Growth, cell cycle progression, and morphology of 3T3 cells following fibroin microsphere ingestion

Maintenance of viability and proliferation of 3T3 cell aggregates incorporating fibroin microspheres into cultures

This study investigated whether micron-sized microspheres can be used as dispersed scaffolds where anchorage-dependent cells can proliferate and survive in suspension culture. Aggregates of murine 3T3 cells in a non-adherent plate cultured remained viable for more than 2 weeks by the presence of 0.5 mg/ml fibroin microspheres. A nucleoside incorporation assay confirmed the proliferation of 3T3 cells in the aggregates only when cultured with microspheres. Under these conditions, the glucose consumption rate of 3T3 cells increased to 66.5 nmol day^-1 cell^-1. Histological analysis demonstrated that the intercellular space of cell aggregates was larger in cultures supplemented with 0.5 mg/ml microspheres than in non-supplemented cultures. The cell aggregates with microspheres also exhibited a reduced arrest in G1 phase. Transmission electron microscopy verified the presence of microspheres in the space between cells in aggregates. Fibroin microspheres maintained the viability and proliferability of 3T3 cells cultured under non-adherent conditions and thus can be used to develop viable suspensions of anchorage-dependent cells.

Cellular uptake and fate of fibroin microspheres loaded with randomly fragmented DNA in 3T3 cells

Purified fibroin protein can be obtained in large quantities from silk fibers and processed to form microscopic particles as delivery vehicles for therapeutic agents. In this study, we demonstrated that fibroin microspheres were taken up by 3T3 cells, localized in the nonlysosomal compartment, and secreted from the cytoplasm after medium replenishment. DNA-loaded microspheres were taken up by >95% of 3T3 cells. DNA cargo had no influence on the intracellular trafficking of microspheres, while fluorescently labeled cargo DNA was observed in the lysosomal compartment and in the microspheres. These results indicate that fibroin microspheres can travel through 3T3 cells without making any contact with the lysosomal compartments. The amount of DNA loaded in the microspheres taken up by 3T3 cells was estimated up to 831.0 pg/cell. Thus, fibroin microspheres can deliver a large amount of randomly fragmented DNA (<10 kb) into the cytoplasmic compartment of 3T3 cells.