Mechanisms of Medial Wall Thinning in Chronic Total Occlusion.

BACKGROUND: The success rate of percutaneous coronary intervention (PCI) for chronic total occlusion (CTO) is lower and the risk for complications higher compared with other non-CTO PCI. Although interventionalists focus on intimal plaque characteristics, the coronary media is an important (especially for techniques involving antegrade dissection and re-entry) but poorly understood structure in CTO PCI. OBJECTIVES: The aim of the present study was to investigate coronary medial wall thinning in CTO lesions and determine how this thinning might affect CTO PCI. METHODS: A total of 2,586 sections were investigated, from arteries with evidence of CTO from 54 subjects (n = 1,383 sections) and arteries without evidence of CTO from 54 subjects with non-coronary-related deaths (n = 1,203 sections) after matching for age, gender, body weight, and body height. RESULTS: The medial thickness in subjects with CTO was lower than that in those with non-coronary-related death (P < 0.001). In subjects with CTO, CTO lesions had thinner medial walls compared with those with lower luminal narrowing (P < 0.001). At the CTO distal segments, the 6- to 12-mm distal segment from the distal end of the CTO had significantly less luminal narrowing (P < 0.001), and similar medial thickness, compared with the distal end of the CTO. Immunohistochemical analysis revealed that short-duration CTO had more cleaved caspase-3-positive cells in media and had significantly more CD3+, CD4+, CD8+, and CD4+CD28null T cells compared with long-duration CTO. CONCLUSIONS: CTO lesions demonstrated coronary medial thinning compared with non-CTO lesions. Further investigation of the cause-and-effect relationship among inflammation, apoptosis, and coronary medial wall thinning is warranted in future mechanistic studies.

CD163+ Macrophages Induce Endothelial-to-Mesenchymal Transition in Atheroma.

BACKGROUND: Cell phenotype switching is increasingly being recognized in atherosclerosis. However, our understanding of the exact stimuli for such cellular transformations and their significance for human atherosclerosis is still evolving. Intraplaque hemorrhage is thought to be a major contributor to plaque progression in part by stimulating the influx of CD163+ macrophages. Here, we explored the hypothesis that CD163+ macrophages cause plaque progression through the induction of proapoptotic endothelial-to-mesenchymal transition (EndMT) within the fibrous cap. METHODS: Human coronary artery sections from CVPath's autopsy registry were selected for pathological analysis. Athero-prone ApoE-/- and ApoE-/-/CD163-/- mice were used for in vivo studies. Human peripheral blood mononuclear cell-induced macrophages and human aortic endothelial cells were used for in vitro experiments. RESULTS: In 107 lesions with acute coronary plaque rupture, 55% had pathological evidence of intraplaque hemorrhage in nonculprit vessels/lesions. Thinner fibrous cap, greater CD163+ macrophage accumulation, and a larger number of CD31/FSP-1 (fibroblast specific protein-1) double-positive cells and TUNEL (terminal deoxynucleotidyl transferase-dUTP nick end labeling) positive cells in the fibrous cap were observed in nonculprit intraplaque hemorrhage lesions, as well as in culprit rupture sections versus nonculprit fibroatheroma sections. Human aortic endothelial cells cultured with supernatants from hemoglobin/haptoglobin-exposed macrophages showed that increased mesenchymal marker proteins (transgelin and FSP-1) while endothelial markers (VE-cadherin and CD31) were reduced, suggesting EndMT induction. Activation of NF-κB (nuclear factor kappa ß) signaling by proinflammatory cytokines released from CD163+ macrophages directly regulated the expression of Snail, a critical transcription factor during EndMT induction. Western blot analysis for cleaved caspase-3 and microarray analysis of human aortic endothelial cells indicated that apoptosis was stimulated during CD163+ macrophage-induced EndMT. Additionally, CD163 deletion in athero-prone mice suggested that CD163 is required for EndMT and plaque progression. Using single-cell RNA sequencing from human carotid endarterectomy lesions, a population of EndMT was detected, which demonstrated significant upregulation of apoptosis-related genes. CONCLUSIONS: CD163+ macrophages provoke EndMT, which may promote plaque progression through fibrous cap thinning.

Clonal Proliferation Within Smooth Muscle Cells in Unstable Human Atherosclerotic Lesions.

BACKGROUND: Studies in humans and mice using the expression of an X-linked gene or lineage tracing, respectively, have suggested that clones of smooth muscle cells (SMCs) exist in human atherosclerotic lesions but are limited by either spatial resolution or translatability of the model. METHODS: Phenotypic clonality can be detected by X-chromosome inactivation patterns. We investigated whether clones of SMCs exist in unstable human atheroma using RNA in situ hybridization (BaseScope) to identify a naturally occurring 24-nucleotide deletion in the 3'UTR of the X-linked BGN (biglycan) gene, a proteoglycan highly expressed by SMCs. BGN-specific BaseScope probes were designed to target the wild-type or deletion mRNA. Three different coronary artery plaque types (erosion, rupture, and adaptive intimal thickening) were selected from heterozygous females for the deletion BGN. Hybridization of target RNA-specific probes was used to visualize the spatial distribution of mutants. A clonality index was calculated from the percentage of each probe in each region of interest. Spatial transcriptomics were used to identify differentially expressed transcripts within clonal and nonclonal regions. RESULTS: Less than one-half of regions of interest in the intimal plaque were considered clonal with the mean percent regions of interest with clonality higher in the intimal plaque than in the media. This was consistent for all plaque types. The relationship of the dominant clone in the intimal plaque and media showed significant concordance. In comparison with the nonclonal lesions, the regions with SMC clonality had lower expression of genes encoding cell growth suppressors such as CD74, SERF-2 (small EDRK-rich factor 2), CTSB (cathepsin B), and HLA-DPA1 (major histocompatibility complex, class II, DP alpha 1), among others. CONCLUSIONS: Our novel approach to examine clonality suggests atherosclerosis is primarily a disease of polyclonally and to a lesser extent clonally expanded SMCs and may have implications for the development of antiatherosclerotic therapies.

Histologic Assessment of Thromboemboli Due to Plaque Rupture, Plaque Erosion, or COVID-19 Microthrombi.

Plaque rupture, plaque erosion, and COVID-19 infection can cause acute coronary syndromes (ACS). We illustrate case examples demonstrating the distinctive and characteristic pathologic findings underlying each of these various causes of acute myocardial infarction. A deeper understanding of the pathophysiology of ACS is necessary for the development of newer agents and techniques to improve outcomes after ACS. (Level of Difficulty: Advanced.).

Local, Downstream, and Systemic Evaluation after Femoral Artery Angioplasty with Kanshas Drug-Coated Balloons In Vitro and in a Healthy Swine Model.

PURPOSE: To evaluate the incidence of distal embolism and local vascular responses after treatment with the Kanshas drug-coated balloon (DCB) in a preclinical model. MATERIALS AND METHODS: A total of 90 femoral arteries from 35 healthy swine were treated with a single-dose (×1) or triple-dose (×3) Kanshas DCB that applies the Unicoat technology with 3.2 µg/mm2 of paclitaxel. An uncoated Kanshas balloon was used as a control. The arterial wall, downstream skeletal muscle, and nontarget organs (kidneys, lungs, lymph nodes, liver, spleen, and heart) were histologically evaluated. For pharmacokinetic evaluation, a total of 40 healthy swine were treated with ×1 Kanshas DCB, and treated vessels were evaluated ex vivo with high-performance liquid chromatography-mass spectrometry. RESULTS: Arteries treated with the Kanshas DCB showed mild proteoglycan deposition accompanied by the loss of smooth muscle cells (SMCs). These changes increased in a dose-dependent manner (medial SMC loss at 28 days in the ×1 vs ×3 groups, in depth, 1 (0.75-1.38) vs 2 (1.63-2.44); P = .0008; in circumference, 0.83 (0.67-1) vs 1.5 (1.19-1.81); P = .0071). No evidence of distal embolization in skeletal muscles (0 of 210 histological sections) and nontarget organs (0 of 345 sections) was observed. The pharmacokinetic evaluation showed high paclitaxel concentration in the treated artery (912 ng/mg, peaking at 3 minutes), which remained detectable at up to 180 days (0.04 ng/mg). CONCLUSIONS: The Kanshas DCB showed a local drug effect in treated arteries up to 180 days with a high concentration of paclitaxel and no histological evidence of distal embolization.

The histological analysis of the coronary medial thickness: Implications for percutaneous coronary intervention.

BACKGROUND: A deeper understanding of coronary medial thickness is important for coronary intervention because media thickness can limit the safety and effectiveness of interventional techniques. However, there is a paucity of detailed data on human coronary medial thickness so far. MATERIALS AND METHODS: We investigated the thickness of the media by histologic analysis. A total of 230 sections from 10 individuals from the CVPath autopsy registry who died from non-coronary deaths were evaluated. We performed pathological analysis on 13 segments of the following primary vessels from coronary arteries: the left main trunk, proximal left anterior descending artery (LAD), mid LAD, distal LAD, proximal left circumflex artery (LCX), mid LCX, distal LCX, proximal right coronary artery (RCA), mid RCA, and the distal RCA. The following side branches were also evaluated: diagonal, obtuse margin, and posterior descending artery branches. RESULTS: The average age of the studied individuals was 60.4±12.3 years. The median medial thickness for all sections was 0.202 (0.149-0.263) mm. The median medial thickness of the main branches was significantly higher compared to that of the side branches (p<0.001). Although the medial thicknesses of the main branch of LAD and LCX were significantly decreased from proximal to distal segments (p = 0.010, p = 0.006, respectively), the medial thickness of the main branch of RCA was not significantly decreased from proximal to distal (p = 0.170). The thickness of the media was positively correlated with vessel diameter, while it was negatively correlated with luminal narrowing (p<0.001 and p<0.001, respectively). CONCLUSIONS: The human coronary arteries demonstrate variation in medial thickness which tends to vary depending upon an epicardial coronary artery itself, as well as its segments and branches. Understanding these variations in medial thickness can be useful for both the interventionalists and interventional product development teams.

CD163+ macrophages restrain vascular calcification, promoting the development of high-risk plaque.

Vascular calcification (VC) is concomitant with atherosclerosis, yet it remains uncertain why rupture-prone high-risk plaques do not typically show extensive calcification. Intraplaque hemorrhage (IPH) deposits erythrocyte-derived cholesterol, enlarging the necrotic core and promoting high-risk plaque development. Pro-atherogenic CD163+ alternative macrophages engulf hemoglobin:haptoglobin (HH) complexes at IPH sites. However, their role in VC has never been examined to our knowledge. Here we show, in human arteries, the distribution of CD163+ macrophages correlated inversely with VC. In vitro experiments using vascular smooth muscle cells (VSMCs) cultured with HH-exposed human macrophage - M(Hb) - supernatant reduced calcification, while arteries from ApoE-/- CD163-/- mice showed greater VC. M(Hb) supernatant-exposed VSMCs showed activated NF-κB, while blocking NF-κB attenuated the anticalcific effect of M(Hb) on VSMCs. CD163+ macrophages altered VC through NF-κB-induced transcription of hyaluronan synthase (HAS), an enzyme that catalyzes the formation of the extracellular matrix glycosaminoglycan, hyaluronan, within VSMCs. M(Hb) supernatants enhanced HAS production in VSMCs, while knocking down HAS attenuated its anticalcific effect. NF-κB blockade in ApoE-/- mice reduced hyaluronan and increased VC. In human arteries, hyaluronan and HAS were increased in areas of CD163+ macrophage presence. Our findings highlight an important mechanism by which CD163+ macrophages inhibit VC through NF-κB-induced HAS augmentation and thus promote the high-risk plaque development.

Understanding the role of alternative macrophage phenotypes in human atherosclerosis.

INTRODUCTION: Atherosclerosis-based ischemic heart disease is still the primary cause of death throughout the world. Over the past decades there has been no significant changes in the therapeutic approaches to atherosclerosis, which are mainly based on lipid lowering therapies and management of comorbid conditions such as diabetes and hypertension. The involvement of macrophages in atherosclerosis has been recognized for decades. More recently, a more detailed and sophisticated understanding of their various phenotypes and roles in the atherosclerotic process has been recognized. This new data is revealing how specific subtypes of macrophage-induced inflammation may have distinct effects on atherosclerosis progression and may provide new approaches for treatment, based upon targeting of specific macrophage subtypes. AREAS COVERED: We will comprehensively review the spectrum of macrophage phenotypes and how they contribute to atherosclerotic plaque development and progression. EXPERT OPINION: Various signals derived from atherosclerotic lesions drive macrophages into complex subsets with different gene expression profiles, phenotypes, and functions, not all of which are understood. Macrophage phenotypes include those that enhance, heal, and regress the atherosclerotic lesions though various mechanisms. Targeting of specific macrophage phenotypes may provide a promising and novel approach to prevent atherosclerosis progression.

Myeloid-associated lipin-1 transcriptional co-regulatory activity is atheroprotective.

BACKGROUND AND AIMS: Atherosclerosis is the most prominent underlying cause of cardiovascular disease (CVD). It is initiated by cholesterol deposition in the arterial intima, which causes macrophage recruitment and proinflammatory responses that promote plaque growth, necrotic core formation, and plaque rupture. Lipin-1 is a phosphatidic acid phosphohydrolase for glycerolipid synthesis. We have shown that lipin-1 phosphatase activity promotes macrophage pro-inflammatory responses when stimulated with modified low-density lipoprotein (modLDL) and accelerates atherosclerosis. Lipin-1 also independently acts as a transcriptional co-regulator where it enhances the expression of genes involved in ß-oxidation. In hepatocytes and adipocytes, lipin-1 augments the activity of transcription factors such as peroxisome proliferator-activated receptor (PPARs). PPARs control the expression of anti-inflammatory genes in macrophages and slow or reduce atherosclerotic progression. Therefore, we hypothesize myeloid-derived lipin-1 transcriptional co-regulatory activity reduces atherosclerosis. METHODS: We used myeloid-derived lipin-1 knockout (lipin-1mKO) and littermate control mice and AAV8-PCSK9 along with high-fat diet to elicit atherosclerosis. RESULTS: Lipin-1mKO mice had larger aortic root plaques than littermate control mice after 8 and 12 weeks of a high-fat diet. Lipin-1mKO mice also had increased serum proinflammatory cytokine concentrations, reduced apoptosis in plaques, and larger necrotic cores in the plaques compared to control mice. CONCLUSIONS: Combined, the data suggest lipin-1 transcriptional co-regulatory activity in myeloid cells is atheroprotective.

AAV8-mediated overexpression of mPCSK9 in liver differs between male and female mice.

BACKGROUND AND AIMS: The recombinant adeno-associated viral vector serotype 8 expressing the gain-of-function mutation of mouse proprotein convertase subtilisin/kexin type 9 (AAV8- PCSK9) is a new model for the induction of hypercholesterolemia. AAV8 preferentially infects hepatocytes and the incorporated liver-specific promoter should ensure expression of PCSK9 in the liver. Since tissue distribution of AAVs can differ between male and female mice, we investigated the differences in PCSK9 expression and hypercholesterolemia development between male and female mice using the AAV8-PCSK9 model. METHODS: Male and female C57BL/6 mice were injected with either a low-dose or high-dose of AAV8-PCSK9 and fed a high-fat diet. Plasma lipid levels were evaluated as a measure of the induction of hypercholesterolemia. RESULTS: Injection of mice with low dose AAV8-PCSK9 dramatically elevated both serum PCSK9 and cholesterol levels in male but not female mice. Increasing the dose of AAV8-PCSK9 threefold in female mice rescued the hypercholesterolemia phenotype but did not result in full restoration of AAV8-PCSK9 transduction of livers in female mice compared to the low-dose male mice. Our data demonstrate female mice respond differently to AAV8-PCSK9 injection compared to male mice. CONCLUSIONS: These differences do not hinder the use of female mice when AAV8-PCSK9 doses are taken into consideration. However, localization to and production of AAV8-PCSK9 in organs besides the liver in mice may introduce confounding factors into studies and should be considered during experimental design.

Absence of Nicotinamide Nucleotide Transhydrogenase in C57BL/6J Mice Exacerbates Experimental Atherosclerosis.

BACKGROUND: Mitochondrial reactive oxygen species (ROS) contribute to inflammation and vascular remodeling during atherosclerotic plaque formation. C57BL/6N (6N) and C57BL/6J (6J) mice display distinct mitochondrial redox balance due to the absence of nicotinamide nucleotide transhydrogenase (NNT) in 6J mice. We hypothesize that differential NNT expression between these animals alters plaque development. METHODS: 6N and 6J mice were treated with AAV8-PCSK9 (adeno-associated virus serotype 8/proprotein convertase subtilisin/kexin type 9) virus leading to hypercholesterolemia, increased low-density lipoprotein, and atherosclerosis in mice fed a high-fat diet (HFD). Mice were co-treated with the mitochondria-targeted superoxide dismutase mimetic MitoTEMPO to assess the contribution of mitochondrial ROS to atherosclerosis. RESULTS: Baseline and HFD-induced vascular superoxide is increased in 6J compared to 6N mice. MitoTEMPO diminished superoxide in both groups demonstrating differential production of mitochondrial ROS among these strains. PCSK9 treatment and HFD led to similar increases in plasma lipids in both 6N and 6J mice. However, 6J animals displayed significantly higher levels of plaque formation. MitoTEMPO reduced plasma lipids but did not affect plaque formation in 6N mice. In contrast, MitoTEMPO surprisingly increased plaque formation in 6J mice. CONCLUSION: These data indicate that loss of NNT increases vascular ROS production and exacerbates atherosclerotic plaque development.

Macrophage-Associated Lipin-1 Enzymatic Activity Contributes to Modified Low-Density Lipoprotein-Induced Proinflammatory Signaling and Atherosclerosis.

OBJECTIVE: Macrophage proinflammatory responses induced by modified low-density lipoproteins (modLDL) contribute to atherosclerotic progression. How modLDL causes macrophages to become proinflammatory is still enigmatic. Macrophage foam cell formation induced by modLDL requires glycerolipid synthesis. Lipin-1, a key enzyme in the glycerolipid synthesis pathway, contributes to modLDL-elicited macrophage proinflammatory responses in vitro. The objective of this study was to determine whether macrophage-associated lipin-1 contributes to atherogenesis and to assess its role in modLDL-mediated signaling in macrophages. APPROACH AND RESULTS: We developed mice lacking lipin-1 in myeloid-derived cells and used adeno-associated viral vector 8 expressing the gain-of-function mutation of mouse proprotein convertase subtilisin/kexin type 9 (adeno-associated viral vector 8-proprotein convertase subtilisin/kexin type 9) to induce hypercholesterolemia and plaque formation. Mice lacking myeloid-associated lipin-1 had reduced atherosclerotic burden compared with control mice despite similar plasma lipid levels. Stimulation of bone marrow-derived macrophages with modLDL activated a persistent protein kinase Cα/ßII-extracellular receptor kinase1/2-jun proto-oncogene signaling cascade that contributed to macrophage proinflammatory responses that was dependent on lipin-1 enzymatic activity. CONCLUSIONS: Our data demonstrate that macrophage-associated lipin-1 is atherogenic, likely through persistent activation of a protein kinase Cα/ßII-extracellular receptor kinase1/2-jun proto-oncogene signaling cascade that contributes to foam cell proinflammatory responses. Taken together, these results suggest that modLDL-induced foam cell formation and modLDL-induced macrophage proinflammatory responses are not independent consequences of modLDL stimulation but rather are both directly influenced by enhanced lipid synthesis.

Lipin-1 contributes to modified low-density lipoprotein-elicited macrophage pro-inflammatory responses.

Atherosclerosis is a chronic inflammatory disease of large and medium-sized arteries and the underlying cause of cardiovascular disease, a major cause of mortality worldwide. The over-accumulation of modified cholesterol-containing low-density lipoproteins (e.g. oxLDL) in the artery wall and the subsequent recruitment and activation of macrophages contributes to the development of atherosclerosis. The excessive uptake of modified-LDL by macrophages leads to a lipid-laden "foamy" phenotype and pro-inflammatory cytokine production. Modified-LDLs promote foam cell formation in part by stimulating de novo lipid biosynthesis. However, it is unknown if lipid biosynthesis directly regulates foam cell pro-inflammatory mediator production. Lipin-1, a phosphatidate phosphohydrolase required for the generation of diacylglycerol during glycerolipid synthesis has recently been demonstrated to contribute to bacterial-induced pro-inflammatory responses by macrophages. In this study we present evidence demonstrating the presence of lipin-1 within macrophages in human atherosclerotic plaques. Additionally, reducing lipin-1 levels in macrophages significantly inhibits both modified-LDL-induced foam cell formation in vitro, as observed by smaller/fewer intracellular lipid inclusions, and ablates modified-LDL-elicited production of the pro-atherogenic mediators tumor necrosis factor-α, interleukin-6, and prostaglandin E2. These findings demonstrate a critical role for lipin-1 in the regulation of macrophage inflammatory responses to modified-LDL. These data begin to link the processes of foam cell formation and pro-inflammatory cytokine production within macrophages.

Natural killer T (NKT) cells accelerate Shiga toxin type 2 (Stx2) pathology in mice.

Shiga toxin-producing Escherichia coli (STEC) is a leading cause of childhood renal disease Hemolytic Uremic Syndrome (HUS). The involvement of renal cytokines and chemokines is suspected to play a critical role in disease progression. In current article, we tested the hypothesis that NKT cells are involved in Stx2-induced pathology in vivo. To address this hypothesis we compared Stx2 toxicity in WT and CD1 knockout (KO) mice. In CD1KO mice, which lack natural killer T (NKT) cells, Stx2-induced pathologies such as weight loss, renal failure, and death were delayed. In WT mice, Stx2-specific selective increase in urinary albumin occurs in later time points, and this was also delayed in NKT cell deficient mice. NKT cell-associated cytokines such as IL-2, IL-4, IFN-γ, and IL-17 were detected in kidney lysates of Stx2-injected WT mice with the peak around 36 h after Stx2 injection. In CD1KO, there was a delay in the kinetics, and increases in these cytokines were observed 60 h post Stx2 injection. These data suggest that NKT cells accelerate Stx2-induced pathology in mouse kidneys. To determine the mechanism by which NKT cells promote Stx2-associated disease, in vitro studies were performed using murine renal cells. We found that murine glomerular endothelial cells and podocytes express functional CD1d molecules and can present exogenous antigen to NKT cells. Moreover, we observed the direct interaction between Stx2 and the receptor Gb3 on the surface of mouse renal cells by 3D STORM-TIRF which provides single molecule imaging. Collectively, these data suggest that Stx2 binds to Gb3 on renal cells and leads to aberrant CD1d-mediated NKT cell activation. Therefore, strategies targeting NKT cells could have a significant impact on Stx2-associated renal pathology in STEC disease.