Clarifying endothelin type B receptor function

High dietary sodium causes dyssynchrony of the renal molecular clock in rats

Speed JS, Hyndman KA, Roth K, Heimlich JB, Kasztan M, Fox BM, Johnston JG, Becker BK, Jin C, Gamble KL, Young ME, Pollock JS, Pollock DM. High dietary sodium causes dyssynchrony of the renal molecular clock in rats. Am J Physiol Renal Physiol 314: F89-F98, 2018. First published September 27, 2017; doi:10.1152/ajprenal.00028.2017.-Dyssynchrony of circadian rhythms is associated with various disorders, including cardiovascular and metabolic diseases. The cell autonomous molecular clock maintains circadian control; however, environmental factors that may cause circadian dyssynchrony either within or between organ systems are poorly understood. Our laboratory recently reported that the endothelin (ET-1) B (ETB) receptor functions to facilitate Na+ excretion in a time of day-dependent manner. Therefore, the present study was designed to determine whether high salt (HS) intake leads to circadian dyssynchrony within the kidney and whether the renal endothelin system contributes to control of the renal molecular clock. We observed that HS feeding led to region-specific alterations in circadian clock components within the kidney. For instance, HS caused a significant 5.5-h phase delay in the peak expression of Bmal1 and suppressed Cry1 and Per2 expression in the renal inner medulla, but not the renal cortex, of control rats. The phase delay in Bmal1 expression appears to be mediated by ET-1 because this phenomenon was not observed in the ETB-deficient rat. In cultured inner medullary collecting duct cells, ET-1 suppressed Bmal1 mRNA expression. Furthermore, Bmal1 knockdown in these cells reduced epithelial Na+ channel expression. These data reveal that HS feeding leads to intrarenal circadian dyssynchrony mediated, in part, through activation of ETB receptors within the renal inner medulla.

Dopamine and renal function and blood pressure regulation

Dopamine is an important regulator of systemic blood pressure via multiple mechanisms. It affects fluid and electrolyte balance by its actions on renal hemodynamics and epithelial ion and water transport and by regulation of hormones and humoral agents. The kidney synthesizes dopamine from circulating or filtered L-DOPA independently from innervation. The major determinants of the renal tubular synthesis/release of dopamine are probably sodium intake and intracellular sodium. Dopamine exerts its actions via two families of cell surface receptors, D1-like receptors comprising D1R and D5R, and D2-like receptors comprising D2R, D3R, and D4R, and by interactions with other G protein-coupled receptors. D1-like receptors are linked to vasodilation, while the effect of D2-like receptors on the vasculature is variable and probably dependent upon the state of nerve activity. Dopamine secreted into the tubular lumen acts mainly via D1-like receptors in an autocrine/paracrine manner to regulate ion transport in the proximal and distal nephron. These effects are mediated mainly by tubular mechanisms and augmented by hemodynamic mechanisms. The natriuretic effect of D1-like receptors is caused by inhibition of ion transport in the apical and basolateral membranes. D2-like receptors participate in the inhibition of ion transport during conditions of euvolemia and moderate volume expansion. Dopamine also controls ion transport and blood pressure by regulating the production of reactive oxygen species and the inflammatory response. Essential hypertension is associated with abnormalities in dopamine production, receptor number, and/or posttranslational modification.

Therapeutic potential of endothelin receptor antagonists for chronic proteinuric renal disease in humans

Diabetes and arterial hypertension continue to be the main causes of chronic renal failure in 2010, with a rising prevalence in part due to the worldwide obesity epidemic. Proteinuria is a main feature of chronic renal disease and mediated by defects in the glomerular filtration barrier and is as a good predictor of cardiovascular events. Indeed, chronic renal disease due to glomerulosclerosis is one of the important risk factors for the development of coronary artery disease and stroke. Glomerulosclerosis develops in response to inflammatory activation and increased growth factor production. Preclinical and first preliminary clinical studies provide strong evidence that endogenous endothelin-1 (ET-1), a 21-amino-acid peptide with strong growth-promoting and vasoconstricting properties, plays a central role in the pathogenesis of proteinuria and glomerulosclerosis via activation of its ET(A) subtype receptor involving podocyte injury. These studies have not only shown that endothelin participates in the disease processes of hypertension and glomerulosclerosis but also that features of chronic renal disease such as proteinuria and glomerulosclerosis are reversible processes. Remarkably, the protective effects of endothelin receptors antagonists (ERAs) are present even on top of concomitant treatments with inhibitors of the renin-angiotensin system. This review discusses current evidence for a role of endothelin for proteinuric renal disease and podocyte injury in diabetes and arterial hypertension and reviews the current status of endothelin receptor antagonists as a potential new treatment option in renal medicine.

Global transcriptional characterization of a mouse pulmonary epithelial cell line for use in genetic toxicology

Prior to its application for in vitro toxicological assays, thorough characterization of a cell line is essential. The present study uses global transcriptional profiling to characterize a lung epithelial cell line (FE1) derived from MutaMouse [White, P.A., Douglas, G.R., Gingerich, J., Parfett, C., Shwed, P., Seligy, V., Soper, L., Berndt, L., Bayley, J., Wagner, S., Pound, K., Blakey, D., 2003. Development and characterization of a stable epithelial cell line from Muta Mouse lung. Environmental and Molecular Mutagenesis 42, 166-184]. Results presented here demonstrate the origin of the FE1 lung cell line as epithelial, presenting both type I and type II alveolar phenotype. An assessment of toxicologically-relevant genes, including those involved in the response to stress and stimuli, DNA repair, cellular metabolism, and programmed cell death, revealed changes in expression of 22-27% of genes in one or more culture type (proliferating and static FE1 cultures, primary epithelial cultures) compared with whole lung isolates. Gene expression analysis at 4 and 24h following benzo(a)pyrene exposure revealed the induction of cyp1a1, cyp1a2, and cyp1b1 in FE1 cells and lung isolates. The use of DNA microarrays for gene expression profiling allows an improved understanding of global, coordinated cellular events arising in cells under different physiological conditions. Taken together, these data indicate that the FE1 cell line is derived from a cell type relevant to toxic responses in vivo, and shows some similarity in response to chemical insult as the original tissue.

Endothelin: 20 years from discovery to therapy

Since its identification as an endothelial cell-derived vasoconstrictor peptide in 1988, endothelin-1, the predominant member of the endothelin peptide family, has received considerable interest in basic medical science and in clinical medicine, which is reflected by more than 20 000 scientific publications on endothelin research in the past 20 years. The story of endothelin is unique as the gene sequences of endothelin receptors and the first receptor antagonists became available within only 4 years of the identification of the peptide sequence. The first clinical study in patients with congestive heart failure was published only 3 years thereafter. Yet, despite convincing experimental evidence of a pathogenetic role for endothelin in development, cell function, and disease, many initial clinical studies on endothelin antagonism were negative. In many of these studies, study designs or patient selection were inadequate. Today, for diseases such as pulmonary hypertension, endothelin antagonist treatment has become reality in clinical medicine, and ongoing clinical studies are evaluating additional indications, such as renal disease and cancer. Twenty years after the discovery of endothelin, its inhibitors have finally arrived in the clinical arena and are now providing us with new options to treat disease and prolong the lives of patients. Possible future indications include resistant arterial hypertension, proteinuric renal disease, cancer, and connective tissue diseases.

Differential effects of ET(A) and ET(B) receptor antagonism on oxidative stress in type 2 diabetes

Endothelin (ET-1) is chronically elevated in diabetes. However, role of ET-1 in increased oxidative stress in type 2 diabetes is less clear. This study tested the hypotheses that: 1) oxidative stress markers are increased and total antioxidant capacity is decreased in diabetes, and 2) activation of ET(A) receptors mediates oxidative stress whereas ET(B) receptors display opposing effects. Plasma total antioxidant status (TAS) and 8-isoprostane (8-iso PGF(2alpha)) as well as total nitrotyrosine levels in mesenteric resistance vessels were measured in control Wistar and diabetic Goto-Kakizaki (GK) rats (n=5-10) treated with vehicle, ET(A) antagonist (atrasentan, 5 mg/kg/day), or ET(B) receptor antagonist (A-192621, 15 or 30 mg/kg/day, low and high dose, respectively) for 4 weeks. 8-iso PGF(2alpha) (pg/ml) levels were significantly higher in low dose A-192621 treatment groups of control and diabetic rats than in atrasentan or high-dose A-192621 treated groups. Protein nitration was increased in diabetes and ET(A) receptor antagonism prevented this increase. TAS levels were similar in all experimental groups. Thus, ET-1 contributes to oxidative stress in type 2 diabetes and ET receptor antagonism with atrasentan or A-192612 displays differential effects depending on dose and receptor subtype.

Endothelin-a receptor blockade improves renal microvascular architecture and function in experimental hypercholesterolemia

Hypercholesterolemia (HC) may trigger early renal injury, partly by impairing the function or the structure of renal microvessels (MV). The endothelin (ET) system is upregulated in HC and can have an impact on the renal microcirculation by regulating MV tone, growth factors, and remodeling. It was hypothesized that ET-A blockade would protect the HC kidney by improving the function and attenuating the damage of intrarenal MV. Single-kidney function and hemodynamic responses to endothelium-dependent challenge were assessed in pigs after 12 wk of experimental HC, HC and chronic supplementation with the ET receptor A blocker ABT-627 (HC+ET-A, 0.75 mg/kg per d), and normal controls. Renal MV architecture then was studied ex vivo using three-dimensional microcomputed tomography imaging, and growth factors and remodeling pathways were explored in renal tissue. The HC kidney showed increased MV density compared with normal (77.68 +/- 5.1 versus 62.9 +/- 4.8 vessels/cm(2); P = 0.04) but blunted endothelial function. Chronic ET-A blockade in HC upregulated renal vascular growth factors, further increased renal MV density (139.9 +/- 8.4 vessels/cm(2); P = 0.001 versus normal and HC), and decreased renal tissue and MV remodeling. Furthermore, ET-A blockade in HC decreased MV tortuosity and improved MV endothelial function, suggesting accelerated stabilization and maturation of neo-vessels. Modulation of renal MV architecture and function in HC is mediated partly by the endogenous ET system. Notably, ET-A blockade enhanced the proliferation and facilitated the maturation of renal MV in the HC kidney and improved renal MV remodeling and function. This study suggests novel renoprotective effects of ET-A blockers and supports further exploration of strategies that target the ET pathway in HC and atherosclerosis.