The Effect of Adenosine on Extracellular Matrix Production in Porcine Intervertebral Disc Cells.

Compressive loading promotes adenosine triphosphate (ATP) production and release by intervertebral disc (IVD) cells. Extracellular ATP can be rapidly hydrolyzed by ectonucleotidases. Adenosine, one of the adenine derivatives of ATP hydrolysis, can modulate diverse cellular actions via adenosine receptors. The objectives of this study were to investigate the effects of exogenous adenosine on the production of extracellular matrix (ECM; i.e., collagen type II and aggrecan) and ATP of IVD cells and explore the underlying mechanism of action. It was found that adenosine treatment significantly upregulated aggrecan and type II collagen gene expression and the ATP level in IVD cells. Dipyridamole, an adenosine transport blocker, completely suppressed the effects of adenosine on the ATP production and ECM gene expression of the IVD cells, whereas antagonists of adenosine receptors did not significantly affect adenosine-treated IVD cells. The findings suggested that elevated intracellular ATP and upregulation of ECM gene expression by adenosine treatment are mainly due to adenosine uptake rather than receptor activation. Since ECM biosynthesis is a high ATP demanding process, supplementing adenosine could be beneficial as IVD cells are able to utilize it to replenish intracellular ATP and sequentially promote ECM production, which is constantly suppressed by limited nutrition supply due to the avascular nature of the IVD.

Effect of endplate calcification and mechanical deformation on the distribution of glucose in intervertebral disc: a 3D finite element study.

The intervertebral disc (IVD) is avascular, receiving nutrition from surrounding vasculature. Theoretical modelling can supplement experimental results to understand nutrition to IVD more clearly. A new, 3D finite element model of the IVD was developed to investigate effects of endplate calcification and mechanical deformation on glucose distributions in IVD. The model included anatomical disc geometry, non-linear coupling of cellular metabolism with pH and oxygen concentration and strain-dependent properties of the extracellular matrix. Calcification was simulated by reducing endplate permeability (∼79%). Mechanical loading was applied based on in vivo disc deformation during the transition from supine to standing positions. Three static strain conditions were considered: supine, standing and weight-bearing standing. Minimum glucose concentrations decreased 45% with endplate calcification, whereas disc deformation led to a 4.8-63% decrease, depending on the endplate condition (i.e. normal vs. calcified). Furthermore, calcification more strongly affected glucose concentrations in the nucleus compared to the annulus fibrous region. This study provides important insight into nutrient distributions in IVD under mechanical deformation.

Osteogenic differentiation of stem cells derived from human periodontal ligaments and pulp of human exfoliated deciduous teeth.

Multipotent stem cells derived from periodontal ligaments (PDLSC) and pulp of human exfoliated deciduous teeth (SHED) represent promising cell sources for bone regeneration. Recent studies have demonstrated that retinoic acid (RA) and dexamethasone (Dex) induce osteogenesis of postnatal stem cells. The objective of this study was to examine the effects of RA and Dex on the proliferation and osteogenic differentiation of SHED and PDLSC and to compare the osteogenic characteristics of SHED and PDLSC under RA treatment. SHED and PDLSC were treated with serum-free medium either alone or supplemented with RA or Dex for 21 days. The proliferation of SHED and PDLSC was significantly inhibited by both RA and Dex. RA significantly upregulated gene expression and the activity of alkaline phosphatase in SHED and PDLSC. Positive Alizarin red and von Kossa staining of calcium deposition was seen on the RA-treated SHED and PDLSC after 21 days of culture. The influences of RA on the osteogenic differentiation of SHED and PDLSC were significantly stronger than with Dex. Supplementation with insulin enhanced RA-induced osteogenic differentiation of SHED. Thus, RA is an effective inducer of osteogenic differentiation of SHED and PDLSC, whereas RA treatment in combination with insulin supplementation might be a better option for inducing osteogenic differentiation. Significantly higher cell proliferation of PDLSC results in greater calcium deposition after 3-week culture, suggesting that PDLSC is a better osteogenic stem cell source. This study provides valuable information for efficiently producing osteogenically differentiated SHED or PDLSC for in vivo bone regeneration.