Aims: Hypothermia therapy has been shown to confer robust protection against brain injury and cardiac arrest. However, the mechanisms underlying endothelial cell protection of hypothermia have not yet been completely elucidated. Here, we investigated molecular effects of hypothermia on tumour necrosis factor-alpha (TNF-alpha)-induced endothelial barrier dysfunction and apoptosis.
Methods and results: Human umbilical vein endothelial cells (HUVECs) treated with TNF-alpha were incubated under normothermia (37 degrees C) or hypothermia (33 degrees C). [corrected] Endothelial permeability, actin alterations, and apoptosis were examined. The protein levels were determined by immunoblot analysis. Treatment of HUVECs with TNF-alpha resulted in a significant increase of permeability, actin reorganization, and apoptosis. Hypothermia markedly attenuated TNF-alpha-induced effects. The inhibitory action of hypothermia on stress fibre formation was mediated via inactivation of p38 mitogen-activated protein kinase (MAPK)/heat shock protein 27 (HSP27), and the decrease in TNF-alpha-induced apoptosis by hypothermia was associated with inhibition of p38 MAPK and c-Jun N-terminal kinase (JNK) activity. Hypothermia had no action on p38 MAPK and JNK upstream kinases MAPK kinase 3/6 (MKK3/6) and MAPK kinase 7 (MKK7), but it markedly induced the expression of MAPK phosphatase-1 (MKP-1). Furthermore, siRNA experiments showed that MKP-1 was an important mediator of hypothermia in reducing TNF-alpha-induced inflammatory responses and activation of p38 MAPK and JNK in HUVECs.
Conclusion: These results for the first time demonstrate that hypothermia protects against TNF-alpha-induced endothelial barrier dysfunction and apoptosis through an MKP-1-dependent mechanism.