THE BIOPHYSICAL PROPERTIES OF MACROMOLECULAR CROWDERS AND THEIR UPTAKE, DISTRIBUTION AND FATE IN CELLS

Abstract

The proliferation and differentiation of mesenchymal stem cells is significantly enhanced under macromolecular crowding. Crowders increase collagen deposition in the extracellular matrix. The diffusion of probes is shown to depend on the microviscosity of Ficoll solutions rather than bulk viscosity. Probes undergo anomalous diffusion in these solutions. The rate of actin polymerisation increases with Ficoll concentration, despite the large increase in bulk viscosity. As a crowder, polyvinylpyrrolidone (PVP) causes more collagen deposition than Ficoll. Ficoll is shown to be spontaneously taken up by cells, dismissing the long-held assumption that it is an inert crowder. The mechanism of uptake is micropinocytosis and occurs rapidly. Ficoll colocalises with mitochondria, a surprising and novel finding. These experiments led to subsequent experiments that proved Ficoll is metabolised by cells, thus providing an alternative explanation for its positive effects on stem cells.