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

A new immune disease: systemic hypertension

Systemic hypertension is the most common medical comorbidity affecting the adult population globally, with multiple associated outcomes including cerebrovascular diseases, cardiovascular diseases, vascular calcification, chronic kidney disease, metabolic syndrome and mortality. Despite advancements in the therapeutic field approximately one in every five adult patients with hypertension is classified as having treatment-resistant hypertension, indicating the need for studies to provide better understanding of the underlying pathophysiology and the need for more therapeutic targets. Recent pre-clinical studies have demonstrated the role of the innate and adaptive immune system including various cell types and cytokines in the pathophysiology of hypertension. Moreover, pre-clinical studies have indicated the potential beneficial effects of immunosuppressant medications in the control of hypertension. Nevertheless, it is unclear whether such pathophysiological mechanisms and therapeutic alternatives are applicable to human subjects, while this area of research is undoubtedly a rapidly growing field.

Responses to Ang II (Angiotensin II), Salt Intake, and Lipopolysaccharide Reveal the Diverse Actions of TNF-α (Tumor Necrosis Factor-α) on Blood Pressure and Renal Function

TNF-α (tumor necrosis factor-alpha) is the best known as a proinflammatory cytokine; yet, this cytokine also has important immunomodulatory and regulatory functions. As the effects of TNF-α on immune system function were being revealed, the spectrum of its activities appeared in conflict with each other before investigators defined the settings and mechanisms by which TNF-α contributed to both host defense and chronic inflammation. These effects reflect self-protective mechanisms that may become harmful when dysregulated. The paradigm of physiological and pathophysiological effects of TNF-α has since been uncovered in the lung, colon, and kidney where its role has been identified in pulmonary edema, electrolyte reabsorption, and blood pressure regulation, respectively. Recent studies on the prohypertensive and inflammatory effects of TNF-α in the cardiovascular system juxtaposed to those related to NaCl and blood pressure homeostasis, the response of the kidney to lipopolysaccharide, and protection against bacterial infections are helping define the mechanisms by which TNF-α modulates distinct functions within the kidney. This review discusses how production of TNF-α by renal epithelial cells may contribute to regulatory mechanisms that not only govern electrolyte excretion and blood pressure homeostasis but also maintain the appropriate local hypersalinity environment needed for optimizing the innate immune response to bacterial infections in the kidney. It is possible that the wide range of effects mediated by TNF-α may be related to severity of disease, amount of inflammation and TNF-α levels, and the specific cell types that produce this cytokine, areas that remain to be investigated further.

Erythropoietin prevented the decreased expression of aquaporin1-3 in ureteral obstructive kidneys in juvenile rats

BACKGROUND

Urinary tract obstruction is associated with impaired renal urinary concentration; even after the release of the obstruction, patients still suffer from polyuria. It has been reported that the decreased expression of aquaporins (AQPs) is associated with postobstructive polyuria, and erythropoietin (EPO) can promote the recovery of decreased AQP2 expression induced by bilateral ureteral obstruction. However, whether EPO can promote the recovery of the expression of AQP1-3 after the release of unilateral ureteral obstruction (UUO) has not yet been reported.

AIMS

To investigate the effects of EPO treatment on the expression of renal AQP1-3 after the release of UUO.

METHODS

UUO was established in rats by 24-h temporary unilateral obstruction of renal ureters. Three days following EPO treatment, the kidneys were removed to determine the expression levels of AQP1-3, NLRP3, caspase-1, and IL-1β via semiquantitative immunoblotting and immunohistochemistry.

RESULTS

EPO inhibited the expression of NLRP3, caspase-1, and IL-1β; reduced plasma creatinine and urea; and promoted the recovery of AQP1-3 expression in UUO rats.

CONCLUSIONS

EPO treatment prevented the decreased expression of renal AQPs and the development of impaired urinary concentration capacity after the release of UUO, which may partially occur by way of anti-inflammasome effects.

IMPACT

EPO treatment could prevent the decreased expression of renal water transporter proteins AQP1-3 and the development of impaired renal functions, which may be associated with its anti-inflammasome effects. EPO regulated the expression of renal water transporter proteins AQP1-3, which could provide the potential for the treatment of postobstructive polyuresis. EPO treatment could be one of the effective methods by participating in multiple dimensions for patients with obstructive nephropathy.

Sex-specific adaptations to high-salt diet preserve electrolyte homeostasis with distinct sodium transporter profiles

Kidneys continuously filter an enormous amount of sodium and adapt kidney Na+ reabsorption to match Na+ intake to maintain circulatory volume and electrolyte homeostasis. Males (M) respond to high-salt (HS) diet by translocating proximal tubule Na+/H+ exchanger isoform 3 (NHE3) to the base of the microvilli, reducing activated forms of the distal NaCl cotransporter (NCC) and epithelial Na+ channel (ENaC). Males (M) and females (F) on normal-salt (NS) diet present sex-specific profiles of "transporters" (cotransporters, channels, pumps, and claudins) along the nephron, e.g., F exhibit 40% lower NHE3 and 200% higher NCC abundance than M. We tested the hypothesis that adaptations to HS diet along the nephron will, likewise, exhibit sexual dimorphisms. C57BL/6J mice were fed for 15 days with 4% NaCl diet (HS) versus 0.26% NaCl diet (NS). On HS, M and F exhibited normal plasma [Na+] and [K+], similar urine volume, Na+, K+, and osmolal excretion rates normalized to body weight. In F, like M, HS lowered abundance of distal NCC, phosphorylated NCC, and cleaved (activated) forms of ENaC. The adaptations associated with achieving electrolyte homeostasis exhibit sex-dependent and independent mechanisms. Sex differences in baseline "transporters" abundance persist during HS diet, yet the fold changes during HS diet (normalized to NS) are similar along the distal nephron and collecting duct. Sex-dependent differences observed along the proximal tubule during HS show that female kidneys adapt differently from patterns reported in males, yet achieve and maintain fluid and electrolyte homeostasis.

Environmental, inflammatory, and anti-inflammatory squad in acne vulgaris pathogenesis: AhR, IL-36, and IL-38

BACKGROUND

Acne vulgaris (AV) is an extraordinarily common skin condition. The high prevalence of AV is linked to the exposure factors, as environmental pollutants and climatic factors, occupational, psychosocial, and lifestyle factors. The AhR plays a critical part in environmental toxic action. The AhR expression and imbalance in the IL-36 & 38 expression may have a role in inflammation and AV pathogenesis.

AIMS

To detect possible links between environmental, inflammatory, and anti-inflammatory factors in AV pathogenesis through measuring AhR, IL-36, and IL-38 mRNA gene expression levels.

PATIENTS AND METHODS

Total of 100 subjects (70 AV patients and 30 apparently healthy control subjects) were tested for AhR, IL-36γ, and IL-38 mRNA levels by quantitative real-time PCR.

RESULTS

The median levels of AhR and IL-36 mRNA gene expression were considerably greater, while that of IL-38 was essentially lower in AV than healthy subjects (p < 0.001, 0.021 and 0.002, respectively). The AhR and IL-36 mRNA gene expression levels increased, while IL-38 decreased significantly with higher grades of severity (p < 0.001, 0.001, and <0.001, respectively). ROC curve showed that AhR mRNA gene expression level had the best AUC for diagnosis of AV, with better sensitivity and specificity than IL-36 and IL-38.

CONCLUSIONS

Higher levels of AhR, IL-36, and lower levels of IL-38 gene expression were significantly associated with AV patients and higher grades of severity. AhR had better diagnostic ability than IL-38 and IL-36.

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.

ETA receptor activation contributes to T cell accumulation in the kidney following ischemia-reperfusion injury

Renal ischemia-reperfusion (IR) injury and acute kidney injury (AKI) increase the risk of developing hypertension, with T cells suspected as a possible mechanistic link. Endothelin promotes renal T cell infiltration in several diseases, predominantly via the ETA receptor, but its contribution to renal T cell infiltration following renal IR injury is poorly understood. To test whether ETA receptor activation promotes T cell infiltration of the kidney following IR injury, male C57BL/6 mice were treated with the ETA receptor antagonist ABT-627 or vehicle, commencing 2 days prior to unilateral renal IR injury. Mice were sacrificed at 24 h or 10 days post-IR for assessment of the initial renal injury and subsequent infiltration of T cells. Vehicle and ABT-627-treated mice displayed significant upregulation of endothelin-1 (ET-1) in the IR compared to contralateral kidney at both 24 h and 10 days post-IR (P < 0.001). Renal CD3+ T cell numbers were increased in the IR compared to contralateral kidneys at 10 days, but ABT-627-treated mice displayed a 35% reduction in this effect in the outer medulla (P < 0.05 vs. vehicle) and a nonsignificant 23% reduction in the cortex compared to vehicle-treated mice. Whether specific T cell subsets were affected awaits confirmation by flow cytometry, but outer medullary expression of the T helper 17 transcription factor RORγt was reduced by ABT-627 (P = 0.06). These data indicate that ET-1 acting via the ETA receptor contributes to renal T cell infiltration post-IR injury. This may have important implications for immune system-mediated long-term consequences of AKI, an area which awaits further investigation.

Combination exposure of melamine and cyanuric acid is associated with polyuria and activation of NLRP3 inflammasome in rats

The molecular mechanisms of melamine-induced renal toxicity have not been fully understood. The purpose of the study aimed to investigate whether melamine and cyanuric acid induced NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome activation in the kidney, which may contribute to abnormal water and sodium handling in a rat model. Wistar rats received melamine (Mel; 200 mg·kg body wt−1·day−1), cyanuric acid (CA; 200 mg·kg body wt−1·day−1), or Mel plus CA (Mel + CA; 100 mg·kg body wt−1·day−1, each) for 2 wk. Mel + CA caused damaged tubular epithelial structure and organelles, dilated tubular lumen, and inflammatory responses. Crystals were observed in urine and serum specimen, also in the lumen of dilated distal renal tubules. The combined ingestion of Mel and CA in rats caused a markedly impaired urinary concentration, which was associated with reduced protein expression of aquaporin (AQP)1, 2, and 3 in inner medulla and α-Na-K-ATPase and Na-K-2Cl transporters in cortex and outer medulla. Mel + CA treatment was associated with increased protein expression of CD3 and mRNA levels of CD68 and F4/80 as well as phosphorylation of NF-κB in the kidney. Mel + CA treatment increased protein and mRNA expression of NLRP3 inflammasome components apoptosis-associated speck-like protein containing a caspase recruitment domain, caspase-1, and IL-1β in the inner medulla of rats. NF-κB inhibitor Bay 11-7082 reduced IL-1β expression induced by Mel + CA and prevented downregulation of AQP2 in inner medullary collecting duct cell suspensions. In conclusion, Mel + CA treatment caused urinary-concentrating defects and reduced expression of renal AQPs and key sodium transporters, which is likely due to the inflammatory responses and activation of NLRP3 inflammasome induced by crystals formed in the kidney.

Interleukin-1β as a driver of renal NGAL production

Neutrophil gelatinase-associated lipocalin (NGAL) is increasingly regarded as a biomarker of acute kidney injury, or kidney injury in general, but the stimuli responsible for its production are incompletely understood. This study tested the relationship between the pro-inflammatory cytokine interleukin-1β (IL-1β) and both circulating and renal NGAL, using chronic subcutaneous infusion of IL-1β in mice and tissue culture of renal cell lines. Following a 14-day subcutaneous infusion of vehicle or IL-1β (10ng/h) in male C57Bl/6 mice, a striking positive correlation (r²=0.94; P<0.01) was observed between plasma IL-1β and NGAL concentrations. NGAL was markedly increased in the kidneys of IL-1β-infused mice compared with vehicle-treated mice, both at the protein and mRNA level, indicating increased local as well as systemic production of NGAL. Immunohistochemical staining revealed prominent increases of NGAL in the proximal tubular epithelium of IL-1β infused mice. These effects occurred in the absence of overt renal injury, with plasma creatinine concentration not significantly different between groups. Further showing that IL-1β has a direct effect on NGAL production by tubular epithelial cells, exposure of a proximal tubular cell line (HK-2 cells) and a cortical collecting duct principal cell line (mpkCCD cells) to IL-1β for 24h produced a significant increase of NGAL mRNA levels (>30-fold). These data indicate IL-1β serves as a powerful stimulus for renal production of NGAL.

Role of IL-38 and its related cytokines in inflammation

Interleukin- (IL-) 38 is a recently discovered cytokine and is the tenth member of the IL-1 cytokine family. IL-38 shares structural features with IL-1 receptor antagonist (IL-1Ra) and IL-36Ra. IL-36R is the specific receptor of IL-38, a partial receptor antagonist of IL-36. IL-38 inhibits the production of T-cell cytokines IL-17 and IL-22. IL-38 also inhibits the production of IL-8 induced by IL-36γ, thus inhibiting inflammatory responses. IL-38-related cytokines, including IL-1Ra and IL-36Ra, are involved in the regulation of inflammation and immune responses. The study of IL-38 and IL-38-related cytokines might provide new insights for developing anti-inflammatory treatments in the near future.

Aliskiren restores renal AQP2 expression during unilateral ureteral obstruction by inhibiting the inflammasome

Ureteral obstruction is associated with reduced expression of renal aquaporins (AQPs), urinary concentrating defects, and an enhanced inflammatory response, in which the renin-angiotensin system (RAS) may play an important role. We evaluated whether RAS blockade by a direct renin inhibitor, aliskiren, would prevent the decreased renal protein expression of AQPs in a unilateral ureteral obstruction (UUO) model and what potential mechanisms may be involved. UUO was performed for 3 days (3UUO) and 7 days (7UUO) in C57BL/6 mice with or without aliskiren injection. In 3UUO and 7UUO mice, aliskiren abolished the reduction of AQP2 protein expression but not AQP1, AQP3, and AQP4. mRNA levels of renal AQP2 and vasopressin type 2 receptor were decreased in obstructed kidneys of 7UUO mice, which were prevented by aliskiren treatment. Aliskiren treatment was also associated with a reduced inflammatory response in obstructed kidneys of UUO mice. Aliskiren significantly decreased mRNA levels of several proinflammatory factors, such as transforming growth factor-β and tumor necrosis factor-α, seen in obstructed kidneys of UUO mice. Interestingly, mRNA and protein levels of the NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome components apoptosis-associated speck-like protein containing a caspase recruitment domain, caspase-1, and IL-1β were dramatically increased in obstructed kidneys of 7UUO mice, which were significantly suppressed by aliskiren. In primary cultured inner medullary collecting duct cells, IL-1β significantly decreased AQP2 expression. In conclusions, RAS blockade with the direct renin inhibitor aliskiren increased water channel AQP2 expression in obstructed kidneys of UUO mice, at least partially by preventing NLRP3 inflammasome activation in association with ureteral obstruction.