Comparative gene-expression analysis of periodontal ligament and dental pulp in the human permanent teeth

Abstract

The periodontal ligament (PDL) and dental pulp tissues of human permanent teeth have a number of differences in their developmental processes, histological characteristics and functions. It can be figured out that these differences are attributable to genetic backgrounds of their cells organized tissues. Meanwhile, most studies were conducted by gene expression analysis using cultured cells of PDL and dental pulp (in vitro), but there have been few studies about their gene expression analysis in tissue level (in vivo). The purpose of this study was to identify the gene-expression profiles and their molecular biological differences of periodontal ligament and dental pulp tissues from the human permanent teeth. To achieve this, cDNA microarray analysis, quantitative real-time polymerase chain reaction and immunohistochemical stain were used. The cDNA Microarray analysis identified 347 genes with a quadruple or greater difference in expression level between PDL and dental pulp tissues of the permanent teeth, 83 and 264 of which were more plentiful in PDL and dental pulp tissues, respectively. Genes associated with collagen degradation such as those that encode matrix metallopeptidase 3 (MMP3), matrix metallopeptidase 9 (MMP9), and matrix metallopeptidase 13 (MMP13) and with collagen synthesis such as those that encode fibroblast activation protein, alpha (FAP) and with bone development and remodeling such as those that encode secreted phosphoprotein 1 (SPP1), bone morphogenetic protein 3 (BMP3), acid phosphatase 5, tartrate resistant (ACP5), cathepsin K (CTSK), and parathyroid hormone-like hormone (PTHLH) were more strongly expressed in PDL tissues of permanent teeth. In dental pulp tissues of permanent teeth, genes associated with calcium ion such as those that encode calbindin 1 (CALB1), cadherin12, type 2 (CDH12), and scinderin (SCIN) and with mineralization and formation of enamel or dentin such as those that encode secreted protein acidic and rich in cystein/osteonectin 3 (SPOCK3), phosphate regulating endopeptidase homolog, X-linked (PHEX), ameloblastin (AMBN), and dentin sialophosphoprotein (DSPP) were more strongly expressed. The quantitative real-time polymerase chain reaction analysis which was conducted for 6 randomly selected genes was consistent with the results of the cDNA microarray assay. The immunohistochemical staining analysis showed that collagen, type XII, alpha 1 (COL12A1), MMP9, and SPP1 was extensively expressed in permanent PDL tissues, but barely expressed in permanent dental pulp tissues. CALB1 was extensively expressed in the permanent dental pulp tissues, but barely expressed in permanent PDL tissues. These results were also coincided with the cDNA microarray assay data.