Glaucoma is a devastating neurodegenerative disease, which can lead to vision loss and is associated with irreversible damage to retinal ganglion cells. Although the mechanism of disease onset remains unknown, we have recently demonstrated that the stiffness of the ocular trabecular meshwork (HTM) increases dramatically in human donor eyes with a history of glaucoma. Here we report that polyacrylamide hydrogels, which mimic the compliant conditions of normal and glaucomatous HTM, profoundly modulate cytoskeletal dynamics and the elastic modulus of the overlying HTM cells. Substratum compliance also modulates HTM cell response to Latrunculin-B, a cytoskeletal disrupting agent currently in human clinical trials for the treatment of glaucoma. Additionally, we observed a compliance-dependent rebound effect of Latrunculin-B with an unexpected increase in HTM cell elastic modulus being observed upon withdrawal of the drug. The results predict that cytoskeletal disrupting drugs may be more potent in advanced stages of glaucoma.
The influence of nucleus shape and orientation on the elastic modulus of epithelial cells was investigated with atomic force microscopy. The shape and orientation were controlled by presenting the epithelial cells with anisotropic parallel ridges and grooves of varying pitch at the cell substratum. As the cells oriented to the underlying topography, the volume of the nucleus increased as the pitch of the topography increased from 400 nm to 2000 nm. The increase in nucleus volume was reflected by an increase in the measured elastic modulus of the topographically aligned cells. Significant alterations in the shape of the nucleus, by intimate contact with the topographic ridge and grooves of the underlying cell, were also observed via confocal microscopy, indicating that the nucleus may also act as a direct mechanosensor of substratum topography.
Cardiovascular disease (CVD) remains a leading cause of death both within the United States (US) as well as globally. In 2006 alone, over one-third of all deaths in the US were attributable to CVD. The high prevalence, mortality, morbidity, and socioeconomic impact of CVD has motivated a significant research effort; however, there remain significant knowledge gaps regarding disease onset and progression as well as pressing needs for improved therapeutic approaches. One critical area of research that has received limited attention is the role of biophysical cues on the modulation of endothelial cell behaviors; specifically, the impact of local compliance, or the stiffness, of the surrounding vascular endothelial extracellular matrix. In this study, the impact of substratum compliance on the modulation of cell behaviors of several human primary endothelial cell types, representing different anatomic sites and differentiation states in vivo, were investigated. Substrates used within our studies span the range of compliance that has been reported for the vascular endothelial basement membrane. Differences in substratum compliance had a profound impact on cell attachment, spreading, elongation, proliferation, and migration. In addition, each cell population responded differentially to changes in substratum compliance, documenting endothelial heterogeneity in the response to biophysical cues. These results demonstrate the importance of incorporating substratum compliance in the design of in vitro experiments as well as future prosthetic design. Alterations in vascular substratum compliance directly influence endothelial cell behavior and may participate in the onset and/or progression of CVDs.
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