Substrate stress relaxation regulates neural stem cell fate commitment.

Adult neural stem cells (NSCs) reside in the dentate gyrus of the hippocampus, and their capacity to generate neurons and glia plays a role in learning and memory. In addition, neurodegenerative diseases are known to be caused by a loss of neurons and glial cells, resulting in a need to better understand stem cell fate commitment processes. We previously showed that NSC fate commitment toward a neuronal or glial lineage is strongly influenced by extracellular matrix stiffness, a property of elastic materials. However, tissues in vivo are not purely elastic and have varying degrees of viscous character. Relatively little is known about how the viscoelastic properties of the substrate impact NSC fate commitment. Here, we introduce a polyacrylamide-based cell culture platform that incorporates mismatched DNA oligonucleotide-based cross-links as well as covalent cross-links. This platform allows for tunable viscous stress relaxation properties via variation in the number of mismatched base pairs. We find that NSCs exhibit increased astrocytic differentiation as the degree of stress relaxation is increased. Furthermore, culturing NSCs on increasingly stress-relaxing substrates impacts cytoskeletal dynamics by decreasing intracellular actin flow rates and stimulating cyclic activation of the mechanosensitive protein RhoA. Additionally, inhibition of motor-clutch model components such as myosin II and focal adhesion kinase partially or completely reverts cells to lineage distributions observed on elastic substrates. Collectively, our results introduce a unique system for controlling matrix stress relaxation properties and offer insight into how NSCs integrate viscoelastic cues to direct fate commitment.