Collecting duct-specific knockout of nitric oxide synthase 3 impairs water excretion in a sex-dependent manner

ApoE/NOS3 Knockout Mice as a Novel Cardiovascular Disease Model of Hypertension and Atherosclerosis

Hypertension is an independent risk factor for atherosclerosis. However, few models of hypertensive atherosclerosis have been established in medical research. In this study, we crossed the ApoE knockout (ApoE-KO; ApoE-/-) atherosclerotic mouse model with the NOS3 knockout (NOS3-KO; NOS3-/-) hypertensive mouse model to establish an ApoE/NOS3 double knockout (ApoE/NOS3-KO; ApoE/NOS3-/-) hypertensive atherosclerosis mouse model. We found that ApoE/NOS3-/- mice reproduced normally, had a blood pressure of 133.00 ± 3.85 mmHg, and developed hypertensive fundus retinopathy and hypertensive nephropathy. In addition, serum total cholesterol (TC) and low-density lipoprotein (LDL) levels in the blood were abnormally elevated, steatosis was observed in the liver cells, and atherosclerotic lesions were observed in the aortic vessels in ApoE/NOS3-/- adult mice. In conclusion, ApoE/NOS3-/- adult mice are a satisfactory model of hypertension and atherosclerosis and can be utilized for studies on cardiovascular diseases.

Sex-Dependent Effects of Nephron Ift88 Disruption on BP, Renal Function, and Cystogenesis

BACKGROUND

Primary cilia regulation of renal function and BP in health and disease is incompletely understood. This study investigated the effect of nephron ciliary loss on renal physiology, BP, and ensuing cystogenesis.

METHODS

Mice underwent doxycycline (DOX)-inducible nephron-specific knockout (KO) of the Ift88 gene at 2 months of age using a Cre-LoxP strategy. BP, kidney function, and renal pathology were studied 2 and 9 months after DOX (Ift88 KO) or vehicle (control).

RESULTS

At 2 months post-DOX, male, but not female, Ift88 KO, compared with sex-matched control, mice had reduced BP, enhanced salt-induced natriuresis, increased urinary nitrite and nitrate (NOx) excretion, and increased kidney NOS3 levels, which localized to the outer medulla; the reductions in BP in male mice were prevented by L-NAME. At 9 months post-DOX, male, but not female, Ift88 KO mice had polycystic kidneys, elevated BP, and reduced urinary NOx excretion. No differences were observed in plasma renin concentration, plasma aldosterone, urine vasopressin, or urine PGE₂ between Ift88 KO and control mice at 2 or 9 months post-DOX.

CONCLUSIONS

Nephron cilia disruption in male, but not female, mice (1) reduces BP prior to cyst formation, (2) increases NOx production that may account for the lower BP prior to cyst formation, and (3) induces polycystic kidneys that are associated with hypertension and reduced renal NO production.

Induction of renal tumor necrosis factor-α and other autacoids and the beneficial effects of hypertonic saline in acute decompensated heart failure

Although administration of hypertonic saline (HSS) in combination with diuretics has yielded improved weight loss, preservation of renal function, and reduction in hospitalization time in the clinical setting of patients with acute decompensated heart failure (ADHF), the mechanisms that underlie these beneficial effects remain unclear and additional studies are needed before this approach can be adopted on a more consistent basis. As high salt conditions stimulate the production of several renal autacoids that exhibit natriuretic effects, renal physiologists can contribute to the understanding of mechanisms by which HSS leads to increased diuresis both as an individual therapy as well as in combination with loop diuretics. For instance, since HSS increases TNF-α production by proximal tubule and thick ascending limb of Henle's loop epithelial cells, this article is aimed at highlighting how the effects of TNF-α produced by these cell types may contribute to the beneficial effects of HSS in patients with ADHF. Although TNF-α produced by infiltrating macrophages and T cells exacerbates and attenuates renal damage, respectively, production of this cytokine within the tubular compartment of the kidney functions as an intrinsic regulator of blood pressure and Na⁺ homeostasis via mechanisms along the nephron related to inhibition of Na⁺-K⁺-2Cl^- cotransporter isoform 2 activity and angiotensinogen expression. Thus, in the clinical setting of ADHF and hyponatremia, induction of TNF-α production along the nephron by administration of HSS may attenuate Na⁺-K⁺-2Cl^- cotransporter isoform 2 activity and angiotensinogen expression as part of a mechanism that prevents excessive Na⁺ reabsorption in the thick ascending limb of Henle's loop, thereby mitigating volume overload.

High salt intake induces collecting duct HDAC1-dependent NO signaling

We reported that high salt (HS) intake stimulates renal collecting duct (CD) endothelin (ET) type B receptor (ETBR)/nitric oxide (NO) synthase 1β (NOS1β)-dependent NO production inhibiting the epithelial sodium channel (ENaC) promoting natriuresis. However, the mechanism underlying the HS-induced increase of NO production is unclear. Histone deacetylase 1 (HDAC1) responds to increased fluid flow, as can occur in the CD during HS intake. The renal inner medulla (IM), in particular the IMCD, has the highest NOS1 activity within the kidney. Hence, we hypothesized that HS intake provokes HDAC1 activation of NO production in the IM. HS intake for 1 wk significantly increased HDAC1 abundance in the IM. Ex vivo treatment of dissociated IM from HS-fed mice with a selective HDAC1 inhibitor (MS-275) decreased NO production with no change in ET-1 peptide or mRNA levels. We further investigated the role of the ET-1/ETBR/NOS1β signaling pathway with chronic ETBR blockade (A-192621). Although NO was decreased and ET-1 levels were elevated in the dissociated IM from HS-fed mice treated with A-192621, ex vivo MS-275 did not further change NO or ET-1 levels suggesting that HDAC1-mediated NO production is regulated at the level or downstream of ETBR activation. In split-open CDs from HS-fed mice, patch clamp analysis revealed significantly higher ENaC activity after MS-275 pretreatment, which was abrogated by an exogenous NO donor. Moreover, flow-induced increases in mIMCD-3 cell NO production were blunted by HDAC1 or calcium inhibition. Taken together, these findings indicate that HS intake induces HDAC1-dependent activation of the ETBR/NO pathway contributing to the natriuretic response.

Renal Autocrine and Paracrine Signaling: A Story of Self-protection

Autocrine and paracrine signaling in the kidney adds an extra level of diversity and complexity to renal physiology. The extensive scientific production on the topic precludes easy understanding of the fundamental purpose of the vast number of molecules and systems that influence the renal function. This systematic review provides the broader pen strokes for a collected image of renal paracrine signaling. First, we recapitulate the essence of each paracrine system one by one. Thereafter the single components are merged into an overarching physiological concept. The presented survey shows that despite the diversity in the web of paracrine factors, the collected effect on renal function may not be complicated after all. In essence, paracrine activation provides an intelligent system that perceives minor perturbations and reacts with a coordinated and integrated tissue response that relieves the work load from the renal epithelia and favors diuresis and natriuresis. We suggest that the overall function of paracrine signaling is reno-protection and argue that renal paracrine signaling and self-regulation are two sides of the same coin. Thus local paracrine signaling is an intrinsic function of the kidney, and the overall renal effect of changes in blood pressure, volume load, and systemic hormones will always be tinted by its paracrine status.

The contribution of collecting duct NOS1 to the concentrating mechanisms in male and female mice

The collecting duct (CD) concentrates the urine, thereby maintaining body water volume and plasma osmolality within a normal range. The endocrine hormone arginine vasopressin acts in the CD to increase water permeability via the vasopressin 2 receptor (V2R)-aquaporin (AQP) axis. Recent studies have suggested that autocrine factors may also contribute to the regulation of CD water permeability. Nitric oxide is produced predominantly by nitric oxide synthase 1 (NOS1) in the CD and acts as a diuretic during salt loading. The present study sought to determine whether CD NOS1 regulates diuresis during changes in hydration status. Male and female control and CD NOS1 knockout (CDNOS1KO) mice were hydrated (5% sucrose water), water deprived, or acutely challenged with the V2R agonist desmopressin. In male mice, water deprivation resulted in decreased urine flow and increased plasma osmolality, copeptin concentration, and kidney AQP2 abundance independent of CD NOS1. In female control mice, water deprivation reduced urine flow, increased plasma osmolality and copeptin, but did not significantly change total AQP2; however, there was increased basolateral AQP3 localization. Surprisingly, female CDNOS1KO mice while on the sucrose water presented with symptoms of dehydration. Fibroblast growth factor 21, an endocrine regulator of sweetness preference, was significantly higher in female CDNOS1KO mice, suggesting that this was reducing their drive to drink the sucrose water. With acute desmopressin challenge, female CDNOS1KO mice failed to appropriately concentrate their urine, resulting in higher plasma osmolality than controls. In conclusion, CD NOS1 plays only a minor role in urine-concentrating mechanisms.

Duloxetine and Angiotensin II Receptor Blocker Combination Potentially Induce Severe Hyponatremia in an Elderly Woman

We encountered a case of syndrome of inappropriate antidiuretic hormone secretion (SIADH) caused by duloxetine, serotonin and norepinephrine reuptake inhibitor (SNRI). A 74-year-old woman complaining of severe lethargy was transferred to our emergency department. Her serum sodium level was 109 mEq/L. Plasma hypo-osmolality with urine normo-osmolality was observed, indicating SIADH. Her essential hypertension had long been treated with telmisartan, and she had just started duloxetine 20 mg/day for chronic musculoskeletal pain 4 days prior to admission. On prescribing duloxetine in the primary care setting, clinicians should be aware of the possibility of duloxetine-induced hyponatremia, particularly in combination with telmisartan.

Nephron-Specific Disruption of Nitric Oxide Synthase 3 Causes Hypertension and Impaired Salt Excretion

BACKGROUND

In vitro studies suggest that nephron nitric oxide synthase 3 (NOS3) modulates tubule Na⁺ transport.

METHODS AND RESULTS

To assess nephron NOS3 relevance in vivo, knockout (KO) mice with doxycycline-inducible nephron-wide deletion of NOS3 were generated. During 1 week of salt loading, KO mice, as compared with controls, had higher arterial pressure and Na⁺ retention, a tendency towards reduced plasma renin concentration, and unchanged glomerular filtration rate. Chronic high salt-treated KO mice had modestly decreased total NCC and total SPAK/OSR1 versus controls, however percent phosphorylation of NCC (at T⁵³) and of SPAK/OSR1 was increased. In contrast, total and phosphorylated NKCC2 (at T^96/101) were suppressed by 50% each in KO versus control mice after chronic salt intake. In response to an acute salt load, KO mice had delayed urinary Na⁺ excretion versus controls; this delay was completely abolished by furosemide, partially reduced by hydrochlorothiazide, but not affected by amiloride. After 4 hours of an acute salt load, phosphorylated and total NCC were elevated in KO versus control mice. Acute salt loading did not alter total NKCC2 or SPAK/OSR1 in KO versus control mice but increased the percent phosphorylation of NKCC2 (at T^96/101 and S¹²⁶) and SPAK/OSR1 in KO versus control mice.

CONCLUSIONS

These findings indicate that nephron NOS3 is involved in blood pressure regulation and urinary Na⁺ excretion during high salt intake. Nephron NOS3 appears to regulate NKCC2 and NCC primarily during acute salt loading. These effects of NOS3 may involve SPAK/OSR1 as well as other pathways.

The Impact of the Nitric Oxide (NO)/Soluble Guanylyl Cyclase (sGC) Signaling Cascade on Kidney Health and Disease: A Preclinical Perspective

Chronic Kidney Disease (CKD) is a highly prevalent disease with a substantial medical need for new and more efficacious treatments. The Nitric Oxide (NO), soluble guanylyl cyclase (sGC), cyclic guanosine monophosphate (cGMP) signaling cascade regulates various kidney functions. cGMP directly influences renal blood flow, renin secretion, glomerular function, and tubular exchange processes. Downregulation of NO/sGC/cGMP signaling results in severe kidney pathologies such as CKD. Therefore, treatment strategies aiming to maintain or increase cGMP might have beneficial effects for the treatment of progressive kidney diseases. Within this article, we review the NO/sGC/cGMP signaling cascade and its major pharmacological intervention sites. We specifically focus on the currently known effects of cGMP on kidney function parameters. Finally, we summarize the preclinical evidence for kidney protective effects of NO-donors, PDE inhibitors, sGC stimulators, and sGC activators.

EHD4 is a novel regulator of urinary water homeostasis

The Eps15-homology domain-containing (EHD) protein family comprises 4 members that regulate endocytic recycling. Although the kidney expresses all 4 EHD proteins, their physiologic roles are largely unknown. This study focused on EHD4, which we found to be expressed differentially across nephron segments with the highest expression in the inner medullary collecting duct. Under baseline conditions, Ehd4^-/- [EHD4-knockout (KO)] mice on a C57Bl/6 background excreted a higher volume of more dilute urine than control C57Bl/6 wild-type (WT) mice while maintaining a similar plasma osmolality. Urine excretion after an acute intraperitoneal water load was significantly increased in EHD4-KO mice compared to WT mice, and although EHD4-KO mice concentrated their urine during 24-h water restriction, urinary osmolality remained significantly lower than in WT mice, suggesting that EHD4 plays a role in renal water handling. Total aquaporin 2 (AQP2) and phospho-S256-AQP2 (pAQP2) protein expression in the inner medulla was similar in the two groups in baseline conditions. However, localization of both AQP2 and pAQP2 in the renal inner medullary principal cells appeared more dispersed, and the intensity of apical membrane staining for AQP2 was reduced significantly (by ∼20%) in EHD4-KO mice compared to WT mice in baseline conditions, suggesting an important role of EHD4 in trafficking of AQP2. Together, these data indicate that EHD4 play important roles in the regulation of water homeostasis.-Rahman, S. S., Moffitt, A. E. J., Trease, A. J., Foster, K. W., Storck, M. D., Band, H., Boesen, E. I. EHD4 is a novel regulator of urinary water homeostasis.

Nitric oxide reduces paracellular resistance in rat thick ascending limbs by increasing Na+ and Cl- permeabilities

About 50% of the Na⁺ reabsorbed in thick ascending limbs traverses the paracellular pathway. Nitric oxide (NO) reduces the permselectivity of this pathway via cGMP, but its effects on absolute Na⁺ ([Formula: see text]) and Cl^- ([Formula: see text]) permeabilities are unknown. To address this, we measured the effect of l-arginine (0.5 mmol/l; NO synthase substrate) and cGMP (0.5 mmol/l) on [Formula: see text] and [Formula: see text] calculated from the transepithelial resistance (R_t) and [Formula: see text]/[Formula: see text] in medullary thick ascending limbs. R_t was 7,722 ± 1,554 ohm·cm in the control period and 6,318 ± 1,757 ohm·cm after l-arginine treatment (P < 0.05). [Formula: see text]/[Formula: see text] was 2.0 ± 0.2 in the control period and 1.7 ± 0.1 after l-arginine (P < 0.04). Calculated [Formula: see text] and [Formula: see text] were 3.52 ± 0.2 and 1.81 ± 0.10 × 10^-5 cm/s, respectively, in the control period. After l-arginine they were 6.65 ± 0.69 (P < 0.0001 vs. control) and 3.97 ± 0.44 (P < 0.0001) × 10^-5 cm/s, respectively. NOS inhibition with N^ω-nitro-l-arginine methyl ester (5 mmol/l) prevented l-arginine's effect on R_t Next we tested the effect of cGMP. R_t in the control period was 7,592 ± 1,470 and 4,796 ± 847 ohm·cm after dibutyryl-cGMP (0.5 mmol/l; db-cGMP) treatment (P < 0.04). [Formula: see text]/[Formula: see text] was 1.8 ± 0.1 in the control period and 1.6 ± 0.1 after db-cGMP (P < 0.03). [Formula: see text] and [Formula: see text] were 4.58 ± 0.80 and 2.66 ± 0.57 × 10^-5 cm/s, respectively, for the control period and 9.48 ± 1.63 (P < 0.007) and 6.01 ± 1.05 (P < 0.005) × 10^-5 cm/s, respectively, after db-cGMP. We modeled NO's effect on luminal Na⁺ concentration along the thick ascending limb. We found that NO's effect on the paracellular pathway reduces net Na⁺ reabsorption and that the magnitude of this effect is similar to that due to NO's inhibition of transcellular transport.

Regulated necrosis-related molecule mRNA expression in humans and mice and in murine acute tissue injury and systemic autoimmunity leading to progressive organ damage, and progressive fibrosis

The species-specific, as well as organ-specific expression of regulated necrosis (RN)-related molecules, is not known. We determined the expression levels of tumour necrosis factor receptor-1 (TNFR1), receptor activated protein kinase (RIPK)1, RIPK3, mixed lineage kinase domain-like (MLKL), CASP8, Fas-associated protein with death domain (FADD), cellular inhibitor of apoptosis protein (CIAP)1, CIAP2, glutathione peroxidase-4 (GPX4), cyclophilin D (CYPD), CASP1, NLRP3 and poly(ADP-ribose) polymerase-1 (PARP1) in human and mouse solid organs. We observed significant differences in expression of these molecules between human and mice. In addition, we characterized their expression profiles in acute as well as persistent tissue injury and chronic tissue remodelling using acute and chronic kidney injury models. We observed that the degree and pattern of induction of RN-related molecules were highly dependent on the trigger and disease pathogenesis. Furthermore, we studied their expression patterns in mice with lupus-like systemic autoimmunity, which revealed that the expression of MLKL, GPX4 and PARP1 significantly increased in the spleen along disease progression and CASP1, RIPK1, RIPK3 and CYPD were higher at the earlier stages but were significantly decreased in the later stages. In contrast, in the kidney, the expression of genes involved in pyroptosis, e.g. NLRP3 and CASP1 were significantly increased and TNFR1, RIPK1, RIPK3, CIAP1/2 and GPX4 were significantly decreased along the progression of lupus nephritis (LN). Thus, the organ- and species-specific expression of RN-related molecules should be considered during designing experiments, interpreting the results as well as extrapolating the conclusions from one species or organ to another species or organ respectively.