Platelet-rich plasma ameliorates cartilage degradation in rat models of osteoarthritis via the OPG/RANKL/RANK system.

Introduction: Osteoarthritis (OA) is one of the most common degenerative joint diseases in the elderly, which is featured by the degradation of articular cartilage. Recently, platelet-rich plasma (PRP) injection into the affected joint has become one biological therapy for OA treatment. The OPG/RANKL/ RANK signalling has been reported to mediate OA progression. Our study aimed to confirm whether PRP injection retards OA development through the regulation of the OPG/RANKL/RANK system.

Material and methods: The OA rat models were induced by medial menisci resection combined with anterior cruciate ligament transection. Four weeks after surgery, OA-induced rats received intra- articular injection with 50 μL PRP once a week for 6 weeks. Rats were euthanised one week after the 6th injection. Rat knee joints were subjected to histopathological examination by haematoxylin- eosin (H&E) and safranin O staining. Osteoprotegerin (OPG), receptor activator of nuclear factor kappa B (RANK), and RANK ligand (RANKL) in the articular cartilage of rats were tested through immunofluorescence staining and western blotting. Serum interleukin-1β (IL-1β) and interleukin-6 (IL-6) levels were measured by enzyme-linked immunosorbent assay (ELISA). Matrix metalloproteinase- 13 (MMP-13), aggrecan, collagen α, IL-1β, IL-6, tumour necrosis factor-alpha (TNF-α), and nuclear factor kappa-B (NF-κB) mRNA and protein expression in rat articular cartilage were examined by real-time quantitative polymerase chain reaction (RT-qPCR) and western blotting, respectively.

Results: Intra-articular injections of PRP significantly improved the structural integrity of the articular cartilage and enhanced the synthesis of glycosaminoglycans. PRP reduced MMP-13 protein level but increased aggrecan and collagen α protein levels in articular cartilage of OA rats. OA-induced increase in serum IL-1β, IL-6, and TNF-α concentrations as well as increased MMP-13, and decreased collagen II mRNA levels were reversed by the administration of PRP. OA increased IL-1β, TNF-α, and NF-κB mRNA expression in rat articular cartilage whereas PRP administration ameliorated these changes. Moreover, in the articular tissue of OA-induced rats the increased OPG protein level was further elevated by PRP injections whereas the protein level of RANK did not change. The increase in the protein level of RANKL in OA-induced articular tissue was offset by PRP administration. PRP elevated OPG mRNA expression and the OPG/RANKL mRNA ratio, but reduced RANKL mRNA expression and the RANKL/RANK mRNA ratio in the articular tissue of OA-induced rats.

Conclusions: PRP mitigates cartilage degradation and inflammation in experimental knee OA by regulating the OPG/RANKL/RANK signalling system.