α2β1 integrin and RhoA mediates electric field‐induced ligament fibroblast migration directionality

Abstract

Guided cell migration is important in tissue development, repair, and engineering. We have previously demonstrated that applied electric fields (EFs) enhanced and directed ligament fibroblast migration and collagen production, depending on EF parameters. Electrical stimulation is widely used for the treatment of pain and to promote wound healing. In orthopaedic practices, applied EFs promote bone healing and ligament repair in vivo. In the current study, stimulation waveforms used in physical therapy for promoting tissue repair were adapted to examine their effects on ACL fibroblast migration. Using different waveform and field strengths, we discovered a decoupling of cell motility and directionality, which suggests disparate mechanisms. Integrin, a major extracellular matrix receptor, polarized in response to applied EFs and controlled cell directionality and signaling. Furthermore, we demonstrated that RhoA is a mediator between integrin aggregation and directed cell migration. Polarization is essential in directed cell migration and our study establishes an outside-in signaling mechanism for EF-induced cell directionality. ß

Lipid rafts sense and direct electric field-induced migration

“…We previously reported that integrin mediates directional cell migration in applied EFs (17). The polarized distribution of integrin in response to EF was abolished with raft disruption, whereas raft polarization in EF was less influenced by functional blocking of integrin (Fig.…”

“…Polarization of intracellular signaling molecules, including RhoA, src, and PI3K, mediates EF-induced directionality (7,17). To understand the role of raft in the polarization of these downstream factors, we examined their distribution in applied EF after raft disruption and found polarization of these signaling proteins was abolished (Fig.…”

“…As the plasma membrane consists of mostly negatively charged molecules that move in the plane of the membrane, the external field induces electrophoresis and electroosmosis of these molecules (11)(12)(13). A number of membrane proteins have been found to polarize in direct current (DC) EF, including acetyl choline receptors, VEGF/EGF receptors, and integrins (14)(15)(16)(17). In addition, electrical stimulations are found to regulate ion channel activities with higher activation toward the cathode (18).…”

“…In addition, electrical stimulations are found to regulate ion channel activities with higher activation toward the cathode (18). Through these polarized surface receptors, the external EFs activate intracellular signaling, such as src kinase (src), small GTPases, and phosphoinositol kinase pathways, which are polarized in the EFinduced migration direction (7,17).…”

“…These results suggest that glycolipid redistribution in EF can be an alternative candidate as the primary EF sensor in cell membrane. Moreover, we previously reported that symmetric alternating current (AC) at 50 Hz drives directional cell migration (17). Glycolipids are capable of congregating into structures such as lipid rafts that can increase in size by recruiting proteins and lipids.…”