Smooth Muscle Cell Phenotypic Modulation Research Articles

Smooth muscle α-actin missense variant promotes atherosclerosis through modulation of intracellular cholesterol in smooth muscle cells.

The variant p.Arg149Cys in ACTA2, which encodes smooth muscle cell (SMC)-specific α-actin, predisposes to thoracic aortic disease and early onset coronary artery disease in individuals without cardiovascular risk factors. This study investigated how this variant drives increased atherosclerosis. Apoe-/- mice with and without the variant were fed a high-fat diet for 12 weeks, followed by evaluation of atherosclerotic plaque formation and single-cell transcriptomics analysis. SMCs explanted from Acta2R149C/+ and wildtype (WT) ascending aortas were used to investigate atherosclerosis-associated SMC phenotypic modulation. Hyperlipidemic Acta2R149C/+Apoe-/- mice have a 2.5-fold increase in atherosclerotic plaque burden compared to Apoe-/- mice with no differences in serum lipid levels. At the cellular level, misfolding of the R149C α-actin activates heat shock factor 1, which increases endogenous cholesterol biosynthesis and intracellular cholesterol levels through increased HMG-CoA reductase (HMG-CoAR) expression and activity. The increased cellular cholesterol in Acta2R149C/+ SMCs induces endoplasmic reticulum stress and activates PERK-ATF4-KLF4 signaling to drive atherosclerosis-associated phenotypic modulation in the absence of exogenous cholesterol, while WT cells require higher levels of exogenous cholesterol to drive phenotypic modulation. Treatment with the HMG-CoAR inhibitor pravastatin successfully reverses the increased atherosclerotic plaque burden in Acta2R149C/+Apoe-/- mice. These data establish a novel mechanism by which a pathogenic missense variant in a smooth muscle-specific contractile protein predisposes to atherosclerosis in individuals without hypercholesterolemia or other risk factors. The results emphasize the role of increased intracellular cholesterol levels in driving SMC phenotypic modulation and atherosclerotic plaque burden.

MiR-342-5p promotes vascular smooth muscle cell phenotypic transition through a negative-feedback regulation of Notch signaling via targeting FOXO3

AimUnder various pathological conditions such as cancer, vascular smooth muscle cells (vSMCs) transit their contractile phenotype into phenotype(s) characterized by proliferation and secretion, a process called vSMC phenotypic transition (vSMC-PT). Notch signaling regulates vSMC development and vSMC-PT. This study aims to elucidate how the Notch signal is regulated. Main methodsGene-modified mice with a SM22α-CreERT2 transgene were generated to activate/block Notch signaling in vSMCs. Primary vSMCs and MOVAS cells were cultured in vitro. RNA-seq, qRT-PCR and Western blotting were used to evaluated gene expression level. EdU incorporation, Transwell and collagen gel contraction assays were conducted to determine the proliferation, migration and contraction, respectively. Key findingsNotch activation upregulated, while Notch blockade downregulated, miR-342-5p and its host gene Evl in vSMCs. However, miR-342-5p overexpression promoted vSMC-PT as shown by altered gene expression profile, increased migration and proliferation, and decreased contraction, while miR-342-5p blockade exhibited the opposite effects. Moreover, miR-342-5p overexpression significantly suppressed Notch signaling, and Notch activation partially abolished miR-342-5p-induced vSMC-PT. Mechanically, miR-342-5p directly targeted FOXO3, and FOXO3 overexpression rescued miR-342-5p-induced Notch repression and vSMC-PT. In a simulated tumor microenvironment, miR-342-5p was upregulated by tumor cell-derived conditional medium (TCM), and miR-342-5p blockade abrogated TCM-induced vSMC-PT. Meanwhile, conditional medium from miR-342-5p-overexpressing vSMCs significantly enhanced tumor cell proliferation, while miR-342-5p blockade had the opposite effects. Consistently, in a co-inoculation tumor model, miR-342-5p blockade in vSMCs significantly delayed tumor growth. SignificancemiR-342-5p promotes vSMC-PT through a negative-feedback regulation of Notch signaling via downregulating FOXO3, which could be a potential target for cancer therapy.

Abstract 703: Dioxin-induced Smooth Muscle Cell Phenotypic Modulation And Atherosclerosis Worsens In The Absence Of AHR

Background: Dioxin (TCDD, 2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin) is an active constituent of tobacco smoke and air pollution that activates the aryl hydrocarbon receptor (AHR). Dioxin has been linked to an increased risk of coronary artery disease (CAD). However, the corresponded molecular mechanisms remain unclear. Smooth muscle cells (SMC) play a critical role in atherosclerotic plaque remodeling due to their phenotypic plasticity. In this study, we aimed to understand the role of AHR in modulating the effect of dioxin on vascular SMC and atherosclerosis phenotype. Methods: SMC lineage-tracing (SMC Lin ) mice ( Tg Myh11-CreERT2 , ROSA tdT/tdT , ApoE -/- ) without any TCDD injection were used as control. TCDD were injected to both SMC Lin mice, and SMC-specific Ahr knockout mice. High fat diet (HFD) and TCDD injection started at 8 weeks of age and aortic roots were harvested at 24 weeks of age for either histology or single-cell sequencing (10X Genomics, triplicates). Histology analysis was performed at the aortic sinus of control mice (n=9), TCDD injected SMC Lin mice (n=12) and TCDD injected SMC-specific Ahr knockout mice (n=9). Immunohistochemistry was performed with anti-SM22α antibody and CD68 antibody. Results: The histological analysis of the aortic sinus showed increased lesion area after TCDD treatment in the SMC Lin control mice. In the SMC-specific knockout of Ahr , the lesion area was significantly larger compared to the SMC Lin control mice when treated with TCDD along with significantly increased presence of Tagln + cells in the lesion. These results indicated TCDD leads to adverse remodeling of atherosclerosis and that the presence of Ahr gene is protective against the athero-promoting effects of dioxin. The scRNA-seq of SMC Lin control mice treated with TCDD exposure showed that the SMC phenotypic modulation was markedly inhibited, leading to the presence of fewer fibromyocytes (FMC). Increased FMC to chondromyocytes (CMC) modulation resulted in further reduction of FMC population in the Ahr -KO mice treated with TCDD. Conclusion: Dioxin adversely remodels atherosclerotic plaque, and the lack of AHR in SMC can exacerbate the atherosclerotic process, suggesting that dioxin may exhibit its harmful effect via non-AHR dependent pathway.

Abstract 341: Study Of ADAR1 Implicates RNA Editing In Vascular Smooth Muscle Cells As A Mechanism Of Coronary Artery Disease Risk

Adenosine-to-inosine (A-to-I) RNA editing is a common RNA modification catalyzed by ADAR (adenosine deaminase acting on RNA) enzymes. ADAR1 serves a crucial function to edit double stranded RNA (dsRNA) molecules to prevent activation of the dsRNA sensor MDA5 ( IFIH1 ) that stimulates an interferon stimulated gene (ISG) response. Discoveries in human genetics now implicate deficient ADAR1 RNA editing as a causal mechanism in coronary artery disease (CAD). We hypothesize that smooth muscle cell (SMC) specific RNA editing is required to prevent vascular calcification and inflammation. Here, we demonstrate that ADAR1 is the master regulator of RNA editing in primary human coronary artery SMC (HCASMC). ADAR1 KD in HCASMC causes an ISG response characterized by massive upregulation of key ISG genes (e.g. ISG15, IFI6, IFIH1 ). Importantly, ADAR1 KD stimulates the upregulation of genes with known roles in SMC phenotypic transition and CAD risk, including KLF4 , TCF21 , ATF3 , and ZEB2 . This effect is dependent on activation of MDA5. Additionally, we demonstrate ADAR1 and MDA5 regulate SMC phenotypic modulation and calcification in vitro where ADAR1 KD inhibits SMC maturation and dysregulates the calcification gene program in an MDA5 dependent manner. Using scRNAseq data collected from human vascular tissue we show that immunogenic dsRNA are disproportionately expressed in human SMC in atherosclerosis. Similarly, in atherosclerosis prone mice, scRNAseq analysis reveals SMC to have increasing ISG expression as cells transition from mature SMC to a more calcified chondromyocyte phenotype — consistent with MDA5 activation. To further evaluate the role for SMC specific RNA editing in vivo, we generated a conditional SMC specific Adar1 KD mouse ( Adar1 flox/flox , Myh11 CreERT2 , ROSA tdT/+ ). At 2 weeks following SMC- Adar1 KD, mice demonstrate a severe phenotype of elastin degradation and disarray, intravascular hemorrhage, and inflammatory cell infiltration in the aortic wall. This effect was not seen with an endothelial cell specific deletion model ( Adar1 flox/flox , Cx40 CreERT2 ). Here we provide key evidence to support the observations from human genetics that the ADAR1-dsRNA-MDA5 axis is a causal mechanism in vascular disease and warrants further investigation.

Abstract 284: Pro-Inflammatory Adventitial Fibroblast Contribute To Aortic Aneurysms In Loeys Dietz Syndrome

Introduction: Vascular smooth muscle cell (SMC) phenotype modulation is implicated in thoracic aneurysm formation, however, the role of adventitial fibroblasts (AdvFib) in aneurysm formation remains poorly characterized. Loeys-Dietz Syndrome (LDS), caused by a spectrum of mutations in the TGF-β signaling cascade, leads to aggressive thoracic aneurysms. Given the ubiquitous nature of TGF-β signaling machinery, the exact cell type(s) responsible for initiation of LDS pathogenesis is poorly understood. Methods: We performed single cell transcriptomic characterization of aortic root and ascending aortic samples from LDS patients ((n=6 LDS (harboring TGFB2 , TGFBR1 , TGFBR2 , or SMAD3 mutation); n=2 Donor control)) as well as root/ascending aorta from a murine model of LDS ( Tgfbr2 G357W/+ ) to understand cell-state transitions and transcriptomic alterations in LDS. Results: Single cell RNA sequencing (scRNAseq) of human and mice LDS samples (in total >40,000 cells) revealed a secondary pattern of cellular activation in LDS as compared to Marfan Syndrome. Instead of SMC phenotypic modulation as seen in MFS, LDS appears to preferentially modulate adventitial fibroblasts (AdvFib) phenotype in the Tgfbr2 G357W/+ mouse model. Human LDS patient’s AdvFib turn on high levels of macrophage-recruiting pro-inflammatory cytokines CCL2 and HLA-B, with a corresponding 1.8-fold increase in LDS aortic wall macrophages compared to Donor. A more extreme pattern was observed in the Tgfbr2 G357W/+ LDS mouse model. While Tgfbr2 G357W/+ SMC are transcriptomically similar to wild type counterparts, AdvFib were activated into a pro-inflammatory state associated with increased aortic macrophage recruitment ( Ccl2 , Il6 , Vcam1, and Cxcl2 ) and fibrotic response ( Col1a1 , Col1a2 , Col3a1, and Fn1 ). A 6-fold increase in the number of aortic wall macrophages was identified in Tgfbr2 G357W/+ compared to WT. Conclusions: LDS mouse and human AdvFib undergo phenotypic alterations into a pro-inflammatory state evidenced by increased expression of numerous cytokines, macrophage recruitment, and ECM deposition. AdvFib, in addition to SMCs, are potentially another important pathological cell population in LDS aneurysm formation.

Smooth Muscle Cell Klf4 Expression Is Not Required for Phenotype Modulation or Aneurysm Formation in Marfan Syndrome Mice-Brief Report.

Smooth muscle cell (SMC) phenotypic reprogramming toward a mixed synthetic-proteolytic state is a central feature of aortic root aneurysm in Marfan syndrome (MFS). Previous work identified Klf4 as a potential mediator of SMC plasticity in MFS. MFS (Fbn1C1041G/+) mouse strains with an inducible vascular SMC fluorescent reporter (MFSSMC) with or without SMC-specific deletion of Klf4 exons 2 to 3 (MFSSMC-Klf4Δ) were generated. Simultaneous SMC tracing and Klf4 loss-of-function (Klf4Δ mice) was induced at 6 weeks of age. Aneurysm growth was assessed via serial echocardiography (4-24 weeks). Twenty-four-week-old mice were assessed via histology, RNA in situ hybridization, and aortic single-cell RNA sequencing. MFS mice demonstrated progressive aortic root dilatation compared with control (WTSMC) mice regardless of Klf4 genotype (P<0.001), but there was no difference in aneurysm growth in MFSSMC-Klf4Δ versus MFSSMC (P=0.884). Efficient SMC Klf4 deletion was confirmed via lineage-stratified genotyping, RNA in situ hybridization, and immunohistochemistry. Single-cell RNA sequencing of traced SMCs revealed a highly similar pattern of phenotype modulation marked by loss of contractile markers (eg, Myh11, Cnn1) and heightened expression of matrix genes (eg, Col1a1, Fn1) between Klf4 genotypes. Pseudotemporal quantitation of SMC dedifferentiation confirmed that Klf4 deletion did not alter the global extent of phenotype modulation, but reduced expression of 23 genes during this phenotype transition in MFSSMC-Klf4Δmice, including multiple chondrogenic genes expressed by only the most severely dedifferentiated SMCs (eg, Cytl1, Tnfrsf11b). Klf4 is not required to initiate SMC phenotype modulation in MFS aneurysm but may exert regulatory control over chondrogenic genes expressed in highly dedifferentiated SMCs.

Meet the First Authors.

Meet the First Authors.

Age-dependent phenotypic modulation of smooth muscle cells in the normal ascending aorta.

Ascending aortic aneurysms are associated with pre-existing conditions, including connective tissue disorders (i.e., Marfan syndrome) and bicuspid aortic valves. The underlying mechanisms remain uncertain. Even less is known regarding ascending aortic aneurysms in individuals with normal (i.e., tricuspid) aortic valves (TAV), and without known aneurysm-associated disorders. Regardless of etiology, the risk of aortic complications increases with biological age. Phenotypic modulation of smooth muscle cells (SMCs) is a feature of ascending aortic aneurysms, whereby contractile SMCs are replaced with synthetic SMCs that are capable of degrading the aortic wall. We asked whether age itself causes dysfunctional SMC phenotype modulation, independent of aortic dilatation or pre-existing aneurysm-associated diseases. Non-dilated ascending aortic samples were obtained intra-operatively from 40 patients undergoing aortic valve surgery (range: 20-82 years old, mean: 59.1 ± 15.2). Patients with known genetic diseases or aortic valve malformations were excluded. Tissue was divided, and a portion was formalin-fixed and immunolabeled for alpha-smooth muscle actin (ASMA), a contractile SMC protein, and markers of synthetic (vimentin) or senescent (p16/p21) SMCs. Another fragment was used for SMC isolation (n = 10). Cultured SMCs were fixed at cell passage 2 and stained for phenotype markers, or were cultured indefinitely to determine replicative capacity. In whole tissue, ASMA decreased (R2 = 0.47, P < 0.0001), while vimentin increased (R2 = 0.33, P = 0.02) with age. In cultured SMCs, ASMA decreased (R2 = 0.35, P = 0.03) and vimentin increased (R2 = 0.25, P = 0.04) with age. p16 (R2 = 0.34, P = 0.02) and p21 (R2 = 0.29, P = 0.007) also increased with age in SMCs. Furthermore, the replicative capacity of SMCs from older patients was decreased compared to that of younger patients (P = 0.03). By investigating non-dilated aortic samples from individuals with normal TAVs, we found that age itself has a negative impact on SMCs in the ascending aortic wall, whereby SMCs switched from the contractile phenotype to maladaptive synthetic or senescent states with increased age. Therefore, based on our findings, modification of SMC phenotype should be studied as a therapeutic consideration against aneurysms in the future, regardless of etiology.

The Autotaxin-LPA Axis Emerges as a Novel Regulator of Smooth Muscle Cell Phenotypic Modulation during Intimal Hyperplasia.

Neointimal hyperplasia is characterized by a loss of the contractile phenotype of vascular smooth muscle cells (VSMCs). Our group has recently shown that VSMC proliferation and migration are mediated by lysophosphatidic acid (LPA) during restenosis, but the role of autotaxin (ATX; lysophospholipase D), which produces LPA, remains unclear. Endothelial denudation of the mouse carotid artery was performed to induce neointimal hyperplasia, and the extent of damage caused by the ATX-LPA axis was assessed in VSMCs. We observed the upregulation of ATX activity (p < 0.0002) in the injured carotid artery using an AR2 probe fluorescence assay. Further, the tissue carotid LPA levels were elevated 2.7-fold in carotid vessels, augmenting neointimal hyperplasia. We used an electrical cell-substrate impedance sensor (ECIS) to measure VSMC proliferation and migration. Treatment with an ATX inhibitor (PF8380) or LPA receptor inhibitor (Ki16425) attenuated VSMC proliferation (extracellular signal-regulated kinases) activity and migration in response to recombinant ATX. Indeed, PF8380 treatment rescued the aggravated post-wire injury neointima formation of carotid arteries. The upregulation of ATX following vessel injury leads to LPA production in VSMCs, favoring restenosis. Our observations suggest that inhibition of the ATX-LPA axis could be therapeutically targeted in restenosis to minimize VSMC phenotypic modulation and inflammation after vascular injury.

MiRNA‑92a inhibits vascular smooth muscle cell phenotypic modulation and may help prevent in‑stent restenosis.

The modulation of vascular smooth muscle cell (VSMC) phenotype during cellular proliferation and migration may represent a potential therapeutic approach for vascular intimal hyperplasia prevention. However, the precise role of this process in VSMC biology and remodeling remains unclear. In the present study, western blotting, PCR, MTT and Transwell assays were used to analyze related protein and mRNA expression, cell viability and cell migration, respectively. It was demonstrated that miR‑92a modulated VSMCs into a synthetic phenotype via the Kruppel‑like factor 4 (KLF4) pathway. Targeting microRNA (miRNA/miR)‑92a in VSMCs using a KLF4 inhibitor suppressed the synthetic phenotype and inhibited VSMC proliferation and migration. To further confirm this finding, the expression levels of miR‑92a were measured in patients undergoing coronary artery intervention. The serum miR‑92a expression levels were significantly higher in patients with in‑stent restenosis (ISR) compared with those in patients without ISR, whereas KLF4 expression was significantly reduced in the non‑ISR group. Bioinformatic analysis and promoter‑luciferase reporter assays were used to examine the regulatory mechanisms underlying KLF4 expression. KLF4 was demonstrated to be transcriptionally upregulated by miR‑92a in VSMCs. miRNA transfection was also performed to regulate the level of miR‑92a expression. miR‑92a overexpression inhibited VSMC proliferation and migration, and also increased the mRNA and protein expression levels of certain differentiated VSMC‑related genes. Finally, miR‑92a inhibition promoted the proliferation and migration of VSMCs, which could be reversed using a KLF4 inhibitor. Collectively, these results indicated that the local delivery of a KLF4 inhibitor may act as a novel therapeutic option for the prevention of ISR.

Abstract 11748: Prophylactic Aortic Arch Replacement in Patients With Loeys-Dietz Syndrome: Surgical Outcomes and Molecular Rationale

Introduction: Loeys-Dietz syndrome (LDS) patients typically develop focal aortic root aneurysm but have substantial risk of distal aortic events (arch aneurysm and type B dissection) after root replacement. We offer prophylactic arch replacement to LDS patients of all genotypes undergoing elective valve-sparing aortic root replacement (VSARR) to prevent late aortic events. We hypothesized that non-dilated LDS aortic arch tissue demonstrates ongoing deterioration at the time of VSARR. Methods: Aortic tissue was anatomically segmented (root, ascending, arch) then examined via histology and single-cell RNA sequencing (‘scRNAseq’, n=4 patients) to comprehensively profile cellular phenotypes. Results: LDS patients (n=8, mean age 37.9 years, 87.5% male) had root aneurysm (mean 45.1 ± 8.9mm) without ascending (35.1± 7.8mm) or arch dilation (28.7 ± 2.8mm) and underwent concurrent VSARR and branched graft total arch replacement. There were no perioperative deaths or strokes and no distal aortic events or reoperations after median 1.26 years follow-up. Histologically, elastin fragmentation and collagen deposition were detectable in each aortic segment (n=4). scRNAseq identified a continuum of smooth muscle cell (SMC) phenotype modulation associated with progressively reduced contractile gene expression. Pathway analysis of 260 genes enriched during SMC modulation identified heightened integrin signaling, transforming growth factor-beta-responsiveness, cell adhesion, and extracellular matrix remodeling. Histologic confirmation using RNA probes specific for modulated SMCs (TGF-beta responsive gene SERPINE1 and glycoprotein TNFRSF11B ) identified these cells in the tunica media layer of each aortic segment, with greatest density in the root aneurysm but extending to the arch. In age-matched donor aortas, TNFRSF11B + cells were restricted to the atherosclerotic tunica intima, confirming specificity of medial SMC modulation in aneurysm. Conclusions: Total arch replacement during elective VSARR is feasible without substantial morbidity. In LDS patients with root aneurysm, matrix deterioration and SMC phenotype modulation are present in the non-dilated aortic arch, providing molecular rationale for aggressive arch replacement.

Abstract 11944: Surfactant Protein a Promotes Smooth Muscle Cell Phenotype Modulation Through Inhibiting the Myocardin-Smad3 Interaction

Vascular smooth muscle cell (SMC) transition from a differentiated to dedifferentiated phenotype and subsequent neointima formation/vascular remodeling plays a critical role in the development of a number of vascular diseases such as atherosclerosis, restenosis after angioplasty or bypass, diabetic vascular complications, arteriopathy transplants, asthma and cancer. However, mechanisms that regulate SMC phenotype modulation and neointima formation are not completely understood. We have found that Surfactant protein A (SPA), an innate immune system collectin that reduces membrane surface tension and protects lung function during exhalation, is critical for SMC phenotype and vascular modeling. SPA is induced during SMC phenotypic modulation and injury-induced vascular remodeling in both rat and mouse carotid arteries. Knockdown of SPA increased contractile protein expression while enhancing the expression of Myocardin and TGF-β1 in SMCs. Moreover, SMCs from SPA knockout mice had increased Smad3 phosphorylation which was blocked by TGF-β1 neutralizing antibody. To understand the contribution of SMC SPA to vascular remodeling, we generated SMC specific SPA-deficient (SPAsm -/- ) mice with hypercholesteremia by injection of AAV-PCSK9. By using mouse carotid artery wire-injury model, we found that SPA deficiency in SMCs markedly inhibits neointimal formation and the Myocardin-Smad3 interaction in the injured artery. Our data demonstrated that SPA mediates proliferative/synthetic phenotype and neointimal hyperplasia by blocking Myocardin-Smad3 interaction.

Dexmedetomidine alleviates inflammatory response and oxidative stress injury of vascular smooth muscle cell via α2AR/GSK-3β/MKP-1/NRF2 axis in intracranial aneurysm

Vascular smooth muscle cell (VSMC) phenotypic modulation regulates the initiation and progression of intracranial aneurysm (IA). Dexmedetomidine (DEX) is suggested to play neuroprotective roles in patients with craniocerebral injury. Therefore, we investigated the biological functions of DEX and its mechanisms against IA formation and progression in the current study. The rat primary VSMCs were isolated from Sprague–Dawley rats. IA and superficial temporal artery (STA) tissue samples were obtained from patients with IA. Flow cytometry was conducted to identify the characteristics of isolated VSMCs. Hydrogen peroxide (H2O2) was used to mimic IA-like conditions in vitro. Cell viability was detected using CCK-8 assays. Wound healing and Transwell assays were performed to detect cell motility. ROS production was determined by immunofluorescence using DCFH-DA probes. Western blotting and RT-qPCR were carried out to measure gene expression levels. Inflammation responses were determined by measuring inflammatory cytokines. Immunohistochemistry staining was conducted to measure α2-adrenergic receptor levels in tissue samples. DEX alleviated the H2O2-induced cytotoxicity, attenuated the promoting effects of H2O2 on cell malignancy, and protected VSMCs against H2O2-induced oxidative damage and inflammation response. DEX regulated the GSK-3β/MKP-1/NRF2 pathway via the α2AR. DEX alleviates the inflammatory responses and oxidative damage of VSMCs by regulating the GSK-3β/MKP-1/NRF2 pathway via the α2AR in IA.

Lack of PI 3-kinase isoform p110alpha impairs SMC differentiation and proliferation and promotes aortic aneurysm formation

Abstract Background Proliferation and phenotypic modulation of vascular smooth muscle cells (SMCs) significantly contribute to the functionality of the aortic wall. Dysregulation of underlying signal transduction pathways impairs the vessel wall structure and promote the development and progression of abdominal aortic aneurysms (AAA). The PI 3-kinase (PI3K) isoform p110α is activated downstream of receptor tyrosine kinases (RTKs) and represents the most relevant PI3K isoform in SMCs. Aim This project follows the hypothesis that p110α deficiency impairs proliferation and phenotypic modulation of SMCs as well as the structure of the extracellular matrix (ECM) and therefore promotes the development and progression of AAA. It was investigated how p110α deficiency affects the plasticity of SMCs, the production and structure of ECM components, and the formation of AAA. Methods and results Western blot analyses showed that SMCs isolated from smooth muscle specific p110α−/− (sm-p110α−/−) mice were characterized by decreased expression of the differentiation markers sm-α-actin, calponin and sm-MHC. Mechanistically, phosphorylation of key modulators of the SMC phenotype – AKT1, AKT2, FOXO1, -3 and -4 as well as GSK3β – was impaired in p110α−/− SMCs after RTK stimulation. These findings indicate that phenotypic modulation of p110α−/− SMCs is restricted. In addition, protein expression of elastin and fibrillin was reduced in p110α−/− SMCs. In silico analysis (MatLab macro CT-FIRE and Curvalign) of the ECM produced by SMCs in vitro revealed a significantly reduced elastin fiber length and width in p110α−/− SMCs compared to fibers produced by WT SMCs (p&amp;lt;0.05). Consistently, aortas from sm-p110α−/− mice showed a significantly higher number of elastic fiber breaks specifically in the thoracic section than WT controls (289±31 mmm–2 versus 190±9 mmm–2, n=5, p=0.015). Aortic aneurysms in sm-p110α−/− mice and wild-type littermates were analyzed using the established porcine pancreatic elastase (PPE) model. PPE was perfused into the infrarenal aorta to induce AAA formation. Ultrasound examination of the aorta revealed an enlarged aortic diameter in all PPE-treated mice. However, the increase in aortic diameter in sm-p110α−/− mice (70.16±10.82% mm, n=9) was significant more pronounced compared to wild-type animals (42.44±5.99%, n=10) (p&amp;lt;0.05). Three days after PPE perfusion, the number of elastic fiber breaks was significantly increased, and amount of proliferating SMCs were decreased in the infrarenal aorta of sm-p110α−/− mice compared to WT controls. Conclusion p110α deficiency in SMCs impairs aortic wall structure and promotes the development and progression of aortic aneurysms. Mechanistically, p110α activity maintains a differentiated SMC phenotype as well as the expression and assembly of ECM components. These data identify p110α signaling as a modifiable target for preventive and therapeutic strategies for aortic aneurysms. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Deutsche Forschungsgemeinschaft

Sox9 mediates autophagy-dependent vascular smooth muscle cell phenotypic modulation and transplant arteriosclerosis

SummaryVascular smooth muscle cell (vSMC) phenotypic modulation is a dynamic pathogenesis process implicated in neointimal formation and transplant arteriosclerosis (TA). Transcription factor Sox9 functions to establish cell type and wound healing, but little is known about its transcriptional regulation in vSMCs and its roles in the development of TA. Here, we found an increased Sox9 expression in aortic allografts and in HMGB1-treated vSMCs in vitro, accompanied by the downregulation of vSMC markers. Notably, vSMC-specific Sox9 knockdown in aortic allografts attenuated neointimal formation through preventing vSMC phenotypic modulation following transplantation. We further indicated that HMGB1 induced Sox9 expression and vSMC phenotypic modulation through activating autophagy to degrade p27Kip1. Mechanistically, p27Kip1 bound to the Sox9 promoter in vSMCs together with p130/E2F4 complex, by which it restrained Sox9 transcriptional expression. These findings uncover a fundamental role of Sox9 in mediating autophagy-dependent vSMC phenotypic modulation and TA, offering a therapeutic approach for vascular pathologies.

Effects of traditional cigarette and electronic cigarette on smooth muscle cell phenotypic modulation

Background and Aims : Cigarette smoke (CS) is a risk factor for cardiovascular disease. Whole traditional cigarette (TC) smoke contains over 7000 chemical components and several are deemed to be toxic. Thus, alternative next-generation tobacco products (E-cigarettes (E-cig)) are being developed as less dangerous. Vascular homeostasis is maintained by differentiated quiescent smooth muscle cells (SMCs) that, following environmental cues, may undergo transcriptional changes affecting contractile proteins and their proliferative phenotype.

The Etiology and Molecular Mechanism Underlying Smooth Muscle Phenotype Switching in Intimal Hyperplasia of Vein Graft and the Regulatory Role of microRNAs.

Mounting evidence suggests that the phenotypic transformation of venous smooth muscle cells (SMCs) from differentiated (contractile) to dedifferentiated (proliferative and migratory) phenotypes causes excessive proliferation and further migration to the intima leading to intimal hyperplasia, which represents one of the key pathophysiological mechanisms of vein graft restenosis. In recent years, numerous miRNAs have been identified as specific phenotypic regulators of vascular SMCs (VSMCs), which play a vital role in intimal hyperplasia in vein grafts. The review sought to provide a comprehensive overview of the etiology of intimal hyperplasia, factors affecting the phenotypic transformation of VSMCs in vein graft, and molecular mechanisms of miRNAs involved in SMCs phenotypic modulation in intimal hyperplasia of vein graft reported in recent years.

Embryologic Origin Influences Smooth Muscle Cell Phenotypic Modulation Signatures in Murine Marfan Syndrome Aortic Aneurysm.

Aortic root smooth muscle cells (SMC) develop from both the second heart field (SHF) and neural crest. Disparate responses to disease-causing Fbn1 variants by these lineages are proposed to promote focal aortic root aneurysm formation in Marfan syndrome (MFS), but lineage-stratified SMC analysis in vivo is lacking. We generated SHF lineage-traced MFS mice and performed integrated multiomic (single-cell RNA and assay for transposase-accessible chromatin sequencing) analysis stratified by embryological origin. SMC subtypes were spatially identified via RNA in situ hybridization. Response to TWIST1 overexpression was determined via lentiviral transduction in human aortic SMCs. Lineage stratification enabled nuanced characterization of aortic root cells. We identified heightened SHF-derived SMC heterogeneity including a subset of Tnnt2 (cardiac troponin T)-expressing cells distinguished by altered proteoglycan expression. MFS aneurysm-associated SMC phenotypic modulation was identified in both SHF-traced and nontraced (neural crest-derived) SMCs; however, transcriptomic responses were distinct between lineages. SHF-derived modulated SMCs overexpressed collagen synthetic genes and small leucine-rich proteoglycans while nontraced SMCs activated chondrogenic genes. These modulated SMCs clustered focally in the aneurysmal aortic root at the region of SHF/neural crest lineage overlap. Integrated RNA-assay for transposase-accessible chromatin analysis identified enriched Twist1 and Smad2/3/4 complex binding motifs in SHF-derived modulated SMCs. TWIST1 overexpression promoted collagen and SLRP gene expression in vitro, suggesting TWIST1 may drive SHF-enriched collagen synthesis in MFS aneurysm. SMCs derived from both SHF and neural crest lineages undergo phenotypic modulation in MFS aneurysm but are defined by subtly distinct transcriptional responses. Enhanced TWIST1 transcription factor activity may contribute to enriched collagen synthetic pathways SHF-derived SMCs in MFS.

Revealing the Critical Regulators of Modulated Smooth Muscle Cells in Atherosclerosis in Mice.

Background: There are still residual risks for atherosclerosis (AS)-associated cardiovascular diseases to be resolved. Considering the vital role of phenotypic switching of smooth muscle cells (SMCs) in AS, especially in calcification, targeting SMC phenotypic modulation holds great promise for clinical implications. Methods: To perform an unbiased and systematic analysis of the molecular regulatory mechanism of phenotypic switching of SMCs during AS in mice, we searched and included several publicly available single-cell datasets from the GEO database, resulting in an inclusion of more than 80,000 cells. Algorithms implemented in the Seurat package were used for cell clustering and cell atlas depiction. The pySCENIC and SCENIC packages were used to identify master regulators of interested cell groups. Monocle2 was used to perform pseudotime analysis. clusterProfiler was used for Gene Ontology enrichment analysis. Results: After dimensionality reduction and clustering, reliable annotation was performed. Comparative analysis between cells from normal artery and AS lesions revealed that three clusters emerged as AS progression, designated as mSMC1, mSMC2, and mSMC3. Transcriptional and functional enrichment analysis established a continuous transitional mode of SMCs’ transdifferentiation to mSMCs, which is further supported by pseudotime analysis. A total of 237 regulons were identified with varying activity scores across cell types. A potential core regulatory network was constructed for SMC and mSMC subtypes. In addition, module analysis revealed a coordinate regulatory mode of regulons for a specific cell type. Intriguingly, consistent with gain of ossification-related transcriptional and functional characteristics, a corresponding small set of regulators contributing to osteochondral reprogramming was identified in mSMC3, including Dlx5, Sox9, and Runx2. Conclusion: Gene regulatory network inference indicates a hierarchical organization of regulatory modules that work together in fine-tuning cellular states. The analysis here provides a valuable resource that can provide guidance for subsequent biological experiments.

SREBP1 regulates Lgals3 activation in response to cholesterol loading

Aberrant smooth muscle cell (SMC) plasticity is etiological to vascular diseases. Cholesterol induces SMC phenotypic transition featuring high LGALS3 (galectin-3) expression. This proatherogenic process is poorly understood for its molecular underpinnings, in particular, the mechanistic role of sterol regulatory-element binding protein-1 (SREBP1), a master regulator of lipid metabolism. Herein we show that cholesterol loading stimulated SREBP1 expression in mouse, rat, and human SMCs. SREBP1 positively regulated LGALS3 expression (and vice versa), whereas Krüppel-like factor-15 (KLF15) acted as a negative regulator. Both bound to the Lgals3 promoter, yet at discrete sites, as revealed by chromatin immunoprecipitation-qPCR and electrophoretic mobility shift assays. SREBP1 and LGALS3 each abated KLF15 protein, and blocking the bromo/extraterminal domain-containing proteins (BETs) family of acetyl-histone readers abolished cholesterol-stimulated SREBP1/LGALS3 protein production. Furthermore, silencing bromodomain protein 2 (BRD2; but not other BETs) reduced SREBP1; endogenous BRD2 co-immunoprecipitated with SREBP1’s transcription-active domain, its own promoter DNA, and that of Lgals3. Thus, results identify a previously uncharacterized cholesterol-responsive dyad—SREBP1 and LGALS3, constituting a feedforward circuit that can be blocked by BETs inhibition. This study provides new insights into SMC phenotypic transition and potential interventional targets.