NG2 proteoglycan expression in mouse skin: altered postnatal skin development in the NG2 null mouse

Evidence for the in vivo existence and mobilisation of myeloid angiogenic cells and pericyte-like cells in wound patients after skin grafting

Myeloid angiogenic cells (MACs) and pericyte-like cells, derived from peripheral blood mononuclear cells (MNCs) by in vitro culturing, are suggested as relevant cell types for angiogenesis and tissue repair. However, the in vivo existence and relevance of these cells has so far remained unknown. Our aim was thus to study, if MACs and pericyte-like cells exist in circulation during the wound healing of skin graft patients, and to evaluate the cellular features of wound repair. MNCs were isolated from blood samples of healthy controls (n = 4) and patients with a traumatic full thickness skin defect (n = 4) before skin grafting and on postoperative days 1 and 6. The numbers of circulating CD14⁺ CD45⁺ CD31⁺ CD34^- MACs and CD14⁺ CD45⁺ NG2⁺ pericyte-like cells were assessed by flow cytometry, and gene expression of various pro-angiogenic factors was analysed by qPCR. Wound bed biopsies were taken on postoperative days 6 and 14, and MAC (CD31, CD14 and CD45) and pericyte-related markers (NG2 and PDGFRβ) were histologically studied. MACs and pericyte-like cells were detected in both healthy controls and in patients. Before reconstruction, on average 18% of all circulating MNCs represented MACs and 2% pericyte-like cells in wound patients. Number of MACs significantly increased 1.1-1.7-fold in all patients 1 day after skin grafting (p < 0.01). In addition, histological analysis demonstrated effective vascularization of skin grafts, as well as presence of pericytes, and CD14 and CD45 expressing myeloid cells during wound healing. In conclusion, our data shows, for the first time, the presence and mobilisation of MACs and pericyte-like cells in human circulation.

Ninjurin1 deletion in neuron-glial antigen 2-positive pericytes prevents microvessel maturation and delays wound healing

The formation of mature vasculature through angiogenesis is essential for adequate wound healing, such that blood-borne cells, nutrients, and oxygen can be delivered to the remodeling skin area. Neovessel maturation is highly dependent on the coordinated functions of vascular endothelial cells and perivascular cells, namely pericytes (PCs). However, the underlying mechanism for vascular maturation has not been completely elucidated, and its role in wound healing remains unclear. In this study, we investigated the role of Ninjurin-1 (Ninj1), a new molecule mediating vascular maturation, in wound healing using an inducible PC-specific Ninj1 deletion mouse model. Ninj1 expression increased temporarily in NG2-positive PCs in response to skin injury. When tamoxifen treatment induced a decreased Ninj1 expression in PCs, the neovessels in the regenerating wound margins were structurally and functionally immature, but the total number of microvessels was unaltered. This phenotypic change is associated with a reduction in PC-associated microvessels. Wound healing was significantly delayed in the NG2-specific Ninj1 deletion mouse model. Finally, we showed that Ninj1 is a crucial molecule that mediates vascular maturation in injured skin tissue through the interaction of vascular endothelial cells and PCs, thereby inducing adequate and prompt wound healing.

Distinct Fibroblast Lineages Give Rise to NG2+ Pericyte Populations in Mouse Skin Development and Repair

We have examined the developmental origins of Ng2+ perivascular cell populations that adhere to the basement membrane of blood vessels, and their contribution to wound healing. Neural/glial antigen 2 (Ng2) labeled most perivascular cells (70-80%) in developing and adult mouse back skin, a higher proportion than expressed by other pericyte markers Tbx18, Nestin and Pdgfrβ. In adult mouse back skin Ng2+ perivascular cells could be categorized into 4 populations based on whether they expressed Pdgfrα and Pdgfrβ individually or in combination or were Pdgfr-negative. Lineage tracing demonstrated that although Ng2+ cells in embryonic and neonatal back skin contributed to multiple cell types they did not give rise to interfollicular fibroblasts within the dermis. Lineage tracing of distinct fibroblast populations during skin development showed that papillary fibroblasts (Lrig1+) gave rise to Ng2+ perivascular cells in the upper dermis, whilst Ng2+ perivascular cells in the lower dermis were primarily derived from reticular Dlk1+ fibroblasts. Following wounding of adult skin, Ng2+ dermal cells only give rise to Ng2+ blood vessel associated cells and did not contribute to other fibroblast lineages. The relative abundance of Ng2+ Pdgfrβ+ perivascular populations was comparable in wounded and non-wounded skin, indicating that perivascular heterogeneity was maintained during full thickness skin repair. In the wound bed Ng2+ perivascular populations were primarily derived from Lrig1+ papillary or Dlk1+ reticular fibroblast lineages, according to the location of the regenerating blood vessels. We conclude that Ng2+ perivascular cells represent a heterogeneous lineage restricted population that is primarily recruited from the papillary or reticular fibroblast lineages during tissue regeneration.

Age-related changes in NG2-expressing telocytes of rat stomach

NG2 immunoreactive cells (NG2 cells) are found in the brain and peripheral tissues including the skin, intestinal tracts, and bladder. In a previous study, we observed the presence of NG2 cells in the stomach using bioluminescence imaging techniques in NG2-firefly luciferase (fLuc) transgenic (Tg) rats. Here, we aimed to identify and characterize NG2 cells in the adult rat stomach. Immunohistochemical studies showed that NG2 cells were mainly present in the lamina propria and most of the cells were gastric telocytes, co-expressing CD34, and platelet-derived growth factor receptor alpha (PDGFRα), with a small oval-shaped cell body and extremely long and thin cellular prolongations. In the rat stomach, NG2-expressing telocytes comprised two subpopulations: NG2+/CD34+/PDGFRα+ and NG2+/CD34+/PDGFRα-. Furthermore, we showed that the expression of NG2 gene in the aged rat stomach decreased relative to that of the young rat stomach and the decline of NG2 expression in aged rats was mainly observed in NG2+/CD34+/PDGFRα+ telocytes. These findings suggested age-related alterations in NG2+/CD34+/PDGFRα+ telocytes of rat stomach.

Photobiomodulation drives pericyte mobilization towards skin regeneration

Photobiomodulation is being widely applied for improving dermal or mucosal wound healing. However, the underlying cellular and molecular processes that directly contribute to its effects remain poorly understood. Pericytes are relevant cells involved in the wound microenvironment and could be one of the main targets of photobiomodulation due to their plasticity and perivascular localization. Herein, we investigate tissue repair under the photobiomodulation stimulus using a pericyte labeled (or reporter) transgenic mice. Using a model of two contralateral back wounds, one the control and the other photoactivated daily (660 nm, 20 mW, 0.71 W/cm2, 5 J/cm2, 7 s, 0.14 J), we showed an overall influx of immune and undifferentiated cells and higher mobilization of a potent pericyte subpopulation (Type-2 pericytes) in the photoactivated wounds in comparison to the controls. Doppler analysis showed a significant increase in the blood flow in the photoactivated wounds, while marked vascular supply was observed histologically. Histochemical analysis has indicated more advanced stages of tissue repair after photoactivation. These data suggest that photobiomodulation significantly accelerates tissue repair through its vascular effects with direct recruitment of pericytes to the injury site.

Biodiversity of CS–proteoglycan sulphation motifs: chemical messenger recognition modules with roles in information transfer, control of cellular behaviour and tissue morphogenesis

Chondroitin sulphate (CS) glycosaminoglycan chains on cell and extracellular matrix proteoglycans (PGs) can no longer be regarded as merely hydrodynamic space fillers. Overwhelming evidence over recent years indicates that sulphation motif sequences within the CS chain structure are a source of significant biological information to cells and their surrounding environment. CS sulphation motifs have been shown to interact with a wide variety of bioactive molecules, e.g. cytokines, growth factors, chemokines, morphogenetic proteins, enzymes and enzyme inhibitors, as well as structural components within the extracellular milieu. They are therefore capable of modulating a panoply of signalling pathways, thus controlling diverse cellular behaviours including proliferation, differentiation, migration and matrix synthesis. Consequently, through these motifs, CS PGs play significant roles in the maintenance of tissue homeostasis, morphogenesis, development, growth and disease. Here, we review (i) the biodiversity of CS PGs and their sulphation motif sequences and (ii) the current understanding of the signalling roles they play in regulating cellular behaviour during tissue development, growth, disease and repair.

In vivo monitoring of hair cycle stages via bioluminescence imaging of hair follicle NG2 cells

Hair growth occurs periodically in a cycle that consists of three different phases: growth, regression, and resting. The length of each phase is regulated by both intrinsic and extrinsic factors throughout life, and influenced by physiological and pathological conditions. Elongation of the resting phase and shortening of the growth phase occur during physiological ageing and in baldness, respectively. In vivo discrimination of each phase of the hair cycle can be used to research for regeneration of hair follicles as well as to evaluate the efficacy of hair regrowth treatments in the same individual. Here we show that NG2+ epithelial cells in the hair follicles encompass bulge stem cells, and that the number of hair follicle NG2 cells underwent dramatic changes during the hair cycle. Transgenic rats with expression of firefly luciferase gene in NG2 cells were generated to monitor the hair cycle in vivo. Hair follicle NG2 cells were clearly visualized via bioluminescence imaging to study each phase of the hair cycle in the rats, from infancy to old age.

The NG2 Proteoglycan in Pericyte Biology

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

NG2 Proteoglycan-Dependent Contributions of Pericytes and Macrophages to Brain Tumor Vascularization and Progression

The NG2 proteoglycan promotes tumor growth as a component of both tumor and stromal cells. Using intracranial, NG2-negative B16F10 melanomas, we have investigated the importance of PC and Mac NG2 in brain tumor progression. Reduced melanoma growth in Mac-NG2ko and PC-NG2ko mice demonstrates the importance of NG2 in both stromal compartments. In each genotype, the loss of PC-endothelial cell interaction diminishes the formation of endothelial junctions and assembly of the basal lamina. Tumor vessels in Mac-NG2ko mice have smaller diameters, reduced patency, and increased leakiness compared to PC-NG2ko mice, thus decreasing tumor blood supply and increasing hypoxia. While the reduced PC interaction with endothelial cells in PC-NG2ko mice results from the loss of PC activation of β1 integrin signaling in endothelial cells, reduced PC-endothelial cell interaction in Mac-NG2ko mice results from 90% reduced Mac recruitment. The absence of Mac-derived signals in Mac-NG2ko mice causes the loss of PC association with endothelial cells. Reduced Mac recruitment may be due to diminished activation of integrins in the absence of NG2, causing decreased Mac interaction with endothelial adhesion molecules that are needed for extravasation. These results reflect the complex interplay that occurs between Mac, PC, and endothelial cells during tumor vascularization.

Epidermal Cells Expressing Putative Cell Markers in Nonglabrous Skin Existing in Direct Proximity with the Distal End of the Arrector Pili Muscle

Inconsistent with the view that epidermal stem cells reside randomly spread along the basal layer of the epidermal rete ridges, we found that epidermal cells expressing stem cell markers in nonglabrous skin exist in direct connection with the distal end of the arrector pili muscle. The epidermal cells that express stem cell markers consist of a subpopulation of basal keratinocytes located in a niche at the lowermost portion of the rete ridges at the distal arrector pili muscle attachment site. Keratinocytes in the epidermal stem cell niche express K15, MCSP, and α6 integrin. α5 integrin marks the distal end of the APM colocalized with basal keratinocytes expressing stem cell markers located in a well-protected and nourished environment at the lowermost point of the epidermis; these cells are hypothesized to participate directly in epidermal renewal and homeostasis and also indirectly in wound healing through communication with the hair follicle bulge epithelial stem cell population through the APM. Our findings, plus a reevaluation of the literature, support the hierarchical model of interfollicular epidermal stem cell units of Fitzpatrick. This new view provides insights into epidermal control and the possible involvement of epidermal stem cells in nonmelanoma skin carcinogenesis.

Role of NG2 proteoglycan in macrophage recruitment to brain tumors and sites of CNS demyelination

Macrophage infiltration is a factor in most if not all inflammatory pathologies. Understanding molecular interactions that underlie this process is therefore important for our ability to modulate macrophage behavior for therapeutic purposes. Our studies show that cell surface expression of the nerveglial antigen 2 (NG2) proteoglycan is important for the ability of macrophages to colonize both brain tumors and sites of central nervous system (CNS) demyelination. Myeloid-specific ablation of NG2 using LysM-Cre deleter mice results in large decreases in macrophage abundance in both an intracranial melanoma model and a lysolecithin model of spinal cord demyelination. In the melanoma model, decreased macrophage recruitment in the NG2 null mice leads to diminished tumor growth. In line with observations in the literature, this phenomenon is based in part on deficits in tumor vascularization that result from loss of pericyte interaction with endothelial cells in the absence of a macrophage-derived factor(s). In the demyelination model, decreased macrophage infiltration in the NG2 null mice is associated with an initial reduction in lesion size, but nevertheless also with deficits in repair of the lesion. Diminished myelin repair is due not only to reduced clearance of myelin debris, but also to decreased proliferation/recruitment of oligodendrocyte progenitor cells in the absence of a macrophage-derived factor(s). Thus, in both models macrophages have secondary effects on other cell types that are important for progression of the specific pathology. Efforts are underway to identify mechanisms by which NG2 influences macrophage recruitment and by which macrophages signal to other cell types involved in the pathologies.

NG2 Proteoglycan Ablation Reduces Foam Cell Formation and Atherogenesis via Decreased Low-Density Lipoprotein Retention by Synthetic Smooth Muscle Cells

OBJECTIVES

Obesity and hyperlipidemia are critical risk factors for atherosclerosis. Because ablation of NG2 proteoglycan in mice leads to hyperlipidemia and obesity, we investigated the impact of NG2 ablation on atherosclerosis in apoE null mice.

APPROACH AND RESULTS

Immunostaining indicates that NG2 expression in plaque, primarily by synthetic smooth muscle cells, increases during atherogenesis. NG2 ablation unexpectedly results in decreased (30%) plaque development, despite aggravated obesity and hyperlipidemia. Mechanistic studies reveal that NG2-positive plaque synthetic smooth muscle cells in culture can sequester low-density lipoprotein to enhance foam-cell formation, processes in which NG2 itself plays direct roles. In agreement with these observations, low-density lipoprotein retention and lipid accumulation in the NG2/ApoE knockout aorta is 30% less than that seen in the control aorta.

CONCLUSIONS

These results indicate that synthetic smooth muscle cell-dependent low-density lipoprotein retention and foam cell formation outweigh obesity and hyperlipidemia in promoting mouse atherogenesis. Our study sheds new light on the role of synthetic smooth muscle cells during atherogenesis. Blocking plaque NG2 or altering synthetic smooth muscle cells function may be promising therapeutic strategies for atherosclerosis.

NG2-proteoglycan-dependent contributions of oligodendrocyte progenitors and myeloid cells to myelin damage and repair

BACKGROUND

The NG2 proteoglycan is expressed by several cell types in demyelinated lesions and has important effects on the biology of these cells. Here we determine the cell-type-specific roles of NG2 in the oligodendrocyte progenitor cell (OPC) and myeloid cell contributions to demyelination and remyelination.

METHODS

We have used Cre-Lox technology to dissect the cell-type-specific contributions of NG2 to myelin damage and repair. Demyelination is induced by microinjection of 1 % lysolecithin into the spinal cord white matter of control, OPC-specific NG2-null (OPC-NG2ko), and myeloid-specific NG2-null (My-NG2ko) mice. The status of OPCs, myeloid cells, axons, and myelin is assessed by light, immunofluorescence, confocal, and electron microscopy.

RESULTS

In OPC-NG2ko mice 1 week after lysolecithin injection, the OPC mitotic index is reduced by 40 %, resulting in 25 % fewer OPCs at 1 week and a 28 % decrease in mature oligodendrocytes at 6 weeks post-injury. The initial demyelinated lesion size is not affected in OPC-NG2ko mice, but lesion repair is delayed by reduced production of oligodendrocytes. In contrast, both the initial extent of demyelination and the kinetics of lesion repair are decreased in My-NG2ko mice. Surprisingly, the OPC mitotic index at 1 week post-injury is also reduced (by 48 %) in My-NG2ko mice, leading to a 35 % decrease in OPCs at 1 week and a subsequent 34 % reduction in mature oligodendrocytes at 6 weeks post-injury. Clearance of myelin debris is also reduced by 40 % in My-NG2ko mice. Deficits in myelination detected by immunostaining for myelin basic protein are confirmed by toluidine blue staining and by electron microscopy. In addition to reduced myelin repair, fewer axons are found in 6-week lesions in both OPC-NG2ko and My-NG2ko mice, emphasizing the importance of myelination for neuron survival.

CONCLUSIONS

Reduced generation of OPCs and oligodendrocytes in OPC-NG2ko mice correlates with reduced myelin repair. Diminished demyelination in My-NG2ko mice may stem from a reduction (approximately 70 %) in myeloid cell recruitment to lesions. Reduced macrophage/microglia numbers may then result in decreased myelin repair via diminished clearance of myelin debris and reduced stimulatory effects on OPCs.

Differential expression of stem cell-like proteins in normal, hyperplastic and dysplastic oral epithelium

Objective

The identification of stem cells (SC) remains challenging. In the human oral mucosal epithelium, these cells are believed to be in the basal layer (stem cell niche), but their exact location is unclear. The aim of this study was to examine the dysplastic oral epithelium for these SC-like proteins in order to assess their diagnostic value as biomarkers complementing the histological grading of dysplasia.

Material and Methods

Thirty oral epithelial dysplasia (OED), 25 oral lichen planus (OLP), 10 oral hyperkeratosis and 5 normal oral epithelium (OE) were immunohistochemically examined for four SC markers [integrin β1, neuron-glial-2 (NG2), notch 1 (N1) and keratin 15 (K15)].

Results

Three of four SC markers were heterogeneously detected in all samples. K15 overexpression in the lower two-thirds of severe OED suggests an expanded SC niche. Integrin β1 distribution pattern was not measurably different between OEDs and control. NG2 was almost negative to absent in all samples examined. N1 expression was weak and highly variable in normal and dysplastic epithelium, making it an unreliable epithelial stem cell marker.

Conclusions

Present findings suggest that these markers were unable to identify individual epithelial stem cells. Instead, subpopulations of cells, most probably stem cells and transit amplifying cells with stem cell-like properties were identified in the dysplastic oral epithelium. The characteristic expressions of K15 might be of diagnostic value for oral dysplasia and should be investigated further.

Proteoglycans in Normal and Healing Skin

Significance: Proteoglycans have a distinct spatial localization in normal skin and are essential for the correct structural development, organization, hydration, and functional properties of this tissue. The extracellular matrix (ECM) is no longer considered to be just an inert supportive material but is a source of directive, spatial and temporal, contextual information to the cells via components such as the proteoglycans. There is a pressing need to improve our understanding of how these important molecules functionally interact with other matrix structures, cells and cellular mediators in normal skin and during wound healing. Recent Advances: New antibodies to glycosaminoglycan side chain components of skin proteoglycans have facilitated the elucidation of detailed localization patterns within skin. Other studies have revealed important proliferative activities of proteinase-generated fragments of proteoglycans and other ECM components (matricryptins). Knockout mice have further established the functional importance of skin proteoglycans in the assembly and homeostasis of the normal skin ECM. Critical Issues: Our comprehension of the molecular and structural complexity of skin as a complex, dynamic, constantly renewing, layered connective tissue is incomplete. The impact of changes in proteoglycans on skin pathology and the wound healing process is recognized as an important area of pathobiology and is an area of intense investigation. Future Directions: Advanced technology is allowing the development of new artificial skins. Recent knowledge on skin proteoglycans can be used to incorporate these molecules into useful adjunct therapies for wound healing and for maintenance of optimal tissue homeostasis in aging skin.

The dynamics of developmental and tumor angiogenesis-a comparison

The blood vasculature in cancers has been the subject of intense interest during the past four decades. Since the original ideas of targeting angiogenesis to treat cancer were proposed in the 1970s, it has become evident that more knowledge about the role of vessels in tumor biology is needed to fully take advantage of such strategies. The vasculature serves the surrounding tissue in a multitude of ways that all must be taken into consideration in therapeutic manipulation. Aspects of delivery of conventional cytostatic drugs, induction of hypoxia affecting treatment by radiotherapy, changes in tumor cell metabolism, vascular leak and trafficking of leukocytes are affected by interventions on vascular function. Many tumors constitute a highly interchangeable milieu undergoing proliferation, apoptosis, and necrosis with abundance of growth factors, enzymes and metabolites. These aspects are reflected by the abnormal tortuous, leaky vascular bed with detached mural cells (pericytes). The vascular bed of tumors is known to be unstable and undergoing remodeling, but it is not until recently that this has been dynamically demonstrated at high resolution, facilitated by technical advances in intravital microscopy. In this review we discuss developmental genetic loss-of-function experiments in the light of tumor angiogenesis. We find this a valid comparison since many studies phenocopy the vasculature in development and tumors.

Proteoglycans in stem cells

The remarkable promise of pluripotent and multipotent stem cells (SCs) imparts tremendous optimism for advancement of regenerative medicine, developmental biology, and drug discovery. Perhaps the greatest challenge is to finely direct, control, and command their differentiation. As those processes are managed on many levels, including genomic, transcriptomic, and epigenomic, examination of all of these components will yield powerful tools for manipulation of SCs. Carbohydrates surround all cells, including SCs as a glycocalyx. Of particular interest is the class of carbohydrates known as proteoglycans (PGs), which are a diverse group of glycoconjugates consisting of core protein with one or more glycosaminoglycan (GAG) chains attached. They are primarily located in the extracellular matrix as well as at cell surfaces, where they are bound or anchored to the membrane through their core proteins. GAG chains are linear, anionic, and highly heterogeneous carbohydrates consisting of repeating disaccharides. PGs facilitate interaction of cells with the extracellular environment by interacting with chemokines, growth factors, and other signaling molecules. Core proteins are involved in many signaling pathways, both individually, as well as through attached proteins via GAG-mediated interactions. These essential and accessible functions make PGs an excellent target for manipulating SCs and guiding their fate. Studying the role of PGs in cell development will yield valuable insight into the mechanism of SC differentiation and suggest approaches toward directing those pathways. Such studies may also help identify valuable markers for distinguishing between various cell populations during differentiation.

Ablation of NG2 proteoglycan leads to deficits in brown fat function and to adult onset obesity

Obesity is a major health problem worldwide. We are studying the causes and effects of obesity in C57Bl/6 mice following genetic ablation of NG2, a chondroitin sulfate proteoglycan widely expressed in progenitor cells and also in adipocytes. Although global NG2 ablation delays early postnatal adipogenesis in mouse skin, adult NG2 null mice are paradoxically heavier than wild-type mice, exhibiting larger white fat deposits. This adult onset obesity is not due to NG2-dependent effects on CNS function, since specific ablation of NG2 in oligodendrocyte progenitors yields the opposite phenotype; i.e. abnormally lean mice. Metabolic analysis reveals that, while activity and food intake are unchanged in global NG2 null mice, O₂ consumption and CO₂ production are decreased, suggesting a decrease in energy expenditure. Since brown fat plays important roles in regulating energy expenditure, we have investigated brown fat function via cold challenge and high fat diet feeding, both of which induce the adaptive thermogenesis that normally occurs in brown fat. In both tests, body temperatures in NG2 null mice are reduced compared to wild-type mice, indicating a deficit in brown fat function in the absence of NG2. In addition, adipogenesis in NG2 null brown pre-adipocytes is dramatically impaired compared to wild-type counterparts. Moreover, mRNA levels for PR domain containing 16 (PRDM16) and peroxisome proliferator-activated receptor γ coactivator (PGC)1-α, proteins important for brown adipocyte differentiation, are decreased in NG2 null brown fat deposits in vivo and NG2 null brown pre-adipocytes in vitro. Altogether, these results indicate that brown fat dysfunction in NG2 null mice results from deficits in the recruitment and/or development of brown pre-adipocytes. As a consequence, obesity in NG2 null mice may occur due to disruptions in brown fat-dependent energy homeostasis, with resulting effects on lipid storage in white adipocytes.

Reduced inflammation accompanies diminished myelin damage and repair in the NG2 null mouse spinal cord

BACKGROUND

Multiple sclerosis (MS) is a demyelinating disease in which blood-derived immune cells and activated microglia damage myelin in the central nervous system. While oligodendrocyte progenitor cells (OPCs) are essential for generating oligodendrocytes for myelin repair, other cell types also participate in the damage and repair processes. The NG2 proteoglycan is expressed by OPCs, pericytes, and macrophages/microglia. In this report we investigate the effects of NG2 on these cell types during spinal cord demyelination/remyelination.

METHODS

Demyelinated lesions were created by microinjecting 1% lysolecithin into the lumbar spinal cord. Following demyelination, NG2 expression patterns in wild type mice were studied via immunostaining. Immunolabeling was also used in wild type and NG2 null mice to compare the extent of myelin damage, the kinetics of myelin repair, and the respective responses of OPCs, pericytes, and macrophages/microglia. Cell proliferation was quantified by studies of BrdU incorporation, and cytokine expression levels were evaluated using qRT-PCR.

RESULTS

The initial volume of spinal cord demyelination in wild type mice is twice as large as in NG2 null mice. However, over the ensuing 5 weeks there is a 6-fold improvement in myelination in wild type mice, versus only a 2-fold improvement in NG2 null mice. NG2 ablation also results in reduced numbers of each of the three affected cell types. BrdU incorporation studies reveal that reduced cell proliferation is an important factor underlying NG2-dependent decreases in each of the three key cell populations. In addition, NG2 ablation reduces macrophage/microglial cell migration and shifts cytokine expression from a pro-inflammatory to anti-inflammatory phenotype.

CONCLUSIONS

Loss of NG2 expression leads to decreased proliferation of OPCs, pericytes, and macrophages/microglia, reducing the abundance of all three cell types in demyelinated spinal cord lesions. As a result of these NG2-dependent changes, the course of demyelination and remyelination in NG2 null mice differs from that seen in wild type mice, with both myelin damage and repair being reduced in the NG2 null mouse. These studies identify NG2 as an important factor in regulating myelin processing, suggesting that therapeutic targeting of the proteoglycan might offer a means of manipulating cell behavior in demyelinating diseases.

Immortalized CNS pericytes are quiescent smooth muscle actin-negative and pluripotent

Despite their identification more than 100 years ago by the French scientist Charles-Marie Benjamin Rouget, microvascular pericytes have proven difficult to functionally characterize, due in part to their relatively low numbers and the lack of specific cell markers. However, recent progress is beginning to shed light on the diverse biological functions of these cells. Pericytes are thought to be involved in regulating vascular homeostasis and hemostasis as well as serving as a local source of adult stem cells. To further define the properties of these intriguing cells, we have isolated pericytes from transgenic mice (Immortomouse®) harboring a temperature-sensitive mutant of the SV40 virus target T-gene. This Immortopericyte (IMP) conditional cell line is stable for long periods of time and, at 33°C in the presence of interferon gamma, does not differentiate. Under these conditions IMPs are alpha muscle actin-negative and exhibit a pluripotent phenotype, but can be induced to differentiate along both mesenchymal and neuronal lineages at 37°C. Alternatively, differentiation of wild type pericytes and IMPs can be induced directly from capillaries in culture. Finally, the addition of endothelial cells to purified IMP cultures augments their rate of self-renewal and differentiation, possibly in a cell-to-cell contact dependent manner.

Endoplasmic reticulum protein BI-1 modulates unfolded protein response signaling and protects against stroke and traumatic brain injury

Bax-Inhibitor-1 (BI-1) is an evolutionarily conserved cytoprotective protein that resides in membranes of the endoplasmic reticulum (ER). BI-1's cytoprotective activity is manifested in the context of ER stress, with previous studies showing that BI-1 modulates several ER-associated functions, including Unfolded Protein Response (UPR) signaling. Here we investigated the role of BI-1 in neuroprotection by generating transgenic mice in which BI-1 was constitutively expressed from a neuronal-specific promoter. Cultured primary cortical neurons from BI-1 transgenic mouse embryos exhibited greater resistance to cell death induced by agents known to cause ER stress compared to their non-transgenic counterparts. While brain morphology and vasculature of BI-1 mice appeared to be unchanged from normal non-transgenic mice, BI-1 transgenic mice showed reduced brain lesion volumes and better performance in motoric tests, compared with non-transgenic littermates, in two models of acute brain injury: stroke caused by middle cerebral artery occlusion (MCAO) and traumatic brain injury (TBI) caused by controlled cortical impact. Furthermore, brain tissue from BI-1 transgenic mice showed reduced levels of apoptotic cells and reduced induction of markers of ER stress after brain injury, including CHOP protein expression. In summary, our findings demonstrate that enforced neuronal expression of BI-1 reduces ER stress and provides protection from acute brain injury, suggesting that strategies for enhancing BI-1 expression or activity should be considered for development of new therapies for counteracting the consequences of stroke and acute brain trauma.

Morphology and properties of pericytes

Pericytes were described in 1873 by the French scientist Charles-Marie Benjamin Rouget and were originally called Rouget cells. The Rouget cell was renamed some years later due to its anatomical location abluminal to the endothelial cell (EC) and luminal to parenchymal cells. In the brain, pericytes are located in precapillary arterioles, capillaries and postcapillary venules. They deposit elements of the basal lamina and are totally surrounded by this vascular component. Pericytes are important cellular constituents of the blood-brain barrier (BBB) and actively communicate with other cells of the neurovascular unit such as ECs, astrocytes, and neurons. Pericytes are local regulatory cells that are important for the maintenance of homeostasis and hemostasis, and are a source of adult pluripotent stem cells. Further understanding of the role played by this intriguing cell may lead to novel targeted therapies for neurovascular diseases.

CSPG4 protein as a new target for the antibody-based immunotherapy of triple-negative breast cancer

BACKGROUND

The cell surface proteoglycan, chondroitin sulfate proteoglycan 4 (CSPG4), is a potential target for monoclonal antibody (mAb)-based immunotherapy for many types of cancer. The lack of effective therapy for triple-negative breast cancer (TNBC) prompted us to examine whether CSPG4 is expressed in TNBC and can be targeted with CSPG4-specific mAb.

METHODS

CSPG4 protein expression was assessed in 44 primary TNBC lesions, in TNBC cell lines HS578T, MDA-MB-231, MDA-MB-435, and SUM149, and in tumor cells in pleural effusions from 12 metastatic breast cancer patients. The effect of CSPG4-specific mAb 225.28 on growth, adhesion, and migration of TNBC cells was tested in vitro. The ability of mAb 225.28 to induce regression of tumor metastases (n = 7 mice) and to inhibit spontaneous metastasis and tumor recurrence (n = 12 mice per group) was tested in breast cancer models in mice. The mechanisms responsible for the antitumor effect of mAb 225.28 were also investigated in the cell lines and in the mouse models. All statistical tests were two-sided.

RESULTS

CSPG4 protein was preferentially expressed in 32 of the 44 (72.7%) primary TNBC lesions tested, in TNBC cell lines, and in tumor cells in pleural effusions from 12 metastatic breast cancer patients. CSPG4-specific mAb 225.28 statistically significantly inhibited growth, adhesion, and migration of TNBC cells in vitro. mAb 225.28 induced 73.1% regression of tumor metastasis in a TNBC cell-derived experimental lung metastasis model (mAb 225.28 vs control, mean area of metastatic nodules = 44590.8 vs 165950.8 μm(2); difference of mean = 121360.0 μm(2), 95% confidence interval = 91010.7 to 151709.4 μm(2); P < .001). Additionally, mAb 225.28 statistically significantly reduced spontaneous lung metastases and tumor recurrences in an orthotopic xenograft mouse model. The mechanisms responsible for antitumor effect included increased apoptosis and reduced mitotic activity in tumor cells, decreased blood vessel density in the tumor microenvironment, and reduced activation of signaling pathways involved in cell survival, proliferation and metastasis.

CONCLUSIONS

This study identified CSPG4 as a new target for TNBC. The antitumor activity of CSPG4-specific mAb was mediated by multiple mechanisms, including the inhibition of signaling pathways crucial for TNBC cell survival, proliferation, and metastasis.

Pericyte deficiencies lead to aberrant tumor vascularizaton in the brain of the NG2 null mouse

Tightly regulated crosstalk between endothelial cells and pericytes is required for formation and maintenance of functional blood vessels. When the NG2 proteoglycan is absent from pericyte surfaces, vascularization of syngeneic tumors growing in the C57Bl/6 mouse brain is aberrant in several respects, resulting in retardation of tumor progression. In the NG2 null mouse brain, pericyte investment of the tumor vascular endothelium is reduced, causing deficiencies in both pericyte and endothelial cell maturation, as well as reduced basal lamina assembly. While part of this deficit may be due to the previously-identified role of NG2 in beta1 integrin-dependent periyte/endothelial cell crosstalk, the ablation of NG2 also appears responsible for loss of collagen VI anchorage, in turn leading to reduced collagen IV deposition. Poor functionality of tumor vessels in NG2 null brain is reflected by reduced vessel patency and increased vessel leakiness, resulting in large increases in tumor hypoxia. These findings demonstrate the importance of NG2-dependent pericyte/endothelial cell interaction in the development and maturation of tumor blood vessels, identifying NG2 as a potential target for anti-angiogenic cancer therapy.

Transmembrane signaling proteoglycans

Virtually all metazoan cells contain at least one and usually several types of transmembrane proteoglycans. These are varied in protein structure and type of polysaccharide, but the total number of vertebrate genes encoding transmembrane proteoglycan core proteins is less than 10. Some core proteins, including those of the syndecans, always possess covalently coupled glycosaminoglycans; others do not. Syndecan has a long evolutionary history, as it is present in invertebrates, but many other transmembrane proteoglycans are vertebrate inventions. The variety of proteins and their glycosaminoglycan chains is matched by diverse functions. However, all assume roles as coreceptors, often working alongside high-affinity growth factor receptors or adhesion receptors such as integrins. Other common themes are an ability to signal through their cytoplasmic domains, often to the actin cytoskeleton, and linkage to PDZ protein networks. Many transmembrane proteoglycans associate on the cell surface with metzincin proteases and can be shed by them. Work with model systems in vivo and in vitro reveals roles in growth, adhesion, migration, and metabolism. Furthermore, a wide range of phenotypes for the core proteins has been obtained in mouse knockout experiments. Here some of the latest developments in the field are examined in hopes of stimulating further interest in this fascinating group of molecules.

The NG2 proteoglycan promotes oligodendrocyte progenitor proliferation and developmental myelination

The NG2 proteoglycan has been shown to promote proliferation and motility in a variety of cell types. The presence of NG2 on oligodendrocyte progenitor cells (OPCs) suggests that the proteoglycan may be a factor in expansion of the OPC pool to fill the entire CNS prior to OPC differentiation to form myelinating oligodendrocytes. Comparisons of postnatal cerebellar myelination in wild type and NG2 null mice reveal reduced numbers of OPCs in developing white matter of the NG2 null mouse. Quantification of BrdU incorporation shows that reduced proliferation is a key reason for this OPC shortage, with the peak of OPC proliferation delayed by 4-5 days in the absence of NG2. As a result of the subnormal pool of OPCs, there is also a delay in production of mature oligodendrocytes and myelinating processes in the NG2 null cerebellum. NG2 may promote OPC proliferation via enhancement of growth factor signaling or mediation of OPC interaction with unmyelinated axons.

A role for the NG2 proteoglycan in glioma progression

Many human gliomas carry markers characteristic of oligodendrocyte progenitor cells (such as Olig-2, PDGF alpha receptor and NG2 proteoglycan), suggesting these progenitors as the cells of origin for glioma initiation. This review considers the potential roles of the NG2 proteoglycan in glioma progression. NG2 is expressed not only by glioma cells and by oligodendrocyte progenitors, but also by pericytes associated with the tumor microvasculature. The proteoglycan may therefore promote tumor vascularization and recruitment of normal progenitors to the tumor mass, in addition to mediating expansion of the transformed cell population. Along with potentiating growth factor signaling and serving as a cell surface receptor for extracellular matrix components, NG2 also has the ability to mediate activation of beta-1 integrins. These molecular interactions allow the proteoglycan to contribute to critical processes such as cell proliferation, cell motility and cell survival.