coli LPS is a potent inducer of the production of MMPs in fibroblast-like synovial cells and rat chondrocytes, as well as other innate host response molecules in HGFs and gingival/oral epithelia [41, 42]. Moreover, it was noted that VX-680 cell line both P. gingivalis LPS1435/1449 and E. coli LPS significantly upregulated the expression of MMP-2 mRNA but not its protein as compared to the controls. A number of factors may account for this

finding, such as the stability of mRNA, its processing and Flavopiridol manufacturer splicing patterns, half-life of the target protein and post-translational modifications [43, 44]. Therefore, in the present study increase in MMP-2 mRNA expression level may not be necessarily reflected at its protein level. TIMPs exhibit high affinity for binding with MMPs and lead to inhibition of their activities. In the present study, TIMP-1 mRNA was upregulated by P. gingivalis LPS1435/1449-treated HGFs, while no significant up-regulation was observed in P. gingivalis LPS1690-stimulated cells. The current results may not be comparable with previous studies in which the structural heterogeneity of LPS was not fully considered [45–49]. This omission may account for the conflicting reports in the literature.

Hence, some studies have observed see more lower TIMP-1 levels in the conditioned media of HGFs in response to P. gingivalis LPS [49]. In contrast, other studies have noted the increased expression level of TIMP-1 in gingival crevicular fluid of periodontitis patients [45, 47]. Moreover, periodontal treatment could alter the balance between MMP-3 and TIMP-1 [46, 48]. Based upon the current findings, further study may be warranted to explore the association of different isoforms of P. gingivalis LPS with periodontal conditions in periodontal oxyclozanide patients and the possible effect of periodontal treatment on the expression of these LPS isoforms by P. gingivalis. In addition, the discrepancy observed

in TIMP-1 mRNA and protein expression following the stimulation of both P. gingivalis LPS1435/1449 and E. coli LPS in HGFs could be due to the complex regulation of transcription and translation [43, 44]. LPS is the major immuno-stimulatory component of P. gingivalis which has shown to be capable of interacting with TLRs. Binding of LPS to TLRs activates the downstream signal transduction pathways such as NF-ĸB and MAPK [50, 51]. Previous studies have suggested that the activation of MMPs could be through both NF-ĸB and MAPK signaling [23, 52–54]. The present study demonstrated that p38 MAPK and ERK are critically involved in P. gingivalis LPS1690- and E. coli LPS-induced expression of MMP-3 in HGFs. This finding is supported by a previous study that p38 MAPK and ERK1/2 pathways are essential for the expression and regulation of MMPs in various cell types in response to LPS [54]. ERK, JNK and p38 MAPK pathways play vital roles in regulating the expression of MMPs induced by various stimulants such as cytokines [53, 55, 56].