Annulus fibrosus cells interact with neuron-like cells to modulate production of growth factors and cytokines in symptomatic disc degeneration

• Published in: Spine (Philadelphia, Pa. 1976) Vol. 37; no. 1; p. 2
• Main Authors: Moon, Hong Joo, Kim, Joo Han, Lee, Hack Sun, Chotai, Silky, Kang, James D, Suh, Jung Keun, Park, Youn-Kwan
• Format: Journal Article
• Language: English
• Published: United States 01.01.2012
• Subjects: Cell Line, Tumor; Coculture Techniques; Culture Media, Conditioned - chemistry; Cytokines - metabolism; Female; Humans; Interleukin-1beta - pharmacology; Intervertebral Disc; Intervertebral Disc Degeneration; Male; Neovascularization, Pathologic - chemically induced; Nerve Growth Factors - metabolism; Neurites - drug effects; Neurites - pathology; Neuroblastoma - metabolism; Neuroblastoma - pathology; Neurons - drug effects; Neurons - metabolism; Neurons - pathology; Recombinant Proteins; Tretinoin - pharmacology; Tumor Necrosis Factor-alpha - pharmacology
• ISSN: 1528-1159
• DOI: 10.1097/BRS.0b013e31820cd2d8

We hypothesized that AF/neuron interactions during annular injury were involved in neovascularization and nerve ingrowth, the pathologic hallmarks of symptomatic disc degeneration. To identify growth factors and inflammatory cytokines related to AF/neuron interactions using in vitro model. Discogenic pain is the chronic intractable pain initiated by tears in the outer annulus fibrosus (AF); this is a unique structure with free nerve endings at outer one-third, located beside dorsal root ganglia. The relationship between AF and neuron cells in annular injury has not been extensively investigated. Human AF cells were cocultured with a retinoic acid (RA)-treated SH-SY5Y human neuroblastoma cell line (neuron-like cells). Conditioned media from cells cultured alone or in coculture were assayed for growth factors and inflammatory cytokines using enzyme-linked immunosorbent assays. The responses of the neuron-like cells, the AF cells, and the cocultured group to IL-1β/TNF-α were compared using the same outcome measures. RA-treated SH-SY5Y cells showed significant neurite outgrowth on the 7th day; this is a typical morphologic finding of neuron-like cells. Neuron-like cells produced vascular endothelial growth factor (VEGF) and IGF-1 under basal conditions and dose-dependently secreted small amounts of IL-8 in response to TNF-α. Coculturing enhanced the secretion of VEGF, TGF-β1, and β-NGF, and suppressed the production of IGF-1. VEGF in the coculture group and the AF cells was downregulated by IL-1β/TNF-α stimulation. IL-1β/TNF-α stimulation enhanced the production of large amounts of IL-6 and IL-8 from AF cells; IL-1β produced a greater response than TNF-α. The neuron-like cells did not produce detectable amounts of IL-6 or IL-8. These studies suggest that AF cells are involved in an inflammatory reaction and that the interactions between AF and neuron-like cells enhance the production of growth factors responsible for neovascularization and nerve ingrowth. AF injury has the potential to initiate neovascularization/nerve ingrowth and an inflammatory reaction through the interactions of AF and neural tissues.