INTRODUCTION: Platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs) serve as two of the most popular potential therapies to enhance cartilage regeneration. Platelets contain alpha granules that house a plethora of growth factors, cytokines, and other molecules that may potentiate tissue healing. Some studies posit that MSCs exert regenerative effects via paracrine signaling [1] which may be mediated by exosomes. Defined as extracellular vesicles released from the fusion of a cytosolic multivesicular body with the cell membrane, exosomes have been implicated in intracellular communication and molecular transport [2]. Early evidence suggests that MSC-derived exosomes possess chondroprotective and anti-inflammatory properties [3]. Similarly, PRP has been shown to increase chondrocyte proliferation and gene expression indicative of extracellular matrix (ECM) production [4]. However, no studies have examined the concomitant effects of PRP and MSC-derived exosomes on chondrocyte gene expression in both a neutral and inflammatory environment. It was hypothesized that chondrocytes cultured in a combination of PRP and exosomes would demonstrate enhanced gene expression suggestive of ECM synthesis and decreased inflammation than chondrocytes grown with PRP or exosomes in isolation.METHODS: Articular chondrocytes were harvested from articular surfaces of bovine ankle joints and cultured in DMEM-F12 medium with 10% fetal bovine serum (FBS) and 1% antibiotic-antimycotic (AA) solution. MSCs were isolated from the bone marrow of Sprague-Dawley rats and cultured in low-glucose DMEM medium with 15% FBS and 1% AA. Both cell lines were incubated with 5% CO2 at 37u00b0C. PRP was obtained from one healthy donor using a Regen PRP kit. Following a previously published protocol [5], exosomes were obtained from MSCs as a 100K pellet. Chondrocytes were seeded at 50,000 cells/well into 24-well plates. They were partitioned into one control (media only) and five experimental conditions: exosomes alone (Exo), 1% unactivated PRP (1u), 5u, combined exosomes and 1% uPRP (Exo1), and Exo5. Exosomes were added to the appropriate treatment groups at a concentration of 10 u03bcg/ml. All conditions were further allocated into one of two environments: with or without IL-1u03b2 (10 ng/ml) to simulate an osteoarthritic or neutral environment respectively. Following 1 and 3 days, RNA was harvested, isolated, and reverse transcribed into cDNA. Quantitative RT-PCR was then performed (n = 3 per condition), using glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as the endogenous control, for the following target genes: aggrecan (ACAN), sex-determining region Y box 9 (SOX9), alpha-1 chain of type I collagen (Col1), alpha-1 chain of type II collagen (Col2), and matrix metalloproteinase 3 (MMP3), thioredoxin-interacting protein (TXNIP), and proliferating cell nuclear antigen (PCNA). The data were analyzed according to the 2-u0394u0394CT method. Because significant deviations from normality were observed, within-day comparisons across conditions and within-condition comparisons across days were analyzed with Kruskal-Wallis tests followed by Conover-Iman post hoc tests. Due to the large number of comparisons performed, the Benjamini-Hochberg procedure was employed to control the false discovery rate. Significance was determined if p