Background: Diabetes imposes an increased risk of microvascular complications. The present study aims to evaluate if diabetes and its disturbances in brain blood microcirculation increases the susceptibility to brain ischemic insults.
Methods and Results: Diabetes was induced by streptozocin in mice expressing green fluorescent protein in endothelial cells (Tie2-GFP mice). Four weeks later the diabetic mice were subjected to transient (20 min) middle cerebral artery occlusion (MCAO). In vivo two-photon laser scanning microscopy (TPLSM) was applied to the brains of the mice, and blood flow was estimated in arteries, capillaries and veins in diabetic and control mice after the MCAO. We found a significant decrease in red blood cell (RBC) velocity in capillaries in diabetic mice (0.93 ± 0.11 mm/s, P<0.001 versus control mice). Despite this no significant changes in regional blood flow was observed by simultaneously performed laser-Doppler flowmetry. Notably, we observed that a further decline in RBC velocity (0.62 ± 0.07 mm/s, P<0.001 versus diabetic or ischemic mice) and capillary volume flux [(2.29 ± 0.27) × 10-5 μl/s, P<0.001 versus diabetic or ischemic mice] in diabetic-MCAO mice, indicating diabetes-aggravated brain ischemia-induced disturbance in cerebral capillary blood flow. Furthermore, our intravital TPLSM data demonstrated that brain capillary flow was more turbulent in diabetic-MCAO mice than in the other groups. Diabetic-MCAO mice also exhibited increased neurological deficit (3.36 ± 0.23, P<0.01 versus MCAO mice), which was accompanied by exaggerated degradation of tight junction proteins and blunted CaMKII phosphorylation.
Conclusions: The present data indicate that diabetic mice are more susceptible to disturbances of cerebral capillary blood flow and neurovascular defects during ischemic conditions.