<i>Tcf21</i> expressing cells are found in atherosclerotic lesions.

<p><i>Tcf21</i>^{<i>lacZ/+</i>}, <i>ApoE</i>^<i>-/-</i> mice were fed HFD from 4 weeks of age for 4, 8, 12, or 20 weeks, proximal aortic tissues were harvested, and <i>Tcf21</i> gene expression evaluated by Xgal staining to visualize β-galactosidase activity, and sections were counterstained with nuclear fast red to visualize disease lesion architecture. For each timepoint, boxes in low-power images at left indicate regions examined at high power in panels to the right. At 4 weeks of HFD there was no expression in the lesions although clusters of <i>lacZ</i> expressing cells identified in the media in regions below the disease lesions (arrows). At the 8-week timepoint cells with β-galactosidase activity were seen extending from the media to the luminal surface of the lesion (black arrows) in the vicinity of the forming fibrous cap (purple arrows). By 12 weeks of HFD there was extensive labeling of cells in lesions, with the appearance of β-galactosidase positive cells in the vicinity of the fibrous cap (purple arrows). Also, there was extensive staining of cells in areas of disrupted medial structure (white arrows). After 20 weeks of HFD, <i>Tcf21</i>-expressing cells had decreased in the lesions but formed a narrow band of cells associated with the fibrous cap (purple arrows).