Can Notochordal Cells Promote Bone Marrow Stromal Cell Potential for Nucleus Pulposus Enrichment? A SimplifiedIn VitroSystem

Abstract

Bone marrow stromal cells (BMSCs) have shown promising potential to stop intervertebral disc degeneration in several animal models. In order to restore a healthy state, though, this potential should be further stimulated. Notochordal cells (NCs), influential in disc development, have been shown to stimulate BMSC differentiation, but it is unclear how this effect will translate in an environment where resident disc cells (nucleus pulposus cells [NPCs]) could also influence BMSCs. The goal of this study was, therefore, to evaluate the effects of NCs on BMSCs when cocultured with NPCs, in a simplified 3D in vitro system. Bovine BMSCs and NPCs were mixed (Mix) and seeded into alginate beads. Using culture inserts, the Mix was then cocultured with porcine NCs (alginate beads) and compared to coculture with empty beads or porcine skin fibroblasts (SFs, alginate beads). NPCs alone were also cocultured with NCs, and BMSCs alone cultured under chondrogenic conditions. The effects of coculture conditions on cell viability, matrix production (proteoglycan and collagen), and gene expression of disc markers (aggrecan, type II collagen, and SOX9) were assessed after 4 weeks of culture. The NC phenotype and gene expression profile were also analyzed. Coculture with NCs did not significantly influence cell viability, proteoglycan production, or disc marker gene expression of the Mix. When compared to NPCs, the Mix produced the same amount of proteoglycan and displayed a higher expression of disc marker, indicating a stimulation of the BMSCs (and/or NPCs) in the Mix. Additionally, during the 4 weeks of culture, the NC phenotype changed drastically (morphology, gene expression profile). These results show that NCs might not be as stimulatory for BMSCs in an NPC-rich environment, as believed from individual cultures. This absence of effects could be explained by a mild stimulation provided by (de)differentiating NCs and the costimulation of BMSCs and NPCs by each other.

Nucleus Pulposus Cell Conditioned Medium Promotes Mesenchymal Stem Cell Differentiation into Nucleus Pulposus-Like Cells under Hypoxic Conditions

“…To obtain a better understanding of MSC differentiation into NP-like cells, we investigated the effects of the 50% or 100% NPC conditioned medium on MSCs. Some previous studies showed that the notochordal cells and notochordal cell conditioned medium had positive effects in the treatment of IVD degeneration [ 31 , 32 ]. However, it remains unclear whether these positive effects apply to MSCs.…”

Co-culturing nucleus pulposus mesenchymal stem cells with notochordal cell-rich nucleus pulposus explants attenuates tumor necrosis factor-α-induced senescence

“…To date, although a number of studies have shown the activating effects of NCs for the treatment of IDD, the regeneration potential was mild or invalid due to the disruption of the physiological organization of NCs [ 4 , 37 , 38 ]. In this study, cell viability and the expression of NC phenotype-related genes after NC-rich NP explant were tested in rabbit L4/5, L5/6, and L6/7 IVDs; the results demonstrated no significant differences, indicating that the NC-rich NP explant model was comparable among the three segments used in this study and that these could be used randomly.…”

A Review: Methodologies to Promote the Differentiation of Mesenchymal Stem Cells for the Regeneration of Intervertebral Disc Cells Following Intervertebral Disc Degeneration

“…The co-culture of MSCs with NPCs is often used to differentiate MSCs into NPClike cells. Both direct co-culture [56,57,[177][178][179][180] and trans-well co-culture [72,[181][182][183] successfully induced the chondrogenic differentiation of MSCs. Wharton's jelly is another source of MSCs [184].…”