Abstract 102: Autophagy Is Differentially Regulated In Leukocyte And Nonleukocyte Foam Cells During Atherosclerosis

Atherosclerosis is characterized by a build-up of foam cells in the arterial wall, resulting from excess cholesterol uptake and accumulation of cytosolic lipid droplets (LDs). Autophagy has been shown to be atheroprotective in part by promoting the catabolism of LDs which liberates free cholesterol for efflux out of foam cells to cholesterol acceptors (ApoA-I or HDL) for removal from the body. Apart from macrophages (MΦ), vascular smooth muscle cells (VSMCs) comprise 50-70% of foam cells in the plaques. Unlike MΦ, the capacity of VSMC foam cells to metabolize cholesterol via autophagy is unknown. Here, w e performed a comparative analysis of the autophagic capacity and cholesterol efflux of arterial foam cell subtypes of the atherosclerotic plaque .

Atherosclerosis was induced in hypercholesterolemic autophagy reporter mice (GFP-LC3 mice receiving PCSK9-AAV and fed a Western diet). Autophagic flux in aortic digests was assessed by quantifying GFP-LC3 fluorescence after ex vivo treatment with the autophagy inhibitor Bafilomycin A1 or vehicle. MΦ foam cells displayed functional autophagy as shown by an accumulation of GFP-LC3 upon autophagy inhibition. In contrast, VSMC foam cells did not similarly accumulate GFP-LC3 upon bafilomycin treatment, suggesting dysfunction autophagy in these cells. Additionally, immunostaining of late-stage aortic roots showed MΦ, but not VSMC, foam cells induction of the active autophagy marker pATG16L1. Cell culture studies of lipid loaded MΦ and VSMC corroborated this inability for VSMCs to initiate autophagy in vivo .

In vitro , MΦ foam cells effluxed cholesterol to ApoA-I (14%) and HDL (50%), whereas VSMC foam cells minimally effluxed cholesterol to HDL (7%) but not apoA-I. However, unlike MΦ foam cells, VSMC efflux was pharmacologically induced by treatment with metformin.

Our data therefore demonstrates a lack of functional autophagy in VSMC, as compared to MΦ foam cells, which impairs their ability to perform cholesterol efflux. This autophagy defect in VSMC foam cells can be increased by autophagy activation using metformin, highlighting both the importance of understanding cholesterol metabolism in all foam cell populations and a new avenue to treat atherosclerosis.

Abstract 207: Autophagy Is Differentially Regulated In Leukocyte And Nonleukocyte Foam Cells During Atherosclerosis

Atherosclerosis is characterized by a build-up of foam cells in the arterial wall, resulting from excess cholesterol uptake and accumulation of cytosolic lipid droplets (LDs). Autophagy has been shown to be atheroprotective in part by promoting the catabolism of LDs which liberates free cholesterol for efflux out of foam cells to cholesterol acceptors (ApoA-I or HDL) for removal from the body. Apart from macrophages (MΦ), vascular smooth muscle cells (VSMCs) comprise 50-70% of foam cells in the plaques. Unlike MΦ, the capacity of VSMC foam cells to metabolize cholesterol via autophagy is unknown. Here, we performed a comparative analysis of the autophagic capacity and cholesterol efflux of arterial foam cell subtypes of the atherosclerotic plaque.

Atherosclerosis was induced in hypercholesterolemic autophagy reporter mice (GFP-LC3 mice receiving PCSK9-AAV and fed a Western diet). Autophagic flux in aortic digests was assessed by quantifying GFP-LC3 fluorescence after ex vivo treatment with the autophagy inhibitor Bafilomycin A1 or vehicle. MΦ foam cells displayed functional autophagy as shown by an accumulation of GFP-LC3 upon autophagy inhibition. In contrast, VSMC foam cells did not similarly accumulate GFP-LC3 upon bafilomycin treatment, suggesting dysfunction autophagy in these cells. Additionally, immunostaining of late-stage aortic roots showed MΦ, but not VSMC, foam cells induction of the active autophagy marker pATG16L1. Cell culture studies of lipid loaded MΦ and VSMC corroborated this inability for VSMCs to initiate autophagy in vivo .

In vitro , MΦ foam cells effluxed cholesterol to ApoA-I (14%) and HDL (50%), whereas VSMC foam cells minimally effluxed cholesterol to HDL (7%) but not apoA-I. However, unlike MΦ foam cells, VSMC efflux was pharmacologically induced by treatment with metformin.

Our data therefore demonstrates a lack of functional autophagy in VSMC, as compared to MΦ foam cells, which impairs their ability to perform cholesterol efflux. This autophagy defect in VSMC foam cells can be increased by autophagy activation using metformin, highlighting both the importance of understanding cholesterol metabolism in all foam cell populations and a new avenue to treat atherosclerosis.

Autophagy Is Differentially Regulated in Leukocyte and Nonleukocyte Foam Cells During Atherosclerosis

RATIONALE

Atherosclerosis is characterized by an accumulation of foam cells within the arterial wall, resulting from excess cholesterol uptake and buildup of cytosolic lipid droplets (LDs). Autophagy promotes LD clearance by freeing stored cholesterol for efflux, a process that has been shown to be atheroprotective. While the role of autophagy in LD catabolism has been studied in macrophage-derived foam cells, this has remained unexplored in vascular smooth muscle cell (VSMC)-derived foam cells that constitute a large fraction of foam cells within atherosclerotic lesions.

OBJECTIVE

We performed a comparative analysis of autophagy flux in lipid-rich aortic intimal populations to determine whether VSMC-derived foam cells metabolize LDs similarly to their macrophage counterparts.

METHODS AND RESULTS

Atherosclerosis was induced in GFP-LC3 transgenic mice by PCSK9 (proprotein convertase subtilisin/kexin type 9)-adeno-associated viral injection and Western diet feeding. Using flow cytometry of aortic digests, we observed a significant increase in dysfunctional autophagy of VSMC-derived foam cells during atherogenesis relative to macrophage-derived foam cells. Using cell culture models of lipid-loaded VSMC and macrophage, we show that autophagy-mediated cholesterol efflux from VSMC foam cells was poor relative to macrophage foam cells, and largely occurs when HDL (high-density lipoprotein) is used as a cholesterol acceptor, as opposed to apoA-1 (apolipoproteinA-1). This was associated with the predominant expression of ABCG1 in VSMC foam cells. Using metformin, an autophagy activator, cholesterol efflux to HDL was significantly increased in VSMC, but not in macrophage, foam cells.

CONCLUSIONS

These data demonstrate that VSMC and macrophage foam cells perform cholesterol efflux by distinct mechanisms, and that autophagy flux is highly impaired in VSMC foam cells, but can be induced by pharmacological means. Further investigation is warranted into targeting autophagy specifically in VSMC foam cells, the predominant foam cell subtype of advanced atherosclerotic plaques, to promote reverse cholesterol transport and resolution of the atherosclerotic plaque.

Surgical Techniques for the Treatment of Anomalous Origin of Right Coronary Artery From the Left Sinus: A Comparative Review

The anomalous aortic origin of the right coronary artery (AAORCA) from the left sinus is a congenital anomaly affecting both the origin and course of the right coronary artery. AAORCA is nowadays easily and increasingly recognized by several cardiac imaging modalities. In most cases, patients remain asymptomatic; however, in some, and especially in young athletes, symptoms start to appear following exertion. A literature review was conducted on the surgical management of AAORCA by searching the Pubmed and Google Scholar databases. The inclusion criteria included manuscripts reporting surgical outcomes of AAORCA for ≥1 of the 3 techniques of interest (unroofing, reimplantation, and coronary artery bypass grafting) and manuscripts written in English and that were published between 2010 and 2020. The surgical management of AAORCA can be done through several techniques, most commonly the unroofing of the intramural segment of the AAORCA, the reimplantation of the native right coronary artery onto the right sinus of the aortic root, and coronary artery bypass grafting with either arterial or venous graft conduits with or without ligation of the proximal right coronary artery. Superiority of one surgical technique has not yet been formally proven because of the rare nature of this condition and the lack of any prospective randomized controlled trial or robust prospective observational studies.

Comprehensive left ventricular outflow tract management beyond septal reduction to relieve obstruction

The surgical management of patients with hypertrophic obstructive cardiomyopathy can be extremely challenging. Relieving the left ventricular outflow tract obstruction in these patients is often achieved by performing a septal myectomy. However, in many instances, septal reduction alone is not enough to relieve the obstruction. Interventions on the sub-valvular apparatus, including the anomalous chordae tendineae and the abnormal papillary muscles, are often required. In this review, we summarize the embryology and the pathophysiology of the different elements that may contribute to the left ventricular outflow tract obstruction in the setting of hypertrophic obstructive cardiomyopathy. In addition, we highlight the different surgical procedures that a surgeon may adopt to relieve the left ventricular outflow tract obstruction, beyond the septal myectomy.

Comparative Analysis Following Implementation of Two Types of Y-Composite Multiarterial Revascularization Strategies at a Single Academic Institution

Background

We compared early outcomes, at a single academic institution, of implementing full coronary revascularization in coronary artery bypass grafting using multiarterial Y‐composite grafts with multiple sequential anastomoses.

Methods and Results

Clinical records of 425 consecutive patients who underwent coronary artery bypass grafting using Y‐grafting with left internal mammary artery and radial artery (Y‐RA group) or right internal mammary artery (Y‐RIMA group) from 2015 to 2019, were reviewed. These were compared with the institutional experience of isolated coronary artery bypass grafting cases (in situ on pump/off pump) for the same period of time. When comparing the 4 groups, the Y‐RIMA/RA groups revealed a higher number of distal anastomosis than the in situ on‐ or off‐pump groups. When the number of distal arterial anastomosis was analyzed, there was a superiority of using the Y‐configuration compared with the in situ approach. Moreover, there were no significant differences among groups for mortality and/or major adverse cardiac and cerebrovascular events in hospital or at 30‐day follow‐up. A subanalysis comparing the Y‐RIMA group with the Y‐RA group showed that complementary grafts to the Y‐construct were required to accomplish full revascularization more frequently in the Y‐RIMA group. Full‐arterial revascularization was achieved in 92.2% of the Y‐RA group and 72.0% of the Y‐RIMA group (P<0.001). In 82.8% of the Y‐RA group and 30.8% of the Y‐RIMA group, revascularization was completed as an anaortic procedure (P<0.001).

Conclusions

The 2 types of arterial Y‐composite grafting were able to be introduced in the routine practice of our institution showing comparable results to the established institutional practice. This procedure allowed for more arterial distal anastomosis to be performed safely without compromising outcomes.

Systematic Approach to the Calcified Mitral Valve Apparatus at Time of Mitral Valve Replacement

Mitral annular calcification (MAC) represents a surgical challenge to mitral valve replacement. The presence of MAC at the time of mitral valve replacement is associated with perivalvular leak and atrial-ventricular groove injury. Although percutaneous and hybrid approaches may offer alternatives to surgical mitral valve replacement, the early and late results from these techniques remain unknown. As such, the surgical management of MAC remains relevant in the contemporary treatment of patients with MAC. Herein, we present a systematic approach to the management of MAC at the time of mitral valve replacement.

GATA6 Regulates Aortic Valve Remodeling, and Its Haploinsufficiency Leads to Right-Left Type Bicuspid Aortic Valve

BACKGROUND

Bicuspid aortic valve (BAV), the most common congenital heart defect affecting 1% to 2% of the population, is a major risk factor for premature aortic valve disease and accounts for the majority of valve replacement. The genetic basis and mechanisms of BAV etiology and pathogenesis remain largely undefined.

METHODS

Cardiac structure and function was assessed in mice lacking a Gata6 allele. Human GATA6 gene variants were analyzed in 452 BAV cases from the BAV consortium and 1849 controls from the Framingham GWAS (Genome Wide Association Study). GATA6 expression was determined in mice and human tissues using quantitative real-time polymerase chain reaction and immunohistochemistry. Mechanistic studies were carried out in cultured cells.

RESULTS

Gata6 heterozygous mice have highly penetrant right-left (RL)-type BAV, the most frequent type in humans. GATA6 transcript levels are lower in human BAV compared with normal tricuspid valves. Mechanistically, Gata6 haploinsufficiency disrupts valve remodeling and extracellular matrix composition through dysregulation of important signaling molecules, including matrix metalloproteinase 9. Cell-specific inactivation of Gata6 reveals an essential role for GATA6 in secondary heart field myocytes because loss of 1 Gata6 allele from Isl- 1-positive cells-but not from endothelial or neural crest cells-recapitulates the phenotype of Gata6 heterozygous mice.

CONCLUSIONS

The data identify a new cellular and molecular mechanism underlying BAV. The availability of an animal model for the most frequent human BAV opens the way for the elucidation of BAV pathogenesis and the development of much needed therapies.

From embryogenesis to adulthood: Critical role for GATA factors in heart development and function

Cardiac development is governed by a complex network of transcription factors (TFs) that regulate cell fates in a spatiotemporal manner. Among these, the GATA family of zinc finger TFs plays prominent roles in regulating the development of the myocardium, endocardium, and outflow tract. This family comprises six members three of which, GATA4, 5, and 6, are predominantly expressed in cardiac cells where they activate specific downstream gene targets via interactions with one another and with other TFs and signaling molecules. Their critical function in heart formation is evidenced by the phenotypes of animal models lacking these factors and by the broad spectrum of human congenital heart diseases associated with mutations in their genes. Similarly, in the postnatal heart, these proteins play significant and nonredundant roles in cardiac function, regulating adaptive stress responses including cardiomyocyte hypertrophy and survival, as well as endothelial homeostasis and angiogenesis. As such, decreased expression of either GATA4, 5, or 6 results in impaired cardiovascular homeostasis and increased risk of premature and serious cardiovascular events such as hypertension, arrhythmia, aortopathy, and heart failure. Although a great deal of progress has been made in understanding GATA-dependent regulatory processes in the heart, the molecular mechanisms underlying the specificity of GATA factors and their upstream regulation remain incompletely understood. The knowledge and tools developed since their discovery 25 years ago should accelerate progress toward further elucidation of their mechanisms of action in health and disease. This in turn will greatly improve diagnosis and care for the millions of individuals affected by congenital and acquired cardiac disease worldwide.

Glutaredoxin-2 controls cardiac mitochondrial dynamics and energetics in mice, and protects against human cardiac pathologies

Glutaredoxin 2 (GRX2), a mitochondrial glutathione-dependent oxidoreductase, is central to glutathione homeostasis and mitochondrial redox, which is crucial in highly metabolic tissues like the heart. Previous research showed that absence of Grx2, leads to impaired mitochondrial complex I function, hypertension and cardiac hypertrophy in mice but the impact on mitochondrial structure and function in intact cardiomyocytes and in humans has not been explored. We hypothesized that Grx2 controls cardiac mitochondrial dynamics and function in cellular and mouse models, and that low expression is associated with human cardiac dysfunction. Here we show that Grx2 absence impairs mitochondrial fusion, ultrastructure and energetics in primary cardiomyocytes and cardiac tissue. Moreover, provision of the glutathione precursor, N-acetylcysteine (NAC) to Grx2-/- mice did not restore glutathione redox or prevent impairments. Using genetic and histopathological data from the human Genotype-Tissue Expression consortium we demonstrate that low GRX2 is associated with fibrosis, hypertrophy, and infarct in the left ventricle. Altogether, GRX2 is important in the control of cardiac mitochondrial structure and function, and protects against human cardiac pathologies.

Inhibition of Cardiomyogenesis in Embryocarcinoma Cells Induced by Long-Term High Level of Glucose

BACKGROUND/AIMS

Cardiac myocytes constitute the first differentiated cell type during mammalian heart formation with the ability to beat spontaneously and rhythmically. Hyperglycemia is a primary risk factor for cardiovascular disease in pre-gestational diabetes mellitus (PGDM). However, the impact that hyperglycemia has on cardiac progenitors or on precursors differentiation remains poorly understood. The aim of the present study is to investigate whether hyperglycemia affects cardiomyogenesis of embryocarcinoma cells.

METHODS

P19CL6 cells differentiation induced by 1% DMSO was evaluated under either normal glucose (5.6 mmol/L) or high level of glucose concentrations (20 mmol/L or 40 mmol/L). To investigate the effect of long-term high level of glucose on cardiomyocytes differentiation, sarcomeric α-actinin, peroxisome proliferator-activated receptor coactivator-1 (PGC-1α), transcription factor GATA4 and Nkx2.5 were assessed by qRT-PCR analysis, western blot and immunofluorescence.

RESULTS

We observed that long-term high level of glucose markedly reduced P19CL6 cells differentiation into cardiomyocytes. The change in PGC-1α expression was consistent with changes in cardiac muscle myosin expression after exposure to 20 mmol/L or 40 mmol/L of glucose. On the other hand, the high level of glucose concentration profoundly decreased both GATA4 and Nkx2-5 expressions from day 6 to day 12 after differentiation, which was induced by 1% DMSO.

CONCLUSION

Our results elucidate that the effect resulting from the long-term exposure of cardiac progenitors to high level of glucose is associated with decreased expression of GATA4 and Nkx2.5, providing a novel mechanism by which high glucose is able to affect cell differentiation.

GATA5 mutation homozygosity linked to a double outlet right ventricle phenotype in a Lebanese patient

Background

GATA transcription factors are evolutionary conserved zinc finger proteins with multiple roles in cell differentiation/proliferation and organogenesis. GATA5 is only transiently expressed in the embryonic heart, and the inactivation of both Gata5 alleles results in a partially penetrant bicuspid aortic valve (BAV) phenotype in mice. We hypothesized that only biallelic mutations in GATA5 could be disease causing.

Methods

A total of 185 patients with different forms of congenital heart disease (CHD) were screened along 150 healthy individuals for GATA4, 5, and 6. All patients' phenotypes were diagnosed with echocardiography.

Results

Sequencing results revealed eight missense variants (three of which are novel) in cases with various conotruncal and septal defects. Out of these, two were inherited in recessive forms: the p.T67P variant, which was found both in patients and in healthy individuals, and the previously described p.Y142H variant which was only found in a patient with a double outlet right ventricle (DORV). We characterized the p.Y142H variant and showed that it significantly reduced the transcriptional activity of the protein over cardiac promoters by 30–40%.

Conclusion

Our results do prove that p.Y142H is associated with DORV and suggests including GATA5 as a potential gene to be screened in patients with this phenotype.

GATA4 loss-of-function mutations underlie familial tetralogy of fallot

Tetralogy of Fallot (TOF) represents the most common form of cyanotic congenital heart disease and accounts for significant morbidity and mortality in humans. Emerging evidence has implicated genetic defects in the pathogenesis of TOF. However, TOF is genetically heterogeneous and the genetic basis for TOF in most patients remains unclear. In this study, the GATA4 gene were sequenced in 52 probands with familial TOF, and three novel heterozygous mutations, including A9P and L51V both located in the putative first transactivational domain and N285S in the C-terminal zinc finger, were identified in three probands, respectively. Genetic analysis of the pedigrees demonstrated that in each family the mutation cosegregated with TOF with complete penetrance. The missense mutations were absent in 800 control chromosomes and the altered amino acids were highly conserved evolutionarily. Functional analysis showed that the GATA4 mutants were consistently associated with diminished DNA-binding affinity and decreased transcriptional activity. Furthermore, the N285S mutation completely disrupted the physical interaction between GATA4 and TBX5. To our knowledge, this report associates GATA4 loss-of-function mutations with familial TOF for the first time, providing novel insight into the molecular mechanism involved in TOF and suggesting potential implications for the early prophylaxis and allele-specific therapy of TOF.