Brice Ongali

Complete Rescue of Cerebrovascular Function in Aged Alzheimer's Disease Transgenic Mice by Antioxidants and Pioglitazone, a Peroxisome Proliferator-Activated Receptor γ Agonist

Accumulating evidence suggests that cerebrovascular dysfunction is an important factor in the pathogenesis of Alzheimers disease (AD). Using aged (∼16 months) amyloid precursor protein (APP) transgenic mice that exhibit increased production of the amyloid-β (Aβ) peptide and severe cerebrovascular and memory deficits, we examined the capacity of in vivo treatments with the antioxidants N-acetyl-l-cysteine (NAC) and tempol, or the peroxisome proliferator-activated receptor γ agonist pioglitazone to rescue cerebrovascular function and selected markers of AD neuropathology. Additionally, we tested the ability of pioglitazone to normalize the impaired increases in cerebral blood flow (CBF) and glucose uptake (CGU) induced by whisker stimulation, and to reverse spatial memory deficits in the Morris water maze. All compounds fully restored cerebrovascular reactivity of isolated cerebral arteries concomitantly with changes in proteins regulating oxidative stress, without reducing brain Aβ levels or Aβ plaque load. Pioglitazone, but not NAC, significantly attenuated astroglial activation and improved, albeit nonsignificantly, the reduced cortical cholinergic innervation. Furthermore, pioglitazone completely normalized the CBF and CGU responses to increased neuronal activity, but it failed to improve spatial memory. Our results are the first to demonstrate that late pharmacological intervention with pioglitazone not only overcomes cerebrovascular dysfunction and altered neurometabolic coupling in aged APP mice, but also counteracts cerebral oxidative stress, glial activation, and, partly, cholinergic denervation. Although early or combined therapy may be warranted to improve cognition, these findings unequivocally point to pioglitazone as a most promising strategy for restoring cerebrovascular function and counteracting several AD markers detrimental to neuronal function.

Simvastatin improves cerebrovascular function and counters soluble amyloid-beta, inflammation and oxidative stress in aged APP mice.

Cerebrovascular dysfunctions appear to contribute to Alzheimers disease (AD) pathogenesis and the associated cognitive decline. Recently, it has been suggested that statins could be beneficial to AD patients independently from their cholesterol-lowering effects. Using 10 month-old amyloid precursor protein transgenic mice (APP mice), we sought to reverse cerebrovascular, neuronal and memory impairments with simvastatin (20 mg/kg/day, 8 weeks). Simvastatin improved reactivity of cerebral arteries, rescued the blood flow response to neuronal activation, attenuated oxidative stress and inflammation, and reduced cortical soluble amyloid-beta (Abeta) levels and the number of Abeta plaque-related dystrophic neurites. However, at such an advanced stage of the pathology, it failed to reduce Abeta plaque load and normalize cholinergic and memory deficits. These findings demonstrate that low-dose simvastatin treatment in aged APP mice largely salvages cerebrovascular function and has benefits on several AD landmarks, which could explain some of the positive effects of statins reported in AD patients.

Oxidative stress and cerebrovascular dysfunction in mouse models of Alzheimer's disease

Several factors have been implicated in Alzheimers disease (AD) but there is no definite conclusion as to the main pathogenic agents. Mutations in the amyloid precursor protein (APP) that lead to increased production of amyloid β peptide (Aβ) are associated with the early‐onset, familial forms of AD. However, in addition to ageing, the most common risk factors for the sporadic, prevalent form of AD are hypertension, hypercholesterolaemia, ischaemic stroke, the ApoE4 allele and diabetes, all characterized by a vascular pathology. In AD, the vascular pathology includes accumulation of Aβ in the vessel wall, vascular fibrosis, and other ultrastructural changes in constituent endothelial and smooth muscle cells. Moreover, the ensuing chronic cerebral hypoperfusion has been proposed as a determinant factor in the accompanying cognitive deficits. In transgenic mice that overexpress mutated forms of the human APP (APP mice), the increased production of Aβ results in vascular oxidative stress and loss of vasodilatory function. The culprit molecule, superoxide, triggers the synthesis of other reactive oxygen species and the sequestration of nitric oxide (NO), thus impairing resting cerebrovascular tone and NO‐dependent dilatations. The Aβ‐induced cerebrovascular dysfunction can be completely abrogated in aged APP mice with antioxidant therapy. In contrast, in mice that overproduce an active form of the cytokine transforming growth factor‐β1 and recapitulate the vascular structural changes seen in AD, antioxidants have no beneficial effect on the accompanying cerebrovascular deficits. This review discusses the beneficial role and limitations of antioxidant therapy in AD cerebrovascular pathology.

Expression of kinin B1 receptors in the spinal cord of streptozotocin-diabetic rat.

Previous studies have reported cardiovascular and nociceptive responses after intrathecal injection of kinin B1 receptor (B1R) agonists in the model of streptozotocin (STZ)-diabetic rat (diabetic). The aim of this study was to measure the early up-regulation of B1R binding sites and mRNA in the thoracic spinal cord of diabetic and control rats. Data show significant increases of specific B1R binding sites in the dorsal horn of diabetic rats 2 days (+315%), 7 days (+303%) and 21 days (+181%) after STZ treatment. Levels of mRNA were significantly increased (+68%) at 2 and 7 days but not at 21 days. These data bring the first molecular evidence for an early up-regulation of B1R in the spinal cord of diabetic rat.

Selective in vivo antagonism of endothelin receptors in transforming growth factor-β1 transgenic mice that mimic the vascular pathology of Alzheimer’s diseaseThis article is one of a selection of papers published in the two-part special issue entitled 20 Years of Endothelin Research.

Increased levels of transforming growth factor-beta1 (TGF-beta1) induce a vascular pathology that shares similarities with that seen in Alzheimers disease, and which possibly contributes to the cognitive decline. In aged transgenic mice that overexpress TGF-beta1 (TGF mice), we previously found reduced dilatory function and selectively impaired endothelin-1 (ET-1)-induced contraction. Here we studied the effects of chronic treatments with selective ETA (ABT-627) or ETB (A-192621) receptor antagonist on cerebrovascular reactivity, cerebral perfusion, or memory performance. The dilatory deficit of TGF mice was not improved by either treatment, but both ET-1 contraction and basal nitric oxide (NO) production were distinctly altered. Although ABT-627 was devoid of any effect in TGF mice, it virtually abolished the ET-1-induced contraction and NO release in wild-type (WT) littermates. In contrast, A-192621 only acted upon TGF mice with full recovery of ET-1 contraction and baseline NO synthesis. TGF mice, treated or not, had no cognitive deficit in the Morris water maze, nor did ABT-627-treated WT controls despite severely impaired vasoreactivity. These findings confirm that ETA receptors primarily mediate the ET-1-induced contraction. Further, they suggest that ETB receptors play a detrimental role in conditions of increased TGF-beta1 and that vascular dysfunction does not inevitably lead to cognitive deficit.

Transforming growth factor-β1 (TGF-β1) induces cerebrovascular dysfunction and astrogliosis through angiotensin II type 1 receptor-mediated signaling pathways.

Transgenic mice constitutively overexpressing the cytokine transforming growth factor-β1 (TGF-β1) (TGF mice) display cerebrovascular alterations as seen in Alzheimers disease (AD) and vascular cognitive impairment and dementia (VCID), but no or only subtle cognitive deficits. TGF-β1 may exert part of its deleterious effects through interactions with angiotensin II (AngII) type 1 receptor (AT1R) signaling pathways. We test such interactions in the brain and cerebral vessels of TGF mice by measuring cerebrovascular reactivity, levels of protein markers of vascular fibrosis, nitric oxide synthase activity, astrogliosis, and mnemonic performance in mice treated (6 months) with the AT1R blocker losartan (10 mg/kg per day) or the angiotensin converting enzyme inhibitor enalapril (3 mg/kg per day). Both treatments restored the severely impaired cerebrovascular reactivity to acetylcholine, calcitonin gene-related peptide, endothelin-1, and the baseline availability of nitric oxide in aged TGF mice. Losartan, but not enalapril, significantly reduced astrogliosis and cerebrovascular levels of profibrotic protein connective tissue growth factor while raising levels of antifibrotic enzyme matrix metallopeptidase-9. Memory was unaffected by aging and treatments. The results suggest a pivotal role for AngII in TGF-β1-induced cerebrovascular dysfunction and neuroinflammation through AT1R-mediated mechanisms. Further, they suggest that AngII blockers could be appropriate against vasculopathies and astrogliosis associated with AD and VCID.

Cerebrovascular and memory deficits in an Alzheimer's disease mouse model overexpressing amyloid precursor protein and transforming growth factor-β1

Background: Vascular dysfunctions and memory loss are two landmarks of Alzheimer’s disease (AD). In AD brain and cerebral vasculature, levels of amyloid-beta (Ab) and transforming growth factor-b1 (TGF-b1) are elevated. When separately overproduced in transgenic mice, Ab and TGF-b1 result in vascular deficits that can be imputed to oxidative stress or alterations in vasomotor signaling pathways respectively, but cognitive deficits only occur in Ab-overexpressing mice. Methods: In young (6-8), adult (w12) and old (18-19 months) APP/TGF mice and age-matched wildtype (wt) littermates, we measured i) cerebrovascular reactivity of isolated, pressurized middle cerebral artery using on-line videomicroscopy; ii) levels of proteins involved in vascular function, structure or oxidative stress regulation by Western blot; iii) cerebral blood flow (CBF) induced by whisker stimulation using Laser doppler flowmetry, iv) astrocyte activation and amyloidosis by immunohistochemistry and, finally, vi) spatial memory in the Morris water maze. Results: Relative to wt controls, APP/TGF mice displayed early and age-dependent decreases in vasodilatory responses to acetylcholine (ACh) and calcitonin gene-related peptide (CGRP) with late reduction in basal synthesis of nitric oxide (NO). These were not attributable to oxidative stress as inhibition of free radicals did not restore function. The deficits in cerebrovascular reactivity measured in vitro translated in vivo to a progressive decrease in the CBF evoked by sensory stimulation. Vessels displayed unchanged levels of the oxidative stress marker superoxide dismutase (SOD2), but those of the vasodilator synthesizing enzyme cyclooxygenase-2 (COX2) were decreased whereas levels of molecules associated with vascular remodeling vascular endothelial growth factor (VEGF), connective tissue growth factor (CTGF), matrix metalloproteinase 9 (MMP9) and collagen were increased. Finally, APP/TGF mice exhibited progressive vascular and senile Ab plaques, astrocyte activation and, with time, developed severe memory deficits. Conclusions: APP/TGF mice display progressive cerebrovascular functional and structural deficits reflective of the TGF-b1 phenotype, in addition to vascular and parenchymal amyloidosis and memory impairment exhibited by Ab-overproducing mice. Hence, APP/TGF mice represent a very attractive model to explore therapeutic strategies that target both aspects of AD pathophysiology.