Isolation, bulk cultivation, and characterization of coronary microvascular pericytes: the second most frequent myocardial cell type in vitro

PBX/Knotted 1 homeobox-2 (PKNOX2) is a novel regulator of myocardial fibrosis

Much effort has been made to uncover the cellular heterogeneities of human hearts by single-nucleus RNA sequencing. However, the cardiac transcriptional regulation networks have not been systematically described because of the limitations in detecting transcription factors. In this study, we optimized a pipeline for isolating nuclei and conducting single-nucleus RNA sequencing targeted to detect a higher number of cell signal genes and an optimal number of transcription factors. With this unbiased protocol, we characterized the cellular composition of healthy human hearts and investigated the transcriptional regulation networks involved in determining the cellular identities and functions of the main cardiac cell subtypes. Particularly in fibroblasts, a novel regulator, PKNOX2, was identified as being associated with physiological fibroblast activation in healthy hearts. To validate the roles of these transcription factors in maintaining homeostasis, we used single-nucleus RNA-sequencing analysis of transplanted failing hearts focusing on fibroblast remodelling. The trajectory analysis suggested that PKNOX2 was abnormally decreased from fibroblast activation to pathological myofibroblast formation. Both gain- and loss-of-function in vitro experiments demonstrated the inhibitory role of PKNOX2 in pathological fibrosis remodelling. Moreover, fibroblast-specific overexpression and knockout of PKNOX2 in a heart failure mouse model induced by transverse aortic constriction surgery significantly improved and aggravated myocardial fibrosis, respectively. In summary, this study established a high-quality pipeline for single-nucleus RNA-sequencing analysis of heart muscle. With this optimized protocol, we described the transcriptional regulation networks of the main cardiac cell subtypes and identified PKNOX2 as a novel regulator in suppressing fibrosis and a potential therapeutic target for future translational studies.

The fate and role of the pericytes in myocardial diseases

The adult mammalian heart contains a large population of pericytes that play important roles in homeostasis and disease. In the normal heart, pericytes regulate microvascular permeability and flow. Myocardial diseases are associated with marked alterations in pericyte phenotype and function. This review manuscript discusses the role of pericytes in cardiac homeostasis and disease. Following myocardial infarction (MI), cardiac pericytes participate in all phases of cardiac repair. During the inflammatory phase, pericytes may secrete cytokines and chemokines and may regulate leukocyte trafficking, through formation of intercellular gaps that serve as exit points for inflammatory cells. Moreover, pericyte contraction induces microvascular constriction, contributing to the pathogenesis of 'no-reflow' in ischemia and reperfusion. During the proliferative phase, pericytes are activated by growth factors, such as transforming growth factor (TGF)-β and contribute to fibrosis, predominantly through secretion of fibrogenic mediators. A fraction of pericytes acquires fibroblast identity but contributes only to a small percentage of infarct fibroblasts and myofibroblasts. As the scar matures, pericytes form a coat around infarct neovessels, promoting stabilization of the vasculature. Pericytes may also be involved in the pathogenesis of chronic heart failure, by regulating inflammation, fibrosis, angiogenesis and myocardial perfusion. Pericytes are also important targets of viral infections (such as SARS-CoV2) and may be implicated in the pathogenesis of cardiac complications of COVID19. Considering their role in myocardial inflammation, fibrosis and angiogenesis, pericytes may be promising therapeutic targets in myocardial disease.

Stromal Cell-SLIT3/Cardiomyocyte-ROBO1 Axis Regulates Pressure Overload-Induced Cardiac Hypertrophy

BACKGROUND

Recently shown to regulate cardiac development, the secreted axon guidance molecule SLIT3 maintains its expression in the postnatal heart. Despite its known expression in the cardiovascular system after birth, SLIT3's relevance to cardiovascular function in the postnatal state remains unknown. As such, the objectives of this study were to determine the postnatal myocardial sources of SLIT3 and to evaluate its functional role in regulating the cardiac response to pressure overload stress.

METHODS

We performed in vitro studies on cardiomyocytes and myocardial tissue samples from patients and performed in vivo investigation with SLIT3 and ROBO1 (roundabout homolog 1) mutant mice undergoing transverse aortic constriction to establish the role of SLIT3-ROBO1 in adverse cardiac remodeling.

RESULTS

We first found that SLIT3 transcription was increased in myocardial tissue obtained from patients with congenital heart defects that caused ventricular pressure overload. Immunostaining of hearts from WT (wild-type) and reporter mice revealed that SLIT3 is secreted by cardiac stromal cells, namely fibroblasts and vascular mural cells, within the heart. Conditioned media from cardiac fibroblasts and vascular mural cells both stimulated cardiomyocyte hypertrophy in vitro, an effect that was partially inhibited by an anti-SLIT3 antibody. Also, the N-terminal, but not the C-terminal, fragment of SLIT3 and the forced overexpression of SLIT3 stimulated cardiomyocyte hypertrophy and the transcription of hypertrophy-related genes. We next determined that ROBO1 was the most highly expressed roundabout receptor in cardiomyocytes and that ROBO1 mediated SLIT3's hypertrophic effects in vitro. In vivo, Tcf21+ fibroblast and Tbx18+ vascular mural cell-specific knockout of SLIT3 in mice resulted in decreased left ventricular hypertrophy and cardiac fibrosis after transverse aortic constriction. Furthermore, α-MHC+ cardiomyocyte-specific deletion of ROBO1 also preserved left ventricular function and abrogated hypertrophy, but not fibrosis, after transverse aortic constriction.

CONCLUSIONS

Collectively, these results indicate a novel role for the SLIT3-ROBO1-signaling axis in regulating postnatal cardiomyocyte hypertrophy induced by pressure overload.

The role of cardiac pericytes in health and disease: therapeutic targets for myocardial infarction

Millions of cardiomyocytes die immediately after myocardial infarction, regardless of whether the culprit coronary artery undergoes prompt revascularization. Residual ischaemia in the peri-infarct border zone causes further cardiomyocyte damage, resulting in a progressive decline in contractile function. To date, no treatment has succeeded in increasing the vascularization of the infarcted heart. In the past decade, new approaches that can target the heart's highly plastic perivascular niche have been proposed. The perivascular environment is populated by mesenchymal progenitor cells, fibroblasts, myofibroblasts and pericytes, which can together mount a healing response to the ischaemic damage. In the infarcted heart, pericytes have crucial roles in angiogenesis, scar formation and stabilization, and control of the inflammatory response. Persistent ischaemia and accrual of age-related risk factors can lead to pericyte depletion and dysfunction. In this Review, we describe the phenotypic changes that characterize the response of cardiac pericytes to ischaemia and the potential of pericyte-based therapy for restoring the perivascular niche after myocardial infarction. Pericyte-related therapies that can salvage the area at risk of an ischaemic injury include exogenously administered pericytes, pericyte-derived exosomes, pericyte-engineered biomaterials, and pharmacological approaches that can stimulate the differentiation of constitutively resident pericytes towards an arteriogenic phenotype. Promising preclinical results from in vitro and in vivo studies indicate that pericytes have crucial roles in the treatment of coronary artery disease and the prevention of post-ischaemic heart failure.

The role of endothelial cell-pericyte interactions in vascularization and diseases

BACKGROUND

Endothelial cells (ECs) and pericytes (PCs) are crucial components of the vascular system, with ECs lining the inner layer of blood vessels and PCs surrounding capillaries to regulate blood flow and angiogenesis. Intercellular communication between ECs and PCs is vital for the formation, stability, and function of blood vessels. Various signaling pathways, such as the vascular endothelial growth factor/vascular endothelial growth factor receptor pathway and the platelet-derived growth factor-B/platelet-derived growth factor receptor-β pathway, play roles in communication between ECs and PCs. Dysfunctional communication between these cells is associated with various diseases, including vascular diseases, central nervous system disorders, and certain types of cancers.

AIM OF REVIEW

This review aimed to explore the diverse roles of ECs and PCs in the formation and reshaping of blood vessels. This review focused on the essential signaling pathways that facilitate communication between these cells and investigated how disruptions in these pathways may contribute to disease. Additionally, the review explored potential therapeutic targets, future research directions, and innovative approaches, such as investigating the impact of EC-PCs in novel systemic diseases, addressing resistance to antiangiogenic drugs, and developing novel antiangiogenic medications to enhance therapeutic efficacy.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Disordered EC-PC intercellular signaling plays a role in abnormal blood vessel formation, thus contributing to the progression of various diseases and the development of resistance to antiangiogenic drugs. Therefore, studies on EC-PC intercellular interactions have high clinical relevance.

Pericytes as the Orchestrators of Vasculature and Adipogenesis

Pericytes (PCs) are located surrounding the walls of small blood vessels, particularly capillaries and microvessels. In addition to their functions in maintaining vascular integrity, participating in angiogenesis, and regulating blood flow, PCs also serve as a reservoir for multi-potent stem/progenitor cells in white, brown, beige, and bone marrow adipose tissues. Due to the complex nature of this cell population, the identification and characterization of PCs has been challenging. A comprehensive understanding of the heterogeneity of PCs may enhance their potential as therapeutic targets for metabolic syndromes or bone-related diseases. This mini-review summarizes multiple PC markers commonly employed in lineage-tracing studies, with an emphasis on their contribution to adipogenesis and functions in different adipose depots under diverse metabolic conditions.

Pericyte loss initiates microvascular dysfunction in the development of diastolic dysfunction

Aims

Microvascular dysfunction has been proposed to drive heart failure with preserved ejection fraction (HFpEF), but the initiating molecular and cellular events are largely unknown. Our objective was to determine when microvascular alterations in HFpEF begin, how they contribute to disease progression, and how pericyte dysfunction plays a role herein.

Methods and results

Microvascular dysfunction, characterized by inflammatory activation, loss of junctional barrier function, and altered pericyte-endothelial crosstalk, was assessed with respect to the development of cardiac dysfunction, in the Zucker fatty and spontaneously hypertensive (ZSF1) obese rat model of HFpEF at three time points: 6, 14, and 21 weeks of age. Pericyte loss was the earliest and strongest microvascular change, occurring before prominent echocardiographic signs of diastolic dysfunction were present. Pericytes were shown to be less proliferative and had a disrupted morphology at 14 weeks in the obese ZSF1 animals, who also exhibited an increased capillary luminal diameter and disrupted endothelial junctions. Microvascular dysfunction was also studied in a mouse model of chronic reduction in capillary pericyte coverage (PDGF-Bret/ret), which spontaneously developed many aspects of diastolic dysfunction. Pericytes exposed to oxidative stress in vitro showed downregulation of cell cycle-associated pathways and induced a pro-inflammatory state in endothelial cells upon co-culture.

Conclusion

We propose pericytes are important for maintaining endothelial cell function, where loss of pericytes enhances the reactivity of endothelial cells to inflammatory signals and promotes microvascular dysfunction, thereby accelerating the development of HFpEF.

COVID-19 and Cardiovascular Diseases: From Cellular Mechanisms to Clinical Manifestations

Coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), quickly spread worldwide and led to over 581 million confirmed cases and over 6 million deaths as 1 August 2022. The binding of the viral surface spike protein to the human angiotensin-converting enzyme 2 (ACE2) receptor is the primary mechanism of SARS-CoV-2 infection. Not only highly expressed in the lung, ACE2 is also widely distributed in the heart, mainly in cardiomyocytes and pericytes. The strong association between COVID-19 and cardiovascular disease (CVD) has been demonstrated by increased clinical evidence. Preexisting CVD risk factors, including obesity, hypertension, and diabetes etc., increase susceptibility to COVID-19. In turn, COVID-19 exacerbates the progression of CVD, including myocardial damage, arrhythmia, acute myocarditis, heart failure, and thromboembolism. Moreover, cardiovascular risks post recovery and the vaccination-associated cardiovascular problems have become increasingly evident. To demonstrate the association between COVID-19 and CVD, this review detailly illustrated the impact of COVID-19 on different cells (cardiomyocytes, pericytes, endothelial cells, and fibroblasts) in myocardial tissue and provides an overview of the clinical manifestations of cardiovascular involvements in the pandemic. Finally, the issues related to myocardial injury post recovery, as well as vaccination-induced CVD, has also been emphasized.

Research advances in cochlear pericytes and hearing loss

Pericytes are specialized mural cells surrounding endothelial cells in microvascular beds. They play a role in vascular development, blood flow regulation, maintenance of blood-tissue barrier integrity, and control of angiogenesis, tissue fibrosis, and wound healing. In recent decades, understanding of the critical role played by pericytes in retina, brain, lung, and kidney has seen significant progress. The cochlea contains a large population of pericytes. However, the role of cochlear pericytes in auditory pathophysiology is, by contrast, largely unknown. The present review discusses recent progress in identifying cochlear pericytes, mapping their distribution, and defining their role in regulating blood flow, controlling the blood-labyrinth barrier (BLB) and angiogenesis, and involvement in different types of hearing loss.

Cardiac Pericytes Acquire a Fibrogenic Phenotype and Contribute to Vascular Maturation After Myocardial Infarction

BACKGROUND

Pericytes have been implicated in tissue repair, remodeling, and fibrosis. Although the mammalian heart contains abundant pericytes, their fate and involvement in myocardial disease remains unknown.

METHODS

We used NG2Dsred;PDGFRαEGFP pericyte:fibroblast dual reporter mice and inducible NG2CreER mice to study the fate and phenotypic modulation of pericytes in myocardial infarction. The transcriptomic profile of pericyte-derived cells was studied using polymerase chain reaction arrays and single-cell RNA sequencing. The role of transforming growth factor-β (TGF-β) signaling in regulation of pericyte phenotype was investigated in vivo using pericyte-specific TGF-β receptor 2 knockout mice and in vitro using cultured human placental pericytes.

RESULTS

In normal hearts, neuron/glial antigen 2 (NG2) and platelet-derived growth factor receptor α (PDGFRα) identified distinct nonoverlapping populations of pericytes and fibroblasts, respectively. After infarction, a population of cells expressing both pericyte and fibroblast markers emerged. Lineage tracing demonstrated that in the infarcted region, a subpopulation of pericytes exhibited transient expression of fibroblast markers. Pericyte-derived cells accounted for ~4% of PDGFRα+ infarct fibroblasts during the proliferative phase of repair. Pericyte-derived fibroblasts were overactive, expressing higher levels of extracellular matrix genes, integrins, matricellular proteins, and growth factors, when compared with fibroblasts from other cellular sources. Another subset of pericytes contributed to infarct angiogenesis by forming a mural cell coat, stabilizing infarct neovessels. Single-cell RNA sequencing showed that NG2 lineage cells diversify after infarction and exhibit increased expression of matrix genes, and a cluster with high expression of fibroblast identity markers emerges. Trajectory analysis suggested that diversification of infarct pericytes may be driven by proliferating cells. In vitro and in vivo studies identified TGF-β as a potentially causative mediator in fibrogenic activation of infarct pericytes. However, pericyte-specific TGF-β receptor 2 disruption had no significant effects on infarct myofibroblast infiltration and collagen deposition. Pericyte-specific TGF-β signaling was involved in vascular maturation, mediating formation of a mural cell coat investing infarct neovessels and protecting from dilative remodeling.

CONCLUSIONS

In the healing infarct, cardiac pericytes upregulate expression of fibrosis-associated genes, exhibiting matrix-synthetic and matrix-remodeling profiles. A fraction of infarct pericytes exhibits expression of fibroblast identity markers. Pericyte-specific TGF-β signaling plays a central role in maturation of the infarct vasculature and protects from adverse dilative remodeling, but it does not modulate fibrotic remodeling.

Coronary No-Reflow after Primary Percutaneous Coronary Intervention-Current Knowledge on Pathophysiology, Diagnosis, Clinical Impact and Therapy

Coronary no-reflow (CNR) is a frequent phenomenon that develops in patients with ST-segment elevation myocardial infarction (STEMI) following reperfusion therapy. CNR is highly dynamic, develops gradually (over hours) and persists for days to weeks after reperfusion. Microvascular obstruction (MVO) developing as a consequence of myocardial ischemia, distal embolization and reperfusion-related injury is the main pathophysiological mechanism of CNR. The frequency of CNR or MVO after primary PCI differs widely depending on the sensitivity of the tools used for diagnosis and timing of examination. Coronary angiography is readily available and most convenient to diagnose CNR but it is highly conservative and underestimates the true frequency of CNR. Cardiac magnetic resonance (CMR) imaging is the most sensitive method to diagnose MVO and CNR that provides information on the presence, localization and extent of MVO. CMR imaging detects intramyocardial hemorrhage and accurately estimates the infarct size. MVO and CNR markedly negate the benefits of reperfusion therapy and contribute to poor clinical outcomes including adverse remodeling of left ventricle, worsening or new congestive heart failure and reduced survival. Despite extensive research and the use of therapies that target almost all known pathophysiological mechanisms of CNR, no therapy has been found that prevents or reverses CNR and provides consistent clinical benefit in patients with STEMI undergoing reperfusion. Currently, the prevention or alleviation of MVO and CNR remain unmet goals in the therapy of STEMI that continue to be under intense research.

Cultured brain pericytes adopt an immature phenotype and require endothelial cells for expression of canonical markers and ECM genes

Pericytes (PCs) are essential components of the blood brain barrier. Brain PCs are critical for dynamically regulating blood flow, for maintaining vascular integrity and their dysregulation is associated with a myriad of disorders such as Alzheimer's disease. To understand their physiological and molecular functions, studies have increasingly focused on primary brain PC isolation and culture. Multiple methods for PC culture have been developed over the years, however, it is still unclear how primary PCs compare to their in vivo counterparts. To address this question, we compared cultured brain PCs at passage 5 and 20 to adult and embryonic brain PCs directly isolated from mouse brains via single cell RNA-seq. Cultured PCs were highly homogeneous, and were most similar to embryonic PCs, while displaying a significantly different transcriptional profile to adult brain PCs. Cultured PCs downregulated canonical PC markers and extracellular matrix (ECM) genes. Importantly, expression of PC markers and ECM genes could be improved by co-culture with brain endothelial cells, showing the importance of the endothelium in maintaining PC identity and function. Taken together, these results highlight key transcriptional differences between cultured and in vivo PCs which should be considered when performing in vitro experiments with brain PCs.

Proteomic profiling of concurrently isolated primary microvascular endothelial cells, pericytes, and vascular smooth muscle cells from adult mouse heart

The microcirculation serves crucial functions in adult heart, distinct from those carried out by epicardial vessels. Microvessels are governed by unique regulatory mechanisms, impairment of which leads to microvessel-specific pathology. There are few treatment options for patients with microvascular heart disease, primarily due to limited understanding of underlying pathology. High throughput mRNA sequencing and protein expression profiling in specific cells can improve our understanding of microvessel biology and disease at the molecular level. Understanding responses of individual microvascular cells to the same physiological or pathophysiological stimuli requires the ability to isolate the specific cell types that comprise the functional units of the microcirculation in the heart, preferably from the same heart, to ensure that different cells have been exposed to the same in-vivo conditions. We developed an integrated process for simultaneous isolation and culture of the main cell types comprising the microcirculation in adult mouse heart: endothelial cells, pericytes, and vascular smooth muscle cells. These cell types were characterized with isobaric labeling quantitative proteomics and mRNA sequencing. We defined microvascular cell proteomes, identified novel protein markers, and confirmed established cell-specific markers. Our results allow identification of unique markers and regulatory proteins that govern microvascular physiology and pathology.

Cardiac pericyte reprogramming by MEK inhibition promotes arteriologenesis and angiogenesis of the ischemic heart

Pericytes (PCs) are abundant yet remain the most enigmatic and ill-defined cell population in the heart. Here, we investigated whether PCs can be reprogrammed to aid neovascularization. Primary PCs from human and mouse hearts acquired cytoskeletal proteins typical of vascular smooth muscle cells (VSMCs) upon exclusion of EGF/bFGF, which signal through ERK1/2, or upon exposure to the MEK inhibitor PD0325901. Differentiated PCs became more proangiogenic, more responsive to vasoactive agents, and insensitive to chemoattractants. RNA sequencing revealed transcripts marking the PD0325901-induced transition into proangiogenic, stationary VSMC-like cells, including the unique expression of 2 angiogenesis-related markers, aquaporin 1 (AQP1) and cellular retinoic acid-binding protein 2 (CRABP2), which were further verified at the protein level. This enabled us to trace PCs during in vivo studies. In mice, implantation of Matrigel plugs containing human PCs plus PD0325901 promoted the formation of αSMA+ neovessels compared with PC only. Two-week oral administration of PD0325901 to mice increased the heart arteriolar density, total vascular area, arteriole coverage by PDGFRβ+AQP1+CRABP2+ PCs, and myocardial perfusion. Short-duration PD0325901 treatment of mice after myocardial infarction enhanced the peri-infarct vascularization, reduced the scar, and improved systolic function. In conclusion, myocardial PCs have intrinsic plasticity that can be pharmacologically modulated to promote reparative vascularization of the ischemic heart.

Ischemia preconditioning alleviates ischemia/reperfusion injury-induced coronary no-reflow and contraction of microvascular pericytes in rats

BACKGROUND

Ischemia preconditioning (IPC) ameliorates coronary no-reflow induced by ischemia/reperfusion (I/R) injury, and pericytes play an important role in microvascular function. However, it is unclear whether IPC exerts a protective effect on coronary microcirculation and regulates the pericytes.

OBJECTIVE

The purpose of this study was to assess whether IPC improves coronary microvascular perfusion and reduces pericyte constriction after myocardial I/R injury.

METHODS

Rats were randomly divided into three groups: the sham group, the I/R group, and the IPC + I/R group. The left anterior descending artery (LAD) of rats in the I/R group were ligated for 45 min, and the rats in the IPC + I/R group received 4 episodes of 6min occlusion followed by 6min reperfusion before the LAD was ligated. After 24 h of reperfusion, the area of no-reflow, and area at risk were evaluated with thioflavin-S and Evens blue staining, and infarct size with triphenyl tetrazolium chloride staining, respectively. Besides, fluorescent microspheres were perfused to enable visualization of the non-obstructed coronary vessels. Cardiac pericytes and microvascular were observed by immunofluorescence, and the diameter of microvascular at the site of the pericyte somata was analyzed.

RESULTS

The infarct size, and area of no-reflow in the IPC + I/R group were significantly reduced compared with the I/R group (infarct size, 33.5% ± 11.9% vs. 49.2% ± 9.4%, p = 0.021；no-reflow, 12.7% ± 5.2% vs. 26.6% ± 5.0%, p < 0.001). IPC improved microvascular perfusion and reduced the percentage of the blocked coronary capillary. Moreover, we found that cardiac pericytes were widely distributed around the microvascular in various regions of the heart, and expressed the contractile protein α-smooth muscle actin. The microvascular lumen diameter at pericyte somata was reduced after I/R (4.3 ± 1.0 μm vs. 6.5 ± 1.2 μm, p < 0.001), which was relieved in IPC + I/R group compared with the I/R group (5.2 ± 1.0 μm vs. 4.3 ± 1.0 μm, p < 0.001). Besides, IPC could reduce the proportion of apoptotic pericytes compared to the I/R group (22.1% ± 8.4% vs. 38.5% ± 7.5%, p < 0.001).

CONCLUSION

IPC reduced no-reflow and inhibited the contraction of microvascular pericytes induced by cardiac I/R injury, suggesting that IPC might play a protective role by regulating the pericyte function.

Myocardial oedema: pathophysiological basis and implications for the failing heart

Myocardial fluid homeostasis relies on a complex interplay between microvascular filtration, interstitial hydration, cardiomyocyte water uptake and lymphatic removal. Dysregulation of one or more of these mechanisms may result in myocardial oedema. Interstitial and intracellular fluid accumulation disrupts myocardial architecture, intercellular communication, and metabolic pathways, decreasing contractility and increasing myocardial stiffness. The widespread use of cardiac magnetic resonance enabled the identification of myocardial oedema as a clinically relevant imaging finding with prognostic implications in several types of heart failure. Furthermore, growing experimental evidence has contributed to a better understanding of the physical and molecular interactions in the microvascular barrier, myocardial interstitium and lymphatics and how they might be disrupted in heart failure. In this review, we summarize current knowledge on the factors controlling myocardial water balance in the healthy and failing heart and pinpoint the new potential therapeutic avenues.

Validation of Specific and Reliable Genetic Tools to Identify, Label, and Target Cardiac Pericytes in Mice

Background In the myocardium, pericytes are often confused with other interstitial cell types, such as fibroblasts. The lack of well-characterized and specific tools for identification, lineage tracing, and conditional targeting of myocardial pericytes has hampered studies on their role in heart disease. In the current study, we characterize and validate specific and reliable strategies for labeling and targeting of cardiac pericytes. Methods and Results Using the neuron-glial antigen 2 (NG2)DsRed reporter line, we identified a large population of NG2+ periendothelial cells in mouse atria, ventricles, and valves. To examine possible overlap of NG2+ mural cells with fibroblasts, we generated NG2DsRed; platelet-derived growth factor receptor (PDGFR) αEGFP pericyte/fibroblast dual reporter mice. Myocardial NG2+ pericytes and PDGFRα+ fibroblasts were identified as nonoverlapping cellular populations with distinct transcriptional signatures. PDGFRα+ fibroblasts expressed high levels of fibrillar collagens, matrix metalloproteinases, tissue inhibitor of metalloproteinases, and genes encoding matricellular proteins, whereas NG2+ pericytes expressed high levels of Pdgfrb, Adamts1, and Vtn. To validate the specificity of pericyte Cre drivers, we crossed these lines with PDGFRαEGFP fibroblast reporter mice. The constitutive NG2Cre driver did not specifically track mural cells, labeling many cardiomyocytes. However, the inducible NG2CreER driver specifically traced vascular mural cells in the ventricle and in the aorta, without significant labeling of PDGFRα+ fibroblasts. In contrast, the inducible PDGFRβCreER line labeled not only mural cells but also the majority of cardiac and aortic fibroblasts. Conclusions Fibroblasts and pericytes are topographically and transcriptomically distinct populations of cardiac interstitial cells. The inducible NG2CreER driver optimally targets cardiac pericytes; in contrast, the inducible PDGFRβCreER line lacks specificity.

Application of Human Induced Pluripotent Stem Cell Technology for Cardiovascular Regenerative Pharmacology

Cardiovascular diseases are one of the leading causes of mortality in the western world. Myocardial infarction is among the most prevalent and results in significant cell loss within the myocardium. Similarly, numerous drugs have been identified as having cardiotoxic side effects. The adult human heart is however unable to instigate an effective repair mechanism and regenerate the myocardium in response to such damage. This is in large part due to the withdrawal of cardiomyocytes (CMs) from the cell cycle. Thus, identifying, screening, and developing agents that could enhance the proliferative capacity of CMs holds great potential in cardiac regeneration. Human induced pluripotent stem cells (hiPSCs) and their cardiovascular derivatives are excellent tools in the search for such agents. This chapter outlines state-of-the art techniques for the two-dimensional differentiation and attainment of hiPSC-derived CMs and endothelial cells (ECs). Bioreactor systems and three-dimensional spheroids derived from hiPSC-cardiovascular derivatives are explored as platforms for drug discovery before focusing on relevant assays that can be employed to assess cell proliferation and viability.

The SARS-CoV-2 Spike protein disrupts human cardiac pericytes function through CD147 receptor-mediated signalling: a potential non-infective mechanism of COVID-19 microvascular disease

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a broad range of clinical responses including prominent microvascular damage. The capacity of SARS-CoV-2 to infect vascular cells is still debated. Additionally, the SARS-CoV-2 Spike (S) protein may act as a ligand to induce non-infective cellular stress. We tested this hypothesis in pericytes (PCs), which are reportedly reduced in the heart of patients with severe coronavirus disease-2019 (COVID-19). Here we newly show that the in vitro exposure of primary human cardiac PCs to the SARS-CoV-2 wildtype strain or the α and δ variants caused rare infection events. Exposure to the recombinant S protein alone elicited signalling and functional alterations, including: (1) increased migration, (2) reduced ability to support endothelial cell (EC) network formation on Matrigel, (3) secretion of pro-inflammatory molecules typically involved in the cytokine storm, and (4) production of pro-apoptotic factors causing EC death. Next, adopting a blocking strategy against the S protein receptors angiotensin-converting enzyme 2 (ACE2) and CD147, we discovered that the S protein stimulates the phosphorylation/activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) through the CD147 receptor, but not ACE2, in PCs. The neutralisation of CD147, either using a blocking antibody or mRNA silencing, reduced ERK1/2 activation, and rescued PC function in the presence of the S protein. Immunoreactive S protein was detected in the peripheral blood of infected patients. In conclusion, our findings suggest that the S protein may prompt PC dysfunction, potentially contributing to microvascular injury. This mechanism may have clinical and therapeutic implications.

The SARS-CoV-2 Spike protein disrupts human cardiac pericytes function through CD147 receptor-mediated signalling: a potential non-infective mechanism of COVID-19 microvascular disease

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a broad range of clinical responses including prominent microvascular damage. The capacity of SARS-CoV-2 to infect vascular cells is still debated. Additionally, the SARS-CoV-2 Spike (S) protein may act as a ligand to induce non-infective cellular stress. We tested this hypothesis in pericytes (PCs), which are reportedly reduced in the heart of patients with severe coronavirus disease-2019 (COVID-19). Here we newly show that the in vitro exposure of primary human cardiac PCs to the SARS-CoV-2 wildtype strain or the α and δ variants caused rare infection events. Exposure to the recombinant S protein alone elicited signalling and functional alterations, including: (1) increased migration, (2) reduced ability to support endothelial cell (EC) network formation on Matrigel, (3) secretion of pro-inflammatory molecules typically involved in the cytokine storm, and (4) production of pro-apoptotic factors causing EC death. Next, adopting a blocking strategy against the S protein receptors angiotensin-converting enzyme 2 (ACE2) and CD147, we discovered that the S protein stimulates the phosphorylation/activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) through the CD147 receptor, but not ACE2, in PCs. The neutralisation of CD147, either using a blocking antibody or mRNA silencing, reduced ERK1/2 activation, and rescued PC function in the presence of the S protein. Immunoreactive S protein was detected in the peripheral blood of infected patients. In conclusion, our findings suggest that the S protein may prompt PC dysfunction, potentially contributing to microvascular injury. This mechanism may have clinical and therapeutic implications.

Coronary microvascular dysfunction pathophysiology in COVID-19

Recently, accumulating evidence has highlighted the role of endothelial dysfunction in COVID-19 progression. Coronary microvascular dysfunction (CMD) plays a pivotal role in cardiovascular disease (CVD) and CVD-related risk factors (eg, age, gender, hypertension, diabetes mellitus, and obesity). Equally, these are also risk factors for COVID-19. The purpose of this review was to explore CMD pathophysiology in COVID-19, based on recent evidence. COVID-19 mechanisms were reviewed in terms of imbalanced renin-angiotensin-aldosterone-systems (RAAS), systemic inflammation and immune responses, endothelial dysfunction, and coagulatory disorders. Based on these mechanisms, we addressed CMD pathophysiology within the context of COVID-19, from five perspectives. The first was the disarrangement of local RAAS and Kallikrein-kinin-systems attributable to SARS-Cov-2 entry, and the concomitant decrease in coronary microvascular endothelial angiotensin I converting enzyme 2 (ACE2) levels. The second was related to coronary microvascular obstruction, induced by COVID-19-associated systemic hyper-inflammation and pro-thrombotic state. The third was focused on how pneumonia/acute respiratory distress syndrome (ARDS)-related systemic hypoxia elicited oxidative stress in coronary microvessels and cardiac sympathetic nerve activation. Fourthly, we discussed how autonomic nerve dysfunction mediated by COVID-19-associated mental, physical, or physiological factors could elicit changes in coronary blood flow, resulting in CMD in COVID-19 patients. Finally, we analyzed reciprocity between the coronary microvascular endothelium and perivascular cellular structures due to viremia, SARS-CoV-2 dissemination, and systemic inflammation. These mechanisms may function either consecutively or intermittently, finally culminating in CMD-mediated cardiovascular symptoms in COVID-19 patients. However, the underlying molecular pathogenesis remains to be clarified.

Emerging Role of Pericytes and Their Secretome in the Heart

Pericytes, as mural cells covering microvascular capillaries, play an essential role in vascular remodeling and maintaining vascular functions and blood flow. Pericytes are crucial participants in the physiological and pathological processes of cardiovascular disease. They actively interact with endothelial cells, vascular smooth muscle cells (VSMCs), fibroblasts, and other cells via the mechanisms involved in the secretome. The secretome of pericytes, along with diverse molecules including proinflammatory cytokines, angiogenic growth factors, and the extracellular matrix (ECM), has great impacts on the formation, stabilization, and remodeling of vasculature, as well as on regenerative processes. Emerging evidence also indicates that pericytes work as mesenchymal cells or progenitor cells in cardiovascular regeneration. Their capacity for differentiation also contributes to vascular remodeling in different ways. Previous studies primarily focused on the roles of pericytes in organs such as the brain, retina, lung, and kidney; very few studies have focused on pericytes in the heart. In this review, following a brief introduction of the origin and fundamental characteristics of pericytes, we focus on pericyte functions and mechanisms with respect to heart disease, ending with the promising use of cardiac pericytes in the treatment of ischemic heart failure.

The vasculature: a therapeutic target in heart failure?

It is well established that the vasculature plays a crucial role in maintaining oxygen and nutrients supply to the heart. Increasing evidence further suggest that the microcirculation has additional roles in supporting a healthy microenvironment. Heart failure is well known to be associated with changes and functional impairment of the microvasculature. The specific ablation of protective signals in endothelial cells in experimental models is sufficient to induce heart failure. Therefore, restoring a healthy endothelium and microcirculation may be a valuable therapeutic strategy to treat heart failure. The present review article will summarize the current understanding of the vascular contribution to heart failure with reduced or preserved ejection fraction. Novel therapeutic approaches including next generation pro-angiogenic therapies and non-coding RNA therapeutics, as well as the targeting of metabolites or metabolic signaling, vascular inflammation and senescence will be discussed.

Implementation of Pericytes in Vascular Regeneration Strategies

For the survival and integration of complex large-sized tissue-engineered (TE) organ constructs that exceed the maximal nutrients and oxygen diffusion distance required for cell survival, graft (pre)vascularization to ensure medium or blood supply is crucial. To achieve this, the morphology and functionality of the microcapillary bed should be mimicked by incorporating vascular cell populations, including endothelium and mural cells. Pericytes play a crucial role in microvascular function, blood vessel stability, angiogenesis, and blood pressure regulation. In addition, tissue-specific pericytes are important in maintaining specific functions in different organs, including vitamin A storage in the liver, renin production in the kidneys and maintenance of the blood-brain-barrier. Together with their multipotential differentiation capacity, this makes pericytes the preferred cell type for application in TE grafts. The use of a tissue-specific pericyte cell population that matches the TE organ may benefit organ function. In this review, we provide an overview of the literature for graft (pre)-vascularization strategies and highlight the possible advantages of using tissue-specific pericytes for specific TE organ grafts. Impact statement The use of a tissue-specific pericyte cell population that matches the tissue-engineered (TE) organ may benefit organ function. In this review, we provide an overview of the literature for graft (pre)vascularization strategies and highlight the possible advantages of using tissue-specific pericytes for specific TE organ grafts.

Cardiac pericytes function as key vasoactive cells to regulate homeostasis and disease

Pericytes (PCs)—mural cells that envelop endothelial cells (ECs) of microvessels—regulate tissue‐specific vasculature development as well as maturation and maintenance of endothelial barrier integrity. However, little is known about their tissue‐specific function in the heart. Specifically, the mechanism by which cardiac PCs constrict coronary capillaries remains undetermined. To gain insights into the function of cardiac PCs at the cellular level, we isolated NG2⁺ PDGFRβ⁺ CD146⁺ CD34⁻ CD31⁻ CD45⁻ PCs for detailed characterization. Functionally, we provide evidence that these PCs increased transepithelial electrical resistance and decreased endothelial permeability. We show for the first time that this population of PCs express contractile proteins, are stimulated by adrenergic signaling, and demonstrate stereotypical contraction and relaxation. Furthermore, we also studied for the first time, the PCs in in vitro models of disease. PCs in hypoxia activated the hypoxia‐inducible factor 1 alpha pathway, increased secretion of angiogenic factors, and caused cellular apoptosis. Supraphysiological levels of low‐density lipoprotein decreased PC proliferation and induced lipid droplet accumulation. Elevated glucose levels triggered a proinflammatory response. Taken together, our study characterizes cardiac PCs under in vitro disease conditions and supports the hypothesis that cardiac PCs are key vasoactive cells that can regulate blood flow in the heart.

Evaluation of serum platelet-derived growth factor receptor-ß and brain-derived neurotrophic factor levels in microvascular angina

Objective:

Microvascular angina (MVA) is a coronary microcirculation disease. Research on microcirculatory dysfunction has revealed several biomarkers involved in the etiopathogenesis of MVA. Platelet-derived growth factor receptor β (PDGFR-β) and brain-derived neurotrophic factor (BDNF) are 2 biomarkers associated with microcirculation, particularly pericytes function. The aim of this study was to investigate the role of PDGFR-β and BDNF in MVA.

Methods:

Ninety-one patients (median age, 56 y; age range, 40–79 y; 36 men) with MVA and 61 control group subjects (median age, 52 y; age range, 38–76 y; 29 men) were included in the study. Serum concentrations of PDGFR-β and BDNF were measured with commercially available enzyme-linked immunosorbent assay kits.

Results:

PDGFR-β [2.82 ng/ml; interquartile range (IQR), 0.57–7.79 ng/ml vs. 2.27 ng/ml; IQR, 0.41–7.16 ng/ml; p<0.0005] and BDNF (2.41 ng/ml; IQR, 0.97–7.97 ng/ml vs. 1.92 ng/ml; IQR, 1.07–6.67 ng/ml; p=0.023) concentrations were significantly higher in patients with MVA compared with the controls. PDGFR-β correlated positively with age (r=0.26, p=0.001), low-density lipoprotein (r=0.18; p=0.02), and BDNF (r=0.47; p<0.001), and BDNF showed a significant positive correlation with age (r=0.20; p=0.01). In binary logistic regression analysis, high-sensitivity C-reactive protein, uric acid, and PDGFR-β values were found to be independent predictors of MVA.

Conclusion:

MVA is associated with higher PDGFR-β and BDNF levels. This association may indicate an abnormality in microvascular function. Future studies are required to determine the role of these biomarkers in the pathogenesis of MVA. (Anatol J Cardiol 2020; 24: 397-404)

Dual Function of iPSC-Derived Pericyte-Like Cells in Vascularization and Fibrosis-Related Cardiac Tissue Remodeling In Vitro

Myocardial interstitial fibrosis (MIF) is characterized by excessive extracellular matrix (ECM) deposition, increased myocardial stiffness, functional weakening, and compensatory cardiomyocyte (CM) hypertrophy. Fibroblasts (Fbs) are considered the principal source of ECM, but the contribution of perivascular cells, including pericytes (PCs), has gained attention, since MIF develops primarily around small vessels. The pathogenesis of MIF is difficult to study in humans because of the pleiotropy of mutually influencing pathomechanisms, unpredictable side effects, and the lack of available patient samples. Human pluripotent stem cells (hPSCs) offer the unique opportunity for the de novo formation of bioartificial cardiac tissue (BCT) using a variety of different cardiovascular cell types to model aspects of MIF pathogenesis in vitro. Here, we have optimized a protocol for the derivation of hPSC-derived PC-like cells (iPSC-PCs) and present a BCT in vitro model of MIF that shows their central influence on interstitial collagen deposition and myocardial tissue stiffening. This model was used to study the interplay of different cell types—i.e., hPSC-derived CMs, endothelial cells (ECs), and iPSC-PCs or primary Fbs, respectively. While iPSC-PCs improved the sarcomere structure and supported vascularization in a PC-like fashion, the functional and histological parameters of BCTs revealed EC- and PC-mediated effects on fibrosis-related cardiac tissue remodeling.

Sirtuin 3, Endothelial Metabolic Reprogramming, and Heart Failure With Preserved Ejection Fraction

The incidences of heart failure with preserved ejection fraction (HFpEF) are increased in aged populations as well as diabetes and hypertension. Coronary microvascular dysfunction has contributed to the development of HFpEF. Endothelial cells (ECs) depend on glycolysis rather than oxidative phosphorylation for generating adenosine triphosphate to maintain vascular homeostasis. Glycolytic metabolism has a critical role in the process of angiogenesis, because ECs rely on the energy produced predominantly from glycolysis for migration and proliferation. Sirtuin 3 (SIRT3) is found predominantly in mitochondria and its expression declines progressively with aging, diabetes, obesity, and hypertension. Emerging evidence indicates that endothelial SIRT3 regulates a metabolic switch between glycolysis and mitochondrial respiration. SIRT3 deficiency in EC resulted in a significant decrease in glycolysis, whereas, it exhibited higher mitochondrial respiration and more prominent production of reactive oxygen species. SIRT3 deficiency also displayed striking increases in acetylation of p53, EC apoptosis, and senescence. Impairment of SIRT3-mediated EC metabolism may lead to a disruption of EC/pericyte/cardiomyocyte communications and coronary microvascular rarefaction, which promotes cardiomyocyte hypoxia, Titin-based cardiomyocyte stiffness, and myocardial fibrosis, thus leading to a diastolic dysfunction and HFpEF. This review summarizes current knowledge of SIRT3 in EC metabolic reprograming, EC/pericyte interactions, coronary microvascular dysfunction, and HFpEF.

PTX3 Predicts Myocardial Damage and Fibrosis in Duchenne Muscular Dystrophy

Pentraxin 3 (PTX3) is a main component of the innate immune system by inducing complement pathway activation, acting as an inflammatory mediator, coordinating the functions of macrophages/dendritic cells and promoting apoptosis/necrosis. Additionally, it has been found in fibrotic regions co-localizing with collagen. In this work, we wanted to investigate the predictive role of PTX3 in myocardial damage and fibrosis of Duchenne muscular dystrophy (DMD). DMD is an X-linked recessive disease caused by mutations of the dystrophin gene that affects muscular functions and strength and accompanying dilated cardiomyopathy. Here, we expound the correlation of PTX3 cardiac expression with age and Toll-like receptors (TLRs)/interleukin-1 receptor (IL-1R)-MyD88 inflammatory markers and its modulation by the so-called alarmins IL-33, high-mobility group box 1 (HMGB1), and S100β. These findings suggest that cardiac levels of PTX3 might have prognostic value and potential in guiding therapy for DMD cardiomyopathy.

Pregnancy-induced Cardiovascular Pathologies: Importance of Structural Components and Lipids

Pregnancy leads to adaptations for maternal and fetal energy needs. The cardiovascular system bears the brunt of the adaptations as the heart and vessels enable nutrient supply to maternal organs facilitated by the placenta to the fetus. The components of the cardiovascular system are critical in the balance between maternal homeostatic and fetus driven homeorhetic regulation. Since lipids intersect maternal cardiovascular function and fetal needs with growth and in stress, factors affecting lipid deposition and mobilization impact risk outcomes. Here, the cardiovascular components and functional derangements associated with cardiovascular pathology in pregnancy, vis-à-vis lipid deposition, mobilization and maternal and/or cardiac and fetal energy needs are detailed. Most reports on the components and associated pathology in pregnancy, are on derangements affecting the extracellular matrix and epicardial fat, followed by the endothelium, vascular smooth muscle, pericytes and myocytes. Targeted studies on all cardiovascular components and pathological outcomes in pregnancy will enhance targeted interventions.

Research advances in pericyte function and their roles in diseases

Pericyte, a kind of pluripotent cell, may regulate the irrigation flow and permeability of microcirculation. Pericytes are similar to the smooth muscle cells, which express several kinds of contractile proteins and have contractility. The dysfunction of pericytes is related to many microvascular diseases, including hypoxia, hypertension, diabetic retinopathy, fibrosis, inflammation, Alzheimer's disease, multiple sclerosis, and tumor formation. For a long time, their existence and function have been neglected. The distribution, structure, biomarker, related signaling pathways as well as the roles of pericytes on vascular diseases will be introduced in this review.

The coronary circulation in acute myocardial ischaemia/reperfusion injury: a target for cardioprotection

The coronary circulation is both culprit and victim of acute myocardial infarction. The rupture of an epicardial atherosclerotic plaque with superimposed thrombosis causes coronary occlusion, and this occlusion must be removed to induce reperfusion. However, ischaemia and reperfusion cause damage not only in cardiomyocytes but also in the coronary circulation, including microembolization of debris and release of soluble factors from the culprit lesion, impairment of endothelial integrity with subsequently increased permeability and oedema formation, platelet activation and leucocyte adherence, erythrocyte stasis, a shift from vasodilation to vasoconstriction, and ultimately structural damage to the capillaries with eventual no-reflow, microvascular obstruction (MVO), and intramyocardial haemorrhage (IMH). Therefore, the coronary circulation is a valid target for cardioprotection, beyond protection of the cardiomyocyte. Virtually all of the above deleterious endpoints have been demonstrated to be favourably influenced by one or the other mechanical or pharmacological cardioprotective intervention. However, no-reflow is still a serious complication of reperfused myocardial infarction and carries, independently from infarct size, an unfavourable prognosis. MVO and IMH can be diagnosed by modern imaging technologies, but still await an effective therapy. The current review provides an overview of strategies to protect the coronary circulation from acute myocardial ischaemia/reperfusion injury. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

Pericytes in the infarcted heart

The adult mammalian heart lacks regenerative capacity and heals through activation of an inflammatory cascade that leads to the formation of a collagen-based scar. Although scar formation is important to preserve the structural integrity of the ventricle, unrestrained inflammation and excessive fibrosis have been implicated in the pathogenesis of adverse post-infarction remodeling and heart failure. Interstitial cells play a crucial role in the regulation of cardiac repair. Although recent studies have explored the role of fibroblasts and immune cells, the cardiac pericytes have been largely ignored by investigators interested in myocardial biology. This review manuscript discusses the role of pericytes in the regulation of inflammation, fibrosis and angiogenesis following myocardial infarction. During the inflammatory phase of infarct healing, pericytes may regulate microvascular permeability and may play an important role in leukocyte trafficking. Moreover, pericyte activation through Toll-like receptor-mediated pathways may stimulate cytokine and chemokine synthesis. During the proliferative phase, pericytes may be involved in angiogenesis and fibrosis. To what extent pericyte to fibroblast conversion and pericyte-mediated growth factor synthesis contribute to the myocardial fibrotic response remains unknown. During the maturation phase of infarct healing, coating of infarct neovessels with pericytes plays an important role in scar stabilization. Implementation of therapeutic approaches targeting pericytes in the infarcted and remodeling heart remains challenging, due to the lack of systematic characterization of myocardial pericytes, their phenotypic heterogeneity and the limited knowledge on their functional role.

Pericytes in the Heart

Mural cells known as pericytes envelop the endothelial layer of microvessels throughout the body and have been described to have tissue-specific functions. Cardiac pericytes are abundantly found in the heart, but they are relatively understudied. Currently, their importance is emerging in cardiovascular homeostasis and dysfunction due to their pleiotropism. They are known to play key roles in vascular tone and vascular integrity as well as angiogenesis. However, their dysfunctional presence and/or absence is critical in the mechanisms that lead to cardiac pathologies such as myocardial infarction, fibrosis, and thrombosis. Moreover, they are targeted as a therapeutic potential due to their mesenchymal properties that could allow them to repair and regenerate a damaged heart. They are also sought after as a cell-based therapy based on their healing potential in preclinical studies of animal models of myocardial infarction. Therefore, recognizing the importance of cardiac pericytes and understanding their biology will lead to new therapeutic concepts.

Maternal Cognitive Impairment Associated with Gestational Diabetes Mellitus-A Review of Potential Contributing Mechanisms

Gestational diabetes mellitus (GDM) carries many risks, where high blood pressure, preeclampsia and future type II diabetes are widely acknowledged, but less focus has been placed on its effect on cognitive function. Although the multifactorial pathogenesis of maternal cognitive impairment is not completely understood, it shares several features with type 2 diabetes mellitus (T2DM). In this review, we discuss some key pathophysiologies of GDM that may lead to cognitive impairment, specifically hyperglycemia, insulin resistance, oxidative stress, and neuroinflammation. We explain how these incidents: (i) impair the insulin-signaling pathway and/or (ii) lead to cognitive impairment through hyperphosphorylation of τ protein, overexpression of amyloid-β and/or activation of microglia. The aforementioned pathologies impair the insulin-signaling pathway primarily through serine phosphorylation of insulin receptor substances (IRS). This then leads to the inactivation of the phosphatidylinositol 3-kinase/Protein kinase B (PI3K/AKT) signaling cascade, which is responsible for maintaining brain homeostasis and normal cognitive functioning. PI3K/AKT is crucial in maintaining normal cognitive function through the inactivation of glycogen synthase kinase 3β (GSκ3β), which hyperphosphorylates τ protein and releases pro-inflammatory cytokines that are neurotoxic. Several biomarkers were also highlighted as potential biomarkers of GDM-related cognitive impairment such as AGEs, serine-phosphorylated IRS-1 and inflammatory markers such as tumor necrosis factor α (TNF-α), high-sensitivity C-reactive protein (hs-CRP), leptin, interleukin 1β (IL-1β), and IL-6. Although GDM is a transient disease, its complications may be long-term, and hence increased mechanistic knowledge of the molecular changes contributing to cognitive impairment may provide important clues for interventional strategies.

Heterocellularity and Cellular Cross-Talk in the Cardiovascular System

Cellular specialization and interactions with other cell types are the essence of complex multicellular life. The orchestrated function of different cell populations in the heart, in combination with a complex network of intercellular circuits of communication, is essential to maintain a healthy heart and its disruption gives rise to pathological conditions. Over the past few years, the development of new biological research tools has facilitated more accurate identification of the cardiac cell populations and their specific roles. This review aims to provide an overview on the significance and contributions of the various cellular components: cardiomyocytes, fibroblasts, endothelial cells, vascular smooth muscle cells, pericytes, and inflammatory cells. It also aims to describe their role in cardiac development, physiology and pathology with a particular focus on the importance of heterocellularity and cellular interaction between these different cell types.

Cellular and Molecular Heterogeneity Associated with Vessel Formation Processes

The microvasculature heterogeneity is a complex subject in vascular biology. The difficulty of building a dynamic and interactive view among the microenvironments, the cellular and molecular heterogeneities, and the basic aspects of the vessel formation processes make the available knowledge largely fragmented. The neovascularisation processes, termed vasculogenesis, angiogenesis, arteriogenesis, and lymphangiogenesis, are important to the formation and proper functioning of organs and tissues both in the embryo and the postnatal period. These processes are intrinsically related to microvascular cells, such as endothelial and mural cells. These cells are able to adjust their activities in response to the metabolic and physiological requirements of the tissues, by displaying a broad plasticity that results in a significant cellular and molecular heterogeneity. In this review, we intend to approach the microvasculature heterogeneity in an integrated view considering the diversity of neovascularisation processes and the cellular and molecular heterogeneity that contribute to microcirculatory homeostasis. For that, we will cover their interactions in the different blood-organ barriers and discuss how they cooperate in an integrated regulatory network that is controlled by specific molecular signatures.

Concise Review: The Regenerative Journey of Pericytes Toward Clinical Translation

Coronary artery disease (CAD) is the single leading cause of death worldwide. Advances in treatment and management have significantly improved patient outcomes. On the other hand, although mortality rates have decreased, more people are left with sequelae that require additional treatment and hospitalization. Moreover, patients with severe nonrevascularizable CAD remain with only the option of heart transplantation, which is limited by the shortage of suitable donors. In recent years, cell-based regenerative therapy has emerged as a possible alternative treatment, with several regenerative medicinal products already in the clinical phase of development and others emerging as competitive preclinical solutions. Recent evidence indicates that pericytes, the mural cells of blood microvessels, represent a promising therapeutic candidate. Pericytes are abundant in the human body, play an active role in angiogenesis, vessel stabilization and blood flow regulation, and possess the capacity to differentiate into multiple cells of the mesenchymal lineage. Moreover, early studies suggest a robustness to hypoxic insult, making them uniquely equipped to withstand the ischemic microenvironment. This review summarizes the rationale behind pericyte-based cell therapy and the progress that has been made toward its clinical application. We present the different sources of pericytes and the case for harvesting them from tissue leftovers of cardiovascular surgery. We also discuss the healing potential of pericytes in preclinical animal models of myocardial ischemia (MI) and current practices to upgrade the production protocol for translation to the clinic. Standardization of these procedures is of utmost importance, as lack of uniformity in cell manufacturing may influence clinical outcome. Stem Cells 2018;36:1295-1310.

Perivascular fibrosis and the microvasculature of the heart. Still hidden secrets of pathophysiology?

Perivascular fibrosis, the deposition of connective tissue around the vessels, has been demonstrated crucially involved in the development of cardiac dysfunction. Although cardiac fibrosis has been shown to be reversible under certain experimental conditions, effective anti-fibrotic therapies remain largely elusive. Therefore, perivascular fibrosis currently represents a major therapeutic target for cardiovascular diseases. The main topic of this review will be to address the mechanisms underlying perivascular fibrosis of the vasculature within the myocardium, with a special focus on perivascular fibrosis of small vessels, microvascular dysfunction and disease.

The Microvascular Pericyte: Approaches to Isolation, Characterization, and Cultivation

The microvascular pericyte was identified in 1873 by the French scientist Charles Benjamin Rouget and originally called the Rouget cell (Rouget.Sciences 88:916-8, 1879). However, it was not until the early 1900s that Rouget's work was confirmed, and the Rouget cell renamed the pericyte by virtue of its peri-endothelial location (Dore. Brit J Dermatol 35:398-404, 1923; Zimmermann. Z Anat Entwicklungsgesch 68:3-109, 1923). Over the years a large number of publications have emerged, but the pericyte has remained a truly enigmatic cell. This is due, in part, by the paucity of easy and reliable methods to isolate and characterize the cell as well as its heterogeneity and pluripotent characteristics. However, more recent advances in molecular genetics and development of novel cell isolation and imaging techniques have enable scientists to more readily define pericyte function. This chapter will discuss general approaches to the isolation, characterization, and propagation of primary pericytes in the establishment of cell lines. We will attempt to dispel misinterpretations about the pericyte that cloud the literature.

Pericytes in Tissue Engineering

Pericytes have crucial roles in blood-brain barrier function, blood vessel function/stability, angiogenesis, endothelial cell proliferation/differentiation, wound healing, and hematopoietic stem cells maintenance. They can be isolated from fetal and adult tissues and have multipotential differentiation capacity as mesenchymal stem cells (MSCs). All of these properties make pericytes as preferred cells in the field of tissue engineering. Current developments have shown that tissue-engineered three-dimensional (3D) systems including multiple cell layers (or types) and a supporting biological matrix represent the in vivo environment better than those monolayers on plastic dishes. Tissue-engineered models are also more ethical and cheaper systems than animal models. This chapter describes the role of pericytes in tissue engineering for regenerative medicine.

Capillary pericytes mediate coronary no-reflow after myocardial ischaemia

After cardiac ischaemia, a prolonged decrease of coronary microvascular perfusion often occurs even after flow is restored in an upstream artery. This 'no-reflow' phenomenon worsens patient prognosis. In the brain, after stroke, a similar post-ischaemic 'no-reflow' has been attributed to capillary constriction by contractile pericytes. We now show that occlusion of a rat coronary artery, followed by reperfusion, blocks 40% of cardiac capillaries and halves perfused blood volume within the affected region. Capillary blockages colocalised strongly with pericytes, where capillary diameter was reduced by 37%. The pericyte relaxant adenosine increased capillary diameter by 21% at pericyte somata, decreased capillary block by 25% and increased perfusion volume by 57%. Thus, cardiac pericytes constrict coronary capillaries and reduce microvascular blood flow after ischaemia, despite re-opening of the culprit artery. Cardiac pericytes are therefore a novel therapeutic target in ischaemic heart disease.

Heart attacks occur when one of the arteries supplying blood to the heart muscle becomes blocked, usually by a blood clot. Doctors unblock the artery and insert an expanding metal cage called a stent to keep it unblocked. This restores blood flow through the artery. Unfortunately, blood flow often does not return to smaller downstream blood vessels called capillaries. This can lead to further damage to the heart.

Scientists have not been able to find a way to reliably open up those capillaries after a heart attack because it is not clear exactly what is keeping them closed. Muscle-like cells called pericytes, which wrap around the capillaries, are one possible culprit for the blockages. Pericytes narrow capillaries in the brain after stroke in animal experiments. These cells are also present on heart capillaries, but scientists do not know much about them.

Now, O’Farrell, Mastitskaya, Hammond-Haley et al. show that pericytes are partly responsible for limiting blood flow in capillaries after a heart attack in rats. In the experiments, blood flow through an artery feeding the hearts of anaesthetized rats was restricted, simulating a heart attack. After the blood flow was later restored, 40% of the animal’s capillaries remained blocked. Many blockages occurred near pericytes that had narrowed the capillary preventing blood flow. Treating the rats with a drug called adenosine, which relaxes the pericytes, reduced capillary blockages and increased blood flow in the heart.

Although adenosine could help to restore blood flow in the capillaries after a heart attack, it may also relax muscles around arteries and lower blood pressure, and so it may not be an ideal treatment. More studies are needed to determine whether drugs that target only the pericytes could complement existing heart attack treatments that unblock the arteries. If these studies are successful, pericyte-targeting drugs might prevent serious complications after a heart attack, including heart failure, heart rhythm abnormalities and future heart attacks.

How Plastic Are Pericytes?

Pericytes are defined by both their anatomical location and molecular markers. Numerous publications have reported their role as stem cells, contributing to the formation of tissues other than blood vessels. However, using cell-lineage tracing in a new transgenic mouse model, a recent study shows that in the context of aging and some pathologies, Tbx18+ pericytes do not function as stem cells in vivo. This study challenges the current view that pericytes can differentiate into other cells and reopen questions about their plasticity. This emerging knowledge is important not only for our understanding of development but may also inform treatments for diseases.

Identification and Functional Characterization of Hypoxia-Induced Endoplasmic Reticulum Stress Regulating lncRNA (HypERlnc) in Pericytes

RATIONALE

Pericytes are essential for vessel maturation and endothelial barrier function. Long noncoding RNAs regulate many cellular functions, but their role in pericyte biology remains unexplored.

OBJECTIVE

Here, we investigate the effect of hypoxia-induced endoplasmic reticulum stress regulating long noncoding RNAs (HypERlnc, also known as ENSG00000262454) on pericyte function in vitro and its regulation in human heart failure and idiopathic pulmonary arterial hypertension.

METHODS AND RESULTS

RNA sequencing in human primary pericytes identified hypoxia-regulated long noncoding RNAs, including HypERlnc. Silencing of HypERlnc decreased cell viability and proliferation and resulted in pericyte dedifferentiation, which went along with increased endothelial permeability in cocultures consisting of human primary pericyte and human coronary microvascular endothelial cells. Consistently, Cas9-based transcriptional activation of HypERlnc was associated with increased expression of pericyte marker genes. Moreover, HypERlnc knockdown reduced endothelial-pericyte recruitment in Matrigel assays (P<0.05). Mechanistically, transcription factor reporter arrays demonstrated that endoplasmic reticulum stress-related transcription factors were prominently activated by HypERlnc knockdown, which was confirmed via immunoblotting for the endoplasmic reticulum stress markers IRE1α (P<0.001), ATF6 (P<0.01), and soluble BiP (P<0.001). Kyoto encyclopedia of genes and gene ontology pathway analyses of RNA sequencing experiments after HypERlnc knockdown indicate a role in cardiovascular disease states. Indeed, HypERlnc expression was significantly reduced in human cardiac tissue from patients with heart failure (P<0.05; n=19) compared with controls. In addition, HypERlnc expression significantly correlated with pericyte markers in human lungs derived from patients diagnosed with idiopathic pulmonary arterial hypertension and from donor lungs (n=14).

CONCLUSIONS

Here, we show that HypERlnc regulates human pericyte function and the endoplasmic reticulum stress response. In addition, RNA sequencing analyses in conjunction with reduced expression of HypERlnc in heart failure and correlation with pericyte markers in idiopathic pulmonary arterial hypertension indicate a role of HypERlnc in human cardiopulmonary disease.

Culture media-based selection of endothelial cells, pericytes, and perivascular-resident macrophage-like melanocytes from the young mouse vestibular system

The vestibular blood-labyrinth barrier (BLB) is comprised of perivascular-resident macrophage-like melanocytes (PVM/Ms) and pericytes (PCs), in addition to endothelial cells (ECs) and basement membrane (BM), and bears strong resemblance to the cochlear BLB in the stria vascularis. Over the past few decades, in vitro cell-based models have been widely used in blood-brain barrier (BBB) and blood-retina barrier (BRB) research, and have proved to be powerful tools for studying cell-cell interactions in their respective organs. Study of both the vestibular and strial BLB has been limited by the unavailability of primary culture cells from these barriers. To better understand how barrier component cells interact in the vestibular system to control BLB function, we developed a novel culture medium-based method for obtaining EC, PC, and PVM/M primary cells from tiny explants of the semicircular canal, sacculus, utriculus, and ampullae tissue of young mouse ears at post-natal age 8-12 d. Each phenotype is grown in a specific culture medium which selectively supports the phenotype in a mixed population of vestibular cell types. The unwanted phenotypes do not survive passaging. The protocol does not require additional equipment or special enzyme treatment. The harvesting process takes less than 2 h. Primary cell types are generated within 7-10 d. The primary culture ECs, PCs, and PVM/M shave consistent phenotypes more than 90% pure after two passages (∼ 3 weeks). The highly purified primary cell lines can be used for studying cell-cell interactions, barrier permeability, and angiogenesis.

Discovering cardiac pericyte biology: From physiopathological mechanisms to potential therapeutic applications in ischemic heart disease

Microvascular pericytes and the more recently discovered adventitial pericyte-like progenitor cells are a subpopulation of vascular stem cells closely associated with small and large blood vessels respectively. These populations of perivascular cells are remarkably abundant in the heart. Pericytes control important physiological processes such as angiogenesis, blood flow and vascular permeability. In the heart, this pleiotropic activity makes pericytes extremely interesting for applications in regenerative medicine. On the other hand, dysfunction of pericytes could participate in the pathogenesis of cardiovascular disease, such as arterial hypertension, fibro-calcific cardiovascular remodeling, myocardial edema and post-ischemic coronary no-reflow. On a therapeutic standpoint, preclinical studies in small animal models of myocardial infarction have demonstrated the healing potential of pericytes transplantation, which has been ascribed to direct vascular incorporation and paracrine pro-angiogenic and anti-apoptotic activities. These promising findings open the door to the clinical use of pericytes for the treatment of cardiovascular diseases.

Skeletal and cardiac muscle pericytes: Functions and therapeutic potential

Pericytes are periendothelial mesenchymal cells residing within the microvasculature. Skeletal muscle and cardiac pericytes are now recognized to fulfill an increasing number of functions in normal tissue homeostasis, including contributing to microvascular function by maintaining vessel stability and regulating capillary flow. In the setting of muscle injury, pericytes contribute to a regenerative microenvironment through release of trophic factors and by modulating local immune responses. In skeletal muscle, pericytes also directly enhance tissue healing by differentiating into myofibers. Conversely, pericytes have also been implicated in the development of disease states, including fibrosis, heterotopic ossication and calcification, atherosclerosis, and tumor angiogenesis. Despite increased recognition of pericyte heterogeneity, it is not yet clear whether specific subsets of pericytes are responsible for individual functions in skeletal and cardiac muscle homeostasis and disease.

Pericytes: Properties, Functions and Applications in Tissue Engineering

Mesenchymal stem cells (MSCs) are one of the most studied adult stem cells and in recent years. They have become attractive agents/cell source for cellular therapy and regenerative medicine applications. During investigations about their origin, researchers hypothesized that perivascular regions are the common anatomical regions where MSCs come from and perivascular cells like pericytes (PCs) (Rouget cells, mural cells) are in vivo counterparts of MSCs. Beside capillaries and microvessels as their most common locations, PCs are also found in large vessels (arteries and veins). They can be isolated from several tissues and organs particularly from retina and brain. There are different approaches about their isolation, characterization and culture but there has been no common protocol yet because of the lack of defined PC-specific marker. They make special contact with endothelial cells in the basement membrane and have very important functions in several tissues and organs. They participate in vascular development, stabilization, maturation, and remodeling, blood pressure control, endothelial cell proliferation and differentiation, contractility of vascular smooth muscle cells, wound healing, vasculogenesis and angiogenesis, long-term maintenance of hematopoietic stem cells in bone marrow niche. Their multipotential differentiation capacity and participation in many events in the body make PCs preferred cells in tissue engineering applications including 3D blood-brain barrier models, skeletal muscle constructs, bone tissue engineering and tissue-engineered vascular grafts.