Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia in the elderly population. In this study, we used the APP/PS1 transgenic mouse model to explore the feasibility of using diffusion kurtosis imaging (DKI) as a tool for the early detection of microstructural changes in the brain due to amyloid-β (Aβ) plaque deposition. We longitudinally acquired DKI data of wild-type (WT) and APP/PS1 mice at 2, 4, 6 and 8 months of age, after which these mice were sacrificed for histological examination. Three additional cohorts of mice were also included at 2, 4 and 6 months of age to allow voxel-based co-registration between diffusion tensor and diffusion kurtosis metrics and immunohistochemistry. Changes were observed in diffusion tensor (DT) and diffusion kurtosis (DK) metrics in many of the 23 regions of interest that were analysed. Mean and axial kurtosis were greatly increased owing to Aβ-induced pathological changes in the motor cortex of APP/PS1 mice at 4, 6 and 8 months of age. Additionally, fractional anisotropy (FA) was decreased in APP/PS1 mice at these respective ages. Linear discriminant analysis of the motor cortex data indicated that combining diffusion tensor and diffusion kurtosis metrics permits improved separation of WT from APP/PS1 mice compared with either diffusion tensor or diffusion kurtosis metrics alone. We observed that mean kurtosis and FA are the critical metrics for a correct genotype classification. Furthermore, using a newly developed platform to co-register the in vivo diffusion-weighted magnetic resonance imaging with multiple 3D histological stacks, we found high correlations between DK metrics and anti-Aβ (clone 4G8) antibody, glial fibrillary acidic protein, ionised calcium-binding adapter molecule 1 and myelin basic protein immunohistochemistry. Finally, we observed reduced FA in the septal nuclei of APP/PS1 mice at all ages investigated. The latter was at least partially also observed by voxel-based statistical parametric mapping, which showed significantly reduced FA in the septal nuclei, as well as in the corpus callosum, of 8-month-old APP/PS1 mice compared with WT mice. Our results indicate that DKI metrics hold tremendous potential for the early detection and longitudinal follow-up of Aβ-induced pathology.

MRI diffusion data suffers from significant inter- and intra-site variability, which hinders multi-site and/or longitudinal diffusion studies. This variability may arise from a range of factors, such as hardware, reconstruction algorithms and acquisition settings. To allow a reliable comparison and joint analysis of diffusion data across sites and over time, there is a clear need for robust data harmonization methods. This review article provides a comprehensive overview of diffusion data harmonization concepts and methods, and their limitations. Overall, the methods for the harmonization of multi-site diffusion images can be categorized in two main groups: diffusion parametric map harmonization (DPMH) and diffusion weighted image harmonization (DWIH). Whereas DPMH harmonizes the diffusion parametric maps (e.g., FA, MD, and MK), DWIH harmonizes the diffusion-weighted images. Defining a gold standard harmonization technique for dMRI data is still an ongoing challenge. Nevertheless, in this paper we provide two classification tools, namely a feature table and a flowchart, which aim to guide the readers in selecting an appropriate harmonization method for their study.

P2Y receptors are G-protein-coupled receptors activated by extracellular nucleotides. The P2Y₆ receptor is selectively activated by UDP, and its transcript has been detected in numerous organs, including the spleen, thymus, intestine, blood leukocytes, and aorta. To investigate the biological functions of this receptor, we generated P2Y₆-null mice by gene targeting. The P2Y₆ knockout (KO) mice are viable and are not distinguishable from the wild-type (WT) mice in terms of growth or fertility. In thioglycollate-elicited macrophages, the production of inositol phosphate in response to UDP stimulation was lost, indicating that P2Y₆ is the unique UDP-responsive receptor expressed by mouse macrophages. Furthermore, the amount of interleukin-6 and macrophage-inflammatory protein-2, but not tumor necrosis factor-α, released in response to lipopolysaccharide stimulation was significantly enhanced in the presence of UDP, and this effect was lost in the P2Y₆ KO macrophages. The endothelium-dependent relaxation of the aorta by UDP was abolished in KO P2Y₆ mice. The contractile effect of UDP on the aorta, observed when endothelial nitric-oxide synthase is blocked, was also abolished in P2Y₆-null mice. In conclusion, we generated P2Y₆-deficient mice and have shown that these mice have a defective response to UDP in macrophages, endothelial cells, and vascular smooth muscle cells. These observations might be relevant to several physiopathological conditions such as atherosclerosis or hypertension.

Objective: Intraplaque neovascularization is an important feature of unstable human atherosclerotic plaques. However, its impact on plaque formation and stability is poorly studied. Because proliferating endothelial cells generate up to 85% of their ATP from glycolysis, we investigated whether pharmacological inhibition of glycolytic flux by the small-molecule 3PO (3-[3-pyridinyl]-1-[4-pyridinyl]-2-propen-1-one) could have beneficial effects on plaque formation and composition. Approach and Results: ApoE ^{−/ −} (apolipoprotein E deficient) mice treated with 3PO (50 µg/g, ip; 4×/wk, 4 weeks) showed a metabolic switch toward ketone body formation. Treatment of ApoE ^−/− Fbn1 ^C1039G+/− mice with 3PO (50 µg/g, ip) either after 4 (preventive, twice/wk, 10 weeks) or 16 weeks of Western diet (curative, 4×/wk, 4 weeks) inhibited intraplaque neovascularization by 50% and 38%, respectively. Plaque formation was significantly reduced in all 3PO-treated animals. This effect was independent of intraplaque neovascularization. In vitro experiments showed that 3PO favors an anti-inflammatory M2 macrophage subtype and suppresses an M1 proinflammatory phenotype. Moreover, 3PO induced autophagy, which in turn impaired NF-κB (nuclear factor-kappa B) signaling and inhibited TNF-α (tumor necrosis factor-alpha)–mediated VCAM-1 (vascular cell adhesion molecule-1) and ICAM-1 (intercellular adhesion molecule-1) upregulation. Consistently, a preventive 3PO regimen reduced endothelial VCAM-1 expression in vivo. Furthermore, 3PO improved cardiac function in ApoE ^−/− Fbn1 ^C1039G+/− mice after 10 weeks of treatment. Conclusions: Partial inhibition of glycolysis restrained intraplaque angiogenesis without affecting plaque composition. However, less plaques were formed, which was accompanied by downregulation of endothelial adhesion molecules—an event that depends on autophagy induction. Inhibition of coronary plaque formation by 3PO resulted in an overall improved cardiac function.

Based on pharmacological criteria, we previously suggested that in the mouse aorta, endothelium‐dependent relaxation by nucleotides is mediated by P2Y₁(adenosine diphosphate (ADP)), P2Y₂(adenosine triphosphate (ATP)) and P2Y₆(uridine diphosphate (UDP)) receptors. For UTP, it was unclear whether P2Y₂, P2Y₆or yet another subtype was involved. Therefore, in view of the lack of selective purinergic agonists and antagonists, we used P2Y₂‐deficient mice to clarify the action of UTP. Thoracic aorta segments (width 2 mm) of P2Y₂‐deficient and wild‐type (WT) mice were mounted in organ baths to measure isometric force development and intracellular calcium signalling. Relaxations evoked by ADP, UDP and acetylcholine were identical in knockout and WT mice, indicating that the receptors for these agonists function normally. P2Y₂‐deficient mice showed impaired ATP‐ and adenosine 5′[γ‐thio] triphosphate (ATPγS)‐evoked relaxation, suggesting that in WT mice, ATP and ATPγS activate predominantly the P2Y₂subtype. The ATP/ATPγS‐evoked relaxation and calcium signals in the knockout mice were partially rescued by P2Y₁, as they were sensitive to 2′‐deoxy‐N⁶‐methyladenosine 3′,5′‐bisphosphate (MRS2179), a P2Y₁‐selective antagonist. In contrast to ATP, the UTP‐evoked relaxation was not different between knockout and WT mice. Moreover, the action of UTP was not sensitive to MRS2179. Therefore, the action of UTP is probably mediated mainly by a P2Y₆(like) receptor subtype. In conclusion, we demonstrated that ATP‐evoked relaxation of the murine aorta is mainly mediated by P2Y₂. But this P2Y₂receptor has apparently no major role in UTP‐evoked relaxation. The vasodilator effect of UTP is probably mediated mainly by a P2Y₆(like) receptor. British Journal of Pharmacology(2006)147, 569–574. doi:10.1038/sj.bjp.0706642