Cellular distribution of the renal bumetanide-sensitive Na-K-2Cl cotransporter BSC-1 in the inner stripe of the outer medulla during the development of hypertension in the spontaneously hypertensive rat

Interactions between diabetic and hypertensive drugs: a pharmacogenetics approach

Diabetes is known to increase susceptibility to hypertension due to increase in inflammation, oxidative stress, and endothelial dysfunction, leading to vascular stiffness. The polytherapy might lead to several drug-drug interactions (DDIs), which cause certain life-threatening complications such as diabetic nephropathy and hypoglycaemia. So, in this review we focused on drug-drug interactions and impact of genetic factors on drug responses for better disease management. Drug-drug interactions (DDIs) may act either synergistically or antagonistically. For instance, a combination of metformin with angiotensin II receptor antagonist or angiotensin-converting enzyme inhibitors (ACEIs) synergistically improves glucose absorption, whereas the same hypertensive drug combination with sulphonylurea might cause severe hypoglycaemia sometimes. Thiazolidinediones (TDZs) can cause fluid retention and heart failure when taken alone, but a combination of angiotensin II receptor antagonist with TZDs prevents these side effects. Interindividual genetic variation affects the DDI response. We found two prominent genes, GLUT4 and PPAR-γ, which are common targets for most of the drug. So, all of these findings established a connection between drug-drug interaction and genetics, which might be used for effective disease management.

Renal denervation and CD161a immune ablation prevent cholinergic hypertension and renal sodium retention

Cholinergic receptor activation leads to premature development of hypertension and infiltration of proinflammatory CD161a⁺/CD68⁺ M1 macrophages into the renal medulla. Renal inflammation is implicated in renal sodium retention and the development of hypertension. Renal denervation is known to decrease renal inflammation. The objective of this study was to determine the role of CD161a⁺/CD68⁺ macrophages and renal sympathetic nerves in cholinergic-hypertension and renal sodium retention. Bilateral renal nerve denervation (RND) and immune ablation of CD161a⁺ immune cells were performed in young prehypertensive spontaneously hypertensive rat (SHR) followed by infusion of either saline or nicotine (15 mg·kg^-1·day^-1) for 2 wk. Immune ablation was conducted by injection of unconjugated azide-free antibody targeting rat CD161a⁺. Blood pressure was monitored by tail cuff plethysmography. Tissues were harvested at the end of infusion. Nicotine induced premature hypertension, renal expression of the sodium-potassium chloride cotransporter (NKCC2), increases in renal sodium retention, and infiltration of CD161a⁺/CD68⁺ macrophages into the renal medulla. All of these effects were abrogated by RND and ablation of CD161a⁺ immune cells. Cholinergic activation of CD161a⁺ immune cells with nicotine leads to the premature development of hypertension in SHR. The effects of renal sympathetic nerves on chemotaxis of CD161a⁺ macrophages to the renal medulla, increased renal expression of NKCC2, and renal sodium retention contribute to cholinergic hypertension. The CD161a⁺ immune cells are necessary and essential for this prohypertensive nicotine-mediated inflammatory response.NEW & NOTEWORTHY This is the first study that describes a novel integrative physiological interaction between the adrenergic, cholinergic, and renal systems in the development of hypertension, describing data for the role of each in a genetic model of essential hypertension. Noteworthy findings include the prevention of nicotine-mediated hypertension following successful immune ablation of CD161a⁺ immune cells and the necessary role these cells play in the overexpression of the sodium-potassium-chloride cotransporter (NKCC2) in the renal medulla and renal sodium retention. Renal infiltration of these cells is demonstrated to be dependent on the presence of renal adrenergic innervation. These data offer a fertile ground of therapeutic potential for the treatment of hypertension as well as open the door for further investigation into the mechanism involved in inflammation-mediated renal sodium transporter expression. Taken together, these findings suggest immune therapy, renal denervation, and, possibly, other new molecular targets as having a potential role in the development and maintenance of essential hypertension.

Thick Ascending Limb Sodium Transport in the Pathogenesis of Hypertension

The thick ascending limb plays a key role in maintaining water and electrolyte balance. The importance of this segment in regulating blood pressure is evidenced by the effect of loop diuretics or local genetic defects on this parameter. Hormones and factors produced by thick ascending limbs have both autocrine and paracrine effects, which can extend prohypertensive signaling to other structures of the nephron. In this review, we discuss the role of the thick ascending limb in the development of hypertension, not as a sole participant, but one that works within the rich biological context of the renal medulla. We first provide an overview of the basic physiology of the segment and the anatomical considerations necessary to understand its relationship with other renal structures. We explore the physiopathological changes in thick ascending limbs occurring in both genetic and induced animal models of hypertension. We then discuss the racial differences and genetic defects that affect blood pressure in humans through changes in thick ascending limb transport rates. Throughout the text, we scrutinize methodologies and discuss the limitations of research techniques that, when overlooked, can lead investigators to make erroneous conclusions. Thus, in addition to advancing an understanding of the basic mechanisms of physiology, the ultimate goal of this work is to understand our research tools, to make better use of them, and to contextualize research data. Future advances in renal hypertension research will require not only collection of new experimental data, but also integration of our current knowledge.

Role of renal transporters and novel regulatory interactions in the TAL that control blood pressure

Hypertension (HTN), a major public health issue is currently the leading factor in the global burden of disease, where associated complications account for 9.4 million deaths worldwide every year. Excessive dietary salt intake is among the environmental factors that contribute to HTN, known as salt sensitivity. The heterogeneity of salt sensitivity and the multiple mechanisms that link high salt intake to increases in blood pressure are of upmost importance for therapeutic application. A continual increase in the kidney's reabsorption of sodium (Na+) relies on sequential actions at various segments along the nephron. When the distal segments of the nephron fail to regulate Na+, the effects on Na+ homeostasis are unfavorable. We propose that the specific nephron region where increased active uptake occurs as a result of variations in Na+ reabsorption is at the thick ascending limb of the loop of Henle (TAL). The purpose of this review is to urge the consideration of the TAL as contributing to the pathophysiology of salt-sensitive HTN. Further research in this area will enable development of a therapeutic application for targeted treatment.

Angiotensin II and Anti Diuretic Hormone Exert Synergistic Effects on Thick Ascending Limb Transport in Spontaneously Hypertensive Rats

BACKGROUND

Sodium reabsorption is increased in the thick ascending limb (TAL) of Henle in several hypertensive models. In this segment, while transport is increased by ADH via cAMP, sodium reabsorption results from Ang II-induced superoxide (O2(-)) production. Surprisingly, it is unknown whether these mechanisms overlap in hypertension. We hypothesized that Ang II and ADH have accumulative effects on TAL's transport during hypertension.

METHODS

The effect of ADH/Ang II in TALs from spontaneously hypertensive rats (SHR) on oxygen consumption (QO2), cAMP and O2(-) was measured.

RESULTS

Basal QO2 was 113.3 ± 14.2 nmol O2/min/mg protein. Addition of ADH (1 nM) increased QO2 by 198%. In the presence of ADH, Ang II (1 nM) elicited a QO2 transient response and then rose to 321.5 ± 28.3 (p = 0.003 vs. ADH). These accumulative effects could be due to nitric oxide synthase (NOS) uncoupling, lower Ang II ability to decrease cAMP or increased O2(-). We first measured QO2 using a NOS inhibitor. Pretreatment with L-NAME did not block the observed interaction (p = 0.001 Ang II vs. ADH). Also, Ang II blocked the ADH-stimulated cAMP accumulation in TAL of SHRs. In the presence of ADH, Ang II increased O2(-) production in TALs from SHR by 309% (p = 0.015 vs. basal). The O2(-) scavenger tempol blocked the Ang II effects on QO2. In the presence of the NADPH oxidase inhibitor apocynin, the accumulative effects of ADH and Ang II were abolished. We conclude that (1) in SHR, Ang II has accumulative effects on ADH-stimulated transport; (2) this effect is mediated by AT1 receptors, and increased O2(-) production.

Na+/K+-ATPase β1-subunit is recruited in Na-K-2Cl co-transporter isoform 2 multiprotein complexes in rat kidneys: possible role in blood pressure regulation

OBJECTIVE

The progression from prehypertensive to hypertensive state in spontaneous hypertensive rats (SHRs) is accompanied by a significant increase in membrane expression of Na-K-2Cl co-transporter isoform 2 (NKCC2), suggesting that the altered NKCC2 trafficking and activity are directly related with the development of hypertension in this strain. The aim of this work is to gain insights on the molecular mechanism that underlies this phenomenon.

METHODS

We performed a comparative analysis of NKCC2 multiprotein complexes (MPCs) in the kidney of SHRs versus Wistar Kyoto rats by Blue Native difference gel electrophoresis combined with mass spectrometry.

RESULTS

We found that the recruitment of the β-subunit isoform 1 of the Na(+)-K(+)-ATPase (β1NK) in NKCC2 MPCs was significantly increased in the kidneys of SHR compared with Wistar Kyoto rat control strain. Co-immunoprecipitation experiments showed that β1NK actually interacts with NKCC2 in the native tissue. The analysis of the physiological role of β1NK-NKCC2 interaction in human embryonic kidney cells showed that β1NK increased the steady-state membrane expression and activity of NKCC2 enhancing NKCC2 trafficking toward the plasma membrane.

CONCLUSION

We identify a new NKCC2-interacting partner involved in the modulation of NKCC2 intracellular trafficking and possibly involved in the regulation of blood pressure.

Vasopressin regulation of sodium transport in the distal nephron and collecting duct

Arginine vasopressin (AVP) is released from the posterior pituitary gland during states of hyperosmolality or hypovolemia. AVP is a peptide hormone, with antidiuretic and antinatriuretic properties. It allows the kidneys to increase body water retention predominantly by increasing the cell surface expression of aquaporin water channels in the collecting duct alongside increasing the osmotic driving forces for water reabsorption. The antinatriuretic effects of AVP are mediated by the regulation of sodium transport throughout the distal nephron, from the thick ascending limb through to the collecting duct, which in turn partially facilitates osmotic movement of water. In this review, we will discuss the regulatory role of AVP in sodium transport and summarize the effects of AVP on various molecular targets, including the sodium-potassium-chloride cotransporter NKCC2, the thiazide-sensitive sodium-chloride cotransporter NCC, and the epithelial sodium channel ENaC.

Identification of moesin as NKCC2-interacting protein and analysis of its functional role in the NKCC2 apical trafficking

BACKGROUND INFORMATION

The renal Na(+) -K(+) -2Cl(-) co-transporter (NKCC2) is expressed in kidney thick ascending limb cells, where it mediates NaCl re-absorption regulating body salt levels and blood pressure.

RESULTS

In this study, we used a well-characterised NKCC2 construct (c-NKCC2) to identify NKCC2-interacting proteins by an antibody shift assay coupled with blue native/SDS-PAGE and mass spectrometry. Among the interacting proteins, we identified moesin, a protein belonging to ezrin, eadixin and moesin family. Co-immunoprecipitation experiments confirmed that c-NKCC2 interacts with the N-terminal domain of moesin in LLC-PK1 cells. Moreover, c-NKCC2 accumulates in intracellular and sub-apical vesicles in cells transfected with a moesin dominant negative green fluorescent protien (GFP)-tagged construct. In addition, moesin knock-down by short interfering RNA decreases by about 50% c-NKCC2 surface expression. Specifically, endocytosis and exocytosis assays showed that moesin knock-down does not affect c-NKCC2 internalisation but strongly reduces exocytosis of the co-transporter.

CONCLUSIONS

Our data clearly demonstrate that moesin plays a critical role in apical membrane insertion of NKCC2, suggesting a possible involvement of moesin in regulation of Na(+) and Cl(-) absorption in the kidney.

Na+-K+-2Cl- cotransporter type 2 trafficking and activity: the role of interacting proteins

The central role of Na+-K+-2Cl- cotransporter type 2 (NKCC2) in vectorial transepithelial salt reabsorption in thick ascending limb cells from Henle's loop in the kidney is evidenced by the effects of loop diuretics, the pharmacological inhibitors of NKCC2, that are amongst the most powerful antihypertensive drugs available to date. Moreover, genetic mutations of the NKCC2 encoding gene resulting in impaired apical targeting and function of NKCC2 transporter give rise to a pathological phenotype known as type I Bartter syndrome, characterised by a severe volume depletion, hypokalaemia and metabolic alkalosis with high prenatal mortality. On the contrary, excessive NKCC2 activity has been linked with inherited hypertension in humans and in rodent models. Interestingly, in animal models of hypertension, NKCC2 upregulation is achieved by post-translational mechanisms underlining the need to analyse the molecular mechanisms involved in the regulation of NKCC2 trafficking and activity to gain insights in the pathogenesis of hypertension.

Molecular regulation of NKCC2 in the thick ascending limb

The kidney plays an essential role in blood pressure regulation by controlling short-term and long-term NaCl and water balance. The thick ascending limb of the loop of Henle (TAL) reabsorbs 25-30% of the NaCl filtered by the glomeruli in a process mediated by the apical Na(+)-K(+)-2Cl(-) cotransporter NKCC2, which allows Na(+) and Cl(-) entry from the tubule lumen into TAL cells. In humans, mutations in the gene coding for NKCC2 result in decreased or absent activity characterized by severe salt and volume loss and decreased blood pressure (Bartter syndrome type 1). Opposite to Bartter's syndrome, enhanced NaCl absorption by the TAL is associated with human hypertension and animal models of salt-sensitive hypertension. TAL NaCl reabsorption is subject to exquisite control by hormones like vasopressin, parathyroid, glucagon, and adrenergic agonists (epinephrine and norepinephrine) that stimulate NaCl reabsorption. Atrial natriuretic peptides or autacoids like nitric oxide and prostaglandins inhibit NaCl reabsorption, promoting salt excretion. In general, the mechanism by which hormones control NaCl reabsorption is mediated directly or indirectly by altering the activity of NKCC2 in the TAL. Despite the importance of NKCC2 in renal physiology, the molecular mechanisms by which hormones, autacoids, physical factors, and intracellular ions regulate NKCC2 activity are largely unknown. During the last 5 years, it has become apparent that at least three molecular mechanisms determine NKCC2 activity. As such, membrane trafficking, phosphorylation, and protein-protein interactions have recently been described in TALs and heterologous expression systems as mechanisms that modulate NKCC2 activity. The focus of this review is to summarize recent data regarding NKCC2 regulation and discuss their potential implications in physiological control of TAL function, renal physiology, and blood pressure regulation.

MAL/VIP17, a new player in the regulation of NKCC2 in the kidney

The renal-specific Na+-K+-2Cl- cotransporter (NKCC2) is the major salt transport pathway of the apical membrane of the mammalian thick ascending limb of Henle's loop. Here, we analyze the role of the tetraspan protein myelin and lymphocytes-associated protein (MAL)/VIP17 in the regulation of NKCC2. We demonstrated that 1) NKCC2 and MAL/VIP17 colocalize and coimmunoprecipitate in Lilly Laboratories cell porcine kidney cells (LLC-PK1) as well as in rat kidney medullae, 2) a 150-amino acid stretch of NKCC2 C-terminal tail is involved in the interaction with MAL/VIP17, 3) MAL/VIP17 increases the cell surface retention of NKCC2 by attenuating its internalization, and 4) this coincides with an increase in cotransporter phosphorylation. Interestingly, overexpression of MAL/VIP17 in the kidney of transgenic mice results in cysts formation in distal nephron structures consistent with the hypothesis that MAL/VIP17 plays an important role in apical sorting or in maintaining the stability of the apical membrane. The NKCC2 expressed in these mice was highly glycosylated and phosphorylated, suggesting that MAL/VIP17 also is involved in the stabilization of NKCC2 at the apical membrane in vivo. Thus, the involvement of MAL/VIP17 in the activation and surface expression of NKCC2 could play an important role in the regulated absorption of Na+ and Cl- in the kidney.