Effects of extracellular matrix compliance on cell morphology and function: Applications to the liver and central nervous system

Mechanical properties of the extracellular matrix change when the balance shifts from a healthy to a pathologic tissue state. The mechanical change can drive cell function in cell types of both the liver and central nervous system. The shear moduli of fibrotic liver and healthy rat brain tissue measured by rheology are mimicked with mechanically controllable polyacrylamide and fibrin gels as cell substrates to model tissue disease states in vitro. A new technique for conjugating proteins to the polyacrylamide gel surface is also described. Astrocytes exhibit compliance-dependent cytoskeletal and focal adhesion reorganization and stellation. Neurons, too, are a mechanosensitive cell-type, but have a lower threshold for mechanical signals than astrocytes. Unlike astrocytes, neurons have fully assembled cytoskeletons and are very adhesive to soft gel. On soft gels, cortical co-cultures are predominantly composed of neurons, while on hard gels, the population is evenly composed of neurons and astrocytes. Focal adhesion kinase (FAK) phosphorylation on soft matrices is also cell-type specific: expression levels of phosphorylated FAK are high in neuron and astrocyte co-cultures on soft materials, but are low in pure astrocyte cultures on soft gels. Finally, there are deficits in synaptogenesis in neurons on soft gels, but restoration is possible with addition of astroglial-conditioned medium (GCM) or the Src-kinase inhibitor, PP2