Regulation of atrial contraction by PKA and PKC during development and regression of eccentric cardiac hypertrophy

Regulation of kinase cascade activation and heat shock protein expression by poly(ADP-ribose) polymerase inhibition in doxorubicin-induced heart failure

Cardiomyopathy is one of the most severe side effects of the chemotherapeutic agent doxorubicin (DOX). The formation of reactive oxygen species plays a critical role in the development of cardiomyopathies, and the pathophysiological cascade activates nuclear enzyme poly(ADP-ribose) polymerase (PARP), and kinase pathways. We characterized the effects of the PARP-inhibitor and kinase-modulator compound L-2286 in DOX-induced cardiac injury models. We studied the effect of the established superoxide dismutase-mimic Tempol and compared the effects of this agent with those of the PARP inhibitor. In the rat H9C2 cardiomyocytes, in which DOX-induced poly(ADP-ribosyl)ation, L-2286 protected them from the DOX-induced injury in a concentration-dependent manner. In the in vivo studies, mice were pretreated (for 1 week) with L-2286 or Tempol before the DOX treatment. Both the agents improved the activation of cytoprotective kinases, Akt, phospho-specific protein kinase C ϵ, ζ/λ and suppressed the activity of cell death promoting kinases glycogen synthase kinase-3β, JNK, and p38 mitogen-activated protein kinase, but the effect of PARP inhibitor was more pronounced and improved the survival as well. L-2286 activated the phosphorylation of proapoptotic transcription factor FKHR1 and promoted the expression of Hsp72 and Hsp90. These data suggest that the mode of the cytoprotective action of the PARP inhibitor may include the modulation of kinase pathways and heat shock protein expression.

Ras dexamethasone-induced protein 1 is a modulator of hormone secretion in the volume overloaded heart

Because of the crucial role of the endocrine heart in maintaining homeostasis, considerable effort has been focused on the elucidation of the mechanistic underlying gene expression and secretion of the cardiac hormones atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP). However, much remains to be determined regarding specific molecular events involved in cardiocyte secretory function. In this work, we identified genes involved in the transcriptional response of the endocrine heart to volume overload (VO) and signaling pathways involved in its regulation. To this end, the cardiac atrial and ventricular transcriptomes were analyzed in the heart of rats subjected to experimentally induced aorto-caval shunt VO. Pathway analysis revealed unique gene expression profiles in the VO atria for G-protein signaling, notably a significant downregulation of Ras dexamethasone-induced protein 1 (RASD1). In vitro, knockdown of RASD1 in the atrial-derived HL-1 cells, significantly increased ANF secretion. Concurrent knockdown of RASD1 and its effectors Gα(o1) or Gβ(1)γ(2) abrogated the endocrine response, demonstrating a previously unknown negative modulator role for RASD1. RASD1 thus emerges as a tonic inhibitor of ANF secretion and illustrates for the first time the concept of inhibitory protein regulators of ANF release. The novel molecular function identified herein for RASD1 is of considerable importance given its therapeutic implications for cardiovascular disease.

Regulation of the instantaneous inward rectifier and the delayed outward rectifier potassium channels by Captopril and Angiotensin II via the Phosphoinositide-3 kinase pathway in volume-overload-induced hypertrophied cardiac myocytes

Background

Early development of cardiac hypertrophy may be beneficial but sustained hypertrophic activation leads to myocardial dysfunction. Regulation of the repolarizing currents can be modulated by the activation of humoral factors, such as angiotensin II (ANG II) through protein kinases. The aim of this work is to assess the regulation of I_K and I_K1 by ANG II through the PI3-K pathway in hypertrophied ventricular myocytes.

Material/Methods

Cardiac eccentric hypertrophy was induced through volume-overload in adult male rats by aorto-caval shunt (3 weeks). After one week half of the rats were given captopril (2 weeks; 0.5 g/l/day) and the other half served as control. The voltage-clamp and western blot techniques were used to measure the delayed outward rectifier potassium current (I_K) and the instantaneous inward rectifier potassium current (I_K1) and Akt activity, respectively.

Results

Hypertrophied cardiomyocytes showed reduction in I_K and I_K1. Treatment with captopril alleviated this difference seen between sham and shunt cardiomyocytes. Acute administration of ANG II (10⁻⁶M) to cardiocytes treated with captopril reduced I_K and I_K1 in shunts, but not in sham. Captopril treatment reversed ANG II effects on I_K and I_K1 in a PI3-K-independent manner. However in the absence of angiotensin converting enzyme inhibition, ANG II increased both I_K and I_K1 in a PI3-K-dependent manner in hypertrophied cardiomyocytes.

Conclusions

Thus, captopril treatment reveals a negative effect of ANG II on I_K and I_K1, which is PI3-K independent, whereas in the absence of angiotensin converting enzyme inhibition I_K and I_K1 regulation is dependent upon PI3-K.

Differential activation of enkephalin, galanin, somatostatin, NPY, and VIP neuropeptide production by stimulators of protein kinases A and C in neuroendocrine chromaffin cells

Neuropeptides function as peptide neurotransmitters and hormones to mediate cell-cell communication. The goal of this study was to understand how different neuropeptides may be similarly or differentially regulated by protein kinase A (PKA) and protein kinase C (PKC) intracellular signaling mechanisms. Therefore, this study compared the differential effects of treating neuroendocrine chromaffin cells with stimulators of PKA and PKC on the production of the neuropeptides (Met)enkephalin, galanin, somatostatin, NPY, and VIP. Significantly, selective increases in production of these neuropeptides were observed by forskolin or phorbol myristate acetate (PMA) which stimulate PKA and PKC mechanisms, respectively. (Met)enkephalin production was stimulated by up to 2-fold by forskolin treatment, but not by PMA. In contrast, PMA treatment (but not forskolin) resulted in a 2-fold increase in production of galanin and somatostatin, and a 3-fold increase in NPY production. Notably, VIP production was highly stimulated by forskolin and PMA, with increases of 3-fold and 10-15-fold, respectively. Differences in elevated neuropeptides occurred in cell extracts compared to secretion media, which consisted of (i) increased NPY primarily in secretion media, (ii) increased (Met)enkephalin and somatostatin in secretion media (not cell extracts), and (iii) increased galanin and VIP in both cell extracts and secretion media. Involvement of PKA or PKC for forskolin or PMA regulation of neuropeptide biosynthesis, respectively, was confirmed with direct inhibitors of PKA and PKC. The selective activation of neuropeptide production by forskolin and PMA demonstrates that PKA and PKC pathways are involved in the differential regulation of neuropeptide production.

S-nitroso-N-acetylcysteine (SNAC) prevents myocardial alterations in hypercholesterolemic LDL receptor knockout mice by antiinflammatory action

We investigated the ability of S-nitroso-N-acetylcyseine (SNAC) to prevent structural and functional myocardial alterations in hypercholesterolemic mice. C57BL6 wild-type (WT) and LDL-R-/- male mice (S) were fed a standard diet for 15 days. LDL-R-/- mice (S) showed an 11% increase in blood pressure, 62% decrease in left atrial contractility, and lower CD40L and eNOS expression relative to WT. LDL-R-/- mice fed an atherogenic diet for 15 days (Chol) showed significant increased left ventricular mass compared to S, which was characterized by: (1) 1.25-fold increase in the LV weight/body weight ratio and cardiomyocyte diameter; (2) enhanced expression of the NOS isoforms, CD40L, and collagen amount; and (3) no alteration in the atrial contractile performance. Administration of SNAC to Chol mice (Chol + SNAC) (0.51 micromol/kg/day for 15 day, IP) prevented increased left ventricular mass, collagen deposit, NOS isoforms, and CD40L overexpression, but it had no effect on the increased blood pressure or atrial basal hypocontractility. Deletion of the LDL receptor gene in mice resulted in hypertension and a marked left atrial contractile deficit, which may be related to eNOS underexpression. Our data show that SNAC treatment has an antiinflammatory action that might contribute to prevention of structural and functional myocardial alterations in atherosclerotic mice independently of changes in blood pressure.

Enhancement of tumor invasion depends on transdifferentiation of skin fibroblasts mediated by reactive oxygen species

Myofibroblasts, pivotal for tumor progression, populate the microecosystem of reactive stroma. Using an in vitro tumor-stroma model of skin carcinogenesis, we report here that tumor-cell-derived transforming growth factor β1 (TGFβ1) initiates reactive oxygen species-dependent expression of α-smooth muscle actin, a biomarker for myofibroblastic cells belonging to a group of late-responsive genes. Moreover, protein kinase C (PKC) is involved in lipid hydroperoxide-triggered molecular events underlying transdifferentiation of fibroblasts to myofibroblasts (mesenchymal-mesenchymal transition, MMT). In contrast to fibroblasts, myofibroblasts secrete large amounts of hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6), resulting in a significant increase in the invasive capacity of tumor cells. The thiol N-acetyl-L-cysteine, the micronutrient selenite as well as selenoprotein P and the lipid peroxidation inhibitors α-tocopherol and butylated hydroxytoluene significantly lower both the number of TGFβ1-initiated myofibroblasts and the secretion of HGF, VEGF and IL-6, correlating with a diminished invasive capacity of tumor cells. This novel concept of stromal therapy, namely the protection of stromal cells against the dominating influence of tumor cells in tumor-stroma interaction by antioxidants and micronutrients, may form the basis for prevention of MMT in strategies for chemoprevention of tumor invasion.