Postischemic brain injury is attenuated in mice lacking the beta2-adrenergic receptor.
BACKGROUND
Several beta-adrenergic receptor (betaAR) antagonists have been shown to have neuroprotective effects against cerebral ischemia. However, clenbuterol, a beta(2)AR agonist, was shown to have neuroprotective activity by increasing nerve growth factor expression. We used beta(2)AR knockout mice and a beta(2) selective antagonist to test the effect of loss of beta(2)ARs on outcome from transient focal cerebral ischemia.


METHODS
Ischemia was induced by the intraluminal suture method, for 60 min of middle cerebral artery occlusion (MCAO) followed by 24 h reperfusion. Neurological score was determined at 24 h reperfusion and infarct size was determined by cresyl violet or 2,3,5-triphenyltetrazolium chloride staining. beta(2)AR knockout mice and wild-type congenic FVB/N controls were studied, as well as 2 groups of wild type mice given either ICI 118,551 (0.2 mg/kg) or 0.9% saline intraperitoneally 30 min before MCAO (n = 10 per group). Changes in expression of heat shock protein (Hsp)72 after ischemia were examined by immunohistochemistry and western blots.


RESULTS
Compared with wild type littermates, infarct volume was decreased by 22.3% in beta(2)AR knockout mice (39.7 +/- 10.7 mm(3) vs 51.0 +/- 11.4 mm(3), n = 10/group, P = 0.034) after 60 min of MCAO followed by 24 h reperfusion. Pretreatment with a beta(2)AR selective antagonist, ICI 118,551, also decreased infarct size significantly, by 25.1%, compared with the saline control (32.8 +/- 11.9 mm(3) vs 43.8 +/- 10.3 mm(3), n = 10/group, P = 0.041). Neurological scores were also significantly improved in mice lacking the beta(2)AR or pretreated with ICI 118,551. After cerebral ischemia, total levels of Hsp72 and the number of Hsp72 immunopositive cells were greater in mice lacking beta(2) AR.


CONCLUSIONS
Brain injury is reduced and neurological outcome improved after MCAO in mice lacking the beta(2)AR, or in wild type mice pretreated with a selective beta(2)AR antagonist. This is consistent with a shift away from prosurvival signaling to prodeath signaling in the presence of beta(2)AR activation in cerebral ischemia. Protection is associated with higher levels of Hsp72, a known antideath protein. The effect of beta(2)AR signaling in the setting of cerebral ischemia is complex and warrants further study.
Han
Ru-Quan
RQ
Department of Anesthesia,Stanford University School of Medicine, Stanford, California 94305-5117, USA.
Ouyang
Yi-Bing
YB
Xu
Lijun
L
Agrawal
Rani
R
Patterson
Andrew J
AJ
Giffard
Rona G
RG
D058672:Adrenergic beta-2 Receptor Antagonists; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D004195:Disease Models, Animal; D050884:HSP72 Heat-Shock Proteins / Q000378:metabolism; D020244:Infarction, Middle Cerebral Artery / Q000150:complications / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D002546:Ischemic Attack, Transient / Q000209:etiology / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009043:Motor Activity / Q000187:drug effects; D018696:Neuroprotective Agents / Q000494:pharmacology*; D011412:Propanolamines / Q000494:pharmacology*; D018343:Receptors, Adrenergic, beta-2 / Q000172:deficiency* / Q000235:genetics; D015854:Up-Regulation
D058672:Adrenergic beta-2 Receptor Antagonists; D000319:Adrenergic beta-Antagonists; D050884:HSP72 Heat-Shock Proteins; D018696:Neuroprotective Agents; D011412:Propanolamines; D018343:Receptors, Adrenergic, beta-2; C026777:ICI 118551