Vasopressin increases expression of UT-A1, UT-A3, and ER chaperone GRP78 in the renal medulla of mice with a urinary concentrating defect.

Activation of V2 receptors (V2R) during antidiuresis increases the permeability of the inner medullary collecting duct to urea and water. Extracellular osmolality is elevated as the concentrating capacity of the kidney increases. Osmolality is known to contribute to the regulation of collecting duct water (aquaporin-2; AQP2) and urea transporter (UT-A1, UT-A3) regulation. AQP1KO mice are a concentrating mechanism knockout, a defect attributed to the loss of high interstitial osmolality. A V2R-specific agonist, deamino-8-D-arginine vasopressin (dDAVP), was infused into wild-type and AQP1KO mice for 7 days. UT-A1 mRNA and protein abundance were significantly increased in the medullas of wild-type and AQP1KO mice following dDAVP infusion. The mRNA and protein abundance of UT-A3, the basolateral urea transporter, was significantly increased by dDAVP in both wild-type and AQP1KO mice. Semiquantitative immunoblots revealed that dDAVP infusion induced a significant increase in the medullary expression of the endoplasmic reticulum (ER) chaperone GRP78. Immunofluorescence studies demonstrated that GRP78 expression colocalized with AQP2 in principal cells of the papillary tip of the renal medulla. Using immunohistochemistry and immunogold electron microscopy, we demonstrate that vasopressin induced a marked apical targeting of GRP78 in medullary principal cells. Urea-sensitive genes, GADD153 and ATF4 (components of the ER stress pathway), were significantly increased in AQP1KO mice by dDAVP infusion. These findings strongly support an important role of vasopressin in the activation of an ER stress response in renal collecting duct cells, in addition to its role in activating an increase in UT-A1 and UT-A3 abundance.

CARMA: A platform for analyzing microarray datasets that incorporate replicate measures.

BACKGROUND: The incorporation of statistical models that account for experimental variability provides a necessary framework for the interpretation of microarray data. A robust experimental design coupled with an analysis of variance (ANOVA) incorporating a model that accounts for known sources of experimental variability can significantly improve the determination of differences in gene expression and estimations of their significance. RESULTS: To realize the full benefits of performing analysis of variance on microarray data we have developed CARMA, a microarray analysis platform that reads data files generated by most microarray image processing software packages, performs ANOVA using a user-defined linear model, and produces easily interpretable graphical and numeric results. No pre-processing of the data is required and user-specified parameters control most aspects of the analysis including statistical significance criterion. The software also performs location and intensity dependent lowess normalization, automatic outlier detection and removal, and accommodates missing data. CONCLUSION: CARMA provides a clear quantitative and statistical characterization of each measured gene that can be used to assess marginally acceptable measures and improve confidence in the interpretation of microarray results. Overall, applying CARMA to microarray datasets incorporating repeated measures effectively reduces the number of gene incorrectly identified as differentially expressed and results in a more robust and reliable analysis.

Vasopressin receptor subtype 2 activation increases cell proliferation in the renal medulla of AQP1 null mice.

Aquaporin (AQP) 1 null mice have a defect in the renal concentrating gradient because of their inability to generate a hyperosmotic medullary interstitium. To determine the effect of vasopressin on renal medullary gene expression, in the absence of high local osmolarity, we infused 1-deamino-8-d-arginine vasopressin (dDAVP), a V(2) receptor (V(2)R)-specific agonist, in AQP1 null mice for 7 days. cDNA microarray analysis was performed on the renal medullary tissue, and 5,140 genes of the possible 12,000 genes on the array were included in the analysis. In the renal medulla of AQP1 null mice, 245 transcripts were identified as increased by dDAVP infusion and 200 transcripts as decreased (1.5-fold or more). Quantitative real-time PCR measurements confirmed the increases seen for cyclin D1, early growth response gene 1, and activating transcription factor 3, genes associated with changes in cell cycle/growth. Changes in mRNA expression were correlated with changes in protein expression by semiquantitative immunoblotting; cyclin D1 and ATF3 were increased significantly in abundance following dDAVP infusion in the renal medulla of AQP1 null mice (161 and 461%, respectively). A significant increase in proliferation of medullary collecting ducts cells, following V(2)R activation, was identified by proliferating cell nuclear antigen immunohistochemistry; colocalization studies with AQP2 indicated that the increase in proliferation was primarily observed in principal cells of the inner medullary collecting duct (IMCD). V(2)R activation, via dDAVP, increased AQP2 and AQP3 protein abundance in the cortical collecting ducts of AQP1 null mice. However, V(2)R activation did not increase AQP2 protein abundance in the IMCD of AQP1 null mice.

Stanniocalcin-1 regulates endothelial gene expression and modulates transendothelial migration of leukocytes.

The mammalian counterpart of the fish calcium-regulating hormone stanniocalcin-1 (STC1) inhibits monocyte chemotactic protein-1- and stromal-derived factor-1alpha (SDF-1alpha)-mediated chemotaxis and diminishes chemokinesis in macrophage-like RAW264.7 and U937 cells in a manner that may involve attenuation of the intracellular calcium signal. STC1 is strongly induced in the kidney following obstructive injury. We hypothesized that STC1 may serve to attenuate the influx of inflammatory cells to the site of tissue injury. In this study, we examined the effect of STC1 on the migration of freshly isolated human macrophages, neutrophils, and T and B lymphocytes through quiescent or IL-1beta-treated human umbilical vein endothelial cell (HUVEC) monolayers. STC1 inhibited transmigration of macrophages and T lymphocytes through quiescent or IL-1beta-activated HUVECs but did not attenuate the transmigration of neutrophils and B lymphocytes. STC1 regulates gene expression in cultured endothelial cells and is detected on the apical surface of endothelial cells in vivo. The data suggest that STC1 plays a critical role in transendothelial migration of inflammatory cells and is involved in the regulation of numerous aspects of endothelial function.

Comparative effects of dehydroepiandrosterone sulfate on ventricular diastolic function with young and aged female mice.

The adrenal steroid hormone dehydroepiandrosterone (DHEA) and its sulfated derivative [DHEA(S)] have been extensively studied for their potential anti-aging effects. Associated with aging, DHEA levels decline in humans, whereas other adrenal hormones remain unchanged, suggesting that DHEA may be important in the aging process. However, the effect of DHEA(S) supplementation on cardiac function in the aged has not been investigated. Therefore, we administered to young and old female mice a 60-day treatment with exogenous DHEA(S) at a dose of 0.1 mg/ml in the drinking water and compared the effects on left ventricular diastolic function and the myocardial extracellular matrix composition. The left ventricular stiffness (beta) was 0.30 +/- 0.06 mmHg/mul in the older control mice compared with 0.17 +/- 0.02 mmHg/mul in young control mice. Treatment with DHEA(S) decreased left ventricular stiffness to 0.12 +/- 0.03 mmHg/mul in the older mice and increased left ventricular stiffness to 0.27 +/- 0.04 mmHg/mul in young mice. The mechanism for the DHEA(S)-induced changes in diastolic function appeared to be associated with altered matrix metalloproteinase activity and the percentage of collagen cross-linking. We conclude that exogenous DHEA(S) supplementation is capable of reversing the left ventricular stiffness and fibrosis that accompanies aging, with a paradoxical increased ventricular stiffness in young mice.

Effects of water restriction on gene expression in mouse renal medulla: identification of 3betaHSD4 as a collecting duct protein.

To identify novel gene targets of vasopressin regulation in the renal medulla, we performed a cDNA microarray study on the inner medullary tissue of mice following a 48-h water restriction protocol. In this study, 4,625 genes of the possible approximately 12,000 genes on the array were included in the analysis, and of these 157 transcripts were increased and 63 transcripts were decreased by 1.5-fold or more. Quantitative, real-time PCR measurements confirmed the increases seen for 12 selected transcripts, and the decreases were confirmed for 7 transcripts. In addition, we measured transcript abundance for many renal collecting duct proteins that were not represented on the array; aquaporin-2 (AQP2), AQP3, Pax-8, and alpha- and beta-Na-K-ATPase subunits were all significantly increased in abundance; the beta- and gamma-subunits of ENaC and the vasopressin type 1A receptor were significantly decreased. To correlate changes in mRNA expression with changes in protein expression, we carried out quantitative immunoblotting. For most of the genes examined, changes in mRNA abundances were not associated with concomitant protein abundance changes; however, AQP2 transcript abundance and protein abundance did correlate. Surprisingly, aldolase B transcript abundance was increased but protein abundance was decreased following 48 h of water restriction. Several transcripts identified by microarray were novel with respect to their expression in mouse renal medullary tissues. The steroid hormone enzyme 3beta-hydroxysteroid dehydrogenase 4 (3betaHSD4) was identified as a novel target of vasopressin regulation, and via dual labeling immunofluorescence we colocalized the expression of this protein to AQP2-expressing collecting ducts of the kidney. These studies have identified several transcripts whose abundances are regulated in mouse inner medulla in response to an increase in endogenous vasopressin levels and could play roles in the regulation of salt and water excretion.

Renal medullary gene expression in aquaporin-1 null mice.

Mice that lack the aquaporin-1 gene (AQP1) lack a functional countercurrent multiplier mechanism, fail to concentrate the inner medullary (IM) interstitium, and present with a urinary concentrating defect. In this study, we use DNA microarrays to identify the gene expression profile of the IM of AQP1 null mice and corresponding changes in gene expression resulting from a loss of a hypertonic medullary interstitium. An ANOVA analysis model, CARMA, was used to isolate the knockout effect while taking into account experimental variability associated with microarray studies. In this study 5,701 genes of the possible approximately 12,000 genes on the array were included in the ANOVA; 531 genes were identified as demonstrating a >1.5-fold up- or downregulation between the wild-type and knockout groups. We randomly selected 35 genes for confirmation by real-time PCR, and 29 of the 35 genes were confirmed using this method. The overall pattern of gene expression in the AQP1 null mice was one of downregulation compared with gene expression in the renal medullas of the wild-type mice. Heat shock proteins 105 and 94, aldose reductase, adenylate kinase 2, aldolase B, aldehyde reductase 6, and p8 were decreased in the AQP1 null mice. Carboxylesterase 3, matrilin 2, lipocalin 2, and transforming growth factor-alpha were increased in IM of AQP1 null mice. In addition, we observed a loss of vasopressin type 2 receptor mRNA expression in renal medullas of the AQP1 null mice. Thus the loss of the hyperosmotic renal interstitium, due to a loss of the concentrating mechanism, drastically altered not only the phenotype of these animals but also their renal medullary gene expression profile.