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Kidney tubuloids are cell models that are derived from human or mouse renal epithelial cells and show high similarities with their in vivo counterparts. Tubuloids grow polarized in 3D, allow for long-term expansion, and represent multiple segments of the nephron, as shown by their gene expression pattern. In addition, human tubuloids form tight, functional barriers and have been succesfully used for drug testing. Our knowledge of mouse tubuloids, on the other hand, is only minimal. In this study, we further characterized mouse tubuloids and differentiated them towards the collecting duct, which led to a significant upregulation of collecting duct-specific mRNAs of genes and protein expression, including the water channel AQP2 and the sodium channel ENaC. Differentiation resulted in polarized expression of collecting duct water channels AQP2 and AQP3. Also, a physiological response to desmopressin and forskolin stimulation by translocation of AQP2 to the apical membrane was demonstrated. Furthermore, amiloride-sensitive ENaC-mediated sodium uptake was shown in differentiated tubuloids using radioactive tracer sodium. This study demonstrates that mouse tubuloids can be differentiated towards the collecting duct and exhibit collecting duct-specific function. This illustrates the potential use of mouse kidney tubuloids as novel in vitro models to study (patho)physiology of kidney diseases.

Background: Heterozygous variants in Transient receptor potential melastatin type 7 ( TRPM7 ), encoding an essential and ubiquitously expressed cation channel, may cause hypomagnesemia, but current evidence is insufficient to draw definite conclusions and it is unclear whether any other phenotypes can occur., Methods: Individuals with unexplained hypomagnesemia underwent whole-exome sequencing which identified TRPM7 variants. Pathogenicity of the identified variants was assessed by combining phenotypic, functional and in silico analyses., Results: We report three new heterozygous missense variants in TRPM7 (p.Met1000Thr, p.Gly1046Arg, p.Leu1081Arg) in individuals with hypomagnesemia. Strikingly, autism spectrum disorder and developmental delay, mainly affecting speech and motor skills, was observed in all three individuals, while two out of three also presented with seizures. The three variants are predicted to be severely damaging by in silico prediction tools and structural modeling. Furthermore, these variants result in a clear loss-of-function of TRPM7-mediated magnesium uptake in vitro , while not affecting TRPM7 expression or insertion into the plasma membrane., Conclusions: This study provides additional evidence for the association between heterozygous TRPM7 variants and hypomagnesemia and adds developmental delay to the phenotypic spectrum of TRPM7 -related disorders. Considering that the TRPM7 gene is relatively tolerant to loss-of-function variants, future research should aim to unravel by what mechanisms specific heterozygous TRPM7 variants can cause disease., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the ERA.)

Background: Hypomagnesaemia with secondary hypocal-caemia (HSH) is a rare autosomal recessive disorder caused by pathogenic variants in TRPM6, encoding the channel-kinase transient receptor potential melastatin type 6. Patients have very low serum magnesium (Mg2+) levels and suffer from muscle cramps and seizures. Despite genetic testing, a subgroup of HSH patients remains without a diagnosis., Methods: In this study, two families with an HSH phenotype but negative for TRPM6 pathogenic variants were subjected to whole exome sequencing. Using a complementary combination of biochemical and functional analyses in overexpression systems and patient-derived fibroblasts, the effect of the TRPM7-identified variants on Mg2+ transport was examined., Results: For the first time, variants in TRPM7 were identified in two families as a potential cause for hereditary HSH. Patients suffer from seizures and muscle cramps due to magnesium deficiency and episodes of hypocalcaemia. In the first family, a splice site variant caused the incorporation of intron 1 sequences into the TRPM7 messenger RNA and generated a premature stop codon. As a consequence, patient-derived fibroblasts exhibit decreased cell growth. In the second family, a heterozygous missense variant in the pore domain resulted in decreased TRPM7 channel activity., Conclusions: We establish TRPM7 as a prime candidate gene for autosomal dominant hypomagnesaemia and secondary hypocalcaemia. Screening of unresolved patients with hypocalcaemia and secondary hypocalcaemia may further establish TRPM7 pathogenic variants as a novel Mendelian disorder., (© The Author(s) 2022. Published by Oxford University Press on behalf of the ERA.)

Mutations in the hepatocyte nuclear factor (HNF)1β gene ( HNF1B ) cause autosomal dominant tubulointerstitial kidney disease, a rare and heterogeneous disease characterized by renal cysts and/or malformation, maturity-onset diabetes of the young, hypomagnesemia, and hypokalemia. The electrolyte disturbances may develop in the distal part of the nephron, which is important for fine-tuning of Mg 2+ and Ca 2+ reabsorption. Therefore, we aimed to study the transcriptional network directed by HNF1β in the distal part of the nephron. We combined HNF1β chromatin immunoprecipitation-sequencing and mRNA expression data to identify direct targets of HNF1β in a renal distal convoluted tubule cell line (mpkDCT). Gene Ontology term pathway analysis demonstrated enrichment of cell polarity, cell-cell junction, and cytoskeleton pathways in the dataset. Genes directly and indirectly regulated by HNF1β within these pathways included members of the apical and basolateral polarity complexes including Crumbs protein homolog 3 ( Crb3 ), partitioning defective 6 homolog-β ( Pard6b ), and LLGL Scribble cell polarity complex component 2 ( Llgl2 ). In monolayers of mouse inner medullary collecting duct 3 cells expressing dominant negative Hnf1b, tight junction integrity was compromised, as observed by reduced transepithelial electrical resistance values and increased permeability for fluorescein (0.4 kDa) compared with wild-type cells. Expression of dominant negative Hnf1b also led to a decrease in height (30%) and an increase in surface (58.5%) of cells grown on membranes. Moreover, three-dimensional spheroids formed by cells expressing dominant negative Hnf1b were reduced in size compared with wild-type spheroids (30%). Together, these findings demonstrate that HNF1β directs a transcriptional network regulating tight junction integrity and cell structure in the distal part of the nephron. NEW & NOTEWORTHY Genetic defects in transcription factor hepatocyte nuclear factor (HNF)1β cause a heterogeneous disease characterized by electrolyte disturbances, kidney cysts, and diabetes. By combining RNA-sequencing and HNF1β chromatin immunoprecipitation-sequencing data, we identified new HNF1β targets that were enriched for cell polarity pathways. Newly discovered targets included members of polarity complexes Crb3, Pard6b, and Llgl2. Functional assays in kidney epithelial cells demonstrated decreased tight junction integrity and a loss of typical cuboidal morphology in mutant Hnf1b cells.

Background: Gitelman syndrome is a salt-losing tubulopathy characterized by hypokalemic alkalosis and hypomagnesemia. It is caused by homozygous recessive or compound heterozygous pathogenic variants in SLC12A3 , which encodes the Na + -Cl - cotransporter (NCC). In up to 10% of patients with Gitelman syndrome, current genetic techniques detect only one specific pathogenic variant. This study aimed to identify a second pathogenic variant in introns, splice sites, or promoters to increase the diagnostic yield., Methods: Long-read sequencing of SLC12A3 was performed in 67 DNA samples from individuals with suspected Gitelman syndrome in whom a single likely pathogenic or pathogenic variant was previously detected. In addition, we sequenced DNA samples from 28 individuals with one variant of uncertain significance or no candidate variant. Midigene splice assays assessed the pathogenicity of novel intronic variants., Results: A second likely pathogenic/pathogenic variant was identified in 45 (67%) patients. Those with two likely pathogenic/pathogenic variants had a more severe electrolyte phenotype than other patients. Of the 45 patients, 16 had intronic variants outside of canonic splice sites (nine variants, mostly deep intronic, six novel), whereas 29 patients had an exonic variant or canonic splice site variant. Midigene splice assays of the previously known c.1670-191C>T variant and intronic candidate variants demonstrated aberrant splicing patterns., Conclusion: Intronic pathogenic variants explain an important part of the missing heritability in Gitelman syndrome. Long-read sequencing should be considered in diagnostic workflows for Gitelman syndrome., (Copyright © 2022 by the American Society of Nephrology.)

Kidney tubuloids are cell models that are derived from human or mouse renal epithelial cells and show high similarities with their in vivo counterparts. Tubuloids grow polarized in 3D, allow for long-term expansion, and represent multiple segments of the nephron, as shown by their gene expression pattern. In addition, human tubuloids form tight, functional barriers and have been succesfully used for drug testing. Our knowledge of mouse tubuloids, on the other hand, is only minimal. In this study, we further characterized mouse tubuloids and differentiated them towards the collecting duct, which led to a significant upregulation of collecting duct-specific mRNAs of genes and protein expression, including the water channel AQP2 and the sodium channel ENaC. Differentiation resulted in polarized expression of collecting duct water channels AQP2 and AQP3. Also, a physiological response to desmopressin and forskolin stimulation by translocation of AQP2 to the apical membrane was demonstrated. Furthermore, amiloride-sensitive ENaC-mediated sodium uptake was shown in differentiated tubuloids using radioactive tracer sodium. This study demonstrates that mouse tubuloids can be differentiated towards the collecting duct and exhibit collecting duct-specific function. This illustrates the potential use of mouse kidney tubuloids as novel in vitro models to study (patho)physiology of kidney diseases., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Olde Hanhof, Dilmen, Yousef Yengej, Latta, Ammerlaan, Schreurs, Hooijmaijers, Jansen, Rookmaaker, Orhon, Verhaar and Hoenderop.)

Cyclin M (CNNM1-4) proteins maintain cellular and body magnesium (Mg 2+ ) homeostasis. Using various biochemical approaches, we have identified members of the CNNM family as direct interacting partners of ADP-ribosylation factor-like GTPase 15 (ARL15), a small GTP-binding protein. ARL15 interacts with CNNMs at their carboxyl-terminal conserved cystathionine-β-synthase (CBS) domains. In silico modeling of the interaction between CNNM2 and ARL15 supports that the small GTPase specifically binds the CBS1 and CNBH domains. Immunocytochemical experiments demonstrate that CNNM2 and ARL15 co-localize in the kidney, with both proteins showing subcellular localization in the endoplasmic reticulum, Golgi apparatus and the plasma membrane. Most importantly, we found that ARL15 is required for forming complex N-glycosylation of CNNMs. Overexpression of ARL15 promotes complex N-glycosylation of CNNM3. Mg 2+ uptake experiments with a stable isotope demonstrate that there is a significant increase of 25 Mg 2+ uptake upon knockdown of ARL15 in multiple kidney cancer cell lines. Altogether, our results establish ARL15 as a novel negative regulator of Mg 2+ transport by promoting the complex N-glycosylation of CNNMs.

Background: Variable definitions and an incomplete understanding of the gradient of reverse cardiac remodeling following continuous flow left ventricular assist device (LVAD) implantation has limited the field of myocardial plasticity. We evaluated the continuum of LV remodeling by serial echocardiographic imaging to define 3 stages of reverse cardiac remodeling following LVAD., Methods: The study enrolled consecutive LVAD patients across 4 study sites. A blinded echocardiographer evaluated the degree of structural (LV internal dimension at end-diastole [LVIDd]) and functional (LV ejection fraction [LVEF]) change after LVAD. Patients experiencing an improvement in LVEF ≥40% and LVIDd ≤6.0 cm were termed responders, absolute change in LVEF of ≥5% and LVEF <40% were termed partial responders, and the remaining patients with no significant improvement in LVEF were termed nonresponders., Results: Among 358 LVAD patients, 34 (10%) were responders, 112 (31%) partial responders, and the remaining 212 (59%) were nonresponders. The use of guideline-directed medical therapy for heart failure was higher in partial responders and responders. Structural changes (LVIDd) followed a different pattern with significant improvements even in patients who had minimal LVEF improvement. With mechanical unloading, the median reduction in LVIDd was -0.6 cm (interquartile range [IQR], -1.1 to -0.1 cm; nonresponders), -1.1 cm (IQR, -1.8 to -0.4 cm; partial responders), and -1.9 cm (IQR, -2.9 to -1.1 cm; responders). Similarly, the median change in LVEF was -2% (IQR, -6% to 1%), 9% (IQR, 6%-14%), and 27% (IQR, 23%-33%), respectively., Conclusions: Reverse cardiac remodeling associated with durable LVAD support is not an all-or-none phenomenon and manifests in a continuous spectrum. Defining 3 stages across this continuum can inform clinical management, facilitate the field of myocardial plasticity, and improve the design of future investigations.

Hypomagnesemia, seizures, and intellectual disability (HSMR) syndrome is a rare disorder caused by mutations in the cyclin M2 (CNNM2) gene. Due to the limited number of cases, extensive phenotype analyses of these patients have not been performed, hindering early recognition of patients. In this study, we established the largest cohort of HSMR to date, aiming to improve recognition and diagnosis of this complex disorder. Eleven novel variants in CNNM2 were identified in nine single sporadic cases and in two families with suspected HSMR syndrome. 25 Mg 2+ uptake assays demonstrated loss-of-function in seven out of nine variants in CNNM2. Interestingly, the pathogenic mutations resulted in decreased plasma membrane expression. The phenotype of those affected by pathogenic CNNM2 mutations was compared with five previously reported cases of HSMR. All patients suffered from hypomagnesemia (0.44-0.72 mmol/L), which could not be fully corrected by Mg 2+ supplementation. The majority of patients (77%) experienced generalized seizures and exhibited mild to moderate intellectual disability and speech delay. Moreover, severe obesity was present in most patients (89%). Our data establish hypomagnesemia, seizures, intellectual disability, and obesity as hallmarks of HSMR syndrome. The assessment of these major features offers a straightforward tool for the clinical diagnosis of HSMR., (© 2021 The Authors. Human Mutation published by Wiley Periodicals LLC.)

Aims: Acute heart failure (AHF) leads to a drastic increase in mortality and rehospitalization. The aim of the study was to identify prognostic variables in a real-life population of AHF patients admitted to the emergency department with acute shortness of breath., Methods and Results: We evaluated potential predictors of mortality in 728 consecutive patients admitted to the emergency department with AHF. Possible predictors of all-cause and cardiovascular (CV) mortality were investigated by Cox and Fine and Gray models at multivariable analysis. Among the 728 patients, 256 died during the entire follow-up, 142 of these due to CV cause. The 1 year mortality rate was 20%, with the highest risk of death during the index hospitalization (with 8% estimate in-hospital mortality at 30 days). A higher risk of events during the index hospitalization was more evident for the CV deaths, for which we found a cumulative 1 year incidence of 12% with a cumulative incidence in the first 30 days of hospitalization of about 5%. At multivariable analysis, age (P < 0.001), New York Heart Association (NYHA) class IV vs. I-II-III (P = 0.001), systolic blood pressure (P < 0.001), non-cardiac co-morbidities (≥3 vs. 0, P = 0.05), oxygen saturation (P = 0.03), serum creatinine (P < 0.001), and left ventricular ejection fraction (LVEF) (40-49% vs. <40%, P = 0.004; ≥50% vs. <40%, P = 0.003) were independent predictors of all-cause mortality during the entire follow-up. Age (P = 0.03), systolic blood pressure (P = 0.01), oxygen saturation (P = 0.03), serum creatinine (P = 0.02), and LVEF (40-49% vs. <40%, P = 0.03; ≥50% vs. <40%, P = 0.004) were independent predictors of CV mortality during the entire follow-up. NYHA class IV vs. I-II-III (P < 0.001), serum creatinine (P = 0.01), and LVEF (40-49% vs. <40%, P = 0.02; ≥50% vs. <40%, P < 0.001) remained independent predictors for in-hospital death, while only serum creatinine (P = 0.04), LVEF (40-49% vs. <40%: 0.32, P = 0.04; ≥50% vs. <40%, P < 0.001), and NYHA class vs. I-II-III (P = 0.02) remained predictors for in-hospital CV mortality., Conclusions: In this real-life cohort of patients with AHF, the results showed a similar mortality rate comparing with other analysis and with the most important registries. Age, NYHA class IV, systolic blood pressure, creatinine levels, sodium levels, and ejection fraction were independent predictors of 1 year mortality, while LVEF <40% was the only predictor of both all-cause mortality and CV mortality., (© 2020 The Authors. ESC Heart Failure published by John Wiley & Sons Ltd on behalf of the European Society of Cardiology.)

Background: Under-reporting of clinical trial results inhibits dissemination of knowledge, limits understanding of therapeutic interventions, and may ultimately harm patients., Objectives: This study examined the rates and predictors of heart failure clinical trial publication and how they have changed over time., Methods: This study assessed cross-sectional analysis of all heart failure clinical trials registered on ClinicalTrials.gov with at least 2 years follow-up after trial completion. The content area was chosen for the robust clinical trial activity in the field. The primary outcome was manuscript publication with multivariable proportional hazards adjustment to identify associations with publication., Results: Of the 1,429 included studies, 806 (56%) were published as manuscripts, 623 were unpublished, and 97 (7%) reported results without manuscript publication. Of the total, 1,243 were completed after 2007, when the mean 1-year publication rate for interventional trials rose from 12.7% to 19.6% (p = 0.049), which was possibly associated with changes in government regulation. However, there was no further sustained improvement over time, and there was no multivariable association between later completion dates and reporting or publication of results. Funding from the National Institutes of Health and use of clinical (death, hospitalization, myocardial infarction, changes in functional classification) rather than nonclinical primary endpoints were associated with earlier publication. Whether the results were consistent with the primary study hypothesis was not associated with likelihood of publication., Conclusions: The rates of heart failure clinical trial publication or reporting of results remain unacceptably low. Additional efforts by all stakeholders, including investigators, sponsors, regulators, societies, editors, and journals are needed to improve data dissemination., (Copyright © 2020 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Heart failure (HF) patients experience a high burden of symptoms and functional limitations, and morbidity and mortality remain high despite successful therapies. The majority of HF drugs in the United States are approved for reducing hospitalization and mortality, while only a few have indications for improving quality of life, physical function, or symptoms. Patient-reported outcomes that directly measure patient's perception of health status (symptoms, physical function, or quality of life) are potentially approvable endpoints in drug development. This paper summarizes the history of endpoints used for HF drug approvals in the United States and reviews endpoints that measure symptoms, physical function, or quality of life in HF patients., (Copyright © 2020. Published by Elsevier Inc.)

Solute carrier family 41 member A1 (SLC41A1) has been suggested to mediate magnesium (Mg 2+ ) transport by several in vitro studies. However, the physiological function of SLC41A1 remains to be elucidated. In this study, cellular Mg 2+ transport assays combined with zebrafish slc41a1 knockdown experiments were performed to disclose SLC41A1 function and its physiological relevance. The gene slc41a1 is ubiquitously expressed in zebrafish tissues and is regulated by water and dietary Mg 2+ availability. Knockdown of slc41a1 in zebrafish larvae grown in a Mg 2+ -free medium resulted in a unique phenotype characterized by a decrease in zebrafish Mg content. This decrease shows that SLC41A1 is required to maintain Mg 2+ balance and its dysfunction results in renal Mg 2+ wasting in zebrafish larvae. Importantly, the Mg content of the larvae is rescued when mouse SLC41A1 is expressed in slc41a1-knockdown zebrafish. Conversely, expression of mammalian SLC41A1-p.Asp262Ala, harboring a mutation in the ion-conducting SLC41A1 pore, did not reverse the renal Mg 2+ wasting. 25 Mg 2+ transport assays in human embryonic kidney 293 (HEK293) cells overexpressing SLC41A1 demonstrated that SLC41A1 mediates cellular Mg 2+ extrusion independently of sodium (Na + ). In contrast, SLC41A1-p.Asp262Ala expressing HEK293 cells displayed similar Mg 2+ extrusion activities than control (mock) cells. In polarized Madin-Darby canine kidney cells, SLC41A1 localized to the basolateral cell membrane. Our results demonstrate that SLC41A1 facilitates renal Mg 2+ reabsorption in the zebrafish model. Furthermore, our data suggest that SLC41A1 mediates both Mg 2+ uptake and extrusion.

Mutations in the KCNA1 gene encoding the voltage-gated potassium (K+) channel Kv1.1 have been linked to rare neurological syndromes, episodic ataxia type 1 (EA1) and myokymia. In 2009, a KCNA1 mutation was identified in a large family with autosomal dominant hypomagnesemia. Despite efforts in establishing a genotype-phenotype correlation for the wide variety of symptoms in EA1, little is known on the serum magnesium (Mg2+) levels in these patients. In the present study, we describe a new de novo KCNA1 mutation in a Polish patient with tetany and hypomagnesemia. Electrophysiological and biochemical analyses were performed to determine the pathogenicity of the mutation. A female patient presented with low serum Mg2+ levels, renal Mg2+ wasting, muscle cramps, and tetanic episodes. Whole exome sequencing identified a p.Leu328Val mutation in KCNA1 encoding the Kv1.1 K+ channel. Electrophysiological examinations demonstrated that the p.Leu328Val mutation caused a dominant-negative loss of function of the encoded Kv1.1 channel. Cell surface biotinylation showed normal plasma membrane expression. Taken together, this is the second report linking KCNA1 with hypomagnesemia, thereby emphasizing the need for further evaluation of the clinical phenotypes observed in patients carrying KCNA1 mutations., (© 2018 S. Karger AG, Basel.)

Isoform 3 of the Na + -Ca 2+ exchanger (NCX3) participates in the Ca 2+ fluxes across the plasma membrane. Among the NCX family, NCX3 carries out a peculiar role due to its specific functions in skeletal muscle and the immune system and to its neuroprotective effect under stress exposure. In this context, proper understanding of the regulation of NCX3 is primordial to consider its potential use as a drug target. In this study, we demonstrated the regulation of NCX3 by protein kinase A (PKA) and C (PKC). Disparity in regulation has been previously reported among the splice variants of NCX3 therefore the activity of Ca 2+ uptake and extrusion of the two murine variants was measured using fura-2-based Ca 2+ imaging and revealed that both variants are similarly regulated. PKC stimulation diminished the Ca 2+ uptake performed by NCX3 in the reverse mode, triggered by a rise in [Ca 2+ ] i or [Na + ] i , whereas an opposite response was observed upon PKA stimulation, with a significant increase of the Ca 2+ uptake after a rise in [Ca 2+ ] i . The latter stimulation affected similarly the efflux capacity of NCX3 whereas Ca 2+ extrusion capacity remained unaffected under activation of PKC. Next, using site-directed mutagenesis, the sensitivity of NCX3 to PKC was abolished by singly mutating its predicted phosphorylation sites T529 or S695. The sensitivity to PKC might be due to the influence of T529 phosphorylation on the Ca 2+ -binding domain 1. Additionally, we showed that stimulation of NCX3 by PKA occurred through residue S524. This effect may well participate in the fight-or-flight response in skeletal muscle and the long-term potentiation in hippocampus., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

In kidney, transcellular transport of Ca 2+ is mediated by transient receptor potential vanilloid 5 and Na + -Ca 2+ exchanger 1 proteins in distal convoluted and connecting tubules (DCTs and CNTs, respectively). It is not yet understood how DCT/CNT cells can adapt to differences in tubular flow rate and, consequently, Ca 2+ load. This study aims to elucidate the molecular mechanisms by which DCT/CNT cells sense fluid dynamics to control transepithelial Ca 2+ reabsorption and whether their primary cilia play an active role in this process. Mouse primary DCT/CNT cultures were subjected to a physiologic fluid shear stress (FSS) of 0.12 dyn/cm 2 Transient receptor potential vanilloid 5 and Na + -Ca 2+ exchanger 1 mRNA levels were significantly increased upon FSS exposure compared with static controls. Functional studies with 45 Ca 2+ demonstrated a significant stimulation of transepithelial Ca 2+ transport under FSS compared with static conditions. Primary cilia removal decreased Ca 2+ transport in both static and FSS conditions, a finding that correlated with decreased expression of genes involved in transepithelial Ca 2+ transport; however, FSS-induced stimulation of Ca 2+ transport was still observed. These results indicate that nephron DCT and CNT segments translate FSS into a physiologic response that implicates an increased Ca 2+ reabsorption. Moreover, primary cilia influence transepithelial Ca 2+ transport in DCTs/CNTs, yet this process is not distinctly coupled to FSS sensing by these organelles.-Mohammed, S. G., Arjona, F. J., Latta, F., Bindels, R. J. M., Roepman, R., Hoenderop, J. G. J. Fluid shear stress increases transepithelial transport of Ca 2+ in ciliated distal convoluted and connecting tubule cells., (© FASEB.)

The transient receptor potential melastatin type 6 (TRPM6) epithelial Mg(2+) channels participate in transcellular Mg(2+) transport in the kidney and intestine. Previous reports suggested a hormonal cAMP-dependent regulation of Mg(2+) reabsorption in the kidney. The molecular details of this process are, however, unknown. Adenylate cyclase 3 (Adcy3) has been shown to colocalize with the Na(+)/Cl(-) cotransporter, a marker of the distal convoluted segment of the kidney, the principal site of TRPM6 expression. Given the critical role of TRPM6 in Mg(2+) reabsorption, an inducible kidney-specific Adcy3 deletion mouse model was characterized for blood and urinary electrolyte disturbances under a normal--and low--Mg(2+) diet. Increased urinary Mg(2+) wasting and Trpm6 mRNA levels were observed in the urine and kidney of Adcy3-deleted animals compared with wild-type controls. Serum Mg(2+) concentration was significantly lower in Adcy3-deleted animals at day 7 on the low Mg(2+) diet. Using patch clamp electrophysiology, cell surface biotinylation, and total internal reflection fluorescence live cell imaging of transfected HEK293 cells, we demonstrated that cAMP signaling rapidly potentiates TRPM6 activity by promoting TRPM6 accumulation at the plasma membrane and increasing its single-channel conductance. Comparison of electrophysiological data from cells expressing the phosphorylation-deficient S1252A or phosphomimetic S1252D TRPM6 mutants suggests that phosphorylation at this intracellular residue participates in the observed stimulation of channel activity. Altogether, these data support a physiologically relevant magnesiotropic role of cAMP signaling in the kidney by a direct stimulatory action of protein kinase A on the plasma membrane trafficking and function of TRPM6 ion channels., (Copyright © 2016 by the American Society of Nephrology.)

Background/aims: Fine-tuning of renal calcium (Ca(2+)) reabsorption takes place in the late distal convoluted and connecting tubules (DCT2/CNT) of the kidney via transcellular Ca(2+) transport. Here, Ca(2+) enters the cell at the apical side via the epithelial Ca(2+) channel transient receptor potential vanilloid 5 and is subsequently extruded at the basolateral side by the concerted actions of the plasma membrane Ca(2+) ATPases and the Na(+)/Ca(2+) exchanger 1 (NCX1). NCX1 is responsible for ∼ 70% of basolateral Ca(2+) extrusion. The aim of this study was to determine the predominant NCX1 variant in the kidney and its role in Ca(2+) transport., Methods: DCT2/CNT specific tubules were used to show the abundance of NCX1 specific isoforms. Renal NCX1 variants were cloned from mouse kidney tissue. Human Embryonic Kidney 293(T) cells were transiently transfected with NCX1.3, and Fura-2 measurements and 45Ca(2+) uptake assays were performed to determine several characteristics of NCX1.3 in the reverse mode., Results: NCX1.3 was demonstrated to be the predominant NCX1 variant in the DCT2/CNT, next to NCX1.2 and NCX1.7. NCX1.3 could be inhibited by SN-6, an NCX-specific inhibitor, whereas stimulation of the cAMP/PKA or PKC-mediated pathway did not affect Ca(2+) influx as measured in the reverse mode. Lowering intracellular Ca(2+) concentrations resulted in a decreased Ca(2+) uptake., Conclusion: NCX1.3 is the predominant NCX variant in the DCT2/CNT tubules. Its function is dependent on intracellular Ca(2+) concentrations., (© 2015 S. Karger AG, Basel.)

Study Objectives: To examine sex effects on sleep stages and electroencephalogram (EEG) spectral power in older adults., Design: Sleep was polygraphically recorded for 2 consecutive nights, and blood was sampled during the last 24 hours., Setting: The University of Chicago Clinical Research Center., Participants: Two groups of healthy nonobese older subjects: 10 men (59 +/- 2 years), and 10 postmenopausal women (63 +/- 2 years)., Interventions: N/A., Measurements and Results: A spectral analysis of the EEG was performed in the delta and alpha bands. There were no sex differences in sleep stages. Blood sampling resulted in reductions of total sleep time, sleep maintenance, slow-wave sleep, and absolute delta activity that were all larger in women than in men. In absolute values, delta and alpha activities in non-rapid eye movement (NREM) and rapid eye movement (REM) sleep were higher in women than in men, but, for delta activity, the sex differences were larger in REM than in NREM sleep. In women, but not in men, absolute delta activity in REM was decreased during blood sampling and was strongly correlated with absolute delta activity in NREM. Delta activity in REM did not dissipate across the night in either group. When normalized for the activity in REM sleep, the sex difference in delta activity in NREM sleep was reversed, with lower activity in women., Conclusions: Sex differences in sleep EEG variables are present in older adults. When normalized, delta activity in older women is lower than in older men, which may be more consistent with sex differences in subjective complaints, in fragility of sleep in the presence of environmental disturbances, and in the relationship to growth-hormone release.

Study Objectives: To examine sex differences in nocturnal growth hormone and prolactin release in older adults., Design: Sleep was polygraphically recorded for 2 consecutive nights, and blood was sampled at frequent intervals during the last 24 hours., Setting: The University of Chicago Clinical Research Center., Participants: Two groups of healthy nonobese older subjects: 10 men (59 +/- 2 years, mean +/- SEM), and 10 postmenopausal women (63 +/- 2 years)., Interventions: N/A., Measurements and Results: A spectral analysis of the electroencephalogram was performed in the delta and alpha bands. When delta activity was normalized for the activity in rapid eye movement sleep, women had lower delta activity than men. Growth hormone secretion was estimated by deconvolution. The prolactin profile was quantified by a best-fit curve. In both sexes, growth hormone was released both before and after sleep onset. In men, there was no relationship between presleep growth hormone release and subsequent sleep quality and postsleep growth hormone release correlated with delta activity. In women, presleep growth hormone release appeared to inhibit both postsleep growth hormone release and sleep consolidation. Prolactin release was related to rapid eye movement sleep and was lower in men than in women. Women with poor sleep maintenance had a lower prolactin acrophase., Conclusions: Major sex differences in the nocturnal profiles of growth hormone and prolactin and their relationship to sleep electroencephalogram variables are present in healthy older adults. Our analyses suggest that lower sleep-onset release of growth hormone in women as compared with men could be related to lower levels of delta activity. Improvements in the homeostatic control of sleep could have hormonal benefits in older adults.

For more than 30 years, growth hormone (GH) has been observed to be preferentially secreted during deep, slow-wave sleep (SWS). However, the mechanisms that underlie this robust relationship that links anabolic processes in the body with behavioral rest and decreased cerebral metabolism remain to be elucidated. Current evidence indicates that GH secretion during the beginning of sleep appears to be primarily regulated by GH-releasing hormone (GHRH) stimulation occurring during a period of relative somatostatin withdrawal, which also is associated with elevated levels of circulating ghrelin. Apparently, two populations of GHRH neurons need to be simultaneously active to stimulate, in a coordinated fashion, SWS and pituitary GH release. Pharmacological interventions that are capable of increasing the duration and/or the intensity of SWS such as oral administration of gamma-hydroxybutyrate (GHB), also increase the rate of GH release. Because the normal negative feedback exerted by GH on central GHRH is inoperative in patients with GH deficiency, it is possible that the decreased energy levels and fatigue often reported by GH-deficient adults partly reflect an alteration in sleep-wake regulation. Preliminary data from a sleep study of adults with GH deficiency using wrist actigraphy for 6 nights at home and polysomnography in the laboratory indeed show decreased total sleep time and increased sleep fragmentation in GH-deficient patients as compared with normal controls.