Abstract
Recapitulating tissue elasticity can direct mesenchymal stromal cell (MSC) differentiation; however, it is unclear how substrate elasticity affects MSC metabolism. It is hypothesized MSCs subjected to stiffnesses, atypical of standard tissue culture plastic, display altered metabolic phenotypes during differentiation. In this study, such alterations in MSC metabolic profiles, based on the fluorescence lifetime of NAD(P)H, a critical co-factor in energy production, were monitored using Fluorescence lifetime imaging microscopy (FLIM) as an evaluation tool. Polyacrylamide substrates with varying stiffnesses were fabricated to model the native elasticity of cartilage and bone. MSCs cultured on these substrates exhibited potent alterations in their metabolic status over a 14-day period that were detectable as early as day 3 using FLIM. Overall, soft substrates induced a more glycolytic response after 10 days of culture that persisted at day 14 (as measured by protein-bound NAD(P)H contributions to the lifetime decay). Similarly, by day 10; MSCs on intermediate-stiffness substrates favoured glycolysis. MSCs on stiffer substrates initially displayed a glycolytic phenotype followed by a transition to oxidative phosphorylation by day 10. Staining for mineralised nodules and glycosaminoglycans verified MSCs on stiffer substrates differentiating towards an osteogenic lineage, while MSCs on intermediate substrates showed similarities with differentiated chondrocytes. Overall, it can be concluded that matrix stiffness can induce metabolic perturbations in MSCs for up to 14 days. From this research, ideal culture conditions in which the metabolics of MSCs could be manipulated to promote maximum potency could potentially be defined in the future.
