Mechanical stress induced cellular orientation and phenotypic modulation of 3-D cultured smooth muscle cells

The effect of periodic stretch on cellular orientation and intracellular ultrastructure of three-dimensionally (3-D) cultured arterial smooth muscle cells (SMCs) was investigated. Ring shaped hybrid tissues were prepared by thermal gelation of a mixed solution of Type I collagen and SMCs derived from bovine aorta. The gels were subjected to three modes of stress loading: floated (control), stretched isometrically (static stress), and periodically stretched and recoiled with 10% amplitude at 60 rpm frequency (dynamic stress). After 4 weeks of stress loading, the gels were morphologically investigated with a light microscope and a transmission electron microscope (TEM). Irrespective of static or dynamic stress loading, SMCs in stress loaded gels exhibited an elongated bipolar spindle shape and were oriented parallel to the direction of stretch, whereas those in control gels were polygonal shaped and randomly oriented. TEM observation showed that SMCs in control and static stress loaded gels were intracellularly filled with organelles, such as rough endoplasmic reticulum, free ribosomes, Golgi complexes, and mitochondria, indicating that the cells were of the synthetic phenotype. On the other hand, SMCs in dynamic stress loaded gels tended to have increased contractile apparatus, such as myofilaments, dense bodies, and basement membranes, suggesting that periodic stretch plays an important role in phenotypic modulation of SMCs from the synthetic to the contractile state, as well as cellular orientation.