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.

The blood-brain barrier (BBB) limits the entry of neurotoxic blood-derived products and cells into the brain that is required for normal neuronal functioning and information processing. Pericytes maintain the integrity of the BBB and degenerate in Alzheimer's disease (AD). The BBB is damaged in AD, particularly in individuals carrying apolipoprotein E4 (APOE4) gene, which is a major genetic risk factor for late-onset AD. The mechanisms underlying the BBB breakdown in AD remain, however, elusive. Here, we show accelerated pericyte degeneration in AD APOE4 carriers >AD APOE3 carriers >non-AD controls, which correlates with the magnitude of BBB breakdown to immunoglobulin G and fibrin. We also show accumulation of the proinflammatory cytokine cyclophilin A (CypA) and matrix metalloproteinase-9 (MMP-9) in pericytes and endothelial cells in AD (APOE4 >APOE3), previously shown to lead to BBB breakdown in transgenic APOE4 mice. The levels of the apoE lipoprotein receptor, low-density lipoprotein receptor-related protein-1 (LRP1), were similarly reduced in AD APOE4 and APOE3 carriers. Our data suggest that APOE4 leads to accelerated pericyte loss and enhanced activation of LRP1-dependent CypA-MMP-9 BBB-degrading pathway in pericytes and endothelial cells, which can mediate a greater BBB damage in AD APOE4 compared with AD APOE3 carriers.

PICALM is highly validated genetic risk factor for Alzheimer’s disease (AD). Here, we report that PICALM reductions in AD and murine brain endothelium correlate with amyloid–β (Aβ) pathology and cognitive impairment. Moreover, Picalm deficiency diminishes Aβ clearance across the murine blood–brain barrier (BBB) and accelerates Aβ pathology that is reversible by endothelial PICALM re–expression. Using human brain endothelial monolayer, we show that PICALM regulates PICALM/clathrin–dependent internalization of Aβ bound to the low density lipoprotein receptor related protein–1, a key Aβ clearance receptor, and guides Aβ trafficking to Rab5 and Rab11 leading to Aβ endothelial transcytosis and clearance. PICALM levels and Aβ clearance were reduced in AD–derived endothelial monolayers, which was reversible by adenoviral–mediated PICALM transfer. iPSC–derived human endothelial cells carrying the rs3851179 protective allele exhibited higher PICALM levels and enhanced Aβ clearance. Thus, PICALM regulates Aβ BBB transcytosis and clearance that has implications for Aβ brain homeostasis and clearance therapy.

Pericytes are perivascular mural cells of brain capillaries that are positioned centrally within the neurovascular unit between endothelial cells, astrocytes and neurons. This unique position allows them to play a major role in regulating key neurovascular functions of the brain. The role of pericytes in the regulation of cerebral blood flow (CBF) and neurovascular coupling remains, however, debatable. Using loss-of-function pericyte-deficient mice, here we show that pericyte degeneration diminishes global and individual capillary CBF responses to neuronal stimulus resulting in neurovascular uncoupling, reduced oxygen supply to brain and metabolic stress. We show that these neurovascular deficits lead over time to impaired neuronal excitability and neurodegenerative changes. Thus, pericyte degeneration as seen in neurological disorders such as Alzheimer’s disease may contribute to neurovascular dysfunction and neurodegeneration associated with human disease.

Activated protein C (APC) is a blood protease with anticoagulant activity and cell-signaling activities mediated by activation of protease-activated receptors 1 and 3 (PAR1, PAR3) via non-canonical cleavage1. Recombinant APC and/or its analogs with reduced (>90%) anticoagulant activity such as 3K3A-APC (Lys191–193Ala), engineered to reduce APC-associated bleeding risk while retaining normal cell signaling activity, have shown benefits in preclinical models of ischemic stroke2–6, brain trauma7, multiple sclerosis8, amyotrophic lateral sclerosis9, sepsis10,11, ischemic/reperfusion injury of heart12, kidney and liver13, pulmonary, kidney and gastrointestinal inflammation1,11, diabetes14 and lethal body radiation15. Based on proof of concept studies and an excellent safety profile in humans, 3K3A-APC has advanced to clinical trials as a neuroprotectant in ischemic stroke16,17. Recently, 3K3A-APC has been shown to stimulate neuronal production by human neural stem/progenitor cells (NSCs) in vitro18 via a PAR1-PAR3-sphingosine-1-phosphate receptor 1-Akt pathway19, suggesting the potential for APC-based treatment as a strategy for structural repair in the human central nervous system. Here, we report that late post-ischemic treatment of mice with 3K3A-APC stimulates neuronal production by transplanted human NSCs, promotes circuit restoration, and improves functional recovery. Thus, 3K3A-APC-potentiated neuronal recruitment from engrafted NSCs may offer a new approach to the treatment of stroke and related neurological disorders.

Cells with reduced origin firing have an increased rate of replication fork progression, whereas fork progression is slowed in cells with excess origins.

he APOE4 variant of apolipoprotein E is the strongest genetic risk factor for AD 1 . One and two APOE4 alleles increase risk for AD by approximately 4-and 15-fold, respectively, compared to the more-common APOE3 gene that carries lower risk for AD 1 . Besides accelerating onset and progression of dementia, APOE4 is associated with different brain pathologies. For example, APOE4 accelerates BBB breakdown and degeneration of brain capillary pericytes 2,3 that maintain BBB integrity [4][5][6] and leads to cerebral blood flow (CBF) reduction 7,8 and dysregulation 7,9,10 . APOE4 is toxic to neurons 11 and accelerates tau-mediated neurodegeneration 12 . Additionally, APOE4 slows down amyloid-β (Aβ) clearance 13,14 and accelerates amyloid deposition [14][15][16] , which promotes development of amyloid pathology.Recent studies focused on very early stages in the Alzheimer's continuum in individuals who are cognitively unimpaired or with mild cognitive impairment (MCI) have shown that individuals bearing an APOE4 variant (APOE3/APOE4 or APOE4/APOE4) are distinguished from APOE3 homozygotes by breakdown in the BBB in the hippocampus and medial temporal lobe, regions responsible for memory encoding and cognitive functions 17 . This finding is apparent in cognitively unimpaired APOE4 carriers and more severe in those with MCI and is independent of Aβ or tau pathology measured in the cerebrospinal fluid or in brain by positron emission tomography 17 . These findings support the growing evidence suggesting that vascular dysfunction, BBB breakdown and vascular disorder contribute to early cognitive impairment and AD [17][18][19][20][21][22][23][24][25][26] . On the other hand, accumulation of Aβ in the brain has also been suggested to occur years before cognitive impairment and continues to increase with disease progression 27 . Although it has been shown that vascular dysfunction contributes to early cognitive impairment in ways that may not be exclusively related to classical AD pathology 17,19,20,26 , the respective contributions of the BBB pathway and vascular disorder versus amyloid-β pathway to advanced disease stage during progression of neurodegenerative disorder and cognitive decline in AD are still poorly understood.To address this question, here we studied vascular dysfunction, Aβ pathology, neuronal dysfunction and behavior in older APOE3 and APOE4 knock-in mice 28 alone and crossed with the 5xFAD line 29 . All mice were derived from the same litters, as previously described 30 . Mice lacking Apoe 3 and/or expressing human APOE4 develop early BBB breakdown 3,[31][32][33] and CBF dysregulation 10 . On the other hand, the 5xFAD line also develops BBB breakdown [34][35][36][37] , CBF reductions 38 and neuron and synaptic loss at a later stage 29,39 , whereas APOE3;5xFAD and APOE4;5xFAD mice (also known as E3FAD and E4FAD lines, respectively 30 ) have comparable Aβ pathology at an older age 40 . These features of the studied models allowed us to interrogate how different pathologies in APOE4 compared to APOE3 mice relat...

The low-density lipoprotein receptor–related protein 1 (LRP1) is an endocytic and cell signaling transmembrane protein. Endothelial LRP1 clears proteinaceous toxins at the blood–brain barrier (BBB), regulates angiogenesis, and is increasingly reduced in Alzheimer’s disease associated with BBB breakdown and neurodegeneration. Whether loss of endothelial LRP1 plays a direct causative role in BBB breakdown and neurodegenerative changes remains elusive. Here, we show that LRP1 inactivation from the mouse endothelium results in progressive BBB breakdown, followed by neuron loss and cognitive deficits, which is reversible by endothelial-specific LRP1 gene therapy. LRP1 endothelial knockout led to a self-autonomous activation of the cyclophilin A–matrix metalloproteinase-9 pathway in the endothelium, causing loss of tight junctions underlying structural BBB impairment. Cyclophilin A inhibition in mice with endothelial-specific LRP1 knockout restored BBB integrity and reversed and prevented neuronal loss and behavioral deficits. Thus, endothelial LRP1 protects against neurodegeneration by inhibiting cyclophilin A, which has implications for the pathophysiology and treatment of neurodegeneration linked to vascular dysfunction.