Exacerbation of Poststroke Dementia by Type 2 Diabetes is Associated with Synergistic Increases of Beta-secretase Activation and Beta-amyloid Generation in Rat Brains

We examined the effect of type 2 diabetes on stroke-induced Alzheimer's disease-like pathological and behavioral changes in rats. Rats were treated for 2 months with high fat diet (HFD) followed by streptozotocin (STZ) injection to induce type 2 diabetes (HFD-STZ model). Middle cerebral artery occlusion (MCAO) was used to induce cerebral focal ischemia. Animals were divided into four groups: Sham-NPD, Sham-HFD-STZ, MCAO-NPD and MCAO-HFD-STZ. The results showed that HFD-STZ treatment induced obesity, hypertriglyceridemia, hypercholesterolemia, hyperinsulinemia, hyperglycemia and insulin resistance, characteristics of type 2 diabetes. The performance of rats in the Morris water maze test was impaired in MCAO-NPD and Sham-HFD-STZ rats, indicating cognitive deficits. Hippocampal caspase-3+ and beta amyloid (Abeta+) cell numbers, as well as beta-site amyloid precursor protein-cleaving enzyme (BACE1) levels and activity, increased in both groups. Moreover, HFD-STZ treatment exacerbated stroke-induced cognitive deficits, additively increased MCAO-induced activation of caspase-3, and increased levels of BACE1, C99 and Abeta. However, the level of insulin decreased in MCAO-HFD-STZ rats. These results suggested that type 2 diabetes deteriorated stroke-induced brain damage and cognitive impairment, which might be associated with increased Abeta generation and cytotoxicity. We concluded that type 2 diabetes exacerbated poststroke dementia possibly due to brain injury and synergistic generation of Abeta via activation of BACE1.