(341b) Elevated Viscosity Drives Enhanced Cancer Cell Migration Via Distinct Traction Force Patterns and YAP Signaling

The tumor microenvironment is highly complex, and unraveling its intricacies is crucial for understanding cancer metastasis. Upon dissociation from primary tumors, cancer cells encounter diverse mechanical stimuli, including extracellular matrix stiffness, spatial confinement, and fluid viscosity. Elevated fluid viscosity within tumors, resulting from extreme molecular crowding and extracellular matrix degradation, significantly influences cancer cell behavior. In this study, we investigated the combined effects of physiologically relevant substrate stiffness and elevated fluid viscosity on triple-negative breast cancer cells, using MDA-MB-231 cells as a model. We employed state-of-the-art 3D Traction Force Microscopy (3D TFM) within compliant, confining microchannels to explore the mechanistic underpinnings of cell migration in response to high viscosity conditions. This innovative approach utilized a platform termed Hydrogel-Encapsulated Microchannel Array (HEMICA), which incorporates a novel method to fabricate polyacrylamide-based microfluidic devices with tunable stiffness.

Consistent with previously reported impacts of viscosity, MDA-MB-231 cells cultured on elastic gels (8 kPa) under elevated viscosity conditions (8 cP) for two days exhibited significantly enhanced migratory behavior within confined microchannels composed of either soft polyacrylamide gel (HEMICA) or stiff PDMS, compared to cells cultured under basal viscosity conditions (0.77 cP). To delineate the mechanisms underlying this increased migratory capacity, we performed comprehensive 2D and 3D TFM analyses. Our 3D TFM experiments within compliant microchannels revealed that most cellular traction forces were oriented normally outward from the cell surface. This finding markedly contrasts with observations from 2D substrates, where traction forces are predominantly contractile and localized at cell peripheries. Furthermore, these normal-directed tractions were dispersed along the entire cell body rather than restricted to polar regions associated with cellular protrusions. Quantification of contractile traction forces on 2D substrates showed that acute exposure to high viscosity conditions induced a substantial increase in traction magnitude relative to controls. Additionally, we elucidated distinct patterns of normal and contractile traction forces resulting from viscosity exposure within 3D confinement environments. Given the known relationship between higher traction forces and the transcription factor Yes-Associated Protein 1 (YAP), we examined its localization in cells cultured on 2D substrates. Analysis of nuclear-to-cytoplasmic ratios revealed increased nuclear accumulation of YAP under high-viscosity conditions, aligning closely with observed traction force patterns and enhanced migratory behavior.

In conclusion, our study demonstrates that elevated fluid viscosity within the tumor microenvironment induces significant changes in cellular mechanics, fostering enhanced migration capabilities through distinct traction force profiles and increased nuclear accumulation of YAP. These findings underscore the importance of mechanical cues in driving cancer cell aggressiveness and suggest that targeting biomechanical interactions could offer promising avenues for therapeutic interventions aimed at mitigating metastasis.