Abstract Body: BACKGROUND: The beneficial effects of the neuregulin/ErbB pathway on the diseased heart have been well-established. The cardioprotective aspects of neuregulin are largely attributable to the activation of the ErbB4 receptor. We recently developed a small-molecule selective ErbB4 agonist, which reduced collagen production in fibroblasts and prevented oxidative-stress induced cardiomyocyte death in vitro.

HYPOTHESIS: We hypothesized that the ErbB4 agonist (referred to as compound, Cpd), would attenuate left ventricular remodeling, reduce interstitial cardiac fibrosis and preserve cardiac function in a murine model of myocardial infarction (MI). Since there is a potential interaction between the ErbB4 receptor and the estrogen receptor, we further hypothesized these effects would be sex-dependent.

METHODS: Mice were divided by sex and then further divided into three experimental groups: a sham group, an MI group receiving Cpd (MI/Cpd), and a control MI group receiving vehicle only (MI/Veh). Mice started treatment with either Cpd (2mg/kg/d) or its vehicle through subcutaneous osmotic minipumps seven days after MI. Cardiac ultrasound was performed weekly until mice were sacrificed after four weeks of treatment. Hearts were excised and stained with Masson’s trichrome to assess interstitial cardiac fibrosis in myocardium remote from the infarction scar.

RESULTS: In females (n=25), Cpd significantly decreased left ventricular end-diastolic volume compared to vehicle (Fig.1A, 80±23 µl vs.108±29µl, p=0.045) and induced a slightly increased left ventricular ejection fraction (Fig.2A, 32±12% vs. 22±9%, p=0.086). In addition, Cpd significantly reduced reactive interstitial fibrosis (fibrotic area, Fig.3A, 1.4±1.0% vs. vehicle: 3.8±3.1%, p=0.036) in females. In males (n=30), Cpd had no significant effects on either of the parameters mentioned above (Fig.1B, 2B, 3B).

CONCLUSION: Treatment with the novel small-molecule ErbB4 agonist attenuates left ventricular dilation and reactive interstitial fibrosis after MI in female mice, but not in males. These data support the premise that small molecule-induced ErbB4 activation is a potential new therapy for heart failure, especially in female patients. The mechanisms underlying the sex-dependent effects warrant further exploration.