Objective: 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 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. However, the effect of ATIP on brain damage has not been clarified. We investigated the possibility that ATIP could enhance the protective effects of compound 21 (C21), a selective direct non-peptidic AT2 receptor agonist, on focal cerebral ischemia.
Method: Ten week-old male ATIP-transgenic (ATIP-Tg) and littermate (WT) mice were subjected to permanent 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 and neurological deficit was assessed. Cerebral blood flow (CBF) was measured by laser speckle flowmetry. Expression of methyl methanesulfonate sensitive 2 (MMS2) as a neuroprotective factor were measured by real-time RT-PCR. Collateral circulation was evaluated by the perfusion of India ink.
Results: Systolic blood pressure did not differ between ATIP-Tg and WT mice with or without C21. There was no significant difference in ischemic size without C21 treatment between two strains. 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. Treatment 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 expression increased in ipsilateral hemisphere of ATIP-Tg mice compared with contralateral hemisphere. C21 treatment tended to increase collateral number in ATIP-Tg mice.
Conclusions: These results suggested that ATIP could enhance the cerebral protective effects of AT2 receptor stimulation at least in part due to the improvement of CBF and increase of MMS2 expression.