Microanatomy of the Human Atherosclerotic Plaque by Single-Cell Transcriptomics

Rationale:Atherosclerotic lesions are known for their cellular heterogeneity, yet the molecular complexity within the cells of human plaques has not been fully assessed.Objective:Using single-cell transcriptomics and chromatin accessibility, we gained a better understanding of the pathophysiology underlying human atherosclerosis.Methods and Results:We performed single-cell RNA and single-cell ATAC sequencing on human carotid atherosclerotic plaques to define the cells at play and determine their transcriptomic and epigenomic characteristics. We identified 14 distinct cell populations including endothelial cells, smooth muscle cells, mast cells, B cells, myeloid cells, and T cells and identified multiple cellular activation states and suggested cellular interconversions. Within the endothelial cell population, we defined subsets with angiogenic capacity plus clear signs of endothelial to mesenchymal transition. CD4(+) and CD8(+) T cells showed activation-based subclasses, each with a gradual decline from a cytotoxic to a more quiescent phenotype. Myeloid cells included 2 populations of proinflammatory macrophages showing IL (interleukin) 1B or TNF (tumor necrosis factor) expression as well as a foam cell-like population expressing TREM2 (triggering receptor expressed on myeloid cells 2) and displaying a fibrosis-promoting phenotype. ATACseq data identified specific transcription factors associated with the myeloid subpopulation and T cell cytokine profiles underlying mutual activation between both cell types. Finally, cardiovascular disease susceptibility genes identified using public genome-wide association studies data were particularly enriched in lesional macrophages, endothelial, and smooth muscle cells.Conclusions:This study provides a transcriptome-based cellular landscape of human atherosclerotic plaques and highlights cellular plasticity and intercellular communication at the site of disease. This detailed definition of cell communities at play in atherosclerosis will facilitate cell-based mapping of novel interventional targets with direct functional relevance for the treatment of human disease

The applications of single-cell RNA sequencing in atherosclerotic research

At the base of the work described here is the overview of all different cell populations present in the carotid atherosclerotic plaque, which were previously not characterized in such detail. We unraveled cell populations such as smooth muscle cells (SMCs), endothelial cells (ECs) and various immune cells via single cell RNA-sequencing (scRNA-seq) which were characterized by examining their specific marker genes. We examined potential ligand-receptor interactions to study cell-cell communications within the plaque and found that myeloid, EC and SMCs are most likely to be interacting. In addition, we compared the human myeloid populations with mouse populations and reported a decent concordance in cell type diversity between species. We leveraged this new knowledge of the cell populations to study the wealth of genome wide association studies (GWAS) loci associated with cardiovascular disease. Identifying the genes from GWAS that are potential candidate genes for clinical care is not straightforward. We describe a two-step approach how we can use scRNA-seq data to translate GWAS susceptibility loci into targets for clinical care by directly examining expression in disease relevant tissue. Loci associated with coronary artery disease are dominantly associated with plaque SMC and EC populations. After identifying (novel) cell- gene pairs, expression of SKI, KANK2 and EDNRA was correlated with migration, proliferation and calcification in vascular SMCs. The molecular mechanisms of endothelial to mesenchymal transition (EndoMT) in human atherosclerosis are poorly understood. We combined the power of in vitro experimental data and scRNA-seq of a lineage tracing mouse model to help study EndoMT in human lesions. We assessed the temporal gene expression under EndoMT promoting conditions and defined assorted patterns of gene expression over the course of time. Next we studied scRNA-seq data from a lineage tracing mouse model were we composed endoMT trajectories. This data was used to demonstrate that the temporal gene expression changes from the in vitro model could identify EndoMT trajectories. Finally, we constructed three candidate EndoMT lineages across multiple subpopulations of ECs and SMCs in human carotid scRNA-seq data, similar to the approach that was applied in mouse data. We examined gene expression over the course of these lineages and identified 73 potential markers for mid-stage EndoMT. From these genes, NRG1 and DEPP1 are associated with mid-stage EndoMT in human atherosclerotic cells. Lastly we studied sex differences in human atherosclerosis via (sc)RNA-seq data. We compared SMC and EC sex-stratified gene expression profiles from 20 female and 26 male atherosclerotic lesions. And used deconvolution to estimate cell population proportions of RNA seq from 169 female and 485 male samples. Differences in sex-related biological pathways in sex stratified scRNA-seq data revealed that the differences in genes found between sexes do not have a common denominator such as “apoptosis” or “endoMT”, but could individually point to different processes. Deconvolution results indicated that female plaques showed a trend towards a higher SMC content compared to males and that males showed a trend towards a higher macrophage and immune cell content. Consequently, females leaned towards a higher ratio of structural vs. immune cells

GWAS to single cell: Intersecting single-cell transcriptomics and genome-wide association studies identifies crucial cell-populations and candidate genes for atherosclerosis.

These are the single-cell RNAseq data from the Athero-Express Biobank Study as used after quality control in the paper referenced below; abstract below. Background Genome-wide association studies (GWAS) have discovered hundreds of common genetic variants for atherosclerotic disease and cardiovascular risk factors. The translation of susceptibility loci into biological mechanisms and targets for drug discovery remains challenging. Intersecting genetic and gene expression data has led to identification of candidate genes. However, the assayed tissues are often non-diseased and heterogeneous in cell composition confounding the candidate prioritization. We collected single-cell transcriptomics (scRNA-seq) from atherosclerotic plaques and aimed to identify cell-type-specific expression of disease-associated genes. Methods and Results To identify disease-associated candidate genes, we applied gene-based analyses using GWAS summary statistics from 46 atherosclerotic, cardiometabolic, and other traits. Next we intersected these candidates with single-cell transcriptomics (scRNA-seq) to identify those genes that are specifically expressed in individual cell (sub)populations of atherosclerotic plaques. We derive an enrichment score and show that loci that associated with coronary artery disease demonstrated a prominent substrate in plaque smooth muscle cells (SKI, KANK2, SORT1), endothelial cells (SLC44A1, ATP2B1), and macrophages (APOE, HNRNPUL1). Further sub clustering of SMC-subtypes revealed genes in risk loci for coronary calcification specifically enriched in a synthetic cluster of SMCs. To verify the robustness of our approach, we used liver-derived scRNAseq-data and showed enrichment of circulating lipids-associated loci in hepatocytes. Conclusion We confirm known gene-cell pairs relevant for atherosclerotic disease, and discovered novel pairs pointing to new biological mechanisms amenable for therapy. We present an intuitive single-cell transcriptomics driven workflow rooted in human large-scale genetic studies to identify putative candidate genes and affected cells associated with cardiovascular traits. Athero-Express Biobank Study The AE started in 2002 and now includes over 3,500 patients who underwent surgery to remove atherosclerotic plaques (endarterectomy) from one (or more) of their major arteries (majority carotids and femorals); this is further described here. The study design and staining protocols are described by Verhoeven et al.. GitHub A link to the public GitHub repository: https://github.com/CirculatoryHealth/gwas2single. This contains all scripts used for the data, which is pseudonymized and shared here. Additional data Additional clinical data is available upon discussion and signing a Data Sharing Agreement (see Terms of Access). PlaqView In collaboration with the http://millerlab.org from the University of Virginia (USA) we created PlaqView.com. You can query any gene of interest in many carotid-plaque datasets, including ours. From our experience we know that usually this suffices most research questions and prevents the lengthy process of obtaining these data through a DSA

The changing landscape of the vulnerable plaque: a call for fine-tuning of preclinical models

For decades, the pathological definition of the vulnerable plaque led to invaluable insights into the mechanisms that underlie myocardial infarction and stroke. Beyond plaque rupture, other mechanisms, such as erosion, may elicit thrombotic events underlining the complexity and diversity of the atherosclerotic disease. Novel insights, based on single-cell transcriptomics and other “omics” methods, provide tremendous opportunities in the ongoing search for cell-specific determinants that will fine-tune the description of the thrombosis prone lesion. It coincides with an increasing awareness that knowledge on lesion characteristics, cell plasticity and clinical presentation of ischemic cardiovascular events have shifted over the past decades. This shift correlates with an observed changes of cell composition towards phenotypical stabilizing of human plaques. These stabilization features and mechanisms are directly mediated by the cells present in plaques and can be mimicked in vitro via primary plaque cells derived from human atherosclerotic tissues. In addition, the rapidly evolving of sequencing technologies identify many candidate genes and molecular mechanisms that may influence the risk of developing an atherosclerotic thrombotic event - which bring the next challenge in sharp focus: how to translate these cell-specific insights into tangible functional and translational discoveries

TRIM46 Organizes Microtubule Fasciculation in the Axon Initial Segment

Selective cargo transport into axons and dendrites over the microtubule network is essential for neuron polarization. The axon initial segment (AIS) separates the axon from the somatodendritic compartment and controls the microtubule-dependent transport into the axon. Interestingly, the AIS has a characteristic microtubule organization; it contains bundles of closely spaced microtubules with electron dense cross-bridges, referred to as microtubule fascicles. The microtubule binding protein TRIM46 localizes to the AIS and when overexpressed in non-neuronal cells forms microtubule arrays that closely resemble AIS fascicles in neurons. However, the precise role of TRIM46 in microtubule fasciculation in neurons has not been studied. Here we developed a novel correlative light and electron microscopy approach to study AIS microtubule organization. We show that in cultured rat hippocampal neurons of both sexes, TRIM46 levels steadily increase at the AIS during early neuronal differentiation and at the same time closely spaced microtubules form, whereas the fasciculated microtubules appear at later developmental stages. Moreover, we localized TRIM46 to the electron dense cross-bridges and show that depletion of TRIM46 causes loss of cross-bridges and increased microtubule spacing. These data indicate that TRIM46 has an essential role in organizing microtubule fascicles in the AIS.SIGNIFICANCE STATEMENT The axon initial segment (AIS) is a specialized region at the proximal axon where the action potential is initiated. In addition the AIS separates the axon from the somatodendritic compartment, where it controls protein transport to establish and maintain neuron polarity. Cargo vesicles destined for the axon recognize specialized microtubule tracks that enter the AIS. Interestingly the microtubules entering the AIS form crosslinked bundles, called microtubule fascicules. Recently we found that the microtubule-binding protein TRIM46 localizes to the AIS, where it may organize the AIS microtubules. In the present study we developed a novel correlative light and electron microscopy approach to study the AIS microtubules during neuron development and identified an essential role for TRIM46 in microtubule fasciculation

TRIM46 Organizes Microtubule Fasciculation in the Axon Initial Segment

Selective cargo transport into axons and dendrites over the microtubule network is essential for neuron polarization. The axon initial segment (AIS) separates the axon from the somatodendritic compartment and controls the microtubule-dependent transport into the axon. Interestingly, the AIS has a characteristic microtubule organization; it contains bundles of closely spaced microtubules with electron dense cross-bridges, referred to as microtubule fascicles. The microtubule binding protein TRIM46 localizes to the AIS and when overexpressed in non-neuronal cells forms microtubule arrays that closely resemble AIS fascicles in neurons. However, the precise role of TRIM46 in microtubule fasciculation in neurons has not been studied. Here we developed a novel correlative light and electron microscopy approach to study AIS microtubule organization. We show that in cultured rat hippocampal neurons of both sexes, TRIM46 levels steadily increase at the AIS during early neuronal differentiation and at the same time closely spaced microtubules form, whereas the fasciculated microtubules appear at later developmental stages. Moreover, we localized TRIM46 to the electron dense cross-bridges and show that depletion of TRIM46 causes loss of cross-bridges and increased microtubule spacing. These data indicate that TRIM46 has an essential role in organizing microtubule fascicles in the AIS.SIGNIFICANCE STATEMENT The axon initial segment (AIS) is a specialized region at the proximal axon where the action potential is initiated. In addition the AIS separates the axon from the somatodendritic compartment, where it controls protein transport to establish and maintain neuron polarity. Cargo vesicles destined for the axon recognize specialized microtubule tracks that enter the AIS. Interestingly the microtubules entering the AIS form crosslinked bundles, called microtubule fascicules. Recently we found that the microtubule-binding protein TRIM46 localizes to the AIS, where it may organize the AIS microtubules. In the present study we developed a novel correlative light and electron microscopy approach to study the AIS microtubules during neuron development and identified an essential role for TRIM46 in microtubule fasciculation

TRIM46 Controls Neuronal Polarity and Axon Specification by Driving the Formation of Parallel Microtubule Arrays

Axon formation, the initial step in establishing neuronal polarity, critically depends on local microtubule reorganization and is characterized by the formation of parallel microtubule bundles. How uniform microtubule polarity is achieved during axonal development remains an outstanding question. Here, we show that the tripartite motif containing (TRIM) protein TRIM46 plays an instructive role in the initial polarization of neuronal cells. TRIM46 is specifically localized to the newly specified axon and, at later stages, partly overlaps with the axon initial segment (AIS). TRIM46 specifically forms closely spaced parallel microtubule bundles oriented with their plus-end out. Without TRIM46, all neurites have a dendrite-like mixed microtubule organization resulting in Tau missorting and altered cargo trafficking. By forming uniform microtubule bundles in the axon, TRIM46 is required for neuronal polarity and axon specification in vitro and in vivo. Thus, TRIM46 defines a unique axonal cytoskeletal compartment for regulating microtubule organization during neuronal development

TRIM46 Controls Neuronal Polarity and Axon Specification by Driving the Formation of Parallel Microtubule Arrays

Axon formation, the initial step in establishing neuronal polarity, critically depends on local microtubule reorganization and is characterized by the formation of parallel microtubule bundles. How uniform microtubule polarity is achieved during axonal development remains an outstanding question. Here, we show that the tripartite motif containing (TRIM) protein TRIM46 plays an instructive role in the initial polarization of neuronal cells. TRIM46 is specifically localized to the newly specified axon and, at later stages, partly overlaps with the axon initial segment (AIS). TRIM46 specifically forms closely spaced parallel microtubule bundles oriented with their plus-end out. Without TRIM46, all neurites have a dendrite-like mixed microtubule organization resulting in Tau missorting and altered cargo trafficking. By forming uniform microtubule bundles in the axon, TRIM46 is required for neuronal polarity and axon specification in vitro and in vivo. Thus, TRIM46 defines a unique axonal cytoskeletal compartment for regulating microtubule organization during neuronal development

Microanatomy of the Human Atherosclerotic Plaque by Single-Cell Transcriptomics

RATIONALE: Atherosclerotic lesions are known for their cellular heterogeneity, yet the molecular complexity within the cells of human plaques has not been fully assessed. OBJECTIVE: Using single-cell transcriptomics and chromatin accessibility, we gained a better understanding of the pathophysiology underlying human atherosclerosis. METHODS AND RESULTS: We performed single-cell RNA and single-cell ATAC sequencing on human carotid atherosclerotic plaques to define the cells at play and determine their transcriptomic and epigenomic characteristics. We identified 14 distinct cell populations including endothelial cells, smooth muscle cells, mast cells, B cells, myeloid cells, and T cells and identified multiple cellular activation states and suggested cellular interconversions. Within the endothelial cell population, we defined subsets with angiogenic capacity plus clear signs of endothelial to mesenchymal transition. CD4+ and CD8+ T cells showed activation-based subclasses, each with a gradual decline from a cytotoxic to a more quiescent phenotype. Myeloid cells included 2 populations of proinflammatory macrophages showing IL (interleukin) 1B or TNF (tumor necrosis factor) expression as well as a foam cell-like population expressing TREM2 (triggering receptor expressed on myeloid cells 2) and displaying a fibrosis-promoting phenotype. ATACseq data identified specific transcription factors associated with the myeloid subpopulation and T cell cytokine profiles underlying mutual activation between both cell types. Finally, cardiovascular disease susceptibility genes identified using public genome-wide association studies data were particularly enriched in lesional macrophages, endothelial, and smooth muscle cells. CONCLUSIONS: This study provides a transcriptome-based cellular landscape of human atherosclerotic plaques and highlights cellular plasticity and intercellular communication at the site of disease. This detailed definition of cell communities at play in atherosclerosis will facilitate cell-based mapping of novel interventional targets with direct functional relevance for the treatment of human disease

Microanatomy of the Human Atherosclerotic Plaque by Single-Cell Transcriptomics

These are the single-cell RNAseq data from the Athero-Express Biobank Study as used after quality control in the paper referenced below; below the abstract. Rationale Atherosclerotic lesions are known for their cellular heterogeneity, yet the molecular complexity within the cells of human plaques has not been fully assessed. Objective Using single-cell transcriptomics and chromatin accessibility, we gained a better understanding of the pathophysiology underlying human atherosclerosis. Methods and Results We performed single-cell RNA and single-cell ATAC sequencing on human carotid atherosclerotic plaques to define the cells at play and determine their transcriptomic and epigenomic characteristics. We identified 14 distinct cell populations including endothelial cells, smooth muscle cells, mast cells, B cells, myeloid cells, and T cells and identified multiple cellular activation states and suggested cellular interconversions. Within the endothelial cell population, we defined subsets with angiogenic capacity plus clear signs of endothelial to mesenchymal transition. CD4+ and CD8+ T cells showed activation-based subclasses, each with a gradual decline from a cytotoxic to a more quiescent phenotype. Myeloid cells included 2 populations of proinflammatory macrophages showing IL (interleukin) 1B or TNF (tumor necrosis factor) expression as well as a foam cell-like population expressing TREM2 (triggering receptor expressed on myeloid cells 2) and displaying a fibrosis-promoting phenotype. ATACseq data identified specific transcription factors associated with the myeloid subpopulation and T cell cytokine profiles underlying mutual activation between both cell types. Finally, cardiovascular disease susceptibility genes identified using public genome-wide association studies data were particularly enriched in lesional macrophages, endothelial, and smooth muscle cells. Conclusions This study provides a transcriptome-based cellular landscape of human atherosclerotic plaques and highlights cellular plasticity and intercellular communication at the site of disease. This detailed definition of cell communities at play in atherosclerosis will facilitate cell-based mapping of novel interventional targets with direct functional relevance for the treatment of human disease. GitHub A link to the public GitHub repository: https://github.com/CirculatoryHealth/MicroanatomyHumanPlaque_scRNAseq. This contains all scripts used for the data, which is pseudonymized and shared here. We also made a private GitHub repository (https://github.com/CirculatoryHealth/AE_TEMPLATE_SCRNASEQ_DATA_SHARE) to enable easy sharing with third parties, publicly or privately. Athero-Express Biobank Study The AE started in 2002 and now includes over 3,500 patients who underwent surgery to remove atherosclerotic plaques (endarterectomy) from one (or more) of their major arteries (majority carotids and femorals); this is further described here. The study design and staining protocols are described by Verhoeven et al.. Additional data Additional clinical data is available upon discussion and signing a Data Sharing Agreement (see Terms of Access). PlaqView In collaboration with the http://millerlab.org from the University of Virginia (USA) we created PlaqView.com. You can query any gene of interest in many carotid-plaque datasets, including ours. From our experience we know that usually this suffices most research questions and prevents the lengthy process of obtaining these data through a DSA