Force-Regulated Multimotor Coordination Drives Bidirectional Lipid Droplets Transport in Tunneling Nanotubes

Tunneling nanotubes (TNTs) mediate intercellular exchange of organelles, yet the mechanical basis of cargo transport in these confined structures remains unclear. Here, we combine optical trapping with confocal imaging to quantify lipid droplet (LD) transport in TNTs. Bidirectional LD movement relies on MTs and is driven by kinesin and dynein. Both transport directions exhibit multimotor cooperation, characterized by trimodal anterograde stall forces (∼2.1, 4.2, 6.3 pN; 1-3 kinesins) and bimodal retrograde forces (∼1.5, 2.9 pN; 1-2 dynins), with conserved ∼8 nm step size. Dynein inhibition eliminated higher-order kinesin force peaks and narrowed step distributions, revealing dynamic force coupling between bidirectional motors. Although the highly viscoelastic microenvironment of TNTs reduces the transport speed of LDs, multimotor engagement sustained long-range transport. These findings define a quantitative description of force-dependent motor coordination in TNTs and clarify how confined intercellular structures regulate organelle transport.