Characterization of Human Chondrocytes Exposed to Simulated Microgravity

Abstract

Background: Tissue engineering is a strategy of cartilage regeneration, but scaffolds, required for 3D growth of chondrocytes, are still a problem. Methods: Searching for possibilities to improve scaffold-free engineering of cartilage, we characterized human chondrocytes incubated on a random positioning machine (RPM) to simulate microgravity (µg). Results: When cultured in simulated µg, human chondrocytes start forming 3D cell assemblies within 5 days. After 24h, we could not detect caspase-3, Fas, p53 or Bcl-2 proteins in these cells, Annexin V flow cytometry, however, revealed 18% of apoptotic chondrocytes in 1g cultures but only 10% on the RPM. Both rates of apoptosis were not changed, when vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF) was added. 24 h, simulated microgravity also had significantly decreased collagen type I and X, but did not change collagen type IV and laminin, while collagen type II, chondroitin sulfate and aggrecan were elevated as compared with 1g controls. The production of collagen type II/X, chondroitin sulfate and aggrecan was modified, when external bFGF or VEGF had been applied. Conclusion: Chondrocytes exposed to simulated µg seem to change their extracellular matrix production behavior, while they rearrange their cytoskeletal proteins prior to forming 3D aggregates.