Is zebrafish heart regeneration "complete"? Lineage-restricted cardiomyocytes proliferate to pre-injury numbers but some fail to differentiate in fibrotic hearts
Is zebrafish heart regeneration "complete"? Lineage-restricted cardiomyocytes proliferate to pre-injury numbers but some fail to differentiate in fibrotic hearts
复制标题
DOI：
10.1016/j.ydbio.2020.12.004
复制
发表时间：
2021-03-01
影响因子：
2.7
通讯作者：
Weidinger, Gilbert
中科院分区：
文献类型：
--
作者：
Bertozzi, Alberto;Wu, Chi-Chung;Weidinger, Gilbert
成年斑马鱼经常被描述为能够“完全”再生心脏。然而，由于心肌细胞增殖的现有证据是间接或非定量的，因此因损伤而损失的心肌细胞被替换的程度尚不清楚。我们建立了体视学方法来量化冷冻损伤后几个时间点的心肌细胞数量。有趣的是，在冷冻损伤杀死约 1/3 的心室心肌细胞后，心肌细胞数量在 30 天内就恢复到了损伤前的水平。然而，许多心脏保留了小的残留疤痕，并且与这些纤维化区域接壤的心肌细胞子集仍然较小，缺乏分化的肌节结构，并且显示出有缺陷的钙信号传导。因此，再生心肌细胞的一个子集未能完全成熟。虽然谱系追踪实验表明再生心肌细胞源自分化的心肌细胞，但技术限制此前无法测试心肌细胞转分化是否有助于非心肌细胞谱系的再生。使用在心脏所有主要细胞类型中表达的 Cre 应答细胞系，我们没有发现心肌细胞转分化为内皮细胞、心外膜、成纤维细胞或免疫细胞谱系的证据。总体而言，我们的结果意味着斑马鱼是否可以完全再生心脏的问题得到了一个精确的答案：为了应对冷冻损伤，损伤前的心肌细胞数量确实通过谱系限制性心肌细胞的增殖而完全再生，而心肌细胞分化和功能的恢复以及疤痕组织的吸收则不太稳健地实现。
Adult zebrafish are frequently described to be able to "completely" regenerate the heart. Yet, the extent to which cardiomyocytes lost to injury are replaced is unknown, since existing evidence for cardiomyocyte proliferation is indirect or non-quantitative. We established stereological methods to quantify the number of cardiomyocytes at several time-points post cryoinjury. Intriguingly, after cryoinjuries that killed about 1/3 of the ventricular cardiomyocytes, pre-injury cardiomyocyte numbers were restored already within 30 days. Yet, many hearts retained small residual scars, and a subset of cardiomyocytes bordering these fibrotic areas remained smaller, lacked differentiated sarcomeric structures, and displayed defective calcium signaling. Thus, a subset of regenerated cardiomyocytes failed to fully mature. While lineage-tracing experiments have shown that regenerating cardiomyocytes are derived from differentiated cardiomyocytes, technical limitations have previously made it impossible to test whether cardiomyocyte trans-differentiation contributes to regeneration of non-myocyte cell lineages. Using Cre responder lines that are expressed in all major cell types of the heart, we found no evidence for cardiomyocyte transdifferentiation into endothelial, epicardial, fibroblast or immune cell lineages. Overall, our results imply a refined answer to the question whether zebrafish can completely regenerate the heart: in response to cryoinjury, preinjury cardiomyocyte numbers are indeed completely regenerated by proliferation of lineage restricted cardiomyocytes, while restoration of cardiomyocyte differentiation and function, as well as resorption of scar tissue, is less robustly achieved.