American journal of physiology. Renal physiology最新文献

Arginine vasopressin (AVP) is a peptide hormone synthesized in the hypothalamus and secreted by the posterior pituitary. Previous studies toward understanding AVP physiology relied heavily on Brattleboro rats, which have a spontaneous mutation in the Avp gene and lack circulating AVP. However, these rats are difficult to breed due to high neonatal death and behavioral issues, causing commercial breeders to stop production. To address this, we developed a mouse line with tamoxifen-inducible deletion of Avp. We used CRISPR/Cas9 to insert loxP sites into the Avp gene. These mice were then bred with mice expressing a tamoxifen-inducible Cre recombinase. The resulting conditional knockout mice (Avp^flx/flxCre⁺) are viable, fertile, and healthy before induction. Administration of tamoxifen in 8-12-wk-old mice successfully deleted Avp, as confirmed by Sanger sequencing. This deletion caused a significant decrease in urine osmolality, a hallmark of AVP deficiency. The kidney structure remained normal, with no signs of medullary atrophy. In addition, these mice exhibited a substantially decreased expression of the aquaporin 2 water channel (AQP2), which is involved in water reabsorption in the kidney inner medulla. We illustrate the use of this model by using RNA-seq to profile the consequences of Avp deletion on gene expression in the kidney. The curated RNA-seq data can be browsed, searched, or downloaded at https://esbl.nhlbi.nih.gov/Databases/AVP-KO/. In conclusion, we successfully created an inducible Avp knockout mouse line that has been made available to the research community. This model will be valuable for studying water balance regulation, polycystic kidney disease, and the neural, vascular, and metabolic functions of vasopressin.NEW & NOTEWORTHY We developed an inducible Avp knockout mouse line that will be shared with the research community and is likely to be useful for further study of the regulation of water balance and polycystic kidney disease, as well as neural, vascular, and metabolic roles of vasopressin.

Mineralocorticoid receptor (MR) overactivation plays a crucial role in the pathogenesis of chronic kidney disease, as well as several cardiovascular and arterial diseases. Current studies determined the mechanisms of the beneficial kidney effects of the nonsteroidal MR antagonist finerenone (FN) in a mouse model of Western diet-induced obesity and insulin resistance. Ten-week-old male C57BL/6J mice were fed a low-fat (LF) or a Western diet (WD) for 12 weeks followed by treatment with either vehicle or FN for another 14 weeks (intervention studies) until they were 36 weeks old. Finerenone treatment prevented 1) the increased albuminuria and kidney injury molecule 1 (KIM1); 2) the expanded extracellular mesangial matrix and synaptopodin coverage; 3) fibronectin, collagen IV, CD45, and CD68 immunostaining; 4) glomerular basement membrane disruption, podocyte foot processes effacement, and mitochondrial structural abnormalities; 5) the proinflammatory cytokines [monocyte chemoattractant protein-1 (MCP-1)], innate immunity pathways [Toll-like receptor-2 (TLR2), stimulator of interferon genes (STING), signal transducer and activator of transcription 3 (STAT3)], and fibrosis markers fibronectin, transforming growth factor-β (TGFβ), and plasminogen activator inhibitor-1 (Pail); and 6) the increased kidney cholesterol levels. There was also reduced expression of nuclear receptor estrogen-related receptor-γ (ERRγ) without changes in ERRα in WD-fed mice, whereas both ERRα and ERRγ expression levels increased after finerenone treatment. NADH lifetime analysis showed decreased bound NADH, compatible with decreased mitochondrial oxidative phosphorylation (OXPHOS) in the kidneys of WD-fed mice compared to controls, which was prevented by finerenone treatment. In conclusion, finerenone treatment exhibits a renal protective role and prevents the progression of kidney disease by regulating mitochondrial function, most likely via ERRγ, and reducing lipid accumulation and inflammation. NEW & NOTEWORTHY Finerenone, a nonsteroidal mineralocorticoid receptor (MR) antagonist, has shown promise in protecting against kidney damage in obese, insulin-resistant mice. It effectively prevents albuminuria, inflammation, fibrosis, and mitochondrial dysfunction, while also restoring estrogen-related receptor-γ (ERRγ) expression. These results suggest that finerenone could play a key role in halting the progression of kidney disease by enhancing mitochondrial function and reducing harmful lipid accumulation, offering a potential therapeutic strategy for managing kidney complications in metabolic disorders.

Acute kidney injury (AKI) is prevalent among hospitalized patients. Novel biomarkers are needed to diagnose AKI and target therapies. Endotrophin (ETP) is a molecule released during collagen type VI formation that may promote injury and fibrosis. Although serum ETP elevation has been associated with adverse outcomes in AKI, urinary ETP has not been assessed in AKI, nor has ETP been evaluated in a pediatric population. Urine samples were collected from a tertiary children's hospital. Medical records were reviewed, and patients who met criteria were sorted into three categories: 1) AKI; 2) hospitalized controls; and 3) outpatient controls. ETP was measured using ELISA, and results were corrected to urine creatinine (uETP:Cre). A multivariate linear regression assessed whether demographic variables were independently associated with uETP:Cre. Odds of AKI were assessed in serial uETP:Cre tertiles using a multivariate logistic regression model that adjusted for patient variables. uETP:Cre was elevated in patients with AKI compared with hospitalized patients without AKI (P < 0.05) and outpatient controls (P < 0.0001). Multivariate analysis revealed that age, but not sex, race, or ethnicity independently correlated with uETP:Cre. After adjustment for these variables, the odds ratio for AKI increased with serial uETP:Cre tertiles. Noninvasive measurement of uETP may deliver meaningful information to aid AKI diagnosis. Given that ETP may be both a biomarker and a clinically actionable stimulus of inflammation and fibrosis, future studies are needed to understand the role of elevated ETP in AKI and whether existing ETP-neutralizing antibodies could represent a new avenue of AKI therapy.NEW & NOTEWORTHY Endotrophin (ETP) is a molecule released during the formation of type VI collagen that may promote fibrosis and inflammation. Serum ETP is elevated in acute kidney injury (AKI) and associates with adverse outcomes. Urine ETP during AKI has never been assessed. For the first time, this study demonstrates that urine ETP is also elevated during episodes of AKI, representing a novel, noninvasive AKI biomarker that may be clinically actionable.

The pregnane X receptor (PXR) is a ligand-activated transcription factor and a member of the nuclear receptor superfamily. PXR is constitutively expressed in the hypothalamus and kidney, with its physiological function incompletely understood. In this study, we found that treatment with pregnenolone-16α-carbonitrile (PCN), an endogenous PXR ligand, significantly reduced urine volume and increased urine osmolarity in C57BL/6 mice. In contrast, PXR gene knockout (PXR^-/-) mice exhibited impaired urine-concentrating ability, leading to a polyuria phenotype. In addition, treatment of mice with PCN significantly upregulated, whereas PXR gene deficiency substantially reduced, arginine vasopressin (AVP) expression in the hypothalamus. Bioinformatic analysis showed that the mouse AVP gene promoter contains a putative PXR response element (PXRE). The luciferase reporter, ChIP, and electrophoretic mobility shift assays further revealed that PXR can bind to the PXRE, resulting in a significant increase in AVP gene transcription. Collectively, the present study demonstrates that hypothalamic PXR plays a critical role in regulating urine volume, and its activation enhances urine-concentrating capacity primarily by upregulating the expression of AVP in the hypothalamus.NEW & NOTEWORTHY Activation of PXR enhances urine concentration, whereas PXR deficiency diminishes this capacity. PXR is coexpressed with AVP in the hypothalamus, where it upregulates AVP transcription to promote renal water reabsorption. These findings reveal a novel role for PXR in regulating urinary concentration and propose its potential as a therapeutic target for water metabolism disorders, such as diabetes insipidus.

In the kidney, the epithelial sodium channel (ENaC) facilitates sodium absorption in polarized epithelia and is required to maintain salt and water homeostasis. ENaC's apical membrane population is strictly controlled, with loss of this control leading to hyper- or hypotensive disorders such as Liddle's syndrome or pseudohypoaldosteronism type 1, respectively. Retromer and retriever are conserved endosome-localized protein trafficking complexes that mediate recycling of membrane proteins to the cell surface either directly, via recycling endosomes, or via the trans-Golgi network. Protein cargo for recycling is linked to retromer or retriever by sorting nexin (SNX) proteins. We hypothesized that SNX proteins are required for ENaC recycling. Using two epithelial cell lines [Fischer rat thyroid (FRT) and mouse cortical collecting duct clone 1 (mCCDcl1)] and the human embryonic kidney 293 (HEK293) cell line, with transient transfection of human ENaC-encoding plasmids into HEK293 and FRT epithelia, we found that siRNA knockdown of retromer- and retriever-associated sorting nexin (SNX1, 2, 3, 5, and 17) proteins reduced ENaC amiloride-sensitive short-circuit current and reduced ENaC cell surface population, observed using cell surface biotinylation. Coimmunoprecipitation experiments using transiently transfected human ENaC demonstrated a protein-protein interaction with SNX3 in FRT cells and with SNX17 in both FRT and HEK293 cells, suggesting that SNX3 and SNX17 act as cargo binding proteins between ENaC and the retromer and retriever complexes, respectively. Together, our findings suggest that SNX proteins associated with both the retromer and retriever recycling complexes play a role in maintaining ENaC cell surface populations in polarized epithelia.NEW & NOTEWORTHY Cell surface levels of the epithelial sodium channel, ENaC, are controlled by endocytosis and exocytosis pathways. Sorting nexin (SNX) family members facilitate the binding of protein cargo to recycling complexes for sequestration into recycling compartments. We show that knockdown of several SNX proteins decreases ENaC current and cell surface population, and both SNX3 and SNX17 coimmunoprecipitate with ENaC. Our data provide new insights into the control of ENaC cell surface levels and activity.

Renal oxygenation is essential for maintaining kidney function. Disruptions in oxygen delivery can lead to renal hypoxia, which can exacerbate kidney injury through multiple pathways, including inflammation, oxidative stress, and ischemia-reperfusion injury. Despite the recognized importance of oxygenation in renal pathology, noninvasive and reliable methods for assessing kidney oxygen levels are limited. Current techniques either lack sensitivity or involve invasive procedures, restricting their use in routine monitoring. Therefore, there is a pressing need for innovative approaches to map renal oxygenation, particularly in kidney injury. This study evaluated electron paramagnetic resonance (EPR)-based oxygen imaging using the paramagnetic tracer Ox071 to map kidney oxygen levels in mice with cyclophosphamide-induced kidney injury. Urine partial pressure of oxygen (Po₂) was also assessed as a potential surrogate marker. EPR oximetry accurately measured kidney oxygen distribution, revealing a temporary increase in Po₂ post-injury. Urine oximetry, however, did not reliably reflect changes in kidney oxygenation. Furthermore, EPR oximetry provided high-resolution spatial mapping of oxygen levels within the kidney, allowing for a detailed understanding of the impact of hypoxia on renal tissue. EPR oximetry is a promising, noninvasive tool for monitoring renal oxygenation, offering high-resolution mapping and longitudinal assessment. Its ability to provide detailed information about oxygen distribution within the kidney makes it a valuable tool for studying the pathophysiology of renal diseases and for developing novel therapeutic strategies.NEW & NOTEWORTHY Quantitative spatially resolved measurement of renal oxygenation has the potential to guide clinical decision making in renal disorders such as acute kidney injury. In this study, we demonstrate the utility of electron paramagnetic resonance imaging to provide noninvasive and quantitative high-resolution mapping of kidney oxygen concentrations.

Transport across cells of the renal tubule differs between females and males, possibly as a consequence of varying abundance of transport proteins along the nephron. We hypothesized that sex-specific differences in the physiological responses and in transport protein abundances exist in the context of acid-base challenges. We used female and male C57Bl/6J mice and challenged them with acid (NH₄Cl) or base (NaHCO₃) in their drinking water for 8 days. Blood and urine samples were collected at baseline and at the end of the experimental period before kidneys were harvested and protein abundances determined. In response to NH₄Cl challenge, the significant decreases in urine pH, blood HCO₃^-, and base excess were similar in both sexes despite a smaller intake of NH₄Cl in male compared with female mice. In response to NaHCO₃ challenge, urine pH significantly increased in both sexes; however, blood pH, HCO₃^-, and base excess were increased significantly and to a greater extent in male compared with female mice. Two-way analysis of variance demonstrated that out of the 12 tested proteins, 7 were significantly affected by sex, 7 were significantly affected by treatment, and the interaction of sex and treatment was significant for Na⁺/K⁺/2Cl^- cotransporter, NKCC2. In summary, our study demonstrates 1) sex differences in protein abundance, 2) proteins are affected differentially in response to acid-base challenges, and 3) NKCC2 is a new and potentially important player in acid-base regulation.NEW & NOTEWORTHY Disturbances in acid-base regulation are common and can have detrimental effects. Here, we provide evidence that acid-base disturbances in males and females are consistent with female mice being able to defend acid and base challenges more effectively. Our data have potential clinical importance in humans regarding the treatment of acidosis and alkalosis in males versus females.