Regulation of Renin Expression by the Orphan Nuclear Receptors Nr2f2 and Nr2f6.
Am J Physiol Renal Physiol. 2012 Jan 25;
Authors: Weatherford ET, Liu X, Sigmund CD
Abstract
Understanding the transcriptional mechanisms of renin expression is key to understanding the regulation of the renin-angiotensin system. We previously identified the nuclear receptors RAR/RXR and Nr2f6 (EAR2) as positive and negative transcriptional regulators of renin expression, respectively. Both mediate their effects through a hormone response element (HRE) within the renin enhancer. Here, we determined whether another nuclear receptor, Nr2f2 (Coup-TFII, Arp-1), identified in a screen of proteins that bind the HRE, also regulates renin expression. Luciferase assays indicate that Nr2f2 negatively regulates the renin promoter more potently than Nr2f6. Gel-shift and chromatin immunoprecipitation (ChIP) indicate that Nr2f2 and Nr2f6 can bind directly to the renin enhancer through the HRE. Surprisingly, baseline expression of endogenous renin was not effected when Nr2f2 was knocked down in As4.1 cells, whereas knockdown of Nr2f6 increased renin expression 2-fold. Interestingly however, knockdown of Nr2f2 augmented the induction of renin expression caused by retinoic acid. This data indicates that both Nr2f6 and Nr2f2 can negatively regulate the renin promoter, under baseline conditions and in response to physiological queues, respectively. Therefore, Nr2f2 may require an initiating signal that results in a change at the chromatin level or activation of another transcription factor to exert its effects. We conclude that both Nr2f2 and Nr2f6 negatively regulate renin promoter activity, but may do so by divergent mechanisms.
PMID: 22278040 [PubMed - as supplied by publisher]
Cytokine Elevation and Transaminitis after Laparoscopic Donor Nephrectomy.
Am J Physiol Renal Physiol. 2012 Jan 18;
Authors: Yap SC, Park SW, Egan B, Lee HT
Abstract
Acute kidney injury (AKI) frequently occurs in the critically ill and often progresses into multi-organ dysfunction syndrome resulting in high mortality. We previously showed that nephrectomized mice had increased IL-6 and TNF-α that directly contributed to systemic inflammation and hepatic injury. In this study, we examined whether patients undergoing laparoscopic donor nephrectomy have increased post-operative cytokine levels with injury to the liver, and whether the remaining kidney sustains injury. Serial serum and urine samples were collected from 32 patients undergoing laparoscopic donor nephrectomy and 17 patients undergoing non-renal laparoscopic surgery. Serum IL-6, IL-18, TNF-α, and MCP-1 (markers of systemic inflammation) and urinary NGAL, KIM-1, MCP-1 and IL-18 (markers of acute kidney injury), were quantified by ELISA. We also analyzed serum creatinine, aspartate transaminase (AST) and alanine transaminase (ALT) to assess liver injury. Patients who underwent donor nephrectomy not only demonstrated increased serum creatinine but also had significant increases in serum IL-6, MCP-1 and AST. Serum TNF-α also trended upwards in donor nephrectomy patients. Finally, the donor nephrectomy group showed increased urinary NGAL but not KIM-1 at 24 hours. Taken together, our findings of increased serum IL-6, MCP-1 and AST after donor nephrectomy suggest that an acute reduction of kidney function induces systemic inflammation and may have distant effects on the liver. Further studies are needed to correlate increased urinary NGAL after donor nephrectomy both as a potential marker for renal tubular stress and/or hypertrophy in the contralateral kidney.
PMID: 22262478 [PubMed - as supplied by publisher]
Regulation of pendrin by cAMP: possible involvement in β adrenergic-dependent NaCl retention.
Am J Physiol Renal Physiol. 2012 Jan 18;
Authors: Azroyan A, Morla L, Crambert G, Laghmani K, Ramakrishnan S, Edwards A, Doucet A
Abstract
The sodium-independent anion exchanger pendrin is expressed in several tissues including the kidney collecting duct (CCD), where it acts as a chloride/bicarbonate exchanger and has been shown to participate in the regulation of acid-base homeostasis and blood pressure. The renal sympathetic nervous system is known to play a key role in the development of salt-induced hypertension. This study aimed to determine whether pendrin may partly mediate the effects of β adrenegic receptors (β-AR) on renal salt handling. We investigated the regulation of pendrin activity by the cAMP/protein kinase A (PKA) signalling pathway, both in vitro in OKP cells stably transfected with pendrin cDNA, and ex vivo in isolated microperfused CCDs stimulated by isoproterenol, a β-AR agonist. We found that stimulation of the cAMP/PKA pathway in OKP cells increased the amount of pendrin at the cell surface as well as its transport activity. These effects stemmed from increased exocytosis of pendrin and were associated with its phosphorylation. Furthermore, cAMP effects on the membrane expression and activity of pendrin were abolished by mutating the serine 49 located in the intracellular N-terminal domain of pendrin. Finally, we showed that isoproterenol increases pendrin trafficking to the apical membrane as well as the reabsorption of both Cl(-) and Na(+) in microperfused CCDs. All together, our results strongly suggest that pendrin activation by the cAMP/PKA pathway underlies isoproterenol-induced stimulation of NaCl reabsorption in the kidney collecting duct, a mechanism likely involved in the sodium-retaining effect of β adrenergic agonists.
PMID: 22262479 [PubMed - as supplied by publisher]
Pre-ischemic Targeting of HIF Prolyl Hydroxylation Inhibits Fibrosis associated with Acute Kidney Injury.
Am J Physiol Renal Physiol. 2012 Jan 18;
Authors: Kapitsinou PP, Jaffe J, Michael M, Swan CE, Duffy KJ, Erickson-Miller CL, Haase VH
Abstract
Acute kidney injury (AKI) due to ischemia is an important contributor to the progression of chronic kidney disease (CKD). Key mediators of cellular adaptation to hypoxia are oxygen-sensitive hypoxia-inducible factors (HIF), which are regulated by prolyl-4-hydroxylase domain (PHD)-containing dioxygenases. While activation of HIF protects from ischemic cell death, HIF has been shown to promote fibrosis in experimental models of CKD. The impact of HIF activation on AKI-induced fibrosis has not been defined. Here we investigated the impact of pharmacologic HIF activation on AKI-associated fibrosis and inflammation. We found that pharmacologic inhibition of HIF prolyl hydroxylation prior to AKI ameliorated fibrosis and prevented anemia, while inhibition of HIF prolyl hydroxylation in the early recovery phase of AKI did not affect short- or long-term clinical outcome. Therefore, pre-ischemic targeting of the PHD/HIF pathway represents an effective therapeutic strategy for the prevention of CKD resulting from AKI, and warrants further investigation in clinical trials.
PMID: 22262480 [PubMed - as supplied by publisher]
Both cyclin I and p35 are required for maximal survival benefit of Cyclin-dependent kinase 5 in kidney podocytes.
Am J Physiol Renal Physiol. 2012 Jan 18;
Authors: Taniguchi Y, Pippin JW, Hagmann H, Krofft RD, Chang AM, Zhang J, Terada Y, Brinkkoetter P, Shankland SJ
Abstract
Cyclin-dependent kinase (Cdk)-5 is activated by both cyclin I and the non-cyclin activator p35 in terminally differentiated cells such as kidney podocytes and neurons. Cyclin I and p35 are restricted to podocytes in the kidney, and each limit podocyte apoptosis by activating Cdk5. To determine if both activators are necessary, or if they serve backup roles, a double cyclin I-p35 null mice was generated. Experimental glomerular disease characterized by podocyte apoptosis was then induced by administering an anti-podocyte antibody. The results showed that under non-stressed conditions double mutants had normal kidney structure and function, and were indistinguishable from wild-type, cyclin I(-/-) or p35(-/-)mice. In contrast, when stressed with disease, podocyte apoptosis was fourfold increased compared to diseased cyclin I(-/-) or p35(-/-) mice. This resulted in a more pronounced decrease in podocyte number, proteinuria and glomerulosclerosis. Under normal states and nephritic states, levels for the pro-survival protein Bcl-2 were lower in double cyclin I(-/-) p35(-/-) mice than the other mice. Likewise, levels of Bcl-xL, another pro-survival member, were lower in normal and nephritic double cyclin I(-/-) p35(-/-) mice, but similar to single cyclin I(-/-) mice. Moreover, levels of ERK1/2 and MEK1/2 activation were lower in nephritic double cyclin I(-/-) p35(-/-) mice, but similar to single cyclin I(-/-) mice. The results demonstrate that the activators of Cdk5, p35 and cyclin I, are not required for normal kidney function. However, they play pivotal coordinated roles in maintaining podocyte survival during stress states in disease.
PMID: 22262481 [PubMed - as supplied by publisher]
Signal Transduction in a Compliant Thick Ascending Limb.
Am J Physiol Renal Physiol. 2012 Jan 18;
Authors: Layton AT, Moore LC, Layton HE
Abstract
In several previous studies, we used a mathematical model of the thick ascending limb (TAL) to investigate nonlinearities in the tubuloglomerular feedback (TGF) loop. That model, which represents the TAL as a rigid tube, predicts that TGF signal transduction by the TAL is a generator of nonlinearities: if a sinusoidal oscillation is added to constant intratubular fluid flow, the time interval required for an element of tubular fluid to traverse the TAL, as a function of time, is oscillatory and periodic but not sinusoidal. As a consequence, NaCl concentration in tubular fluid alongside the macula densa will be nonsinusoidal and thus contain harmonics of the original sinusoidal frequency. We hypothesized that the complexity found in power spectra based on in vivo time series of key TGF variables arises in part from those harmonics and that nonlinearities in TGF-mediated oscillations may result in increased NaCl delivery to the distal nephron. To investigate the possibility that a more realistic model of the TAL would damp the harmonics, we have conducted new studies in a model TAL that has compliant walls and thus a tubular radius that depends on transmural pressure. These studies predict that compliant TAL walls do not damp, but instead intensify, the harmonics. In addition, our results predict that mean TAL flow strongly influences the shape of the NaCl concentration waveform at the macula densa. This is a consequence of the inverse relationship between flow and transit time, which produces asymmetry between up- and down-slopes of the oscillation, and the nonlinearity of TAL NaCl absorption at low flow rates, which broadens the trough of the oscillation relative to the peak. The dependence of waveform shape on mean TAL flow may be the source of the variable degree of distortion, relative to a sine wave, seen in experimental recordings of TGF-mediated oscillations.
PMID: 22262482 [PubMed - as supplied by publisher]
CARCINOGENS INDUCE LOSS OF THE PRIMARY CILIUM IN PROXIMAL TUBULAR EPITHELIAL CELLS INDEPENDENT OF EFFECTS ON CELL CYCLE.
Am J Physiol Renal Physiol. 2012 Jan 18;
Authors: Radford R, Slattery C, Jennings P, Blacque O, Pfaller W, Gmuender H, Van Delft J, Ryan MP, McMorrow T
Abstract
Background: The primary cilium is an immotile sensory and signalling organelle found on the majority of mammalian cell types. Of the multitude of roles that the primary cilium performs, perhaps some of the most important include maintenance of differentiation, quiescence and cellular polarity. Given that the progression of cancer requires disruption of all of these processes we have investigated the effects of renal carcinogens on the primary cilium of the RPTEC/TERT1 human proximal tubular epithelial cell line. Methods & results: Using both scanning electron microscopy and immunofluorescent labelling of the ciliary markers acetylated tubulin and Arl13b we confirmed that RPTEC/TERT1 cells express primary cilium upon confluency. Treatment with the carcinogens ochratoxin A and KBrO3 caused a significant reduction in the number of ciliated cells while exposure to nifedipine, a non-carcinogenic renal toxin had no effect on primary cilium expression. Flow cytometric analysis of the effects of all three compounds on the cell cycle revealed that only KBrO3 resulted in an increase in the proportion of cells entering the cell cycle. Microarray analysis identified dysregulation of multiple pathways affecting ciliogenesis and ciliary maintenance following OTA and KBrO3 exposure, which were unaffected by nifedipine exposure. Discussion: The primary cilium represents a unique physical checkpoint with relevance to carcinogenesis. The results of this study suggest that the renal carcinogens OTA and KBrO3 caused significant deciliation in tubular epithelial cells. With KBrO3, this was followed by re-entry into the cell cycle, however deciliation did not coincide with re-entry into the cell cycle following OTA exposure. Transcriptomic analysis identified dysregulation of Wnt signalling and ciliary trafficking in response to OTA and KBrO(3) exposure.
PMID: 22262483 [PubMed - as supplied by publisher]
Renal handling of sodium and water is abnormal in chronic kidney diseases. In order to study the function and regulation of the aquaporin-2 water channel (AQP2) and the epithelial sodium channel (ENaC) in autosomal dominant polycystic kidney disease (ADPKD), we measured urinary excretion of AQP2 (u-AQP2), β-subunit of ENaC (u-ENaC(β)), c-AMP (u-cAMP) and prostaglandin E2 (u-PGE(2)), free water clearance (C(H2O)), fractional sodium excretion (FE(Na)), and plasma vasopressin (p-AVP), renin (p-Renin), angiotensin II (p-Ang II), aldosterone (p-Aldo), and atrial and brain natriuretic peptide (p-ANP, p-BNP) in patients with ADPKD and healthy controls during 24-h urine collection and after hypertonic saline infusion during high sodium intake (HS, 300 mmol sodium/day) and low sodium intake (LS, 30 mmol sodium/day). No difference in u-AQP2, u-ENaC(β), u-cAMP, u-PGE(2), C(H2O), and vasoactive hormones was found between patients and controls at baseline, but during HS the patients had higher FE(Na). The saline caused higher increases in FE(Na) in patients than controls during LS, but the changes in u-ENaC(β), p-Aldo, p-ANP, p-BNP, p-Renin, and p-Ang II were similar. Higher increases in u-AQP2 and p-AVP were seen in patients during both diets. In conclusion, u-AQP2 and u-ENaC(β) were comparable in patients with ADPKD and controls at baseline. In ADPKD, the larger increase in u-AQP2 and p-AVP in response to saline could reflect an abnormal water absorption in the distal nephron. During LS, the larger increase in FE(Na) in response to saline could reflect a defective renal sodium retaining capacity in ADPKD, unrelated to changes in u-ENaC(β). ClinicalTrials.gov ID: NCT00410007.
PMID: 22262484 [PubMed - as supplied by publisher]
Dual RAS Blockade Normalizes Angiotensin-Converting Enzyme-2 Expression, Prevents Hypertension and Tubular Apoptosis in Akita Angiotensinogen-Transgenic Mice.
Am J Physiol Renal Physiol. 2011 Dec 28;
Authors: Lo CS, Liu F, Shi Y, Maachi H, Chenier I, Godin N, Filep JG, Ingelfinger JR, Zhang SL, Chan JS
Abstract
We investigated the effects of dual renin-angiotensin system (RAS) blockade on angiotensin-converting enzyme-2 (Ace2) expression, hypertension and renal proximal tubular cell (RPTC) apoptosis in type 1 diabetic Akita angiotensinogen (Agt)-transgenic (Tg) mice that specifically overexpress Agt in their RPTCs. Adult (8 weeks old) male Akita and Akita Agt-Tg mice were treated with 2 RAS blockers (angiotensin II (Ang II)-receptor type 1 blocker losartan (30 mg/kg/day) and angiotensin-converting enzyme (ACE) inhibitor perindopril (4 mg/kg/day)) in drinking water. Same-age non-Akita littermates and Agt-Tg mice served as controls. Blood pressure, blood glucose and albuminuria were monitored weekly. The animals were euthanized at age 16 weeks. The left kidneys were processed for immunohistochemistry and apoptosis studies. Renal proximal tubules were isolated from the right kidneys to assess gene and protein expression. Urinary Ang II and Ang 1-7 were quantified by ELISA. RAS blockade normalized renal Ace2 expression and urinary Ang 1-7 levels (both of which were low in untreated Akita and Akita Agt-Tg), prevented hypertension, albuminuria, tubulointerstitial fibrosis and tubular apoptosis, and inhibited pro-fibrotic and pro-apoptotic gene expression in RPTCs of Akita and Akita Agt-Tg mice as compared to non-Akita controls. Our results demonstrate the effectiveness of RAS blockade in preventing intrarenal RAS activation, hypertension and nephropathy progression in diabetes and support the important role of intrarenal Ace2 expression in modulating hypertension and renal injury in diabetes.
PMID: 22205225 [PubMed - as supplied by publisher]
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