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High concentrations of urinary calcium counteract vasopressin action via the activation of the Calcium‐Sensing Receptor (CaSR) expressed in the luminal membrane of the collecting duct cells, which impairs the trafficking of aquaporin‐2 (AQP2). In line with these findings, we provide evidence that, with respect to wild‐type mice, CaSR knock‐in (KI) mice mimicking autosomal dominant hypocalcaemia, display a significant decrease in the total content of AQP2 associated with significantly higher levels of AQP2 phosphorylation at Ser261, a phosphorylation site involved in AQP2 degradation. Interestingly, KI mice also had significantly higher levels of phosphorylated p38MAPK, a downstream effector of CaSR and known to phosphorylate AQP2 at Ser261. Moreover, ATF1 phosphorylated at Ser63, a transcription factor downstream of p38MAPK, was significantly higher in KI. In addition, KI mice had significantly higher levels of AQP2‐targeting miRNA137 consistent with a post‐transcriptional downregulation of AQP2. In vivo treatment of KI mice with the calcilytic JTT‐305, a CaSR antagonist, increased AQP2 expression and reduced AQP2‐targeting miRNA137 levels in KI mice. Together, these results provide direct evidence for a critical role of CaSR in impairing both short‐term vasopressin response by increasing AQP2‐pS261, as well as AQP2 abundance, via the p38MAPK‐ATF1‐miR137 pathway. Key points: Calcium‐Sensing Receptor (CaSR) activating mutations are the main cause of autosomal dominant hypocalcaemia (ADH) characterized by inappropriate renal calcium excretion leading to hypocalcaemia and hypercalciuria. Current treatments of ADH patients with parathyroid hormone, although improving hypocalcaemia, do not improve hypercalciuria or nephrocalcinosis.In vivo treatment with calcilytic JTT‐305/MK‐5442 ameliorates most of the ADH phenotypes of the CaSR knock‐in mice including hypercalciuria or nephrocalcinosis and reverses the downregulation of the vasopressin‐sensitive aquaporin‐2 (AQP2) expression, providing direct evidence for a critical role of CaSR in impairing vasopressin response.The beneficial effect of calcilytic in reducing the risk of renal calcification may occur in a parathyroid hormone‐independent action through vasopressin‐dependent inhibition of cAMP synthesis in the thick ascending limb and in the collecting duct.The amelioration of most of the abnormalities in calcium metabolism including hypercalciuria, renal calcification, and AQP2‐mediated osmotic water reabsorption makes calcilytic a good candidate as a novel therapeutic agent for ADH. [ABSTRACT FROM AUTHOR]

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a rare X‐linked disease caused by gain‐of‐function mutations of arginine vasopressin receptor 2 (V2R). Patients with NSIAD are characterized by the inability to excrete a free water load and by inappropriately increased urinary osmolality despite very low levels of plasma vasopressin, resulting in euvolaemic hyponatraemia. To dissect the signalling downstream V2R constitutively active variants, Flp‐In T‐REx Madin‐Darby canine kidney (FTM) cells, stably transfected with V2R mutants (R137L, R137C and F229V) and AQP2‐wt or non‐phosphorylatable AQP2‐S269A/AQP2‐S256A, were used as cellular models. All three activating V2R mutations presented constitutive plasma membrane expression of AQP2‐wt and significantly higher basal water permeability. In addition, V2R‐R137L/C showed significantly higher activity of Rho‐associated kinase (ROCK), a serine/threonine kinase previously suggested to be involved in S269‐AQP2 phosphorylation downstream of these V2R mutants. Interestingly, FTM cells expressing V2R‐R137L/C mutants and AQP2‐S269A showed a significant reduction in AQP2 membrane abundance and a significant reduction in ROCK activity, indicating the crucial importance of S269‐AQP2 phosphorylation in the gain‐of‐function phenotype. Conversely, V2R‐R137L/C mutants retained the gain‐of‐function phenotype when AQP2‐S256A was co‐expressed. In contrast, cells expressing the F229V mutant and the non‐phosphorylatable AQP2‐S256A had a significant reduction in AQP2 membrane abundance along with a significant reduction in basal osmotic water permeability, indicating a crucial role of Ser256 for this mutant. These data indicate that the constitutive AQP2 trafficking associated with the gain‐of‐function V2R‐R137L/C mutants causing NSIAD is protein kinase A independent and requires an intact Ser269 in AQP2 under the control of ROCK phosphorylation. Key points: Nephrogenic syndrome of inappropriate antidiuresis is caused by two constitutively active variant phenotypes of AVPR2, one sensitive to vaptans (V2R‐F229V) and the other vaptan resistant (V2R‐R137C/L). In renal cells, all three activating arginine vasopressin receptor 2 (V2R) variants display constitutive AQP2 plasma membrane expression and high basal water permeability.In cells expressing V2R‐R137L/C mutants, disruption of the AQP2‐S269 phosphorylation site caused the loss of the gain‐of‐function phenotype, which, in contrast, was retained in V2R‐F229V‐expressing cells.Cells expressing the V2R‐F229V mutant were instead sensitive to disruption of the AQP2‐S256 phosphorylation site.The serine/threonine kinase Rho‐associated kinase (ROCK) was found to be involved in AQP2‐S269 phosphorylation downstream of the V2R‐R137L/C mutants.These findings might have clinical relevance for patients with nephrogenic syndrome of inappropriate antidiuresis. [ABSTRACT FROM AUTHOR]

Acute pyelonephritis (APN) is most frequently caused by uropathogenic Escherichia coli (UPEC), which ascends from the bladder to the kidneys during a urinary tract infection. Patients with APN have been reported to have reduced renal concentration capacity under challenged conditions, polyuria, and increased aquaporin-2 (AQP2) excretion in the urine. We have recently shown increased AQP2 accumulation in the plasma membrane in cell cultures exposed to E. coli lysates and in the apical plasma membrane of inner medullary collecting ducts in a 5-day APN mouse model. This study aimed to investigate if AQP2 expression in host cells increases UPEC infection efficiency and to identify specific bacterial components that mediate AQP2 plasma membrane insertion. As the transepithelial water permeability in the collecting duct is codetermined by AQP3 and AQP4, we also investigated whether AQP3 and AQP4 localization is altered in the APN mouse model. We show that AQP2 expression does not increase UPEC infection efficiency and that AQP2 was targeted to the plasma membrane in AQP2-expressing cells in response to the two pathogen-associated molecular patterns (PAMPs), lipopolysaccharide and peptidoglycan. In contrast to AQP2, the subcellular localizations of AQP1, AQP3, and AQP4 were unaffected both in lysate-incubated cell cultures and in the APN mouse model. Our finding demonstrated that cellular exposure to lipopolysaccharide and peptidoglycan can trigger the insertion of AQP2 in the plasma membrane revealing a new regulatory pathway for AQP2 plasma membrane translocation, which may potentially be exploited in intervention strategies. NEW & NOTEWORTHY: Acute pyelonephritis (APN) is associated with reduced renal concentration capacity and increased aquaporin-2 (AQP2) excretion. Uropathogenic Escherichia coli (UPEC) mediates changes in the subcellular localization of AQP2 and we show that in vitro, these changes could be elicited by two pathogen-associated molecular patterns (PAMPs), namely, lipopolysaccharide and peptidoglycan. UPEC infection was unaltered by AQP2 expression and the other renal AQPs (AQP1, AQP3, and AQP4) were unaltered in APN. [ABSTRACT FROM AUTHOR]

The text is an editorial discussing the 72nd Annual Meeting of the Italian Society of Physiology, which brought together leading physiologists to discuss innovative research directions. The meeting covered a wide range of topics, including cell physiology, neurobiology, and cardiovascular health. Some notable findings presented at the meeting include the potential therapeutic use of autophagy modulation in neurological disorders, the protective effects of botanical extracts and dietary supplements against oxidative stress-related pathologies, the role of cellular communication in disease pathogenesis and therapeutic interventions, and the impact of environmental pollutants on human health. The editorial emphasizes the importance of collaboration and curiosity in advancing scientific knowledge and expresses gratitude to the authors, reviewers, and contributors who made the research topic possible. [Extracted from the article]

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