A multifactorial intervertebral disc degeneration model: Integrating inflammation, structural disruption,...

Intervertebral disc (IVD) degeneration (IVDD) is a major cause of low back pain, yet treatment options remain limited. Robust IVDD models are essential for discovering and validating new regenerative treatments. Ex vivo whole organ bioreactor cultures using bovine IVDs are a well-established approach, with various degeneration models developed on this platform. However, most existing models replicate only isolated aspects of IVDD, failing to reflect its complex nature. There is a critical need for in vitro models that more accurately simulate the full spectrum of degeneration phenotypes observed in patients. Combining multiple well-established degeneration models offers a promising strategy. In this study, we investigated the combined effects of enzyme (papain) and cytokine (tumor necrosis factor alpha [TNFα]) based degeneration inducers on bioreactor loaded bovine IVDs. While papain injection led to a 5.5-fold higher glycosaminoglycan loss and tissue void formation, TNFα induced inflammatory and catabolic changes relevant to IVDD, including significant aggrecanase-1 (ADAMTS4) upregulation and a 2.65-fold increase in interleukin 6 release. Both effects were evident when combined, enabling the manifestation of multiple aspects of IVDD in one model. To also explore implications on nociception, primary bovine dorsal root ganglion neurons were cultured and treated with conditioned medium from the induced degenerative IVDs. Nociceptors treated with degenerative medium showed a 1.51-fold higher proportion of neurons with a response compared to treatment with control IVD medium. By expanding the range of degenerative changes and bridging them to pain-associated features, this model provides a valuable platform for testing novel regenerative therapies.