Comparative gene expression analysis of the human dental pulp in deciduous and permanent teeth

Abstract

Human deciduous and permanent teeth exhibit different developmental processes, morphologies, histological characteristics and life cycles. In addition, their pulp tissues react differently to external stimuli, such as the pulp sensitivity test, dental trauma and pulp therapy materials. These differences are attributable to their genetic backgrounds. Gene expression profiles of the human dental pulp from deciduous and permanent teeth were compared using cDNA microarray analysis, quantitative real-time polymerase chain reaction (RT-PCR) and immunohistochemical staining. Microarray analysis identified 263 genes with a twofold or greater difference in expression level between the 2 types of tooth, 43 and 220 of which were more abundant in deciduous and permanent dental pulp tissues, respectively. Genes related to enamel mineralization and secondary and/or reparative dentin formation such as those encoding calbindin 1 (CALB1), secreted protein acidic and rich in cysteine/osteonectin (SPOCK3), and integrin-binding sialoprotein (IBSP) and to neurotransmission such as those that encode glutamate receptor ionotropic kainite 1 (GRIK1), gamma-aminobutyric acid A receptor beta 1 (GABRB1), ST8 alpha-N-acetyl-neuraminide alpha-2,8-sialytransferase 1 (ST8SIA1), and potassium channel subfamily K member 10 (KCNK10) were more strongly expressed in permanent dental pulp tissue than in deciduous dental pulp tissue. Most of the genes that were abundantly expressed in the deciduous dental pulp tissue have barely been discussed with respect to tooth and dental pulp tissue. Of particular note, most of these genes are involved in the development of other organs or cancer, such as those that encode insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1), and teashirt zinc finger homeobox 2 (TSHZ2), or are associated with the immune system, such as those that encode major histocompatibility complex class II DQ alpha 1 (HLA-DQA1), and deoxyribonuclease 1-like 3 (DNASE1L3). This may be attributable to the self-destruction characteristic of deciduous teeth. Quantitative RT-PCR analysis was conducted for eight randomly selected genes, and the findings were consistent with the results of the cDNA microarray assay. The immunohistochemical staining revealed that IGF2BP1 was broadly expressed in deciduous dental pulp tissue, but barely expressed in permanent dental pulp tissue. CALB1, LGR5 (which encodes leucine-rich repeat-containing G-protein-coupled receptor 5), and GABRB1 were abundantly expressed in the permanent predentin/odontoblast area, but only barely expressed in deciduous dental pulp tissue. These results were also consistent with the microarray data.