Exploring the role of galectin 3 in kidney function: a genetic approach.

Galectin 3 belongs to a family of glycoconjugate-binding proteins that participate in cellular homeostasis by modulating cell growth, adhesion, and signaling. We studied adult galectin 3 null mutant (Gal 3-/-) and wild-type (WT) mice to gain insights into the role of galectin 3 in the kidney. By immunofluorescence, galectin 3 was found in collecting duct (CD) principal and intercalated cells in some regions of the kidney, as well as in the thick ascending limbs at lower levels. Compared to WT mice, Gal 3-/- mice had approximately 11% fewer glomeruli (p < 0.04), associated with kidney hypertrophy (p < 0.006). In clearance experiments, urinary chloride excretion was found to be higher in Gal 3-/- than in WT mice (p < 0.04), but there was no difference in urinary bicarbonate excretion, in glomerular filtration, or urinary flow rates. Under chronic low sodium diet, Gal 3-/- mice had lower extracellular fluid (ECF) volume than WT mice (p < 0.05). Plasma aldosterone concentration was higher in Gal 3-/- than in WT mice (p < 0.04), which probably caused the observed increase in alpha-epithelial sodium channel (alpha-ENaC) protein abundance in the mutant mice (p < 0.001). Chronic high sodium diet resulted paradoxically in lower blood pressure (p < 0.01) in Gal 3-/- than in WT. We conclude that Gal 3-/- mice have mild renal chloride loss, which causes chronic ECF volume contraction and reduced blood pressure levels.

Impaired 11-beta hydroxysteroid dehydrogenase type 2 activity in sweat gland ducts in human essential hypertension.

The enzyme 11-beta hydroxysteroid dehydrogenase type 2 plays a major role in blood pressure regulation. It metabolizes glucocorticoid hormones into derivatives with low affinity for the mineralocorticoid receptor, preventing its permanent occupancy by circulating cortisol, which is 100- to 1000-fold more abundant than aldosterone in the plasma. Inactivating mutations of the enzyme result in severe hypertension, as seen in children with apparent mineralocorticoid excess syndrome. In patients with essential hypertension, however, attempts to evidence enzyme deficiency have been inconclusive. In this pilot study, its catalytic activity was measured directly in aldosterone-sensitive sweat gland ducts collected from skin biopsy samples of 10 male normotensive subjects and 10 subjects with essential hypertension (more than 140 to 90 mm Hg) with no sign of hypermineralocorticism. Isolated ducts were assayed for nicotinamide-dinucleotide-dependent dehydrogenase activity (transformation of tritiated corticosterone into tritiated-11 dehydrocorticosterone, as measured by high-pressure liquid chromatography). Hypertensive patients exhibited significantly lower 11-beta hydroxysteroid dehydrogenase type 2 activity (9.7+/-4.7 femtomoles per 3 mm length of duct and per 10 minutes incubation, median+/-SD) than did normotensive subjects (15.9+/-2.6). Such defect was undetectable using the classical urinary corticosteroid metabolism indexes, probably because of compensatory mechanisms. Relations between these findings and blood pressure levels should benefit from direct enzyme measurements in the vasculature. In conclusion, this cross-sectional study points to partial 11-beta hydroxysteroid dehydrogenase type 2 deficiency as a novel feature of essential hypertension, which should stimulate search for new signaling pathways and therapeutical targets.

Basolateral translocation by vasopressin of the aldosterone-induced pool of latent Na-K-ATPases is accompanied by alpha1 subunit dephosphorylation: study in a new aldosterone-sensitive rat cortical collecting duct cell line.

The regulation of plasma membrane Na(+)-K(+)-ATPases (NKA) expression by aldosterone and arginin vasopressin (AVP) in the cortical collecting duct (CCD) has been examined in a new rat CCD cell line, designated as RCCD(2). This cell line has maintained many characteristics of the CCD-in particular, the expression of the mineralocorticoid receptor. Mineralocorticoid receptor is expressed at the protein level and binds (3)H-aldosterone (approximately 15 to 20 fmol/mg protein). Short-circuit current (Isc) experiments showed approximately a twofold increase in Isc associated with a decrease in transepithelial resistance when cells were treated with aldosterone concentrations as low as 10(-9) M. This effect on Isc was significant 2 h after aldosterone addition and was still present after 24 h. It was accompanied by an increase in the amount of mRNA encoding for the alpha subunit of the epithelial sodium channel (sixfold) and the alpha1 subunit of NKA (fourfold) after 24 h of hormone treatment. In addition, mRNA expression of the serum- and glucocorticoid-induced kinase (Sgk) was increased by 10(-9) M aldosterone treatment as early as 45 min after hormone addition. As had already been documented in native CCD obtained by microdissection, incubation of RCCD(2) cells for 24 h with aldosterone resulted in the constitution of a latent pool of NKA that could be rapidly recruited by AVP (15 min). NKA biotinylation experiments and preparation of membrane fractions show that this latent pool of NKA is present in the intracellular compartment of the cells and is recruited by AVP in the basolateral membrane through a translocation process. This mechanism is accompanied by dephosphorylation of the alpha(1) catalytic subunit of NKA.