Strain and strain rate mechanotransduction in human vascular smooth muscle cells

Vascular smooth muscle cells exist in a dynamic mechanical environment and are able to independently sense and respond to mechanical stimuli. Mechanotransduction is an important event in many tissues and is a deciding factor in the control of smooth muscle function. Still in debate, however, is which components of a physical force are sensed by the cell. The viscoelastic nature of biological materials creates the possibility that strain rate may influence the cellular response to stretch. The following dissertation investigated mechanotransduction of strain rate and amplitude in aligned human vascular smooth muscle cells.; To best represent in vivo smooth muscle tissue in a controlled mechanical environment, a procedure was developed to align smooth muscle cells in the direction of an applied uniaxial stretch. This procedure generated two dimensional cultures of human smooth muscle cells with in vivo-like architecture and allowed the investigation into the importance of cell alignment on strain rate mechanotransduction.; ERK1/2 is important to both the short term contractile behavior of smooth muscle and its long term proliferative or differentiated phenotype. Phosphorylation of ERK1/2 has also become a stereotypical marker of mechanical stimulation. Strain rate has a profound affect on changes in stretch induced changes in ERK1/2 phosphorylation. Sub-physiologic strain rate induced dephosphorylation while physiologic and super-physiologic rates elicited increased phosphorylation at all strain amplitudes examined.; Dephosphorylation at the slow strain rate was dependent on cell orientation matching the strain field. The activity of GTP binding proteins is required for ERK1/2 phosphorylation but not dephosphorylation. Apyrase, an ATP and ADP hydrolyzing enzyme, demonstrated a complex affect on stretch regulation of ERK1/2. Stretch induced release of an intracellular protein in a strain rate dependent manner supports the hypothesis that physiologic mechanical stimuli induce changes in plasma membrane integrity. Direct evidence of heterotrimeric and small GTPase activity in mechanotransduction is also presented.