Background: In order to elucidate the expression pattern of L-type amino acid transporter 1 (LAT1) in the bone formation process, the expressions of LAT1 and its subunit 4F2 heavy chain (4F2hc) were investigated in the healing process after the implantation of a tooth ash-plaster of Paris mixture in rats with calvarial osseous defect.
Materials and methods: Circular calvarial defects (8 mm in diameter) were made midparietally. The rats were divided into 2 groups, 1 control group and 1 experimental group. In the control group, the defect was only covered with a soft tissue flap (control group); in the experimental group, it was filled with a mixture of tooth ash and plaster of Paris (2:1 by weight; mixture group). The rats were sacrificed at 1, 2, 4 and 8 weeks after operation and RT-PCR and immunohistochemical analyses were performed.
Results: In the RT-PCR analysis, the expressions of the LAT1 and 4F2hc mRNAs were slightly stronger in the experimental group than in the control group. In the immunohistochemical analysis, at 1 week after operation, the LAT1 protein and its subunit 4F2hc protein were mainly expressed in the osteoblasts, osteocytes and interstitial tissues of the area around the defect and the inner part of newly forming bone in both groups. The expressions of LAT1 and 4F2hc proteins were decreased at 2 and 4 weeks after operation. The LAT1 and 4F2hc proteins were scarcely expressed at 8 weeks after operation in both groups. The expressions of LAT1 and 4F2hc proteins were slightly stronger in the mixture group than in the control group.
Conclusion: These results suggest that the LAT1 and its subunit 4F2hc are highly expressed in the early stage of new bone formation and may have an important role in providing cells with neutral amino acids, including several essential amino acids, at that stage.