Cardiac-Specific Over-Expression of Epidermal Growth Factor Receptor 2 (ErbB2) Induces Pro-Survival Pathways and Hypertrophic Cardiomyopathy in Mice

Abstract

BackgroundEmerging evidence shows that ErbB2 signaling has a critical role in cardiomyocyte physiology, based mainly on findings that blocking ErbB2 for cancer therapy is toxic to cardiac cells. However, consequences of high levels of ErbB2 activity in the heart have not been previously explored.Methodology/Principal FindingsWe investigated consequences of cardiac-restricted over-expression of ErbB2 in two novel lines of transgenic mice. Both lines develop striking concentric cardiac hypertrophy, without heart failure or decreased life span. ErbB2 transgenic mice display electrocardiographic characteristics similar to those found in patients with Hypertrophic Cardiomyopathy, with susceptibility to adrenergic-induced arrhythmias. The hypertrophic hearts, which are 2–3 times larger than those of control littermates, express increased atrial natriuretic peptide and β-myosin heavy chain mRNA, consistent with a hypertrophic phenotype. Cardiomyocytes in these hearts are significantly larger than wild type cardiomyocytes, with enlarged nuclei and distinctive myocardial disarray. Interestingly, the over-expression of ErbB2 induces a concurrent up-regulation of multiple proteins associated with this signaling pathway, including EGFR, ErbB3, ErbB4, PI3K subunits p110 and p85, bcl-2 and multiple protective heat shock proteins. Additionally, ErbB2 up-regulation leads to an anti-apoptotic shift in the ratio of bcl-xS/xL in the heart. Finally, ErbB2 over-expression results in increased activation of the translation machinery involving S6, 4E-BP1 and eIF4E. The dependence of this hypertrophic phenotype on ErbB family signaling is confirmed by reduction in heart mass and cardiomyocyte size, and inactivation of pro-hypertrophic signaling in transgenic animals treated with the ErbB1/2 inhibitor, lapatinib.Conclusions/SignificanceThese studies are the first to demonstrate that increased ErbB2 over-expression in the heart can activate protective signaling pathways and induce a phenotype consistent with Hypertrophic Cardiomyopathy. Furthermore, our work suggests that in the situation where ErbB2 signaling contributes to cardiac hypertrophy, inhibition of this pathway may reverse this process.

ErbB2 overexpression upregulates antioxidant enzymes, reduces basal levels of reactive oxygen species, and protects against doxorubicin cardiotoxicity

“…Our previous studies on ErbB2 overexpression in the heart showed a concurrent upregulation of EGFR (62), as this phenomena has been observed in cancer cells with ErbB2 upregulation (22,28). Furthermore, in addition to ErbB2, EGFR is also known to bind and activate Abl kinases in breast cancer cells; consequently, the activities of EGFR cannot be excluded here (59).…”

“…However, the specific role of ErbB2 as it is related to ROS-scavenging mechanisms has not been defined, and critical in vivo studies to investigate how ErbB2 affects ROS defenses and mitochondrial function in the heart have not been done, largely because ErbB2 knockout mice die prematurely, precluding the study of specific mechanisms of cardiac protection. We therefore sought to further investigate the possible protective role of cardiac ErbB2 upregulation using a recently developed transgenic murine model that selectively overexpresses ErbB2 in cardiomyocytes (62). Specifically, we used this transgenic mouse model to examine the role of ErbB2 upregulation on mitochondrial function and antioxidant defense mechanisms in the heart.…”

“…A-3273-01). The wild-type (WT) and transgenic (TG; ErbB2 tg ) mice used in this study were developed as described previously (62).…”

“…Densitometry was performed using ImageJ (NIH) software. Levels of Akt (62) and GAPDH proteins were measured to normalize protein quantities across tissue and cell lysate samples, respectively.…”

“…Lysates from heart tissue and H9c2 cells were prepared for immunoprecipitation as previously described (62). Briefly, lysates were incubated with antibodies directed against ErbB2 (Santa Cruz Biotechnology), c-Abl (Santa Cruz Biotechnology), or Arg (US Biological) at 4°C overnight.…”