Chondrogenic differentiation is not inhibited by Fe-Pro labeling. Both unlabeled (A) and Fe-Pro-labeled (B) MSC pellets exhibited similar distributions of Alcian blue-stained glycosaminoglycans. Inset shows magnified view (× 100). Staining with collagen X (normally present only in hypertrophic chondrocytes, fetal cartilage, cartilage at growth plates of long bones, and neoplasms arising from chondrocytes) followed by Prussian Blue (PB) shows positive collagen X expression both in unlabeled (C) and Fe-Pro-labeled (D) MSC pellets.4 Magnified view shows collagen X expression in iron-positive cells (E, multiple arrows). Note the lack of Alcian blue stain and expression of collagen X in the cells around extracellular iron oxide complexes (arrow in B, arrow in D). The bars on A-D represent 100 μm and the bar on E represents 20 μm. Photomicrographs were visualized under a Zeiss Axioplan Imaging II microscope (Carl Zeiss, Oberkochen, Germany) equipped with 10×/0.50 (A-D) or 100×/1.30 (A inset, B inset, E) oil immersion objective lenses (Carl Zeiss). Images were acquired with Axiovision 4 software (Carl Zeiss) and processed with Adobe Photoshop 7.0 software (Adobe, San Jose, CA).
