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Did you know that viruses, nucleic acids, and even entire mitochondria can be transferred between cells?
In the microscopic world of biology, there is an amazing structure called "Tunneling Nanotubes (TNTs)". These intercellular connections not only enable the transmission of messages, but can even transport important cellular components such as nucleic acids and mitochondria. This advanced method of cell-to-cell communication is important for our understanding of how cells interact.
Channel nanotubes range in diameter from 0.05 microns to 1.5 microns, can extend to lengths of several cell diameters, and can be divided into open and closed types.
These tiny structures not only exist between certain animal cells, but also exhibit powerful functions. These channels allow cells to connect over distances of up to 100 microns and can pass parts of the cell membrane between two cells, forming a direct cellular connection. In addition to basic cell-to-cell communication, they are also capable of transferring nucleic acids such as mRNA and miRNA, as well as transmitting pathogens such as HIV and prions.
The history of channel nanotubes
The concept of channel nanotubes was first proposed in 1999. The research purpose at that time was to explore the morphological development of the wings of Drosophila melanogaster. As research continued to deepen, a 2004 paper further described the connection structures formed between PC12 cells and named these structures "channel nanotubes" for the first time. These preliminary studies show that nanotube formation is closely related to the transfer of cell membranes and organelles.
Formation of nanotubes
The formation mechanism of channel nanotubes is still under study, and there are two main hypotheses. One is that direct contact between cells allows the cytoplasmic protrusions to extend toward another cell and eventually fuse with the membrane of the target cell. The other is when two interconnected cells separate, leaving behind nanotubes that act as bridges to keep each other connected.
The study found that certain dendritic cells and THP-1 monocytes connected through channel nanotubes and showed evidence of calcium flow when stimulated by bacteria or machinery.
Transfer of substances between cells
Transfer of mitochondria
Channel nanotubes have been shown to be a mechanism capable of transferring entire mitochondria between cells. In some studies, cancer cells have been found to be able to steal mitochondria from immune cells through these nanotubes. When cells are damaged, damaged mitochondria release reactive oxygen species, triggering nearby mesenchymal stem cells to provide them with healthy mitochondria via nanotubes, a process thought to aid heart repair.
Propagation of action potential
Recent studies have shown that channel nanotubes are capable of propagating action potentials through their extended endoplasmic reticulum. Such a process can promote active diffusion of calcium ions into other cells, thereby facilitating intercellular signaling.
Transmission of pathogens
Not only can mitochondria be transported through channel nanotubes, many viruses can also use these structures to spread. For example, research has shown that the SARS-CoV-2 virus is able to build channel nanotubes to spread from cells in the nose to other parts of the body. In addition, the spread of HIV virus between dendritic cells also relies on the presence of these nanotubes.
Compared with patients whose HIV had not progressed over a long period of time, their dendritic cells were defective in their ability to form channel nanotubes, which may explain the virus's transmission path.
Applications in nanomedicine
Channel nanotubes show potential for applications in nanomedicine. On the one hand, researchers might consider blocking nanotube formation to reduce the toxicity of treatments; on the other hand, promoting nanotube formation might enhance the effectiveness of treatments.
Conclusion
Channel nanotubes provide a unique way for cells to communicate, demonstrating how cells interact across distances. This emerging field of research not only gives us a deeper understanding of cell biology, but also provides new perspectives for future medical technologies. What undiscovered potentials are hidden in such a microscopic world?
