p38 MAPK: a mediator of hypoxia-induced cerebrovascular inflammation

Vascular perturbations and hypoxia are increasingly implicated in Alzheimer's disease (AD) pathogenesis. Cerebral hypoxia induces a large number of inflammatory proteins in brain endothelial cells via signaling pathways that have not been defined. The p38 mitogen-activated protein kinase (MAPK) signaling system has been implicated in endothelial injury and inflammation. The objective of this study is to examine p38 MAPK levels in the cerebromicrovasulature in AD and AD animal models and determine the role of p38 MAPK signaling in hypoxia-mediated effects on brain endothelial cells. Western blot analysis of isolated human brain microvessels show that the phosphorylated (active) form of p38 MAPK (pp38 MAPK) is increased in vessels derived from AD brains compared to control-derived vessels. Similarly, immunofluorescent analysis reveals an increase in cerebrovascular pp38 MAPK as well as inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in transgenic AD mice. Exposure of brain endothelial cells to hypoxia (2-6 hours) shows a time-dependent increase in pp38 MAPK. Examination of these cultures at 6 hours hypoxia shows that iNOS and COX-2 are significantly elevated and that the selective p38 MAPK inhibitor SB203580 significantly reduces the hypoxia-mediated increase in their expression. Inhibition of p38 MAPK in cultured brain endothelial cells also significantly decreases the hypoxia-induced increase in the inflammatory proteins, matrix metalloproteinase-2 and angiopoietin-2. These data demonstrate that pp38 MAPK is a key regulator of hypoxia in the cerebrovasculature and suggest that control of this signaling pathway could have therapeutic value in AD and other disorders where hypoxia is involved.