Adipogenic differentiation was inhibited by downregulation of PPAR gamma signaling pathway in aging tendon stem/progenitor cells

Background Tendon stem/progenitor cells (TSPCs) play a vital role in tendon repair and regeneration. Previously we found more adipocytes accumulated in the patellar tendon injury sites in aging rats compared with the young ones, of which the mechanism is still unknown. Here, we want to identify whether erroneous differentiation of TSPCs by aging accounts for the adipocyte accumulation. Methods TSPCs from young and aging rats were isolated and propagated. Both young and aging TSPCs were induced to differentiate into adipocytes, and Oil red O staining, quantitative real-time polymerase chain reaction (qRT-PCR), western-blot and immunofluorescent staining were used to evaluate the capability of TSPCs. RNA sequencing was utilized to screen out different genes and signaling pathways related to adipogenesis between young and aging TSPCs. Results The Oil red O staining showed there were more adipocytes formed in young TSPCs. Besides, adipogenic markers perilipin, peroxisome proliferator-activated receptor gamma (PPAR gamma), CCAAT/enhancer-binding proteins alpha (C/EBP alpha) and Fatty acid-binding protein 4 (FABP4) were elevated both at gene and protein level. PPAR gamma signaling pathway was selected as our target via RNA sequencing. After adding the signaling activators, Rosiglitazone maleate (RM), inhibited adipogenesis of aging TSCs was reversed. Conclusions In conclusion, aging inhibited adipogenesis of TSPCs by down-regulating PPAR gamma signaling. It is not likely that the adipocyte accumulation in aging tendon during repair was due to the aging of TSPCs. This may provide new targets for curing aging tendon injuries or tendinopathies.