Effects of Oscillatory Shear Stress on Early Differentiation and Mechanotransduction
The efficacy of using pluripotent embryonic stem cells (ESCs) as a potential source for cell-based therapies depends on the ability to direct differentiation. Differentiation can be achieved through biochemical factors, mechanical forces, electrical stimulation, and cell-cell binding. The physical connection of the extracellular matrix and the nucleus achieved by actin filaments facilitates mechanotransduction. In this way, mechanical cues can alter gene transcription at a faster rate than propagation of biochemical signaling. While the application of steady laminar shear stress (SLSS) in 2D culture has been shown to promote mesoderm differentiation, the effect of oscillatory shear stress (OSS) on early differentiation has not been characterized. Here, a method for applying both SLSS and OSS to differentiating ESCs was developed and used to explore the reliance of cell response to flow profile. ESCs seeded on collagen-coated surfaces will experience a magnitude of 5 dynes/cm2 shear stress. Signal transduction through the mechanosensitive Hippo pathway and preliminary differentiation will be studied after the application of OSS. Results will be compared to both SLSS samples and static controls. Results show that OSS has a greater affect of the Hippo pathway in comparison to SLSS, and OSS causes the disruption of cell polarity as seen by the down-regulation of polarity genes that serve to regulate the Hippo pathway. Both OSS and SLSS consistently induced the same trends in mesodermal and cytoskeletal gene expression. It is unclear whether the heterogeneity of cell population used in this study suppresses the differential between OSS and SLSS in markers of early gene lineage specification. Further understanding of force-mediated stem cell differentiation can be established by using the same approach with different shear stress flow profiles.