Partial characterization of matrix components interacting with cartilage proteoglycans

The effect of paraformaldehyde fixation on the delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) measurement

The delayed Gadolinium-Enhanced Magnetic Resonance Imaging of Cartilage (dGEMRIC) method allows for both qualitative and quantitative measurement of the spatial distribution of glycosaminoglycan [GAG] in excised cartilage. The objective of this study was to determine the effect of paraformaldehyde fixation on dGEMRIC measurements. Five bovine and seven human cartilage pieces were punched into 5-mm plugs, fixed for 18 h in 4% paraformaldehyde solution, and washed. The magnetic resonance imaging (MRI) parameter T1 was measured prior and post fixation in cartilage without (T1(0)) and with (T1(Gd)), the ionically charged MRI contrast agent Gd(DTPA)(2-). Images of tissue before and after fixation were qualitatively very similar. The ratios of T1(0), T1(Gd), and calculated [GAG] after fixation, relative to before fixation, were near or slightly higher than 1 for both bovine cartilage (1.01 +/- 0.01, 1.04 +/- 0.02, 1.05 +/- 0.03, respectively) and for human cartilage (0.96 +/- 0.11, 1.03 +/- 0.05, 1.09 +/- 0.13). Thus, these data suggest that dGEMRIC can be used on previously fixed samples to assess the three dimensional spatial distribution of GAG.

A robust method for proteomic characterization of mouse cartilage using solubility-based sequential fractionation and two-dimensional gel electrophoresis

Identification of protein expression differences using two-dimensional electrophoresis (2-DE) and multidimensional liquid chromatography (MDLC)-based proteomics depends critically on reproducibility throughout sample preparation and analysis. This applies particularly where sample fractionation is used to remove high abundance or interfering components to facilitate deeper mining of the proteome. Here we present a procedure for solubility-based cartilage fractionation using sequential extraction with 1 M sodium chloride followed by 4 M guanidinium hydrochloride. We characterized the extracts by 1-D electrophoresis and immunoblotting for individual cellular and matrix components and more globally by 2-DE. In general, NaCl extracts were highly enriched for cellular proteins and GuHCl extracts were predominantly matrix components, with some interesting exceptions. Importantly, we observed high inter-sample reproducibility and strong correlation between targeted and global analysis, indicating that our method can be applied to differential proteomic analysis of normal and pathological cartilage sub-proteomes.

A bimodular polyconvex anisotropic strain energy function for articular cartilage

A strain energy function for finite deformations is developed that has the capability to describe the nonlinear, anisotropic, and asymmetric mechanical response that is typical of articular cartilage. In particular, the bimodular feature is employed by including strain energy terms that are only mechanically active when the corresponding fiber directions are in tension. Furthermore, the strain energy function is a polyconvex function of the deformation gradient tensor so that it meets material stability criteria. A novel feature of the model is the use of bimodular and polyconvex "strong interaction terms" for the strain invariants of orthotropic materials. Several regression analyses are performed using a hypothetical experimental dataset that captures the anisotropic and asymmetric behavior of articular cartilage. The results suggest that the main advantage of a model employing the strong interaction terms is to provide the capability for modeling anisotropic and asymmetric Poisson's ratios, as well as axial stress-axial strain responses, in tension and compression for finite deformations.

Tracking chondrocytes and assessing their proliferation with PKH26: effects on secretion of proteoglycan 4 (PRG4)

Distinguishing between implanted and host-derived cells, as well as between distinct cell phenotypes, would be useful in assessing the mechanisms of cell-based repair of cartilage. The fluorescent tracker dye, PKH26, was previously applied to several cell types to assess proliferation in vitro and to track cells in vivo. The objectives of this study were to assess the utility of PKH26 for tracking chondrocytes from superficial and middle zones and their proliferation, and determine the effects of PKH26 on chondrocyte functions, in particular, proliferation and secretion of Proteoglycan 4 (PRG4). PKH26-labeled and unlabeled superficial and middle zone chondrocytes were plated in either low- or high-density monolayer culture and analyzed for retention of PKH26 by flow cytometry and fluorescence microscopy at days 0 and 7. Cell suspensions and conditioned media were analyzed for DNA and secretion of PRG4, respectively. Flow cytometric histograms were deconvolved so that the number of cells in each doubling generation contributing to the final cell population could be estimated. Chondrocytes were consistently and intensely labeled with PKH26 through 7 cycles of division. At day 7 of culture, >97% of superficial zone cells seeded at low or high density could be distinguished as fluorescent, as could middle zone cells seeded at high density. Retention of cell fluorescence after PKH26 labeling and lack of adverse effects on cell proliferation and synthesis of PRG4 suggest that PKH26 can be useful in determining the fate and function of implanted chondrocytes in vivo, as well as monitoring proliferation in vitro.