A Growth Tonic for Heart Failure?∗

Many organs rely on undifferentiated stem and progenitor cells for tissue regeneration. Whether differentiated cells themselves can contribute to cell replacement and tissue regeneration is a controversial question. Here, we show that differentiated heart muscle cells, cardiomyocytes, can be induced to proliferate and regenerate. We identify an underlying molecular mechanism for controlling this process that involves the growth factor neuregulin1 (NRG1) and its tyrosine kinase receptor, ErbB4. NRG1 induces mononucleated, but not binucleated, cardiomyocytes to divide. In vivo, genetic inactivation of ErbB4 reduces cardiomyocyte proliferation, whereas increasing ErbB4 expression enhances it. Injecting NRG1 in adult mice induces cardiomyocyte cell-cycle activity and promotes myocardial regeneration, leading to improved function after myocardial infarction. Undifferentiated progenitor cells did not contribute to NRG1-induced cardiomyocyte proliferation. Thus, increasing the activity of the NRG1/ErbB4 signaling pathway may provide a molecular strategy to promote myocardial regeneration.

The purpose of this study was to assess the safety and efficacy of recombinant human neuregulin-1 (rhNRG-1) in chronic heart failure (CHF) patients. Neuregulin-1 plays important roles in maintaining cardiomyocyte structure and cardiac pumping functionality and physiology. Previously, rhNRG-1 was proven to be effective in treating heart failure in animals by reducing end-diastolic volume (EDV) and end-systolic volume (ESV) and increasing left ventricular ejection fraction (LVEF%). A total of 44 CHF patients designated as New York Heart Association functional class II or III were enrolled in a double-blind, randomized manner and treated with a placebo or rhNRG-1 (0.3, 0.6, or 1.2 microg/kg/day) for 10 days, in addition to standard therapies. The follow-up period was 90 days; left ventricular function and structure measured by magnetic resonance imaging were the primary end points. Although not statistically different from placebo, the LVEF% was significantly increased by 27.11 +/- 31.12% (p = 0.009) at day 30 after rhNRG-1 treatment in the 0.6-microg/kg group, whereas it was only increased 5.83 +/- 25.75% in the placebo group (p = 0.49). In addition, there were decreases in ESV (-11.58 +/- 12.74%, p = 0.002) and EDV (-5.64 +/- 10.03%, p = 0.05) in the 0.6-microg/kg/day group at day 30; more importantly, both ESV and EDV levels continued to decrease at day 90 (-20.79 +/- 17.03% and -14.03 +/- 13.17%, respectively), accompanied by a sustained increase in LVEF%. This suggests that short-term treatment with rhNRG-1 results in a long-term reversal of remodeling. The effective dose was proven to be tolerable and safe for CHF patients. rhNRG-1 improved the cardiac function of CHF patients by increasing the LVEF% and showed the capability of antiremodeling by decreasing ESV and EDV compared with pre-treatment. (A Randomized, Double-Blind, Multi-Center, Placebo Parallel controlled, Standard Therapy Based Phase II Clinical Trial to Evaluate the Efficacy and Safety of Recombinant Human Neuregulin-1 for Injection in Patients with Chronic Heart Failure; ChiCTR-TRC-00000414). Copyright 2010 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.

Neuregulins (i.e. neuregulin-1 (NRG1), also called neu differentiation factor, heregulin, glial growth factor, and acetylcholine receptor-inducing activity) are known to induce growth and differentiation of epithelial, glial, neuronal, and skeletal muscle cells. Unexpectedly, mice with loss of function mutations of NRG1 or of either of two of their cognate receptors, ErbB2 and ErbB4, die during midembryogenesis due to the aborted development of myocardial trabeculae in ventricular muscle. To examine the role of NRG and their receptors in developing and postnatal myocardium, we studied the ability of a soluble NRG1 (recombinant human glial growth factor 2) to promote proliferation, survival, and growth of isolated neonatal and adult rat cardiac myocytes. Both ErbB2 and ErbB4 receptors were found to be expressed by neonatal and adult ventricular myocytes and activated by rhGGF2. rhGGF2 (30 ng/ml) provoked an approximate 2-fold increase in embryonic cardiac myocyte proliferation. rhGGF2 also promoted survival and inhibited apoptosis of subconfluent, serum-deprived myocyte primary cultures and also induced hypertrophic growth in both neonatal and adult ventricular myocytes, which was accompanied by enhanced expression of prepro-atrial natriuretic factor and skeletal alpha-actin. Moreover, NRG1 mRNA could be detected in coronary microvascular endothelial cell primary cultures prepared from adult rat ventricular muscle. NRG1 expression in these cells was increased by endothelin-1, another locally acting cardiotropic peptide within the heart. The persistent expression of both a neuregulin and its cognate receptors in the postnatal and adult heart suggests a continuing role for neuregulins in the myocardial adaption to physiologic stress or injury.