Dynamics of Mechanosensitive Neural Stem Cell Differentiation

Stem cell differentiation can be highly sensitive to mechanical inputs from the extracellular matrix (ECM). Identifying temporal windows during which lineage commitment responds to ECM stiffness, and the signals that mediate these decisions, would advance both mechanistic insights and translational efforts. To address these questions, we investigate adult neural stem cell (NSC) fate commitment using an oligonucleotide‐crosslinked ECM platform that for the first time offers dynamic and reversible control of stiffness. “Stiffness pulse” studies in which the ECM was transiently or permanently softened or stiffened at specified initiation times and durations pinpoint a 24‐hour window in which ECM stiffness maximally impacts neurogenic commitment. Overexpression of the transcriptional coactivator Yes‐associated protein (YAP) within this window suppressed neurogenesis, and silencing YAP enhanced it. Moreover, ablating YAP‐β‐catenin interaction rescued neurogenesis. This work reveals that ECM stiffness dictates NSC lineage commitment by signaling via a YAP and β‐catenin interaction during a defined temporal window. Stem Cells 2017;35:497–506 In this study, we have shown that NSCs are maximally sensitive to mechanical inputs from 12–36 hours after the introduction of soluble differentiation cues, and become insensitive to further changes in the elastic modulus of their microenvironment after this window closes. These findings were enabled by further innovation of a polyacrylamide gel whose stiffness can be dynamically and reversibly controlled by addition of DNA oligonucleotides. We subsequently correlated this time window with increased expression of the transcriptional co‐activator YAP, and implicated YAP as the messenger of mechanical cues from the extracellular matrix. Overexpression of YAP specifically during this time window was sufficient to override soft matrix cues and suppress neurogenesis, while silencing of YAP ablated the ability of stiff microenvironments to suppress neurogenesis. However, we observe that YAP does not exhibit mesenchymal‐like changes in nuclear translocation in response to stiffness cues, and we link YAP's capacity to block neuronal differentiation to an inhibitor interaction with β‐catenin. Our data thus support a model where a protein protein‐level interaction between YAP and β‐catenin independent of nuclear translocation is responsible for transducing mechanical cues to NSC differentiation programs. Our study thereby advances our