Background —Left ventricular hypertrophy (LVH) represents both an adaptive response to increased cardiac work load and a precursor state of heart failure. Recent evidence linked cardiac myocyte death by apoptosis with LVH and heart failure. It remained unclear, however, whether apoptosis participated in the transition from LVH to left ventricular dysfunction (LVD). Methods and Results —Cardiac myocyte apoptotic events and changes in apoptosis-specific genes were studied in a rat model of chronic pressure overload induced by transverse aortic constriction. The changes in left ventricular geometry and function were assessed by echocardiography. Transverse aortic constriction rats progressively developed “concentric” LVH and subsequently, LVD. A similar distribution of LVH and LVD was found 18 weeks after surgery. At this time point, we determined the occurrence of myocyte apoptosis by DNA laddering, in situ DNA TUNEL labeling, and light and electron microscopy. The monitoring of proapoptotic and antiapoptotic genes was determined by Western blot and immunohistochemistry. Our data demonstrated that cardiomyocyte apoptotic events increased from virtually undetectable (in sham-operated controls, SH) to 0.8/10 ³ and 1.5/10 ³ positive nuclei in LVH and LVD, respectively. Fibrosis also increased in the subendocardial and midwall regions of LVH and LVD rats compared with SH. Expression of the proapoptotic gene bax increased, whereas that of antiapoptotic gene bcl -2 decreased in LVH and LVD compared with SH. Conclusions —These data suggest that in response to chronic pressure overload, cardiomyocyte-specific apoptosis contributed to the transition from LVH to LVD. LVH and LVD were accompanied by a dramatic cardiomyocyte upregulation of the proapoptotic gene bax and reduced bcl -2/ bax ratio, predisposing cardiomyocytes to apoptosis.

We examined the mechanism of atrial natriuretic factor (ANF) transcription by isoproterenol (ISO), an agonist for the beta-adrenergic receptor (betaAR), in cardiac myocytes. ISO only modestly activated members of the mitogen-activated protein kinase family. ISO-induced ANF transcription was not affected by inhibition of mitogen-activated protein kinases, whereas it was significantly inhibited by KN93, an inhibitor of Ca(2+)/calmodulin-dependent kinase (CaM kinase II). Production of 3'-phosphorylated phosphatidylinositides (3 phosphoinositides) was also required for ISO-induced ANF transcription. ISO caused phosphorylation (Ser-473) and activation of Akt through CaM kinase II- and 3 phosphoinositides-dependent mechanisms. Constitutively active Akt increased myocyte surface area, total protein content, and ANF expression, whereas dominant negative Akt blocked ISO-stimulated ANF transcription. ISO caused Ser-9 phosphorylation and decreased activities of GSK3beta. Overexpression of GSK3beta inhibited ANF transcription, which was reversed by ISO. ISO failed to reverse the inhibitory effect of GSK3beta(S9A), an Akt-insensitive mutant. Kinase-inactive GSK3beta increased ANF transcription. Cyclosporin A partially inhibited ISO-stimulated ANF transcription, indicating that calcineurin only partially mediates ANF transcription. These results suggest that both CaM kinase II and 3 phosphoinositides mediate betaAR-induced Akt activation and ANF transcription in cardiac myocytes. Furthermore, betaAR-stimulated ANF transcription is predominantly mediated by activation of Akt and subsequent phosphorylation/inhibition of GSK3beta.

Epidemiological studies have documented a high incidence of diabetes in hypertensive patients.Insulin resistance is defined as a less than expected biologic response to a given concentration of the hormone and plays a pivotal role in the pathogenesis of diabetes. However, over the last decades, it became evident that insulin resistance is not merely a metabolic abnormality, but is a complex and multifaceted syndrome that can also affect blood pressure homeostasis. The dysregulation of neuro-humoral and neuro-immune systems is involved in the pathophysiology of both insulin resistance and hypertension. These mechanisms induce a chronic low grade of inflammation that interferes with insulin signalling transduction. Molecular abnormalities associated with insulin resistance include the defects of insulin receptor structure, number, binding affinity, and/or signalling capacity. For instance, hyperglycaemia impairs insulin signalling through the generation of reactive oxygen species, which abrogate insulin-induced tyrosine autophosphorylation of the insulin receptor. Additional mechanisms have been described as responsible for the inhibition of insulin signalling, including proteasome-mediated degradation of insulin receptor substrate 1/2, phosphatase-mediated dephosphorylation and kinase-mediated serine/threonine phosphorylation of both insulin receptor and insulin receptor substrates. Insulin resistance plays a key role also in the pathogenesis and progression of hypertension-induced target organ damage, like left ventricular hypertrophy, atherosclerosis and chronic kidney disease. Altogether these abnormalities significantly contribute to the increase the risk of developing type 2 diabetes.

Inflammation is a key mechanism of cardiovascular diseases. It is an essential component of atherosclerosis and a significant risk factor for the development of cardiovascular events. In the crosstalk between inflammation and cardiovascular diseases, the transcription factor NFκB seems to be a key player since it is involved in the development and progression of both inflammation and cardiac and vascular damage. In this review, we deal with the recent findings of the role of inflammation in cardiac diseases, focusing, in particular, on NFκB as a functional link. We describe strategies for the therapeutic targeting of NFκB as a potential strategy for the failing heart.

Inactivation of glycogen synthase kinase 3β (GSK3β) is critical for transcription of atrial natriuretic factor (ANF) by β-adrenergic receptors in cardiac myocytes. We examined the mechanism by which GSK3β regulates ANF transcription. Stimulation of β-adrenergic receptors induced nuclear accumulation of GATA4, whereas β-adrenergic ANF transcription was suppressed by dominant negative GATA4, suggesting that GATA4 plays an important role in β-adrenergic ANF transcription. Interestingly, GATA4-mediated transcription was markedly attenuated by GSK3β. GSK3β physically associates with GATA4 and phosphorylates GATA4 in vitro. Overexpression of GSK3β suppressed both basal and β-adrenergic increases in nuclear expression of GATA4, whereas inhibition of GSK3β by LiCl caused nuclear accumulation of GATA4, suggesting that GSK3β negatively regulates nuclear expression of GATA4. The nuclear exportin Crm1 reduced nuclear expression of GATA4, and the reduction was enhanced by GSK3β but not by kinase-inactive GSK3β. Leptomycin B, an inhibitor for Crm1, increased basal nuclear GATA4 and suppressed GSK3β-induced decreases in nuclear GATA4. These results suggest that GSK3β negatively regulates nuclear expression of GATA4 by stimulating Crm1-dependent nuclear export. Inhibition of GSK3β by β-adrenergic stimulation abrogates GSK3β-induced nuclear export of GATA4, causing nuclear accumulation of GATA4, which may represent an important signaling mechanism mediating cardiac hypertrophy.

Myocardial beta-adrenergic receptors (beta -ARs) consist of beta(1)- and beta(2)-subtypes, which mediate distinct signaling mechanisms. We examined which beta-AR subtype mediates cardiac hypertrophy. The beta(2)-subtype is predominant in neonatal rat cardiac myocytes (beta(1), 36%vbeta(2), 64%), while the beta(1)-subtype predominates in the adult rat heart (59%v 41%). Stimulation of cultured cardiac myocytes in vitro with isoproterenol (ISO), an agonist for beta(1)- and beta(2)-ARs, caused hypertrophy of myocytes along with increases in transcription of atrial natriuretic factor (ANF) and actin reorganization. All of these ISO-mediated myocyte responses in vitro were inhibited by a beta(1)-AR antagonist, betaxolol, but not by a beta(2)-AR antagonist, ICI 118551. Pertussis toxin failed to affect ISO-induced increases in total protein/DNA content and ANF transcription in vitro. ISO increased LV weight/body weight and ANF transcription in the adult rat in vivo, which were also inhibited by betaxolol but not by ICI 118551. These results suggest that beta -AR stimulated hypertrophy is mediated by the beta(1)-subtype and by a pertussis toxin-insensitive mechanism