Shockwave Triggers Cultured Mesenhcymal Stem Cell Proliferation via Activating mTOR-FAK Signaling Axis

Shockwave Triggers Cultured Mesenhcymal Stem Cell Proliferation via Activating mTOR-FAK Signaling Axis
Fan-Yen Lee (1), Yen-Yi Zhen (2), Hon-Kan Yip (2)

Institution:
(1) Dept. of Surgery, (2) Dept. of Internal Medicine, Kaohsiung Chang Gung Memorial Hospital, Taiwan

Device and producing company:
Evotron, Switzerland

Introduction:
Previous studies demonstrated extracorporeal shockwave therapy (ESWT) has a significant positive effect on accelerating diabetic (DM) wound healing. However, the systemic effect after ESWT is still unclear.

Methods:
To elucidate the role of cytoskeletons in SW-induced FAK phosphorylation, we administered cytochalasin D to depolymerize actin filament before applying the optimal energy of 0.12 mJ/mm2 to MSCs.

Results:
The results showed a failure in stimulating FAK phosphorylation, highlighting the essential role of microfilament in SW-induced FAK phosphorylation. To further identify the upstream regulator, three kinases, namely GSK-3β, Akt, and mTORC1, which are activated in pressure-stimulated mechanotransduction, are assayed for SW- stimulated FAK phosphorylation. Of the three specific inhibitors, only rapamycin, an inhibitor of mTORC1, was found to inhibit FAK phosphorylation, suggesting that mTORC1 is the upstream regulator in SW-elicited FAK phosphorylation. Microscopic examination revealed not only SW-induced increase in the number of actin stress fibers, but also alternative subcellular localization of mTORC1 as vesicle-like inclusions on microfilaments. Besides, rapamycin was found to destruct the vesicle-like pattern of mTORC1, while dissociation between actin and mTORC1 was noted after cytochalasin D administration.

Discussion:
Since mTORC1 is essential for cell proliferation, we performed proliferation assay for MSCs with and without SW/rapamycin treatment. The results demonstrated significant enhancement of cell proliferation after SW treatment.

Conclusion:
Our findings suggest that mTORC1 and microfilament synergistically regulate FAK phosphorylation and mTORC1-FAK signalling participates in MSC proliferation.