Matrix modification for enhancing the transport properties of the human cartilage endplate to improve disc nutrition

Abstract

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.

Effects of Glucose Deprivation on ATP and Proteoglycan Production of Intervertebral Disc Cells under Hypoxia

“…Several methods have been proposed to promote nutrient transport and energy production in the IVD 32,[70][71][72] , especially dynamic compression that can enhance not only anabolic gene expression 73 but also energy production in the IVD 72,74 . Furthermore, besides PG production, protein synthesis is also one of the most energy costly processes 45 .…”

Characterization of bovine and canine animal model cartilage endplates and comparison to human cartilage endplate structure, matrix composition, and cell phenotype

“…Differences in CEP thickness observed between human and canine or bovine may have implications for use in studying CEP transport or mechanical properties. For example, human CEPs with poor diffusive properties have higher amounts of matrix constituents, such as collagen, aggrecan, and mineral, 10 and treating the CEP with MMP‐8 reduces these matrix constituents and increases diffusivity 31 . Diffusivity of the CEP is essential for proper IVD nutrition and waste removal.…”

“…We have previously as collagen, aggrecan, and mineral, 10 and treating the CEP with MMP-8 reduces these matrix constituents and increases diffusivity. 31 Diffusivity of the CEP is essential for proper IVD nutrition and waste removal. Transport properties of thinner CEPs may be better than thicker CEPs due to a smaller distance for metabolites to travel.…”

Electrospinning and 3D bioprinting for intervertebral disc tissue engineering

“…47 Furthermore, it will be crucial to achieve suitable EP diffusivity to maintain cell viability, especially in the center of the engineered IVD. 48…”

“…Although 3D bioprinting can be a valuable tool to create EP structures, low printing resolutions may hamper their structural functionality 47 . Furthermore, it will be crucial to achieve suitable EP diffusivity to maintain cell viability, especially in the center of the engineered IVD 48 …”