Pericyte contractility controls endothelial cell cycle progression and sprouting: insights into angiogenic switch mechanics

Characterization of Proteome Changes in Aged and Collagen VI-Deficient Human Pericyte Cultures

Pericytes are a distinct type of cells interacting with endothelial cells in blood vessels and contributing to endothelial barrier integrity. Furthermore, pericytes show mesenchymal stem cell properties. Muscle-derived pericytes can demonstrate both angiogenic and myogenic capabilities. It is well known that regenerative abilities and muscle stem cell potential decline during aging, leading to sarcopenia. Therefore, this study aimed to investigate the potential of pericytes in supporting muscle differentiation and angiogenesis in elderly individuals and in patients affected by Ullrich congenital muscular dystrophy or by Bethlem myopathy, two inherited conditions caused by mutations in collagen VI genes and sharing similarities with the progressive skeletal muscle changes observed during aging. The study characterized pericytes from different age groups and from individuals with collagen VI deficiency by mass spectrometry-based proteomic and bioinformatic analyses. The findings revealed that aged pericytes display metabolic changes comparable to those seen in aging skeletal muscle, as well as a decline in their stem potential, reduced protein synthesis, and alterations in focal adhesion and contractility, pointing to a decrease in their ability to form blood vessels. Strikingly, pericytes from young patients with collagen VI deficiency showed similar characteristics to aged pericytes, but were found to still handle oxidative stress effectively together with an enhanced angiogenic capacity.

The contribution of β-amyloid, Tau and α-synuclein to blood-brain barrier damage in neurodegenerative disorders

Central nervous system (CNS) accumulation of fibrillary deposits made of Amyloid β (Aβ), hyperphosphorylated Tau or α-synuclein (α-syn), present either alone or in the form of mixed pathology, characterizes the most common neurodegenerative diseases (NDDs) as well as the aging brain. Compelling evidence supports that acute neurological disorders, such as traumatic brain injury (TBI) and stroke, are also accompanied by increased deposition of toxic Aβ, Tau and α-syn species. While the contribution of these pathological proteins to neurodegeneration has been experimentally ascertained, the cellular and molecular mechanisms driving Aβ, Tau and α-syn-related brain damage remain to be fully clarified. In the last few years, studies have shown that Aβ, Tau and α-syn may contribute to neurodegeneration also by inducing and/or promoting blood-brain barrier (BBB) disruption. These pathological proteins can affect BBB integrity either directly by affecting key BBB components such as pericytes and endothelial cells (ECs) or indirectly, by promoting brain macrophages activation and dysfunction. Here, we summarize and critically discuss key findings showing how Aβ, Tau and α-syn can contribute to BBB damage in most common NDDs, TBI and stroke. We also highlight the need for a deeper characterization of the role of these pathological proteins in the activation and dysfunction of brain macrophages, pericytes and ECs to improve diagnosis and treatment of acute and chronic neurological disorders.

MEK1-ERK1/2 signaling regulates the cardiomyocyte non-sarcomeric actin cytoskeletal network

During select pathological conditions, the heart can hypertrophy and remodel in either a dilated or concentric ventricular geometry, which is associated with lengthening or widening of cardiomyocytes, respectively. The mitogen-activated protein kinase kinase 1 (MEK1) and extracellular signal-related kinase 1 and 2 (ERK1/2) pathway has been implicated in these differential types of growth such that cardiac overexpression of activated MEK1 causes profound concentric hypertrophy and cardiomyocyte thickening, while genetic ablation of the genes encoding ERK1/2 in the mouse heart causes dilation and cardiomyocyte lengthening. However, the mechanisms by which this kinase signaling pathway controls cardiomyocyte directional growth as well as its downstream effectors are poorly understood. To investigate this, we conducted an unbiased phosphoproteomic screen in cultured neonatal rat ventricular myocytes treated with an activated MEK1 adenovirus, the MEK1 inhibitor U0126, or an eGFP adenovirus control. Bioinformatic analysis identified cytoskeletal-related proteins as the largest subset of differentially phosphorylated proteins. Phos-tag and traditional Western blotting were performed to confirm that many cytoskeletal proteins displayed changes in phosphorylation with manipulations in MEK1-ERK1/2 signaling. From this, we hypothesized that the actin cytoskeleton would be changed in vivo in the mouse heart. Indeed, we found that activated MEK1 transgenic mice and gene-deleted mice lacking ERK1/2 protein had enhanced non-sarcomeric actin expression in cardiomyocytes compared with wild-type control hearts. Consistent with these results, cytoplasmic β- and γ-actin were increased at the subcortical intracellular regions of adult cardiomyocytes. Together, these data suggest that MEK1-ERK1/2 signaling influences the non-sarcomeric cytoskeletal actin network, which may be important for facilitating the growth of cardiomyocytes in length and/or width.NEW & NOTEWORTHY Here, we performed an unbiased analysis of the total phosphoproteome downstream of MEK1-ERK1/2 kinase signaling in cardiomyocytes. Pathway analysis suggested that proteins of the non-sarcomeric cytoskeleton were the most differentially affected. We showed that cytoplasmic β-actin and γ-actin isoforms, regulated by MEK1-ERK1/2, are localized to the subcortical space at both lateral membranes and intercalated discs of adult cardiomyocytes suggesting how MEK1-ERK1/2 signaling might underlie directional growth of adult cardiomyocytes.

Emerging Links between Cerebral Blood Flow Regulation and Cognitive Decline: A Role for Brain Microvascular Pericytes

Cognitive impairment associated with vascular etiology has been of considerable interest in the development of dementia. Recent studies have started to uncover cerebral blood flow deficits in initiating cognitive deterioration. Brain microvascular pericytes, the only type of contractile cells in capillaries, are involved in the precise modulation of vascular hemodynamics due to their ability to regulate resistance in the capillaries. They exhibit potential in maintaining the capillary network geometry and basal vascular tone. In addition, pericytes can facilitate better blood flow supply in response to neurovascular coupling. Their dysfunction is thought to disturb cerebral blood flow causing metabolic imbalances or structural injuries, leading to consequent cognitive decline. In this review, we summarize the characteristics of microvascular pericytes in brain blood flow regulation and outline the framework of a two-hit hypothesis in cognitive decline, where we emphasize how pericytes serve as targets of cerebral blood flow dysregulation that occurs with neurological challenges, ranging from genetic factors, aging, and pathological proteins to ischemic stress.

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.

Biology of vascular mural cells

The vasculature consists of vessels of different sizes that are arranged in a hierarchical pattern. Two cell populations work in concert to establish this pattern during embryonic development and adopt it to changes in blood flow demand later in life: endothelial cells that line the inner surface of blood vessels, and adjacent vascular mural cells, including smooth muscle cells and pericytes. Despite recent progress in elucidating the signalling pathways controlling their crosstalk, much debate remains with regard to how mural cells influence endothelial cell biology and thereby contribute to the regulation of blood vessel formation and diameters. In this Review, I discuss mural cell functions and their interactions with endothelial cells, focusing on how these interactions ensure optimal blood flow patterns. Subsequently, I introduce the signalling pathways controlling mural cell development followed by an overview of mural cell ontogeny with an emphasis on the distinguishing features of mural cells located on different types of blood vessels. Ultimately, I explore therapeutic strategies involving mural cells to alleviate tissue ischemia and improve vascular efficiency in a variety of diseases.

Highlighting In Vitro the Role of Brain-like Endothelial Cells on the Maturation and Metabolism of Brain Pericytes by SWATH Proteomics

Within the neurovascular unit, brain pericytes (BPs) are of major importance for the induction and maintenance of the properties of the blood-brain barrier (BBB) carried by the brain microvessel endothelial cells (ECs). Throughout barriergenesis, ECs take advantage of soluble elements or contact with BPs to maintain BBB integrity and the regulation of their cellular homeostasis. However, very few studies have focused on the role of ECs in the maturation of BPs. The aim of this study is to shed light on the proteome of BPs solocultured (hBP-solo) or cocultured with ECs (hBP-coc) to model the human BBB in a non-contact manner. We first generated protein libraries for each condition and identified 2233 proteins in hBP-solo versus 2492 in hBP-coc and 2035 common proteins. We performed a quantification of the enriched proteins in each condition by sequential window acquisition of all theoretical mass spectra (SWATH) analysis. We found 51 proteins enriched in hBP-solo related to cell proliferation, contractility, adhesion and extracellular matrix element production, a protein pattern related to an immature cell. In contrast, 90 proteins are enriched in hBP-coc associated with a reduction in contractile activities as observed in vivo in ‘mature’ BPs, and a significant gain in different metabolic functions, particularly related to mitochondrial activities and sterol metabolism. This study highlights that BPs take advantage of ECs during barriergenesis to make a metabolic switch in favor of BBB homeostasis in vitro.

The Multiple Roles of Pericytes in Vascular Formation and Microglial Functions in the Brain

In the capillary walls, vascular endothelial cells are covered with mural cells, such as smooth muscle cells and pericytes. Although pericytes had been thought to play simply a structural role, emerging evidence has highlighted their multiple functions in the embryonic, postnatal, and adult brain. As the central nervous system (CNS) develops, the brain's vascular structure gradually matures into a hierarchical network, which is crucial for the proper development of neural lineage cells by providing oxygen and nutrients. Pericytes play an essential role in vascular formation and regulate blood‒brain barrier (BBB) integrity as a component of the neurovascular unit (NVU), in collaboration with other cells, such as vascular endothelial cells, astrocytes, neurons, and microglia. Microglia, the resident immune cells of the CNS, colonize the brain at embryonic day (E) 9.5 in mice. These cells not only support the development and maturation of neural lineage cells but also help in vascular formation through their extensive migration. Recent studies have demonstrated that pericytes directly contact microglia in the CNS, and their interactions have a profound effect on physiological and pathological aspects. This review summarizes the function of pericytes, focusing on the interplay between pericytes and microglia.

Comparison of the Behavior of Perivascular Cells (Pericytes and CD34+ Stromal Cell/Telocytes) in Sprouting and Intussusceptive Angiogenesis

Perivascular cells in the pericytic microvasculature, pericytes and CD34+ stromal cells/telocytes (CD34+SCs/TCs), have an important role in angiogenesis. We compare the behavior of these cells depending on whether the growth of endothelial cells (ECs) from the pre-existing microvasculature is toward the interstitium with vascular bud and neovessel formation (sprouting angiogenesis) or toward the vascular lumen with intravascular pillar development and vessel division (intussusceptive angiogenesis). Detachment from the vascular wall, mobilization, proliferation, recruitment, and differentiation of pericytes and CD34+SCs/TCs, as well as associated changes in vessel permeability and functionality, and modifications of the extracellular matrix are more intense, longer lasting over time, and with a greater energy cost in sprouting angiogenesis than in intussusceptive angiogenesis, in which some of the aforementioned events do not occur or are compensated for by others (e.g., sparse EC and pericyte proliferation by cell elongation and thinning). The governing mechanisms involve cell-cell contacts (e.g., peg-and-socket junctions between pericytes and ECs), multiple autocrine and paracrine signaling molecules and pathways (e.g., vascular endothelial growth factor, platelet-derived growth factor, angiopoietins, transforming growth factor B, ephrins, semaphorins, and metalloproteinases), and other factors (e.g., hypoxia, vascular patency, and blood flow). Pericytes participate in vessel development, stabilization, maturation and regression in sprouting angiogenesis, and in interstitial tissue structure formation of the pillar core in intussusceptive angiogenesis. In sprouting angiogenesis, proliferating perivascular CD34+SCs/TCs are an important source of stromal cells during repair through granulation tissue formation and of cancer-associated fibroblasts (CAFs) in tumors. Conversely, CD34+SCs/TCs have less participation as precursor cells in intussusceptive angiogenesis. The dysfunction of these mechanisms is involved in several diseases, including neoplasms, with therapeutic implications.

Pericyte-mediated constriction of renal capillaries evokes no-reflow and kidney injury following ischaemia

Acute kidney injury is common, with ~13 million cases and 1.7 million deaths/year worldwide. A major cause is renal ischaemia, typically following cardiac surgery, renal transplant or severe haemorrhage. We examined the cause of the sustained reduction in renal blood flow ('no-reflow'), which exacerbates kidney injury even after an initial cause of compromised blood supply is removed. Adult male Sprague-Dawley rats, or NG2-dsRed male mice were used in this study. After 60 min kidney ischaemia and 30-60 min reperfusion, renal blood flow remained reduced, especially in the medulla, and kidney tubule damage was detected as Kim-1 expression. Constriction of the medullary descending vasa recta and cortical peritubular capillaries occurred near pericyte somata, and led to capillary blockages, yet glomerular arterioles and perfusion were unaffected, implying that the long-lasting decrease of renal blood flow contributing to kidney damage was generated by pericytes. Blocking Rho kinase to decrease pericyte contractility from the start of reperfusion increased the post-ischaemic diameter of the descending vasa recta capillaries at pericytes, reduced the percentage of capillaries that remained blocked, increased medullary blood flow and reduced kidney injury. Thus, post-ischaemic renal no-reflow, contributing to acute kidney injury, reflects pericytes constricting the descending vasa recta and peritubular capillaries. Pericytes are therefore an important therapeutic target for treating acute kidney injury.

The Important Role of Endothelium and Extracellular Vesicles in the Cellular Mechanism of Aortic Aneurysm Formation

Homeostasis is a fundamental property of biological systems consisting of the ability to maintain a dynamic balance of the environment of biochemical processes. The action of endogenous and exogenous factors can lead to internal balance disorder, which results in the activation of the immune system and the development of inflammatory response. Inflammation determines the disturbances in the structure of the vessel wall, connected with the change in their diameter. These disorders consist of accumulation in the space between the endothelium and the muscle cells of low-density lipoproteins (LDL), resulting in the formation of fatty streaks narrowing the lumen and restricting the blood flow in the area behind the structure. The effect of inflammation may also be pathological dilatation of the vessel wall associated with the development of aneurysms. Described disease entities strongly correlate with the increased migration of immune cells. Recent scientific research indicates the secretion of specific vesicular structures during migration activated by the inflammation. The review focuses on the link between endothelial dysfunction and the inflammatory response and the impact of these processes on the development of disease entities potentially related to the secretion of extracellular vesicles (EVs).

Hexokinase 2-driven glycolysis in pericytes activates their contractility leading to tumor blood vessel abnormalities

Defective pericyte-endothelial cell interaction in tumors leads to a chaotic, poorly organized and dysfunctional vasculature. However, the underlying mechanism behind this is poorly studied. Herein, we develop a method that combines magnetic beads and flow cytometry cell sorting to isolate pericytes from tumors and normal adjacent tissues from patients with non-small cell lung cancer (NSCLC) and hepatocellular carcinoma (HCC). Pericytes from tumors show defective blood vessel supporting functions when comparing to those obtained from normal tissues. Mechanistically, combined proteomics and metabolic flux analysis reveals elevated hexokinase 2(HK2)-driven glycolysis in tumor pericytes, which up-regulates their ROCK2-MLC2 mediated contractility leading to impaired blood vessel supporting function. Clinically, high percentage of HK2 positive pericytes in blood vessels correlates with poor patient overall survival in NSCLC and HCC. Administration of a HK2 inhibitor induces pericyte-MLC2 driven tumor vasculature remodeling leading to enhanced drug delivery and efficacy against tumor growth. Overall, these data suggest that glycolysis in tumor pericytes regulates their blood vessel supporting role.

Pericyte-endothelial cells interaction defines tumor vasculature and has implications in tumorigenesis development and therapy efficacy. Here, the authors show that hexokinase 2- driven glycolysis activates ROCK1-MLC2 mediated contractility in pericytes leading to tumor blood vessel abnormality.

Pericyte Contractile Responses to Endothelin-1 and Aβ Peptides: Assessment by Electrical Impedance Assay

Pericytes are vascular mural cells that contract and relax in response to vasoactive stimuli to regulate neurovascular coupling and cerebral blood flow. Pericytes are damaged and degenerate in Alzheimer's disease (AD). We previously showed that the level of the regulatory vasoconstrictor, endothelin-1 (EDN1), is elevated in AD cerebral cortex and upregulated by amyloid-beta (Aβ). We have used electrical impedance analysis to monitor the contractile and proliferative response of cultured human fetal and adult brain-derived pericytes to EDN1 in real-time. EDN1 caused transient, dose-dependent contraction of fetal and adult brain pericytes that was mediated by EDN1 type A receptors and increased the subsequent proliferation of fetal but not adult cells. The contractile responses to EDN1 were weaker in the adult pericytes. The EDN1-mediated contractile response of fetal pericytes was unchanged after exposure to Aβ_{1 - 40} or Aβ_{1 - 42} (0.1-10 μM) for 1 h but both contraction and subsequent relaxation were significantly impaired upon exposure to Aβ for 24 h. These data suggest that chronic exposure to Aβ interferes with EDN1-mediated pericyte contractility, potentially contributing to neurovascular uncoupling and reduced cerebral blood flow in AD.

Blood-Brain Barrier and Neurodegenerative Diseases-Modeling with iPSC-Derived Brain Cells

The blood-brain barrier (BBB) regulates the delivery of oxygen and important nutrients to the brain through active and passive transport and prevents neurotoxins from entering the brain. It also has a clearance function and removes carbon dioxide and toxic metabolites from the central nervous system (CNS). Several drugs are unable to cross the BBB and enter the CNS, adding complexity to drug screens targeting brain disorders. A well-functioning BBB is essential for maintaining healthy brain tissue, and a malfunction of the BBB, linked to its permeability, results in toxins and immune cells entering the CNS. This impairment is associated with a variety of neurological diseases, including Alzheimer's disease and Parkinson's disease. Here, we summarize current knowledge about the BBB in neurodegenerative diseases. Furthermore, we focus on recent progress of using human-induced pluripotent stem cell (iPSC)-derived models to study the BBB. We review the potential of novel stem cell-based platforms in modeling the BBB and address advances and key challenges of using stem cell technology in modeling the human BBB. Finally, we highlight future directions in this area.

Chemokine-Cytokine Networks in the Head and Neck Tumor Microenvironment

Head and neck squamous cell carcinomas (HNSCCs) are aggressive diseases with a dismal patient prognosis. Despite significant advances in treatment modalities, the five-year survival rate in patients with HNSCC has improved marginally and therefore warrants a comprehensive understanding of the HNSCC biology. Alterations in the cellular and non-cellular components of the HNSCC tumor micro-environment (TME) play a critical role in regulating many hallmarks of cancer development including evasion of apoptosis, activation of invasion, metastasis, angiogenesis, response to therapy, immune escape mechanisms, deregulation of energetics, and therefore the development of an overall aggressive HNSCC phenotype. Cytokines and chemokines are small secretory proteins produced by neoplastic or stromal cells, controlling complex and dynamic cell-cell interactions in the TME to regulate many cancer hallmarks. This review summarizes the current understanding of the complex cytokine/chemokine networks in the HNSCC TME, their role in activating diverse signaling pathways and promoting tumor progression, metastasis, and therapeutic resistance development.

Pericyte mechanics and mechanobiology

Pericytes are mural cells of the microvasculature, recognized by their thin processes and protruding cell body. Pericytes wrap around endothelial cells and play a central role in regulating various endothelial functions, including angiogenesis and inflammation. They also serve as a vascular support and regulate blood flow by contraction. Prior reviews have examined pericyte biological functions and biochemical signaling pathways. In this Review, we focus on the role of mechanics and mechanobiology in regulating pericyte function. After an overview of the morphology and structure of pericytes, we describe their interactions with both the basement membrane and endothelial cells. We then turn our attention to biophysical considerations, and describe contractile forces generated by pericytes, mechanical forces exerted on pericytes, and pericyte responses to these forces. Finally, we discuss 2D and 3D engineered in vitro models for studying pericyte mechano-responsiveness and underscore the need for more evolved models that provide improved understanding of pericyte function and dysfunction.

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.

Picturing Breast Cancer Brain Metastasis Development to Unravel Molecular Players and Cellular Crosstalk

Simple Summary

Breast cancer is a devastating disorder affecting millions of women worldwide. With improved therapeutics for the primary tumor, the appearance of metastasis has been increasing. Breast cancer frequently metastasizes to the brain, constituting a major hurdle without cure and with a poor survival. It is imperative to better understand the mechanisms involved in malignant cell transposition of the brain microvasculature and parenchymal colonization by deciphering the alterations occurring in the tumor and microvascular cells, as well as the occurrence of intercellular communication during the process. We aimed to profile the process of the formation of breast cancer brain metastasis and the timeline of events governing it. We used a specific mouse model of the disease to perform extensive microscopic analyses. We identified phenotypic changes and the activation of relevant molecular players in tumorigenesis, together with vascular alterations, and the occurrence of crosstalk. Our findings unravel putative therapeutic targets to tackle breast cancer brain metastasis.

Abstract

With breast cancer (BC) therapy improvements, the appearance of brain metastases has been increasing, representing a life-threatening condition. Brain metastasis formation involves BC cell (BCC) extravasation across the blood–brain barrier (BBB) and brain colonization by unclear mechanisms. We aimed to disclose the actors involved in BC brain metastasis formation, focusing on BCCs’ phenotype, growth factor expression, and signaling pathway activation, correlating with BBB alterations and intercellular communication. Hippocampi of female mice inoculated with 4T1 BCCs were examined over time by hematoxylin-eosin, immunohistochemistry and immunofluorescence. Well-established metastases were observed at seven days, increasing thereafter. BCCs entering brain parenchyma presented mesenchymal, migratory, and proliferative features; however, with time, they increasingly expressed epithelial markers, reflecting a mesenchymal–epithelial transition. BCCs also expressed platelet-derived growth factor-B, β₄ integrin, and focal adhesion kinase, suggesting autocrine and/or paracrine regulation with adhesion signaling activation, while balance between Rac1 and RhoA was associated with the motility status. Intercellular communication via gap junctions was clear among BCCs, and between BCCs and endothelial cells. Thrombin accumulation, junctional protein impairment, and vesicular proteins increase reflect BBB alterations related with extravasation. Expression of plasmalemma vesicle-associated protein was increased in BCCs, along with augmented vascularization, whereas pericyte contraction indicated mural cells’ activation. Our results provide further understanding of BC brain metastasis formation, disclosing potential therapeutic targets.

Heart failure impairs the mechanotransduction properties of human cardiac pericytes

The prominent impact that coronary microcirculation disease (CMD) exerts on heart failure symptoms and prognosis, even in the presence of macrovascular atherosclerosis, has been recently acknowledged. Experimental delivery of pericytes in non-revascularized myocardial infarction improves cardiac function by stimulating angiogenesis and myocardial perfusion. Aim of this work is to verify if pericytes (Pc) residing in ischemic failing human hearts display altered mechano-transduction properties and to assess which alterations of the mechano-sensing machinery are associated with the observed impaired response to mechanical cues. RESULTS: Microvascular rarefaction and defects of YAP/TAZ activation characterize failing human hearts. Although both donor (D-) and explanted (E-) heart derived cardiac Pc support angiogenesis, D-Pc exert this effect significantly better than E-Pc. The latter are characterized by reduced focal adhesion density, decreased activation of the focal adhesion kinase (FAK)/ Crk-associated substrate (CAS) pathway, low expression of caveolin-1, and defective transduction of extracellular stiffness into cytoskeletal stiffening, together with an impaired response to both fibronectin and lysophosphatidic acid. Importantly, Mitogen-activated protein kinase kinase inhibition restores YAP/TAZ nuclear translocation. CONCLUSION: Heart failure impairs Pc mechano-transduction properties, but this defect could be reversed pharmacologically.

The hallmarks of ovarian cancer: Focus on angiogenesis and micro-environment and new models for their characterisation

Cancers develop by sustained growth, migration and invasion properties of tumour cells, supported by complex interactions with stromal cells within the tumour micro-environment. This review is focused on the latest discoveries regarding the highlighted role of angiogenesis and tumour micro-environment in ovarian cancer. This cancer milieu encompasses non-cancerous cells present in the tumour or nearby, including vessel-forming cells, fibroblasts and immune cells amongst others that work in a cooperative way with cancer cells, impacting tumour behaviour. Angiogenesis, migration and invasion, and more recently immune evasion, are cancer hallmarks clearly dependent on these supporting cells. Moreover, these stromal cells are more genetically stable than tumour cells and thus represent an attractive therapeutic target. A better understanding of the stromal cells function, and their complex interplay with cancer cells, will open additional areas to target, as the tumour-host interface.

CD73+ extracellular vesicles inhibit angiogenesis through adenosine A2B receptor signalling

Pathological angiogenesis is a hallmark of several conditions including eye diseases, inflammatory diseases, and cancer. Stromal cells play a crucial role in regulating angiogenesis through the release of soluble factors or direct contact with endothelial cells. Here, we analysed the properties of the extracellular vesicles (EVs) released by bone marrow mesenchymal stromal cells (MSCs) and explored the possibility of using them to therapeutically target angiogenesis. We demonstrated that in response to pro-inflammatory cytokines, MSCs produce EVs that are enriched in TIMP-1, CD39 and CD73 and inhibit angiogenesis targeting both extracellular matrix remodelling and endothelial cell migration. We identified a novel anti-angiogenic mechanism based on adenosine production, triggering of A2B adenosine receptors, and induction of NOX2-dependent oxidative stress within endothelial cells. Finally, in pilot experiments, we exploited the anti-angiogenic EVs to inhibit tumour progression in vivo. Our results identify novel pathways involved in the crosstalk between endothelial and stromal cell and suggest new therapeutic strategies to target pathological angiogenesis.

Brain Microvascular Pericytes in Vascular Cognitive Impairment and Dementia

Pericytes are unique, multi-functional mural cells localized at the abluminal side of the perivascular space in microvessels. Originally discovered in 19th century, pericytes had drawn less attention until decades ago mainly due to lack of specific markers. Recently, however, a growing body of evidence has revealed that pericytes play various important roles: development and maintenance of blood–brain barrier (BBB), regulation of the neurovascular system (e.g., vascular stability, vessel formation, cerebral blood flow, etc.), trafficking of inflammatory cells, clearance of toxic waste products from the brain, and acquisition of stem cell-like properties. In the neurovascular unit, pericytes perform these functions through coordinated crosstalk with neighboring cells including endothelial, glial, and neuronal cells. Dysfunction of pericytes contribute to a wide variety of diseases that lead to cognitive impairments such as cerebral small vessel disease (SVD), acute stroke, Alzheimer’s disease (AD), and other neurological disorders. For instance, in SVDs, pericyte degeneration leads to microvessel instability and demyelination while in stroke, pericyte constriction after ischemia causes a no-reflow phenomenon in brain capillaries. In AD, which shares some common risk factors with vascular dementia, reduction in pericyte coverage and subsequent microvascular impairments are observed in association with white matter attenuation and contribute to impaired cognition. Pericyte loss causes BBB-breakdown, which stagnates amyloid β clearance and the leakage of neurotoxic molecules into the brain parenchyma. In this review, we first summarize the characteristics of brain microvessel pericytes, and their roles in the central nervous system. Then, we focus on how dysfunctional pericytes contribute to the pathogenesis of vascular cognitive impairment including cerebral ‘small vessel’ and ‘large vessel’ diseases, as well as AD. Finally, we discuss therapeutic implications for these disorders by targeting pericytes.

Postnatal development of cerebrovascular structure and the neurogliovascular unit

The unceasing metabolic demands of brain function are supported by an intricate three-dimensional network of arterioles, capillaries, and venules, designed to effectively distribute blood to all neurons and to provide shelter from harmful molecules in the blood. The development and maturation of this microvasculature involves a complex interplay between endothelial cells with nearly all other brain cell types (pericytes, astrocytes, microglia, and neurons), orchestrated throughout embryogenesis and the first few weeks after birth in mice. Both the expansion and regression of vascular networks occur during the postnatal period of cerebrovascular remodeling. Pial vascular networks on the brain surface are dense at birth and are then selectively pruned during the postnatal period, with the most dramatic changes occurring in the pial venular network. This is contrasted to an expansion of subsurface capillary networks through the induction of angiogenesis. Concurrent with changes in vascular structure, the integration and cross talk of neurovascular cells lead to establishment of blood-brain barrier integrity and neurovascular coupling to ensure precise control of macromolecular passage and metabolic supply. While we still possess a limited understanding of the rules that control cerebrovascular development, we can begin to assemble a view of how this complex process evolves, as well as identify gaps in knowledge for the next steps of research. This article is categorized under: Nervous System Development > Vertebrates: Regional Development Vertebrate Organogenesis > Musculoskeletal and Vascular Nervous System Development > Vertebrates: General Principles.

Glioblastoma Stem Cells: Driving Resilience through Chaos

Glioblastoma is an aggressive and heterogeneous tumor in which glioblastoma stem cells (GSCs) are at the apex of an entropic hierarchy and impart devastating therapy resistance. The high entropy of GSCs is driven by a permissive epigenetic landscape and a mutational landscape that revokes crucial cellular checkpoints. The GSC population encompasses a complex array of diverse microstates that are defined and maintained by a wide variety of attractors including the complex tumor ecosystem and therapeutic intervention. Constant dynamic transcriptional fluctuations result in a highly adaptable and heterogeneous entity primed for therapy evasion and survival. Analyzing the transcriptional, epigenetic, and metabolic landscapes of GSC dynamics in the context of a stochastically fluctuating tumor network will provide novel strategies to target resistant populations of GSCs in glioblastoma.

Microphysiological systems for recapitulating physiology and function of blood-brain barrier

Central nervous system (CNS) diseases are emerging as a major issue in an aging society. Although extensive research has focused on the development of CNS drugs, the limited transport of therapeutic agents across the blood-brain barrier (BBB) remains a major challenge. Conventional two-dimensional culture dishes do not recapitulate in vivo physiology and real-time observations of molecular transport are not possible in animal models. Recent advances in engineering techniques have enabled the generation of more physiologically relevant in vitro BBB models, and their applications have expanded from fundamental biological research to practical applications in the pharmaceutical industry. In this article, we provide an overview of recent advances in the development of in vitro BBB models, with a particular focus on the recapitulation of BBB function. The development of biomimetic BBB models is postulated to revolutionize not only fundamental biological studies but also drug screening.

The role of pericytes in brain disorders: from the periphery to the brain

It is becoming increasingly apparent that disorders of the brain microvasculature contribute to many neurological disorders. In recent years it has become clear that a major player in these events is the capillary pericyte which, in the brain, is now known to control the blood-brain barrier, regulate blood flow, influence immune cell entry and be crucial for angiogenesis. In this review we consider the under-explored possibility that peripheral diseases which affect the microvasculature, such as hypertension, kidney disease and diabetes, produce central nervous system (CNS) dysfunction by mechanisms affecting capillary pericytes within the CNS. We highlight how cellular messengers produced peripherally can act via signalling pathways within CNS pericytes to reshape blood vessels, restrict blood flow or compromise blood-brain barrier function, thus causing neuronal dysfunction. Increased understanding of how renin-angiotensin, Rho-kinase and PDGFRβ signalling affect CNS pericytes may suggest novel therapeutic approaches to reducing the CNS effects of peripheral disorders.

Angiogenic Endothelial Cell Signaling in Cardiac Hypertrophy and Heart Failure

Endothelial cells are, by number, one of the most abundant cell types in the heart and active players in cardiac physiology and pathology. Coronary angiogenesis plays a vital role in maintaining cardiac vascularization and perfusion during physiological and pathological hypertrophy. On the other hand, a reduction in cardiac capillary density with subsequent tissue hypoxia, cell death and interstitial fibrosis contributes to the development of contractile dysfunction and heart failure, as suggested by clinical as well as experimental evidence. Although the molecular causes underlying the inadequate (with respect to the increased oxygen and energy demands of the hypertrophied cardiomyocyte) cardiac vascularization developing during pathological hypertrophy are incompletely understood. Research efforts over the past years have discovered interesting mediators and potential candidates involved in this process. In this review article, we will focus on the vascular changes occurring during cardiac hypertrophy and the transition toward heart failure both in human disease and preclinical models. We will summarize recent findings in transgenic mice and experimental models of cardiac hypertrophy on factors expressed and released from cardiomyocytes, pericytes and inflammatory cells involved in the paracrine (dys)regulation of cardiac angiogenesis. Moreover, we will discuss major signaling events of critical angiogenic ligands in endothelial cells and their possible disturbance by hypoxia or oxidative stress. In this regard, we will particularly highlight findings on negative regulators of angiogenesis, including protein tyrosine phosphatase-1B and tumor suppressor p53, and how they link signaling involved in cell growth and metabolic control to cardiac angiogenesis. Besides endothelial cell death, phenotypic conversion and acquisition of myofibroblast-like characteristics may also contribute to the development of cardiac fibrosis, the structural correlate of cardiac dysfunction. Factors secreted by (dysfunctional) endothelial cells and their effects on cardiomyocytes including hypertrophy, contractility and fibrosis, close the vicious circle of reciprocal cell-cell interactions within the heart during pathological hypertrophy remodeling.

Rho-Associated Coiled-Coil Kinase (ROCK) in Molecular Regulation of Angiogenesis

Identified as a major downstream effector of the small GTPase RhoA, Rho-associated coiled-coil kinase (ROCK) is a versatile regulator of multiple cellular processes. Angiogenesis, the process of generating new capillaries from the pre-existing ones, is required for the development of various diseases such as cancer, diabetes and rheumatoid arthritis. Recently, ROCK has attracted attention for its crucial role in angiogenesis, making it a promising target for new therapeutic approaches. In this review, we summarize recent advances in understanding the role of ROCK signaling in regulating the permeability, migration, proliferation and tubulogenesis of endothelial cells (ECs), as well as its functions in non-ECs which constitute the pro-angiogenic microenvironment. The therapeutic potential of ROCK inhibitors in angiogenesis-related diseases is also discussed.

Agent-based computational model of retinal angiogenesis simulates microvascular network morphology as a function of pericyte coverage

OBJECTIVE

Define a role for perivascular cells during developmental retinal angiogenesis in the context of EC Notch1-DLL4 signaling at the multicellular network level.

METHODS

The retinal vasculature is highly sensitive to growth factor-mediated intercellular signaling. Although EC signaling has been explored in detail, it remains unclear how PC function to modulate these signals that lead to a diverse set of vascular network patterns in health and disease. We have developed an ABM of retinal angiogenesis that incorporates both ECs and PCs to investigate the formation of vascular network patterns as a function of pericyte coverage. We use our model to test the hypothesis that PC modulate Notch1-DLL4 signaling in endothelial cell-endothelial cell interactions.

RESULTS

Agent-based model (ABM) simulations that include PCs more accurately predict experimentally observed vascular network morphologies than simulations that lack PCs, suggesting that PCs may influence sprouting behaviors through physical blockade of endothelial intercellular connections.

CONCLUSIONS

This study supports a role for PCs as a physical buffer to signal propagation during vascular network formation-a barrier that may be important for generating healthy microvascular network patterns.

Where's the Leak in Vascular Barriers? A Review

Edema is typically presented as a secondary effect from injury, illness, disease, or medication, and its impact on patient wellness is nested within the underlying etiology. Therefore, it is often thought of more as an amplifier to current preexisting conditions. Edema, however, can be an independent risk factor for patient deterioration. Improper management of edema is costly not only to the patient, but also to treatment and care facilities, as mismanagement of edema results in increased lengths of hospital stay. Direct tissue trauma, disease, or inappropriate resuscitation and/or ventilation strategies result in edema formation through physical disruption and chemical messenger-based structural modifications of the microvascular barrier. Derangements in microvascular barrier function limit tissue oxygenation, nutrient flow, and cellular waste removal. Recent studies have sought to elucidate cellular signaling and structural alterations that result in vascular hyperpermeability in a variety of critical care conditions to include hemorrhage, burn trauma, and sepsis. These studies and many others have highlighted how multiple mechanisms alter paracellular and/or transcellular pathways promoting hyperpermeability. Roles for endothelial glycocalyx, extracellular matrix and basement membrane, vesiculo-vacuolar organelles, cellular junction and cytoskeletal proteins, and vascular pericytes have been described, demonstrating the complexity of microvascular barrier regulation. Understanding these basic mechanisms inside and out of microvessels aid in developing better treatment strategies to mitigate the harmful effects of excessive edema formation.

Pericytes regulate VEGF-induced endothelial sprouting through VEGFR1

Pericytes adhere to the abluminal surface of endothelial tubules and are required for the formation of stable vascular networks. Defective endothelial cell-pericyte interactions are frequently observed in diseases characterized by compromised vascular integrity such as diabetic retinopathy. Many functional properties of pericytes and their exact role in the regulation of angiogenic blood vessel growth remain elusive. Here we show that pericytes promote endothelial sprouting in the postnatal retinal vasculature. Using genetic and pharmacological approaches, we show that the expression of vascular endothelial growth factor receptor 1 (VEGFR1) by pericytes spatially restricts VEGF signalling. Angiogenic defects caused by pericyte depletion are phenocopied by intraocular injection of VEGF-A or pericyte-specific inactivation of the murine gene encoding VEGFR1. Our findings establish that pericytes promote endothelial sprouting, which results in the loss of side branches and the enlargement of vessels when pericyte function is impaired or lost.

Pericytes and cardiac stem cells: Common features and peculiarities

Clinical data and basic research indicate that the structural and functional alterations that characterize the evolution of cardiac disease towards heart failure may be, at least in part, reversed. This paradigm shift is due to the accumulation of evidence indicating that, in peculiar settings, cardiomyocytes may be replenished. Moving from the consideration that cardiomyocytes are rapidly withdrawn from the cell cycle after birth, independent laboratories have tested the hypothesis that cardiac resident stem/progenitor cells resided in mammalian hearts and were important for myocardial repair. After almost two decades of intensive investigation, several (but partially overlapping) cardiac resident stem/progenitor cell populations have been identified. These primitive cells are characterized by mesenchymal features, unique properties that distinguish them from mesodermal progenitors residing in other tissues, and heterogeneous embryological origins (that include the neural crest and the epicardium). A further layer of complexity is related to the nature, in vivo localization and properties of mesodermal progenitors residing in adult tissues. Intriguingly, these latter, whose possible perivascular pericyte/mural cell origin has been shown, have been identified in human hearts too. However, their exact anatomical localization, pathophysiological role, and their relationship with cardiac stem/progenitor cells are emerging only recently. Therefore, aim of this review is to discuss the different origin, the distinct nature, and the complementary effect of cardiac stem cells and pericytes supporting regenerative strategies based on the combined use of both myogenic and angiogenic factors.

Inhibiting the Migration of M1 Microglia at Hyperacute Period Could Improve Outcome of tMCAO Rats

AIM

To study whether inhibiting microglia migration to the ischemic boundary zone (IBZ) at the early phase could improve neurological outcomes after stroke.

METHODS

The transient middle cerebral artery occlusion (tMCAO) was induced in adult male Sprague-Dawley rats. AMD3100, a highly selective CXC-chemokine receptor 4 (CXCR4) antagonist, was used to inhibit microglia migration. Microglia was evaluated by immunofluorescence in vivo, and their migration was tested by transwell assay in vitro. Expressions of cytokines were detected by real-time PCR. Infarct volume was determined by triphenyltetrazolium chloride (TTC) staining. Functional recovery of tMCAO rats was evaluated by behavior tests.

RESULTS

M1 microglia in the IBZ was rapidly increased within 3 days after tMCAO, accompanied with enhanced expression of CXCR4. Chemokine CXC motif chemokine ligand 12 (CXCL12) was also increased in the IBZ. And AMD3100 could obviously decline M1 microglia migration induced by CXCL12 and secretion of related inflammatory cytokines in the IBZ after stroke. This was accompanied by significant attenuated infarct volume and improved neurological outcomes.

CONCLUSION

This study confirms the protective efficacy of inhibiting microglia migration at the hyperacute phase as a therapeutic strategy for ischemic stroke in tMCAO model of rats, and its therapeutic time window could last for 24 h after cerebral ischemia reperfusion.

Static mechanical strain induces capillary endothelial cell cycle re-entry and sprouting

Vascular endothelial cells are known to respond to a range of biochemical and time-varying mechanical cues that can promote blood vessel sprouting termed angiogenesis. It is less understood how these cells respond to sustained (i.e., static) mechanical cues such as the deformation generated by other contractile vascular cells, cues which can change with age and disease state. Here we demonstrate that static tensile strain of 10%, consistent with that exerted by contractile microvascular pericytes, can directly and rapidly induce cell cycle re-entry in growth-arrested microvascular endothelial cell monolayers. S-phase entry in response to this strain correlates with absence of nuclear p27, a cyclin-dependent kinase inhibitor. Furthermore, this modest strain promotes sprouting of endothelial cells, suggesting a novel mechanical 'angiogenic switch'. These findings suggest that static tensile strain can directly stimulate pathological angiogenesis, implying that pericyte absence or death is not necessarily required of endothelial cell re-activation.

Glioma Stem Cells and Their Microenvironments: Providers of Challenging Therapeutic Targets

Malignant gliomas are aggressive brain tumors with limited therapeutic options, possibly because of highly tumorigenic subpopulations of glioma stem cells. These cells require specific microenvironments to maintain their “stemness,” described as perivascular and hypoxic niches. Each of those niches induces particular signatures in glioma stem cells (e.g., activation of Notch signaling, secretion of VEGF, bFGF, SDF1 for the vascular niche, activation of HIF2α, and metabolic reprogramming for hypoxic niche). Recently, accumulated knowledge on tumor-associated macrophages, possibly delineating a third niche, has underlined the role of immune cells in glioma progression, via specific chemoattractant factors and cytokines, such as macrophage-colony stimulation factor (M-CSF). The local or myeloid origin of this new component of glioma stem cells niche is yet to be determined. Such niches are being increasingly recognized as key regulators involved in multiple stages of disease progression, therapy resistance, immune-escaping, and distant metastasis, thereby substantially impacting the future development of frontline interventions in clinical oncology. This review focuses on the microenvironment impact on the glioma stem cell biology, emphasizing GSCs cross talk with hypoxic, perivascular, and immune niches and their potential use as targeted therapy.

Pericyte chemomechanics and the angiogenic switch: insights into the pathogenesis of proliferative diabetic retinopathy?

PURPOSE

To establish the regulatory roles that pericytes have in coordinating retinal endothelial cell (EC) growth and angiogenic potential.

METHODS

Pericytes were derived from donor diabetic (DHuRP) or normal (NHuRP) human retinae, and characterized using vascular markers, coculture, contraction, morphogenesis, and proliferation assays. To investigate capillary "cross-talk," pericyte-endothelial coculture growth, and connexin-43 (Cx43) expression assays were performed. Paracrine effects were examined via treating EC with pericyte-derived conditioned media (CM) in proliferation, angiogenesis, and angiocrine assays. The effects of sphingosine 1-phosphate (S1P) were assessed using receptor antagonists.

RESULTS

The DHuRP exhibit unique proliferative and morphologic properties, reflecting distinctive cytoskeletal and isoactin expression patterns. Unlike NHuRP, DHuRP are unable to sustain EC growth arrest in coculture and display reduced Cx43 expression. Further, CM from DHuRP (DPCM) markedly stimulates EC proliferation and tube formation. Treatment with S1P receptor antagonists mitigates DPCM growth-promotion in EC and S1P-mediated pericyte contraction. Angiocrine assays on normal and diabetic pericyte secretomes reveal factors involved in angiogenic control, inflammation, and metabolism.

CONCLUSIONS

Effects from the diabetic microenvironment appear sustainable in cell culture: pericytes derived from diabetic donor eyes seemingly possess a "metabolic memory" in vitro, which may be linked to original donor health status. Diabetes- and pericyte-dependent effects on EC growth and angiogenesis may reflect alterations in bioactive lipid, angiocrine, and chemomechanical signaling. Altogether, our results suggest that diabetes alters pericyte contractile phenotype and cytoskeletal signaling, which ultimately may serve as a key, initiating event required for retinal endothelial reproliferation, angiogenic activation, and the pathological neovascularization accompanying proliferative diabetic retinopathy.

Combined effects of pericytes in the tumor microenvironment

Pericytes are multipotent perivascular cells whose involvement in vasculature development is well established. Evidences in the literature also suggest that pericytes display immune properties and that these cells may serve as an in vivo reservoir of stem cells, contributing to the regeneration of diverse tissues. Pericytes are also capable of tumor homing and are important cellular components of the tumor microenvironment (TME). In this review, we highlight the contribution of pericytes to some classical hallmarks of cancer, namely, tumor angiogenesis, growth, metastasis, and evasion of immune destruction, and discuss how collectively these hallmarks could be tackled by therapies targeting pericytes, providing a rationale for cancer drugs aiming at the TME.