Intercellular Communication through Tunneling Nanotubes

Abstract

Cell-cell communication is an essential process for the life activities of multicellular organisms. This communication includes direct mechanisms for short distances and indirect mechanisms for long distances. Tunneling nanotubes (TNTs) are a newly discovered pathway for cell-cell communication, providing a direct mechanism for the transfer of various substances and signals between cells over long distances. This study aims to elucidate the structural characteristics and formation mechanisms of TNTs using super-resolution imaging techniques such as Super- Resolution Localization Microscopy (STORM) and Super-Resolution Radial Fluctuation (SRRF) Microscopy. The results revealed that TNTs exhibit a helical structure during their formation process, expanding our understanding of the dynamic movements involved in TNT formation. Detailed analysis showed that the motor protein Myosin-V contributes to the formation of the helical structure of the filopodia bridge, ultimately leading to the formation of TNTs. Additionally, the role of pannexin channels in calcium ion transfer through close- ended TNTs was investigated. Through calcium uncaging experiments, we observed the transfer of calcium ions between cells connected by TNTs by irradiating one cell with UV light and measuring the calcium ion transfer to the other cell. Blocking experiments with probenecid and octanol demonstrated that pannexins play a more significant role than connexins in this transfer process. Our results indicate that pannexin channels facilitate calcium ion transfer through close-ended TNTs, broadening the perspective on cell-cell communication via close-ended TNTs. Quantum dot transfer experiments were conducted to investigate the presence of open-ended TNTs, characterized by the absence of cadherin clusters. The successful transfer of quantum dots, which are too large to pass through pannexin channels, confirmed the possibility of open-ended TNTs. These findings emphasize the interplay between actin polymerization and myosin motor proteins in mediating membrane fusion and nanotube stability, providing a comprehensive model for TNT formation. We propose that the pushing force generated by actin polymerization at the tips of filopodia, combined with the resisting force of Myosin-II, plays a crucial role in overcoming the energy barrier required for membrane fusion, leading to the formation of open-ended TNTs. This research advances the understanding of TNT-mediated cell-cell communication, providing new insights into the structural dynamics and functional roles of TNTs in cellular processes. These discoveries have significant implications for targeted drug delivery and therapeutic interventions, particularly in diseases where cell-cell communication is disrupted. Identifying specific proteins involved in TNT formation and function offers new therapeutic targets in conditions with impaired cell-cell communication. Leveraging advanced imaging techniques and detailed experimental analysis, this study provides a foundational understanding of the mechanisms underlying TNT formation and function, contributing to the broader fields of cellular biology and intercellular communication.