Background/Purpose:

Bone erosion is a characteristic feature of inflammatory arthritides, such as rheumatoid arthritis (RA). Death Receptor 3 (DR3) and its only known ligand TNF-like protein 1A (TL1A) have been identified as key regulators of osteoclastogenesis in murine models of arthritis (Bull MJ, Williams AS et.al. J.Exp.Med. 2008). We investigated the potential mechanisms by which the DR3/TL1A pathway orchestrates osteoclast (OC) formation in humans and assessed the impact of DR3 signalling upon bone pathology in RA.

Methods:

CD14⁺ monocytes were obtained from healthy females (n=8). Cells were cultured on ivory discs (with macrophage-colony-stimulating factor (M) and receptor activator of nuclear factor-κB ligand (R)) for 7, 10 and 14 days ± TL1A (10 and 100ng/ml). Osteoclastogenesis and area of disc resorbed were quantified. Levels of TNFα and MMP-9 were measured by ELISA. Serum samples were obtained from consenting normal human volunteers (n=12) and RA patients (n=36) attending outpatient clinic who fulfilled the ACR classification criteria.TL1A and TNFα were measured by ELISA. Ethical approval for this study was granted by the Bro-Taf Health Authority. All data is expressed as mean±SEM value.

Results:

A significant dose-dependent increase in osteoclastogenesis was observed after addition of exogenous TL1A (P<0.01; 2-way ANOVA) in our in vitro human system. Cell counts per mm², at end-point, were comparable for each condition tested (M+R=480±49; M+R+TL1A-10=517±62 and M+R+TL1A-100=475±59). However, TL1A (100ng/ml) doubled the number of OC observed on each ivory disk (12±3; OC per mm²) when compared against controls (6.8±2; P<0.05). These OC were functionally active, evidenced by their capacity to resorb a bone substrate. TL1A (100ng/ml) induced a potent 5-fold increase in bone resorption (5.19±3%) over control cultures (1.33±0.43%, P<0.01); the effect was dose-dependent. This was accompanied by a significant (P<0.01; 2-way ANOVA) dose and time dependent elevation in bone-matrix degrading MMP-9 secretion. MMP-9(μg/ml) increased from 4.8±1.1 to 7.5±1 for controls versus TL1A (100ng/ml) activated cultures on day 14. These data reveal a new mechanism for DR3’s resorptive function in bone. This action was independent of TNFα ; the cytokine was not detected in any of culture conditions studied. In serum collected from RA patients, TL1A levels were significantly elevated (P<0.05) over normal healthy individuals (3.0±0.6 versus 0.2±0.2 ng/ml). Serum levels of TL1A were also significantly higher in RA (rheumatoid factor positive) patients with erosive disease over those who had no detectable radiographic changes at time of sampling (3.9±0.8 and 0.5±0.2 ng/ml). TNFα was not detected in any of the samples assayed.

Conclusion:

Our findings reveal TL1A to be a key regulator in osteoclastogenesis and imply that the TL1A/DR3 pathway contributes to osteoclast-driven bone pathology associated with RA.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/tnf-like-protein-1adeath-receptor-3-pathway-regulates-osteoclastogenesis-and-is-associated-with-erosive-disease-in-rheumatoid-arthritis/