Cardiomyocyte contractile status is associated with differences in fibronectin and integrin interactions

Area of Science:

• Cardiovascular Biology
• Cellular Mechanics
• Biophysics

Background:

• Integrins mediate cell-extracellular matrix (ECM) interactions, crucial for mechanotransduction.
• Quantitative data linking cardiomyocyte mechanical state to specific ECM-integrin interactions are limited.
• Understanding these interactions is vital for cardiac function and disease research.

Purpose of the Study:

• To characterize fibronectin (FN)-integrin interactions in cardiomyocytes.
• To test if these interactions vary with cardiomyocyte contraction and relaxation states.
• To correlate integrin-FN binding with cellular mechanical properties.

Main Methods:

• Atomic force microscopy (AFM) to measure unbinding force and adhesion probability between integrins and FN.
• Experiments conducted on isolated mouse cardiomyocytes in physiological, high-K+ (contracted), and low-Ca2+ (relaxed) solutions.
• Assessment of cell stiffness and use of antibodies and inhibitors (Cytochalasin D, BDM) to probe binding specificity and cytoskeletal involvement.

Main Results:

• Adhesion force between FN and cardiomyocyte alpha3beta1/alpha5beta1-integrins was ~40 pN under normal conditions.
• Monoclonal antibodies against integrin subunits significantly inhibited FN binding.
• Cell stiffness increased dramatically during tonic contraction, and integrin-FN adhesion was modulated by the contractile state, independent of actin cytoskeleton or myofilament function disruption.

Conclusions:

• Integrin binding to fibronectin is dynamically modulated by the contractile state of cardiac myocytes.
• Cardiomyocyte contraction influences integrin-ECM interactions, suggesting a role in cardiac mechanotransduction.
• Findings provide quantitative insights into the mechanical regulation of cell adhesion in the heart.