Background: Intervertebral disc (IVD) degeneration is suggested as a major cause of chronic low back pain (LBP). Intradiscal delivery of growth factors has been proposed as a promising strategy for IVD repair and regeneration. Previously, BMP-4 was shown to be more potent in promoting extracellular matrix (ECM) production than other BMPs and TGF-β in human nucleus pulposus (NP) cells, suggesting its applicability for disc regeneration.
Methods: The effects of BMP-4 on ECM deposition and cell proliferation were assessed in sheep NP and annulus fibrosus (AF) cells in a pellet culture model. Further, a nuclectomy induced sheep lumbar IVD degeneration model was used to evaluate the safety and effects of intradiscal BMP-4 injection on IVD regeneration. Outcomes were assessed by magnetic resonance imaging, micro-computed tomography, histological and biochemical measurements.
Results: In vitro, BMP-4 significantly increased the production of proteoglycan and deposition of collagen type II and proliferation of NP and AF cells. Collagen type I deposition was not affected in NP cells, while in AF cells it was high at low BMP-4 concentrations, and decreased with increasing concentration of BMP-4. Intradiscal injection of BMP-4 induced extradiscal new bone formation and Schmorl's node-like changes in vivo. No regeneration in the NP nor AF was observed.
Conclusion: Our study demonstrated that although BMP-4 showed promising regenerative effects in vitro, similar effects were not observed in a large IVD degeneration animal model.
The translational potential of this article: The contradictory results of using BMP-4 on IVD regeneration between in vitro and in vivo demonstrate that direct BMP-4 injection for disc degeneration-associated human chronic low back pain should not be undertaken. In addition, our results may also shed light on the mechanisms behind pathological endplate changes in human patients as a possible target for therapy.
Keywords: AB/PR, Alcian blue and picrosirius red; ADAMTS, A disintegrin and metalloproteinase with thrombospondin motifs; AF, Annulus fibrosus; Annulus fibrosus; BMP-4; BMPs, Bone morphogenetic proteins; Bone formation; CLBP, Chronic low back pain; DHI, Disc height index; ECM, Extracellular matrix; EP, Endplate; GAG, Glycosaminoglycan; GDF-8, Growth and differentiation factor-8; H&E, Hematoxylin and eosin; IVD, Intervertebral disc; IVDD, Intervertebral disc degeneration; Intervertebral disc regeneration; Ki-67, Nuclear Ki-67 protein; LBP, Low back pain; MMPs, Matrix metalloproteinases; MRI, Magnetic resonance imaging; Micro-CT, Micro-computed tomography; NP, Nucleus pulposus; Nucleus pulposus; RPL19, Ribosomal protein L19; SOX-9, SRY-box transcription factor-9; Saf-O FG, Safranin-O and fast green; Subchondral bone remodeling; TGF-β, Transforming growth factor-beta; TRAP, Tartrate-resistant acid phosphatase.
© 2022 The Authors.