The NF-κB/FXR/TonEBP pathway protects renal medullary interstitial cells against hypertonic stress.

Farnesoid X receptor (FXR), a ligand-activated transcription factor, plays an important role in maintaining water homeostasis by up-regulating aquaporin 2 (AQP2) expression in renal medullary collecting ducts; however, its role in the survival of renal medullary interstitial cells (RMICs) under hypertonic conditions remains unclear. We cultured primary mouse RMICs and found that the FXR was expressed constitutively in RMICs, and that its expression was significantly up-regulated at both mRNA and protein levels by hypertonic stress. Using luciferase and ChIP assays, we found a potential binding site of nuclear factor kappa-B (NF-κB) located in the FXR gene promoter which can be bound and activated by NF-κB. Moreover, hypertonic stress-induced cell death in RMICs was significantly attenuated by FXR activation but worsened by FXR inhibition. Furthermore, FXR increased the expression and nuclear translocation of hypertonicity-induced tonicity-responsive enhance-binding protein (TonEBP), the expressions of its downstream target gene sodium myo-inositol transporter (SMIT), and heat shock protein 70 (HSP70). The present study demonstrates that the NF-κB/FXR/TonEBP pathway protects RMICs against hypertonic stress.

Unexpected localization of AQP3 and AQP4 induced by migration of primary cultured IMCD cells.

Aquaporin-2-4 (AQP) are expressed in the principal cells of the renal collecting duct (CD). Beside their role in water transport across membranes, several studies showed that AQPs can influence the migration of cells. It is unknown whether this also applies for renal CD cells. Another fact is that the expression of these AQPs is highly modulated by the external osmolality. Here we analyzed the localization of AQP2-4 in primary cultured renal inner medullary CD (IMCD) cells and how osmolality influences the migration behavior of these cells. The primary IMCD cells showed a collective migration behavior and there were no differences in the migration speed between cells cultivated either at 300 or 600 mosmol/kg. Acute increase from 300 to 600 mosmol/kg led to a marked reduction and vice versa an acute decrease from 600 to 300 mosmol/kg to a marked increase in migration speed. Interestingly, none of the analyzed AQPs were localized at the leading edge. While AQP3 disappeared within the first 2-3 rows of cells, AQP4 was enriched at the rear end. Further analysis indicated that migration induced lysosomal degradation of AQP3. This could be prevented by activation of the protein kinase A, inducing localization of AQP3 and AQP2 at the leading edge and increasing the migration speed.

Renal medullary carcinoma involving serous cavity fluids: a cytomorphologic study of 12 cases.

INTRODUCTION: Renal medullary carcinoma (RMC) is a highly lethal adenocarcinoma with a propensity for widespread metastatic disease in young patients. It is strongly associated with sickle cell trait and shows the loss of SMARCB1 (also known as INI1 or BAF47) protein expression. In the present study, we reviewed a series of 12 patients for whom the cytology specimens played a significant role in patient treatment. MATERIALS AND METHODS: We performed a retrospective case review of patients with a history of RMC from 3 large tertiary care pathology practices. RESULTS: A total of 12 patients were identified with histologically confirmed RMC who had had pleural, pericardial, or urine specimens involved by their disease or had undergone initial kidney fine needle aspiration. Patient age ranged from 13 to 37 years (median, 21.5 years). All 12 patients were black or of African descent, and 10 had a confirmed history of sickle cell trait. Of the 12 patients, 11 (92%) had fluid specimens involved by metastatic tumor at some point in their clinical course, and 4 (33%) had initially presented with pericardial and/or pleural effusions or urine specimens that were positive for malignancy. Cytologic examination predominantly showed fragments of 3-dimensional "tumor balls" with smooth borders, fine pale cytoplasm with vacuolization, and highly pleomorphic nuclei with irregular nuclear membranes and coarse to vesicular chromatin and single prominent nucleoli. CONCLUSIONS: The cytomorphology of RMC involving serous fluids is nonspecific and in keeping with metastatic high-grade adenocarcinoma. In a young patient presenting with no history of malignancy and a pleural or pericardial effusion, triaging the material for ancillary studies and a nuanced assessment of patient history and radiologic findings will be critical.

Renomedullary Interstitial Cell Endothelin A Receptors Regulate BP and Renal Function.

BACKGROUND: The physiologic role of renomedullary interstitial cells, which are uniquely and abundantly found in the renal inner medulla, is largely unknown. Endothelin A receptors regulate multiple aspects of renomedullary interstitial cell function in vitro. METHODS: To assess the effect of targeting renomedullary interstitial cell endothelin A receptors in vivo, we generated a mouse knockout model with inducible disruption of renomedullary interstitial cell endothelin A receptors at 3 months of age. RESULTS: BP and renal function were similar between endothelin A receptor knockout and control mice during normal and reduced sodium or water intake. In contrast, on a high-salt diet, compared with control mice, the knockout mice had reduced BP; increased urinary sodium, potassium, water, and endothelin-1 excretion; increased urinary nitrite/nitrate excretion associated with increased noncollecting duct nitric oxide synthase-1 expression; increased PGE2 excretion associated with increased collecting duct cyclooxygenase-1 expression; and reduced inner medullary epithelial sodium channel expression. Water-loaded endothelin A receptor knockout mice, compared with control mice, had markedly enhanced urine volume and reduced urine osmolality associated with increased urinary endothelin-1 and PGE2 excretion, increased cyclooxygenase-2 protein expression, and decreased inner medullary aquaporin-2 protein content. No evidence of endothelin-1-induced renomedullary interstitial cell contraction was observed. CONCLUSIONS: Disruption of renomedullary interstitial cell endothelin A receptors reduces BP and increases salt and water excretion associated with enhanced production of intrinsic renal natriuretic and diuretic factors. These studies indicate that renomedullary interstitial cells can modulate BP and renal function under physiologic conditions.

Hepatocyte nuclear factor-1ß regulates Wnt signaling through genome-wide competition with ß-catenin/lymphoid enhancer binding factor.

Hepatocyte nuclear factor-1ß (HNF-1ß) is a tissue-specific transcription factor that is essential for normal kidney development and renal tubular function. Mutations of HNF-1ß produce cystic kidney disease, a phenotype associated with deregulation of canonical (ß-catenin-dependent) Wnt signaling. Here, we show that ablation of HNF-1ß in mIMCD3 renal epithelial cells produces hyperresponsiveness to Wnt ligands and increases expression of Wnt target genes, including Axin2, Ccdc80, and Rnf43 Levels of ß-catenin and expression of Wnt target genes are also increased in HNF-1ß mutant mouse kidneys. Genome-wide chromatin immunoprecipitation sequencing (ChIP-seq) in wild-type and mutant cells showed that ablation of HNF-1ß increases by 6-fold the number of sites on chromatin that are occupied by ß-catenin. Remarkably, 50% of the sites that are occupied by ß-catenin in HNF-1ß mutant cells colocalize with HNF-1ß-occupied sites in wild-type cells, indicating widespread reciprocal binding. We found that the Wnt target genes Ccdc80 and Rnf43 contain a composite DNA element comprising a ß-catenin/lymphoid enhancer binding factor (LEF) site overlapping with an HNF-1ß half-site. HNF-1ß and ß-catenin/LEF compete for binding to this element, and thereby HNF-1ß inhibits ß-catenin-dependent transcription. Collectively, these studies reveal a mechanism whereby a transcription factor constrains canonical Wnt signaling through direct inhibition of ß-catenin/LEF chromatin binding.

Novel cellular mechanism that mediates the collecting duct formation during postnatal renal development.

We have previously demonstrated that kidney embryonic structures are present in rats, and are still developing until postnatal Day 20. Consequently, at postnatal Day 10, the rat renal papilla contains newly formed collecting duct (CD) cells and others in a more mature stage. Performing primary cultures, combined with immunocytochemical and time-lapse analysis, we investigate the cellular mechanisms that mediate the postnatal CD formation. CD cells acquired a greater degree of differentiation, as we observed that they gradually lose the ability to bind BSL-I lectin, and acquire the capacity to bind Dolichos biflorus. Because CD cells retain the same behavior in culture than in vivo, and by using DBA and BSL-I as markers of cellular lineage besides specific markers of epithelial/mesenchymal phenotype, the experimental results strongly suggest the existence of mesenchymal cell insertion into the epithelial CD sheet. We propose such a mechanism as an alternative strategy for CD growing and development.

Race and renal cell carcinoma stage at diagnosis: an analysis of the Surveillance, Epidemiology, and End Results data.

To study racial differences in tumor stage at diagnosis among Black and White patients with renal cell carcinoma (RCC) by histologic type and time period. The patients were Black and White patients with RCC from 1999 to 2011 derived from the National Cancer Institute's Surveillance, Epidemiology, and End Results Program. Multinomial logistic regression was used to assess the associations between cancer stage and race and then stratified by histology and diagnosis year. Compared to Whites, Blacks were less likely to be diagnosed with regional disease [odds ratio (OR)=0.67; 95% confidence interval (CI)=0.60-0.73] or distant disease (OR=0.82; 95% CI=0.74-0.90) after adjusting for age, sex, year of diagnosis, and tumor grade. When stratified by RCC histology, similar results were observed for clear cell (OR=0.71; 95% CI=0.63-0.80), chromophobe (OR=0.51; 95% CI=0.32-0.81), and other histologic type (OR=0.63; 95% CI=0.42-0.96) while the association was not significant for papillary histology. The analyses by time showed a lower likelihood to have regional disease in Black than White in 2003-2006 (OR=0.66; 95% CI=0.55-0.79) and 2007-2011 (OR=0.57; 95% CI=0.49-0.67). Black patients were also less likely to have distant disease in 2007-2011 period (OR=0.76; 95% CI=0.65-0.88). In conclusion, blacks were less likely to be diagnosed at a later stage RCC than Whites regardless of cancer histology. This racial disparity may exist over time during the study period.

Tonicity inversely modulates lipocalin-2 (Lcn2/24p3/NGAL) receptor (SLC22A17) and Lcn2 expression via Wnt/ß-catenin signaling in renal inner medullary collecting duct cells: implications for cell fate and bacterial infection.

BACKGROUND: We have previously evidenced apical expression of the 24p3/NGAL/lipocalin-2 receptor (Lcn2-R; SLC22A17) in inner medullary collecting duct (IMCD) cells, which are present in vivo in a hyperosmotic/-tonic environment that activates canonical Wnt/ß-catenin signaling. The localization of Lcn2-R in the inner medulla is intriguing considering local bacterial infections trigger toll-like receptor-4 (TLR-4)-mediated secretion of the bacteriostatic Fe3+-free (apo-)Lcn2. AIM: To determine the effects of osmolarity/tonicity changes, Wnt/ß-catenin and TLR-4 activation on Lcn2-R and Lcn2 expression and cell viability in rat primary IMCD and mouse (m)IMCD3 cells. METHODS: Normosmolarity/-tonicity was 300 mosmol/l whereas hyperosmolarity/-tonicity was induced by adding 100 mmol/l NaCl + 100 mmol/l urea (600 mosmol/l, 1-7 days). Lcn2-R and Lcn2 expression were determined by qPCR, immunoblotting, flow cytometry and immunofluorescence microscopy. ß-catenin was silenced by RNAi. Cell viability/death was determined with MTT and LDH release assays. TLR-4 was activated by bacterial lipopolysaccharides (LPS). RESULTS: Hyperosmotic/-tonic media upregulated Lcn2-R by ~4-fold and decreased Lcn2 expression/secretion, along with Wnt/ß-catenin activation, in IMCD cells. These effects of hyperosmotic/-tonic media on Lcn2-R/Lcn2 expression were reverted by normosmolarity/-tonicity, ß-catenin silencing and/or LPS. Exposure of cells with endogenous or stably overexpressing Lcn2-R to apo-Lcn2 or LPS decreased cell viability. CONCLUSIONS: Lcn2-R upregulation and Lcn2 downregulation via Wnt/ß-catenin may promote adaptive osmotolerant survival of IMCD cells in response to hyperosmolarity/-tonicity whereas Lcn2 upregulation and Lcn2-R downregulation via TLR-4 and/or normosmolarity/-tonicity may protect IMCD cells against bacterial infections and prevent autocrine death induction by Lcn2.

Metabolic Phenotyping of Anks3 Depletion in mIMCD-3 cells - a Putative Nephronophthisis Candidate.

Nephronophthisis (NPH) is an autosomal recessive form of cystic kidney disease and the leading cause of hereditary kidney failure in children and young adults. Like other NPH proteins, the NPHP16/Anks6-interacting protein Anks3 has been identified to cause laterality defects in humans. However, the cellular functions of Anks3 remain enigmatic. We investigated the metabolic impact of Anks3 depletion in cultured murine inner medullary collecting duct cells via GC-MS profiling and LC-MS/MS analysis. Combined metabolomics successfully identified 155 metabolites; 48 metabolites were identified to be significantly altered by decreasing Anks3 levels. Especially, amino acid and purine/pyrimidine metabolism were affected by loss of Anks3. Branched-chain amino acids were identified to be significantly downregulated suggesting disrupted nutrient signalling. Tryptophan and 1-ribosyl-imidazolenicotinamide accumulated whereas NAD+ and NADP+ concentrations were diminished indicating disturbances within the tryptophan-niacin pathway. Most strikingly, nucleosides were reduced upon Anks3 depletion, while 5-methyluridine and 6-methyladenosine accumulated over time. Hence, elevated PARP1 and cleaved PARP1 levels could be detected. Furthermore, living cell number and viability was significantly declined. In combination, these results suggest that Anks3 may be involved in DNA damage responses by balancing the intracellular nucleoside pool.

Farnesoid X receptor is essential for the survival of renal medullary collecting duct cells under hypertonic stress.

Hypertonicity in renal medulla is critical for the kidney to produce concentrated urine. Renal medullary cells have to survive high medullary osmolarity during antidiuresis. Previous study reported that farnesoid X receptor (FXR), a nuclear receptor transcription factor activated by endogenous bile acids, increases urine concentrating ability by up-regulating aquaporin 2 expression in medullary collecting duct cells (MCDs). However, whether FXR is also involved in the maintenance of cell survival of MCDs under dehydration condition and hypertonic stress remains largely unknown. In the present study, we demonstrate that 24-hours water restriction selectively up-regulated renal medullary expression of FXR with little MCD apoptosis in wild-type mice. In contrast, water deprivation caused a massive apoptosis of MCDs in both global FXR gene-deficient mice and collecting duct-specific FXR knockout mice. In vitro studies showed that hypertonicity significantly increased FXR and tonicity response enhancer binding protein (TonEBP) expression in mIMCD3 cell line and primary cultured MCDs. Activation and overexpression of FXR markedly increased cell viability and decreased cell apoptosis under hyperosmotic conditions. In addition, FXR can increase gene expression and nuclear translocation of TonEBP. We conclude that FXR protects MCDs from hypertonicity-induced cell injury very likely via increasing TonEBP expression and nuclear translocation. This study provides insights into the molecular mechanism by which FXR enhances urine concentration via maintaining cell viability of MCDs under hyperosmotic condition.

Renal papillary tip extract stimulates BNP production and excretion from cardiomyocytes.

BACKGROUND: Brain natriuretic peptide (BNP) is an important biomarker for patients with cardiovascular diseases, including heart failure, hypertension and cardiac hypertrophy. It is also known that BNP levels are relatively higher in patients with chronic kidney disease and no heart disease; however, the mechanism remains unclear. METHODS AND RESULTS: We developed a BNP reporter mouse and occasionally found that this promoter was activated specifically in the papillary tip of the kidneys, and its activation was not accompanied by BNP mRNA expression. No evidence was found to support the existence of BNP isoforms or other nucleotide expression apart from BNP and tdTomato. The pBNP-tdTomato-positive cells were interstitial cells and were not proliferative. Unexpectedly, both the expression and secretion of BNP increased in primary cultured neonatal cardiomyocytes after their treatment with an extract of the renal papillary tip. Intraperitoneal injection of the extract of the papillary tips reduced blood pressure from 210 mmHg to 165 mmHg, the decrease being accompanied by an increase in serum BNP and urinary cGMP production in stroke-prone spontaneously hypertensive (SHR-SP) rats. Furthermore the induction of BNP by the papillary extract from rats with heart failure due to myocardial infarction was increased in cardiomyocytes. CONCLUSIONS: These results suggested that the papillary tip express a substance that can stimulate BNP production and secretion from cardiomyocytes.

Molecular phenotypes of the human kidney: Myoid stromal cells/telocytes and myoepithelial cells.

The connective stromal and epithelial compartments of the kidney have regenerative potential and phenotypic flexibility. A few studies have shown that cells appertaining to both compartments can exhibit myoid phenotypes. The purpose of our study was to investigate the myoid pattern of kidney and its association with the kidney niches containing stromal cells/telocytes (SC/TCs). We performed an immunohistochemical study using a panel of endothelial, myoid, mesenchymal and stem/progenitor markers, namely CD31, CD34, CD105 (endoglin), CD117/c-kit, nestin, desmin, α-smooth muscle actin (α-SMA) and the heavy chain of smooth muscle myosin (SMM). We used histologically normal kidney samples, obtained after nephrectomy, from nine adult patients. The capsular SC/TCs had a strong CD34 and partial nestin and CD105 immunopositivity. Subcapsular and interstitial SC/TCs expressed c-kit, nestin, CD105, but also α-SMA and SMM, therefore having a myoid phenotype. The endothelial SC/TCs phenotype was CD31+/CD34+/CD105+/nestin±/SMM±/α-SMA±. All three myoid markers were expressed in periendothelial SC/TCs. We also found a scarce expression of nestin in parietal epithelial cells of Bowman's capsule, and in podocytes. In epithelial cells, we found a positive expression for CD31, CD117/c-kit, desmin, CD34, SMM, and CD105. In epithelial tubular cells, we found a predominant basal expression of the myoid markers (SMM and desmin). In conclusion, myoepithelial tubular cells, myoid endothelial cells and myoid SC/TCs are normal constituents of the kidney.

Epithelium Lining Rat Renal Papilla: Nomenclature and Association with Chronic Progressive Nephropathy (CPN).

Chronic progressive nephropathy (CPN) occurs commonly in rats, more frequently and severely in males than females. High-grade CPN is characterized by increased layers of the renal papilla lining, designated as urothelial hyperplasia in the International Harmonization of Nomenclature and Diagnostic Criteria classification. However, urothelium lining the pelvis is not equivalent to the epithelium lining the papilla. To evaluate whether the epithelium lining the renal papilla is actually urothelial in nature and whether CPN-associated multicellularity represents proliferation, kidney tissues from aged rats with CPN, from rats with multicellularity of the renal papilla epithelium of either low-grade or marked severity, and from young rats with normal kidneys were analyzed and compared. Immunohistochemical staining for uroplakins (urothelial specific proteins) was negative in the papilla epithelium in all rats with multicellularity or not, indicating these cells are not urothelial. Mitotic figures were rarely observed in this epithelium, even with multicellularity. Immunohistochemical staining for Ki-67 was negative. Papilla lining cells and true urothelium differed by scanning electron microscopy. Based on these findings, we recommend that the epithelium lining the papilla not be classified as urothelial, and the CPN-associated lesion be designated as vesicular alteration of renal papilla instead of hyperplasia and distinguished in diagnostic systems from kidney pelvis urothelial hyperplasia.

Hyaluronan Production by Renomedullary Interstitial Cells: Influence of Endothelin, Angiotensin II and Vasopressin.

The content of hyaluronan (HA) in the interstitium of the renal medulla changes in relation to body hydration status. We investigated if hormones of central importance for body fluid homeostasis affect HA production by renomedullary interstitial cells in culture (RMICs). Simultaneous treatment with vasopressin and angiotensin II (Ang II) reduced HA by 69%. No change occurred in the mRNA expressions of hyaluronan synthase 2 (HAS2) or hyaluronidases (Hyals), while Hyal activity in the supernatant increased by 67% and CD44 expression reduced by 42%. The autocoid endothelin (ET-1) at low concentrations (10-10 and 10-8 M) increased HA 3-fold. On the contrary, at a high concentration (10-6 M) ET-1 reduced HA by 47%. The ET-A receptor antagonist BQ123 not only reversed the reducing effect of high ET-1 on HA, but elevated it to the same level as low concentration ET-1, suggesting separate regulating roles for ET-A and ET-B receptors. This was corroborated by the addition of ET-B receptor antagonist BQ788 to low concentration ET-1, which abolished the HA increase. HAS2 and Hyal2 mRNA did not alter, while Hyal1 mRNA was increased at all ET-1 concentrations tested. Hyal activity was elevated the most by high ET-1 concentration, and blockade of ET-A receptors by BQ123 prevented about 30% of this response. The present study demonstrates an important regulatory influence of hormones involved in body fluid balance on HA handling by RMICs, thereby supporting the concept of a dynamic involvement of interstitial HA in renal fluid handling.

Impaired AQP2 trafficking in Fxyd1 knockout mice: A role for FXYD1 in regulated vesicular transport.

The final adjustment of urine volume occurs in the inner medullary collecting duct (IMCD), chiefly mediated by the water channel aquaporin 2 (AQP2). With vasopressin stimulation, AQP2 accumulation in the apical plasma membrane of principal cells allows water reabsorption from the lumen. We report that FXYD1 (phospholemman), better known as a regulator of Na,K-ATPase, has a role in AQP2 trafficking. Daytime urine of Fxyd1 knockout mice was more dilute than WT despite similar serum vasopressin, but both genotypes could concentrate urine during water deprivation. FXYD1 was found in IMCD. In WT mice, phosphorylated FXYD1 was detected intracellularly, and vasopressin induced its dephosphorylation. We tested the hypothesis that the dilute urine in knockouts was caused by alteration of AQP2 trafficking. In WT mice at baseline, FXYD1 and AQP2 were not strongly co-localized, but elevation of vasopressin produced translocation of both FXYD1 and AQP2 to the apical plasma membrane. In kidney slices, baseline AQP2 distribution was more scattered in the Fxyd1 knockout than in WT. Apical recruitment of AQP2 occurred in vasopressin-treated Fxyd1 knockout slices, but upon vasopressin washout, there was more rapid reversal of apical AQP2 localization and more heterogeneous cytoplasmic distribution of AQP2. Notably, in sucrose gradients, AQP2 was present in a detergent-resistant membrane domain that had lower sedimentation density in the knockout than in WT, and vasopressin treatment normalized its density. We propose that FXYD1 plays a role in regulating AQP2 retention in apical membrane, and that this involves transfers between raft-like membrane domains in endosomes and plasma membranes.

Infusion of Valproic Acid Into the Renal Medulla Activates Stem Cell Population and Attenuates Salt-Sensitive Hypertension in Dahl S Rats.

BACKGROUND: Our previous study has detected a stem cell deficiency in the renal medulla in Dahl salt-sensitive (S) rats. This study determined whether infusion of valproic acid (VA), an agent known to stimulate the stem cell function, attenuated salt-sensitive hypertension in Dahl S rats. METHODS: Uninephrectomized Dahl S rats were infused with vehicle or VA (50mg/kg/d) into the renal medulla and fed with a low (LS) or high salt diet (HS). Stem cell marker and number were analyzed by immunohistochemistry, Real-time RT-PCR and Western blot. Sodium excretion and blood pressure were measured. RESULTS: VA significantly increased the mRNA and protein levels of FGF2, a stem cell niche factor, and CD133, a stem cell marker. The number of CD133+ cells was significantly increased in the renal medulla in VA-treated rats. Meanwhile, high salt-induced increases in the mRNA level of proinflammatory factors interleukin-1ß and interleukin-6 were blocked in VA-treated rats. Functionally, sodium excretion in response to the blood pressure increase and acute sodium loading was significantly enhanced, sodium retention attenuated, high salt-induced increase of blood pressure reduced in VA-treated rats. CONCLUSION: Activation of stem cell function by VA inhibits the activation of proinflammatory factors and attenuates salt-sensitive hypertension in Dahl S rats.

Sustained hyperosmolarity increses TGF-ß1 and Egr-1 expression in the rat renal medulla.

BACKGROUND: Although TGF-ß and the transcription factor Egr-1 play an important role in both kidney fibrosis and in response to acute changes of renal medullary osmolarity, their role under sustained hypo- or hyperosmolar conditions has not been elucidated. We investigated the effects of chronic hypertonicity and hypotonicity on the renal medullary TGF-ß and Egr-1 expression. METHODS: Male adult Sprague Dawley rats (n = 6/group) were treated with 15 mg/day furosemide, or the rats were water restricted to 15 ml/200 g body weight per day. Control rats had free access to water and rodent chow. Kidneys were harvested after 5 days of treament. In cultured inner medullary collecting duct (IMCD) cells, osmolarity was increased from 330 mOsm to 900 mOsm over 6 days. Analyses were performed at 330, 600 and 900 mOsm. RESULTS: Urine osmolarity has not changed due to furosemide treatment but increased 2-fold after water restriction (p < 0.05). Gene expression of TGF-ß and Egr-1 increased by 1.9-fold and 7-fold in the hypertonic medulla, respectively (p < 0.05), accompanied by 6-fold and 2-fold increased c-Fos and TIMP-1 expression, respectively (p < 0.05) and positive immunostaining for TGF-ß and Egr-1 (p < 0.05). Similarly, hyperosmolarity led to overexpression of TGF-ß and Egr-1 mRNA in IMCD cells (2.5-fold and 3.5-fold increase from 330 to 900 mOsm, respectively (p < 0.05)) accompanied by significant c-Fos and c-Jun overexpressions (p < 0.01), and increased Col3a1 and Col4a1 mRNA expression. CONCLUSION: We conclude that both TGF-ß and Egr-1 are upregulated by sustained hyperosmolarity in the rat renal medulla, and it favors the expression of extracellular matrix components.

Endocrine functions of the renal interstitium.

This review aims to summarize the knowledge about the sensor and endocrine response functions of resident interstitial cells of the kidney. By the production of renin, erythropoietin and arachidonate metabolites (medullipin) subsets of renal interstitial fibroblasts and pericytes in different kidney zones play a central role in salt, blood pressure and oxygen homeostasis of the body. Common to these endocrine functions is that their regulation mainly occurs by (de)recruitment of active cells.

Highly suggestive preliminary evidence that the renal interstitium contracts in vivo.

To learn more about controlling renal interstitial hydrostatic pressure (RIHP), we assessed its response to renal medullary direct interstitial volume expansion (rmDIVE = 100 µL bolus infusion/30 sec). Three experimental series (S) were performed in hydropenic, anesthetized, right-nephrectomized, acute left renal-denervated and renal perfusion pressure-controlled rats randomly assigned to groups in each S. S1: Rats without hormonal clamp were contrasted before and after rmDIVE induced via 0.9% saline solution bolus (SS group) or 2% albumin in SS bolus (2% ALB + SS group). Subcapsular ΔRIHP rose slowly, progressively and similarly in both groups by ~3 mmHg. S2: Rats under hormonal clamp were contrasted before and after sham rmDIVE (time CTR group) and real rmDIVE induced via either SS bolus (SS group) or SS bolus containing the subcutaneous tissue fibroblast relaxant dibutyryl-cAMP (SS + db-cAMP group). ΔRIHP showed time, group, and time*group interaction effects with a biphasic response (early: ~1 mmHg; late: ~4 mmHg) in the SS group that was absent in the SS + db-cAMP group. S3: Two groups of rats (SS and SS + db-cAMP) under hormonal clamp were contrasted as in S2, producing similar ΔRIHP results to those of S2 but showing a slow, progressive, and indistinct decrease in renal outer medullary blood flow in both groups. These results provide highly suggestive preliminary evidence that the renal interstitium is capable of contracting reactively in vivo in response to rmDIVE with SS and demonstrate that such a response is abolished when db-cAMP is interstitially and concomitantly infused.

Aldosterone does not alter endothelin B receptor signaling in the inner medullary collecting duct.

Recent studies suggest that aldosterone-mediated sulfenic acid modification of the endothelin B receptor (ETB) promotes renal injury in an ischemia/reperfusion model through reduced ETB-stimulated nitric oxide production. Similarly, aldosterone inactivation of ETB signaling promotes pulmonary artery hypertension. Consequently, we asked whether aldosterone inhibits collecting duct ETB signaling; this could promote fluid retention since CD ETB exerts natriuretic and diuretic effects. A mouse inner medullary collecting duct cell line (IMCD3) was treated with aldosterone for 48 h followed by sarafotoxin-6c, an ETB-selective agonist, and extracellular signal-related kinase 1/2 (ERK) phosphorylation assessed. S6c increased the phospho/total-ERK ratio similarly in control and aldosterone-treated cells (aldosterone alone increased phospho/total-ERK). Since cultured IMCD cell lines lack ETB inhibited AVP signaling, the effect of S6c on AVP-stimulated cAMP in acutely isolated IMCD was assessed. Rats (have much higher CD ETB expression than mice) were exposed to 3 days of a normal or low Na+ diet, or low Na+ diet + desoxycorticosterone acetate. S6c inhibited AVP-stimulated cAMP in rat IMCD by the same degree in the high mineralocorticoid groups compared to controls. Finally, S6c-stimulated cGMP accumulation in cultured IMCD, or S6c-stimulated nitric oxide or cGMP in acutely isolated IMCD, was not affected by prior aldosterone exposure. These findings provide evidence that aldosterone does not modify ETB effects on ERK phosphorylation, AVP-dependent cAMP inhibition, or NO/cGMP accumulation in the IMCD Thus, while aldosterone can inhibit endothelial cell ETB activity to promote hypertension and injury, this response does not appear to occur in the IMCD.