Human annulus cells regulate PAPP-A and IGFBP-4 expression, and thereby insulin-like growth factor bioavailability, in response to proinflammatory cytokine exposure in vitro

Abstract

Pregnancy-associated plasma protein-A (PAPP-A) is a metalloproteinase which cleaves IGF binding protein (BP)-4 in the extracellular matrix, making IGF available to nearby cells. We have shown that PAPP-A is present in the human intervertebral disc, and is significantly upregulated in more degenerated discs where increased proinflammatory cytokine levels are present. We hypothesized that increased proinflammatory cytokines present in the degenerating disc might be related to PAPP-A expression. Experiments exposed human annulus cells to IL-1-β or TNF-α to test this hypothesis. Treated cells showed significantly increased PAPP-A in conditioned media versus controls (p < 0.001). PAPP-A production following exposure to IL-1β was significantly greater in cells derived from more degenerated versus healthier discs (p = 0.05). PAPP-A gene expression (microarray analysis) was significantly upregulated in IL-1β- or TNF-α-exposed cells (p = 0.01–0.004). Quantitative RT-PCR confirmed significant upregulation of IGFBP-4 in IL-1β- or TNF-α-exposed cells. Data have potential relevance to future cell-based biologic therapies for disc degeneration.

• IL-1-β
• intervertebral disc
• PAPP-A
• TNF-α

Acknowledgements

We also acknowledge the support of the Brooks Back Pain Research Endowment for general laboratory support. We also thank Nury Steuerwald, Ph.D. and Judy Parsons, B.S. in the Cannon Research Molecular Biology Core Facility for their expert assistance with molecular procedures, and Synthia Bethea, B.S. and Ray Deepe, M.S. in our department for expert cell culture.