Bone morphogenetic protein-7 antagonizes tumor necrosis factor-α-induced activation of nuclear factor κB and up-regulation of the ADAMTS, leading to decreased degradation of disc matrix macromolecules aggrecan and collagen II

Abstract

Background context: Tumor necrosis factor-α (TNF-α) is a regulatory cytokine that can increase the activity of enzymes such as ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs), which degrade disc matrix. ADAMTS are enzymes that break down disc matrix and thereby mediate disc degeneration. Bone morphogenetic protein-7 (BMP-7), on the other hand, stimulates synthesis of the disc extracellular matrix and is a potential therapeutic molecule for the treatment of disc degeneration. However, the effects of BMP-7 on TNF-α and ADAMTS are unknown.

Purpose: We investigated the effects of BMP-7 on the catabolic regulators such as TNF-α and ADAMTS and evaluated the molecular mechanism by which BMP-7 affects the catabolic regulators.

Study design: This was an in vitro study in which we used human intervertebral disc cells cultured in alginate beads.

Methods: Human intervertebral disc cells were cultured in alginate beads, and treated with TNF-α, or TNF- α plus BMP-7, pharmacological inhibitor of ERK1/2 (U0126), p38 (SB203580), or NFκB (BAY 11-7082). The mRNA levels of target genes were measured by real-time polymerase chain reaction, and the protein levels were determined by the Western blots. The nuclear factor (NF)κB activity was analyzed by measured phosphorylation and nuclear translocation of the NFκB protein p65.

Results: TNF-α activated NFκB signaling and induced up-regulation of the catabolic regulators ADAMTS-4 and ADAMTS-5, contributing to degradation of the disc matrix macromolecules aggrecan and collagen II. BMP-7 antagonized the TNF-α-induced activation of NFκB protein p65 and blocked TNF-α-induced up-regulation of ADAMTS-4 and ADAMTS-5, leading to reversing TNF-α-mediated degradation of aggrecan and collagen II. Moreover, BMP-7 antagonized the TNF-α-induced activation of NFκB signaling by suppressing phosphorylation and nucleus translocation of NFκB protein p65.

Conclusion: BMP-7 antagonizes TNF-α-induced activation of NFκB and up-regulation of ADAMTS, leading to decreased degradation of disc matrix macromolecules. These data indicate that BMP-7 has a dual mechanism of action on disc metabolism: (1) the previously well-described positive effect on disc matrix synthesis and (2) an anticatabolic effect that is described here. This understanding is important as BMP-7 is being considered for treatment of disc degeneration.

Keywords: ADAMTS; BMP-7; Intervertebral discs; NF-κB; TNF-α.