A New Autosomal Myh11-CreERT2 Smooth Muscle Cell Lineage Tracing and Gene Knockout Mouse Model-Brief Report

Generation of a novel constitutive smooth muscle cell-specific Myh11-driven Cre mouse model

Dysfunction in either embryonic or postnatal smooth muscle cells (SMCs) significantly contributes to the progression of various cardiovascular and visceral diseases. Therefore, elucidating the molecular mechanisms governing SMC development and homeostasis is crucial. MYH11 is the most reliable lineage gene for SMCs and has been utilized to develop tamoxifen-inducible Cre driver lines for achieving SMC-specific gene manipulation by crossing with mice carrying the loxP-flanked gene, particularly in adult mice. For studies involving SMCs during embryogenesis, the commonly used constitutive Cre driver is controlled by the Tagln (also known as SM22α) promoter. However, this Cre driver exhibits activity in multiple non-SMC populations, including cardiomyocytes and skeletal muscle precursors, introducing confounding effects. Additionally, most existing SMC-specific Cre drivers are generated using a transgenic approach, raising concerns about random site integration and variable gene copy numbers. To address these limitations, we report a novel Cre mouse model generated by knock-in (KI) of a nuclear-localized Cre recombinase into the Myh11 gene locus using homologous recombination. We confirmed that the Cre activity precisely recapitulates endogenous Myh11 expression by crossing with Rosa26 mTmG or tdTomato reporter mice. Moreover, Myh11-driven Cre can efficiently delete the floxed allele of the transcription factor Tead1 specifically in SMCs. The Tead1 SMC-specific knockout mice did not exhibit an overt phenotype, thereby circumventing the embryonic lethal phenotype mediated by Tagln-driven Cre, as we previously reported. These findings establish this novel Cre driver line as a robust tool for tracing the Myh11-positive SMC lineage and manipulating gene function specifically in SMCs during embryonic development in both male and female mice.

Vascular cell types in progeria: victims or villains?

Hutchinson-Gilford progeria syndrome (HGPS) is an ultrarare genetic disease caused by progerin, a broadly expressed mutant variant of lamin A protein that accelerates aging and leads to premature death typically in adolescence. Progerin affects many organs and reproduces many characteristics of physiological aging, with the main cause of death in HGPS being atherosclerotic cardiovascular disease (CVD). Due to the rarity of HGPS, advances in understanding the disease and progress toward new therapeutic approaches are crucially dependent on preclinical models. We discuss recent research developments from a variety of HGPS experimental systems, with a special focus on in vivo studies of the role of vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) that are key players in atherosclerosis.

Depletion of Mitochondrial Cyclophilin D in Endothelial and Smooth Muscle Cells Attenuates Vascular Dysfunction and Hypertension

Hypertension is a major risk factor of cardiovascular disease affecting nearly half of adult population. It is associated with mitochondrial dysfunction and understanding these mechanisms is important to develop new therapies. Cyclophilin D (CypD) promotes mitochondrial swelling and dysfunction. The objective of this study is to test if CypD depletion attenuates vascular dysfunction and hypertension using endothelial and smooth muscle-specific CypD knockout mice in angiotensin II model of vascular dysfunction and hypertension. Our results show that depletion of endothelial CypD prevents angiotensin II-induced impairment of endothelial-dependent vasorelaxation, preserves endothelial nitric oxide and mitochondrial respiration, attenuates hypertension, vascular oxidative stress and vascular metabolic glycolytic-switch. Depletion of smooth muscle CypD slightly reduces angiotensin II-induced hypertension, protects vascular nitric oxide and vasorelaxation, decreases vascular superoxide, diminishes angiotensin II-induced vascular glycolysis, hypertrophy and fibrosis. These data suggest "metabolic" and "redox" crosstalk between endothelial and smooth muscle cells. Endothelial CypD depletion reduces not only endothelial glycolysis but also attenuates smooth muscle cell glycolytic switch. Smooth muscle CypD depletion reduced not only smooth muscle glycolysis, but it also attenuated endothelial glycolysis. Vascular oxidative stress was inhibited both in EcCypDKO and SmcCypDKO mice, therefore, cell-specific CypD depletion had "global" antioxidant effect in vasculature. Our results support a novel function of mitochondrial CypD in regulation of superoxide and metabolism in vascular smooth muscle and endothelial cells which affect endothelial barrier and smooth muscle vascular functions. We suggest that blocking vascular CypD reduces vascular oxidative stress, improves vascular metabolism and vascular function which may be beneficial in cardiovascular disease.

Hypercholesterolemia-induced LXR signaling in smooth muscle cells contributes to vascular lesion remodeling and visceral function

Vascular smooth muscle cells (VSMC) are the most abundant cell type in the artery's media layer and regulate vascular tone and lesion remodeling during atherogenesis. Like monocyte-derived macrophages, VSMCs accumulate excess lipids and contribute to the total intimal foam cell population in human coronary plaques and mouse aortic atheroma. While there are extensive studies characterizing the contribution of lipid metabolism in macrophage immunometabolic responses in atherosclerotic plaques, the role of VSMC lipid metabolism in regulating vascular function and lesion remodeling in vivo remains poorly understood. Here, we report that the liver X receptor (LXR) signaling pathway in VSMC is continuously activated during atherogenesis. Notably, we found that LXR deficiency in SMCs under hypercholesterolemic conditions influenced lesion remodeling by altering the fate of dedifferentiated SMCs and promoting the accumulation of VSMC-derived transitional cells. This phenotypic switching was accompanied by reduced indices of plaque stability, characterized by a larger necrotic core area and reduced fibrous cap thickness. Moreover, SMC-specific LXR deficiency impaired vascular function and caused visceral myopathy characterized by maladaptive bladder remodeling and gut lipid malabsorption. Mechanistically, we found that the expression of several genes involved in cholesterol efflux and FA synthesis including Abca1, Srebf1, Scd1, Scd2, Acsl3, and Mid1ip1 was downregulated in mice lacking LXRαβ in SMCs, likely contributing to the phenotypic switching of VSMC in the atherosclerotic lesions.

Exploring Origin-Dependent Susceptibility of Smooth Muscle Cells to Aortic Diseases Through Intersectional Genetics

BACKGROUND

The developmental diversity among smooth muscle cells (SMCs) plays a crucial role in segment-specific aortic diseases. However, traditional genetic approaches are inadequate for enabling in vivo analysis of disease susceptibility associated with cellular origin. There is an urgent need to build genetic technologies that target different developmental origins to investigate the mechanisms of aortopathies, thereby facilitating the development of effective therapeutics.

METHODS

To address this challenge, we developed an advanced dual recombinase-mediated intersectional genetic system, specifically designed to precisely target SMCs from various developmental origins in mice. Specifically, we used Isl1-Dre, Wnt1-Dre, Meox1-DreER, and Upk3b-Dre to target SMC progenitors from the second heart field, cardiac neural crest, somites, and mesothelium, respectively. This system was combined with single-cell RNA sequencing to investigate the impact of TGF-β (transforming growth factor-β) signaling in different segments of the aorta by selectively knocking out Tgfbr2 in the ascending aorta and Smad4 in the aortic arch, respectively.

RESULTS

Through intersectional genetic approaches, we use the Myh11-Cre(ER) driver along with origin-specific Dre drivers to trace cells of diverse developmental origins within the SMC population. We found that a deficiency of Tgfbr2 in SMCs of the ascending aorta leads to aneurysm formation in this specific region. We also demonstrate the critical role of Smad4 in preserving aortic wall integrity and homeostasis in SMCs of the aortic arch.

CONCLUSIONS

Our approach to genetically targeting SMC subtypes provides a novel platform for exploring origin-dependent or location-specific aortic vascular diseases. This genetic system enables comprehensive analysis of contributions from different cell lineages to SMC behavior and pathology, thereby paving the way for targeted research and therapeutic interventions in the future.

A 5-lncRNA signature predicts clinical prognosis and demonstrates a different mRNA expression in adult soft tissue sarcoma

Background

Adult soft tissue sarcoma (SARC) is a highly aggressive malignancy. A growing number of long non-coding RNAs (lncRNAs) have been linked to malignancies, and many researchers consider lncRNAs potential biomarkers for prognosis. However, there is limited evidence available to determine the role of lncRNAs in the prognosis of SARC. In this study, we collected The Cancer Genome Atlas (TCGA) data to identify prognosis-related lncRNAs for SARC and explore the relationship between lncRNAs and gene expression.

Methods

TCGA datasets, which included 259 samples, served as data sources in this study. Univariable Cox regression analysis, robust analysis, and multivariable Cox regression analysis were used to construct a 5-lncRNA signature Cox regression model. Then, based on the median risk score, high- and low-risk groups were identified. The Kaplan-Meier method was applied to survival analysis in the training set, testing set, complete set, and different pathological type sets. To explore the relationship between lncRNAs and messenger RNAs (mRNAs), differentially expressed mRNAs (DEmRNAs) between the high- and low-risk groups were identified. The function of DEmRNAs was predicted using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. The relationships between the 5 lncRNAs and DEmRNAs were calculated using the Spearman correlation coefficient. A total of 18 DEmRNAs that showed a strong correlation with risk score (|Spearman's r|>0.6) in leiomyosarcoma (LMS) samples were identified, and a protein-protein interaction (PPI) network was built using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database.

Results

A Cox regression model was built in this study with the risk score= (-0.5698*AC018645.2) + 0.1732*LINC02454 + 0.387*ERICD + 0.6262*DSCR9 + 0.9781*AL031770.1. The study found that this 5-lncRNA signature could predict prognosis well, especially in LMS, a subtype of SARC, with P value =1.19e-06 [hazard ratio (HR) 6.134, 95% confidence interval (CI): 2.951-12.752]. Additionally, 44 DEmRNAs were observed between the high- and low-risk groups, and the expression levels of DEmRNAs in LMS samples differed from other pathology types. The PPI network analysis revealed that MYH11, MYLK, and CNN1 were the most important hub genes among the 18 DEmRNAs, all of which are essential for muscle function.

Conclusions

In this study, a predictive clinical model for SARC was successfully established, showing better prediction accuracy in patients with LMS. Importantly, we identified MYH11, MYLK, and CNN1 as potential therapeutic targets for SARC.

Inhibition of vascular smooth muscle cell PERK/ATF4 ER stress signaling protects against abdominal aortic aneurysms

Abdominal aortic aneurysms (AAA) are a life-threatening cardiovascular disease for which there is a lack of effective therapy preventing aortic rupture. During AAA formation, pathological vascular remodeling is driven by vascular smooth muscle cell (VSMC) dysfunction and apoptosis, for which the mechanisms regulating loss of VSMCs within the aortic wall remain poorly defined. Using single-cell RNA-Seq of human AAA tissues, we identified increased activation of the endoplasmic reticulum stress response pathway, PERK/eIF2α/ATF4, in aortic VSMCs resulting in upregulation of an apoptotic cellular response. Mechanistically, we reported that aberrant TNF-α activity within the aortic wall induces VSMC ATF4 activation through the PERK endoplasmic reticulum stress response, resulting in progressive apoptosis. In vivo targeted inhibition of the PERK pathway, with VSMC-specific genetic depletion (Eif2ak3fl/fl Myh11-CreERT2) or pharmacological inhibition in the elastase and angiotensin II-induced AAA model preserved VSMC function, decreased elastin fragmentation, attenuated VSMC apoptosis, and markedly reduced AAA expansion. Together, our findings suggest that cell-specific pharmacologic therapy targeting the PERK/eIF2α/ATF4 pathway in VSMCs may be an effective intervention to prevent AAA expansion.

Cellular communication network factor 2 regulates smooth muscle cell transdifferentiation and lipid accumulation in atherosclerosis

AIMS

Accruing evidence illustrates an emerging paradigm of dynamic vascular smooth muscle cell (SMC) transdifferentiation during atherosclerosis progression. However, the molecular regulators that govern SMC phenotype diversification remain poorly defined. This study aims to elucidate the functional role and underlying mechanisms of cellular communication network factor 2 (CCN2), a matricellular protein, in regulating SMC plasticity in the context of atherosclerosis.

METHODS AND RESULTS

In both human and murine atherosclerosis, an up-regulation of CCN2 is observed in transdifferentiated SMCs. Using an inducible murine SMC CCN2 deletion model, we demonstrate that SMC-specific CCN2 knockout mice are hypersusceptible to atherosclerosis development as evidenced by a profound increase in lipid-rich plaques along the entire aorta. Single-cell RNA sequencing studies reveal that SMC deficiency of CCN2 positively regulates machinery involved in endoplasmic reticulum stress, endocytosis, and lipid accumulation in transdifferentiated macrophage-like SMCs during the progression of atherosclerosis, findings recapitulated in CCN2-deficient human aortic SMCs.

CONCLUSION

Our studies illuminate an unanticipated protective role of SMC-CCN2 against atherosclerosis. Disruption of vascular wall homeostasis resulting from vascular SMC CCN2 deficiency predisposes mice to atherosclerosis development and progression.

Generation of a novel constitutive smooth muscle cell-specific Myh11 -driven Cre mouse model

Dysfunction in either embryonic or postnatal vascular smooth muscle cells (SMCs) significantly contributes to the progression of various cardiovascular diseases. Therefore, elucidating the molecular mechanisms governing VSMC development and homeostasis is crucial. MYH11 is the most reliable lineage gene for SMCs and has been utilized to develop tamoxifen-inducible Cre driver lines for achieving SMC-specific gene manipulation by crossing with mice carrying the lox P -flanked gene, particularly in adult mice. For studies involving SMCs during embryogenesis, the commonly used constitutive Cre driver is controlled by the Tagln ( Sm22α ) promoter. However, this Cre driver exhibits activity in multiple non-SMC populations, including cardiomyocytes and skeletal muscle precursors, introducing confounding effects. Additionally, most existing SMC-specific Cre drivers are generated using a transgenic approach, raising concerns about random site integration and variable gene copy numbers. To address these limitations, we report a novel Cre mouse model generated by knock-in (KI) of a nuclear-localized Cre recombinase into the Myh11 gene locus using homologous recombination. We confirmed that the Cre activity precisely recapitulates endogenous Myh11 expression by crossing with Rosa26 mTmG or tdTomato reporter mice. Moreover, Myh11 -driven Cre can efficiently delete the floxed allele of the transcription factor Tead1 specifically in SMCs. The Tead1 SMC-specific knockout mice did not exhibit an overt phenotype, thereby circumventing the embryonic lethal phenotype mediated by Tagln -driven Cre, as we previously reported. These findings establish this novel Cre driver line as a robust tool for tracing the Myh11 -positive SMC lineage and manipulating gene function specifically in SMCs during embryonic development in mice.

Integrative gene regulatory network analysis discloses key driver genes of fibromuscular dysplasia

Fibromuscular dysplasia (FMD) is a poorly understood disease affecting 3-5% of adult females. The pathobiology of FMD involves arterial lesions of stenosis, dissection, tortuosity, dilation and aneurysm, which can lead to hypertension, stroke, myocardial infarction and even death. Currently, there are no animal models for FMD and few insights as to its pathobiology. In this study, by integrating DNA genotype and RNA sequence data from primary fibroblasts of 83 patients with FMD and 71 matched healthy controls, we inferred 18 gene regulatory co-expression networks, four of which were found to act together as an FMD-associated supernetwork in the arterial wall. After in vivo perturbation of this co-expression supernetwork by selective knockout of a top network key driver, mice developed arterial dilation, a hallmark of FMD. Molecular studies indicated that this supernetwork governs multiple aspects of vascular cell physiology and functionality, including collagen/matrix production. These studies illuminate the complex causal mechanisms of FMD and suggest a potential therapeutic avenue for this challenging disease.

Novel Mouse Model of Myocardial Infarction, Plaque Rupture, and Stroke Shows Improved Survival With Myeloperoxidase Inhibition

BACKGROUND

Thromboembolic events, including myocardial infarction (MI) or stroke, caused by the rupture or erosion of unstable atherosclerotic plaques are the leading cause of death worldwide. Although most mouse models of atherosclerosis develop lesions in the aorta and carotid arteries, they do not develop advanced coronary artery lesions. Moreover, they do not undergo spontaneous plaque rupture with MI and stroke or do so at such a low frequency that they are not viable experimental models to study late-stage thrombotic events or to identify novel therapeutic approaches for treating atherosclerotic disease. This has stymied the development of more effective therapeutic approaches for reducing these events beyond what has been achieved with aggressive lipid lowering. Here, we describe a diet-inducible mouse model that develops widespread advanced atherosclerosis in coronary, brachiocephalic, and carotid arteries with plaque rupture, MI, and stroke.

METHODS

We characterized a novel mouse model with a C-terminal mutation in the scavenger receptor class B, type 1 (SR-BI), combined with Ldlr knockout (designated SR-BI∆CT/∆CT/Ldlr-/-). Mice were fed Western diet (WD) for 26 weeks and analyzed for MI and stroke. Coronary, brachiocephalic, and carotid arteries were analyzed for atherosclerotic lesions and indices of plaque stability. To validate the utility of this model, SR-BI∆CT/∆CT/Ldlr-/- mice were treated with the drug candidate AZM198, which inhibits myeloperoxidase, an enzyme produced by activated neutrophils that predicts rupture of human atherosclerotic lesions.

RESULTS

SR-BI∆CT/∆CT/Ldlr-/- mice show high (>80%) mortality rates after 26 weeks of WD feeding because of major adverse cardiovascular events, including spontaneous plaque rupture with MI and stroke. Moreover, WD-fed SR-BI∆CT/∆CT/Ldlr-/- mice displayed elevated circulating high-sensitivity cardiac troponin I and increased neutrophil extracellular trap formation within lesions compared with control mice. Treatment of WD-fed SR-BI∆CT/∆CT/Ldlr-/- mice with AZM198 showed remarkable benefits, including >90% improvement in survival and >60% decrease in the incidence of plaque rupture, MI, and stroke, in conjunction with decreased circulating high-sensitivity cardiac troponin I and reduced neutrophil extracellular trap formation within lesions.

CONCLUSIONS

WD-fed SR-BI∆CT/∆CT/Ldlr-/- mice more closely replicate late-stage clinical events of advanced human atherosclerotic disease than previous models and can be used to identify and test potential new therapeutic agents to prevent major adverse cardiac events.

Epsins oversee smooth muscle cell reprograming by influencing master regulators KLF4 and OCT4

Smooth muscle cells in major arteries play a crucial role in regulating coronary artery disease. Conversion of smooth muscle cells into other adverse cell types in the artery propels the pathogenesis of the disease. Curtailing artery plaque buildup by modulating smooth muscle cell reprograming presents us a new opportunity to thwart coronary artery disease. Here, our report how Epsins, a family of endocytic adaptor proteins oversee the smooth muscle cell reprograming by influencing master regulators OCT4 and KLF4. Using single-cell RNA sequencing, we characterized the phenotype of modulated smooth muscle cells in mouse atherosclerotic plaque and found that smooth muscle cells lacking epsins undergo profound reprogramming into not only beneficial myofibroblasts but also endothelial cells for injury repair of diseased endothelium. Our work lays concrete groundwork to explore an uncharted territory as we show that depleting Epsins bolsters smooth muscle cells reprograming to endothelial cells by augmenting OCT4 activity but restrain them from reprograming to harmful foam cells by destabilizing KLF4, a master regulator of adverse reprograming of smooth muscle cells. Moreover, the expression of Epsins in smooth muscle cells positively correlates with the severity of both human and mouse coronary artery disease. Integrating our scRNA-seq data with human Genome-Wide Association Studies (GWAS) identifies pivotal roles Epsins play in smooth muscle cells in the pathological process leading to coronary artery disease. Our findings reveal a previously unexplored direction for smooth muscle cell phenotypic modulation in the development and progression of coronary artery disease and unveil Epsins and their downstream new targets as promising novel therapeutic targets for mitigating metabolic disorders.

Loss of anoctamin 1 reveals a subtle role for BK channels in lymphatic muscle action potentials

Ca2+ signalling plays a crucial role in determining lymphatic muscle cell excitability and contractility through its interaction with the Ca2+-activated Cl- channel anoctamin 1 (ANO1). In contrast, the large-conductance (BK) Ca2+-activated K+ channel (KCa) and other KCa channels have prominent vasodilatory actions by hyperpolarizing vascular smooth muscle cells. Here, we assessed the expression and contribution of the KCa family to mouse and rat lymphatic collecting vessel contractile function. The BK channel was the only KCa channel consistently expressed in fluorescence-activated cell sorting-purified mouse lymphatic muscle cell lymphatic muscle cells. We used a pharmacological inhibitor of BK channels, iberiotoxin, and small-conductance Ca2+-activated K+ channels, apamin, to inhibit KCa channels acutely in ex vivo isobaric myography experiments and intracellular membrane potential recordings. In basal conditions, BK channel inhibition had little to no effect on either mouse inguinal-axillary lymphatic vessel (MIALV) or rat mesenteric lymphatic vessel contractions or action potentials (APs). We also tested BK channel inhibition under loss of ANO1 either by genetic ablation (Myh11CreERT2-Ano1 fl/fl, Ano1ismKO) or by pharmacological inhibition with Ani9. In both Ano1ismKO MIALVs and Ani9-pretreated MIALVs, inhibition of BK channels increased contraction amplitude, increased peak AP and broadened the peak of the AP spike. In rat mesenteric lymphatic vessels, BK channel inhibition also abolished the characteristic post-spike notch, which was exaggerated with ANO1 inhibition, and significantly increased the peak potential and broadened the AP spike. We conclude that BK channels are present and functional on mouse and rat lymphatic muscle cells but are otherwise masked by the dominance of ANO1. KEY POINTS: Mouse and rat lymphatic muscle cells express functional BK channels. BK channels make little contribution to either rat or mouse lymphatic collecting vessel contractile function in basal conditions across a physiological pressure range. ANO1 limits the peak membrane potential achieved in the action potential and sets a plateau potential limiting the voltage-dependent activation of BK. BK channels are activated when ANO1 is absent or blocked and slightly impair contractile strength by reducing the peak membrane potential achieved in the action potential spike and accelerating the post-spike repolarization.

Extracellular cancer‑associated fibroblasts: A novel subgroup in the cervical cancer microenvironment that exhibits tumor‑promoting roles and prognosis biomarker functions

Tumor invasion and metastasis are the processes that primarily cause adverse outcomes in patients with cervical cancer. Cancer-associated fibroblasts (CAFs), which participate in cancer progression and metastasis, are novel targets for the treatment of tumors. The present study aimed to assess the heterogeneity of CAFs in the cervical cancer microenvironment through single-cell RNA sequencing. After collecting five cervical cancer samples and obtaining the CAF-associated gene sets, the CAFs in the cervical cancer microenvironment were divided into myofibroblastic CAFs and extracellular (ec)CAFs. The ecCAFs appeared with more robust pro-tumorigenic effects than myCAFs according to enrichment analysis. Subsequently, through combining the ecCAF hub genes and bulk gene expression data for cervical cancer obtained from The Cancer Genome Atlas and Gene Ontology databases, univariate Cox regression and least absolute shrinkage and selection operator analyses were performed to establish a CAF-associated risk signature for patients with cancer. The established risk signature demonstrated a stable and strong prognostic capability in both the training and validation cohorts. Subsequently, the association between the risk signature and clinical data was evaluated, and a nomogram to facilitate clinical application was established. The risk score was demonstrated to be associated with both the tumor immune microenvironment and the therapeutic responses. Moreover, the signature also has predictive value for the prognosis of head and neck squamous cell carcinoma, and bladder urothelial carcinoma, which were also associated with human papillomavirus infection. In conclusion, the present study assessed the heterogeneity of CAFs in the cervical cancer microenvironment, and a subgroup of CAFs that may be closely associated with tumor progression was defined. Moreover, a signature based on the hub genes of ecCAFs was shown to have biomarker functionality in terms of predicting survival rates, and therefore this CAF subgroup may become a therapeutic target for cervical cancer in the future.

Clonal Expansion in Cardiovascular Pathology

Clonal expansion refers to the proliferation and selection of advantageous "clones" that are better suited for survival in a Darwinian manner. In recent years, we have greatly enhanced our understanding of cell clonality in the cardiovascular context. However, our knowledge of the underlying mechanisms behind this clonal selection is still severely limited. There is a transpiring pattern of clonal expansion of smooth muscle cells and endothelial cells-and, in some cases, macrophages-in numerous cardiovascular diseases irrespective of their differing microenvironments. These findings indirectly suggest the possible existence of stem-like vascular cells which are primed to respond during disease. Subsequent clones may undergo further phenotypic changes to adopt either protective or detrimental roles. By investigating these clone-forming vascular cells, we may be able to harness this inherent clonal nature for future therapeutic intervention. This review comprehensively discusses what is currently known about clonal expansion across the cardiovascular field. Comparisons of the clonal nature of vascular cells in atherosclerosis (including clonal hematopoiesis of indeterminate potential), pulmonary hypertension, aneurysm, blood vessel injury, ischemia- and tumor-induced angiogenesis, and cerebral cavernous malformations are evaluated. Finally, we discuss the potential clinical implications of these findings and propose that proper understanding and specific targeting of these clonal cells may provide unique therapeutic options for the treatment of these cardiovascular conditions.

A single-cell atlas of the aging mouse ovary

Ovarian aging leads to diminished fertility, dysregulated endocrine signaling and increased chronic disease burden. These effects begin to emerge long before follicular exhaustion. Female humans experience a sharp decline in fertility around 35 years of age, which corresponds to declines in oocyte quality. Despite a growing body of work, the field lacks a comprehensive cellular map of the transcriptomic changes in the aging mouse ovary to identify early drivers of ovarian decline. To fill this gap we performed single-cell RNA sequencing on ovarian tissue from young (3-month-old) and reproductively aged (9-month-old) mice. Our analysis revealed a doubling of immune cells in the aged ovary, with lymphocyte proportions increasing the most, which was confirmed by flow cytometry. We also found an age-related downregulation of collagenase pathways in stromal fibroblasts, which corresponds to rises in ovarian fibrosis. Follicular cells displayed stress-response, immunogenic and fibrotic signaling pathway inductions with aging. This report provides critical insights into mechanisms responsible for ovarian aging phenotypes. The data can be explored interactively via a Shiny-based web application.

IP3R1 underlies diastolic ANO1 activation and pressure-dependent chronotropy in lymphatic collecting vessels

Pressure-dependent chronotropy of murine lymphatic collecting vessels relies on the activation of the Ca2+-activated chloride channel encoded by Anoctamin 1 (Ano1) in lymphatic muscle cells. Genetic ablation or pharmacological inhibition of ANO1 results in a significant reduction in basal contraction frequency and essentially complete loss of pressure-dependent frequency modulation by decreasing the rate of the diastolic depolarization phase of the ionic pacemaker in lymphatic muscle cells (LMCs). Oscillating Ca2+ release from sarcoendoplasmic reticulum Ca2+ channels has been hypothesized to drive ANO1 activity during diastole, but the source of Ca2+ for ANO1 activation in smooth muscle remains unclear. Here, we investigated the role of the inositol triphosphate receptor 1 (Itpr1; Ip3r1) in this process using pressure myography, Ca2+ imaging, and membrane potential recordings in LMCs of ex vivo pressurized inguinal-axillary lymphatic vessels from control or Myh11CreERT2;Ip3r1fl/fl (Ip3r1ismKO) mice. Ip3r1ismKO vessels had significant reductions in contraction frequency and tone but an increased contraction amplitude. Membrane potential recordings from LMCs of Ip3r1ismKO vessels revealed a depressed diastolic depolarization rate and an elongation of the plateau phase of the action potential (AP). Ca2+ imaging of LMCs using the genetically encoded Ca2+ sensor GCaMP6f demonstrated an elongation of the Ca2+ flash associated with an AP-driven contraction. Critically, diastolic subcellular Ca2+ transients were absent in LMCs of Ip3r1ismKO mice, demonstrating the necessity of IP3R1 activity in controlling ANO1-mediated diastolic depolarization. These findings indicate a critical role for IP3R1 in lymphatic vessel pressure-dependent chronotropy and contractile regulation.

Tissue-specific Cre driver mice to study vascular diseases

Vascular diseases, including atherosclerosis and abdominal aneurysms, are the primary cause of mortality and morbidity among the elderly worldwide. The life quality of patients is significantly compromised due to inadequate therapeutic approaches and limited drug targets. To expand our comprehension of vascular diseases, gene knockout (KO) mice, especially conditional knockout (cKO) mice, are widely used for investigating gene function and mechanisms of action. The Cre-loxP system is the most common method for generating cKO mice. Numerous Cre driver mice have been established to study the main cell types that compose blood vessels, including endothelial cells, smooth muscle cells, and fibroblasts. Here, we first discuss the characteristics of each layer of the arterial wall. Next, we provide an overview of the representative Cre driver mice utilized for each of the major cell types in the vessel wall and their most recent applications in vascular biology. We then go over Cre toxicity and discuss the practical methods for minimizing Cre interference in experimental outcomes. Finally, we look into the future of tissue-specific Cre drivers by introducing the revolutionary single-cell RNA sequencing and dual recombinase system.

Phenotypic Switching of Vascular Smooth Muscle Cells in Atherosclerosis

The medial layer of the arterial wall is composed mainly of vascular smooth muscle cells (VSMCs). Under physiological conditions, VSMCs assume a contractile phenotype, and their primary function is to regulate vascular tone. In contrast with terminally differentiated cells, VSMCs possess phenotypic plasticity, capable of transitioning into other cellular phenotypes in response to changes in the vascular environment. Recent research has shown that VSMC phenotypic switching participates in the pathogenesis of atherosclerosis, where the various types of dedifferentiated VSMCs accumulate in the atherosclerotic lesion and participate in the associated vascular remodeling by secreting extracellular matrix proteins and proteases. This review article discusses the 9 VSMC phenotypes that have been reported in atherosclerotic lesions and classifies them into differentiated VSMCs, intermediately dedifferentiated VSMCs, and dedifferentiated VSMCs. It also provides an overview of several methodologies that have been developed for studying VSMC phenotypic switching and discusses their respective advantages and limitations.

Generating endogenous Myh11-driven Cre mice for sex-independent gene deletion in smooth muscle cells

Specific and efficient smooth muscle cell-targeted (SMC-targeted) gene deletion is typically achieved by pairing SMMHC-CreERT2-Tg mice with mice carrying the loxP-flanked gene. However, the transgene, CreERT2, is not controlled by the endogenous Myh11 gene promoter, and the codon-modified iCreERT2 exhibits significant tamoxifen-independent leakage. Furthermore, because the Cre-bearing bacterial artificial chromosome (BAC) is inserted onto the Y chromosome, the SMMHC-CreERT2-Tg mice strain can only exhibit gene deletions in male mice. Additionally, there is a lack of Myh11-driven constitutive Cre mice when tamoxifen usage is a concern. We used CRISPR/Cas9-mediated homologous recombination between a donor vector carrying the CreNLSP2A or CreERT2-P2A sequence and homologous arm surrounding the translation start site of the Myh11 gene to generate Cre-knockin mice. The P2A sequence enables the simultaneous translation of Cre and endogenous proteins. Using reporter mice, we assessed Cre-mediated recombination efficiency, specificity, tamoxifen-dependent controllability, and functionality in both sexes. Both constitutive (Myh11-CreNLSP2A) and inducible (Myh11-CreERT2-P2A) Cre mice demonstrated efficient, SMC-specific, sex-independent Cre recombinase activity without confounding endogenous gene expression. Combined with recently generated BAC transgenic Myh11-CreERT2-RAD mice and the Itga8-CreERT2 mouse models, our models will help expand the research toolbox, facilitating unbiased and comprehensive research in SMCs and SMC-dependent cardiovascular diseases.