CD34 and CD43 inhibit mast cell adhesion and are required for optimal mast cell reconstitution

Staphylococcal superantigen-like protein 3 triggers murine mast cell adhesion by binding to CD43 and augments mast cell activation

Staphylococcus aureus is a noteworthy pathogen in allergic diseases, as four staphylococcal exotoxins activate mast cells, a significant contributor to inflammation, in an IgE-independent manner. Although the adhesion of mast cells is an essential process for their immune responses, only a small number of exotoxins have been reported to affect the process. Here, we demonstrated that staphylococcal superantigen-like (SSL) 3, previously identified as a toll-like receptor 2 agonist, induced the adhesion of murine bone marrow-derived mast cells to culture substratum. SSL3-induced adhesion was mediated by fibronectin in an Arg-Gly-Asp (RGD) sequence-dependent manner, suggesting the integrins were involved in the process. Additionally, SSL3 was found to bind to an anti-adhesive surface protein CD43. SSL3 induced the adhesion of HEK293 cells expressing exogenous CD43, suggesting that CD43 is the target molecule for adhesion induced by SSL3. Evaluation of SSL3-derived mutants showed that the C-terminal region (253-326), specifically T285 and H307, are necessary to induce adhesion. SSL3 augmented the IL-13 production of mast cells in response to immunocomplex and SSL12. These findings reveal a novel function of SSL3, triggering cell adhesion and enhancing mast cell activation. This study would clarify the correlation between S. aureus and allergic diseases such as atopic dermatitis.

Differential expression of mast cells in the small airways and alveolar septa of current smokers and patients with small airway disease and COPD

Background

COPD patients suffer from dysregulated and suppressed immune functionality, determined by their loss of degranulating capacity. Here we provide crucial information on the presence of degranulated mast cells (MCs) in COPD airways and demonstrate their relationship to lung physiology and airway remodelling.

Methods

Small airway lung resections from non-smoking controls (NC), normal lung function smokers (NLFS), small airway disease (SAD), and mild-to-moderate COPD current smokers (COPD-CS) and ex-smokers (COPD-ES) were dual immuno-stained with MC tryptase and degranulation marker lysosome-associated membrane protein (LAMP)-1. Total MCs, degranulating MCs and non-MCs were enumerated in small airway epithelium and subepithelium, and in alveolar septa.

Results

In the small airway wall subepithelial areas, COPD-CS and COPD-ES patients had significantly lower MCs than the NC group (p<0.05), although the numbers were considerably higher in the small airway epithelium (p<0.01). Degranulating non-MCs were higher in SAD (p<0.05) than in COPD in the small airway subepithelium. In contrast, there were significant increases in total MCs (degranulated and non-degranulated) and degranulated non-MCs in the alveolar septum of COPD patients compared with the NC group (p<001). The lower numbers of MCs in the subepithelium correlated with lower forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) and forced expiratory flow at 25-75% of FVC (FEF25-75%), higher smoking rates in COPD patients, and increased small airway wall thickness and extracellular matrix. The increase in MCs in the alveolar septum negatively correlated with FEF25-75%.

Conclusions

This study is the first to assess the differential pattern of MC, degranulating MC and non-MC populations in the small airways and alveoli of COPD patients. The spatial positioning of the MCs within the airways showed variable correlations with lung function.

Osimertinib Covalently Binds to CD34 and Eliminates Myeloid Leukemia Stem/Progenitor Cells

Osimertinib is a third-generation covalent EGFR inhibitor that is used in treating non-small cell lung cancer. First-generation EGFR inhibitors were found to elicit pro-differentiation effect on acute myeloid leukemia (AML) cells in preclinical studies, but clinical trials yielded mostly negative results. Here, we report that osimertinib selectively induced apoptosis of CD34+ leukemia stem/progenitor cells but not CD34- cells in EGFR-negative AML and chronic myeloid leukemia (CML). Covalent binding of osimertinib to CD34 at cysteines 199 and 177 and suppression of Src family kinases (SFK) and downstream STAT3 activation contributed to osimertinib-induced cell death. SFK and STAT3 inhibition induced synthetic lethality with osimertinib in primary CD34+ cells. CD34 expression was elevated in AML cells compared with their normal counterparts. Genomic, transcriptomic, and proteomic profiling identified mutation and gene expression signatures of patients with AML with high CD34 expression, and univariate and multivariate analyses indicated the adverse prognostic significance of high expression of CD34. Osimertinib treatment induced responses in AML patient-derived xenograft models that correlated with CD34 expression while sparing normal CD34+ cells. Clinical responses were observed in two patients with CD34high AML who were treated with osimertinib on a compassionate-use basis. These findings reveal the therapeutic potential of osimertinib for treating CD34high AML and CML and describe an EGFR-independent mechanism of osimertinib-induced cell death in myeloid leukemia.

SIGNIFICANCE

Osimertinib binds CD34 and selectively kills CD34+ leukemia cells to induce remission in preclinical models and patients with AML with a high percentage of CD34+ blasts, providing therapeutic options for myeloid leukemia patients.

Clinical Characteristics and Local Histopathological Modulators of Endometriosis and Its Progression

Endometriosis (E) and adenomyosis (A) are associated with a wide spectrum of symptoms and may present various histopathological transformations, such as the presence of hyperplasia, atypia, and malignant transformation occurring under the influence of local inflammatory, vascular and hormonal factors and by the alteration of tumor suppressor proteins and the inhibition of cell apoptosis, with an increased degree of lesion proliferation.

MATERIAL AND METHODS

This retrospective study included 243 patients from whom tissue with E/A or normal control uterine tissue was harvested and stained by histochemical and classical immunohistochemical staining. We assessed the symptomatology of the patients, the structure of the ectopic epithelium and the presence of neovascularization, hormone receptors, inflammatory cells and oncoproteins involved in lesion development. Atypical areas were analyzed using multiple immunolabeling techniques.

RESULTS

The cytokeratin (CK) CK7+/CK20- expression profile was present in E foci and differentiated them from digestive metastases. The neovascularization marker cluster of differentiation (CD) 34+ was increased, especially in areas with malignant transformation of E or A foci. T:CD3+ lymphocytes, B:CD20+ lymphocytes, CD68+ macrophages and tryptase+ mast cells were abundant, especially in cases associated with malignant transformation, being markers of the proinflammatory microenvironment. In addition, we found a significantly increased cell division index (Ki67+), with transformation and inactivation of tumor suppressor genes p53, B-cell lymphoma 2 (BCL-2) and Phosphatase and tensin homolog (PTEN) in areas with E/A-transformed malignancy.

CONCLUSIONS

Proinflammatory/vascular/hormonal changes trigger E/A progression and the onset of cellular atypia and malignant transformation, exacerbating symptoms, especially local pain and vaginal bleeding. These triggers may represent future therapeutic targets.

Extracellular vesicle-derived TP53BP1, CD34, and PBX1 from human peripheral blood serve as potential biomarkers for the assessment and prediction of vascular aging

BACKGROUND

Vascular aging is an important pathophysiological basis for the senescence of various organs and systems in the human body, and it is a common pathogenetic trigger for many chronic diseases in the elderly.

METHODS

The extracellular vesicles (EVs) from young and aged umbilical vein endothelial cells were isolated and identified by qPCR the differential expression levels of 47 mRNAs of genes closely related to aging in the two groups.

RESULTS

There were significant differences in the expression levels of 18 genes (we noted upregulation in PLA2G12A, TP53BP1, CD144, PDE11A, FPGT, SERPINB4, POLD1, and PPFIBP2 and downregulation in ATP2C2, ROBO2, RRM2, GUCY1B1, NAT1-14, VEGFR2, WTAPP1, CD146, DMC1, and GRIK2). Subsequent qPCR identification of the above-mentioned genes in PBMCs and plasma-EVs from the various age groups revealed that the trend in expression levels in peripheral blood plasma-EVs of the different age groups was approximately the same as that in PBMCs. Of these mRNAs, the expression of four genes-PLA2G12A, TP53BP1, OPRL1, and KIAA0895-was commensurate with increasing age. In contradistinction, the expression trend of four genes (CREG1, PBX1, CD34, and SLIT2) was inversely proportional to the increase in age. Finally, by taking their intersection, we determined that the expression of TP53BP1 was upregulated with increasing human age and that CD34 and PBX1 were downregulated with increasing age.

CONCLUSION

Our study indicates that human peripheral blood plasma-EV-derived TP53BP1, CD34, and PBX1 potentially comprise a noninvasive biomarker for assessing and predicting vascular aging.

CD34 Protein: Its expression and function in inflammation

CD34 has spear-headed the field of basic research and clinical transplantation since the first reports of its expression on hematopoietic stem cells (HSCs). Expressed in mice, humans, rats and other species, CD34 has been used for more than 40 years as a hematopoietic stem and progenitor cell marker. It was later found that muscle satellite cells and epidermal precursors can also be identified with the aid of CD34. Despite the usefulness of CD34 as a marker of HSCs, its overall purpose in animal physiology has remained unclear. This review recaptures CD34 structure, evolutionary conservation, proposed functions, and role in lung inflammation, to describe current research findings and to provide guidance for future studies on CD34.

CD34-Structure, Functions and Relationship with Cancer Stem Cells

The CD34 protein was identified almost four decades ago as a biomarker for hematopoietic stem cell progenitors. CD34 expression of these stem cells has been exploited for therapeutic purposes in various hematological disorders. In the last few decades, studies have revealed the presence of CD34 expression on other types of cells with non-hematopoietic origins, such as interstitial cells, endothelial cells, fibrocytes, and muscle satellite cells. Furthermore, CD34 expression may also be found on a variety of cancer stem cells. Nowadays, the molecular functions of this protein have been involved in a variety of cellular functions, such as enhancing proliferation and blocking cell differentiation, enhanced lymphocyte adhesion, and cell morphogenesis. Although a complete understanding of this transmembrane protein, including its developmental origins, its stem cell connections, and other functions, is yet to be achieved. In this paper, we aimed to carry out a systematic analysis of the structure, functions, and relationship with cancer stem cells of CD34 based on the literature overview.

Role of CD34 in inflammatory bowel disease

Inflammatory bowel disease (IBD) is caused by a variety of pathogenic factors, including chronic recurrent inflammation of the ileum, rectum, and colon. Immune cells and adhesion molecules play an important role in the course of the disease, which is actually an autoimmune disease. During IBD, CD34 is involved in mediating the migration of a variety of immune cells (neutrophils, eosinophils, and mast cells) to the inflammatory site, and its interaction with various adhesion molecules is involved in the occurrence and development of IBD. Although the function of CD34 as a partial cell marker is well known, little is known on its role in IBD. Therefore, this article describes the structure and biological function of CD34, as well as on its potential mechanism in the development of IBD.

The immune cell profile of the developing rat brain

Little is known about the peripheral immune cell (PIC) profile of the developing brain despite growing appreciation for these cells in the mature nervous system. To address this gap, the PIC profile, defined as which cells are present, where they are located, and for how long, was examined in the developing rat using spectral flow cytometry. Select regions of the rat brain (cerebellum, hippocampus, and hypothalamus) were examined at embryonic day 20, and postnatal days 0, 7 and 16. At their peak (E20), PICs were most abundant in the cerebellum, then the hippocampus and hypothalamus. Within the PIC pool, monocytes were most prevalent in all regions and time points, and shifted from being majority classical at E20 to non-classical by PN7. T cells increased over time, and shifted from majority cytotoxic to T-helper cells by PN7. This suggests the PIC profile transitions from reactive to adaptive and surveilling in the second postnatal week. NK cells and mast cells increased temporarily, and mast cells were restricted to the hippocampus and hypothalamus, suggesting they may play a specific role in the development of those regions. Mimicking a viral infection by administration of Poly I:C increased the influx of PICs into the neonatal brain, particularly of NK cells and in the case of males only, non-classical monocytes. This work provides a map for researchers as they study immune cell contributions to healthy and pathological brain development.

Specific Local Predictors That Reflect the Tropism of Endometriosis-A Multiple Immunohistochemistry Technique

Ectopic endometrial epithelium associates a wide spectrum of symptomatology. Their evolution can be influenced by inflammatory and vascular changes, that affect not only the structure and cell proliferation rate, but also symptoms. This prospective study involved tissue samples from surgically treated patients, stained using classical histotechniques and immunohistochemistry. We assessed ectopic endometrial glands (CK7+, CK20-), adjacent blood vessels (CD34+), estrogen/progesterone hormone receptors (ER+, PR+), inflammatory cells (CD3+, CD20+, CD68+, Tryptase+), rate of inflammatory cells (Ki67+) and oncoproteins (BCL2+, PTEN+, p53+) involved in the development of endometriosis/adenomyosis. A CK7+/CK20- expression profile was present in the ectopic epithelium and differentiated it from digestive metastases. ER+/PR+ were present in all cases analyzed. We found an increased vascularity (CD34+) in the areas with abdominal endometriosis and CD3+-:T-lymphocytes, CD20+-:B-lymphocytes, CD68+:macrophages, and Tryptase+: mastocytes were abundant, especially in cases with adenomyosis as a marker of proinflammatory microenvironment. In addition, we found a significantly higher division index-(Ki67+) in the areas with adenomyosis, and inactivation of tumor suppressor genes-p53+ in areas with neoplastic changes. The inflammatory/vascular/hormonal mechanisms trigger endometriosis progression and neoplastic changes increasing local pain. Furthermore, they may represent future therapeutic targets. Simultaneous-multiple immunohistochemical labelling represents a valuable technique for rapidly detecting cellular features that facilitate comparative analysis of the studied predictors.

Mycobacterium bovis Wild-Type BCG or Recombinant BCG Secreting Murine IL-18 (rBCG/IL-18) Strains in Driving Immune Responses in Immunocompetent or Immunosuppressed Mice

Mycobacterium tuberculosis infections remain a global health problem in immunosuppressed patients. The effectiveness of BCG (Bacillus Calmette−Guérin), an anti-tuberculosis vaccine, is unsatisfactory. Finding a new vaccine candidate is a priority. We compared numerous immune markers in BCG-susceptible C57BL/6 and BCG-resistant C3H mice who had been injected with 0.9% NaCl (control) or with wild-type BCG or recombinant BCG secreting interleukin (IL)-18 (rBCG/IL-18) and in immunized mice who were immunocompromised with cyclophosphamide (CTX). The inoculation of rBCG/IL-18 in immunocompetent mice increased the percentage of bone marrow myeloblasts and promyelocytes, which were further elevated in the rBCG/IL-18/CTX-treated mice: C57BL/6 mice—3.0% and 11.4% (control) vs. 18.6% and 42.4%, respectively; C3H mice—1.1% and 7.7% (control) vs. 18.4% and 44.9%, respectively, p < 0.05. The bone marrow cells showed an increased mean fluorescence index (MFI) in the CD34 adhesion molecules: C57BL/6 mice—4.0 × 103 (control) vs. 6.2 × 103; C3H mice—4.0 × 103 (control) vs. 8.0 × 103, p < 0.05. Even in the CTX-treated mice, the rBCG/IL-18 mobilized macrophages for phagocytosis, C57BL/6 mice—4% (control) vs. 8%; C3H mice—2% (control) vs. 6%, and in immunocompetent mice, C57BL/6 induced the spleen homing of effector memory CD4+ and CD8+ T cells (TEM), 15% (control) vs. 28% and 8% (control) vs. 22%, respectively, p < 0.05. In conclusion, rBCG/IL-18 effectively induced selected immune determinants that were maintained even in immunocompromised mice.

Immunoprofiling Reveals Novel Mast Cell Receptors and the Continuous Nature of Human Lung Mast Cell Heterogeneity

Background

Immunohistochemical analysis of granule-associated proteases has revealed that human lung mast cells constitute a heterogeneous population of cells, with distinct subpopulations identified. However, a systematic and comprehensive analysis of cell-surface markers to study human lung mast cell heterogeneity has yet to be performed.

Methods

Human lung mast cells were obtained from lung lobectomies, and the expression of 332 cell-surface markers was analyzed using flow cytometry and the LEGENDScreen™ kit. Markers that exhibited high variance were selected for additional analyses to reveal whether they were correlated and whether discrete mast cell subpopulations were discernable.

Results

We identified the expression of 102 surface markers on human lung mast cells, 23 previously not described on mast cells, of which several showed high continuous variation in their expression. Six of these markers were correlated: SUSD2, CD49a, CD326, CD34, CD66 and HLA-DR. The expression of these markers was also correlated with the size and granularity of mast cells. However, no marker produced an expression profile consistent with a bi- or multimodal distribution.

Conclusions

LEGENDScreen analysis identified more than 100 cell-surface markers on mast cells, including 23 that, to the best of our knowledge, have not been previously described on human mast cells. The comprehensive expression profiling of the 332 surface markers did not identify distinct mast cell subpopulations. Instead, we demonstrate the continuous nature of human lung mast cell heterogeneity.

Mast cell surfaceome characterization reveals CD98 heavy chain is critical for optimal cell function

BACKGROUND

Mast cells are involved in many distinct pathologic conditions, suggesting that they recognize and respond to various stimuli and thus require a rich repertoire of cell surface proteins. However, mast cell surface proteomes have not been comprehensively characterized.

OBJECTIVE

We aimed to further characterize the mast cell surface proteome to obtain a better understanding of how mast cells function in health and disease.

METHODS

We enriched for glycosylated surface proteins expressed in mouse bone marrow-derived cultured mast cells (BMCMCs) and identified them using mass spectrometry analysis. The presence of novel surface proteins in mast cells was validated by real-time quantitative PCR and flow cytometry analysis in BMCMCs and peritoneal mast cells (PMCs). We developed a clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) gene editing approach to disrupt genes of interest in BMCMCs.

RESULTS

The glycoprotein enrichment approach resulted in the identification of 1270 proteins in BMCMCs, 378 of which were localized to the plasma membrane. The most common protein classes among plasma membrane proteins were small GTPases, receptors, and transporters. One such cell surface protein was CD98 heavy chain (CD98hc), encoded by the Slc3a2 gene. Slc3a2 gene disruption resulted in a significant reduction in CD98hc expression, adhesion, and proliferation.

CONCLUSIONS

Glycoprotein enrichment coupled with mass spectrometry can be used to identify novel surface molecules in mast cells. Moreover, CD98hc plays an important role in mast cell function.

Trial watch: Prognostic and predictive value of the immune infiltrate in cancer

Solid tumors are constituted of a variety of cellular components, including bona fide malignant cells as well as endothelial, structural and immune cells. On one hand, the tumor stroma exerts major pro-tumorigenic and immunosuppressive functions, reflecting the capacity of cancer cells to shape the microenvironment to satisfy their own metabolic and immunological needs. On the other hand, there is a component of tumor-infiltrating leucocytes (TILs) that has been specifically recruited in the attempt to control tumor growth. Along with the recognition of the critical role played by the immune system in oncogenesis, tumor progression and response to therapy, increasing attention has been attracted by the potential prognostic and/or predictive role of the immune infiltrate in this setting. Data from large clinical studies demonstrate indeed that a robust infiltration of neoplastic lesions by specific immune cell populations, including (but not limited to) CD8⁺ cytotoxic T lymphocytes, Th1 and Th17 CD4⁺ T cells, natural killer cells, dendritic cells, and M1 macrophages constitutes an independent prognostic indicator in several types of cancer. Conversely, high levels of intratumoral CD4⁺CD25⁺FOXP3⁺ regulatory T cells, Th2 CD4⁺ T cells, myeloid-derived suppressor cells, M2 macrophages and neutrophils have frequently been associated with dismal prognosis. So far, only a few studies have addressed the true predictive potential of TILs in cancer patients, generally comforting the notion that—at least in some clinical settings—the immune infiltrate can reliably predict if a specific patient will respond to therapy or not. In this Trial Watch, we will summarize the results of clinical trials that have evaluated/are evaluating the prognostic and predictive value of the immune infiltrate in the context of solid malignancies.

CD34 positive cells isolated from traumatized human skeletal muscle require the CD34 protein for multi-potential differentiation

The CD34 protein is regarded as a marker of stem cells from multiple origins. Recently a mesenchymal progenitor CD34 positive cell identified from traumatized human skeletal muscle demonstrates differentiation capability into vascular endothelial cells, osteoblasts and adipocytes. Here they were treated with a small inhibitory RNA for CD34, which significantly reduced the cellular level of the CD34 protein. These treated cells had a reduced capacity to proliferate, and migrate. They were both unable to differentiation down multiple pathways and to undergo vascular endothelial differentiation as reflected by a lack of expression of VE cadherin, Tie 2 and CD31. Additionally the cells were unable to form tube-like structures in an endothelial tube assay. These treated cells were also unable to undergo osteogenesis, as revealed by lack of alizarin red and alkaline phosphatase staining and were unable to undergo adipogenesis as revealed by lack of oil red O staining. Finally, when CD34 was expressed in cells lacking this protein, the cells were able to undergo vascular endothelial differentiation as revealed by expression of Tie2, VE-cadherin and CD31. These data indicate that in cells derived from traumatized muscle the CD34 protein is required for enhanced proliferation, migration and differentiation down multiple pathways.

A sticky wicket: Defining molecular functions for CD34 in hematopoietic cells

The CD34 cell surface antigen is widely expressed in tissues on cells with progenitor-like properties and on mature vascular endothelia. In adult human bone marrow, CD34 marks hematopoietic stem and progenitor cells (HSPCs) starting from the bulk of hematopoietic stem cells with long-term repopulating potential (LT-HSCs) throughout expansion and differentiation of oligopotent and unipotent progenitors. CD34 protein surface expression is typically lost as cells mature into terminal effectors. Because of this expression pattern of HSPCs, CD34 has had a central role in the evaluation or selection of donor graft tissue in HSC transplant (HSCT). Given its clinical importance, it is surprising that the biological functions of CD34 are still poorly understood. This enigma is due, in part, to CD34's context-specific role as both a pro-adhesive and anti-adhesive molecule and its potential functional redundancy with other sialomucins. Moreover, there are also critical differences in the regulation of CD34 expression on HSPCs in humans and experimental mice. In this review, we highlight some of the more well-defined functions of CD34 in HSPCs with a focus on proposed functions most relevant to HSCT biology.

CD34 cells in somatic, regenerative and cancer stem cells: Developmental biology, cell therapy, and omics big data perspective

The transmembrane phosphoglycoprotein protein CD34 has conventionally been regarded as a marker for hematopoietic progenitors. Its expression on these cells has been leveraged for cell therapy applications in various hematological disorders. More recently, the expression of CD34 has also been reported on cells of nonhematopoietic origin. The list includes somatic cells such as endothelial cells, fibrocytes and interstitial cells and regenerative stem cells such as corneal keratocytes, muscle satellite cells, and muscle-derived stem cells. Furthermore, its expression on some cancer stem cells (CSCs) has also been reported. Till date, the functional roles of this molecule have been implicated in a multitude of cellular processes including cell adhesion, signal transduction, and maintenance of progenitor phenotype. However, the complete understanding about this molecule including its developmental origins, its embryonic connection, and associated functions is far from complete. Here, we review our present understanding of the structure and putative functions of the CD34 molecule based upon our literature survey. We also probed various biological databases to retrieve data related to the expression and associated molecular functions of CD34. Such information, upon synthesis, is hence likely to provide the suitability of such cells for cell therapy. Moreover, we have also covered the existing cell therapy and speculated cell therapy applications of CD34⁺ cells isolated from various lineages. We have also attempted here to speculate the role(s) of CD34 on CSCs. Finally, we discuss number of large-scale proteomics and transcriptomics studies that have been performed using CD34⁺ cells.

Activation of PKC induces leukocyte adhesion by the dephosphorylation of ERM

Although circulating leukocytes are non-adherent cells, they also undergo adhesion in response to external stimuli. To elucidate this switch mechanism, we investigated PMA-induced cell adhesion in myelomonocytic KG-1 cells. PMA induced microvillius collapse, decrease of cell surface rigidity and exclusion of sialomucin from adhesion sites. All these adhesion-contributing events are linked to dephosphorylation of Ezrin/Radixin/Moesin (ERM) proteins. Indeed, PMA-treatment induced quick decrease of phosphorylated ERM proteins, while expression of Moesin-T558D, a phospho-mimetic mutant, inhibited PMA-induced cell adhesion. PMA-induced cell adhesion and ERM-dephophorylation were inhibited by PKC inhibitors or by a phosphatase inhibitor, indicating the involvement of PKC and protein phophatase in these processes. In peripheral T lymphocytes, ERM-dephosphorylation by adhesion-inducing stimuli was inhibited by a PKC inhibitor. Combined, these findings strongly suggest that external stimuli induce ERM-dephosphorylation via the activation of PKC in leukocytes and that ERM-dephosphorylation leads to leukocytes' adhesion.

Sialomucin and phosphorylated-ERM are inhibitors for cadherin-mediated aggregate formation

Cell adhesion is mediated by adhesion molecules, but also regulated by adhesion inhibitory molecules. Molecules such as leukocyte sialomucin and phosphorylated-Ezrin/Radixin/Moesin (ERM) inhibit cell-substratum adhesion. Here we show that these adhesion inhibitory molecules also inhibit aggregate formation of adherent cells in suspension culture. Expression of sialomucin, CD43 or CD34, inhibited formation of packed aggregates in HEK293T cells. Deletion mutant analysis and enzymatic cleavage indicated the significance of the extracellular sialomucin domain for this inhibition. Meanwhile, phosphorylated-ERM were decreased coincidently with aggregate formation. Combined with the inhibition of aggregate formation by the expression of phospho-mimetic Moesin mutant (Moesin-T558D), phosphorylated-ERM are inhibitors for aggregate formation. Increase of phosphorylated-ERM by CD43 and sialomucin-dependence of Moesin-T558D's inhibition indicate that sialomucin and phosphorylated-ERM collaborate to inhibit aggregate formation. Because aggregate formation of HEK293T cells is mediated by N-cadherin, sialomucin and phosphorylated-ERM inhibit cadherin-mediated cell-cell adhesion. Thus, sialomucin and phosphorylated-ERM are inhibitors for both cell-cell adhesion and cell-substratum adhesion, and regulation of these inhibitory molecules is essential for cell adhesion.

Immunohistochemical expression of P53, Ki-67, and CD34 in psoriasis and psoriasiform dermatitis

BACKGROUND

Psoriasis is the prime example of psoriasiform tissue pattern and should be differentiated from other psoriasiform dermatoses both clinically and histopathologically.

AIM

To evaluate immunohistochemical expression of P53, Ki-67, and CD34 in psoriasis and psoriasiform dermatitis for diagnostic purposes.

METHODS

An analytical cross-sectional study was performed on the paraffin blocks of 60 psoriasis and 31 psoriasiform dermatitis patients between 2014 and 2017. The selected formalin-fixed paraffin-embedded tissues from each biopsy specimen were cut into 4-micron sections. Initial sections were stained by hematoxylin and eosin staining. Primary antihuman antibodies against P53, Ki-67, and CD34 were applied. Positive control samples for biomarkers were received from former strongly positive samples of papillary endothelial hyperplasia, high grade lymphoma, and breast ductal carcinoma for CD34, Ki-67, and P53, respectively.

RESULTS

Out of 60 psoriasis patients, 56.7% were men, with the mean age of 36.8 years. From 31 psoriasiform patients, 45.2% were men, with the mean age of 37.5 years. Both groups were matched in terms of sex and age. The mean staining of three markers was more significant in psoriasiform dermatitis than psoriasis.

CONCLUSION

In spite of some other researches, the present study showed expression of P53, Ki-67, and CD34 biomarkers were significantly higher in psoriasiform dermatitis than psoriasis.

Glycan Markers of Human Stem Cells Assigned with Beam Search Arrays

Glycan antigens recognized by monoclonal antibodies have served as stem cell markers. To understand regulation of their biosynthesis and their roles in stem cell behavior precise assignments are required. We have applied state-of-the-art glycan array technologies to compare the glycans bound by five antibodies that recognize carbohydrates on human stem cells. These are: FC10.2, TRA-1-60, TRA-1-81, anti-i and R-10G. Microarray analyses with a panel of sequence-defined glycans corroborate that FC10.2, TRA-1-60, TRA-1-81 recognize the type 1-(Galβ-3GlcNAc)-terminating backbone sequence, Galβ-3GlcNAcβ-3Galβ-4GlcNAcβ-3Galβ-4GlcNAc, and anti-i, the type 2-(Galβ-4GlcNAc) analog, Galβ-4GlcNAcβ-3Galβ-4GlcNAcβ-3Galβ-4GlcNAc, and we determine substituents they can accommodate. They differ from R-10G, which requires sulfate. By Beam Search approach, starting with an antigen-positive keratan sulfate polysaccharide, followed by targeted iterative microarray analyses of glycan populations released with keratanases and mass spectrometric monitoring, R-10G is assigned as a mono-sulfated type 2 chain with 6-sulfation at the penultimate N-acetylglucosamine, Galβ-4GlcNAc(6S)β-3Galβ-4GlcNAcβ-3Galβ-4GlcNAc. Microarray analyses using newly synthesized glycans corroborate the assignment of this unique determinant raising questions regarding involvement as a ligand in the stem cell niche.

MiR-665 aggravates heart failure via suppressing CD34-mediated coronary microvessel angiogenesis

BACKGROUND

Heart failure (HF) is a major public health problem worldwide. The development of HF was related to coronary microvessel dysfunction. Whether miRNAs participate in HF by regulating coronary microvessel function remain unclear.

METHODS

The potential targets of miR-665 were predicted by rnahybrid software, then verified through anti-Ago2 co-immunoprecipitation, Western blotting and luciferase reporter assays. rAAV9 system was used to manipulate the expression of miR-665 in vivo.

RESULTS

Significant increase of miR-665 was observed in endothelial cells of human heart with heart failure. In vitro over-expression of miR-665 in endothelial cells resulted in decreased proliferation but enhanced apoptosis. rAAV-mediated delivery of miR-665 reduced coronary microvessel angiogenesis and cardiac microvessel density, then further impaired cardiac function in vivo. Furthermore, CD34 was confirmed as one of the miR-665 targets. Consistently, re-expression of CD34 attenuated miR-665-mediated damage effects in vitro and in vivo. We also found that Sp1 regulated miR-665 expression in endothelial cells.

CONCLUSION

Our findings demonstrated that miR-665 played an important role in heart failure via damaging coronary microvessel angiogenesis, and suggested that miRNA-based therapeutics may protect against coronary microvessel dysfunction and heart failure.

Genetic and Imaging Approaches Reveal Pro-Inflammatory and Immunoregulatory Roles of Mast Cells in Contact Hypersensitivity

Contact hypersensitivity (CHS) is a common T cell-mediated skin disease induced by epicutaneous sensitization to haptens. Mast cells (MCs) are widely deployed in the skin and can be activated during CHS responses to secrete diverse products, including some with pro-inflammatory and anti-inflammatory functions. Conflicting results have been obtained regarding pathogenic versus protective roles of MCs in CHS, and this has been attributed in part to the limitations of certain models for studying MC functions in vivo. This review discusses recent advances in the development and analysis of mouse models to investigate the roles of MCs and MC-associated products in vivo. Notably, fluorescent avidin-based two-photon imaging approaches enable in vivo selective labeling and simultaneous tracking of MC secretory granules (e.g., during MC degranulation) and MC gene activation by real-time longitudinal intravital microscopy in living mice. The combination of such genetic and imaging tools has shed new light on the controversial role played by MCs in mouse models of CHS. On the one hand, they can amplify CHS responses of mild severity while, on the other hand, can limit the inflammation and tissue injury associated with more severe or chronic models, in part by representing an initial source of the anti-inflammatory cytokine IL-10.

Not just a marker: CD34 on human hematopoietic stem/progenitor cells dominates vascular selectin binding along with CD44

CD34 is routinely used to identify and isolate human hematopoietic stem/progenitor cells (HSPCs) for use clinically in bone marrow transplantation, but its function on these cells remains elusive. Glycoprotein ligands on HSPCs help guide their migration to specialized microvascular beds in the bone marrow that express vascular selectins (E- and P-selectin). Here, we show that HSPC-enriched fractions from human hematopoietic tissue expressing CD34 (CD34^pos) bound selectins, whereas those lacking CD34 (CD34^neg) did not. An unbiased proteomics screen identified potential glycoprotein ligands on CD34^pos cells revealing CD34 itself as a major vascular selectin ligand. Biochemical and CD34 knockdown analyses highlight a key role for CD34 in the first prerequisite step of cell migration, suggesting that it is not just a marker on these cells. Our results also entice future potential strategies to investigate the glycoforms of CD34 that discriminate normal HSPCs from leukemic cells and to manipulate CD34^neg HSPC-enriched bone marrow or cord blood populations as a source of stem cells for clinical use.

Loss of Vascular CD34 Results in Increased Sensitivity to Lung Injury

Survival during lung injury requires a coordinated program of damage limitation and rapid repair. CD34 is a cell surface sialomucin expressed by epithelial, vascular, and stromal cells that promotes cell adhesion, coordinates inflammatory cell recruitment, and drives angiogenesis. To test whether CD34 also orchestrates pulmonary damage and repair, we induced acute lung injury in wild-type (WT) and Cd34^-/- mice by bleomycin administration. We found that Cd34^-/- mice displayed severe weight loss and early mortality compared with WT controls. Despite equivalent early airway inflammation to WT mice, CD34-deficient animals developed interstitial edema and endothelial delamination, suggesting impaired endothelial function. Chimeric Cd34^-/- mice reconstituted with WT hematopoietic cells exhibited early mortality compared with WT mice reconstituted with Cd34^-/- cells, supporting an endothelial defect. CD34-deficient mice were also more sensitive to lung damage caused by influenza infection, showing greater weight loss and more extensive pulmonary remodeling. Together, our data suggest that CD34 plays an essential role in maintaining vascular integrity in the lung in response to chemical- and infection-induced tissue damage.

Human haematopoietic stem cell development: from the embryo to the dish

Haematopoietic stem cells (HSCs) emerge during embryogenesis and give rise to the adult haematopoietic system. Understanding how early haematopoietic development occurs is of fundamental importance for basic biology and medical sciences, but our knowledge is still limited compared with what we know of adult HSCs and their microenvironment. This is particularly true for human haematopoiesis, and is reflected in our current inability to recapitulate the development of HSCs from pluripotent stem cells in vitro In this Review, we discuss what is known of human haematopoietic development: the anatomical sites at which it occurs, the different temporal waves of haematopoiesis, the emergence of the first HSCs and the signalling landscape of the haematopoietic niche. We also discuss the extent to which in vitro differentiation of human pluripotent stem cells recapitulates bona fide human developmental haematopoiesis, and outline some future directions in the field.

Light Guided In-vivo Activation of Innate Immune Cells with Photocaged TLR 2/6 Agonist

The complexity of the immune system creates challenges in exploring its importance and robustness. To date, there have been few techniques developed to manipulate individual components of the immune system in an in vivo environment. Here we show a light-based dendritic cell (DC) activation allowing spatial and temporal control of immune activation in vivo. Additionally, we show time dependent changes in RNA profiles of the draining lymph node, suggesting a change in cell profile following DC migration and indicating that the cells migrating have been activated towards antigen presentation.

Matrix-Embedded Endothelial Cells Attain a Progenitor-Like Phenotype

Culture of endothelial cells (ECs) embedded in 3D scaffolds of denatured collagen has shown tremendous therapeutic potential in clinical trials of tissue repair. It is postulated that these matrix-embedded ECs (MEECs) attain a differential phenotype similar to early progenitor forms, which cannot be attained in 2D culture. MEECs are compared to 2D-ECs and endothelial progenitor cells (EPCs) by secretome, phenotype, and genetic fingerprint, and are found to be altered from 2D-ECs on all levels, adopting an EPC-like phenotype. This manifests in elevation of CD34 expression-a progenitor cell marker-and protein secretion and gene expression pro-files that are similar to EPCs. Even more striking is that EPCs in 2D lose their phenotype, evident by the loss of CD34 expression, but are able to regain expression over time when embedded in the same 3D matrices, suggesting that future in vitro EPC work should use ME-EPCs to recapitulate in vivo phenotype. These findings elucidate the relationship between EPCs and the substratum-dependent regulation imparted by ECs which is critical to understand in order to optimize MEEC therapy and propel it into the clinic.

Cancer stem cell marker glycosylation: Nature, function and significance

Glycans are essential for the maintenance of normal biological function, with alterations in glycan expression being a hallmark of cancer. Cancer stem cells (CSCs) are a subset of cells within a tumour capable of self-renewal, cellular differentiation and resistances to conventional therapies. As is the case with stem cells, marker proteins present on the cell surface are frequently used to identify and enrich CSCs, with the expression of these markers statistical correlating with the likelihood of cancer recurrence and overall patient survival. As such CSC markers are of high clinical relevance. The majority of markers currently used to identify CSC populations are glycoproteins, and although the diverse biological roles for many of these markers are known, the nature and function of the glycan moiety on these glycoproteins remains to be fully elucidated. This mini-review summarises our current knowledge regarding the types and extent of CSC marker glycosylation, and the various roles that these glycans play in CSC biology, including in mediating cell adhesion, metastasis, evading apoptosis, tear shear resistance, tumour growth, maintaining pluripotency, self-renewal, trafficking, maintaining stability, maintaining enzymatic activity and aiding epithelial mesenchymal transitioning. Given that CSCs markers have multiple diverse biological functions, and are potentially of significant diagnostic and therapeutic benefit the search for new markers that are uniquely expressed on CSCs is vital to selectively target/identify this subset of cancer cells. As such we have also outlined how high-throughput lectin microarrays can be used to successfully profile the glycosylation status of CSC and to identify glyco-markers unique to CSCs.

Biomarkers of Human Pluripotent Stem Cell-Derived Cardiac Lineages

Human pluripotent stem cells (hPSCs) offer a practical source for the de novo generation of cardiac tissues and a unique opportunity to investigate cardiovascular lineage commitment. Numerous strategies have focused on the in vitro production of cardiomyocytes, smooth muscle, and endothelium from hPSCs. However, these differentiation protocols often yield undesired cell types. Thus, establishing a set of stage-specific markers for pure cardiac subpopulations will assist in defining the hierarchy of cardiac differentiation, aid in the development of cellular therapy, and facilitate drug screening and disease modeling. The recent characterization of many such markers is enabling the isolation of major cardiac lineages and subpopulations from differentiating hPSCs. We provide here a comprehensive review detailing the suite of biomarkers used to differentiate cardiac lineages from mixed hPSC-derived populations.

Extracellular matrix and α5β1 integrin signaling control the maintenance of bone formation capacity by human adipose-derived stromal cells

Stromal vascular fraction (SVF) cells of human adipose tissue have the capacity to generate osteogenic grafts with intrinsic vasculogenic properties. However, adipose-derived stromal/stem cells (ASC), even after minimal monolayer expansion, display poor osteogenic capacity in vivo. We investigated whether ASC bone-forming capacity may be maintained by culture within a self-produced extracellular matrix (ECM) that recapitulates the native environment. SVF cells expanded without passaging up to 28 days (Unpass-ASC) deposited a fibronectin-rich extracellular matrix and displayed greater clonogenicity and differentiation potential in vitro compared to ASC expanded only for 6 days (P0-ASC) or for 28 days with regular passaging (Pass-ASC). When implanted subcutaneously, Unpass-ASC produced bone tissue similarly to SVF cells, in contrast to P0- and Pass-ASC, which mainly formed fibrous tissue. Interestingly, clonogenic progenitors from native SVF and Unpass-ASC expressed low levels of the fibronectin receptor α₅ integrin (CD49e), which was instead upregulated in P0- and Pass-ASC. Mechanistically, induced activation of α₅β₁ integrin in Unpass-ASC led to a significant loss of bone formation in vivo. This study shows that ECM and regulation of α₅β₁-integrin signaling preserve ASC progenitor properties, including bone tissue-forming capacity, during in vitro expansion.

CD34 Promotes Pathological Epi-Retinal Neovascularization in a Mouse Model of Oxygen-Induced Retinopathy

The sialomucins CD34 and podocalyxin (PODXL) are anti-adhesive molecules expressed at the luminal membrane of endothelial cells of small blood vessels and facilitate vascular lumen formation in the developing mouse aorta. CD34 transcript and protein levels are increased during human angiogenesis, its expression is particularly enriched on endothelial tip cell filopodia and CD34 is a marker for tip cells in vitro. Here, we investigated whether CD34 merely marks endothelial tip cells or has a functional role in tip cells and angiogenesis. We assessed that silencing CD34 in human microvascular endothelial cells has little effect on endothelial cell migration or invasion, but has a significant effect on vascular-endothelial growth factor-induced angiogenic sprouting activity in vitro. In vivo, the absence of CD34 reduced the density of filopodia on retinal endothelial tip cells in neonatal mice, but did not influence the overall architecture of the retinal vascular network. In oxygen-induced retinopathy, Cd34^-/- mice showed normal intra-retinal regenerative angiogenesis but the number of pathological epi-retinal neovascular tufts were reduced. We conclude that CD34 is not essential for developmental vascularization in the retina, but its expression promotes the formation of pathological, invasive vessels during neovascularization.

Interaction of extravillous trophoblast galectin-1 and mucin(s)-Is there a functional relevance?

In the course of embryo implantation extensive interaction of the trophoblast with uterine tissue is crucial for adequate trophoblast invasion. This interaction is highly controlled, and it has been pointed out that a specific glycocode and changes in glycosylation may be important for successful implantation and maintenance of pregnancy. Both uterine and trophoblast cells have been shown to express cell surface glycoconjugates and sugar binding proteins, such as mucins (MUC) and galectins (gals). An increasing number of studies have investigated potential candidates interacting in this process. However, knowledge about the biochemical nature of the interactions and their importance for trophoblast cell function, and, consequently, for pregnancy outcome are still lacking. This review is aimed at deliberating the possibility that mucins, as heavily glycosylated proteins, might be among the functionally relevant galectin ligands in human trophoblast, based on both published data and our original research.

In situ hematopoiesis: a regulator of TH2 cytokine-mediated immunity and inflammation at mucosal surfaces

Hematopoiesis refers to the development of blood cells in the body through the differentiation of pluripotent stem cells. Although hematopoiesis is a multifocal process during embryonic development, under homeostatic conditions it occurs exclusively within the bone marrow. There, a limited number of hematopoietic stem cells differentiate into a rapidly proliferating population of lineage-restricted progenitors that serve to replenish circulating blood cells. However, emerging reports now suggest that under inflammatory conditions, alterations in hematopoiesis that occur outside of the bone marrow appear to constitute a conserved mechanism of innate immunity. Moreover, recent reports have identified previously unappreciated pathways that regulate the egress of hematopoietic progenitor cells from the bone marrow, alter their activation status, and skew their developmental potential. These studies suggest that progenitor cells contribute to inflammatory response by undergoing in situ hematopoiesis (ISH). In this review, we highlight the differences between homeostatic hematopoiesis, which occurs in the bone marrow, and ISH, which occurs at mucosal surfaces. Further, we highlight factors produced at local sites of inflammation that regulate hematopoietic progenitor cell responses and the development of TH2 cytokine-mediated inflammation. Finally, we discuss the therapeutic potential of targeting ISH in preventing the development of inflammation at mucosal sites.

Concise review: evidence for CD34 as a common marker for diverse progenitors

CD34 is a transmembrane phosphoglycoprotein, first identified on hematopoietic stem and progenitor cells. Clinically, it is associated with the selection and enrichment of hematopoietic stem cells for bone marrow transplants. Due to these historical and clinical associations, CD34 expression is almost ubiquitously related to hematopoietic cells, and it is a common misconception that CD34-positive (CD34⁺) cells in nonhematopoietic samples represent hematopoietic contamination. The prevailing school of thought states that multipotent mesenchymal stromal cells (MSC) do not express CD34. However, strong evidence demonstrates CD34 is expressed not only by MSC but by a multitude of other nonhematopoietic cell types including muscle satellite cells, corneal keratocytes, interstitial cells, epithelial progenitors, and vascular endothelial progenitors. In many cases, the CD34⁺ cells represent a small proportion of the total cell population and also indicate a distinct subset of cells with enhanced progenitor activity. Herein, we explore common traits between cells that express CD34, including associated markers, morphology and differentiation potential. We endeavor to highlight key similarities between CD34⁺ cells, with a focus on progenitor activity. A common function of CD34 has yet to be elucidated, but by analyzing and understanding links between CD34⁺ cells, we hope to be able to offer an insight into the overlapping properties of cells that express CD34. Stem Cells2014;32:1380–1389

Human mast cell and basophil/eosinophil progenitors

Mast cell, basophil, and eosinophil lineages all derive from CD34(+) hemopoietic stem cells; however, mast cells are derived from a distinct, nonmyeloid progenitor, while eosinophils and basophils share a common myeloid progenitor. These progenitors likely evolved from an ancestral leukocyte population involved in innate immunity and currently play a central role in the pathology of allergic disease. Advances in isolation and analysis of mast cell and basophil/eosinophil progenitor populations have been critical to understanding lineage commitment, differentiation, function, and transcriptional regulation of these cells and have provided a way of monitoring the effect of novel investigational therapies on these cell populations in samples of blood, bone marrow, and airway secretions.

Tracing the origin of the HSC hierarchy reveals an SCF-dependent, IL-3-independent CD43(-) embryonic precursor

Definitive hematopoietic stem cells (HSCs) develop in the aorta gonad mesonephros (AGM) region in a stepwise manner. Type I pre-HSCs express CD41 but lack CD45 expression, which is subsequently upregulated in type II pre-HSCs prior to their maturation into definitive HSCs. Here, using ex vivo modeling of HSC development, we identify precursors of definitive HSCs in the trunk of the embryonic day 9.5 (E9.5) mouse embryo. These precursors, termed here pro-HSCs, are less mature than type I and II pre-HSCs. Although pro-HSCs are CD41(+), they lack the CD43 marker, which is gradually upregulated in the developing HSC lineage. We show that stem cell factor (SCF), but not interleukin-3 (IL-3), is a major effector of HSC maturation during E9-E10. This study extends further the previously established hierarchical organization of the developing HSC lineage and presents it as a differentially regulated four-step process and identifies additional targets that could facilitate the generation of transplantable HSCs from pluripotent cells for clinical needs.

Mast cells aggravate sepsis by inhibiting peritoneal macrophage phagocytosis

Controlling the overwhelming inflammatory reaction associated with polymicrobial sepsis remains a prevalent clinical challenge with few treatment options. In septic peritonitis, blood neutrophils and monocytes are rapidly recruited into the peritoneal cavity to control infection, but the role of resident sentinel cells during the early phase of infection is less clear. In particular, the influence of mast cells on other tissue-resident cells remains poorly understood. Here, we developed a mouse model that allows both visualization and conditional ablation of mast cells and basophils to investigate the role of mast cells in severe septic peritonitis. Specific depletion of mast cells led to increased survival rates in mice with acute sepsis. Furthermore, we determined that mast cells impair the phagocytic action of resident macrophages, thereby allowing local and systemic bacterial proliferation. Mast cells did not influence local recruitment of neutrophils and monocytes or the release of inflammatory cytokines. Phagocytosis inhibition by mast cells involved their ability to release prestored IL-4 within 15 minutes after bacterial encounter, and treatment with an IL-4-neutralizing antibody prevented this inhibitory effect and improved survival of septic mice. Our study uncovers a local crosstalk between mast cells and macrophages during the early phase of sepsis development that aggravates the outcome of severe bacterial infection.

Regulation of cell shape and adhesion by CD34

We previously reported that expression of CD43/leukosialin induces cell rounding and microvillus formation via inhibition of cell adhesion. Here, we found that CD34, a cell surface sialomucin and marker for hematopoietic progenitor cells, also inhibited cell adhesion and induced cell rounding and microvillus formation. Forced expression of CD34-induced cell rounding, microvillus formation, and phosphorylation of ezrin/radixin/moesin (ERM) proteins in HEK293T cells, while inhibiting integrin-mediated cell re-attachment. Furthermore, CD34+ blood cells and KG-1 cells, which express endogenous CD34 on their surface, were spherical in shape, surrounded by microvilli, and non-adherent to substrata. In addition, cleavage of O-sialomucin augmented integrin-mediated cell adhesion of KG-1 cells. These results suggest the involvement of CD34 in the inhibition of integrin-mediated cell adhesion and formation of the cell surface structure. The inhibitory function of CD34 in cell adhesion may affect cell shape organization via phosphorylation of ERM proteins. Cellular structures such as the spherical shape and microvilli of CD34+ cells may also contribute to regulation of cell adhesion.

Requirement for core 2 O-glycans for optimal resistance to helminth infection

The migration of lymphocytes to the small intestine is controlled by expression of the integrin α4β7 and the chemokine receptor CCR9. However, the molecules that specifically regulate migration to the large intestine remain unclear. Immunity to infection with the large intestinal helminth parasite Trichuris muris is dependent upon CD4⁺ T cells that migrate to the large intestine. We examine the role of specific chemokine receptors, adhesion molecules and glycosyltransferases in the development of protective immunity to Trichuris. Mice deficient in expression of the chemokine receptors CCR2 or CCR6 were resistant to infection with Trichuris. Similarly, loss of CD34, CD43, CD44 or PSGL-1 had no effect on resistance to infection. In contrast, simultaneous deletion of the Core2 β1,6-N-acetylglucosaminyltransferase (C2GnT) enzymes C2GnT1 and C2Gnt2 resulted in delayed expulsion of worms. These results suggest that C2GnT-dependent modifications may play a role in migration of protective immune cells to the large intestine.

A familiar stranger: CD34 expression and putative functions in SVF cells of adipose tissue

Human adipose tissue obtained by liposuction is easily accessible and an abundant potential source of autologous cells for regenerative medicine applications. After digestion of the tissue and removal of differentiated adipocytes, the so-called stromal vascular fraction (SVF) of adipose, a mix of various cell types, is obtained. SVF contains mesenchymal fibroblastic cells, able to adhere to culture plastic and to generate large colonies in vitro, that closely resemble bone marrow-derived colony forming units-fibroblastic, and whose expanded progeny, adipose mesenchymal stem/stromal cells (ASC), show strong similarities with bone marrow mesenchymal stem cells. The sialomucin CD34, which is well known as a hematopoietic stem cell marker, is also expressed by ASC in native adipose tissue but its expression is gradually lost upon standard ASC expansion in vitro. Surprisingly little is known about the functional role of CD34 in the biology and tissue forming capacity of SVF cells and ASC. The present editorial provides a short introduction to the CD34 family of sialomucins and reviews the data from the literature concerning expression and function of these proteins in SVF cells and their in vitro expanded progeny.

Mouse models to evaluate the function of genes associated with allergic airway disease

PURPOSE OF REVIEW

In recent years, considerable effort has been invested in developing mouse models of allergic airway disease, as a means of evaluating the role of select genes in its pathophysiology. Here, we review the principal models used in this field, including models of allergic asthma and hypersensitivity pneumonitis. As an example of how these models can reveal novel functional roles for genes, we review our work showing a role for the stem-cell-associated gene, Cd34. Through this example, we illustrate the genetic and immunological strategies available in the field to better understand allergic airway inflammation.

RECENT FINDINGS

CD34 was found to play an important role in the development of two different models of allergic disease, that is, Th2-driven allergic asthma and Th17-driven hypersensitivity pneumonitis. Using a combination of genetically modified mice as well as cell transfers and chimeric mice, we showed that CD34 is important for the efficient trafficking of hematopoietic subsets into and out of the lung, including mast cells, eosinophils and dendritic cells.

SUMMARY

The currently available array of mutant mice and animal models of allergic disease now offers an opportunity to make profound insights into these diseases and provide preclinical models for the development of therapeutics.

IL-7Rα and L-selectin, but not CD103 or CD34, are required for murine peanut-induced anaphylaxis

Background

Allergy to peanuts results in severe anaphylactic responses in affected individuals, and has dramatic effects on society and public policy. Despite the health impacts of peanut-induced anaphylaxis (PIA), relatively little is known about immune mechanisms underlying the disease. Using a mouse model of PIA, we evaluated mice with deletions in four distinct immune molecules (IL7Rα, L-selectin, CD34, CD103), for perturbed responses.

Methods

PIA was induced by intragastric sensitization with peanut antigen and cholera toxin adjuvant, followed by intraperitoneal challenge with crude peanut extract (CPE). Disease outcome was assessed by monitoring body temperature, clinical symptoms, and serum histamine levels. Resistant mice were evaluated for total and antigen specific serum IgE, as well as susceptibility to passive systemic anaphylaxis.

Results

PIA responses were dramatically reduced in IL7Rα^−/− and L-selectin^−/− mice, despite normal peanut-specific IgE production and susceptibility to passive systemic anaphylaxis. In contrast, CD34^−/− and CD103^−/− mice exhibited robust PIA responses, indistinguishable from wild type controls.

Conclusions

Loss of L-selectin or IL7Rα function is sufficient to impair PIA, while CD34 or CD103 ablation has no effect on disease severity. More broadly, our findings suggest that future food allergy interventions should focus on disrupting sensitization to food allergens and limiting antigen-specific late-phase responses. Conversely, therapies targeting immune cell migration following antigen challenge are unlikely to have significant benefits, particularly considering the rapid kinetics of PIA.

CD34 promotes satellite cell motility and entry into proliferation to facilitate efficient skeletal muscle regeneration

Expression of the cell surface sialomucin CD34 is common to many adult stem cell types, including muscle satellite cells. However, no clear stem cell or regeneration-related phenotype has ever been reported in mice lacking CD34, and its function on these cells remains poorly understood. Here, we assess the functional role of CD34 on satellite cell-mediated muscle regeneration. We show that Cd34(-/-) mice, which have no obvious developmental phenotype, display a defect in muscle regeneration when challenged with either acute or chronic muscle injury. This regenerative defect is caused by impaired entry into proliferation and delayed myogenic progression. Consistent with the reported antiadhesive function of CD34, knockout satellite cells also show decreased motility along their host myofiber. Altogether, our results identify a role for CD34 in the poorly understood early steps of satellite cell activation and provide the first evidence that beyond being a stem cell marker, CD34 may play an important function in modulating stem cell activity.

Rb and nucleolin antagonize in controlling human CD34 gene expression

Retinoblastoma protein (Rb) controls cell proliferation, differentiation, survival and gene expression and it has a central role in the signaling network that provides a cell cycle checkpoint in the G1 phase of the cell cycle. Studies in mice have shown that Rb regulates interactions between hematopoietic stem cells and their bone marrow microenvironment and it acts as a critical regulator of hematopoietic stem and progenitor cells under stress. In human hematopoiesis, the CD34 protein is expressed on a subset of progenitor cells capable of self-renewal, multilineage differentiation, and hematopoietic reconstitution, and CD34 has a role in the differentiation of hematopoietic cells. Here we find that, in CD34-positive hematopoietic cells, Rb controls the human CD34 promoter region by antagonizing the CD34 promoter factor nucleolin to provide a mechanism that links expression of endogenous CD34 to cell cycle progression. Our study suggests a direct involvement of Rb in the transcriptional program of human CD34-positive hematopoietic stem/progenitor cells, thus providing further insights into the molecular network relevant to the features of these cells.

CD34 mediates intestinal inflammation in Salmonella-infected mice

CD34 is a highly glycosylated sialomucin expressed on a variety of cells, ranging from vascular endothelial cells to haematopoietic stem cells. Depending on its glycosylation state, CD34 has been shown to promote or inhibit cell adhesion and migration; however, a functional role for CD34 in the gut has not been determined. Using a model of Salmonella-induced gastroenteritis, we investigated the role of CD34 in the context of infection. Upon oral infection, the number of CD34+ cells detected in the submucosa, vascular endothelium and lamina propria significantly increased in S. Typhimurium-infected C57Bl/6 mice. The pathology of S. Typhimurium-infected C57Bl/6 mice was characterized by recruitment of neutrophils to the site of inflammation, submucosal oedema and crypt destruction. In contrast, Cd34(-/-) mice showed a delayed pathology, a defect in inflammatory cell migration into the intestinal tissue and enhanced survival. Importantly, this was not due to a lack of chemotactic signals in Cd34(-/-) mice as these mice had either similar or significantly higher levels of pro-inflammatory cytokines and chemokines post infection when compared with infected C57/Bl6 control mice. In summary, we demonstrate a novel role for CD34 in enhancing migration of inflammatory cells and thereby exacerbating host-mediated immunopathology in the intestine of S. Typhimurium-infected mice.

Opposing roles for CD34 in B16 melanoma tumor growth alter early stage vasculature and late stage immune cell infiltration

Tumor growth and metastasis are determined by the complex interplay of factors, including those intrinsic to tumor cells and extrinsic factors associated with the tumor microenvironment. Our previous work demonstrated key roles for CD34 in the maintenance of vascular integrity and eosinophil and mast cell homing. Since both of these functions affect tumor development, we characterized the effect of CD34 ablation on tumor growth using the B16F1 melanoma model. Intriguingly, we found that CD34 plays a biphasic role in tumor progression. In early growth, both subcutaneous-injected tumors and intravenous-injected lung metastases grew more slowly in Cd34^−/− mice. This correlated with abnormal vessel morphology and increased vascular permeability in these mice. Bone marrow transplantation experiments confirmed that this reflects a non-hematopoietic function of CD34. At later stages, subcutaneous tumor growth was accelerated in Cd34^−/− mice and surpassed growth in wildtype mice. Bone marrow chimera experiments demonstrated this difference was due to a hematopoietic function for CD34 and, correspondingly we found reduced intra-tumor mast cell numbers in Cd34^−/− mice. In aggregate, our analysis reveals a novel role for CD34 in both early and late tumor growth and provides novel insights into the role of the tumor microenvironment in tumor progression.