STAT5b is a key effector of NRG-1/ERBB4-mediated cardiomyocyte growth

The growth factor neuregulin-1 (NRG-1) regulates hypertrophic and hyperplastic myocardial growth and is currently under clinical investigation as a treatment for heart failure. We have previously demonstrated that an isoform of the NRG-1 receptor ERBB4 (ERBB4 JM-b) expressed in cardiomyocytes selectively regulates the activation of STAT5b. To explore the role of STAT5b in NRG-1/EBBB4 mediated cardiomyocyte growth, several in vitro and in vivo models were utilized. The downregulation of NRG-1/ERBB4 signaling consistently reduced STAT5b activation and transcription of STAT5b target genes Igf1, Myc and Cdkn1a in murine in vitro and in vivo models of myocardial growth. Stat5b knock-down in primary cardiomyocytes ablated NRG-1-induced cardiomyocyte hypertrophy. Stat5b was activated during NRG-1-induced hyperplastic myocardial growth and chemical inhibition of the Nrg-1/Erbb4 pathway led to the loss of myocardial growth and Stat5 activation in zebrafish embryos. Moreover, CRISPR/Cas9-mediated knock-down of stat5b in zebrafish embryos resulted in reduced myocardial growth and heart failure as indicated by reduced ventricular ejection fraction. Dynamin-2 was discovered to control the cell surface localization of ERBB4 and the chemical inhibition of dynamin-2 downregulated NRG-1/ERBB4/STAT5b signaling in models of hypertrophic and hyperplastic myocardial growth. Finally, the activation of the NRG-1/ERBB4/STAT5b signaling pathway was explored in clinical samples representing pathological cardiac hypertrophy. The NRG-1/ERBB4/STAT5b signaling pathway was differentially regulated both at the mRNA and protein levels in the myocardium of patients with pathological cardiac hypertrophy as compared to myocardium of control subjects. These results establish the role for STAT5b, and dynamin-2 in NRG-1/ERBB4-mediated myocardial growth.