Glucocorticoid-induced tumour necrosis factor receptor family-related protein (GITR) drives atherosclerosis in mice and is associated with an unstable plaque phenotype and cerebrovascular events in humans

AIMS

GITR-a co-stimulatory immune checkpoint protein-is known for both its activating and regulating effects on T-cells. As atherosclerosis bears features of chronic inflammation and autoimmunity, we investigated the relevance of GITR in cardiovascular disease (CVD).

METHODS AND RESULTS

GITR expression was elevated in carotid endarterectomy specimens obtained from patients with cerebrovascular events (n = 100) compared to asymptomatic patients (n = 93) and correlated with parameters of plaque vulnerability, including plaque macrophage, lipid and glycophorin A content, and levels of interleukin (IL)-6, IL-12, and C-C-chemokine ligand 2. Soluble GITR levels were elevated in plasma from subjects with CVD compared to healthy controls. Plaque area in 28-week-old Gitr-/-Apoe-/- mice was reduced, and plaques had a favourable phenotype with less macrophages, a smaller necrotic core and a thicker fibrous cap. GITR deficiency did not affect the lymphoid population. RNA sequencing of Gitr-/-Apoe-/- and Apoe-/- monocytes and macrophages revealed altered pathways of cell migration, activation, and mitochondrial function. Indeed, Gitr-/-Apoe-/- monocytes displayed decreased integrin levels, reduced recruitment to endothelium, and produced less reactive oxygen species. Likewise, GITR-deficient macrophages produced less cytokines and had a reduced migratory capacity.

CONCLUSION

Our data reveal a novel role for the immune checkpoint GITR in driving myeloid cell recruitment and activation in atherosclerosis, thereby inducing plaque growth and vulnerability. In humans, elevated GITR expression in carotid plaques is associated with a vulnerable plaque phenotype and adverse cerebrovascular events. GITR has the potential to become a novel therapeutic target in atherosclerosis as it reduces myeloid cell recruitment to the arterial wall and impedes atherosclerosis progression.

Abstract 586: CD40L on T Cells is a Major Contributor to Atherosclerosis in Hyperlipidemic Mice

Atherosclerosis is a lipid driven chronic inflammatory disease of the arterial wall, involving both innate and adaptive immune responses. Specialized immune cells such as monocytes, B cells, T cells and dendritic cells (DCs) contribute to disease progression or control the inflammatory responses. The CD40-CD40L dyad was identified as an efficient modulator of cellular immune responses. CD40 is a member of the tumor necrosis factor receptor (TNFR) superfamily and is activated by CD40 ligand (CD40L). CD40 and CD40L both are expressed on the majority of immune and non-immune cells associated with atherosclerosis. However, the specific contribution of CD40-CD40L signaling on the different single cell types towards atherosclerosis progression remains undefined. Here, we aimed to investigate the cell type-specific mechanisms of CD40-CD40L interactions in atherosclerosis by generating mice with a conditional ablation of CD40L on T cells. Hyperlipidemic mice with a T cell-specific deficiency of CD40L developed significantly smaller atherosclerotic lesions in the ascending after 28 weeks of chow diet, and following 6 weeks of a cholesterol-enriched diet when compared to their littermate controls. Changes in lesion size were accompanied by a modified anti-inflammatory plaque phenotype, characterized by an increased proportion of smooth muscle cells and a reduced number of pro-inflammatory immune cells, such as macrophages and T cells. T cell CD40L-deficient mice displayed systematically reduced expression of pro-inflammatory cytokines such as IL-1β, IL-2, IL-12, and IFNγ, and increased expression of anti-inflammatory cytokines IL-10 and TGFβ. This anti-inflammatory milieu was paralleled a change in the development and activation status of the T cells with mice lacking CD40L on T cells displaying a reduction in the expression of cytokines and gene markers associated with the activation of T cells (e.g., IL-2, CD69). This change was also reflected within the T cell populations which had a reduced proportion of activated effector T cells and an increased ratio of naïve T cells. Thus, our study ascribes CD40L on T cells a central role in atherosclerosis.

Comparing nonrigid registration techniques for motion corrected MR prostate diffusion imaging

PURPOSE

T2-weighted magnetic resonance imaging (MRI) is commonly used for anatomical visualization in the pelvis area, such as the prostate, with high soft-tissue contrast. MRI can also provide functional information such as diffusion-weighted imaging (DWI) which depicts the molecular diffusion processes in biological tissues. The combination of anatomical and functional imaging techniques is widely used in oncology, e.g., for prostate cancer diagnosis and staging. However, acquisition-specific distortions as well as physiological motion lead to misalignments between T2 and DWI and consequently to a reduced diagnostic value. Image registration algorithms are commonly employed to correct for such misalignment.

METHODS

The authors compare the performance of five state-of-the-art nonrigid image registration techniques for accurate image fusion of DWI with T2.

RESULTS

Image data of 20 prostate patients with cancerous lesions or cysts were acquired. All registration algorithms were validated using intensity-based as well as landmark-based techniques.

CONCLUSIONS

The authors' results show that the "fast elastic image registration" provides most accurate results with a target registration error of 1.07 ± 0.41 mm at minimum execution times of 11 ± 1 s.

Mammalian target of rapamycin and its downstream signalling components are activated in psoriatic skin

BACKGROUND

Mammalian target of rapamycin (mTOR) signalling integrates signals leading to cellular growth, proliferation and differentiation. Disturbance of this tightly regulated interplay leads to malignancies, as reflected by altered mTOR signalling in epidermal tumours. As psoriatic keratinocytes also show features of perturbed cell growth and differentiation, the question arises as to whether mTOR signalling also plays a role in the pathogenesis of psoriasis.

OBJECTIVES

To investigate the activation status of mTOR signalling components in psoriasis.

METHODS

Biopsies from lesional and nonlesional skin of patients with psoriasis (n = 10), as well as samples from healthy donors (n = 3), were analysed by immunohistochemistry and Western blot, utilizing antibodies detecting phosphorylated mTOR, phospho-S6 kinase and phospho-S6 ribosomal protein.

RESULTS

We found mTOR and its downstream signalling molecule, the ribosomal protein S6, to be activated in lesional psoriatic skin. While mTOR is activated throughout the whole epidermis, with particularly strong activation in the basal layer, S6 is active in suprabasal layers of differentiating keratinocytes.

CONCLUSIONS

Altogether these results suggest a role for mTOR signalling in the epidermal changes leading to the psoriatic phenotype. mTOR inhibition might be a mode of action to explore in developing innovative antipsoriatic drugs.

The effect of regularization in motion compensated PET image reconstruction: a realistic numerical 4D simulation study

Following continuous improvement in PET spatial resolution, respiratory motion correction has become an important task. Two of the most common approaches that utilize all detected PET events to motion-correct PET data are the reconstruct-transform-average method (RTA) and motion-compensated image reconstruction (MCIR). In RTA, separate images are reconstructed for each respiratory frame, subsequently transformed to one reference frame and finally averaged to produce a motion-corrected image. In MCIR, the projection data from all frames are reconstructed by including motion information in the system matrix so that a motion-corrected image is reconstructed directly. Previous theoretical analyses have explained why MCIR is expected to outperform RTA. It has been suggested that MCIR creates less noise than RTA because the images for each separate respiratory frame will be severely affected by noise. However, recent investigations have shown that in the unregularized case RTA images can have fewer noise artefacts, while MCIR images are more quantitatively accurate but have the common salt-and-pepper noise. In this paper, we perform a realistic numerical 4D simulation study to compare the advantages gained by including regularization within reconstruction for RTA and MCIR, in particular using the median-root-prior incorporated in the ordered subsets maximum a posteriori one-step-late algorithm. In this investigation we have demonstrated that MCIR with proper regularization parameters reconstructs lesions with less bias and root mean square error and similar CNR and standard deviation to regularized RTA. This finding is reproducible for a variety of noise levels (25, 50, 100 million counts), lesion sizes (8 mm, 14 mm diameter) and iterations. Nevertheless, regularized RTA can also be a practical solution for motion compensation as a proper level of regularization reduces both bias and mean square error.

Nonrigid motion modeling of the liver from 3-D undersampled self-gated golden-radial phase encoded MRI

Magnetic resonance imaging (MRI) has been commonly used for guiding and planning image guided interventions since it provides excellent soft tissue visualization of anatomy and allows motion modeling to predict the position of target tissues during the procedure. However, MRI-based motion modeling remains challenging due to the difficulty of acquiring multiple motion-free 3-D respiratory phases with adequate contrast and spatial resolution. Here, we propose a novel retrospective respiratory gating scheme from a 3-D undersampled high-resolution MRI acquisition combined with fast and robust image registrations to model the nonrigid deformation of the liver. The acquisition takes advantage of the recently introduced golden-radial phase encoding (G-RPE) trajectory. G-RPE is self-gated, i.e., the respiratory signal can be derived from the acquired data itself, and allows retrospective reconstructions of multiple respiratory phases at any arbitrary respiratory position. Nonrigid motion modeling is applied to predict the liver deformation of an average breathing cycle. The proposed approach was validated on 10 healthy volunteers. Motion model accuracy was assessed using similarity-, surface-, and landmark-based validation methods, demonstrating precise model predictions with an overall target registration error of TRE = 1.70 ± 0.94 mm which is within the range of the acquired resolution.

Thoracic respiratory motion estimation from MRI using a statistical model and a 2-D image navigator

Respiratory motion models have potential application for estimating and correcting the effects of motion in a wide range of applications, for example in PET-MR imaging. Given that motion cycles caused by breathing are only approximately repeatable, an important quality of such models is their ability to capture and estimate the intra- and inter-cycle variability of the motion. In this paper we propose and describe a technique for free-form nonrigid respiratory motion correction in the thorax. Our model is based on a principal component analysis of the motion states encountered during different breathing patterns, and is formed from motion estimates made from dynamic 3-D MRI data. We apply our model using a data-driven technique based on a 2-D MRI image navigator. Unlike most previously reported work in the literature, our approach is able to capture both intra- and inter-cycle motion variability. In addition, the 2-D image navigator can be used to estimate how applicable the current motion model is, and hence report when more imaging data is required to update the model. We also use the motion model to decide on the best positioning for the image navigator. We validate our approach using MRI data acquired from 10 volunteers and demonstrate improvements of up to 40.5% over other reported motion modelling approaches, which corresponds to 61% of the overall respiratory motion present. Finally we demonstrate one potential application of our technique: MRI-based motion correction of real-time PET data for simultaneous PET-MRI acquisition.

Does Linezolid Inhibit Its Own Metabolism?—Population Pharmacokinetics As a Tool to Explain the Observed Nonlinearity in Both Healthy Volunteers and Septic Patients

Few studies investigating the population pharmacokinetics of linezolid in critically ill patients have been reported, yielding controversial results. Therefore, a population pharmacokinetic analysis using NONMEM was performed to thoroughly understand the pharmacokinetics of unbound linezolid in plasma. Data were obtained from 10 healthy volunteers and 24 septic patients. Intensive sampling was performed after single and multiple dosing. The pharmacokinetics of unbound linezolid was best described by a two-compartment model with an absorption rate constant (K(A), 1.81 h(-1)), clearance (CL, 11.1 l/h), volumes of distribution (V(2) and V(3), 20.0 and 28.9 liters, respectively), and intercompartmental clearance Q, 75.0 l/h). However, clearance was inhibited over time to 76.4% of its original value, dependent on the concentration in an empirical inhibition compartment. Overall, imprecision of parameter estimates was low to moderate. Comparison of goodness of fit graphics and of the predictive performance revealed that the presented model was superior to previously published models using linear elimination or parallel linear and Michaelis-Menten elimination and also to other of our own investigated model alternatives. The observed nonlinearity in linezolid pharmacokinetics might be a result of an inhibition of the formation of the major linezolid metabolite due to the inhibition of respiratory chain enzyme activity. To our knowledge, this study presents the first attempt to mechanistically explain the observed nonlinearity in linezolid pharmacokinetics. Finally, simulations demonstrated that the model might also serve as a tool to predict concentration-time profiles of linezolid, thus providing a rationale for a more targeted antimicrobial therapy.