CCL19-CCR7-dependent reverse transendothelial migration of myeloid cells clears Chlamydia muridarum from the arterial intima.

Regions of the normal arterial intima predisposed to atherosclerosis are sites of ongoing monocyte trafficking and also contain resident myeloid cells with features of dendritic cells. However, the pathophysiological roles of these cells are poorly understood. Here we found that intimal myeloid cells underwent reverse transendothelial migration (RTM) into the arterial circulation after systemic stimulation of pattern-recognition receptors (PRRs). This process was dependent on expression of the chemokine receptor CCR7 and its ligand CCL19 by intimal myeloid cells. In mice infected with the intracellular pathogen Chlamydia muridarum, blood monocytes disseminated infection to the intima. Subsequent CCL19-CCR7-dependent RTM was critical for the clearance of intimal C. muridarum. This process was inhibited by hypercholesterolemia. Thus, RTM protects the normal arterial intima, and compromised RTM during atherogenesis might contribute to the intracellular retention of pathogens in atherosclerotic lesions.

Radiation Impacts Early Atherosclerosis by Suppressing Intimal LDL Accumulation.

RATIONALE: Bone marrow transplantation (BMT) is used frequently to study the role of hematopoietic cells in atherosclerosis, but aortic arch lesions are smaller in mice after BMT. OBJECTIVE: To identify the earliest stage of atherosclerosis inhibited by BMT and elucidate potential mechanisms. METHODS AND RESULTS: Ldlr-/- mice underwent total body γ-irradiation, bone marrow reconstitution, and 6-week recovery. Atherosclerosis was studied in the ascending aortic arch and compared with mice without BMT. In BMT mice, neutral lipid and myeloid cell topography were lower in lesions after feeding a cholesterol-rich diet for 3, 6, and 12 weeks. Lesion coalescence and height were suppressed dramatically in mice post-BMT, whereas lateral growth was inhibited minimally. Targeted radiation to the upper thorax alone reproduced the BMT phenotype. Classical monocyte recruitment, intimal myeloid cell proliferation, and apoptosis did not account for the post-BMT phenotype. Neutral lipid accumulation was reduced in 5-day lesions, thus we developed quantitative assays for LDL (low-density lipoprotein) accumulation and paracellular leakage using DiI-labeled human LDL and rhodamine B-labeled 70 kD dextran. LDL accumulation was dramatically higher in the intima of Ldlr-/- relative to Ldlr+/+ mice, and was inhibited by injection of HDL mimics, suggesting a regulated process. LDL, but not dextran, accumulation was lower in mice post-BMT both at baseline and in 5-day lesions. Since the transcript abundance of molecules implicated in LDL transcytosis was not significantly different in the post-BMT intima, transcriptomics from whole aortic arch intima, and at single-cell resolution, was performed to give insights into pathways modulated by BMT. CONCLUSIONS: Radiation exposure inhibits LDL entry into the aortic intima at baseline and the earliest stages of atherosclerosis. Single-cell transcriptomic analysis suggests that LDL uptake by endothelial cells is diverted to lysosomal degradation and reverse cholesterol transport pathways. This reduces intimal accumulation of lipid and impacts lesion initiation and growth.

Role of myeloid-derived chemokine CCL5/RANTES at an early stage of atherosclerosis.

One of the hallmarks of atherosclerosis is ongoing accumulation of macrophages in the artery intima beginning at disease onset. Monocyte recruitment contributes to increasing macrophage abundance at early stages of atherosclerosis. Although the chemokine CCL5 (RANTES) has been studied in atherosclerosis, its role in the recruitment of monocytes to early lesions has not been elucidated. We show that expression of Ccl5 mRNA, as well as other ligands of the CCR5 receptor (Ccl3 and Ccl4), is induced in the aortic intima of Ldlr-/- mice 3 weeks after the initiation of cholesterol-rich diet (CRD)-induced hypercholesterolemia. En face immunostaining revealed that CCL5 protein expression is also upregulated at 3 weeks of CRD. Blockade of CCR5 significantly reduced monocyte recruitment to 3-week lesions, suggesting that chemokine signaling through CCR5 is critical. However, we observed that Ccl5-deficiency had no effect on early lesion formation and CCL5-blockade did not affect monocyte recruitment in Ldlr-/- mice. Immunostaining of the lesions in Ldlr-/- mice and reciprocal bone marrow transplantation (BMT) of Ccl5+/+ and Ccl5-/- mice revealed that CCL5 is expressed by both myeloid and endothelial cells. BMT experiments were carried out to determine if CCL5 produced by distinct cells has functions that may be concealed in Ccl5-/-Ldlr-/- mice. We found that hematopoietic cell-derived CCL5 regulates monocyte recruitment and the abundance of intimal macrophages in 3-week lesions of Ldlr-/- mice but plays a minor role in 6-week lesions. Our findings suggest that there is a short window in early lesion formation during which myeloid cell-derived CCL5 has a critical role in monocyte recruitment and macrophage abundance.

Glycogen Synthase Kinase-3 Modulates Cbl-b and Constrains T Cell Activation.

The decision between T cell activation and tolerance is governed by the spatial and temporal integration of diverse molecular signals and events occurring downstream of TCR and costimulatory or coinhibitory receptor engagement. The PI3K-protein kinase B (PKB; also known as Akt) signaling pathway is a central axis in mediating proximal signaling events of TCR and CD28 engagement in T cells. Perturbation of the PI3K-PKB pathway, or the loss of negative regulators of T cell activation, such as the E3 ubiquitin ligase Cbl-b, have been reported to lead to increased susceptibility to autoimmunity. In this study, we further examined the molecular pathway linking PKB and Cbl-b in murine models. Our data show that the protein kinase GSK-3, one of the first targets identified for PKB, catalyzes two previously unreported phosphorylation events at Ser476 and Ser480 of Cbl-b. GSK-3 inactivation by PKB abrogates phosphorylation of Cbl-b at these two sites and results in reduced Cbl-b protein levels. We further show that constitutive activation of PKB in vivo results in a loss of tolerance that is mediated through the downregulation of Cbl-b. Altogether, these data indicate that the PI3K-PKB-GSK-3 pathway is a novel regulatory axis that is important for controlling the decision between T cell activation and tolerance via Cbl-b.

Hypoxia-inducible factor 1 alpha limits dendritic cell stimulation of CD8 T cell immunity.

Dendritic cells are sentinels of the immune system and represent a key cell in the activation of the adaptive immune response. Hypoxia-inducible factor 1 alpha (HIF-1α)-a crucial oxygen sensor stabilized during hypoxic conditions-has been shown to have both activating and inhibitory effects in immune cells in a context- and cell-dependent manner. Previous studies have demonstrated that in some immune cell types, HIF-1α serves a pro-inflammatory role. Genetic deletion of HIF-1α in macrophages has been reported to reduce their pro-inflammatory function. In contrast, loss of HIF-1α enhanced the pro-inflammatory activity of dendritic cells in a bacterial infection model. In this study, we aimed to further clarify the effects of HIF-1α in dendritic cells. Constitutive expression of HIF-1α resulted in diminished immunostimulatory capacity of dendritic cells in vivo, while conditional deletion of HIF-1α in dendritic cells enhanced their ability to induce a cytotoxic T cell response. HIF-1α-expressing dendritic cells demonstrated increased production of inhibitory mediators including IL-10, iNOS and VEGF, which correlated with their reduced capacity to drive effector CD8+ T cell function. Altogether, these data reveal that HIF-1α can promote the anti-inflammatory functions of dendritic cells and provides insight into dysfunctional immune responses in the context of HIF-1α activation.

Single-trial classification of NIRS signals during emotional induction tasks: towards a corporeal machine interface.

BACKGROUND: Corporeal machine interfaces (CMIs) are one of a few available options for restoring communication and environmental control to those with severe motor impairments. Cognitive processes detectable solely with functional imaging technologies such as near-infrared spectroscopy (NIRS) can potentially provide interfaces requiring less user training than conventional electroencephalography-based CMIs. We hypothesized that visually-cued emotional induction tasks can elicit forehead hemodynamic activity that can be harnessed for a CMI. METHODS: Data were collected from ten able-bodied participants as they performed trials of positively and negatively-emotional induction tasks. A genetic algorithm was employed to select the optimal signal features, classifier, task valence (positive or negative emotional value of the stimulus), recording site, and signal analysis interval length for each participant. We compared the performance of Linear Discriminant Analysis and Support Vector Machine classifiers. The latency of the NIRS hemodynamic response was estimated as the time required for classification accuracy to stabilize. RESULTS: Baseline and activation sequences were classified offline with accuracies upwards of 75.0%. Feature selection identified common time-domain discriminatory features across participants. Classification performance varied with the length of the input signal, and optimal signal length was found to be feature-dependent. Statistically significant increases in classification accuracy from baseline rates were observed as early as 2.5 s from initial stimulus presentation. CONCLUSION: NIRS signals during affective states were shown to be distinguishable from baseline states with classification accuracies significantly above chance levels. Further research with NIRS for corporeal machine interfaces is warranted.

A review of emerging access technologies for individuals with severe motor impairments.

Research and development in the field of access technologies for individuals with severe motor impairments has accelerated over the past 10 years. Many emergent alternatives to conventional mechanical switches, such as infrared sensing, electromyography, oculography, and computer vision, have been investigated for those retaining some limited volitional motor ability. At the same time, electroencephalography, electrocorticography, intracortical recordings, and electrodermal activity have been explored for those presenting as locked in. The relevant literature is scattered across many disciplines, obfuscating the strength of the clinical evidence in support of the different access technologies currently in development. This article systematically organizes the literature on the aforementioned access technologies, summarizing their underlying operational mechanisms while reviewing the clinical evidence reported between 1996 and 2006. Research evidence within this period is generally found to be at the case study or uncontrolled study level, with very modest sample sizes. Novel mechanical switches and electroencephalography-based access systems dominate the literature, whereas many other movement-based access modalities have emerged with promising early findings. Access methods for those without extant physical movement constitute a critical direction for future and ongoing research efforts.