Extracellular Calcium Ion Concentration Regulates Chondrocyte Elastic Modulus and Adhesion Behavior

Area of Science:

• Biomedical Engineering
• Cell Biology
• Biophysics

Background:

• Osteoarthritis (OA) is a degenerative joint disease associated with altered extracellular calcium ion concentration ([Ca2+]) in human joints.
• The mechanical implications of elevated [Ca2+], particularly on the biomechanical properties of primary human OA chondrocytes, are not fully understood.

Purpose of the Study:

• To investigate the effect of varying extracellular calcium ion concentration ([Ca2+]) on the mechanical properties of primary human OA chondrocytes.
• To elucidate the relationship between [Ca2+], chondrocyte stiffness, cell-extracellular matrix (ECM) adhesion, and cell migration.

Main Methods:

• Atomic Force Microscopy (AFM) was used to measure the elastic modulus and cell-ECM adhesion forces of human OA chondrocytes at different [Ca2+] levels.
• Quantitative Polymerase Chain Reaction (qPCR) and immunofluorescence were employed to assess gene and protein expression.
• Scratch assays were performed to evaluate chondrocyte migration ability.

Main Results:

• Increasing [Ca2+] led to a biphasic change in chondrocyte elastic modulus, with a peak increase of 37% at 2.75 mM.
• Cell-ECM unbinding force significantly increased by up to 72% with elevated [Ca2+].
• Dose-dependent changes in myosin and integrin β1 expression correlated with altered cell stiffness and adhesion; chondrocyte migration speed decreased as stiffness and adhesion increased.

Conclusions:

• Extracellular calcium ion concentration ([Ca2+]) significantly modulates the mechanical properties of human OA chondrocytes, including stiffness and cell-ECM adhesion.
• These calcium-induced mechanical changes influence chondrocyte migration, a critical factor in cartilage repair processes.
• The findings highlight a novel regulatory role of [Ca2+] in chondrocyte biomechanics relevant to OA pathogenesis and potential therapeutic strategies.