Ultrasound stimulation of different dental stem cell populations: role of mitogen-activated protein kinase signaling

Introduction:
Mesenchymal stem cells (MSCs) from dental tissues may respond to low-intensity pulsed ultrasound (LIPUS) treatment, potentially providing a therapeutic approach to promoting dental tissue regeneration. This work aimed to study compare LIPUS effects on the proliferation and MAPK signaling in MSCs from rodent dental pulp (DPSCs), compared with MSCs from periodontal ligament (PDLSCs) and bone marrow (BMSCs).
Methods:
Isolated MSCs were treated with 1 MHz LIPUS at an intensity of 250 or 750 mW/cm2 for 5 or 20 min. Cell proliferation was evaluated by BrdU staining after 24h culture following single LIPUS treatment. Specific ELISAs were used to determine total and activated p38, ERK1/2, JNK MAPK signaling proteins up to 4h post-treatment. Selective MAPK inhibitors PD98059 (ERK1/2), SB203580 (p38) and SP600125 (JNK), were used to determine the role of activation of the particular MAPK pathways.
Results:
Proliferation of all MSC types was significantly increased following LIPUS treatment. LIPUS at 750 mW/cm2 dose induced the greatest effects on DPSCs. BMSC proliferation was stimulated in equal measures by both intensities, whilst 250 mW/cm2 LIPUS exposure exerted maximum effects on PDLSCs. ERK1/2 was activated immediately in DPSCs post-treatment. Concomitantly, DPSC proliferation was specifically modulated by ERK1/2 inhibition, whilst p38 and JNK inhibition exerted no effects. In BMSCs, JNK MAPK signaling was LIPUS-activated, and the increase in proliferation was blocked by specific inhibition of the JNK pathway. In PDLSCs, JNK MAPK signaling was activated immediately post-LIPUS, while p-p38 MAPK increased significantly in these cells 4h after exposure. Correspondingly, JNK and p38 inhibition modulated the LIPUS-stimulated PDLSC proliferation.
Conclusions:
LIPUS promoted MSC proliferation in an intensity and cell-specific dependent manner via activation of distinct MAPK pathways.