Reduced 11beta-hydroxysteroid dehydrogenase activity in the remaining kidney following nephrectomy

Ultrastructural changes and nestin expression accompanying compensatory renal growth after unilateral nephrectomy in adult rats

Background

Several renal disorders affect the glomerular podocytes. Compensatory structural and functional changes have been observed in animals that have undergone unilateral renal ablation. These changes occur as a pliant response to quench the increased functional demand to maintain homeostasis of fluid and solutes. Nestin is an intermediate filament protein present in the glomerular podocytes of the adult kidney and is linked with the maintenance of its foot process structure. Structural changes in the podocytes ultimately restructure the filtration barrier. Very few studies related to the ultrastructural and histopathologic changes of the podocytes are documented. The present study aimed to assess the histopathologic changes at the ultrastructural level in the adapted kidney at different time intervals following unilateral renal ablation in adult rats and its relation with nestin.

Methods

Forty-eight rats were divided into four groups (n=12 in each group). The animals of Group A were control naïve rats, while the group B, group C and group D animals underwent left unilateral nephrectomy and the remaining right kidney was removed on days 10, 20 and 30, respectively. Each group included four sham-operated rats, which were sacrificed at the same time as the naïve rats. Each nephrectomized sample was weighed and its sections were subjected to hematoxylin and eosin examination, transmission electron microscopic study as well as immunostaining using the intermediate filament protein nestin.

Results

No difference was found between the kidney sections from the control group and the sham-operated groups. A significant increase in the weight of the right kidneys was noted in groups B, C and D (P<0.001). The ultrastructural adaptive changes seen in the glomeruli of group B were subsequently reduced in groups C and D. This finding corresponded to a similar pattern of nestin expression in the podocytes, which showed significant increase in group B followed by reduced expression in groups C and D. Histopathologic and transmission electron microscopic evaluation of group B showed signs of kidney injury. On the other hand, group C animals showed markedly reduced renal adaptive changes and similar changes were also noted in group D.

Conclusion

Correlation between nestin expression and the ultrastructural changes confirms that nestin has a role in increasing the mechanical stability of the podocytes in order to enhance their morphologic changes in response to the tensile glomerular capillary wall. However, further studies investigating more remote ultrastructural changes and their relation with nestin expression are needed to confirm this relationship.

Regulation of 11β-hydroxysteroid dehydrogenase type 2 by microRNA

The enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) is selectively expressed in aldosterone target tissues, conferring aldosterone selectivity for the mineralocorticoid receptor. A diminished activity causes salt-sensitive hypertension. The mechanism of the variable and distinct 11β-hydroxysteroid dehydrogenase type 2 gene (HSD11B2) expression in the cortical collecting duct is poorly understood. Here, we analyzed for the first time whether the 11β-HSD2 expression is modulated by microRNAs (miRNAs). In silico analysis revealed 53 and 27 miRNAs with potential binding sites on human or rat HSD11B2 3'-untranslated region. A reporter assay demonstrated 3'-untranslated region-dependent regulation of human and rodent HSD11B2. miRNAs were profiled from cortical collecting ducts and proximal convoluted tubules. Bioinformatic analyses showed a distinct clustering for cortical collecting ducts and proximal convoluted tubules with 53 of 375 miRNAs, where 13 were predicted to bind to the rat HSD11B2 3'-untranslated region. To gain insight into potentially relevant miRNAs in vivo, we investigated 2 models with differential 11β-HSD2 activity linked with salt-sensitive hypertension. (1) Comparing Sprague-Dawley with low and Wistar rats with high 11β-HSD2 activity revealed rno-miR-20a-5p, rno-miR-19b-3p, and rno-miR-190a-5p to be differentially expressed. (2) Uninephrectomy lowered 11β-HSD2 activity in the residual kidney with differentially expressed rno-miR-19b-3p, rno-miR-29b-3p, and rno-miR-26-5p. In conclusion, miRNA-dependent mechanisms seem to modulate 11β-HSD2 dosage in health and disease states.

High salt intake down-regulates colonic mineralocorticoid receptors, epithelial sodium channels and 11β-hydroxysteroid dehydrogenase type 2

Besides the kidneys, the gastrointestinal tract is the principal organ responsible for sodium homeostasis. For sodium transport across the cell membranes the epithelial sodium channel (ENaC) is of pivotal relevance. The ENaC is mainly regulated by mineralocorticoid receptor mediated actions. The MR activation by endogenous 11β-hydroxy-glucocorticoids is modulated by the 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2). Here we present evidence for intestinal segment specific 11β-HSD2 expression and hypothesize that a high salt intake and/or uninephrectomy (UNX) affects colonic 11β-HSD2, MR and ENaC expression. The 11β-HSD2 activity was measured by means of 3H-corticosterone conversion into 3H-11-dehydrocorticosterone in Sprague Dawley rats on a normal and high salt diet. The activity increased steadily from the ileum to the distal colon by a factor of about 3, an observation in line with the relevance of the distal colon for sodium handling. High salt intake diminished mRNA and protein of 11β-HSD2 by about 50% (p<0.001) and reduced the expression of the MR (p<0.01). The functionally relevant ENaC-β and ENaC-γ expression, a measure of mineralocorticoid action, diminished by more than 50% by high salt intake (p<0.001). The observed changes were present in rats with and without UNX. Thus, colonic epithelial cells appear to contribute to the protective armamentarium of the mammalian body against salt overload, a mechanism not modulated by UNX.

Altered Regulation of Type II 11β-hydroxysteroid Dehydrogenase in the Kidney of Rats with Experimental Hypertension

The present study was aimed at investigating the role of type II 11β-hydroxysteroid dehydrogenase (IIβ-HSD II) in the development of hypertension. Two-kidney, one-clip (2K1C), deoxycorticosterone acetate (DOCA)/salt, or N^G-nitro-L-arginine methyl ester (L-NAME) hypertension was induced in male Sprague-Dawley rats. Four weeks later, the expression of 11β-HSD II mRNA was determined in the kidney by Northern blot analysis. The plasma level of aldosterone was measured by radioimmunoassay. In 2K1C hypertension, the expression of 11β-HSD II was decreased in the clipped kidney and increased in the non-clipped kidney. The expression was increased in the remnant kidney of DOCA/salt hypertension, while decreased in the kidneys of L-NAME hypertension. The plasma level of aldosterone was increased, decreased, and remained unchanged in 2K1C, DOCA/salt, and L-NAME hypertension, respectively. The down-regulation of 11β-HSD II may contribute to the sodium retention, thereby increasing the blood pressure in 2K1C and L-NAME hypertension. On the contrary, the up-regulation in DOCA/salt hypertension may play a compensatory role to dissipate the sodium retention.

Renal interstitial corticosterone and 11-dehydrocorticosterone in conscious rats

Deficiencies in the conversion between active and inactive glucocorticoids in the kidney can lead to hypertension. However, the significance of glucocorticoid metabolism in specific kidney regions in vivo is not clear, possibly in part due to the difficulty in measuring glucocorticoid levels in kidney regions in vivo. We used microdialysis techniques to sample renal interstitial fluid from conscious rats. The levels of corticosterone (active) and 11-dehydrocorticosterone (inactive) were analyzed by liquid chromatography-tandem mass spectrometry. Direct infusion of the 11β-hydroxysteroid dehydrogenase (11β-HSD) inhibitor carbenoxolone into the renal medulla induced hypertension, and significantly increased corticosterone levels and the corticosterone/11-dehydrocorticosterone ratio, an index of 11β-HSD activity, in the renal medullary microdialysate, but not in urine or the plasma. Further characterization of conscious, untreated rats ( n = 13–16) indicated that corticosterone concentrations (ng/ml) were 0.8 ± 0.1, 1.0 ± 0.1, 66.7 ± 8.1, and 7.9 ± 1.1 in cortical microdialysate, medullary microdialysate, the plasma, and urine, respectively. The corticosterone/11-dehydrocorticosterone ratios were 0.8 ± 0.1, 0.6 ± 0.1, 10.6 ± 1.4, and 1.7 ± 0.1, respectively, in these 4 types of sample. The expression level of 11β-HSD1 was higher in the medulla than in the cortex, whereas 11β-HSD2 was most enriched in the outer medulla. Microdialysate levels of corticosterone were ∼1.6-fold higher in afternoons than in mornings, whereas plasma levels differed by 2.8-fold. These results demonstrated that corticosterone excess in the renal medulla might be sufficient to cause hypertension and provided the first characterization of renal interstitial glucocorticoids.

Glucocorticoid-mediated mineralocorticoid receptor activation and hypertension

PURPOSE OF REVIEW

Traditionally, the mineralocorticoid receptor was thought to be activated by the mineralocorticoid hormone aldosterone, and to exhibit its main action on epithelia by promoting renal sodium retention, potassium excretion and inducing hypertension upon excessive activation. Recently, evidence appeared that mineralocorticoid receptors are expressed in nonepithelial cells and activated by endogenous glucocorticoids including cortisol. Therefore, the prereceptor regulation of cortisol access to the mineralocorticoid receptors by 11beta-hydroxysteroid dehydrogenase enzymes (11beta-HSDs), a mechanism absent in most nonepithelial cells, appears to be relevant for disease states with cortisol-induced mineralocorticoid action. The present review focuses on direct and indirect effects attributable to mineralocorticoid receptor activation by glucocorticoids.

RECENT FINDINGS

The determination of the intracellular topology of 11beta-HSD1, facing the endoplasmic reticulum lumen, and 11beta-HSD2, facing the cytoplasm, suggests that 11beta-HSD1 acts as a prereceptor mechanism in the local activation of glucocorticoid receptors, whereas 11beta-HSD2 controls mineralocorticoid receptors by interacting with the receptor in the absence of aldosterone. Downregulation of 11beta-HSD2 was observed with various stimuli including hypoxia, shear stress, angiotensin II and tumor necrosis factor alpha. The corresponding signal transcription pathways and some relevant transcription factors have been identified. Renal sodium retention in liver cirrhosis, nephrotic syndrome and hypoxia have been linked to 11beta-HSD2 reduced activity. Overexpression of 11beta-HSD1 specifically in adipose tissue in mice caused central obesity, a metabolic syndrome and hypertension due to increased intracellular cortisol concentrations. Peroxisome proliferator-activated receptor gamma agonists reduce 11beta-HSD1 activity and diminish the intracellular availability of cortisol, an effect accompanied by a decline in blood pressure. Three individuals with loss-of-function mutations of peroxisome proliferator-activated receptor gamma developed early hypertension. A potential mechanism might be glucocorticoid dependent mineralocorticoid receptor-mediated downregulation of endothelial nitric oxide synthase.

SUMMARY

Recently, mineralocorticoid receptor antagonists have been used in the randomized aldactone evaluation study (RALES) with spironolactone, the eplerenone post-AMI heart failure efficacy and survival study (EPHESUS), and in severe and postmyocardial infarct heart failure, respectively. These investigations cannot be understood on the basis of the present physiological knowledge and underscore the relevance of focusing on mineralocorticoid receptor activation by ligands other than aldosterone.

Glucocorticoids and 11 beta-hydroxysteroid dehydrogenase type 2 gene expression in the aging kidney

BACKGROUND

Aging is associated with increased concentrations of circulating glucocorticoids, a situation expected to induce a glucocorticoid-mediated mineralocorticoid effect, resulting in sodium retention and hypertension unless counteracting mechanisms are operative. Conversion of glucocorticoids to inert 11 beta-keto compounds by the enzyme 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD2) is one of these mechanisms. We hypothesized therefore that 11 beta-HSD2 gene expression and/or activity increase with age in male WAG/Rij rats, a strain without increased blood pressure with age or senescence-related obesity or kidney disease.

MATERIALS AND METHODS

Corticosterone (B) concentrations in plasma and urinary excretion of corticosterone and dehydrocorticosterone (A) tetrahydro metabolites, THB + 5 alpha-THB + THA, were assessed by gas chromatography-mass spectrometry (GC-MS) in 10-month-old-rats (n = 6) and in 30-month-old rats (n = 6). Renal 11 beta-HSD2 messenger ribonucleic acid (mRNA) abundance was measured by real-time quantitative TaqMan polymerase chain reaction and microarray assays.

RESULTS

Thirty-month-old rats had significantly higher corticosterone concentrations in plasma and increased urinary excretion of corticosterone and dehydrocorticosterone tetrahydro metabolites. Conversion of B to A in kidney microsomes from 30-month-old rats was moderately but not significantly increased compared with 10-month-old rats. The urinary ratios of (THB + 5 alpha-THB)/THA and free B/A and renal 11 beta-HSD2 mRNA abundance were equal in 10- and 30-month-old rats.

CONCLUSIONS

There is no evidence for an enhanced gene expression or activity of renal 11 beta-HSD2 in these aging rats, suggesting either that endogenous 11 beta-HSD2 is able to cope with the increased corticosterone concentrations characteristic of the aging process or that alternative mechanisms contribute to the maintenance of a normal sodium excretion in these animals.

In vivo footprinting of the human 11beta-hydroxysteroid dehydrogenase type 2 promoter: evidence for cell-specific regulation by Sp1 and Sp3

11beta-Hydroxysteroid dehydrogenase type 2 is selectively expressed in aldosterone target tissues, where it confers aldosterone selectivity for the mineralocorticoid receptor by inactivating 11beta-hydroxyglucocorticoids with a high affinity for the mineralocorticoid receptor. The present investigation aimed to elucidate the mechanisms accounting for the rigorous control of the HSD11B2 gene in humans. Using dimethyl sulfate in vivo footprinting via ligation-mediated PCR, we identified potentially important regions for HSD11B2 regulation in human cell lines: two GC-rich regions in the first exon (I and II) and two upstream elements (III and IV). The footprints suggest a correlation between the extent of in vivo protein occupancy at three of these regions (I, II, and III) and the rate of HSD11B2 transcription in cells with high (SW620), intermediate (HCD, MCF-7, and HK-2), or low HSD11B2 mRNA levels (SUT). Moreover, gel shift assays with nuclear extracts from these cell lines revealed that decreased HSD11B2 expression is related to a decreased binding activity with oligonucleotides containing the putative regulatory elements. Antibody supershifts identified the majority of the components of the binding complexes as the transcription factors Sp1 and Sp3. Finally, transient transfections with various deletion mutant reporters define positive regulatory elements that might account for basal and selective expression of 11beta-hydroxysteroid dehydrogenase type 2.

TNF-alpha enhances intracellular glucocorticoid availability

For understanding the mechanism(s) relating inflammation to corticosteroid action, the effect of tumour necrosis factor-alpha (TNF-alpha) on 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), the enzyme regulating access of 11beta-hydroxycorticosteroids to receptors, was studied in LLC-PK(1) cells. We observed (i) NAD-dependent enzyme activity and mRNA for 11beta-HSD2, but not 11beta-HSD1, (ii) increasing 11beta-HSD2 activity with increasing degree of differentiation and (iii) a concentration-dependent down-regulation by TNF-alpha, phorbol myristate acetate (PMA) or glucose of activity and mRNA of 11beta-HSD2. The decrease of activity and mRNA by glucose and PMA, but not that by TNF-alpha, was abrogated by the protein kinase C inhibitor GF-109203X. The effect of TNF-alpha on 11beta-HSD2 was reversed by inhibiting the mitogen-activated protein kinases ERK with PD-098050 and p38 by SB-202190, or by activating protein kinase A with forskolin. Overexpression of MEK1, an ERK activator, down-regulated the 11beta-HSD2 activity. In conclusion, TNF-alpha decreases 11beta-HSD2 activity and thereby enhances glucocorticoid access to glucocorticoid receptors to modulate the inflammatory response.

Effect of angiotensin II on rat renal cortical 11beta-hydroxysteroid dehydrogenase

Renal 11beta-hydroxysteroid dehydrogenases (11beta-HSDs) are subject to modulation by various endogenous factors. 11beta-HSDs convert glucocorticoids into inactive 11-ketones and thereby determine tissue levels of active glucocorticoids and thus the extent of glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) activation. As such, modulation of the activity of renal 11beta-HSDs may contribute to the cascade of regulatory events involved in renal electrolyte water handling. We investigated whether renal 11beta-HSDs are modulated by elevated circulating angiotensin II. In rats infused for 2 wk with angiotensin II (250 ng/[kg x min] subcutaneously), plasma angiotensin II, aldosterone, and corticosterone were raised 5.1-, 10.7-, and 2.3-fold, respectively, compared with control rats. Angiotensin II infusion raised corticosterone 11beta-oxidation 1.46- and 1.35-fold in renal cortical proximal and distal tubules (enriched by Percoll centrifugation), respectively, but had no effect on 11beta-HSD1 and 11beta-HSD2 mRNA levels (semiquantitative reverse transcriptase polymerase chain reaction), except for distal tubular 11beta-HSD1 mRNA, which was decreased to 50%. In vitro treatment of freshly isolated tubules with angiotensin II for 45 min prior to assessment of 11beta-HSD activity showed no direct acute effects of angiotensin II on tubular corticosterone 11beta-oxidation. The enhanced renal tubular corticosterone 11beta-oxidation in vivo may partly protect renal GR and MR from elevated plasma corticosterone on angiotensin II infusion.

The N-terminal anchor sequences of 11beta-hydroxysteroid dehydrogenases determine their orientation in the endoplasmic reticulum membrane

11beta-Hydroxysteroid dehydrogenase enzymes (11beta- HSD) regulate the ratio of active endogenous glucocorticoids to their inactive keto-metabolites, thereby controlling the access of glucocorticoids to their cognate receptors. In this study, the topology and intracellular localization of 11beta-HSD1 and 11beta-HSD2 have been analyzed by immunohistochemistry and protease protection assays of in vitro transcription/translation products. 11beta-HSD constructs, tagged with the FLAG epitope, were transiently expressed in HEK-293 cells. The enzymatic characteristics of tagged and native enzymes were indistinguishable. Fluorescence microscopy demonstrated the localization of both 11beta-HSD1 and 11beta-HSD2 exclusively to the endoplasmic reticulum (ER) membrane. To examine the orientation of tagged 11beta-HSD enzymes within the ER membrane, we stained selectively permeabilized HEK-293 cells with anti-FLAG antibody. Immunohistochemistry revealed that the N terminus of 11beta-HSD1 is cytoplasmic, and the catalytic domain containing the C terminus is protruding into the ER lumen. In contrast, the N terminus of 11beta-HSD2 is lumenal, and the catalytic domain is facing the cytoplasm. Chimeric proteins where the N-terminal anchor sequences of 11beta-HSD1 and 11beta-HSD2 were exchanged adopted inverted orientation in the ER membrane. However, both chimeric proteins were not catalytically active. Furthermore, mutation of a tyrosine motif to alanine in the transmembrane segment of 11beta-HSD1 significantly reduced V(max). The subcellular localization of 11beta-HSD1 was not affected by mutations of the tyrosine motif or of a di-lysine motif in the N terminus. However, residue Lys(5), but not Lys(6), turned out to be critical for the topology of 11beta-HSD1. Mutation of Lys(5) to Ser inverted the orientation of 11beta-HSD1 in the ER membrane without loss of catalytic activity. Our results emphasize the importance of the N-terminal transmembrane segments of 11beta-HSD enzymes for their proper function and demonstrate that they are sufficient to determine their orientation in the ER membrane.

Inhibition of 11beta-hydroxysteroid dehydrogenase by bile acids in rats with cirrhosis

Renal sodium retention and potassium loss occur early, in many instances in the preascitic state of cirrhosis, an observation that cannot be fully explained by increased aldosterone concentrations. We therefore hypothesize that 11beta-hydroxysteroid dehydrogenase 2 (11beta-HSD2), which protects mineralocorticoid receptors (MR) from glucocorticosteroids, is down-regulated in cirrhosis. Cirrhosis was induced by bile duct ligation in rats. The urinary ratio of (tetrahydrocorticosterone + 5alpha-tetrahydrocorticosterone)/ 11-dehydro-tetrahydrocorticosterone [(THB+5alpha-THB)/THA] was measured by gas chromatography. Cortical collecting tubules (CCT) were isolated by microdissection and used for measurements of the activity of 11beta-HSD2 by assessing the conversion of corticosterone to dehydrocorticosterone. The mRNA content of 11beta-HSD2 was determined by reverse-transcription polymerase chain reaction (RT-PCR) in CCTs. The urinary ratio of (THB+5alpha-THB)/THA increased concomitantly with the urinary excretion of bile acids following bile duct ligation. Chenodeoxycholic acid (CDCA) dose-dependently inhibited 11beta-HSD2 in CCT with a Ki of 19.9 micromol/L. Four weeks after bile duct ligation, 11beta-HSD2 activity was decreased in CCT, an observation preceded by a reduced mRNA content at weeks 2 and 3. In cirrhosis, the MR-protecting effect by 11beta-HSD2 is diminished, and therefore, endogenous glucocorticoids can induce MR-mediated sodium retention and potassium loss.