Partial characterization of matrix components interacting with cartilage proteoglycans.

Area of Science:

• Biochemistry
• Biomaterials Science
• Orthopedics

Background:

• Cartilage extracellular matrix is primarily composed of proteoglycans and collagen.
• The charge content of cartilage influences its mechanical and osmotic properties.
• Understanding charge distribution is crucial for comprehending cartilage structure and function.

Purpose of the Study:

• To determine the charge content of milled cartilage samples using colloid titration.
• To compare charge content estimations from titration with chemical analyses.
• To investigate the role of basic proteins in articular cartilage charge.

Main Methods:

• Colloid titration technique with a particle charge detector for aqueous cartilage suspensions.
• Chemical analyses for estimating charge content.
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for protein analysis.
• Extraction of articular cartilage with 0.1 M and 1.2 M NaCl.

Main Results:

• A strong correlation between titration and chemical analyses was observed for nonarticular cartilage (nasal septa).
• This correlation was absent in articular cartilages (metacarpalphalangeal joint, patella).
• Extraction with NaCl increased the availability of negative groups in articular cartilage.
• SDS-PAGE revealed basic proteins (chondrocalcin, proline-arginine-rich protein, pleiotrophin, histone-H2b) in NaCl extracts.

Conclusions:

• Electrostatic interactions between basic proteins and proteoglycans likely occur in articular cartilage.
• These interactions significantly impact cartilage osmotic properties and structural organization.
• Charge heterogeneity in cartilage is influenced by the presence of specific basic proteins.