Stimulation of serglycin and CD44 mRNA expression in endothelial cells exposed to TNF-alpha and IL-1alpha

Tenogenic Induction From Induced Pluripotent Stem Cells Unveils the Trajectory Towards Tenocyte Differentiation

The musculoskeletal system is integrated by tendons that are characterized by the expression of scleraxis (Scx), a functionally important transcription factor. Here, we newly developed a tenocyte induction method using induced pluripotent stem cells established from ScxGFP transgenic mice by monitoring fluorescence, which reflects a dynamic differentiation process. Among several developmentally relevant factors, transforming growth factor-beta 2 (TGF-β2) was the most potent inducer for differentiation of tenomodulin-expressing mature tenocytes. Single-cell RNA sequencing (scRNA-seq) revealed 11 distinct clusters, including mature tenocyte population and tenogenic differentiation trajectory, which recapitulated the in vivo developmental process. Analysis of the scRNA-seq dataset highlighted the importance of retinoic acid (RA) as a regulatory pathway of tenogenic differentiation. RA signaling was shown to have inhibitory effects on entheseal chondrogenic differentiation as well as TGF-β2-dependent tenogenic/fibrochondrogenic differentiation. The collective findings provide a new opportunity for tendon research and further insight into the mechanistic understanding of the differentiation pathway to a tenogenic fate.

Platelet α-granule cargo packaging and release are affected by the luminal proteoglycan, serglycin

BACKGROUND

Serglycin (SRGN) is an intragranular, sulfated proteoglycan in hematopoietic cells that affects granule composition and function.

OBJECTIVE

To understand how SRGN affects platelet granule packaging, cargo release, and extra-platelet microenvironments.

METHODS

Platelets and megakaryocytes from SRGN-/- mice were assayed for secretion kinetics, cargo levels, granule morphology upon activation, and receptor shedding.

RESULTS

Metabolic, 35 SO4 labeling identified SRGN as a major sulfated macromolecule in megakaryocytes. SRGN colocalized with α-granule markers (platelet factor 4 [PF4], von Willebrand factor [VWF], and P-selectin), but its deletion did not affect α-granule morphology or number. Platelet α-granule composition was altered, with a reduction in basic proteins (pI ≥8; e.g., PF4, SDF-1, angiogenin) and constitutive release of PF4 from SRGN-/- megakaryocytes. P-Selectin, VWF, and fibrinogen were unaffected. Serotonin (5-HT) uptake and β-hexosaminidase (HEXB) were slightly elevated. Thrombin-induced exocytosis of PF4 from platelets was defective; however, release of RANTES/CCL5 was normal and osteopontin secretion was more rapid. Release of 5-HT and HEXB (from dense granules and lysosomes, respectively) were unaffected. Ultrastructural studies showed distinct morphologies in activated platelets. The α-granule lumen of SRGN-/- platelet had a grainy staining pattern, whereas that of wild-type granules had only fibrous material remaining. α-Granule swelling and decondensation were reduced in SRGN-/- platelets. Upon stimulation of platelets, a SRGN/PF4 complex was released in a time- and agonist-dependent manner. Shedding of GPVI from SRGN-/- platelets was modestly enhanced. Shedding of GP1b was unaffected.

CONCLUSION

The polyanionic proteoglycan SRGN influences α-granule packaging, cargo release, and shedding of platelet membrane proteins.

Transcriptome Profile of Human Fibroblasts in an Ex Vivo Culture

Implantation of autologous fibroblasts is a method used to correct age-related changes in facial skin. The aim of this study was to establish the optimal population of cultured human fibroblasts according to the organization of the extracellular matrix in the dermis. Transcriptome profile analysis of cells derived from three consecutive passages indicated that fibroblasts after the second passage were the population with the greatest number of upregulated genes encoding the critical biological processes responsible for skin regeneration, such as extracellular matrix organization, collagen fibril organization, and cell adhesion. Furthermore, genes encoding proteinases responsible for the degradation of dermal extracellular matrix proteins were noticeably downregulated at this stage of culture. Autologous fibroblasts seem to be an optimal and safe biological filler for the renewal of all skin structures.

Increased levels of serum serglycin and agrin is associated with adverse perinatal outcome in early onset preeclampsia

Goal: Our aim was to determine whether alterations in serum serglycin and agrin levels in early-onset preeclampsia (EOPE) are useful in predicting adverse perinatal outcomes such as fetal growth restriction (FGR), intrauterine fetal demise (IUFD), preterm delivery and/or neonatal unit admission. Materials and Methods: A prospective case-controlled study enrolled 88 pregnant patients (44 EOPE and 44 controls). Maternal serum serglycin and agrin levels were determined before the 34th gestational week by enzyme-linked immunosorbent assay. Results: Compared with controls, women with EOPE had significantly higher serglycin and agrin levels (p = .018; p = .048). Multivariable logistic regression analysis revealed serglycin was independently associated with FGR in EOPE (OR 0.866; 95% CI 0.779-0.953). Agrin was independently associated with IUFD in EOPE (OR 0.757, 95% CI 0.636-0.879). Conclusions: The current study suggests that increased maternal serum serglycin is associated with FGR, and increased maternal serum agrin is associated with IUFD in EOPE.

Serglycin as part of IL-1β induced inflammation in human chondrocytes

Serglycin (SRGN) is an intracellular proteoglycan produced and secreted by several cell types. The increased expression of SRGN was associated with greater aggressiveness in cancer and inflammation. In this study, we demonstrated that SRGN is increased in human chondrocytes after IL-β stimulation. Furthermore, we found that secreted SRGN was able to bind the CD44 receptor thus participating in the extension of the inflammatory response. Using SRGN knockdown cells we observed a significantly decrease in specific inflammatory markers and NF-kB activation. Similar results were observed by blocking the CD44 receptor. These data provide further evidences for a direct involvement of SRGN in the mechanisms regulating the non-infectious chondrocytes damage, and the consequent joint inflammation and cartilage destruction in arthritis.

Tumorigenic functions of serglycin: Regulatory roles in epithelial to mesenchymal transition and oncogenic signaling

Numerous studies point out serglycin as an important regulator of tumorigenesis in a variety of malignancies. Serglycin expression correlates with the aggressive phenotype of tumor cells and serves as a poor prognostic indicator for disease progression. Although serglycin is considered as an intracellular proteoglycan, it is also secreted in the extracellular matrix by tumor cells affecting cell properties, oncogenic signaling and exosomes cargo. Serglycin directly interacts with CD44 and possibly other cell surface receptors including integrins, evoking cell adhesion and signaling. Serglycin also creates a pro-inflammatory and pro-angiogenic tumor microenvironment by regulating the secretion of proteolytic enzymes, IL-8, TGFβ2, CCL2, VEGF and HGF. Hence, serglycin activates multiple signaling cascades that drive angiogenesis, tumor cell growth, epithelial to mesenchymal transition, cancer cell stemness and metastasis. The interference with the tumorigenic functions of serglycin emerges as an attractive prospect to target malignancies.

Serglycin protects against high fat diet-induced increase in serum LDL in mice

Proteoglycans have been implicated in regulation of lipoprotein metabolism. However, the impact of serglycin, the major proteoglycan expressed by many hematopoietic- and endothelial cells, on lipoprotein metabolism has not been explored. Here we addressed this issue by comparing several parameters of lipid metabolism in wild type (WT) and serglycin-/- mice, both at baseline and after feeding mice the Paigen diet. We show that, after feeding this diet for 20 weeks, serglycin deficient mice exhibited elevated concentrations of serum LDL in comparison with WT mice, thus suggesting that serglycin protects against an elevation of serum LDL levels after intake of a high-fat diet. Body weight increased in both groups, but only significantly in the serglycin-/- group. To explore the mechanism underlying this phenotype, genome-wide expression analysis was performed on liver tissues from WT and serglycin-/- mice. This analysis showed that serglycin-deficiency is associated with differential expression of numerous genes involved in the regulation of lipid metabolism, suggesting that the impact of serglycin on LDL levels may be related to effects at the gene expression level. In particular, several members of the CYP gene family were differently regulated in serglycin-/- compared with WT mice. Moreover, upstream regulator analysis suggested that several pro-inflammatory pathways, including the NFκB pathway, could contribute to the impact of serglycin on LDL. Hence, the elevation of serum LDL seen in serglycin-/- mice may be linked to dysregulated inflammatory responses. Taken together, our findings introduce serglycin as a novel player in processes that regulate lipid metabolism.

Serglycin: at the crossroad of inflammation and malignancy

Serglycin has been initially characterized as an intracellular proteoglycan expressed by hematopoietic cells. All inflammatory cells highly synthesize serglycin and store it in granules, where it interacts with numerous inflammatory mediators, such as proteases, chemokines, cytokines, and growth factors. Serglycin is implicated in their storage into the granules and their protection since they are secreted as complexes and delivered to their targets after secretion. During the last decade, numerous studies have demonstrated that serglycin is also synthesized by various non-hematopoietic cell types. It has been shown that serglycin is highly expressed by tumor cells and promotes their aggressive phenotype and confers resistance against drugs and complement system attack. Apart from its direct beneficial role to tumor cells, serglycin may promote the inflammatory process in the tumor cell microenvironment thus enhancing tumor development. In the present review, we discuss the role of serglycin in inflammation and tumor progression.

Serglycin proteoglycan is required for multiple myeloma cell adhesion, in vivo growth, and vascularization

Recently, it was discovered that serglycin, a hematopoietic cell proteoglycan, is the major proteoglycan expressed and constitutively secreted by multiple myeloma (MM) cells. High levels of serglycin are present in the bone marrow aspirates of at least 30% of newly diagnosed MM patients. However, its contribution to the pathophysiology of MM is unknown. Here, we show that serglycin knockdown (by ∼85% compared with normal levels), using lentiviral shRNA, dramatically attenuated MM tumor growth in mice with severe combined immunodeficiency. Tumors formed from cells deficient in serglycin exhibited diminished levels of hepatocyte growth factor expression and impaired development of blood vessels, indicating that serglycin may affect tumor angiogenesis. Furthermore, knockdown of serglycin significantly decreased MM cell adhesion to bone marrow stromal cells and collagen I. Even though serglycin proteoglycan does not have a transmembrane domain, flow cytometry showed that serglycin is present on the MM cell surface, and attachment to the cell surface is, at least in part, dependent on its chondroitin sulfate side chains. Co-precipitation of serglycin from conditioned medium of MM cells using a CD44-Fc chimera suggests that CD44 is the cell surface-binding partner for serglycin, which therefore may serve as a major ligand for CD44 at various stages during myeloma progression. Finally, we demonstrate that serglycin mRNA expression in MM cells is up-regulated by activin, a predominant cytokine among those increased in MM patients with osteolytic lesions. These studies provide direct evidence for a critical role for serglycin in MM pathogenesis and show that targeting serglycin may provide a novel therapeutic approach for MM.

Heparan sulfate expression is affected by inflammatory stimuli in primary human endothelial cells

In diabetes the endothelium is either chronically or transiently exposed to hyperglycemic conditions. In addition, endothelial dysfunction in diabetes is related to changes in the inflammatory response and the turnover of extracellular matrix. This study was undertaken to study the effects of inflammatory stimuli on one particular matrix component, the heparan sulfate (HS) proteoglycans (PGs) synthesized by primary human umbilical cord vein endothelial cells (HUVEC). Such cells were cultured in vitro in 5 mM and 25 mM glucose. The latter concentration was used to mimic hyperglycemic conditions in short-term experiments. HUVEC were also cultured in the presence of the inflammatory agents tumor necrosis factor α (TNF-α), interleukin 1α (IL-1α), interleukin 1β (IL-1β) and transforming growth factor β (TGF-β). The cells were labeled with (35)S-sulfate and (35)S-PGs were recovered for further analyses. The major part of the (35)S-PGs was secreted to the medium, irrespective of type of stimuli. Secreted (35)S-PGs were therefore isolated and subjected to further analyses. TNF-α and IL-1α slightly increased the release of (35)S-PGs to the culture medium, whereas IL-1β treatment gave a significant increase. The different treatments neither changed the ratio of (35)S-HS and (35)S-chondroitin sulfate (CS) nor the macromolecular properties of the (35)S-PGs. However, the (35)S-HS chains were slightly increased in size after TNF-α treatment, and slightly decreased after TGF-β treatment, but not affected by the other treatments. Compositional analysis of labeled disaccharides showed changes in the amount of 6-O-sulfated glucosamine residues after treatment with TNF-α, IL-1α and IL-1β. Western immunoblotting showed that major HSPGs recovered from these cells were collagen XVIII, perlecan and agrin, and that secretion of these distinct PGs was increased after IL-1β stimulation. Hence, short term inflammatory stimuli increased the release of HSPGs in HUVEC and affected both the size and sulfation pattern of HS, depending on type of stimuli.

Identification of specific chondroitin sulfate species in cutaneous autoimmune disease

Cutaneous lupus erythematosus and dermatomyositis (DM) are chronic inflammatory diseases of the skin with accumulated dermal mucin. Earlier work has shown chondroitin sulfate (CS) accumulation within the dermis of discoid lupus erythematosus (DLE), subacute cutaneous lupus erythematosus (SCLE), and DM lesions compared with control skin. Immunohistochemistry for C4S revealed a greater density in DLE and DM lesions, whereas SCLE lesions did not differ from controls. Scleredema and scleromyxedema are attributed to increased hyaluronic acid, and lesional samples from these diseases also demonstrated accumulated dermal C4S. Interferon-γ and interleukin-1α, but not interferon-α, treatment of cultured dermal fibroblasts induced mRNA expression of CHST-11, which attaches sulfates to the 4-position of unsulfated chondroitin. These studies on possible CS core proteins revealed that serglycin, known to have C6S side chains in endothelial cells, had greater density within DM dermal endothelia but not in DLE or SCLE, following the pattern of C6S overexpression reported previously. CD44 variants expand the CS binding repertoire of the glycoprotein; CD44v7 co-localized to the distribution of C4S in DLE lesions, a finding not observed in DM, SCLE lesions, or controls. Because C4S and C6S have immunologic effects, their dysregulation in cutaneous mucinoses may contribute to the pathogenesis of these disorders.

Ultraviolet irradiation induces the accumulation of chondroitin sulfate, but not other glycosaminoglycans, in human skin

Ultraviolet (UV) light alters cutaneous structure and function. Prior work has shown loss of dermal hyaluronan after UV-irradiation of human skin, yet UV exposure increases total glycosaminoglycan (GAG) content in mouse models. To more fully describe UV-induced alterations to cutaneous GAG content, we subjected human volunteers to intermediate-term (5 doses/week for 4 weeks) or single-dose UV exposure. Total dermal uronyl-containing GAGs increased substantially with each of these regimens. We found that UV exposure substantially increased dermal content of chondroitin sulfate (CS), but not hyaluronan, heparan sulfate, or dermatan sulfate. UV induced the accumulation of both the 4-sulfated (C4S) and 6-sulfated (C6S) isoforms of CS, but in distinct distributions. Next, we examined several CS proteoglycan core proteins and found a significant accumulation of dermal and endothelial serglycin, but not of decorin or versican, after UV exposure. To examine regulation in vitro, we found that UVB in combination with IL-1α, a cytokine upregulated by UV radiation, induced serglycin mRNA in cultured dermal fibroblasts, but did not induce the chondroitin sulfate synthases. Overall, our data indicate that intermediate-term and single-dose UVB exposure induces specific GAGs and proteoglycan core proteins in human skin in vivo. These molecules have important biologic functions and contribute to the cutaneous response to UV.

Serglycin is a major proteoglycan in polarized human endothelial cells and is implicated in the secretion of the chemokine GROalpha/CXCL1

Proteoglycan (PG) expression was studied in primary human umbilical vein endothelial cells (HUVEC). RT-PCR analyses showed that the expression of the PG serglycin core protein was much higher than that of the extracellular matrix PG decorin and the cell surface PG syndecan-1. PG biosynthesis was further studied by biosynthetic [(35)S]sulfate labeling of polarized HUVEC. Interestingly, a major part of (35)S-PGs was secreted to the apical medium. A large portion of these PGs was trypsin-resistant, a typical feature of serglycin. The trypsin-resistant PGs were mainly of the chondroitin/dermatan sulfate type but also contained a minor heparan sulfate component. Secreted serglycin was identified by immunoprecipitation as a PG with a core protein of ∼30 kDa. Serglycin was furthermore shown to be present in perinuclear regions and in two distinct types of vesicles throughout the cytoplasm using immunocytochemistry. To search for possible serglycin partner molecules, HUVEC were stained for the chemokine growth-related oncogene α (GROα/CXCL1). Co-localization with serglycin could be demonstrated, although not in all vesicles. Serglycin did not show overt co-localization with tissue-type plasminogen activator-positive vesicles. When PG biosynthesis was abrogated using benzyl-β-D-xyloside, serglycin secretion was decreased, and the number of vesicles with co-localized serglycin and GROα was reduced. The level of GROα in the apical medium was also reduced after xyloside treatment. Together, these findings indicate that serglycin is a major PG in human endothelial cells, mainly secreted to the apical medium and implicated in chemokine secretion.

Serglycin proteoglycan deletion in mouse platelets: physiological effects and their implications for platelet contributions to thrombosis, inflammation, atherosclerosis, and metastasis

Serglycin is found in all nucleated hematopoietic cells and platelets, blood vessels, various reproductive and developmental tissues, and in chondrocytes. The serglycin knockout mouse has demonstrated that this proteoglycan is required for proper generation and function of secretory granules in several hematopoietic cells. The effects on platelets are profound, and include diminishing platelet aggregation responses and formation of platelet thrombi. This chapter will review cell-specific aspects of serglycin structure, its gene regulation, cell and tissue localization, and the effects of serglycin deletion on hematopoietic cell granule structure and function. The effects of serglycin knockout on platelets are described and discussed in detail. Rationales for further investigations into the contribution of serglycin to the known roles of platelets in thrombosis, inflammation, atherosclerosis, and tumor metastasis are presented.

The role of CD44 in cutaneous inflammation

CD44 is a transmembrane glycoprotein expressed in various tissues including the skin. Previous studies indicated that CD44 is required for epidermal permeability barrier homeostasis and keratinocyte differentiation. Yet, while some studies have demonstrated that CD44 is critical for the development of inflammation, others have shown that CD44 is not essential for the development of cutaneous inflammation. In this study, we evaluated the changes in epidermal CD44 expression in a variety of skin inflammatory models and determined whether CD44 is required for the development of cutaneous inflammation. Inflammatory responses were compared in CD44 KO versus wild-type mice in acute models of irritant and allergic contact dermatitis, as well as in a subacute allergic contact dermatitis induced by repeated hapten treatment. Inflammatory responses were assessed by measuring ear thickness and epidermal hyperplasia in haematoxylin & eosin-stained sections. Our results demonstrate that: (i) epidermal CD44 expression increases in both acute and subacute cutaneous inflammatory models; and (ii) acute disruption of the epidermal permeability barrier function increases epidermal CD44 expression. Whereas inflammatory responses did not differ between CD44 KO and wild-type mice in acute models of irritant and allergic contact dermatitis, both inflammatory responses and epidermal hyperplasia increased in CD44 KO mice following repeated hapten challenges. These results show first, that permeability barrier disruption and inflammation stimulate epidermal CD44 expression, and second, that CD44 modulates epidermal proliferation and inflammatory responses in a subacute murine allergic contact dermatitis model.

Interleukin-1β selectively decreases the synthesis of versican by arterial smooth muscle cells

Proteoglycans accumulate in lesions of atherosclerosis but little is known as to which factors regulate the synthesis of these molecules. Interleukin-1beta (IL-1beta) is a cytokine involved in vascular lesion development but it is not clear whether it has specific effects on proteoglycan synthesis by arterial smooth muscle cells (ASMC). Monkey ASMC were treated with IL-1beta and proteoglycan synthesis assessed using [(35)S]-sulfate and [(35)S]-Trans amino acid labeling. Four prominent size populations of proteoglycans, as determined by SDS-PAGE gradient gel electrophoresis, were observed in the culture medium and identified as versican, biglycan, decorin, and an unknown population that migrated to the gel interface. IL-1beta treatment decreased significantly the synthesis of versican, while increasing the synthesis of decorin, but having no effect on biglycan synthesis. Northern blot analyses confirmed this selective effect on versican and decorin mRNA transcripts. Nuclear run-on and RNA inhibition studies showed that decreased mRNA for versican was due to increased mRNA degradation and not to changes in transcription. In addition, IL-1beta increased the synthesis of the population of proteoglycans that separated at the SDS-PAGE gel interface. Chondroitinase ABC lyase digestion of this population revealed a complex of proteins composed of versican (350 kDa), an unidentified protein (215 kDa), and a 23 kDa protein identified by sequence analyses as serglycin. These data demonstrate that IL-1beta selectively downregulates versican synthesis by ASMC, while positively regulating the synthesis of other proteoglycans.

Endocan or endothelial cell specific molecule-1 (ESM-1): a potential novel endothelial cell marker and a new target for cancer therapy

Endocan, previously called endothelial cell specific molecule-1, is a soluble proteoglycan of 50 kDa, constituted of a mature polypeptide of 165 amino acids and a single dermatan sulphate chain covalently linked to the serine residue at position 137. This dermatan sulphate proteoglycan, which is expressed by the vascular endothelium, has been found freely circulating in the bloodstream of healthy subjects. Experimental evidence is accumulating that implicates endocan as a key player in the regulation of major processes such as cell adhesion, in inflammatory disorders and tumor progression. Inflammatory cytokines such as TNF-alpha, and pro-angiogenic growth factors such as VEGF, FGF-2 and HGF/SF, strongly increased the expression, synthesis or the secretion of endocan by human endothelial cells. Endocan is clearly overexpressed in human tumors, with elevated serum levels being observed in late-stage lung cancer patients, as measured by enzyme-linked immunoassay, and with its overexpression in experimental tumors being evident by immunohistochemistry. Recently, the mRNA levels of endocan have also been recognized as being one of the most significant molecular signatures of a bad prognosis in several types of cancer including lung cancer. Overexpression of this dermatan sulphate proteoglycan has also been shown to be directly involved in tumor progression as observed in mouse models of human tumor xenografts. Collectively, these results suggest that endocan could be a biomarker for both inflammatory disorders and tumor progression as well as a validated therapeutic target in cancer. On the basis of the recent successes of immunotherapeutic approaches in cancer, the preclinical data on endocan suggests that an antibody raised against the protein core of endocan could be a promising cancer therapy.

Expression of CD44v3 protein in human endothelial cells in vitro and in tumoral microvessels in vivo

The most universal angiogenic cytokines (VEGF, bFGF, HGF) are all heparin-binding proteins, the function of which is dependent on cell surface heparan sulfate proteoglycans (HSPG). Several proteoglycans have been demonstrated in endothelial cells, but only glypican-1 from the cell surface HSPG subfamily was documented at protein level. Here, we show that CD44v3 is expressed in human immortalized endothelial cells [anchorage-dependent human umbilical vein endothelial cells (HUVEC) and anchorage-independent Kaposi sarcoma (KS-Imm)] at mRNA and protein level, but is absent from the primary culture of human brain microvascular endothelial cells. We have shown that CD44v3 has a large cytoplasmic pool in endothelial cells, but a limited surface expression, mainly at filopodia, colocalized with MMP-2. Angiogenic factors like VEGF or bFGF did not affect surface detection of CD44v3 suggesting a constitutive expression. The putative functional role for endothelial cell surface CD44v3 was identified in chemotaxis assay when anti-CD44v3 antibody pretreatment proved to be inhibitory for HUVEC. Furthermore, we provided evidence for the CD44v3 protein expression in human endothelial cells in vivo in peritumoral microvessels of both human melanoma and glottic cancers, suggesting a role for this part-time heparan sulfate proteoglycan in tumor induced angiogenesis.

Enhanced expression of CD44 variants in human atheroma and abdominal aortic aneurysm: possible role for a feedback loop in endothelial cells

CD44, a polymorphic hyaluronate receptor, may participate in chronic inflammation. We hypothesized that CD44 variants contribute to the development of arterial diseases. CD44 levels vary in normal and diseased arterial tissues in the following order: unaffected arteries < fibrous plaques < or = abdominal aortic aneurysm < atheromatous plaques; and correlate with macrophage content. Furthermore, plaque microvessels express CD44, and anti-CD44v3 or anti-CD44v6 treatment reduces endothelial cell proliferation but not apoptosis in vitro, suggesting functionality of these receptors. Endothelial cells express CD44H and CD44v6 after exposure to interleukin-1beta and tumor necrosis factor-alpha. Macrophages, a major source of abundant CD44 in vitro, express not only CD44H but also variants CD44v4/5, CD44v6, and CD44v7/8, isoforms distinctively regulated by proinflammatory cytokines. Several proinflammatory cytokines induce shedding of CD44 from the surface of macrophages and endothelial cells. Soluble CD44 stimulates the expression and release of interleukin-1beta from endothelial cells, suggesting a positive feedback loop of this cytokine. By demonstrating augmented expression of CD44 and variants within human atheroma and in abdominal aortic aneurysm as well as the vascular cell release of sCD44, a process regulated by proinflammatory cytokines, this study provides new insights on the functions of CD44 in arterial diseases.

Intracellular proteoglycans

Proteoglycans (PGs) are proteins with glycosaminoglycan chains, are ubiquitously expressed and have a wide range of functions. PGs in the extracellular matrix and on the cell surface have been the subject of extensive structural and functional studies. Less attention has so far been given to PGs located in intracellular compartments, although several reports suggest that these have biological functions in storage granules, the nucleus and other intracellular organelles. The purpose of this review is, therefore, to present some of these studies and to discuss possible functions linked to PGs located in different intracellular compartments. Reference will be made to publications relevant for the topics we present. It is beyond the scope of this review to cover all publications on PGs in intracellular locations.

Differentiation of stress, metabolism, communication, and defense responses following transplantation

The biological complexity of allograft rejection and alloantigen-independent mechanisms is poorly understood. Therefore, we analyzed four components of the biological response following transplantation by global gene analysis. A comparative and kinetic approach was used to identify gene expression profiles. Biological processes were assigned to genes displaying the largest alterations in expression. Metabolism, stress response, and cell organization were the predominant, biological processes associated with ischemia and systemic stress. Innate and adaptive immune responses induced a transcriptional shift toward defense and cell communication. The kinetic analysis showed a shift from innate toward adaptive responses in the post-transplant course.

Serglycin proteoglycan expression and synthesis in embryonic stem cells

The serglycin proteoglycan is expressed in most hematopoietic cells and is packaged into secretory vesicles for constitutive or regulated secretion. We have now shown serglycin mRNA expression in undifferentiated murine embryonic stem (ES) cells and in embryoid bodies, and synthesis and secretion in undifferentiated ES cells. Serglycin was localized to ES cell cytoplasm by immunostaining. Serglycin mRNA is expressed in tal-1((-/-)) ES cells and embryoid bodies; tal-1((-/-)) mice cannot produce hematopoietic cells. Thus, ES serglycin expression is probably not associated with hematopoiesis. Serglycin expression was increased by treatment of ES cells with retinoic acid (RA) and dibutyryl cAMP (dbcAMP). The serglycin core protein obtained from control ES culture medium after chondroitinase digestion appears as a doublet. Only the lower Mr band is present in serglycin secreted from RA-treated and the higher Mr band in RA+dbcAMP-treated cells, suggesting that core protein structure is affected by differentiation.

Serglycin proteoglycan is sorted into zymogen granules of rat pancreatic acinar cells

Serglycin is known as a secretory granule proteoglyean in hematopoietic cells. In this study we identified a high-molecular-weight molecule in aggregated content proteins of zymogen granules of pancreatic acinar cells. The amino acid composition of the isolated protein showed high similarity to serglycin proteoglycan core protein. To confirm the expression of serglycin proteoglycan in pancreatic acinar cells we cloned the rat pancreas cDNA of serglycin core protein and detected the serglycin mRNA in pancreas tissue and AR4-2J cells by reverse transcription-PCR. In AR4-2J cells, transfected with serglycin fused to green fluorescent protein (EGFP), serglycin localized within a web-like pattern in the perinuclear space as well as with a punctate pattern distributed in the cytoplasm. The perinuclear structures colocalized with the Golgi membrane-associated protein p115 and the punctate structures with the secretory enzyme procarboxypeptidase A, indicating that the serglycin-EGFP fusion protein travels through compartments of the secretory pathway and is sorted into secretory granules. Using an antiserum against serglycin core protein immunofluorescence as well as immunogold electron microscopy analysis conrirmed the subcellular distribution of serglycin proteoglycan in zymogen granules of pancreatic acinar cells. To prevent glycosylation of serglycin core protein we incubated AR4-2J cells with 2 mM p-nitrophenyl-beta-D-xylopyranoside (PNP-xyloside), which serves as alternate substrate for glycosaminoglycan chain attachment. Furthermore, we deleted the serine/glycine repeat region in the serglycin core protein. In both approaches the transfected serglycin-EGFP fusion protein could be detected predominantly in perinuclear Golgi membrane structures, while in control cells the serglycin fusion protein was mostly sorted into the secretory granules. Additionally, we show that sorting of secretory enzymes like amylase

Monoclonal antibodies to CD44 epitopes on mouse endothelium

CD44 is a widely expressed, plasma membrane protein. Many molecular forms of CD44 are possible as it is encoded by a gene with multiple exons that can be alternatively spliced and its deduced protein sequence contains numerous glycosylation sites. Through its role as an adhesion molecule, CD44 is involved in many and diverse biological processes, including angiogenesis, lymphogenesis, wound healing, inflammation, and cancer metastasis. We have developed a new panel of rat monoclonal antibodies (MAbs) to murine CD44 by immunization with mouse lung endothelial cells (LEII cells). The antibodies were characterized using immunoprecipitation, mass spectrometry, competition binding, and cross Western blot experiments with MAb 133-13A, which recognizes CD44 expressed on tumor cells. The new MAbs recognize three distinct epitope groups. MAbs 531-2A and 531-32A compete for binding with the MAb 133-13A that was described previously. MAb 531-30A identifies a CD44 epitope found on low molecular weight forms expressed in vivo, while MAb 531-22A appears to recognize an epitope specific for endothelial cells. This novel panel of anti-CD44 antibodies has potential for investigating the role of CD44 in disease pathogenesis models in the mouse. They may be particularly useful for examining the role of endothelial cells in these models.

Analysis of the innate and adaptive phases of allograft rejection by cluster analysis of transcriptional profiles

Both clinical and experimental observations suggest that allograft rejection is a complex process with multiple components that are, at least partially, functionally redundant. Studies using graft recipients deficient in various genes including chemokines, cytokines, and other immune-associated genes frequently produce a phenotype of delayed, but not indefinitely prevented, rejection. Only a small subset of genetic deletions (for example, TCR(alpha) or beta, MHC I and II, B7-1 and B7-2, and recombinase-activating gene) permit permanent graft acceptance suggesting that rejection is orchestrated by a complex network of interrelated inflammatory and immune responses. To investigate this complex process, we have used oligonucleotide microarrays to generate quantitative mRNA expression profiles following transplantation. Patterns of gene expression were confirmed with real-time PCR data. Hierarchical clustering algorithms clearly differentiated the early and late phases of rejection. Self-organizing maps identified clusters of coordinately regulated genes. Genes up-regulated during the early phase included genes with prior biological functions associated with ischemia, injury, and Ag-independent innate immunity, whereas genes up-regulated in the late phase were enriched for genes associated with adaptive immunity.

Vascular genomics of the human brain

The microvasculature of the human brain plays an important role in the development and maintenance of the central nervous system and in the pathogenesis of brain diseases, and is the site of differential gene expression within the brain. However, human brain microvascular-specific genes may not be detected in whole-brain gene microarray because the volume of the brain microvascular endothelium is relatively small (0.1%) compared with the whole brain. Therefore, the differential gene expression within the human brain microvasculature was evaluated using suppression subtractive hybridization with RNA isolated from human brain microvessels. Gene identification was restricted to the first 71 clones that were differentially expressed at the brain microvasculature. Twenty of these were genes encoding proteins with known function that were involved in angiogenesis, neurogenesis, molecular transport, and maintenance of endothelial tight junctions or the cytoskeleton. Eighteen genes coding for proteins of an unknown function were identified, including five genes containing satellite DNA sequences. The results provide the initial outline of the genomics of the human brain microvasculature, and have implications for the identification of both targets for brain-specific drug transport and changes in microvascular gene expression in brain diseases.

The distribution pattern of the hyaluronan receptor CD44 during human tooth development

The aim was to investigate the expression pattern of the major cell-surface hyaluronan receptor CD44, as there are no existing data on its presence or absence in human dental structures at different developmental stages. Immunohistochemical localization of CD44 was studied using a monoclonal antibody, H3, that specifically recognizes an epitope in the common backbone of all CD44 isoforms. The dental lamina displayed a strong CD44 signal; the external enamel epithelium was negative. In the coronal region of the tooth germ the presecretory ameloblasts showed an intense reaction whereas the less differentiated inner enamel epithelial cells showed no signal at the cervical loop where they meet the external enamel epithelium. In the stellate reticulum a moderate reaction was detected. The secretory ameloblasts and the stratum intermedium showed a strong cell-surface CD44 signal. A strong signal was also observed on the odontoblasts and their processes. In the pulp, close to the odontoblastic layer, weak labelling was seen in the walls of capillary vessels. The distribution of CD44 in the human tooth germ corresponds to that of hyaluronan in most locations, suggesting that during tooth development this transmembrane protein plays an important part in hyaluronan-mediated events.

Promoter regulatory elements and DNase I-hypersensitive sites involved in serglycin proteoglycan gene expression in human erythroleukemia, CHRF 288-11, and HL-60 cells

We have compared regulation of the serglycin gene in human erythroleukemia (HEL) and CHRF 288-11 cells, which have megakaryocytic characteristics, with promyelocytic HL-60 cells. Deletion constructs were prepared from the region -1123/+42 to -20/+42, and putative regulatory sites were mutated. In all three cell lines, the two major regulatory elements for constitutive expression were the (-80)ets site and the cyclic AMP response element (CRE) half-site at -70. A protein from HEL and CHRF, but not HL60, nuclear extracts bound to the (-80)ets site. Another protein from all three cell lines bound to the (-70)CRE. Phorbol 12-myristate 13-acetate (PMA) and dibutyryl cyclic AMP (dbcAMP) increased expression of the reporter in HEL cells 2.5-3- and 4.5-fold, respectively, from all constructs except those with (-70)CRE mutations. PMA virtually eliminated expression of serglycin mRNA and promoter constructs, but dbcAMP increased expression in HL-60 cells. The effects of PMA and dbcAMP on promoter expression correlated with mRNA expression. The strengths of two DNase I-hypersensitive sites in the 5'-flanking region and the first intron in all three cells correlated with relative endogenous serglycin mRNA expression. An additional DNase I-hypersensitive site in HL60 DNA in the first intron may be related to the high serglycin expression in HL60 relative to HEL or CHRF cells.

Use of suppression subtractive hybridization for differential gene expression in stroke: discovery of CD44 gene expression and localization in permanent focal stroke in rats

BACKGROUND AND PURPOSE

CD44 is a transmembrane glycoprotein involved in endothelial cell recognition, lymphocyte trafficking, and regulation of cytokine gene expression in inflammatory diseases. The present report describes the discovery of upregulated CD44 gene expression and its spatial and temporal distribution in the brain after focal stroke.

METHODS

Rats were subjected to permanent occlusion of the middle cerebral artery (MCAO). Suppression subtractive hybridization (SSH) strategy was used to identify differentially expressed genes. Northern blotting and real-time polymerase chain reaction were used to evaluate the expression of CD44 and hyaluronan synthase 2 (HAS-2) mRNA. Western blotting and immunohistochemistry were used to examine CD44 expression and cellular distribution.

RESULTS

CD44 upregulation after focal stroke was discovered by the SSH approach and confirmed by DNA sequencing. Northern blot using a pooled poly(A)+ RNA revealed 3 splice variants of CD44 mRNA, and their inducible expression started at 6 hours (5.3-fold increase over sham operation), peaked at 24 hours (28.6-fold increase), and persisted up to 72 hours (17.8-fold increase) after MCAO. A parallel induction profile of HAS-2 mRNA was observed in the ischemic brain tissue. The levels of CD44 were markedly elevated at 6 hours (1.8-fold increase over sham; n=3), 24 hours (2.9-fold, peak induction; P<0.01), and 72 hours (2.4-fold increase; P<0.05) after MCAO by means of Western analysis. Immunohistochemical and confocal microscopy confirmed that constitutive expression of CD44 is limited to microvessels in normal brain but is strongly induced after ischemia, where the immunoreactive signal mainly resided in endothelial cells and monocytes. Double-labeling immunohistochemistry demonstrated that a marked induction of CD44 in the ischemic lesion is dominantly located in microglia and a subset of macrophages.

CONCLUSIONS

The discovery of concomitant induction of CD44 and HAS-2 mRNA expression and the localization of CD44 in the microglia, macrophages, and microvessels of the ischemic brain tissue suggest that an active interaction between CD44 and hyaluronan may occur and play a role in the known inflammatory response and tissue remodeling after stroke.

Synthesis, secretion, and subcellular localization of serglycin proteoglycan in human endothelial cells

The serglycin proteoglycan is best known as a hematopoietic cell granule proteoglycan. It has been found that serglycin is synthesized by endothelial cells, is localized to cytoplasmic vesicles, and is constitutively secreted. Serglycin messenger RNA in human umbilical vein endothelial cells (HUVECs) and cultured human aortic endothelial cells was detected by reverse transcription-polymerase chain reaction. (35)S-sulfate-labeled secreted and intracellular proteoglycans were analyzed. It was found that 85% of the proteoglycans synthesized during culture were secreted. A core protein of the appropriate size for serglycin was detected by analysis of the chondroitinase-digested (35)S-sulfate-labeled HUVEC proteoglycans. This was the major core protein of the secreted chondroitin sulfate proteoglycans. Recombinant serglycin core protein was used to generate an antibody in chickens. A core protein identified by Western blotting of chondroitinase digests of HUVEC proteoglycans corresponded to the major (35)S-sulfate- labeled core protein. Identical results were obtained with 2 hematopoietic cell lines. Cyto-immunofluorescence showed cytoplasmic vesicular and perinuclear labeling in hematopoietic cells and HUVECs. The serglycin-containing vesicles in HUVECs are distinct from the Weibel-Palade bodies, which contain von Willebrand factor. Confocal microscopy showed that tissue plasminogen activator was distributed similarly to serglycin. Serglycin may be important for the function of these vesicles and, once secreted, for the modulation of the activity of their constituents.

CD39 modulates IL-1 release from activated endothelial cells

The activation of endothelial cells (EC) and monocyte-macrophages (M&phi;) by lipopolysaccharide (LPS) is considered an important element of the vascular injury observed in endotoxemia. Interleukin-1 (IL-1) beta release from M&phi; in response to LPS, appears to be mediated by the autocrine/paracrine release of ATP via P2X7 receptor activation. In EC, similar nucleotide-mediated signaling pathways may be influenced by high levels of expression of CD39, the vascular nucleoside triphosphate diphosphohydrolase (NTPDase; ENTPD I). To determine whether CD39 modulates ATP-mediated release of IL-1 from EC, we stimulated human EC with LPS and measured levels of ATP secretion and IL-1 release. LPS triggered ATP secretion from EC that was soon followed by IL-1alpha release. Overexpression of CD39 following infection with recombinant CD39 adenoviral vectors (AdCD39) abrogated the initial phase of ATP secretion and inhibited IL-1alpha release; comparable results were obtained with soluble NTPDase. These data demonstrate that CD39/NTPDase modulates IL-1alpha release from LPS stimulated human EC.