The beta(2)-adrenoceptor agonist clenbuterol modulates Bcl-2, Bcl-xl and Bax protein expression following transient forebrain ischemia

It is well known that proteins encoded by the Bcl-2 gene family play a majo r role in the regulation of apoptosis. We have demonstrated previously that neuronal apoptosis can be induced in the hippocampus and striatum after gl obal ischemia. Clenbuterol, a Pz-adrenoceptor agonist, showed considerable activity against neuronal apoptosis. In the present study, we attempted to find out whether the members of the Bcl-2 family are induced after ischemia , and whether expression of these genes could be altered by clenbuterol. Tr ansient forebrain ischemia was performed in male Wistar rats by clamping bo th common carotid arteries and reducing the blood pressure to 40 mmHg for 1 0 min. Clenbuterol (0.5 mg/kg, i.p.) or vehicle were injected 3 h before on set of ischemia or in non-ischemic rats. The hippocampus and striatum were taken from non-ischemic rats 3, 6 and 24 h after injection of clenbuterol, as well as from drug-treated and untreated rats 6 and 24 h after ischemia. Eighty micrograms/lane total protein were loaded on a 15% sodium dodecyl su lfate-polyacrylamide gel for western blotting. Bcl-2, Bar and Bcl-xl protei ns were detectable in the non-ischemic hippocampus and the striatum. Clenbu terol upregulated the expression of Bcl-2 protein at 3, 6 and 24 h after ad ministration. Enhanced Bcl-xl signals were found in the non-ischemic striat um 3, 6 and 24 h after clenbuterol treatment, but no change of Bcl-xl expre ssion by clenbuterol was seen in the non-ischemic hippocampus. Bar expressi on was not altered by clenbuterol in the non-ischemic hippocampus and stria tum. Bcl-2 was up-regulated in both detected regions at 24 h after ischemia , while the increase in Bar and Bcl-xl protein expression had appeared alre ady at 6 h and also 24 h after ischemia. Clenbuterol further increased the expression of Bcl-2 at 6 and 24 h after ischemia. In contrast, Bar protein level was down-regulated by clenbuterol at 6 and 24 h after ischemia. Clenb uterol also increased Bcl-xl level in the ischemic striatum. The results suggest that global ischemia induces proto-oncogenes which are associated with apoptosis. Clenbuterol not only increased Bcl-2 expression in the non-ischemic hippocampus and striatum, but also up-regulated Bcl-2 a nd down-regulated Bar expression in the ischemic hippocampus and striatum. The increase in the ratio of Bcl-2 and Bar may contribute to the anti-apopt otic effect of clenbuterol. The present study indicates that pharmacologica l modulation of Bcl-2 family member expression could become a new strategy to interfere with neuronal damage. (C) 1999 IBRO. Published by Elsevier Sci ence Ltd.