Biology of vascular mural cells

Single-cell RNA sequencing for characterizing the immune communication and iron metabolism roles in CD31+ glioma cells

Background

Gliomas are aggressive brain tumors marked by complex cellular interactions and significant immune cell infiltration. This study investigated the role of CD31+ immune cells, specifically macrophages and T cells, in the glioma microenvironment through single-cell RNA sequencing (scRNA-seq).

Methods

We employed the CellChat framework to map cell-cell communication pathways and used Monocle3 for pseudotime trajectory analysis to characterize the signaling and developmental progressions within CD31+ cells. Pathways such as osteopontin (SPP1) and major histocompatibility complex class II (MHC-II) were analyzed in terms of their role in immune regulation, and we examined the expression of ferritin, an iron-binding protein, to assess its potential function in modulating CD31+ cell activity.

Results

Our findings highlight the expression of key pathways, including SPP1 and MHC-II, influencing immune regulation. Ferritin was found to be highly expressed in CD31+ cells, suggesting a dual role in iron metabolism and immune modulation within the glioma microenvironment.

Conclusions

This study clarified the distinct roles of CD31+ immune cells in glioma progression and identified ferritin as a potential therapeutic target for modulating immune responses in gliomas. These findings may offer new directions in glioma research and the development of immunotherapy, which can aid in improving treatment outcomes.

Origins of Aortic Coarctation: A Vascular Smooth Muscle Compartment Boundary Model

Compartment boundaries divide the embryo into segments with distinct fates and functions. In the vascular system, compartment boundaries organize endothelial cells into arteries, capillaries, and veins that are the fundamental units of a circulatory network. For vascular smooth muscle cells (SMCs), such boundaries produce mosaic patterns of investment based on embryonic origins with important implications for the non-uniform distribution of vascular disease later in life. The morphogenesis of blood vessels requires vascular cell movements within compartments as highly-sensitive responses to changes in fluid flow shear stress and wall strain. These movements underline the remodeling of primitive plexuses, expansion of lumen diameters, regression of unused vessels, and building of multilayered artery walls. Although the loss of endothelial compartment boundaries can produce arterial-venous malformations, little is known about the consequences of mislocalization or the failure to form SMC-origin-specific boundaries during vascular development. We propose that the failure to establish a normal compartment boundary between cardiac neural-crest-derived SMCs of the 6th pharyngeal arch artery (future ductus arteriosus) and paraxial-mesoderm-derived SMCs of the dorsal aorta in mid-gestation embryos leads to aortic coarctation observed at birth. This model raises new questions about the effects of fluid flow dynamics on SMC investment and the formation of SMC compartment borders during pharyngeal arch artery remodeling and vascular development.

CXCL12 drives natural variation in coronary artery anatomy across diverse populations

Coronary arteries have a specific branching pattern crucial for oxygenating heart muscle. Among humans, there is natural variation in coronary anatomy with respect to perfusion of the inferior/posterior left heart, which can branch from either the right arterial tree, the left, or both-a phenotype known as coronary dominance. Using angiographic data for >60,000 US veterans of diverse ancestry, we conducted a genome-wide association study of coronary dominance, revealing moderate heritability and identifying ten significant loci. The strongest association occurred near CXCL12 in both European- and African-ancestry cohorts, with downstream analyses implicating effects on CXCL12 expression. We show that CXCL12 is expressed in human fetal hearts at the time dominance is established. Reducing Cxcl12 in mice altered coronary dominance and caused septal arteries to develop away from Cxcl12 expression domains. These findings indicate that CXCL12 patterns human coronary arteries, paving the way for "medical revascularization" through targeting developmental pathways.

Location, Location, Location: Spatial Immune-Stroma Crosstalk Drives Pathogenesis in Asthma

Chronic lung diseases including asthma are characterized by an abnormal immune response and active tissue remodeling. These changes in the architecture of the tissue are a fundamental part of the pathology across the life course of patients suffering from asthma. Current treatments aim at dampening the immune system hyperactivation, but effective drugs targeting stromal or acellular structures are still lacking. This is mainly due to the lack of a detailed understanding of the composition of the large airways and the cellular interactions taking place in this niche. We and others have revealed multiple aspects of the spatial architecture of the airway wall in response to airborne insults. In this review, we discuss four elements that we believe should be the focus of future asthma research across the life course, to increase understanding and improve therapies: (i) specialized lung niches, (ii) the 3D architecture of the epithelium, (iii) the extracellular matrix, and (iv) the vasculature. These components comprise the main stromal structures at the airway wall, each playing a key role in the development of asthma and directing the immune response. We summarize promising future directions that will enhance lung research, ultimately benefiting patients with asthma.

Alk1/Endoglin signaling restricts vein cell size increases in response to hemodynamic cues

Hemodynamic cues are thought to control blood vessel hierarchy through a shear stress set point, where flow increases lead to blood vessel diameter expansion, while decreases in blood flow cause blood vessel narrowing. Aberrations in blood vessel diameter control can cause congenital arteriovenous malformations (AVMs). We show in zebrafish embryos that while arteries behave according to the shear stress set point model, veins do not. This behavior is dependent on distinct arterial and venous endothelial cell (EC) shapes and sizes. We show that arterial ECs enlarge more strongly when experiencing higher flow, as compared to vein cells. Through the generation of chimeric embryos, we discover that this behavior of vein cells depends on the bone morphogenetic protein (BMP) pathway components Endoglin and Alk1. Endoglin (eng) or alk1 (acvrl1) mutant vein cells enlarge when in normal hemodynamic environments, while we do not observe a phenotype in either acvrl1 or eng mutant ECs in arteries. We further show that an increase in vein diameters initiates AVMs in eng mutants, secondarily leading to higher flow to arteries. These enlarge in response to higher flow through increasing arterial EC sizes, fueling the AVM. This study thus reveals a mechanism through which BMP signaling limits vein EC size increases in response to flow and provides a framework for our understanding of how a small number of mutant vein cells via flow-mediated secondary effects on wildtype arterial ECs can precipitate larger AVMs in disease conditions, such as hereditary hemorrhagic telangiectasia (HHT).

In vitro vascularization of 3D cell aggregates in microwells with integrated vascular beds

Most human tissues possess vascular networks supplying oxygen and nutrients. Engineering of functional tissue and organ models or equivalents often require the integration of artificial vascular networks. Several approaches, such as organs on chips and three-dimensional (3D) bioprinting, have been pursued to obtain vasculature and vascularized tissues in vitro. This technical feasibility study proposes a new approach for the in vitro vascularization of 3D microtissues. For this, we thermoform arrays of round-bottom microwells into thin non-porous and porous polymer films/membranes and culture vascular beds on them from which endothelial sprouting occurs in a Matrigel-based 3D extra cellular matrix. We present two possible culture configurations for the microwell-integrated vascular beds. In the first configuration, human umbilical vein endothelial cells (HUVECs) grow on and sprout from the inner wall of the non-porous microwells. In the second one, HUVECs grow on the outer surface of the porous microwells and sprout through the pores toward the inside. These approaches are extended to lymphatic endothelial cells. As a proof of concept, we demonstrate the in vitro vascularization of spheroids from human mesenchymal stem cells and MG-63 human osteosarcoma cells. Our results show the potential of this approach to provide the spheroids with an abundant outer vascular network and the indication of an inner vasculature.

Single-cell transcriptomics reveals aberrant skin-resident cell populations and identifies fibroblasts as a determinant in rosacea

Rosacea is a chronic inflammatory skin disorder, whose underlying cellular and molecular mechanisms remain obscure. Here, we generate a single-cell atlas of facial skin from female rosacea patients and healthy individuals. Among keratinocytes, a subpopulation characterized by IFNγ-mediated barrier function damage is found to be unique to rosacea lesions. Blocking IFNγ signaling alleviates rosacea-like phenotypes and skin barrier damage in mice. The papulopustular rosacea is featured by expansion of pro-inflammatory fibroblasts, Schwann, endothelial and macrophage/dendritic cells. The frequencies of type 1/17 and skin-resident memory T cells are increased, and vascular mural cells are characterized by activation of inflammatory pathways and impaired muscle contraction function in rosacea. Most importantly, fibroblasts are identified as the leading cell type producing pro-inflammatory and vasodilative signals in rosacea. Depletion of fibroblasts or knockdown of PTGDS, a gene specifically upregulated in fibroblasts, blocks rosacea development in mice. Our study provides a comprehensive understanding of the aberrant alterations of skin-resident cell populations and identifies fibroblasts as a key determinant in rosacea development.

GLP-1 programs the neurovascular landscape

Readily available nutrient-rich foods exploit our inherent drive to overconsume, creating an environment of overnutrition. This transformative setting has led to persistent health issues, such as obesity and metabolic syndrome. The development of glucagon-like peptide-1 receptor (GLP-1R) agonists reveals our ability to pharmacologically manage weight and address metabolic conditions. Obesity is directly linked to chronic low-grade inflammation, connecting our metabolic environment to neurodegenerative diseases. GLP-1R agonism in curbing obesity, achieved by impacting appetite and addressing associated metabolic defects, is revealing additional benefits extending beyond weight loss. Whether GLP-1R agonism directly impacts brain health or does so indirectly through improved metabolic health remains to be elucidated. In exploring the intricate connection between obesity and neurological conditions, recent literature suggests that GLP-1R agonism may have the capacity to shape the neurovascular landscape. Thus, GLP-1R agonism emerges as a promising strategy for addressing the complex interplay between metabolic health and cognitive well-being.

Robust differentiation of human pluripotent stem cells into mural progenitor cells via transient activation of NKX3.1

Mural cells are central to vascular integrity and function. In this study, we demonstrate the innovative use of the transcription factor NKX3.1 to guide the differentiation of human induced pluripotent stem cells into mural progenitor cells (iMPCs). By transiently activating NKX3.1 in mesodermal intermediates, we developed a method that diverges from traditional growth factor-based differentiation techniques. This approach efficiently generates a robust iMPC population capable of maturing into diverse functional mural cell subtypes, including smooth muscle cells and pericytes. These iMPCs exhibit key mural cell functionalities such as contractility, deposition of extracellular matrix, and the ability to support endothelial cell-mediated vascular network formation in vivo. Our study not only underscores the fate-determining significance of NKX3.1 in mural cell differentiation but also highlights the therapeutic potential of these iMPCs. We envision these insights could pave the way for a broader use of iMPCs in vascular biology and regenerative medicine.

A systems view of the vascular endothelium in health and disease

The dysfunction of blood-vessel-lining endothelial cells is a major cause of mortality. Although endothelial cells, being present in all organs as a single-cell layer, are often conceived as a rather inert cell population, the vascular endothelium as a whole should be considered a highly dynamic and interactive systemically disseminated organ. We present here a holistic view of the field of vascular research and review the diverse functions of blood-vessel-lining endothelial cells during the life cycle of the vasculature, namely responsive and relaying functions of the vascular endothelium and the responsive roles as instructive gatekeepers of organ function. Emerging translational perspectives in regenerative medicine, preventive medicine, and aging research are developed. Collectively, this review is aimed at promoting disciplinary coherence in the field of angioscience for a broader appreciation of the importance of the vasculature for organ function, systemic health, and healthy aging.

Semaphorin 3A promotes the long-term persistence of human SVF-derived microvascular networks in engineered grafts

Introduction

The stromal vascular fraction (SVF) of human adipose tissue is an attractive cell source for engineering grafts with intrinsic vascularization potential, as it is rich in vasculogenic progenitors. However, in order to maintain their functional perfusion it is important to promote the in vivo stabilization of newly assembled microvascular networks. We previously found that Semaphorin 3A (Sema3A) promotes the rapid stabilization of new blood vessels induced by VEGF overexpression in skeletal muscle. Here we investigated whether Sema3A could promote the assembly, connection to circulation and persistence of human SVF-derived microvascular networks in engineered grafts.

Methods

Recombinant Sema3A was engineered with a transglutaminase substrate sequence (TG-Sema3A) to allow cross-linking into fibrin hydrogels. Grafts were prepared with freshly isolated human SVF cells in fibrin hydrogels decorated with 0, 0.1 or 100 μg/ml TG-Sema3A and implanted subcutaneously in immune-deficient mice.

Results

After 1 week in vivo, the assembly of human-derived networks was similar in all conditions. The outer part of the grafts was populated by blood vessels of both human and mouse origin, which formed abundant hybrid structures within a common basal lamina. About 90% of human-derived blood vessels were functionally connected to the host circulation in all conditions. However, in the control samples human vessels were unstable. In fact, they significantly regressed by 6 weeks and could no longer be found by 12 weeks. In contrast, a low Sema3A dose (0.1 μg/ml) promoted further human vascular expansion by about 2-fold at 6 weeks and protected them from regression until 12 weeks. From a mechanistic point of view, the stabilization of SVF-derived vessels by 0.1 μg/ml of Sema3A correlated with the recruitment of a specific population of monocytes expressing its receptor Neuropilin-1.

Discussion

In conclusion, Sema3A is a potent stimulator of in vivo long-term persistence of microvascular networks derived from human SVF. Therefore, decoration of matrices with Sema3a can be envisioned to promote the functional support of tissue engineered grafts.

Astrocytic activation increases blood flow in the adult olfactory bulb

Activation of astrocytes after sensory stimulation has been reported to be involved in increased blood flow in the central nervous system. In the present study, using a chemogenetic method to induce astrocyte activation in mice without sensory stimulation, we found that astrocytic activation led to increased blood flow in the olfactory bulb, suggesting that astrocyte activation is sufficient for increasing blood flow in the olfactory bulb. The technique established here will be useful for studying the mechanisms underlying sensory input-dependent blood flow increases.

High-resolution 3D ultrastructural analysis of developing mouse neocortex reveals long slender processes of endothelial cells that enter neural cells

The development of the neocortex involves an interplay between neural cells and the vasculature. However, little is known about this interplay at the ultrastructural level. To gain a 3D insight into the ultrastructure of the developing neocortex, we have analyzed the embryonic mouse neocortex by serial block-face scanning electron microscopy (SBF-SEM). In this study, we report a first set of findings that focus on the interaction of blood vessels, notably endothelial tip cells (ETCs), and the neural cells in this tissue. A key observation was that the processes of ETCs, located either in the ventricular zone (VZ) or subventricular zone (SVZ)/intermediate zone (IZ), can enter, traverse the cytoplasm, and even exit via deep plasma membrane invaginations of the host cells, including apical progenitors (APs), basal progenitors (BPs), and newborn neurons. More than half of the ETC processes were found to enter the neural cells. Striking examples of this ETC process "invasion" were (i) protrusions of apical progenitors or newborn basal progenitors into the ventricular lumen that contained an ETC process inside and (ii) ETC process-containing protrusions of neurons that penetrated other neurons. Our observations reveal a - so far unknown - complexity of the ETC-neural cell interaction.

Dural mural cells paint an anti-inflammatory picture

Mural cells directly contact macrophages in the dural layer of the meninges to suppress pro-inflammatory phenotypes, including antigen presentation and lymphocyte differentiation. These mechanisms represent new targets for modulating CNS immune surveillance and pathological inflammation (Min et al. 2024. J. Exp. Med.https://doi.org/10.1084/jem.20230326).