Background:The human heart has limited capacity to generate new cardiomyocytes and this capacity declines with age. Because loss of cardiomyocytes may contribute to heart failure, it is crucial to explore stimuli of endogenous cardiac regeneration to favorably shift the balance between loss of cardiomyocytes and the birth of new cardiomyocytes in the aged heart. We have previously shown that cardiomyogenesis can be activated by exercise in the young adult mouse heart. Whether exercise also induces cardiomyogenesis in aged hearts, however, is still unknown. Here, we aim to investigate the effect of exercise on the generation of new cardiomyocytes in the aged heart.Methods:Aged (20-month-old) mice were subjected to an 8-week voluntary running protocol, and age-matched sedentary animals served as controls. Cardiomyogenesis in aged hearts was assessed on the basis of ¹⁵N-thymidine incorporation and multi-isotope imaging mass spectrometry. We analyzed 1793 cardiomyocytes from 5 aged sedentary mice and compared these with 2002 cardiomyocytes from 5 aged exercised mice, followed by advanced histology and imaging to account for ploidy and nucleation status of the cell. RNA sequencing and subsequent bioinformatic analyses were performed to investigate transcriptional changes induced by exercise specifically in aged hearts in comparison with young hearts.Results:Cardiomyogenesis was observed at a significantly higher frequency in exercised compared with sedentary aged hearts on the basis of the detection of mononucleated/diploid ¹⁵N-thymidine–labeled cardiomyocytes. No mononucleated/diploid ¹⁵N-thymidine–labeled cardiomyocyte was detected in sedentary aged mice. The annual rate of mononucleated/diploid ¹⁵N-thymidine–labeled cardiomyocytes in aged exercised mice was 2.3% per year. This compares with our previously reported annual rate of 7.5% in young exercised mice and 1.63% in young sedentary mice. Transcriptional profiling of young and aged exercised murine hearts and their sedentary controls revealed that exercise induces pathways related to circadian rhythm, irrespective of age. One known oscillating transcript, however, that was exclusively upregulated in aged exercised hearts, was isoform 1.4 of regulator of calcineurin, whose regulation and functional role were explored further.Conclusions:Our data demonstrate that voluntary running in part restores cardiomyogenesis in aged mice and suggest that pathways associated with circadian rhythm may play a role in physiologically stimulated cardiomyogenesis.

中文翻译：

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通过自愿运动恢复老年小鼠心脏的心肌生成

背景：人类心脏产生新心肌细胞的能力有限，并且这种能力随着年龄的增长而下降。由于心肌细胞的丢失可能导致心力衰竭，因此探索内源性心脏再生的刺激以有利地改变衰老心脏中心肌细胞的丢失和新心肌细胞的诞生之间的平衡至关重要。我们之前已经证明，年轻成年小鼠心脏的运动可以激活心肌生成。然而，运动是否也会诱导老年心脏的心肌生成仍然未知。在这里，我们的目的是研究运动对老年心脏中新心肌细胞生成的影响。方法：对老年（20 个月大）小鼠进行为期 8 周的自愿跑步方案，并让年龄匹配的久坐动物进行训练作为控件。根据¹⁵ N-胸苷掺入和多同位素成像质谱法评估老年心脏的心肌发生。我们分析了来自 5 只老年久坐小鼠的 1793 个心肌细胞，并将其与来自 5 只老年运动小鼠的 2002 个心肌细胞进行了比较，然后采用先进的组织学和成像技术来解释细胞的倍性和成核状态。通过 RNA 测序和随后的生物信息分析，研究运动引起的转录变化，特别是与年轻心脏相比，在老年心脏中引起的转录变化。结果：根据单核细胞的检测，与久坐的老年心脏相比，运动的老年心脏中心肌生成的频率显着更高。 /二倍体¹⁵ N-胸苷标记的心肌细胞。在久坐的老年小鼠中未检测到单核/二倍体¹⁵ N-胸苷标记的心肌细胞。老年运动小鼠中单核/二倍体¹⁵ N-胸苷标记心肌细胞的年增长率为 2.3%。相比之下，我们之前报道的年轻运动小鼠的年增长率为 7.5%，年轻久坐小鼠的年增长率为 1.63%。对年轻和老年运动小鼠心脏及其久坐控制的转录谱分析表明，无论年龄如何，运动都会诱导与昼夜节律相关的通路。然而，一种已知的振荡转录本在老年运动心脏中专门上调，它是钙调神经磷酸酶调节剂的亚型 1.4，其调节和功能作用已得到进一步探索。结论：我们的数据表明，自愿跑步部分恢复了老年小鼠的心肌生成，并表明与昼夜节律相关的通路可能在生理刺激的心肌生成中发挥作用。