HUMAN INTERVERTEBRAL DISC AGGRECAN INHIBITS ENDOTHELIAL CELL MIGRATION IN VITRO.

Abstract

Background: Increased nerve growth into degenerated intervertebral discs is associated with discogenic low back pain [1]. Many of these growing nerves are in neo-vascularised areas of the tissue [1,2] and endothelial cells that penetrate the disc express neurotrophic factors [3]. Thus, disc neovascularisation and disc innervation may be closely linked. Whilst disc aggrecan has been found to inhibit sensory nerve growth in vitro [4], the effects of disc aggrecan on endothelial cells are unknown.

Methods/Results: Adapting in vitro assays used previously [4], with HMEC-1 and EAhy-926 cell lines as models of endothelial cell growth, we found that disc aggrecan inhibited endothelial cell migration in a dose-dependent manner. Endothelial cells traversed over collagen substrates until they encountered disc aggrecan substrates (1mg/ml human aggrecan), where they either stopped migrating or, more commonly, changed their direction of movement and aligned to the collagen:aggrecan border (Figure 1). After reaching the aggrecan border, some endothelial cells also migrated away from the disc aggrecan. At lower concentrations of disc aggrecan (0.01mg/ml), no such inhibition of endothelial cell growth was seen.

Conclusions: Loss of aggrecan, increased innervation and neovascularisation are all marked features of disc degeneration [1,2,5]. This study provides evidence that disc aggrecan inhibits endothelial migration and therefore supports a hypothesis that a loss of aggrecan from degenerated discs predisposes the tissue to vascular invasion.