Gene expression analysis of toll like receptor 2 and 4, Dectin-1, Osteopontin and inflammatory cytokines in human dental pulp ex-vivo

BACKGROUND

Toll like receptors (TLR) 2 and 4 present on innate immune cells of the dental pulp detect cariogenic bacteria. Along with bacteria, C. albicans may also be present in dental caries. The presence of C. albicans can be detected by Dectin-1 a C type Lectin receptor. Expression of Dectin-1 in human pulpits has not been reported. Similarly, cytokines are released as a consequence of dental pulp inflammation caused by cariogenic bacteria. The T helper (Th) 1 inflammatory response leads to exacerbation of inflammation and its relationship with Osteopontin (OPN) is not known in pulp inflammation.

OBJECTIVE

The aim of this study was to observe the expression of Dectin-1, TLR-2, OPN and pro-inflammatory cytokines in irreversibly inflamed human dental pulp and to observe relationship between Dectin-1/TLR-2 and OPN/Pro-inflammatory cytokines in the presence of appropriate controls.

METHODS

A total of 28 subjects diagnosed with irreversible pulpitis were included in this ex-vivo study. Fifteen samples were subjected to standard hematoxylin and Eosin (H&E) and immunohistochemistry staining. Whereas, gene expression analysis was performed on 13 samples to observe mRNA expression of pro-inflammatory cytokines; tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1 beta (ß), IL-6 Dectin-1, OPN, TLR-2 and TLR-4. SPSS version 21 was used for statistical analysis. One way analysis of variance (ANOVA), Pearson correlation and Chi-square test were used at p ≤ 0.05.

RESULTS

Gene expressions of Dectin-1, TLR-2 and TLR-4 were observed in all samples. Dectin-1 and TLR-2 expressions were significantly correlated (r = 0.5587, p = 0.0002). Similarly, OPN and TNF-α expression showed a significant correlation (r = 0.5860, p = 0001). The agreement between histologic and clinical diagnosis was 69.2% in the cases of irreversible pulpitis.

CONCLUSION

Dectin-1 was expressed by inflamed human dental pulp. Dectin-1 and TLR-2 expression pattern was suggestive of a collaborative receptor response in inflamed pulp environment. OPN and TNF-α expressions showed a positive correlation indicating a possible relationship.

The dectin 1 agonist curdlan regulates osteoclastogenesis by inhibiting nuclear factor of activated T cells cytoplasmic 1 (NFATc1) through Syk kinase

Several immune system cell surface receptors are reported to be associated with osteoclastogenesis. Dectin 1, a lectin receptor for β-glucan, is found predominantly on cells of the myeloid lineage. In this study, we examined the effect of the dectin 1 agonist curdlan on osteoclastogenesis. In mouse bone marrow cells and dectin 1-overexpressing RAW 264.7 cells (d-RAWs), curdlan suppressed receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation, bone resorption, and actin ring formation in a dose-dependent manner. This was achieved within non-growth inhibitory concentrations at the early stage. Conversely, curdlan had no effect on macrophage colony-stimulating factor-induced differentiation. Furthermore, curdlan inhibited RANKL-induced nuclear factor of activated T cell cytoplasmic 1 (NFATc1) expression, thereby decreasing osteoclastogenesis-related marker gene expression, including tartrate-resistant acid phosphatase, osteoclast stimulatory transmembrane protein, cathepsin K, and matrix metallopeptidase 9. Curdlan inhibited RANKL-induced c-fos expression, followed by suppression of NFATc1 autoamplification, without significantly affecting the NF-κB signaling pathway. We also observed that curdlan treatment decreased Syk protein in d-RAWs. Inhibition of the dectin 1-Syk kinase pathway by Syk-specific siRNA or chemical inhibitors suppressed osteoclast formation and NFATc1 expression stimulated by RANKL. In conclusion, our results demonstrate that curdlan potentially inhibits osteoclast differentiation, especially NFATc1 expression, and that Syk kinase plays a crucial role in the transcriptional pathways. This suggests that the activation of dectin 1-Syk kinase interaction critically regulates the genes required for osteoclastogenesis.