Gene Expression in Early Stages of Low-Intensity Pulsed Ultrasound Exposure on Bone Marrow Cells

: The aim of this study was to identify genes that are prominently expressed in rat bone marrow cell-derived osteoblasts during the initial phase of low-intensity pulsed ultrasound (LIPUS) exposure. Bone marrow cells were obtained from three Sprague-Dawley rats (8-week-old, male), and cell cultures were prepared by suspension in osteogenic medium. After cultures were established, test cultures were exposed to LIPUS from the bottom of the cell culture plate for 15 min/d on days 1–4 (LIPUS group). LIPUS signals were transmitted at a frequency of 3 MHz and a spatial average intensity of 40 mW/cm 2 . The control group was not exposed to LIPUS. On day 14, alizarin red S staining was performed to detect calcifi -cation. On day 4, total RNA was extracted from both cultures, hybridized to microarray slides, and the resulting data set was analyzed. Genes exhibiting a fold-change ≥2 and a p-value <0.05 (LIPUS vs. control) were identified as differentially expressed genes. Pathway analysis was performed on genes whose expression increased in the LIPUS group. The cellular areas stained with alizarin red S were significantly larger in the LIPUS group than in the control group on day 14. LIPUS exposure increased the expression of genes related to type II interferon signaling, and endochondral ossification was ob served after 4 d of culture. The results demonstrated that LIPUS exposure activated the immune response and promoted osteoblast differentiation.