UC San Diego

The mechanical forces surrounding cells can have far reaching influences on cellular function. In particular, differentiation of stem cells into the cardiovascular lineages can be impacted by numerous environmental factors, including stiffness of surrounding ECM, stretch or strain on cellular attachment, and contraction of the cells themselves. However, the cardiovascular lineage cells themselves induce mechanical forces on their surroundings as well, notably with regards to cardiomyocyte or smooth muscle cell contraction. In combination with induced pluripotent stem cells and the use of genetic modifications, studying the connection of mechanical function to disease risk genetics can be well documented in vitro. In looking into how the cardiovascular 9p21 risk haplotype influences smooth muscle cells, we found iPSC-derived SMCs with homozygous risk (R/R) haplotype were found to have lower cellular adhesion as well as global contractility through spinning disk shear and collagen gel contractility assays, respectively. We then examined how the 9p21 risk haplotype influences endothelial cell function in relation to coronary artery disease. In a static environment, iPSC-derived ECs of R/R haplotype exhibited greater permeability and showed greater reactive oxygen species generation compared to knockout (KO) and non-risk (N/N) haplotypes. In the presence of inflammatory cytokine TNFα, EC monolayers showed greater permeability independent of haplotype. However when grown in a 3D microvessel environment with pathological wall shear stress levels, R/R ECs showed greater permeability and vessel wall detachment. The genomic expression of these R/R ECs also displayed decreased EC adhesion genes and ECM genes but also a reversal into greater CAD associated transcriptomic expression compared to static conditions as established by a subset of previously identified CAD risk genes. These data suggests the presence of pathological shear stress may regulate the 9p21.3 non-coding risk loci in the context of CAD. While the research detailed here applies to cardiovascular disease in particular, the concepts behind cellular mechanics and their surroundings are far reaching, applying to other diseases and homeostatic conditions. The use of 3D microfluidic vessel formation and application of in vitro fluidic shear modeling is a tool that can hopefully be applied to further human disease ailments and research in the future.