G protein-coupled receptor (GPCR) gene variants and human genetic disease.

Genetic variations in the genes encoding G protein-coupled receptors (GPCRs) can disrupt receptor structure and function, which can result in human genetic diseases. Disease-causing mutations have been reported in at least 55 GPCRs for more than 66 monogenic diseases in humans. The spectrum of pathogenic and likely pathogenic variants includes loss of function variants that decrease receptor signaling on one extreme and gain of function that may result in biased signaling or constitutive activity, originally modeled on prototypical rhodopsin GPCR variants identified in retinitis pigmentosa, on the other. GPCR variants disrupt ligand binding, G protein coupling, accessory protein function, receptor desensitization and receptor recycling. Next generation sequencing has made it possible to identify variants of uncertain significance (VUS). We discuss variants in receptors known to result in disease and in silico strategies for disambiguation of VUS such as sorting intolerant from tolerant and polymorphism phenotyping. Modeling of variants has contributed to drug development and precision medicine, including drugs that target the melanocortin receptor in obesity and interventions that reverse loss of gonadotropin-releasing hormone receptor from the cell surface in idiopathic hypogonadotropic hypogonadism. Activating and inactivating variants of the calcium sensing receptor (CaSR) gene that are pathogenic in familial hypocalciuric hypercalcemia and autosomal dominant hypocalcemia have enabled the development of calcimimetics and calcilytics. Next generation sequencing has continued to identify variants in GPCR genes, including orphan receptors, that contribute to human phenotypes and may have therapeutic potential. Variants of the CaSR gene, some encoding an arginine-rich region that promotes receptor phosphorylation and intracellular retention, have been linked to an idiopathic epilepsy syndrome. Agnostic strategies have identified variants of the pyroglutamylated RF amide peptide receptor gene in intellectual disability and G protein-coupled receptor 39 identified in psoriatic arthropathy. Coding variants of the G protein-coupled receptor L1 (GPR37L1) orphan receptor gene have been identified in a rare familial progressive myoclonus epilepsy. The study of the role of GPCR variants in monogenic, Mendelian phenotypes has provided the basis of modeling the significance of more common variants of pharmacogenetic significance.

Long-term multisystemic efficacy of migalastat on Fabry-associated clinical events, including renal, cardiac and cerebrovascular outcomes.

BACKGROUND: Fabry disease is a rare, multisystemic disorder caused by GLA gene variants that lead to alpha galactosidase A deficiency, resulting in accumulation of glycosphingolipids and cellular dysfunction. Fabry-associated clinical events (FACEs) cause significant morbidity and mortality, yet the long-term effect of Fabry therapies on FACE incidence remains unclear. METHODS: This posthoc analysis evaluated incidence of FACEs (as a composite outcome and separately for renal, cardiac and cerebrovascular events) in 97 enzyme replacement therapy (ERT)-naïve and ERT-experienced adults with Fabry disease and amenable GLA variants who were treated with migalastat for up to 8.6 years (median: 5 years) in Phase III clinical trials of migalastat. Associations between baseline characteristics and incidence of FACEs were also evaluated. RESULTS: During long-term migalastat treatment, 17 patients (17.5%) experienced 22 FACEs and there were no deaths. The incidence rate of FACEs was 48.3 events per 1000 patient-years overall. Numerically higher incidence rates were observed in men versus women, patients aged >40 years versus younger patients, ERT-naïve versus ERT-experienced patients and men with the classic phenotype versus men and women with all other phenotypes. There was no statistically significant difference in time to first FACE when analysed by patient sex, phenotype, prior treatment status or age. Lower baseline estimated glomerular filtration rate (eGFR) was associated with an increased risk of FACEs across patient populations. CONCLUSIONS: The overall incidence of FACEs for patients during long-term treatment with migalastat compared favourably with historic reports involving ERT. Lower baseline eGFR was a significant predictor of FACEs.

Vaptans or voluntary increased hydration to protect the kidney: how do they compare?

The adverse effects of vasopressin (AVP) in diverse forms of chronic kidney disease have been well described. They depend on the antidiuretic action of AVP mediated by V2 receptors (V2R). Tolvaptan, a selective V2R antagonist, is now largely used for the treatment of patients with autosomal dominant polycystic kidney disease. Another way to reduce the adverse effects of AVP is to reduce endogenous AVP secretion by a voluntary increase in fluid intake. These two approaches differ in several ways, including the level of thirst and AVP. With voluntary increased drinking, plasma osmolality will decline and so will AVP secretion. Thus, not only will V2R-mediated effects be reduced, but also those mediated by V1a and V1b receptors (V1aR and V1bR). In contrast, selective V2R antagonism will induce a loss of fluid that will stimulate AVP secretion and thus increase AVP's influence on V1a and V1b receptors. V1aR is expressed in the luminal side of the collecting duct (CD) and in inner medullary interstitial cells, and their activation induces the production of prostaglandins, mostly prostaglandin E2 (PGE2). Intrarenal PGE2 has been shown to reduce sodium and water reabsorption in the CD and increase blood flow in the renal medulla, both effects contributing to increase sodium and water excretion and reduce urine-concentrating activity. Conversely, non-steroidal anti-inflammatory drugs have been shown to induce significant water and sodium retention and potentiate the antidiuretic effects of AVP. Thus, during V2R antagonism, V1aR-mediated actions may be responsible for part of the diuresis observed with this drug. These V1aR-dependent effects do not take place with a voluntary increase in fluid intake. In summary, while both strategies may have beneficial effects, the information reviewed here leads us to assume that pharmacological V2R antagonism, with resulting stimulation of V1aR and increased PGE2 production, may provide greater benefit than voluntary high water intake. The influence of tolvaptan on the PGE2 excretion rate and the possibility to use somewhat lower tolvaptan doses than presently prescribed remain to be evaluated.

Regulation of Thirst and Vasopressin Release.

Recent experiments using optogenetic tools facilitate the identification and functional analysis of thirst neurons and vasopressin-producing neurons. Four major advances provide a detailed anatomy and physiology of thirst, taste for water, and arginine-vasopressin (AVP) release: ( a) Thirst and AVP release are regulated by the classical homeostatic, interosensory plasma osmolality negative feedback as well as by novel, exterosensory, anticipatory signals. These anticipatory signals for thirst and vasopressin release concentrate on the same homeostatic neurons and circumventricular organs that monitor the composition of blood. ( b) Acid-sensing taste receptor cells (TRCs) expressing otopetrin 1 on type III presynaptic TRCs on the tongue, which were previously suggested as the sour taste sensors, also mediate taste responses to water. ( c) Dehydration is aversive, and median preoptic nucleus (MnPO) neuron activity is proportional to the intensity of this aversive state. ( d) MnPOGLP1R neurons serve as a central detector that discriminates fluid ingestion from solid ingestion, which promotes acute satiation of thirst through the subfornical organ and other downstream targets.

Mass Spectrometry Analysis of Globotriaosylsphingosine and Its Analogues in Dried Blood Spots.

Fabry disease (FD) is an X-linked lysosomal storage disorder where impaired α-galactosidase A enzyme activity leads to the intracellular accumulation of undegraded glycosphingolipids, including globotriaosylsphingosine (lyso-Gb3) and related analogues. Lyso-Gb3 and related analogues are useful biomarkers for screening and should be routinely monitored for longitudinal patient evaluation. In recent years, a growing interest has emerged in the analysis of FD biomarkers in dried blood spots (DBSs), considering the several advantages compared to venipuncture as a technique for collecting whole-blood specimens. The focus of this study was to devise and validate a UHPLC-MS/MS method for the analysis of lyso-Gb3 and related analogues in DBSs to facilitate sample collection and shipment to reference laboratories. The assay was devised in conventional DBS collection cards and in Capitainer®B blood collection devices using both capillary and venous blood specimens from 12 healthy controls and 20 patients affected with FD. The measured biomarker concentrations were similar in capillary and venous blood specimens. The hematocrit (Hct) did not affect the correlation between plasma and DBS measurements in our cohort (Hct range: 34.3-52.2%). This UHPLC-MS/MS method using DBS would facilitate high-risk screening and the follow-up and monitoring of patients affected with FD.

Assessment of plasma lyso-Gb3 for clinical monitoring of treatment response in migalastat-treated patients with Fabry disease.

PURPOSE: To assess the utility of globotriaosylsphingosine (lyso-Gb3) for clinical monitoring of treatment response in patients with Fabry disease receiving migalastat. METHODS: A post hoc analysis evaluated data from 97 treatment-naive and enzyme replacement therapy (ERT)-experienced patients with migalastat-amenable GLA variants from FACETS (NCT00925301) and ATTRACT (NCT01218659) and subsequent open-label extension studies. The relationship between plasma lyso-Gb3 and measures of Fabry disease progression (left ventricular mass index [LVMi], estimated glomerular filtration rate [eGFR], and pain) and the relationship between lyso-Gb3 and incidence of Fabry-associated clinical events (FACEs) were assessed in both groups. The relationship between changes in lyso-Gb3 and kidney interstitial capillary (KIC) globotriaosylceramide (Gb3) inclusions was assessed in treatment-naive patients. RESULTS: No significant correlations were identified between changes in lyso-Gb3 and changes in LVMi, eGFR, or pain. Neither baseline lyso-Gb3 levels nor the rate of change in lyso-Gb3 levels during treatment predicted FACE occurrences in all patients or those receiving migalastat for ≥24 months. Changes in lyso-Gb3 correlated with changes in KIC Gb3 inclusions in treatment-naive patients. CONCLUSIONS: Although used as a pharmacodynamic biomarker in research and clinical studies, plasma lyso-Gb3 may not be a suitable biomarker for monitoring treatment response in migalastat-treated patients.

Independent Registries Are Cost-Effective Tools to Provide Mandatory Postauthorization Surveillance for Orphan Medicinal Products.

OBJECTIVES: Orphan medicinal products (OMPs) often receive market authorization under conditions imposed by regulators for ongoing postauthorization surveillance (PAS) to answer questions that remain at the time of market entry. This surveillance may be provided through industry-funded registries (IFRs). Nevertheless, data in these registries may not be of sufficient quality to answer these questions and may not always be accessible for regulatory review. We propose that a mandatory independent registry is an efficient and cost-effective tool for PAS for OMPs. METHODS: Using data from the Canadian Fabry Disease Initiative, we reviewed costs per unique patient from sites participating in both the independent national registry and IFRs for Fabry disease and compared data completeness from the Canadian Fabry Disease Initiative to that in published documents from IFRs. RESULTS: The costs of data collection through the independent registry were 17% to 36% (depending on site) lower than costs to collect data in the IFRs, and completeness of data collected through the independent registry was higher than that through the IFRs. Data from the independent registry were reviewed annually to guide indications for publicly funded Fabry disease therapy. Even when enrollment ceased to be a requirement to receive therapy, 77% of patients continued to enroll in the registry, suggesting the structure was acceptable to patients. CONCLUSIONS: Independent registries are cost-effective and efficient tools and should be mandated by regulatory agencies as the preferred tool for PAS for OMPs. Countries with publicly funded health systems should consider investment in registry infrastructure for OMPs.

Use of a rare disease registry for establishing phenotypic classification of previously unassigned GLA variants: a consensus classification system by a multispecialty Fabry disease genotype-phenotype workgroup.

BACKGROUND: Fabry disease (α-galactosidase deficiency) is an X-linked genetic disease caused by a variety of pathogenic GLA variants. The phenotypic heterogeneity is considerable, with two major forms, classic and later-onset disease, but adjudication of clinical phenotype is currently lacking for many variants. We aimed to determine consensus phenotypic classification for previously unclassified GLA variants from the GLA-specific fabry-database.org database. METHODS: A Fabry disease genotype-phenotype workgroup developed a five-stage iterative system based on expert clinical assessment, published literature and clinical evidence of pathogenicity using a 2-point scoring system based on clinical hallmarks of classic disease. Kaplan-Meier (KM) analysis of severe clinical event-free survival was used as final validation. Results were compared with those from web-based disease databases and in silico pathogenicity prediction programmes. RESULTS: Final consensus on classifications of 'pathogenic' was achieved for 32 of 33 GLA variants (26 'classic' phenotype, 171 males; 6 'later-onset' phenotype, 57 males). One variant remained of uncertain significance. KM curves were similar for the known fabry-database.org database phenotypes and when workgroup consensus classifications were added, and the curves retained the same separation between 'classic' and 'later-onset' phenotypes. CONCLUSION: The iterative system implemented by a Fabry disease genotype-phenotype workgroup achieved phenotypic classifications for variants that were previously unclassified. Clinical pathogenicity associated with a particular GLA variant defined in affected males appears to have predictive value and also generally correlates with risk for affected females. The newly established classifications can be of benefit to the clinical care of Fabry patients harbouring these variants.

Diurnal Variation of Urinary Fabry Disease Biomarkers during Enzyme Replacement Therapy Cycles.

Fabry disease is an X-linked lysosomal storage disorder caused by mutations in the GLA gene encoding the α-galactosidase A enzyme. This enzyme cleaves the last sugar unit of glycosphingolipids, including globotriaosylceramide (Gb3), globotriaosylsphingosine (lyso-Gb3), and galabiosylceramide (Ga2). Enzyme impairment leads to substrate accumulation in different organs, vascular endothelia, and biological fluids. Enzyme replacement therapy (ERT) is a commonly used treatment. Urinary analysis of Gb3 isoforms (different fatty acid moieties), as well as lyso-Gb3 and its analogues, is a reliable way to monitor treatment. These analogues correspond to lyso-Gb3 with chemical modifications on the sphingosine moiety (-C2H4, -C2H4+O, -H2, -H2+O, +O, +H2O2, and +H2O3). The effects of sample collection time on urinary biomarker levels between ERT cycles were not previously documented. The main objective of this project was to analyze the aforementioned biomarkers in urine samples from seven Fabry disease patients (three treated males, three treated females, and one ERT-naïve male) collected twice a day (morning and evening) for 42 days (three ERT cycles). Except for one participant, our results show that the biomarker levels were generally more elevated in the evening. However, there was less variability in samples collected in the morning. No cyclic variations in biomarker levels were observed between ERT infusions.

What can copeptin tell us in patients with autosomal dominant polycystic disease?

Vasopressin is known to contribute to disease progression in autosomal dominant polycystic disease (ADPKD) by its influence on cyclic adenosine monophosphate that directly promotes cyst growth. In addition, vasopressin probably contributes to progression by inducing glomerular hyperfiltration as shown in other forms of chronic kidney diseases. The measurement of plasma copeptin, a marker of vasopressin secretion, could help identify patients at higher risk of fast progression and those expected to benefit the most from vasopressin V2 receptor blockade. Further studies should evaluate the optimal level of suppression of vasopressin effects in autosomal dominant polycystic disease.

Treatment of Fabry's Disease with the Pharmacologic Chaperone Migalastat.

BACKGROUND: Fabry's disease, an X-linked disorder of lysosomal α-galactosidase deficiency, leads to substrate accumulation in multiple organs. Migalastat, an oral pharmacologic chaperone, stabilizes specific mutant forms of α-galactosidase, increasing enzyme trafficking to lysosomes. METHODS: The initial assay of mutant α-galactosidase forms that we used to categorize 67 patients with Fabry's disease for randomization to 6 months of double-blind migalastat or placebo (stage 1), followed by open-label migalastat from 6 to 12 months (stage 2) plus an additional year, had certain limitations. Before unblinding, a new, validated assay showed that 50 of the 67 participants had mutant α-galactosidase forms suitable for targeting by migalastat. The primary end point was the percentage of patients who had a response (≥50% reduction in the number of globotriaosylceramide inclusions per kidney interstitial capillary) at 6 months. We assessed safety along with disease substrates and renal, cardiovascular, and patient-reported outcomes. RESULTS: The primary end-point analysis, involving patients with mutant α-galactosidase forms that were suitable or not suitable for migalastat therapy, did not show a significant treatment effect: 13 of 32 patients (41%) who received migalastat and 9 of 32 patients (28%) who received placebo had a response at 6 months (P=0.30). Among patients with suitable mutant α-galactosidase who received migalastat for up to 24 months, the annualized changes from baseline in the estimated glomerular filtration rate (GFR) and measured GFR were -0.30±0.66 and -1.51±1.33 ml per minute per 1.73 m(2) of body-surface area, respectively. The left-ventricular-mass index decreased significantly from baseline (-7.7 g per square meter; 95% confidence interval [CI], -15.4 to -0.01), particularly when left ventricular hypertrophy was present (-18.6 g per square meter; 95% CI, -38.2 to 1.0). The severity of diarrhea, reflux, and indigestion decreased. CONCLUSIONS: Among all randomly assigned patients (with mutant α-galactosidase forms that were suitable or not suitable for migalastat therapy), the percentage of patients who had a response at 6 months did not differ significantly between the migalastat group and the placebo group. (Funded by Amicus Therapeutics; ClinicalTrials.gov numbers, NCT00925301 [study AT1001-011] and NCT01458119 [study AT1001-041].).

Efficacy of the pharmacologic chaperone migalastat in a subset of male patients with the classic phenotype of Fabry disease and migalastat-amenable variants: data from the phase 3 randomized, multicenter, double-blind clinical trial and extension study.

PURPOSE: Outcomes in patients with Fabry disease receiving migalastat during the phase 3 FACETS trial (NCT00925301) were evaluated by phenotype. METHODS: Data were evaluated in two subgroups of patients with migalastat-amenable GLA variants: "classic phenotype" (n = 14; males with residual peripheral blood mononuclear cell α-galactosidase A <3% normal and multiorgan system involvement) and "other patients" (n = 36; males not meeting classic phenotype criteria and all females). Endpoints included estimated glomerular filtration rate (eGFR), left ventricular mass index (LVMi), Gastrointestinal Symptoms Rating Scale diarrhea subscale (GSRS-D), renal peritubular capillary (PTC) globotriaosylceramide (GL-3) inclusions, and plasma globotriaosylsphingosine (lyso-Gb3). RESULTS: Baseline measures in the classic phenotype patients suggested a more severe phenotype. At month 24, mean (SD) annualized change in eGFRCKD-EPI with migalastat was -0.3 (3.76) mL/min/1.73 m2 in the classic phenotype subgroup; changes in LVMi, GSRS-D, and lyso-Gb3 were -16.7 (18.64) g/m2, -0.9 (1.66), and -36.8 (35.78) nmol/L, respectively. At month 6, mean PTC GL-3 inclusions decreased with migalastat (-0.8) and increased with placebo (0.3); switching from placebo to migalastat, PTC inclusions decreased by -0.7. Numerically smaller changes in these endpoints were observed in the other patients. CONCLUSION: Migalastat provided clinical benefit to patients with Fabry disease and amenable variants, regardless of disease severity.

Low-dose agalsidase beta treatment in male pediatric patients with Fabry disease: A 5-year randomized controlled trial.

BACKGROUND: Fabry disease is a rare, X-linked, lifelong progressive lysosomal storage disorder. Severely deficient α-galactosidase A activity in males is associated with the classic phenotype with early-onset, multisystem manifestations evolving to vital organ complications during adulthood. We assessed the ability of 2 low-dose agalsidase beta regimens to lower skin, plasma, and urine globotriaosylceramide (GL-3) levels, and influence clinical manifestations in male pediatric Fabry patients. METHODS: In this multicenter, open-label, parallel-group, phase 3b study, male patients aged 5-18 years were randomized to receive agalsidase beta at 0.5 mg/kg 2-weekly (n = 16) or 1.0 mg/kg 4-weekly (n = 15) for 5 years. All had plasma/urine GL-3 accumulation but no clinically evident organ involvement. The primary outcome was GL-3 accumulation in superficial skin capillary endothelium (SSCE). RESULTS: The mean age was 11.6 (range: 5-18) years and all but one of the 31 patients had classic GLA mutations. In the overall cohort, shifts from non-0 to 0-scores for SSCE GL-3 were significant at years 1, 3, and 5, but results were variable. Plasma GL-3 normalized and urine GL-3 reduced substantially. Higher anti-agalsidase beta antibody titers were associated with less robust SSCE GL-3 clearance and higher urine GL-3 levels. Renal function remained stable and normal. Most Fabry signs and symptoms tended to stabilize; abdominal pain was significantly reduced (-26.3%; P = .0215). No new clinical major organ complications were observed. GL-3 accumulation and cellular and vascular injury were present in baseline kidney biopsies (n = 7). Treatment effects on podocyte GL-3 content and foot process width were highly variable. Fabry arteriopathy overall increased in severity. Two patients withdrew and 2 had their agalsidase beta dose increased. CONCLUSIONS: Our findings increase the limited amount of available data on long-term effects of enzyme replacement therapy in pediatric, classic Fabry patients. The low-dose regimens studied here over a period of 5 years did not demonstrate a consistent benefit among the patients in terms of controlling symptomatology, urine GL-3 levels, and pathological histology. The current available evidence supports treatment of pediatric, classic male Fabry patients at the approved agalsidase beta dose of 1.0 mg/kg 2-weekly if these patients are considered for enzyme replacement therapy with agalsidase beta.

Agalsidase alfa versus agalsidase beta for the treatment of Fabry disease: an international cohort study.

BACKGROUND: Two recombinant enzymes (agalsidase alfa 0.2 mg/kg/every other week and agalsidase beta 1.0 mg/kg/every other week) have been registered for the treatment of Fabry disease (FD), at equal high costs. An independent international initiative compared clinical and biochemical outcomes of the two enzymes. METHODS: In this multicentre retrospective cohort study, clinical event rate, left ventricular mass index (LVMI), estimated glomerular filtration rate (eGFR), antibody formation and globotriaosylsphingosine (lysoGb3) levels were compared between patients with FD treated with agalsidase alfa and beta at their registered dose after correction for phenotype and sex. RESULTS: 387 patients (192 women) were included, 248 patients received agalsidase alfa. Mean age at start of enzyme replacement therapy was 46 (±15) years. Propensity score matched analysis revealed a similar event rate for both enzymes (HR 0.96, P=0.87). The decrease in plasma lysoGb3 was more robust following treatment with agalsidase beta, specifically in men with classical FD (ß: -18 nmol/L, P<0.001), persisting in the presence of antibodies. The risk to develop antibodies was higher for patients treated with agalsidase beta (OR 2.8, P=0.04). LVMI decreased in a higher proportion following the first year of agalsidase beta treatment (OR 2.27, P=0.03), while eGFR slopes were similar. CONCLUSIONS: Treatment with agalsidase beta at higher dose compared with agalsidase alfa does not result in a difference in clinical events, which occurred especially in those with more advanced disease. A greater biochemical response, also in the presence of antibodies, and better reduction in left ventricular mass was observed with agalsidase beta.

Oral pharmacological chaperone migalastat compared with enzyme replacement therapy in Fabry disease: 18-month results from the randomised phase III ATTRACT study.

BACKGROUND: Fabry disease is an X-linked lysosomal storage disorder caused by GLA mutations, resulting in α-galactosidase (α-Gal) deficiency and accumulation of lysosomal substrates. Migalastat, an oral pharmacological chaperone being developed as an alternative to intravenous enzyme replacement therapy (ERT), stabilises specific mutant (amenable) forms of α-Gal to facilitate normal lysosomal trafficking. METHODS: The main objective of the 18-month, randomised, active-controlled ATTRACT study was to assess the effects of migalastat on renal function in patients with Fabry disease previously treated with ERT. Effects on heart, disease substrate, patient-reported outcomes (PROs) and safety were also assessed. RESULTS: Fifty-seven adults (56% female) receiving ERT (88% had multiorgan disease) were randomised (1.5:1), based on a preliminary cell-based assay of responsiveness to migalastat, to receive 18 months open-label migalastat or remain on ERT. Four patients had non-amenable mutant forms of α-Gal based on the validated cell-based assay conducted after treatment initiation and were excluded from primary efficacy analyses only. Migalastat and ERT had similar effects on renal function. Left ventricular mass index decreased significantly with migalastat treatment (-6.6 g/m2 (-11.0 to -2.2)); there was no significant change with ERT. Predefined renal, cardiac or cerebrovascular events occurred in 29% and 44% of patients in the migalastat and ERT groups, respectively. Plasma globotriaosylsphingosine remained low and stable following the switch from ERT to migalastat. PROs were comparable between groups. Migalastat was generally safe and well tolerated. CONCLUSIONS: Migalastat offers promise as a first-in-class oral monotherapy alternative treatment to intravenous ERT for patients with Fabry disease and amenable mutations. TRIAL REGISTRATION NUMBER: NCT00925301; Pre-results.

Vasopressin and the Regulation of Thirst.

Recent experiments using optogenetic tools allow the identification and functional analysis of thirst neurons and vasopressin producing neurons. Two major advances provide a detailed anatomy of taste for water and arginine-vasopressin (AVP) release: (1) thirst and AVP release are regulated not only by the classical homeostatic, intero-sensory plasma osmolality negative feedback, but also by novel, extero-sensory, anticipatory signals. These anticipatory signals for thirst and vasopressin release converge on the same homeostatic neurons of circumventricular organs that monitor the composition of the blood; (2) acid-sensing taste receptor cells (which express polycystic kidney disease 2-like 1 protein) on the tongue that were previously suggested as the sour taste sensors also mediate taste responses to water. The tongue has a taste for water. The median preoptic nucleus (MnPO) of the hypothalamus could integrate multiple thirst-generating stimuli including cardiopulmonary signals, osmolality, angiotensin II, oropharyngeal and gastric signals, the latter possibly representing anticipatory signals. Dehydration is aversive and MnPO neuron activity is proportional to the intensity of this aversive state.

Hepatocyte Nuclear Factor-1ß Regulates Urinary Concentration and Response to Hypertonicity.

The transcription factor hepatocyte nuclear factor-1ß (HNF-1ß) is essential for normal kidney development and function. Inactivation of HNF-1ß in mouse kidney tubules leads to early-onset cyst formation and postnatal lethality. Here, we used Pkhd1/Cre mice to delete HNF-1ß specifically in renal collecting ducts (CDs). CD-specific HNF-1ß mutant mice survived long term and developed slowly progressive cystic kidney disease, renal fibrosis, and hydronephrosis. Compared with wild-type littermates, HNF-1ß mutant mice exhibited polyuria and polydipsia. Before the development of significant renal structural abnormalities, mutant mice exhibited low urine osmolality at baseline and after water restriction and administration of desmopressin. However, mutant and wild-type mice had similar plasma vasopressin and solute excretion levels. HNF-1ß mutant kidneys showed increased expression of aquaporin-2 mRNA but mislocalized expression of aquaporin-2 protein in the cytoplasm of CD cells. Mutant kidneys also had decreased expression of the UT-A urea transporter and collectrin, which is involved in apical membrane vesicle trafficking. Treatment of HNF-1ß mutant mIMCD3 cells with hypertonic NaCl inhibited the induction of osmoregulated genes, including Nr1h4, which encodes the transcription factor FXR that is required for maximal urinary concentration. Chromatin immunoprecipitation and sequencing experiments revealed HNF-1ß binding to the Nr1h4 promoter in wild-type kidneys, and immunoblot analysis revealed downregulated expression of FXR in HNF-1ß mutant kidneys. These findings reveal a novel role of HNF-1ß in osmoregulation and identify multiple mechanisms, whereby mutations of HNF-1ß produce defects in urinary concentration.