Assessment of the cell cycle in the condyle using microarray technology

Abstract

AIM: Mechanical strain produced by mandibular advancement has been linked to condylar growth. A close correlation exists between replicating mesenchymal cells and condylar growth. However, the factors regulating such a process have not yet been identified. The aims of this study were to investigate the expression profile of cell cycle genes in the mandibular condyle during natural growth and upon mechanical strain, to identify those key regulatory genes, and to quantify their expression intensity. MATERIAL AND METHODS: Two hundred and eighty 35-day-old female Sprague-Dawley rats were randomly divided into seven experimental and seven control groups. The experimental groups were fitted with bite-jumping appliances. Each group of rats was sacrificed on the following experimental days: 1, 3, 7, 9, 14, 30 and 33. Total RNA was extracted from condylar cartilage for oligonucleotide microarray analysis. Validation was undertaken by RT-PCR and immunolocalization to determine the protein distribution in the condylar cartilage. RESULTS: Thirty-nine known cell cycle genes were present in the condyle, where Cyclin D1, PCNA and Wnt5a were found to be differentially expressed. RT-PCR confirmed that Cyclin D1 reached a 2-fold increase on day 1 and a 3-fold increase on day 14 of advancement, whereas Cyclin D1 shortened the G1 phase of the cell cycle and accelerated entry into the S phase. PCNA showed a 2.2 fold increase on both experimental days 9 and 30 to facilitate the replication of mesenchymal cells during the S-phase. Wnt5a showed a 2-fold increase on experimental day 1, which helped to recruit replicating mesenchymal cells into the chondrogenic lineage. CONCLUSION: Changes in the biophysical environment of the temporomandibular joint produced by mandibular advancement trigger a cascade of events that leads to a significant increase in cellular proliferation leading to condylar growth through Cyclin D1, PCNA and Wnt5a pathway.