In Situ Regenerative Potential of Notochordal Cells in a Nucleus Pulposus Explant Model

Introduction Because current treatments for symptomatic intervertebral disk degeneration focus on pain rather than its cause, with only modest success in the long term, there is a need for new therapies. Since the earliest signs of intervertebral disk degeneration have been observed in the nucleus pulposus (NP), cell therapies focusing on NP regeneration are of great interest. Very early in life, the NP is populated with two cell types: NP cells and notochordal cells (NCs). Incidence and onset of disk degeneration is less and later in certain species that retain their NCs throughout adulthood vs. those that lose their NCs before adolescence.2 Consequently, it has been proposed that NCs might be involved in the maintenance of a healthy NP, and both direct3 and indirect coculture4 of NCs and NP cells have shown increased proteoglycan synthesis by NP cells in the presence of NCs. However, translation of such effects on isolated NP cells to NP tissue may not be straightforward. Thus, in this study, we investigated the in situ effects of NC therapy using an NP explant culture model developed previously in our group.5 Similar to cell cultures, we hypothesized that an injection of NCs in a NP explant would increase the extracellular matrix protein synthesis over 6 weeks in culture. Materials and Methods Porcine lumbar and thoracic NPs (n = 4 donors,