Vulnerable vasculature and increased inflammation contribute to the exacerbation of transient focal ischemia in a genetic mouse model of type 1 diabetes

Abstract

PURPOSE: Epidemiological studies showed that type 1 diabetic patients are much more prone to cerebrovascular mortality from stroke and the median survival is only half when compared with those in the general population. It has been suggested that type 1 diabetes is a risk factor for stroke; however, the underlying mechanisms are still unclear. In the current study, we aim to elucidate the potential mechanisms contributing to the exacerbation. METHOD: Ins2Akita/+ mice, a type 1 diabetic murine model, and their wildtype (Ins2+/+) littermates at 12 weeks of age were challenged with experimental stroke by middle cerebral artery occlusion (MCAO) for 2h followed by 2h of reperfusion. Survival rate and neurological deficits were accessed at the end of reperfusion. Brain slices were prepared and stained with 2, 3, 5-triphenyltetrazolium chloride for estimating the infarction, hemispheric swelling, and hemorrhagic area. Blood vessel integrity (ZO-1) and inflammatory response (VEGF and pErk) were compared between Ins2Akita/+ and Ins2+/+ ipsilateral brains using Western blot analysis. ER-stress (ATF6, BiP, CHOP, PERK and IRE-1α) and autophagy (Atg12, Bcn1, LC3-a, LC3-b and p62) response were also compared using real-time PCR. RESULTS: Ins2Akita/+ mice showed a decreased survival rate and increased neurological deficits after MCAO, together with a significant increase in infarction and hemorrhage size. Down-regulation of ZO-1 protein and remarkable up-regulation of VEGF and pErk protein were observed in Ins2Akita/+ mice when compared with Ins2+/+ mice. mRNA expression of CHOP was significantly increased in both mice after MCAO challenge and was further augmented in Ins2Aktia/+ mice. Atg12, Bcn1 and LC3-b mRNA expressions were significantly lower in the Ins2+/+ mice after MCAO when compared with the sham-operated controls but there was no difference between the post-MCAO Ins2Akita/+ and Ins2+/+ groups. CONCLUSION: We showed that induction of MCAO in Ins2Akita/+ mice could mimic the clinical observations of high mortality in type 1 diabetic patients upon stroke. Decrease in ZO-1 expression and augmented hemorrhage indicated that blood vessel integrity was more vulnerable in the Ins2Akita/+ mice. Provoked inflammatory response and ER-stress may play important roles in the exacerbation of the ischemic brain, which was evidenced in increased infarction in Ins2Akita/+ mice.