Expression of the bumetanide-sensitive Na-K-Cl cotransporter BSC2 is differentially regulated by fluid mechanical and inflammatory cytokine stimuli in vascular endothelium

Time-dependent effects of tumor necrosis factor α on Ca2+-dependent secretion in murine small intestinal organoids

Background

Intestinal organoids are stem cell-derived, 3D "mini-guts" with similar functions as the native intestinal epithelium such as electrolyte transport or establishment of an epithelial barrier. During intestinal inflammation, epithelial functions are dysregulated by proinflammatory cytokines like tumor necrosis factor α (TNFα) and other messengers from the immune system resulting in a loss of electrolytes and water due to an impaired epithelial barrier and higher net secretion.

Methods

A murine small intestinal organoid model was established to study (long-term) effects of TNFα on the intestinal epithelium in vitro using live imaging, immunohistochemical staining and qPCR.

Results

TNFα induced apoptosis in intestinal organoids as indicated by an increased number of cells with immunoreactivity for cleaved caspase 3. Furthermore, TNFα exposure led to swelling of the organoids which was inhibited by bumetanide and was concomitant with an upregulation of the bumetanide-sensitive Na+-K+-2Cl- symporter 1 (NKCC1) as shown by qPCR. Fura-2 imaging experiments revealed time-dependent changes in Ca2+ signaling consisting of a rise in the basal cytosolic Ca2+ concentration at day 1 and an increase of the carbachol-induced Ca2+ response after 3 days TNFα exposure. This was prevented by preincubation with La3+, an inhibitor of non-selective cation channels, or by using a Ca2+-free buffer indicating an enhancement of the Ca2+ influx from the extracellular side by the cytokine. No significant changes in cDNA levels of epithelial barrier proteins could be observed in the presence of TNFα.

Conclusion

Intestinal organoids are a useful tool to study the mechanism underlying the TNFα-induced secretion on enterocytes such as the regulation of NKCC1 expression or the modulation of cellular Ca2+ signaling.

Revealing the Angiopathy of Lacrimal Gland Lesion in Type 2 Diabetes

For a better understanding of diabetic angiopathy (DA), the potential biomarkers in lacrimal DA and its potential mechanism, we evaluated the morphological and hemodynamic alterations of lacrimal glands (LGs) in patients with type 2 diabetes and healthy counterparts by color Doppler flow imaging (CDFI). We further established a type 2 diabetic mice model and performed hematoxylin-eosin (HE) staining, immunofluorescence staining of CD31, RNA-sequencing analysis, and connectivity map (CMap) analysis. We found atrophy and ischemia in patients with type 2 diabetes and mice models. Furthermore, we identified 846 differentially expressed genes (DEGs) between type 2 diabetes mellitus (T2DM) and vehicle mice by RNA-seq. The gene ontology (GO) analysis indicated significant enrichment of immune system process, regulation of blood circulation, apoptotic, regulation of secretion, regulation of blood vessel diameter, and so on. The molecular complex detection (MCODE) showed 17 genes were involved in the most significant module, and 6/17 genes were involved in vascular disorders. CytoHubba revealed the top 10 hub genes of DEGs, and four hub genes (App, F5, Fgg, and Gas6) related to vascular regulation were identified repeatedly by MCODE and cytoHubba. GeneMANIA analysis demonstrated functions of the four hub genes above and their associated molecules were primarily related to the regulation of circulation and coagulation. CMap analysis found several small molecular compounds to reverse the altered DEGs, including disulfiram, bumetanide, genistein, and so on. Our outputs could empower the novel potential targets to treat lacrimal angiopathy, diabetes dry eye, and other diabetes-related diseases.

The GABA Developmental Shift Is Abolished by Maternal Immune Activation Already at Birth

Epidemiological and experimental studies suggest that maternal immune activation (MIA) leads to developmental brain disorders, but whether the pathogenic mechanism impacts neurons already at birth is not known. We now report that MIA abolishes in mice the oxytocin-mediated delivery γ-aminobutyric acid (GABA) shift from depolarizing to hyperpolarizing in CA3 pyramidal neurons, and this is restored by the NKCC1 chloride importer antagonist bumetanide. Furthermore, MIA hippocampal pyramidal neurons at birth have a more exuberant apical arbor organization and increased apical dendritic length than age-matched controls. The frequency of spontaneous glutamatergic postsynaptic currents is also increased in MIA offspring, as well as the pairwise correlation of the synchronized firing of active cells in CA3. These alterations produced by MIA persist, since at P14-15 GABA action remains depolarizing, produces excitatory action, and network activity remains elevated with a higher frequency of spontaneous glutamatergic postsynaptic currents. Therefore, the pathogenic actions of MIA lead to important morphophysiological and network alterations in the hippocampus already at birth.

Designing Single-Molecule Magnets as Drugs with Dual Anti-Inflammatory and Anti-Diabetic Effects

We have designed and synthesized two novel cobalt coordination compounds using bumetanide (bum) and indomethacin (ind) therapeutic agents. The anti-inflammatory effects of cobalt metal complexes with ind and bum were assayed in lipopolysaccharide stimulated RAW 264.7 macrophages by inhibition of nitric oxide production. Firstly, we determined the cytotoxicity and the anti-inflammatory potential of the cobalt compounds and ind and bum ligands in RAW 264.7 cells. Indomethacin-based metal complex was able to inhibit the NO production up to 35% in a concentration-dependent manner without showing cytotoxicity, showing around 6–37 times more effective than indomethacin. Cell cycle analysis showed that the inhibition of NO production was accompanied by a reversion of the differentiation processes in LPS-stimulated RAW 264.7 cells, due to a decreased of cell percentage in G0/G1 phase, with the corresponding increase in the number of cells in S phase. These two materials have mononuclear structures and show slow relaxation of magnetization. Moreover, both compounds show anti-diabetic activity with low in vitro cell toxicities. The formation of metal complexes with bioactive ligands is a new and promising strategy to find new compounds with high and enhanced biochemical properties and promises to be a field of great interest.

Comparison of efficacy of SHENQI compound and rosiglitazone in the treatment of diabetic vasculopathy analyzing multi-factor mediated disease-causing modules

Atherosclerosis-predominant vasculopathy is a common complication of diabetes with high morbidity and high mortality, which is ruining the patient's daily life. As is known to all, traditional Chinese medicine (TCM) SHENQI compound and western medicine rosiglitazone play an important role in the treatment of diabetes. In particular, SHENQI compound has a significant inhibitory effect on vascular lesions. Here, to explore and compare the therapeutic mechanism of SHENQI compound and rosiglitazone on diabetic vasculopathy, we first built 7 groups of mouse models. The behavioral, physiological and pathological morphological characteristics of these mice showed that SHENQI compound has a more comprehensive curative effect than rosiglitazone and has a stronger inhibitory effect on vascular lesions. While rosiglitazone has a more effective but no significant effect on hypoglycemic. Further, based on the gene expression of mice in each group, we performed differential expression analysis. The functional enrichment analysis of these differentially expressed genes (DEGs) revealed the potential pathogenesis and treatment mechanisms of diabetic angiopathy. In addition, we found that SHENQI compound mainly exerts comprehensive effects by regulating MCM8, IRF7, CDK7, NEDD4L by pivot regulator analysis, while rosiglitazone can rapidly lower blood glucose levels by targeting PSMD3, UBA52. Except that, we also identified some pivot TFs and ncRNAs for these potential disease-causing DEG modules, which may the mediators bridging drugs and modules. Finally, similar to pivot regulator analysis, we also identified the regulation of some drugs (e.g. bumetanide, disopyramide and glyburide etc.) which have been shown to have a certain effect on diabetes or diabetic angiopathy, proofing the scientific and objectivity of this study. Overall, this study not only provides an in-depth comparison of the efficacy of SHENQI compound and rosiglitazone in the treatment of diabetic vasculopathy, but also provides clinicians and drug designers with valuable theoretical guidance.

Inhibition of NKCC1 Modulates Alveolar Fluid Clearance and Inflammation in Ischemia-Reperfusion Lung Injury via TRAF6-Mediated Pathways

Background: The expression of Na-K-2Cl cotransporter 1 (NKCC1) in the alveolar epithelium is responsible for fluid homeostasis in acute lung injury (ALI). Increasing evidence suggests that NKCC1 is associated with inflammation in ALI. We hypothesized that inhibiting NKCC1 would attenuate ALI after ischemia-reperfusion (IR) by modulating pathways that are mediated by tumor necrosis-associated factor 6 (TRAF6).

Methods: IR-ALI was induced by producing 30 min of ischemia followed by 90 min of reperfusion in situ in an isolated and perfused rat lung model. The rats were randomly allotted into four groups comprising two control groups and two IR groups with and without bumetanide. Alveolar fluid clearance (AFC) was measured for each group. Mouse alveolar MLE-12 cells were cultured in control and hypoxia-reoxygenation (HR) conditions with or without bumetanide. Flow cytometry and transwell monolayer permeability assay were carried out for each group.

Results: Bumetanide attenuated the activation of p-NKCC1 and lung edema after IR. In the HR model, bumetanide decreased the cellular volume and increased the transwell permeability. In contrast, bumetanide increased the expression of epithelial sodium channel (ENaC) via p38 mitogen-activated protein kinase (p38 MAPK), which attenuated the reduction of AFC after IR. Bumetanide also modulated lung inflammation via nuclear factor-κB (NF-κB). TRAF6, which is upstream of p38 MAPK and NF-κB, was attenuated by bumetanide after IR and HR.

Conclusions: Inhibition of NKCC1 by bumetanide reciprocally modulated epithelial p38 MAPK and NF-κB via TRAF6 in IR-ALI. This interaction attenuated the reduction of AFC via upregulating ENaC expression and reduced lung inflammation.

Na+ -K+ -2Cl- Cotransporter (NKCC) Physiological Function in Nonpolarized Cells and Transporting Epithelia

Two genes encode the Na+ -K+ -2Cl- cotransporters, NKCC1 and NKCC2, that mediate the tightly coupled movement of 1Na+ , 1K+ , and 2Cl- across the plasma membrane of cells. Na+ -K+ -2Cl- cotransport is driven by the chemical gradient of the three ionic species across the membrane, two of them maintained by the action of the Na+ /K+ pump. In many cells, NKCC1 accumulates Cl- above its electrochemical potential equilibrium, thereby facilitating Cl- channel-mediated membrane depolarization. In smooth muscle cells, this depolarization facilitates the opening of voltage-sensitive Ca2+ channels, leading to Ca2+ influx, and cell contraction. In immature neurons, the depolarization due to a GABA-mediated Cl- conductance produces an excitatory rather than inhibitory response. In many cell types that have lost water, NKCC is activated to help the cells recover their volume. This is specially the case if the cells have also lost Cl- . In combination with the Na+ /K+ pump, the NKCC's move ions across various specialized epithelia. NKCC1 is involved in Cl- -driven fluid secretion in many exocrine glands, such as sweat, lacrimal, salivary, stomach, pancreas, and intestine. NKCC1 is also involved in K+ -driven fluid secretion in inner ear, and possibly in Na+ -driven fluid secretion in choroid plexus. In the thick ascending limb of Henle, NKCC2 activity in combination with the Na+ /K+ pump participates in reabsorbing 30% of the glomerular-filtered Na+ . Overall, many critical physiological functions are maintained by the activity of the two Na+ -K+ -2Cl- cotransporters. In this overview article, we focus on the functional roles of the cotransporters in nonpolarized cells and in epithelia. © 2018 American Physiological Society. Compr Physiol 8:871-901, 2018.

Cytokine-Regulation of Na+-K+-Cl- Cotransporter 1 and Cystic Fibrosis Transmembrane Conductance Regulator-Potential Role in Pulmonary Inflammation and Edema Formation

Pulmonary edema, a major complication of lung injury and inflammation, is defined as accumulation of extravascular fluid in the lungs leading to impaired diffusion of respiratory gases. Lung fluid balance across the alveolar epithelial barrier protects the distal airspace from excess fluid accumulation and is mainly regulated by active sodium transport and Cl^- absorption. Increased hydrostatic pressure as seen in cardiogenic edema or increased vascular permeability as present in inflammatory lung diseases such as the acute respiratory distress syndrome (ARDS) causes a reversal of transepithelial fluid transport resulting in the formation of pulmonary edema. The basolateral expressed Na⁺-K⁺-2Cl^- cotransporter 1 (NKCC1) and the apical Cl^- channel cystic fibrosis transmembrane conductance regulator (CFTR) are considered to be critically involved in the pathogenesis of pulmonary edema and have also been implicated in the inflammatory response in ARDS. Expression and function of both NKCC1 and CFTR can be modulated by released cytokines; however, the relevance of this modulation in the context of ARDS and pulmonary edema is so far unclear. Here, we review the existing literature on the regulation of NKCC1 and CFTR by cytokines, and-based on the known involvement of NKCC1 and CFTR in lung edema and inflammation-speculate on the role of cytokine-dependent NKCC1/CFTR regulation for the pathogenesis and potential treatment of pulmonary inflammation and edema formation.

Inhibition of Na-K-Cl cotransporter isoform 1 reduces lung injury induced by ischemia-reperfusion

OBJECTIVES

Ischemia-reperfusion acute lung injury is characterized by increased vascular permeability, lung edema, and neutrophil sequestration. Ischemia-reperfusion acute lung injury occurs in lung transplantation and other major surgical procedures. Effective regulation of alveolar fluid balance is critical for pulmonary edema. Sodium-potassium-chloride co-transporter regulates alveolar fluid and is associated with inflammation. We hypothesized that sodium-potassium-chloride co-transporter is important in ischemia-reperfusion acute lung injury. Bumetanide, a sodium-potassium-chloride co-transporter inhibitor, is used to treat pulmonary edema clinically. We studied the effect of bumetanide in ischemia-reperfusion acute lung injury.

METHODS

Isolated perfusion of mouse lungs in situ was performed. The main pulmonary artery and left atrium were catheterized for lung perfusion and effluent collection for recirculation, respectively, with perfusate consisting of 1 mL blood and 9 mL physiologic solution. Ischemia-reperfusion was induced by 120 minutes of ischemia (no ventilation or perfusion) and reperfused for 60 minutes. Wild-type, SPAK knockout (SPAK^-/-), and WNK4 knockin (WNK4^D561A/+) mice were divided into control, ischemia-reperfusion, and ischemia-reperfusion + bumetanide groups (n = 6 per group). Bumetanide was administered via perfusate during reperfusion. Measurements were taken of lung wet/dry weight, microvascular permeability, histopathology, cytokine concentrations, and activity of the nuclear factor-κB pathway.

RESULTS

In wild-type mice, ischemia-reperfusion caused lung edema (wet/dry weight 6.30 ± 0.36) and hyperpermeability (microvascular permeability, 0.29 ± 0.04), neutrophil sequestration (255.0 ± 55.8 cells/high-power field), increased proinflammatory cytokines, and nuclear factor-κB activation (1.33 ± 0.13). Acute lung injury was more severe in WNK4 mice with more lung edema, permeability, neutrophil sequestration, and nuclear factor-κB activation. Severity of acute lung injury was attenuated in SPAK^-/-mice. Bumetanide decreased pulmonary edema (wild-type: wet/dry weight 5.05 ± 0.44, WNK4: wet/dry weight 5.13 ± 0.70), neutrophil sequestration (wild-type: 151.7 ± 27.8 cells/high-power field, WNK4: 135.3 ± 19.1 cells/high-power field), permeability (wild-type: 0.19 ± 0.01, WNK4: 0.21 ± 0.03), cytokines, and nuclear factor-κB activation after ischemia-reperfusion.

CONCLUSIONS

Functional reduction of sodium-potassium-chloride co-transporter by genetic or pharmacologic treatment to inhibit sodium-potassium-chloride co-transporter resulted in lower severity of acute lung injury induced by ischemia-reperfusion. Sodium-potassium-chloride co-transporter may present a promising target for therapeutic interventions in a clinical setting.

Expressions of ion co-transporter genes in salicylate-induced tinnitus and treatment effects of spirulina

BACKGROUND

Although the activity of tinnitus-related ion co-transporter are known, their mRNA expressions has seldom been reported. We aimed to investigate the mRNA expressions of tinnitus-related ion co-transporter genes, and treatment effects of Spirulina.

METHODS

The mRNA expressions of K(+)-Cl(-) co-transporter (KCC2) and Na-K-2Cl co-transporter 1 (NKCC1) genes in the cochlea and brain of mice were evaluated after tinnitus was induced by intraperitoneal injection of salicylate. The effects of spirulina water extract on these gene expressions were investigated.

RESULTS

Compared to the control group, the tinnitus scores increased significantly, however, the salicylate-induced tinnitus could be reduced significantly by spirulina water extract. The tinnitus group had higher of borderline significance mRNA expression of KCC2 gene in the cochlear, significantly higher in the temporal lobes and in the frontal lobes. Meanwhile, compared to the tinnitus group, the spirulina group had significantly lower mRNA expression of KCC2 gene in the cochlear, temporal lobes, frontal lobes and parahippocampus/hippocampus. However, the NKCC1 mRNA expression was not significantly different between three groups in the cochlea and these brain areas.

CONCLUSION

Salicylate-induced tinnitus might be associated with increased mRNA expression of KCC2 gene, but not with mRNA expressions of NKCC1 gene in the cochlear and some tinnitus-related brain areas. Spirulina reduced the expression of KCC2 genes in salicylate-induced tinnitus.

Everything we always wanted to know about furosemide but were afraid to ask

Furosemide is a widely used, potent natriuretic drug, which inhibits the Na(+)-K(+)-2Cl(-) cotransporter (NKCC)-2 in the ascending limb of the loop of Henle applied to reduce extracellular fluid volume expansion in heart and kidney disease. Undesirable consequences of furosemide, such as worsening of kidney function and unpredictable effects on sodium balance, led to this critical evaluation of how inhibition of NKCC affects renal and cardiovascular physiology. This evaluation reveals important knowledge gaps, involving furosemide as a drug, the function of NKCC2 (and NKCC1), and renal and systemic indirect effects of NKCC inhibition. Regarding renal effects, renal blood flow and glomerular filtration rate could become compromised by activation of tubuloglomerular feedback or by renin release, particularly if renal function is already compromised. Modulation of the intrarenal renin angiotensin system, however, is ill-defined. Regarding systemic effects, vasodilation followed by nonspecific NKCC inhibition and changes in venous compliance are not well understood. Repetitive administration of furosemide induces short-term (braking phenomenon, acute diuretic resistance) and long-term (chronic diuretic resistance) adaptations, of which the mechanisms are not well known. Modulation of NKCC2 expression and activity in kidney and heart failure is ill-defined. Lastly, furosemide's effects on cutaneous sodium stores and on uric acid levels could be beneficial or detrimental. Concluding, a considerable knowledge gap is identified regarding a potent drug with a relatively specific renal target, NKCC2, and renal and systemic actions. Resolving these questions would increase the understanding of NKCCs and their actions and improve rational use of furosemide in pathophysiology of fluid volume expansion.

With-No-Lysine Kinase 4 Mediates Alveolar Fluid Regulation in Hyperoxia-Induced Lung Injury

OBJECTIVES

To investigate mechanisms involved in the regulation of epithelial ion channels and alveolar fluid clearance in hyperoxia-induced lung injury.

DESIGN

Laboratory animal experiments.

SETTING

Animal care facility procedure room in a medical center.

SUBJECTS

Wild-type, STE20/SPS1-related proline/alanine-rich kinase knockout (SPAK(-/-)), and with-no-lysine kinase 4 knockin (WNK4(D561A/+)) mice.

INTERVENTIONS

Mice were exposed to room air or 95% hyperoxia for 60 hours.

MEASUREMENTS AND MAIN RESULTS

Exposure to hyperoxia for 60 hours increased the lung expression of with-no-lysine kinase 4 and led to STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter phosphorylation, which resulted in the suppression of alveolar fluid clearance and increase of lung edema. WNK4(D561A/+) mice at the baseline presented an abundance of epithelium sodium channel and high levels of STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter phosphorylation. Compared with the wild-type group, hyperoxia caused greater epithelium sodium channel expression in WNK4(D561A/+) mice, but no significant difference in STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter phosphorylation. The functional inactivation of sodium-potassium-chloride cotransporter by gene knockout in SPAK(-/-) mice yielded a lower severity of lung injury and longer animal survival, whereas constitutive expression of with-no-lysine kinase 4 exacerbated the hyperoxia-induced lung injury. Pharmacologic inhibition of sodium-potassium-chloride cotransporter by inhaled furosemide improved animal survival in WNK4(D561A/+) mice. By contrast, inhibition of epithelium sodium channel exacerbated the hyperoxia-induced lung injury and animal death.

CONCLUSIONS

With-no-lysine kinase 4 plays a crucial role in the regulation of epithelial ion channels and alveolar fluid clearance, mainly via phosphorylation and activation of STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter.

Protein kinases are potential targets to treat inflammatory bowel disease

Protein kinases play a crucial role in the pathogenesis of inflammatory bowel disease (IBD), the two main forms of which are ulcerative colitis and Crohn’s disease. In this article, we will review the mechanisms of involvement of protein kinases in the pathogenesis of and intervention against IBD, in terms of their effects on genetics, microbiota, mucous layer and tight junction, and the potential of protein kinases as therapeutic targets against IBD.

Hypertonic saline alleviates cerebral edema by inhibiting microglia-derived TNF-α and IL-1β-induced Na-K-Cl Cotransporter up-regulation

Background

Hypertonic saline (HS) has been successfully used clinically for treatment of various forms of cerebral edema. Up-regulated expression of Na-K-Cl Cotransporter 1 (NKCC1) and inflammatory mediators such as tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) has been demonstrated to be closely associated with the pathogenesis of cerebral edema resulting from a variety of brain injuries. This study aimed to explore if alleviation of cerebral edema by 10% HS might be effected through down-regulation of inflammatory mediator expression in the microglia, and thus result in decreased NKCC1 expression in astrocytes in the cerebral cortex bordering the ischemic core.

Methods

The Sprague-Dawley (SD) rats that underwent right-sided middle cerebral artery occlusion (MCAO) were used for assessment of NKCC1, TNF-α and IL-1β expression using Western blotting, double immunofluorescence and real time RT-PCR, and the model also was used for evaluation of brain water content (BWC) and infarct size. SB203580 and SP600125, specific inhibitors of the p38 and JNK signaling pathways, were used to treat primary microglia cultures to determine whether the two signaling pathways were required for the inhibition of HS on microglia expressing and secreting TNF-α and IL-1β using Western blotting, double immunofluorescence and enzyme-linked immunosorbent assay (ELISA). The effect of TNF-α and IL-1β on NKCC1 expression in primary astrocyte cultures was determined. In addition, the direct inhibitory effect of HS on NKCC1 expression in primary astrocytes was also investigated by Western blotting, double immunofluorescence and real time RT-PCR.

Results

BWC and infarct size decreased significantly after 10% HS treatment. TNF-α and IL-1β immunoexpression in microglia was noticeably decreased. Concomitantly, NKCC1 expression in astrocytes was down-regulated. TNF-α and IL-1β released from the primary microglia subjected to hypoxic exposure and treatment with 100 mM HS were decreased. NKCC1 expression in primary astrocytes was concurrently and progressively down-regulated with decreasing concentration of exogenous TNF-α and IL-1β. Additionally, 100 mM HS directly inhibited NKCC1 up-regulation in astrocytes under hypoxic condition.

Conclusions

The results suggest that 10% HS alleviates cerebral edema through inhibition of the NKCC1 Cotransporter, which is mediated by attenuation of TNF-α and IL-1β stimulation on NKCC1.

Molecular physiology of SPAK and OSR1: two Ste20-related protein kinases regulating ion transport

SPAK (Ste20-related proline alanine rich kinase) and OSR1 (oxidative stress responsive kinase) are members of the germinal center kinase VI subfamily of the mammalian Ste20 (Sterile20)-related protein kinase family. Although there are 30 enzymes in this protein kinase family, their conservation across the fungi, plant, and animal kingdom confirms their evolutionary importance. Already, a large volume of work has accumulated on the tissue distribution, binding partners, signaling cascades, and physiological roles of mammalian SPAK and OSR1 in multiple organ systems. After reviewing this basic information, we will examine newer studies that demonstrate the pathophysiological consequences to SPAK and/or OSR1 disruption, discuss the development and analysis of genetically engineered mouse models, and address the possible role these serine/threonine kinases might have in cancer proliferation and migration.

Diuretics and epilepsy: will the past and present meet?

Clinical studies from over half a century ago suggested efficacy of a variety of diuretics in focal and generalized epilepsies as well as in status epilepticus, but these findings have not been translated into modern epilepsy training or practice. Recent advances in our understanding of neuronal maturation and the pathophysiology of neonatal seizures provide fresh insight into the mechanisms by which diuretics might reduce susceptibility to seizures. In vitro and in vivo rodent studies and human epilepsy surgical cases have shown that specific diuretic agents targeting the cation-chloride cotransporters decrease neuronal synchrony and neuronal hyperexcitability. These agents are thought to convey their antiepileptic activity by either expanding the extracellular space or promoting a cellular chloride transport balance that reflects a more developmentally "mature," less excitable state. It may be time to reexamine whether diuretics could serve as adjunctive therapies in the treatment of refractory epilepsies.

Cytokine regulation of OCTN2 expression and activity in small and large intestine

BACKGROUND

The organic cation transporter OCTN2 is located on the IBD5 risk allele and has been implicated in the pathogenesis of inflammatory bowel diseases (IBD). OCTN2 is expressed in the apical membrane and transports many solutes including bacteria-derived mediators that may be involved in host-microbial interactions. To explore its role further, we examined potential regulatory factors in human IBD and in experimental models of OCTN2 expression.

METHODS

Human colonic epithelial cells (Caco2BBE) were used to investigate the effects of inflammatory mediators on OCTN2 activity and expression. Apical membrane expression of OCTN2 was assessed by surface biotinylation. Rag-1(-/-) -deficient mice were used to determine the potential role of adaptive immune cells in the regulation of OCTN2 expression. C57Bl/6 mice were treated with the cytokines interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) to determine the effects on OCTN2 expression and activity. OCTN2 expression in human IBD specimens was assessed by Western blotting and immunohistochemistry.

RESULTS

OCTN2 activity and expression are regulated by the state of intestinal inflammation. OCTN2 expression in colonic tissues of Rag-1(-/-) -deficient mice was reduced. Treatment with IFN-γ and TNF-α increased intestinal OCTN2 expression, particularly in the colon. IFN-γ increased both total and apical membrane expression of Caco2BBE OCTN2, whereas TNF-α stimulated apical expression. Colonic epithelial OCTN2 expression was increased in actively inflamed areas of both Crohn's disease and ulcerative colitis.

CONCLUSIONS

Intestinal epithelial OCTN2 expression is increased by intestinal inflammation, most likely through increased levels of proinflammatory cytokines. These findings suggest that OCTN2 may participate to restoration of intestinal homeostasis under conditions of inflammation-associated stress.

Transcriptional remodeling of ion channel subunits by flow adaptation in human coronary artery endothelial cells

Endothelial cells (ECs) are constantly exposed to blood flow-induced shear forces in the vessels and this is a major determinant of endothelial function. Ion channels have a major role in endothelial function and in the control of vascular tone. We hypothesized that shear force is a general regulator of ion channel expression, which will have profound effects on endothelial function. We examined this hypothesis using large-scale quantitative real-time RT-PCR. Human coronary artery ECs were exposed to two levels of flow-induced shear stress for 24 h, while control cells were grown under static conditions. The expression of ion channel subunits was compared between control and flow-adapted cells. We used primers against 55 ion channel and exchanger subunits and were able to detect 54 subunits. Five dyn/cm(2) of shear induced downregulation of 1 (NCX1) and upregulation of 18 subunits, including K(Ca)2.2, K(Ca)2.3, CX37, K(v)1.5 and HCN2. Fifteen dyn/cm(2) of shear stress induced the expression of 30 ion channel subunits, including K(Ca)2.3, K(Ca)2.2, CX37, K(ir)2.3 and K(Ca)3.1. Our data demonstrate that substantial remodeling of endothelial ion channel subunit expression occurs with flow adaptation and suggest that altered ion channel expression may significantly contribute to vascular pathology associated with flow-induced alterations.

Secretome of human endothelial cells under shear stress

Endothelial cells are exposed to different types of shear stress which triggers the secretion of subsets of proteins. In this study, we analyzed the secretome of endothelial cells under static, laminar, and oscillatory flow. To differentiate between endogenously expressed and added proteins, isolated human umbilical vein endothelial cells were labeled with l-Lysine-(13)C(6),(15)N(2) and l-Arginine-(13)C(6),(15)N(4). Shear stress was applied for 24 h using a cone-and-plate viscometer. Proteins from the supernatants were isolated, trypsinized, and finally analyzed using LC-MS/MS (LTQ). Under static control condition 395 proteins could be identified, of which 78 proteins were assigned to the secretome according to Swiss-Prot database. Under laminar shear stress conditions, 327 proteins (83 secreted) and under oscillatory shear stress 507 proteins (79 secreted) were measured. We were able to identify 6 proteins specific for control conditions, 8 proteins specific for laminar shear stress, and 5 proteins specific for oscillatory shear stress. In addition, we identified flow-specific secretion patterns like the increased secretion of cell adhesion proteins and of proteins involved in protein binding. In conclusion, the identification of shear stress specific secreted proteins (101 under different flow conditions) emphasizes the role of endothelial cells in modulating the plasma composition according to the physiological requirements.

Ste20-related proline/alanine-rich kinase (SPAK) regulated transcriptionally by hyperosmolarity is involved in intestinal barrier function

The Ste20-related protein proline/alanine-rich kinase (SPAK) plays important roles in cellular functions such as cell differentiation and regulation of chloride transport, but its roles in pathogenesis of intestinal inflammation remain largely unknown. Here we report significantly increased SPAK expression levels in hyperosmotic environments, such as mucosal biopsy samples from patients with Crohn's disease, as well as colon tissues of C57BL/6 mice and Caco2-BBE cells treated with hyperosmotic medium. NF-kappaB and Sp1-binding sites in the SPAK TATA-less promoter are essential for SPAK mRNA transcription. Hyperosmolarity increases the ability of NF-kappaB and Sp1 to bind to their binding sites. Knock-down of either NF-kappaB or Sp1 by siRNA reduces the hyperosmolarity-induced SPAK expression levels. Furthermore, expression of NF-kappaB, but not Sp1, was upregulated by hyperosmolarity in vivo and in vitro. Nuclear run-on assays showed that hyperosmolarity increases SPAK expression levels at the transcriptional level, without affecting SPAK mRNA stability. Knockdown of SPAK expression by siRNA or overexpression of SPAK in cells and transgenic mice shows that SPAK is involved in intestinal permeability in vitro and in vivo. Together, our data suggest that SPAK, the transcription of which is regulated by hyperosmolarity, plays an important role in epithelial barrier function.

TNF-alpha modulates the Na+/ K+ ATPase and the Na+K+2Cl- symporter in LLC-PK cells

BACKGROUND

Tumour necrosis factor alpha (TNF-alpha) has been implicated in the development of diabetic nephropathy and the accompanying increase in sodium retention. Inhibition of renal Na(+)/K(+) ATPase was reported to accompany cell death. As TNF is known to induce both apoptosis and cell survival, this work investigated the effect and mechanism of action of TNF-alpha on the Na(+)/K(+) ATPase and the Na(+)K(+)2Cl(-) symporter using LLC-PK(1) cells, a porcine renal proximal tubules cell line.

MATERIALS AND METHODS

Cells were incubated for 2 h with TNF-alpha in presence and absence of pyrrolidinedithiocarbamate, SP600125 and FK009, respective inhibitors of the transcription factor nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappaB), c-Jun N-terminal kinase (JNK) and caspases. The activity of the pump was assayed by measuring the ouabain-inhibitable release of inorganic phosphate. Changes in its expression and the expression of the symporter were monitored by western blot analysis.

RESULTS

TNF-alpha up-regulated both transporters. NF-kappaB, JNK and the caspases were all mediators of the cytokine action. TNF up-regulated the Na(+)/K(+) pump by stimulating JNK which in turn, activated NF-kappaB and inhibited the caspases. TNF effect on the cotransporter was also mediated via activation of JNK which however inhibited NF-kappaB and by so doing prevented activation of caspases. As caspases were demonstrated to down-regulate the two transporters, their inhibition by TNF is responsible for the observed up-regulatory effect.

CONCLUSIONS

It was concluded that the Na(+)/K(+) ATPase and Na(+)K(+)2Cl(-) are both targets of TNF-alpha and the effect of the cytokine favours cell survival over cell death.

Ste20-related proline/alanine-rich kinase: A novel regulator of intestinal inflammation

Recently, inflammatory bowel disease (IBD) has been the subject of considerable research, with increasing attention being paid to the loss of intestinal epithelial cell barrier function as a mechanism of pathogenesis. Ste20-related proline/alanine-rich kinase (SPAK) is involved in regulating barrier function. SPAK is known to interact with inflammation-related kinases (such as p38, JNK, NKCC1, PKCtheta;, WNK and MLCK), and with transcription factor AP-1, resulting in diverse biological phenomena, including cell differentiation, cell transformation and proliferation, cytoskeleton rearrangement, and regulation of chloride transport. This review examines the involvement of Ste20-like kinases and downstream mitogen-activated protein kinases (MAPKs) pathways in the pathogenesis and control of intestinal inflammation. The primary focus will be on the molecular features of intestinal inflammation, with an emphasis on the interaction between SPAK and other molecules, and the effect of these interactions on homeostatic maintenance, cell volume regulation and increased cell permeability in intestinal inflammation.

Nuclear factor-kappaB is a critical mediator of Ste20-like proline-/alanine-rich kinase regulation in intestinal inflammation

Inflammatory bowel disease (IBD) is thought to result from commensal flora, aberrant cellular stress, and genetic factors. Here we show that the expression of colonic Ste20-like proline-/alanine-rich kinase (SPAK) that lacks a PAPA box and an F-alpha helix loop is increased in patients with IBD. The same effects were observed in a mouse model of dextran sodium sulfate-induced colitis and in Caco2-BBE cells treated with the pro-inflammatory cytokine tumor necrosis factor (TNF)-alpha. The 5'-flanking region of the SPAK gene contains two transcriptional start sites, three transcription factor Sp1-binding sites, and one transcription factor nuclear factor (NF)-kappaB-binding site, but no TATA elements. The NF-kappaB-binding site was essential for stimulated SPAK promoter activity by TNF-alpha, whereas the Sp1-binding sites were important for basal promoter activity. siRNA-induced knockdown of NF-kappaB, but not of Sp1, reduced TNF-alpha-induced SPAK expression. Nuclear run-on and mRNA decay assays demonstrated that TNF-alpha directly increased SPAK mRNA transcription without affecting SPAK mRNA stability. Furthermore, up-regulation of NF-kappaB expression and demethylation of the CpG islands induced by TNF-alpha also played roles in the up-regulation of SPAK expression. In conclusion, our data indicate that during inflammatory conditions, TNF-alpha is a key regulator of SPAK expression. The development of compounds that can either modulate or disrupt the activity of SPAK-mediated pathways is therefore important for the control and attenuation of downstream pathological responses, particularly in IBD.

Shear stress and 17β-estradiol modulate cerebral microvascular endothelial Na-K-Cl cotransporter and Na/H exchanger protein levels

Ion transporters of blood-brain barrier (BBB) endothelial cells play an important role in regulating the movement of ions between the blood and brain. During ischemic stroke, reduction in cerebral blood flow is accompanied by transport of Na and Cl from the blood into the brain, with consequent brain edema formation. We have shown previously that a BBB Na-K-Cl cotransporter (NKCC) participates in ischemia-induced brain Na and water uptake and that a BBB Na/H exchanger (NHE) may also participate. While the abrupt reduction of blood flow is a prominent component of ischemia, the effects of flow on BBB NKCC and NHE are not known. In the present study, we examined the effects of changes in shear stress on NKCC and NHE protein levels in cerebral microvascular endothelial cells (CMECs). We have shown previously that estradiol attenuates both ischemia-induced cerebral edema and CMEC NKCC activity. Thus, in the present study, we also examined the effects of estradiol on NKCC and NHE protein levels in CMECs. Exposing CMECs to steady shear stress (19 dyn/cm2) increased the abundance of both NKCC and NHE. Estradiol abolished the shear stress-induced increase in NHE but not NKCC. Abrupt reduction of shear stress did not alter NKCC or NHE abundance in the absence of estradiol, but it decreased NKCC abundance in estradiol-treated cells. Our results indicate that changes in shear stress modulate BBB NKCC and NHE protein levels. They also support the hypothesis that estradiol attenuates edema formation in ischemic stroke in part by reducing the abundance of BBB NKCC protein.

Interleukin-1beta upregulates Na+-K+-2Cl- cotransporter in human middle ear epithelia

Disruption of periciliary fluid homeostasis is the main pathogenesis of otitis media with effusion (OME), one of the most common childhood diseases. Although the underlying molecular mechanisms are unclear, it has been suggested that the altered functions of ion channels and transporters are involved in the fluid collection of middle ear cavity of OME patients. In the present study, we analyzed the effects of a major cytokine interleukin (IL)-1beta, which was known to be involved in the pathogenesis of OME, on Na(+)-K(+)-2Cl(-) cotransporter (NKCC) in human middle ear cells. Intracellular pH (pH(i)) was measured in primary cultures of normal human middle ear epithelial (NHMEE) cells using a double perfusion chamber, which enabled us to analyze the membrane-specific transporter activities. NKCC activities were estimated by the pH(i) reduction due to bumetanide-sensitive intracellular uptake of NH(4) (+). In NHMEE cells, NKCC activities were observed only in the basolateral membrane, and immunoblotting using specific antibodies revealed the expression of NKCC1. Interestingly, IL-1beta treatments augmented the basolateral NKCC activities and increased NKCC1 expression. In addition, IL-1beta treatments stimulated bumetanide-sensitive fluid transport across the NHMEE cell monolayers. Furthermore, an elevated NKCC1 expression was observed in middle ear cells from OME patients when compared to those from control individuals. The above results provide in vitro and in vivo evidence that the inflammatory cytokine IL-1beta upregulates NKCC1 in middle ear epithelial cells, which would be one of the important underlying mechanisms of excess fluid collection in OME patients.

Neuroinflammatory response of the choroid plexus epithelium in fatal diabetic ketoacidosis

A systemic inflammatory response (SIR) occurs prior to and during the treatment of severe diabetic ketoacidosis (DKA). IL-1beta, TNF-alpha and C5b-9 are components of SIR and have been speculated to be involved in the clinical brain edema (BE) of DKA. We studied IL-1beta, TNF-alpha, C5b-9, inducible nitric oxide (iNOS), ICAM-1, IL-10 and Hsp70 expression in the brains of two patients who died as the result of clinical BE during the treatment of DKA. IL-1beta was strongly expressed in the choroid plexus epithelium (CPE) and ependyma, and to a lesser extent in the hippocampus, caudate, white matter radiation of the pons, molecular layer of the cerebellum and neurons of the cortical gray matter. TNF-alpha was expressed to a lesser extent than IL-1beta, and only in the CP. C5b-9, previously shown to be deposited on neurons and oligodendrocytes, was found on CPE and ependymal cells. iNOS and ICAM-1 had increased expression in the CPE and ependyma. Hsp70 and IL-10 were also expressed in the CPE of the case with the shorter duration of treatment. Our data demonstrate the presence of a multifaceted neuroinflammatory cytotoxic insult of the CPE, which may play a role in the pathophysiology of the fatal brain edema of DKA.

Tumor necrosis factor-α and interferon-γ increase PepT1 expression and activity in the human colon carcinoma cell line Caco-2/bbe and in mouse intestine

A major mechanism for apical peptide absorption by small intestine is via the proton-coupled transporter PepT1. PepT1 is expressed at a high level in proximal small intestine, but it is not expressed in the healthy colon. However, in chronic states of intestinal inflammation, such as in Crohn's disease and ulcerative colitis, PepT1 expression in colonic epithelia is increased, serving as a pathway for entry of bacteria-derived molecules such as muramyl dipeptide (MDP) and fMet-Leu-Phe (fMLP). As little is known of how inflammation induces PepT1, we investigated whether or not inflammatory cytokines and mediators such as interleukins (IL)-1beta, IL-2, IL-8, IL-10, tumor necrosis factor-alpha, (TNF-alpha) and interferon-gamma (IFN-gamma ) up-regulate PepT1 activity and expression. Uptake of the PepT1 substrate glycylsarcosine [(3)H]-Gly-Sar was studied in vitro in the human colon carcinoma cell line Caco2/bbe monolayers as well as in vivo in mice injected with cytokines. TNF-alpha and IFN-gamma increased the activity, and total and apical membrane protein expression of PepT1 protein in a concentration- and time-dependent fashion. No changes in PepT1 mRNA were observed, suggesting post-transcriptional regulation. All three cytokines increased PepT1 protein expression in mouse proximal and distal colon but not in jejunum or ileum. TNF-alpha and IFN-gamma, but not IL-1beta, increased Gly-Sar uptake in mouse proximal and distal colon; however, no changes were observed in the small intestine with any cytokine treatment. Whereas neither TNF-alpha nor IFN-gamma increased PepT1 mRNA expression in any segment of the intestine, treatment with IL-1beta increased PepT1 mRNA expression in mouse proximal and distal colon and decreased PepT1 mRNA expression in jejunum and ileum. Since PepT1 transports bacteria-derived peptides, the up-regulation of protein expression and activity observed after treatment with TNF-alpha or IFN-gamma may play a role in activating host responses in involved colon.

Characterization of the interaction of the stress kinase SPAK with the Na+-K+-2Cl- cotransporter in the nervous system: evidence for a scaffolding role of the kinase

Activity of heterologously expressed NKCC1 was analyzed under basal and activated conditions in the presence and absence of binding of Ste20-related proline-alanine-rich kinase (SPAK). Mutant NKCC1 that lacks the ability to bind to this kinase showed K+ transport function identical to wild-type NKCC1. Thus, preventing the binding of the kinase to the cotransporter does not affect cotransporter function. In contrast, several experiments suggest a possible role for SPAK as a scaffolding protein. First, Western blot analysis revealed the presence, and in some tissues abundance, of truncated forms of SPAK and OSR1 in which the kinase domains are affected and thus lack kinase activity. Second, a yeast two-hybrid screen of proteins that interact with the regulatory (binding) domain of SPAK identified several proteins all involved in cellular stress pathways. Third, p38, one of the three major MAPKs, can be coimmunoprecipitated with SPAK and with NKCC1 in an activity-dependent manner. The amount of p38 coimmunoprecipitated with the kinase and the cotransporter significantly decreases upon cellular stress, whereas the interaction of the kinase with NKCC1 remains unchanged. These findings suggest that cation-chloride cotransporters might act as "sensors" for cellular stress, and SPAK, by interacting with the cotransporter, serves as an intermediate in the response to cellular stress.

Immunolocalization of a Na-K-2Cl cotransporter in human tracheobronchial smooth muscle

Inhibition of the Na-K-2Cl (NKCC) cotransporter by loop diuretics is associated with airway relaxation, but there has been no direct evidence for the expression of this protein in airway smooth muscle. Thus we hypothesized that a NKCC cotransporter is present and functional in airway smooth muscle cells. Monoclonal and polyclonal antibodies were used first to demonstrate the presence of a NKCC cotransporter protein in isolated human fetal trachea and normal human bronchial smooth muscle cells (BSMC) by Western blotting. The cotransporter protein was then localized by immunohistochemical staining to airway smooth muscle cells in culture and in situ. The localization was confirmed by indirect immunofluorescence and laser confocal microscopy in the BSMC. Cotransporter function in BSMC was also confirmed in vitro by bumetanide-mediated inhibition of rubidium uptake. Our present findings thus document the presence of a functional NKCC cotransporter in human airway smooth muscle, providing a basis for defining the role of this ion cotransporter in airway smooth muscle function.

Fluid shear stress and the vascular endothelium: for better and for worse

As blood flows, the vascular wall is constantly subjected to physical forces, which regulate important physiological blood vessel responses, as well as being implicated in the development of arterial wall pathologies. Changes in blood flow, thus generating altered hemodynamic forces are responsible for acute vessel tone regulation, the development of blood vessel structure during embryogenesis and early growth, as well as chronic remodeling and generation of adult blood vessels. The complex interaction of biomechanical forces, and more specifically shear stress, derived by the flow of blood and the vascular endothelium raise many yet to be answered questions:How are mechanical forces transduced by endothelial cells into a biological response, and is there a "shear stress receptor"?Are "mechanical receptors" and the final signaling pathways they evoke similar to other stimulus-response transduction systems?How do vascular endothelial cells differ in their response to physiological or pathological shear stresses?Can shear stress receptors or shear stress responsive genes serve as novel targets for the design of diagnostic and therapeutic modalities for cardiovascular pathologies?The current review attempts to bring together recent findings on the in vivo and in vitro responses of the vascular endothelium to shear stress and to address some of the questions raised above.

Amiloride blockades lipopolysaccharide-induced proinflammatory cytokine biosynthesis in an IkappaB-alpha/NF-kappaB-dependent mechanism. Evidence for the amplification of an antiinflammatory pathway in the alveolar epithelium

It has been previously reported that amiloride suppresses inflammatory cytokine biosynthesis. However, the molecular mechanism involved has yet to be ascertained. Therefore, the immunoregulatory potential mediated by amiloride and the underlying signaling transduction pathway was investigated. Exposure of alveolar epithelial cells to amiloride or its analog, 5-(N,N-hexamethylene)-amiloride (HMA), reduced, in a dose-dependent manner, lipopolysaccharide (LPS)-induced secretion of interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. This inhibitory effect was associated with the augmentation of a counter antiinflammatory response, mediated by IL-6 and IL-10. Analysis of the mechanism implicated revealed the involvement of an inhibitory kappaB (IkappaB-alpha)/nuclear factor kappaB (NF- kappaB)-sensitive pathway. Amiloride and HMA suppressed the phosphorylation of IkappaB-alpha mediated by LPS, thereby allowing its cytosolic accumulation. Furthermore, both inhibitors interfered with the nuclear translocation of selective NF-kappaB subunits, an effect associated with blockading the DNA-binding activity of NF-kappaB. Recombinant IL-10 blockaded LPS-induced biosynthesis of IL-1beta and TNF-alpha and reduced NF-kappaB activation. Immunoneutralization of endogenous IL-10 reversed the inhibitory effect of amiloride on proinflammatory cytokines and restored the DNA-binding activity of NF-kappaB. These results indicate that amiloride acts as a novel dual immunoregulator in the alveolar epithelium: it downregulates an inflammatory signal and at the same time upregulates an antiinflammatory response. This biphasic effect is IL-10 sensitive and is associated with the selective targeting of the IkappaB-alpha/NF-kappaB signaling transduction pathway.

Differential regulation of Cl- transport proteins by PKC in Calu-3 cells

Cl- transport proteins expressed in a Calu-3 airway epithelial cell line were differentiated by function and regulation by protein kinase C (PKC) isotypes. mRNA expression of Cl- transporters was semiquantitated by RT-PCR after transfection with a sense or antisense oligonucleotide to the PKC isotypes that modulate the activity of the cystic fibrosis transmembrane conductance regulator [CFTR (PKC-epsilon)] or of the Na/K/2Cl (NKCC1) cotransporter (PKC-delta). Expression of NKCC1 and CFTR mRNAs and proteins was independent of antisense oligonucleotide treatment. Transport function was measured in cell monolayers grown on a plastic surface or on filter inserts. With both culture methods, the antisense oligonucleotide to PKC-epsilon decreased the amount of PKC-epsilon and reduced cAMP-dependent activation of CFTR but not alpha(1)-adrenergic activation of NKCC1. The antisense oligonucleotide to PKC-delta did not affect CFTR function but did block alpha(1)-adrenergic activation of NKCC1 and reduce PKC-delta mass. These results provide the first evidence for mRNA and protein expression of NKCC1 in Calu-3 cells and establish the differential regulation of CFTR and NKCC1 function by specific PKC isotypes at a site distal to mRNA expression and translation in airway epithelial cells.

Flow-induced expression of endothelial Na-K-Cl cotransport: dependence on K(+) and Cl(-) channels

Steady laminar shear stress has been shown previously to markedly increase Na-K-Cl cotransporter mRNA and protein in human umbilical vein endothelial cells and also to rapidly increase endothelial K(+) and Cl(-) channel conductances. The present study was done to evaluate the effects of shear stress on Na-K-Cl cotransporter activity and protein expression in bovine aortic endothelial cells (BAEC) and to determine whether changes in cotransporter expression may be dependent on early changes in K(+) and Cl(-) channel conductances. Confluent BAEC monolayers were exposed in a parallel-plate flow chamber to either steady shear stress (19 dyn/cm(2)) or purely oscillatory shear stress (0 +/- 19 dyn/cm(2)) for 6-48 h. After shearing, BAEC monolayers were assessed for Na-K-Cl cotransporter activity or were subjected to Western blot analysis of cotransporter protein. Steady shear stress led to a 2- to 4-fold increase in BAEC cotransporter protein levels and a 1.5- to 1.8-fold increase in cotransporter activity, increases that were sustained over the longest time periods studied. Oscillatory flow, in contrast, had no effect on cotransporter protein levels. In the presence of flow-sensitive K(+) and Cl(-) channel pharmacological blockers, the steady shear stress-induced increase in cotransporter protein was virtually abolished. These results suggest that shear stress modulates the expression of the BAEC Na-K-Cl cotransporter by mechanisms that are dependent on flow-activated ion channels.

Regulation of Na(+)-K(+)-Cl(-) cotransporter in primary astrocytes by dibutyryl cAMP and high [K(+)](o)

In this study, we examined the Na(+)-K(+)-Cl(-) cotransporter activity and expression in rat cortical astrocyte differentiation. Astrocyte differentiation was induced by dibutyryl cAMP (DBcAMP, 0. 25 mM) for 7 days, and cells changed from a polygonal to process-bearing morphology. Basal activity of the cotransporter was significantly increased in DBcAMP-treated astrocytes (P < 0.05). Expression of an approximately 161-kDa cotransporter protein was increased by 91% in the DBcAMP-treated astrocytes. Moreover, the specific [(3)H]bumetanide binding was increased by 67% in the DBcAMP-treated astrocytes. Inhibition of protein synthesis by cyclohexamide (2-3 microgram/ml) significantly attenuated the DBcAMP-mediated upregulation of the cotransporter activity and expression. The Na(+)-K(+)-Cl(-) cotransporter in astrocytes has been suggested to play a role in K(+) uptake. In 75 mM extracellular K(+) concentration, the cotransporter-mediated K(+) influx was stimulated by 147% in nontreated cells and 79% in DBcAMP-treated cells (P < 0.05). To study whether this high K(+)-induced stimulation of the cotransporter is attributed to membrane depolarization and Ca(2+) influx, the role of the L-type voltage-dependent Ca(2+) channel was investigated. The high-K(+)-mediated stimulation of the cotransporter activity was abolished in the presence of either 0.5 or 1.0 microM of the L-type channel blocker nifedipine or Ca(2+)-free HEPES buffer. A rise in intracellular free Ca(2+) in astrocytes was observed in high K(+). These results provide the first evidence that the Na(+)-K(+)-Cl(-) cotransporter protein expression can be regulated selectively when intracellular cAMP is elevated. The study also demonstrates that the cotransporter in astrocytes is stimulated by high K(+) in a Ca(2+)-dependent manner.

Protein kinase C activation downregulates the expression and function of the basolateral Na+/K+/2Cl(-) cotransporter

The basolateral Na+/K+/2Cl(-) cotransporter (NKCC1) has been shown to be an independent regulatory site for electrogenic Cl(-) secretion. The proinflammatory phorbol ester, phorbol 12-myristate 13-acetate (PMA), which activates protein kinase C (PKC), inhibits basal and cyclic adenosine monophosphate (cAMP)-stimulated NKCC1 activity in T84 intestinal epithelial cells and decreases the steady state levels of NKCC1 mRNA in a time- and dose-dependent manner. The levels of NKCC1 protein also fall in accordance with the NKCC1 mRNA transcript and these levels are unaffected by 4alpha-phorbol, which does not activate PKC. Inhibition of maximal (cAMP-stimulated) NKCC1 functional activity by PMA was first detected by 1 h, whereas decreases in the steady state levels of NKCC1 mRNA were not detectable until 4 h. NKCC1 mRNA expression recovers toward control levels with extended treatment of cells with PMA suggesting that the PMA effects on NKCC1 expression are mediated through activation of PKC. Although NKCC1 mRNA and protein levels return to control values after extended PMA exposure, NKCC1 functional activity does not recover. Immunofluorescence imaging suggest that the absence of functional recovery is due to failure of newly synthesized NKKC1 protein to reach the cell surface. We conclude that NKCC1 has the capacity to be regulated at the level of de novo expression by PKC, although decreased NKCC1 expression alone cannot account for either early or late loss of NKCC1 function.

A spatial approach to transcriptional profiling: mechanotransduction and the focal origin of atherosclerosis

The initiation and progression of focal atherosclerotic lesions has long been known to be associated with regions of disturbed blood flow. Improved precision in experimental models of spatially defined flow has recently been combined with regional and single-cell gene-expression profiling to investigate the relationships linking haemodynamics to vessel-wall pathobiology.

Fluid shear stress as a regulator of gene expression in vascular cells: possible correlations with diabetic abnormalities

Diabetes mellitus is associated with increased frequency, severity and more rapid progression of cardiovascular diseases. Metabolic perturbations from hyperglycemia result in disturbed endothelium-dependent relaxation, activation of coagulation pathways, depressed fibrinolysis, and other abnormalities in vascular homeostasis. Atherosclerosis is localized mainly at areas of geometric irregularity at which blood vessels branch, curve and change diameter, and where blood is subjected to sudden changes in velocity and/or direction of flow. Shear stress resulting from blood flow is a well known modulator of vascular cell function. This paper presents what is currently known regarding the molecular mechanisms responsible for signal transduction and gene regulation in vascular cells exposed to shear stress. Considering the importance of the hemodynamic environment of vascular cells might be vital to increasing our understanding of diabetes.

Special communicationthe critical role of mechanical forces in blood vessel development, physiology and pathology

The following extended abstracts were presented at the Research Initiatives in Vascular Disease Conference, Movers and Shakers in the Vascular Tree-Hemodynamic and Biomechanical Factors in Blood Vessel Pathology, sponsored by The Lifeline Foundation and the Cardiovascular & Interventional Radiology Research and Educational Foundation; jointly sponsored by the International Society for Cardiovascular Surgery, North American Chapter, The Society for Vascular Surgery, and The Society of Cardiovascular and Interventional Radiology; in cooperation with the National Institutes of Health-National Heart, Lung &Blood Institute on Mar 11-12, 1999, in Bethesda, Md.

Cloning, characterization, and chromosomal location of a novel human K+-Cl- cotransporter

Differential display polymerase chain reaction has been used to isolate genes regulated in vascular endothelial cells by the angiogenic factor vascular endothelial cell growth factor (VEGF). Analysis of one of the bands consistently up-regulated by VEGF led us to the identification of a cDNA from a human umbilical vein endothelial cell library that is 77% identical to the human K+-Cl- cotransporter1 (KCC1). We have referred to the predicted protein as K+-Cl- cotransporter 3 (KCC3). Hydrophobicity analysis of the KCC3 amino acid sequence showed an almost identical pattern to KCC1, suggesting 12 membrane-spanning segments, a large extracellular loop with potential N-glycosylation sites, and cytoplasmic N- and C-terminal regions. The KCC3 mRNA was highly expressed in brain, heart, skeletal muscle, and kidney, showing a distinct pattern and size from KCC1 and KCC2. The KCC3 mRNA level in endothelial cells increased on treatment with VEGF and decreased with the proinflammatory cytokine tumor necrosis factor alpha, whereas KCC1 mRNA levels remained unchanged. Stable overexpression of KCC3 cDNA in HEK293 cells produced a glycoprotein of approximately 150 kDa, which was reduced to 120 kDa by glycosidase digestion. An increased initial uptake rate of 86Rb was seen in clones with high KCC3 expression, which was dependent on extracellular Cl- but not Na+ and was inhibitable by the loop diuretic agent furosemide. The KCC3 genomic localization was shown to be 15q13 by fluorescence in situ hybridization. Radiation hybrid analysis placed KCC3 within an area associated with juvenile myoclonic epilepsy. These results suggest KCC3 is a new member of the KCC family that is under distinct regulation from KCC1.

Blood flow and vascular gene expression: fluid shear stress as a modulator of endothelial phenotype

Vascular endothelium, the cellular monolayer lining the entire cardiovascular system, is exposed to a variety of biochemical and biomechanical stimuli. Fluid shear stresses generated by blood flow in the vasculature can profoundly influence the phenotype of the endothelium by regulating the activity of certain flow-sensitive proteins (for example, enzymes), as well as by modulating gene expression. The finding that specific fluid mechanical forces can alter endothelial structure and function has provided a framework for a mechanistic understanding of flow-dependent processes, ranging from vascular remodeling in response to hemodynamic changes, to the initiation and localization of chronic vascular diseases such as atherosclerosis.

Human prostaglandin transporter gene (hPGT) is regulated by fluid mechanical stimuli in cultured endothelial cells and expressed in vascular endothelium in vivo

BACKGROUND

biomechanical forces generated by blood flow within the cardiovascular system have been proposed as important modulators of regional endothelial phenotype and function. This process is thought to involve the regulation of vascular gene expression by physiological fluid mechanical stimuli such as fluid shear stresses.

METHODS AND RESULTS

We demonstrate sustained upregulation of a recently identified gene encoding a human prostaglandin transporter (hPGT) in cultured human vascular endothelium exposed to a physiological fluid mechanical stimulus in vitro. This biomechanical induction is selective in that steady laminar shear stress is sufficient to upregulate the hPGT gene at the level of transcriptional activation, whereas a comparable level of turbulent shear stress (a nonphysiological stimulus) is not. Various biochemical stimuli, such as bacterial endotoxin and the inflammatory cytokines recombinant human interleukin 1beta cytokines (rhIL-1beta) and tumor necrosis factor-alpha (TNF-alpha), did not significantly induce hPGT. Using a specific antiserum to hPGT, we demonstrate endothelial expression within the arterial vasculature and the microcirculation of highly vascularized tissues such as the heart.

CONCLUSIONS

Our results identify hPGT as an inducible gene in vascular endothelium and suggest that biomechanical stimuli generated by blood flow in vivo may be important determinants of hPGT expression. Furthermore, this demonstration of regulated endothelial expression of hPGT implicates this molecule in the regional metabolism of prostanoids within the cardiovascular system.

Na+-K+-Cl- cotransport in human fibroblasts is inhibited by cytomegalovirus infection

We examined the effects of human cytomegalovirus (HCMV) infection on the Na+-K+-Cl- cotransporter (NKCC) in a human fibroblast cell line. Using the Cl--sensitive dye MQAE, we showed that the mock-infected MRC-5 cells express a functional NKCC. 1) Intracellular Cl- concentration ([Cl-]i) was significantly reduced from 53.4 +/- 3.4 mM to 35.1 +/- 3.6 mM following bumetanide treatment. 2) Net Cl- efflux caused by replacement of external Cl- with gluconate was bumetanide sensitive. 3) In Cl--depleted mock-infected cells, the Cl- reuptake rate (in HCO-3-free media) was reduced in the absence of external Na+ and by treatment with bumetanide. After HCMV infection, we found that although [Cl-]i increased progressively [24 h postexposure (PE), 65.2 +/- 4.5 mM; 72 h PE, 80.4 +/- 5.0 mM], the bumetanide and Na+ sensitivities of [Cl-]i and net Cl- uptake and loss were reduced by 24 h PE and abolished by 72 h PE. Western blots using the NKCC-specific monoclonal antibody T4 showed an approximately ninefold decrease in the amount of NKCC protein after 72 h of infection. Thus HCMV infection resulted in the abolition of NKCC function coincident with the severe reduction in the amount of NKCC protein expressed.

Fluid shear stress activation of egr-1 transcription in cultured human endothelial and epithelial cells is mediated via the extracellular signal-related kinase 1/2 mitogen-activated protein kinase pathway

The primary response transcription factor, early growth response-1 (Egr-1), is rapidly activated by a variety of extracellular stimuli. Egr-1 binds to a sequence found in the promoters of genes involved in vascular injury, such as PDGF-A and tissue factor, and trans-activates their expression in endothelial cells in response to fluid shear stress. Here we show that egr-1 mRNA is increased after 30 min of flow in human aortic endothelial cell and HeLa cell cultures. Transient transfection of HeLa cells with reporter gene constructs driven by the murine or human egr-1 5' flanking sequence revealed a five- and ninefold induction, respectively, in transcriptional activity after exposure to a shear stress of 5 dynes/cm2 for 3 h. Deletion of sequences in the murine promoter containing two AP1 sites and an inhibitory Egr-1 binding sequence, did not reduce shear stress inducibility. However, progressive deletion of five serum response elements, reduced both the basal promoter activity and its capacity to be activated by shear stress. Further examination indicated that the three upstream serum response elements are predominantly responsible for shear stress activation of the egr-1 promoter. Treatment of cells with PD98059, a specific inhibitor of mitogen-activated protein kinase-1 inhibited shear stress activation of egr-1. We suggest that egr-1 activation by shear stress involves activation of Elk-1 but not c-jun activity. These data, which are consistent with previous findings for shear mediated signaling via the mitogen-activated protein kinase cascade, now implicate shear modulation of the Egr-1 transcription factor in this pathway.

Laminar shear stress: mechanisms by which endothelial cells transduce an atheroprotective force

Mechanical forces are important modulators of cellular function in many tissues and are particularly important in the cardiovascular system. The endothelium, by virtue of its unique location in the vessel wall, responds rapidly and sensitively to the mechanical conditions created by blood flow and the cardiac cycle. In this study, we examine data which suggest that steady laminar shear stress stimulates cellular responses that are essential for endothelial cell function and are atheroprotective. We explore the ability of shear stress to modulate atherogenesis via its effects on endothelial-mediated alterations in coagulation, leukocyte and monocyte migration, smooth muscle growth, lipoprotein uptake and metabolism, and endothelial cell survival. We also propose a model of signal transduction for the endothelial cell response to shear stress including possible mechanotransducers (integrins, caveolae, ion channels, and G proteins), intermediate signaling molecules (c-Src, ras, Raf, protein kinase C) and the mitogen activated protein kinases (ERK1/2, JNK, p38, BMK-1), and effector molecules (nitric oxide). The endothelial cell response to shear stress may also provide a mechanism by which risk factors such as hypertension, diabetes, hypercholesterolemia, and sedentary lifestyle act to promote atherosclerosis.