Low Intensity Pulsed Ultrasound Enhanced Mesenchymal Stem Cell Recruitment through Stromal Derived Factor-1 Signaling in Fracture Healing

Abstract

Low intensity pulsed ultrasound (LIPUS) has been proven effective in promoting fracture healing but the underlying mechanisms are not fully depicted. We examined the effect of LIPUS on the recruitment of mesenchymal stem cells (MSCs) and the pivotal role of stromal cell-derived factor-1/C-X-C chemokine receptor type 4 (SDF-1/CXCR4) pathway in response to LIPUS stimulation, which are essential factors in bone fracture healing. For in vitro study, isolated rat MSCs were divided into control or LIPUS group. LIPUS treatment was given 20 minutes/day at 37°C for 3 days. Control group received sham LIPUS treatment. After treatment, intracellular CXCR4 mRNA, SDF-1 mRNA and secreted SDF-1 protein levels were quantified, and MSCs migration was evaluated with or without blocking SDF-1/CXCR4 pathway by AMD3100. For in vivo study, fractured 8-week-old young rats received intracardiac administration of MSCs were assigned to LIPUS treatment, LIPUS+AMD3100 treatment or vehicle control group. The migration of transplanted MSC to the fracture site was investigated by ex vivo fluorescent imaging. SDF-1 protein levels at fracture site and in serum were examined. Fracture healing parameters, including callus morphology, micro-architecture of the callus and biomechanical properties of the healing bone were investigated. The in vitro results showed that LIPUS upregulated SDF-1 and CXCR4 expressions in MSCs, and elevated SDF-1 protein level in the conditioned medium. MSCs migration was promoted by LIPUS and partially inhibited by AMD3100. In vivo study demonstrated that LIPUS promoted MSCs migration to the fracture site, which was associated with an increase of local and serum SDF-1 level, the changes in callus formation, and the improvement of callus microarchitecture and mechanical properties; whereas the blockade of SDF-1/CXCR4 signaling attenuated the LIPUS effects on the fractured bones. These results suggested SDF-1 mediated MSCs migration might be one of the crucial mechanisms through which LIPUS exerted influence on fracture healing.

Ultrasound-assisted liposuction provides a source for functional adipose-derived stromal cells

“…These findings are strengthened by a study published by Panetta et al comparing SAL and VASER derived lipoaspirates also showing tendencies of higher expression of Runx-2 and OCN in VASER samples [21]. This osteogenic tendency of VASER ASCs is consistent with published reports on the benefits of ultrasound treatment for bone regeneration and MSC function in fracture healing [22, 23]. Additionally, some effect can be observed in the expression of adipogenic markers and the 36kHZ deployed by the VASER device again seem to be more stimulating than the lower frequency of Lysonix.…”

Low-intensity pulsed ultrasound (LIPUS) prevents periprosthetic inflammatory loosening through FBXL2-TRAF6 ubiquitination pathway

“…The average intensity was 200 mW/cm 2 , the pulsed frequency was 1.5 MHz, the repetition rate was 250 Hz, and the pulse lasted 0.2 ms16. The LIPUS generating system with six individual ultrasound transducers was previously described3738. The culture plate was placed above these transducers with a thin layer of coupling gel3940.…”

Low-intensity pulsed ultrasound promotes cell motility through vinculin-controlled Rac1 GTPase activity

“…Enhanced cell migration is a widely reported response to LIPUS stimulation, occurring in several cell types including mesenchymal stem cells (Wei et al, 2014), chondrogenic progenitor cells (Jang et al, 2014), primary human endothelial cells (Katano et al, 2011), human chondrocytes (Uddin et al, 2016) and MC3T3 mouse osteoblasts (Fig. S1C) (Sawai et al, 2012).…”