Mechanical properties of intercellular tunneling nanotubes formed by different mechanisms.

Tunneling nanotubes (TNTs) that connect cells have been recognized as a pathway for long-range intercellular transport of diverse cargoes, including viruses, lysosomes or other organelles, Ca and electrical signals. TNTs can initially be formed from thin finger-like actin assembly-driven protrusions or cell contacts and dislodgment. However, it remains unclear whether the mechanical properties of TNTs formed by these two mechanisms are the same. Here, we developed novel microoperation methods to investigate the mechanical properties of TNTs in HEK293 cells, in which the TNTs form from thin finger-like actin assembly-driven protrusions and C2C12 cells, in which the TNTs form through contact and cell dislodgment. We found that TNTs formed by the two mechanisms represent elastic elements with similar tensile strength. In both the HEK and C2C12 cells, the tensile strength of TNTs exhibited a distinct size dependence on their lengths and diameters. Disturbing the cytoskeleton or removing extracellular Ca also changed their tensile strength. In addition, the stiffening of the extracellular matrix (ECM) enhanced the length, diameter and tensile strength of TNTs both in both HEK and C2C12 cells. Finally, a theoretical model was established to reveal the changes in the TNT's mechanical properties with its length, diameter and individual tunneling nanotubes (iTNT) number. This work not only gains insights into the properties of TNTs but also helps understand the dynamics of various cells.