MODULATION OF CARDIAC MYOCYTE PHENOTYPE IN-VITRO BY THE COMPOSITION AND ORIENTATION OF THE EXTRACELLULAR-MATRIX

Cellular phenotype is the result of a dynamic interaction between a ce ll's intrinsic genetic program and the morphogenetic signals that serv e to modulate the extent to which that program is expressed. In the pr esent study we have examined how morphogenetic information might be st ored in the extracellular matrix (ECM) and communicated to the neonata l heart cell (NHC) by the cardiac alpha(1) beta(1) integrin molecule. A thin film of type I collagen (T1C) was prepared with a defined orien tation. This was achieved by applying T1C to the peripheral edge of a 100 mm culture dish. The T1C was then drawn across the surface of the dish in a continuous stroke with a sterile cell scraper and allowed to polymerize. When NHCs were cultured on this substrate, they spread, a s a population, along a common axis in parallel with the gel lattice a nd expressed an in vivo-like phenotype. Individual NHCs displayed an e longated, rod-like shape and disclosed parallel arrays of myofibrils. These phenotypic characteristics were maintained for at least 4 weeks in primary culture. The evolution of this tissue-like organizational p attern was dependant upon specific interactions between the NHCs and t he collagen-based matrix that were mediated by the cardiac alpha(1) be ta(1) integrin complex. This conclusion was supported by a variety of experimental results. Altering the tertiary structure of the matrix or blocking the extracellular domains of either the cardiac alpha(1) or beta(1) integrin chain inhibited the expression of the tissue-like pat tern of organization. Neither cell-to-cell contact or contractile func tion were necessary to induce the formation of the rod-like cell shape . However, beating activity was necessary for the assembly of a well-d ifferentiated myofibrillar apparatus. These data suggest that the card iac alpha(1) beta(1) integrin complex serves to detect and transduce p henotypic information stored within the tertiary structure of the surr ounding matrix. (C) 1994 Wiley-Liss, Inc.