Increased transglutaminase activity was associated with IL-6 release in cultured human gingival fibroblasts exposed to dental cast alloys

Transglutaminase 2 up-regulation is associated with RANKL/OPG pathway in cultured HPDL cells and THP-1-differentiated macrophages

Recent evidence emphasized that transglutaminase 2 (TG2), a protein cross-linking enzyme, may play a role in the early phase of inflammation. High levels of TG2 have been associated with the constitutive activation of nuclear factor-kappa B (NF-κB) that is considered the main regulator of inflammation. In this context, the receptor activator of NF-kappa B ligand (RANKL) and receptor activator of NF-κB have extensive functions in the regulation of cytokine secretion associated with different pathological conditions. The human periodontal ligament (HPDL) cells, which express and secrete osteoprotegerin (OPG) and RANKL, represent an useful "ex vivo" model for monitoring cell response in inflammatory microenvironments, such as periodontitis-dependent tissue response. Thus, we evaluated TG2 expression and alterations in RANKL/OPG ratio occurring in cultured HPDL cells. The HPDL cells were obtained from patients with chronic periodontitis (CP) and healthy subjects. We observed the up-regulation of some inflammatory markers, such as IL-6, TNF-α, and HMGB-1, and at the same time an increase in TG2 mRNA levels in HPDL cells from CP patients compared with healthy subjects. We found a positive correlation between RANKL/OPG ratio and TG2 mRNA levels in HPDL cells from CP patients. In the parallel experiments, we demonstrated that TG2 inhibition reduced RANKL expression in both HPDL cells from CP patients and monocytes differentiated to macrophages by tetradecanoyl phorbol acetate treatment. Given the RANKL key role in NF-κB pathway and the observed up-regulation of pro-inflammatory cytokines, our data suggest that TG2 may be involved in molecular mechanisms of inflammatory response occurring in periodontal disease.

Transglutaminase regulation of cell function

Transglutaminases (TGs) are multifunctional proteins having enzymatic and scaffolding functions that participate in regulation of cell fate in a wide range of cellular systems and are implicated to have roles in development of disease. This review highlights the mechanism of action of these proteins with respect to their structure, impact on cell differentiation and survival, role in cancer development and progression, and function in signal transduction. We also discuss the mechanisms whereby TG level is controlled and how TGs control downstream targets. The studies described herein begin to clarify the physiological roles of TGs in both normal biology and disease states.