织PTH1R mRNA的表达量分别为0.27±0.08和0.29±0.06,PTH1R蛋白表达分别为0.87±0.07和0.31±0.09;PDTC组分别为0.57±0.27和0.37±0.11,1.13±0.17和0.68±0.15,两组差异显著(P<0.05).ANP组NF-κB活性较对照组明显升高,PTH1R表达明显下降;与ANP组比较,PDTC组NF-κB活性降低,血清钙水平明显升高,PTH1R的表达上调(P<0.05).结论 NF-κB可能通过间接下调组织PTH1R的表达,致血清钙显著下降.PDTC对改善ANP低钙血症有一定意义.     

高脂高糖饮食对自发性高血压大鼠内皮素表达及肾功能的影响

目的探讨高脂高糖饮食对自发性高血压大鼠(SHR)内皮素1表达和肾功能的影响。方法 24只6周龄雄性SHR随机分为高脂高糖组和普通饲料组,每组12只。观察高脂高糖饮食对体质量、血糖、血脂、胰岛素、内皮素1和肾功能等的影响,计算胰岛素抵抗指数(HOMA-IR)、肌酐清除率(Ccr)、尿白蛋白/肌酐比值(ACR)的变化。提取肾脏总RNA,实时定量RT-PCR检测内皮素1mRNA,HE染色观察肾脏的病理变化。结果与普通饲料组比较,高脂高糖组大鼠干预后第12周体质量增加24%,TC、TG水平、胰岛素及HOMA-IR升高,内皮素1增高[(45.0±0.2)ng/L vs(25.0±0.1)ng/L];Ccr降低[(0.3±0.2)ml/min vs(0.6±0.1)ml/min],差异有统计学意义(P<0.05,P<0.01)。ACR升高(P<0.05);肾脏内皮素1mRNA增高(197.9±22.2)vs(100.3±11.4),差异有统计学意义(P<0.05)。结论长期高脂高糖饮食可加重SHR肾损害,其机制可能与胰岛素升高、HOMA-IR增加及肾脏内皮素1mRNA表达上调相关。     

参附注射液对脓毒症老龄大鼠肾脏组织炎症因子表达的影响

目的探讨参附注射液对脓毒症大鼠肾组织的保护作用。方法取80只SD大鼠,分别为正常组,假手术组,模型组,参附注射液组(高、中、低),阳性药组;分别于给药后12、24、36、48 h后,采集大鼠血清、肾脏及尿液标本。利用自动生化分析仪测定血清中肌酐(Cr)、尿素氮(BUN)、谷氨酸氨基转移酶(ALT)、K+及尿液中N-乙酰-β-D-葡萄糖苷酶(NAG)、Na~+含量,以及血清中白细胞介素(IL)-6及肾组织中IL-6、CD14、IL-18蛋白含量。结果模型组大鼠血清和肾组织中的IL-6蛋白表达水平明显升高;给予参附注射液治疗后,12~48 h大鼠血清中IL-6蛋白表达水平明显降低(P<0.05),12 h肾脏组织中IL-6水平却无显著变化,而24~36h肾脏组织中IL-6蛋白表达水平明显降低(P<0.05);模型组大鼠CD14、IL-18蛋白表达水平明显增高(P<0.01);与模型组相比,参附注射液高、中、低3组中肾脏组织中CD14、IL-18蛋白表达水平明显减少(P<0.01)。结论参附注射液对脓毒症大鼠肾脏具有明显的保护作用,其机制可能与调节血清与肾组织中的IL-6、CD14、IL-18蛋白表达水平,从而对炎症反应相关代谢产生调节有关。     

脂联素与醛固酮介导的SD大鼠心脏损害的关系

目的 探讨脂联素与醛固酮介导的SD大鼠心肌损害的关系.方法 雄性SD大鼠0.75μg/h皮下持续输注醛固酮4周,观察血压、心肌结构改变,测定血浆脂联素水平和附睾脂肪垫脂肪组织脂联素基因表达.体外培养3T3-L1脂肪细胞,10-8和10-6 mol/L醛固酮作用24和48 h,观察脂联素基因表达和培养液中脂联素浓度的变化.结果 醛固酮作用SD大鼠4周,血压轻微上升[(123±7)mm Hg,P<0.05],但心肌超微结构已有明显损伤如线粒体肿胀、内部结构不清等;同时,大鼠血浆脂联素水平较对照组降低22.8%(P<0.05).10-8和10-6mol/L醛固酮干预3T3-L1脂肪细胞24 h,培养液中脂联素浓度分别降低21.8%和27.2%(P<0.05);干预48 h,脂联素mRNA表达分别降低22.1%和37.4%(P<0.05).螺内酯可逆转醛固酮对心肌的影响.结论 脂联素水平的降低可能与醛固酮介导的心脏损伤有关.     

血管加压素对大鼠肾脏水孔蛋白2表达的影响

背景和目的水孔蛋白2(AQP2)是调节机体水平衡的通道蛋白,与多种具水盐代谢异常疾病的病理发生发展密切相关,本文观察血管加压素(AVP)对 WKY 大鼠肾脏 AQP2表达的影响。方法 WKY 大鼠16只,随机分成2组,一组 AVP[2.5 U/(kg·d)]腹腔注射,等量的生理盐水腹腔注射为对照。7天后处死大鼠,RT-PCR法检测两组大鼠。肾脏 AQP2的 mRNA 表达,免疫组化法检测 AQP2蛋白表达水平,放射免疫法检测大鼠血浆 AVP浓度。结果 AVP 注射组大鼠血浆 AVP 浓度明显升高[(65.7±7.9)vs 对照组(51.2±7.9)pg/mL,P<0.05],肾脏 AQP2 mRNA(0.68±0.14 vs 0.39±0.11,P<0.05)和 AQP2蛋白表达水平(0.71±0.09 vs 0.42±0.12,P<0.05)均显著高于对照组。结论 AVP 可刺激肾脏 AQP2的表达,AQP2可能是 AVP 调节肾脏水代谢的机制之一。提示水通道蛋白2表达的调节可能成为干预某些心血管疾病,如充血性心力衰竭、高血压的靶点。     

An SGK1 site in WNK4 regulates Na+ channel and K+ channel activity and has implications for aldosterone signaling and K+ homeostasis

The steroid hormone aldosterone is secreted both in the setting of intravascular volume depletion and hyperkalemia, raising the question of how the kidney maximizes NaCl reabsorption in the former state while maximizing K(+) secretion in the latter. Mutations in WNK4 cause pseudohypoaldosteronism type II (PHAII), a disease featuring increased renal NaCl reabsorption and impaired K(+) secretion. PHAII-mutant WNK4 achieves these effects by increasing activity of the Na-Cl cotransporter (NCC) and the Na(+) channel ENaC while concurrently inhibiting the renal outer medullary K(+) channel (ROMK). We now describe a functional state for WNK4 that promotes increased, rather than decreased, K(+) secretion. We show that WNK4 is phosphorylated by SGK1, a mediator of aldosterone signaling. Whereas wild-type WNK4 inhibits the activity of both ENaC and ROMK, a WNK4 mutation that mimics phosphorylation at the SGK1 site (WNK4(S1169D)) alleviates inhibition of both channels. The net result of these effects in the kidney would be increased K(+) secretion, because of both increased electrogenic Na(+) reabsorption and increased apical membrane K(+) permeability. Thus, modification at the PHAII and SGK1 sites in WNK4 impart opposite effects on K(+) secretion, decreasing or increasing ROMK activity and net K(+) secretion, respectively. This functional state for WNK4 would thus promote the desired physiologic response to hyperkalemia, and the fact that it is induced downstream of aldosterone signaling implicates WNK4 in the physiologic response to aldosterone with hyperkalemia. Together, the different states of WNK4 allow the kidney to provide distinct and appropriate integrated responses to intravascular volume depletion and hyperkalemia.     

A novel protein kinase signaling pathway essential for blood pressure regulation in humans.

The discovery that mutations in WNK4 [encoding a member of the WNK family - so named because of the unique substitution of cysteine for lysine at a nearly invariant residue within subdomain II of its catalytic core: with no K (lysine)] cause pseudohypoaldosteronism type II, an autosomal dominant form of human hypertension, provided the initial clue that this serine/threonine kinase is a crucial part of a complex renal salt regulatory system. Recent findings from physiological studies of WNK4 in Xenopus laevis oocytes, mammalian cell systems and in vivo in mouse models have provided novel insights into the mechanisms by which the kidney regulates salt homeostasis, and therefore blood pressure, downstream of aldosterone signaling in mammals. The current evidence supports a model in which WNK4 coordinates the activities of diverse aldosterone-sensitive mediators of ion transport in the distal nephron to promote normal homeostasis in response to physiological perturbation.     

Src-family protein tyrosine kinase phosphorylates WNK4 and modulates its inhibitory effect on KCNJ1 (ROMK)

With-no-lysine kinase 4 (WNK4) inhibits the activity of the potassium channel KCNJ1 (ROMK) in the distal nephron, thereby contributing to the maintenance of potassium homeostasis. This effect is inhibited via phosphorylation at Ser1196 by serum/glucocorticoid-induced kinase 1 (SGK1), and this inhibition is attenuated by the Src-family protein tyrosine kinase (SFK). Using Western blot and mass spectrometry, we now identify three sites in WNK4 that are phosphorylated by c-Src: Tyr¹⁰⁹², Tyr¹⁰⁹⁴, and Tyr¹¹⁴³, and show that both c-Src and protein tyrosine phosphatase type 1D (PTP-1D) coimmunoprecipitate with WNK4. Mutation of Tyr¹⁰⁹² or Tyr¹¹⁴³ to phenylalanine decreased the association of c-Src or PTP-1D with WNK4, respectively. Moreover, the Tyr1092Phe mutation markedly reduced ROMK inhibition by WNK4; this inhibition was completely absent in the double mutant WNK4^Y1092/1094F. Similarly, c-Src prevented SGK1-induced phosphorylation of WNK4 at Ser¹¹⁹⁶, an effect that was abrogated in the double mutant. WNK4^Y1143F inhibited ROMK activity as potently as wild-type (WT) WNK4, but unlike WT, the inhibitory effect of WNK4^Y1143F could not be reversed by SGK1. The failure to reverse WNK4^Y1143F-induced inhibition of ROMK by SGK1 was possibly due to enhancing endogenous SFK effect on WNK4 by decreasing the WNK4–PTP-1D association because inhibition of SFK enabled SGK1 to reverse WNK4^Y1143F-induced inhibition of ROMK. We conclude that WNK4 is a substrate of SFKs and that the association of c-Src and PTP-1D with WNK4 at Tyr¹⁰⁹² and Tyr¹¹⁴³ plays an important role in modulating the inhibitory effect of WNK4 on ROMK.With-no-lysine kinase 4 (WNK4) is expressed in the connecting tubule (CNT) and cortical collecting duct (CCD) (1, 2) and plays an important role in modulating the balance between renal K secretion and Na reabsorption (3–8). The effect of WNK4 on renal K secretion is partially mediated through inhibition of KCNJ1 (ROMK) channels in the CNT and in the CCD. ROMK inhibition is achieved by a stimulation of clathrin-mediated endocytosis (1), an effect that is dependent on intersectin, a scaffold protein containing two Eps15 homology domains (9).Serum/glucocorticoid-induced kinase 1 (SGK1), a downstream mediator of aldosterone signaling, suppresses the inhibitory effect of WNK4 on ROMK channels through phosphorylation of WNK4 at Ser¹¹⁶⁹ (2) and Ser¹¹⁹⁶ (5). Both volume depletion and high K intake increase aldosterone and SGK1 levels (10). However, it is not clear why a high K intake or volume depletion modulates differently the effect of SGK1 on ROMK channels.Candidate regulators of differential ROMK expression in hyperkalemia and hypovolemia should be regulated in a potassium-dependent manner. One such protein is the protein tyrosine kinase c-Src, whose expression in renal cortex is reduced in states of high potassium intake (11). We have previously demonstrated a key role of c-Src in determining the effect of SGK1 on WNK4 (12). C-Src abolishes SGK1-induced phosphorylation of WNK4 and restores the inhibitory effect of WNK4 on ROMK channels in the presence of SGK1 (13). This effect may play a role in preventing K secretion in the absence of hyperkalemia. High potassium intake, in contrast, will diminish c-Src levels, restore SGK1-induced phosphorylation of WNK4, and lead to increased renal potassium secretion via ROMK.Whereas protein phosphatase activity has been shown to be involved in c-Src–mediated modulation of the interaction between SGK1 and WNK4 (13), the molecular mechanism of c-Src’s interaction with WNK4 has been elusive. We here identify previously undescribed tyrosine phosphorylation sites in WNK4 that are targets of c-Src. We characterize the effects of tyrosine phosphorylation on the SGK1–WNK4 interaction, as well as WNK4-mediated ROMK inhibition.     

WNK4 regulates apical and basolateral Cl- flux in extrarenal epithelia

Mutations in the serine-threonine kinase WNK4 [with no lysine (K) 4] cause pseudohypoaldosteronism type II, a Mendelian disease featuring hypertension with hyperkalemia. In the kidney, WNK4 regulates the balance between NaCl reabsorption and K(+) secretion via variable inhibition of the thiazide-sensistive NaCl cotransporter and the K(+) channel ROMK. We now demonstrate expression of WNK4 mRNA and protein outside the kidney. In extrarenal tissues, WNK4 is found almost exclusively in polarized epithelia, variably associating with tight junctions, lateral membranes, and cytoplasm. Epithelia expressing WNK4 include sweat ducts, colonic crypts, pancreatic ducts, bile ducts, and epididymis. WNK4 is also expressed in the specialized endothelium of the blood-brain barrier. These epithelia and endothelium all play important roles in Cl(-) transport. Because WNK4 is known to regulate renal Cl(-) handling, we tested WNK4's effect on the activity of mediators of epithelial Cl(-) flux whose extrarenal expression overlaps with WNK4. WNK4 proved to be a potent inhibitor of the activity of both the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) and the Cl(-)/base exchanger SLC26A6 (CFEX) (>95% inhibition of NKCC1-mediated (86)Rb influx, P < 0.001; >80% inhibition of CFEX-mediated [(14)C] formate uptake, P < 0.001), mediators of Cl(-) flux across basolateral and apical membranes, respectively. In contrast, WNK4 showed no inhibition of pendrin, a related Cl(-)/base exchanger. These findings indicate a general role for WNK4 in the regulation of electrolyte flux in diverse epithelia. Moreover, they reveal that WNK4 regulates the activities of a diverse group of structurally unrelated ion channels, cotransporters, and exchangers.     

Decreased ENaC expression compensates the increased NCC activity following inactivation of the kidney-specific isoform of WNK1 and prevents hypertension

Mutations in WNK1 and WNK4 lead to familial hyperkalemic hypertension (FHHt). Because FHHt associates net positive Na(+) balance together with K(+) and H(+) renal retention, the identification of WNK1 and WNK4 led to a new paradigm to explain how aldosterone can promote either Na(+) reabsorption or K(+) secretion in a hypovolemic or hyperkalemic state, respectively. WNK1 gives rise to L-WNK1, an ubiquitous kinase, and KS-WNK1, a kinase-defective isoform expressed in the distal convoluted tubule. By inactivating KS-WNK1 in mice, we show here that this isoform is an important regulator of sodium transport. KS-WNK1(-/-) mice display an increased activity of the Na-Cl cotransporter NCC, expressed specifically in the distal convoluted tubule, where it participates in the fine tuning of sodium reabsorption. Moreover, the expression of the ROMK and BKCa potassium channels was modified in KS-WNK1(-/-) mice, indicating that KS-WNK1 is also a regulator of potassium transport in the distal nephron. Finally, we provide an alternative model for FHHt. Previous studies suggested that the activation of NCC plays a central role in the development of hypertension and hyperkalemia. Even though the increase in NCC activity in KS-WNK1(-/-) mice was less pronounced than in mice overexpressing a mutant form of WNK4, our study suggests that the activation of Na-Cl cotransporter is not sufficient by itself to induce a hyperkalemic hypertension and that the deregulation of other channels, such as the Epithelial Na(+) channel (ENaC), is probably required.     

Activation of the renal Na+:Cl- cotransporter by angiotensin II is a WNK4-dependent process

Pseudohypoaldosteronism type II is a salt-sensitive form of hypertension with hyperkalemia in humans caused by mutations in the with-no-lysine kinase 4 (WNK4). Several studies have shown that WNK4 modulates the activity of the renal Na(+)Cl(-) cotransporter, NCC. Because the renal consequences of WNK4 carrying pseudoaldosteronism type II mutations resemble the response to intravascular volume depletion (promotion of salt reabsorption without K(+) secretion), a condition that is associated with high angiotensin II (AngII) levels, it has been proposed that AngII signaling might affect WNK4 modulation of the NCC. In Xenopus laevis oocytes, WNK4 is required for modulation of NCC activity by AngII. To demonstrate that WNK4 is required in the AngII-mediated regulation of NCC in vivo, we used a total WNK4-knockout mouse strain (WNK4(-/-)). WNK4 mRNA and protein expression were absent in WNK4(-/-) mice, which exhibited a mild Gitelman-like syndrome, with normal blood pressure, increased plasma renin activity, and reduced NCC expression and phosphorylation at T-58. Immunohistochemistry revealed normal morphology of the distal convoluted tubule with reduced NCC expression. Low-salt diet or infusion of AngII for 4 d induced phosphorylation of STE20/SPS1-related proline/alanine-rich kinase (SPAK) and of NCC at S-383 and T-58, respectively, in WNK4(+/+) but not WNK4(-/-) mice. Thus, the absence of WNK4 in vivo precludes NCC and SPAK phosphorylation promoted by a low-salt diet or AngII infusion, suggesting that AngII action on the NCC occurs via a WNK4-SPAK-dependent signaling pathway. Additionally, stimulation of aldosterone secretion by AngII, but not by a high-K(+) diet, was impaired in WNK4(-/-) mice.     

Paracellular Cl- permeability is regulated by WNK4 kinase: insight into normal physiology and hypertension

Paracellular ion flux across epithelia occurs through selective and regulated pores in tight junctions; this process is poorly understood. Mutations in the kinase WNK4 cause pseudohypoaldosteronism type II (PHAII), a disease featuring hypertension and hyperkalemia. Whereas WNK4 is known to regulate several transcellular transporters and channels involved in NaCl and K+ homeostasis, its localization to tight junctions suggests it might also regulate paracellular flux. We performed electrophysiology on mammalian kidney epithelia with inducible expression of various WNK4 constructs. Induction of wild-type WNK4 reduced transepithelial resistance by increasing absolute chloride permeability. PHAII-mutant WNK4 produced markedly larger effects, whereas kinase-mutant WNK4 had no effect. The electrochemical and pharmacologic properties of these effects indicate they are attributable to the paracellular pathway. The effects of WNK4 persist when induction is delayed until after tight-junction formation, demonstrating a dynamic effect. WNK4 did not alter the flux of uncharged solutes, or the expression or localization of selected tight-junction proteins. Transmission and freeze-fracture electron microscopy showed no effect of WNK4 on tight-junction structure. These findings implicate WNK signaling in the coordination of transcellular and paracellular flux to achieve NaCl and K+ homeostasis, explain PHAII pathophysiology, and suggest that modifiers of WNK signaling may be potent antihypertensive agents.     

WNK1, a kinase mutated in inherited hypertension with hyperkalemia,localizes to diverse Cl- -transporting epithelia

Mutations in WNK1 and WNK4, genes encoding members of a novel family of serine-threonine kinases, have recently been shown to cause pseudohypoaldosteronism type II (PHAII), an autosomal dominant disorder featuring hypertension, hyperkalemia, and renal tubular acidosis. The localization of these kinases in the distal nephron and the Cl(-) dependence of these phenotypes suggest that these mutations increase renal Cl(-) reabsorption. Although WNK4 expression is limited to the kidney, WNK1 is expressed in many tissues. We have examined the distribution of WNK1 in these extrarenal tissues. Immunostaining using WNK1-specific antibodies demonstrated that WNK1 is not present in all cell types; rather, it is predominantly localized in polarized epithelia, including those lining the lumen of the hepatic biliary ducts, pancreatic ducts, epididymis, sweat ducts, colonic crypts, and gallbladder. WNK1 is also found in the basal layers of epidermis and throughout the esophageal epithelium. The subcellular localization of WNK1 varies among these epithelia. WNK1 is cytoplasmic in kidney, colon, gallbladder, sweat duct, skin, and esophagus; in contrast, it localizes to the lateral membrane in bile ducts, pancreatic ducts, and epididymis. These epithelia are all notable for their prominent role in Cl(-) flux. Moreover, these sites largely coincide with those involved in the pathology of cystic fibrosis, a disease characterized by deranged epithelial Cl(-) flux. Together with the known pathophysiology of PHAII, these findings suggest that WNK1 plays a general role in the regulation of epithelial Cl(-) flux, a finding that suggests the potential of new approaches to the selective modulation of these processes.