Endogenous endothelin 1 mediates angiotensin II-induced hypertrophy in electrically paced cardiac myocytes through EGFR transactivation, reactive oxygen species and NHE-1

Pioglitazone Modulates the Vascular Contractility in Hypertension by Interference with ET-1 Pathway

Endothelin-1 (ET-1) is an important modulator of the vascular tone and a proinflammatory molecule that contributes to the vascular damage observed in hypertension. Peroxisome-proliferator activated receptors-γ (PPARγ) agonists show cardioprotective properties by decreasing inflammatory molecules such as COX-2 and reactive oxygen species (ROS), among others. We investigated the possible modulatory effect of PPARγ activation on the vascular effects of ET-1 in hypertension. In spontaneously hypertensive rats (SHR), but not in normotensive rats, ET-1 enhanced phenylephrine-induced contraction through ET_A by a mechanism dependent on activation of TP receptors by COX-2-derived prostacyclin and reduction in NO bioavailability due to enhanced ROS production. In SHR, the PPARγ agonist pioglitazone (2.5 mg/Kg·day, 28 days) reduced the increased ET_A levels and increased those of ET_B. After pioglitazone treatment of SHR, ET-1 through ET_B decreased ROS levels that resulted in increased NO bioavailability and diminished phenylephrine contraction. In vascular smooth muscle cells from SHR, ET-1 increased ROS production through AP-1 and NFκB activation, leading to enhanced COX-2 expression. These effects were blocked by pioglitazone. In summary, in hypertension, pioglitazone shifts the vascular ET_A/ET_B ratio, reduces ROS/COX-2 activation and increases NO availability; these changes explain the effect of ET-1 decreasing phenylephrine-induced contraction.

Cardiac GPCR-Mediated EGFR Transactivation: Impact and Therapeutic Implications

G protein-coupled receptors (GPCRs) remain primary therapeutic targets for numerous cardiovascular disorders, including heart failure (HF), because of their influence on cardiac remodeling in response to elevated neurohormone signaling. GPCR blockers have proven to be beneficial in the treatment of HF by reducing chronic G protein activation and cardiac remodeling, thereby extending the lifespan of patients with HF. Unfortunately, this effect does not persist indefinitely, thus next-generation therapeutics aim to selectively block harmful GPCR-mediated pathways while simultaneously promoting beneficial signaling. Transactivation of epidermal growth factor receptor (EGFR) has been shown to be mediated by an expanding repertoire of GPCRs in the heart, and promotes cardiomyocyte survival, thus may offer a new avenue of HF therapeutics. However, GPCR-dependent EGFR transactivation has also been shown to regulate cardiac hypertrophy and fibrosis by different GPCRs and through distinct molecular mechanisms. Here, we discuss the mechanisms and impact of GPCR-mediated EGFR transactivation in the heart, focusing on angiotensin II, urotensin II, and β-adrenergic receptor systems, and highlight areas of research that will help us to determine whether this pathway can be engaged as future therapeutic strategy.

Nitric oxide/cyclic GMP pathway mediates the endothelin-1-upregulation of adiponectin expression in rat cardiomyocytes

Endothelin-1 (ET-1) serves an important role in the development of cardiac dysfunction and heart failure. ET-1 and angiotensin II (AngII) comprise a mutually reciprocal signalling network in the myocardium and serve similar or additive roles in the development of heart failure. Our previous study previously demonstrated that AngII upregulated the expression of APN in cardiomyocytes through an AngII receptor type 2/nitric oxide (NO)/cyclic GMP(cGMP)-dependent pathway. The purpose of the present study was to determine the effects of ET-1 and the additive effects of ET-1 and AngII on the gene expression and secretion of APN, and the underlying mechanisms involved. ELISA was used to determine the secretion of adiponectin (APN) and reverse transcription-quantitative polymerase chain reaction was used to evaluate the gene expression of APN. ET-1 induced APN secretion in a time- and dose-dependent manner, and induced APN secretion with AngII simultaneously, as determined via APN mRNA analyses. ETA and ETB receptors were also involved. The use of a NO synthase inhibitor and an analogue of cGMP antagonist resulted in a diminished ET-1- and/or AngII-mediated APN induction in cardiomyocytes. These results suggested that ET-1, as well as AngII, upregulated the gene expression and secretion of APN via the common NO/cGMP-mediated mechanism.