Characterization of novel resident heart cells identified as atypically-shaped cardiomyocytes(ACMs)

我们研究了成年小鼠中存在的与心肌细胞不同的常驻心脏细胞。冠状动脉灌注酶，切除两个心室进一步消化。旋转心室肌细胞后，上清部分（心肌细胞耗尽部分，CMDF）在甲基纤维素基半固体培养基中培养。三到五天后，一些附着在培养皿底部的小细胞逐渐形成形状，并开始自发地跳动。这些细胞大多是多核的，具有良好的肉瘤组织并表达心脏特异性蛋白，被定义为一种新型的心脏细胞，非典型形状心肌细胞（ACMs）。ACMs的细胞数量在新生儿期最高，在前5周内显著下降，在成虫期达到平稳期。从新生和老年小鼠中获得的ACMs均表达胎儿心脏基因产物，如心房利钠肽（ANP）和电压门控Ca2+通道CaV3.2。我们检测了CMDF细胞（包括ACMs）在模拟致死性缺血后能否发育为跳动细胞。预缺血CMDF细胞培养6 d后，跳动的ACMs细胞数约为常温下的50%。电镜分析显示，即使在常压条件下，在培养过程中，ACMs也具有组成性的自噬活性。结果表明，即使存活的细胞数量很少，在受伤的心脏中也可能发生跳动的ACMs。

We have investigated the presence of resident heart cells that are distinct from cardiomyocytes in adult mice. The heart was coronary perfused with enzymes and both ventricles were excised and further digested. After spinning the ventricular myocytes down, the supernatant fraction (cardiac myocyte-depleted fraction, CMDF) was cultured in methylcellulose-based semisolid culture medium. Three to five days after plating, some of the small cells adhered to the bottom of the dishes gradually developed their shapes and started beating spontaneously. These cells were mostly multinucleated, well sarcomeric-organized and expressed cardiac specific proteins, defined as a novel type of heart cells, atypically-shaped cardiomyocytes (ACMs). The cell population of ACMs was highest at neonatal period and significantly decreased within the first 5 weeks and reached a plateau in the adult stage. The ACMs obtained from both newborn and aged mice express the fetal cardiac gene products, such as atrial natriuretic peptide (ANP) and voltage-gated Ca2+channel CaV3.2. We examined whether CMDF cells, including ACMs, that underwent simulated lethal ischemia could develop into beating cells. When CMDF cells pre-exposed to ischemia were cultured for 6 days, the cell number of beating ACMs was ~50% of normoxic preparations. Electron microscopic analyses of ACMs displayed constitutively active autophagy during the culture even in the normoxic conditions. The results suggest the possibility that the development of beating ACMs could occur in injured heart, even if the surviving cell population is small.