Intramuscular injection of bone marrow mononuclear cells contributes to bone repair following midpalatal expansion in rats

Healing from injury requires the activation and proliferation of stem cells for tissue repair. Previous studies have demonstrated that bone marrow is a central pool of stem cells. The present study aimed to investigate the route undertaken by bone marrow mononuclear cells (BMMCs) following BMMC transplantation by masseter injection in a rat model of midpalatal expansion. The rats were divided into five groups according to the types of midpalatal expansion, incision and BMMC transplantation. Samples of midpalatal bone from the rats in each group were used for histological and immunohistochemical assessments to track and evaluate the differential potentials of the transplanted BMMCs in the masseter muscle and midpalatal bone. Bromodeoxyuridine was used as a BMMC tracing label, and M-cadherin was used to detect muscle satellite cells. The BMMCs injected into the masseter were observed, not only in the masseter, but also in the blood vessels and oral mucosa, and enveloped the midpalatal bone. A number of the BMMCs transformed into osteoblasts at the boundary of the neuromuscular bundle, and were embedded in the newly formed bone during midpalatal bone regeneration. The results of the present study suggested that BMMCs entered the circulation and migrated from muscle to the bone tissue, where they were involved in bone repair. Therefore, BMMCs may prove useful in the treatment of various types of cancer.