2025-03-17 ヒューストン大学(UH)
<関連情報>
- https://uh.edu/news-events/stories/2025/march/03172025-heart-formation-layers-wu.php
- https://www.science.org/doi/10.1126/science.add3417
トンネリングナノチューブ様構造が心臓形成時の遠隔細胞間相互作用を制御する Tunneling nanotube–like structures regulate distant cellular interactions during heart formation
Lianjie Miao, Yangyang Lu, Anika Nusrat, Guizhen Fan, […], and Mingfu Wu
Science Published:14 Mar 2025
DOI:https://doi.org/10.1126/science.add3417
Editor’s summary
During cardiac development, heart muscle cells (the myocardium) and inner lining cells (the endocardium) are separated by a space filled with cardiac jelly. Miao et al. discovered that despite this physical separation, the two cell types communicate with each other through tiny structures called tunneling nanotube-like microstructures (TNTLs) (see the Perspective by de la Pompa). TNTLs extend across the cardiac jelly, allowing direct cell-cell contact, signal transduction, and selective protein transfer. Disrupting TNTLs leads to abnormal heart wall formation, highlighting the importance of TNTLs in cardiac development. —Stella M. Hurtley
Structured Abstract
INTRODUCTION
Heart development is a highly orchestrated process dependent on dynamic interactions between the myocardium and the endocardium. The two layers are separated by a noncellular matrix called cardiac jelly and communicate through signaling pathways involving membrane-bound receptors and ligands. However, the mechanisms enabling such signaling interaction over physical distances remain poorly understood. In this work, we characterized tunneling nanotube–like structures (TNTLs), which we found physically connecting cardiomyocytes (CMs) in the myocardium to endocardial cells (ECs) in the endocardium. These structures likely help to facilitate long-distance intercellular communication essential for heart formation.
RATIONALE
Heart formation relies on precise signaling interactions between the myocardium and endocardium, particularly during trabecular development. Signaling pathways, such as Notch1, Vegf, and Nrg1, have ligands and receptors segregated across these two cardiac layers. The mechanisms enabling these long-distance interactions across the intervening cardiac jelly are unclear. We hypothesized that TNTL structures exist between the cardiac layers and could mediate intercellular long-distance communication in the developing heart, allowing for the transport of signaling molecules and cytoplasmic proteins between them.
RESULTS
We used genetic labeling, contact-tracing techniques, and advanced imaging to demonstrate the existence of TNTLs in mouse embryonic hearts. These TNTLs extended from CMs to ECs across the cardiac jelly, establishing direct connections that enable signal transduction and cytoplasmic protein transfer.
The TNTLs were identified in the heart through the genetic labeling of cellular protrusions. During mouse development TNTLs were shown to form between CMs and ECs as early as embryonic day 8.0. The filamentous structures inside TNTL were characterized by three-dimensional imaging and the reconstruction of the electron microscopy (EM) and cryo-EM images.
The TNTLs contained actin filaments, and TNTL formation depended on actin polymerization. The presence of actin filaments in TNTLs was confirmed in a transgenic mouse line that could label actin filaments with a fluorescent marker. Inhibiting actin polymerization chemically or by ablating the small guanosine triphosphatase, Cdc42, eliminated TNTLs.
The TNTLs were involved in regulating Notch1 signaling and other signaling pathways. TNTLs were sufficient to activate Notch1 signaling in ECs, with ligands from CMs transported through these microstructures to ECs. Loss of TNTLs resulted in reduced Notch signaling and other signaling pathways. TNTLs were able to transport signaling molecules, cytoplasmic proteins, and trafficking vesicles, underscoring their role as conduits for intercellular communication.
The TNTLs were essential in cardiac morphogenesis. Disruption of TNTLs in embryonic hearts resulted in impaired ventricular wall morphogenesis, evidenced by loss of trabeculae and defective myocardial growth.
CONCLUSION
In this work, we identified TNTLs as a critical mechanism for long-distance intercellular communication during heart development. These actin-rich structures physically bridge the myocardium and endocardium, allowing for the efficient exchange of signaling molecules necessary for trabecular formation and ventricular wall morphogenesis. Disruption of TNTLs compromises these interactions, highlighting their essential role in heart patterning. This work provides insights into mechanisms of cellular communication and suggests that TNTL formation might help cells to regulate long-distance cell-cell communication and modulate tissue patterning in mammalian systems. Future research should explore the molecular machinery governing TNTL formation, the structural basis of the interface between TNTLs and endocardial cells (see summary figure), the molecular mechanism of protein trafficking inside the TNTL, the potential functions of cytoplasmic protein transfer between myocardium and endocardium during heart formation, and the potential therapeutic implications of modulating these structures in congenital heart defects and heart failure.
Microstructure regulates signaling interaction and cytoplasmic proteins transfer between CMs and ECs.
TNTLs linking CMs to ECs function as a bridge across the cardiac jelly for signaling molecule trafficking, cytoplasmic protein transferring, and Myosin X shuttling. Trafficking vesicles and cytoplasmic proteins but not Myosin X can be transferred from CMs to ECs. Disruption of TNTL affects Notch1 signaling activation and several other signaling interaction between CMs and ECs, leading to trabeculation defects. NICD, Notch1 intracellular domain.
Abstract
In the developing mammalian heart, the endocardium and the myocardium are separated by so-called cardiac jelly. Communication between the endocardium and the myocardium is essential for cardiac morphogenesis. How membrane-localized receptors and ligands achieve interaction across the cardiac jelly is not understood. Working in developing mouse cardiac morphogenesis models, we used a variety of cellular, imaging, and genetic approaches to elucidate this question. We found that myocardium and endocardium interacted directly through microstructures termed tunneling nanotube–like structures (TNTLs). TNTLs extended from cardiomyocytes (CMs) to contact endocardial cells (ECs) directly. TNTLs transported cytoplasmic proteins, transduced signals between CMs and ECs, and initiated myocardial growth toward the heart lumen to form ventricular trabeculae-like structures. Loss of TNTLs disturbed signaling interactions and, subsequently, ventricular patterning.
