Abstract-Since the discovery that neuregulin-1 (NRG-1)/ErbB signaling is indispensable in cardiac development, evidence has shown that this system also plays a crucial role in the adult heart. In patients, an inhibitory ErbB2 antibody, trastuzumab, used in the treatment of mammary carcinomas, increases the risk for the development of cardiotoxic cardiomyopathy. Postnatal disruption of NRG-1/ErbB signaling by gene targeting in mice leads to dilated cardiomyopathy. Initially, the search for the mechanisms behind these observations focused mainly on the effects of NRG-1 on cardiomyocyte growth and survival and revealed that NRG-1 has Akt-dependent antiapoptotic effects in cultured cardiomyocytes. In vivo studies, however, did not uniformly reinforce a role for apoptosis in the development of cardiomyopathy induced by impaired NRG-1/ErbB signaling. More recent studies have revealed that NRG-1 is involved in the regulation of cardiac sympathovagal balances by counterbalancing adrenergic stimulation of the adult myocardium and through an obligatory interaction with the muscarinic cholinergic system. NRG-1 is synthesized and released by the endocardial and cardiac microvascular endothelium, dynamically controlled by neurohormonal and biomechanical stimuli. The physiology of the cardiac NRG-1/ErbB system has implications for the treatment of both cancer and heart failure. Clinical studies in breast cancer with novel ErbB inhibitors are currently underway. Novel oncological indications for ErbB inhibition are emerging; cardiovascular side effects need to be carefully monitored. On the other hand, pharmacological activation of ErbB signaling is likely an unrecognized and beneficial effect of currently used drugs in heart failure and a promising therapeutic approach to prevent or reverse myocardial dysfunction. Key Words: endothelium Ⅲ receptors, ErbB-2 Ⅲ heart failure Ⅲ neuregulins N euregulin-1 (NRG-1) is a member of the epidermal growth factor (EGF) family known to activate proliferation, differentiation, and survival of many tissue types, including breast epithelial cells, glial cells, neurons, and myocytes. 1-4 Its biological effects are mediated by a set of tyrosine kinase receptors (ErbB2, ErbB3, and ErbB4) that dimerize on ligand binding, leading to phosphorylation and downstream signaling. 5 NRG-1 biology is complicated by the fact that multiple splice variants are produced from the NRG-1 gene (for review, see elsewhere 6 ). These NRG-1 isoforms can be divided into 3 types. Type I and II NRGs contain an immunoglobulin-like domain and are single-pass transmembrane proteins. Type III NRGs, containing a cysteine-rich domain, are 2-pass transmembrane proteins. Proteolytic cleavage of type I and II NRGs by members of the a-disintegrin and metalloprotease (ADAM) family such as tumor necrosis factor-␣ converting enzyme (ADAM17) and meltrin-␤ (ADAM19) 7,8 results in the release of a bioactive fragment. Cleavage of type III isoforms generates a transmembrane N-terminal fragment (Figure 1). 9 A common motif to all NRG isofo...

Neuregulin-1 (NRG-1), a cardioactive growth factor released from endothelial cells, has been shown to be indispensable for the normal function of the adult heart by binding to ErbB4 receptors on cardiomyocytes. In the present study, we have investigated to what extent ErbB2, the favored co-factor of ErbB4 for heterodimerization, participates in the cardiac effects of endothelium-derived NRG-1. In addition, in view of our previously described anti-adrenergic effects of NRG-1, we have studied which neurohormonal stimuli affect endothelial NRG-1 expression and release and how this may fit into a broader frame of cardiovascular physiology. Immunohistochemical staining of rat heart and aorta showed that NRG-1 expression was restricted to the endocardial endothelium and the cardiac microvascular endothelium (CMVE); by contrast, NRG-1 expression was absent in larger coronary arteries and veins and in aortic endothelium. In rat CMVE in culture, NRG-1 mRNA and protein expression was down-regulated by angiotensin II and phenylephrine and up-regulated by endothelin-1 and mechanical strain. CMVE-derived NRG-1 was shown to phosphorylate cardiomyocyte ErbB2, an event prevented by a 24-h preincubation of myocytes with monoclonal ErbB2 antibodies. Pretreating cardiomyocytes with these inhibitory anti-ErbB2 antibodies significantly attenuated CMVE-induced cardiomyocyte hypertrophy and abolished the protective actions of CMVE against cardiomyocyte apoptosis. Accordingly, ErbB2 signaling participated in the paracrine survival and growth controlling effects of NRG-1 on cardiomyocytes in vitro, explaining the cardiotoxicity of ErbB2 antibodies in patients. Cardiac NRG-1 synthesis occurs in endothelial cells adjacent to cardiac myocytes and is sensitive to factors related to the regulation of blood pressure.In the adult heart, the neuregulin (NRG) 3 receptors ErbB2 and ErbB4, but not ErbB3, are found on cardiomyocytes, whereas NRG-1 has been detected in the endothelium (1). Binding of NRG-1 to its receptor induces the formation of homo-and heterodimers, which is crucial for signaling (2). Although NRG-1 does not bind directly to ErbB2, it is the favored co-receptor for heterodimerization (3). This means that, in the adult heart, NRG-1 signaling can occur through ErbB2/ErbB4 heterodimers and/or ErbB4/ErbB4 homodimers. The importance of NRG/ErbB signaling in the adult heart was revealed by an unforeseen side effect of trastuzumab (Herceptin), a monoclonal antibody against ErbB2 used in the treatment of breast cancer. Unexpectedly, trastuzumab induced dilated cardiomyopathy and heart failure in human patients when combined with a treatment of anthracycline (4, 5). In addition, postnatal conditional mutation of cardiac ErbB2 leads to dilated cardiomyopathy in the mouse (6).Despite these observations, the specific role of ErbB2 in the cardioprotective actions of NRG-1 has remained controversial. Hence, the interpretation of the cardiotoxic effects of trastuzumab in patients has remained difficult. For example, Grazette et al. (7) indica...

. Mesenchymal stem cell adhesion to cardiac microvascular endothelium: activators and mechanisms.

In this review, we address clinical aspects and mechanisms of ventricular dysfunction induced byanticancer drugs targeted to the ErbB2 receptor. ErbB2 antagonists prolong survival in cancer, but also interfere with homeostatic processes in the heart. ErbB2 is a coreceptor for ErbB4, which is activated by neuregulin-1. This epidermal growth factor-like growth factor is released from endothelial cells in the endocardium and in the myocardial microcirculation, hence contributing to intercellular crosstalk in the ventricle. We look at the physiological aspects of neuregulin-1/ErbB signaling in the ventricle, and review its (mal)adaptive responses in chronic heart failure. We also compare structural aspects of

Background— Because of global aging, the prevalence of heart failure with preserved ejection fraction (HFpEF) continues to rise. Although HFpEF pathophysiology remains incompletely understood, endothelial inflammation is stated to play a central role. Cellular senescence is a process of cellular growth arrest linked with aging and inflammation. We used mice with accelerated aging to investigate the role of cellular senescence in HFpEF development. Methods and Results— Senescence-accelerated mice (SAM, n=18) and control mice with normal senescence (n=15) were fed normal chow or a high-fat, high-salt diet (WD). Vascular and cardiac function was assessed at 8, 16, and 24 weeks of age. At 24 weeks, both SAM on WD (SAM-WD) and SAM on regular diet displayed endothelial dysfunction, as evidenced by impaired acetylcholine-induced relaxation of aortic segments and reduced basal nitric oxide. At week 24, SAM-WD had developed HFpEF, characterized by diastolic dysfunction, left ventricular hypertrophy, left atrial dilatation, and interstitial fibrosis. Also, exercise capacity was reduced and lung weight increased. Cardiovascular inflammation and senescence were assessed by immunohistochemical and immunofluorescence staining of hearts and aortas. SAM-WD showed increased endothelial inflammation (intercellular adhesion molecule 1 expression) and increased endothelial senescence (acetyl-p53/CD31 costaining). The latter correlated with diastolic function and intercellular adhesion molecule 1 expression. Conclusions— SAM develop endothelial dysfunction. Adding a high-salt, high-fat diet accelerates endothelial senescence and instigates endothelial inflammation. This coincides with hemodynamic and structural changes typical of HFpEF. Targeting endothelial senescence could be a new therapeutic avenue in HFpEF.