Isolated Anxa5+/Sca-1+ perivascular cells from mouse meningeal vasculature retain their perivascular phenotype in vitro and in vivo

Recovery of Therapeutically Ablated Engineered Blood-Vessel Networks on a Plug-and-Play Platform

Limiting the availability of key angiogenesis-promoting factors is a successful strategy to ablate tumor-supplying blood vessels or to reduce excessive vasculature in diabetic retinopathy. However, the efficacy of such anti-angiogenic therapies (AATs) varies with tumor type, and regrowth of vessels is observed upon termination of treatment. The ability to understand and develop AATs remains limited by a lack of robust in vitro systems for modeling the recovery of vascular networks. Here, complex 3D micro-capillary networks are engineered by sequentially seeding human bone marrow-derived mesenchymal stromal cells and human umbilical vein endothelial cells (ECs) on a previously established, synthetic plug-and-play hydrogel platform. In the tightly interconnected vascular networks that form this way, the two cell types share a basement membrane-like layer and can be maintained for several days of co-culture. Pre-formed networks degrade in the presence of bevacizumab. Upon treatment termination, vessel structures grow back to their original positions after replenishment with new ECs, which also integrate into unperturbed established networks. The data suggest that this plug-and-play platform enables the screening of drugs with blood-vessel inhibiting functions. It is believed that this platform could be of particular interest in studying resistance or recovery mechanisms to AAT treatment.

Fungal brain infection modelled in a human-neurovascular-unit-on-a-chip with a functional blood-brain barrier

The neurovascular unit, which consists of vascular cells surrounded by astrocytic end-feet and neurons, controls cerebral blood flow and the permeability of the blood-brain barrier (BBB) to maintain homeostasis in the neuronal milieu. Studying how some pathogens and drugs can penetrate the human BBB and disrupt neuronal homeostasis requires in vitro microphysiological models of the neurovascular unit. Here we show that the neurotropism of Cryptococcus neoformans-the most common pathogen causing fungal meningitis-and its ability to penetrate the BBB can be modelled by the co-culture of human neural stem cells, brain microvascular endothelial cells and brain vascular pericytes in a human-neurovascular-unit-on-a-chip maintained by a stepwise gravity-driven unidirectional flow and recapitulating the structural and functional features of the BBB. We found that the pathogen forms clusters of cells that penetrate the BBB without altering tight junctions, suggesting a transcytosis-mediated mechanism. The neurovascular-unit-on-a-chip may facilitate the study of the mechanisms of brain infection by pathogens, and the development of drugs for a range of brain diseases.

Chorioallantoic Membrane Models of Various Avian Species: Differences and Applications

The chorioallantoic membrane model (CAM) of an avian embryo is used as an experimental model in various fields of research, including angiogenesis research and drug testing, xenografting and cancer research, and other scientific and commercial disciplines in microbiology, biochemistry, cosmetics, etc. It is a low-cost, low-maintenance, and well-available in vivo animal model that is non-sentient and can be used as an alternative for other mammal experimental models. It respects the principles of the "3R" rule (Replacement, Reduction, and Refinement)-conditions set out for scientific community providing an essential framework for conducting a more human animal research, which is also in line with constantly raising public awareness of welfare and the ethics related to the use of animal experimental models. In this review, we describe the chorioallantoic membrane of an avian embryo, focusing on its properties and development, its advantages and disadvantages as an experimental model, and the possibilities of its application in various fields of biological research. Since the most common chicken CAM model is already well known and described in many publications, we are particularly focusing on the advantages and application of less known avian species that are used for the CAM model-quail, turkey, and duck.

Basement membrane and stroke

Located at the interface of the circulation system and the CNS, the basement membrane (BM) is well positioned to regulate blood-brain barrier (BBB) integrity. Given the important roles of BBB in the development and progression of various neurological disorders, the BM has been hypothesized to contribute to the pathogenesis of these diseases. After stroke, a cerebrovascular disease caused by rupture (hemorrhagic) or occlusion (ischemic) of cerebral blood vessels, the BM undergoes constant remodeling to modulate disease progression. Although an association between BM dissolution and stroke is observed, how each individual BM component changes after stroke and how these components contribute to stroke pathogenesis are mostly unclear. In this review, I first briefly introduce the composition of the BM in the brain. Next, the functions of the BM and its major components in BBB maintenance under homeostatic conditions are summarized. Furthermore, the roles of the BM and its major components in the pathogenesis of hemorrhagic and ischemic stroke are discussed. Last, unsolved questions and potential future directions are described. This review aims to provide a comprehensive reference for future studies, stimulate the formation of new ideas, and promote the generation of new genetic tools in the field of BM/stroke research.

The role of non-endothelial cells on the penetration of nanoparticles through the blood brain barrier

The blood brain barrier (BBB) is a well-established cell-based membrane that circumvents the central nervous system (CNS), protecting it from harmful substances. Due to its robustness and cell integrity, it is also an outstanding opponent when it comes to the delivery of several therapeutic agents to the brain, which requires the crossing through its highly-organized structure. This regulation and cell-cell communications occur mostly between astrocytes, pericytes and endothelial cells. Therefore, alternative ways to deliver drugs to the CNS, overcoming the BBB are required, to improve the efficacy of brain target drugs. Nanoparticles emerge here as a promising drug delivery strategy, due to their ability of high drug loading and the capability to exploit specific delivery pathways that most drugs are unable to when administered freely, increasing their bioavailability in the CNS. Thus, further attempts to assess the possible influence of non-endothelial may have on the BBB translocation of nanoparticles are here revised. Furthermore, the use of macrophages and/or monocytes as nanoparticle delivery cells are also approached. Lastly, the temporarily disruption of the overall organization and normal structure of the BBB to promote the penetration of nanoparticles aimed at the CNS is described, as a synergistic path.

Mimicking Angiogenesis in vitro: Three-dimensional Co-culture of Vascular Endothelial Cells and Perivascular Cells in Collagen Type I Gels

Angiogenesis defines the process of formation of new vascular structures form existing blood vessels, involved during development, repair processes like wound healing but also linked to pathological changes. During angiogenic processes, endothelial cells build a vascular network and recruit perivascular cells to form mature, stable vessels. Endothelial cells and perivascular cells secret and assemble a vascular basement membrane and interact via close cell-cell contacts. To mimic these processes in vitro we have developed a versatile three-dimensional culture system where perivascular cells (PVC) are co-cultured with human umbilical cord vascular endothelial cells (HUVEC) in a collagen type I gel. This co-culture system can be used to determine biochemical and cellular processes during neoangiogenic events with a wide range of analyses options.

The role of pericytic laminin in blood brain barrier integrity maintenance

Laminin, a major component of the basement membrane, plays an important role in blood brain barrier regulation. At the neurovascular unit, brain endothelial cells, astrocytes, and pericytes synthesize and deposit different laminin isoforms into the basement membrane. It has been shown that laminin α4 (endothelial laminin) regulates vascular integrity at embryonic/neonatal stage, while astrocytic laminin maintains vascular integrity in adulthood. Here, we investigate the function of pericyte-derived laminin in vascular integrity. Using a conditional knockout mouse line, we report that loss of pericytic laminin leads to hydrocephalus and BBB breakdown in a small percentage (10.7%) of the mutants. Interestingly, BBB disruption always goes hand-in-hand with hydrocephalus in these mutants, and neither symptom is observed in the rest 89.3% of the mutants. Further mechanistic studies show that reduced tight junction proteins, diminished AQP4 expression, and decreased pericyte coverage are responsible for the BBB disruption. Together, these data suggest that pericyte-derived laminin is involved in the maintenance of BBB integrity and regulation of ventricular size/development.

Induction of initial steps of angiogenic differentiation and maturation of endothelial cells by pericytes in vitro and the role of collagen IV

Activation of endothelial cells and recruitment of mural cells define critical steps during the formation of stable vascular elements. Both events are reflected by cocultures of endothelial cells and isolated murine pericyte-like cells and define a versatile platform for the analysis of distinct steps during the angiogenic process in vitro. Isolated pericyte-like cells promote the survival of endothelial cells, induce the assembly of endothelial cells as well as establish direct contacts with forming endothelial alignments. More importantly, they also induce characteristic steps of maturation including the assembly of stable cell-cell junctions, deposition of basement membrane-like matrices and local formation of a central lumen. The presence of pericyte-like cells induces the secretion of extracellular matrices enriched in collagen IV by endothelial cells, which improves endothelial tube formation and provides the adhesive substrate for mural cell recruitment. Collagen-binding integrins contribute differentially to the process, with α1β1 involved in the adhesion of pericyte-like cells to collagen IV and α2β1 mainly involved in endothelial cord formation. These data indicate that pericyte-like cells are essential for the survival of endothelial cells, the efficient formation of endothelial alignments as well as initial steps of maturation of capillary-like structures.

Emerging roles of pericytes in the regulation of the neurovascular unit in health and disease

Pericytes of the central nervous system (CNS) are uniquely positioned within a multicellular structure termed the neurovascular unit (NVU) to provide crucial support to blood brain barrier (BBB) formation, maintenance, and stability. Numerous CNS diseases are associated with some aspect of BBB dysfunction. A dysfunction can manifest as one or multiple disruptions to any of the following barriers: physical, metabolic, immunological and transport barrier. A breach in the BBB can notably result in BBB hyper-permeability, endothelial activation and enhanced immune-endothelial interaction. How the BBB is regulated within this integrated unit remains largely unknown, especially as it relates to pericyte-endothelial interaction. We summarize the latest findings on pericyte origin, possible marker expression, and availability within different organ systems. We highlight pericyte-endothelial cell interactions, concentrating on extra- and intra- cellular signaling mechanisms linked to platelet derived growth factor-B, transforming growth factor -β, angiopoietins, Notch, and gap junctions. We discuss the role of pericytes in the NVU under inflammatory insult, focusing on how pericytes may indirectly affect leukocyte CNS infiltration, the direct role of pericyte-mediated basement membrane modifications, and immune responses. We review new findings of pericyte actions in CNS pathologies including Alzheimer's disease, stroke, multiple sclerosis, diabetic retinopathy, and HIV-1 infection. The uncovering of the regulatory role of pericytes on the BBB will provide key insight into how barrier integrity can be re-established during neuroinflammation.

PECAM1(+)/Sca1(+)/CD38(+) vascular cells transform into myofibroblast-like cells in skin wound repair

Skin injury induces the formation of new blood vessels by activating the vasculature in order to restore tissue homeostasis. Vascular cells may also differentiate into matrix-secreting contractile myofibroblasts to promote wound closure. Here, we characterize a PECAM1⁺/Sca1⁺ vascular cell population in mouse skin, which is highly enriched in wounds at the peak of neoangiogenesis and myofibroblast formation. These cells express endothelial and perivascular markers and present the receptor CD38 on their surface. PECAM1⁺/Sca1⁺/CD38⁺ cells proliferate upon wounding and could give rise to α-SMA⁺ myofibroblast-like cells. CD38 stimulation in immunodeficient mice reduced the wound size at the peak of neoangiogenesis and myofibroblast formation. In humans a corresponding cell population was identified, which was enriched in sprouting vessels of basal cell carcinoma biopsies. The results indicate that PECAM1⁺/Sca1⁺/CD38⁺ vascular cells could proliferate and differentiate into myofibroblast-like cells in wound repair. Moreover, CD38 signaling modulates PECAM1⁺/Sca1⁺/CD38⁺ cell activation in the healing process implying CD38 as a target for anti-angiogenic therapies in human basal cell carcinoma.

Desminopathies: pathology and mechanisms

The intermediate filament protein desmin is an essential component of the extra-sarcomeric cytoskeleton in muscle cells. This three-dimensional filamentous framework exerts central roles in the structural and functional alignment and anchorage of myofibrils, the positioning of cell organelles and signaling events. Mutations of the human desmin gene on chromosome 2q35 cause autosomal dominant, autosomal recessive, and sporadic myopathies and/or cardiomyopathies with marked phenotypic variability. The disease onset ranges from childhood to late adulthood. The clinical course is progressive and no specific treatment is currently available for this severely disabling disease. The muscle pathology is characterized by desmin-positive protein aggregates and degenerative changes of the myofibrillar apparatus. The molecular pathophysiology of desminopathies is a complex, multilevel issue. In addition to direct effects on the formation and maintenance of the extra-sarcomeric intermediate filament network, mutant desmin affects essential protein interactions, cell signaling cascades, mitochondrial functions, and protein quality control mechanisms. This review summarizes the currently available data on the epidemiology, clinical phenotypes, myopathology, and genetics of desminopathies. In addition, this work provides an overview on the expression, filament formation processes, biomechanical properties, post-translational modifications, interaction partners, subcellular localization, and functions of wild-type and mutant desmin as well as desmin-related cell and animal models.

Laminin isoforms in endothelial and perivascular basement membranes

Laminins, one of the major functional components of basement membranes, are found underlying endothelium, and encasing pericytes and smooth muscle cells in the vessel wall. Depending on the type of blood vessel (capillary, venule, postcapillary venule, vein or artery) and their maturation state, both the endothelial and mural cell phenotype vary, with associated changes in laminin isoform expression. Laminins containing the α4 and α5 chains are the major isoforms found in the vessel wall, with the added contribution of laminin α2 in larger vessels. We here summarize current data on the precise localization of these laminin isoforms and their receptors in the different layers of the vessel wall, and their potential contribution to vascular homeostasis.

Depletion of annexin A5, annexin A6, and collagen X causes no gross changes in matrix vesicle-mediated mineralization, but lack of collagen X affects hematopoiesis and the Th1/Th2 response

Numerous biochemical studies have pointed to an essential role of annexin A5 (AnxA5), annexin A6 (AnxA6), and collagen X in matrix vesicle-mediated biomineralization during endochondral ossification and in osteoarthritis. By binding to the extracellular matrix protein collagen X and matrix vesicles, annexins were proposed to anchor matrix vesicles in the extracellular space of hypertrophic chondrocytes to initiate the calcification of cartilage. However, mineralization appears to be normal in mice lacking AnxA5 and AnxA6, whereas collagen X-deficient mice show only subtle alterations in the growth plate organization. We hypothesized that the simultaneous lack of AnxA5, AnxA6, and collagen X in vivo induces more pronounced changes in the growth plate development and the initiation of mineralization. In this study, we generated and analyzed mice deficient for AnxA5, AnxA6, and collagen X. Surprisingly, mice were viable, fertile, and showed no obvious abnormalities. Assessment of growth plate development indicated that the hypertrophic zone was expanded in Col10a1(-/-) and AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) newborns, whereas endochondral ossification and mineralization were not affected in 13-day- and 1-month-old mutants. In peripheral quantitative computed tomography, no changes in the degree of biomineralization were found in femora of 1-month- and 1-year-old mutants even though the diaphyseal circumference was reduced in Col10a1(-/-) and AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) mice. The percentage of naive immature IgM(+) /IgM(+) B cells and peripheral T-helper cells were increased in Col10a1(-/-) and AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) mutants, and activated splenic T cells isolated from Col10a1(-/-) mice secreted elevated levels of IL-4 and GM-CSF. Hence, collagen X is needed for hematopoiesis during endochondral ossification and for the immune response, but the interaction of annexin A5, annexin A6, and collagen X is not essential for physiological calcification of growth plate cartilage. Therefore, annexins and collagen X may rather fulfill functions in growth plate cartilage not directly linked to the mineralization process.

Extracellular matrix and matrix receptors in blood-brain barrier formation and stroke

The blood-brain barrier (BBB) is formed primarily to protect the brain microenvironment from the influx of plasma components, which may disturb neuronal functions. The BBB is a functional unit that consists mainly of specialized endothelial cells (ECs) lining the cerebral blood vessels, astrocytes, and pericytes. The BBB is a dynamic structure that is altered in neurologic diseases, such as stroke. ECs and astrocytes secrete extracellular matrix (ECM) proteins to generate and maintain the basement membranes (BMs). ECM receptors, such as integrins and dystroglycan, are also expressed at the brain microvasculature and mediate the connections between cellular and matrix components in physiology and disease. ECM proteins and receptors elicit diverse molecular signals that allow cell adaptation to environmental changes and regulate growth and cell motility. The composition of the ECM is altered upon BBB disruption and directly affects the progression of neurologic disease. The purpose of this review is to discuss the dynamic changes of ECM composition and integrin receptor expression that control BBB functions in physiology and pathology.

The possible roles of brain pericytes in brain ischemia and stroke

Brain pericytes regulate a variety of functions, such as microcirculation, angiogenesis, and the blood brain barrier in the brain. Recent studies have also shown that they are pluripotent in a manner similar to mesenchymal stem cells. Since, brain pericytes actively control these functions, these cells probably play an important role not only during brain ischemia, but also in the post-stroke period.

Annexin-A5 assembled into two-dimensional arrays promotes cell membrane repair

Eukaryotic cells possess a universal repair machinery that ensures rapid resealing of plasma membrane disruptions. Before resealing, the torn membrane is submitted to considerable tension, which functions to expand the disruption. Here we show that annexin-A5 (AnxA5), a protein that self-assembles into two-dimensional (2D) arrays on membranes upon Ca²⁺ activation, promotes membrane repair. Compared with wild-type mouse perivascular cells, AnxA5-null cells exhibit a severe membrane repair defect. Membrane repair in AnxA5-null cells is rescued by addition of AnxA5, which binds exclusively to disrupted membrane areas. In contrast, an AnxA5 mutant that lacks the ability of forming 2D arrays is unable to promote membrane repair. We propose that AnxA5 participates in a previously unrecognized step of the membrane repair process: triggered by the local influx of Ca²⁺, AnxA5 proteins bind to torn membrane edges and form a 2D array, which prevents wound expansion and promotes membrane resealing.

Eukaryotic cell plasma membranes possess a mechanism to repair tears caused by stimuli such as mechanical stress. The authors demonstrate that annexin-A5, when assembled into two-dimensional arrays in the presence of calcium, is required for membrane repair.

Brain pericytes: emerging concepts and functional roles in brain homeostasis

Brain pericytes are an important constituent of neurovascular unit. They encircle endothelial cells and contribute to the maturation and stabilization of the capillaries in the brain. Recent studies have revealed that brain pericytes play pivotal roles in a variety of brain functions, such as regulation of capillary flow, angiogenesis, blood brain barrier, immune responses, and hemostasis. In addition, brain pericytes are pluripotent and can differentiate into different lineages similar to mesenchymal stem cells. The brain pericytes are revisited as a key player to maintain brain function and repair brain damage.

Pericyte-derived MFG-E8 regulates pathologic angiogenesis

OBJECTIVE

MFG-E8 (also called lactadherin and SED1) is a secreted glycoprotein that has been previously implicated in enhancement of vascular endothelial growth factor-dependent angiogenesis. Major sources of MFG-E8 in vivo and precise mechanisms of MFG-E8 action remain undetermined. The objective of this study was to identify important sources of MFG-E8 in vivo and further elucidate the role(s) of MFG-E8 in the regulation of angiogenesis.

METHODS AND RESULTS

We used knockout mice and anti-MFG-E8 antibodies to study MFG-E8 function in vivo. In melanomas and in retinas of mice with oxygen-induced retinopathy, MFG-E8 colocalized with pericytes rather than endothelial cells, and platelet-derived growth factor receptor β+ pericytes/pericyte precursors purified from tumors contained large amounts of MFG-E8 mRNA. Tumor- and retinopathy-associated angiogenesis was diminished in MFG-E8 knockout mice, and pericyte coverage of neovessels was reduced. Inhibition of MFG-E8 production by 10T1/2 cells (surrogate pericyte/pericyte precursors) using small interfering RNAs and short hairpin RNAs, or inhibition of MFG-E8 action with some anti-MFG-E8 antibodies, selectively attenuated migration in vitro. Significantly, the anti-MFG-E8 antibodies that inhibited 10T1/2 cell migration in vitro also inhibited pathological angiogenesis in vivo.

CONCLUSIONS

These studies strongly implicate MFG-E8 in pericyte/pericyte precursor function and indicate that MFG-E8-directed therapeutics may merit further development.

Isolation and perivascular localization of mesenchymal stem cells from mouse brain

BACKGROUND

Although originally isolated from the bone marrow, mesenchymal stem cells (MSCs) have recently been detected in other tissues. However, little is known about MSCs in the brain.

OBJECTIVE

To determine the extent to which cells with the features of MSCs exist in normal brain tissue and to determine the location of these cells in the brain.

METHODS

Single-cell suspensions from mouse brains were cultured according to the same methods used for culturing bone marrow-derived MSCs (BM-MSCs). These brain-derived cells were analyzed by fluorescence-activated cell sorting for surface markers associated with BM-MSCs (stem cell antigen 1 [Sca-1+], CD9+, CD45-, CD11b-, and CD31-). Brain-derived cells were exposed to mesenchymal differentiation conditions. To determine the locations of these cells within the brain, sections of normal brains were analyzed by immunostaining for Sca-1, CD31, and nerve/glial antigen 2.

RESULTS

Cells morphologically similar to mouse BM-MSCs were identified and called brain-derived MSCs (Br-MSCs). Fluorescence-activated cell sorting indicated that the isolated cells had a surface marker profile similar to BM-MSCs, ie, Sca-1V+, CD9+, CD45-, and CD11b-. Like BM-MSCs, Br-MSCs were capable of differentiation into adipocytes, osteocytes, and chondrocytes. Immunostaining indicated that Sca-1+ Br-MSCs are located around blood vessels and may represent progenitor cells that serve as a source of mesenchymal elements (eg, pericytes) within the brain.

CONCLUSION

Our results indicate that cells similar to BM-MSCs exist in the brain. These Br-MSCs appear to be located within the vascular niche and may provide the mesenchymal elements of this niche. Because MSCs may be part of the cellular response to tissue injury, Br-MSCs may represent targets in the therapy of pathological processes such as stroke, trauma, and tumorigenesis.

Glioblastoma-dependent differentiation and angiogenic potential of human mesenchymal stem cells in vitro

Tumor angiogenesis is of central importance in the malignancy of glioblastoma multiforme (GBM). As previously shown, human mesenchymal stem cells (hMSC) migrate towards GBM and are incorporated into tumor microvessels. However, phenotype and function of recruited hMSC remain unclear. We evaluated the differentiation and angiogenic potential of hMSC after stimulation with glioblastoma-conditioned medium in vitro. Immunostaining with endothelial, smooth muscle cell and pericyte markers was used to analyze hMSC differentiation in different concentrations of tumor-conditioned medium (CM), and the angiogenic potential was evaluated by matrigel-based tube-formation assay (TFA). Immunofluorescence staining revealed that tumor-conditioned hMSC (CM-hMSC) expressed CD 151, VE-cadherin, desmin, α-smooth muscle actin, nestin, and nerval/glial antigen 2 (NG2) in a CM concentration-dependent manner, whereas no expression of von-Willebrand factor (vWF) and smooth myosin could be detected. These findings are indicative of GBM-dependent differentiation of hMSC into pericyte-like cells, rather than endothelial or smooth muscle cells. Furthermore, TFA of hMSC and CM-hMSC revealed CM-dependent formation of capillary-like networks, which differed substantially from those formed by human endothelial cells (HUVEC), also implying pericyte-like tube formation. These results are indicative of GBM-derived differentiation of hMSC into pericyte-like mural cells, which might contribute to the neovascularization and stabilization of tumor vessels.

Reversible transdifferentiation of blood vascular endothelial cells to a lymphatic-like phenotype in vitro

Blood vascular cells and lymphatic endothelial cells (BECs and LECs, respectively) form two separate vascular systems and are functionally distinct cell types or lineages with characteristic gene expression profiles. Interconversion between these cell types has not been reported. Here, we show that in conventional in vitro angiogenesis assays, human BECs of fetal or adult origin show altered gene expression that is indicative of transition to a lymphatic-like phenotype. This change occurs in BECs undergoing tubulogenesis in fibrin, collagen or Matrigel assays, but is independent of tube formation per se, because it is not inhibited by a metalloproteinase inhibitor that blocks tubulogenesis. It is also reversible, since cells removed from 3D tubules revert to a BEC expression profile upon monolayer culture. Induction of the lymphatic-like phenotype is partially inhibited by co-culture of HUVECs with perivascular cells. These data reveal an unexpected plasticity in endothelial phenotype, which is regulated by contact with the ECM environment and/or cues from supporting cells.

Sorting of growth plate chondrocytes allows the isolation and characterization of cells of a defined differentiation status

Axial growth of long bones occurs through a coordinated process of growth plate chondrocyte proliferation and differentiation. This maturation of chondrocytes is reflected in a zonal change in gene expression and cell morphology from resting to proliferative, prehypertrophic, and hypertrophic chondrocytes of the growth plate followed by ossification. A major experimental limitation in understanding growth plate biology and pathophysiology is the lack of a robust technique to isolate cells from the different zones, particularly from small animals. Here, we report on a new strategy for separating distinct chondrocyte populations from mouse growth plates. By transcriptome profiling of microdissected zones of growth plates, we identified novel, zone-specific cell surface markers and used these for flow cytometry and immunomagnetic cell separation to quantify, enrich, and characterize chondrocytes populations with respect to their differentiation status. This approach provides a novel platform to study cartilage development and characterize mouse growth plate chondrocytes to reveal unique cellular phenotypes of the distinct subpopulations within the growth plate.

Deficiency of annexins A5 and A6 induces complex changes in the transcriptome of growth plate cartilage but does not inhibit the induction of mineralization

Initiation of mineralization during endochondral ossification is a multistep process and has been assumed to correlate with specific interactions of annexins A5 and A6 and collagens. However, skeletal development appears to be normal in mice deficient for either A5 or A6, and the highly conserved structures led to the assumption that A5 and A6 may fulfill redundant functions. We have now generated mice deficient of both proteins. These mice were viable and fertile and showed no obvious abnormalities. Assessment of skeletal elements using histologic, ultrastructural, and peripheral quantitative computed tomographic methods revealed that mineralization and development of the skeleton were not significantly affected in mutant mice. Otherwise, global gene expression analysis showed subtle changes at the transcriptome level of genes involved in cell growth and intermediate metabolism. These results indicate that annexins A5 and A6 may not represent the essential annexins that promote mineralization in vivo.

The blood-brain and the blood-cerebrospinal fluid barriers: function and dysfunction

The central nervous system (CNS) is tightly sealed from the changeable milieu of blood by the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier (BCSFB). While the BBB is considered to be localized at the level of the endothelial cells within CNS microvessels, the BCSFB is established by choroid plexus epithelial cells. The BBB inhibits the free paracellular diffusion of water-soluble molecules by an elaborate network of complex tight junctions (TJs) that interconnects the endothelial cells. Combined with the absence of fenestrae and an extremely low pinocytotic activity, which inhibit transcellular passage of molecules across the barrier, these morphological peculiarities establish the physical permeability barrier of the BBB. In addition, a functional BBB is manifested by a number of permanently active transport mechanisms, specifically expressed by brain capillary endothelial cells that ensure the transport of nutrients into the CNS and exclusion of blood-borne molecules that could be detrimental to the milieu required for neural transmission. Finally, while the endothelial cells constitute the physical and metabolic barrier per se, interactions with adjacent cellular and acellular layers are prerequisites for barrier function. The fully differentiated BBB consists of a complex system comprising the highly specialized endothelial cells and their underlying basement membrane in which a large number of pericytes are embedded, perivascular antigen-presenting cells, and an ensheathment of astrocytic endfeet and associated parenchymal basement membrane. Endothelial cell morphology, biochemistry, and function thus make these brain microvascular endothelial cells unique and distinguishable from all other endothelial cells in the body. Similar to the endothelial barrier, the morphological correlate of the BCSFB is found at the level of unique apical tight junctions between the choroid plexus epithelial cells inhibiting paracellular diffusion of water-soluble molecules across this barrier. Besides its barrier function, choroid plexus epithelial cells have a secretory function and produce the CSF. The barrier and secretory function of the choroid plexus epithelial cells are maintained by the expression of numerous transport systems allowing the directed transport of ions and nutrients into the CSF and the removal of toxic agents out of the CSF. In the event of CNS pathology, barrier characteristics of the blood-CNS barriers are altered, leading to edema formation and recruitment of inflammatory cells into the CNS. In this review we will describe current knowledge on the cellular and molecular basis of the functional and dysfunctional blood-CNS barriers with focus on CNS autoimmune inflammation.

Role of the extracellular matrix in lymphocyte migration

The extracellular matrix (ECM) exists in various biochemical and structural forms that can act either as a barrier to migrating leukocytes, in the case of basement membranes, or provide a physical scaffold supporting or guiding migration (interstitial matrix). This review focuses on basement membranes and our current knowledge of the way that leukocytes transmigrate this protein barrier, with emphasis on T lymphocytes. Recent data suggest that the classical concept of cell-matrix adhesion requires revision with respect to leukocyte-ECM interactions. Whereas specific receptors may be required for leukocyte recognition of ECM molecules or three-dimensional structural domains, the role of adhesion in migration as perceived from the traditional studies of adherent cell-ECM interactions is less clear. Further, the indirect effects of ECM such as the binding and presentation of cytokines or chemotactic factors may more profoundly influence the directed migration of normally non-adherent leukocytes than the migration of adherent cells such as epithelial cells or fibroblasts. Proteases (in particular matrix metalloproteinases) released at sites of inflammation can selectively process ECM, cell surface molecules or soluble factors, which may result in the release of bioactive fragments that can function as chemoattractants for different leukocyte subsets or may modulate the activity/function of resident mesenchymal and immune cells. Current findings suggest that different leukocyte types employ different mechanisms to migrate across or through the ECM; this might be determined by the composition and organization of the ECM itself.

The immune reaction against allogeneic necrotic cells is reduced in Annexin A5 knock out mice whose macrophages display an anti-inflammatory phenotype

Proteins of the annexin family bind to phospholipids in a Ca²⁺ dependent manner. The exposure of phosphatidylserine (PS) by apoptotic as well as necrotic cells is one major eat-me-signal for macrophages. Annexin A5 (Anx A5) preferentially binds to PS. The availability of Anx A5 knock out (KO) mice allowed us to investigate for the first time if endogenous Anx A5 modulates the immune response towards allogeneic cells. Furthermore, the effect of Anx A5 gene deletion on the phagocytic process as well as on the inflammatory reaction of macrophages was explored. We found that Anx A5 KO mice have a strongly reduced allogeneic cellular immune reaction against primary as well as secondary necrotic cells. In vivo phagocytosis experiments revealed that macrophages of Anx A5 KO mice displayed an increased uptake of necrotic cells. Additionally, an increased secretion of the anti-inflammatory cytokine IL-10 of isolated macrophages of Anx A5 KO mice after contact with necrotic cells was observed. Furthermore, the promoter activity of the Anx A5 gene was enhanced after stimulation of macrophages. The tumour size of an allogeneic tumour regressed faster when endogenous Anx A5 was present. These data demonstrate that endogenous Anx A5 influences the phagocytosis of necrotic cells, modulates the immune response towards allogeneic cells and acts as an inflammatory protein.