Circulating NRG‐1b does not contribute to plasma ErbB3‐activating activity

Abstract

Neuregulin‐1b (NRG‐1b) is a membrane‐bound or secreted growth and differentiation factor that mediates its action by binding to ErbB receptors. Circulating levels of NRG‐1b are characterized by large inter‐individual variability with the range of absolute values covering two orders of magnitude, from hundreds to tens of thousands of picograms per milliliter of blood. NRG‐1b signaling via ErbB receptors contributes to the survival of endothelial and other cells and downregulation of the inflammatory response. A higher level of circulating NRG‐1b may indicate increased expression and secretion or shedding of membrane‐bound NRG‐1b, which in turn can contribute to better protection against cardiovascular stress or injury. However, it is unknown whether circulating NRG‐1b can induce activation of ErbB receptors.Here, we performed an analysis of circulating NRG‐1b functional activity using a cell‐based ELISA to measure ErbB3‐activating activity in blood plasma obtained from healthy donors and subjects undergoing coronary artery bypass grafting (CABG) surgery. Activation of ErbB3 receptors, expressed at high level in the MCF‐7 breast cancer cell line, was determined by measuring ErbB3 phosphorylation (Tyr1289).High levels of plasma ErbB3‐activating activity were detected in healthy donors and CABG subjects. However, no correlations were found between the levels of plasma NRG‐1b and ErbB3‐activating activity. To determine the direct effect of circulating NRG‐1b we incubated blood plasma with an NRG‐1 neutralizing antibody, which prevented the stimulatory effect of recombinant NRG‐1b on activation of ErbB3 receptors. No effect of neutralizing antibody was found on the ErbB3‐activating activity of plasma obtained from healthy donors or CABG subjects. Analysis of plasma before and after CABG revealed a significant decrease in the levels of ErbB3‐activating activity but not circulating NRG‐1b at 24 hours after surgery.Our results demonstrate that circulating NRG‐1b cannot induce ErbB3 activation and emphasize the importance of functional testing of NRG‐1b proteins in biological samples. Further investigation of post‐translational modifications of circulating NRG‐1b is warranted.Support or Funding InformationThis work was supported by the Maine Medical Center Cardiovascular Research Institute 2015 Pilot Project Program, the National Heart, Lung, and Blood Institute of the National Institutes of Health under grant R01 HL136560 and the American Heart Association under grant 17POST33410474.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.