RRAGD-Associated Autosomal Dominant Kidney Hypomagnesemia with Cardiomyopathy: A Review on the Clinical Manifestations and Therapeutic Options.

BACKGROUND: A hereditary condition primarily affecting the kidneys and heart has newly been identified: the RRAGD-associated autosomal dominant kidney hypomagnesemia with cardiomyopathy (ADKH-RRAGD). This disorder is characterized by renal loss of magnesium and potassium, coupled with varying degrees of cardiac dysfunction. These range from arrhythmias to severe dilated cardiomyopathy, which may require heart transplantation. Mutations associated with RRAGD significantly disrupt the non-canonical branch of the mechanistic target of rapamycin complex 1 pathway. This disruption hinders the nuclear translocation and transcriptional activity of the transcription factor EB a crucial regulator of lysosomal and autophagic function. SUMMARY: All identified RRAGD variants compromise kidney function, leading to hypomagnesemia and hypokalemia of various severity. The renal phenotype for most of the variants (i.e., S76L, I221K, P119R, P119L) typically manifests in the second decade of life occasionally preceded by childhood symptoms of dilated cardiomyopathy. In contrast, the P88L variant is associated to dilated cardiomyopathy manifesting in adulthood. To date, the T97P variant has not been linked to cardiac involvement. The most severe manifestations of ADKH-RRAGD, particularly concerning electrolyte imbalance and heart dysfunction requiring transplantation in childhood appear to be associated with the S76L, I221K, P119R variants. KEY MESSAGES: This review aimed to provide an overview of the clinical presentation for ADKH-RRAGD, aiming to enhance awareness, promote early diagnosis, and facilitate proper treatment. It also reports on the limited experience in patient management with diuretics, magnesium and potassium supplements, metformin, or calcineurin and SGLT2 inhibitors.

Animal models to study cognitive impairment of chronic kidney disease.

Mild cognitive impairment (MCI) is common in people with chronic kidney disease (CKD), and its prevalence increases with progressive loss of kidney function. MCI is characterized by a decline in cognitive performance greater than expected for an individual age and education level but with minimal impairment of instrumental activities of daily living. Deterioration can affect one or several cognitive domains (attention, memory, executive functions, language, and perceptual motor or social cognition). Given the increasing prevalence of kidney disease, more and more people with CKD will also develop MCI causing an enormous disease burden for these individuals, their relatives, and society. However, the underlying pathomechanisms are poorly understood, and current therapies mostly aim at supporting patients in their daily lives. This illustrates the urgent need to elucidate the pathogenesis and potential therapeutic targets and test novel therapies in appropriate preclinical models. Here, we will outline the necessary criteria for experimental modeling of cognitive disorders in CKD. We discuss the use of mice, rats, and zebrafish as model systems and present valuable techniques through which kidney function and cognitive impairment can be assessed in this setting. Our objective is to enable researchers to overcome hurdles and accelerate preclinical research aimed at improving the therapy of people with CKD and MCI.

Renal Cystinuria and Immune Cells (T Lymphocytes) Dysfunction: What We Know about?

INTRODUCTION: Cystinuria (CYS) is the most common monogenic kidney stone disease. METHODS: Starting from an unusual case of CYS associated to primary sclerosing cholangitis, inflammatory bowel disease (IBD), and autoimmune hepatitis in a young male, we carefully review the literature and propose here a working hypothesis regarding the potential risk of cystinuric patients to develop conditions due to immune system dysregulation. To corroborate this hypothesis, we retrospectively evaluate the frequency of dysimmunity in a monocentric cohort including 36 cystinuric patients compared to healthy and disease controls. RESULTS: CYS patients have an increased prevalence of atopic disease compared to disease controls (p = 0.03) and 16.7% of CYS subjects were diagnosed with allergic disease to a variety of antigens. CONCLUSION: Further studies are needed to define the relationship between proximal tubular transport defect of CYS and dysregulated immunity.

The SGLT2 inhibitor dapagliflozin improves kidney function in glycogen storage disease XI.

Glycogen storage disease XI, also known as Fanconi-Bickel syndrome (FBS), is a rare autosomal recessive disorder caused by mutations in the SLC2A2 gene that encodes the glucose-facilitated transporter type 2 (GLUT2). Patients develop a life-threatening renal proximal tubule dysfunction for which no treatment is available apart from electrolyte replacement. To investigate the renal pathogenesis of FBS, SLC2A2 expression was ablated in mouse kidney and HK-2 proximal tubule cells. GLUT2Pax8Cre+ mice developed time-dependent glycogen accumulation in proximal tubule cells and recapitulated the renal Fanconi phenotype seen in patients. In vitro suppression of GLUT2 impaired lysosomal autophagy as shown by transcriptomic and biochemical analysis. However, this effect was reversed by exposure to a low glucose concentration, suggesting that GLUT2 facilitates the homeostasis of key cellular pathways in proximal tubule cells by preventing glucose toxicity. To investigate whether targeting proximal tubule glucose influx can limit glycogen accumulation and correct symptoms in vivo, we treated mice with the selective SGLT2 inhibitor dapagliflozin. Dapagliflozin reduced glycogen accumulation and improved metabolic acidosis and phosphaturia in the animals by normalizing the expression of Napi2a and NHE3 transporters. In addition, in a patient with FBS, dapagliflozin was safe, improved serum potassium and phosphate concentrations, and reduced glycogen content in urinary shed cells. Overall, this study provides proof of concept for dapagliflozin as a potentially suitable therapy for FBS.

[Hyponatremia and Electrolyte Disorders in Cancer Patients].

Onconephrology is a rising and rapidly expanding field of medicine in which nephrology and oncology meet each other. Besides multidisciplinary meetings, oncologists and nephrologists often discuss on timing of the treatment, dosage, and side effects management. Cancer patients often encounter different electrolyte disorders. They are mostly secondary to the tumor itself or consequences of its treatment. In the last years, the great efforts to find new therapies like targeted, immune, and cell-based led us to many new side effects. Hyponatremia, hypokalemia, hyperkalemia, hypercalcemia, and hypomagnesemia are among the most common electrolyte disorders. Data have shown a worse prognosis in patients with electrolytic imbalances. Additionally, they cause a delay in chemotherapy or even an interruption. It is important to diagnose promptly these complications and treat them. In this review, we provide a special focus on hyponatremia and its treatment as the most common electrolytes disorder in cancer patients, but also on newly described cases of hypo- and hyperkalemia and metabolic acidosis.

Thromboembolic Events after COVID-19 Vaccination: An Italian Retrospective Real-World Safety Study.

INTRODUCTION: Real-world safety studies can provide important evidence on the thromboembolic risk associated with COVID-19 vaccines, considering that millions of people have been already vaccinated against COVID-19. In this study, we aimed to estimate the incidence of thromboembolic events after COVID-19 vaccination and to compare the Oxford-AstraZeneca vaccine with other COVID-19 vaccines. METHODS: We conducted a retrospective real-world safety study using data from two different data sources: the Italian Pharmacovigilance database (Rete Nazionale di Farmacovigilanza, RNF) and the Campania Region Health system (Sistema INFOrmativo saNità CampanIA, SINFONIA). From the start date of the COVID-19 vaccination campaign (27 December 2021) to 27 September 2022, information on COVID-19 vaccinations and thromboembolic events were extracted from the two databases. The reporting rate (RR) and its 95% confidence interval (95%CI) of thromboembolic events for 10,000 doses was calculated for each COVID-19 vaccine. Moreover, the odds of being vaccinated with the Oxford-AstraZeneca vaccine vs. the other COVID-19 vaccines in cases with thromboembolic events vs. controls without thromboembolic events were computed. RESULTS: A total of 12,692,852 vaccine doses were administered in the Campania Region, of which 6,509,475 (51.28%) were in females and mostly related to the Pfizer-BioNtech vaccine (65.05%), followed by Moderna (24.31%), Oxford-AstraZeneca (9.71%), Janssen (0.91%), and Novavax (0.02%) vaccines. A total of 641 ICSRs with COVID-19 vaccines and vascular events were retrieved from the RNF for the Campania Region, of which 453 (70.67%) were in females. Most ICSRs reported the Pfizer-BioNtech vaccine (65.05%), followed by Oxford-AstraZeneca (9.71%), Moderna (24.31%), and Janssen (0.91%). A total of 2451 events were reported in the ICSRs (3.8 events for ICSRs), of which 292 were thromboembolic events. The higher RRs of thromboembolic events were found with the Oxford-AstraZeneca vaccine (RR: 4.62, 95%CI: 3.50-5.99) and Janssen vaccine (RR: 3.45, 95%CI: 0.94-8.82). Thromboembolic events were associated with a higher likelihood of exposure to the Oxford-AstraZeneca vaccine compared to Pfizer-BioNtech (OR: 6.06; 95%CI: 4.22-8.68) and Moderna vaccines (OR: 6.46; 95%CI: 4.00-10.80). CONCLUSION: We observed a higher reporting of thromboembolic events with viral-vector-based vaccines (Oxford-AstraZeneca and Janssen) and an increased likelihood of being exposed to the Oxford-AstraZeneca vaccine compared to the mRNA vaccines (Pfizer-BioNtech and Moderna) among thromboembolic cases.

Kidney and blood pressure regulation-latest evidence for molecular mechanisms.

Hypertension is one of the major health problems leading to the development of cardiovascular diseases. Despite a rapid expansion in global hypertension prevalence, molecular mechanisms leading to hypertension are not fully understood largely due to the complexity of pathogenesis involving several factors. Salt intake is recognized as a leading determinant of blood pressure, since reduced dietary salt intake is related to lower morbidity and mortality, and hypertension in relation to cardiovascular events. Compared with salt-resistant populations, salt-sensitive individuals exhibit high sensitivity in blood pressure responses according to changes in salt intake. In this setting, the kidney plays a major role in the maintenance of blood pressure under the hormonal control of the renin-angiotensin-aldosterone system. In the present review, we summarize the current overview on the molecular mechanisms for modulation of blood pressure associated with renal ion channels/transporters including sodium-hydrogen exchanger isoform 3 (NHE3), Na+-K+-2Cl- cotransporter (NKCC2), sodium-chloride cotransporter (NCC), epithelial sodium channel (ENaC) and pendrin expressed in different nephron segments. In particular, recent studies on experimental animal models with deletion of renal ion channels led to the identification of several crucial physiological mechanisms and molecules involved in hypertension. These findings could further provide a potential for novel therapeutic approaches applicable on human patients with hypertension.

miRNA-23a modulates sodium-hydrogen exchanger 1 expression: studies in medullary thick ascending limb of salt-induced hypertensive rats.

BACKGROUND: The kidney is the main organ in the pathophysiology of essential hypertension. Although most bicarbonate reabsorption occurs in the proximal tubule, the medullary thick ascending limb (mTAL) of the nephron also maintains acid-base balance by contributing to 25% of bicarbonate reabsorption. A crucial element in this regulation is the sodium-hydrogen exchanger 1 (NHE1), a ubiquitous membrane protein controlling intracellular pH, where proton extrusion is driven by the inward sodium flux. MicroRNA (miRNA) expression of hypertensive patients significantly differs from that of normotensive subjects. The aim of this study was to determine the functional role of miRNA alterations at the mTAL level. METHODS: By miRNA microarray analysis, we identified miRNA expression profiles in isolated mTALs from high sodium intake-induced hypertensive rats (HSD) versus their normotensive counterparts (NSD). In vitro validation was carried out in rat mTAL cells. RESULTS: Five miRNAs involved in the onset of salt-sensitive hypertension were identified, including miR-23a, which was bioinformatically predicted to target NHE1 mRNA. Data demonstrated that miRNA-23a is downregulated in the mTAL of HSD rats while NHE1 is upregulated. Consistently, transfection of an miRNA-23a mimic in an mTAL cell line, using a viral vector, resulted in NHE1 downregulation. CONCLUSION: NHE1, a protein involved in sodium reabsorption at the mTAL level and blood pressure regulation, is upregulated in our model. This was due to a downregulation of miRNA-23a. Expression levels of this miRNA are influenced by high sodium intake in the mTALs of rats. The downregulation of miRNA-23a in humans affected by essential hypertension corroborate our data and point to the potential role of miRNA-23a in the regulation of mTAL function following high salt intake.

Telemedicine: A cornerstone of healthcare assistance during the SARS-Cov2 pandemic outbreak but also a great opportunity for the near future.

At the end of 2019, Wuhan, China, experienced an outbreak of a novel coronavirus. The SARS-CoV2 epidemiologic burden was constantly evolving, with numbers of infected persons, hospital admissions and deaths growing near exponentially. The pandemic outbreak of COVID-19 worldwide caught the health care systems in every country by storm and without a proper defense mechanism to cope and control such a pandemic, causing an overwhelming burden of illnesses that stressed the Health System capacity. In this context, telemedicine has been promoted and scaled up to reduce the risk of transmission. During the "lockdown", the AOU "Federico II" was forced to create peculiar pathways to ensure the safety of the patients and medical staff, and to keep an appropriate medical assistance, therefore it was introduced the telemedicine, wherever possible, by modifying the Information Technology (IT) related to the waiting times, rescheduling all booked visits and identifying several outpatient clinics suitable for telemedicine activities. In this paper the Authors reports their own experience with Telemedicine.

Safety and immunogenicity of the COVID-19 vaccine BNT162b2 for patients with breast and gynecological cancer on active anticancer therapy: Results of a prospective observational study.

Background: Vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are highly effective. Nevertheless, immunocompromised participants were excluded from randomized controlled clinical trials. This study evaluates the efficacy and safety of the Pfizer/BioNTech BNT162b2 (BNT162b2) vaccine in patients with breast and gynecological cancer treated with active anticancer therapy versus a control cohort of healthy participants. Methods: Immune responses to the BNT162b2 vaccine in patients with breast cancer (n = 44) or a gynecological malignancy (n = 6) on active anticancer therapy (28 on chemotherapy, mostly anthracycline- or taxane-based, and 22 on target therapy) and in a control cohort of participants without cancer (n = 67) were investigated by SARS-CoV-2 neutralizing antibody titers measured by S1-binding immunoglobulin G (IgG) concentrations assessed using the LIAISON XL tools (DiaSorin S.p.A.). Response was assessed after a second dose of the BNT162b2 vaccine administered before and at least 3 weeks after the vaccine dose. Results: Overall, 43/50 (86%) patients of the cancer cohort (74% in the breast cancer group and 100% in the gynecological malignancy group) developed IgG antibodies after the second dose of the BNT162b2 vaccine. There were no statistically significant differences in responder rates between patients treated with chemotherapy and those on target therapy. The majority of patients who received chemotherapy with or without target therapy, 21/28 (75%), developed a reliable antibody titer after a vaccine. All seven non-responder patients were undergoing an anthracycline-based regimen. Based on IgG levels (0-400 AU/ml), patients were classified as negative ('non-responders'), weakly positive, or strongly positive ('responders'). No delay in cancer therapy schedule or reported side effects were recorded after BNT162b2 vaccine administration. All healthy participants were strongly positive. Responder rates differed significantly between the two study cohorts (p < 0.001). Conclusions: Most patients develop antibody titers after the second immunization. However, given the persistence of non-responders or weak responders, additional immunization booster seems to be required, along with proactive planning in the vaccination schedule, with vaccine administration spaced out over time with respect to chemotherapy.

Dapagliflozin Prevents Kidney Glycogen Accumulation and Improves Renal Proximal Tubule Cell Functions in a Mouse Model of Glycogen Storage Disease Type 1b.

BACKGROUND: Mutations in SLC37A4, which encodes the intracellular glucose transporter G6PT, cause the rare glycogen storage disease type 1b (GSD1b). A long-term consequence of GSD1b is kidney failure, which requires KRT. The main protein markers of proximal tubule function, including NaPi2A, NHE3, SGLT2, GLUT2, and AQP1, are downregulated as part of the disease phenotype. METHODS: We utilized an inducible mouse model of GSD1b, TM-G6PT-/-, to show that glycogen accumulation plays a crucial role in altering proximal tubule morphology and function. To limit glucose entry into proximal tubule cells and thus to prevent glycogen accumulation, we administered an SGLT2-inhibitor, dapagliflozin, to TM-G6PT-/- mice. RESULTS: In proximal tubule cells, G6PT suppression stimulates the upregulation and activity of hexokinase-I, which increases availability of the reabsorbed glucose for intracellular metabolism. Dapagliflozin prevented glycogen accumulation and improved kidney morphology by promoting a metabolic switch from glycogen synthesis toward lysis and by restoring expression levels of the main proximal tubule functional markers. CONCLUSION: We provide proof of concept for the efficacy of dapagliflozin in preserving kidney function in GSD1b mice. Our findings could represent the basis for repurposing this drug to treat patients with GSD1b.

Single nephron glomerular filtration rate measured by linescan multiphoton microscopy compared to conventional micropuncture.

Renal micropuncture, which requires the direct access to the renal tubules, has for long time been the technique of choice to measure the single nephron glomerular filtration rate (SNGFR) in animal models. This approach is challenging by virtue of complex animal preparation and numerous technically difficult steps. The introduction of intravital multiphoton microscopy (MPM) offers another approach to the measure of the SNGFR by mean of the high laser-tissue penetration and the optical sectioning capacity. Previous MPM studies measuring SNGFR in vivo relied on fast full-frame acquisition during the filtration process obtainable with high performance resonant scanners. In this study, we describe an innovative linescan-based MPM method. The new method can discriminate SNGFR variations both in conditions of low and high glomerular filtration, and shows results comparable to conventional micropuncture both for rats and mice. Moreover, this novel approach has improved spatial and time resolution and is faster than previous methods, thus enabling the investigation of SNGFR from more tubules and improving options for data-analysis.

The DiaCoVAb Study in South Italy: Immune Response to SARS-CoV-2 Vaccination in Dialysis Patients.

INTRODUCTION: Since the pandemic of COVID-19 started from December 2019, remarkable numbers of infections and deaths associated with COVID-19 have been recorded worldwide. End-stage kidney disease patients on dialysis are particularly at high risk of infections due to impairments in the innate and adaptive immune systems. Vaccination on dialysis patients (DP) still remains challenging because of the variable response and a low seroconversion rate compared with healthy participants (HP). Therefore, it is urgently necessary to establish a different vaccination strategy for DP, in terms of the dose and administration time. METHODS: Here, we report an observational prospective cohort study in which the immunogenic efficacies of SARS-CoV-2 vaccine BNT162b2 on DP and HP were evaluated by absolute quantification of IgG levels in the blood. RESULTS: DP showed a delayed seroconversion after two vaccine doses, with a low absolute IgG levels compared to HP. While HP reached complete seroconversion within 10 days from the administration of a second dose, only 76% of DP were seropositive. After the booster dose, DP had a strongly improved seroconversion rate as well as antibody levels, reaching 97% seropositivity and 50 times enhancement on antibody levels. DISCUSSION/CONCLUSION: These results prompt to suggest an additional vaccine dose in DP, reducing the interval of time from the second dose. Since limited data are available on immune response in DP overtime after three vaccine doses currently, our study is among the first reports demonstrating the improved seropositivity and IgG levels in DP after the booster vaccine dose.

Basilar Artery Occlusion (BAO) revascularization after more than 12 hours from the onset of symptoms with excellent outcome: Report of a case.

This paper reports a case of basilar artery occlusion (BAO), a relatively rare event associated with high mortality rate and high risk of disability. A 77-year-old man arrived at our Stroke Unit approximately 14 hours after the onset of symptoms (dysarthria and complete left hemiparesis) with progressive worsening up to coma and with a National Institute Health Stroke Scale (NIHSS) of 22. The patient was treated and, at discharge, the modified Rankin scale and NIHSS were 2 and 5, respectively. The aim of this paper is to illustrate how revascularization treatment, also after 12 hours, could be a viable option to ensure survival and a good life quality for the patient. Furthermore, it is essential to encourage the publication of a greater number of trials about the posterior circulation emphasizing how many favorable prognosis indicators are now recognized.

Efficacy of a Virtual Reality Program in Pediatric Surgery to Reduce Anxiety and Distress Symptoms in the Preoperative Phase: A Prospective Randomized Clinical Trial.

Background: Virtual reality (VR) experience is the most adopted form of video-gaming to reduce preoperative anxiety. This prospective randomized clinical trial aimed to examine the feasibility and efficacy of preoperative VR experience in children undergoing elective surgery. Materials and Methods: All patients older than 13 years and scheduled for elective surgery between March and June 2021 were enrolled. Preoperative VR experience consisted in watching a 5-minute video using a head-mounted display. Four parameters were evaluated and compared between the two groups: (1) patient heart rate (HR) before anesthesia; (2) patient evaluation of preoperative anxiety using facial affective scale (FAS); (3) anesthesiologist evaluation of preoperative anxiety using FAS; and (4) subjective stress scoring using a 5-item Likert-type scale. Results: A total of 40 patients (23 boys) with a median age of 14.5 years (range 12-17) participated in the study. The patients were randomized in two groups, each of 20 patients, according to preoperative VR experience: VR group (G1) and control group (G2). No adverse events related to VR occurred. The patient median HR was significantly lower in G1 (72 bpm) than in G2 (101 bpm) (P = .001). The very relaxed/relaxed face selection rate using FAS was significantly higher in G1 than in G2, in both patient and anesthesiologist evaluations (P = .001). Finally, the subjective patient scoring of operating room experience was significantly greater in G1 [4.6 ± 0.4] than in G2 [2.15 ± 1.07] (P = .001). Conclusions: Our preliminary results showed that VR is safe and effective to relieve anxiety and improve relaxation in the preoperative period in pediatric patients undergoing elective surgery. The VR experience resulted in decreased overall anxiety and increased overall positive affect during the preoperative period in VR group compared with the control group. Further studies are needed to investigate this technology in the postoperative phase and on a larger patient cohort.

Evaluation of endogenous miRNA reference genes across different zebrafish strains, developmental stages and kidney disease models.

The majority of kidney diseases arise from the loss of podocytes and from morphological changes of their highly complex foot process architecture, which inevitably leads to a reduced kidney filtration and total loss of kidney function. It could have been shown that microRNAs (miRs) play a pivotal role in the pathogenesis of podocyte-associated kidney diseases. Due to their fully functioning pronephric kidney, larval zebrafish have become a popular vertebrate model, to study kidney diseases in vivo. Unfortunately, there is no consensus about a proper normalization strategy of RT-qPCR-based miRNA expression data in zebrafish. In this study we analyzed 9 preselected candidates dre-miR-92a-3p, dre-miR-206-3p, dre-miR-99-1, dre-miR-92b-3p, dre-miR-363-3p, dre-let-7e, dre-miR-454a, dre-miR-30c-5p, dre-miR-126a-5p for their capability as endogenous reference genes in zebrafish experiments. Expression levels of potential candidates were measured in 3 different zebrafish strains, different developmental stages, and in different kidney disease models by RT-qPCR. Expression values were analyzed with NormFinder, BestKeeper, GeNorm, and DeltaCt and were tested for inter-group differences. All candidates show an abundant expression throughout all samples and relatively high stability. The most stable candidate without significant inter-group differences was dre-miR-92b-3p making it a suitable endogenous reference gene for RT-qPCR-based miR expression zebrafish studies.

Atorvastatin does not ameliorate nephrogenic diabetes insipidus induced by lithium or potassium depletion in mice.

Acquired forms of nephrogenic diabetes insipidus (NDI) include lithium (Li)-induced and hypokalemia-induced NDI. Both forms are associated with AQP2 downregulation and collecting duct (CD) cellular remodeling. Statins are cholesterol-lowering drugs appearing to increase AQP2 membrane-translocation and improve urine concentration in other NDI models. We have investigated if statins are able to prevent or rescue the Li-induced changes in mice and in a mouse cortical CD cell line (mCCDc1l ). Biotinylation assays showed that acute (1hr) atorvastatin, simvastatin, or fluvastatin increased AQP2 membrane accumulation in mCCDc1l cells showing that the cell line responds to acute statin treatment. To see whether chronic statin treatment abolish the Li effects, mCCDc1l cells were treated with 48 h Li, combined Li/atorvastatin or combined Li/simvastatin. Li reduced AQP2, but combined Li/atorvastatin or Li/simvastatin did not prevent AQP2 downregulation. In mice, chronic (21 days) Li increased urine output and reduced urine osmolality, but combined Li/atorvastatin did not prevent these effects. In inner medulla (IM), Li reduced total AQP2 and increased pS261-AQP2. Combined Li/atorvastatin did not abolish these changes. Atorvastatin did not prevent a Li-induced increase in intercalated cells and proliferation in IM. In mice with already established NDI, atorvastatin had no effect on the Li-induced changes either. Mice subjected to 14 days of potassium-deficient diet developed polyuria and AQP2 downregulation in IM. Co-treatment with atorvastatin did not prevent this. In conclusion, atorvastatin does not appear to be able to prevent or rescue Li-NDI or to prevent hypokalemic-induced NDI.

Dysregulation of Principal Cell miRNAs Facilitates Epigenetic Regulation of AQP2 and Results in Nephrogenic Diabetes Insipidus.

BACKGROUND: MicroRNAs (miRNAs), formed by cleavage of pre-microRNA by the endoribonuclease Dicer, are critical modulators of cell function by post-transcriptionally regulating gene expression. METHODS: Selective ablation of Dicer in AQP2-expressing cells (DicerAQP2Cre+ mice) was used to investigate the role of miRNAs in the kidney collecting duct of mice. RESULTS: The mice had severe polyuria and nephrogenic diabetes insipidus, potentially due to greatly reduced AQP2 and AQP4 levels. Although epithelial sodium channel levels were decreased in cortex and increased in inner medulla, amiloride-sensitive sodium reabsorption was equivalent in DicerAQP2Cre+ mice and controls. Small-RNA sequencing and proteomic analysis revealed 31 and 178 significantly regulated miRNAs and proteins, respectively. Integrated bioinformatic analysis of the miRNAome and proteome suggested alterations in the epigenetic machinery and various transcription factors regulating AQP2 expression in DicerAQP2Cre+ mice. The expression profile and function of three miRNAs (miR-7688-5p, miR-8114, and miR-409-3p) whose predicted targets were involved in epigenetic control (Phf2, Kdm5c, and Kdm4a) or transcriptional regulation (GATA3, GATA2, and ELF3) of AQP2 were validated. Luciferase assays could not demonstrate direct interaction of AQP2 or the three potential transcription factors with miR-7688-5p, miR-8114, and miR-409-3p. However, transfection of respective miRNA mimics reduced AQP2 expression. Chromatin immunoprecipitation assays demonstrated decreased Phf2 and significantly increased Kdm5c interactions at the Aqp2 gene promoter in DicerAQP2Cre+ mice, resulting in decreased RNA Pol II association. CONCLUSIONS: Novel evidence indicates miRNA-mediated epigenetic regulation of AQP2 expression.

Characterization of five novel vasopressin V2 receptor mutants causing nephrogenic diabetes insipidus reveals a role of tolvaptan for M272R-V2R mutation.

Nephrogenic diabetes insipidus (NDI) is a rare tubulopathy characterized by urinary concentration defect due to renal resistance to vasopressin. Loss-of-function mutations of vasopressin V2 receptor (V2R) gene (AVPR2) is the most common cause of the disease. We have identified five novel mutations L86P, R113Q, C192S, M272R, and W323_I324insR from NDI-affected patients. Functional characterization of these mutants revealed that R113Q and C192S were normally localized at the basolateral membrane of polarized Madin-Darby Canine Kidney (MDCK) cells and presented proper glycosylation maturation. On the other side, L86P, M272R, and W323_I324insR mutants were retained in endoplasmic reticulum and exhibited immature glycosylation and considerably reduced stability. All five mutants were resistant to administration of vasopressin analogues as evaluated by defective response in cAMP release. In order to rescue the function of the mutated V2R, we tested VX-809, sildenafil citrate, ibuprofen and tolvaptan in MDCK cells. Among these, tolvaptan was effective in rescuing the function of M272R mutation, by both allowing proper glycosylation maturation, membrane sorting and response to dDAVP. These results show an important proof of concept for the use of tolvaptan in patients affected by M272R mutation of V2R causing NDI.