Strategies for intervertebral disc regeneration

Abstract

Chronic low back pain (CLBP) affects a large population worldwide. Intervertebral disc (IVD) degeneration is a leading case of CLBP. To date, the clinical treatments are limited to pain relief strategies, and to date, no efficient therapy was developed aiming at IVD regeneration. This thesis aimed to understand the degenerative processes of IVD and propose potential therapeutic routes to halt degeneration and achieve regeneration. Blocking inflammation is considered a viable strategy to relieve pain and delay disc degeneration. Pro-inflammatory cytokine, TNF-α, is highly associated with inflammation and pain in IVD degeneration. Therefore, in Chapter 2, a TNF-α-induced ex vivo IVD degenerative model was established on the bovine whole caudal IVD culture system under mechanical loading. This model can be used to further elucidate the mechanisms of TNF-α-induced IVD degeneration, and importantly, can serve as a model for screening of bioactives targeting TNF-a inhibition. A previous study reported that bone morphogenetic protein- 4 (BMP-4) has potent effects on NP matrix regeneration, as shown in a co-culture of human NP cells and mesenchymal stem cells. In Chapter 3, the effects of BMP-4 on IVD regeneration were evaluated in vitro and in vivo sheep models. The regenerative effects of BMP-4 on NP and AF cells were shown by improved cell proliferation and ECM production. However, no regeneration in the NP nor AF was observed in vivo. These results suggest that direct intradiscal injection of BMP-4 may not be a suitable strategy for IVD regeneration. More factors should be considered before attempting translation BMP-4 for IVD regeneration, for instance, the delivery method. To restore the function of the IVD, keeping its structural integrity is essential. Although the AF is a crucial component of IVD, this structure is often overlooked in therapy development. In Chapter 4, AF analog scaffolds were explored and evaluated in vitro and ex vivo. Our findings demonstrate that the combination of cellular, biomaterial, and bioactive strategies has excellent potential for AF regeneration. In Chapter 5, we found that CD146 is essential for the contractility of AF cells. Furthermore, we partly elucidated the underlying signaling pathway of CD146 upregulation by TGF-β in AF cells and suggest that CD146 can potentially be used as a functional marker in AF repair strategies. Intradiscal administration has been proposed as a desirable strategy for drug delivery to increase local drug concentration, prolong drug retention, and reduce systemic side effects because of the isolated nature of IVD. In Chapter 6, this study provides evidence of drug release and retention profiles in the IVD by using different methods (nuclear magnetic resonance spectroscopy, near-infrared imaging) and models (ex vivo, and in vivo on sheep and rats). Results showed that drug retention in IVD can be affected by degeneration and that a proper drug release system could prolong drug retention in IVD, which theoretically may improve treatment outcomes.