HIF-1α Stabilization Hampers the Chondrogenic Differentiation of Aged Bone Marrow Mesenchymal Stem Cells by Adenosine A 2A /A 2B Receptors Imbalance

Trauma and excessive motion are deleterious to cartilage by triggering HIF-1α stabilization, leading to changes in extracellular adenosine formation via CD73. How these changes affect adenosine A2A/A2B receptors activation balance in chondrogenesis is unclear. We used bone marrow mesenchymal stem cells (BM-MSCs) from aged women to investigate the impact of HIF-1α overactivation on adenosine formation from ATP breakdown and subsequent A2A/A2B receptor tone-regulating chondrogenesis. The chondrogenic differentiation of BM-MSCs from 27 postmenopausal (Pm) women was induced for 14 days with or without DMOG, a prolyl-4-hydroxylase (PHD) inhibitor that increases HIF-1α intracellular accumulation. Chondrogenesis was ascertained by the nuclear translocation of SOX9, type II/X collagen, and MMP13 production and by transcriptomic RNAseq analysis. Changes in the density of adenosine receptors, ecto-NTPDases, and CD73 were assessed by immunofluorescence confocal microscopy. The kinetics of ATP hydrolysis and adenosine formation was performed by HPLC. DMOG-induced HIF-1α transcriptional activity increased cartilage damage biomarkers (MMP13 and type X collagen), while decreasing cell viability, SOX9 nuclear translocation, and type II collagen production. DMOG upregulated pro-inflammatory genes and down-regulated chondrogenic gene transcripts determined by RNAseq. HIF-1α stabilization decreased CD39/CD73 amounts and activity, thus reducing adenosine formation. Hence, changes in the A2A/A2B receptor tone resulted in preferential activation of the SCH 442416-sensitive A2A receptor, which is deleterious to the cartilage. In conclusion, HIF-1α overactivation hampers the chondrogenic differentiation of aged BM-MSCs by decreasing adenosine formation from ATP hydrolysis via CD39/CD73, leading to preferential activation of the high-affinity A2A versus the chondroprotective A2B receptor.