Reuter Sean, Soonpaa Mark H, Firulli Anthony B, Chang Audrey N, Field Loren J
The Krannert Institute of Cardiology, and the Riley Heart Research Center, Wells Center for Pediatric Research, and Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
PLoS One. 2014 Dec 29;9(12):e115871. doi: 10.1371/journal.pone.0115871. eCollection 2014.
Neuregulin 1 signaling plays an important role in cardiac trabecular development, and in sustaining functional integrity in adult hearts. Treatment with neuregulin 1 enhances adult cardiomyocyte differentiation, survival and/or function in vitro and in vivo. It has also been suggested that recombinant neuregulin 1β1 (NRG1β1) induces cardiomyocyte proliferation in normal and injured adult hearts. Here we further explore the impact of neuregulin 1 signaling on adult cardiomyocyte cell cycle activity.
Adult mice were subjected to 9 consecutive daily injections of recombinant NRG1β1 or vehicle, and cardiomyocyte DNA synthesis was quantitated via bromodeoxyuridine (BrdU) incorporation, which was delivered using mini-osmotic pumps over the entire duration of NRG1β1 treatment. NRG1β1 treatment inhibited baseline rates of cardiomyocyte DNA synthesis in normal mice (cardiomyocyte labelling index: 0.019±0.005% vs. 0.003±0.001%, saline vs. NRG1β1, P<0.05). Acute NRG1β1 treatment did result in activation of Erk1/2 and cardiac myosin regulatory light chain (down-stream mediators of neuregulin signalling), as well as activation of DNA synthesis in non-cardiomyocytes, validating the biological activity of the recombinant protein. In other studies, mice were subjected to permanent coronary artery occlusion, and cardiomyocyte DNA synthesis was monitored via tritiated thymidine incorporation which was delivered as a single injection 7 days post-infarction. Daily NRG1β1 treatment had no impact on cardiomyocyte DNA synthesis in the infarcted myocardium (cardiomyocyte labelling index: 0.039±0.011% vs. 0.027±0.021%, saline vs. NRG1β1, P>0.05).
These data indicate that NRG1β1 treatment does not increase cardiomyocyte DNA synthesis (and consequently does not increase the rate of cardiomyocyte renewal) in normal or infarcted adult mouse hearts. Thus, any improvement in cardiac structure and function observed following neuregulin treatment of injured hearts likely occurs independently of overt myocardial regeneration.
神经调节蛋白1信号通路在心脏小梁发育以及维持成年心脏功能完整性方面发挥重要作用。用神经调节蛋白1进行治疗可增强成年心肌细胞在体外和体内的分化、存活及/或功能。也有研究表明，重组神经调节蛋白1β1（NRG1β1）可诱导正常及受损成年心脏中的心肌细胞增殖。在此，我们进一步探究神经调节蛋白1信号通路对成年心肌细胞细胞周期活性的影响。
对成年小鼠连续9天每日注射重组NRG1β1或溶剂，通过溴脱氧尿苷（BrdU）掺入法对心肌细胞DNA合成进行定量，BrdU通过微型渗透泵在NRG1β1治疗的整个期间给药。NRG1β1治疗抑制了正常小鼠心肌细胞DNA合成的基线速率（心肌细胞标记指数：生理盐水组为0.019±0.005%，NRG1β1组为0.003±0.001%，P<0.05）。急性NRG1β1治疗确实导致了细胞外信号调节激酶1/2（Erk1/2）和心肌肌球蛋白调节轻链（神经调节蛋白信号的下游介质）的激活，以及非心肌细胞中DNA合成的激活，从而验证了重组蛋白的生物活性。在其他研究中，对小鼠进行永久性冠状动脉闭塞，并在心肌梗死后7天通过单次注射氚标记胸腺嘧啶核苷来监测心肌细胞DNA合成。每日NRG1β1治疗对梗死心肌中的心肌细胞DNA合成没有影响（心肌细胞标记指数：生理盐水组为0.039±0.011%，NRG1β1组为0.027±0.021%，P>0.05）。
这些数据表明，在正常或梗死的成年小鼠心脏中，NRG1β1治疗不会增加心肌细胞DNA合成（因此不会增加心肌细胞更新率）。因此，在用神经调节蛋白治疗受损心脏后观察到的心脏结构和功能的任何改善可能独立于明显的心肌再生而发生。
