Bone Abstracts

When cells detach from or re-attach to the substrates, there is a drastic change in shape. Molecular mechanism by which controls shape upon cell attachment to the substrates was studied in osteoblastic MC3T3-E1 cells in vitro. Most striking feature found in the ovoid cells detached from the substrates was densely packed cortical actin bundles (CAB) encircling cells. Cells lost the CAB upon attachment and spreading on to the substrates. CABs were under control of small GTPase RhoA (RhoA)/Rho-associated kinase (ROCK) signaling. Cells less spread showed a higher RhoA activity as well as richer CAB on the substrates of lower adhesion strength. Inhibition of adhesion signaling by FAK inhibitor showed the same feature of cells seeded on to the substrates of lower adhesion strength. However, detaching cells of which RhoA or ROCK activity was inhibited maintained their spreaded shape of attached cells without developing CAB. On contrary, attaching cells of which RhoA activity was stimulated by overexpressing constitutively active RhoA maintained ovoid shape of the detached cells. Furthermore, cells spreading on the substrates activated Rac1. Increase of Rac1 activity was also clear in the spread cells which were induced by RhoA-ROCK inhibition on the substrates of low adhesion strength. However, cells overexpressing dominant negative Rac1 did not spread despite of RhoA-ROCK inhibition. Furthermore, without chemico-mechanical improvement of the substrate condition, Rho-ROCK inhibition enhanced the cell attachment and spreading on to the substrates of which adhesion strength is extremely low. These results indicate that inhibition of RhoA-ROCK by adhesion signaling makes cells spread by eliminating contraction force of the CAB and activating Rac1. Rho-ROCK inhibition can be a way to enhance the cell attachment and spreading on to the substrates for the bone tissue engineering which generally uses hydrophobic scaffolds of much low adhesion strength as carriers for cells.