PECAM1 and obesity due to melanocortin 4 receptor deficiency: To ascertain its impact on FAP biology in vitro, we isolated FAPs with fluorescence-activated cell sorting (FACS) using an established surface marker profile (Sca-1+, CD31–, CD45–, integrin α7–) (28, 29), then applied THBS1 at a concentration observed in the plasma of humans with obesity (44).