Xanthine oxidase-derived extracellular superoxide anions stimulate activator protein 1 activity and hypertrophy in human vascular smooth muscle via c-Jun N-terminal kinase and p38 mitogen-activated protein kinases

Abstract

Vascular xanthine oxidase (XO) activity has been found to be elevated in chronic vascular disease. Although a role for XO in endothelial dysfunction has been proposed, little is known about its influence on vascular smooth muscle maladaptive growth. The proliferative and hypertrophic response of human aortic smooth muscle cells (HASMC) stimulated with xanthine/xanthine oxidase (X/XO) was quantified by determining cell number, cell size and protein synthesis. The levels and activity of the growth-related transcription factor activator protein 1 (AP-1) and the activation of mitogen-activated protein kinase (MAPK) by X/XO were determined by either Western blot or transient transfection experiments. X/XO did not affect HASMC proliferation, but led to enhanced planar cell surface area and protein synthesis. In addition, X/XO enhanced c-jun levels and AP-1 transcriptional activity. Although X/XO did not modify extracellular signal-regulated protein kinases 1/2 MAPK or Akt/PKB activity, it promoted the activation of c-Jun N-terminal kinase and p38 MAPK, which were both necessary for X/XO to increase AP-1 activity and cell size in HASMC cultures. Finally, the effects of X/XO on MAPK activation, AP-1 activity and cell size were dependent on the extracellular release of superoxide anions through the enzymatic activity of XO, as they were prevented by both superoxide dismutase and allopurinol. X/XO exhibits hypertrophic properties for human vascular smooth muscle, which are mediated by redox-sensitive pathways involving MAPK activation. XO can therefore participate in the maladaptive vascular remodeling observed in chronic cardiovascular diseases exhibiting elevated vascular XO activity.