Lipid accumulation in arterial smooth muscle cells. Influence of phenotype

Universal cell membrane camouflaged nano-prodrugs with right-side-out orientation adapting for positive pathological vascular remodeling in atherosclerosis

A right-side-out orientated self-assembly of cell membrane-camouflaged nanotherapeutics is crucial for ensuring their biological functionality inherited from the source cells. In this study, a universal and spontaneous right-side-out coupling-driven ROS-responsive nanotherapeutic approach, based on the intrinsic affinity between phosphatidylserine (PS) on the inner leaflet and PS-targeted peptide modified nanoparticles, has been developed to target foam cells in atherosclerotic plaques. Considering the increased osteopontin (OPN) secretion from foam cells in plaques, a bioengineered cell membrane (OEM) with an overexpression of integrin α9β1 is integrated with ROS-cleavable prodrugs, OEM-coated ETBNPs (OEM-ETBNPs), to enhance targeted drug delivery and on-demand drug release in the local lesion of atherosclerosis. Both in vitro and in vivo experimental results confirm that OEM-ETBNPs are able to inhibit cellular lipid uptake and simultaneously promote intracellular lipid efflux, regulating the positive cellular phenotypic conversion. This finding offers a versatile platform for the biomedical applications of universal cell membrane camouflaging biomimetic nanotechnology.

Phenotypic switching of vascular smooth muscle cells in atherosclerosis, hypertension, and aortic dissection

Vascular smooth muscle cells (VSMCs) play a critical role in regulating vasotone, and their phenotypic plasticity is a key contributor to the pathogenesis of various vascular diseases. Two main VSMC phenotypes have been well described: contractile and synthetic. Contractile VSMCs are typically found in the tunica media of the vessel wall, and are responsible for regulating vascular tone and diameter. Synthetic VSMCs, on the other hand, are typically found in the tunica intima and adventitia, and are involved in vascular repair and remodeling. Switching between contractile and synthetic phenotypes occurs in response to various insults and stimuli, such as injury or inflammation, and this allows VSMCs to adapt to changing environmental cues and regulate vascular tone, growth, and repair. Furthermore, VSMCs can also switch to osteoblast-like and chondrocyte-like cell phenotypes, which may contribute to vascular calcification and other pathological processes like the formation of atherosclerotic plaques. This provides discusses the mechanisms that regulate VSMC phenotypic switching and its role in the development of vascular diseases. A better understanding of these processes is essential for the development of effective diagnostic and therapeutic strategies.

Lipid droplets, autophagy, and ageing: A cell-specific tale

Lipid droplets are the essential organelle for storing lipids in a cell. Within the variety of the human body, different cells store, utilize and release lipids in different ways, depending on their intrinsic function. However, these differences are not well characterized and, especially in the context of ageing, represent a key factor for cardiometabolic diseases. Whole body lipid homeostasis is a central interest in the field of cardiometabolic diseases. In this review we characterize lipid droplets and their utilization via autophagy and describe their diverse fate in three cells types central in cardiometabolic dysfunctions: adipocytes, hepatocytes, and macrophages.

OxLDL induces the release of IL-1β from primed human endothelial and smooth muscle cells via different caspase -1-dependent mechanisms

Atherosclerosis is characterised by abnormal lipid and cell accumulation within arterial layers that leads to disturbed blood flow. Modified cholesterol forms such as oxidised low-density lipoprotein (oxLDL) enter cells altering their phenotype, triggering over-exuberant repair and arterial occlusion, myocardial infarction or stroke. We hypothesised that oxLDL enters vascular wall cells and induces interleukin-1β (IL-1β) secretion, potentially via a caspase-1/NLRP3 mechanism. Human coronary artery endothelial cells (HCAEC) and smooth muscle cells (HCASMC), isolated from different donors, were cultured and stimulated (primed) with pro-inflammatory cytokines TNFα and IL-1α (10 ng/mL each, for 48 h), followed by incubation with human oxLDL (10-50 ug/mL) for up to 6 h. Inhibitors of caspase-1 (YVAD), NLRP3 (MCC950) and gasdermin D (disulfiram) were added 1 h before oxLDL. Cell lysates and culture supernatants were collected and analysed for IL-1β using ELISA. Microscopy imaging showed oxLDL entered stimulated cells and formed particles. OxLDL at 20 and 50 ug/mL induced the maximum release of IL-1β from stimulated HCASMCs and HCAECs, respectively, compared to control. Inhibition of either NLRP3, caspase-1 or gasdermin D significantly reduced the release of IL-1β (4-fold, P < 0.0001; 14-fold, P < 0.0001, 1.5-fold, P < 0.0003, respectively) in HCAEC. In contrast, in HCASMCs, only caspase-1 inhibition reduced the release of IL-1β (2.1-fold, P < 0.0001). HCAECs and HCASMCs elicited the release of IL-1β in response to the same stimulus via different mechanisms. In HCAECs, released IL-1β potentially exits via a GSDMD-induced membrane pore. These data suggest that caspase-1 or gasdermin D inhibition is likely to be effective vessel wall cell-specific strategies for the reduction of atherosclerosis.

Insight into the Evolving Role of PCSK9

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is the last discovered member of the family of proprotein convertases (PCs), mainly synthetized in hepatic cells. This serine protease plays a pivotal role in the reduction of the number of low-density lipoprotein receptors (LDLRs) on the surface of hepatocytes, which leads to an increase in the level of cholesterol in the blood. This mechanism and the fact that gain of function (GOF) mutations in PCSK9 are responsible for causing familial hypercholesterolemia whereas loss-of-function (LOF) mutations are associated with hypocholesterolemia, prompted the invention of drugs that block PCSK9 action. The high efficiency of PCSK9 inhibitors (e.g., alirocumab, evolocumab) in decreasing cardiovascular risk, pleiotropic effects of other lipid-lowering drugs (e.g., statins) and the multifunctional character of other proprotein convertases, were the cause for proceeding studies on functions of PCSK9 beyond cholesterol metabolism. In this article, we summarize the current knowledge on the roles that PCSK9 plays in different tissues and perspectives for its clinical use.

Role of advanced glycation end products on vascular smooth muscle cells under diabetic atherosclerosis

Atherosclerosis (AS) is a chronic inflammatory disease and leading cause of cardiovascular diseases. The progression of AS is a multi-step process leading to high morbidity and mortality. Hyperglycemia, dyslipidemia, advanced glycation end products (AGEs), inflammation and insulin resistance which strictly involved in diabetes are closely related to the pathogenesis of AS. A growing number of studies have linked AGEs to AS. As one of the risk factors of cardiac metabolic diseases, dysfunction of VSMCs plays an important role in AS pathogenesis. AGEs are increased in diabetes, participate in the occurrence and progression of AS through multiple molecular mechanisms of vascular cell injury. As the main functional cells of vascular, vascular smooth muscle cells (VSMCs) play different roles in each stage of atherosclerotic lesions. The interaction between AGEs and receptor for AGEs (RAGE) accelerates AS by affecting the proliferation and migration of VSMCs. In addition, increasing researches have reported that AGEs promote osteogenic transformation and macrophage-like transformation of VSMCs, and affect the progression of AS through other aspects such as autophagy and cell cycle. In this review, we summarize the effect of AGEs on VSMCs in atherosclerotic plaque development and progression. We also discuss the AGEs that link AS and diabetes mellitus, including oxidative stress, inflammation, RAGE ligands, small noncoding RNAs.

The consequences of PCSK9 inhibition in selected tissues

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is one of nine members of the proprotein convertase family. These serine proteases play a pivotal role in the post-translational modification of proteins and the activation of hormones, enzymes, transcription factors and growth factors. As a result, they participate in many physiological processes like embryogenesis, activity of central nervous system and lipid metabolism. Scientific studies show that the family of convertases is also involved in the pathogenesis of viral and bacterial infections, osteoporosis, hyperglycaemia, cardiovascular diseases, neurodegenerative disorders and cancer. The inhibition of PCSK9 by two currently approved for use monoclonal antibodies (alirocumab, evolocumab) slows down the degradation of low-density lipoprotein cholesterol receptors (LDLRs). This leads to increased density of LDLRs on the surface of hepatocytes, resulting in decreased level of low-density lipoprotein cholesterol (LDL-C) in the bloodstream, which is connected with the reduction of cardiovascular risk. PCSK9 inhibitors (PCSK9i) were created for the patients who could not achieve appropriate level of LDL-C using current statin and ezetimibe therapy. It seems that high therapeutic efficacy of PCSK9i will make them more common in the clinical use. The pleiotropic effects of previously mentioned lipid-lowering therapies were the reasons for literature review of possible positive and negative effects of PCSK9 inhibition beyond cholesterol metabolism.

An Update on the Role of PCSK9 in Atherosclerosis

Atherosclerosis is initiated by functional changes in the endothelium accompanied by accumulation, oxidation, and glycation of LDL-cholesterol in the inner layer of the arterial wall and continues with the expression of adhesion molecules and release of chemoattractants. PCSK9 is a proprotein convertase that increases circulating LDL levels by directing hepatic LDL receptors into lysosomes for degradation. The effects of PCSK9 on hepatic LDL receptors and contribution to atherosclerosis via the induction of hyperlipidemia are well defined. Monoclonal PCSK9 antibodies that block the effects of PCSK9 on LDL receptors demonstrated beneficial results in cardiovascular outcome trials. In recent years, extrahepatic functions of PCSK9, particularly its direct effects on atherosclerotic plaques have received increasing attention. Experimental trials have revealed that PCSK9 plays a significant role in every step of atherosclerotic plaque formation. It contributes to foam cell formation by increasing the uptake of LDL by macrophages via scavenger receptors and inhibiting cholesterol efflux from macrophages. It induces the expression of inflammatory cytokines, adhesion molecules, and chemoattractants, thereby increasing monocyte recruitment, inflammatory cell adhesion, and inflammation at the atherosclerotic vascular wall. Moreover, low shear stress is associated with increased PCSK9 expression. PCSK9 may induce endothelial cell apoptosis and autophagy and stimulate the differentiation of smooth muscle cells from the contractile phenotype to synthetic phenotype. Increasing evidence indicates that PCSK9 is a molecular target in the development of novel approaches toward the prevention and treatment of atherosclerosis. This review focuses on the molecular roles of PCSK9 in atherosclerotic plaque formation.

Lipid efflux mechanisms, relation to disease and potential therapeutic aspects

Lipids are hydrophobic and amphiphilic molecules involved in diverse functions such as membrane structure, energy metabolism, immunity, and signaling. However, altered intra-cellular lipid levels or composition can lead to metabolic and inflammatory dysfunction, as well as lipotoxicity. Thus, intra-cellular lipid homeostasis is tightly regulated by multiple mechanisms. Since most peripheral cells do not catabolize cholesterol, efflux (extra-cellular transport) of cholesterol is vital for lipid homeostasis. Defective efflux contributes to atherosclerotic plaque development, impaired β-cell insulin secretion, and neuropathology. Of these, defective lipid efflux in macrophages in the arterial walls leading to foam cell and atherosclerotic plaque formation has been the most well studied, likely because a leading global cause of death is cardiovascular disease. Circulating high density lipoprotein particles play critical roles as acceptors of effluxed cellular lipids, suggesting their importance in disease etiology. We review here mechanisms and pathways that modulate lipid efflux, the role of lipid efflux in disease etiology, and therapeutic options aimed at modulating this critical process.

Vascular smooth muscle cells in atherosclerosis

Vascular smooth muscle cells (VSMCs) are a major cell type present at all stages of an atherosclerotic plaque. According to the 'response to injury' and 'vulnerable plaque' hypotheses, contractile VSMCs recruited from the media undergo phenotypic conversion to proliferative synthetic cells that generate extracellular matrix to form the fibrous cap and hence stabilize plaques. However, lineage-tracing studies have highlighted flaws in the interpretation of former studies, revealing that these studies had underestimated both the content and functions of VSMCs in plaques and have thus challenged our view on the role of VSMCs in atherosclerosis. VSMCs are more plastic than previously recognized and can adopt alternative phenotypes, including phenotypes resembling foam cells, macrophages, mesenchymal stem cells and osteochondrogenic cells, which could contribute both positively and negatively to disease progression. In this Review, we present the evidence for VSMC plasticity and summarize the roles of VSMCs and VSMC-derived cells in atherosclerotic plaque development and progression. Correct attribution and spatiotemporal resolution of clinically beneficial and detrimental processes will underpin the success of any therapeutic intervention aimed at VSMCs and their derivatives.

Smooth muscle cell fate and plasticity in atherosclerosis

Current knowledge suggests that intimal smooth muscle cells (SMCs) in native atherosclerotic plaque derive mainly from the medial arterial layer. During this process, SMCs undergo complex structural and functional changes giving rise to a broad spectrum of phenotypes. Classically, intimal SMCs are described as dedifferentiated/synthetic SMCs, a phenotype characterized by reduced expression of contractile proteins. Intimal SMCs are considered to have a beneficial role by contributing to the fibrous cap and thereby stabilizing atherosclerotic plaque. However, intimal SMCs can lose their properties to such an extent that they become hard to identify, contribute significantly to the foam cell population, and acquire inflammatory-like cell features. This review highlights mechanisms of SMC plasticity in different stages of native atherosclerotic plaque formation, their potential for monoclonal or oligoclonal expansion, as well as recent findings demonstrating the underestimated deleterious role of SMCs in this disease.

Identification of a Klf4-dependent upstream repressor region mediating transcriptional regulation of the myocardin gene in human smooth muscle cells

Phenotypic switching of smooth muscle cells (SMCs) plays a central role in the development of vascular diseases such as atherosclerosis and restenosis. However, the factors regulating expression of the human myocardin (Myocd) gene, the master gene regulator of SMC differentiation, have yet to be identified. In this study, we sought to identify the critical factors regulating Myocd expression in human SMCs. Using deletion/genetic reporter analyses, an upstream repressor region (URR) was localised within the Myocd promoter, herein termed PrmM. Bioinformatic analysis revealed three evolutionary conserved Klf4 sites within the URR and disruption of those elements led to substantial increases in PrmM-directed gene expression. Furthermore, ectopic expression established that Klf4 significantly decreased Myocd mRNA levels and PrmM-directed gene expression while electrophoretic mobility shift assays and chromatin immunoprecipitation (ChIP) assays confirmed specific binding of endogenous Klf4, and not Klf5 or Klf2, to the URR of PrmM. Platelet-derived growth factor BB (PDGF-BB), a potent inhibitor of SMC differentiation, reduced Myocd mRNA levels and PrmM-directed gene expression in SMCs. A PDGF-BB-responsive region (PRR) was also identified within PrmM, overlapping with the previously identified URR, where either siRNA knockdown of Klf4 or the combined disruption of the Klf4 elements completely abolished PDGF-BB-mediated repression of PrmM-directed gene expression in SMCs. Moreover, ChIP analysis established that PDGF-BB-induced repression of Myocd gene expression is most likely regulated by enhanced binding of Klf4 and Klf5 to a lesser extent, to the PRR of PrmM. Taken together, these data provide critical insights into the transcriptional regulation of the Myocd gene in vascular SMCs, including during SMC differentiation.

Endothelin-1 signalling in vascular smooth muscle: pathways controlling cellular functions associated with atherosclerosis

Atherosclerosis is the primary ischaemic vascular condition underlying a majority of cardiovascular disease related deaths. Endothelin-1 is a vasoactive peptide agent upregulated in atherosclerosis and in conjunction with its G protein-coupled receptors exerts diverse actions on all cells of the vasculature in particular vascular smooth muscle cells (VSMC). The effects of endothelin-1 include cell proliferation, migration and contraction, and the induction of extracellular matrix components and growth factors. VSMC as the major component of the neointima in atherosclerotic plaques accordingly play a key role in atherogenesis. In this review we examine classic and novel signalling pathways activated by endothelin-1 in VSMC (including phospholipase C, adenylate cyclase, Rho kinase, transactivation of receptor tyrosine kinases, mitogen activated protein kinase cascades and beta-arrestin) and their likely impact on the development and progression of atherosclerosis.

Mechanopathobiology of Atherogenesis: A Review

Cardiovascular disease is the number one cause of mortality in the United States. Atherosclerosis, the primary etiology of cardiovascular disease is hypothesized to be a time-dependent response to arterial injury. Although risk factors for atherosclerosis are systemic in nature, certain arteries (e.g., coronary arteries) are more susceptible to plaque formation than others. The heterogeneous distribution of atherosclerosis in the vasculature is thought to be related to biomechanical factors. A review of the relevant pathological features of atherogenesis and how physiologically-consistent mechanical stimuli can impact those processes supports this notion. However, specific investigations geared toward finding the mechanistic link between mechanical stimuli and early atherogenic processes are required to differentiate those stimuli that facilitate and those that inhibit atherogenesis. Such knowledge is required for intelligent direction in the search for potential targets for clinical intervention.

Changes in gene expression in atherosclerotic plaques analyzed using DNA array

A better understanding of atherogenesis at the level of gene expression could lead to the identification of new therapeutic strategies for vascular diseases. With DNA array technology, it is possible to identify multiple, simultaneous changes in gene expression in small tissue samples from atherosclerotic arteries. We analyzed gene expression in normal arteries and in immunohistologically characterized human advanced atherosclerotic lesions using an array of 18376 cDNA fragments. The array method was first validated by detecting a group of genes (n=17) that were already known to be connected to atherogenesis. These genes included e.g. Apolipoprotein E, CD68, TIMP and phospholipase D. Next we detected 75 differentially expressed genes that were previously not connected to atherogenesis. A subgroup of genes involved in cell signaling and proliferation was selected for further analyzes with in situ hybridization and RT-PCR which confirmed array results by showing induction in advanced lesions of Janus kinase 1 (JAK-1) which is an important signaling molecule in activated macrophages; VEGF receptor-2 which mediates angiogenic and vasculoprotective effects of VEGF; and an unknown gene, which mapped on chromosome 19. It is concluded that DNA array technology enables fast screening of gene expression in small samples of atherosclerotic lesions. The technique will be useful for the identification of new factors, such as JAK-1 and VEGF receptor-2, which may play an important role in atherogenesis.

Differences in caveolae dynamics in vascular smooth muscle cells of different phenotypes

Vascular smooth muscle cells shift between two major differentiated states with distinct morphological and functional properties, a contractile and a synthetic phenotype. Here, primary cultures were used to study caveolae expression and dynamics in these cells. The results demonstrate that caveolae are more numerous and more actively interact with intracellular organelles in contractile than in synthetic cells. Immunohistochemistry showed that caveolin-1 was mainly localized to caveolae in contractile cells and partly shifted to Golgi-associated vesicles in synthetic cells, whereas caveolin-2 chiefly appeared in cytoplasmic vesicles in both cases. Cholera toxin B subunit, a ligand of GM1 ganglioside, was internalized via caveolae and carried to endosomes and Golgi-associated vesicles. In contractile cells, it later moved into Golgi and endoplasmic reticulum (ER) cisternae and thus had access to the entire endocytic and exocytic pathways. In contrast, in synthetic cells, the tracer was restricted to the endocytic pathway. Filipin staining similarly disclosed that cholesterol was more widely distributed in contractile than in synthetic cells, with strong labeling of both caveolae and adjacent ER portions. Although no direct continuity between caveolae and ER was detected, it is suggested that cholesterol and other molecules may be translocated between these compartments. The observed differences in caveolae expression and dynamics are likely to be significant for the differences in proliferative capacity and cholesterol transport between contractile and synthetic smooth muscle cells.

Differentiated properties and proliferation of arterial smooth muscle cells in culture

The smooth muscle cell is the sole cell type normally found in the media of mammalian arteries. In the adult, it is a terminally differentiated cell that expresses cytoskeletal marker proteins like smooth muscle alpha-actin and smooth muscle myosin heavy chains, and contracts in response to chemical and mechanical stimuli. However, it is able to revert to a proliferative and secretory active state equivalent to that seen during vasculogenesis in the fetus, and this is a prerequisite for the involvement of the smooth muscle cell in the formation of atherosclerotic and restenotic lesions. A similar transition from a contractile to a synthetic phenotype occurs when smooth muscle cells are established in culture. Accordingly, an in vitro system has been used extensively to study the regulation of differentiated properties and proliferation of these cells. During the first few days after seeding, the cells are reorganized structurally with a loss of myofilaments and formation of a widespread endoplasmic reticulum and a prominent Golgi complex. In parallel, they lose their contractility and instead become competent to divide in response to a large variety of mitogens, including platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF). After entering the cell cycle, they start to produce these and other mitogens on their own, and continue to replicate in the absence of exogenous stimuli for a restricted number of generations. Furthermore, they start to secrete extracellular matrix components such as collagen, elastin, and proteoglycans. The mechanisms that control this change in morphology and function of the smooth muscle cells are still poorly understood. Adhesive proteins such as fibronectin and laminin apparently have an important role in determining the basic phenotypic state of the cells and exert their effects via integrin receptors. The proliferative and secretory activities of the cells are influenced by a multitude of growth factors, cytokines, and other molecules. Although much work remains before an integrated view of this regulatory machinery can be achieved, there is no doubt that the cell culture technique has contributed substantially to our knowledge of smooth muscle differentiation and growth. At the same time, it has been crucial in exploring the role of these cells in vascular disease and developing new therapeutic strategies to cope with major causes of human death and disability.

Mast cell granule remnants carry LDL into smooth muscle cells of the synthetic phenotype and induce their conversion into foam cells

We report the effect of mast cells on the uptake of LDL by smooth muscle cells (SMCs) and their conversion into foam cells in vitro. The mast cells were stimulated to exocytose their cytoplasmic secretory granules, and the granule remnants formed were recovered from the extracellular fluid and added to cultures of SMCs of either the synthetic or contractile phenotype in LDL-containing medium. In the presence but not in the absence of granule remnants, SMCs of the synthetic phenotype took up LDL with ensuing stimulation of intracellular cholesteryl ester synthesis and cytoplasmic accumulation of neutral lipid droplets. Using methylated LDL (mLDL), a modified species of LDL that binds to granule remnants but not to LDL receptors, we demonstrated that this uptake (leading to foam cell formation) occurred only when LDL was bound to granule remnants. After the addition of colloidal gold-LDL and granule remnants to the incubation system, electron microscopy revealed that within phagosomes of the SMCs there were granule remnants (diameter, 0.5 to 1 micron) coated with LDL, confirming that LDL had been carried into the cells with the remnants. SMCs of the contractile phenotype were less efficient than their synthetic counterparts at phagocytosing LDL-coated granule remnants and were not converted into foam cells. This difference in the rate of phagocytosis of granule remnants was present even in the absence of LDL, revealing that the more active phagocytosis by SMCs of the synthetic phenotype was not specifically related to uptake of lipids but rather reflected a general phenotype characteristic of these cells. These observations indicate a phagocytic mechanism by which SMCs of the synthetic phenotype are converted into cholesteryl ester-filled foam cells, and they also suggest that degranulation of mast cells plays a role in the development of fatty streak lesions.

Decrease in high density lipoprotein binding sites is associated with decrease in intracellular cholesterol efflux in dedifferentiated aortic smooth muscle cells

One of the key features of atherosclerosis formation and progression is 'dedifferentiation' of contractile arterial smooth muscle cells (SMC) in synthetic cells. In primary cultures and subcultures before 10 and after 200 passages, SMC exhibit contractile-like, synthetic and transformed phenotypes, respectively, providing a good model for studying dedifferentiation process in vitro: the rationale for comparing these phenotypes of SMC in vivo rests in similar changes in cytoenzymatic and cytoskeletal features. In vivo, dedifferentiated SMC are transformed into foam cells by accumulating lipids. Thus, the aim of this study was to determine whether cholesterol metabolism undergoes changes in dedifferentiated cells and the three cultured phenotypes were compared in regard to their cholesterol efflux mechanisms. Phenotypic changes were shown to be associated with decrease in intracellular cholesterol apoprotein mediated efflux and translocation but also with decrease in high affinity binding sites for native HDL. Thus, the dedifferentiation process triggers a need for increased supply of cholesterol for membrane synthesis and efflux down-regulation mechanisms are aimed at maximizing cholesterol availability to the cell. Plasma membrane cholesterol efflux, which seems to be apoprotein-independent, decrease slightly with cell dedifferentiation suggesting either modifications in the dedifferentiated cell membranes physical properties. Taken together, these different results showed that dedifferentiation of arterial SMC is associated with decrease in the different steps of the efflux process, which could constitute one of the early events in their foam cell transformation.

Perindopril inhibits both the development of atherosclerosis in the cholesterol-fed rabbit and lipoprotein binding to smooth muscle cells in culture

The aim of the study was to examine the effect of low doses of perindopril, approximating those used therapeutically and sub-therapeutically in human hypertensives, on the development of atherosclerosis in the cholesterol-fed rabbit. The right carotid artery of 12 week old rabbits was balloon de-endothelialized to induce the formation of a myointimal thickening. After 14 weeks rabbits were placed into 6 groups, 6 rabbits per group. Groups I, II and III were fed a 1% cholesterol diet for the following 6 week experimental period, while Groups IV, V and VI received a normolipemic diet. In addition, Groups II and V rabbits received in their drinking water 0.3 mg/kg per day perindopril, and Groups III and VI 0.01 mg/kg per day. At the end of 6 weeks' treatment, the mean arterial pressure (MAP) in Groups II and V decreased by about 12%, while that in Groups III and VI decreased by 13%. Plasma cholesterol levels of rabbits on a normolipemic diet (Groups IV, V, VI) averaged 1.3 mmol/l while those on a cholesterol-enriched diet (Groups I, II, III) averaged 10.5 mmol/l. Plasma perindoprilat concentrations and percentage of plasma angiotensin converting enzyme (ACE) inhibition in Groups II and V averaged 14 ng/ml and 92.1% respectively, while in Groups III and VI they were 5.7 ng/ml and 80.5%, respectively. The percentage luminal surface area of the thoracic aorta covered by lipid-filled plaques (as observed by en face staining with Oil-Red-O) averaged 26.3% in Group I, 4.7% in Group II and 20.0% in Group III. No lesions developed in Groups IV, V and VI. Microscopic examination of the right (manipulated) carotid arteries of Group I rabbits revealed lesions of large, lipid-filled cells radially oriented, overlying the pre-formed myointimal thickening. Both doses of perindopril in the cholesterol-fed rabbits (Groups II and III) decreased the amount of lipid-filled cells which were oriented circumferentially. More extracellular matrix was present in the lesions of Groups II and III than of Group I. No lesions were observed in the right carotid arteries of Groups IV, V and VI (normal diet) or in the unmanipulated left carotid arteries of all 6 groups. The sizes of the neointima plus lesion in Groups I, II and III were, however, not significantly different, being 42.4%, 48.5% and 46.9% of the cross-sectional area of the artery wall.(ABSTRACT TRUNCATED AT 400 WORDS)

Enzyme cytochemical expression of aortic smooth muscle cell modulation in primary and secondary cultures

"Contractile" arterial smooth muscle cells (SMC) return to a less differentiated "synthetic" state during adaptative and proliferative processes in vitro and in cell cultures. At present, the enzyme expression of the modulation of cultured SMC is partially unknown. In order to define metabolic events associated with cell modulation in vitro, we studied 16 enzyme activities in primary and secondary (P1-P3-P10) SMC cultures in comparison to in situ SMC in fetal and adult rat aorta. The "contractile" SMC in aorta of 2 months old rat showed very high nucleotide hydrolase activities (5'-nucleotidase, Mg-ATPase, Ca-ATPase), and naphthylesterase activities and weak lysosomal acid phosphatase activity; the glycolysis-linked dehydrogenases were expressed with higher activities than Krebs cycle-linked enzymes. In primary cultures, the SMC near the explant expressed a "contractile-like" enzyme behaviour, in opposite to cells in the peripheral part of growing area enzymatically similar to sub-cultured SMC. Proliferating SMC in secondary cultures were characterized by increased lysosomal activities and by the decrease or disappearance of Ca-ATPase, Mg-ATPase, 5'-nucleotidase, and butyrylcholinesterase activities like fetal SMC in vivo. These enzyme changes in subcultures might be related to a deficiency of nucleotide ester hydrolysis, abnormal adenosine and AMP levels, lowered lipolytic capability and increased lysosomal reactivity. In conclusion, subcultured "synthetic" SMC expressed enzyme cytochemical patterns different from those of "contractile" SMC and similar to those of fetal immature SMC. Their enzyme behaviour is unfavourable to contractile function and favourable to cell proliferation and lipid accumulation, two characteristic features of SMC in atherosclerotic plaques.

Localization and smooth muscle cell composition of atherosclerotic lesions in Watanabe heritable hyperlipidemic rabbits

Morphological techniques (histology and electron microscopy), as well as immunofluorescence assays, were applied to the study of the localization and smooth muscle cell (SMC) composition of atherosclerotic lesions in Watanabe heritable hyperlipidemic (WHHL) rabbits during a 4.5-month period. Vascular segments from different arteries (carotid, coronary, and iliac arteries) or from the same vessel at different levels (aorta) of animals at days 7, 15, 30, 40, 60, 90, and 135 showed that the atherosclerotic lesion first became visible at the level of the aortic arch in 60-day-old WHHL animals. Histological examination of serial cryosections from this vascular region indicated that the vascular lesion arose from a cavity in the media layer, located anatomically at the level of the juncture of the ligamentum arteriosum with the aortic arch. This aortic arch cavity is formed during the postnatal closure of the ductus arteriosus and is characterized by the presence of a thickened intima, which was absent in the other vascular regions examined. Immunofluorescence comparison of normal and atherosclerotic tissues from the aortic arch cavity wall with the use of monoclonal antibodies specific for smooth muscle and nonmuscle myosin isoforms revealed the existence of distinct SMC populations. SMCs in the thickened intima showed a myosin isoform pattern peculiar to cells with a degree of maturation intermediate between the fully differentiated and the developing (fetal) aortic SMCs. By contrast, SMCs present in atherosclerotic lesions displayed a predominant fetal-type pattern of myosin isoform expression. The achievement of this myosin isoform content seems to be correlated with the accumulation of lipids in the intima. In the media subjacent to the intimal thickening or atherosclerotic lesion, SMCs primarily displayed an intermediate degree of maturation. In older WHHL animals and at this aortic level, the SMC composition of the atherosclerotic lesion did not change, whereas in the subjacent media, the cells of intermediate type almost disappeared. In the vascular regions in which the atherosclerotic lesion appeared at later stages, such as near the aortic bifurcation, the distribution of fetal and intermediate cell types in the atherosclerotic wall was similar to that taken at the aortic arch level. These results indicate that there is 1) a preferential anatomic site from which atherogenesis initiates in WHHL rabbits; 2) a time correlation between the accumulation of lipids in the wall and the phenotypic change of SMCs toward a poorly differentiated cell type; and 3) the tendency for SMCs to follow the same differentiation pattern in early atherosclerotic lesions, irrespective of the site and time at which they develop.

Long-term treatment of neonatal aortic smooth muscle cells with beta VLDL induces cholesterol accumulation

A model for smooth muscle derived foam cells was developed by treating smooth muscle cells isolated from the aortae of neonatal rabbits with beta VLDL for up to 1 month. Hyperlipidemic beta VLDL isolated from cholesterol fed rabbits induced proliferation of the cells that were maintained in lipid deficient serum. In addition, the lipoprotein fraction stimulated [14C]oleic acid incorporation into [14C]cholesteryl ester, even in cultures that had been chronically exposed to the lipoprotein. The accumulation of cholesterol was evaluated and small amounts of cholesteryl ester were demonstrated in cultures treated for 3 days with beta VLDL. However, continued exposure to the lipoprotein resulted in larger elevations in total cholesterol, approximately 65% of which was in the esterified form in cultures treated with 100 micrograms beta VLDL/ml for 24 days. When cholesterol levels were examined as a function of time, it was determined that both total cholesterol and cholesteryl ester levels increased. Approximately 2-3 weeks after lipoprotein was introduced to the culture, maximum levels were attained. Triglyceride levels were also measured and found to increase more than two-fold in cultures that had been incubated in the presence of beta VLDL for 24 days, when compared to cultures incubated in its absence. Examination of the cultures by electron microscopy revealed intracytoplasmic lipid droplets in beta VLDL treated cells. These results suggest that beta VLDL treatment of neonatal aortic smooth muscle cells provides an ideal model in which to study the lipid laden smooth muscle cells that characterize the atherosclerotic plaque.

Heparan sulfate-degrading enzymes induce modulation of smooth muscle phenotype

Macrophages cocultured with rabbit aortic smooth muscle cells at a ratio of 1:3 degraded all the 35S-labeled heparan sulfate proteoglycan from the smooth muscle surface into free sulfate (Kav of 0.84 on Sepharose 6B). Concomitantly, the same macrophages induced a decrease in the volume fraction of myofilaments (Vvmyo) of the smooth muscle cells and a decrease in alpha-actin mRNA as a percentage of total actin mRNA. Both macrophage lysosomal lysate at neutral pH and heparinase degraded cell-free 35S-labeled matrix deposited by smooth muscle cells into fragments which eluted at a Kav of 0.63 and which were identified as heparan sulfate chains by their complete degradation in the presence of low pH nitrous acid. At acid pH the macrophage lysosomal lysate completely degraded the heparan sulfate to free sulfate (Kav 0.84). Both macrophage lysosomal lysate and commercial heparinase at neutral pH induced smooth muscle phenotypic change while other enzymes such as trypsin and chondroitin ABC lyase had no effect. It was therefore suggested that the active factor present in the macrophages is a lysosomal heparan sulfate-degrading endoglycosidase (heparinase). Only a small amount of heparan sulfate-degrading activity was released into the incubation medium by living macrophages, and there was no heparinase activity on their isolated plasma membranes, although proteolytic enzymes were evident in both instances. In pulse-chase studies, high Vvmyo smooth muscle cells were seen to constantly internalize and degrade 35S-labeled heparan sulfate proteoglycan from their own pericellular compartment, suggesting that this may be the mechanism by which smooth muscle phenotype is maintained under normal circumstances and that removal of heparan sulfate from the surface of smooth muscle cells and its degradation by macrophages temporarily interrupts this process, inducing smooth muscle phenotypic change.

Effect of conditioning of beta-migrating very low-density lipoprotein with macrophages on the accumulation of cholesteryl esters in smooth muscle cells

The mechanism of cholesteryl ester accumulation in smooth muscle cells was investigated. Incubation of smooth muscle cells with beta-migrating very low-density lipoprotein (beta-VLDL, d less than 1.006) for 24 h did not result in accumulation of oil red O-stained particles in the cells. However, incubation of smooth muscle cells with beta-VLDL in the presence of rat peritoneal macrophages induced accumulation of oil red O-stained granules in smooth muscle cells. Medium containing [3H]-cholesteryl linoleate-labelled beta-VLDL ([3H]beta-VLDL) that was conditioned with rat peritoneal macrophages increased the incorporation of [3H]-cholesterol and the cholesteryl ester content in smooth muscle cells, whereas unconditioned [3H]beta-VLDL did not. On zonal ultracentrifugation of conditioned medium containing [3H]beta-VLDL with macrophages, radioactivity was found at two peaks of density 1.150 and less than 1.006. This new fraction with d = 1.150 (peak II) migrated at beta-positions, the same as that of low-density lipoprotein (LDL) on agarose gel electrophoresis, and contained cholesteryl esters (28%), free cholesterol (15%) and phospholipid (43%). When smooth muscle cells were incubated with the peak II fraction, the radioactivity incorporated into smooth muscle cells and the cholesterol ester content of the cells increased. These results show that aortic smooth muscle cells in cooperation with macrophages can accumulate cholesteryl ester from beta-VLDL.

Effects of hypercholesterolemia on monokine-induced smooth muscle cell proliferation

Macrophage/smooth muscle cell interactions play a role in atherogenesis and foreign body reactions to biomaterials. This study investigates the effect of a hypercholesterolemic diet on the ability of smooth muscle cells (SMCs) to respond to monokines which are produced in response to hypercholesterolemia, biomaterials or both. Peritoneal macrophages were harvested from rabbits fed either a normal (M phi NL) or a 2% cholesterol/6% peanut oil diet (M phi ATH) (plasma cholesterol 2840 vs 42.3 [p less than 0.005]). The macrophages were then cultured in the presence of either 1) polyglactin 910 (PG910), 2) Dacron, or 3) no biomaterial (control), and the media collected and pooled by week for the smooth muscle cell mitogenesis assays. Rabbit aortic smooth muscle cells were harvested and cultured from the same two groups of rabbits (SMCNL or SMCATH), quiesced in serum free media (48 h) followed by addition of the test media and 3H-TdR. The addition of either biomaterial to M phi NL-conditioned media increased 3H-TdR incorporation in both smooth muscle lines as compared to controls. PG910 resulted in significantly higher 3H-TdR incorporation than Dacron (weeks 3-5, p less than 0.005). The addition of either biomaterial to M phi ATH also increased 3H-TdR incorporation in both smooth muscle cell lines, however, the magnitude of the response was decreased as compared to the M phi NL-conditioned media in both cell lines (p less than 0.001 for either SMC line). In contrast to the M phi NL-conditioned media, the addition of Dacron to M phi ATH resulted in the highest level of 3H-TdR incorporation in both cell lines as compared to the media without biomaterial. The SMCNL had a higher response to both the monokines in conditioned media (2-fold) and to fetal bovine serum (3-fold) than the SMCATH (p less than 0.001). Although there is a generalized decrease in release of mitogens active on SMCs from M phi ATH, the M phi ATH exposed to Dacron release increased amounts of mitogenic factors, most active on the SMCATH cell line. A common mode of failure of small diameter Dacron grafts in man is pseudointimal hyperplasia, and it is inviting to postulate that the Dacron/macrophage/smooth muscle cell interactions in this atherosclerotic group of patients plays a role in the pathogenesis of this lesion.

Excess membrane cholesterol alters calcium movements, cytosolic calcium levels, and membrane fluidity in arterial smooth muscle cells

The relations between membrane cholesterol content, basal (unstimulated) transmembrane 45Ca2+ movements, cytosolic calcium levels, and membrane fluidity were investigated in cultured rabbit aortic smooth muscle cells (SMCs) and isolated SMC plasma membrane microsomes. SMCs were enriched with unesterified (free) cholesterol (FC) for 18-24 hours with medium containing human low density lipoprotein and FC-rich phospholipid (PL) liposomes. This procedure increased cholesterol mass without affecting PL mass, resulting in an increase in the FC/PL molar ratio compared with controls in cells (67% FC increase, p less than 0.001; 43% FC/PL ratio increase, p less than 0.01) and in SMC microsomes (52% FC increase, p less than 0.05; 43% FC/PL ratio increase, p less than 0.05). Cholesterol enrichment also increased unstimulated 45Ca2+ influx (p less than 0.001) and efflux (p less than 0.05). Cellular cholesterol content correlated in a linear fashion with these changes (influx: r = 0.722, p less than 0.01; efflux: r = 0.951, p less than 0.05). In addition, cytosolic calcium levels increased approximately 34% (p less than 0.01) with cholesterol enrichment. The cholesterol-induced increase in 45Ca2+ influx was reversible with time and demonstrated sensitivity to the channel blockers. Fluorescence anisotropy measured from 5 degrees C to 40 degrees C using the fluorophore diphenylhexatriene showed decreased membrane fluidity in microsomal membranes obtained from cholesterol-enriched SMCs compared with controls (p less than 0.02). These results suggest that the SMC plasma membrane is very sensitive to cholesterol enrichment with liposomes or human low density lipoprotein and that increases in membrane cholesterol content increase cytosolic calcium levels in SMCs, are associated with a decrease in membrane fluidity, and unmask a new, or otherwise silent, dihydropyridine-sensitive calcium channel that may be involved in altered arterial wall properties with serum hypercholesterolemia.

Importance of the phenotypic state of vascular smooth muscle cells on the binding and the mitogenic activity of endothelin

Smooth muscle cells of the rabbit aorta, when grown in vitro, express distinguishable forms of phenotypes (contractile and synthetic). On contractile cells, ET-1 specifically bound to a single class of high affinity (KD = 128 pM) and high capacity (Bmax = 66,000 sites/cell) binding sites. But, whereas affinity of [125I]-ET-1 was not significantly affected by phenotypic modulation, synthetic cells displayed a 10-fold lower [125I]-ET-1 binding capacity than contractile smooth muscle cells. Similarly, the mitogenic effect of ET-1 on smooth muscle cells was considerably lower for synthetic than for contractile cells. The ET-1 receptor on primary cells was recognized by sarafotoxin S6b and the different ET-related peptides with an order of potency [ET-1 greater than S6b greater than ET-3 greater than Big ET-1 much greater than ET(16-21)] identical to that inducing smooth muscle cell growth. Therefore, these data indicate that the binding and the mitogenic effects of ET-1 on smooth muscle cells might be of different magnitudes depending on the phenotypic state of these cells.

Myointimal hyperplasia: pathogenesis and implications. 1. In vitro characteristics

Myointimal hyperplasia (MIH) is an arterial wall smooth muscle cell (SMC) proliferative disorder. This process is responsible for a significant number of early and long-term arterial reconstructive and graft failures. Histopathologically, this process is characterized by a proliferation of SMC in the intima of traumatized arteries resulting in arterial and/or anastomatic stenosis with secondary thrombosis. In vitro studies of cultured SMC have allowed the evaluation of SMC response to factors suspected of being clinically associated with MIH. Principal among these is platelet derived growth factor (PDGF), which is known to be secreted by several cell types including endothelial cells (ECs) and monocytes as well as being stored and secreted by platelets. PDGF, somatomedin-C, epithelial growth factor, insulin, and other factors have been found to significantly increase SMC replication in vitro. Lipoproteins may be important substrates for SMC proliferation in contrast to heparin, which may directly inhibit SMC protein synthesis. Unlike SMCs, whose continued growth in culture is dependent on various growth factors and nutrients, ECs essentially cease to proliferate after the cells have formed a monolayer over the available surface. Extracellular matrix proteins, polypeptide mitogens, and heparin have been shown to modify EC migration and proliferation in vitro. Wounding of EC monolayers by scratching results in increased replication and migration, processes which require plasma factors that remain poorly defined. However, two general forms of EC growth factor have been isolated from many body tissues, are potent stimulators of capillary endothelial growth, and appear important both for normal EC monolayer homeostasis and for the response to injury. Cultured ECs produce mitogens for SMC. Production of the principal mitogen, PDGF, is significantly increased in sparse versus confluent cell cultures as well as by toxic agents such as endotoxin and phorbol esters. Acetyl low density lipoprotein as well as omega-3 fatty acids may significantly and selectively inhibit EC PDGF production, a finding with potentially profound implications for the clinical control of MIH in vivo.

Phenotypic expression of surface antigens of rabbit aortic smooth muscle cells in culture. Monoclonal antibody, 2P1A2, characteristic of smooth muscle cells present in atherosclerotic plaque, is not correlated with cell proliferation

The expression of smooth muscle cell (SMC) antigens was studied in culture by immunofluorescence and immunoelectron microscopy. As specific SMC markers, we used 2 monoclonal antibodies (MAb), 1PC1 and 2P1A2 which are able to detect atherosclerotic plaques in the rabbit. MAb 1PC1 recognizes an antigen expressed on the cell surface, starting on the 7th day in primary culture after serum activation, and then secreted. On a confluent SMC monolayers this antigen appears outside the cell as an important filamentous network. The kinetics of secretion of this external protein recognized by 1PC1 corresponds to the kinetics of the secretory phenotype described by Chamley-Campbell and Campbell (Atherosclerosis, 40 (1981) 347). 2P1A2 MAb is specific for SMCs exclusively present in the rabbit atherosclerotic plaque. We studied the degree of reactivity of 2P1A2 with SMCs during primary cell culture. This "atherosclerotic" antigen of SMCs recognized by 2P1A2 is expressed in culture conditions by SMCs from rabbit normal media. This antigen appears after 3 days of serum activation, and heparin growth inhibition does not interfere with its expression. 2P1A2 recognized antigen is expressed during all cell cycle phases without amplification. 3 days after fetal calf serum (FCS) stimulation of cells which are in G0/G1, 89% are labelled by 2P1A2, 4 days later G0/G1 positive cells constitute 49%. We conclude that 2P1A2 immunolabelling on the SMC surface reflects an activated state which is not correlated with SMC proliferation.

Cell constitution and characteristics of human atherosclerotic plaques selectively removed by percutaneous atherectomy

The Simpson atherectomy device used for the recanalization of severely stenosed peripheral arteries is able to collect plaque material which can be further characterized. This study reports histological, immunohistochemical and transmission electron microscopic findings on advanced human primary atherosclerotic plaques of peripheral arteries percutaneously removed by a Simpson atherectomy catheter. Material from stenosing plaques consisted of dense connective tissue with abundant amounts of concentrically arranged elastic fibers and lamellae. This meshwork contained numerous cells, often arranged in clusters and oriented with their longer axis parallel to the direction of blood flow. The vast majority of these cells could be easily identified as vimentin-positive and desmin-negative smooth muscle cells containing lipid deposits in the perinuclear region and numerous glycogen particles. Monocytes/macrophages were observed only very infrequently. Plaque tissue contained a range of smooth muscle cell phenotypes. Most of the cells were of an intermediate phenotype, i.e. sparsely filled with myofilament bundles at the cell periphery and a high amount of organelles such as mitochondria, rough endoplasmic reticulum and Golgi cisterns. An intact lining of pieces of intimal tissue with endothelial cells was not observed. Two-dimensional gel electrophoresis of plaque tissue showed the presence of alpha-, beta- and gamma-actin isoforms with a clear predominance of the beta-isoform.

Effects of zinc and cholesterol/choleate on serum lipoproteins and the liver in rats

The effects of short-term treatment with orally-administered zinc sulphate and/or a mixture of cholesterol/choleate on serum lipoprotein and hepatic enzyme levels were studied. Administration of graded doses of zinc sulphate (20 or 40 mg/kg, as zinc ion) for 5 days, dose-dependently increased serum and hepatic zinc levels but depressed the serum high-density lipoprotein-cholesterol (HDL-C) concentration and liver cytochrome P-450 activity. However, it did not affect hepatic concentrations of malondialdehyde and free beta-glucuronidase. Cholesterol/choleate treatment for 5 days markedly damaged the liver, as reflected by elevations of hepatic concentrations of malondialdehyde (both in the mitochondrial and microsomal fractions) and of free beta-glucuronidase; total cholesterol and low-density lipoprotein-cholesterol in the blood were increased, whereas HDL-C was decreased significantly. Concomitant administration of zinc sulphate with cholesterol/choleate further lowered HDL-C levels, but reversed the high hepatic concentrations of both malondialdehyde and free beta-glucuronidase. The present study indicates that both zinc ions and cholesterol can decrease circulatory HDL-C levels and that zinc protects against cholesterol-induced hepatic damage by reducing lysosomal enzyme release and preventing lipid peroxidation in the liver.

Quantitative ultrastructural analysis of coronary atherosclerotic involvement in two macaque species

Ultrastructural analyses were employed to observe and to compare in detail lesions of the coronary artery of cynomolgus and rhesus monkeys. Animals were fed individually with the same atherogenic ration under identical conditions for 4, 8, and 12 months, and controls of each species were fed with a low fat, cholesterol-free ration. Transmission electron microscopic studies of coronary arteries from these animals led to the following conclusions: (1) Synthetic smooth muscle cells (SMC) without lipid and macrophages without lipid appeared more frequently in the cynomolgus lesions than in the rhesus lesions. Furthermore, phenotypic expression of synthetic SMCs in the cynomolgus was more active with greater diversity, while the rhesus showed less phenotypic modulation. Macrophages without lipid appeared frequently in the cynomolgus media. (2) Increased percentages of both synthetic SMCs with lipid and macrophages with lipid were demonstrated in the cynomolgus lesions as compared to those in the rhesus. This indicates that foam cells, including SMC- and macrophage-derived foam cells, are more prevalent in cynomolgus than in rhesus. They are considered to play an important role in atherogenesis. (3) Medial disruption, synthetic SMCs, and macrophages containing lipid appeared more often in cynomolgus media than in rhesus media. (4) There were greater percentages of both synthetic SMCs and macrophages in the intima of the myocardial side of coronary arteries in both species. (5) Approximately 42% of all foam cells in the cynomolgus lesions were derived from SMCs. There were fewer macrophages in rhesus lesions. (6) The difference in expression between the two macaque species reflects different responses of macrophages to medial smooth muscle cell (SMC) components. The configuration of the artery wall could be one of the important indicators of these different expressions.

Studies on aorta during development. I. Fetal rabbit aorta under ex vivo and in vitro conditions: rapid changes in smooth muscle cell phenotype, cell proliferation and cholesterol content with organ culture

The structural development of the already well defined fetal rabbit aortic wall from 22 to 31 days of gestation in vivo consists of increasing aortic wall thickness, elastic lamina continuities, extracellular matrix deposition, and maturing of the fine structure of the medial smooth muscle cells. In vivo at term (31 days), the mature aortic smooth muscle cells demonstrated the characteristic thin, thick and intermediate filaments, dense plaques, endoplasmic reticulum, golgi, plasmalemma vesicles and an incomplete basal lamina. The fetal aorta rapidly responded to organ culture with various changes. Fetal smooth muscle cells modified their phenotype to the synthetic state when cultured in both serum-supplemented and serum-free media. This smooth muscle cell modification occurred after 3 days of culture in fetal explants. The synthetic type smooth muscle cells (fetal) began to proliferate after 6 days of culture. This proliferation resulted in a peripheral outgrowth after 9 days of 10-20 layers in fetal cultures from serum-supplemented media and of 2-4 layers in serum-free media. The orderly arrangement of the internal elastic lamina and alternating medial layers of smooth muscle cells and elastic lamina seen in vivo was disrupted along with increased matrix after 9 days of fetal explant culture. Significant numbers of 'modified' synthetic phenotype smooth muscle cells were not observed in adult aortic explants until after 15 days in culture in serum supplemented media. The mature contractile phenotype smooth muscle cell predominated in adult explants cultured in serum-free media. Significant synthetic phenotype smooth muscle cell proliferation only occurred in adult explants after 15 days culture in serum-supplemented media. When compared to aorta in vivo evidence for increases in cholesterol esterification were observed in both fetal (9 days) and adult (15 days) explants cultured in both serum-supplemented and serum-free media. The fetal aorta in organ culture appeared to be more susceptible than the adult aorta to (a) phenotypic modulation of smooth muscle cells to the synthetic state, (b) smooth muscle cell proliferation, and (c) early cholesteryl ester accumulation.

A possible antiatherogenic role for phosphocitrate through modulation of low density lipoprotein uptake and degradation in aortic smooth muscle cells

The present study reports the influence of a phosphorylated polycarboxylic acid, phosphocitrate, on low density lipoprotein (LDL) metabolism in cultured rabbit aortic smooth muscle cells. Phosphocitrate profoundly influenced both LDL binding and degradation. At the maximal effective concentration (2 mM), phosphocitrate released approximately 90% of the receptor-bound [125I]LDL whilst the total amount of [125I]LDL degraded was reduced by 60%. Measurement of total cholesterol accumulation revealed that even in the presence of high concentrations of added LDL, phosphocitrate (2 mM) diminished cholesterol levels close to the basal levels seen in incubations in lipoprotein-deficient serum. Further, this inhibitory effect of phosphocitrate was demonstrable after 24 h at 37 degrees C. Phosphocitrate, a recognized anticalcifying agent, possesses a strong negative charge to size ratio at physiological pH. It is postulated that the observed effects probably arise from charge interference and/or its ability to modulate cellular calcium concentration.

Atherosclerotic lesions in the coronary arteries of hyperlipidemic swine. Part 1. Cell increases, divisions, losses and cells of origin in first 90 days on diet

The intima of the proximal portion of the coronary arteries of young swine is normally thickened by accumulations of cells about 90% of which are smooth muscle cells (SMC) and about 10% are of probable monocyte origin. Extracellular components such as collagen and elastic tissue are also present but we have chosen to emphasize their cellular nature by calling the regions of thickened intima, intimal cell masses (ICM). We have previously shown that atherosclerotic lesions produced in the coronary arteries of swine by 90 days of feeding a hyperlipidemic (HL) diet arise almost exclusively in the normally occurring ICM. We are reporting here a study of the pathogenesis of these lesions following killing at 0, 14, 49 and 90 HL diet days with comparisons between ICM in control mash-fed swine and ICM-lesions in the HL swine. We found that in the ICM: lipid accumulation was present by 14 days and increased thereafter; the lipid was mostly in SMC but percentage wise the monocyte-macrophages were involved as much or more, cell division activity was increased 3-4-fold by 49 days, cell numbers in ICM were similar in HL and control swine at 49 days but were about 6-fold greater in the HL swine at 90 days, (now in ICM-lesions), at 90 days, circa 90% of the cells appeared to be of SMC and circa 10% of monocyte origin both in the ICM-lesions of the HL swine and in the normal ICM of the controls. The data suggest but do not prove that early lipid accumulation precedes increased cell divisions especially among the SMC component and this in turn precedes increased numbers of cells in the ICM. Although SMC constitute the major cell component of the ICM-lesion at 90 days, the monocyte-macrophage-like cells also increase in number as a result of the HL diet and constitute a small but definite minor component. One possible explanation for the increased cell division activity is that one of the lipid constituents is acting as mitogen; another possibility is that the effect of a well known mitogen such as platelet-derived growth factor is enhanced by the lipid; another is that the monocytes are being stimulated to produce monocyte-derived growth factor. In any event in the very early stage of atherogenesis in the coronary arteries in these experiments excessive proliferation of resident SMC in the ICM appears to be the predominant feature.

Replication of smooth muscle cells in vascular disease

Smooth muscle proliferation has been recognized as central to the pathology of both major forms of vascular disease: atherosclerosis and hypertension. Recent advances in our knowledge of mechanisms of control of proliferation suggest that events occurring in adult animals may recapitulate portions of the developmental biology of the smooth muscle cell. This review attempts to consider the current state of knowledge of the mechanisms controlling smooth muscle proliferation in these two diseases, to put that knowledge into the context of what is known about smooth muscle biology, and to offer two hypotheses on the possible roles of smooth muscle developmental biology in manifestations of atherosclerosis and hypertension in adult humans.

Cell population kinetics in atherogenesis. Cell births and losses in intimal cell mass-derived lesions in the abdominal aorta of swine

Atherosclerotic lesions may arise in a number of different ways. The two most notable, perhaps, are by monocyte infiltration of the intima and by hyperplasia of normally occurring intimal cell masses. This report is limited to the ICM-derived lesion type induced by a hyperlipidemic diet in the abdominal aorta of swine. The HL diet results, by 49 days, in accumulation of lipid in about 50% of the ICM cells and increases in cell division activity, as indicated by tritiated thymidine LI fourfold greater than in ICM of control swine. Cell numbers are not significantly increased over controls at 49 days, but by 90 HL diet days, they have increased to eightfold over control values. Throughout the 90 days, about 95% of the cells in the ICM or ICM-lesions are smooth muscle cells. Monocytes appear to constitute no more than 5% of the cells. Calculated lesion cell deaths are small during the 90 days, and foci of necrosis are rarely found. By scanning electron microscopy, the endothelial cell integrity appears to be maintained even over the ICM-lesions at 90 days. Calculations from tritiated thymidine LI indicate endothelial cell losses equivalent to 50% of the LI, but they are not significantly greater for the HL swine than for controls. We suggest, then, that the lipid in the ICM (or something associated with it) is the most likely candidate for the SMC growth stimulatory agent accounting for the increased tritiated thymidine LI and the great increase in ICM-lesion cell numbers between HL diet days 49 and 90. Platelet- and/or monocyte-derived growth factors may also be involved in some subtle fashion, but this study provides no positive evidence to support this hypothesis. Progression of the ICM-derived lesions to the advanced atheromatous phase by 300 days on HL diet appears to be a much more complex process. By 300 days in the specific experiment cited, approximately 65% of the atherosclerotic lesion volume consisted of lipid-rich calcific necrotic debris; calculated death rates of lesion cells were very high compared to that at 90 days; calculated endothelial cell loss rates were considerably higher than in controls; and, large numbers of monocyte-macrophages were present in many areas generally associated with necrotic foci. These changes in the aggregate suggest a much more complex mode of pathogenesis for progression to advanced stages than for initiation and early development.

Metabolism of atherogenic lipoproteins by smooth muscle cells of different phenotype in culture

Smooth muscle cells of the rabbit aorta, when grown in vitro, express three distinguishable forms of phenotype (contractile, reversible synthetic, and irreversible synthetic). We compared the interactions of these three smooth muscle phenotypes with rabbit very low density lipoprotein (VLDL), low density lipoprotein (LDL), and very low density lipoprotein from cholesterol-fed rabbits (beta-VLDL). beta-VLDL showed saturable. high-affinity binding characteristics with each phenotype predominantly through the B/E receptor. The irreversible synthetic cells displayed the greatest binding capacity and the contractile cells, the least. Binding and degradation of normal VLDL was less than that of beta-VLDL and higher than that of LDL. Only the irreversible synthetic cells showed substantial (about threefold) cholesteryl ester formation and cholesterol accumulation, and then only when incubated with beta-VLDL. Substantial stainable lipid, shown chemically to include triglyceride, cholesterol and cholesteryl ester, was also observed only when irreversible synthetic cells were exposed to beta-VLDL. The high capacity of irreversible synthetic-state, smooth muscle cells to bind and accumulate beta-VLDL in contrast to the relative immunity of contractile cells may be relevant to the genesis of atherosclerosis in the rabbit and possibly also in humans.