The effect of the pro-inflammatory cytokine tumor necrosis factor-alpha on human joint capsule myofibroblasts

Introduction: Previous studies have shown that the number of
myoblastically differentiated fibroblasts known as myofibroblasts
(MFs) is significantly increased in stiff joint capsules,
indicating their crucial role in the pathogenesis of post-traumatic
joint stiffness. Although the mode of MFs' function has been well
defined for different diseases associated with tissue fibrosis, the
underlying mechanisms of their regulation in the pathogenesis of
post-traumatic joint capsule contracture are largely unknown.
Methods: In this study, we examined the impact of the
pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha)
on cellular functions of human joint capsule MFs. MFs were
challenged with different concentrations of TNF-alpha with or
without both its specifically inactivating antibody infliximab
(IFX) and cyclooxygenase-2 (COX2) inhibitor diclofenac. Cell
proliferation, gene expression of both alpha-smooth muscle actin
(alpha-SMA) and collagen type I, the synthesis of prostaglandin
derivates E(2), F(1A), and F(2A), as well as the ability to
contract the extracellular matrix were assayed in monolayers and in
a three-dimensional collagen gel contraction model. The a-SMA and
COX2 protein expressions were evaluated by immunofluorescence
staining and Western blot analysis. Results: The results indicate
that TNF-alpha promotes cell viability and proliferation of MFs,
but significantly inhibits the contraction of the extracellular
matrix in a dose-dependent manner. This effect was associated with
downregulation of a-SMA and collagen type I by TNF-alpha
application. Furthermore, we found a significant time-dependent
upregulation of prostaglandin E(2) synthesis upon TNF-alpha
treatment. The effect of TNF-alpha on COX2-positive MFs could be
specifically prevented by IFX and partially reduced by the COX2
inhibitor diclofenac. Conclusions: Our results provide evidence
that TNF-alpha specifically modulates the function of MFs through
regulation of prostaglandin E(2) synthesis and therefore may play a
crucial role in the pathogenesis of joint capsule contractures.