Interleukin-9 Promotes TNF-α and PGE2 Release in Human Degenerated Intervertebral Disc Tissues

Based on human disc surgical samples and isolated cells in vitro, we undertook a descriptive and mechanistic investigation of proinflammatory effects of interleukin (IL)-9 in intervertebral disc (IVD) degeneration.

To investigate the proinflammatory role of IL-9 in the pathological process of IVD degeneration.

IL-9 is known as a pleiotropic cytokine that regulates the human pathogenesis of inflammatory and autoimmune diseases. However, whether IL-9 cytokine is involved in the immuno-inflammatory pathogenesis of IVD degeneration is unclear.

The IVD samples were obtained from 45 patients. Immunohistochemistry, western blot, and real-time Polymerase Chain Reaction (PCR) were performed to detect the expression of IL-9 and tumor necrosis factor alpha (TNF-α) in the degenerated IVDs. Moreover, nucleus pulposus (NP) cells were treated with 0, 1, 10, and 100 ng/mL IL-9 cytokine and stimulated with IL-9 alone at 100 ng/mL for 0, 12, 24, and 48 hours. TNF-α expression was determined by immunofluorescence staining, western blot, and real-time PCR, respectively. The amounts of TNF-α and prostaglandin E2 (PGE2) in the supernatant were quantified by enzyme-linked immunosorbent assay. Additionally, Spearman correlation analyses were performed to analyze the correlation between Pfirrmann grading score of the involved degenerated IVDs and serum levels of IL-9.

The expressions of IL-9 and TNF-α in degenerated IVD tissues were dramatically elevated in comparison with the control. IL-9 significantly up-regulated the TNF-α and PGE2 secretion of NP cells in dose- and time-dependent manner. Moreover, there is a positive correlation between IL-9 serum level and severity of involved IVD degeneration.

Our findings suggest that IL-9 may play a potential role in the inflammatory processes of IVD degeneration. IL-9 may be involved in the IVD degeneration, at least in part, though stimulating the release of TNF-α and PGE2 in NP cells.

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