Mechanisms of hypothermia-induced cell protection mediated by microglial cells in vitro.

Despite the widespread interest in the clinical applications of hypothermia, the cellular mechanisms of hypothermia-induced neuroprotection have not yet been clearly understood. Therefore, the aim of this study was to elucidate the cellular effects of clinically relevant hypothermia and rewarming on the morphological and functional characteristics of microglia. Microglial cells were exposed to a dynamic cooling and rewarming protocol. For stimulation, microglial cells were treated with 1 microg/mL lipopolysaccharide (LPS). We found that hypothermia led to morphological changes from ramified to ameboid cell shapes. At 2 h after hypothermia and rewarming, microglial cells were again ramified with extended branches. Moreover, we found enhanced cell activation after rewarming, accompanied by increased phagocytosis and adenosine triphosphate consumption. Interestingly, hypothermia and rewarming led to a time-dependent significant up-regulation of the anti-inflammatory cytokines interleukin-10 and interleukin-1 receptor antagonist in stimulated microglial cells. This is in line with the reduced proliferation and time-dependent down-regulation of the pro-inflammatory cytokines tumor necrosis factor-alpha and monocyte chemotactic protein-1 in comparison to normothermic control cells after LPS stimulation. Furthermore, degradation of the inhibitor of the nuclear transcription factor-kappaB (IkappaB-alpha) was diminished and delayed under conditions of cooling and rewarming in LPS-stimulated microglial cells. Thus, our results show that hypothermia and rewarming activate microglial cells, increase phagocytosis and shift the balance of cytokine release in stimulated microglial cells towards the anti-inflammatory cytokines. This could be a new cellular mechanism of hypothermia-induced neuroprotection mediated by activated microglial cells.

Methylprednisolone and tacrolimus prevent hypothermia-induced endothelial dysfunction.

BACKGROUND: Hypothermia is used to preserve organs for transplantation and is the oldest method to protect organs during complex pediatric cardiac surgery. Loss of tissue function and tissue edema are common complications in children undergoing corrective cardiac surgery and heart transplantation. The present study was designed to examine the effects of methylprednisolone and tacrolimus on endothelial cell function and morphology after deep hypothermia and rewarming. METHODS: Human umbilical vein endothelial cells were pre-treated with methylprednisolone or tacrolimus, or both, incubated within a specially designed bioreactor or in monolayers, and then exposed to a dynamic cooling and rewarming protocol. Immunocytochemistry, time-lapse video microscopy, cell permeability and adherence assays, and Western blot analysis were performed. RESULTS: Confluent endothelial cells exposed to hypothermia displayed elongated cell shapes with intercellular gap formation, increased endothelial cell-layer permeability, and loss in adherence. Upon rewarming, however, endothelial cell integrity was restored. Opening and closing of intercellular gaps was dependent on extracellular signal-regulated kinase 1 and 2 (ERK 1/2) activation and connexin 43 expression. The combined treatment with methylprednisolone and tacrolimus inhibited these hypothermia-induced changes. CONCLUSIONS: These results suggest that methylprednisolone and tacrolimus inhibit hypothermia-induced endothelial gap formation by phosphorylated ERK 1/2 inhibition and connexin 43 stabilization. Application of combined drugs that affect multiple targets may therefore be considered as a possible new therapeutic strategy to prevent endothelial dysfunction after hypothermia and rewarming.