Interleukin-1 inhibition of Na(+)-K(+)-ATPase in inner medullary collecting duct cells: role of PGE2

SOCS-1 rescues IL-1β-mediated suppression of epithelial sodium channel in mouse lung epithelial cells via ASK-1

Background

Acute lung injury (ALI) is characterized by alveolar damage, increased levels of pro-inflammatory cytokines and impaired alveolar fluid clearance. Recently, we showed that the deletion of Apoptosis signal-regulating kinase 1 (ASK1) protects against hyperoxia-induced acute lung injury (HALI) by suppressing IL-1β and TNF-α. Previously, our data revealed that the suppressor of cytokine signaling-1 (SOCS-1) overexpression restores alveolar fluid clearance in HALI by inhibiting ASK-1 and suppressing IL-1β levels. Furthermore, IL-1β is known to inhibit the expression of epithelial sodium channel α-subunit (ENaC) via a p38 MAPK signaling pathway.

Objective

To determine whether SOCS-1 overexpression in MLE-12 cells would protect against IL-1β-mediated depletion of αENaC by suppressing ASK-1 expression.

Methods

We co-transfected MLE-12 cells with SOCS-1 overexpressing plasmid with or without IL-1β in the presence or absence of sodium channel inhibitor, amiloride. We measured potential difference, transepithelial current, resistance, and sodium uptake levels across MLE-12 cells. We studied the effect of ASK-1 depletion, as well as ASK-1 and SOCS-1 overexpression on αENaC expression.

Results

SOCS-1 overexpression sufficiently restored transepithelial current and resistance in MLE-12 cells treated with either IL-1β or amiloride. The αENaC mRNA levels and sodium transport were increased in SOCS-1 overexpressing MLE-12 cells exposed to IL-1β. Depletion of ASK-1 in MLE-12 cells increased αENaC mRNA levels. Interestingly, SOCS-1 overexpression restored αENaC expression in MLE-12 cells in the presence of ASK-1 overexpression.

Conclusion

Collectively, these findings suggest that SOCS-1 may exert its protective effect by rescuing αENaC expression via suppression of ASK-1.

Inflammatory cytokines regulate renal sodium transporters: how, where, and why?

Hypertension is growing in epidemic proportions worldwide and is now the leading preventable cause of premature death. For over a century, we have known that the kidney plays a critical role in blood pressure regulation. Specifically, abnormalities in renal sodium transport appear to be a final common pathway that gives rise to elevated blood pressure regardless of the nature of the initial hypertensive stimulus. However, it is only in the past decade that we have come to realize that inflammatory cytokines secreted by innate and adaptive immune cells, as well as renal epithelial cells, can modulate the expression and activity of sodium transporters all along the nephron, leading to alterations in pressure natriuresis, sodium and water balance, and ultimately hypertension. This mini-review highlights specific cytokines and the transporters that they regulate and discusses why inflammatory cytokines may have evolved to serve this function.

Hyponatremia in patients with systemic lupus erythematosus

The aim of this study was to determine whether decreased serum sodium concentration could be associated with the disease activity in SLE. We retrospectively analyzed the data of the two independent cohorts of children and adults with SLE in two centers. Hyponatremia was associated with serum chloride (p = 0.004), albumin (p = 0.002) and SLE disease activity index (SLEDAI) (p = 0.026) in children with SLE. Serum sodium levels were correlated negatively with ESR (p =0.001) and positively with serum albumin levels (p < 0.0001) and C3 (p = 0.008) in children with SLE and those levels were correlated negatively with serum interleukin-6 levels (p = 0.003) in adults with SLE. Independent risk factors for the development of hyponatremia were the decreased serum C3 levels (OR 1.069, p = 0.031), the decreased serum chloride levels (OR 2.054, p = 0.006) and increased erythrocyte sedimentation rate (ESR) (OR 1.066, p = 0.03) in children with SLE and increased C-reactive protein (CRP) (OR 1.480, p = 0.023) in combined cohorts with SLE by multiple logistic regression analyses. Our study firstly showed that hyponatremia could reflect a disease activity and severe inflammation of SLE.

Epithelial transport during septic acute kidney injury

A goal for scientists studying septic acute kidney injury (AKI) should be to formulate a conceptual model of disease that is able to coherently reconcile the molecular and inflammatory consequences of sepsis with impaired epithelial tubular function, diminished glomerular filtration rate (GFR) and ultimately kidney failure. Recent evidence has shed light on how sepsis modulates the tubular regulation of ion, glucose, urea and water transport and acid-base homeostasis in the kidney. The present review summarizes recent discoveries on changes in epithelial transport under septic and endotoxemic conditions as well as the mechanisms that link inflammation with impaired tubular membrane transport. This paper also proposes that the tubular dysfunction that is mediated by inflammation in sepsis ultimately leads to increased sodium and chloride delivery to the distal tubule and macula densa, contributing to tubuloglomerular feedback and impaired GFR. We feel that this conceptual model resolves many of the physiologic and clinical paradoxes that septic AKI presents to practicing researchers and clinicians.

Chronic elevation of IL-1β induces diuresis via a cyclooxygenase 2-mediated mechanism

Chronic renal inflammation is an increasingly recognized phenomenon in multiple disease states, but the impact of specific cytokines on renal function is unclear. Previously, we found that 14-day interleukin-1β (IL-1β) infusion increased urine flow in mice. To determine the mechanism by which this occurs, the current study tested the possible involvement of three classical prodiuretic pathways. Chronic IL-1β infusion significantly increased urine flow (6.5 ± 1 ml/day at day 14 vs. 2.3 ± 0.3 ml/day in vehicle group; P < 0.05) and expression of cyclooxygenase (COX)-2, all three nitric oxide synthase (NOS) isoforms, and endothelin (ET)-1 in the kidney (P < 0.05 in all cases). Urinary prostaglandin E metabolite (PGEM) excretion was also significantly increased at day 14 of IL-1β infusion (1.21 ± 0.26 vs. 0.29 ± 0.06 ng/day in vehicle-infused mice; P = 0.001). The selective COX-2 inhibitor celecoxib markedly attenuated urinary PGEM excretion and abolished the diuretic response to chronic IL-1β infusion. In contrast, deletion of NOS3, or inhibition of NOS1 with L-VNIO, did not blunt the diuretic effect of IL-1β, nor did pharmacological blockade of endothelin ETA and ETB receptors with A-182086. Consistent with a primary effect on water transport, IL-1β infusion markedly reduced inner medullary aquaporin-2 expression (P < 0.05) and did not alter urinary Na⁺ or K⁺ excretion. These data indicate a critical role for COX-2 in mediating the effects of chronic IL-1β elevation on the kidney.

Tumor necrosis factor-alpha is an endogenous inhibitor of Na+-K+-2Cl- cotransporter (NKCC2) isoform A in the thick ascending limb

The effects of TNF gene deletion on renal Na(+)-K(+)-2Cl(-) cotransporter (NKCC2) expression and activity were determined. Outer medulla from TNF(-/-) mice exhibited a twofold increase in total NKCC2 protein expression compared with wild-type (WT) mice. This increase was not observed in TNF(-/-) mice treated with recombinant human TNF (hTNF) for 7 days. Administration of hTNF had no effect on total NKCC2 expression in WT mice. A fourfold increase in NKCC2A mRNA accumulation was observed in outer medulla from TNF(-/-) compared with WT mice; NKCC2F and NKCC2B mRNA accumulation was similar between genotypes. The increase in NKCC2A mRNA accumulation was attenuated when TNF(-/-) mice were treated with hTNF. Bumetanide-sensitive O(2) consumption, an in vitro correlate of NKCC2 activity, was 2.8 ± 0.2 nmol·min(-1)·mg(-1) in medullary thick ascending limb tubules from WT, representing ∼40% of total O(2) consumption, whereas, in medullary thick ascending limb tubules from TNF(-/-) mice, it was 5.6 ± 0.3 nmol·min(-1)·mg(-1), representing ∼60% of total O(2) consumption. Administration of hTNF to TNF(-/-) mice restored the bumetanide-sensitive component to ∼30% of total O(2) consumption. Ambient urine osmolality was higher in TNF(-/-) compared with WT mice (2,072 ± 104 vs. 1,696 ± 153 mosmol/kgH(2)O, P < 0.05). The diluting ability of the kidney, assessed by measuring urine osmolality before and after 1 h of water loading also was greater in TNF(-/-) compared with WT mice (174 ± 38 and 465 ± 81 mosmol/kgH(2)O, respectively, P < 0.01). Collectively, these findings suggest that TNF plays a role as an endogenous inhibitor of NKCC2 expression and function.

Ion channels in inflammation

Most physical illness in vertebrates involves inflammation. Inflammation causes disease by fluid shifts across cell membranes and cell layers, changes in muscle function and generation of pain. These disease processes can be explained by changes in numbers or function of ion channels. Changes in ion channels have been detected in diarrhoeal illnesses, pyelonephritis, allergy, acute lung injury and systemic inflammatory response syndromes involving septic shock. The key role played by changes in ion transport is directly evident in inflammation-induced pain. Expression or function of all major categories of ion channels like sodium, chloride, calcium, potassium, transient receptor potential, purinergic receptor and acid-sensing ion channels can be influenced by cyto- and chemokines, prostaglandins, leukotrienes, histamine, ATP, reactive oxygen species and protons released in inflammation. Key pathways in this interaction are cyclic nucleotide, phosphoinositide and mitogen-activated protein kinase-mediated signalling, direct modification by reactive oxygen species like nitric oxide, ATP or protons and disruption of the cytoskeleton. Therapeutic interventions to modulate the adverse and overlapping effects of the numerous different inflammatory mediators on each ion transport system need to target adversely affected ion transport systems directly and locally.

Potential involvement of P2Y2 receptor in diuresis of postobstructive uropathy in rats

AVP resistance of the medullary collecting duct (mCD) in postobstructive uropathy (POU) has been attributed to increased production of PGE2. P2Y2 receptor activation causes production of PGE2 by the mCD. We hypothesize that increased P2Y2 receptor expression and/or activity may contribute to the diuresis of POU. Sprague-Dawley rats were subjected to bilateral ureteral obstruction for 24 h followed by release (BUO/R, n = 17) or sham operation (SHM/O, n = 15) and euthanized after 1 wk or 12 days. BUO/R rats developed significant polydipsia, polyuria, urinary concentration defect, and increased urinary PGE2 and decreased aquaporin-2 protein abundance in the inner medulla compared with SHM/O rats. After BUO/R, the relative mRNA expression of P2Y2 and P2Y6 receptors was increased by 2.7- and 4.9-fold, respectively, without significant changes in mRNA expression of P2Y1 or P2Y4 receptor. This was associated with a significant 3.5-fold higher protein abundance of the P2Y2 receptor in BUO/R than SHM/O rats. When freshly isolated mCD fractions were challenged with different types of nucleotides (ATPgammaS, ADP, UTP, or UDP), BUO/R and SHM/O rats responded to only ATPgammaS and UTP and released PGE2, consistent with involvement of the P2Y2, but not P2Y6, receptor. ATPgammaS- or UTP-stimulated increases in PGE2 were much higher in BUO/R (3.20- and 2.28-fold, respectively, vs. vehicle controls) than SHM/O (1.68- and 1.30-fold, respectively, vs. vehicle controls) rats. In addition, there were significant 2.4- and 2.1-fold increases in relative mRNA expression of prostanoid EP1 and EP3 receptors, respectively, in the inner medulla of BUO/R vs. SHM/O rats. Taken together, these data suggest that increased production of PGE2 by the mCD in POU may be due to increased expression and activity of the P2Y2 receptor. Increased mRNA expression of EP1 and EP3 receptors in POU may also help accentuate PGE2-induced signaling in the mCD.

Interleukin-1beta, but not interleukin-6, enhances renal and systemic endothelin production in vivo

The inflammatory cytokines IL-1beta and IL-6 have been shown to stimulate production of endothelin-1 (ET-1) by several cell types in vitro, but their effects on renal ET-1 production in vivo are not known. To test whether IL-1beta and IL-6 stimulate renal ET-1 production and release in vivo, urine was collected from male C57BL/6 mice over 24-h periods at baseline and on days 7 and 14 of a 14-day subcutaneous infusion of IL-1beta (10 ng/h), IL-6 (16 ng/h), or vehicle. By day 14, plasma ET-1 was significantly increased by IL-1beta infusion (1.7 +/- 0.1 vs. 0.8 +/- 0.1 pg/ml for vehicle, P < 0.001). Compared with vehicle infusion, IL-1beta infusion induced significant increases in urinary ET-1 excretion rate and urine flow but did not affect conscious mean arterial pressure (telemetry). IL-1beta infusion significantly increased renal cortical and medullary IL-1beta content (ELISA) and prepro-ET-1 mRNA expression (quantitative real-time PCR). In contrast, 14 days of IL-6 infusion had no significant effect on plasma ET-1 or urinary ET-1 excretion rate. To determine whether IL-1beta stimulates ET-1 release via activation of NF-kappaB, inner medullary collecting duct (IMCD-3) cells were incubated for 24 h with IL-1beta, and ET-1 release and NF-kappaB activation were measured (ELISA). IL-1beta activated NF-kappaB and increased ET-1 release in a concentration-dependent manner. The effect of IL-1beta on ET-1 release could be partially inhibited by pretreatment of IMCD-3 cells with an inhibitor of NF-kappaB activation (BAY 11-7082). These results indicate that IL-1beta stimulates renal and systemic ET-1 production in vivo, providing further evidence that ET-1 participates in inflammatory responses.

Changes in ion transport in inflammatory disease

Ion transport is essential for maintenance of transmembranous and transcellular electric potential, fluid transport and cellular volume. Disturbance of ion transport has been associated with cellular dysfunction, intra and extracellular edema and abnormalities of epithelial surface liquid volume. There is increasing evidence that conditions characterized by an intense local or systemic inflammatory response are associated with abnormal ion transport. This abnormal ion transport has been involved in the pathogenesis of conditions like hypovolemia due to fluid losses, hyponatremia and hypokalemia in diarrhoeal diseases, electrolyte abnormalities in pyelonephritis of early infancy, septicemia induced pulmonary edema, and in hypersecretion and edema induced by inflammatory reactions of the mucosa of the upper respiratory tract. Components of membranous ion transport systems, which have been shown to undergo a change in function during an inflammatory response include the sodium potassium ATPase, the epithelial sodium channel, the Cystic Fibrosis Transmembrane Conductance Regulator and calcium activated chloride channels and the sodium potassium chloride co-transporter. Inflammatory mediators, which influence ion transport are tumor necrosis factor, gamma interferon, interleukins, transforming growth factor, leukotrienes and bradykinin. They trigger the release of specific messengers like prostaglandins, nitric oxide and histamine which alter ion transport system function through specific receptors, intracellular second messengers and protein kinases. This review summarizes data on in vivo measurements of changes in ion transport in acute inflammatory conditions and in vitro studies, which have explored the underlying mechanisms. Potential interventions directed at a correction of the observed abnormalities are discussed.

The signal transduction pathway that mediates the effect of interleukin-1 beta on the Na+-K+-ATPase in LLC-PK1 cells

IL-1beta reduces the activity and protein expression of Na(+)-K(+)-ATPase in rat kidney cells. The aim of the present study was to elucidate the signalling pathway involved, using the LLC-PK(1) cell line. In these cells IL-1beta caused a time and concentration-dependent decrease in the protein expression of the Na(+)-K(+)-ATPase. Inhibition of extracellular signal-regulated kinase (ERK), nuclear factor-kappaB (NF-kappaB) and cyclooxygenase (COX), but not p38 mitogen-activated kinase (MAPK), abolished the effect of the cytokine on the pump. The activation of NF-kappaB by IL-1beta was maximal at 20 min and declined thereafter. Inhibition of the transcription factor by pyrrolidinediethyldithiocarbamate (PDTC) down-regulated the ATPase. The effects of IL-1beta on the pump and NF-kappaB were prevented by the COX inhibitor indomethacin. Exogenous PGE(2) reduced protein expression of the ATPase within 15 min, even in presence of an ERK inhibitor. It is concluded that IL-1beta stimulates the mitogen and extracellular signal regulated protein kinase kinase/extracellular signal regulated protein kinase (MEK/ERK) pathway. This activates NF-kappaB, thus leading to increased COX-2 expression and PGE(2) release. PGE(2) in turn inhibits NF-kappaB and reduces the protein expression of Na(+)-K(+)-ATPase.

Mechanisms of sodium pump regulation

The Na(+)-K(+)-ATPase, or sodium pump, is the membrane-bound enzyme that maintains the Na(+) and K(+) gradients across the plasma membrane of animal cells. Because of its importance in many basic and specialized cellular functions, this enzyme must be able to adapt to changing cellular and physiological stimuli. This review presents an overview of the many mechanisms in place to regulate sodium pump activity in a tissue-specific manner. These mechanisms include regulation by substrates, membrane-associated components such as cytoskeletal elements and the gamma-subunit, and circulating endogenous inhibitors as well as a variety of hormones, including corticosteroids, peptide hormones, and catecholamines. In addition, the review considers the effects of a range of specific intracellular signaling pathways involved in the regulation of pump activity and subcellular distribution, with particular consideration given to the effects of protein kinases and phosphatases.

Intracellular signaling in the regulation of renal Na-K-ATPase. II. Role of eicosanoids

We recently reported a novel intracellular mechanism of renal Na-K-ATPase regulation by agents that increase cell cAMP, which involves protein kinase A-phospholipase A2 and is mediated by one or more arachidonic acid metabolites (Satoh, T., H. T. Cohen, and A. I. Katz. 1992. J. Clin. Invest. 89:1496). The present studies were, therefore, designed to assess the role of eicosanoids in the modulation of Na-K-ATPase activity in the rat cortical collecting duct. The effect of various cAMP agonists (dopamine, fenoldopam, vasopressin, forskolin, and dibutyryl cAMP), which inhibited the pump to a similar extent (approximately 50%), was independent of altered Na entry as it was elicited in the presence of amiloride or nystatin, or when NaCl was replaced with choline Cl. This effect was completely blocked by SKF 525A or ethoxyresorufin, two inhibitors of the cytochrome P450-dependent monooxygenase pathway, or by pretreating the animals with CoCl2, which depletes cytochrome P450. Equimolar concentrations (10(-7) M) of the cyclooxygenase inhibitors indomethacin or meclofenamate caused only a partial inhibition of the cAMP agonists' effect on the pump, whereas nordihydroguaiaretic acid or A 63162, two inhibitors of the lipoxygenase pathway, were without effect. Furthermore, two products of this pathway, leukotriene B4 and leukotriene D4, had no effect on Na-K-ATPase activity, and ICI 198615, a leukotriene receptor antagonist, did not alter pump inhibition by cAMP agonists. Several P450 monoxygenase arachidonic acid metabolites (5,6-epoxyeicosatrienoic acid; 11,12-epoxyeicosatrienoic acid; 11,12-dihydroxyeicosatrienoic acid; and 12(R)-hydroxyeicosatetraenoic acid) as well as PGE2 inhibited the Na:K pump in dose-dependent manner, but the effect of PGE2 was blocked when Na availability was altered, whereas that of 12(R)-HETE remained unchanged. We conclude that the cytochrome P450-monooxygenase pathway of the arachidonic acid cascade plays a major role in the modulation of Na:K pump activity by eicosanoids in the rat cortical collecting duct, and that products of the cyclooxygenase pathway may contribute to pump inhibition indirectly, by decreasing intracellular Na.