Podoplanin: emerging functions in development, the immune system, and cancer

Assessment of Proliferative Potential of Odontogenic Keratocyst and Dentigerous Cyst using Podoplanin: An Immunohistochemical Study

INTRODUCTION

Odontogenic cysts are commonly encountered lesions among head and neck pathologies. Odontogenic keratocyst (OKC) has unique features of recurrence and local aggressiveness. Podoplanin (PDP) is a lymphatic endothelial marker and is shown to be expressed in a variety of tissues. Hence, we planned to assess the significance of PDP in OKC and dentigerous cyst (DC).

MATERIALS AND METHODS

The present study included assessment of immunoexpression of PDP in OKC and DC. Twenty specimens each of OKC and DC were included in the present study and were stained with D2-40 antibody. All the sections were analyzed and were categorized as negative staining, weakly positive staining, and strongly positive staining. All the results were analyzed by Statistical Package for the Social Sciences (SPSS) software.

RESULTS

We detected PDP-positive staining in the cell membrane and cytoplasm of the cells of basal cell layer and supra-basal cell layers. In DC cases, we observed positive staining only in cases associated with inflammation.

CONCLUSION

Podoplanin does play a significant role in enhancing the local invasive and neoplastic properties of OKC.

CLINICAL SIGNIFICANCE

Podoplanin expression in OKC is potentially associated with moderate invasive nature of the neighboring structures.

Effect of anti-podoplanin antibody administration during lipopolysaccharide-induced lung injury in mice

Introduction

Acute respiratory distress syndrome (ARDS) is a devastating pulmonary condition in the critically ill patient. A therapeutic intervention is yet to be found that can prevent progression to ARDS. We recently demonstrated that the interaction between podoplanin expressed on inflammatory alveolar macrophages (iAMs) and its endogenous ligand, platelet C-type lectin-like 2 (CLEC-2), protects against exaggerated lung inflammation during a mouse model of ARDS. In this study, we aim to investigate the therapeutic use of a crosslinking/activating anti-podoplanin antibody (α-PDPN, clone 8.1.1) during lipopolysaccharide (LPS)-induced lung inflammation in mice.

Methods

Intravenous administration of α-PDPN was performed 6 hours after intratracheal LPS in wildtype, C57Bl/6 mice. Lung function decline was measured by pulse oximetry as well as markers of local inflammation including bronchoalveolar lavage neutrophilia and cytokine/chemokine expression. In parallel, alveolar macrophages were isolated and cultured in vitro from haematopoietic-specific podoplanin-deficient mice (Pdpn^fl/flVAV1cre⁺) and floxed-only controls treated with or without LPS in the presence or absence of α-PDPN.

Results

Lung function decline as well as alveolar neutrophil recruitment was significantly decreased in mice treated with the crosslinking/activating α-PDPN in vivo. Furthermore, we demonstrate that, in vitro, activation of podoplanin on iAMs regulates their secretion of proinflammatory cytokines and chemokines.

Conclusions

These data confirm the importance of the CLEC-2–podoplanin pathway during intratracheal (IT)-LPS and demonstrate the beneficial effect of targeting podoplanin during IT-LPS in mice possibly via modulation of local cytokine/chemokine expression. Moreover, these data suggest that podoplanin-targeted therapies may have a beneficial effect in patients at risk of developing ARDS.

Tailoring Natural Killer cell immunotherapy to the tumour microenvironment

Natural killer (NK) cells are cytotoxic and cytokine-secreting cells that can mediate potent anti-tumour activity. Accumulating evidence indicates that NK cell functions are severely compromised within the confines of the tumour microenvironment thus impairing the efficacy and development of NK cell-based therapies. Here we review the various cellular and molecular pathways that tumours have supplanted to evade NK cell surveillance. We highlight novel strategies designed to alleviate or circumvent the immunosuppressive conditions of the tumour microenvironment in order to emancipate NK cell function and stifle the inexorable growth and metastasis of malignant cells.

Podoplanin is a negative regulator of Th17 inflammation

Recent data indicate that there are different subpopulations of Th17 cells that can express a regulatory as opposed to an inflammatory gene signature. The transmembrane glycoprotein PDPN is critical in the development of multiple organs including the lymphatic system and has been described on T cells in mouse models of autoimmune Th17 inflammation. Here, we demonstrate that unlike in mice, PDPN+ T cells induced under classic Th17-polarizing conditions express transcription factors associated with Th17 cells but do not produce IL-17. Moreover, these cells express a transcriptional profile enriched for immunosuppressive and regulatory pathways and express a distinct cytokine profile compared with potentially pathogenic PDPN- Th17 cells. Ligation of PDPN by its ligand CLEC-2 ameliorates the Th17 inflammatory response. IL-17 secretion is restored with shRNA gene silencing of PDPN. Furthermore, PDPN expression is reduced via an Sgk1-mediated pathway under proinflammatory, high sodium chloride conditions. Finally, CD3+PDPN+ T cells are devoid of IL-17 in skin biopsies from patients with candidiasis, a prototypical Th17-driven skin disease. Thus, our data support the hypothesis that PDPN may serve as a marker of a nonpathogenic Th17 cell subset and may also functionally regulate pathogenic Th17 inflammation.

Disrupted fibroblastic reticular cells and interleukin-7 expression in tumor draining lymph nodes

The immune system of patients with cancer is usually in an inhibitory state. Lymph node (LN) draining of pathological sites provides a suitable microenvironment where adaptive immune responses mainly occur. However, the microenvironment in the tumor draining lymph nodes (TDLNs) of patients with cancer appears to be in favor of tolerance. The effects of tumor cells on TDLNs have not been elaborated clearly. The present results have indicated that tumor cells may directly affect TDLNs by decreasing the fibroblastic reticular cell population that led to less interleukin-7 secretion. As a result, the number of T cells in TDLNs declined with reduced survival signals. A decreased number of T cells in TDLNs means weakened ability of immune surveillance. Clinically, these results were also confirmed in LN biopsies from patients with colon cancer at different clinical stages. Results of the present study showed that tumor cells may directly inhibit the immunological function of TDLNs.

Oncostatin M drives intestinal inflammation and predicts response to tumor necrosis factor-neutralizing therapy in patients with inflammatory bowel disease

Inflammatory bowel diseases (IBD), including Crohn's disease (CD) and ulcerative colitis (UC), are complex chronic inflammatory conditions of the gastrointestinal tract that are driven by perturbed cytokine pathways. Anti-tumor necrosis factor-α (TNF) antibodies are mainstay therapies for IBD. However, up to 40% of patients are nonresponsive to anti-TNF agents, which makes the identification of alternative therapeutic targets a priority. Here we show that, relative to healthy controls, inflamed intestinal tissues from patients with IBD express high amounts of the cytokine oncostatin M (OSM) and its receptor (OSMR), which correlate closely with histopathological disease severity. The OSMR is expressed in nonhematopoietic, nonepithelial intestinal stromal cells, which respond to OSM by producing various proinflammatory molecules, including interleukin (IL)-6, the leukocyte adhesion factor ICAM1, and chemokines that attract neutrophils, monocytes, and T cells. In an animal model of anti-TNF-resistant intestinal inflammation, genetic deletion or pharmacological blockade of OSM significantly attenuates colitis. Furthermore, according to an analysis of more than 200 patients with IBD, including two cohorts from phase 3 clinical trials of infliximab and golimumab, high pretreatment expression of OSM is strongly associated with failure of anti-TNF therapy. OSM is thus a potential biomarker and therapeutic target for IBD, and has particular relevance for anti-TNF-resistant patients.

Lymphatic and vascular markers in an optic nerve crush model in rat

Only few tissues lack lymphatic supply, such as the CNS or the inner eye. However, if the scleral border is compromised due to trauma or tumor, lymphatics are detected in the eye. Since the situation in the optic nerve (ON), part of the CNS, is not clear, the aim of this study is to screen for the presence of lymphatic markers in the healthy and lesioned ON. Brown Norway rats received an unilateral optic nerve crush (ONC) with defined force, leaving the dura intact. Lesioned ONs and unlesioned contralateral controls were analyzed 7 days (n = 5) and 14 days (n = 5) after ONC, with the following markers: PDGFRb (pericyte), Iba1 (microglia), CD68 (macrophages), RECA (endothelial cell), GFAP (astrocyte) as well as LYVE-1 and podoplanin (PDPN; lymphatic markers). Rat skin sections served as positive controls and confocal microscopy in single optical section mode was used for documentation. In healthy ONs, PDGFRb is detected in vessel-like structures, which are associated to RECA positive structures. Some of these PDGFRb⁺/RECA⁺ structures are closely associated with LYVE-1⁺ cells. Homogenous PDPN-immunoreactivity (IR) was detected in healthy ON without vascular appearance, showing no co-localization with LYVE-1 or PDGFRb but co-localization with GFAP. However, in rat skin controls PDPN-IR was co-localized with LYVE-1 and further with RECA in vessel-like structures. In lesioned ONs, numerous PDGFRb⁺ cells were detected with network-like appearance in the lesion core. The majority of these PDGFRb⁺ cells were not associated with RECA-IR, but were immunopositive for Iba1 and CD68. Further, single LYVE-1⁺ cells were detected here. These LYVE-1⁺ cells were Iba1-positive but PDPN-negative. PDPN-IR was also clearly absent within the lesion site, while LYVE-1⁺ and PDPN⁺ structures were both unaltered outside the lesion. In the lesioned area, PDGFRb⁺/Iba1⁺/CD68⁺ network-like cells without vascular association might represent a subtype of microglia/macrophages, potentially involved in repair and phagocytosis. PDPN was detected in non-lymphatic structures in the healthy ON, co-localizing with GFAP but lacking LYVE-1, therefore most likely representing astrocytes. Both, PDPN and GFAP positive structures are absent in the lesion core. At both time points investigated, no lymphatic structures can be identified in the lesioned ON. However, single markers used to identify lymphatics, detected non-lymphatic structures, highlighting the importance of using a panel of markers to properly identify lymphatic structures.

Mice with a deficiency in CLEC-2 are protected against deep vein thrombosis

Deep vein thrombosis (DVT) with its major complication, pulmonary embolism, is a global health problem. Mechanisms of DVT remain incompletely understood. Platelets play a role in DVT, but the impact of specific platelet receptors remains unclear. Platelet C-type lectin-like receptor 2 (CLEC-2) is known to maintain the physiological state of blood vasculature under inflammatory conditions. DVT is a thromboinflammatory disorder developing largely as sterile inflammation in the vessel wall. We hypothesized therefore that CLEC-2 might play a role in DVT. Here, using a murine DVT model of inferior vena cava (IVC) stenosis, we demonstrate that mice with general inducible deletion of CLEC-2 or platelet-specific deficiency in CLEC-2 are protected against DVT. No phenotype in the complete stasis model was observed. Transfusion of wild-type platelets into platelet-specific CLEC-2 knockout mice restored thrombosis. Deficiency in CLEC-2 as well as inhibition of podoplanin, a ligand of CLEC-2, was associated with reduced platelet accumulation at the IVC wall after 6 hours of stenosis. Podoplanin was expressed in the IVC wall, where it was localized in the vicinity of the abluminal side of the endothelium. The level of podoplanin in the IVC increased after 48 hours of stenosis to a substantially higher extent in mice with a thrombus vs those without a thrombus. Treatment of animals with an anti-podoplanin neutralizing antibody resulted in development of smaller thrombi. Thus, we propose a novel mechanism of DVT, whereby CLEC-2 and upregulation of podoplanin expression in the venous wall trigger thrombus formation.

The brain-tumor related protein podoplanin regulates synaptic plasticity and hippocampus-dependent learning and memory

INTRODUCTION

Podoplanin is a cell-surface glycoprotein constitutively expressed in the brain and implicated in human brain tumorigenesis. The intrinsic function of podoplanin in brain neurons remains however uncharacterized.

MATERIALS AND METHODS

Using an established podoplanin-knockout mouse model and electrophysiological, biochemical, and behavioral approaches, we investigated the brain neuronal role of podoplanin.

RESULTS

Ex-vivo electrophysiology showed that podoplanin deletion impairs dentate gyrus synaptic strengthening. In vivo, podoplanin deletion selectively impaired hippocampus-dependent spatial learning and memory without affecting amygdala-dependent cued fear conditioning. In vitro, neuronal overexpression of podoplanin promoted synaptic activity and neuritic outgrowth whereas podoplanin-deficient neurons exhibited stunted outgrowth and lower levels of p-Ezrin, TrkA, and CREB in response to nerve growth factor (NGF). Surface Plasmon Resonance data further indicated a physical interaction between podoplanin and NGF.

DISCUSSION

This work proposes podoplanin as a novel component of the neuronal machinery underlying neuritogenesis, synaptic plasticity, and hippocampus-dependent memory functions. The existence of a relevant cross-talk between podoplanin and the NGF/TrkA signaling pathway is also for the first time proposed here, thus providing a novel molecular complex as a target for future multidisciplinary studies of the brain function in the physiology and the pathology. Key messages Podoplanin, a protein linked to the promotion of human brain tumors, is required in vivo for proper hippocampus-dependent learning and memory functions. Deletion of podoplanin selectively impairs activity-dependent synaptic strengthening at the neurogenic dentate-gyrus and hampers neuritogenesis and phospho Ezrin, TrkA and CREB protein levels upon NGF stimulation. Surface plasmon resonance data indicates a physical interaction between podoplanin and NGF. On these grounds, a relevant cross-talk between podoplanin and NGF as well as a role for podoplanin in plasticity-related brain neuronal functions is here proposed.

Stromal Fibroblasts in Tertiary Lymphoid Structures: A Novel Target in Chronic Inflammation

Tertiary lymphoid structures (TLS) are organized aggregates of lymphocytes, myeloid, and stromal cells that provide ectopic hubs for acquired immune responses. TLS share phenotypical and functional features with secondary lymphoid organs (SLO); however, they require persistent inflammatory signals to arise and are often observed at target sites of autoimmune disease, chronic infection, cancer, and organ transplantation. Over the past 10 years, important progress has been made in our understanding of the role of stromal fibroblasts in SLO development, organization, and function. A complex and stereotyped series of events regulate fibroblast differentiation from embryonic life in SLOs to lymphoid organ architecture observed in adults. In contrast, TLS-associated fibroblasts differentiate from postnatal, locally activated mesenchyme, predominantly in settings of inflammation and persistent antigen presentation. Therefore, there are critical differences in the cellular and molecular requirements that regulate SLO versus TLS development that ultimately impact on stromal and hematopoietic cell function. These differences may contribute to the pathogenic nature of TLS in the context of chronic inflammation and malignant transformation and offer a window of opportunity for therapeutic interventions in TLS associated pathologies.

Postnatal Deletion of Podoplanin in Lymphatic Endothelium Results in Blood Filling of the Lymphatic System and Impairs Dendritic Cell Migration to Lymph Nodes

OBJECTIVE

The lymphatic vascular system exerts major physiological functions in the transport of interstitial fluid from peripheral tissues back to the blood circulation and in the trafficking of immune cells to lymph nodes. Previous studies in global constitutive knockout mice for the lymphatic transmembrane molecule podoplanin reported perinatal lethality and a complex phenotype with lung abnormalities, cardiac defects, lymphedema, blood-filled lymphatic vessels, and lack of lymph node organization, reflecting the importance of podoplanin expression not only by the lymphatic endothelium but also by a variety of nonendothelial cell types. Therefore, we aimed to dissect the specific role of podoplanin expressed by adult lymphatic vessels.

APPROACH AND RESULTS

We generated an inducible, lymphatic-specific podoplanin knockout mouse model (Pdpn^ΔLEC) and induced gene deletion postnatally. Pdpn^ΔLEC mice were viable, and their lymphatic vessels appeared morphologically normal with unaltered fluid drainage function. Intriguingly, Pdpn^ΔLEC mice had blood-filled lymph nodes and vessels, most frequently in the neck and axillary region, and displayed a blood-filled thoracic duct, suggestive of retrograde filling of blood from the blood circulation into the lymphatic system. Histological and fluorescence-activated cell sorter analyses revealed normal lymph node organization with the presence of erythrocytes within lymph node lymphatic vessels but not surrounding high endothelial venules. Moreover, fluorescein isothiocyanate painting experiments revealed reduced dendritic cell migration to lymph nodes in Pdpn^ΔLEC mice.

CONCLUSIONS

These results reveal an important role of podoplanin expressed by lymphatic vessels in preventing postnatal blood filling of the lymphatic vascular system and in contributing to efficient dendritic cell migration to the lymph nodes.

Platelets: No longer bystanders in liver disease

Growing lines of evidence recognize that platelets play a central role in liver homeostasis and pathobiology. Platelets have important roles at every stage during the continuum of liver injury and healing. These cells contribute to the initiation of liver inflammation by promoting leukocyte recruitment through sinusoidal endothelium. They can activate effector cells, thus amplifying liver damage, and by modifying the hepatic cellular and cytokine milieu drive both hepatoprotective and hepatotoxic processes.

CONCLUSION

In this review we summarize how platelets drive such pleiotropic actions and attempt to reconcile the paradox of platelets being both deleterious and beneficial to liver function; with increasingly novel methods of manipulating platelet function at our disposal, we highlight avenues for future therapeutic intervention in liver disease. (Hepatology 2016;64:1774-1784).

Angiogenesis in the skin of SHARPIN-deficient mice with chronic proliferative dermatitis

Angiogenesis is a common feature of pathological processes including wound healing, tumor formation, and chronic inflammation. Chronic inflammation can also be associated with dilation or proliferation of lymph vessels. We examined blood vessels and lymphatics and the expression of pro- and anti-angiogenic genes in the skin of SHARPIN-deficient mice which spontaneously develop a chronic proliferative dermatitis (cpdm). The number of blood vessels in the dermis of cpdm mice increased with age as the inflammation progressed. Lymphatics identified by labeling for LYVE1 and podoplanin were moderately dilated, but they were not increased in number. The expression of proangiogenic Vegfa, Flt1 and anti-angiogenic Sema3a mRNA was increased. VEGFA was primarily localized in keratinocytes of cpdm skin. There was also increased expression of Ece1 and Pdpn mRNA. Podoplanin was restricted to lymphatic endothelial cells in normal skin, but fibroblasts in cpdm skin also reacted with anti-podoplanin antibodies indicating that they were activated. The expression of other angiogenic and lymphangiogenic factors was not altered or decreased. These results indicate that cpdm mice may be a useful model to study the pathogenesis of angiogenesis in chronic inflammation.

Identification of a novel platelet antagonist that binds to CLEC-2 and suppresses podoplanin-induced platelet aggregation and cancer metastasis

Podoplanin (PDPN) enhances tumor metastases by eliciting tumor cell-induced platelet aggregation (TCIPA) through activation of platelet C-type lectin-like receptor 2 (CLEC-2). A novel and non-cytotoxic 5-nitrobenzoate compound 2CP was synthesized that specifically inhibited the PDPN/CLEC-2 interaction and TCIPA with no effect on platelet aggregation stimulated by other platelet agonists. 2CP possessed anti-cancer metastatic activity in vivo and augmented the therapeutic efficacy of cisplatin in the experimental animal model without causing a bleeding risk. Analysis of the molecular action of 2CP further revealed that Akt1/PDK1 and PKCμ were two alternative CLEC-2 signaling pathways mediating PDPN-induced platelet activation. 2CP directly bound to CLEC-2 and, by competing with the same binding pocket of PDPN in CLEC-2, inhibited PDPN-mediated platelet activation. This study provides evidence that 2CP is the first defined platelet antagonist with CLEC-2 binding activity. The augmentation in the therapeutic efficacy of cisplatin by 2CP suggests that a combination of a chemotherapeutic agent and a drug with anti-TCIPA activity such as 2CP may prove clinically effective.

Polypeptide N-Acetylgalactosaminyltransferase 13 Contributes to Neurogenesis via Stabilizing the Mucin-type O-Glycoprotein Podoplanin

Mucin-type O-glycosylation is initiated by an evolutionarily conserved family of polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts). Previously, it was reported that ppGalNAc-T13 is restrictively expressed at a high level in the brain. Here we provide evidence for the critical role of ppGalNAc-T13 in neural differentiation. In detail, we show that the expression of ppGalNAc-T13 was dramatically up-regulated during early neurogenesis in mouse embryonic brains. Similar changes were also observed in cell models of neuronal differentiation by using either primary mouse cortical neural precursor cells or murine embryonal carcinoma P19 cells. Knockout of ppGalNAc-T13 in P19 cells suppressed not only neural induction but also neuronal differentiation. These effects are at least partly mediated by the mucin-type O-glycoprotein podoplanin (PDPN), as knockdown of PDPN led to a similar inhibition of neuronal differentiation and PDPN was significantly reduced at the posttranscriptional level after ppGalNAc-T13 knockout. Further data demonstrate that PDPN acts as a substrate of ppGalNAc-T13 and that the ppGalNAc-T13-mediated O-glycosylation on PDPN is important for its stability. Taken together, this study suggests that ppGalNAc-T13 contributes to neuronal differentiation through glycosylating and stabilizing PDPN, which provides insights into the regulatory roles of O-glycosylation in mammalian neural development.

The Hepatic Lymphatic Vascular System: Structure, Function, Markers, and Lymphangiogenesis

The lymphatic vascular system has been minimally explored in the liver despite its essential functions including maintenance of tissue fluid homeostasis. The discovery of specific markers for lymphatic endothelial cells has advanced the study of lymphatics by methods including imaging, cell isolation, and transgenic animal models and has resulted in rapid progress in lymphatic vascular research during the last decade. These studies have yielded concrete evidence that lymphatic vessel dysfunction plays an important role in the pathogenesis of many diseases. This article reviews the current knowledge of the structure, function, and markers of the hepatic lymphatic vascular system as well as factors associated with hepatic lymphangiogenesis and compares liver lymphatics with those in other tissues.

Altered Dermal Fibroblasts in Systemic Sclerosis Display Podoplanin and CD90

Tissue injury triggers the activation and differentiation of multiple cell types to minimize damage and initiate repair processes. In systemic sclerosis, these repair processes appear to run unchecked, leading to aberrant remodeling and fibrosis of the skin and multiple internal organs, yet the fundamental pathological defect remains unknown. We describe herein a transition wherein the abundant CD34(+) dermal fibroblasts present in healthy human skin disappear in the skin of systemic sclerosis patients, and CD34(-), podoplanin(+), and CD90(+) fibroblasts appear. This transition is limited to the upper dermis in several inflammatory skin diseases, yet in systemic sclerosis, it can occur in all regions of the dermis. In vitro, primary dermal fibroblasts readily express podoplanin in response to the inflammatory stimuli tumor necrosis factor and IL-1β. Furthermore, we show that on acute skin injury in both human and murine settings, this transition occurs quickly, consistent with a response to inflammatory signaling. Transitioned fibroblasts partially resemble the cells that form the reticular networks in organized lymphoid tissues, potentially linking two areas of fibroblast research. These results allow for the visualization and quantification of a basic stage of fibroblast differentiation in inflammatory and fibrotic diseases in the skin.

Role of podoplanin in the high interleukin-17A secretion resulting from interactions between activated lymphocytes and psoriatic skin-derived mesenchymal cells

In the context of psoriasis, T helper type 17 (Th17) cells infiltrate the inflammatory site and interact with local mesenchymal cells, including skin fibroblasts. The aim of this work was to study the interactions of skin-derived fibroblasts with peripheral blood mononuclear cells (PBMC) with a focus on the Th17 pathway and to identify a mechanism which leads to a high interleukin (IL)-17 secretion. A co-culture system between PBMC and skin fibroblasts was developed. Healthy and patient PBMC were added to non-lesional or lesional skin fibroblasts at a 5:1 ratio for 48 h in the presence or not of activation with phytohaemagglutinin (PHA). Monocytes were removed or not by adherence before the co-culture. An anti-podoplanin antibody was also used during the co-culture. Cytokine production (IL-8, IL-6, IL-1β and IL-17) was measured by enzyme-linked immunosorbent assay (ELISA) and cell staining (CD3, CD4, IL-17 and podoplanin) by flow cytometry. Without T cell receptor (TCR) activation, IL-8, IL-6 and IL-1β production increased in PBMC-fibroblast co-culture compared to PBMC alone. No additional effect was observed with TCR activation, with no difference in the Th17 cell percentage in activated-PBMC alone or co-cultured. Conversely, IL-17 production was increased highly only in co-cultures between control and patient activated-PBMC and skin fibroblasts. Removal of monocytes decreased cytokine production, notably that of IL-17. Addition of an anti-podoplanin antibody decreased IL-17 secretion by 60%. Interactions between resting PBMC and fibroblasts induce the IL-8, IL-6 and IL-1β production. PBMC activation and cell interactions are critical for a high IL-17 secretion. Podoplanin contributes largely to this massive IL-17 secretion.

Epithelial deletion of podoplanin is dispensable for re-epithelialization of skin wounds

The mucin-like transmembrane protein podoplanin (PDPN) is prominently represented in tumor-associated gene expression signatures of numerous types of cancer including squamous cell carcinoma, and gain-of-function and knockdown approaches in tissue culture strongly suggested an important role of PDPN in cell proliferation, migration and adhesion. PDPN is absent during epidermal homeostasis but is highly expressed in basal keratinocytes during cutaneous wound healing. Enhanced motility of immortalized keratinocytes upon ectopic PDPN overexpression argues for wound healing defects upon podoplanin deficiency in keratinocytes; however, in vivo data that unequivocally define the impact of PDPN by functional studies in a physiologically relevant system are still missing. Here, we have applied an in vivo loss-of-function approach by generating a novel transgenic mouse line with keratinocyte-specific podoplanin deficiency. Performing cutaneous full-thickness excisional wounds to examine re-epithelialization capacity, unexpectedly, no defects were observed in wound healing properties of mutant mice. Similarly, PDPN-deficient primary keratinocytes showed no impairment in migration, adhesion or proliferation. Thus, PDPN function is not rate-limiting for re-epithelialization but may be functionally compensated by an as yet unknown protein. Our data also call for in vivo functional studies on PDPN in settings of skin tumor development and progression to clarify PDPN's role in skin pathology.

Immunohistochemical Expression of VEGF and Podoplanin in Uterine Cervical Squamous Intraepithelial Lesions

VEGF and podoplanin (PDPN) have been identified as angiogenesis and/or lymphangiogenesis regulators and might be essential to restrict tumor growth, progression, and metastasis. In the present study, we evaluate the association between the expression of these markers and CIN grade. Immunohistochemistry was performed in 234 uterine cervical samples using conventional histologic sections or TMA with the monoclonal antibodies to VEGF (C-1 clone) and podoplanin (D2-40 clone). Positive-staining rates of VEGF in 191 CIN specimens were significantly associated with histological grade (P < 0.001). Negative and/or focal immunostaining for PDPN were more frequent in CIN 3 (P = 0.016). We found that patients with CIN 3 more frequently had strong and more diffuse staining for VEGF and diminished staining for PDPN (P = 0.018). Strong and more diffuse VEGF immunoexpressions in CIN 2 and CIN 3 were detected when compared to CIN 1. Negative and/or focal PDPN immunoexpression appear to be more frequent in CIN 3. Moderate to strong VEGF expression may be a tendency among patients with high-grade lesions and diminished PDPN expression.

Platelet immunoreceptor tyrosine-based activation motif (ITAM) and hemITAM signaling and vascular integrity in inflammation and development

Platelets are essential for maintaining hemostasis following mechanical injury to the vasculature. Besides this established function, novel roles of platelets are becoming increasingly recognized, which are critical in non-injury settings to maintain vascular barrier integrity. For example, during embryogenesis platelets act to support the proper separation of blood and lymphatic vessels. This role continues beyond birth, where platelets prevent leakage of blood into the lymphatic vessel network. During the course of inflammation, platelets are necessary to prevent local hemorrhage due to neutrophil diapedesis and disruption of endothelial cell-cell junctions. Surprisingly, platelets also work to secure tumor-associated blood vessels, inhibiting excessive vessel permeability and intra-tumor hemorrhaging. Interestingly, many of these novel platelet functions depend on immunoreceptor tyrosine-based activation motif (ITAM) signaling but not on signaling via G protein-coupled receptors, which plays a crucial role in platelet plug formation at sites of mechanical injury. Murine platelets express two ITAM-containing receptors: the Fc receptor γ-chain (FcRγ), which functionally associates with the collagen receptor GPVI, and the C-type lectin-like 2 (CLEC-2) receptor, a hemITAM receptor for the mucin-type glycoprotein podoplanin. Human platelets express an additional ITAM receptor, FcγRIIA. These receptors share common downstream effectors, including Syk, SLP-76 and PLCγ2. Here we will review the recent literature that highlights a critical role for platelet GPVI/FcRγ and CLEC-2 in vascular integrity during development and inflammation in mice and discuss the relevance to human disease.

Podoplanin-expressing cancer-associated fibroblasts inhibit small cell lung cancer growth

Cancer-associated fibroblasts (CAFs) expressing podoplanin (PDPN) are a favorable prognosticator in surgically resected small cell lung cancer (SCLC). Here we explore whether CAFs expressing PDPN influence proliferation of SCLC cells. Compared with control group (SCLC cells co-cultured with CAFs-Ctrl), numbers of SCLC cells co-cultured with CAFs overexpressing PDPN were decreased. Suppression of PDPN expression by shRNA in CAFs resulted in increased numbers of SCLC cells. In surgically resected human SCLC specimens, the frequency of Geminin-positive cancer cells was significantly higher in the cases with PDPN-positive CAFs than in the cases with PDPN-negative CAFs. Thus CAFs expressing PDPN inhibit growth of SCLC cells, suggesting that CAFs expressing PDPN represent a tumor inhibitory stromal cell component in SCLC.

SATB2 expression increased anchorage-independent growth and cell migration in human bronchial epithelial cells

The special AT-rich sequence-binding protein 2 (SATB2) is a protein that binds to the nuclear matrix attachment region of the cell and regulates gene expression by altering chromatin structure. In our previous study, we reported that SATB2 gene expression was induced in human bronchial epithelial BEAS-2B cells transformed by arsenic, chromium, nickel and vanadium. In this study, we show that ectopic expression of SATB2 in the normal human bronchial epithelial cell-line BEAS-2B increased anchorage-independent growth and cell migration, meanwhile, shRNA-mediated knockdown of SATB2 significantly decreased anchorage-independent growth in Ni transformed BEAS-2B cells. RNA sequencing analyses of SATB2 regulated genes revealed the enrichment of those involved in cytoskeleton, cell adhesion and cell-movement pathways. Our evidence supports the hypothesis that SATB2 plays an important role in BEAS-2B cell transformation.

Inflammation drives thrombosis after Salmonella infection via CLEC-2 on platelets

Thrombosis is a common, life-threatening consequence of systemic infection; however, the underlying mechanisms that drive the formation of infection-associated thrombi are poorly understood. Here, using a mouse model of systemic Salmonella Typhimurium infection, we determined that inflammation in tissues triggers thrombosis within vessels via ligation of C-type lectin-like receptor-2 (CLEC-2) on platelets by podoplanin exposed to the vasculature following breaching of the vessel wall. During infection, mice developed thrombi that persisted for weeks within the liver. Bacteria triggered but did not maintain this process, as thrombosis peaked at times when bacteremia was absent and bacteria in tissues were reduced by more than 90% from their peak levels. Thrombus development was triggered by an innate, TLR4-dependent inflammatory cascade that was independent of classical glycoprotein VI-mediated (GPVI-mediated) platelet activation. After infection, IFN-γ release enhanced the number of podoplanin-expressing monocytes and Kupffer cells in the hepatic parenchyma and perivascular sites and absence of TLR4, IFN-γ, or depletion of monocytic-lineage cells or CLEC-2 on platelets markedly inhibited the process. Together, our data indicate that infection-driven thrombosis follows local inflammation and upregulation of podoplanin and platelet activation. The identification of this pathway offers potential therapeutic opportunities to control the devastating consequences of infection-driven thrombosis without increasing the risk of bleeding.

Modes of Antigen Presentation by Lymph Node Stromal Cells and Their Immunological Implications

Antigen presentation is no longer the exclusive domain of cells of hematopoietic origin. Recent works have demonstrated that lymph node stromal cell (LNSC) populations, such as fibroblastic reticular cells, lymphatic and blood endothelial cells, not only provide a scaffold for lymphocyte interactions but also exhibit active immunomodulatory roles that are critical to mounting and resolving effective immune responses. Importantly, LNSCs possess the ability to present antigens and establish antigen-specific interactions with T cells. One example is the expression of peripheral tissue antigens, which are presented on major histocompatibility complex (MHC)-I molecules with tolerogenic consequences on T cells. Additionally, exogenous antigens, including self and tumor antigens, can be processed and presented on MHC-I complexes, which result in dysfunctional activation of antigen-specific CD8⁺ T cells. While MHC-I is widely expressed on cells of both hematopoietic and non-hematopoietic origins, antigen presentation via MHC-II is more precisely regulated. Nevertheless, LNSCs are capable of endogenously expressing, or alternatively, acquiring MHC-II molecules. Transfer of antigen between LNSC and dendritic cells in both directions has been recently suggested to promote tolerogenic roles of LNSCs on the CD4⁺ T cell compartment. Thus, antigen presentation by LNSCs is thought to be a mechanism that promotes the maintenance of peripheral tolerance as well as generates a pool of diverse antigen-experienced T cells for protective immunity. This review aims to integrate the current and emerging literature to highlight the importance of LNSCs in immune responses, and emphasize their role in antigen trafficking, retention, and presentation.

Expression of Podoplanin in Different Grades of Oral Squamous Cell Carcinoma

Background:

The expression of podoplanin is up-regulated in a number of different human cancers, including squamous cell carcinoma of the oral cavity and its relationship with tumor invasion raises the possibility that podoplanin expression could be used as a biomarker for diagnosis and prognosis.

Aim:

The aim of the present study is to evaluate the expression of podoplanin in different grades of squamous cell carcinoma (SCC) and to correlate the expression of podoplanin with relevant clinical features such as age, sex, site and associated habits.

Materials and Methods:

Retrospective study was carried on formalin fixed, paraffin embedded blocks of oral SCC (OSCC) from the archives of Department of Oral and Maxillofacial Pathology, Vishnu Dental College, Bhimavaram. Thirty diagnosed cases were included, of which 10 were well-differentiated SCC (WDSCC) (n = 10), 10 moderately DSCC and 10 poorly DSCC. Demographics including age, sex, gender and associated habit history, were recorded. Immunohistochemical staining was done with podoplanin anti D2–40 antibody, for all the cases of OSCC and assessed qualitatively. The data obtained were tabulated and subjected to statistical analysis.

Results:

In the present study, 27 cases of SCC showed podoplanin expression and remaining three cases showed no expression. The scoring criterion suggested by Yuan et al. was followed for semi-quantitative assessment. OSCC, seven cases presented weak expression (Immunoreactive score [IRS] 0–3), 15 presented moderate expression (IRS Score 4–7) and 5 presented high expression (IRS Score > 8). The assessment of podoplanin expression in the cytoplasm, the membrane and the cytoplasm and membrane (both) of tumor cells showed overall high positivity in the cytoplasmic followed by both and the membrane.

Conclusion:

Podoplanin could be a potent biomarker in assessing the cytoplasm/membrane staining of tumor cells. Furthermore, a high level of podoplanin expression is suggestive of high frequency of lymph node metastasis and immature status in the differentiation process of OSCC.

Macrophage heterogeneity in tissues: phenotypic diversity and functions

During development and throughout adult life, macrophages derived from hematopoietic progenitors are seeded throughout the body, initially in the absence of inflammatory and infectious stimuli as tissue-resident cells, with enhanced recruitment, activation, and local proliferation following injury and pathologic insults. We have learned a great deal about macrophage properties ex vivo and in cell culture, but their phenotypic heterogeneity within different tissue microenvironments remains poorly characterized, although it contributes significantly to maintaining local and systemic homeostasis, pathogenesis, and possible treatment. In this review, we summarize the nature, functions, and interactions of tissue macrophage populations within their microenvironment and suggest questions for further investigation.

A dendritic-cell-stromal axis maintains immune responses in lymph nodes

Within secondary lymphoid tissues, stromal reticular cells support lymphocyte function, and targeting reticular cells is a potential strategy for controlling pathogenic lymphocytes in disease. However, the mechanisms that regulate reticular cell function are not well understood. Here we found that during an immune response in lymph nodes, dendritic cells (DCs) maintain reticular cell survival in multiple compartments. DC-derived lymphotoxin beta receptor (LTβR) ligands were critical mediators, and LTβR signaling on reticular cells mediated cell survival by modulating podoplanin (PDPN). PDPN modulated integrin-mediated cell adhesion, which maintained cell survival. This DC-stromal axis maintained lymphocyte survival and the ongoing immune response. Our findings provide insight into the functions of DCs, LTβR, and PDPN and delineate a DC-stromal axis that can potentially be targeted in autoimmune or lymphoproliferative diseases.

Akt and mitogen-activated protein kinase enhance C-type lectin-like receptor 2-mediated platelet activation by inhibition of glycogen synthase kinase 3α/β

BACKGROUND

The C-type lectin-like receptor 2 (CLEC-2) and the collagen receptor glycoprotein (GP)VI activate platelets through Src and Syk tyrosine kinases, and phospholipase Cγ2. The initial events in the two signaling cascades, however, are distinct, and there are quantitative differences in the roles of proteins downstream of Syk activation. The activation of Akt and mitogen-activated protein kinases (MAPKs) has been shown to enhance platelet activation by GPVI, but their role in CLEC-2 signaling is not known.

OBJECTIVES

We sought to investigate the role of the Akt and MAPK pathways in platelet activation by CLEC-2.

RESULTS

The CLEC-2 agonist rhodocytin stimulated phosphorylation of Akt and p38 and extracellular signal-related kinase (ERK) MAPKs, but with a delay relative to Syk. Phosphorylation of these proteins was markedly inhibited in the combined presence of apyrase and indomethacin, consistent with the reported feedback action of ADP and thromboxane A2 in CLEC-2 signaling. Phosphorylation of Akt and phosphorylation of ERK were blocked by the phosphoinositide 3-kinase (PI3K) inhibitor wortmannin and the protein kinase C (PKC) inhibitor Ro31-8220, respectively, whereas Syk phosphorylation was not altered. On the other hand, both inhibitors reduced phosphorylation of the Akt substrate glycogen synthase kinase 3α/β (GSK3α/β). Phosphorylation of GSK3α/β was also blocked by the Akt inhibitor MK2206, and reduced at late, but not early, times by the MEK inhibitor PD0325901. MK2206 and PD0325901 inhibited aggregation and secretion in response to a low concentration of rhodocytin, which was restored by GSK3α/β inhibitors.

CONCLUSIONS

These results demonstrate that CLEC-2 regulates Akt and MAPK downstream of PI3K and PKC, leading to phosphorylation and inhibition of GSK3α/β, and enhanced platelet aggregation and secretion.

PKA and CDK5 can phosphorylate specific serines on the intracellular domain of podoplanin (PDPN) to inhibit cell motility

Podoplanin (PDPN) is a transmembrane glycoprotein that promotes tumor cell migration, invasion, and cancer metastasis. In fact, PDPN expression is induced in many types of cancer. Thus, PDPN has emerged as a functionally relevant cancer biomarker and chemotherapeutic target. PDPN contains 2 intracellular serine residues that are conserved between species ranging from mouse to humans. Recent studies indicate that protein kinase A (PKA) can phosphorylate PDPN in order to inhibit cell migration. However, the number and identification of specific residues phosphorylated by PKA have not been defined. In addition, roles of other kinases that may phosphorylate PDPN to control cell migration have not been investigated. We report here that cyclin dependent kinase 5 (CDK5) can phosphorylate PDPN in addition to PKA. Moreover, results from this study indicate that PKA and CDK5 cooperate to phosphorylate PDPN on both intracellular serine residues to decrease cell motility. These results provide new insight into PDPN phosphorylation dynamics and the role of PDPN in cell motility. Understanding novel mechanisms of PDPN intracellular signaling could assist with designing novel targeted chemotherapeutic agents and procedures.

Are podoplanin and ezrin involved in the invasion process of the ameloblastomas?

The association between podoplanin and ezrin in the process of odontogenic tumors invasion has been suggested, but was not studied yet. Our purpose was to investigate the relationship between podoplanin and ezrin expressions in the odontogenic epithelium of ameloblastomas. Forty-seven ameloblastomas were analyzed by immunohistochemistry using anti-podoplanin and anti-ezrin antibodies. The expressions of both proteins were evaluated using a score method and the comparison and association between these proteins were verified, respectively, by Wilcoxon Signed-Rank test and by Spearman’s rank correlation coefficient, using a statistical significance level of 0.05. The majority of tumors (87.2%) exhibited strong membranous expression of podoplanin in the peripheral cells. Cytoplasmic expression of ezrin in the peripheral cells of ameloblastomas was stronger than its membranous expression. No statistically significant correlation was observed between podoplanin and ezrin. However, there was statistically significant difference between membranous podoplanin and membranous ezrin expressions, between cytoplasmic podoplanin and membranous ezrin expressions, and between cytoplasmic podoplanin and cytoplasmic ezrin expressions. There was no statistical difference between membranous podoplanin and cytoplasmic ezrin expressions. These results suggest a synergistic role of both proteins in the process of invasion of ameloblastomas.

Podoplanin: a marker for reactive gliosis in gliomas and brain injury

Reactive astrogliosis is associated with many pathologic processes in the central nervous system, including gliomas. The glycoprotein podoplanin (PDPN) is upregulated in malignant gliomas. Using a syngeneic intracranial glioma mouse model, we show that PDPN is highly expressed in a subset of glial fibrillary acidic protein-positive astrocytes within and adjacent to gliomas. The expression of PDPN in tumor-associated reactive astrocytes was confirmed by its colocalization with the astrocytic marker S100β and with connexin43, a major astrocytic gap junction protein. To determine whether the increase in PDPN is a general feature of gliosis, we used 2 mouse models in which astrogliosis was induced either by a needle injury or ischemia and observed similar upregulation of PDPN in reactive astrocytes in both models. Astrocytic PDPN was also found to be coexpressed with nestin, an intermediate filament marker for neural stem/progenitor cells. Our findings confirm that expression of PDPN is part of the normal host response to brain injury and gliomas, and suggest that it may be a novel cell surface marker for a specific population of reactive astrocytes in the vicinity of gliomas and nonneoplastic brain lesions. The findings also highlight the heterogeneity of glial fibrillary acidic protein-positive astrocytes in reactive gliosis.

Mutation of threonine 34 in mouse podoplanin-Fc reduces CLEC-2 binding and toxicity in vivo while retaining antilymphangiogenic activity

The lymphatic system plays an important role in cancer metastasis and inhibition of lymphangiogenesis could be valuable in fighting cancer dissemination. Podoplanin (Pdpn) is a small, transmembrane glycoprotein expressed on the surface of lymphatic endothelial cells (LEC). During mouse development, binding of Pdpn to the C-type lectin-like receptor 2 (CLEC-2) on platelets is critical for the separation of the lymphatic and blood vascular systems. Competitive inhibition of Pdpn functions with a soluble form of the protein, Pdpn-Fc, leads to reduced lymphangiogenesis in vitro and in vivo. However, the transgenic overexpression of human Pdpn-Fc in mouse skin causes disseminated intravascular coagulation due to platelet activation via CLEC-2. In the present study, we produced and characterized a mutant form of mouse Pdpn-Fc, in which threonine 34, which is considered essential for CLEC-2 binding, was mutated to alanine (PdpnT34A-Fc). Indeed, PdpnT34A-Fc displayed a 30-fold reduced binding affinity for CLEC-2 compared with Pdpn-Fc. This also translated into fewer side effects due to platelet activation in vivo. Mice showed less prolonged bleeding time and fewer embolized vessels in the liver, when PdpnT34A-Fc was injected intravenously. However, PdpnT34A-Fc was still as active as wild-type Pdpn-Fc in inhibiting lymphangiogenesis in vitro and also inhibited lymphangiogenesis in vivo. These data suggest that the function of Pdpn in lymphangiogenesis does not depend on threonine 34 in the CLEC-2 binding domain and that PdpnT34A-Fc might be an improved inhibitor of lymphangiogenesis with fewer toxic side effects.

The CLEC-2-podoplanin axis controls the contractility of fibroblastic reticular cells and lymph node microarchitecture

In lymph nodes, fibroblastic reticular cells (FRCs) form a collagen-based reticular network that supports migratory dendritic cells (DCs) and T cells and transports lymph. A hallmark of FRCs is their propensity to contract collagen, yet this function is poorly understood. Here we demonstrate that podoplanin (PDPN) regulates actomyosin contractility in FRCs. Under resting conditions, when FRCs are unlikely to encounter mature DCs expressing the PDPN receptor CLEC-2, PDPN endowed FRCs with contractile function and exerted tension within the reticulum. Upon inflammation, CLEC-2 on mature DCs potently attenuated PDPN-mediated contractility, which resulted in FRC relaxation and reduced tissue stiffness. Disrupting PDPN function altered the homeostasis and spacing of FRCs and T cells, which resulted in an expanded reticular network and enhanced immunity.

Stromal infrastructure of the lymph node and coordination of immunity

The initiation of adaptive immune responses depends upon the careful maneuvering of lymphocytes and antigen into and within strategically placed lymph nodes (LNs). Non-hematopoietic stromal cells form the cellular infrastructure that directs this process. Once regarded as merely structural features of lymphoid tissues, these cells are now appreciated as essential regulators of immune cell trafficking, fluid flow, and LN homeostasis. Recent advances in the identification and in vivo targeting of specific stromal populations have resulted in striking new insights to the function of stromal cells and reveal a level of complexity previously unrealized. We discuss here recent discoveries that highlight the pivotal role that stromal cells play in orchestrating immune cell homeostasis and adaptive immunity.

Podoplanin mediates ECM degradation by squamous carcinoma cells through control of invadopodia stability

Invadopodia are actin-rich cell membrane projections used by invasive cells to penetrate the basement membrane. Control of invadopodia stability is critical for efficient degradation of the extracellular matrix (ECM); however, the underlying molecular mechanisms remain poorly understood. Here, we uncover a new role for podoplanin, a transmembrane glycoprotein closely associated with malignant progression of squamous cell carcinomas (SCCs), in the regulation of invadopodia-mediated matrix degradation. Podoplanin downregulation in SCC cells impairs invadopodia stability, thereby reducing the efficiency of ECM degradation. We report podoplanin as a novel component of invadopodia-associated adhesion rings, where it clusters prior to matrix degradation. Early podoplanin recruitment to invadopodia is dependent on lipid rafts, whereas ezrin/moesin proteins mediate podoplanin ring assembly. Finally, we demonstrate that podoplanin regulates invadopodia maturation by acting upstream of the ROCK-LIMK-Cofilin pathway through the control of RhoC GTPase activity. Thus, podoplanin has a key role in the regulation of invadopodia function in SCC cells, controlling the initial steps of cancer cell invasion.

Podoplanin negatively regulates CD4+ effector T cell responses

Podoplanin (PDPN, also known as Gp38) is highly expressed on the surface of lymphatic endothelial cells, where it regulates development of lymphatic vessels. We have recently observed that PDPN is also expressed on effector T cells that infiltrate target tissues during autoimmune inflammation; however, the function of PDPN in T cells is largely unclear. Here, we demonstrated that global deletion of Pdpn results in exaggerated T cell responses and spontaneous experimental autoimmune encephalomyelitis (EAE) in mice with a susceptible genetic background. In contrast, T cell-specific overexpression of PDPN resulted in profound defects in IL-7-mediated T cell expansion and survival. Consequently, these animals exhibited a more rapid resolution of CNS inflammation, characterized by a reduced effector CD4+ T cell population in the CNS. Mice harboring a T cell-specific deletion of Pdpn developed exacerbated EAE, with increased accumulation of effector CD4+ T cells in the CNS. Transcriptional profiling of naturally occurring PDPN+ effector T cells in the CNS revealed increased expression of other inhibitory receptors, such as Pd1 and Tim3, and decreased expression of prosurvival factors, including Il7ra. Together, our data suggest that PDPN functions as an inhibitory molecule on T cells, thereby promoting tissue tolerance by limiting long-term survival and maintenance of CD4+ effector T cells in target organs.

Syk and Src family kinases regulate C-type lectin receptor 2 (CLEC-2)-mediated clustering of podoplanin and platelet adhesion to lymphatic endothelial cells

The interaction of C-type lectin receptor 2 (CLEC-2) on platelets with Podoplanin on lymphatic endothelial cells initiates platelet signaling events that are necessary for prevention of blood-lymph mixing during development. In the present study, we show that CLEC-2 signaling via Src family and Syk tyrosine kinases promotes platelet adhesion to primary mouse lymphatic endothelial cells at low shear. Using supported lipid bilayers containing mobile Podoplanin, we further show that activation of Src and Syk in platelets promotes clustering of CLEC-2 and Podoplanin. Clusters of CLEC-2-bound Podoplanin migrate rapidly to the center of the platelet to form a single structure. Fluorescence lifetime imaging demonstrates that molecules within these clusters are within 10 nm of one another and that the clusters are disrupted by inhibition of Src and Syk family kinases. CLEC-2 clusters are also seen in platelets adhered to immobilized Podoplanin using direct stochastic optical reconstruction microscopy. These findings provide mechanistic insight by which CLEC-2 signaling promotes adhesion to Podoplanin and regulation of Podoplanin signaling, thereby contributing to lymphatic vasculature development.

B cell homeostasis and follicle confines are governed by fibroblastic reticular cells

Naive B and T cells exist in discrete zones in lymph nodes. Turley and colleagues demonstrate that a distinct subset of fibroblastic reticular cells reside in B cell zones, where they sustain B cell survival by providing BAFF.

Fibroblastic reticular cells (FRCs) are known to inhabit T cell–rich areas of lymphoid organs, where they function to facilitate interactions between T cells and dendritic cells. However, in vivo manipulation of FRCs has been limited by a dearth of genetic tools that target this lineage. Here, using a mouse model to conditionally ablate FRCs, we demonstrated their indispensable role in antiviral T cell responses. Unexpectedly, loss of FRCs also attenuated humoral immunity due to impaired B cell viability and follicular organization. Follicle-resident FRCs established a favorable niche for B lymphocytes via production of the cytokine BAFF. Thus, our study indicates that adaptive immunity requires an intact FRC network and identifies a subset of FRCs that control B cell homeostasis and follicle identity.

Expression of podoplanin in oral premalignant and malignant lesions and its potential as a biomarker

AIM

To analyze and compare the expression of podoplanin in normal oral tissues, leukoplakia and oral squamous cell carcinoma (OSCC) and to predict its use as a biomarker.

MATERIALS AND METHODS

Ninety-two formalin fixed paraffin embedded tissue samples comprising of 32 cases of leukoplakia, 50 cases of OSCCs and ten normal gingival samples. The samples were retrieved from archives and immunohistochemically analyzed using podoplanin. Appendix tissue samples were used for control purposes. The results were tabulated and statistically analyzed using ANOVA/Kruskal-Wallis test with post-hoc tests, where demographic details are compared and analyzed using Pearson Chi-square test.

RESULTS

The study results showed, absence of podoplanin expression in the epithelium of all the gingival samples (Group I). Positive podoplanin expression noticed in 19 out of 32 (59.4%) cases of leukoplakia (Group II) and 41 out of 50 (82%) cases of OSCCs (Group III). The expression of podoplanin among different groups was highly significant (P = 0.000).

CONCLUSION

The podoplanin may be considered as a predictor marker in assessing malignant transformation of premalignancies and prognosis of oral malignancy. Indeed it is believed that podoplanin might play a role in tumor progression though exact mechanism is not fully elucidated. Further research is required to understand its exact pathophysiology.

Lymphomania

In this issue of Blood, Bénézech and colleagues demonstrate a role for platelets beyond fetal development, to maintaining integrity of the adult lymphatic system.

Platelets direct monocyte differentiation into epithelioid-like multinucleated giant foam cells with suppressive capacity upon mycobacterial stimulation

BACKGROUND

Epithelioid, foam, and multinucleated giant cells (MNGCs) are characteristics of tuberculosis granulomas, yet the precise genesis and functions of these transformed macrophages are unclear. We evaluated the role of platelets as drivers of macrophage transformation in mycobacterial infection.

METHODS

We employed flow cytometry and microscopy to assess cellular phenotype and phagocytosis. Immune assays allowed quantification of cytokines and chemokines, whereas gene microarray technology was applied to estimate global transcriptome alterations. Immunohistochemical investigations of tuberculosis granulomas substantiated our findings at the site of infection.

RESULTS

Monocytes differentiated in presence of platelets (MP-Macs) acquired a foamy, epithelioid appearance and gave rise to MNGCs (MP-MNGCs). MP-Macs up-regulated activation markers, phagocytosed mycobacteria, and released abundant interleukin 10. Upon extended culture, MP-Macs shared transcriptional features with epithelioid cells and M2 macrophages and up-regulated CXCL5 transcripts. In line with this, CXCL5 concentrations were significantly increased in airways of active tuberculosis patients. The platelet-specific CD42b antigen was detected in MP-Macs, likewise in macrophages, MNGCs, and epithelioid cells within tuberculosis granulomas, along with the platelet aggregation-inducing factor PDPN.

CONCLUSIONS

Platelets drive macrophage differentiation into MNGCs with characteristics of epithelioid, foam, and giant cells observed in tuberculosis granulomas. Our data define platelets as novel participants in tuberculosis pathogenesis.

Galectin-8: a matricellular lectin with key roles in angiogenesis

Galectin-8 (gal-8) is a "tandem-repeat"-type galectin, containing two carbohydrate recognition domains connected by a linker peptide. gal-8 is expressed both in the cytoplasm and nucleus in vascular endothelial cells (ECs) from normal and tumor-associated blood vessels, and in lymphatic endothelial cells. Herein, we describe a novel role for gal-8 in the regulation of vascular and lymphatic angiogenesis and provide evidence of its critical implications in tumor biology. Functional assays revealed central roles for gal-8 in the control of capillary-tube formation, EC migration and in vivo angiogenesis. So far, two endothelial ligands have been described for gal-8, namely podoplanin in lymphatic vessels and CD166 (ALCAM, activated leukocyte cell adhesion molecule) in vascular ECs. Other related gal-8 functions are also summarized here, including cell adhesion and migration, which collectively demonstrate the multi-functionality of this complex lectin. Thus, gal-8 is an important component of the angiogenesis network, and an essential molecule in the extracellular matrix by providing molecular anchoring to this surrounding matrix. The implications of gal-8 in tumor angiogenesis remain to be further explored, but it is exciting to speculate that modulating gal-8-glycan interactions could be used to block lymphatic-vascular connections vital for metastasis.

Up-regulation of podoplanin involves in neuronal apoptosis in LPS-induced neuroinflammation

Podoplanin (PDPN) is a mucin-type transmembrane sialoglycoprotein expressed in multiple tissues in adult animals, including the brain, lungs, kidney, and lymphoid organs. Studies of this molecule have demonstrated its great importance in tumor metastasis, platelet aggregation, and lymphatic vessel formation. However, information regarding its regulation and possible function in the central nervous system is still limited. In this study, we performed a neuroinflammatory model by lipopolysaccharide (LPS) lateral ventral injection in adult rats and detected increased expression of PDPN in the brain cortex. Immunofluorescence indicated that PDPN was located in the neurons, but not astrocytes. Moreover, there was a concomitant up-regulation of active caspase-3, cyclin D1, and CDK4 in vivo and vitro studies. In addition, the expression of these three proteins in cortical primary neurons was decreased after knocking down PDPN by siRNA. Collectively, all these results suggested that the up-regulation of PDPN might be involved in neuronal apoptosis in neuroinflammation after LPS injection.