Effects of enzymatic degradation after loading in temporomandibular joint

Abstract

Synovial fluid of the joint decreases friction between the cartilage surfaces and reduces cartilage wear during articulation. Characteristic changes of synovial fluid have been shown in patients with osteoarthritis (OA) in the temporomandibular joint (TMJ). OA is generally considered to be induced by excessive mechanical stress. However, whether the changes in synovial fluid precede the mechanical overloading or vice versa remains unclear. In the present study, our purpose was to examine if the breakdown of joint lubrication affects the frictional properties of mandibular condylar cartilage and leads to subsequent degenerative changes in TMJ. We measured the frictional coefficient in porcine TMJ by a pendulum device after digestion with hyaluronidase (HAase) or trypsin. Gene expressions of interleukin-1β (IL-1β), cyclooxygenase-2 (COX-2), matrix metalloproteinases (MMPs), type II collagen, and histology were examined after prolonged cyclic loading by an active pendulum system. The results showed that the frictional coefficient increased significantly after HAase (35%) or trypsin (74%) treatment. Gene expression of IL-1β, COX-2, and MMPs-1, -3, and -9 increased significantly in enzyme-treated TMJs after cyclic loading. The increase in the trypsin-treated group was greater than that in the HAase-treated group. Type II collagen expression was reduced in both enzyme-treated groups. Histology revealed surface fibrillation and increased MMP-1 in the trypsin-treated group, as well as increased IL-1β in both enzyme-treated groups after cyclic loading. The findings demonstrated that the compromised lubrication in TMJ is associated with altered frictional properties and surface wear of condylar cartilage, accompanied by release of pro-inflammatory and matrix degradation mediators under mechanical loading.

Keywords: cyclic loading; hyaluronan; lubrication; matrix metalloproteases; osteoarthritis; superficial zone protein.

Figure 1.

Schematic illustration of device used in the experiment. Pendulum-type tester for measuring frictional coefficient (A) and a sample of damping curve recorded by the angle sensor (B). Active cyclic loading device modified from the friction tester is used to apply mechanical load (C).

Figure 2.

Effects of enzyme treatment on frictional coefficient of temporomandibular joint (TMJ). Frictional coefficient of TMJ after 1 h of phosphate-buffered solution (PBS) or hyaluronidase (HAase) (3,000 U/mL) or trypsin (0.5%) treatment. Data are expressed as means ± SD, n = 10, ** P < 0.01.

Figure 3.

Effects of enzyme treatment on gene expression in TMJ cartilage. Gene expression of IL-1β (A), COX-2 (B), MMP-1 (C), MMP-3 (D), MMP-9 (E), and type II collagen (F) in TMJ cartilage after 24 h of PBS, HAase (3,000 U/mL), or trypsin (0.5%) treatment with or without cyclic loading. Data are expressed as means ± SD, n = 3, * P < 0.05, ** P < 0.01.

Figure 4.

Effects of enzymatic degradation on histologic changes in TMJ cartilage. Representative IHC staining of IL-1β (A), MMP-1 (B), and SZP (C) of TMJ cartilage after 24 h of PBS, HAase (3,000 U/mL), or trypsin (0.5%) treatment with or without cyclic loading. Extensive staining areas are indicated by arrowheads.