Cooperative coupling of cell-matrix and cell–cell adhesions in cardiac muscle

Abstract

Adhesion between cardiac myocytes is essential for the heart to function as an electromechanical syncytium. Although cell-matrix and cell-cell adhesions reorganize during development and disease, the hierarchical cooperation between these subcellular structures is poorly understood. We reasoned that, during cardiac development, focal adhesions mechanically stabilize cells and tissues during myofibrillogenesis and intercalated disc assembly. As the intercalated disc matures, we postulated that focal adhesions disassemble as systolic stresses are transmitted intercellularly. Finally, we hypothesized that pathological remodeling of cardiac microenvironments induces excessive mechanical loading of intercalated discs, leading to assembly of stabilizing focal adhesions adjacent to the junction. To test our model, we engineered μtissues composed of two ventricular myocytes on deformable substrates of tunable elasticity to measure the dynamic organization and functional remodeling of myofibrils, focal adhesions, and intercalated discs as cooperative ensembles. Maturing μtissues increased systolic force while simultaneously developing into an electromechanical syncytium by disassembling focal adhesions at the cell-cell interface and forming mature intercalated discs that transmitted the systolic load. We found that engineering the microenvironment to mimic fibrosis resulted in focal adhesion formation adjacent to the cell-cell interface, suggesting that the intercalated disc required mechanical reinforcement. In these pathological microenvironments, μtissues exhibited further evidence of maladaptive remodeling, including lower work efficiency, longer contraction cycle duration, and weakened relationships between cytoskeletal organization and force generation. These results suggest that the cooperative balance between cell-matrix and cell-cell adhesions in the heart is guided by an architectural and functional hierarchy established during development and disrupted during disease.adherens junctions | sarcomere | mechanotransduction | extracellular matrix I n the adult heart, healthy ventricular tissue is characterized by spatial segregation of cell-matrix adhesions to transverse myocyte borders (1) and cell-cell adhesions to longitudinal myocyte borders (2). Many cardiomyopathies are characterized by lateralization of cell-cell adhesions (3-5), increased expression of cell-matrix adhesions (6, 7), and arrhythmogenesis (8), suggesting that spatially organized adhesion is essential for effective eletromechanical coupling (9). Although in vivo studies have shown that localization of cell-matrix and cell-cell adhesions is developmentally regulated (10-13), the factors that regulate their assembly and disassembly are not well understood.Cell-matrix adhesions are especially important during organogenesis, anchoring developing cells and tissues to the extracellular matrix (ECM) (14) and directing cell migration (15-17). As development progresses, cell-matrix adhesions must selectively disassemble so that cell-cell adhesions can f...

Cadherin-based intercellular adhesions organize epithelial cell–matrix traction forces

“…Focal adhesions have been observed to disappear underneath cell-cell contacts (31,52), but this effect may depend on substrate stiffness (29) and the extent of cell spreading (53). Recent work has also suggested that forces transmitted through focal adhesions can modulate intercellular forces (25,29), which in turn can modulate intercellular-junction assembly and disassembly (15).…”

“…We and others have shown that epithelial cell clusters with strong cell-cell adhesions exhibit coordinated mechanical behavior over length scales much larger than a single cell (24)(25)(26)(27). Several studies have implicated cross talk between cell-ECM and cell-cell adhesions (28,29) that can be modulated by actomyosin contractility (30). Recent data suggest that integrinmediated adhesions can modulate the composition (31,32) and tension (25, 33, 34) of cell-cell junctions.…”

Mechanical signaling coordinates the embryonic heartbeat

“…We treat CMs as elastic inclusions embedded in the ECM, in accord with recent experiments of CMs embedded in 3D hydrogels (20). We ignore direct cell-cell mechanical coupling; experimental evidence indicates that stresses are transmitted primarily through cell-matrix adhesions rather than cell-cell contacts during development (21), likely due to the prevalence of cell-junction remodeling. In addition, collagenase treatment indicates that ECM is the primary component of tissue structural integrity (10).…”

Engineering Cardiac Cell JunctionsIn Vitroto Study the Intercalated Disc

“…To better understand the spatiotemporal co-development of ID structures with the cytoskeleton, we cultured pairs of cardiac myocytes on micropatterned islands of fi bronectin on compliant polyacrylamide gels with physiological elastic moduli ( Figure 1A). With this technique, we could independently modulate tissue geometry and extracelluar matrix elasticity and monitor cytoskeletal maturation, force generation, and cell -cell junction formation over time in culture in a controlled setting (McCain et al, 2012a). At early time points in culture, myocytes were contracting but not well-coupled, as contractile forces were transmitted through focal adhesions to the extracellular matrix near the cell -cell interface.…”