Single-cell analysis reveals an Angpt4-initiated EPDC-EC-CM cellular coordination cascade during heart regeneration

Mammals exhibit limited heart regeneration ability, which can lead to heart failure after myocardial infarction. In contrast, zebrafish exhibit remarkable cardiac regeneration capacity. Several cell types and signaling pathways have been reported to participate in this process. However, a comprehensive analysis of how different cells and signals interact and coordinate to regulate cardiac regeneration is unavailable. We collected major cardiac cell types from zebrafish and performed high-precision single-cell transcriptome analyses during both development and post-injury regeneration. We revealed the cellular heterogeneity as well as the molecular progress of cardiomyocytes during these processes, and identified a subtype of atrial cardiomyocyte exhibiting a stem-like state which may transdifferentiate into ventricular cardiomyocytes during regeneration. Furthermore, we identified a regeneration-induced cell (RIC) population in the epicardium-derived cells (EPDC), and demonstrated Angiopoietin 4 (Angpt4) as a specific regulator of heart regeneration. angpt4 expression is specifically and transiently activated in RIC, which initiates a signaling cascade from EPDC to endocardium through the Tie2-MAPK pathway, and further induces activation of cathepsin K in cardiomyocytes through RA signaling. Loss of angpt4 leads to defects in scar tissue resolution and cardiomyocyte proliferation, while overexpression of angpt4 accelerates regeneration. Furthermore, we found that ANGPT4 could enhance proliferation of neonatal rat cardiomyocytes, and promote cardiac repair in mice after myocardial infarction, indicating that the function of Angpt4 is conserved in mammals. Our study provides a mechanistic understanding of heart regeneration at single-cell precision, identifies Angpt4 as a key regulator of cardiomyocyte proliferation and regeneration, and offers a novel therapeutic target for improved recovery after human heart injuries.

Correlation between activation of transforming growth factor signal in muscle fibers and inflammatory response to acute muscle injury / 中华创伤骨科杂志

Objective:To investigate the effect of transforming growth factor (TGF- β) signal in muscle fiber itself during inflammation/immunity response on intramuscular inflammation. Methods:Sixteen wild C57BL/6 mice (wild group) and sixteen mice with skeletal muscle-specific deficiency of T βRⅡ (knock-out group) between 4-8 weeks of age were selected for this study. Acute muscle injury in mice was induced by injection of myotoxin cardiotoxin (CTX) into gastrocnemius. The differences in intramuscular inflammation were compared between the wild and knock-out groups on 0, 4, 7 and 10 d after CTX injection by observing exudation of mononuclear phagocytes, macrophages, M1 type macrophages, CD4 +T cells and helpers T cells (Th1, 2&17). Two newborn C57BL/6 wild mice and 2 SM TGF- βr2-/- knock-out mice were selected to culture primary myoblasts in vitro which were divided into 2 groups: an interferon group subjected to interferon simulation and a control group subjected to addition of an equal amount of solvent. The differences in expression of IL-6, IL-10, MCP-1, MIP-1α, H-2K b, H2-Ea, Toll-like receptor (TLR)3 and TLR7 were compared between the interferon and control groups, as well as between the wild and knock-out groups. Results:On 4&7 d after CTX injection, the ratios of mononuclear/macrophage (75.73%±3.62%, 45.27%± 2.32%), macrophages (38.67%±2.76%, 24.87%±2.19%), M1 macrophages (43.21%±0.11%, 30.43%±2.19%), CD4 +T cells (20.13%±1.62%, 5.67%±0.32%) in the muscle tissue from the knock-out mice were significantly higher than those from the wild mice (58.52%±2.43%, 29.21%±2.45%; 20.63%±2.32%, 16.23%±1.25%; 24.98%±0.35%, 14.23%±1.69%; 10.70%±0.43%, 2.50%±0.45%), with a majority of Th1&Th17 ( P<0.05). In vitro results showed that the levels of IL-6, MCP-1, MIP-1α, H-2K b, H2-Ea and TLR3 were significantly upregulated in the interferon group compared with the control group and that such upregulation in the nock-out mice was more significant than in the wild mice ( P<0.05). Conclusions:Endogenous TGF- β signal activation plays a role in the functional recovery after muscle trauma, because it is involved in the regulation of immune behavior of muscle fibers, thus affecting intramuscular inflammation and muscle regeneration.