Angiotensin II AT1 Receptor Blockade Changes Expression of Renal Sodium Transporters in Rats with Chronic Renal Failure

We aimed to examine the effects of angiotensin II AT1 receptor blocker on the expression of major renal sodium transporters and aquaporin-2 (AQP2) in rats with chronic renal failure (CRF). During 2 wks after 5/6 nephrectomy or sham operation, both CRF rats (n=10) and sham-operated control rats (n=7) received a fixed amount of low sodium diet and had free access to water. CRF rats (n=10) were divided into two groups which were either candesartan-treated (CRF-C, n=4) or vehicletreated (CRF-V, n=6). Both CRF-C and CRF-V demonstrated azotemia, decreased GFR, polyuria, and decreased urine osmolality compared with sham-operated rats. When compared with CRF-V, CRF-C was associated with significantly higher BUN levels and lower remnant kidney weight. Semiquantitative immunoblotting demonstrated decreased AQP2 expression in both CRF-C (54% of control levels) and CRF-V (57%), whereas BSC-1 expression was increased in both CRF groups. Particularly, CRF-C was associated with higher BSC-1 expression (611%) compared with CRF-V (289%). In contrast, the expression of NHE3 (25%) and TSC (27%) was decreased in CRF-C, whereas no changes were observed in CRF-V. In conclusion, 1) candesartan treatment in an early phase of CRF is associated with decreased renal hypertrophy and increased BUN level; 2) decreased AQP2 level in CRF is likely to play a role in the decreased urine concentration, and the downregulation is not altered in response to candesartan treatment; 3) candesartan treatment decreases NHE3 and TSC expression; and 4) an increase of BSC-1 is prominent in candesartan-treated CRF rats, which could be associated with the increased delivery of sodium and water to the thick ascending limb

Gene Expression Programs of Mouse Endothelial Cells in Kidney Development and Disease

Endothelial cells are remarkably heterogeneous in both morphology and function, and they play critical roles in the formation of multiple organ systems. In addition endothelial cell dysfunction can contribute to disease processes, including diabetic nephropathy, which is a leading cause of end stage renal disease. In this report we define the comprehensive gene expression programs of multiple types of kidney endothelial cells, and analyze the differences that distinguish them. Endothelial cells were purified from Tie2-GFP mice by cell dissociation and fluorescent activated cell sorting. Microarrays were then used to provide a global, quantitative and sensitive measure of gene expression levels. We examined renal endothelial cells from the embryo and from the adult glomerulus, cortex and medulla compartments, as well as the glomerular endothelial cells of the db/db mutant mouse, which represents a model for human diabetic nephropathy. The results identified the growth factors, receptors and transcription factors expressed by these multiple endothelial cell types. Biological processes and molecular pathways were characterized in exquisite detail. Cell type specific gene expression patterns were defined, finding novel molecular markers and providing a better understanding of compartmental distinctions. Further, analysis of enriched, evolutionarily conserved transcription factor binding sites in the promoters of co-activated genes begins to define the genetic regulatory network of renal endothelial cell formation. Finally, the gene expression differences associated with diabetic nephropathy were defined, providing a global view of both the pathogenic and protective pathways activated. These studies provide a rich resource to facilitate further investigations of endothelial cell functions in kidney development, adult compartments, and disease

Multiple Cross Talk between Angiotensin II, Bradykinin, and Insulin Signaling in the Cortical Thick Ascending Limb of Rat Kidney

International audienceCortical thick ascending limb (CTAL) naturally expresses the angiotensin II (AngII) receptor type 1A (AT1 -R), the bradykinin (BK) receptor type 2 (B2 -R), and the insulin receptor. This segment is made of a single morphologically distinct cell type. AngII and BK are involved in same transduction pathways but differ markedly in their physiological actions on Na transport. Besides, the insulin signaling intersects with those of AngII and BK at multiple levels and especially by stimulation on Na reabsorption. Thus, the CTAL is a biologically suitable model to study the cross talk between G protein-coupled receptors or G protein-coupled receptors and receptor tyrosine kinase. In this work, the cross talks between AngII, BK, and insulin signaling are studied in rat CTAL by measuring changes in [Ca2]i . We show that BK exerts negative modulatory effects on AngII-induced [Ca2]i responses dependent on tyrosine kinase and MAPK pathways. Moreover, in the presence of BK, AngII-induced Na transport is suppressed. These effects suggest an interaction between AT1 -R and B 2 -R. We show a positive interaction between the insulin receptor and the AT1 -R through a protein kinase A-dependent mechanism that involves MAPK cascade, leading to the stimulation of the Ca2 influx induced by AngII. The presence of such interactions brings additional arguments for a complex and fine regulation of CTAL functions and puts forward the potentially beneficial effect of BK across this segment, in case of hyperinsulinemia or insulin resistance, by its negative feedback on AngII actions

Tyrosine kinase and mitogen-activated protein kinase/extracellularly regulated kinase differentially regulate intracellular calcium concentration responses to angiotensin II/III and bradykinin in rat cortical thick ascending limb.

International audienceThe cortical thick ascending limb (CTAL) coexpresses angiotensin (Ang) II/Ang III receptor type 1A (AT(1A)-R) and bradykinin (BK) receptor type 2 (B2-R). In several cell types, these two receptors share the same signaling pathways, although their physiological functions are often opposite. In CTAL, little is known about the intracellular transduction events leading to the final physiological response induced by these two peptides. We investigated and compared in this segment the action of Ang II/III and BK on intracellular calcium concentration ([Ca2+]i) response and metabolic CO2 production, an index of Na+ transport, by using inhibitors of protein kinase C (bisindolylmaleimide), Src tyrosine kinase (herbimycin A and PP2), and MAPK/ERK (PD98059 and UO126). Ang II/III and BK (10(-7) mol/liter) released Ca2+ from the same intracellular pools but activated different Ca2+ entry pathways. Ang II/III- or BK-induced [Ca2+]i increases were similarly potentiated by bisindolylmaleimide. Herbimycin A and PP2 decreased similarly the [Ca2+]i responses induced by Ang II/III and BK. In contrast, PD98059 and UO126 affected the effects of BK to a larger extent than those of Ang II/III. Especially, the Ca2+ influx induced by BK was more strongly inhibited than that induced by Ang II/III in the presence of both compounds. The Na+ transport was inhibited by BK and stimulated by Ang II/III. The inhibitory action of BK on Na+ transport was blocked by UO126, whereas the stimulatory response of Ang II/III was potentiated by UO126 but blocked by bisindolylmaleimide. These data suggest that the inhibitory effect of BK on Na+ transport seems to be directly mediated by an increase in Ca2+ influx dependent on MAPK/ERK pathway activation. In contrast, the stimulatory effect of Ang II/III on Na+ transport is more complex and involves PKC and MAPK/ERK pathways

Effect of apelin on glomerular hemodynamic function in the rat kidney.

International audienceApelin is a vasoactive peptide identified as the endogenous ligand of an orphan G protein-coupled receptor called APJ. Apelin and its receptor have been found in the brain and the cardiovascular system. Here we show that the apelin receptor mRNA is highly expressed in the glomeruli while its level of expression is lower in all nephron segments including collecting ducts that express vasopressin V2 receptors. Intravenous injection of apelin 17 into lactating rats induced a significant diuresis. Apelin receptor mRNA was also found in endothelial and vascular smooth muscle cells of glomerular arterioles. Apelin administration caused vasorelaxation of angiotensin II-preconstricted efferent and afferent arterioles as shown by an increase in their diameter. Activation of endothelial apelin receptors caused release of nitric oxide which inhibited angiotensin II-induced rise in intracellular calcium. In addition, it appears that apelin had a direct receptor-mediated vasoconstrictive effect on vascular smooth muscle. These results show that apelin has complex effects on the pre- and post glomerular microvasculature regulating renal hemodynamics. Its role on tubular function (if any) remains to be determined

Characterization of a Functional V1B Vasopressin Receptor in the Male Rat Kidney: Evidence for Cross Talk Between V1B and V2 Receptor Signaling Pathways

Although vasopressin V-1B receptor (V1BR) mRNA has been detected in the kidney, the precise renal localization as well as pharmacological and physiological properties of this receptor remain unknown. Using the selective V-1B agonist d[Leu(4), Lys(8)]VP, either fluorescent or radioactive, we showed that V1BR is mainly present in principal cells of the inner medullary collecting duct (IMCD) in the male rat kidney. Protein and mRNA expression of V1BR were very low compared with the V2 receptor (V2R). On the microdissected IMCD, d[Leu(4), Lys(8)]VP had no effect on cAMP production but induced a dose-dependent and saturable intracellular Ca2+ concentration increase mobilization with an EC50 value in the nanomolar range. This effect involved both intracellular Ca2+ mobilization and extracellular Ca2+ influx. The selective V1B antagonist SSR149415 strongly reduced the ability of vasopressin to increase intracellular Ca2+ concentration but also cAMP, suggesting a cooperation between V1BR and V2R in IMCD cells expressing both receptors. This cooperation arises from a cross talk between second messenger cascade involving PKC rather than receptor heterodimerization, as supported by potentiation of arginine vasopressin-stimulated cAMP production in human embryonic kidney-293 cells coexpressing the two receptor isoforms and negative results obtained by bioluminescence resonance energy transfer experiments. In vivo, only acute administration of high doses of V1B agonist triggered significant diuretic effects, in contrast with injection of selective V2 agonist. This study brings new data on the localization and signaling pathways of V1BR in the kidney, highlights a cross talk between V1BR and V2R in the IMCD, and suggests that V1BR may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V2R activation. New & Noteworthy: Although V1BR mRNA has been detected in the kidney, the precise renal localization as well as pharmacological and physiological properties of this receptor remain unknown. Using original pharmaceutical tools, this study brings new data on the localization and signaling pathways of V1BR, highlights a cross talk between V1BR and V-2 receptor (V2R) in the inner medullary collecting duct, and suggests that V1BR may counterbalance in some pathophysiological conditions the antidiuretic effect triggered by V2R activation