Collecting Duct Gene Expression in a Mouse Vasopressin-Excess Model without Hyponatremia

Introduction. States of vasopressin excess can exist either with or without hyponatremia, depending on water intake. Here, we set up a mouse model of vasopressin-excess without hyponatremia to address the consequences of vasopressin excess that are independent of serum sodium. Methods. A mouse vasopressin-excess model was created by infusing desmopressin for 5 days without a forced water load. Control mice were infused with vehicle. Results. RNA-seq in microdissected cortical collecting ducts (CCDs) from vasopressin-excess mice showed significant changes in 153 transcripts including the expected increases in aquaporin-2 (AQP2) and AQP3 along with increases in several other targets of V2-receptor-mediated signaling in principal cells. In addition, there were decreases in abundances of many transcripts known to be targets of regulation by the Wnt/frizzled/β-catenin pathway. The vasopressin-excess model also manifested marked increases in phosphorylation of β-catenin at a known protein kinase A (PKA) site, viz. Ser552. CRISPR-mediated mutation of this PKA-target site in mice resulted in extensive changes in the transcriptomes of microdissected CCDs after desmopressin-infusion, heavily weighted toward increases in known transcriptional targets of the Wnt/β-catenin pathway. ATAC-seq in microdissected CCDs from DDAVP-infused mice revealed decreases in chromatin accessibility at promoters of many genes regulated in the Wnt/β-catenin pathway. Conclusion. We conclude that vasopressin-excess is associated with vasopressin/PKA-dependent repression of Wnt/Frizzled/β-catenin target gene expression, mediated in part by PKA-dependent phosphorylation of Ser552 of β-catenin. The repression is associated with decreasing chromatin accessibility in the promoter-TSS regions of target genes. The findings suggest that normonatremic vasopressin-excess is not necessarily benign. Hyponatremia is quite common in hospitalized patients. A frequent cause is the syndrome of inappropriate antidiuresis (SIAD), originally described by William Schwartz and colleagues in 1957, in two patients with bronchogenic carcinoma. Studies in animals have demonstrated that in SIAD, hyponatremia requires two causal elements: an unregulated source of antidiuretic hormone (either arginine vasopressin or some other antidiuretic substance) and excess water intake. Consistent with the latter element, restriction of water intake has been found to be an effective means of treatment in many SIAD patients. Other therapeutic approaches include treatment with vaptans or urea, which alter water balance by increasing free water excretion. Such therapies can eliminate or reduce the hyponatremia, but do not likely eliminate the source of excess antidiuretic hormone. A relevant question in this context is, “Does antidiuretic hormone excess without hyponatremia have physiological consequences?” If so, mere correction of the hyponatremia in SIAD may not restore normality. To begin to address the question, we have set up a vasopressin-excess model without hyponatremia in mice by continuous infusion of the vasopressin analog, dDAVP (desmopressin). We focus on changes in gene expression in the cortical collecting duct (CCD), employing RNA-seq in microdissected CCD segments. WT and MT ("PKA-target-site β-catenin S552 mutation").