Electrolyte Homeostasis Research Articles

Neuropilin-1 regulates renin synthesis in juxtaglomerular cells.

Renin is the key enzyme of the systemic renin-angiotensin-aldosterone system, which plays an essential role in regulating blood pressure and maintaining electrolyte and extracellular volume homeostasis. Renin is mainly produced and secreted by specialized juxtaglomerular (JG) cells in the kidney. In the present study, we report for the first time that the conserved transmembrane receptor neuropilin-1 (NRP1) participates in the development of JG cells and plays a key role in renin production. We used the myelin protein zero-Cre (P0-Cre) to abrogate Nrp1 constitutively in P0-Cre lineage-labelled cells of the kidney. We found that the P0-Cre precursor cells differentiate into renin-producing JG cells. We employed a lineage-tracing strategy combined with RNAscope quantification and metabolic studies to reveal a cell-autonomous role for NRP1 in JG cell function. Nrp1-deficient animals displayed abnormal levels of tissue renin expression and failed to adapt properly to a homeostatic challenge to sodium balance. These findings provide new insights into cell fate decisions and cellular plasticity operating in P0-Cre-expressing precursors and identify NRP1 as a novel key regulator of JG cell maturation. KEY POINTS: Renin is a centrepiece of the renin-angiotensin-aldosterone system and is produced by specialized juxtaglomerular cells (JG) of the kidney. Neuropilin-1 (NRP1) is a conserved membrane-bound receptor that regulates vascular and neuronal development, cancer aggressiveness and fibrosis progression. We used conditional mutagenesis and lineage tracing to show that NRP1 is expressed in JG cells where it regulates their function. Cell-specific Nrp1 knockout mice present with renin paucity in JG cells and struggle to adapt to a homeostatic challenge to sodium balance. The results support the versatility of renin-producing cells in the kidney and may open new avenues for therapeutic approaches.

Terapias de reemplazo renal agudo en pacientes críticos

Acute kidney injury (AKI) is defined as the abrupt deterioration of renal excretory function, often observed in critically ill patients. The incidence of AKI worldwide ranges between 20 and 200 cases per million population. Sepsis and septic shock contribute to 25-75% of AKI cases. Regardless of the cause, loss of fluid and electrolyte homeostasis and the accumulation of nitrogenous wastes lead to uremia, hyperkalemia, water and sodium retention, and metabolic acidosis. Renal replacement therapies (RRT) aim to mitigate these effects and prevent death associated with kidney failure. There are various modalities of RRT, including intermittent hemodialysis, continuous RRT, as well as different solute elimination techniques. There have been significant advances in membrane technologies and the addition of substances to improve biocompatibility, in addition to new anticoagulation strategies. The aim of this article is to review current RRT alternatives and comment on recommendations regarding their dosage and timing for starting and discontinuing therapy.

Compositional Aspects of Beverages Designed to Promote Hydration Before, During, and After Exercise: Concepts Revisited.

Hypohydration can impair aerobic performance and deteriorate cognitive function during exercise. To minimize hypohydration, athletes are recommended to commence exercise at least euhydrated, ingest fluids containing sodium during long-duration and/or high-intensity exercise to prevent body mass loss over 2% and maintain elevated plasma osmolality, and rapidly restore and retain fluid and electrolyte homeostasis before a second exercise session. To achieve these goals, the compositions of the fluids consumed are key; however, it remains unclear what can be considered an optimal formulation for a hydration beverage in different settings. While carbohydrate-electrolyte solutions such as sports drinks have been extensively explored as a source of carbohydrates to meet fuel demands during intense and long-duration exercise, these formulas might not be ideal in situations where fluid and electrolyte balance is impaired, such as practicing exercise in the heat. Alternately, hypotonic compositions consisting of moderate to high levels of electrolytes (i.e., ≥45 mmol/L), mainly sodium, combined with low amounts of carbohydrates (i.e., <6%) might be useful to accelerate intestinal water absorption, maintain plasma volume and osmolality during exercise, and improve fluid retention during recovery. Future studies should compare hypotonic formulas and sports drinks in different exercise settings, evaluating different levels of sodium and/or other electrolytes, blends of carbohydrates, and novel ingredients for addressing hydration and rehydration before, during, and after exercise.

Tangram of Sodium and Fluid Balance.

Homeostasis of fluid and electrolytes is a tightly controlled physiological process. Failure of this process is a hallmark of hypertension, chronic kidney disease, heart failure, and other acute and chronic diseases. While the kidney remains the major player in the control of whole-body fluid and electrolyte homeostasis, recent discoveries point toward more peripheral mechanisms leading to sodium storage in tissues, such as skin and muscle, and a link between this sodium and a range of diseases, including the conditions above. In this review, we describe multiple facets of sodium and fluid balance from traditional concepts to novel discoveries. We examine the differences between acute disruption of sodium balance and the longer term adaptation in chronic disease, highlighting areas that cannot be explained by a kidney-centric model alone. The theoretical and methodological challenges of more recently proposed models are discussed. We acknowledge the different roles of extracellular and intracellular spaces and propose an integrated model that maintains fluid and electrolyte homeostasis and can be distilled into a few elemental players: the microvasculature, the interstitium, and tissue cells. Understanding their interplay will guide a more precise treatment of conditions characterized by sodium excess, for which primary aldosteronism is presented as a prototype.

Bile acid receptors and renal regulation of water homeostasis.

The kidney is the key organ responsible for maintaining the body's water and electrolyte homeostasis. About 99% of the primary urine filtered from the Bowman's capsule is reabsorbed along various renal tubules every day, with only 1-2L of urine excreted. Aquaporins (AQPs) play a vital role in water reabsorption in the kidney. Currently, a variety of molecules are found to be involved in the process of urine concentration by regulating the expression or activity of AQPs, such as antidiuretic hormone, renin-angiotensin-aldosterone system (RAAS), prostaglandin, and several nuclear receptors. As the main bile acid receptors, farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor 1 (TGR5) play important roles in bile acid, glucose, lipid, and energy metabolism. In the kidney, FXR and TGR5 exhibit broad expression across all segments of renal tubules, and their activation holds significant therapeutic potential for numerous acute and chronic kidney diseases through alleviating renal lipid accumulation, inflammation, oxidative stress, and fibrosis. Emerging evidence has demonstrated that the genetic deletion of FXR or TGR5 exhibits increased basal urine output, suggesting that bile acid receptors play a critical role in urine concentration. Here, we briefly summarize the function of bile acid receptors in renal water reabsorption and urine concentration.

The condition of electrolyte homeostasis in children with hereditary hemolytic anemia

Objective. Determine the content of electrolytes in the blood serum depending on the severity of anemia in children with hereditary hemolytic anemia.Material and methods. Observations were made on 36 children with hereditary hemolytic anemia (NGA) aged between 3 to 14 years. The distribution by gender was as follows: 16 girls (44.5%) and 20 boys (55.5%). The average age of the participants during the study was 9.5±0.45 years. These children were categorized into three groups based on anemia severity. Primary school-aged children formed the majority, followed by preschoolers, with senior school-aged children being the least in number. Upon admission to the clinic, a thorough examination of each child was conducted, encompassing a detailed complete blood count, erythrocyte morphology, biochemical blood tests (measuring total bilirubin and its fractions), blood serum electrolyte levels (K+, Na+, Ca+, Fe+), and an analysis of bone marrow punctate.Results and discussion. Electrolyte analysis yielded these findings: In children with mild HHA (14 patients), compared with the control group, the concentration of blood electrolytes (K+, Na+, Ca+, Fe+) were within the normal range. In children with moderate HHA (12 patients), the concentration of Fe+ was slightly higher compared with the control and the first group, respectively, and there was also a slight increase in the concentrations of K+, Na+, Ca+ compared with healthy children and children with mild HHA. In children with severe HHA (10 patients), as a result of the development of a hemolytic crisis, the concentration of electrolytes in the blood serum is significantly higher than K+, Na+, Ca+, Fe+ compared with children in the control group K+, Na+, Ca+, Fe+ and patients with mild and moderate, respectively.Conclusion. The study revealed significant clinical changes in the internal organs, as well as pronounced metabolic disorders in the body, due to chronic hemic hypoxia and impaired blood electrolyte composition.

Implications of deltamethrin on hematology, cardiac pathology, and gene expression in Nile tilapia (Oreochromis niloticus) and its possible amelioration with Shatavari (Asparagus racemosus).

Deltamethrin (DM) is one of the extensively used pyrethroids for controlling ectoparasites. Unfortunately, DM is highly toxic to fish as it primarily targets the sodium channels of the plasma membrane thereby affecting their cardiac and nervous systems. The present study investigated the protective efficacy of Shatavari (Asparagus racemosus) against DM-induced cardiotoxicity in Nile tilapia (Oreochromis niloticus). The fish were segregated into nine groups having 36 fish/group maintained in triplicates exposed to DM (1µg/L) and fed with a diet containing three different concentrations (10g, 20g, and 30g/kg feed) of aqueous extract of A. racemosus (ARE) for 21 days. DM caused significant alterations in the blood and serum parameters, and expression of cardiac and apoptotic genes compared to the control group. The ARE cotreatment significantly reduced the increase in serum transaminases, creatine kinase, and lactate dehydrogenase levels induced by DM. ARE facilitated the regain of electrolyte (sodium, potassium, chloride) homeostasis and antioxidants such as catalase, superoxide dismutase, glutathione peroxidase, and glutathione in DM-exposed fish. The cardiac histology exhibited loose separation of the cardiomyocytes and myofibrillar loss in the DM group which was ameliorated in the DM-ARE cotreatment group. Significant modulations were observed in the expression of cardiac-specific genes (gata4, myh6, tnT, cox1) and apoptosis signaling genes and proteins (HSP70, bax, bcl-2, caspase3), in the cotreatment group compared to the DM-exposed group. The current study suggests that ARE possesses potential cardioprotective properties that are effective in mitigating the toxic effects induced by DM via ameliorating oxidative stress, electrolyte imbalance, and apoptosis in tilapia.

Sensorineural Hearing Loss in Patients With Chronic Kidney Disease: A Comprehensive Review.

This article aims to ascertain the prevalence of loss of hearing in patients with chronic kidney disease (CKD) and also to examine potential causes of sensorineural hearing loss (SNHL) in patients suffering from CKD. It has been discovered in recent years that there is a relationship between the occurrence of SNHL and CKD. Nowadays many people are suffering from CKD. These patients deal with several otorhinolaryngological issues, such as SNHL, candidiasis, epistaxis, halitosis, dysgeusia, xerostomia, and lip and thyroid malignancies. One of the most frequent otorhinolaryngological complications is audiovestibular system impairment. There are various proposed mechanisms for the appearance of loss of hearing in people suffering from CKD. The kidney and the inner ear have multiple functional and structural similarities, which may be the cause of these problems in CKD patients. In addition, changes in the homeostasis of water and electrolytes can affect the endolymphatic fluid and result in endolymphatic hydrops. Finally, some medications, like aminoglycosides and loop diuretics, are well known for their ototoxicity and are utilized to treat patients with CKD. Only a small number of population-based research have so far been able to show a connection between CKD and audiovestibular system impairment. Some investigationhasshown that CKD patients are more likely than healthy people to experience vestibular impairment. The quality of life of a patient can be reduced by hearing loss. People with hearing loss experience communication issues in daily life, which negatively affects their cognitive and psychosocial functioning. Social isolation and a poor quality of life in terms of health can all result from hearing loss. In addition, decreased renal function has also been linked to poor quality of life, hospitalization, and cognitive dysfunction.

Utilizing a Machine Learning Approach to Define Racial Difference in Multi-Systemic Impact of Monoclonal Protein in Patient with Multiple Myeloma

Multiple myeloma (MM) is the second common hematologic malignancy characterized by the clonal proliferation of plasma cells. While the clinical outcomes of MM have been improved significantly, there remains an intriguing observation regarding the potential influence of race on disease biology and treatment response. In MM, the malignant plasma cell clone not only disrupts the local bone marrow microenvironment but also exerts a systemic impact on various physiological processes result in significant derangements in immune function, hematopoiesis, renal function, bone metabolism, and electrolyte homeostasis. Understanding the extent of this systemic impact and its potential variation between racial groups is crucial for optimizing patient care and treatment strategies. Here, we hypothesized that the systemic impact of the plasma cell clone does not differ significantly between African American and Caucasian patients. We employed a machine learning approach to capture the full spectrum of systemic effects comprehensively. Our novel model was trained to predict the magnitude of the plasma cell clone, as represented by serum monoclonal protein levels. By systematically comparing model performance with and without the inclusion of race as a variable, we sought to evaluate the potential influence of race on the systemic impact of the plasma cell clone. Method: A total of 171 patients with plasma cell dyscrasias including 1,472 observations were analyzed. where the upper limit of the observed M-spike was 3.5 gr/dL. Forty three clinical and lab variables as predictors of M-spike were fed into the machine learning model. Two lagged variables as the last two preceding M-spike values by the same subject were included. The random forest model was used, where regression forests are an ensemble of different regression trees and are used for nonlinear multiple regression. The goal of using a large number of trees was to train enough that each feature had a chance to appear in several models. The data was randomly split into a training set (80%) and a test set (20%), and a regression tree was built with the training set and then validated using the test set. Bootstrapping was used to generate a collection of data sets (n=500). Importance was measured by leaving a covariate out of models and comparing performance with its inclusion. Result: The training set used to develop the ML algorithm comprised 749 patient-based observations, which represented ~50% of the patient-based observations. The number of observations at each M-Spike value and the distribution of M-Spike values measured by SPEP are shown (Fig. 1). The residual distribution of the RF model indicated that nearly all M-spike values determined using the 43 variables distributed equally on either side of zero. The addition of race as variables did not significantly change the residual plots. The weighted value of each of the 43 independent variables was determined by individually removing a variable from the ML algorithm and measuring its effect on the mean squared error (MSE). As shown, removal of the first lagged M-spike, serum total protein, second-lagged M-spike, serum IgG, serum IgM, and serum IgA, had the greatest effects on the ML algorithm. The effect of race was then added to the ML algorithm. However, patient race had a low weighted value compared to the other variables included in the ML algorithm (Fig-2). M-spike values determined using the ML algorithm correlated highly with M-spike values determined using the laboratory measured SPEP values as indicated by the proximity of the Pearson and Spearman correlation coefficients to +1 . Using the 43 independent variables, the Pearson coefficient was 0.96 and the Spearman coefficient was 0.91, when M-spike values determined using the ML algorithm were compared to laboratory determined M-spike values. When race was added as a variable in the ML algorithm, the Pearson coefficient was 0.95 and the Spearman coefficient was 0.94 which is not significantly different. Conclusion: Here, we present the results of our machine learning analysis, which further supports our hypothesis and sheds light on the potential racial difference in the overall systemic impact of MM. Understanding the factors underlying racial disparities in MM will pave the way for more personalized and equitable treatment strategies, ultimately improving patient outcomes and overall disease management.

Sex differences in renal transporters: assessment and functional consequences.

Mammalian kidneys are specialized to maintain fluid and electrolyte homeostasis. The epithelial transport processes along the renal tubule that match output to input have long been the subject of experimental and theoretical study. However, emerging data have identified a new dimension of investigation: sex. Like most tissues, the structure and function of the kidney is regulated by sex hormones and chromosomes. Available data demonstrate sex differences in the abundance of kidney solute and electrolyte transporters, establishing that renal tubular organization and operation are distinctly different in females and males. Newer studies have provided insights into the physiological consequences of these sex differences. Computational simulations predict that sex differences in transporter abundance are likely driven to optimize reproduction, enabling adaptive responses to the nutritional requirements of serial pregnancies and lactation - normal life-cycle changes that challenge the ability of renal transporters to maintain fluid and electrolyte homeostasis. Later in life, females mayalso undergo menopause, which is associated with changes in disease risk. Although numerous knowledge gaps remain, ongoing studies will provide further insights into the sex-specific mechanisms of sodium, potassium, acid-base and volume physiology throughout the life cycle, which may lead to therapeutic opportunities.

Abstract P103: Higher Preoperative Plasma Aldosterone Concentrations Are Associated With Elevated Risk Of Atrial Fibrillation After Chronic Total Occlusion Percutaneous Coronary Intervention

Background: Postoperative atrial fibrillation (POAF) is associated with poor outcomes in patients with coronary chronic total occlusions (CTO). Aldosterone is a steroid hormone that regulates fluid and electrolyte homeostasis and is known to increase the risk of proarrhythmia. This study aimed to explore the additional value of preoperative plasma aldosterone levels for predicting POAF after CTO percutaneous coronary intervention (PCI). Methods: We conducted a prospective cohort study involving consecutive patients with a left ventricular ejection fraction (LVEF) greater than 50% requiring CTO-PCI in the First Affiliated Hospital of Chengdu Medical College. Patients were excluded if they had a history of AF, preoperative endocarditis and/or a ventricular assist device. Plasma aldosterone levels, echocardiography and transforming growth factor beta1 (TGF-β1) examination were assessed before percutaneous recanalization. The primary endpoint was the occurrence of POAF within 30 days after percutaneous recanalization. New-onset POAF after CTO-PCI was defined as any episode detected via continuous in-hospital electrocardiogram/telemetry monitoring and documented by a physician in the chart, regardless of duration or need for treatment. Results: Thirty-eight of 268 (14.2%) patients had POAF. Compared with controls, patients experiencing POAF were significantly older, had a higher body mass index, had diabetes and hypertension, and had higher preoperative plasma aldosterone levels. In logistic regression analysis, higher plasma aldosterone levels exhibited 1.75-fold higher odds (95% confidence interval [CI], 1.15-2.32, P=0.004) for the presence of POAF, which was significant in the adjusted model (odds ratio [OR], 1.82 [95% CI, 1.21-2.45], P=0.007). Reverse transcriptase PCR analysis performed on the left atrial appendage and plasma examination revealed that TGF-β1 was activated in POAF patients. Conclusion: Higher plasma aldosterone levels are associated with increased odds for POAF in patients with CTO-PCI, even in the absence of primary aldosteronism, implying that plasma aldosterone levels might be a target for POAF risk stratification after CTO-PCI.

Abstract P385: Sex-specific Long Non-coding Gene Expression In Rat Nephron Segments

Transcriptomic and proteomic approaches have identified electrolyte transporters, channels and claudins with sex-specific expression along the nephron which adapt to physiological stressors in a sex-specific manner to maintain proper fluid and electrolyte homeostasis. Yet, less is known how long non-coding gene expression in specific nephron segments differs between sexes. We performed polyA-independent RNA-seq on manually isolated proximal tubule (PT) and medullary thick ascending limb (mTAL) from 6-7-week-old male and female Dahl salt sensitive rats. Sex specific gene expression differences [log2(fold change) ≥ 0.5 or ≤ -0.5; p adj ≤ 0.05] are summarized in the table. More sex-specific differences of both protein coding and lncRNA genes were detected in PT compared to mTAL. lncRNAs were less likely to demonstrate sex-specific differences than protein coding genes (p=2.59e-12 for PT and p=5.68e-3 for mTAL). Rare lncRNAs were expressed in one sex or the other (sex-exclusive). An interesting example is ENSRNOG00000069167 and ENSRNOG00000063718 which are transcribed on opposite strands from an overlapping sequence in male or female mTAL, respectively. Multiple sex-exclusive lncRNAs were colocalized with protein coding genes significantly enriched in the same sex, suggesting they may be co-regulated within a specific chromatin domain. For example, ENSRNOG00000068738 was exclusively expressed in male PT and is colocalized in a ~560-kbp region with Pcnx1 and Sipa1l1, both of which were also enriched in male PT. Collectively, these results extend our understanding of sex-specific gene expression differences in these nephron segments to include long non-coding genes.

Dysregulation of intestinal epithelial electrolyte transport in canine chronic inflammatory enteropathy and the role of the renin-angiotensin-aldosterone-system.

Chronic diarrhea is a hallmark sign of canine chronic inflammatory enteropathy (CIE), leading to fluid and electrolyte losses. Electrolyte homeostasis is regulated by the renin-angiotensin-aldosterone-system (RAAS), which might be involved in (counter-)regulating electrolyte losses in canine CIE. Whether and which electrolyte transporters are affected or if RAAS is activated in canine CIE is unknown. Thus, intestinal electrolyte transporters and components of the RAAS were investigated in dogs with CIE. Serum RAAS fingerprint analysis by mass spectrometry was performed in 5 CIE dogs and 5 healthy controls, and mRNA levels of intestinal electrolyte transporters and local RAAS pathway components were quantified by RT-qPCR in tissue biopsies from the ileum (7 CIE, 10 controls) and colon (6 CIE, 12 controls). Concentrations of RAAS components and mRNA expression of electrolyte transporters were compared between both groups of dogs and were tested for associations among each other. In dogs with CIE, associations with clinical variables were also tested. Components of traditional and alternative RAAS pathways were higher in dogs with CIE than in healthy controls, with statistical significance for Ang I, Ang II, and Ang 1-7 (all p < 0.05). Expression of ileal, but not colonic electrolyte transporters, such as Na+/K+-ATPase, Na+/H+-exchanger 3, Cl- channel 2, down-regulated in adenoma, and Na+-glucose-cotransporter (all p < 0.05) was increased in CIE. Our results suggest that the dys- or counter-regulation of intestinal electrolyte transporters in canine CIE might be associated with a local influence of RAAS. Activating colonic absorptive reserve capacities may be a promising therapeutic target in canine CIE.

Estrogen-induced signalling and the renal contribution to salt and water homeostasis

The kidney is considered to be one of the most estrogen-responsive, not reproductive organs in the body. Different estrogen receptors (ERs) show sex-specific differences in expression along the nephron and the expression of different ERs also changes with the estrous cycle of the female. The kidney becomes more estrogen-sensitive when estradiol levels are at their highest, just prior to ovulation. This review discusses the different mechanisms by which estradiol can modify the salt and water conservation processes of the kidney through transporter regulation to support the fluid and electrolyte homeostasis changes required in mammalian reproduction. The kidney plays a critical role in regulating blood pressure by controlling fluid homeostasis, and so protects the female cardiovascular system from dramatic changes in whole body fluid volume that occur at critical points in the human menstrual cycle and in pregnancy. This is augmented by the direct actions of estradiol on the cardiovascular system, for example through the direct stimulation of endothelial nitric oxide (NO) synthase, which releases NO to promote vasodilation. This and other mechanisms are less evident in the male and give women a degree of cardiovascular protection up until menopause, when the risks of cardiovascular disease and chronic kidney disease begin to match the risks experienced by males.

Osteocalcin: A Multifaceted Bone-Derived Hormone.

Together, loss- and gain-of-function experiments have identified the bone-derived secreted molecule osteocalcin as a hormone with a broad reach in rodents and primates. Following its binding to one of three receptors, osteocalcin exerts a profound influence on various aspects of energy metabolism as well as steroidogenesis, neurotransmitter biosynthesis and thereby male fertility, electrolyte homeostasis, cognition, the acute stress response, and exercise capacity. Although this review focuses mostly on the regulation of energy metabolism by osteocalcin, it also touches on its other functions. Lastly, it proposes what could be a common theme between the functions of osteocalcin and between these functions and the structural functions of bone.

Inhibition of serum- and glucocorticoid-induced kinase 1 ameliorates hydrocephalus in preclinical models

BackgroundHydrocephalus is a pathological accumulation of cerebrospinal fluid (CSF), leading to ventriculomegaly. Hydrocephalus may be primary or secondary to traumatic brain injury, infection, or intracranial hemorrhage. Regardless of cause, current treatment involves surgery to drain the excess CSF. Importantly, there are no long-term, effective pharmaceutical treatments and this represents a clinically unmet need. Many forms of hydrocephalus involve dysregulation in water and electrolyte homeostasis, making this an attractive, druggable target.MethodsIn vitro, a combination of electrophysiological and fluid flux assays was used to elucidate secretory transepithelial electrolyte and fluid flux in a human cell culture model of the choroid plexus epithelium and to determine the involvement of serum-, glucocorticoid-induced kinase 1 (SGK1). In vivo, MRI studies were performed in a genetic rat model of hydrocephalus to determine effects of inhibition of SGK1 with a novel inhibitor, SI113.ResultsIn the cultured cell line, SI113 reduced secretory transepithelial electrolyte and fluid flux. In vivo, SI113 blocks the development of hydrocephalus with no effect on ventricular size of wild-type animals and no overt toxic effects. Mechanistically, the development of hydrocephalus in the rat model involves an increase in activated, phosphorylated SGK1 with no change in the total amount of SGK1. SI113 inhibits phosphorylation with no changes in total SGK1 levels in the choroid plexus epithelium.ConclusionThese data provide a strong preclinical basis for the use of SGK1 inhibitors in the treatment of hydrocephalus.

Circulating renin-angiotensin systems mediated feedback controls over the mean-arterial pressure

The renin-angiotensin systems play pivotal role in cardiovascular physiology through its effects on regulating blood pressure and electrolyte homeostasis. Components of circulating RAS (cRAS) that include precursor angiotensinogen, two critical enzymes (renin and angiotensin-converting enzyme, ACE), their bioactive products, angiotensin- I, II together with its receptors (AT1R and AT2R) essentially determine this homeostasis. Most classical studies, however, showed the deleterious role of cRAS in elevating the blood pressure. Contemporary discovery of non-canonical components of the RAS has challenged this classic hypothesis that it can only exert deleterious effects on the cardiovascular systems. Using the classic cRAS model, we have designed in-silico experiments to test the hypothesis that AT2R-mediated feedback effects play pivotal role for maintaining the normal variation of the mean-arterial pressure (MAP).Beside the AT2R-mediation of downstream singling pathways consisting of several non-canonical RAS components, this study first time illustrated AT2R mediated feedback controls over the blood pressure regulation: one that impedes AT1R activity, and the other that downregulates renin. It has been shown that relatively stronger suppression of renin activity significantly contributes in maintaining the normal MAP and that tight AT2R-mediated regulation is relaxed in hyper-and hypotension. This control mechanism is noted to be robustly maintained with the MAP variations through an established linear steady-state relationship among renin, angiotensin I and angiotensin II. This examination suggests that AT2R-mediated downregulation of renin activities potentially counteracts the AT1R-mediated deleterious actions of Ang II. This study, therefore, provides a solid ground for considering different AT2 receptor adaptor protein and direct agonism at AT2R that can cause greater effects along with contemporary approaches of blocking AT1R mediation to attenuate hypertension or other cardiovascular disorders.

Elucidating the Proximal Tubule HNF4A Gene Regulatory Network in Human Kidney Organoids.

HNF4 genes promote proximal tubule differentiation in mice, but their function in human nephrogenesis is not fully defined. This study uses human pluripotent stem cell (PSC)-derived kidney organoids as a model to investigate HNF4A and HNF4G functions. The loss of HNF4A , but not HNF4G , impaired reabsorption-related molecule expression and microvilli formation in human proximal tubules. Cleavage under targets and release using nuclease (CUT&RUN) sequencing and CRISPR-mediated transcriptional activation (CRISPRa) further confirm that HNF4A directly regulates its target genes. Human kidney organoids provide a good model for studying transcriptional regulation in human kidney development. The proximal tubule plays a major role in electrolyte homeostasis. Previous studies have shown that HNF4A regulates reabsorption-related genes and promotes proximal tubule differentiation during murine kidney development. However, the functions and gene regulatory mechanisms of HNF4 family genes in human nephrogenesis have not yet been investigated. We generated HNF4A -knock out (KO), HNF4G -KO, and HNF4A/4G -double KO human pluripotent stem cell lines, differentiated each into kidney organoids, and used immunofluorescence analysis, electron microscopy, and RNA-seq to analyze them. We probed HNF4A-binding sites genome-wide by cleavage under targets and release using nuclease sequencing in both human adult kidneys and kidney organoid-derived proximal tubular cells. Clustered Regularly Interspaced Short Palindromic Repeats-mediated transcriptional activation validated HNF4A and HNF4G function in proximal tubules during kidney organoid differentiation. Organoids lacking HNF4A , but not HNF4G , showed reduced expression of transport-related, endocytosis-related, and brush border-related genes, as well as disorganized brush border structure in the apical lumen of the organoid proximal tubule. Cleavage under targets and release using nuclease revealed that HNF4A primarily bound promoters and enhancers of genes that were downregulated in HNF4A -KO, suggesting direct regulation. Induced expression of HNF4A or HNF4G by CRISPR-mediated transcriptional activation drove increased expression of selected target genes during kidney organoid differentiation. This study reveals regulatory mechanisms of HNF4A and HNF4G during human proximal tubule differentiation. The experimental strategy can be applied more broadly to investigate transcriptional regulation in human kidney development.

Development of cochlear spiral ligament fibrocytes of the common marmoset, a nonhuman model animal

Spiral ligament fibrocytes generate potassium gradients, which hair cells require to convert mechanical sound waves into electrical palsy. Together with the stria vascularis, they regulate endolymph electrolyte homeostasis. Developing spiral ligament fibrocytes and generating endocochlear potential with an appropriate endolymph ion composition are essential for hearing. Understanding spiral ligament fibrocyte development is useful for studying age-related and genetic hearing loss, as well as for regenerative therapy and cochlear immunology. Despite interspecies differences, most studies of cochlear development have been conducted in rodent models due to the difficulty of using human fetal samples. This study investigated the cochlear development of spiral ligament fibrocytes in a small New World monkey species, the common marmoset (Callithrix jacchus). We examined the developmental expression of specific genes in spiral ligament fibrocytes, including those essential for the generation of endolymphatic potential. Our results showed that this animal model of spiral ligament fibrocyte development is similar to that of humans and is a suitable alternative for the analysis of human cochlear development. The time course established in this study will be useful for studying the primate-specific developmental biology of the inner ear, which may lead to novel treatment strategies for human hearing loss.

Time to eRAASe chronic inflammation: current advances and future perspectives on renin-angiotensin-aldosterone-system and chronic intestinal inflammation in dogs and humans.

Chronic idiopathic intestinal inflammation is an increasing worldwide problem that affects companion animals, especially dogs, and human patients. Although these disease entities have been intensely investigated recently, many questions remain, and alternative therapeutic options are needed. Diarrhea caused by dysregulation of intestinal electrolyte transport and subsequent fluid and electrolyte losses often leads to secondary consequences for the patient. Currently, it is not exactly clear which mechanisms are involved in the dysregulation of intestinal fluid absorption, but differences in intestinal electrolyte shifts between human and canine patients suggest species-specific regulatory or counterregulatory mechanisms. Several intestinal electrolyte transporters are differentially expressed in human patients with inflammatory bowel disease (IBD), whereas there are virtually no studies on electrolyte transporters and their endocrine regulation in canine chronic inflammatory enteropathy. An important mechanism involved in regulating fluid and electrolyte homeostasis is the renin-angiotensin-aldosterone-system (RAAS), which may affect intestinal Na+ transport. While RAAS has previously been considered a systemic regulator of blood pressure, additional complex roles of RAAS in inflammatory processes have been unraveled. These alternative RAAS pathways may pose attractive therapeutic targets to address diarrhea and, thus, electrolyte shifts in human IBD and canine chronic inflammatory enteropathy. This article comparatively summarizes the current knowledge about electrolyte transport in human IBD and canine chronic inflammatory enteropathy and the role of RAAS and offers perspectives for novel therapeutic avenues.