Validation of specificity of SMC Col15a1 knockout, SMC lineage tracing mice. A: excision of Col15a1 occurs only in presence of tamoxifen and shows nearly complete recombination in SMCs. B: SMC Col15a1 knockout is highly specific to SMC-rich vessels (aorta and carotid). C and D: staining for COL15A1 in advanced lesions from 18 wk Western diet-fed SMC lineage tracing [yellow fluorescent protein (YFP)]+/+ Col15a1wt/wt, apoliprotein E (Apoe)−/− (n = 11) and SMC YFP+/+ Col15a1Δ/Δ, Apoe−/− (n = 13) mice shows a significant reduction of COL15A1 in both the media and lesion of SMC YFP+/+ Col15a1Δ/Δ, Apoe−/− mice. Values represent means ± SE. Scale bars = 100 µm. ‘P value was determined by an unpaired, two-tailed t-test with Welch’s correction; ^P value was determined by Mann-Whitney U-test.