Daniel Paris

Inflammatory cytokine levels correlate with amyloid load in transgenic mouse models of Alzheimer's disease

BackgroundInflammation is believed to play an important role in the pathology of Alzheimers disease (AD) and cytokine production is a key pathologic event in the progression of inflammatory cascades. The current study characterizes the cytokine expression profile in the brain of two transgenic mouse models of AD (TgAPPsw and PS1/APPsw) and explores the correlations between cytokine production and the level of soluble and insoluble forms of Aβ.MethodsOrganotypic brain slice cultures from 15-month-old mice (TgAPPsw, PS1/APPsw and control littermates) were established and multiple cytokine levels were analyzed using the Bio-plex multiple cytokine assay system. Soluble and insoluble forms of Aβ were quantified and Aβ-cytokine relationships were analyzed.ResultsCompared to control littermates, transgenic mice showed a significant increase in the following pro-inflammatory cytokines: TNF-α, IL-6, IL-12p40, IL-1β, IL-1α and GM-CSF. TNF-α, IL-6, IL-1α and GM-CSF showed a sequential increase from control to TgAPPsw to PS1/APPsw suggesting that the amplitude of this cytokine response is dependent on brain Aβ levels, since PS1/APPsw mouse brains accumulate more Aβ than TgAPPsw mouse brains. Quantification of Aβ levels in the same slices showed a wide range of Aβ soluble:insoluble ratio values across TgAPPsw and PS1/APPsw brain slices. Aβ-cytokine correlations revealed significant relationships between Aβ1–40, 1–42 (both soluble and insoluble) and all the above cytokines that changed in the brain slices.ConclusionOur data confirm that the brains of transgenic APPsw and PS1/APPsw mice are under an active inflammatory stress, and that the levels of particular cytokines may be directly related to the amount of soluble and insoluble Aβ present in the brain suggesting that pathological accumulation of Aβ is a key driver of the neuroinflammatory response.

Reduction of β-amyloid pathology by celastrol in a transgenic mouse model of Alzheimer's disease

BackgroundAβ deposits represent a neuropathological hallmark of Alzheimers disease (AD). Both soluble and insoluble Aβ species are considered to be responsible for initiating the pathological cascade that eventually leads to AD. Therefore, the identification of therapeutic approaches that can lower Aβ production or accumulation remains a priority. NFκB has been shown to regulate BACE-1 expression level, the rate limiting enzyme responsible for the production of Aβ. We therefore explored whether the known NFκB inhibitor celastrol could represent a suitable compound for decreasing Aβ production and accumulation in vivo.MethodsThe effect of celastrol on amyloid precursor protein (APP) processing, Aβ production and NFκB activation was investigated by western blotting and ELISAs using a cell line overexpressing APP. The impact of celastrol on brain Aβ accumulation was tested in a transgenic mouse model of AD overexpressing the human APP695sw mutation and the presenilin-1 mutation M146L (Tg PS1/APPsw) by immunostaining and ELISAs. An acute treatment with celastrol was investigated by administering celastrol intraperitoneally at a dosage of 1 mg/Kg in 35 week-old Tg PS1/APPsw for 4 consecutive days. In addition, a chronic treatment (32 days) with celastrol was tested using a matrix-driven delivery pellet system implanted subcutaneously in 5 month-old Tg PS1/APPsw to ensure a continuous daily release of 2.5 mg/Kg of celastrol.ResultsIn vitro, celastrol dose dependently prevented NFκB activation and inhibited BACE-1 expression. Celastrol potently inhibited Aβ1-40 and Aβ1-42 production by reducing the β-cleavage of APP, leading to decreased levels of APP-CTFβ and APPsβ. In vivo, celastrol appeared to reduce the levels of both soluble and insoluble Aβ1-38, Aβ1-40 and Aβ1-42. In addition, a reduction in Aβ plaque burden and microglial activation was observed in the brains of Tg PS1/APPsw following a chronic administration of celastrol.ConclusionsOverall our data suggest that celastrol is a potent Aβ lowering compound that acts as an indirect BACE-1 inhibitor possibly by regulating BACE-1 expression level via an NFκB dependent mechanism. Additional work is required to determine whether chronic administration of celastrol can be safely achieved with cognitive benefits in a transgenic mouse model of AD.

Impaired angiogenesis in a transgenic mouse model of cerebral amyloidosis

Abeta peptides are naturally occurring peptides, which are thought to play a key role in the pathophysiology of Alzheimers disease (AD). In AD cases, levels of soluble and insoluble Abeta peptides increase in the brain as well as in the cerebrovasculature, a phenomenon that does not occur in extra-cranial vessels. There are frequently anomalies in the cerebrovasculature in AD, and despite increases in several pro-angiogenic factors in AD brain, evidence for increased vascularity is lacking; in fact there is evidence to the contrary. It has also been recently shown that Abeta peptides may have profound anti-angiogenic effects in vitro and in vivo. We therefore investigated whether there is evidence for altered angiogenesis in the vasculature in a transgenic mouse model of Abeta amyloidosis (Tg APPsw line 2576). In vitro, the formation of capillary-like structures on a reconstituted extracellular matrix by endothelial cells isolated from Tg APPsw is impaired. Ex vivo, the sprouting of new capillaries from arterial explants (over expressing Abeta) isolated from 9-month-old Tg APPsw is reduced compared to arterial explants isolated from control littermates. In addition, Tg APPsw mice show a reduction in vascular density in the cortex and hippocampus compared to control littermates. Altogether, our data suggest that the over expression of APPsw in the vasculature may oppose angiogenesis.

Inhibition of Aβ production by NF-κB inhibitors

bstract The transcription factor nuclear factor B (NFB) is widely expressed in the nervous system and increased NFB immunoreactivity has been bserved in Alzheimer’s disease (AD) brains in the nuclei of neurons within the vicinity of diffuse -amyloid plaques. -Amyloid (A ) peptides re the main constituent of senile plaques and are known to stimulate NFB activity. In the present study, we investigated the effect of various FB inhibitors on the production of A 1–40, A 1–42, secreted APP (sAPP and sAPP ) and APP C-terminal fragments (APP-CTF) using CHO ells overexpressing the -amyloid precursor protein (APP). Our data show that NFB inhibitors decrease both A 1–40 and A 1–42 production.

Inhibition of angiogenesis by Abeta peptides.

Aβ peptides are naturally occurring peptides forming β-sheet aggregates that constitute an integral component of senile plaques and vascular deposits in Alzheimers disease. Since several peptides adopting a β-sheet conformation have been shown to be anti-angiogenic, we investigated the effect of Aβ on angiogenesis. We show that in vitro, Aβ dose-dependently inhibits the formation of capillaries by human brain endothelial cells plated on Matrigel and stimulates capillary degeneration at high doses. Preparations of Aβ peptides containing a higher content of β-sheet structures are more potently anti-angiogenic in vitro. Ex vivo, Aβ dose-dependently opposes angiogenesis in rat aortae and in human middle cerebral arteries. In vivo, Aβ dose dependently inhibits angiogenesis in the chick chorioallantoic membrane assay and suppresses bFGF-induced blood vessel formation in the corneal micropocket and Matrigel plug assays. Since angiogenesis is required for tumor growth, we explored the effect of Aβ on human glioblastoma (U87MG) and human lung adenocarcinoma (A549) tumors. We show that intra-tumoral injection of Aβ potently inhibits the growth and vascularization of human glioblastoma and human lung adenocarcinoma tumor xenografts in nude mice. Similarly to the intra-tumoral injection regimen, Aβ delivered intraperitoneally also suppressed the growth of human lung adenocarcinoma tumor xenografts. Altogether our data show that Aβ is an angiogenesis inhibitor.

Inhibition of Angiogenesis by Aβ Peptides

Aβ peptides are naturally occurring peptides forming β-sheet aggregates that constitute an integral component of senile plaques and vascular deposits in Alzheimers disease. Since several peptides adopting a β-sheet conformation have been shown to be anti-angiogenic, we investigated the effect of Aβ on angiogenesis. We show that in vitro, Aβ dose-dependently inhibits the formation of capillaries by human brain endothelial cells plated on Matrigel and stimulates capillary degeneration at high doses. Preparations of Aβ peptides containing a higher content of β-sheet structures are more potently anti-angiogenic in vitro. Ex vivo, Aβ dose-dependently opposes angiogenesis in rat aortae and in human middle cerebral arteries. In vivo, Aβ dose dependently inhibits angiogenesis in the chick chorioallantoic membrane assay and suppresses bFGF-induced blood vessel formation in the corneal micropocket and Matrigel plug assays. Since angiogenesis is required for tumor growth, we explored the effect of Aβ on human glioblastoma (U87MG) and human lung adenocarcinoma (A549) tumors. We show that intra-tumoral injection of Aβ potently inhibits the growth and vascularization of human glioblastoma and human lung adenocarcinoma tumor xenografts in nude mice. Similarly to the intra-tumoral injection regimen, Aβ delivered intraperitoneally also suppressed the growth of human lung adenocarcinoma tumor xenografts. Altogether our data show that Aβ is an angiogenesis inhibitor.

Selective antihypertensive dihydropyridines lower Aβ accumulation by targeting both the production and the clearance of Aβ across the blood-brain barrier.

Several large population-based or clinical trial studies have suggested that certain dihydropyridine (DHP) L-type calcium channel blockers (CCBs) used for the treatment of hypertension may confer protection against the development of Alzheimer disease (AD). However, other studies with drugs of the same class have shown no beneficial clinical effects. To determine whether certain DHPs are able to impact underlying disease processes in AD (specifically the accumulation of the Alzheimer Aβ peptide), we investigated the effect of several antihypertensive DHPs and non-DHP CCBs on Aβ production. Among the antihypertensive DHPs tested, a few, including nilvadipine, nitrendipine and amlodipine inhibited Aβ production in vitro, whereas others had no effect or raised Aβ levels. In vivo, nilvadipine and nitrendipine acutely reduced brain Aβ levels in a transgenic mouse model of AD (Tg PS1/APPsw) and improved Aβ clearance across the blood-brain barrier (BBB), whereas amlodipine and nifedipine were ineffective showing that the Aβ-lowering activity of the DHPs is independent of their antihypertensive activity Chronic oral treatment with nilvadipine decreased Aβ burden in the brains of Tg APPsw (Tg2576) and Tg PS1/APPsw mice, and also improved learning abilities and spatial memory. Our data suggest that the clinical benefit conferred by certain antihypertensive DHPs against AD is unrelated to their antihypertensive activity, but rely on their ability to lower brain Aβ accumulation by affecting both Aβ production and Aβ clearance across the BBB.

Alzheimer’s β‐amyloid peptide blocks vascular endothelial growth factor mediated signaling via direct interaction with VEGFR‐2

J. Neurochem. (2010) 112, 66–76.

Nilvadipine antagonizes both Aβ vasoactivity in isolated arteries, and the reduced cerebral blood flow in APPsw transgenic mice

The development of Alzheimers disease (AD) is generally thought to correlate with cerebral accumulation of Abeta. It has previously been shown that Abeta peptides enhance vasoconstriction in isolated arteries and oppose certain vasorelaxants. Moreover, exogenous application of Abeta peptides causes cerebral vasoconstriction in rodents and in transgenic mouse models of AD that overexpress Abeta there is reduced cerebral blood flow. In the present study, we investigated the effect of nilvadipine, a dihydropyridine-type calcium channel blocker, on Abeta induced vasoconstriction in isolated arteries and in vivo on cerebral blood flow (CBF) of an AD transgenic mouse model overexpressing Abeta (Tg APPsw line 2576). Nilvadipine completely inhibited the vasoactivity elicited by Abeta in rat aortae and in human middle cerebral arteries. The effect of a short treatment duration (2 weeks) with nilvadipine on regional CBF was investigated in 13-month-old Tg APPsw mice and control littermates using a laser Doppler imager. Additionally, CBF was also measured in 20-month-old Tg APPsw mice and control littermates that were chronically treated with nilvadipine for 7 months. Untreated Tg APPsw mice showed a reduction of regional CBF compared to their untreated control littermates. Nilvadipine restored cortical perfusion levels in Tg APPsw to values similar to those observed in control littermates without notably affecting the CBF of control mice. All together, these data suggest that nilvadipine might be useful for the treatment of oligemia associated with AD.

Stimulation of the Retinoid X Receptor Facilitates Beta-Amyloid Clearance Across the Blood–Brain Barrier

Alzheimer’s disease (AD) is a neurodegenerative process characterized, in part, by the accumulation of beta-amyloid proteins (Aβ) in the brain. Evidence now suggests that the excessive Aβ accumulation is the result of impaired clearance from the brain. Recent studies have indicated that retinoid X receptor (RXR) activation stimulates the metabolic clearance of Aβ and rapidly reverses Aβ-induced behavioral deficits, doing so in an apoE-dependent manner. Previously, we reported that soluble apoE (i.e., not bound to Aβ) facilitated Aβ transit across the blood–brain barrier (BBB). As Aβ clearance from the brain involves both metabolic and BBB-mediated processes, the current studies investigated the impact of RXR stimulation on Aβ clearance across the BBB. Treatment with RXR agonists increased Aβ clearance across the BBB both in vitro and in vivo. Moreover, this processes appeared to involve apoE as RXR agonism did not stimulate Aβ BBB clearance when apoE was absent. Thus, RXR activation could mitigate Aβ brain burden by promoting both the metabolic and BBB clearance of Aβ, offering a novel approach to the treatment of AD.