Abstract 222: Hyperglycemia Reduces Levels of Soluble Amyloid Precursor Protein-α in Mouse Hippocampus and Cortex - Role of Cerebral Microvessels

Abstract

In the present study, we tested hypothesis that hyperglycemia impairs the neuro-protective function of cerebral microvessels. Type 1 diabetes (T1D) was induced by treatment of mice with streptozotocin (blood glucose >300 mg/dL for 2 months). Brain tissues and cerebral microvessels were isolated from diabetic and control mice. We observed significant decrease in the protein levels of soluble amyloid precursor protein-α (sAPPα, a product of α-cleavage of APP and a neurotrophic and neuroprotective molecule) in the total brain tissue of diabetic mice (n=5, P<0.05). Further examination of brain regions revealed that the reduction of protein levels of sAPPα was only detected in hippocampus and cortex but not in cerebellum (n=6, P<0.05). Our studies also revealed that there were no significant differences in the protein expression of APP and its non-amyloidogenic processing enzymes, α-secretases (a disintegrin and metalloprotease 10 [ADAM10], ADAM9, and ADAM17) in total brain tissue between T1D mice and control mice (n=5-6, P>0.05). The protein level of β-processing enzyme BACE1 was also not changed in T1D mouse brain. In contrast, the protein levels of APP and ADAM10 were significantly decreased in cerebral microvasculature of T1D mice, as compared to control mice (n=9-10, P<0.05). Immunofluorescent confocal microscopy also demonstrated that expressions of APP and ADAM10 in cerebral microvasculature (identified by co-staining with CD31) in hippocampus and cortex were reduced in T1D mice. Of note, cerebrovascular protein levels of ADAM9, ADAM17 and BACE1 were not affected by hyperglycemia (n=5-7, P>0.05). These results suggest that hyperglycemia impairs APP expression and α-processing in brain vasculature, thereby leading to the reduction of brain content of sAPPα. The selective loss of neuro-protective molecule sAPPα in hippocampus and cortex may be an important mechanism contributing to the development of cognitive dysfunction in diabetes.