The origin and mechanisms of smooth muscle cell development in vertebrates

Identification of distinct vascular mural cell populations during zebrafish embryonic development

BACKGROUND

Mural cells are an essential perivascular cell population that associate with blood vessels and contribute to vascular stabilization and tone. In the embryonic zebrafish vasculature, pdgfrb and tagln are commonly used as markers for identifying pericytes and vascular smooth muscle cells. However, the overlapping and distinct expression patterns of these markers in tandem have not been fully described.

RESULTS

Here, we used the Tg(pdgfrb:Gal4FF; UAS:RFP) and Tg(tagln:NLS-EGFP) transgenic lines to identify single- and double-positive perivascular cell populations on the cranial, axial, and intersegmental vessels between 1 and 5 days postfertilization. From this comparative analysis, we discovered two novel regions of tagln-positive cell populations that have the potential to function as mural cell precursors. Specifically, we found that the hypochord-a reportedly transient structure-contributes to tagln-positive cells along the dorsal aorta. We also identified a unique mural cell progenitor population that resides along the midline between the neural tube and notochord and contributes to intersegmental vessel mural cell coverage.

CONCLUSION

Together, our findings highlight the variability and versatility of tracking both pdgfrb and tagln expression in mural cells of the developing zebrafish embryo and reveal unexpected embryonic cell populations that express pdgfrb and tagln.

A Novel Tendon Injury Model, Induced by Collagenase Administration Combined with a Thermo-Responsive Hydrogel in Rats, Reproduces the Pathogenesis of Human Degenerative Tendinopathy

Patellar tendinopathy is a common clinical problem, but its underlying pathophysiology remains poorly understood, primarily due to the absence of a representative experimental model. The most widely used method to generate such a model is collagenase injection, although this method possesses limitations. We developed an optimized rat model of patellar tendinopathy via the ultrasound-guided injection of collagenase mixed with a thermo-responsive Pluronic hydrogel into the patellar tendon of sixty male Wistar rats. All analyses were carried out at 3, 7, 14, 30, and 60 days post-injury. We confirmed that our rat model reproduced the pathophysiology observed in human patients through analyses of ultrasonography, histology, immunofluorescence, and biomechanical parameters. Tendons that were injured by the injection of the collagenase-Pluronic mixture exhibited a significant increase in the cross-sectional area (p < 0.01), a high degree of tissue disorganization and hypercellularity, significantly strong neovascularization (p < 0.01), important changes in the levels of types I and III collagen expression, and the organization and presence of intra-tendinous calcifications. Decreases in the maximum rupture force and stiffness were also observed. These results demonstrate that our model replicates the key features observed in human patellar tendinopathy. Collagenase is evenly distributed, as the Pluronic hydrogel prevents its leakage and thus, damage to surrounding tissues. Therefore, this model is valuable for testing new treatments for patellar tendinopathy.

Single-cell analysis of shared signatures and transcriptional diversity during zebrafish development

During development, animals generate distinct cell populations with specific identities, functions, and morphologies. We mapped transcriptionally distinct populations across 489,686 cells from 62 stages during wild-type zebrafish embryogenesis and early larval development (3-120 h post-fertilization). Using these data, we identified the limited catalog of gene expression programs reused across multiple tissues and their cell-type-specific adaptations. We also determined the duration each transcriptional state is present during development and identify unexpected long-term cycling populations. Focused clustering and transcriptional trajectory analyses of non-skeletal muscle and endoderm identified transcriptional profiles and candidate transcriptional regulators of understudied cell types and subpopulations, including the pneumatic duct, individual intestinal smooth muscle layers, spatially distinct pericyte subpopulations, and recently discovered best4+ cells. To enable additional discoveries, we make this comprehensive transcriptional atlas of early zebrafish development available through our website, Daniocell.

Smooth Muscle Actin as a Criterion for Gravisensitivity of Stomach and Jejunum in Laboratory Rodents

Smooth muscle tissue (SMT) is one of the main structural components of visceral organs, acting as a key factor in the development of adaptive and pathological conditions. Despite the crucial part of SMT in the gastrointestinal tract activity, the mechanisms of its gravisensitivity are still insufficiently studied. The study evaluated the content of smooth muscle actin (α-SMA) in the membranes of the gastric fundus and jejunum in C57BL/6N mice (30-day space flight), in Mongolian gerbils Meriones unguiculatus (12-day orbital flight) and after anti-orthostatic suspension according to E.R. Morey-Holton. A morphometric analysis of α-SMA in the muscularis externa of the stomach and jejunum of mice and Mongolian gerbils from space flight groups revealed a decreased area of the immunopositive regions, a fact indicating a weakening of the SMT functional activity. Gravisensitivity of the contractile structures of the digestive system may be due to changes in the myofilament structural components of the smooth myocytes or myofibroblast actin. A simulated antiorthostatic suspension revealed no significant changes in the content of the α-SMA expression level, a fact supporting an alteration in the functional properties of the muscularis externa of the digestive hollow organs under weightless environment. The data obtained contribute to the novel mechanisms of the SMT contractile apparatus remodeling during orbital flights and can be used to improve preventive measures in space biomedicine.

Bioprocessing Considerations towards the Manufacturing of Therapeutic Skeletal and Smooth Muscle Cells

Tissue engineering approaches within the muscle context represent a promising emerging field to address the current therapeutic challenges related with multiple pathological conditions affecting the muscle compartments, either skeletal muscle or smooth muscle, responsible for involuntary and voluntary contraction, respectively. In this review, several features and parameters involved in the bioprocessing of muscle cells are addressed. The cell isolation process is depicted, depending on the type of tissue (smooth or skeletal muscle), followed by the description of the challenges involving the use of adult donor tissue and the strategies to overcome the hurdles of reaching relevant cell numbers towards a clinical application. Specifically, the use of stem/progenitor cells is highlighted as a source for smooth and skeletal muscle cells towards the development of a cellular product able to maintain the target cell's identity and functionality. Moreover, taking into account the need for a robust and cost-effective bioprocess for cell manufacturing, the combination of muscle cells with biomaterials and the need for scale-up envisioning clinical applications are also approached.

Cardiac competence of the paraxial head mesoderm fades concomitant with a shift towards the head skeletal muscle programme

The vertebrate head mesoderm provides the heart, the great vessels, some smooth and most head skeletal muscle, in addition to parts of the skull. It has been speculated that the ability to generate cardiac and smooth muscle is the evolutionary ground-state of the tissue. However, whether indeed the entire head mesoderm has generic cardiac competence, how long this may last, and what happens as cardiac competence fades, is not clear. Bone morphogenetic proteins (Bmps) are known to promote cardiogenesis. Using 41 different marker genes in the chicken embryo, we show that the paraxial head mesoderm that normally does not engage in cardiogenesis has the ability to respond to Bmp for a long time. However, Bmp signals are interpreted differently at different time points. Up to early head fold stages, the paraxial head mesoderm is able to read Bmps as signal to engage in the cardiac programme; the ability to upregulate smooth muscle markers is retained slightly longer. Notably, as cardiac competence fades, Bmp promotes the head skeletal muscle programme instead. The switch from cardiac to skeletal muscle competence is Wnt-independent as Wnt caudalises the head mesoderm and also suppresses Msc-inducing Bmp provided by the prechordal plate, thus suppressing both the cardiac and the head skeletal muscle programmes. Our study for the first time suggests a specific transition state in the embryo when cardiac competence is replaced by skeletal muscle competence. It sets the stage to unravel the cardiac-skeletal muscle antagonism that is known to partially collapse in heart failure.

Crk/Crkl regulates early angiogenesis in mouse embryos by accelerating endothelial cell maturation

Rationale

Ubiquitously expressed cytoplasmic adaptors CRK and CRKL mediate multiple signaling pathways in mammalian embryogenesis. They are also associated with cardiovascular defects occurring in Miller-Dieker syndrome and 22q11.2 deletion syndrome, respectively. The embryonic mesoderm contributes to the formation of the cardiovascular system, yet the roles that Crk and Crkl play there are not understood on a single cell level.

Objectives

To determine functions of Crk and Crkl in the embryonic mesoderm during early mouse vascular development. Secondly, we will examine the molecular mechanisms responsible for early embryonic endothelial cell (EC) defects by performing single cell RNA-sequencing (scRNA-seq) and in vivo validation experiments.

Methods and Results

Inactivation of both Crk and Crkl together using Mesp1 ^Cre resulted embryonic lethality with severe vascular defects. Although vasculogenesis appeared normal, angiogenesis was disrupted both in the yolk sac and embryo proper, leading to disorganized vascular networks. We performed scRNA-seq of the Mesp1 ^Cre mesodermal lineage and found that there was upregulation of a great number of angiogenesis and cell migration related genes in ECs in the mutants, including NOTCH signaling genes such as Dll4 and Hey1 . Further bioinformatic analysis of EC subpopulations identified a relative increase in the number of more differentiated angiogenic ECs and decrease in EC progenitors. Consistent with this, we identified an expansion of Dll4 expressing cells within abnormal arteries, in vivo . Also, our bioinformatic data indicates that there is dysregulated expression of lineage genes that promote EC differentiation causing accelerated cell fate progression during EC differentiation.

Conclusions

Our results show that Crk and Crkl are crucial for regulating early embryonic angiogenesis. Combined inactivation of Crk/Crkl caused precocious EC maturation with an increase of atypical differentiated angiogenic ECs and failed vascular remodeling. This is in part due to increased NOTCH signaling and altered expression of cell migration genes.

The critical role of cardiolipin in metazoan differentiation, development, and maturation

Cardiolipins are phospholipids that are central to proper mitochondrial functioning. Because mitochondria play crucial roles in differentiation, development, and maturation, we would also expect cardiolipin to play major roles in these processes. Indeed, cardiolipin has been implicated in the mechanism of three human diseases that affect young infants, implying developmental abnormalities. In this review, we will: (1) Review the biology of cardiolipin; (2) Outline the evidence for essential roles of cardiolipin during organismal development, including embryogenesis and cell maturation in vertebrate organisms; (3) Place the role(s) of cardiolipin during embryogenesis within the larger context of the roles of mitochondria in development; and (4) Suggest avenues for future research.

Combined Transcriptome and Metabolome Analysis of Smooth Muscle of Myostatin Knockout Cattle

Myostatin (MSTN), a growth and differentiation factor, plays an important role in regulating skeletal muscle growth and development. MSTN knockout (MSTN-KO) leads to skeletal muscle hypertrophy and regulates metabolic homeostasis. Moreover, MSTN is also detected in smooth muscle. However, the effect of MSTN-KO on smooth muscle has not yet been reported. In this study, combined metabolome and transcriptome analyses were performed to investigate the metabolic and transcriptional profiling in esophageal smooth muscles of MSTN-KO Chinese Luxi Yellow cattle (n = 5, 24 months, average body weight 608.5 ± 17.62 kg) and wild-type (WT) Chinese Luxi Yellow cattle (n = 5, 24 months, average body weight 528.25 ± 11.03 kg). The transcriptome was sequenced using the Illumina Novaseq™ 6000 sequence platform. In total, 337 significantly up- and 129 significantly down-regulated genes were detected in the MSTN-KO cattle compared with the WT Chinese Luxi Yellow cattle. Functional enrichment analysis indicated that the DEGs were mainly enriched in 67 signaling pathways, including cell adhesion molecules, tight junction, and the cGMP-PKG signaling pathway. Metabolomics analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) identified 130 differential metabolites between the groups, with 56 up-regulated and 74 down-regulated in MSTN knockout cattle compared with WT cattle. Differential metabolites were significantly enriched in 31 pathways, including glycerophospholipid metabolism, histidine metabolism, glutathione metabolism, and purine metabolism. Transcriptome and metabolome were combined to analyze the significant enrichment pathways, and there were three metabolically related pathways, including histidine metabolism, purine metabolism, and arginine and proline metabolism. These results provide important references for in-depth research on the effect of MSTN knockout on smooth muscle.

Single-cell analysis of shared signatures and transcriptional diversity during zebrafish development

During development, animals generate distinct cell populations with specific identities, functions, and morphologies. We mapped transcriptionally distinct populations across 489,686 cells from 62 stages during wild-type zebrafish embryogenesis and early larval development (3-120 hours post-fertilization). Using these data, we identified the limited catalog of gene expression programs reused across multiple tissues and their cell-type-specific adaptations. We also determined the duration each transcriptional state is present during development and suggest new long-term cycling populations. Focused analyses of non-skeletal muscle and the endoderm identified transcriptional profiles of understudied cell types and subpopulations, including the pneumatic duct, individual intestinal smooth muscle layers, spatially distinct pericyte subpopulations, and homologs of recently discovered human best4+ enterocytes. The transcriptional regulators of these populations remain unknown, so we reconstructed gene expression trajectories to suggest candidates. To enable additional discoveries, we make this comprehensive transcriptional atlas of early zebrafish development available through our website, Daniocell.

Identification of overlapping and distinct mural cell populations during early embryonic development

Mural cells are an essential perivascular cell population that associate with blood vessels and contribute to vascular stabilization and tone. In the embryonic zebrafish vasculature, pdgfrb and tagln are commonly used as markers for identifying pericytes and vascular smooth muscle cells (vSMCs). However, the expression patterns of these markers used in tandem have not been fully described. Here, we used the Tg(pdgfrb:Gal4FF; UAS:RFP) and Tg(tagln:NLS-EGFP) transgenic lines to identify single- and double-positive perivascular populations in the cranial, axial, and intersegmental vessels between 1 and 5 days post-fertilization. From this comparative analysis, we discovered two novel regions of tagln-positive cell populations that have the potential to function as mural cell precursors. Specifically, we found that the hypochord- a reportedly transient structure-contributes to tagln-positive cells along the dorsal aorta. We also identified a unique sclerotome-derived mural cell progenitor population that resides along the midline between the neural tube and notochord and contributes to intersegmental vessel mural cell coverage. Together, our findings highlight the variability and versatility of tracking pdgfrb and tagln expression in mural cells of the developing zebrafish embryo.

A hiPSC-derived lineage-specific vascular smooth muscle cell-on-a-chip identifies aortic heterogeneity across segments

Aortic aneurysm (AA), a potentially lethal condition with the characteristic of aortic dilatation, can only be treated by surgical or endovascular procedures. The underlying mechanisms of AA are unclear and early preventive treatment is still insufficient due to segmental aortic heterogeneity and the limitations of current disease models. Here, we firstly established a comprehensive lineage-specific vascular smooth muscle cell (SMC)-on-a-chip model using human induced pluripotent stem cells to yield cell lineages representing different segments of the aorta and tested the constructed organ-on-a-chip model under various tensile stress conditions. Bulk RNA sequencing, RT-qPCR, immunofluorescence, western blot and FACS analyses were performed to discover the segmental aortic heterogeneity of response for tensile stress and drug testing. The appropriate stretching frequency for all lineages of SMCs was 1.0 Hz, paraxial mesoderm (PM) SMCs were more sensitive to tensile stress than lateral mesoderm (LM) SMCs and neural crest (NC) SMCs. These differences may be related to the different transcriptional profiles of the tension-stressed distinct lineage-specific vascular SMCs, specifically in relation to the PI3K-Akt signaling pathway. Also, the organ-on-a-chip displayed contractile physiology, perfect fluid coordination, and was conducive to drug testing, displaying heterogeneous segmental aortic responses. Compared with LM-SMCs and NC-SMCs, PM-SMCs were more sensitive to ciprofloxacin. The model is evaluated as a novel and suitable supplement to AA animal models for determining differential physiology and drug response in different parts of the aorta. Furthermore, this system could pave the way for disease modeling, drug testing, and the personalized treatment of patients with AA in the future.

Plasticity in airway smooth muscle differentiation during mouse lung development

It has been proposed that smooth muscle differentiation may physically sculpt airway epithelial branches in mammalian lungs. Serum response factor (SRF) acts with its co-factor myocardin to activate the expression of contractile smooth muscle markers. In the adult, however, smooth muscle exhibits a variety of phenotypes beyond contractile, and these are independent of SRF/myocardin-induced transcription. To determine whether a similar phenotypic plasticity is exhibited during development, we deleted Srf from the mouse embryonic pulmonary mesenchyme. Srf-mutant lungs branch normally, and the mesenchyme displays mechanical properties indistinguishable from controls. scRNA-seq identified an Srf-null smooth muscle cluster, wrapping the airways of mutant lungs, which lacks contractile smooth muscle markers but retains many features of control smooth muscle. Srf-null embryonic airway smooth muscle exhibits a synthetic phenotype, compared with the contractile phenotype of mature wild-type airway smooth muscle. Our findings identify plasticity in embryonic airway smooth muscle and demonstrate that a synthetic smooth muscle layer promotes airway branching morphogenesis.

Pulmonary Vascular Remodeling in Pulmonary Hypertension

Pulmonary vascular remodeling is the critical structural alteration and pathological feature in pulmonary hypertension (PH) and involves changes in the intima, media and adventitia. Pulmonary vascular remodeling consists of the proliferation and phenotypic transformation of pulmonary artery endothelial cells (PAECs) and pulmonary artery smooth muscle cells (PASMCs) of the middle membranous pulmonary artery, as well as complex interactions involving external layer pulmonary artery fibroblasts (PAFs) and extracellular matrix (ECM). Inflammatory mechanisms, apoptosis and other factors in the vascular wall are influenced by different mechanisms that likely act in concert to drive disease progression. This article reviews these pathological changes and highlights some pathogenetic mechanisms involved in the remodeling process.

The Molecular Signature of Human Testicular Peritubular Cells Revealed by Single-Cell Analysis

Peritubular cells of the human testis form a small compartment surrounding the seminiferous tubules. They are crucial for sperm transport, and they emerge as contributors to the spermatogonial stem cell niche. They are among the least known cell types of the human body. We employed single-cell RNA sequencing of cultured human testicular peritubular cells (HTPCs), which had been isolated from testicular samples of donors with normal spermatogenesis. The significant overlap between our results and recently published ex vivo data indicates that HTPCs are a highly adequate cellular model to define and study these cells. Thus, based on the expression of several markers, HTPCs can be classified as testicular smooth muscle cells. Small differences between the in vivo/in vitro expressed genes may be due to cellular plasticity. Plasticity was also shown upon addition of FCS to the culture medium. Based on transcriptome similarities, four cellular states were identified. Further analyses confirmed the presence of known stem cell niche-relevant factors (e.g., GDNF) and identified unknown functions, e.g., the ability to produce retinoic acid. Therefore, HTPCs allow us to define the signature(s) and delineate the functions of human testicular peritubular cells. The data may also serve as a resource for future studies to better understand male (in)fertility.

GATA6 is a crucial factor for Myocd expression in the visceral smooth muscle cell differentiation program of the murine ureter

Smooth muscle cells (SMCs) are a crucial component of the mesenchymal wall of the ureter, as they account for the efficient removal of the urine from the renal pelvis to the bladder by means of their contractile activity. Here, we show that the zinc-finger transcription factor gene Gata6 is expressed in mesenchymal precursors of ureteric SMCs under the control of BMP4 signaling. Mice with a conditional loss of Gata6 in these precursors exhibit a delayed onset and reduced level of SMC differentiation and peristaltic activity, as well as dilatation of the ureter and renal pelvis (hydroureternephrosis) at birth and at postnatal stages. Molecular profiling revealed a delayed and reduced expression of the myogenic driver gene Myocd, but the activation of signaling pathways and transcription factors previously implicated in activation of the visceral SMC program in the ureter was unchanged. Additional gain-of-function experiments suggest that GATA6 cooperates with FOXF1 in Myocd activation and SMC differentiation, possibly as pioneer and lineage-determining factors, respectively.

Immunohistochemical Study of Smooth Muscle Cells and Elastin in Goose Lungs

There are many differences (morphological, physiological and mechanical) between the lungs of birds and the lungs of mammals. Birds have a more efficient exchange of oxygen and carbon dioxide than mammals. In this article, we studied the presence of four antibodies (actin, α-smooth muscle actin, desmin and elastin) in the lungs of geese. Smooth muscle cells (SMCs) immunoreactive to actin, α-SMA and desmin were observed in the primary and secondary bronchi and arranged as a continuous layer. In the tertiary bronchus (parabronchus), immunoreactive cells on α-SMA and desmin were observed as aggregations of smooth muscle cells in the septum tips in atrial opening. A small number of α-SMA and desmin-positive cells were observed on the periphery of the parabronchi and between the air and blood capillaries. The elastic fibres were found in the large bronchi in connection with smooth muscle bands. In the parabronchi the elastic fibres form an elastic membrane lining the parabronchial lumen. In the blood vessels, the elastic fibres form the inner and outer elastic membrane. The individual elastic membranes connect neighbouring blood vessels.

Notch signaling is a novel regulator of visceral smooth muscle cell differentiation in the murine ureter

The contractile phenotype of smooth muscle cells (SMCs) is transcriptionally controlled by a complex of the DNA-binding protein SRF and the transcriptional co-activator MYOCD. The pathways that activate expression of Myocd and of SMC structural genes in mesenchymal progenitors are diverse, reflecting different intrinsic and extrinsic signaling inputs. Taking the ureter as a model, we analyzed whether Notch signaling, a pathway previously implicated in vascular SMC development, also affects visceral SMC differentiation. We show that mice with a conditional deletion of the unique Notch mediator RBPJ in the undifferentiated ureteric mesenchyme exhibit altered ureter peristalsis with a delayed onset, and decreased contraction frequency and intensity at fetal stages. They also develop hydroureter 2 weeks after birth. Notch signaling is required for precise temporal activation of Myocd expression and, independently, for expression of a group of late SMC structural genes. Based on additional expression analyses, we suggest that a mesenchymal JAG1-NOTCH2/NOTCH3 module regulates visceral SMC differentiation in the ureter in a biphasic and bimodal manner, and that its molecular function differs from that in the vascular system.