Quantification of local matrix deposition during muscle stem cell activation using engineered hydrogels
Adult stem cells occupy a niche that contributes to their function but how stem cells remodel their microenvironment remains an open-ended question. Herein, biomaterials-based systems and metabolic labeling were utilized to evaluate how skeletal muscle stem cells and mesenchymal progenitors (fibro-adipogenic progenitors) deposit and remodel extracellular matrix. Differences in matrix production of muscle stem cells on substrates with different stiffness were then evaluated and linked with stem cell activation state. Reducing the ability to deposit new matrix attenuated function and mimicked impairments observed from muscle stem cells isolated in old age. Rescuing nascent protein deposition in old age stem cells with therapeutic supplementation rescued extracellular protein deposition and highlight how important this feature of niche remodeling is towards maintaining healthy stem cell function. Overall design: To determine mechanisms related to the impaired nascent matrix, MuSCs from young and old mice were isolated via magnetic activated cell sorting and seeded on the norbornene-hyaluronic acid hydrogels at a cell density of 7500 cells/ cm2.   After 5 days on culture, cells were trypsinized and processed for bulk RNA-seq .