Differentially expressed genes and signalling pathways are involved in mouse osteoblast-like MC3T3-E1 cells exposed to 17-ß estradiol.

Oestrogen is essential for maintaining bone mass, and it has been demonstrated to induce osteoblast proliferation and bone formation. In this study, complementary DNA (cDNA) microarrays were used to identify and study the expression of novel genes that may be involved in MC3T3-E1 cells' response to 17-ß estradiol. MC3T3-E1 cells were inoculated in minimum essential media alpha (α-MEM) cell culture supplemented with 17-ß estradiol at different concentrations and for different time periods. MC3T3-E1 cells treated with 10⁻8 mol⋅L⁻¹ 17-ß estradiol for 5 days exhibited the highest proliferation and alkaline phosphatase (ALP) activity; thus, this group was chosen for microarray analysis. The harvested RNA was used for microarray hybridisation and subsequent real-time reverse transcription polymerase chain reaction (RT-PCR) to validate the expression levels for selected genes. The microarray results were analysed using both functional and pathway analysis. In this study, microarray analysis detected 5403 differentially expressed genes, of which 1996 genes were upregulated and 3407 genes were downregulated, 1553 different functional classifications were identified by gene ontology (GO) analysis and 53 different pathways were involved based on pathway analysis. Among the differentially expressed genes, a portion not previously reported to be associated with the osteoblast response to oestrogen was identified. These findings clearly demonstrate that the expression of genes related to osteoblast proliferation, cell differentiation, collagens and transforming growth factor beta (TGF-ß)-related cytokines increases, while the expression of genes related to apoptosis and osteoclast differentiation decreases, following the exposure of MC3T3-E1 cells to α-MEM supplemented with 17-ß estradiol. Microarray analysis with functional gene classification is critical for a complete understanding of complementary intracellular processes. This microarray analysis provides large-scale gene expression data that require further confirmatory studies.

The early phase response of rat alveolar bone to traumatic occlusion.

OBJECTIVES: Occlusal trauma is an important factor to influence alveolar bone remodelling, the effect of which includes many cytokines and signalling pathways. However, the exact mechanism of the traumatic stimulus for alveolar remodelling is still unclear. The purpose of the present study was to investigate the early responses of alveolar osteocytes to occlusal trauma through genome-wide microarray. METHODS: The occlusal surface of the upper left first molar of rat was raised by placing a stainless steel wire to induce occlusal trauma in the lower left first molar. After 24 h, we took out the alveolar bone tissue of the first molars at the both sides of rats' lower jaws under anaesthesia. The different gene expressions were showed by genome-wide microarray, which comprises about 27,000 genes and the results were examined by quantitative RT-PCR. RESULT: Of the approximately 27,000 genes, the expression of 586 genes was strongly changed. These findings clearly demonstrated that in the early response of the alveolar bone to occlusal trauma, the expression of osteoblast, collagens, bone mineralization, bone remodelling and WNT, TGF-ß pathway related cytokines decreased, and osteoclast-specific cytokines have no significant changes in expression. CONCLUSION: These results suggested that at early phase of the occlusal trauma, osteogenesis in rat's alveolar bone was inhibited, and osteoclastogenesis was not significant.