Matrix modification for enhancing the transport properties of the human cartilage endplate to improve disc nutrition.
Dolor Aaron,Sampson Sara L,Lazar Ann A,Lotz Jeffrey C,Szoka Francis C,Fields Aaron J
Poor solute transport through the cartilage endplate (CEP) impairs disc nutrition and could be a key factor that limits the success of intradiscal biologic therapies. Here we demonstrate that treating the CEP with matrix metalloproteinase-8 (MMP-8) reduces the matrix constituents that impede solute uptake and thereby improves nutrient diffusion. Human CEP tissues harvested from four fresh cadaveric lumbar spines (age range: 38-66 years old) were treated with MMP-8. Treatment caused a dose-dependent reduction in sGAG, localized reductions to the amount of collagen, and alterations to collagen structure. These matrix modifications corresponded with 16-24% increases in the uptake of a small solute (376 Da). Interestingly, the effects of MMP-8 treatment depended on the extent of non-enzymatic glycation: treated CEPs with high concentrations of advanced glycation end products (AGEs) exhibited the lowest uptake compared to treated CEPs with low concentrations of AGEs. Moreover, AGE concentrations were donor-specific, and the donor tissues with the highest AGE concentrations appeared to have lower uptake than would be expected based on the initial amounts of collagen and sGAG. Finally, increasing solute uptake in the CEP improved cell viability inside diffusion chambers, which supports the nutritional relevance of enhancing the transport properties of the CEP. Taken together, our results provide new insights and in vitro proof-of-concept for a treatment approach that could improve disc nutrition for biologic therapy: specifically, matrix reduction by MMP-8 can enhance solute uptake and nutrient diffusion through the CEP, and AGE concentration appears to be an important, patient-specific factor that influences the efficacy of this approach.
Evaluation of nucleus pulposus fluid velocity and pressure alteration induced by cartilage endplate sclerosis using a poro-elastic finite element analysis.
Hassan Chaudhry Raza,Lee Wonsae,Komatsu David Edward,Qin Yi-Xian
Biomechanics and modeling in mechanobiology
The nucleus pulposus (NP) in the intervertebral disk (IVD) depends on diffusive fluid transport for nutrients through the cartilage endplate (CEP). Disruption in fluid exchange of the NP is considered a cause of IVD degeneration. Furthermore, CEP calcification and sclerosis are hypothesized to restrict fluid flow between the NP and CEP by decreasing permeability and porosity of the CEP matrix. We performed a finite element analysis of an L3-L4 lumbar functional spine unit with poro-elastic constitutive equations. The aim of the study was to predict changes in the solid and fluid parameters of the IVD and CEP under structural changes in CEP. A compressive load of 500 N was applied followed by a 10 Nm moment in extension, flexion, lateral bending, and axial rotation to the L3-L4 model with fully saturated IVD, CEP, and cancellous bone. A healthy case of L3-L4 physiology was then compared to two cases of CEP sclerosis: a calcified cartilage endplate and a fluid constricted sclerotic cartilage endplate. Predicted NP fluid velocity increased for the calcified CEP and decreased for the calcified + less permeable CEP. Decreased NP fluid velocity was prominent in the axial direction through the CEP due to a less permeable path available for fluid flux. Fluid pressure and maximum principal stress in the NP were predicted to increase in both cases of CEP sclerosis compared to the healthy case. The porous medium predictions of this analysis agree with the hypothesis that CEP sclerosis decreases fluid flow out of the NP, builds up fluid pressure in the NP, and increases the stress concentrations in the NP solid matrix.
Collagen-Derived N-Acetylated Proline-Glycine-Proline in Intervertebral Discs Modulates CXCR1/2 Expression and Activation in Cartilage Endplate Stem Cells to Induce Migration and Differentiation Toward a Pro-Inflammatory Phenotype.
Feng Chencheng,Zhang Yang,Yang Minghui,Huang Bo,Zhou Yue
Stem cells (Dayton, Ohio)
The factors that regulate the migration and differentiation of cartilage endplate stem cells (CESCs) remain unknown. N-Acetylated proline-glycine-proline (N-Ac-PGP) is a chemokine that is involved in inflammatory diseases. The purpose of this study was to detect N-Ac-PGP in degenerative intervertebral discs (IVDs) and to determine its roles in the migration and differentiation of CESCs. Enzyme-linked immunosorbent assay (ELISA) and liquid chromatography-mass spectrometry results indicated that the levels of the proteases that generate N-Ac-PGP as well as N-Ac-PGP levels themselves increase with the progression of IVD degeneration. Immunohistochemistry and an N-Ac-PGP generation assay demonstrated that nucleus pulposus (NP) cells generate N-Ac-PGP from collagen. The effects of N-Ac-PGP on the migration and differentiation of CESCs were determined using migration assays, RT-PCR, immunoblot analysis, and ELISA. The results showed that the expression of N-Ac-PGP receptors (CXCR1 and CXCR2) in CESCs was upregulated by N-Ac-PGP. Additionally, N-Ac-PGP induced F-actin cytoskeletal rearrangement in CESCs and increased CESC chemotaxis. Furthermore, N-Ac-PGP recruited chondrocytes and spindle-shaped cells from the cartilage endplate (CEP) into the NP in vivo. These spindle-shaped cells expressed CD105 and Stro-1 (mesenchymal stem cell markers). N-Ac-PGP induced the differentiation of CESCs toward a pro-inflammatory phenotype with increased production of inflammatory cytokines rather than toward an NP-like phenotype. Our study indicated that, in the complex microenvironment of a degenerative disc, N-Ac-PGP is generated by NP cells and induces the migration of CESCs from the CEP into the NP. N-Ac-PGP induces a pro-inflammatory phenotype in CESCs, and these cells promote the inflammatory response in degenerative discs.