The Role of Fatty Acid Synthase in the Vascular Smooth Muscle Cell to Foam Cell Transition

Vascular smooth muscle cells (VSMCs), in their contractile and differentiated state, are fundamental for maintaining vascular function. Upon exposure to cholesterol (CHO), VSMCs undergo dedifferentiation, adopting characteristics of foam cells-lipid-laden, macrophage-like cells pivotal in atherosclerotic plaque formation. CHO uptake by VSMCs leads to two primary pathways: ABCA1-mediated efflux or storage in lipid droplets as cholesterol esters (CEs). CE formation, involving the condensation of free CHO and fatty acids, is catalyzed by sterol O-acyltransferase 1 (SOAT1). The necessary fatty acids are synthesized by the lipogenic enzyme fatty acid synthase (FASN), which we found to be upregulated in atherosclerotic human coronary arteries. This observation led us to hypothesize that FASN-mediated fatty acid biosynthesis is crucial in the transformation of VSMCs into foam cells. Our study reveals that CHO treatment upregulates FASN in human aortic SMCs, concurrent with increased expression of CD68 and upregulation of KLF4, markers associated with the foam cell transition. Crucially, downregulation of FASN inhibits the CHO-induced upregulation of CD68 and KLF4 in VSMCs. Additionally, FASN-deficient VSMCs exhibit hindered lipid accumulation and an impaired transition to the foam cell phenotype following CHO exposure, while the addition of the fatty acid palmitate, the main FASN product, exacerbates this transition. FASN-deficient cells also show decreased SOAT1 expression and elevated ABCA1. Notably, similar effects are observed in KLF4-deficient cells. Our findings demonstrate that FASN plays an essential role in the CHO-induced upregulation of KLF4 and the VSMC to foam cell transition and suggest that targeting FASN could be a novel therapeutic strategy to regulate VSMC phenotypic modulation.

Exploring the Mechanism of Buyang Huanwu Decoction Alleviating Restenosis by Regulating VSMC Phenotype Switching and Proliferation by Network Pharmacology and Molecular Docking

BACKGROUND

Buyang Huanwu Decoction (BHD) is used to regulate blood circulation and clear collaterals and is widely used in coronary heart disease. However, the active compounds and the mechanism of BHD used to treat restenosis are less understood.

OBJECTIVE

The study aimed to explore the potential mechanism of Buyang Huanwu decoction (BHD) for the treatment of restenosis using network pharmacology and molecular docking experiments. Methods： The bioactive components of BHD and their corresponding targets were retrieved from the Traditional Chinese Medicine Systems Pharmacology (TCMSP) and Encyclopaedia of Traditional Chinese Medicine (ETCM) databases as well as literature. Restenosis-associated therapeutic genes were identified from the OMIM, Drugbank, GEO, and DisGeNET databases. Genes related to the vascular smooth muscle cell (VSMC) phenotype were obtained from the gene ontology (GO) database and literature. The core target genes for the drug-disease-VSMC phenotype were identified using the Venn tool and Cytoscape software. Moreover, the "drug-component-target-pathway" network was constructed and analyzed, and pathway enrichment analysis was performed. The connection between the main active components and core targets was analyzed using the AutoDock tool, and PyMOL was used to visualize the results. Result：The "compound-target-disease" network included 80 active ingredients and 599 overlapping targets. Among the bioactive components, quercetin, ligustrazine, ligustilide, hydroxysafflor yellow A, and dihydrocapsaicin had high degree values, and the core targets included TP53, MYC, APP, UBC, JUN, EP300, TGFB1, UBB, SP1, MAPK1, SMAD2, CTNNB1, FOXO3, PIN1, EGR1, TCF4, FOS, SMAD3, and CREBBP. A total of 365 items were obtained from the GO functional enrichment analysis (P < 0.05), whereas the enrichment analysis of the KEGG pathway identified 30 signaling pathways (P < 0.05), which involved the TGF-β signaling pathway, Wnt signaling pathway, TRAF6-mediated induction of NF-κB and MAPK pathway, TLR7/8 cascade, and others. The molecular docking results revealed quercetin, luteolin, and ligustilide to have good affinity with the core targets MYC and TP53. Conclusion：The active ingredients in BHD might act on TP53, MYC, APP, UBC, JUN, and other targets through its active components (such as quercetin, ligustrazine, ligustilide, hydroxysafflor yellow A, and dihydrocapsaicin). This action of BHD may be transmitted via the involvement of multiple signaling pathways, including the TGF-β signaling pathway, Wnt signaling pathway, TRAF6-mediated induction of NF-κB and MAPK pathway, and TLR7/8 cascade, to treat restenosis by inhibiting the phenotype switching and proliferation of VSMC.

Tracing G-Protein-Mediated Contraction and Relaxation in Vascular Smooth Muscle Cell Spheroids

Analyses of G-protein-mediated contraction and relaxation of vascular smooth muscle cells (VSMCs) are usually hampered by a rigid growth surface and culture conditions promoting cell proliferation and a less contractile phenotype. Our studies indicated that mouse aortic VSMCs cultured in three-dimensional spheroids acquire a quiescent contractile status while decreasing the baseline G-protein-dependent inositolphosphate formation and increasing the expression of endothelin receptor type A (Ednra). Endothelin-1 (ET-1) promoted inositolphosphate formation in VSMC spheroids, but not in VSMCs cultured under standard conditions. To trace ET-1-mediated contraction of VSMC spheroids, we developed an assay by adhering them to collagen hydrogels and recording structural changes by time-lapse microscopy. Under these conditions, mouse and human VSMC spheroids contracted upon treatment with ET-1 and potassium chloride or relaxed in response to caffeine and the prostacyclin analogue Iloprost. ET-1 activated AKT-, MKK1-, and MKK3/6-dependent signaling cascades, which were inhibited by an overexpressing regulator of G-protein signaling 5 (Rgs5) to terminate the activity of Gα subunits. In summary, culture of VSMCs in three-dimensional spheroids lowers baseline G-protein activity and enables analyses of both contraction and relaxation of mouse and human VSMCs. This model serves as a simple and versatile tool for drug testing and investigating G-protein-depending signaling.

RGS5 Attenuates Baseline Activity of ERK1/2 and Promotes Growth Arrest of Vascular Smooth Muscle Cells

The regulator of G-protein signaling 5 (RGS5) acts as an inhibitor of Gαq/11 and Gαi/o activity in vascular smooth muscle cells (VSMCs), which regulate arterial tone and blood pressure. While RGS5 has been described as a crucial determinant regulating the VSMC responses during various vascular remodeling processes, its regulatory features in resting VSMCs and its impact on their phenotype are still under debate and were subject of this study. While Rgs5 shows a variable expression in mouse arteries, neither global nor SMC-specific genetic ablation of Rgs5 affected the baseline blood pressure yet elevated the phosphorylation level of the MAP kinase ERK1/2. Comparable results were obtained with 3D cultured resting VSMCs. In contrast, overexpression of RGS5 in 2D-cultured proliferating VSMCs promoted their resting state as evidenced by microarray-based expression profiling and attenuated the activity of Akt- and MAP kinase-related signaling cascades. Moreover, RGS5 overexpression attenuated ERK1/2 phosphorylation, VSMC proliferation, and migration, which was mimicked by selectively inhibiting Gαi/o but not Gαq/11 activity. Collectively, the heterogeneous expression of Rgs5 suggests arterial blood vessel type-specific functions in mouse VSMCs. This comprises inhibition of acute agonist-induced Gαq/11/calcium release as well as the support of a resting VSMC phenotype with low ERK1/2 activity by suppressing the activity of Gαi/o.

Oxidative stress modulates vascular smooth muscle cell phenotype via CTGF in thoracic aortic aneurysm

AIMS

Dissection and rupture of the ascending aorta are life-threatening conditions resulting in 80% mortality. Ascending aortic replacement in patients presenting with thoracic aortic aneurysm (TAA) is determined by metric measurement. However, a significant number of dissections occur outside of the parameters suggested by the current guidelines. We investigate the correlation among altered haemodynamic condition, oxidative stress, and vascular smooth muscle cell (VSMC) phenotype in controlling tissue homoeostasis.

METHODS AND RESULTS

We demonstrate using finite element analysis (FEA) based on computed tomography geometries that TAA patients have higher wall stress in the ascending aorta than non-dilated patients. We also show that altered haemodynamic conditions are associated with increased levels of reactive oxygen species (ROS), direct regulators of the VSMC phenotype in the microregional area of the ascending aorta. Using in vitro and ex vivo studies on human tissues, we show that ROS accumulation correlates with media layer degeneration and increased connective tissue growth factor (CTGF) expression, which modulate the synthetic VSMC phenotype. Results were validated by a murine model of TAA (C57BL/6J) based on Angiotensin II infusion showing that medial thickening and luminal expansion of the proximal aorta is associated with the VSMC synthetic phenotype as seen in human specimens.

CONCLUSIONS

Increased peak wall stress correlates with change in VSMC towards a synthetic phenotype mediated by ROS accumulation via CTGF. Understanding the molecular mechanisms that regulate VSMC towards a synthetic phenotype could unveil new regulatory pathways of aortic homoeostasis and impact the risk-stratification tool for patients at risk of aortic dissection and rupture.