The glucose transporter GLUT1 at the blood-brain barrier (BBB) mediates glucose transport into the brain. Alzheimer's disease is characterized by early reductions in glucose transport associated with diminished GLUT1 expression at the BBB. Whether GLUT1 reduction influences disease pathogenesis remains, however, elusive. Here, we show that GLUT1 deficiency in mice overexpressing amyloid β-petpide (Aβ) precursor protein leads to: 1) early cerebral microvascular degeneration, blood flow reductions and dysregulation, and BBB breakdown; and (2) accelerated amyloid β-peptide (Aβ) pathology, reduced Aβ clearance, diminished neuronal activity, behavioral deficits, and progressive neuronal loss and neurodegeneration that develop after initial cerebrovascular degenerative changes. We also show that GLUT1 deficiency in endothelium, but not in astrocytes, initiates the vascular phenotype as shown by BBB breakdown. Thus, reduced BBB GLUT1 expression worsens Alzheimer's disease cerebrovascular degeneration, neuropathology and cognitive function suggesting that GLUT1 may represent a novel therapeutic target for Alzheimer's disease vasculo-neuronal dysfunction and degeneration.

Neurovascular dysfunction contributes to Alzheimer’s disease (AD). Cerebrovascular abnormalities and blood-brain barrier (BBB) damage have been shown in AD. The BBB dysfunction can lead to leakage of potentially neurotoxic plasma components in brain that may contribute to neuronal injury. Pericytes are integral in maintaining the BBB integrity. Pericyte-deficient mice develop a chronic BBB damage preceding neuronal injury. Moreover, loss of pericytes was associated with BBB breakdown in patients with amyotrophic lateral sclerosis. Here, we demonstrate a decrease in mural vascular cells in AD, and show that pericyte number and coverage in the cortex and hippocampus of AD subjects compared to neurologically-intact controls are reduced by 59% and 60% (p<0.01), and 32 and 33% (p<0.01), respectively. An increase in extravascular immunoglobulin G and fibrin deposition correlated with reductions in pericyte coverage in AD cases compared to controls; the Pearson’s correlation coefficient r for the magnitude of BBB breakdown to IgG and fibrin versus reduction in pericyte coverage was − 0.96 (p<0.01) and − 0.81 (p<0.01) in the cortex, respectively, and − 0.86 (p<0.01) and − 0.98 (p<0.01) in the hippocampus, respectively. Thus, deficiency in mural vascular cells may contribute to disrupted vascular barrier properties and resultant neuronal dysfunction during AD pathogenesis.

The blood–brain barrier and blood–spinal cord barrier (BSCB) limit the entry of plasma components and erythrocytes into the central nervous system (CNS). Pericytes play a key role in maintaining blood–CNS barriers. The BSCB is damaged in patients with amyotrophic lateral sclerosis (ALS). Moreover, transgenic ALS rodents and pericyte-deficient mice develop BSCB disruption with erythrocyte extravasation preceding motor neuron dysfunction. Here, we studied whether BSCB disruption with erythrocyte extravasation and pericyte loss are present in human ALS. We show that 11 of 11 cervical cords from ALS patients, but 0 of 5 non-neurodegenerative disorders controls, possess perivascular deposits of erythrocyte-derived hemoglobin and hemosiderin typically 10–50 μm in diameter suggestive of erythrocyte extravasation. Immunostaining for CD235a, a specific marker for erythrocytes, confirmed sporadic erythrocyte extravasation in ALS, but not controls. Quantitative analysis revealed a 3.1-fold increase in perivascular hemoglobin deposits in ALS compared to controls showing hemoglobin confined within the vascular lumen, which correlated with 2.5-fold increase in hemosiderin deposits (r = 0.82, p < 0.01). Spinal cord parenchymal accumulation of plasma-derived immunoglobulin G, fibrin and thrombin was demonstrated in ALS, but not controls. Immunostaining for platelet-derived growth factor receptor-β, a specific marker for CNS pericytes, indicated a 54 % (p < 0.01) reduction in pericyte number in ALS patients compared to controls. Pericyte reduction correlated negatively with the magnitude of BSCB damage as determined by hemoglobin abundance (r = −0.75, p < 0.01). Thus, the BSCB disruption with erythrocyte extravasation and pericyte reductions is present in ALS. Whether similar findings occur in motor cortex and affected brainstem motor nuclei remain to be seen.

The blood–spinal cord barrier (BSCB) regulates molecular exchange between blood and spinal cord. Pericytes are presumed to be important cellular constituents of the BSCB. However, the regional abundance and vascular functions of spinal cord pericytes have yet to be determined. Utilizing wild-type mice, we show that spinal cord pericyte capillary coverage and number compared with the brain regions are reduced most prominently in the anterior horn. Regional pericyte variations are highly correlated with: (1) increased capillary permeability to 350 Da, 40,000 Da, and 150,000 Da, but not 2,000,000 Da fluorescent vascular tracers in cervical, thoracic, and lumbar regions and (2) diminished endothelial zonula occludens-1 (ZO-1) and occludin tight junction protein expression. Pericyte-deficient mutations (PdgfrβF7/F7 mice) resulted in additional pericyte reductions in spinal cord capillaries leading to overt BSCB disruption to serum proteins, accumulation in motor neurons of cyotoxic thrombin and fibrin and motor neuron loss. Barrier disruption in perciyte-deficient mice coincided with further reductions in ZO-1 and occludin. These data suggest that pericytes contribute to proper function of the BSCB at the capillary level. Regional reductions in spinal cord pericytes may provide a cellular basis for heightened spinal cord barrier capillary permeability and motor neuron loss.