PECAM1 and type 2 diabetes mellitus: In vitro sitagliptin, an inhibitor of Dpp4 used clinically to treat diabetes mellitus type 2, promotes osteogenesis, but does not affect the angiogenesis of either CD45-CD31-Sca1+CD24+ cells or CD45-CD31-Sca1-PDGFRα+ osteochondroprogenitors.