Fiona Crawford

Role of CD40 ligand in amyloidosis in transgenic Alzheimer's mice

We have shown that interaction of CD40 with CD40L enables microglial activation in response to amyloid-β peptide (Aβ), which is associated with Alzheimers disease (AD)-like neuronal tau hyperphosphorylation in vivo. Here we report that transgenic mice overproducing Aβ, but deficient in CD40L, showed decreased astrocytosis and microgliosis associated with diminished Aβ levels and β-amyloid plaque load. Furthermore, in the PSAPP transgenic mouse model of AD, a depleting antibody against CD40L caused marked attenuation of Aβ/β-amyloid pathology, which was associated with decreased amyloidogenic processing of amyloid precursor protein (APP) and increased circulating levels of Aβ. Conversely, in neuroblastoma cells overexpressing wild-type human APP, the CD40–CD40L interaction resulted in amyloidogenic APP processing. These findings suggest several possible mechanisms underlying mitigation of AD pathology in response to CD40L depletion, and validate the CD40–CD40L interaction as a target for therapeutic intervention in AD.

Genetics and molecular advances in Alzheimer's disease

Abstract The abnormal deposition of amyloid β protein (Aβ) in the brain is the major neuropathological characteristic of Alzheimers disease (AD). The disease in some early-onset familial cases develops as a result of mutations in the gene coding for the β-amyloid precursor protein (βAPP) and in the majority of the rest appears to be caused by an unidentified gene on chromosome 14. Only one of the βAPP gene mutations has been associated with aberrant βAPP processing, resulting in an excess production of Aβ in vitro, a result suggesting that there might be excessive Aβ cleavage from βAPP in AD in vivo. By contrast with the βAPP mutants, no particular allele of the apolipoprotein E (APOE) gene predicts the disease completely but one allele is associated with the disease suggesting APOE is a risk locus for AD. This discovery has been linked to increased deposition of Aβ in those cases carrying the risk allele. However, the genetic evidence is currently not sufficient to indicate whether βAPP mismetabolism, direct or indirect Aβ neurotoxicity or dysfunction of βAPP (or its derivatives) are central to the AD process.

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.

Chronic neuropathological and neurobehavioral changes in a repetitive mild traumatic brain injury model

Traumatic brain injury (TBI) is a recognized risk factor for later development of neurodegenerative disease. However, the mechanisms contributing to neurodegeneration following TBI remain obscure.

Walk in to work out: a randomised controlled trial of a self help intervention to promote active commuting

Study objective: To determine if a self help intervention, delivered via written interactive materials (the “Walk in to Work Out” pack), could increase active commuting behaviour (walking and cycling). Design: Randomised controlled trial. The intervention group received the “Walk in to Work Out” pack, which contained written interactive materials based on the transtheoretical model of behaviour change, local information about distances and routes, and safety information. The control group received the pack six months later. Focus groups were also conducted after six months. Setting: Three workplaces in the city of Glasgow, Scotland, UK. Participants: 295 employees who had been identified as thinking about, or doing some irregular, walking or cycling to work. Main results: The intervention group was almost twice as likely to increase walking to work as the control group at six months (odds ratio of 1.93, 95% confidence intervals 1.06 to 3.52). The intervention was not successful at increasing cycling. There were no distance travelled to work, gender, or age influences on the results. Twenty five per cent (95% confidence intervals 17% to 32%) of the intervention group, who received the pack at baseline, were regularly actively commuting at the 12 month follow up. Conclusion: The “Walk in to Work Out” pack was successful in increasing walking but not cycling. The environment for cycling must be improved before cycling will become a popular option.

Repetitive mild traumatic brain injury in a mouse model produces learning and memory deficits accompanied by histological changes

Concussion or mild traumatic brain injury (mTBI) represents the most common type of brain injury. However, in contrast with moderate or severe injury, there are currently few non-invasive experimental studies that investigate the cumulative effects of repetitive mTBI using rodent models. Here we describe and compare the behavioral and pathological consequences in a mouse model of single (s-mTBI) or repetitive injury (r-mTBI, five injuries given at 48 h intervals) administered by an electromagnetic controlled impactor. Our results reveal that a single mTBI is associated with transient motor and cognitive deficits as demonstrated by rotarod and the Barnes Maze respectively, whereas r-mTBI results in more significant deficits in both paradigms. Histology revealed no overt cell loss in the hippocampus, although a reactive gliosis did emerge in hippocampal sector CA1 and in the deeper cortical layers beneath the injury site in repetitively injured animals, where evidence of focal injury also was observed in the brainstem and cerebellum. Axonal injury, manifest as amyloid precursor protein immunoreactive axonal profiles, was present in the corpus callosum of both injury groups, though more evident in the r-mTBI animals. Our data demonstrate that this mouse model of mTBI is reproducible, simple, and noninvasive, with behavioral impairment after a single injury and increasing deficits after multiple injuries accompanied by increased focal and diffuse pathology. As such, this model may serve as a suitable platform with which to explore repetitive mTBI relevant to human brain injury.

Characteristics of thein VitroVasoactivity of β-Amyloid Peptides

The β-amyloid (Aβ1–40) peptide has previously been shown to enhance phenylephrine contraction of aortic ringsin vitro.We have employed a novel observation, that Aβ peptides enhance endothelin-1 (ET-1) contraction, to examine the relationship between vasoactivity and potential amyloidogenicity of Aβ peptides, the role played by free radicals and calcium in the vasoactive mechanism, and the requirement of an intact endothelial layer for enhancement of vasoactivity. Rings of rat aortae were constricted with ET-1 before and after addition of amyloid peptide and/or other compounds, and a comparison was made between post- and pretreatment contractions. In this system, vessel constriction is consistently dramatically enhanced by Aβ1–40, is enhanced less so by Aβ1–42, and is not enhanced by Aβ25–35. The endothelium isnotrequired for Aβ vasoactivity, and calcium channel blockers have a greater effect than antioxidants in blocking enhancement of vasoconstriction by Aβ peptides. In contrast to Aβ-induced cytotoxicity, Aβ-induced vasoactivity is immediate, occurs in response to low doses of freshly solubilized peptide, and appears to be inversely related to the amyloidogenic potential of the Aβ peptides. We conclude that the mechanism of Aβ vasoactivity is distinct from that of Aβ cytotoxicity. Although free radicals appear to modulate the vasoactive effects, the lack of requirement for endothelium suggests that loss of the free radical balance (between NO and O−2) may be a secondary influence on Aβ enhancement of vasoconstriction. These effects of Aβ on isolated vessels, and reported effects of Aβ in cells of the vasculature, suggest that Aβ-induced disruption of vascular tone may be a factor in the pathogenesis of cerebral amyloid angiopathy and Alzheimers disease. Although the mechanism of enhanced vasoconstriction is unknown, it is reasonable to propose thatin vivocontact of Aβ peptides with small cerebral vessels may increase their tendency to constrict and oppose their tendency to relax. The subclinical ischemia resulting from this would be expected to up-regulate βAPP production in and around the vasculature with further increase in Aβ formation and deposition. The disruptive and degenerative effects of such a cycle would lead to the complete destruction of cerebral vessels and consequently neuronal degeneration in the affected areas.

CD40 is expressed and functional on neuronal cells.

We show here that CD40 mRNA and protein are expressed by neuronal cells, and are increased in differentiated versus undifferentiated N2a and PC12 cells as measured by RT–PCR, western blotting and immunofluorescence staining. Additionally, immunohistochemistry reveals that neurons from adult mouse and human brain also express CD40 in situ. CD40 ligation results in a time‐dependent increase in p44/42 MAPK activation in neuronal cells. Furthermore, ligation of CD40 opposes JNK phosphorylation and activity induced by NGF‐β removal from differentiated PC12 cells or serum withdrawal from primary cultured neurons. Importantly, CD40 ligation also protects neuronal cells from NGF‐β or serum withdrawal‐induced injury and affects neuronal differentiation. Finally, adult mice deficient for the CD40 receptor demonstrate neuronal dysfunction as evidenced by decreased neurofilament isoforms, reduced Bcl‐xL:Bax ratio, neuronal morphological change, increased DNA fragmentation, and gross brain abnormality. These changes occur with age, and are clearly evident at 16 months. Taken together, these data demonstrate a role of CD40 in neuronal development, maintenance and protection in vitro and in vivo.

Soluble Alzheimers β-amyloid constricts the cerebral vasculature in vivo

Abstract Bilateral temporoparietal hypoperfusion has been frequently observed early in the Alzheimers disease (AD) process. An increased β-amyloid (Aβ) peptide is believed to play a central role in the pathogenesis of AD. In vitro experiments have shown that freshly solubilized Aβ enhances constriction of cerebral and peripheral vessels. We propose that in vivo the Aβ vasoactive property may contribute to cerebral hypoperfusion of AD patients. To test this hypothesis, we intra-arterially infused freshly solubilized Aβ1–40 in rats and observed changes in cerebral blood flow and cerebrovascular resistance using fluorescent microspheres. We found that infusion of Aβ in vivo resulted in a decreased blood flow and increased vascular resistance specifically in cerebral cortex but not in heart or kidneys. These data suggest that Aβ has a direct and specific constrictive effect on cerebral vessels in vivo, which may contribute to the cerebral hypoperfusion observed early in the AD process.

Association of a functional μ‐opioid receptor allele (+118A) with alcohol dependency

Genetic association studies have implicated the TaqI A1 allele of the human dopamine D2 receptor gene (DRD2) as a risk-determining factor for alcohol dependency. However, as alcoholism is a disease of polygenic inheritance, the percentage of overall disease variance explained by the TaqI A1 allele is small. In searching for other genetic loci that may, either alone or in combination with DRD2, enhance prediction of alcoholism, we have found a novel association between a functional coding variant (+118A) within the human mu-opioid receptor gene and alcohol dependency. However, no association was detected between the DRD2 TaqI A1 allele and alcoholism in our sample nor did we find synergy between +118A and TaqI A1 alleles on prediction of risk for the disease. These results suggest that, at the molecular level, the endogenous mu-opioid receptor system is a contributing factor to the etiology of alcoholism.