Context Blood-based analytes as indicators of pathological processes in Alzheimer's disease (AD). Objective Combined proteomic and neuroimaging approach to identify plasma proteins associated with AD pathology. Design Discovery-phase proteomic experiments to identify plasma proteins associated with correlates of AD pathology including evidence of atrophy using neuroimaging and more rapid clinical progression, followed by replication using quantitative immunoassay. Extension studies in older non-demented humans using 11C-PiB amyloid imaging and transgenic mice with amyloid pathology. Setting Multi-center European study, AddNeuroMed, and the Baltimore Longitudinal Study of Aging (BLSA) in United States. Participants AD patients, mild cognitive impairment (MCI) subjects and healthy controls with standardized clinical assessments and structural neuroimaging. Plasma samples from non-demented older BLSA participants with brain amyloid imaging by PET. Main outcome measures Association of plasma proteins with brain atrophy, disease severity and rate of clinical progression. Extension studies in man and transgenic mice tested association between plasma proteins and brain amyloid. Results Clusterin/apolipoprotein-J was associated with atrophy of the entorhinal cortex, baseline disease severity and rapid clinical progression in AD. Increased plasma concentration of clusterin was predictive of greater beta amyloid (Aβ) burden in the medial temporal lobe. Subjects with AD had increased clusterin mRNA in blood but there was no effect of SNPs in the gene encoding clusterin (CLU) with gene or protein expression. Finally, APP/PS1 transgenic mice showed increased plasma clusterin, age-dependent increase in brain clusterin and amyloid and clusterin co-localisation in plaques. Conclusions Clusterin/apolipoprotein-J is a known amyloid chaperone associated with Alzheimer's disease severity, pathology and progression. Increased plasma concentration of clusterin is also associated with greater burden of fibrillar Aβ in the brain. These results demonstrate an important role of clusterin in the pathogenesis of AD and suggest that alterations in amyloid chaperone proteins may be a biologically relevant peripheral signature of Alzheimer's disease.

Alzheimer's disease (AD) is characterized by the presence of neurofibrillary tangles of hyperphosphorylated, aggregated tau protein and extracellular deposits of beta-amyloid peptide. Increased beta-amyloid levels are thought to precede tangle formation, but tau pathology is more closely related to neuronal death. Minocycline, a tetracycline derivative, has potent antiinflammatory, antiapoptotic, and neuroprotective effects in several models of neurodegenerative disease, including models of AD with amyloid pathology. We have used both in vitro and in vivo models of AD to determine whether minocycline may have therapeutic efficacy against tau pathology. In primary cortical neurons, minocycline prevents beta-amyloid-induced neuronal death, reduces caspase-3 activation, and lowers generation of caspase-3-cleaved tau fragments. Treatment of tangle-forming transgenic mice (htau line) with minocycline results in reduced levels of tau phosphorylation and insoluble tau aggregates. The in vivo effects of minocycline are also associated with reduced caspase-3 activation and lowered tau cleavage by caspase-3. In tau mice, we find that conformational changes in tau are susceptible to minocycline treatment, but are not directly associated with the amount of tau fragments produced, highlighting a dissociation between the development of these pathological tau species. These results suggest a possible novel therapeutic role for minocycline in the treatment of AD and related tauopathies.

Recent genetic and proteomic studies demonstrate that clusterin/apolipoprotein-J is associated with risk, pathology, and progression of Alzheimer’s disease (AD). Our main aim was to examine associations between plasma clusterin concentration and longitudinal changes in brain volume in normal aging and mild cognitive impairment (MCI). A secondary objective was to examine associations between peripheral concentration of clusterin and its concentration in the brain within regions that undergo neuropathological changes in AD. Non-demented individuals (N = 139; mean baseline age 70.5 years) received annual volumetric MRI (912 MRI scans in total) over a mean six-year interval. Sixteen participants (92 MRI scans in total) were diagnosed during the course of the study with amnestic MCI. Clusterin concentration was assayed by ELISA in plasma samples collected within a year of the baseline MRI. Mixed effects regression models investigated whether plasma clusterin concentration was associated with rates of brain atrophy for control and MCI groups and whether these associations differed between groups. In a separate autopsy sample of individuals with AD (N=17) and healthy controls (N=4), we examined the association between antemortem clusterin concentration in plasma and postmortem levels in the superior temporal gyrus, hippocampus and cerebellum. The associations of plasma clusterin concentration with rates of change in brain volume were significantly different between MCI and control groups in several volumes including whole brain, ventricular CSF, temporal gray matter as well as parahippocampal, superior temporal and cingulate gyri. Within the MCI but not control group, higher baseline concentration of plasma clusterin was associated with slower rates of brain atrophy in these regions. In the combined autopsy sample of AD and control cases, representing a range of severity in AD pathology, we observed a significant association between clusterin concentration in the plasma and that in the superior temporal gyrus. Our findings suggest that clusterin, a plasma protein with roles in amyloid clearance, complement inhibition and apoptosis, is associated with rate of brain atrophy in MCI. Furthermore, peripheral concentration of clusterin also appears to reflect its concentration within brain regions vulnerable to AD pathology. These findings in combination suggest an influence of this multi-functional protein on early stages of progression in AD pathology.

Protease-activated receptors (PAR1-4) are activated by proteases released by cell damage or blood clotting, and are known to be involved in promoting pain and hyperalgesia. Previous studies have shown that PAR2 receptors enhance activation of TRPV1 but the role of other PARs is less clear. In this paper we investigate the expression and function of the PAR1, 3 and 4 thrombin-activated receptors in sensory neurones. Immunocytochemistry and in situ hybridization show that PAR1 and PAR4 are expressed in 10 - 15% of neurons, distributed across all size classes. Thrombin or a specific PAR1 or PAR4 activating peptide (PAR1/4-AP) caused functional effects characteristic of activation of the PLCβ/PKC pathway: intracellular calcium release, sensitisation of TRPV1, and translocation of the epsilon isoform of PKC (PKCε) to the neuronal cell membrane. Sensitisation of TRPV1 was significantly reduced by PKC inhibitors. Neurons responding to thrombin or PAR1-AP were either small nociceptive neurones of the peptidergic subclass, or larger neurones which expressed markers for myelinated fibres. Sequential application of PAR1-AP and PAR4-AP showed that PAR4 is expressed in a subset of the PAR1-expressing neurons. Calcium responses to PAR2-AP were by contrast seen in a distinct population of small IB4+ nociceptive neurones. PAR3 appears to be non-functional in sensory neurones. In a skin-nerve preparation the release of the neuropeptide CGRP by heat was potentiated by PAR1-AP. Culture with nerve growth factor (NGF) increased the proportion of thrombin-responsive neurons in the IB4- population, while glial-derived neurotropic factor (GDNF) and neurturin upregulated the proportion of thrombin-responsive neurons in the IB4+ population. We conclude that PAR1 and PAR4 are functionally expressed in large myelinated fibre neurons, and are also expressed in small nociceptors of the peptidergic subclass, where they are able to potentiate TRPV1 activity.

Peripheral biomarkers of Alzheimer's disease (AD) reflecting early neuropathological change are critical to the development of treatments for this condition. The most widely used indicator of AD pathology in life at present is neuroimaging evidence of brain atrophy. We therefore performed a proteomic analysis of plasma to derive biomarkers associated with brain atrophy in AD. Using gel based proteomics we previously identified seven plasma proteins that were significantly associated with hippocampal volume in a combined cohort of subjects with AD (N = 27) and MCI (N = 17). In the current report, we validated this finding in a large independent cohort of AD (N = 79), MCI (N = 88) and control (N = 95) subjects using alternative complementary methods—quantitative immunoassays for protein concentrations and estimation of pathology by whole brain volume. We confirmed that plasma concentrations of five proteins, together with age and sex, explained more than 35% of variance in whole brain volume in AD patients. These proteins are complement components C3 and C3a, complement factor-I, γ-fibrinogen and alpha-1-microglobulin. Our findings suggest that these plasma proteins are strong predictors of in vivo AD pathology. Moreover, these proteins are involved in complement activation and coagulation, providing further evidence for an intrinsic role of these pathways in AD pathogenesis.