Gene Expression Profile in LPS-Induced Mouse Pulpitis

Objectives: Pulpal inflammation is mostly caused by bacterial infection, the extent of which may be modified by many mediators. Using traditional methods, the expression of only a limited number of specific mediators associated with pulpal inflammation can be analyzed. In contrast, DNA array methodology makes possible a survey of the expression of a large number of genes. In this study, we used DNA arrays to examine LPS-induced gene expression in the inflamed pulp. Methods: Six-wk-old C57Bl/6 mice (n=6) were used. Experimental pulpitis was induced by applying LPS (2-3 ug) to the exposed pulp of the mouse upper incisors for 6 hrs (n=3); non-pulp-exposed incisors served as controls (n=3). Then, mice were sacrificed and total RNA was extracted from the incisor pulps. DNA arrays (Mouse Cytokine Gene Array System: R&D systems) were hybridized with RI-labeled cDNA probes, according to the manufacturer's protocol. The level of gene expression was determined and normalized to housekeeping genes using GENe Array Scrip^TM software. Results: The expression of many genes was detectable in the normal pulp. In inflamed pulps, the expression of TGFb super family genes, including SMAD family genes and some chemokines, was up-regulated compared to normal pulps. Conclusions: These results suggest that the expression of many mediators was associated with the process of pulpitis, some of which may serve to limit the severity of inflammation. Analysis of the gene expression profile may also be important in elucidating the heterogeneity in pulpal pathosis. This work supported by grants DE-09018 and DE-11664 (P.S.) from the N.I.D.C.R.