P-selectin Glycoprotein Ligand-1 Research Articles

Mechanical regulation of calcium signaling of HL-60 on P-selectin under flow.

BackgroundBinding of P-selectin to P-selectin glycoprotein ligand-1 (PSGL-1) makes neutrophils roll on and adhere to inflammatory site. Intracellular calcium bursting of adhered neutrophils is a key event for subsequent arresting firmly at and migrating into the injured tissue. But, it remains unclear how the cytoplasmic calcium signaling of the cells were modulated by the fluid shear stress. Here, we focus on mechanical regulation of P-selectin-induced calcium signaling of neutrophil-like HL-60 cells under flow.MethodsHL-60 cells were loaded with Fluo-4 AM for fluorescent detection of intracellular calcium ion, and then perfused over P-selectin-coated bottom of parallel-plate flow chamber. The intracellular calcium concentration of firmly adhered cell under flow was observed in real time by fluorescence microscopy.ResultsForce triggered, enhanced and quickened cytoplasmic calcium bursting of HL-60 on P-selectin. This force-dependent calcium signaling was induced by the immobilized P-selectin coated on substrates in absence of chemokine. Increasing of both shear stress and P-selectin concentration made the calcium signaling intensive, through quickening the cytosolic calcium release and upregulating both probability and peak level of calcium signaling.ConclusionsImmobilized P-selectin-induced calcium signaling of HL-60 cells is P-selectin concentration- and mechanical force-dependent. The higher both the P-selectin concentration and the external force on cell, the more intensive the calcium signaling. It might provide a novel insight into the mechano-chemical regulation mechanism for intracellular signaling pathways induced by adhesion molecules.

Novel therapeutic strategies against cancer and chronic infection by targeting P-selectin glycoprotein ligand-1 as an immune T cells response regulator

P-selectin glycoprotein ligand-1 (PSGL-1) is a homodimeric mucin-like glycoprotein primarily restricted to cells of hematopoietic origin. Although, it may be present on some non-immune cells such as epithelial cells lining the fallopian tube, microvascular endothelial cells, and platelets, PSGL-1 is broadly expressed on most immune cells including neutrophils, monocytes, dendritic cells and lymphocytes (1,2). PSGL-1 on leukocytes mediates interactions with P-selectin and E-selectin present in activated endothelium with a major role in leukocyte adhesion and transmigration as it is responsible for the initial steps of the extravasation cascade (1,2).

Imaging flow cytometry in the assessment of leukocyte-platelet aggregates

Platelets are subcellular blood elements with a well-established role in haemostasis. Upon activation platelets undergo granule exocytosis, resulting in α-granule P-Selectin being expressed on the cell membrane. This allows binding of activated platelets to P-Selectin glycoprotein ligand 1 (PSGL-1) expressing leukocytes, forming leukocyte-platelet aggregates (LPAs). Whole blood flow cytometry (FCM) has demonstrated that elevated circulating LPAs (especially monocyte LPAs) are linked to atherothrombosis in high risk patients, and that activated platelet binding influences monocytes towards a pro-adhesive and pro-atherogenic phenotype. However, a limitation of conventional FCM is the potential for coincident events to resemble LPAs despite no tethering. Imaging cytometry can be used to characterize LPA formation and distinguish circulating MPAs from coincidental events. Platelets and leukocyte subsets are identified by expression of surface markers (e.g. the lipopolysachharide receptor CD14 on monocytes, glycoprotein Ib CD42b on platelets). In conventional FCM, all events with both leukocyte and platelet characteristics are designated as LPAs. However, by using an ‘internal’ mask based on the brightfield image and the fluorescent platelet identifier, imaging flow cytometry is able to distinguish leukocytes with tethered platelets (genuine LPAs) from leukocyte with coincidental, untethered platelets nearby. Mechanisms (e.g. adhesion molecules) or consequences (e.g. signal transduction) can then be separately analysed in platelet tethered and untethered leukocytes. Imaging flow cytometry therefore provides a more accurate approach for both enumeration and analysis of LPAs than conventional FCM.

Immune checkpoint regulator: a new assignment proposed for the classic adhesion molecule P-selectin glycoprotein ligand-1.

P-selectin glycoprotein ligand-1 (PSGL-1) is a major selectin ligand expressed by hematopoietic cells and well known for its role in mediating leukocyte trafficking into inflamed tissue. A recent report by Tinoco et al . examines chronic viral infection and melanoma in PSGL-1 deficient mice ( Selplg −/− ) and suggests a previously unknown and selectin-independent function for PSGL-1 as an immune checkpoint regulator that promotes T cell exhaustion (1).

Whole Blood Analysis of Leukocyte-Platelet Aggregates.

In inflammatory and thrombotic syndromes, platelets aggregate with circulating leukocytes, especially monocytes and neutrophils. This leukocyte-platelet aggregate formation is initiated primarily through platelet surface expression of P-selectin (CD62P), following activation-dependent degranulation of α-granules, binding to its constitutively expressed counter-receptor, P-selectin glycoprotein ligand 1 (PSGL-1), on leukocytes. Monocyte-platelet aggregates are a more sensitive marker of platelet activation than platelet surface P-selectin. Detection of leukocyte-platelet aggregates is relatively simple by whole-blood flow cytometry. Light scatter and at least one leukocyte-specific antibody are used to gate the desired population, and the presence of associated platelets is detected by immunostaining for abundant platelet-specific markers. © 2016 by John Wiley & Sons, Inc.

Novel therapeutic strategies against cancer and chronic infection by targeting P-selectin glycoprotein ligand-1 as an immune T cells response regulator

Novel therapeutic strategies against cancer and chronic infection by targeting P-selectin glycoprotein ligand-1 as an immune T cells response regulator

Inhibition of soluble epoxide hydrolase alleviated atherosclerosis by reducing monocyte infiltration in Ldlr−/− mice

RationaleCirculating monocytes play pivotal roles in chronic inflammatory diseases. Epoxyeicosatrienoic acids (EETs), metabolites of arachidonic acid, are known to have anti-inflammatory effects and are hydrolyzed by soluble epoxide hydrolase (sEH). ObjectiveWe aimed to investigate the effect of sEH inhibition in atherogenesis. Methods and resultsMice with low-density lipoprotein receptor deficiency (Ldlr−/−) with or without sEH inhibitor, and Ldlr/sEH double-knockout (DK) mice were fed a Western-type diet (WTD) for 6weeks to induce arteriosclerosis. Both sEH inhibition and gene depletion decreased the WTD–induced hyperlipidemia, plaque area and macrophage infiltration in mice arterial wall. Ly6Chi infiltration of monocytes remained similar in blood, spleen and bone marrow of DK mice, but was decreased in aortic lesions. To further assess the role of sEH or EETs in monocyte/macrophage infiltration in atherogenesis, we transplanted DK bone marrow into Ldlr−/− recipients, and then fed mice the WTD. Aortic lesions and Ly6Chi monocyte infiltration were reduced in mice with transplanted bone marrow of DK mice without diminishing the cholesterol level. Furthermore, sEH inhibition or gene depletion increased the ratio of EETs/DHETs and diminished the expression of P-selectin glycoprotein ligand 1 (PSGL-1) in mice peripheral-blood mononuclear cells. Monocyte adhesion to P-selectin and to tumor necrosis factor α–activated endothelial cells was also diminished by sEH inhibition. ConclusionsEH inhibition and gene depletion attenuated atherosclerosis in mice by decreasing the infiltration of monocytes into the artery wall. EET and PSGL-1 may play pivotal roles in monocyte/macrophage infiltration and atherogenesis.

Intravascular Inflammation Triggers Intracerebral Activated Microglia and Contributes to Secondary Brain Injury After Experimental Subarachnoid Hemorrhage (eSAH).

Activation of innate immunity contributes to secondary brain injury after experimental subarachnoid hemorrhage (eSAH). Microglia accumulation and activation within the brain has recently been shown to induce neuronal cell death after eSAH. In isolated mouse brain capillaries after eSAH, we show a significantly increased gene expression for intercellular adhesion molecule-1 (ICAM-1) and P-selectin. Hence, we hypothesized that extracerebral intravascular inflammatory processes might initiate the previously reported microglia accumulation within the brain tissue. We therefore induced eSAH in knockout mice for ICAM-1 (ICAM-1-/-) and P-selectin glycoprotein ligand-1 (PSGL-1-/-) to find a significant decrease in neutrophil-endothelial interaction within the first 7days after the bleeding in a chronic cranial window model. This inhibition of neutrophil recruitment to the endothelium results in significantly ameliorated microglia accumulation and neuronal cell death in knockout animals in comparison to controls. Our results suggest an outside-in activation of the CNS innate immune system at the vessel/brain interface following eSAH. Microglia cells, as part of the brain's innate immune system, are triggered by an inflammatory reaction in the microvasculature after eSAH, thus contributing to neuronal cell death. This finding offers a whole range of new research targets, as well as possible therapy options for patients suffering from eSAH.

Sepsis-Induced Thymic Atrophy Is Associated with Defects in Early Lymphopoiesis.

Impaired T lymphopoiesis is associated with immunosuppression of the adaptive immune response and plays a role in the morbidity and mortality of patients and animal models of sepsis. Although previous studies examined several intrathymic mechanisms that negatively affect T lymphopoiesis, the extrathymic mechanisms remain poorly understood. Here, we report a dramatic decrease in the percentage of early T lineage progenitors (ETPs) in three models of sepsis in mice (cecal ligation and puncture, lipopolysaccharide continuous injection, and poly I:C continuous injection). However, septic mice did not show a decrease in the number of bone marrow (BM) precursor cells. Instead, the BM progenitors for ETPs expressed reduced mRNA levels of CC chemokine receptor (CCR) 7, CCR9 and P-selectin glycoprotein ligand 1, and exhibited impaired homing capacity in vitro and in vivo. Furthermore, RNA-Seq analysis and real-time PCR showed a marked downregulation of several lymphoid-related genes in hematopoietic stem and progenitor cells. Hematopoietic stem and progenitor cells differentiated into myeloid cells but failed to generate T lymphocytes in vitro and in vivo. Our results indicate that the depletion of ETPs in septic mice might be a consequence of an impaired migration of BM progenitors to the thymus, as well as a defect in lymphoid lineage commitment. Stem Cells 2016;34:2902-2915.

Abstract 3744: Targeted therapy for breast cancer bone metastases using mRNA engineered mesenchymal stem cells

Abstract Bone is a primary metastatic site in breast cancer, and bone metastases are associated with poor survival and a dramatic decrease of patient's quality of life. Current treatments lack specificity for bone metastatic niches, leading to poor drug delivery and systemic toxicity. Mesenchymal stem/stromal cells (MSCs) represent ideal trophic vehicles for drug delivery to bone metastases as they are readily available, easy to expand, and display a natural, although inefficient, homing to bone and tumor sites. This work aimed to develop MSCs that are engineered through simple mRNA transfection with both bone vasculature-homing ligands and therapeutics to improve targeted delivery and efficacy. The transfection of protein-coding mRNA is an effective tool to engineer simultaneously and transiently cells with multiple factors to control the fate of transplanted cells, while mitigating risks associated with viral-based engineering. Human bone marrow-derived MSCs from healthy donors were engineered with synthetic mRNA to express homing ligands P-selectin glycoprotein ligand-1 (PSGL-1)/Sialyl Lewis X (sLeX), and anti-tumor agents cytosine deaminase (CD) and osteoprotegerin (OPG). PSGL-1/sLeX allow MSCs to efficiently target bone tumor vasculatures that overexpress P- and E-selectins. CD is a convertase that locally converts inactive pro-drug 5-Fluorocytosine (5-FC) to active drug 5-Fluorouracil. OPG is a natural decoy receptor for one of the main bone resorptive factors expressed in bone metastases, RANKL (Receptor activator of nuclear factor kappa-B ligand), and thus blocks the vicious cycle existing between tumor growth and bone resorption. First, we demonstrated that MSCs could be efficiently engineered through mRNA transfection to express simultaneously homing ligands PSGL-1 and sLeX, CD and OPG. We evaluated improved cell homing and anti-tumor functions of engineered stem cells in vitro. Expression of PSGL-1 and sLeX increased MSC rolling and tethering on an activated endothelium under shear flow condition. When co-cultured with human breast cancer cells MDA-MB231 in presence of 5-FC, engineered MSCs induced both breast cancer and MSC death within 5 days. Finally, secreted OPG is able to prevent osteoclastogenesis in vitro using murine osteoclast precursors. We are currently evaluating biodistribution, homing to bone metastatic niches and anti-tumor efficacy of engineered MSCs in vivo using establish models of breast cancer bone metastases (intratibial and intracardiac injection of MDA-MB-231 cells). As bone metastases are osteolytic lesions, bone remodeling will also be measured using histomorphometry. To conclude, our engineered MSCs can potentially be safer vectors to effectively target and treat bone metastases, thus decreasing off-target systemic toxicity. This next-generation of engineered MSCs has the potential to address an unmet challenge for bone metastases treatment. Citation Format: Aude Segaliny, Jason Cheng, Weian Zhao. Targeted therapy for breast cancer bone metastases using mRNA engineered mesenchymal stem cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3744.

Rapid and label-free microfluidic neutrophil purification and phenotyping in diabetes mellitus.

Advanced management of dysmetabolic syndromes such as diabetes will benefit from a timely mechanistic insight enabling personalized medicine approaches. Herein, we present a rapid microfluidic neutrophil sorting and functional phenotyping strategy for type 2 diabetes mellitus (T2DM) patients using small blood volumes (fingerprick ~100 μL). The developed inertial microfluidics technology enables single-step neutrophil isolation (>90% purity) without immuno-labeling and sorted neutrophils are used to characterize their rolling behavior on E-selectin, a critical step in leukocyte recruitment during inflammation. The integrated microfluidics testing methodology facilitates high throughput single-cell quantification of neutrophil rolling to detect subtle differences in speed distribution. Higher rolling speed was observed in T2DM patients (P < 0.01) which strongly correlated with neutrophil activation, rolling ligand P-selectin glycoprotein ligand 1 (PSGL-1) expression, as well as established cardiovascular risk factors (cholesterol, high-sensitive C-reactive protein (CRP) and HbA1c). Rolling phenotype can be modulated by common disease risk modifiers (metformin and pravastatin). Receiver operating characteristics (ROC) and principal component analysis (PCA) revealed neutrophil rolling as an important functional phenotype in T2DM diagnostics. These results suggest a new point-of-care testing methodology, and neutrophil rolling speed as a functional biomarker for rapid profiling of dysmetabolic subjects in clinical and patient-oriented settings.

Psgl-1 Deficiency is Protective against Stroke in a Murine Model of Lupus.

Systemic lupus erythematosus (SLE) is associated with an elevated risk of vascular complications, including premature stroke. Therapies targeting leukocyte recruitment may be beneficial in reducing vascular complications associated with SLE. Lupus was induced in female wild-type (WT) and P-selectin glycoprotein ligand-1 deficient (Psgl-1−/−) mice with pristane. Stroke was induced following photochemical injury to the middle cerebral artery (MCA). Stroke size was increased in pristane-treated WT mice compared to non-pristane-treated WT controls. However, stroke size was not increased in pristane-treated Psgl-1−/− mice compared to controls, despite evidence of increased nephritis in Psgl-1−/− mice. Pristane-treated WT mice showed elevated anti-dsDNA, anti-snRNP, CXCL1, and MCP-1 levels compared to untreated mice; however levels of anti-snRNP, MCP-1, and CXCL1 were reduced in pristane-treated Psgl-1−/− mice compared to pristane-treated WT mice. Infiltration of neutrophils and macrophages at the cerebral infarction site were reduced in pristane-treated Psgl-1−/− mice compared to pristane-treated WT mice. In conclusion, the increase in stroke size associated with lupus is prevented by Psgl-1 deficiency while nephritis is exacerbated. Therapies targeting Psgl-1 may be useful in the management of SLE patients at high risk of acute vascular complications although elucidation of downstream pathways will be necessary to identify targets that do not promote nephritis.

Echocardiographic Ischemic Memory Imaging Through Complement-Mediated Vascular Adhesion of Phosphatidylserine-Containing Microbubbles

ObjectivesThis study hypothesized that microvascular retention of phosphatidylserine-containing microbubbles (MB-PS) would allow detection of recent but resolved myocardial ischemia with myocardial contrast echocardiographic (MCE) molecular imaging. BackgroundTechniques for ischemic memory imaging which can detect and spatially assess resolved myocardial ischemia are being developed for rapid evaluation of patients with chest pain. MethodsMCE molecular imaging with MB-PS was performed 1.5 h, 3.0 h, and 6.0 h after brief (10 min) myocardial ischemia in mice; data were compared to selectin-targeted microbubbles. MCE molecular imaging with Sonazoid (GE Healthcare, Amersham, United Kingdom), a commercially produced phosphatidylserine (PS) − containing agent, was performed in separate mice at 1.5 h and 3.0 h after ischemia-reperfusion; and in dogs undergoing 135 min of ischemia and 60 min of reflow as well as in closed-chest nonischemic control dogs. The mechanism for MB-PS attachment was assessed by intravital microscopy of post-ischemic muscle and by flow cytometry analysis of cell-MB interactions. ResultsIn mice undergoing ischemia-reperfusion without infarction, signal enhancement in the risk area for MB-PS and p-selectin glycoprotein ligand-1−targeted microbubbles was similar at reflow times of 1.5 h (23.3 ± 7.3 IU vs. 30.7 ± 4.1 IU), 3.0 h (42.2 ± 6.2 IU vs. 33.9 ± 7.4 IU), and 6.0 h (24.1 ± 4.3 IU vs. 25.5 ± 4.7 IU). For both agents, signal in the risk area was significantly (p < 0.05) higher than remote region at all reflow times. Sonazoid also produced strong risk area enhancement at 1.5 h (34.7 ± 5.0 IU) and 3.0 h (52.5 ± 4.5 IU) which was approximately 3-fold greater than in the control region, and which correlated spatially with the microsphere-derived risk area. In dogs, Sonazoid signal in the risk area was >5-fold higher than in closed-chest control myocardium (42.2 ± 8.1 IU vs. 7.9 ± 3.3 IU; p < 0.001). Mechanistic studies indicated that MB-PS attached directly to venular endothelium and adherent leukocytes which was dependent on serum complement components C1q and C3. ConclusionsIschemic memory imaging with MCE is possible using MB-PS which may obviate the need for ligand-directed targeting.

Cell adhesion during bullet motion in capillaries.

A numerical analysis is presented of cell adhesion in capillaries whose diameter is comparable to or smaller than that of the cell. In contrast to a large number of previous efforts on leukocyte and tumor cell rolling, much is still unknown about cell motion in capillaries. The solid and fluid mechanics of a cell in flow was coupled with a slip bond model of ligand-receptor interactions. When the size of a capillary was reduced, the cell always transitioned to "bullet-like" motion, with a consequent decrease in the velocity of the cell. A state diagram was obtained for various values of capillary diameter and receptor density. We found that bullet motion enables firm adhesion of a cell to the capillary wall even for a weak ligand-receptor binding. We also quantified effects of various parameters, including the dissociation rate constant, the spring constant, and the reactive compliance on the characteristics of cell motion. Our results suggest that even under the interaction between P-selectin glycoprotein ligand-1 (PSGL-1) and P-selectin, which is mainly responsible for leukocyte rolling, a cell is able to show firm adhesion in a small capillary. These findings may help in understanding such phenomena as leukocyte plugging and cancer metastasis.

Base-modified UDP-sugars reduce cell surface levels of P-selectin glycoprotein 1 (PSGL-1) on IL-1β-stimulated human monocytes.

P-selectin glycoprotein ligand-1 (PSGL-1, CD162) is a cell-surface glycoprotein that is expressed, either constitutively or inducibly, on all myeloid and lymphoid cell lineages. PSGL-1 is implicated in cell–cell interactions between platelets, leukocytes and endothelial cells, and a key mediator of inflammatory cell recruitment and transmigration into tissues. Here, we have investigated the effects of the β-1,4-galactosyltransferase inhibitor 5-(5-formylthien-2-yl) UDP-Gal (5-FT UDP-Gal, compound 1) and two close derivatives on the cell surface levels of PSGL-1 on human peripheral blood mononuclear cells (hPBMCs). PSGL-1 levels were studied both under basal conditions, and upon stimulation of hPBMCs with interleukin-1β (IL-1β). Between 1 and 24 hours after IL-1β stimulation, we observed initial PSGL-1 shedding, followed by an increase in PSGL-1 levels on the cell surface, with a maximal window between IL-1β-induced and basal levels after 72 h. All three inhibitors reduce PSGL-1 levels on IL-1β-stimulated cells in a concentration-dependent manner, but show no such effect in resting cells. Compound 1 also affects the cell surface levels of adhesion molecule CD11b in IL-1β-stimulated hPBMCs, but not of glycoproteins CD14 and CCR2. This activity profile may be linked to the inhibition of global Sialyl Lewis presentation on hPBMCs by compound 1, which we have also observed. Although this mechanistic explanation remains hypothetical at present, our results show, for the first time, that small molecules can discriminate between IL-1β-induced and basal levels of cell surface PSGL-1. These findings open new avenues for intervention with PSGL-1 presentation on the cell surface of primed hPBMCs and may have implications for anti-inflammatory drug development.

Correlations of platelet-leukocyte aggregates with P-selectin S290N and P-selectin glycoprotein ligand-1 M62I genetic polymorphisms in patients with acute ischemic stroke

BackgroundPlatelet-leukocyte aggregations (PLA) play key roles in acute ischemic stroke (AIS) process and they are formed by the combination of P-selectin (SELP) expressed on the surface of the platelet membranes with P-selectin glycoprotein ligand-1(PSGL-1) expressed on the surface of the leukocytes. There are genetic polymorphisms in SELP and PSGL-1. We tested the differences in all kinds of PLA among subtypes of AIS and the association of SELP S290N and PSGL-1 M62I polymorphism with AIS to assess the correlations of PLA with SELP S290N and PSGL-1 M62I genetic polymorphisms. MethodsOne hundred and forty-eight patients with acute ischemic stroke, including thirty patients with large artery atherosclerosis stroke (LAA), twenty-four patients with cardioembolism (CE) and ninety-four patients with small artery occlusion stroke (SAO), and eighty-eight control subjects were evaluated. The lab parameters and levels of PLA were measured within 3h after the ischemic event in the case subjects and within empty stomach in the control subjects. In all subjects, SELP S290N and PSGL-1 M62I polymorphisms were also measured. ResultsPlatelet-monocyte aggregates (PMA), platelet-lymphocyte aggregates (PLyA) and platelet-neutrophil aggregates (PNA) in LAA group, CE group and SAO group were all higher than that in control group (P=0.000 for all comparisons). Compared with LAA group, PMA and PLyA in CE group were significantly higher (P=0.018 and P=0.003, respectively). Compared with SAO group, PMA and PLyA in CE group were also significantly higher (P=0.041 and P=0.019, respectively). Compared with control group, there were significantly differences of I allele frequencies of PSGL-1 M62I in LAA group and SAO group (OR=2.249, 95%CI: 1.175–4.304, P=0.021 and OR=2.055, 95%CI: 1.269–3.328, P=0.004, respectively). In SAO group, there were significantly differences of PNA among MM, MI and II genotype of PSGL-1 M62I (P=0.008). ConclusionsPLA increased in AIS patients rapidly within 3h. The I allele of PSGL-1 M62I was associated with risk of developing AIS, especially LAA and SAO. SAO patients with the II genotype of PSGL-1 M62I have the higher level of PNA.

PSGL-1 Is an Immune Checkpoint Regulator that Promotes T Cell Exhaustion

Chronic viruses and cancers thwart immune responses in humans by inducing Tcell dysfunction. Using a murine chronic virus that models human infections, we investigated the function of the adhesion molecule, P-selectin glycoprotein ligand-1 (PSGL-1), that is upregulated on responding Tcells. PSGL-1-deficient mice cleared the virus due to increased intrinsic survival of multifunctional effector Tcells that had downregulated PD-1 as well as other inhibitory receptors. Notably, this response resulted in CD4(+)-T-cell-dependent immunopathology. Mechanistically, PSGL-1 ligation on exhausted CD8(+) Tcells inhibited Tcell receptor (TCR) and interleukin-2 (IL-2) signaling and upregulated PD-1, leading to diminished survival with TCR stimulation. In models of melanoma cancer in which Tcell dysfunction occurs, PSGL-1 deficiency led to PD-1 downregulation, improved Tcell responses, and tumor control. Thus, PSGL-1 plays a fundamental role in balancing viral control and immunopathology and also functions to regulate Tcell responses in the tumor microenvironment.

The adhesion molecule PSGL-1 is a checkpoint regulator that promotes T cell dysfunction in melanoma tumors

Abstract The tumor microenvironment can promote tumor growth by suppressing effector T cell responses. Using a melanoma model that recapitulates aspects of human disease, we investigated the role of the adhesion molecule, P-selectin glycoprotein ligand-1 (PSGL-1) in tumor infiltrating lymphocytes (TILs). We found that PSGL-1 was highly expressed on TILs that also expressed high PD-1 and TIM-3 inhibitory receptors. PSGL-1-deficiency did not impact T cell recruitment in tumors but instead resulted in a greater TIL accumulation. Furthermore, PSGL-1-deficient T cells had reduced PD-1 expression and increased production of effector cytokines that resulted in delayed tumor growth. We did not find differences in Treg recruitment but instead had an increased effector to Treg ratio in tumors. Our findings show that PSGL-1 does not have a nonredundant role in the trafficking of TILs into melanoma tumors, but can act as an immune checkpoint inhibitor to limit anti-tumor T cell responses in the tumor microenvironment thereby promoting tumor growth.

Homing in on the Sweet Side of Immune Checkpoint Biology

P-selectin glycoprotein ligand-1 (PSGL-1) and its glycostructural determinants facilitate responses to infection and cancer by promoting immune effector-cell trafficking into inflamed tissue. In this issue of Immunity, Tinoco etal. (2016) report homing-independent functions of PSGL-1 in immune checkpoint regulation and Tcell effector activity, in models of chronic viral infection and melanoma.

Thromboxane A synthase enhances blood flow recovery from hindlimb ischemia

BackgroundThromboxane A synthase (TXAS) is the enzyme that converts the arachidonic acid derivative prostaglandin H2 to thromboxane A2 (TXA2). TXA2 induces platelet aggregation, vasoconstriction, and proliferation. TXAS and TXA2 receptors or thromboxane prostanoid (TP) receptors are elevated in numerous cardiovascular and inflammatory diseases. Platelets contain numerous angiogenesis stimulating factors. However, the involvement of TXAS on recovery from an ischemic condition is not well understood. We hypothesized that the TXAS–TXA2–TP receptor axis would induce blood flow recovery by platelet activation. Material and methodsThe model of hindlimb ischemia was made by the right femoral artery ligation. The blood flow was estimated by laser Doppler images. Angiogenesis was estimated by the plasma level of the vascular endothelial growth factor and the stromal cell-derived factor-1 and by immunofluorescence analysis against CD31 and P-selectin glycoprotein ligand-1 (PSGL-1). ResultsIn wild-type mice, blood flow recovery was enhanced by treatment with murine TXAS-overexpressing fibroblasts (C57-mTXAS) compared with empty vector- (EV) treated fibroblasts (C57-EV). Compared with C57-EV-treated mice, activated platelets (P-selectin+ platelets) and plasma levels of vascular endothelial growth factor and stromal cell-derived factor-1 were increased in C57-mTXAS-treated mice. The enhanced-blood flow recovery by C57-mTXAS treatment was suppressed in the TP knockout mice (TP−/−). The expression of PSGL-1 in endothelial cells around the ischemic area was enhanced by C57-mTXAS treatment in wild-type but not in TP−/−. ConclusionsThese results indicated that local administration of C57-mTXAS-induced angiogenesis by activated platelets that bind to PSGL-1 on ischemic endothelial cells.