Introduction
Activation of tumor necrosis factor (TNF) and Fas receptor signaling cascades has been implicated in various pathologies of central nervous system. Our previous work has shown that moderate traumatic brain injury (TBI) upregulates TNF-alpha mRNA and protein, increases the protein levels of TNF receptor 1 (TNFR1), its signaling intermediates, and increases recruitment of TNFR1 into plasma membrane specialized microdomains, lipid rafts 1 . Redistribution of TNFR1 in the plasma membrane altered association of TNFR1 with downstream intermediates that may signal death. Recent data have shown that therapeutic hypothermia significantly reduces TNF alpha mRNA expression in rat hippocampus 2 . Multiple studies indicate that hypothermia is protective, however, it is not known whether hypothermia alters the expression and protein levels of TNF receptor family members and their signaling intermediates.
Methods
We performed immunoblot analysis of brain cortical lysates of adult male Sprague Dawley naïve (N) rats (N=3), rats subjected to normothermic (TN) (37 C) moderate (1.8 – 2.2 atm) fluid-percussion TBI with 30 min survival (N=3). Another group was subjected to moderate TBI with 30 min of pre- and post-traumatic hypothermia (TH) (33 C) (N=3).
Results
TBI resulted in the increased levels of TNFR1, caspase-8 and Fas as previously observed 1 . In contrast, mild hypothermia decreased protein levels of TNFR1, TNFR2, Fas, and an upstream, activated caspase-8, compared to normothermic levels. Protein levels of TNFR signaling intermediates including FADD and RIP did not appear to be significantly altered by hypothermia at this study period.
Conclusions
These data provide evidence that hypothermia affects not only TNF but also Fas signaling in the rat cortices early after TBI. Therapeutic hypothermia may improve histopathological and behavioral outcomes after TBI by targeting death signaling cascades. (See Figure 1).
Footnotes
Acknowledgements
Supported by NIH grants NS42133 and NS30291.