Unlike adult cardiomyocytes, neonatal cardiomyocytes can readily proliferate that contributes to a transient regenerative potential after myocardial injury in mice. We have recently reported that CD4⁺ regulatory T-cells promote this process; however, the role of other CD4⁺ T-cell subsets as well as CD8⁺ T-cells in postnatal heart regeneration has been less studied. Methods: by comparing the regenerating postnatal day (P) 3 and the non-regenerating P8 heart after injury, we revealed the heterogeneity of CD4⁺ and CD8⁺ T-cells in the myocardium through single cell analysis. We also specifically ablated CD4⁺ and CD8⁺ T-cells using the lytic anti-CD4 and -CD8 monoclonal antibodies, respectively, in juvenile mice at P8 after myocardial injury. Results: we observe significantly more CD4⁺FOXP3^- conventional T-cells in the P8 heart when compared to that of the P3 heart within a week after injury. Surprisingly, such a difference is not seen in CD8⁺ T-cells that appear to have no function as their depletion does not reactivate heart regeneration. On the other hand, specific ablation of CD4⁺ T-cells contributes to mitigated cardiac fibrosis and increased cardiomyocyte proliferation after injury in juvenile mice. Single-cell transcriptomic profiling reveals a pro-fibrotic CD4⁺ T-cell subset in the P8 but not P3 heart. Moreover, there are likely more Th1 and Th17 cells in the P8 than P3 heart. We further demonstrate that cytokines of Th1 and Th17 cells can directly reduce the proliferation and increase the apoptosis of neonatal cardiomyocytes. Moreover, ablation of CD4⁺ T-cells can directly or indirectly facilitate the polarization of macrophages away from the pro-fibrotic M2-like signature in the juvenile heart. Nevertheless, ablation of CD4⁺ T-cells alone does not offer the same protection in the adult heart after myocardial infarction, suggesting a developmental change of immune cells including CD4⁺ T-cells in the regulation of age-related mammalian heart repair. Conclusions: our results demonstrate that ablation of CD4⁺ but not CD8⁺ T-cells promotes heart regeneration in juvenile mice; and CD4⁺ T-cells play a distinct role in the regulation of heart regeneration and repair during development.

中文翻译：

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CD4 + T细胞的特定消融促进幼年小鼠的心脏再生。

与成年心肌细胞不同，新生心肌细胞易于增殖，有助于小鼠心肌损伤后的短暂再生潜力。最近我们报道CD4 ⁺调节性T细胞促进了这一过程。然而，其他CD4 ⁺ T细胞亚群以及CD8 ⁺ T细胞在产后心脏再生中的作用还没有得到研究。方法：通过比较受伤后再生的出生后第3天和非再生的P8心脏，我们通过单细胞分析揭示了心肌中CD4 ⁺和CD8 ⁺ T细胞的异质性。我们还专门烧蚀了CD4 ⁺和CD8 ⁺在心肌损伤后的P8幼鼠中，分别使用裂解性抗CD4和-CD8单克隆抗体的T细胞。结果：我们显著更多的观察CD4 ⁺ FOXP3 ^-相比于伤后一周内P3心脏的当传统的T细胞在心脏P8。令人惊讶的是，在似乎没有功能的CD8 ⁺ T细胞中没有看到这种差异，因为它们的耗竭并不能重新激活心脏再生。另一方面，CD4 ⁺ T细胞的特异性消融有助于减轻幼年小鼠受伤后的心脏纤维化和增加心肌细胞的增殖。单细胞转录组谱分析显示纤维化CD4 ⁺T细胞亚群位于P8心脏，而非P3心脏。此外，P8心脏中的Th1和Th17细胞可能多于P3心脏。我们进一步证明Th1和Th17细胞的细胞因子可以直接减少新生心肌细胞的增殖并增加其凋亡。此外，CD4 ⁺ T细胞的消融可以直接或间接促进巨噬细胞的极化，使其远离幼年心脏中的纤维化性M2样信号。然而，单独的CD4 ⁺ T细胞消融在心肌梗塞后不能在成年心脏中提供相同的保护，这表明包括CD4 ⁺ T细胞在内的免疫细胞在调节与年龄相关的哺乳动物心脏修复中的发展变化。结论：我们的研究结果表明，消融CD4 ⁺而不是CD8 ⁺ T细胞可促进幼年小鼠的心脏再生；CD4 ⁺ T细胞在发育过程中对心脏再生和修复的调节中起着独特的作用。