Neuroimmune cardiovascular interfaces control atherosclerosis.

Atherosclerotic plaques develop in the inner intimal layer of arteries and can cause heart attacks and strokes1. As plaques lack innervation, the effects of neuronal control on atherosclerosis remain unclear. However, the immune system responds to plaques by forming leukocyte infiltrates in the outer connective tissue coat of arteries (the adventitia)2-6. Here, because the peripheral nervous system uses the adventitia as its principal conduit to reach distant targets7-9, we postulated that the peripheral nervous system may directly interact with diseased arteries. Unexpectedly, widespread neuroimmune cardiovascular interfaces (NICIs) arose in mouse and human atherosclerosis-diseased adventitia segments showed expanded axon networks, including growth cones at axon endings near immune cells and media smooth muscle cells. Mouse NICIs established a structural artery-brain circuit (ABC): abdominal adventitia nociceptive afferents10-14 entered the central nervous system through spinal cord T6-T13 dorsal root ganglia and were traced to higher brain regions, including the parabrachial and central amygdala neurons; and sympathetic efferent neurons projected from medullary and hypothalamic neurons to the adventitia through spinal intermediolateral neurons and both coeliac and sympathetic chain ganglia. Moreover, ABC peripheral nervous system components were activated: splenic sympathetic and coeliac vagus nerve activities increased in parallel to disease progression, whereas coeliac ganglionectomy led to the disintegration of adventitial NICIs, reduced disease progression and enhanced plaque stability. Thus, the peripheral nervous system uses NICIs to assemble a structural ABC, and therapeutic intervention in the ABC attenuates atherosclerosis.

Cardiovascular Brain Circuits.

The cardiovascular system is hardwired to the brain via multilayered afferent and efferent polysynaptic axonal connections. Two major anatomically and functionally distinct though closely interacting subcircuits within the cardiovascular system have recently been defined: The artery-brain circuit and the heart-brain circuit. However, how the nervous system impacts cardiovascular disease progression remains poorly understood. Here, we review recent findings on the anatomy, structures, and inner workings of the lesser-known artery-brain circuit and the better-established heart-brain circuit. We explore the evidence that signals from arteries or the heart form a systemic and finely tuned cardiovascular brain circuit: afferent inputs originating in the arterial tree or the heart are conveyed to distinct sensory neurons in the brain. There, primary integration centers act as hubs that receive and integrate artery-brain circuit-derived and heart-brain circuit-derived signals and process them together with axonal connections and humoral cues from distant brain regions. To conclude the cardiovascular brain circuit, integration centers transmit the constantly modified signals to efferent neurons which transfer them back to the cardiovascular system. Importantly, primary integration centers are wired to and receive information from secondary brain centers that control a wide variety of brain traits encoded in engrams including immune memory, stress-regulating hormone release, pain, reward, emotions, and even motivated types of behavior. Finally, we explore the important possibility that brain effector neurons in the cardiovascular brain circuit network connect efferent signals to other peripheral organs including the immune system, the gut, the liver, and adipose tissue. The enormous recent progress vis-à-vis the cardiovascular brain circuit allows us to propose a novel neurobiology-centered cardiovascular disease hypothesis that we term the neuroimmune cardiovascular circuit hypothesis.

Artery Tertiary Lymphoid Organs Control Aorta Immunity and Protect against Atherosclerosis via Vascular Smooth Muscle Cell Lymphotoxin ß Receptors.

Tertiary lymphoid organs (TLOs) emerge during nonresolving peripheral inflammation, but their impact on disease progression remains unknown. We have found in aged Apoe(-/-) mice that artery TLOs (ATLOs) controlled highly territorialized aorta T cell responses. ATLOs promoted T cell recruitment, primed CD4(+) T cells, generated CD4(+), CD8(+), T regulatory (Treg) effector and central memory cells, converted naive CD4(+) T cells into induced Treg cells, and presented antigen by an unusual set of dendritic cells and B cells. Meanwhile, vascular smooth muscle cell lymphotoxin ß receptors (VSMC-LTßRs) protected against atherosclerosis by maintaining structure, cellularity, and size of ATLOs though VSMC-LTßRs did not affect secondary lymphoid organs: Atherosclerosis was markedly exacerbated in Apoe(-/-)Ltbr(-/-) and to a similar extent in aged Apoe(-/-)Ltbr(fl/fl)Tagln-cre mice. These data support the conclusion that the immune system employs ATLOs to organize aorta T cell homeostasis during aging and that VSMC-LTßRs participate in atherosclerosis protection via ATLOs.

Novel mechanisms and therapeutic targets in atherosclerosis: inflammation and beyond.

This review based on the ESC William Harvey Lecture in Basic Science 2022 highlights recent experimental and translational progress on the therapeutic targeting of the inflammatory components in atherosclerosis, introducing novel strategies to limit side effects and to increase efficacy. Since the validation of the inflammatory paradigm in CANTOS and COLCOT, efforts to control the residual risk conferred by inflammation have centred on the NLRP3 inflammasome-driven IL-1ß-IL6 axis. Interference with the co-stimulatory dyad CD40L-CD40 and selective targeting of tumour necrosis factor-receptor associated factors (TRAFs), namely the TRAF6-CD40 interaction in macrophages by small molecule inhibitors, harbour intriguing options to reduce established atherosclerosis and plaque instability without immune side effects. The chemokine system crucial for shaping immune cell recruitment and homoeostasis can be fine-tuned and modulated by its heterodimer interactome. Structure-function analysis enabled the design of cyclic, helical, or linked peptides specifically targeting or mimicking these interactions to limit atherosclerosis or thrombosis by blunting myeloid recruitment, boosting regulatory T cells, inhibiting platelet activity, or specifically blocking the atypical chemokine MIF without notable side effects. Finally, adventitial neuroimmune cardiovascular interfaces in advanced atherosclerosis show robust restructuring of innervation from perivascular ganglia and employ sensory neurons of dorsal root ganglia to enter the central nervous system and to establish an atherosclerosis-brain circuit sensor, while sympathetic and vagal efferents project to the celiac ganglion to create an atherosclerosis-brain circuit effector. Disrupting this circuitry by surgical or chemical sympathectomy limited disease progression and enhanced plaque stability, opening exciting perspectives for selective and tailored intervention beyond anti-inflammatory strategies.

Animal Models, Pathogenesis, and Potential Treatment of Thoracic Aortic Aneurysm.

Thoracic aortic aneurysm (TAA) has a prevalence of 0.16-0.34% and an incidence of 7.6 per 100,000 person-years, accounting for 1-2% of all deaths in Western countries. Currently, no effective pharmacological therapies have been identified to slow TAA development and prevent TAA rupture. Large TAAs are treated with open surgical repair and less invasive thoracic endovascular aortic repair, both of which have high perioperative mortality risk. Therefore, there is an urgent medical need to identify the cellular and molecular mechanisms underlying TAA development and rupture to develop new therapies. In this review, we summarize animal TAA models including recent developments in porcine and zebrafish models: porcine models can assess new therapeutic devices or intervention strategies in a large mammal and zebrafish models can employ large-scale small-molecule suppressor screening in microwells. The second part of the review covers current views of TAA pathogenesis, derived from recent studies using these animal models, with a focus on the roles of the transforming growth factor-beta (TGFß) pathway and the vascular smooth muscle cell (VSMC)-elastin-contractile unit. The last part discusses TAA treatment options as they emerge from recent preclinical studies.

The Wilms tumor protein Wt1 contributes to female fertility by regulating oviductal proteostasis.

Although the zinc finger transcription factor Wt1 has been linked to female fertility, its precise role in this process has not yet been understood. We have sequenced the WT1 exons in a panel of patients with idiopathic infertility and have identified a missense mutation in WT1 in one patient out of eight. This mutation leads to an amino acid change within the zinc finger domain and results in reduced DNA binding. We utilized Wt1+/- mice as a model to mechanistically pinpoint the consequences of reduced Wt1 levels for female fertility. Our results indicate that subfertility in Wt1+/- female mice is a maternal effect caused by the Wt1-dependent de-regulation of Prss29, encoding a serine protease. Notably, blocking Prss29 activity was sufficient to rescue subfertility in Wt1+/- mice indicating Prss29 as a critical factor in female fertility. Molecularly, Wt1 represses expression of Prss29. De-repression and precocious expression of Prss29 in the oviduct of Wt1+/- mice interferes with pre-implantation development. Our study reveals a novel role for Wt1 in early mammalian development and identifies proteases as critical mediators of the maternal-embryonic interaction. Our data also suggest that the role of Wt1 in regulating fertility is conserved in mammals.

Limited Macrophage Positional Dynamics in Progressing or Regressing Murine Atherosclerotic Plaques-Brief Report.

Objective- Macrophages play important roles in the pathogenesis of atherosclerosis, but their dynamics within plaques remain obscure. We aimed to quantify macrophage positional dynamics within progressing and regressing atherosclerotic plaques. Approach and Results- In a stable intravital preparation, large asymmetrical foamy macrophages in the intima of carotid artery plaques were sessile, but smaller rounded cells nearer plaque margins, possibly newly recruited monocytes, mobilized laterally along plaque borders. Thus, to test macrophage dynamics in plaques over a longer period of time in progressing and regressing disease, we quantified displacement of nondegradable phagocytic particles within macrophages for up to 6 weeks. In progressing plaques, macrophage-associated particles appeared to mobilize to deeper layers in plaque, whereas in regressing plaques, the label was persistently located near the lumen. By measuring the distance of the particles from the floor of the plaque, we discovered that particles remained at the same distance from the floor regardless of plaque progression or regression. The apparent deeper penetration of labeled cells in progressing conditions could be attributed to monocyte recruitment that generated new superficial layers of macrophages over the labeled phagocytes. Conclusions- Although there may be individual exceptions, as a population, newly differentiated macrophages fail to penetrate significantly deeper than the limited depth they reside on initial entry, regardless of plaque progression, or regression. These limited dynamics may prevent macrophages from escaping areas with unfavorable conditions (such as hypoxia) and pose a challenge for newly recruited macrophages to clear debris through efferocytosis deep within plaque.

Artery Tertiary Lymphoid Organs Control Multilayered Territorialized Atherosclerosis B-Cell Responses in Aged ApoE-/- Mice.

OBJECTIVE: Explore aorta B-cell immunity in aged apolipoprotein E-deficient (ApoE(-/-)) mice. APPROACH AND RESULTS: Transcript maps, fluorescence-activated cell sorting, immunofluorescence analyses, cell transfers, and Ig-ELISPOT (enzyme-linked immunospot) assays showed multilayered atherosclerosis B-cell responses in artery tertiary lymphoid organs (ATLOs). Aging-associated aorta B-cell-related transcriptomes were identified, and transcript atlases revealed highly territorialized B-cell responses in ATLOs versus atherosclerotic lesions: ATLOs showed upregulation of bona fide B-cell genes, including Cd19, Ms4a1 (Cd20), Cd79a/b, and Ighm although intima plaques preferentially expressed molecules involved in non-B effector responses toward B-cell-derived mediators, that is, Fcgr3 (Cd16), Fcer1g (Cd23), and the C1q family. ATLOs promoted B-cell recruitment. ATLO B-2 B cells included naive, transitional, follicular, germinal center, switched IgG1(+), IgA(+), and IgE(+) memory cells, plasmablasts, and long-lived plasma cells. ATLOs recruited large numbers of B-1 cells whose subtypes were skewed toward interleukin-10(+) B-1b cells versus interleukin-10(-) B-1a cells. ATLO B-1 cells and plasma cells constitutively produced IgM and IgG and a fraction of plasma cells expressed interleukin-10. Moreover, ApoE(-/-) mice showed increased germinal center B cells in renal lymph nodes, IgM-producing plasma cells in the bone marrow, and higher IgM and anti-MDA-LDL (malondialdehyde-modified low-density lipoprotein) IgG serum titers. CONCLUSIONS: ATLOs orchestrate dichotomic, territorialized, and multilayered B-cell responses in the diseased aorta; germinal center reactions indicate generation of autoimmune B cells within the diseased arterial wall during aging.

Artery tertiary lymphoid organs contribute to innate and adaptive immune responses in advanced mouse atherosclerosis.

Tertiary lymphoid organs emerge in tissues in response to nonresolving inflammation. Recent research characterized artery tertiary lymphoid organs in the aorta adventitia of aged apolipoprotein E-deficient mice. The atherosclerosis-associated lymphocyte aggregates are organized into distinct compartments, including separate T-cell areas harboring conventional, monocyte-derived, lymphoid, and plasmacytoid dendritic cells, as well as activated T-cell effectors and memory cells; B-cell follicles containing follicular dendritic cells in activated germinal centers; and peripheral niches of plasma cells. Artery tertiary lymphoid organs show marked neoangiogenesis, aberrant lymphangiogenesis, and extensive induction of high endothelial venules. Moreover, newly formed lymph node-like conduits connect the external lamina with high endothelial venules in T-cell areas and also extend into germinal centers. Mouse artery tertiary lymphoid organs recruit large numbers of naïve T cells and harbor lymphocyte subsets with opposing activities, including CD4(+) and CD8(+) effector and memory T cells, natural and induced CD4(+) regulatory T cells, and memory B cells at different stages of differentiation. These data suggest that artery tertiary lymphoid organs participate in primary immune responses and organize T- and B-cell autoimmune responses in advanced atherosclerosis. In this review, we discuss the novel concept that pro- and antiatherogenic immune responses toward unknown arterial wall-derived autoantigens may be organized by artery tertiary lymphoid organs and that disruption of the balance between pro- and antiatherogenic immune cell subsets may trigger clinically overt atherosclerosis.

Systemic analysis of PPARγ in mouse macrophage populations reveals marked diversity in expression with critical roles in resolution of inflammation and airway immunity.

Although peroxisome proliferator-activated receptor γ (PPARγ) has anti-inflammatory actions in macrophages, which macrophage populations express PPARγ in vivo and how it regulates tissue homeostasis in the steady state and during inflammation remains unclear. We now show that lung and spleen macrophages selectively expressed PPARγ among resting tissue macrophages. In addition, Ly-6C(hi) monocytes recruited to an inflammatory site induced PPARγ as they differentiated to macrophages. When PPARγ was absent in Ly-6C(hi)-derived inflammatory macrophages, initiation of the inflammatory response was unaffected, but full resolution of inflammation failed, leading to chronic leukocyte recruitment. Conversely, PPARγ activation favored resolution of inflammation in a macrophage PPARγ-dependent manner. In the steady state, PPARγ deficiency in red pulp macrophages did not induce overt inflammation in the spleen. By contrast, PPARγ deletion in lung macrophages induced mild pulmonary inflammation at the steady state and surprisingly precipitated mortality upon infection with Streptococcus pneumoniae. This accelerated mortality was associated with impaired bacterial clearance and inability to sustain macrophages locally. Overall, we uncovered critical roles for macrophage PPARγ in promoting resolution of inflammation and maintaining functionality in lung macrophages where it plays a pivotal role in supporting pulmonary host defense. In addition, this work identifies specific macrophage populations as potential targets for the anti-inflammatory actions of PPARγ agonists.

Identification of a non-canonical chemokine-receptor pathway suppressing regulatory T cells to drive atherosclerosis.

CCL17 is produced by conventional dendritic cells (cDCs), signals through CCR4 on regulatory T cells (Tregs), and drives atherosclerosis by suppressing Treg functions through yet undefined mechanisms. Here we show that cDCs from CCL17-deficient mice display a pro-tolerogenic phenotype and transcriptome that is not phenocopied in mice lacking its cognate receptor CCR4. In the plasma of CCL17-deficient mice, CCL3 was the only decreased cytokine/chemokine. We found that CCL17 signaled through CCR8 as an alternate high-affinity receptor, which induced CCL3 expression and suppressed Treg functions in the absence of CCR4. Genetic ablation of CCL3 and CCR8 in CD4+ T cells reduced CCL3 secretion, boosted FoxP3+ Treg numbers, and limited atherosclerosis. Conversely, CCL3 administration exacerbated atherosclerosis and restrained Treg differentiation. In symptomatic versus asymptomatic human carotid atheroma, CCL3 expression was increased, while FoxP3 expression was reduced. Together, we identified a non-canonical chemokine pathway whereby CCL17 interacts with CCR8 to yield a CCL3-dependent suppression of atheroprotective Tregs.

Neuroimmune cardiovascular interfaces in atherosclerosis.

Two pairs of biological systems acting over long distances have recently been defined as major participants in the regulation of physiological and pathological tissue reactions: i) the nervous and vascular systems form various blood-brain barriers and control axon growth and angiogenesis; and ii) the nervous and immune systems emerge as key players to direct immune responses and maintain blood vessel integrity. The two pairs have been explored by investigators in relatively independent research areas giving rise to the concepts of the rapidly expanding topics of the neurovascular link and neuroimmunology, respectively. Our recent studies on atherosclerosis led us to consider a more inclusive approach by conceptualizing and combining principles of the neurovascular link and neuroimmunology: we propose that the nervous system, the immune system and the cardiovascular system undergo complex crosstalks in tripartite rather than bipartite interactions to form neuroimmune cardiovascular interfaces (NICIs).

The Impact of the Nervous System on Arteries and the Heart: The Neuroimmune Cardiovascular Circuit Hypothesis.

Three systemic biological systems, i.e., the nervous, the immune, and the cardiovascular systems, form a mutually responsive and forward-acting tissue network to regulate acute and chronic cardiovascular function in health and disease. Two sub-circuits within the cardiovascular system have been described, the artery brain circuit (ABC) and the heart brain circuit (HBC), forming a large cardiovascular brain circuit (CBC). Likewise, the nervous system consists of the peripheral nervous system and the central nervous system with their functional distinct sensory and effector arms. Moreover, the immune system with its constituents, i.e., the innate and the adaptive immune systems, interact with the CBC and the nervous system at multiple levels. As understanding the structure and inner workings of the CBC gains momentum, it becomes evident that further research into the CBC may lead to unprecedented classes of therapies to treat cardiovascular diseases as multiple new biologically active molecules are being discovered that likely affect cardiovascular disease progression. Here, we weigh the merits of integrating these recent observations in cardiovascular neurobiology into previous views of cardiovascular disease pathogeneses. These considerations lead us to propose the Neuroimmune Cardiovascular Circuit Hypothesis.

Pairing of single-cell RNA analysis and T cell antigen receptor profiling indicates breakdown of T cell tolerance checkpoints in atherosclerosis.

Atherosclerotic plaques form in the inner layer of arteries triggering heart attacks and strokes. Although T cells have been detected in atherosclerosis, tolerance dysfunction as a disease driver remains unexplored. Here we examine tolerance checkpoints in atherosclerotic plaques, artery tertiary lymphoid organs and lymph nodes in mice burdened by advanced atherosclerosis, via single-cell RNA sequencing paired with T cell antigen receptor sequencing. Complex patterns of deteriorating peripheral T cell tolerance were observed being most pronounced in plaques followed by artery tertiary lymphoid organs, lymph nodes and blood. Affected checkpoints included clonal expansion of CD4+, CD8+ and regulatory T cells; aberrant tolerance-regulating transcripts of clonally expanded T cells; T cell exhaustion; Treg-TH17 T cell conversion; and dysfunctional antigen presentation. Moreover, single-cell RNA-sequencing profiles of human plaques revealed that the CD8+ T cell tolerance dysfunction observed in mouse plaques was shared in human coronary and carotid artery plaques. Thus, our data support the concept of atherosclerosis as a bona fide T cell autoimmune disease targeting the arterial wall.

Aging impairs the neurovascular interface in the heart.

Aging is a major risk factor for impaired cardiovascular health. Because the aging myocardium is characterized by microcirculatory dysfunction, and because nerves align with vessels, we assessed the impact of aging on the cardiac neurovascular interface. We report that aging reduces nerve density in the ventricle and dysregulates vascular-derived neuroregulatory genes. Aging down-regulates microRNA 145 (miR-145) and derepresses the neurorepulsive factor semaphorin-3A. miR-145 deletion, which increased Sema3a expression or endothelial Sema3a overexpression, reduced axon density, mimicking the aged-heart phenotype. Removal of senescent cells, which accumulated with chronological age in parallel to the decline in nerve density, rescued age-induced denervation, reversed Sema3a expression, preserved heart rate patterns, and reduced electrical instability. These data suggest that senescence-mediated regulation of nerve density contributes to age-associated cardiac dysfunction.

Comparison of gene expression profiles between human and mouse monocyte subsets.

Blood of both humans and mice contains 2 main monocyte subsets. Here, we investigated the extent of their similarity using a microarray approach. Approximately 270 genes in humans and 550 genes in mice were differentially expressed between subsets by 2-fold or more. More than 130 of these gene expression differences were conserved between mouse and human monocyte subsets. We confirmed numerous of these differences at the cell surface protein level. Despite overall conservation, some molecules were conversely expressed between the 2 species' subsets, including CD36, CD9, and TREM-1. Other differences included a prominent peroxisome proliferator-activated receptor gamma (PPARgamma) signature in mouse monocytes, which is absent in humans, and strikingly opposed patterns of receptors involved in uptake of apoptotic cells and other phagocytic cargo between human and mouse monocyte subsets. Thus, whereas human and mouse monocyte subsets are far more broadly conserved than currently recognized, important differences between the species deserve consideration when models of human disease are studied in mice.

Laser Capture Microdissection-Based mRNA Expression Microarrays and Single-Cell RNA Sequencing in Atherosclerosis Research.

A major goal of methodologies related to large scale gene expression analyses is to initiate comprehensive information on transcript signatures in single cells within the tissue's anatomy. Until now, this could be achieved in a stepwise experimental approach: (1) identify the majority of transcripts in a single cell (single cell transcriptome); (2) provide information on transcripts on multiple cell subtypes in a complex sample (cell heterogeneity); and (3) give information on each cell's spatial location within the tissue (zonation transcriptomics). Such genetic information will allow construction of functionally relevant gene expression maps of single cells of a given anatomically defined tissue compartment and thus pave the way for subsequent analyses, including their epigenetic modifications. Until today these aims have not been achieved in the area of cardiovascular disease research though steps toward these goals become apparent: laser capture microdissection (LCM)-based mRNA expression microarrays of atherosclerotic plaques were applied to gain information on local gene expression changes during disease progression, providing limited spatial resolution. Moreover, while LCM-derived tissue RNA extracts have been shown to be highly sensitive and covers a range of 10-16,000 genes per array/small amount of RNA, its original promise to isolate single cells from a tissue section turned out not to be practicable because of the inherent contamination of the cell's RNA of interest with RNA from neighboring cells. Many shortcomings of LCM-based analyses have been overcome using single-cell RNA sequencing (scRNA-seq) technologies though scRNA-seq also has several limitations including low numbers of transcripts/cell and the complete loss of spatial information. Here, we describe a protocol toward combining advantages of both techniques while avoiding their flaws.

Combined Single-Cell RNA and Single-Cell α/ß T Cell Receptor Sequencing of the Arterial Wall in Atherosclerosis.

Although various pro- and anti-inflammatory T cell subsets have been observed in murine and human atherosclerosis, principal issues of T cell immunity remain unanswered: Is atherosclerosis progression critically affected by aberrant T cell responses? Are tolerance checkpoints compromised during atherosclerosis progression? Answers to these questions will determine if we are at the cusp of developing T cell-dependent therapeutic strategies. Rapid advances in single cell RNA sequencing (scRNA-seq) and single cell α/ß T cell receptor (TCR) (scTCR) sequencing allows to address these issues in unprecedented ways. The majority of T cells recognize peptide antigen-MHC complexes presented by antigen-presenting cells which, in turn, trigger activation and proliferation (clonal expansion) of cognate TCR-carrying T cells. Thus, clonal expansion and their corresponding transcriptome are two similarly important sides of T cell immunity and both will-as hypothesized-affect the outcome of atherosclerosis. Here, we combined scRNA-seq and scTCR-seq in single cells. Moreover, we provide single T cell transcriptomes and TCR maps of three important tissues involved in atherosclerosis This approach is anticipated to address principal questions concerning atherosclerosis autoimmunity that are likely to pave the long sought way to T cell-dependent therapeutic approaches.

In vivo Visualization of M2 Macrophages in the Myocardium After Myocardial Infarction (MI) Using 68 Ga-NOTA-Anti-MMR Nb: Targeting Mannose Receptor (MR, CD206) on M2 Macrophages.

Introduction and Objectives: Wound healing after myocardial infarction (MI) is a dynamic and complex multiple phase process, and a coordinated cellular response is required for proper scar formation. The current paradigm suggests that pro-inflammatory monocytes infiltrate the MI zone during the initial pro-inflammatory phase and differentiate into inflammatory macrophages, and then switch their phenotypes to anti-inflammatory during the reparative phase. Visualization of the reparative phase post-MI is of great interest because it may reveal delayed resolution of inflammation, which in turn predicts adverse cardiac remodeling. Imaging of anti-inflammatory macrophages may also be used to assess therapy approaches aiming to modulate the inflammatory response in order to limit MI size. Reparative macrophages can be distinguished from inflammatory macrophages by the surface marker mannose receptor (MR, CD206). In this study we evaluated the feasibility of 68Ga-NOTA-anti-MMR Nb for imaging of MR on alternatively activated macrophages in murine MI models. Methods: Wildtype and MR-knockout mice and Wistar rats were subjected to MI via permanent ligation of the left coronary artery. Non-operated or sham-operated animals were used as controls. MR expression kinetics on cardiac macrophages was measured in mice using flow cytometry. PET/CT scans were performed 1 h after intravenous injection of 68Ga-NOTA-anti-MMR Nb. Mice and rats were euthanized and hearts harvested for ex vivo PET/MRI, autoradiography, and staining. As a non-targeting negative control, 68Ga-NOTA-BCII10 was used. Results: In vivo-PET/CT scans showed focal radioactivity signals in the infarcted myocardium for 68Ga-NOTA-anti-MMR Nb which were confirmed by ex vivo-PET/MRI scans. In autoradiography images, augmented uptake of the tracer was observed in infarcts, as verified by the histochemistry analysis. Immunofluorescence staining demonstrated the presence and co-localization of CD206- and CD68-positive cells, in accordance to infarct zone. No in vivo or ex vivo signal was observed in the animals injected with control Nb or in the sham-operated animals. 68Ga-NOTA-anti-MMR Nb uptake in the infarcts of MR-knockout mice was negligibly low, confirming the specificity of 68Ga-NOTA-anti-MMR Nb to MR. Conclusion: This exploratory study highlights the potential of 68Ga-NOTA-anti-MMR Nb to image MR-positive macrophages that are known to play a pivotal role in wound healing that follows acute MI.

Tissue Clearing Approaches in Atherosclerosis.

Recent advances in cardiovascular research have led to a more comprehensive understanding of molecular mechanisms of atherosclerosis. It has become apparent that the disease involves three layers of the arterial wall: the intima, the media, and a connective tissue coat termed the adventitia. It is also now appreciated that arteries are surrounded by adipose and neuronal tissues. In addition, adjacent to and within the adventitia, arteries are embedded in a loose connective tissue containing blood vessels (vasa vasora) and lymph vessels, artery-draining lymph nodes and components of the peripheral nervous system, including periarterial nerves and ganglia. During atherogenesis, each of these tissues undergoes marked structural and cellular alterations. We propose that a better understanding of these cell-cell and cell-tissue interactions may considerably advance our understanding of cardiovascular disease pathogenesis. Methods to acquire subcellular optical access to the intact tissues surrounding healthy and diseased arteries are urgently needed to achieve these aims. Tissue clearing is a landmark next-generation, three-dimensional (3D) microscopy technique that allows to image large-scale hitherto inaccessible intact deep tissue compartments. It allows for detailed reconstructions of arteries by a combination of labelling, clearing, advanced microscopies and other imaging and data-analysis tools. Here, we describe two distinct tissue clearing protocols; solvent-based modified three-dimensional imaging of solvent-cleared organs (3DISCO) clearing and another using aqueous-based 2,2'-thiodiethanol (TDE) clearing, both of which complement each other.