Age dependence of expression of growth factor receptors in porcine ACL fibroblasts.

Tissue engineering approaches that harness the stimulatory power of platelet-rich plasma have produced encouraging results in anterior cruciate ligament (ACL) repair. However, a number of recent studies have demonstrated age-dependent differences in cellular responses to such an approach. Identifying the reasons for these differences would allow counteracting them and consequently improve outcomes. In this study we hypothesized that these age-related effects are caused by differences in the expression of the receptors for growth factors released from platelet-rich plasma (PRP). Porcine ACL fibroblasts from a predetermined number of animals of different ages were obtained, and mRNA levels of the receptors of platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-beta), fibroblast growth factor (FGF), and vascular endothelial growth factor (VEGF) were determined. Expression levels were compared across age groups (young and adolescent) and regressed on age in days. While no significant difference was seen across groups, the regression analysis showed decreases in receptor expression with increasing age. These differences were statistically significant for TGF-beta receptor 1, FGF receptor, and VEGF receptor 2; and borderline significant for TGF-beta receptor 3 and PDGF receptor. The only receptor that was not associated with age was VEGF receptor 1, a regulator of VEGF receptor 2. These findings suggest that the decrease in growth factor receptor expression as a likely reason for reduced PRP action with increasing age.