PECAM1 and diabetes mellitus: Immunofluorescence co-staining for Cldn5 and the endothelial marker CD31 further illustrated a significant increase in the ratio of Cldn5-stained TJs to CD31-stained endothelium in MSC-treated DM mice compared to untreated DM mice (Figure 5F,G), indicating a recovery of TJ density and structural complexity in DM mice following MSC transplantation.