Endocrine Abstracts

AMP-activated protein kinase (AMPK) acts as a sensor and regulator of cellular energy homeostasis. Once activated, AMPK influences a number of responses including inhibition of anabolic pathways and the switching-on of catabolic pathways. Regulation of AMPK, which responds to an increase in the AMP/ATP ratio, could have an important role in chondrocyte function particularly in response to hormones and to stress such as occurs in osteoarthritis. Therefore, we sought to investigate the effects of activators of AMPK on immortalised human chondrocyte cell lines. Three cell lines (T/C28a2, C20/A4 and C28/I2) were incubated with activators of AMPK to assess their effects on cell proliferation and apoptosis. These were also compared to effects on breast cancer cells which are known to respond to these drugs. Cell proliferation was assessed by a modified MTT assay and apoptosis was assayed by time-lapse video microscopy and Annexin V binding. AICAR (5-aminoimidazole-4-carboximide-1-beta-D-ribofuranoside), which is converted intracellularly to an AMP analogue, induced a maximal inhibitory effect of between 80 and 90% on cellular proliferation at 0.4 mM in both T/C28a2 and C28/I2 cells, whereas in C20/A4 cells the effect was less pronounced. AICAR and Akt Inhibitor VIII elicited additive, but not synergistic effects. Phenformin, another AMPK activator, strongly inhibited cell proliferation similarly in all 3 cell types; metformin, a drug currently used for diabetes, was not as effective in inhibiting proliferation. Measurement of apoptosis revealed that AICAR elicited a significant apoptotic response after 16–20 h, whereas the action of phenformin was more rapid, effects being observed as early as 3 h of administration. These data are the first, to our knowledge, to indicate a possible role for the AMPK pathway in chondrocyte biology. This may also raise important potential implications for the role of the AMPK cascade in hormonal influences in osteoarthritis and other cartilage disorders.