L‐arginine uptake is necessary for lipopolysaccharide/tumor necrosis factor‐α‐induced apoptotic cell death in pulmonary endothelial cells

We have previously found that L‐arginine uptake mediated by the cationic amino acid transporter (CAT) is up‐regulated by LPS/TNF‐α (L/T) in bovine pulmonary arterial endothelial cells (bPAEC). Treatment of bPAEC with L/T led to an increase in cell death and this effect was attenuated by inhibiting CAT‐mediated L‐arginine uptake. We hypothesized that L‐arginine uptake is necessary for the pro‐apoptotic effects of L/T in bPAEC. We tested this hypothesis by treating bPAEC with L/T or vehicle (control) in the presence of absence of 10 mM L‐leucine (L‐leu; competitive inhibitor of CAT). L/T treatment resulted in fewer viable cells than in controls after 24 hours, and L‐leu prevented L/T‐induced cell death. L/T treatment resulted in activation of both caspase 3 and caspase 9, and this effect was attenuated by adding L‐leu to the L/T. Caspase 8 activity was 5‐fold greater in L/T‐treated bPAEC then in controls, and addition of L‐leu to the L/T treatment returned caspase 8 activity to control levels. Expression of bcl‐2 was inhibited by L/T treatment, and addition of L‐leu to the L/T treatment maintained bcl‐2 expression. Our results indicate that L/T induces both the intrinsic and extrinsic apoptotic pathways, and our findings suggest that the activation of apoptosis pathways in bPAEC by L/T requires CAT‐mediated L‐arginine uptake. Funded by NHLBI R01 HL075261