Phenotype of podoplanin-positive cells in the fibrotic tissue.
Thin cardiac sections were indirectly immunolabeled with antibodies that recognize podoplanin (red) and either fibronectin and vimentin (A; green and grey, respectively), VEGFR-2 and CD34 (B and C; green and grey, respectively), or α-SMA (D; grey). Nuclei, blue. Time after MI is indicated. Areas in rectangles are shown at higher magnifications in the adjacent images for each color channel. Note that vimentin (A) or α-SMA (D) labeling is rarely detectable in podoplanin-expressing cells (examples are pointed by yellow arrowheads). In B and C, the podoplanin-presenting cells show minimal VEGFR-2 labeling. At 2 days after MI, the podoplanin-bearing cells mostly do not co-stain with CD34 (exemplified by yellow arrowheads). Starting 2 weeks after MI, the CD34 staining is present in irregular capillary-like structures (examples are indicated by white arrows). In C, quantitative image analysis demonstrating changes in the podoplanin co-labeling with CD34 at indicated times after MI is included in the graph (lower panel). Data represent mean and SD of the co-localization coefficient; n = 5–6 image fields per group. By one-way ANOVA, *P < 0.02 for 2 weeks vs. 2 days; **P < 0.0001 for 1 month vs. 2 days; ns, not-significant for 1 month vs. 2 weeks.