Loss of the neuroprotective factor Sphingosine 1-phosphate early in Alzheimer\u27s disease pathogenesis

Background The greatest genetic risk factor for late-onset Alzheimer\u27s disease (AD) is the ϵ4 allele of Apolipoprotein E (ApoE). ApoE regulates secretion of the potent neuroprotective signaling lipid Sphingosine 1-phosphate (S1P). S1P is derived by phosphorylation of sphingosine, catalysed by sphingosine kinases 1 and 2 (SphK1 and 2), and SphK1 positively regulates glutamate secretion and synaptic strength in hippocampal neurons. S1P and its receptor family have been subject to intense pharmacological interest in recent years, following approval of the immunomodulatory drug Fingolimod, an S1P mimetic, for relapsing multiple sclerosis. Results We quantified S1P levels in six brain regions that are differentially affected by AD pathology, in a cohort of 34 post-mortem brains, divided into four groups based on Braak neurofibrillary tangle staging. S1P declined with increasing Braak stage, and this was most pronounced in brain regions most heavily affected by AD pathology. The S1P/sphingosine ratio was 66% and 64% lower in Braak stage III/IV hippocampus (p = 0.010) and inferior temporal cortex (p = 0.014), respectively, compared to controls. In accordance with this change, both SphK1 and SphK2 activity declined with increasing Braak pathology in the hippocampus (p = 0.032 and 0.047, respectively). S1P/sphingosine ratio was 2.5-fold higher in hippocampus of ApoE2 carriers compared to ApoE4 carriers, and multivariate regression showed a significant association between APOE genotype and hippocampal S1P/sphingosine (p = 0.0495), suggesting a new link between APOE genotype and pre-disposition to AD. Conclusions This study demonstrates loss of S1P and sphingosine kinase activity early in AD pathogenesis, and prior to AD diagnosis. Our findings establish a rationale for further exploring S1P receptor pharmacology in the context of AD therapy

Investigation of the Sphingolipid pathway in the early stages of Alzheimer's disease

Alzheimer’s disease (AD) is a debilitating neurodegenerative disease and a significant burden on families and society. A major hallmark of AD is lipid occlusions within neural cell types, indicating dysfunctional lipid metabolism. Sphingolipids (SL), a subgroup of lipids, play a vast array of functions in the CNS, including as essential components of myelin, a hydrophobic barrier insulating axons and facilitating action potential propagation. SL dysregulation has been studied in post mortem AD affected brain tissues compared to controls, however, SL changes in pre-clinical stages of AD has not been investigated.Applying liquid chromatography tandem mass spectrometry, this thesis describes the sphingolipid profile of six AD affected brain regions infiltrated to varying degrees by neurofibrillary tangle (NFT) pathology, indicated by Braak staging I-VI. A pronounced loss in myelin lipids galactosylceramide (GalCer) and sulfatide from frontal and temporal grey matter (GM) and hippocampus was observed, leading to investigation of de novo synthesis of the precursor ceramide. Activity of the enzyme ceramide synthase 2 (CERS2), essential for very long chain ceramide synthesis and myelin lipid production, was significantly reduced in multiple brain regions at a stage of disease preceding characteristic NFT pathology. Lipid analysis also showed a marked decline of the neuroprotective signalling lipid sphingosine 1-phosphate (S1P) in hippocampus and temporal GM that tracked closely with NFT pathology. S1P loss was attributed to loss of activity in sphingosine kinases 1 and 2, required for S1P synthesis.The major genetic risk factor of AD is expression of the E4 isoform of the apolipoprotein E (ApoE) lipid transporter, which aids in brain lipid delivery and clearance. Despite no correlation between APOE genotype and ceramide levels, a positive correlation between age and C16 ceramide, recently associated with systemic insulin resistance, was observed.Overall we hypothesise that CERS2 activity loss destabilises myelin, triggering neurological decline and sensitising neurons to AD induced neurotoxicity. The effect of insulin resistance in the AD affected brain including cognitive function is garnering interest in AD research, warranting further investigation into the study of C16 ceramide levels with age. Pharmacological restoration of deficient S1P signalling could also open therapeutic perspectives for AD

Investigation of motility and biofilm formation by intestinal <it>Campylobacter concisus</it> strains

<p>Abstract</p> <p>Motility helps many pathogens swim through the highly viscous intestinal mucus. Given the differing outcomes of <it>Campylobacter concisus</it> infection, the motility of eight <it>C</it>. <it>concisus</it> strains isolated from patients with Crohn’s disease (n=3), acute (n=3) and chronic (n=1) gastroenteritis and a healthy control (n=1) were compared. Following growth on solid or liquid media the eight strains formed two groups; however, the type of growth medium did not affect motility. In contrast, following growth in viscous liquid medium seven of the eight strains demonstrated significantly decreased motility. In media of increasing viscosities the motility of <it>C</it>. <it>concisus</it> UNSWCD had two marked increases at viscosities of 20.0 and 74.7 centipoises. Determination of the ability of UNSWCD to swim through a viscous medium, adhere to and invade intestinal epithelial cells showed that while adherence levels significantly decreased with increasing viscosity, invasion levels did not significantly change. In contrast, adherence to and invasion of UNSWCD to mucus-producing intestinal cells increased upon accumulation of mucus, as did bacterial aggregation. Given this aggregation, we determined the ability of the eight <it>C</it>. <it>concisus</it> strains to form biofilms, and showed that all strains formed biofilms. In conclusion, the finding that <it>C</it>. <it>concisus</it> strains could be differentiated into two groups based on their motility may suggest that strains with high motility have an increased ability to swim through the intestinal mucus and reach the epithelial layer.</p

Increased apolipoprotein D dimer formation in Alzheimer\u27s disease hippocampus is associated with lipid conjugated diene levels

Previous studies indicate that apolipoprotein D (apoD) may have a lipid antioxidant function in the brain. We have shown that apoD can reduce free radical-generating lipid hydroperoxides to inert lipid hydroxides in a reaction that involves conversion of surface exposed apoD methione-93 (Met93) residue to Met93-sulfoxide (Met93-SO). One consequence of this reaction is the formation of a stable dimerized form of apoD. As cerebral lipid peroxidation is associated with Alzheimer\u27s disease (AD), in the present study we aimed to assess the possible presence of apoD dimers in postmortem hippocampal and cerebellar tissues derived from a cohort of pathologically defined cases ranging from control to late stage AD. Both soluble and insoluble (requiring guanidine HCl extraction) fractions of tissue homogenates were analyzed for apoD and its dimerized form. We also assessed amyloid-β levels by ELISA and levels of lipid peroxidation by lipid conjugated diene and F2-isoprostane analysis. Our studies reveal a significant association between soluble apoD levels and AD Braak stage whereas apoD dimer formation appears to increase predominantly in the advanced stages of disease. The formation of apoD dimers is closely correlated to lipid conjugated diene levels and occurs in the hippocampus but not in the cerebellum. These results are consistent with the hypothesis that apoD acts as a lipid antioxidant in the brain

Loss of ceramide synthase 2 activity, necessary for myelin biosynthesis, precedes tau pathology in the cortical pathogenesis of Alzheimer\u27s disease

The anatomical progression of neurofibrillary tangle pathology throughout Alzheimer\u27s disease (AD) pathogenesis runs inverse to the pattern of developmental myelination, with the disease preferentially affecting thinly myelinated regions. Myelin is comprised 80% of lipids, and the prototypical myelin lipids, galactosylceramide, and sulfatide are critical for neurological function. We observed severe depletion of galactosylceramide and sulfatide in AD brain tissue, which can be traced metabolically to the loss of their biosynthetic precursor, very long chain ceramide. The synthesis of very long chain ceramides is catalyzed by ceramide synthase 2 (CERS2). We demonstrate a significant reduction in CERS2 activity as early as Braak stage I/II in temporal cortex, and Braak stage III/IV in hippocampus and frontal cortex, indicating that loss of myelin-specific ceramide synthase activity precedes neurofibrillary tangle pathology in cortical regions. These findings open a new vista on AD pathogenesis by demonstrating a defect in myelin lipid biosynthesis at the preclinical stages of the disease. We posit that, over time, this defect contributes significantly to myelin deterioration, synaptic dysfunction, and neurological decline