Autocrine stimulation of osteoblast activity by Wnt5a in response to TNF-α in human mesenchymal stem cells

Abstract

a b s t r a c tAlthough anti-tumor necrosis factor (TNF)-a treatments efficiently block inflammation in ankylosing spondylitis (AS), they are inefficient to prevent excessive bone formation. In AS, ossification seems more prone to develop in sites where inflammation has resolved following anti-TNF therapy, suggesting that TNF-a indirectly stimulates ossification. In this context, our objectives were to determine and compare the involvement of Wnt proteins, which are potent growth factors of bone formation, in the effects of TNF-a on osteoblast function. In human mesenchymal stem cells (MSCs), TNF-a significantly increased the levels of Wnt10b and Wnt5a. Associated with this effect, TNF-a stimulated tissue-non specific alkaline phosphatase (TNAP) and mineralization. This effect was mimicked by activation of the canonical bcatenin pathway with either anti-Dkk1 antibodies, lithium chloride (LiCl) or SB216763. TNF-a reduced, and activation of b-catenin had little effect on expression of osteocalcin, a late marker of osteoblast differentiation. Surprisingly, TNF-a failed to stabilize b-catenin and Dkk1 did not inhibit TNF-a effects. In fact, Dkk1 expression was also enhanced in response to TNF-a, perhaps explaining why canonical signaling by Wnt10b was not activated by TNF-a. However, we found that Wnt5a also stimulated TNAP in MSCs cultured in osteogenic conditions, and increased the levels of inflammatory markers such as COX-2. Interestingly, treatment with anti-Wnt5a antibodies reduced endogenous TNAP expression and activity. Collectively, these data suggest that increased levels of Dkk1 may blunt the autocrine effects of Wnt10b, but not that of Wnt5a, acting through non-canonical signaling. Thus, Wnt5a may be potentially involved in the effects of inflammation on bone formation.

Wnt5a Promotes Inflammatory Responses via Nuclear Factor κB (NF-κB) and Mitogen-activated Protein Kinase (MAPK) Pathways in Human Dental Pulp Cells

“…TNF-␣ has been reported previously to enhance the expression of both Wnt5a and its receptor in BMSCs. BMSCderived Wnt5a is considered to act during a critical step in the regulation of inflammatory processes (23,37). In inflamed dental pulp tissue, high levels of TNF-␣ and IL-1␤ have been detected (27).…”

“…Several studies report that Wnt5a plays a critical role in inflammatory processes associated with skeletal tissue (19,23,37). Osteoblast cells express Wnt5a, whereas osteoclast precursors express Ror2.…”

Wnt5a is expressed in spondyloarthritis and exerts opposite effects on enthesis and bone in murine organ and cell cultures

“…29 In relation to ossification, we previously observed an autocrine stimulation of osteoblast activity by Wnt5a in response to TNF-a in human MSCs. 30 Similarly, IL-1b and IL-6 induce osteogenic differentiation of these cells via the Wnt5a-Ror2 pathway. 31,32 Collectively, these data suggested that Wnt5a may be involved in inflammation-dependent bone formation in SpA.…”

Role of stem cells in spondyloarthritis: Pathogenesis, treatment and complications

“…In addition, a more recent study further supported the role of TNF-α in osteoblastic function and excessive bone formation by demonstrating autocrine stimulation of osteoblast activity by Wnt5a in response to TNF-α in human MSCs. TNF-α was shown to significantly increase the levels of Wnt10b and Wnt5a, accompanied by stimulation of TNAP and mineralisation, an effect which could be mimicked by activating the canonical β-catenin pathway [48], suggesting the effects of inflammation on bone formation may potentially be mediated by Wnt5a . This may help explain partly why anti-TNF-α therapy is inefficient in preventing excessive bone formation in AS as the process involves indirect stimulation of ossification via the MSCs.…”