Basic mechanism of three-dimensional collagen fibre transport by fibroblasts

Collagen remodelling by fibroblasts has a crucial role in organizing tissue structures that are essential to motility during wound repair, development and regulation of cell growth. However, the mechanism of collagen fibre movement in three-dimensional (3D) matrices is not understood. Here, we show that fibroblast lamellipodia extend along held collagen fibres, bind, and retract them in a 'hand-over-hand' cycle, involving alpha2beta1 integrin. Wild-type fibroblasts move collagen fibres three to four times farther per cycle than fibroblasts lacking myosin II-B (myosin II- B-/-). Similarly, myosin II-B-/- fibroblasts contract 3D collagen gels threefold less than controls. On two-dimensional (2D) substrates, however, rates of collagen bead and cell movement are not affected by loss of myosin II- B. Green fluorescent protein (GFP)-tagged myosin II- B, but not II- A, restores normal function in knockout cells and localizes to cell processes, whereas myosin II- A is more centrally located. Additionally, GFP - myosin II- B moves out to the periphery and back during hand-over-hand fibre movement, whereas on 2D collagen, myosin II- B is more centrally distributed. Thus, we suggest that cyclic myosin II- B assembly and contraction in lamellipodia power 3D fibre movements.