Elevation of galectin-9 as an inflammatory response in the periodontal ligament cells exposed to Porphylomonas gingivalis lipopolysaccharide in vitro and in vivo

Considerable evidence suggests that periodontal disease not only is caused by bacterial infection but also is associated with host susceptibility. Using in-house cDNA microarray analysis, we attempted to identify gene expression changes in human periodontal ligament (PDL)-derived cells with and without treatment with lipopolysaccharide (LPS) extracted from Porphylomonas gingivalis (P. gingivalis LPS). Of the five up-regulated genes in the PDLs treated with P. gingivalis LPS, galectin-9, which was reported to have eosinophil chemoattraction, was selected for further analyses. By semiquantitative reverse transcriptase-polymerase chain reaction (sqRT-PCR), real-time quantitative RT-PCR, and Western blot analyses, elevated galectin-9 gene expression was detected in LPS-treated PDL-derived cells. Consequently, it was confirmed that the LPS enhances the expression level of galectin-9 mRNA and protein in a time-dependent manner together with interleukin-8. In addition, strong immunoreaction for galectin-9 was detected in the PDL consisting of the periodontal pocket of a patient with severe periodontal disease. Furthermore, significant up-regulation of galectin-9 mRNA expression was detected in the mRNA from PDLs of patients with periodontal disease when compared with healthy donors (P < 0.05). These results suggest that galectin-9 expression is associated with inflammatory reactions in the PDL.