Carbonic Anhydrase 2 is Required for Maintaining Metabolic Homeostasis of Human Articular Chondrocytes

Objective: To examine the role of carbonic anhydrase II (CA2 gene), the most efficient isoform in the CA family of zinc-containing metalloenzymes, in chondrocyte metabolism. Methods: CA2 expression was measured in human and mouse osteoarthritic cartilage. RNA-seq was performed in C28/I2 cells in which CA2 was silenced. Normal human chondrocytes were cultured under normoxia (21% oxygen) or hypoxia (2% oxygen) following CA2 knockdown. Cell metabolism was studied by measuring extracellular lactate production, glucose consumption, intracellular ADP/ATP, intracellular pH, and ROS production. Glycolysis was measured using Seahorse XF96 analyzer. The effect of CA2 knockdown on anabolic and catabolic markers was measured following treatment with IL-1. Effects of CA2 was examined on cell proliferation, cell-cycle distribution, colony-formation, and migration. Results: CA2 was highly elevated in human and murine osteoarthritic cartilage. RNA-seq analysis revealed that processes related to glycolysis, apoptosis and TNF signaling were perturbed in cells lacking CA2. CA2 expression was 10-fold higher under hypoxia and its knockdown caused decreased extracellular lactate production, increased ADP/ATP ratio, impaired glycolysis, decreased glycolytic capacity and lowered the expression of glycolysis rate-limiting enzymes, but did not affect intracellular pH and ROS production. CA2 deficiency disturbed chondrocyte anabolic and catabolic equilibrium. CA2 knockdown suppressed chondrocyte migration and proliferation and induced cell-cycle arrest. Conclusion: This study unravels a novel role of CA2 in chondrocyte metabolism and inflammation. These findings indicate that CA2 is required for the maintenance of chondrocyte metabolic homeostasis. Future work is needed to further illuminate the mechanistic and functional role of CA2 in osteoarthritis development. RNA-Seq analysis of cells transduced with CA2 shRNA