Intranasal delivery of RGD-motif containing osteopontin icosamer confers neuroprotection in the postischemic brain

초록

Osteopontin (OPN) is a phosphorylated glycoprotein possessing an arginine-glycine-aspartate (RGD)-motif, through which it binds to several cell surface integrins that mediate a wide range of cellular processes, such as, adhesion, migration, and survival. Furthermore, the delayed, sustained, and differential inductions of OPN have been reported in different cell types in the postischemic brain, and the neuroprotective effects of recombinant OPN protein have been demonstrated in animal models of stroke. In the present study, we found that an RGD-containing icosamer OPN peptide (OPNpt20) had a robust neuroprotective effect in a rat model of focal cerebral ischemia induced by middle cerebral artery occlusion (MCAO). After it was administered intranasally at 1 hr-post-MCAO (100 ng), OPNpt20 reduced mean infarct volume by 79.7% as compared to that in MCAO control animals and markedly ameliorated neurological deficits. However, a mutant peptide (OPNpt20-RAA), in which RGD was replaced by RAA, failed to suppress infarct volumes, indicating that the RGD motif is required for its neuroprotective effect. It was also found that the anti-inflammatory effects of OPNpt20 were responsible for these protective effects, since RGD-containing OPNpt20 significantly suppressed the inductions of iNOS and of other inflammatory markers in postischemic brains and in primary microglial cultures, whereas OPNpt20-RAA did not. These results suggest iNOS suppression by OPNpt20 is mediated by OPNpt20-endogenous v3 integrin interaction and RGD-containing OPN icosamer has therapeutic potential related to its anti-inflammatory effects in the postischemic brain.