Effect of Lyso-phosphatidylcholine and Schnurri-3 on Osteogenic Transdifferentiation of Vascular Smooth Muscle Cells to Calcifying Vascular Cells in 3D Culture

Background: In vitro cell culture is a widely used technique for investigating a range of processes such as stem cell behavior, regenerative medicine, tissue engineering, and drug discovery. Conventional cell culture is performed in Petri dishes or flasks where cells typically attach to a flat glass or plastic surface as a cell monolayer. However, 2D cell monolayers do not provide a satisfactory representation of in vivo conditions. A 3D culture could be a much better system for representing the conditions that prevail in vivo. Methods and results: To simulate 3D conditions, vascular smooth muscle cells (VSMCs) were loaded with gold-polyvmer-iron oxide hydrogel, enabling levitation of the cells by using spatially varying magnetic fields. These magnetically levitated 3D cultures appeared as freely suspended, clustered cells which proliferated 3-4 times faster than cells in conventional 2D cultures. When the levitated cells were treated with 10 nM lysophosphatidylcholine (LPC), for 3 days, cell clusters exhibited translucent extensions/rods 60-80 mu m wide and 200-250 mu m long. When 0.5 mu g/mu l Schnurri-3 was added to the culture containing LPC, these extensions were smaller or absent. When excited with 590-650 nm light, these extensions emitted intrinsic fluorescence at >667 nm. When the 3D cultures were treated with a fluorescent probe specific for calcium hydroxyapatite (FITC-HABP-19), the cell extensions/rods emitted intensely at 518 nm, the lambda(max) for FITC emission. Pellets of cells treated with LPC were more enriched in calcium, phosphate, and glycosaminoglycans than cells treated with LPC and Schnurri-3. Conclusions: In 3D cultures, VSMCs grow more rapidly and form larger calcification clusters than cells in 2D cultures. Transdifferentiation of VSMC into calcifying vascular cells is enhanced by LPC and attenuated by Schnurri-3. General significance: The formation of calcified structures in 3D VSMC cultures suggests that similar structures may be formed in vivo. (C) 2013 Elsevier B.V. All rights reserved.