Vulnerable vasculature and increased inflammation contribute to earlier death and higher mortality after transient focal ischemia in type 1 diabetic mice

Abstract

Type 1 diabetic patients are found to be more prone to cerebrovascular mortality from stroke in epidemiological studies, with half median survival when compared with those in the general population. It has been suggested that type 1 diabetes is a risk factor for stroke, but with unclear underlying mechanisms. In this study, we aim to elucidate the potential mechanisms contributing to the exacerbation. Ins2Akita/+ mice, a type 1 diabetic murine model, and their wildtype(Ins2+/+) littermates at 12 weeks of age were challenged with experimental stroke induced by middle cerebral artery occlusion(MCAO)(2h ischemia and 2h or 22 h reperfusion). Survival was recorded at selected intervals and neurological deficits were accessed at the end of reperfusion. Two mm-thick brain slices were stained with 2, 3, 5-triphenyltetrazolium chloride for estimation of the infarct volume, hemispheric swelling and hemorrhagic area. Western blot analyses were performed to compare blood vessel integrity(ZO-1, VEGF, MMP,-2 and MMP-9) and inflammatory response(p Erk and p-p38) in the infarct core and penumbra region. Our results showed that after 2h of reperfusion, the neurological deficit and infarct volume were significantly increased in the Ins2Akita/+ mice. A higher mortality rate and a shorter survival were also observed. Hemorrhage was significantly increased and further advanced with longer reperfusion. VEGF and p Erk were remarkably up-regulated and ZO-1 was down-regulated in the Ins2Akita/+ mice. A trend of increase in MMP-2, MMP-9 and p-p38 were also observed. At 22 h after reperfusion, the expressions of p-Erk and p-p38 still persisted at a significant level. Here, we showed that induction of transient focal ischemia in Ins2Akita/+ mice could mimic the clinical observations of high mortality and shortened survival in type 1 diabetic patients upon stroke. The increased hemorrhage together with VEGF up-regulation and ZO-1 down-regulation indicated that blood vessels were more vulnerable in the Ins2Akita/+ mice. The effect of hemorrhagic transformation was observed as early as 2 h after reperfusion and was further provoked with longer reperfusion. Inflammatory response may also play an important role in the exacerbation of the ischemic injury in Ins2Akita/+ mice.