Alloreactive T cell proliferation is suppressed by 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) independent of AMP-activated protein kinase

The benefits of hematopoietic stem cell transplantation, a therapy used to treat a variety of hematologic and immunologic disorders, are often outweighed by the risks of acute graft-versus-host disease (GVHD), where donor T cells attack and destroy host tissues. Our lab has previously shown that targeting lymphocyte metabolism is a promising and novel strategy for the treatment of GVHD. More recently, we have found that AMP-activated protein kinase (AMPK), a major cellular energy sensor, plays a significant role in T-cell proliferation during disease pathogenesis. To explore this relationship further, we treated alloreactive T cells generated during a mixed leukocyte reaction (MLR) with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), an AMP mimetic that strongly activates AMPK. AICAR treatment of MLR cultures strongly repressed T cell proliferation, with a 70% decrease in total cells by 96 hours. Interestingly this decrease in T cell proliferation was independent of AMPK, as similar results were obtained using AMPK−/− cells. Mechanistically AICAR repressed AKT signaling in stimulated T cells, with a 50% decrease in AKT phosphorylation when cells were concurrently treated with 100 μM AICAR. Cytokine driven STAT5 activation was also significantly blunted by simultaneous AICAR exposure. In summary, despite its wide use as an AMPK agonist, we found that AICAR exerts significant inhibitory effects on T cell allo-activation independent of AMPK. This inhibition occurs, at least in part, through decreased phosphorylation of AKT and down-regulation of STAT signaling, making AICAR a potential therapy to combat GVHD and similar inflammatory disorders.