Navigating the Gradient: Melanoma Cell Durotaxis on Gradient Stiffness Substrates

Abstract

The migratory behavior of A2058 human metastatic melanoma cells is investigated on substrates with a gradient in their mechanical stiffness, a process known as durotaxis. New methods were developed to fabricate hydrogel substrates with a gradient in stiffness using a bio-mimetic collagen protein to ensure physiological relevance. The impact of suppressing the protein FMNL2, a protein relevant to melanoma cell motility, was also studied. On isotropic substrates, A2058 cells underwent pronounced changes in their morphology and motility with increasing stiffness. They adopted more elongated shapes as substrate stiffness increased, and their motility decreased as well. The cells displayed a biphasic relationship with stiffness, as an optimal substrate modulus was determined for their motion. The FMNL2 knockdown cells showed similar behavior, but they were continuously more elongated and less motile than the control cells. On the gradient stiffness substrates, A2058 cells displayed a biphasic durotactic behavior. In soft regions (1-15kPa), the cells underwent positive durotaxis, migrating towards a stiffer region, while in stiff regions (≥ 25kPa), they underwent negative durotaxis towards soft regions. Adurotactic motion was noticed between the soft and stiff regions. The FMNL2 knockdown cells showed noticeable decreases in their motility however, they still underwent durotaxis, suggesting that FMNL2 does not impact the mechanosensing abilities of A2058 cells. We then systematically studied the impact of altering the gradient strength of the substrates using new analytical techniques, and increasing gradient strength enhanced durotactic behavior. Overall, we show that local stiffness, within a physiologically relevant range, can have a dramatic impact on the durotactic behavior of A2058 skin cancer cells.