Molecular Adhesion between Cartilage Extracellular Matrix Macromolecules

Abstract

In this study, we investigated the molecular adhesion between the major constituents of cartilage extracellular matrix, namely, the highly negatively charged proteoglycan aggrecan and the type II/IX/XI fibrillar collagen network, in simulated physiological conditions. Colloidal force spectroscopy was applied to measure the maximum adhesion force and total adhesion energy between aggrecan end-attached spherical tips (end radius R ≈ 2.5 μm) and trypsin-treated cartilage disks with undamaged collagen networks. Studies were carried out in various aqueous solutions to reveal the physical factors that govern aggrecan–collagen adhesion. Increasing both ionic strength and [Ca2+] significantly increased adhesion, highlighting the importance of electrostatic repulsion and Ca2+-mediated ion bridging effects. In addition, we probed how partial enzymatic degradation of the collagen network, which simulates osteoarthritic conditions, affects the aggrecan–collagen interactions. Interestingly, we found a significant increase in aggrecan–collagen adhesion even when there were no detectable changes at the macro- or microscales. It is hypothesized that the aggrecan–collagen adhesion, together with aggrecan–aggrecan self-adhesion, works synergistically to determine the local molecular deformability and energy dissipation of the cartilage matrix, in turn, affecting its macroscopic tissue properties.

Biomechanical properties of murine meniscus surface via AFM-based nanoindentation

“…Immediately after nanoindentation, menisci were incubated in 0.1 mg/mL bovine pancreatic trypsin (Sigma-Aldrich, St. Louis, MO) in PBS (pH = 7.4) at 37 °C for 24 h to remove proteoglycans, as previously described (Rojas et al, 2014). Tissues were then incubated in 0.4 U/mL hyaluronidase (Sigma-Aldrich) in PBS with 10mM sodium acetate (pH = 6.0) at 37 °C for 24 h to remove hyaluronan (Vanden Berg-Foels et al, 2012).…”

Multicomponent analysis of T1 relaxation in bovine articular cartilage at low magnetic fields

“…Trypsin digestion removes proteoglycans (PGs) while keeping the collagen fibrils mostly intact; hence, the increase in water mobility can be related to the depletion of PGs. 21 On the one hand, it is known that PG in the form of aggrecans is able to uptake 40% weight of water, 22 so that a considerable amount of water in natural cartilage can be physically entrapped within the aggrecans, and as such, has a slower dynamics compared with the trypsin-treated cartilage in which the depleted aggrecans are replaced with protein-free water. On the other hand, PGs are known to interact with collagen fibrils in such a way that they affect the exchange of water between intrafibrillar and extrafibrillar space.…”

“…On ILT histograms, it manifests as a shift of the long‐T 1 peak toward larger values, which is assigned to the transitional and the radial zones of cartilage (Figure ), thus suggesting enhanced water mobility in those zones. Trypsin digestion removes proteoglycans (PGs) while keeping the collagen fibrils mostly intact; hence, the increase in water mobility can be related to the depletion of PGs . On the one hand, it is known that PG in the form of aggrecans is able to uptake 40% weight of water, so that a considerable amount of water in natural cartilage can be physically entrapped within the aggrecans, and as such, has a slower dynamics compared with the trypsin‐treated cartilage in which the depleted aggrecans are replaced with protein‐free water.…”

“…According to Ref 23, the early‐stage OA can be characterized “as increased water contents, slightly decreased PGs and reorganized collagens.” Seeking a suitable relaxation characteristic that would be sensible to these particular changes in cartilage biochemistry, we investigated T 1 relaxation in bovine AC at low magnetic fields (B 0 < 600 mT) using the FFC technique. The early‐stage OA conditions were simulated by enzymatic digestion of cartilage with trypsin . Using the low fields reveals a T 1 relaxation‐time distribution that is attributed to morphological zones of articular cartilage—a benefit of the low‐field relaxometry as opposed to the single‐exponential T 1 relaxation typically observed in stronger fields of 1 T and above.…”

Biomechanical properties of murine TMJ articular disc and condyle cartilage via AFM-nanoindentation

“…First, tissues were incubated in 0.1 mg/mL bovine pancreatic trypsin (Sigma-Aldrich, St. Louis, MO) in PBS (pH = 7.4) at 37 °C for 24 h to remove the proteoglycans, as previously described (Rojas et al, 2014). Second, samples were then incubated in 0.4 U/mL hyaluronidase (Sigma-Aldrich, St. Louise, MO) in PBS with 10 mM sodium acetate (pH = 6.0) at 37 °C for 24 h to remove the proteoglycans and expose the collagen fibril architecture.…”