Increased hemorrhage and mortality rate after transient focal ischemia in a genetic mouse model of type 1 diabetes

Abstract

PURPOSE: Epidemiological studies showed that type 1 diabetic patients have a higher risk of cerebrovascular mortality from stroke. Amongst those who survived after stroke, the median survival is only half as 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 not clear. 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 induced by middle cerebral artery occlusion (MCAO) (2h ischemia and 22h reperfusion). Mortality rate was calculated at 1, 2, 4, and 22h of reperfusion and neurological deficits were accessed by the end of the 22h-reperfusion. Brain slices were prepared and stained with 2, 3, 5-triphenyltetrazolium chloride for estimating the infarct area, infarct volume, hemispheric swelling, and hemorrhagic area. Immunohistochemical experiments using antibodies against immunoglobulin G, aquaporin 4 and occludin were performed on brain sections to compare blood vessel integrity. RESULTS: A higher mortality rate and a shorter survival period were observed in Ins2Akita/+ mice after the MCAO challenge when compared with Ins2+/+ mice. In the survived Ins2Akita/+ mice, hemorrhage was observed in almost every individual (90%). The hemorrhagic areas were remarkably increased in Ins2Akita/+ mice, with the majority localizing in the infarct core while a small proportion residing in the penumbra. However, no significant difference was found in neurological deficits, infarct area, infarct volume or hemispheric swelling when compared with Ins2+/+ mice. Immunohistochemistry results showed similar staining pattern and intensity of proteins associated with blood vessel integrity, including immunoglobulin G, aquaporin 4 and occludin, in both Ins2Akita/+ and Ins2+/+ mice. CONCLUSION: We showed that induction of MCAO in Ins2Akita/+ mice could mimic the clinical observations of high mortality and shortened survival in type 1 diabetic patients upon stroke. The presence of hemorrhage, which was associated with blood vessel leakage and extravasation, may be a potential cause of the exacerbation in the injured brains. The similarities in infarct size, hemispheric swelling as well as blood vessel integrity may possibly be due to a selection of surviving animals that were relatively more resistant to ischemic insult.