Background:
Psoriatic arthritis (PsA) results from joint destruction by osteoclasts. Promising efficacy of TNF-α blockage indicates its important role in osteoclastogenesis of PsA. WNT ligands actively regulate osteoclastogenesis. We investigated how WNT ligands activate osteoclasts amid the TNF-α milieu in PsA.
Methods:
We first profiled the expression of WNT ligands in CD14+ monocyte-derived osteoclasts (MDOC) from 3 PsA patients and 3 healthy controls (HC) and then validated the candidate WNT ligands in 32 PsA patients and 16 HC. Through RNA interference against WNT ligands in MDOC, we determined the mechanisms by which TNF-α exerts its effects on osteclastogenesis or chemotaxis.
Results:
The results showed numbers of CD68+WNT5A+ osteoclasts are increased in PsA joints. WNT5A was selectively upregulated by TNF-α in MDOC from PsA patients. However, direct osteoclastogenesis effect (RANK expression) by TNF-αwas not inhibited by WNT5A siRNA. Instead, CXCL1, CXCL16, and MCP-1 was selectively increased in supernatants of MDOC from PsA patients. RNA interference against WNT5A abolished the increased MCP-1 from MDOC and THP-1-cell-derived osteoclasts. The increased migration of osteoclast precursors (OCP) induced by supernatant from PsA MDOC was abolished by MCP-1 neutralizing antibody. WNT5A and MCP-1 expressions were decreased in MDOC from PsA patients treated by biologics against TNF-a but not IL-17.
Conclusion:
We conclude TNF-α recruits OCP by WNT5A-mediated MCP-1 production but not directly activates osteoclastogenesis in PsA.