Transforming growth factor beta-1 attenuates endothelin-1-induced functions in neonatal cardiac myocytes

Endothelin-1 induces alveolar epithelial-mesenchymal transition through endothelin type A receptor-mediated production of TGF-beta1

Endothelin-1 (ET-1) is implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF), but the cellular mechanisms underlying the role it plays in this disease are not well characterized. Epithelial-mesenchymal transition (EMT), which was recently demonstrated in alveolar epithelial cells (AEC), may play an important role in the pathogenesis of IPF and other forms of pulmonary fibrosis. Whether ET-1 contributes to the induction of EMT in AEC is unknown. The aims of this study were to evaluate AEC production of ET-1 and to determine if ET-1 induces EMT in AEC. We demonstrate that ET-1 is produced at physiologically relevant levels by primary AEC and is secreted preferentially toward the basolateral surface. We also demonstrate that AEC express high levels of endothelin type A receptors (ET-A) and, to a lesser extent, type B receptors (ET-B), suggesting autocrine or paracrine function for alveolar ET-1. In addition, ET-1 induces EMT through ET-A activation. Furthermore, TGF-beta1 synthesis is increased by ET-1, ET-1 induces Smad3 phosphorylation, and ET-1-induced EMT is attenuated by a TGF-beta1-neutralizing antibody. Thus, ET-1 is an important mediator of EMT in AEC, acting through ET-A-mediated TGF-beta1 production. These findings increase our basic understanding of the role of ET-1 in pulmonary fibrosis and suggest potential roles for AEC-derived ET-1 in the pathogenesis of other alveolar epithelial-mediated lung diseases.

Localized methylation in the key regulator gene endothelin-1 is associated with cell type-specific transcriptional silencing

DNA methylation can contribute to the stable transcriptional silencing of mammalian genes. Often times, these genes are important developmental regulators, and their silencing in cell types where they are not supposed to be active is important for the phenotypic stability of the cells. To identify key developmental regulator genes whose expression in terminally differentiated cells may be inhibited by DNA methylation, mouse dermal fibroblasts were demethylated with 5-aza-2'-deoxycytidine, and changes in gene expression monitored by microarray analysis. Endothelin-1 (Et1 or Edn1), which encodes a cytokine with diverse regulatory functions, was among the genes upregulated following demethylation. We found that CpG dinucleotides within a short region in intron 1 of the gene have dramatically higher levels of methylation in Et1-non-expressing fibroblasts and chondrocytes as compared to the Et1-expressing mouse cell line, mIMCD-3. Strong evolutionary conservation of this region implies its role in the cis-regulation of Et1 transcription. To confirm that should Et1 in dermal fibroblasts become aberrantly activated, it could indeed lead to the dysregulation of many downstream genes, we exposed fibroblasts to exogenous ET1 peptide and assayed for transcriptional changes by microarray. ET1 treatment resulted in significant expression changes - primarily downregulation - of a significant number of genes. In particular, Tgfbeta2 and Tgfbeta3 were among the downregulated genes, which in turn alter the expression status of their many target genes. These data suggest that the stable silencing of Et1 through its associated DNA methylation in intron 1 is critical for the developmental stability of dermal fibroblasts, and perhaps other cell types as well.

Vascular remodeling versus amyloid beta-induced oxidative stress in the cerebrovascular dysfunctions associated with Alzheimer's disease

The roles of oxidative stress and structural alterations in the cerebrovascular dysfunctions associated with Alzheimer's disease (AD) were investigated in transgenic mice overexpressing amyloid precusor protein (APP+) or transforming growth factor-beta1 (TGF+). Age-related impairments and their in vitro reversibility were evaluated, and underlying pathogenic mechanisms were assessed and compared with those seen in AD brains. Vasoconstrictions to 5-HT and endothelin-1 were preserved, except in the oldest (18-21 months of age) TGF+ mice. Despite unaltered relaxations to sodium nitroprusside, acetylcholine (ACh) and calcitonin gene-related peptide-mediated dilatations were impaired, and there was an age-related deficit in the basal availability of nitric oxide (NO) that progressed more gradually in TGF+ mice. The expression and progression of these deficits were unrelated to the onset or extent of thioflavin-S-positive vessels. Manganese superoxide dismutase (SOD2) was upregulated in pial vessels and around brain microvessels of APP+ mice, pointing to a role of superoxide in the dysfunctions elicited by amyloidosis. In contrast, vascular wall remodeling associated with decreased levels of endothelial NO synthase and cyclooxygenase-2 and increased contents of vascular endothelial growth factor and collagen-I and -IV characterized TGF+ mice. Exogenous SOD or catalase normalized ACh dilatations and NO availability in vessels from aged APP+ mice but had no effect in those of TGF+ mice. Increased perivascular oxidative stress was not evidenced in AD brains, but vascular wall alterations compared well with those seen in TGF+ mice. We conclude that brain vessel remodeling and associated alterations in levels of vasoactive signaling molecules are key contributors to AD cerebrovascular dysfunctions.

Epsilon protein kinase C lengthens the quiescent period between spontaneous contractions in rat ventricular cardiac myocytes and trabecula

We have observed a lengthening of the duration between spontaneous cardiac contractions under conditions that preferentially activate the epsilon protein kinase C (epsilonPKC) isozyme. Therefore, we investigated whether this response could be selectively mediated by epsilonPKC in neonatal cardiac myocytes (NCMs) and adult rat ventricular trabeculae. Contraction of NCMs was monitored using light scattering techniques and trabecular force generation was monitored in tissue baths using a force transducer. The involvement of the epsilonPKC isozyme was confirmed using an epsilonPKC-selective translocation inhibitor and Western blot translocation assays. In NCMs 3 nM 4-beta phorbol 12-myristate-13-acetate (PMA) treatment preferentially activates (translocates) epsilonPKC. In this study 3 nM 4-beta PMA induced a 2-fold increase in contractile amplitude and a approximately 14-fold increase in the quiescent period between contractions in NCMs. Extracellular adenosine 5'-triphosphate (ATP) also enhanced contractile amplitude by 1.7-fold and the quiescent period duration by 8-fold. The enhancement of quiescent period duration was attenuated by an epsilonPKC-selective translocation inhibitor. To investigate these relationships in intact myocardium, we studied spontaneously beating adult rat ventricular trabecula. In these fibers contractile amplitude was only modestly enhanced; however, the quiescent period was lengthened by 4.5-fold following a 15-min exposure to 3 nM 4-beta PMA. 4-beta PMA treatment also promoted arrhythmogenesis and increased the association of epsilonPKC with the particulate fraction in these fibers. Our results suggest that epsilonPKC may influence a specific phase of ventricular myocyte spontaneous beating. A better understanding of epsilonPKC modulation of spontaneous cardiac contraction may improve our understanding of the molecular events contributing to ventricular automaticity.