PECAM1 and peripheral arterial disease: Since we previously showed that IL-21R was upregulated in the endothelial cells under ischemia in both mouse and human PAD muscle [10,11], we isolated CD31-expressing cells from ischemic hind-limb muscles of Il21r−/− or wild-type (WT) mice, as described, [10] and measured the expression level of miR-let7a-2, miR-300, miR-30b, miR-503 and miR-3572.