Peculiarities of cell composition and cell proliferation in different type atherosclerotic lesions in carotid and coronary arteries

Ex Vivo Study Using Diffusion Tensor Imaging to Identify Biomarkers of Atherosclerotic Disease in Human Cadaveric Carotid Arteries

BACKGROUND

This study aims to address the potential of ex vivo diffusion tensor imaging to provide insight into the microstructural composition and morphological arrangement of aged human atherosclerotic carotid arteries.

METHODS

In this study, whole human carotid arteries were investigated both anatomically and by comparing healthy and diseased regions. Nonrigid image registration was used with unsupervised segmentation to investigate the influence of elastin, collagen, cell density, glycosaminoglycans, and calcium on diffusion tensor imaging derived metrics (fractional anisotropy and mean diffusivity). Early stage atherosclerotic features were also investigated in terms of microstructural components and diffusion tensor imaging metrics.

RESULTS

All vessels displayed a dramatic decrease in fractional anisotropy compared with healthy animal arterial tissue, while the mean diffusivity was sensitive to regions of advanced disease. Elastin content strongly correlated with both fractional anisotropy (r>0.7, P<0.001) and mean diffusivity (r>-0.79, P<0.0002), and the thickened intima was also distinguishable from arterial media by these metrics.

CONCLUSIONS

These different investigations point to the potential of diffusion tensor imaging to identify characteristics of arterial disease progression, at early and late-stage lesion development.

Reciprocal regulation of endothelial-mesenchymal transition by MAPK7 and EZH2 in intimal hyperplasia and coronary artery disease

Endothelial-mesenchymal transition (EndMT) is a form of endothelial dysfunction wherein endothelial cells acquire a mesenchymal phenotype and lose endothelial functions, which contributes to the pathogenesis of intimal hyperplasia and atherosclerosis. The mitogen activated protein kinase 7 (MAPK7) inhibits EndMT and decreases the expression of the histone methyltransferase Enhancer-of-Zeste homologue 2 (EZH2), thereby maintaining endothelial quiescence. EZH2 is the catalytic subunit of the Polycomb Repressive Complex 2 that methylates lysine 27 on histone 3 (H3K27me3). It is elusive how the crosstalk between MAPK7 and EZH2 is regulated in the endothelium and if the balance between MAPK7 and EZH2 is disturbed in vascular disease. In human coronary artery disease, we assessed the expression levels of MAPK7 and EZH2 and found that with increasing intima/media thickness ratio, MAPK7 expression decreased, whereas EZH2 expression increased. In vitro, MAPK7 activation decreased EZH2 expression, whereas endothelial cells deficient of EZH2 had increased MAPK7 activity. MAPK7 activation results in increased expression of microRNA (miR)-101, a repressor of EZH2. This loss of EZH2 in turn results in the increased expression of the miR-200 family, culminating in decreased expression of the dual-specificity phosphatases 1 and 6 who may repress MAPK7 activity. Transfection of endothelial cells with miR-200 family members decreased the endothelial sensitivity to TGFβ1-induced EndMT. In endothelial cells there is reciprocity between MAPK7 signaling and EZH2 expression and disturbances in this reciprocal signaling associate with the induction of EndMT and severity of human coronary artery disease.

Emerging Role of Pericytes and Their Secretome in the Heart

Pericytes, as mural cells covering microvascular capillaries, play an essential role in vascular remodeling and maintaining vascular functions and blood flow. Pericytes are crucial participants in the physiological and pathological processes of cardiovascular disease. They actively interact with endothelial cells, vascular smooth muscle cells (VSMCs), fibroblasts, and other cells via the mechanisms involved in the secretome. The secretome of pericytes, along with diverse molecules including proinflammatory cytokines, angiogenic growth factors, and the extracellular matrix (ECM), has great impacts on the formation, stabilization, and remodeling of vasculature, as well as on regenerative processes. Emerging evidence also indicates that pericytes work as mesenchymal cells or progenitor cells in cardiovascular regeneration. Their capacity for differentiation also contributes to vascular remodeling in different ways. Previous studies primarily focused on the roles of pericytes in organs such as the brain, retina, lung, and kidney; very few studies have focused on pericytes in the heart. In this review, following a brief introduction of the origin and fundamental characteristics of pericytes, we focus on pericyte functions and mechanisms with respect to heart disease, ending with the promising use of cardiac pericytes in the treatment of ischemic heart failure.

Single-Cell Transcriptomic Atlas of Different Human Cardiac Arteries Identifies Cell Types Associated With Vascular Physiology

[Figure: see text].

Heteroplasmic Variants of Mitochondrial DNA in Atherosclerotic Lesions of Human Aortic Intima

Mitochondrial dysfunction and oxidative stress are likely involved in atherogenesis. Since the mitochondrial genome variation can alter functional activity of cells, it is necessary to assess the presence in atherosclerotic lesions of mitochondrial DNA (mtDNA) heteroplasmic mutations known to be associated with different pathological processes and ageing. In this study, mtDNA heteroplasmy and copy number (mtCN) were evaluated in the autopsy-derived samples of aortic intima differing by the type of atherosclerotic lesions. To detect mtDNA heteroplasmic variants, next generation sequencing was used, and mtCN measurement was performed by qPCR. It was shown that mtDNA heteroplasmic mutations are characteristic for particular areas of intimal tissue; in 83 intimal samples 55 heteroplasmic variants were found; mean minor allele frequencies level accounted for 0.09, with 12% mean heteroplasmy level. The mtCN variance measured in adjacent areas of intima was high, but atherosclerotic lesions and unaffected intima did not differ significantly in mtCN values. Basing on the ratio of minor and major nucleotide mtDNA variants, we can conclude that there exists the increase in the number of heteroplasmic mtDNA variants, which corresponds to the extent of atherosclerotic morphologic phenotype.

Macrophages and Their Contribution to the Development of Atherosclerosis

Atherosclerosis can be regarded as chronic inflammatory disease driven by lipid accumulation in the arterial wall. Macrophages play a key role in the development of local inflammatory response and atherosclerotic lesion growth. Atherosclerotic plaque is a complex microenvironment, in which different subsets of macrophages coexist executing distinct, although in some cases overlapping functions. According to the classical simplified nomenclature, lesion macrophages can belong to pro-inflammatory or anti-inflammatory or alternatively activated types. While the former promote the inflammatory response and participate in lipid accumulation, the latter are responsible for the inflammation resolution and plaque stabilisation. Atherosclerotic lesion dynamics depends therefore on the balance between these macrophages populations. The diverse functions of macrophages make them an attractive therapeutic target for the development of novel anti-atherosclerotic treatments. In this chapter, we discuss different types of macrophages and their roles in atherosclerotic lesion dynamics and describe the results of several experiments studying macrophage polarisation in atherosclerosis.

Immune Functions and Properties of Resident Cells in the Heart and Cardiovascular System: Pericytes

This chapter provides an introduction to pericyte physiology. Pericytes are smooth muscle-like cells that wrap around vessels and arterioles. Here, we discuss their structure, function, contractility and interaction with other cells including immune cells and finally their role in pathological processes. Additionally, we discuss recent studies describing pericyte populations in the heart and their potential as targets for future cardiac therapeutic interventions.

Histological changes in the umbilical artery following severe chorioamnionitis and funisitis may be indicative of early atherosclerosis

We investigated whether histological evidence of early atherosclerosis was present in the umbilical artery of 21 pregnancies complicated by severe perinatal inflammation, and 21 controls matched for gestational age, sex and birth weight. Severe chorioamnionitis with funisitis was associated with increased numbers of CD68 and CD45 positive cells (both P < 0.01), indicating accumulation of monocyte-derived macrophages in lesion-susceptible regions. A down-regulation of SMA expression (P = 0.01) was also observed. These preliminary findings suggest that chorioamnionitis with funisitis may promote changes in the intima and media of the umbilical artery similar to that seen in early atherosclerosis.

Cellular mechanisms of human atherosclerosis: Role of cell-to-cell communications in subendothelial cell functions

The present study was undertaken in order to extend of our earlier work, focusing on the analysis of roles of cell-to-cell communications in the regulation of the subendothelial cell function. In present study, we have found that the expression of connexin43 (Cx43) is dramatically reduced in human atherosclerotic lesions, compared with undiseased intima. In atherosclerotic lesions, the number of so-called 'connexin plaques' was found to be lower in lipid-laden cells than in cells which were free from lipid inclusions. In primary cell culture, subendothelial intimal cells tended to create multicellular structures in the form of clusters. Cluster creation was accompanied by the formation of gap junctions between cells; the degree of gap junctional communication correlated with the density of cells in culture. We found that atherosclerosis-related processes such as DNA synthesis, protein synthesis and accumulation of intracellular cholesterol correlated with the degree of cell-to-cell communication. The relation of DNA and protein synthesis with cell-to-cell communication could be described as "bell-shaped". We further incubated cells, cultured from undiseased subendothelial intima, with various forms of modified LDL causing intracellular cholesterol accumulation. After the incubation of intimal cells with modified LDL, intercellular communication has "dropped" considerably. The findings indicate that intracellular lipid accumulation might be a reason for a decrease of the number of gap junctions. The findings also suggest that the disintegration of cellular network is associated with foam cell formation, the process known as a key event of atherogenesis.

Intimal pericytes as the second line of immune defence in atherosclerosis

Inflammation plays an essential role in the development of atherosclerosis. The initiation and growth of atherosclerotic plaques is accompanied by recruitment of inflammatory and precursor cells from the bloodstream and their differentiation towards pro-inflammatory phenotypes. This process is orchestrated by the production of a number of pro-inflammatory cytokines and chemokines. Human arterial intima consists of structurally distinct leaflets, with a proteoglycan-rich layer lying immediately below the endothelial lining. Recent studies reveal the important role of stellate pericyte-like cells (intimal pericytes) populating the proteoglycan-rich layer in the development of atherosclerosis. During the pathologic process, intimal pericytes may participate in the recruitment of inflammatory cells by producing signalling molecules and play a role in the antigen presentation. Intimal pericytes are also involved in lipid accumulation and the formation of foam cells. This review focuses on the role of pericyte-like cells in the development of atherosclerotic lesions.

Study of the activated macrophage transcriptome

Transcriptome analysis is a powerful modern tool to study possible alterations of gene expression associated with human diseases. It turns out to be especially promising for evaluation of gene expression changes in immunopathology, as immune cells have flexible gene expression patterns that can be switched in response to infection, inflammatory stimuli and exposure to various cytokines. In particular, macrophage polarization towards pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes can be successfully studied using the modern transcriptome analysis approaches. The two mostly used techniques for transcriptome analysis are microarray and next generation sequencing. In this review we will provide an overview of known gene expression changes associated with immunopathology and discuss the advantage and limitations of different methods of transcriptome analysis.

The impact of uric acid on long-term mortality in patients with asymptomatic carotid atherosclerotic disease

BACKGROUND

Serum uric acid (SUA) has been discussed to be related to cardiovascular (CV) disease and outcome. We investigated whether levels of SUA predict long-term mortality in neurologically asymptomatic patients with carotid atherosclerotic disease.

METHODS

We prospectively studied 959 consecutive patients with carotid atherosclerosis as evaluated by duplex Doppler sonography for all-cause and CV death, respectively.

RESULTS

During a median follow-up time of 6.3 years (interquartile range [IQR], 5.4-7.1 years), 246 deaths (25.7%), including 160 CV deaths (16.7%), were recorded. Median baseline SUA levels were 5.9 mg/dL (IQR, 5.0-7.0 mg/dL). SUA was significantly associated with all-cause death and CV death. Adjusted hazard ratios (HRs) for an increase of 1 mg/dL of SUA levels were 1.12 (95% confidence interval [CI], 1.04-1.21; P = .003) and 1.20 (95% CI, 1.11-1.30; P < .001) for all-cause and CV death, respectively. Quartiles of SUA levels showed a significant association with CV mortality (log-rank P = .002). For CV death, adjusted HRs for quartiles of increasing SUA levels were 1.45 (95% CI, .87-2.43), 1.44 (95% CI, .85-2.46), and 2.26 (95% CI, 1.36-3.76; P < .01), compared with the lowest quartile, respectively. Patients with baseline carotid stenosis of more than 50% and/or increased levels of SUA (≥median) had an approximately 2-fold increase in risk of (CV) death, compared with patients with carotid narrowing of less than 50% and/or SUA levels less than the median (P < .001).

CONCLUSIONS

Levels of SUA represent independent predictors for CV mortality in a cohort of patients with asymptomatic carotid atherosclerosis.

The complexity of cell composition of the intima of large arteries: focus on pericyte-like cells

Pericytes, which are also known as Rouget cells or perivascular cells, are considered to represent a likely distinct pool of vascular cells that are extremely branched and located mostly in the periphery of the vascular system. The family of pericytes is a heterogeneous cell population that includes pericytes and pericyte-like cells. Accumulated data indicate that networks of pericyte-like cells exist in normal non-atherosclerotic intima, and that pericyte-like cells can be involved in the development of atherosclerotic lesions from the very early stages of disease. The pathogenic role of arterial pericytes and pericyte-like cells also might be important in advanced and complicated atherosclerotic lesions via realizing mechanisms of vascular remodelling, ectopic ossification, intraplaque neovascularization, and probably thrombosis.

Association of the level of heteroplasmy of the 15059G>A mutation in the MT-CYB mitochondrial gene with essential hypertension

AIM

To examine whether the heteroplasmy level for 15059G>A mutation in the mitochondrial genome might be associated with essential hypertension.

METHODS

This cross-sectional study involved 196 unrelated participants randomly selected from general population (90 males and 106 females) who underwent a regular medical check-up at the Institute for Atherosclerosis Research (Moscow, Russia). One hundred and twenty of them (61%) had essential hypertension, and 76 (39%) were apparently healthy normotensive persons. The level of heteroplasmy for 15059G>A mutation occurring in the coding region of cytochrome b gene (MT-CYB) of mtDNA isolated from the blood leukocytes, was quantified using DNA pyrosequencing method.

RESULTS

The 15059G>A heteroplasmy level ranged between 4% and 83%, with a median level of 31%. Between the upper and lower quartiles of 15059G>A heteroplasmy distribution, significant differences were observed for patients' age, systolic blood pressure, and triglyceride levels. 15059G>A heteroplasmy correlated both with age (r = 0.331, P < 0.001) and the presence of hypertension (r = 0.228, P = 0.002). Regression analysis revealed that the age explains 12% variability of 15059G>A heteroplasmy, and hypertension independently explains more 5% variability. The 15059G>A heteroplasmy exceeding 31% was found to be significantly associated with a higher risk of essential hypertension (odds ratio 2.76; P (Fisher) 0.019]. The study participants with high 15059G>A heteroplasmy level were found to have significantly higher age (P < 0.001) and the prevalence of essential hypertension (P = 0.033), as compared to those with low 15059G>A heteroplasmy level. These observations suggested a positive correlation between the level of 15059G>A heteroplasmy and essential hypertension.

CONCLUSION

This study provides the evidence of association of mtDNA 15059G>A mutation heteroplasmy with essential hypertension.

Changes of lysosomes in the earliest stages of the development of atherosclerosis

One of hypotheses of atherosclerosis is based on a presumption that the zones prone to the development of atherosclerosis contain lysosomes which are characterized by enzyme deficiency and thus, are unable to dispose of lipoproteins. The present study was undertaken to investigate the characteristics and changes of lysosomes in the earliest stages of the development of atherosclerosis. Electron microscopic immunocytochemistry revealed that there were certain changes in the distribution of CD68 antigen in lysosomes along the ‘normal intima-initial lesion-fatty streak’ sequence. There were no significant changes found in the key mRNAs encoding for the components of endosome/lysosome compartment in initial atherosclerotic lesions, but in fatty streaks, the contents of EEA1 and Rab5a mRNAs were found to be diminished while the contents of CD68 and p62 mRNAs were increased, compared with the intact tissue. The study reinforces a view that changes occurring in lysosomes play a role in atherogenesis from the very earlier stages of the disease.

Diagnostic and prognostic value of low density lipoprotein-containing circulating immune complexes in atherosclerosis

Recently, it has been shown that increased level of LDL-containing circulating immune complexes (LDL-CIC) possess high diagnostic significance in clinically manifested atherosclerosis, but little is known about its diagnostic and prognostic significance in early atherosclerosis. Two-years prospective study was performed in 98 asymptomatic men aged 40-74. The rate of atherosclerosis progression was estimated by high-resolution B-mode ultrasonography as the increase in intima-media thickness (IMT) of common carotid arteries. The patients with elevated baseline levels of LDL-CIC were characterized by significantly higher levels of total and LDL cholesterol as well as significantly increased mean IMT of common carotid arteries. Among all baseline lipid parameters, only LDL-CIC and LDL cholesterol were contingent with the extent of early carotid atherosclerosis (p = 0.042 and p = 0.049, respectively) and had the highest levels of relative risk and odds ratio. During the follow up, significant IMT increase was registered in 53.1 % (n = 52) patients, IMT significant reduction was observed in 21.4 % (n = 21) patients. The increased levels of LDL-CIC, total serum cholesterol and LDL cholesterol had similar prognostic significance with the respect of atherosclerosis progression. The normal level of LDL-CIC (below than 16.0 μg/ml) was the only lipid parameter that predicted the absence of carotid atherosclerosis progression for two following years at prognostic value of 78.3 %. The results of the study allow assuming that LDL-CIC level may be employed not only as a marker of early atherosclerosis, but also has a sufficient prognostic value for clinical implications.

Mutation C3256T of mitochondrial genome in white blood cells: novel genetic marker of atherosclerosis and coronary heart disease

This study was undertaken to examine the association between the level of heteroplasmy for the mutation C3256T in human white blood cells and the extent of carotid atherosclerosis, as well as the presence of coronary heart disease (CHD), the major clinical manifestation of atherosclerosis. Totally, 191 participants (84 men, 107 women) aged 65.0 years (SD 9.4) were recruited in the study; 45 (24%) of them had CHD. High-resolution B-mode ultrasonography of carotids was used to estimate the extent of carotid atherosclerosis by measuring of the carotid intima-media thickness (cIMT). DNA samples were obtained from whole venous blood, and then PCR and pyrosequencing were carried out. On the basis of pyrosequencing data, the levels of C3256T heteroplasmy in DNA samples were calculated. The presence of the mutant allele was detected in all study participants; the level of C3256T heteroplasmy in white blood cells ranged from 5% to 74%. The highly significant relationship between C3256T heteroplasmy level and predisposition to atherosclerosis was revealed. In individuals with low predisposition to atherosclerosis the mean level of C3256T heteroplasmy was 16.8%, as compared to 23.8% in moderately predisposed subjects, and further to 25.2% and 28.3% in significantly and highly predisposed subjects, respectively. The level of C3256T heteroplasmy of mitochondrial genome in human white blood cells is a biomarker of mitochondrial dysfunction and risk factor for atherosclerosis; therefore, it can be used as an informative marker of genetic susceptibility to atherosclerosis, coronary heart disease and myocardial infarction.

Mitochondrial dysfunction and mitochondrial DNA mutations in atherosclerotic complications in diabetes

Mitochondrial DNA (mtDNA) is particularly prone to oxidation due to the lack of histones and a deficient mismatch repair system. This explains an increased mutation rate of mtDNA that results in heteroplasmy, e.g., the coexistence of the mutant and wild-type mtDNA molecules within the same mitochondrion. In diabetes mellitus, glycotoxicity, advanced oxidative stress, collagen cross-linking, and accumulation of lipid peroxides in foam macrophage cells and arterial wall cells may significantly decrease the mutation threshold required for mitochondrial dysfunction, which in turn further contributes to the oxidative damage of the diabetic vascular wall, endothelial dysfunction, and atherosclerosis.

Testing of serum atherogenicity in cell cultures: questionable data published

In a large series of studies was reported that culturing of smooth muscle cells with serum from atherosclerosis patients caused intracellular lipid accumulation, while serum from healthy controls had no such effect. Cultures were used for evaluation of antiatherogenic drugs. Numerous substances were reported to lower serum atherogenicity: statins, trapidil, calcium antagonists, garlic derivatives etc. On the contrary, beta-blockers, phenothiazines and oral hypoglycemics were reported to be pro-atherogenic. Known antiatherogenic agents can influence lipid metabolism and cholesterol synthesis, intestinal absorption or endothelium-related mechanisms. All these targets are absent in cell monocultures. Inflammatory factors, addressed by some antiatherogenic drugs, are also not reproduced. In vivo, relationship between cholesterol uptake by cells and atherogenesis must be inverse rather than direct: in familial hypercholesterolemia, inefficient clearance of LDL-cholesterol by cells predisposes to atherosclerosis. Accordingly, if a pharmacological agent reduces cholesterol uptake by cells in vitro, it should be expected to elevate cholesterol in vivo. Validity of clinical recommendations, based on serum atherogenicity testing in cell monocultures, is therefore questionable. These considerations pertain also to the drugs developed on the basis of the cell culture experiments.

Correlation between lipid deposition, immune-inflammatory cell content and MHC class II expression in diffuse intimal thickening of the human aorta

Inflammatory reactions driven by an accumulation in the intima of immune-inflammatory cells and focal lipid depositions are the hallmarks of atherogenesis. It is commonly accepted that immune-inflammatory cell accumulation and lipid deposition are associated with the very earlier stage of atherosclerosis but no study has yet focused on the determination of quantitative values of this association. The present study examined correlations between lipid deposition, immune-inflammatory cell content and major histocompatibility complex (MHC) class II molecule HLA-DR expression in diffuse intimal thickening (DIT), which is thought to represent the earliest macroscopic manifestation of atherosclerosis. In parallel consecutive tissue sections of DIT, lipids were examined by chromatographic analysis (including triglycerides, cholesteryl esters, free cholesterol and phospholipids), histochemically, using Oil Red O staining, and by electron microscopy. Immune-inflammatory cells and HLA-DR expression were examined immunohistochemically in consecutive sections of the same tissue specimens. The study revealed that lipids exhibited a non-uniform distribution throughout the intima. In the juxtaluminal sublayer, lipids were localized both intracellularly and extracellularly, whereas in the juxtamedial musculoelastic sublayer, lipids were present predominantly along elastic fibers. Lipid deposits were found to positively correlate with HLA-DR expression (r=0.79; p<0.001). The study also identified a positive correlation between lipid deposition and immune-inflammatory cell content but the correlation values varied between different sublayers of the tunica intima. The correlation between lipid deposition and immune-inflammatory cell content in the juxtaluminal sublayer of the intima was notably stronger (r=0.69; p<0.001) than in the juxtamedial musculoelastic layer (r=0.28; p<0.001). The findings of the present study support a view that lipid accumulation in the intima plays a role in the initiation of inflammatory reaction and that at the pre-lesional stage in the development of atherosclerosis, lipid-associated immune cell activation might occur primarily in the juxtaluminal portion of the intima.

Widespread distribution of HLA-DR-expressing cells in macroscopically undiseased intima of the human aorta: a possible role in surveillance and maintenance of vascular homeostasis

The architectonics and cell composition of the human large arteries are not sufficiently understood. The present study is the first to undertake an analysis of the distribution and quantities of HLA-DR-expressing cells in grossly undiseased human intima using immunohistochemical and immunofluorescent analysis, complemented by the advantages of confocal microscopy. The study revealed a widespread distribution of HLA-DR-expressing cells throughout the intimal space where the cells were integrated into continuous networks via long cell processes. Numbers of HLA-DR+ cells were found to be significantly larger in the middle third of the intima than in the superficial and deep intimal portions. We speculate that a widespread distribution of HLA-DR-expressing cells in the intima of normal human aorta might play a role in the surveillance and maintenance of vascular homeostasis.