Cabaud Award Winner: Platelet rich plasma activates pro-inflammatory signaling pathways and induces oxidative stress in tendon fibroblasts

BACKGROUND: Tendon disorders are among the most common musculoskeletal conditions in active patients. Platelet rich plasma (PRP) has been used in the treatment of tendon disorders, but little is known as to the mechanisms by which PRP acts. PRP contains numerous different growth factors and cytokines which activate various cellular signaling cascades, but it has been difficult to determine precisely which signaling pathways and cellular responses are activated following PRP treatment. Additionally, macrophages are important in modulating tendon regeneration, but the influence of PRP on determining whether macrophages assume a proinflammatory or antiinflammatory phenotype remains unknown. Our objectives were to use genome wide expression profiling, bioinformatics and protein analysis to determine the cellular pathways activated in fibroblasts treated with PRP, and to also evaluate the effect of PRP on macrophage polarization. METHODS: Tendon fibroblasts or macrophages from rats were cultured and treated with either platelet poor plasma (PPP) or PRP. RNA or protein was isolated from cells and analyzed using microarrays, qPCR, immunoblot or bioinformatics techniques. RESULTS: Bioinformatics analysis determined that the two signaling pathways predicted to be activated by PRP were the TNFα and NFκB pathways. PRP also downregulated several ECM genes, and induced the expression of autophagy related genes and reactive oxygen species (ROS) genes, as well as markers of protein oxidation in tendon fibroblasts. PRP failed to have a major impact on markers of macrophage polarization. CONCLUSIONS: PRP induces an inflammatory response in tendon fibroblasts which leads to the formation of ROS and activation of oxidative stress pathways. PRP does not appear to significantly modulate macrophage polarization. CLINICAL RELEVANCE: PRP might act by inducing a transient inflammatory event which could then trigger a tissue regeneration response.