Biomechanical Forces Inhibit NF-kappaB Transcriptional Activity in TMJ: Mathematical Analysis

Objectives: Temporal mandibular joint (TMJ) disorders are complex painful disorders, where jaw mobilization provides comfort to many patients. However, the mechanisms underlying the effectiveness of jaw mobilization remain obscure. TMJ disc undergoes compressive and tensile forces during joint movement. We show that dynamic tensile forces of low/ physiological magnitudes (LowDTS) are potent inhibitors of inflammation, whereas at high magnitudes (HiDTS) these signals become proinflammatory. Mathematical models show that intracellular actions of mechanical signals are predictable.

Methods: Fibrochondrocytes (200,000 cells/scaffold) were grown in DMEM with 10% FBS, 1% pen/strep and 2mM Glutamine on Bioflex II plates. Cells were subjected to CTS at a magnitude of 6% or 20% at 0.025 Hz for various times. The inducible NO synthase (NOS2A), matrix metalloproteinase (MMP-13), NF-kappaB p65, I-kBa and I-kBb mRNA expression were analyzed by real time PCR, and activation of NF-kappaB signaling cascade by Western blots and immunofluorescence. Statistical analysis was done by ANOVA and Student's T-test.

Results: The experiments demonstrated that: 1) LowDTF rapidly inhibited IL-1-induced nuclear translocation of NF-kappaB, that was paralleled by suppression of NF-kappaB dependent genes NOS2A, IL-R1, IL-R2, TRAF-1 and TRAF-2; 2) LowDTF inhibited IL-1beta induced I-kBa and I-kBb degradation and upregulated its mRNA expression; 3) LowDTF inhibited IL-1beta-induced TAK-1 activation a key point to inhibit IKK-beta activation; 4) HiDTF induced nuclear translocation of NF-kappaB and NOS2A induction; 5) Mathematical models to generate predictions using IKK activation in response to lowDCF and HiDCF, showed that the dynamics of the system that could be simulated with predictability.

Conclusions: The results demonstrate that LowDTF inhibits TAK-1 activation, the key initial event responsible for NF-kappaB transactivation. Thus, biomechanical forces generate complex magnitude-dependent signals within the inflamed microenvironment of the TMJ, that allow the significant and beneficial effects that can be realized by appropriate TMJ mobilization. Acknowledgement NIAMS AR04878, NIDCR DE15399.