Mechanotransduction of matrix remodeling-directed lineage specification*

Cells build their microenvironments by producing and depositing the extracellular matrix (ECM). Advances in biomaterial design have revealed profound roles of predefined matrix properties in directing various biological processes. However, the relationship between nascent matrix production and preexisting matrix properties in the microenvironment remains generally unclear. Fundamentally, it is unknown how cells make a decision to produce new matrix molecules, and how this process directs cellular functions. To address this question, we leveraged a droplet-based microfluidic approach to deposit a predefined amount of minimal soft hydrogel matrix with an integrin adhesion ligand around single cells. Remarkably, mesenchymal stem cells (MSCs) deposit more nascent proteins when they are surrounded by a smaller predefined amount of minimal matrix. This occurs due to increased cell volume expansion and membrane tension, followed by activation of a transcriptional program that leads to synthesis of matrix molecules. In contrast, this program is not activated with increased matrix rigidity where membrane tension is increased without cell volume expansion. This program is essential to promote osteogenic differentiation of MSCs over adipogenic lineage. Together, our work reveals a mechanism where stem cells sense the preexisting amount of their surrounding matrix, and build a new one to direct lineage specification.