TNF-α induces MMP2 gelatinase activity and MT1-MMP expression in an in vitro model of nucleus pulposus tissue degeneration

Abstract

STUDY DESIGN. In vitro-formed bovine nucleus pulposus (NP) tissues were used as a model for tumor necrosis factor-α (TNF-α) induced NP degeneration. OBJECTIVE. To elucidate the signal transduction mechanisms regulating TNF-α induced matrix metalloproteinase (MMP) activity. SUMMARY OF BACKGROUND DATA. TNF-α is thought to contribute to the pathophysiology of intervertebral disc (IVD) degeneration by up-regulating MMPs, such as MMP-2. MMP-2 has been implicated in influencing disease progression and in the induction of neovascularization. METHODS. In vitro-formed bovine NP tissues were treated with TNF-α to examine its effect on MMP-2 gene and protein levels and activity. The effect of TNF-α on membrane type (MT)1-MMP, an activator of MMP-2, was also assessed. MT1-MMP functional activation by TNF-α was confirmed using promoter-reporter luciferase constructs. Immunoblots and electrophoretic mobility shift assays were used to examine the expression and DNA binding activity of transcription factors known to regulate transcriptional activation of MT1-MMP. RESULTS. TNF-α treatment induced MMP-2 gelatinase activity, which occurred in the absence of any change in MMP-2 gene or protein expression, but did correlate with increased MT1-MMP mRNA and protein levels. Up-regulation of MMP-2 activity was dependent on the ERK-MAPK pathway. ERK-1/2 activation up-regulated early growth factor (Egr-1) expression and its DNA binding activity to the MT1-MMP promoter. There was no effect on Sp-1 binding activity. Reporter constructs demonstrated that TNF-α induced MT1-MMP transcriptional activation and that this response was dependant on ERK MAPK and Egr-1. CONCLUSION. TNF-α induced MMP-2 gelatinase activity correlated with induction of MT1-MMP and not MMP-2 expression. MMP-2 activation was dependent on the ERK-MAPK pathway. As ERK also appeared to regulate MT1-MMP production, this suggests that TNF-α induction of MMP-2 gelatinase activity may be regulated by MT1-MMP. These findings elucidate the regulation of gelatinase activity and identify a mechanism whereby TNF-α may contribute to matrix degradation in NP tissue. © 2008 Lippincott Williams & Wilkins, Inc.