Significance of the Wnt signaling pathway in coronary artery atherosclerosis.

Introduction: The progression of coronary atherosclerosis is an active and regulated process. The Wnt signaling pathway is thought to play an active role in the pathogenesis of several cardiovascular diseases; however, a better understanding of this system in atherosclerosis is yet to be unraveled. Methods: In this study, real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting were used to quantify the expression of Wnt3a, Wnt5a, and Wnt5b in the human coronary plaque, and immunohistochemistry was used to identify sites of local expression. To determine the pathologic significance of increased Wnt, human vascular smooth muscle cells (vSMCs) were treated with Wnt3a, Wnt5a, and Wnt5b recombinant proteins and assessed for changes in cell differentiation and function. Results: RT-PCR and Western blotting showed a significant increase in the expression of Wnt3a, Wnt5a, Wnt5b, and their receptors in diseased coronary arteries compared with that in non-diseased coronary arteries. Immunohistochemistry revealed an abundant expression of Wnt3a and Wnt5b in diseased coronary arteries, which contrasted with little or no signals in normal coronary arteries. Immunostaining of Wnt3a and Wnt5b was found largely in inflammatory cells and myointimal cells. The treatment of vSMCs with Wnt3a, Wnt5a, and Wnt5b resulted in increased vSMC differentiation, migration, calcification, oxidative stress, and impaired cholesterol handling. Conclusions: This study demonstrates the upregulation of three important members of canonical and non-canonical Wnt signaling pathways and their receptors in coronary atherosclerosis and shows an important role for these molecules in plaque development through increased cellular remodeling and impaired cholesterol handling.

Chymase Inhibition Resolves and Prevents Deep Vein Thrombosis Without Increasing Bleeding Time in the Mouse Model.

Background Deep vein thrombosis (DVT) is the primary cause of pulmonary embolism and the third most life-threatening cardiovascular disease in North America. Post-DVT anticoagulants, such as warfarin, heparin, and direct oral anticoagulants, reduce the incidence of subsequent venous thrombi. However, all currently used anticoagulants affect bleeding time at various degrees, and there is therefore a need for improved therapeutic regimens in DVT. It has recently been shown that mast cells play a crucial role in a DVT murine model. The underlying mechanism involved in the prothrombotic properties of mast cells, however, has yet to be identified. Methods and Results C57BL/6 mice and mouse mast cell protease-4 (mMCP-4) genetically depleted mice (mMCP-4 knockout) were used in 2 mouse models of DVT, partial ligation (stenosis) and ferric chloride-endothelial injury model of the inferior vena cava. Thrombus formation and impact of genetically repressed or pharmacologically (specific inhibitor TY-51469) inhibited mMCP-4 were evaluated by morphometric measurements of thrombi immunochemistry (mouse and human DVT), color Doppler ultrasound, bleeding times, and enzymatic activity assays ex vivo. Recombinant chymases, mMCP-4 (mouse) and CMA-1 (human), were used to characterize the interaction with murine and human plasmin, respectively, by mass spectrometry and enzymatic activity assays. Inhibiting mast cell-generated mMCP-4, genetically or pharmacologically, resolves and prevents venous thrombus formation in both DVT models. Inferior vena cava blood flow obstruction was observed in the stenosis model after 6 hours of ligation, in control- but not in TY-51469-treated mice. In addition, chymase inhibition had no impact on bleeding times of healthy or DVT mice. Furthermore, endogenous chymase limits plasmin activity in thrombi ex vivo. Recombinant mouse or human chymase degrades/inactivates purified plasmin in vitro. Finally, mast cell-containing immunoreactive chymase was identified in human DVT. Conclusions This study identified a major role for mMCP-4, a granule-localized protease of chymase type, in DVT formation. These findings support a novel pharmacological strategy to resolve or prevent DVT without affecting the coagulation cascade through the inhibition of chymase activity.

Extracellular Vesicles as a Cell-free Therapy for Cardiac Repair: a Systematic Review and Meta-analysis of Randomized Controlled Preclinical Trials in Animal Myocardial Infarction Models.

Stem cell therapy for cardiac regeneration has been gaining traction as a possible intervention for the reduction of the burden associated with MI and heart failure. However, stem cell therapies have several shortcomings, including poor engraftment, limited improvements in cardiac function, and possible teratogenicity. Recently, extracellular vesicles (EVs) from stem cell sources have been explored as a novel therapy to regenerate the injured myocardium in several animal MI trials. In this systematic review and meta-analysis, we investigate the use of stem cell-derived EVs for cardiac repair preclinical trials in animal MI models. Cochrane Library, Medline, Embase, PubMed, Scopus and Web of Science and grey literature (Canadian Agency for Drugs, Technologies in Health, and Google Scholar) were searched through August 20, 2020 and 37 articles were included in the final analysis. The overall effect size observed in EV-treated small animals after MI for ejection fraction (EF) was 10.85 [95 %CI: 8.79, 12.90] and for fractional shortening (FS) was 7.19 [95 %CI: 5.43, 8.96] compared to control-treated animals. The most abundant stem cell source used were mesenchymal stem cells which showed robust improvements in EF and FS (MD = 11.89 [95 % CI: 9.44, 14.34] and MD = 6.96 [95 % CI: 4.97, 8.96], respectively). Significant publication bias was detected for EF and FS outcomes. This study supports the use of EVs derived from stem cells as a novel therapy for cardiac repair after MI. Further investigation in larger animal studies may be necessary before clinical trials.PROSPERO registration number: CRD42019142218.

Bioactive Scaffolds in Stem Cell-Based Therapies for Myocardial Infarction: a Systematic Review and Meta-Analysis of Preclinical Trials.

The use of bioactive scaffolds in conjunction with stem cell therapies for cardiac repair after a myocardial infarction shows significant promise for clinical translation. We performed a systematic review and meta-analysis of preclinical trials that investigated the use of bioactive scaffolds to support stem cell-aided cardiac regeneration, in comparison to stem cell treatment alone. Cochrane Library, Medline, Embase, PubMed, Scopus, Web of Science, and grey literature were searched through April 23, 2020 and 60 articles were included in the final analysis. The overall effect size observed in scaffold and stem cell-treated small animals compared to stem cell-treated controls for ejection fraction (EF) was 7.98 [95% confidence interval (CI): 6.36, 9.59] and for fractional shortening (FS) was 5.50 [95% CI: 4.35, 6.65] in small animal models. The largest improvements in EF and FS were observed when hydrogels were used (MD = 8.45 [95% CI: 6.46, 10.45] and MD = 5.76 [95% CI: 4.46, 7.05], respectively). Subgroup analysis revealed that cardiac progenitor cells had the largest effect size for FS, and was significant from pluripotent, mesenchymal and endothelial stem cell types. In large animal studies, the overall improvement of EF favoured the use of stem cell-embedded scaffolds compared to direct injection of cells (MD = 10.49 [95% CI: 6.30, 14.67]). Significant publication bias was present in the small animal trials for EF and FS. This study supports the use of bioactive scaffolds to aid in stem cell-based cardiac regeneration. Hydrogels should be further investigated in larger animal models for clinical translation.

Amniotic stromal stem cell-loaded hydrogel repairs cardiac tissue in infarcted rat hearts via paracrine mediators.

The use of stem cells to repair the heart after a myocardial infarction (MI) remains promising, yet clinical trials over the past 20 years suggest that cells fail to integrate into the native tissue, resulting in limited improvements in cardiac function. Here, we demonstrate the cardioprotective potential of a composite inserting human amniotic stromal mesenchymal stem cells (ASMCs) in a chitosan and hyaluronic acid (C/HA) based hydrogel in a rat MI model. Mechanical characterization of the C/HA platform indicated a swift elastic conversion at 40°C and a rapid sol-gel transition time at 37°C. Cell viability assay presented active and proliferating AMSCs in the C/HA. The ASMCs + C/HA injected composite significantly increased left ventricular ejection fraction, fractional shortening, and neovessel formation. The encapsulated AMSCs were abundantly detected in the infarcted myocardium 6 weeks post-administration and co-expressed cardiac proteins and notably proliferative markers. Proteomic profiling revealed that extracellular vesicles released from hypoxia preconditioned ASMCs contained proteins involved in cytoprotection, angiogenesis, cardiac differentiation and non-canonical Wnt-signaling. Independent activation of non-canonical Wnt-signaling pathways in ASMCs induced cardiogenesis. Despite a low injected cellular density at baseline, the encapsulated AMSCs were abundantly retained and increased cardiac function. Furthermore, the C/HA hydrogel provided an active milieu for the AMSCs to proliferate, co-express cardiac proteins, and induce new vessel formation. Hence, this novel composite of AMSCs + C/HA scaffold is a conceivable candidate that could restore cardiac function and reduce remodeling.

COVID-19 and the cardiovascular system: insights into effects and treatments.

Coronavirus disease 2019 (COVID-19), an acute and highly transmissible infectious disease, has reached a pandemic level since 11 March 2020 and continues to challenge the healthcare system worldwide. The pathogenesis of COVID-19 is a complex process involving mechanisms that suppress the host antiviral and innate immune response, while triggering marked activation of coagulation and hyperinflammation leading to cytokine storm in severe COVID-19. This review summarizes current evidence related to COVID-19-associated cardiovascular severe illness and mortality, which encompasses life-threatening clinical manifestations, including myocardial injury, fulminant myocarditis, cardiac arrhythmia, and ischemic stroke. The onset of hypercoagulable state is consistent with increased venous thromboembolism including deep vein thrombosis and pulmonary embolism. Thromboembolic manifestations include arterial thrombotic events such as stroke, myocardial infarction, and limb ischemia. Several treatment strategies have been investigated to mitigate COVID-19-associated cardiovascular clinical manifestations. The prevalence of thrombo-inflammatory syndrome and subsequent cardiovascular dysfunction prompted the implementation of antithrombotic therapy and strategies targeting major pro-inflammatory cytokines involved in COVID-19 cytokine storm. The development of new guidelines for effective treatment strategies requires concerted efforts to refine our understanding of the mechanisms underlying cardiovascular disease and large-scale clinical trials to reduce the burden of COVID-19 hospitalization and mortality.

Urotensin II, urotensin-related peptide, and their receptor in aortic valve stenosis.

OBJECTIVES: Aortic valve stenosis (AVS) is the most common cause of surgical valve replacement worldwide. The vasoactive peptide urotensin II (UII) is upregulated in atherosclerosis and several other cardiovascular diseases; however, its role in the pathogenesis of AVS remains to be determined. Here, we investigated the expression of UII, urotensin-related peptide (URP), and the urotensin receptor (UT) and the role this system plays in AVS. METHODS: Immunohistochemistry and reverse-transcriptase polymerase chain reaction were used to examine the cellular localization and mRNA expression, of UII, URP, and UT in calcified and noncalcified aortic valves. Human aortic valve interstitial cells were isolated from normal valves and treated with UII or URP, and changes in cell proliferation, cholesterol efflux, calcium deposition, and ß-catenin translocation were assessed. RESULTS: The mRNA expression of UII, URP, and UT was significantly greater in patients with AVS. There was abundant presence of UII, URP, and UT immunostaining in diseased compared with nondiseased valves and correlated significantly with presence of calcification (P < .0001) and fibrosis (P < .0001). Treating human aortic valve interstitial cells with UII or URP significantly increased cell proliferation (P < .0001) and decreased cholesterol efflux (P = .0011 and P = .0002, respectively). UII also significantly reduced ABCA1 protein expression (P = .0457) and increased ß-catenin nuclear translocation (P < .0001) and mineral deposition (P < .0001). CONCLUSIONS: Together, these data suggest that the urotensin system plays a role in the pathogenesis of AVS and warrants further investigation.

The Role of Wnt/ß-Catenin Pathway Mediators in Aortic Valve Stenosis.

Aortic valve stenosis (AVS) is a prevailing and life-threatening cardiovascular disease in adults over 75 years of age. However, the molecular mechanisms governing the pathogenesis of AVS are yet to be fully unraveled. With accumulating evidence that Wnt signaling plays a key role in the development of AVS, the involvement of Wnt molecules has become an integral study target in AVS pathogenesis. Thus, we hypothesized that the Wnt/ß-catenin pathway mediators, SFRP2, DVL2, GSK3ß and ß-catenin are dysregulated in patients with AVS. Using immunohistochemistry, Real-Time qPCR and Western blotting, we investigated the presence of SFRP2, GSK-3ß, DVL2, and ß-catenin in normal and stenotic human aortic valves. Markedly higher mRNA and protein expression of GSK-3ß, DVL2, ß-catenin and SFRP2 were found in stenotic aortic valves. This was further corroborated by observation of their abundant immunostaining, which displayed strong immunoreactivity in diseased aortic valves. Proteomic analyses of selective GSK3b inhibition in calcifying human aortic valve interstitial cells (HAVICs) revealed enrichment of proteins involved organophosphate metabolism, while reducing the activation of pathogenic biomolecular processes. Lastly, use of the potent calcification inhibitor, Fetuin A, in calcifying HAVICs significantly reduced the expression of Wnt signaling genes Wnt3a, Wnt5a, Wnt5b, and Wnt11. The current findings of altered expression of canonical Wnt signaling in AVS suggest a possible role for regulatory Wnts in AVS. Hence, future studies focused on targeting these molecules are warranted to underline their role in the pathogenesis of the disease.

Differences in mineral composition and morphology between men and women in aortic valve calcification.

Aortic valve calcification leads to the deposition of calcium phosphate minerals in the extracellular matrix of the aortic valve leaflets. The mineral deposits can severely narrow the opening of the aortic valve, leading to aortic stenosis. There are no therapies to halt or slow down disease progression and the mechanisms governing aortic valve calcification are still poorly understood. Recently, several studies have shown that for the same aortic stenosis severity, women present significantly lower calcification loads than men. The cause of this sex-related difference is unknown. To understand this difference, we analyzed mineral deposits from surgically excised calcified human aortic valves with different material characterization techniques. We find profound differences in mineral composition and morphology between sexes, which strongly suggest that minerals form slower in women than in men and follow a different mineralization pathway. This finding paves the way for new approaches specifically geared towards men or women in the diagnosis and treatment of aortic valve calcification. STATEMENT OF SIGNIFICANCE: Aortic valve calcification is a health disorder with increasing prevalence and high morbidity and mortality. Currently there is no approved effective treatment; the only available therapeutic option is invasive valve replacement, to which not all patients are suited. The main reason for such lack of treatment options is our lack of understanding of the calcification mechanism. In this study, we show profound differences in mineral composition and morphology between sexes, suggesting that aortic valve calcification follows different mineralization pathways in men and women. These findings pave the way for new approaches specifically geared towards men or women in the diagnosis and treatment of aortic valve calcification.

A Notch more: Molecular players in bicuspid aortic valve disease.

The prevalence of calcification of human aortic valve in populations 65 years old and greater is estimated to be 2-3%. Bicuspid aortic valve disease (BAVD) is a common etiology of aortic stenosis in populations aged 60-75 years of age; 30-50% of operated cases of aortic stenosis were due to calcified BAVD. Dysregulation of the Notch and the canonical Wnt pathway has been well documented to be associated with calcification of the aortic valve. However, recent studies have increased this scope to include the non-canonical pathway where Wnt5a, Wnt5b and Wnt 11 levels were significantly greater in calcified human aortic valves than normal valves, and with Wnt5b specifically being implicated in BAVD pathogenesis. More recently, Lipoprotein(a) [Lp(a)] has been implicated as a key player in the pathogenesis of calcific aortic valve disease. It has been shown that the osteogenic effect of Lp(a) is mediated through the oxidized phospholipid pathway as well as oxidized phospholipid independent pathways involving mitogen-activated protein kinases (MAPK), glycogen synthase kinase (GSK) and Wnt. Moving forward, further work needs to be conducted in order to elucidate the crosstalk between the different signaling cascades, specifically with regard to BAVD.

Bioactive scaffolds in stem-cell-based therapies for cardiac repair: protocol for a meta-analysis of randomized controlled preclinical trials in animal myocardial infarction models.

BACKGROUND: Acute myocardial infarction (MI) remains one of the leading causes of death worldwide with no curative therapy available. Stem cell therapies have been gaining interest as a means to repair the cardiac tissue after MI and prevent the onset of heart failure. Many in vivo reports suggest that the use of stem cells is promising, yet clinical trials suggest that the cells fail to integrate into the native tissue, resulting in limited improvements in cardiac function and repair. To battle this limitation, the combination of using stem cells embedded in a bioactive scaffold that promotes cell retention is growing in interest. Yet, a systematic review of the literature on the use of stem cells embedded in bioactive scaffolds for cardiac repair has not yet been performed. In this protocol, we outline a systematic review and meta-analysis of preclinical trials in animal MI models that utilize stem cell-embedded scaffolds for cardiac repair and compare their effects to stem cell-treated animals without the use of a scaffold. METHODS/DESIGN: We will search the following electronic databases: Cochrane Library, MEDLINE, Embase, PubMed, Scopus and Web of Science, and gray literature: Canadian Agency for Drugs and Technologies in Health and Google Scholar. We will only include randomly controlled preclinical trials that have directly investigated the effects of stem cells embedded in a scaffold for cardiac repair in an animal MI model. Two investigators will independently review each article included in the final analysis. The primary endpoint that will be investigated is left ventricular ejection fraction. Secondary endpoints will include infarct size, end systolic volume, end diastolic volume, fractional shortening and left ventricular wall thickness. Pooled analyses will be conducted using the DerSimonian-Laird random effects and Mantel-Haenszel fixed-effect models. Between-studies heterogeneity will be quantified and determined using the Tau2 and I2 statistics. Publication bias will be assessed using visual inspection of funnel plots and complemented by Begg's and Egger's statistical tests. Possible sources of heterogeneity will be assessed using subgroup-meta analysis and meta-regression. DISCUSSION: To date, the use of scaffolds in myocardial repair has not yet been systematically reviewed. The results of this meta-analysis will aid in determining the efficacy of stem cell-embedded scaffolds for cardiac repair and help bring this therapy to the clinic.

Mouse Mast Cell Protease 4 Deletion Protects Heart Function and Survival After Permanent Myocardial Infarction.

Chymase, a mast cell serine protease involved in the generation of multiple cardiovascular factors, such as angiotensin II and endothelin-1 (ET-1), is elevated and participates in tissue degeneration after permanent myocardial infarction (PMI). Anesthetized 4-month old male wild-type (WT) C57BL/6J mice and mouse mast cell protease-4 knockout (mMCP-4 KO) congeners were subjected to ligation of the left anterior descending (LAD) coronary artery. A group of mice was then subjected to Kaplan-Meier 28-day survival analysis. In another group of mice, 18F-fluorodeoxyglucose positron emission tomography (PET) was performed to evaluate heart function and the infarcted zone 3 days post-PMI surgery. Cardiac morphology following PMI was evaluated on formalin-fixed heart slices and glycoproteomic analysis was performed using mass spectrometry. Finally, cardiac and lung tissue content of immunoreactive ET-1 was determined. PMI caused 60% mortality in WT mice, due to left ventricular wall rupture, and 7% in mMCP-4 KO mice. Cardiac PET analysis revealed a significant reduction in left ventricular volume (systolic and diastolic) and preserved the ejection fraction in mMCP-4 KO compared to WT animals. The infarcted area, apoptotic signaling and wall remodeling were significantly decreased in mMCP-4 KO mice compared to their WT congeners, while collagen deposition was increased. Glycoproteomic analysis showed an increase in apolipoprotein A1, an established chymase substrate in mMCP-4 KO mice compared to WT mice post-PMI. ET-1 levels were increased in the lungs of WT, but not mMCP-4 KO mice, 24 h post-PMI. Thus, the genetic deletion of mMCP-4 improved survival and heart function post-PMI.

Pathological significance of lipoprotein(a) in aortic valve stenosis.

BACKGROUND AND AIMS: Aortic valve stenosis (AVS) affects a significant percentage of our elderly population and younger subjects with familial hypercholesterolemia. Lipoprotein(a) [Lp(a)] has been associated with AVS in recent genetic studies. The purpose of this study was to determine the effects of Lp(a) on human aortic valve interstitial cells (HAVICs), and to identify apolipoproteins and phospholipids in diseased human aortic valves. METHODS: We examined the effects of Lp(a) on HAVICs mineralization and oxidant formation. Proteomic analyses were used to determine the effects of Lp(a) on downstream intracellular markers. We also used mass spectroscopy to identify the different lipoproteins and oxidized phospholipids in calcified aortic valves. RESULTS: HAVICs incubated with either LDL or Lp(a) had significantly higher calcium deposition, compared to control (p<0.001), with Lp(a) having the most significant effect (p<0.01) compared to LDL. Proteomic analysis after 10 days of treatment with Lp(a) resulted in enrichment of proteins involved in calcium deposition and vesicle biogenesis. Treatment of HAVICs with Lp(a) significantly increased ROS formation (p<0.05). Patients with calcific aortic stenosis had higher plasma Lp(a) concentrations compared to non-CAD individuals (p<0.001). LC-MS/MS revealed the presence of apolipoproteins and phospholipids in calcified human aortic valves. CONCLUSIONS: The present study outlines an association between Lp(a) and AVS, and suggests that Lp(a) may serve as a potential target for therapeutic purposes to manage the progression of AVS.

HDLs and the pathogenesis of atherosclerosis.

PURPOSE OF REVIEW: Plasma levels of HDL cholesterol are a biomarker of cardiovascular health but not a therapeutic target, as demonstrated by the failure of pharmacological modulation of HDL cholesterol to prevent or treat atherosclerotic cardiovascular disease. In health, HDL particles exert pleiotropic effects against atherosclerosis, including cholesterol removal from foam cells, vasodilatory effects through vascular endothelial cell nitric oxide production, decreased vascular inflammation and oxidative damage, endothelial cell proliferation and antiapoptotic effects. RECENT FINDINGS: These functional effects of HDL are independent of the cholesterol mass and are related to the proteome and lipidome. In disease states and with the ageing process, HDL components are extensively modified and may no longer play a beneficial role but are retained in the atheroma and contribute to atherosclerosis. We have recently shown that desmocollin 1 (DSC1) acts as an apolipoprotein (apo) A-I binding protein that is highly expressed in atherosclerotic plaques and inhibits atheroprotective HDL functions by retaining apoA-I. The apoA-I retention hypothesis proposes that macrophages express DSC1 in a maladaptive process that renders apoA-I inactive and contributes to atherosclerosis. SUMMARY: HDL loses their beneficial properties in ageing and disease states. Novel pathways may present new therapeutic avenues to restore their biological functions.

Desmocollin 1 is abundantly expressed in atherosclerosis and impairs high-density lipoprotein biogenesis.

Aims: The biogenesis of high-density lipoprotein (HDL) particles by cholesterol-laden foam cells in atherosclerotic lesions is crucial for the removal of excess cholesterol from the lesions. Impairment in the HDL biogenic process contributes to the progression of atherosclerosis. The aim of this study is to identify novel cellular factors regulating HDL biogenesis. Methods and results: HDL biogenesis is a process of apolipoprotein (apo)-mediated solubilization of specific plasma membrane (PM) microdomains generated in cholesterol-accumulated cells. We established a new method to isolate PM microdomains interacting with the major HDL protein constituent, apoA-I. Lipidomic and proteomic analyses of an isolated PM microdomain revealed that apoA-I binds to cholesterol-rich and desmocollin 1 (DSC1)-containing microdomains. In this novel apoA-I binding microdomain, DSC1 binds and prevents apoA-I from interacting with another PM microdomain created by adenosine triphosphate-binding cassette transporter A1 (ABCA1) for the formation of HDL. Inhibition of apoA-I-DSC1 binding by silencing DSC1 expression or using DSC1 blocking antibodies increases apoA-I accessibility to ABCA1-created microdomains and thus enhances HDL biogenesis. Importantly, DSC1 is abundantly expressed in macrophages and human atherosclerotic lesions, suggesting that DSC1 may contribute to cholesterol accumulation in atherosclerotic lesions by sequestering apoA-I and impairing HDL biogenesis. Conclusions: The binding of apoA-I to two functionally opposing PM microdomains, ABCA1 and DSC1 domains, suggests that HDL biogenesis and PM cholesterol levels may be regulated by the relative abundance of the two domains and that novel HDL biogenic therapies may be developed by targeting DSC1.

Membrane microdomains and the regulation of HDL biogenesis.

PURPOSE OF REVIEW: The major cardio-protective function of HDL is to remove excess cellular cholesterol in the process of HDL particle formation and maturation. The HDL biogenic procedure requiring protein-lipid interactions has been incompletely understood, and here we discuss recent progress and insights into the mechanism of HDL biogenesis. RECENT FINDINGS: The initial and rate-limiting step of HDL biogenesis is the interaction between apoA-I and plasma membrane microdomains created by ATP-binding cassette transporter A1 (ABCA1) transporter. Computer simulation of molecular dynamics suggests that ABCA1 translocates phospholipids from the inner to the outer leaflet of the plasma membrane to create a transbilayer density gradient leading to the formation of an exovesiculated plasma membrane microdomain. The cryo-electron microscopy structure of ABCA1 suggests that an elongated hydrophobic tunnel formed by the extracellular domain of ABCA1 may function as a passageway to deliver lipids to apoA-I. In contrast to ABCA1-created plasma membrane microdomains, desmocollin 1 (DSC1) contained in a cholesterol-rich plasma membrane microdomain binds apoA-I to prevent HDL biogenesis. The identification of DSC1-containing plasma membrane microdomains as a negative regulator of HDL biogenesis may offer potential therapeutic avenues. SUMMARY: Isolation and characterization of plasma membrane microdomains involved in HDL biogenesis may lead to a better understanding of the molecular mechanism of HDL biogenesis.

Expression of the Frizzled receptors and their co-receptors in calcified human aortic valves.

The cellular mechanisms that induce calcific aortic stenosis are yet to be unraveled. Wnt signaling is increasingly being considered as a major player in the disease process. However, the presence of Wnt Frizzled (Fzd) receptors and co-receptors LRP5 and 6 in normal and diseased human aortic valves remains to be elucidated. Immunohistochemistry and quantitative polymerase chain reaction were used to determine Fzd receptor expression in normal and calcified human aortic valve tissue, as well as human aortic valve interstitial cells (HAVICs) isolated from calcified and normal human aortic valves. There was significantly higher mRNA expression of 4 out of the 10 Fzd receptors in calcified aortic valve tissues and 8 out of the 10 in HAVICs, and both LRP5/6 co-receptors in calcified aortic valves (P < 0.05). These results were confirmed by immunohistochemistry, which revealed abundant increase in immunoreactivity for Fzd3, 7, and 8, mainly in areas of lipid core and calcified nodules of diseased aortic valves. The findings of abundant expression of Fzd and LRP5/6 receptors in diseased aortic valves suggests a potential role for both canonical and noncanonical Wnt signaling in the pathogenesis of human aortic valve calcification. Future investigations aimed at targeting these molecules may provide potential therapies for aortic valve stenosis.

High-Density Lipoproteins: Biology, Epidemiology, and Clinical Management.

High-density lipoproteins (HDLs) have multiple pleiotropic effects against arteriosclerosis. Most are independent of the cholesterol mass within HDL particles. Yet, HDL cholesterol (HDL-C) remains a biomarker to assess cardiovascular risk. Whereas the epidemiological association between HDL-C and cardiovascular risk is strong, graded and coherent across populations, Mendelian randomization studies cast doubt on whether HDL-C is causally related to atherosclerotic cardiovascular disease. The apparent failure of HDL-C-raising therapies (fibrates, niacin, and cholesteryl ester transfer protein inhibitors) raises questions about the HDL-C hypothesis. HDL particles are heterogeneous in lipid and protein composition, and thus in size and function. Multiple factors related to oxidation and inflammation might render HDL particles malfunctional or proatherogenic. HDL functionality might be a preferred biomarker and therapeutic target. However, most of the beneficial events of HDL particles occur in the subendothelial layer of arteries and not in plasma. In this report, we review the complexity and controversies surrounding HDL and atherosclerotic cardiovascular disease. Importantly, intimal HDL biogenesis, function, and egress from the arterial wall might hold the key to unlocking the therapeutic potential of HDL.