To explore the effects of ultrasound-exposed microbubbles (UM) on the expression of CXC chemokine receptor 4 (CXCR4) in bone marrow mesenchymal stem cells (BMSCs) and the mechanisms involved.

Mesenchymal stem cells were isolated from bone marrow taken from male Sprague-Dawley rats. They were divided into a control group, an ultrasound (US) group, an ultrasound-exposed microbubbles (UM) group, a UM plus catalase (UMC) group, a UM plus AMD3100 (UMA) group, and a UM plus anti-CXCR4 antibody (UMCX) group. The control group was not given any treatment. The US group was treated with 1 MHz ultrasound at 1 Watt per square centimetre for 30 seconds. The UM group was treated with ultrasound plus microbubbles. The UMC group was treated with catalase, microbubbles and ultrasound. The UMA group was treated with AMD3100, microbubbles and ultrasound. The UMCX group was treated with anti-CXCR4 antibody, microbubbles and ultrasound. Quantitative polymerase chain reaction (qPCR) and Western blotting were performed to determine the levels of CXCR4 mRNA transcription and the expression of BMSCs in the control, US, UM and UMC groups. Immediately, 5 minutes and 15 minutes after the intervention, fluorescence intensities were observed in the cells labeled with Fluo-4/AM of the control group, US group and UM group under a fluorescence microscope. Migration assays were conducted to determine the chemotactic ability of the BMSCs with respect to stromal-derived factor-1α (SDF-1α) in all six groups.

No significant differences were found in the levels of CXCR4 mRNA transcription and protein expression between the US and control groups(P>0.05), but the levels in those groups and the UMC group were lower than those observed in the UM group. Fluorescence intensity in the cells of the US group was not significantly different from that in the control group (P>0.05), but those levels were both significantly lower than that in the UM group (P<0.05). There was no significant difference in the number of cells migrating to the SDF-1α between the US (22.4±2.2) and control group (20.5±2.3). However, the number of cells migrating to SDF-1α in the UM group (53.1±3.8) was significantly larger than that in the US group, the control group, the UMC group (35.2±3.1), the UMA group (32.5±2.8) and the UMCX group (30.7±2.9) (P<0.05).

UM can increase mRNA transcription and the expression of CXCR4 protein in BMSCs, and promote BMSCs migration to SDF-1α. This may in part be mediated by an increase in calcium influx.

Ultrasound-exposed microbubbles; Bone marrow mesenchymal stem cells; CXCR4; Calcium ion