Abstract
Articular cartilage is an avascular tissue with significantly reduced levels of oxygen and nutrients compared to plasma and synovial fluid. Therefore, chondrocyte survival and cartilage homeostasis require effective mechanisms for oxygen and nutrient signaling. To gain a better understanding of the mechanisms responsible for oxygen and nutrient sensing in chondrocytes, we investigated the effects of hypoxic stimulation induced by cobalt chloride treatment (a hypoxia-mimetic) on glucose uptake and lactate production in chondrocytes. We also studied the effects of cobalt chloride and glucose deprivation on the expression and secretion of active MMP-2. Primary cultures of articular chondrocytes were either maintained in 20% O(2) (normoxia) or exposed to the hypoxia-mimetic cobalt chloride for up to 24 h at the following concentrations: 15 microM, 37.5 microM, and 75 microM. Glucose transport was determined by measuring the net uptake of nonmetabolizable 2-deoxy-D-[2, 6-(3)H] glucose into chondrocytes. Active MMP-2 secretion was assayed by gelatin zymography. Lactic acid production was assayed using a lactate kit. Exposure to cobalt chloride significantly increased the uptake of 2-deoxy-D-[2, 6-(3)H] glucose and the production of lactate. Glucose deprivation and cobalt chloride treatment increased levels of active MMP-2 in the culture medium. Our results suggest that these metabolic alterations are important events during adaptation to hypoxia. Upregulation of MMP-2 and the build-up of lactic acid will have detrimental effects on the extracellular matrix and may contribute to the pathogenesis and progression of osteoarthritis (OA).