Background/Purpose: Osteoarthritis (OA) is the most common form of arthritis, affecting nearly 10% of the US population. There is no therapy to prevent the progression of or reverse OA pathology. Endogenous adenosine 2A receptor (A2AR) stimulation is crucial for chondrocyte viability and cartilage homeostasis as its downstream signaling mediates inflammation. In recent preliminary studies we have found that mice lacking the A2AR or ecto-5’nucleotidase (CD73, an ectoenzyme critical for extracellular adenosine production) develop spontaneous OA. These findings suggest that diminished extracellular adenosine levels promote the development of OA. Since human OA chondrocytes have been found to have diminished mitochondrial content, we propose to test the hypothesis that OA pathogenesis deregulates A2AR signaling at least in part by affecting the cell’s capacity for ATP production via reduced number or functionality of mitochondria.

Methods: A human chondrocyte cell line, TC28a2, was used to determine the effects of IL1B-induced inflammation and A2AR stimulation in vitro. Cells were treated with IL1B (5ng/mL) and with the A2AR-specific agonist, CGS21680 (CGS; 1uM). Mitochondrial content was measured by mtDNA to nDNA ratios and MitoTracker mean cellular intensity. Mitochondrial health and functionality was assessed by mean pixel intensity (MPI) of a fluorescent probe for monitoring mitochondrial membrane potential, TMRM, and by measuring oxygen consumption rates (OCR) on Seahorse Mito Stress Kit Assays. The role of A2AR ligation on mitochondrial health was also studied by histology for 8hydroxyguanosine (8OH-G) residues as a marker for reactive oxygen species (ROS) in A2ARKO mice and Sprague Dawly rats that underwent ACL rupture (post-traumatic OA model) and subsequently received CGS-filled liposomal injections.

Results: A2AR agonism increases mitochondrial content in vitro. IL1B incubation for 3 hours followed by A2AR ligation increases mitochondrial membrane potential (2867±165.5 MPI) compared to control (1582±183.9 MPI), IL1B alone (1483±120.6 MPI) and CGS alone (1788±137.8 MPI) as measured by TMRM staining (p≤0.0001). IL1B incubation for 4 hours with a last hour of A2AR stimulation increases basal oxygen consumption rate and maximal respiratory rate. IL1B+CGS treated cells had significantly increased ATP production (113.04±13.44 of OCR) than the control (83.86±11.89 of OCR), IL1B (81.00±12.80 of OCR) and CGS (76.04± 23.52 of OCR) treated cells as measured by one-way ANOVA (p values =**0.0088, *0.0128, and *0.0259 respectively). A2ARKO mice exhibit increased 8OG-G staining in histology as early as 8 weeks. A2AR stimulation after ACL rupture in rats, results in preserved cartilage volumes, improved OARSI scores (p<0.001) and reduced ROS as seen by reduced 8OH-G staining in histology.

Conclusion: A2AR ligation improves mitochondrial functionality during inflammation and OA progression. Increased mitochondrial function is not seen when the chondrocytes are treated with IL1B or CGS alone; perhaps suggesting that A2AR stimulation is necessary to maintain homeostasis when cells are already under physiological or pathological stress.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-effect-of-adenosine-a2a-receptor-stimulation-on-mitochondrial-metabolism-in-the-pathogenesis-and-treatment-of-osteoarthritis/