The role of erythropoietin (EPO) has extended beyond hematopoiesis to include cytoprotection, inotropy, and neurogenesis. Extra-renal EPO has been reported for multiple tissue/cell types, but the physiological relevance remains unknown. Although the EPO receptor is expressed by multiple cardiac cell types and human recombinant EPO increases contractility and confers cytoprotection against injury, whether the heart produces physiologically meaningful amounts of EPO in vivo is unclear. We show a distinct circadian rhythm of cardiac EPO mRNA expression in adult mice and increased mRNA expression during embryogenesis, suggesting physiological relevance to cardiac EPO production throughout life. We then generated constitutive, cardiomyocyte-specific EPO knockout mice driven by the Mlc2v promoter (EPOfl/fl:Mlc2v-cre+/−; EPO). During cardiogenesis, cardiac EPO mRNA expression and cellular proliferation were reduced in EPO hearts. However, in adult EPO mice, total heart weight was preserved through increased cardiomyocyte cross-sectional area, indicating the reduced cellular proliferation was compensated for by cellular hypertrophy. Echocardiography revealed no changes in cardiac dimensions, with modest reductions in ejection fraction, stroke volume, and tachycardia, whereas invasive hemodynamics showed increased cardiac contractility and lusitropy. Paradoxically, EPO mRNA expression in the heart was elevated in adult EPO, along with increased serum EPO protein content and hematocrit. Using RNA fluorescent in situ hybridization, we found that Epo RNA colocalized with endothelial cells in the hearts of adult EPO mice, identifying the endothelial cells as a cell responsible for the EPO hyper-expression. Collectively, these data identify the first physiological roles for cardiomyocyte-derived EPO. We have established cardiac EPO mRNA expression is a complex interplay of multiple cell types, where loss of embryonic cardiomyocyte EPO production results in hyper-expression from other cells within the adult heart.

中文翻译：

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心源性促红细胞生成素在心脏发育和功能中的新作用

促红细胞生成素 (EPO) 的作用已超出造血作用，还包括细胞保护、正性肌力和神经发生。据报道，肾外 EPO 可用于多种组织/细胞类型，但其生理相关性仍不清楚。尽管 EPO 受体由多种心脏细胞类型表达，并且人重组 EPO 可以增加收缩性并提供细胞保护以防止损伤，但心脏在体内是否产生具有生理意义的量的 EPO 尚不清楚。我们发现成年小鼠心脏 EPO mRNA 表达具有明显的昼夜节律，并且在胚胎发生过程中 mRNA 表达增加，这表明其与整个生命周期中心脏 EPO 产生的生理相关性。然后，我们生成了由 Mlc2v 启动子（EPOfl/fl：Mlc2v-cre+/-；EPO）驱动的组成型心肌细胞特异性 EPO 敲除小鼠。在心脏发生过程中，EPO 心脏中的心脏 EPO mRNA 表达和细胞增殖减少。然而，在成年 EPO 小鼠中，心脏总重量通过增加心肌细胞横截面积得以保留，表明细胞增殖的减少被细胞肥大所补偿。超声心动图显示心脏尺寸没有变化，射血分数、每搏输出量和心动过速适度降低，而有创血流动力学显示心脏收缩力和松弛性增加。矛盾的是，成人 EPO 中心脏中的 EPO mRNA 表达升高，同时血清 EPO 蛋白含量和血细胞比容也升高。使用RNA荧光原位杂交，我们发现Epo RNA与成年EPO小鼠心脏中的内皮细胞共定位，从而确定内皮细胞是负责EPO超表达的细胞。总的来说，这些数据确定了心肌细胞衍生的 EPO 的第一个生理作用。我们已经确定心脏 EPO mRNA 表达是多种细胞类型复杂的相互作用，其中胚胎心肌细胞 EPO 产生的丧失导致成人心脏内其他细胞的过度表达。