Early contribution of pericytes to angiogenic sprouting and tube formation

Dynamic changes in structure and function of brain mural cells around chronically implanted microelectrodes

Integration of neural interfaces with minimal tissue disruption in the brain is ideal to develop robust tools that can address essential neuroscience questions and combat neurological disorders. However, implantation of intracortical devices provokes severe tissue inflammation within the brain, which requires a high metabolic demand to support a complex series of cellular events mediating tissue degeneration and wound healing. Pericytes, peri-vascular cells involved in blood-brain barrier maintenance, vascular permeability, waste clearance, and angiogenesis, have recently been implicated as potential perpetuators of neurodegeneration in brain injury and disease. While the intimate relationship between pericytes and the cortical microvasculature have been explored in other disease states, their behavior following microelectrode implantation, which is responsible for direct blood vessel disruption and dysfunction, is currently unknown. Using two-photon microscopy we observed dynamic changes in the structure and function of pericytes during implantation of a microelectrode array over a 4-week implantation period. Pericytes respond to electrode insertion through transient increases in intracellular calcium and underlying constriction of capillary vessels. Within days following the initial insertion, we observed an influx of new, proliferating pericytes which contribute to new blood vessel formation. Additionally, we discovered a potentially novel population of reactive immune cells in close proximity to the electrode-tissue interface actively engaging in encapsulation of the microelectrode array. Finally, we determined that intracellular pericyte calcium can be modulated by intracortical microstimulation in an amplitude- and frequency-dependent manner. This study provides a new perspective on the complex biological sequelae occurring the electrode-tissue interface and will foster new avenues of potential research consideration and lead to development of more advanced therapeutic interventions towards improving the biocompatibility of neural electrode technology.

Cerebral endothelial cells mediated enhancement of brain pericyte number and migration in oxygen-glucose deprivation involves the HIF-1α/PDGF-β signaling

The present study focused on whether hypoxia-inducible factor-1alpha (HIF-1α) and platelet-derived factor-beta (PDGF-β) are involved in the crosstalk between brain microvascular endothelial cells (BMECs) and brain vascular pericytes (BVPs) under ischaemic-hypoxic conditions. Mono-cultures or co-cultures of BVPs and BMECs were made for the construction of the blood-brain barrier (BBB) model in vitro and then exposed to control and oxygen-glucose deprivation (OGD) conditions. BBB injury was determined by assessing the ability, apoptosis, and migration of BVPs and the transendothelial electrical resistance and horseradish peroxidase permeation of BMECs. Relative mRNA and protein levels of HIF-1α and PDGF-β, as well as tight junction proteins ZO-1 and claudin-5 were analyzed by western blotting, reverse transcription quantitative PCR, and/or immunofluorescence staining. Dual-luciferase reporter assays assessed the relationship between PDGF-β and HIF-1α. Co-culturing with BMECs alleviated OGD-induced reduction in BVP viability, elevation in BVP apoptosis, and repression in BVP migration. Co-culturing with BVPs protected against OGD-induced impairment on BMEC permeability. OGD-induced HIF-1α upregulation enhanced PDGF-β expression in mono-cultured BMECs and co-cultured BMECs with BVPs. Knockdown of HIF-1α impaired the effect of BMECs on BVPs under OGD conditions, and PDGFR-β silencing in BVPs blocked the crosstalk between BMECs and BVPs under OGD conditions. The crosstalk between BMECs and BVPs was implicated in OGD-induced BBB injury through the HIF-1α/PDGF-β signaling.

Neutralization of Interleukin 1-beta is associated with preservation of thalamic capillaries after experimental traumatic brain injury

Introduction

Traumatic brain injury to thalamo-cortical pathways is associated with posttraumatic morbidity. Diffuse mechanical forces to white matter tracts and deep grey matter regions induce an inflammatory response and vascular damage resulting in progressive neurodegeneration. Pro-inflammatory cytokines, including interleukin-1β (IL-1β), may contribute to the link between inflammation and the injured capillary network after TBI. This study investigates whether IL-1β is a key contributor to capillary alterations and changes in pericyte coverage in the thalamus and cortex after TBI.

Methods

Animals were subjected to central fluid percussion injury (cFPI), a model of TBI causing widespread axonal and vascular pathology, or sham injury and randomized to receive a neutralizing anti-IL-1β or a control, anti-cyclosporin A antibody, at 30 min post-injury. Capillary length and pericyte coverage of cortex and thalamus were analyzed by immunohistochemistry at 2- and 7-days post-injury.

Results and Conclusion

Our results show that early post-injury attenuation of IL-1β dependent inflammatory signaling prevents capillary damage by increasing pericyte coverage in the thalamus.

Pericytes modulate endothelial inflammatory response during bacterial infection

Pericytes are located around blood vessels, in close contact with endothelial cells. We discovered that pericytes dampen pro-inflammatory endothelial cell responses. Endothelial cells co-cultured with pericytes had markedly reduced expression of adhesion molecules (PECAM-1 and ICAM-1) and proinflammatory cytokines (CCL-2 and IL-6) in response to bacterial stimuli (Brucella ovis, Listeria monocytogenes, or Escherichia coli lipopolysaccharide). Pericyte-depleted mice intraperitoneally inoculated with either B. ovis, a stealthy pathogen that does not trigger detectable inflammation, or Listeria monocytogenes, developed peritonitis. Further, during Citrobacter rodentium infection, pericyte-depleted mice developed severe intestinal inflammation, which was not evident in control mice. The anti-inflammatory effect of pericytes required connexin 43, as either chemical inhibition or silencing of connexin 43 abrogated pericyte-mediated suppression of endothelial inflammatory responses. Our results define a mechanism by which pericytes modulate inflammation during infection, which shifts our understanding of pericyte biology: from a structural cell to a pro-active player in modulating inflammation.

IMPORTANCE

A previously unknown mechanism by which pericytes modulate inflammation was discovered. The absence of pericytes or blocking interaction between pericytes and endothelium through connexin 43 results in stronger inflammation, which shifts our understanding of pericyte biology, from a structural cell to a player in controlling inflammation.

Glial-restricted progenitor cells: a cure for diseased brain?

The central nervous system (CNS) is home to neuronal and glial cells. Traditionally, glia was disregarded as just the structural support across the brain and spinal cord, in striking contrast to neurons, always considered critical players in CNS functioning. In modern times this outdated dogma is continuously repelled by new evidence unravelling the importance of glia in neuronal maintenance and function. Therefore, glia replacement has been considered a potentially powerful therapeutic strategy. Glial progenitors are at the center of this hope, as they are the source of new glial cells. Indeed, sophisticated experimental therapies and exciting clinical trials shed light on the utility of exogenous glia in disease treatment. Therefore, this review article will elaborate on glial-restricted progenitor cells (GRPs), their origin and characteristics, available sources, and adaptation to current therapeutic approaches aimed at various CNS diseases, with particular attention paid to myelin-related disorders with a focus on recent progress and emerging concepts. The landscape of GRP clinical applications is also comprehensively presented, and future perspectives on promising, GRP-based therapeutic strategies for brain and spinal cord diseases are described in detail.

Platelet-derived Growth Factor Activates Pericytes in the Microvessels of Chronic Subdural Hematoma Outer Membranes

Angiogenesis is one of the growth mechanisms of chronic subdural hematoma (CSDH). Pericytes have been implicated in the capillary sprouting during angiogenesis and are involved in brain ischemia and diabetic retinopathy. This study examined the pericyte expressions in CSDH outer membranes obtained during trepanation surgery. Eight samples of CSDH outer membranes and 35 samples of CSDH fluid were included. NG2, N-cadherin, VE-cadherin, Tie-2, endothelial nitric oxide synthase (eNOS), platelet-derived growth factor (PDGF) receptor-β (PDGFR-β), a well-known marker of pericytes, phosphorylated PDGFR-β at Tyr751, and β-actin expressions, were examined using western blot analysis. PDGFR-β, N-cadherin, and Tie-2 expression levels were also examined using immunohistochemistry. The concentrations of PDGF-BB in CSDH fluid samples were measured using enzyme-linked immunosorbent assay kits. NG2, N-cadherin, VE-cadherin, Tie-2, eNOS, PDGFR-β, and eNOS expressions in CSDH outer membranes were confirmed in all cases. Furthermore, phosphorylated PDGFR-β at Tyr751 was also detected. In addition, PDGFR-β, N-cadherin, and Tie-2 expressions were localized to the endothelial cells of the vessels within CSDH outer membranes by immunohistochemistry. The concentration of PDGF-BB in CSDH fluids was significantly higher than that in cerebrospinal fluid. These findings indicate that PDGF activates pericytes in the microvessels of CSDH outer membranes and suggest that pericytes are crucial in CSDH angiogenesis through the PDGF/PDGFR-β signaling pathway.

The participation of tumor residing pericytes in oral squamous cell carcinoma

Pericytes are perivascular cells related to vessel structure and angiogenesis that can interact with neoplastic cells, interfering with cancer progression and outcomes. This study focused on the characterization of pericytes in oral squamous cell carcinoma (OSCC) using clinical samples and a transgenic mouse model of oral carcinogenesis. Nestin^-/NG2⁺ (type-1) and nestin⁺/NG2⁺ (type-2) pericytes were analyzed by direct fluorescence after induction of oral carcinogenesis (4-nitroquinoline-1-oxide). Gene expression of neuron glial antigen-2 (NG2), platelet-derived growth factor receptor beta (PDGFR-β), and cluster of differentiation 31 (CD31) was examined in human OSCC tissues. The protein expression of von Willebrand factor and NG2 was assessed in oral leukoplakia (i.e., oral potentially malignant disorders) and OSCC samples. Additionally, clinicopathological aspects and survival data were correlated and validated by bioinformatics using The Cancer Genome Atlas (TCGA). Induction of carcinogenesis in mice produced an increase in both NG2⁺ pericyte subsets. In human OSCC, advanced-stage tumors showed a significant reduction in CD31 mRNA and von Willebrand factor-positive vessels. Low PDGFR-β expression was related to a shorter disease-free survival time, while NG2 mRNA overexpression was associated with a reduction in overall survival, consistent with the TCGA data. Herein, oral carcinogenesis resulted in an increase in NG2⁺ pericytes, which negatively affected survival outcomes.

Molecular Regulation of the Response of Brain Pericytes to Hypoxia

The brain needs sufficient oxygen in order to function normally. This is achieved by a large vascular capillary network ensuring that oxygen supply meets the changing demand of the brain tissue, especially in situations of hypoxia. Brain capillaries are formed by endothelial cells and perivascular pericytes, whereby pericytes in the brain have a particularly high 1:1 ratio to endothelial cells. Pericytes not only have a key location at the blood/brain interface, they also have multiple functions, for example, they maintain blood–brain barrier integrity, play an important role in angiogenesis and have large secretory abilities. This review is specifically focused on both the cellular and the molecular responses of brain pericytes to hypoxia. We discuss the immediate early molecular responses in pericytes, highlighting four transcription factors involved in regulating the majority of transcripts that change between hypoxic and normoxic pericytes and their potential functions. Whilst many hypoxic responses are controlled by hypoxia-inducible factors (HIF), we specifically focus on the role and functional implications of the regulator of G-protein signaling 5 (RGS5) in pericytes, a hypoxia-sensing protein that is regulated independently of HIF. Finally, we describe potential molecular targets of RGS5 in pericytes. These molecular events together contribute to the pericyte response to hypoxia, regulating survival, metabolism, inflammation and induction of angiogenesis.

DPP-4 Inhibitor and Sulfonylurea Differentially Reverse Type 2 Diabetes-Induced Blood-Brain Barrier Leakage and Normalize Capillary Pericyte Coverage

Microvascular pathology in the brain is one of the suggested mechanisms underlying the increased incidence and progression of neurodegenerative diseases in people with type 2 diabetes (T2D). Although accumulating data suggest a neuroprotective effect of antidiabetics, the underlying mechanisms are unclear. Here, we investigated whether two clinically used antidiabetics, the dipeptidyl peptidase-4 inhibitor linagliptin and the sulfonylurea glimepiride, which restore T2D-induced brain vascular pathology. Microvascular pathology was examined in the striatum of mice fed for 12 months with either normal chow diet or a high-fat diet (HFD) to induce T2D. A subgroup of HFD-fed mice was treated with either linagliptin or glimepiride for 3 months before sacrifice. We demonstrate that T2D caused leakage of the blood-brain barrier (BBB), induced angiogenesis, and reduced pericyte coverage of microvessels. However, linagliptin and glimepiride recovered the BBB integrity and restored the pericyte coverage differentially. Linagliptin normalized T2D-induced angiogenesis and restored pericyte coverage. In contrast, glimepiride enhanced T2D-induced angiogenesis and increased pericyte density, resulting in proper vascular coverage. Interestingly, glimepiride reduced microglial activation, increased microglial-vascular interaction, and increased collagen IV density. This study provides evidence that both DPP-4 inhibition and sulfonylurea reverse T2D-induced BBB leakage, which may contribute to antidiabetic neurorestorative effects.

Flow-dependent shear stress affects the biological properties of pericyte-like cells isolated from human dental pulp

BACKGROUND

Human dental pulp stem cells represent a mesenchymal stem cell niche localized in the perivascular area of dental pulp and are characterized by low immunogenicity and immunomodulatory/anti-inflammatory properties. Pericytes, mural cells surrounding the endothelium of small vessels, regulate numerous functions including vessel growth, stabilization and permeability. It is well established that pericytes have a tight cross talk with endothelial cells in neoangiogenesis and vessel stabilization, which are regulated by different factors, i.e., microenvironment and flow-dependent shear stress. The aim of this study was to evaluate the effects of a pulsatile unidirectional flow in the presence or not of an inflammatory microenvironment on the biological properties of pericyte-like cells isolated from human dental pulp (hDPSCs).

METHODS

Human DPSCs were cultured under both static and dynamic conditions with or without pre-activated peripheral blood mononuclear cells (PBMCs). Pulsatile unidirectional flow shear stress was generated by using a specific peristaltic pump. The angiogenic potential and inflammatory properties of hDPSCs were evaluated through reverse phase protein microarrays (RPPA), confocal immunofluorescence and western blot analyses.

RESULTS

Our data showed that hDPSCs expressed the typical endothelial markers, which were up-regulated after endothelial induction, and were able to form tube-like structures. RPPA analyses revealed that these properties were modulated when a pulsatile unidirectional flow shear stress was applied to hDPSCs. Stem cells also revealed a downregulation of the immune-modulatory molecule PD-L1, in parallel with an up-regulation of the pro-inflammatory molecule NF-kB. Immune-modulatory properties of hDPSCs were also reduced after culture under flow-dependent shear stress and exposure to an inflammatory microenvironment. This evidence was strengthened by the detection of up-regulated levels of expression of pro-inflammatory cytokines in PBMCs.

CONCLUSIONS

In conclusion, the application of a pulsatile unidirectional flow shear stress induced a modulation of immunomodulatory/inflammatory properties of dental pulp pericyte-like cells.

Approaches for the isolation and long-term expansion of pericytes from human and animal tissues

Pericytes surround capillaries in every organ of the human body. They are also present around the vasa vasorum, the small blood vessels that supply the walls of larger arteries and veins. The clinical interest in pericytes is rapidly growing, with the recognition of their crucial roles in controlling vascular function and possible therapeutic applications in regenerative medicine. Nonetheless, discrepancies in methods used to define, isolate, and expand pericytes are common and may affect reproducibility. Separating pure pericyte preparations from the continuum of perivascular mesenchymal cells is challenging. Moreover, variations in functional behavior and antigenic phenotype in response to environmental stimuli make it difficult to formulate an unequivocal definition of bona fide pericytes. Very few attempts were made to develop pericytes as a clinical-grade product. Therefore, this review is devoted to appraising current methodologies' pros and cons and proposing standardization and harmonization improvements. We highlight the importance of developing upgraded protocols to create therapeutic pericyte products according to the regulatory guidelines for clinical manufacturing. Finally, we describe how integrating RNA-seq techniques with single-cell spatial analysis, and functional assays may help realize the full potential of pericytes in health, disease, and tissue repair.

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.

Chondroitin Sulfate Proteoglycan 4 as a Marker for Aggressive Squamous Cell Carcinoma

Chondroitin sulfate (CS) proteoglycan 4 (CSPG4) is a cell surface proteoglycan that is currently under investigation as a marker of cancer malignancy, and as a potential target of anticancer drug treatment. CSPG4 acts as a driver of tumourigenesis by regulating turnover of the extracellular matrix (ECM) to promote tumour cell invasion, migration as well as inflammation and angiogenesis. While CSPG4 has been widely studied in certain malignancies, such as melanoma, evidence is emerging from global gene expression studies, which suggests a role for CSPG4 in squamous cell carcinoma (SCC). While relatively treatable, lack of widely agreed upon diagnostic markers for SCCs is problematic, especially for clinicians managing certain patients, including those who are aged or infirm, as well as those with underlying conditions such as epidermolysis bullosa (EB), for which a delayed diagnosis is likely lethal. In this review, we have discussed the structure of CSPG4, and quantitatively analysed CSPG4 expression in the tissues and pathologies where it has been identified to determine the usefulness of CSPG4 expression as a diagnostic marker and therapeutic target in management of malignant SCC.

Angiogenic Potential of Human Adipose-Derived Mesenchymal Stromal Cells in Nanofibrillated Cellulose Hydrogel

Adipose-derived mesenchymal stromal cells (ASCs) hold great potential for cellular therapies by having immunomodulatory behavior and tissue regenerative properties. Due to the capability of ASCs to differentiate into endothelial cells (ECs) and other angiogenic cell types, such as pericytes, ASCs are a highly valuable source for stimulating angiogenesis. However, cellular therapies in tissue engineering have faced challenges in poor survival of the cells after transplantation, which is why a protective biomaterial scaffold is required. In this work, we studied the potential of nanofibrillated cellulose (NFC) hydrogel to be utilized as a suitable matrix for three-dimensional (3D) cell culturing of human-derived ASCs (hASCs) and studied their angiogenic properties and differentiation potential in ECs and pericytes. In addition, we tested the effect of hASC-conditioned medium and stimulation with angiopoietin-1 (Ang-1) on human umbilical vein endothelial cells (HUVECs) to induce blood vessel-type tube formation in NFC hydrogel. The hASCs were successfully 3D cell cultured in NFC hydrogel as they formed spheroids and had high cell viability with angiogenic features. Most importantly, they showed angiogenic potential by having pericyte-like characteristics when differentiated in EC medium, and their conditioned medium improved HUVEC viability and tube formation, which recalls the active paracrine properties. This study recommends NFC hydrogel for future use as an animal-free biomaterial scaffold for hASCs in therapeutic angiogenesis and other cell therapy purposes.

Preclinical study of Shen Qi Li Xin formula in improving the development of chronic heart failure

Chronic heart failure (CHF) is a common clinical heart disease. In recent years, traditional Chinese medicines have shown good outcomes in CHF treatment. We aimed to explore the therapeutic effect of Shen Qi Li Xin formula (SQLXF) in CHF. CHF rats were treated with SQLXF at the doses of 8.48, 16.96, and 33.92 g/kg/d once a day for 4 weeks by intragastric administration. The hemodynamic and cardiac function parameters of the rats were monitored by conduction echocardiography. In our results, SQLXF treatment at the doses of 16.96 and 33.92 g/kg/d significantly improved the haemodynamics and cardiac function of CHF rats by enhancing the levels of LVSP, +dp/dtmax, -dp/dtmax, LVEF and LVFS and reducing the levels of LVEDP, LVEDD and LVESD. SQLXF treatment at 16.96 and 33.92 g/kg/d also attenuated the damage of myocardial tissues in CHF rats. In addition, compared with normal rats, the number of pericytes was reduced in myocardial tissues of CHF rats. SQLXF treatment at the doses of 16.96 and 33.92 g/kg/d obviously increased the number of pericytes and proliferation of endothelial cells and promoted angiogenesis in myocardial tissues of CHF rats. In vitro, SQLXF impaired low-oxygen-induced inhibition of cell viability and promotion of apoptosis in primary pericytes. Importantly, SQLXF enhanced the adhesion ability of pericytes to endothelial cells. In conclusion, SQLXF improved myocardial injury in CHF rats by enhancing the interaction between pericytes and endothelial cells, suggesting that SQLXF may be a potential drug for CHF treatment.

Glyoxal Fixation Is Optimal for Immunostaining of Brain Vessels, Pericytes and Blood-Brain Barrier Proteins

Brain vascular staining is very important for understanding cerebrovascular pathologies. 4% paraformaldehyde is considered the gold standard fixation technique for immunohistochemistry and it revolutionized the examination of proteins in fixed tissues. However, this fixation technique produces inconsistent immunohistochemical staining results due to antigen masking. Here, we test a new fixation protocol using 3% glyoxal and demonstrate that this method improves the staining of the brain vasculature, pericytes, and tight junction proteins compared to 4% paraformaldehyde. Use of this new fixation technique will provide more detailed information about vascular protein expressions, their distributions, and colocalizations with other proteins at the molecular level in the brain vasculature.

Central Nervous System Pericytes Contribute to Health and Disease

Successful neuroprotection is only possible with contemporary microvascular protection. The prevention of disease-induced vascular modifications that accelerate brain damage remains largely elusive. An improved understanding of pericyte (PC) signalling could provide important insight into the function of the neurovascular unit (NVU), and into the injury-provoked responses that modify cell–cell interactions and crosstalk. Due to sharing the same basement membrane with endothelial cells, PCs have a crucial role in the control of endothelial, astrocyte, and oligodendrocyte precursor functions and hence blood–brain barrier stability. Both cerebrovascular and neurodegenerative diseases impair oxygen delivery and functionally impair the NVU. In this review, the role of PCs in central nervous system health and disease is discussed, considering their origin, multipotency, functions and also dysfunction, focusing on new possible avenues to modulate neuroprotection. Dysfunctional PC signalling could also be considered as a potential biomarker of NVU pathology, allowing us to individualize therapeutic interventions, monitor responses, or predict outcomes.

Temporal alterations in pericytes at the acute phase of ischemia/reperfusion in the mouse brain

Pericytes, as the mural cells surrounding the microvasculature, play a critical role in the regulation of microcirculation; however, how these cells respond to ischemic stroke remains unclear. To determine the temporal alterations in pericytes after ischemia/reperfusion, we used the 1-hour middle cerebral artery occlusion model, which was examined at 2, 12, and 24 hours after reperfusion. Our results showed that in the reperfused regions, the cerebral blood flow decreased and the infarct volume increased with time. Furthermore, the pericytes in the infarct regions contracted and acted on the vascular endothelial cells within 24 hours after reperfusion. These effects may result in incomplete microcirculation reperfusion and a gradual worsening trend with time in the acute phase. These findings provide strong evidence for explaining the "no-reflow" phenomenon that occurs after recanalization in clinical practice.

Rebuilding the Vascular Network: In vivo and in vitro Approaches

As the material transportation system of the human body, the vascular network carries the transportation of materials and nutrients. Currently, the construction of functional microvascular networks is an urgent requirement for the development of regenerative medicine and in vitro drug screening systems. How to construct organs with functional blood vessels is the focus and challenge of tissue engineering research. Here in this review article, we first introduced the basic characteristics of blood vessels in the body and the mechanism of angiogenesis in vivo, summarized the current methods of constructing tissue blood vessels in vitro and in vivo, and focused on comparing the functions, applications and advantages of constructing different types of vascular chips to generate blood vessels. Finally, the challenges and opportunities faced by the development of this field were discussed.

Neural crest cell-derived pericytes act as pro-angiogenic cells in human neocortex development and gliomas

Central nervous system diseases involving the parenchymal microvessels are frequently associated with a ‘microvasculopathy’, which includes different levels of neurovascular unit (NVU) dysfunction, including blood–brain barrier alterations. To contribute to the understanding of NVU responses to pathological noxae, we have focused on one of its cellular components, the microvascular pericytes, highlighting unique features of brain pericytes with the aid of the analyses carried out during vascularization of human developing neocortex and in human gliomas. Thanks to their position, centred within the endothelial/glial partition of the vessel basal lamina and therefore inserted between endothelial cells and the perivascular and vessel-associated components (astrocytes, oligodendrocyte precursor cells (OPCs)/NG2-glia, microglia, macrophages, nerve terminals), pericytes fulfil a central role within the microvessel NVU. Indeed, at this critical site, pericytes have a number of direct and extracellular matrix molecule- and soluble factor-mediated functions, displaying marked phenotypical and functional heterogeneity and carrying out multitasking services. This pericytes heterogeneity is primarily linked to their position in specific tissue and organ microenvironments and, most importantly, to their ontogeny. During ontogenesis, pericyte subtypes belong to two main embryonic germ layers, mesoderm and (neuro)ectoderm, and are therefore expected to be found in organs ontogenetically different, nonetheless, pericytes of different origin may converge and colonize neighbouring areas of the same organ/apparatus. Here, we provide a brief overview of the unusual roles played by forebrain pericytes in the processes of angiogenesis and barriergenesis by virtue of their origin from midbrain neural crest stem cells. A better knowledge of the ontogenetic subpopulations may support the understanding of specific interactions and mechanisms involved in pericyte function/dysfunction, including normal and pathological angiogenesis, thereby offering an alternative perspective on cell subtype-specific therapeutic approaches.

Neural crest cell-derived pericytes act as pro-angiogenic cells in human neocortex development and gliomas

Central nervous system diseases involving the parenchymal microvessels are frequently associated with a ‘microvasculopathy’, which includes different levels of neurovascular unit (NVU) dysfunction, including blood–brain barrier alterations. To contribute to the understanding of NVU responses to pathological noxae, we have focused on one of its cellular components, the microvascular pericytes, highlighting unique features of brain pericytes with the aid of the analyses carried out during vascularization of human developing neocortex and in human gliomas. Thanks to their position, centred within the endothelial/glial partition of the vessel basal lamina and therefore inserted between endothelial cells and the perivascular and vessel-associated components (astrocytes, oligodendrocyte precursor cells (OPCs)/NG2-glia, microglia, macrophages, nerve terminals), pericytes fulfil a central role within the microvessel NVU. Indeed, at this critical site, pericytes have a number of direct and extracellular matrix molecule- and soluble factor-mediated functions, displaying marked phenotypical and functional heterogeneity and carrying out multitasking services. This pericytes heterogeneity is primarily linked to their position in specific tissue and organ microenvironments and, most importantly, to their ontogeny. During ontogenesis, pericyte subtypes belong to two main embryonic germ layers, mesoderm and (neuro)ectoderm, and are therefore expected to be found in organs ontogenetically different, nonetheless, pericytes of different origin may converge and colonize neighbouring areas of the same organ/apparatus. Here, we provide a brief overview of the unusual roles played by forebrain pericytes in the processes of angiogenesis and barriergenesis by virtue of their origin from midbrain neural crest stem cells. A better knowledge of the ontogenetic subpopulations may support the understanding of specific interactions and mechanisms involved in pericyte function/dysfunction, including normal and pathological angiogenesis, thereby offering an alternative perspective on cell subtype-specific therapeutic approaches.

Telocytes are major constituents of the angiogenic apparatus

The current study investigated role of telocytes (TCs) in angiogenesis during embryonic development of quail using immunohistochemistry (IHC), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The angiogenic apparatus consisted of TCs, endothelial cells, and macrophages. TCs were identified morphologically by their telopodes and podoms using TEM and SEM and immunohistochemically using CD34, and vascular endothelial growth factor (VEGF). TCs also expressed CD68. TCs formed a three-dimensional network and established direct contact with blood vessels, sprouting endothelial cells, and active macrophages, while exerting their effect through paracrine signaling. VEGF was also expressed by endothelial cells and macrophages. Matrix metalloproteinase–9 (MMP-9) was expressed by TCs, endothelial cells, and macrophages. In conclusion, the expression of VEGF by TCs, endothelial cells, and macrophages is required for the proliferation and migration of endothelial cells and vascular growth. The expression of MMP-9 by TCs, endothelial cells, and macrophages is essential for the degradation of extracellular matrix (ECM) components during neoangiogenesis. Macrophages may facilitate phagocytosis and elimination of the degraded ECM components.

Human α-synuclein overexpression in a mouse model of Parkinson's disease leads to vascular pathology, blood brain barrier leakage and pericyte activation

The pathological hallmark of Parkinson's disease (PD) is the formation of Lewy bodies containing aggregated alpha-synuclein (α-syn). Although PD is associated with these distinct histological changes, other pathological features such as microvascular alterations have been linked to neurodegeneration. These changes need to be investigated as they create a hostile brain microenvironment and may contribute to the development and progression of the disease. We use a human α-syn overexpression mouse model that recapitulates some of the pathological features of PD in terms of progressive aggregation of human α-syn, impaired striatal dopamine fiber density, and an age-dependent motor deficit consistent with an impaired dopamine release. We demonstrate for the first time in this model a compromised blood-brain barrier integrity and dynamic changes in vessel morphology from angiogenesis at earlier stages to vascular regression at later stages. The vascular alterations are accompanied by a pathological activation of pericytes already at an early stage without changing overall pericyte density. Our data support and further extend the occurrence of vascular pathology as an important pathophysiological aspect in PD. The model used provides a powerful tool to investigate disease-modifying factors in PD in a temporal sequence that might guide the development of new treatments.

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.

Beta secretase 1-dependent amyloid precursor protein processing promotes excessive vascular sprouting through NOTCH3 signalling

Amyloid beta peptides (Aβ) proteins play a key role in vascular pathology in Alzheimer’s Disease (AD) including impairment of the blood–brain barrier and aberrant angiogenesis. Although previous work has demonstrated a pro-angiogenic role of Aβ, the exact mechanisms by which amyloid precursor protein (APP) processing and endothelial angiogenic signalling cascades interact in AD remain a largely unsolved problem. Here, we report that increased endothelial sprouting in human-APP transgenic mouse (TgCRND8) tissue is dependent on β-secretase (BACE1) processing of APP. Higher levels of Aβ processing in TgCRND8 tissue coincides with decreased NOTCH3/JAG1 signalling, overproduction of endothelial filopodia and increased numbers of vascular pericytes. Using a novel in vitro approach to study sprouting angiogenesis in TgCRND8 organotypic brain slice cultures (OBSCs), we find that BACE1 inhibition normalises excessive endothelial filopodia formation and restores NOTCH3 signalling. These data present the first evidence for the potential of BACE1 inhibition as an effective therapeutic target for aberrant angiogenesis in AD.

Hydrogel cross-linking-programmed release of nitric oxide regulates source-dependent angiogenic behaviors of human mesenchymal stem cell

Angiogenesis is stimulated by nitric oxide (NO) production in endothelial cells (ECs). Although proangiogenic actions of human mesenchymal stem cells (hMSCs) have been extensively studied, the mechanistic role of NO in this action remains obscure. Here, we used a gelatin hydrogel that releases NO upon crosslinking by a transglutaminase reaction ("NO gel"). Then, the source-specific behaviors of bone marrow versus adipose tissue-derived hMSCs (BMSCs versus ADSCs) were monitored in the NO gels. NO inhibition resulted in significant decreases in their angiogenic activities. The NO gel induced pericyte-like characteristics in BMSCs in contrast to EC differentiation in ADSCs, as evidenced by tube stabilization versus tube formation, 3D colocalization versus 2D coformation with EC tube networks, pericyte-like wound healing versus EC-like vasculogenesis in gel plugs, and pericyte versus EC marker production. These results provide previously unidentified insights into the effects of NO in regulating hMSC source-specific angiogenic mechanisms and their therapeutic applications.

Vascular Wall-Mesenchymal Stem Cells Differentiation on 3D Biodegradable Highly Porous CaSi-DCPD Doped Poly (α-hydroxy) Acids Scaffolds for Bone Regeneration

Vascularization is a crucial factor when approaching any engineered tissue. Vascular wall-mesenchymal stem cells are an excellent in vitro model to study vascular remodeling due to their strong angiogenic attitude. This study aimed to demonstrate the angiogenic potential of experimental highly porous scaffolds based on polylactic acid (PLA) or poly-e-caprolactone (PCL) doped with calcium silicates (CaSi) and dicalcium phosphate dihydrate (DCPD), namely PLA-10CaSi-10DCPD and PCL-10CaSi-10DCPD, designed for the regeneration of bone defects. Vascular wall-mesenchymal stem cells (VW-MSCs) derived from pig thoracic aorta were seeded on the scaffolds and the expression of angiogenic markers, i.e. CD90 (mesenchymal stem/stromal cell surface marker), pericyte genes α-SMA (alpha smooth muscle actin), PDGFR-β (platelet-derived growth factor receptor-β), and NG2 (neuron-glial antigen 2) was evaluated. Pure PLA and pure PCL scaffolds and cell culture plastic were used as controls (3D in vitro model vs. 2D in vitro model). The results clearly demonstrated that the vascular wall mesenchymal cells colonized the scaffolds and were metabolically active. Cells, grown in these 3D systems, showed the typical gene expression profile they have in control 2D culture, although with some main quantitative differences. DNA staining and immunofluorescence assay for alpha-tubulin confirmed a cellular presence on both scaffolds. However, VW-MSCs cultured on PLA-10CaSi-10DCPD showed an individual cells growth, whilst on PCL-10CaSi-10DCPD scaffolds VW-MSCs grew in spherical clusters. In conclusion, vascular wall mesenchymal stem cells demonstrated the ability to colonize PLA and PCL scaffolds doped with CaSi-DCPD for new vessels formation and a potential for tissue regeneration.

Chondroitin Sulphate Proteoglycans in the Tumour Microenvironment

Proteoglycans are macromolecules that are essential for the development of cells, human diseases and malignancies. In particular, chondroitin sulphate proteoglycans (CSPGs) accumulate in tumour stroma and play a key role in tumour growth and invasion by driving multiple oncogenic pathways in tumour cells and promoting crucial interactions in the tumour microenvironment (TME). These pathways involve receptor tyrosine kinase (RTK) signalling via the mitogen-activated protein kinase (MAPK) cascade and integrin signalling via the activation of focal adhesion kinase (FAK), which sustains the activation of extracellular signal-regulated kinases 1/2 (ERK1/2).Human CSPG4 is a type I transmembrane protein that is associated with the growth and progression of human brain tumours. It regulates cell signalling and migration by interacting with components of the extracellular matrix, extracellular ligands, growth factor receptors, intracellular enzymes and structural proteins. Its overexpression by tumour cells, perivascular cells and precursor/progenitor cells in gliomas suggests that it plays a role in their origin, progression and neo-angiogenesis and its aberrant expression in tumour cells may be a promising biomarker to monitor malignant progression and patient survival.The aim of this chapter is to review and discuss the role of CSPG4 in the TME of human gliomas, including its potential as a druggable therapeutic target.

Dynamic Interplay between Pericytes and Endothelial Cells during Sprouting Angiogenesis

Vascular physiology relies on the concerted dynamics of several cell types, including pericytes, endothelial, and vascular smooth muscle cells. The interactions between such cell types are inherently dynamic and are not easily described with static, fixed, experimental approaches. Pericytes are mural cells that support vascular development, remodeling, and homeostasis, and are involved in a number of pathological situations including cancer. The dynamic interplay between pericytes and endothelial cells is at the basis of vascular physiology and few experimental tools exist to properly describe and study it. Here we employ a previously developed ex vivo murine aortic explant to study the formation of new blood capillary-like structures close to physiological situation. We develop several mouse models to culture, identify, characterize, and follow simultaneously single endothelial cells and pericytes during angiogenesis. We employ microscopy and image analysis to dissect the interactions between cell types and the process of cellular recruitment on the newly forming vessel. We find that pericytes are recruited on the developing sprout by proliferation, migrate independently from endothelial cells, and can proliferate on the growing capillary. Our results help elucidating several relevant mechanisms of interactions between endothelial cells and pericytes.

Mesenchymal Regulation of the Microvascular Niche in Chronic Lung Diseases

The adult lung is comprised of diverse vascular, epithelial, and mesenchymal progenitor cell populations that reside in distinct niches. Mesenchymal progenitor cells (MPCs) are intimately associated with both the epithelium and the vasculature, and new evidence is emerging to describe their functional roles in these niches. Also emerging, following lineage analysis and single cell sequencing, is a new understanding of the diversity of mesenchymal cell subpopulations in the lung. However, several gaps in knowledge remain, including how newly defined MPC lineages interact with cells in the vascular niche and the role of adult lung MPCs during lung repair and regeneration following injury, especially in chronic lung diseases. Here we summarize how the current evidence on MPC regulation of the microvasculature during tissue homeostasis and injury may inform studies on understanding their role in chronic lung disease pathogenesis or repair. © 2019 American Physiological Society. Compr Physiol 9:1431-1441, 2019.

Delivery of silver sulfadiazine and adipose derived stem cells using fibrin hydrogel improves infected burn wound regeneration

Infection control is necessary for improved burn wound regeneration. In this study contact burn wounds were induced on the dorsum of the rats and were infected with Pseudomonas aeruginosa (107cfu/ml of saline) and left overnight (12-14 hours) to establish the infection. After 12 hours, the wounds were treated with PEGylated fibrin hydrogel containing 50 mgs of silver sulfadiazine (SSD) loaded chitosan microsphere (SSD-CSM-FPEG). On day 9, SSD-CSM-FPEG treated burn wounds further received adipose derived stem cell (5×104 ASCs cells/ml) embedded in PEGylated fibrin hydrogel. Wounds were assessed for the healing outcomes such as neovascularization, granulation tissue formation, wound closure and collagen maturation. Analysis of bacterial load in the burn wound biopsies, demonstrated that SSD-CSM-FPEG significantly reduced bacterial infection, while overt infection was still observed in the untreated groups on day 14. Sequential treatment of infected wounds with SSD-CSM-FPEG followed by ASC-FPEGs (SSD-CSM-ASC-FPEG) significantly reduced bacterial colonization (9 log reduction) and pro-inflammatory cytokine (TNF-α) expression. A significant increase in neovascularization markers; NG2 and vWF was also observed. Histological analysis indicated the wounds treated with SSD-CSM-ASC-FPEG increased amount of dermal collagen matrix deposition, a thicker granulation tissue on day 21 and more mature collagen on day 28. This work demonstrates that the sequential treatment of infected burn wounds with SSD-CSM-FPEG followed by ASC-FPEG reduces bacterial infection as well as promotes neo-vascularization with improved matrix remodeling.

Microvascular bioengineering: a focus on pericytes

Capillaries within the microcirculation are essential for oxygen delivery and nutrient/waste exchange, among other critical functions. Microvascular bioengineering approaches have sought to recapitulate many key features of these capillary networks, with an increasing appreciation for the necessity of incorporating vascular pericytes. Here, we briefly review established and more recent insights into important aspects of pericyte identification and function within the microvasculature. We then consider the importance of including vascular pericytes in various bioengineered microvessel platforms including 3D culturing and microfluidic systems. We also discuss how vascular pericytes are a vital component in the construction of computational models that simulate microcirculation phenomena including angiogenesis, microvascular biomechanics, and kinetics of exchange across the vessel wall. In reviewing these topics, we highlight the notion that incorporating pericytes into microvascular bioengineering applications will increase their utility and accelerate the translation of basic discoveries to clinical solutions for vascular-related pathologies.

Vascular regeneration in adult mouse cochlea stimulated by VEGF-A165 and driven by NG2-derived cells ex vivo

Can damaged or degenerated vessels be regenerated in the ear? The question is clinically important, as disruption of cochlear blood flow is seen in a wide variety of hearing disorders, including in loud sound-induced hearing loss (endothelial injury), ageing-related hearing loss (lost vascular density), and genetic hearing loss (e.g., Norrie disease: strial avascularization). Progression in cochlear blood flow (CBF) pathology can parallel progression in hair cell and hearing loss. However, neither new vessel growth in the ear, nor the role of angiogenesis in hearing, have been investigated. In this study, we used an established ex vivo tissue explant model in conjunction with a matrigel matrix model to demonstrate for the first time that new vessels can be generated by activating a vascular endothelial growth factor (VEGF-A) signal. Most intriguingly, we found that the pattern of the newly formed vessels resembles the natural 'mesh pattern' of in situ strial vessels, with both lumen and expression of tight junctions. Sphigosine-1-phosphate (S1P) in synergy with VEGF-A control new vessel size and growth. Using transgenic neural/glial antigen 2 (NG2) fluorescent reporter mice, we have furthermore discovered that the progenitors of "de novo" strial vessels are NG2-derived cells. Taken together, our data demonstrates that damaged strial microvessels can be regenerated by reprogramming NG2-derived angiogenic cells. Restoration of the functional vasculature may be critical for recovery of vascular dysfunction related hearing loss.

Targeting pericytes for neurovascular regeneration

Pericytes, as a key cellular part of the blood-brain barrier, play an important role in the maintenance of brain neurovascular unit. These cells participate in brain homeostasis by regulating vascular development and integrity mainly through secreting various factors. Pericytes per se show different restorative properties after blood-brain barrier injury. Upon the occurrence of brain acute and chronic diseases, pericytes provoke immune cells to regulate neuro-inflammatory conditions. Loss of pericytes in distinct neurologic disorders intensifies blood-brain barrier permeability and leads to vascular dementia. The therapeutic potential of pericytes is originated from the unique morphological shape, location, and their ability in providing vast paracrine and juxtacrine interactions. A subset of pericytes possesses multipotentiality and exhibit trans-differentiation capacity in the context of damaged tissue. This review article aimed to highlight the critical role of pericytes in restoration of the blood-brain barrier after injury by focusing on the dynamics of pericytes and cross-talk with other cell types.

Pericytes in Ischemic Stroke

Recent stroke research has shifted the focus to the microvasculature from neuron-centric views. It is increasingly recognized that a successful neuroprotection is not feasible without microvascular protection. On the other hand, recent studies on pericytes, long-neglected cells on microvessels have provided insight into the regulation of microcirculation. Pericytes play an essential role in matching the metabolic demand of nervous tissue with the blood flow in addition to regulating the development and maintenance of the blood-brain barrier (BBB), leukocyte trafficking across the BBB and angiogenesis. Pericytes appears to be highly vulnerable to injury. Ischemic injury to pericytes on cerebral microvasculature unfavorably impacts the stroke-induced tissue damage and brain edema by disrupting microvascular blood flow and BBB integrity. Strongly supporting this, clinical imaging studies show that tissue reperfusion is not always obtained after recanalization. Therefore, prevention of pericyte dysfunction may improve the outcome of recanalization therapies by promoting microcirculatory reperfusion and preventing hemorrhage and edema. In the peri-infarct tissue, pericytes are detached from microvessels and promote angiogenesis and neurogenesis, and hence positively effect stroke outcome. Expectedly, we will learn more about the place of pericytes in CNS pathologies including stroke and devise approaches to treat them in the next decades.

The Significance of Chondroitin Sulfate Proteoglycan 4 (CSPG4) in Human Gliomas

Neuron glial antigen 2 (NG2) is a chondroitin sulphate proteoglycan 4 (CSPG4) that occurs in developing and adult central nervous systems (CNSs) as a marker of oligodendrocyte precursor cells (OPCs) together with platelet-derived growth factor receptor α (PDGFRα). It behaves variably in different pathological conditions, and is possibly involved in the origin and progression of human gliomas. In the latter, NG2/CSPG4 induces cell proliferation and migration, is highly expressed in pericytes, and plays a role in neoangiogenesis. NG2/CSPG4 expression has been demonstrated in oligodendrogliomas, astrocytomas, and glioblastomas (GB), and it correlates with malignancy. In rat tumors transplacentally induced by N-ethyl-N-nitrosourea (ENU), NG2/CSPG4 expression correlates with PDGFRα, Olig2, Sox10, and Nkx2.2, and with new vessel formation. In this review, we attempt to summarize the normal and pathogenic functions of NG2/CSPG4, as well as its potential as a therapeutic target.

Blood-brain barrier development: Systems modeling and predictive toxicology

The blood-brain barrier (BBB) serves as a gateway for passage of drugs, chemicals, nutrients, metabolites, and hormones between vascular and neural compartments in the brain. Here, we review BBB development with regard to the microphysiology of the neurovascular unit (NVU) and the impact of BBB disruption on brain development. Our focus is on modeling these complex systems. Extant in silico models are available as tools to predict the probability of drug/chemical passage across the BBB; in vitro platforms for high-throughput screening and high-content imaging provide novel data streams for profiling chemical-biological interactions; and engineered human cell-based microphysiological systems provide empirical models with which to investigate the dynamics of NVU function. Computational models are needed that bring together kinetic and dynamic aspects of NVU function across gestation and under various physiological and toxicological scenarios. This integration will inform adverse outcome pathways to reduce uncertainty in translating in vitro data and in silico models for use in risk assessments that aim to protect neurodevelopmental health.

Assessing the Minimum Time-Period of Normoxic Preincubation for Stable Adipose Stromal Cell-Derived Vascular Networks

Introduction

Pre-vascularization of tissue engineered grafts is a promising strategy to facilitate their improved viability following in vivo implantation. In this process, endothelial cells (ECs) form capillary-like networks that can anastomose with host vasculature. Adipose-derived stromal cells (ASCs) are a commonly used cell population for tissue engineering and contain a subpopulation of ECs capable of assembling into robust vascular networks and anastomosing with the host. However, their initial vascular assembly is significantly impaired in hypoxic conditions (2% O₂). In this study, we explored the minimum period of normoxic (20% O₂) pre-treatment required to enable the formation of stable vascular networks.

Methods

ASC-derived vascular structures were allowed to preassemble in fibrin hydrogels in normoxia for 0, 2, 4, or 6 days and then transplanted into hypoxic environments for 6 days. Total vascular length, pericyte coverage, cell proliferation, apoptosis rates, and ECM production was assessed.

Results

Vascular assembly increased with time over the 6 days of culture. We found that 4 days was the minimum period of time required for stable vascular assembly. We compared the major differences in cell behavior and network structure at Days 2 and 4. Neither proliferation nor apoptosis differed, however, the Day 4 time-point was associated with a significant increase in pericyte coverage (46.1 ± 2.6%) compared to Day 2 (24.3 ± 5.3%).

Conclusions

These data suggest oxygen tension may be a mediator of EC-pericyte interactions during vascular assembly. Pre-vascularization strategies should incorporate a normoxic period of to enable successful vascular formation and development.

Spatiotemporal endothelial cell - pericyte association in tumors as shown by high resolution 4D intravital imaging

Endothelial cells and pericytes are integral cellular components of the vasculature with distinct interactive functionalities. To study dynamic interactions between these two cells we created two transgenic animal lines. A truncated eNOS (endothelial nitric oxide synthase) construct was used as a GFP tag for endothelial cell evaluation and an inducible Cre-lox recombination, under control of the Pdgfrb (platelet derived growth factor receptor beta) promoter, was created for pericyte assessment. Also, eNOStag-GFP animals were crossed with the already established Cspg4-DsRed mice expressing DsRed fluorescent protein in pericytes. For intravital imaging we used tumors implanted in the dorsal skinfold of these transgenic animals. This setup allowed us to study time and space dependent complexities, such as distribution, morphology, motility, and association between both vascular cell types in all angiogenetic stages, without the need for additional labeling. Moreover, as fluorescence was still clearly detectable after fixation, it is possible to perform comparative histology following intravital evaluation. These transgenic mouse lines form an excellent model to capture collective and individual cellular and subcellular endothelial cell – pericyte dynamics and will help answer key questions on the cellular and molecular relationship between these two cells.

Cell surface chondroitin sulphate proteoglycan 4 (CSPG4) binds to the basement membrane heparan sulphate proteoglycan, perlecan, and is involved in cell adhesion

Chondroitin sulphate proteoglycan 4 (CSPG4) is a cell surface proteoglycan highly expressed by tumour, perivascular and oligodendrocyte cells and known to be involved cell adhesion and migration. This study showed that CSPG4 was present as a proteoglycan on the cell surface of two melanoma cell lines, MM200 and Me1007, as well as shed into the conditioned medium. CSPG4 from the two melanoma cell lines differed in the amount of chondroitin sulphate (CS) decoration, as well as the way the protein core was fragmented. In contrast, the CSPG4 expressed by a colon carcinoma cell line, WiDr, was predominantly as a protein core on the cell surface lacking glycosaminoglycan (GAG) chains. This study demonstrated that CSPG4 immunopurified from the melanoma cell lines formed a complex with perlecan synthesized by the same cultured cells. Mechanistic studies showed that CSPG4 bound to perlecan via hydrophobic protein-protein interactions involving multiple sites on perlecan including the C-terminal region. Furthermore, this study revealed that CSPG4 interacted with perlecan to support cell adhesion and actin polymerization. Together these data suggest a novel mechanism by which CSPG4 expressing cells might attach to perlecan-rich matrices so as those found in connective tissues and basement membranes.

Vascular Calcification: Is it rather a Stem/Progenitor Cells Driven Phenomenon?

Vascular calcification (VC) has witnessed a surge of interest. Vasculature is virtually an omnipresent organ and has a notably high capacity for repair throughout embryonic and adult life. Of the vascular diseases, atherosclerosis is a leading cause of morbidity and mortality on account of ectopic cartilage and bone formation. Despite the identification of a number of risk factors, all the current theories explaining pathogenesis of VC in atherosclerosis are far from complete. The most widely accepted response to injury theory and smooth muscle transdifferentiation to explain the VC observed in atherosclerosis is being challenged. Recent focus on circulating and resident progenitor cells in the vasculature and their role in atherogenesis and VC has been the driving force behind this review. This review discusses intrinsic cellular players contributing to fate determination of cells and tissues to form ectopic cartilage and bone formation.

A 3D in vitro pericyte-supported microvessel model: visualisation and quantitative characterisation of multistep angiogenesis

Angiogenesis, which refers to the formation of new blood vessels from already existing vessels, is a promising therapeutic target and a complex multistep process involving many different factors. Pericytes (PCs) are attracting attention as they are considered to make significant contributions to the maturation and stabilisation of newly formed vessels, although not much is known about the precise mechanisms involved. Since there is no single specific marker for pericytes, in vivo models may complicate PC identification and the study of PCs in angiogenesis would benefit from in vitro models recapitulating the interactions between PCs and endothelial cells (ECs) in a three-dimensional (3D) configuration. In this study, a 3D in vitro co-culture microvessel model incorporating ECs and PCs was constructed by bottom-up tissue engineering. Angiogenesis was induced in the manner of sprout formation by the addition of a vascular endothelial cell growth factor. It was found that the incorporation of PCs prevented expansion of the parent vessel diameter and enhanced sprout formation and elongation. Physical interactions between ECs and PCs were visualised by immunostaining and it disclosed that PCs covered the EC monolayer from its basal side in the parent vessel as well as angiogenic sprouts. Furthermore, the microvessels were visualized in 3D by using a non-invasive optical coherence tomography (OCT) imaging system and sprout features were quantitatively assessed. It revealed that the sprouts in EC-PC co-culture vessels were longer and tighter than those in EC mono-culture vessels. The combination of the microvessel model and the OCT system analysis can be useful for the visualisation and demonstration of the multistep process of angiogenesis, which incorporates PCs.

VEGF pathway targeting agents, vessel normalization and tumor drug uptake: from bench to bedside

Vascular endothelial growth factor (VEGF) pathway targeting agents have been combined with other anticancer drugs, leading to improved efficacy in carcinoma of the cervix, stomach, lung, colon and rectum, ovary, and breast. Vessel normalization induced by VEGF pathway targeting agents influences tumor drug uptake. Following bevacizumab treatment, preclinical and clinical studies have shown a decrease in tumor delivery of radiolabeled antibodies and two chemotherapeutic drugs. The decrease in vessel pore size during vessel normalization might explain the decrease in tumor drug uptake. Moreover, the addition of bevacizumab to cetuximab, or panitumumab in colorectal cancer patients or to trastuzumab in breast cancer patients, did not improve efficacy. However, combining bevacizumab with chemotherapy did increase efficacy in some cancer types. Novel biomarkers to select patients who may benefit from combination therapies, such as the effect of an angiogenesis inhibitor on tumor perfusion, requires innovative trial designs and large clinical trials. Small imaging studies with radiolabeled drugs could be used in the interphase to gain further insight into the interplay between VEGF targeted therapy, vessel normalization and tumor drug delivery.

The NG2 Proteoglycan in Pericyte Biology

Studies of pericytes have been retarded by the lack of appropriate markers for identification of these perivascular mural cells. Use of antibodies against the NG2 proteoglycan as a pericyte marker has greatly facilitated recent studies of pericytes, emphasizing the intimate spatial relationship between pericytes and endothelial cells, allowing more accurate quantification of pericyte/endothelial cell ratios in different vascular beds, and revealing the participation of pericytes throughout all stages of blood vessel formation. The functional importance of NG2 in pericyte biology has been established via NG2 knockdown (in vitro) and knockout (in vivo) strategies that reveal significant deficits in blood vessel formation when NG2 is absent from pericytes. NG2 influences pericyte proliferation and motility by acting as an auxiliary receptor that enhances signaling through integrins and receptor tyrosine kinase growth factor receptors. By acting in a trans orientation, NG2 also activates integrin signaling in closely apposed endothelial cells, leading to enhanced maturation and formation of endothelial cell junctions. NG2 null mice exhibit reduced growth of both mammary and brain tumors that can be traced to deficits in tumor vascularization. Use of Cre-Lox technology to produce pericyte-specific NG2 null mice has revealed specific deficits in tumor vessels that include decreased pericyte ensheathment of endothelial cells, diminished assembly of the vascular basement membrane, reduced vessel patency, and increased vessel leakiness. Interestingly, myeloid-specific NG2 null mice exhibit even larger deficits in tumor vascularization, leading to correspondingly slower tumor growth. Myeloid-specific NG2 null mice are deficient in their ability to recruit macrophages to tumors and other sites of inflammation. This absence of macrophages deprives pericytes of a signal that is crucial for their ability to interact with endothelial cells. The interplay between pericytes, endothelial cells, and macrophages promises to be an extremely fertile area of future study.

Proliferating NG2-Cell-Dependent Angiogenesis and Scar Formation Alter Axon Growth and Functional Recovery After Spinal Cord Injury in Mice

Spinal cord injury (SCI) induces a centralized fibrotic scar surrounded by a reactive glial scar at the lesion site. The origin of these scars is thought to be perivascular cells entering lesions on ingrowing blood vessels and reactive astrocytes, respectively. However, two NG2-expressing cell populations, pericytes and glia, may also influence scar formation. In the periphery, new blood vessel growth requires proliferating NG2⁺ pericytes; if this were also true in the CNS, then the fibrotic scar would depend on dividing NG2⁺ pericytes. NG2⁺ glial cells (also called oligodendrocyte progenitors or polydendrocytes) also proliferate after SCI and accumulate in large numbers among astrocytes in the glial scar. Their effect there, if any, is unknown. We show that proliferating NG2⁺ pericytes and glia largely segregate into the fibrotic and glial scars, respectively; therefore, we used a thymidine kinase/ganciclovir paradigm to ablate both dividing NG2⁺ cell populations to determine whether either scar was altered. Results reveal that loss of proliferating NG2⁺ pericytes in the lesion prevented intralesion angiogenesis and completely abolished the fibrotic scar. The glial scar was also altered in the absence of acutely dividing NG2⁺ cells, displaying discontinuous borders and significantly reduced GFAP density. Collectively, these changes enhanced edema, prolonged hemorrhage, and impaired forelimb functional recovery. Interestingly, after halting GCV at 14 d postinjury, scar elements and vessels entered the lesions over the next 7 d, as did large numbers of axons that were not present in controls. Collectively, these data reveal that acutely dividing NG2⁺ pericytes and glia play fundamental roles in post-SCI tissue remodeling.SIGNIFICANCE STATEMENT Spinal cord injury (SCI) is characterized by formation of astrocytic and fibrotic scars, both of which are necessary for lesion repair. NG2⁺ cells may influence both scar-forming processes. This study used a novel transgenic mouse paradigm to ablate proliferating NG2⁺ cells after SCI to better understand their role in repair. For the first time, our data show that dividing NG2⁺ pericytes are required for post-SCI angiogenesis, which in turn is needed for fibrotic scar formation. Moreover, loss of cycling NG2⁺ glia and pericytes caused significant multicellular tissue changes, including altered astrocyte responses and impaired functional recovery. This work reveals previously unknown ways in which proliferating NG2⁺ cells contribute to endogenous repair after SCI.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.