We previously reported that the ischemic brain area was significantly larger in angiotensin II type 2 (AT2) receptor-deficient mice after middle cerebral artery (MCA) occlusion compared to wild-type (WT) mice. We have cloned ATIP (AT2 receptor interacting protein) as a protein interacting specifically with the C-terminal tail of the AT2 receptor, and suggest that ATIP might play key roles in diverse mechanisms of AT2 receptor signaling. We investigated the possibility that ATIP could enhance the protective effects compound 21 (C21), a selective non-peptidic AT2 receptor agonist, on focal cerebral ischemia.Design and method:
Ten week-old male ATIP1-transgenic (ATIP1-Tg) and littermate (WT) mice were subjected to (MCA) occlusion with silicon-coated micro-filament. C21 (10 μg/kg/day) was administered 2 weeks before MCA occlusion. Twenty-four hours after MCA occlusion, ischemic area was assessed by triphenylterazolium chloride staining. Neurological deficit after MCA occlusion was evaluated using a neurological score. Cerebral blood flow (CBF) was measured by laser speckle flowmetry. Expression of inflammatory cytokines and methyl methanesulfonate sensitive 2 (MMS2) as a neuroprotective factor were measured by real-time RT-PCR.Results:
Administration of C21 did not influence the blood pressure measured by tail-cuff method. There was no significant difference in ischemic size without C21 treatment between WT and ATIP-Tg mice. Treatment with C21 decreased ischemic size and improved neurological deficit in both strains. These protective effects by C21 were more marked in ATIP-Tg mice compared with WT mice. Administration of C21 did not affect CBF in the core region of ischemic area after MCA occlusion in both strains; however, the reduction of CBF in penumbra region was markedly attenuated in ATIP-Tg mice treated with C21. MMS2 tended to increase in ATIP1-Tg mice compared with WT mice. Expression of inflammatory cytokines such as TNF-α and MCP-1 was increased in ipsilateral hemisphere compared with in contralateral hemisphere. Treatment of C21 tended to reduce inflammatory cytokine expression in ipsilateral hemisphere.Conclusions:
These results suggested that ATIP1 could enhance the cerebral protective effects of AT2 receptor stimulation at least in part due to the improvement of CBF.