Measurement of soluble C-type lectin-like receptor 2 in human plasma

Abnormalities in C-type lectin-like receptor 2 in a patient with Gorham-Stout disease: the first case report

Background

Gorham-Stout disease (GSD) is a form of lymphangiomatosis of unknown etiology, characterized by abnormal distribution of lymphatic vessels. Platelets and lymphangiogenesis are closely related via C-type lectin-like receptor 2 (CLEC-2)/podoplanin.

Key Clinical Question

Despite similarities between abnormal lymphatic vessels in CLEC-2-deficient mice and patients with GSD, whether CLEC-2 on platelets is involved in GSD pathogenesis is unknown.

Clinical Approach

We examined CLEC-2 expression in platelets of a patient with lethal GSD. Most of the patient's platelets expressed aberrant CLEC-2 that was not detectable by certain monoclonal antibodies for human CLEC-2. Further, this population was not activated by a CLEC-2-activating snake venom, rhodocytin. Possible causes of abnormal CLEC-2 including anti-CLEC-2 autoantibodies, podoplanin binding to CLEC-2, and pathogenic CLEC1B gene alteration were excluded.

Conclusions

We believe that this is the first report of a patient with structurally and functionally abnormal CLEC-2. CLEC-2 abnormality may be associated with dysregulated lymphangiogenesis in GSD.

Super Formula for Soluble C-Type Lectin-Like Receptor 2 × D-Dimer in Patients With Acute Cerebral Infarction

Acute cerebral infarction (ACI) includes atherosclerotic and cardiogenic ACI and involves a thrombotic state, requiring antithrombotic treatment. However, the thrombotic state in ACI cannot be evaluated using routine hemostatic examinations. Plasma soluble C-type lectin-like receptor 2 (sCLEC-2) and D-dimer levels were measured in patients with ACI. Plasma sCLEC-2 and D-dimer levels were significantly higher in patients with ACI than in those without it. The sCLEC-2 × D-dimer formula was significantly higher in patients with ACI than in those without it. A receiver operating characteristic curve showed a high sensitivity, area under the curve, and odds for diagnosing ACI in the sCLEC-2 × D-dimer formula. Although the sCLEC-2 and D-dimer levels were useful for the differential diagnosis between cardiogenic and atherosclerotic ACI, the sCLEC-2 × D-dimer formula was not useful. sCLEC2 and D-dimer levels are useful for the diagnosis of ACI and the sCLEC2 × D-dimer formula can enhance the diagnostic ability of ACI, and sCLEC2 and D-dimer levels may be useful for differentiating between atherosclerotic and cardioembolic ACI.

High plasma soluble CLEC-2 level predicts oxygen therapy requirement in patients with COVID-19

Predicting the clinical course and allocating limited medical resources appropriately is crucial during the COVID-19 pandemic. Platelets are involved in microthrombosis, a critical pathogenesis of COVID-19; however, the role of soluble CLEC-2 (sCLEC-2), a novel platelet activation marker, in predicting the prognosis of COVID-19 remains unexplored. We enrolled 108 patients with COVID-19, hospitalized between January 2021 and May 2022, to evaluate the clinical use of sCLEC-2 as a predictive marker. sCLEC-2 levels were measured in plasma sampled on admission, as well as interleukin-6, cell-free DNA, von Willebrand factor, and thrombomodulin. We retrospectively classified the patients into two groups - those who required oxygenation during hospitalization (oxygenated group) and those who did not (unoxygenated group) - and compared their clinical and laboratory characteristics. The correlation between sCLEC-2 and the other parameters was validated. The sCLEC-2 level was significantly higher in the oxygenated group (188.8 pg/mL vs. 296.1 pg/mL). Multivariate analysis identified high sCLEC-2 levels (odds ratio per 10 pg/mL:1.25) as an independent predictor of oxygen therapy requirement. sCLEC-2 was positively correlated with cell-free DNA, supporting the association between platelet activation and neutrophil extracellular traps. In conclusion, sCLEC-2 is a clinically valuable marker in predicting oxygen therapy requirements for patients with COVID-19.

Soluble C-type lectin-like receptor 2 in stroke (CLECSTRO) study: protocol of a multicentre, prospective cohort of a novel platelet activation marker in acute ischaemic stroke and transient ischaemic attack

INTRODUCTION

Soluble C-type lectin-like receptor 2 (sCLEC-2) is a new biomarker for platelet activation, which can be easily measured by usual blood collection. We conducted the CLECSTRO, a prospective, observational cohort study, to evaluate the clinical implications of sCLEC-2 in patients with acute ischaemic stroke (AIS) and transient ischaemic attack (TIA).

METHODS AND ANALYSIS

The participants are patients with AIS/TIA and control patients required for differentiation from AIS/TIA. The target population is 600, including the patients and controls, who would be recruited from eight stroke centres across Japan. The inclusion criteria are AIS within 24 hours of onset and a modified Rankin Scale (mRS) score of 0-2, TIA within 7 days of onset, and contemporary patients required for differentiation from AIS/TIA. Plasma sCLEC-2 will be measured by high-sensitive chemiluminescent enzyme immunoassay using residual blood samples from routine laboratory examinations at the first visit in all patients and 7 days later or at discharge in patients with AIS/TIA. The outcomes include plasma levels of sCLEC-2 in patients with AIS/TIA and controls, sCLEC-2/D-dimer ratio in non-cardioembolic and cardioembolic AIS/TIA, correlation of sCLEC-2 with recurrence or worsening of stroke, severity of stroke, infarct size, ABCD2 score in TIA and outcome (mRS) at 7 days and 3 months.

ETHICS AND DISSEMINATION

This study was approved by the Ethical Committee of the University of Yamanashi as the central ethical committee in agreement with the ethical committees of all collaborative stroke centres. Informed consent will be obtained by an opt-out form from the patients at each stroke centre according to the Ethical Guidelines for Medical and Biological Research Involving Human Subjects by the Japanese Ministry of Health, Labour and Welfare.

TRIAL REGISTRATION NUMBERS

NCT05579405, UMIN000048954.

Super Formula for Diagnosing Disseminated Intravascular Coagulation Using Soluble C-Type Lectin-like Receptor 2

The scoring systems for disseminated intravascular coagulation (DIC) criteria require several adequate cutoff values, vary, and are complicated. Accordingly, a simpler and quicker diagnostic method for DIC is needed. Under such circumstances, soluble C-type lectin-like receptor 2 (sCLEC-2) received attention as a biomarker for platelet activation.

MATERIALS AND METHODS

The diagnostic usefulness of sCLEC-2 and several formulas, including sCLEC-2xD-dimer, sCLEC-2/platelet count (sCLEC-2/PLT), and sCLEC-2/PLT × D-dimer (sCLEC-2xD-dimer/PLT), were evaluated among 38 patients with DIC, 39 patients with pre-DIC and 222 patients without DIC or pre-DIC (non-DIC).

RESULTS

Although the plasma level of sCLEC-2 alone was not a strong biomarker for the diagnosis of DIC or pre-DIC, the sCLEC-2xD-dimer/PLT values in patients with DIC were significantly higher than those in patients without DIC, and in a receiver operating characteristic (ROC) analysis for the diagnosis of DIC, sCLEC-2xD-dimer/PLT showed the highest AUC, sensitivity, and odds ratio. This formula is useful for the diagnosis of both pre-DIC and DIC. sCLEC-2xD-dimer/PLT values were significantly higher in non-survivors than in survivors.

CONCLUSION

The sCLEC-2xD-dimer/PLT formula is simple, easy, and highly useful for the diagnosis of DIC and pre-DIC without the use of a scoring system.

Co-Expression of Podoplanin and CD44 in Proliferative Vitreoretinopathy Epiretinal Membranes

Epiretinal membranes (ERMs) are sheets of tissue that pathologically develop in the vitreoretinal interface leading to progressive vision loss. They are formed by different cell types and by an exuberant deposition of extracellular matrix proteins. Recently, we reviewed ERMs' extracellular matrix components to better understand molecular dysfunctions that trigger and fuel the onset and development of this disease. The bioinformatics approach we applied delineated a comprehensive overview on this fibrocellular tissue and on critical proteins that could really impact ERM physiopathology. Our interactomic analysis proposed the hyaluronic-acid-receptor cluster of differentiation 44 (CD44) as a central regulator of ERM aberrant dynamics and progression. Interestingly, the interaction between CD44 and podoplanin (PDPN) was shown to promote directional migration in epithelial cells. PDPN is a glycoprotein overexpressed in various cancers and a growing body of evidence indicates its relevant function in several fibrotic and inflammatory pathologies. The binding of PDPN to partner proteins and/or its ligand results in the modulation of signaling pathways regulating proliferation, contractility, migration, epithelial-mesenchymal transition, and extracellular matrix remodeling, all processes that are vital in ERM formation. In this context, the understanding of the PDPN role can help to modulate signaling during fibrosis, hence opening a new line of therapy.

Elevated ratio of C-type lectin-like receptor 2 level and platelet count (C2PAC) aids in the diagnosis of post-operative venous thromboembolism in IDH-wildtype gliomas

INTRODUCTION

Podoplanin (PDPN) is known to induce platelet aggregation via interacting with the C-type lectin-like receptor-2 on platelets and is involved in postoperative venous thromboembolism (VTE) formation. In this study, we investigate the correlation between soluble C-type lectin-like receptor (sCLEC-2) levels and PDPN expression in patients with high grade gliomas and the relationship between sCLEC-2 levels and the occurrence of VTE.

MATERIALS AND METHODS

Forty-four patients harboring high grade gliomas, treated surgically at the Department of Neurosurgery, Niigata University from April 2018 to August 2020, were included. Patients with high grade gliomas were divided into isocitrate dehydrogenase (IDH)- wildtype and mutant groups, and the presence or absence of VTE and the intensity of PDPN by immunohistochemistry were confirmed. Platelet counts, as well as plasma sCLEC-2 and PDPN were measured in these patients. Furthermore, the levels of sCLEC-2 concentration were divided by the platelet count (C2PAC index) for comparison.

RESULTS

IDH-wildtype glioma patients highly expressed PDPN (P < 0.001) compared to IDH-mutant glioma patients. In total, 9 (20.5 %) patients were diagnosed with VTE during the follow-up period, of which 8 patients harbored IDH-wildtype gliomas, and one patient an IDH-mutant glioma. Mean sCLEC-2 levels and C2PAC index in patients with IDH-wildtype gliomas were significantly higher than that of low or no PDPN expression group, which included patients with IDH-mutant gliomas (P = 0.0004, P = 0.0002). In patients with IDH-wildtype gliomas, the C2PAC index in patients with VTE was significantly higher than in patients without VTE (P = 0.0492). The optimal cutoff point of C2PAC for predicting VTE in IDH-wildtype glioma patients was 3.7 with a sensitivity of 87.5 % and specificity of 51.9 %.

CONCLUSION

Platelet activation is strongly involved in the development of VTE in patients with IDH-wildtype high grade gliomas, and C2PAC index is a potential marker to detect VTE formation after surgery.

C-type lectin-like receptor (CLEC)-2, the ligand of podoplanin, induces morphological changes in podocytes

Podoplanin (PDPN) is intensely expressed on the podocyte membrane in an evolutionally conserved manner. CLEC-2, the endogenous ligand of PDPN, is highly expressed in platelets and also exists in a soluble form in plasma. Normally, podocytes are sequestered from CLEC-2, but when the glomerular barrier is injured, podocytes gain access to CLEC-2. We tested the effects of CLEC-2 in podocytes in vitro and in vivo. Cultured podocytes treated with Fc-CLEC-2 demonstrated that CLEC-2 induced the dephosphorylation of ezrin, radixin, and moesin (ERM) proteins. Podocytes treated with Fc-CLEC-2 also showed the dissociation of F-actin filaments from PDPN, F-actin degradation, detachment, and round morphology. Next, we perfused normal mouse kidney in vivo with FLAG-CLEC-2. CLEC-2 induced dephosphorylation of ERM and widening of the foot processes of podocytes. Platelets were detected by immunostaining for CD41 in the urine of mice with podocyte injury, indicating that podocytes can encounter platelets when glomeruli are injured. Collectively, these observations suggest that when platelets leak through the injured glomeruli, CLEC-2 from the platelets acts on PDPN in podocytes and induces morphological change and detachment, which may further aggravate podocyte injury. Thus, PDPN on podocytes may work as a leaked-platelet sensor.

Association between c-type lectin-like receptor 2 and microsatellite instability in colorectal cancer: a cross-sectional study

Background

As a transmembrane protein, C-type lectin-like receptor 2 (CLEC-2) is mainly expressed on platelets and released into plasma after platelet activation. Activated platelets participate in the regulation of innate immune cells. Patients with different microsatellite statuses have distinct immune profiles. This study aimed to investigate the association of plasma CLEC-2 levels with microsatellite status among colorectal cancer (CRC) patients.

Methods

A cross-sectional analysis of 430 CRC patients from Harbin Medical University Cancer Hospital was conducted. CLEC-2 levels were measured with fasting venous blood samples drawn from each participant before any treatment. The microsatellite status was evaluated with DNA obtained from fresh frozen tumor tissue samples. The other clinical data were collected and recorded based on the medical system records.

Results

CLEC-2 levels were significantly higher among patients with high microsatellite instability phenotype than the stable microsatellite group, adjusting for other confounding variables.

Conclusions

The increased CLEC-2 is associated with the high microsatellite instability subtype of CRC.

Early recognition of sepsis-induced coagulopathy using the C2PAC index: a ratio of soluble type C lectin-like receptor 2 (sCLEC-2) level and platelet count

C-type lectin-like receptor 2 (CLEC-2) is a platelet-activated receptor expressed on the surface of platelet membranes. Soluble CLEC-2 (sCLEC-2) has been receiving attention as a predictive marker for thrombotic predisposition. The present study examined the relationship between sCLEC-2 level and degree of coagulation disorder in septic patients. Seventy septic patients were divided into the sepsis-induced disseminated intravascular coagulation (DIC) (SID) group (n = 44) and non-SID group (n = 26). The sCLEC-2 levels were compared between the two groups. Because we suspected that the sCLEC-2 level was affected by the platelet count, we calculated the sCLEC-2/platelet count ratio (C2PAC index). We further divided septic patients into four groups using the Japanese Association for Acute Medicine (JAAM) DIC scoring system (DIC scores: 0-1, 2-3, 4-5, and 6-8). The C2PAC index was significantly higher in the SID group (2.6 ± 1.7) compared with the non-SID group (1.2 ± 0.5) (P < .001). The C2PAC indexes in the four JAAM DIC score groups were 0.9 ± 0.3, 1.1 ± 0.3, 1.7 ± 0.7, and 3.6 ± 1.0, respectively, and this index increased significantly as the DIC score increased (P < .001). According to the receiver-operating curve analysis, the area under the curve (AUC) and optimal cutoff value for the diagnosis of SID were 0.8051 and 1.4 (sensitivity, 75.0%; specificity, 76.9%), respectively. When the C2PAC index and D-dimer level, one of the main fibrinolytic markers, were selected as predictive markers for SID diagnosis in stepwise multiple logistic regression analysis, it was possible to diagnose SID with a high probability (AUC, 0.9528; sensitivity, 0.9545; specificity, 0.8846). The C2PAC index is a useful predictor of SID progression and diagnosis in septic patients.

Correlation of CLEC1B haplotypes with plasma levels of soluble CLEC-2 in healthy individuals

Binding of podoplanin to the C-type lectin-like receptor 2 (CLEC-2) promotes platelet activation and soluble CLEC-2 (sCLEC-2) is shed from activated platelets. The role of sCLEC-2 in the plasma is unknown. The expression level and plasma concentration of sCLEC-2 could be affected by variants of the corresponding gene, CLEC1B. Here, we genotyped SNVs in the promoter and coding region of CLEC1B and determined plasma levels of sCLEC-2 in healthy individuals. We genotyped 516 healthy blood donors for 7 SNVs (rs10505743, rs11053538, rs4764178, rs76016091, rs2273986, rs2273987, rs521040) by using PCR methods and calculated haplotypes from the SNV genotypes. For 313 of the donors we measured the sCLEC-2 concentration in EDTA plasma samples by using a commercial ELISA. SNV typing revealed allele frequencies comparable to database information. None of the SNVs showed significant correlation with sCLEC-2 plasma levels. Haplotype analysis indicated 6 haplotypes with frequencies >1% and haplotype h3 was the most frequent (33.8%). Donors homozygous for h3 (n = 37) showed significantly lower sCLEC-2 plasma levels (median 0.95 ng/mL) than donors being h3 negative or heterozygous (n = 276; 1.44 ng/mL; p = .0203). We found that the sCLEC-2 plasma concentration is variable in healthy individuals and the CLEC1B genotype contributes to the expression level.

The Mannose Receptor: From Endocytic Receptor and Biomarker to Regulator of (Meta)Inflammation

The mannose receptor is a member of the C-type lectin (CLEC) family, which can bind and internalize a variety of endogenous and pathogen-associated ligands. Because of these properties, its role in endocytosis as well as antigen processing and presentation has been studied intensively. Recently, it became clear that the mannose receptor can directly influence the activation of various immune cells. Cell-bound mannose receptor expressed by antigen-presenting cells was indeed shown to drive activated T cells towards a tolerogenic phenotype. On the other hand, serum concentrations of a soluble form of the mannose receptor have been reported to be increased in patients suffering from a variety of inflammatory diseases and to correlate with severity of disease. Interestingly, we recently demonstrated that the soluble mannose receptor directly promotes macrophage proinflammatory activation and trigger metaflammation. In this review, we highlight the role of the mannose receptor and other CLECs in regulating the activation of immune cells and in shaping inflammatory responses.

Soluble C-Type Lectin-Like Receptor 2 Elevation in Patients with Acute Cerebral Infarction

Background: Acute cerebral infarction (ACI) includes cardiogenic ACI treated with anticoagulants and atherosclerotic ACI treated with antiplatelet agents. The differential diagnosis between cardiogenic and atherosclerotic ACI is still difficult. Materials and Methods: The plasma sCLEC-2 and D-dimer levels were measured using the STACIA system. Results: The plasma sCLEC-2 level was significantly high in patients with ACI, especially those in patients with atherosclerotic or lacunar ACI, and plasma D-dimer levels were significantly high in patients with cardioembolic ACI. The plasma levels of sCLEC-2 and the sCLEC-2/D-dimer ratios in patients with atherosclerotic or lacunar ACI were significantly higher than those in patients with cardioembolic ACI. The plasma D-dimer levels in patients with atherosclerotic or lacunar ACI were significantly lower than those in patients with cardioembolic ACI. The plasma levels of sCLEC-2 and the sCLEC-2/D-dimer ratios were significantly higher in patients with atherosclerotic or lacunar ACI or acute myocardial infarction in comparison to patients with cardioembolic ACI or those with deep vein thrombosis. Conclusion: Using both the plasma sCLEC-2 and D-dimer levels may be useful for the diagnosis of ACI, and differentiating between atherosclerotic and cardioembolic ACI.

Plasma soluble C-type lectin-like receptor-2 is associated with the risk of coronary artery disease

Accumulating evidence suggests that C-type lectin-like receptor-2 (CLEC-2) plays an important role in atherothrombosis. In this case-control study, we investigated the association between CLEC-2 and incidence of coronary artery disease (CAD). A total of 216 patients, including 14 cases of stable angina pectoris (SAP, non-ACS) and 202 cases of acute coronary syndrome (ACS), and 89 non-CAD control subjects were enrolled. Plasma levels of soluble CLEC-2 (sCLEC-2) were measured using the enzyme-linked immunosorbent assay (ELISA). Compared with the control group (65.69 (55.36-143.22) pg/mL), the plasma levels of sCLEC-2 were significantly increased in patients with CAD (133.67 (88.76-220.09) pg/mL) and ACS (134.16 (88.88-225.81) pg/mL). The multivariate adjusted odds ratios (95% confidence interval) of CAD reached 2.01 (1.52-2.66) (P_trend < 0.001) for each 1-quartile increase in sCLEC-2. Restricted cubic splines showed a positive dose-response association between sCLEC2 and CAD incidence (P_linearity < 0.001). The addition of sCLEC-2 to conventional risk factors improved the C statistic (0.821 vs. 0.761, P = 0.004) and reclassification ability (net reclassification improvement: 57.45%, P < 0.001; integrated discrimination improvement: 8.27%, P < 0.001) for CAD. In conclusion, high plasma sCLEC-2 is independently associated with CAD risk, and the prognostic value of sCLEC-2 may be evaluated in future prospective studies.

Plasma C-type lectin-like receptor 2 as a predictor of death and vascular events in patients with acute ischemic stroke

BACKGROUND AND PURPOSE

C-type lectin-like receptor 2 (CLEC-2) has prominent involvement in platelet activation, which is increased in coronary heart disease and acute ischaemic stroke (AIS) and is associated with stroke progression and stroke prognosis. Here, the aim was to examine the prognostic value of CLEC-2 in death and vascular event recurrence in AIS patients.

METHODS

In all, 352 patients with AIS were studied prospectively. All patients were followed up for 1 year. Death for all vascular events and a combination of death and vascular diseases (recurrent stroke, myocardial infarction, hospitalized and treated angina, hospitalized and treated peripheral arterial disease) were recorded.

RESULTS

During 1 year of follow-up, 46 patients (14.2%) experienced death or combined end-points (23 death and 46 combined end-points). Plasma CLEC-2 (pCLEC-2) was significantly associated with an increased risk of death and combined events of death and vascular diseases after adjusting for age, sex, history of hypertension, diabetes mellitus and coronary artery disease, and National Institutes of Health Stroke Scale scores. Each 1 SD higher log-transformed pCLEC-2 was associated with a 4.27-fold (hazard ratio 4.27, 95% confidence interval 1.71-10.65) increased risk for death and a 2.42-fold increased risk for combined end-points (hazard ratio 2.42, 95% confidence interval 1.52-3.86). The optimal cut-off point of pCLEC-2 for predicting death was 184.38 pg/ml.

CONCLUSIONS

Higher pCLEC-2 levels at admission were associated with increased risk of death and combined events of death and vascular diseases in patients with AIS, which indicated that pCLEC-2 is an important prognostic factor for AIS.

Soluble CLEC-2 is generated independently of ADAM10 and is increased in plasma in acute coronary syndrome: comparison with soluble GPVI

Soluble forms of platelet membrane proteins are released upon platelet activation. We previously reported that soluble C-type lectin-like receptor 2 (sCLEC-2) is released as a shed fragment (Shed CLEC-2) or as a whole molecule associated with platelet microparticles (MP-CLEC-2). In contrast, soluble glycoprotein VI (sGPVI) is released as a shed fragment (Shed GPVI), but not as a microparticle-associated form (MP-GPVI). However, mechanism of sCLEC-2 generation or plasma sCLEC-2 has not been fully elucidated. Experiments using metalloproteinase inhibitors/stimulators revealed that ADAM10/17 induce GPVI shedding, but not CLEC-2 shedding, and that shed CLEC-2 was partially generated by MMP-2. Although MP-GPVI was not generated, it was generated in the presence of the ADAM10 inhibitor. Moreover, antibodies against the cytoplasmic or extracellular domain of GPVI revealed the presence of the GPVI cytoplasmic domain, but not the extracellular domain, in the microparticles. These findings suggest that most of the GPVI on microparticles are induced to shed by ADAM10; MP-GPVI is thus undetected. Plasma sCLEC-2 level was 1/32 of plasma sGPVI level in normal subjects, but both soluble proteins significantly increased in plasma of patients with acute coronary syndrome. Thus, sCLEC-2 and sGPVI are released by different mechanisms and released in vivo upon platelet activation.

Elevated plasma levels of soluble C-type lectin-like receptor 2 (CLEC2) in patients with thrombotic microangiopathy

BACKGROUND

Thrombotic microangiopathy (TMA) is caused by activated platelets. The plasma C-type lectin-like receptor 2 (CLEC2) levels in 58 patients with TMA were examined and compared with those in healthy volunteers and other diseases.

MATERIALS AND METHODS

The plasma levels of soluble platelet surface glycoprotein VI (GPVI) and CLEC2 were measured in patients with TMA.

RESULTS

Plasma CLEC2 levels in patients with DIC and TMA were significantly higher (p < 0.001) than those in thrombocytopenic patients with other hematological diseases, but no significant differences in the plasma CLEC2 levels were observed among patients with thrombotic thrombocytopenic purpura, hemolytic uremic syndrome (HUS), atypical HUS and other TMA. The plasma CLEC2 levels after the remission were significantly lower than those before treatment (p < 0.001). The plasma CLEC2 levels were poorly correlated with the levels of soluble GPVI in the plasma of patients with TMA. The plasma CLEC2 levels were not significantly differ between survivor and non-survivor in TMA patients, but were significantly higher in non-survivor in overall population (p < 0.001).

CONCLUSION

The measurement of the plasma CLEC2 level is considered to be important for the diagnosis and evaluation of TMA.

Functional significance of the platelet immune receptors GPVI and CLEC-2

Although platelets are best known for their role in hemostasis, they are also crucial in development, host defense, inflammation, and tissue repair. Many of these roles are regulated by the immune-like receptors glycoprotein VI (GPVI) and C-type lectin receptor 2 (CLEC-2), which signal through an immunoreceptor tyrosine-based activation motif (ITAM). GPVI is activated by collagen in the subendothelial matrix, by fibrin and fibrinogen in the thrombus, and by a remarkable number of other ligands. CLEC-2 is activated by the transmembrane protein podoplanin, which is found outside of the vasculature and is upregulated in development, inflammation, and cancer, but there is also evidence for additional ligands. In this Review, we discuss the physiological and pathological roles of CLEC-2 and GPVI and their potential as targets in thrombosis and thrombo-inflammatory disorders (i.e., disorders in which inflammation plays a critical role in the ensuing thrombosis) relative to current antiplatelet drugs.

Podoplanin-positive periarteriolar stromal cells promote megakaryocyte growth and proplatelet formation in mice by CLEC-2

BM FRC-like cells regulate megakaryocytic clonal expansion via CLEC-2/PDPN interactions. CLEC-2/PDPN binding stimulates BM FRC-like cells to secrete the proplatelet formation-promoting factor, CCL5.