Activated Platelets Upregulate β2 Integrin Mac-1 (CD11b/CD18) on Dendritic Cells, Which Mediates Heterotypic Cell-Cell Interaction

Extracellular vesicles from the lung pro-thrombotic niche drive cancer-associated thrombosis and metastasis via integrin beta 2

Cancer is a systemic disease with complications beyond the primary tumor site. Among them, thrombosis is the second leading cause of death in patients with certain cancers (e.g., pancreatic ductal adenocarcinoma [PDAC]) and advanced-stage disease. Here, we demonstrate that pro-thrombotic small extracellular vesicles (sEVs) are secreted by C-X-C motif chemokine 13 (CXCL13)-reprogrammed interstitial macrophages in the non-metastatic lung microenvironment of multiple cancers, a niche that we define as the pro-thrombotic niche (PTN). These sEVs package clustered integrin β2 that dimerizes with integrin αX and interacts with platelet-bound glycoprotein (GP)Ib to induce platelet aggregation. Blocking integrin β2 decreases both sEV-induced thrombosis and lung metastasis. Importantly, sEV-β2 levels are elevated in the plasma of PDAC patients prior to thrombotic events compared with patients with no history of thrombosis. We show that lung PTN establishment is a systemic consequence of cancer progression and identify sEV-β2 as a prognostic biomarker of thrombosis risk as well as a target to prevent thrombosis and metastasis.

Platelets in Alcohol-Associated Liver Disease: Interaction With Neutrophils

Alcohol-associated liver disease (ALD) is a major contributor to liver-related mortality globally. An increasing body of evidence underscores the pivotal role of platelets throughout the spectrum of liver injury and recovery, offering unique insights into liver homeostasis and pathobiology. Alcoholic-associated steatohepatitis is characterized by the infiltration of hepatic neutrophils. Recent studies have highlighted the extensive distance neutrophils travel through sinusoids to reach the liver injury site, relying on a platelet-paved endothelium for efficient crawling. The adherence of platelets to neutrophils is crucial for accurate migration from circulation to the inflammatory site. A gradual decline in platelet levels leads to diminished neutrophil recruitment. Platelets exhibit the ability to activate neutrophils. Platelet activation is heightened upon the release of platelet granule contents, which synergistically activate neutrophils through their respective receptors. The sequence culminates in the formation of platelet-neutrophil complexes and the release of neutrophil extracellular traps intensifies liver damage, fosters inflammatory immune responses, and triggers hepatotoxic processes. Neutrophil infiltration is a hallmark of alcohol-associated steatohepatitis, and the roles of neutrophils in ALD pathogenesis have been studied extensively, however, the involvement of platelets in ALD has received little attention. The current review consolidates recent findings on the intricate and diverse roles of platelets and neutrophils in liver pathophysiology and in ALD. Potential therapeutic strategies are highlighted, focusing on targeting platelet-neutrophil interactions and activation in ALD. The anticipation is that innovative methods for manipulating platelet and neutrophil functions will open promising avenues for future ALD therapy.

Integrins in Health and Disease-Suitable Targets for Treatment?

Integrin receptors are heterodimeric surface receptors that play multiple roles regarding cell-cell communication, signaling, and migration. The four members of the β2 integrin subfamily are composed of an alternative α (CD11a-d) subunit, which determines the specific receptor properties, and a constant β (CD18) subunit. This review aims to present insight into the multiple immunological roles of integrin receptors, with a focus on β2 integrins that are specifically expressed by leukocytes. The pathophysiological role of β2 integrins is confirmed by the drastic phenotype of patients suffering from leukocyte adhesion deficiencies, most often resulting in severe recurrent infections and, at the same time, a predisposition for autoimmune diseases. So far, studies on the role of β2 integrins in vivo employed mice with a constitutive knockout of all β2 integrins or either family member, respectively, which complicated the differentiation between the direct and indirect effects of β2 integrin deficiency for distinct cell types. The recent generation and characterization of transgenic mice with a cell-type-specific knockdown of β2 integrins by our group has enabled the dissection of cell-specific roles of β2 integrins. Further, integrin receptors have been recognized as target receptors for the treatment of inflammatory diseases as well as tumor therapy. However, whereas both agonistic and antagonistic agents yielded beneficial effects in animal models, the success of clinical trials was limited in most cases and was associated with unwanted side effects. This unfavorable outcome is most probably related to the systemic effects of the used compounds on all leukocytes, thereby emphasizing the need to develop formulations that target distinct types of leukocytes to modulate β2 integrin activity for therapeutic applications.

Thromboinflammatory challenges in stroke pathophysiology

Despite years of encouraging translational research, ischemic stroke still remains as one of the highest unmet medical needs nowadays, causing a tremendous burden to health care systems worldwide. Following an ischemic insult, a complex signaling pathway emerges leading to highly interconnected thrombotic as well as neuroinflammatory signatures, the so-called thromboinflammatory cascade. Here, we thoroughly review the cell-specific and time-dependent role of different immune cell types, i.e., neutrophils, macrophages, T and B cells, as key thromboinflammatory mediators modulating the neuroinflammatory response upon stroke. Similarly, the relevance of platelets and their tight crosstalk with a variety of immune cells highlights the relevance of this cell-cell interaction during microvascular dysfunction, neovascularization, and cellular adhesion. Ultimately, we provide an up-to-date overview of therapeutic approaches mechanistically targeting thromboinflammation currently under clinical translation, especially focusing on phase I to III clinical trials.

Carbohydrate ligand engagement with CD11b enhances differentiation of tumor-associated myeloid cells for immunotherapy of solid cancers

BACKGROUND

Efforts to modulate the function of tumor-associated myeloid cell are underway to overcome the challenges in immunotherapy and find a cure. One potential therapeutic target is integrin CD11b, which can be used to modulate the myeloid-derived cells and induce tumor-reactive T-cell responses. However, CD11b can bind to multiple different ligands, leading to various myeloid cell functions such as adhesion, migration, phagocytosis, and proliferation. This has created a major challenge in understanding how CD11b converts the differences in the receptor-ligand binding into subsequent signaling responses and using this information for therapeutic development.

METHODS

This study aimed to investigate the antitumor effect of a carbohydrate ligand, named BG34-200, which modulates the CD11b⁺ cells. We have applied peptide microarrays, multiparameter FACS (fluorescence-activated cell analysis) analysis, cellular/molecular immunological technology, advanced microscopic imaging, and transgenic mouse models of solid cancers, to study the interaction between BG34-200 carbohydrate ligand and CD11b protein and the resulting immunological changes in the context of solid cancers, including osteosarcoma, advanced melanoma, and pancreatic ductal adenocarcinoma (PDAC).

RESULTS

Our results show that BG34-200 can bind directly to the activated CD11b on its I (or A) domain, at previously unreported peptide residues, in a multisite and multivalent manner. This engagement significantly impacts the biological function of tumor-associated inflammatory monocytes (TAIMs) in osteosarcoma, advanced melanoma, and PDAC backgrounds. Importantly, we observed that the BG34-200-CD11b engagement triggered endocytosis of the binding complexes in TAIMs, which induced intracellular F-actin cytoskeletal rearrangement, effective phagocytosis, and intrinsic ICAM-1 (intercellular adhesion molecule I) clustering. These structural biological changes resulted in the differentiation in TAIMs into monocyte-derived dendritic cells, which play a crucial role in T-cell activation in the tumor microenvironment.

CONCLUSIONS

Our research has advanced the current understanding of the molecular basis of CD11b activation in solid cancers, revealing how it converts the differences in BG34 carbohydrate ligands into immune signaling responses. These findings could pave the way for the development of safe and novel BG34-200-based therapies that modulate myeloid-derived cell functions, thereby enhancing immunotherapy for solid cancers.

Platelet, a key regulator of innate and adaptive immunity

Platelets, anucleate blood components, represent the major cell type involved in the regulation of hemostasis and thrombosis. In addition to performing haemostatic roles, platelets can influence both innate and adaptive immune responses. In this review, we summarize the development of platelets and their functions in hemostasis. We also discuss the interactions between platelet products and innate or adaptive immune cells, including neutrophils, monocytes, macrophages, T cells, B cells and dendritic cells. Activated platelets and released molecules regulate the differentiation and function of these cells via platelet-derived receptors or secreting molecules. Platelets have dual effects on nearly all immune cells. Understanding the exact mechanisms underlying these effects will enable further application of platelet transfusion.

Effects of the interactions between platelets with other cells in tumor growth and progression

It has been confirmed that platelets play a key role in tumorigenesis. Tumor-activated platelets can recruit blood cells and immune cells to migrate, establish an inflammatory tumor microenvironment at the sites of primary and metastatic tumors. On the other hand, they can also promote the differentiation of mesenchymal cells, which can accelerate the proliferation, genesis and migration of blood vessels. The role of platelets in tumors has been well studied. However, a growing number of studies suggest that interactions between platelets and immune cells (e.g., dendritic cells, natural killer cells, monocytes, and red blood cells) also play an important role in tumorigenesis and tumor development. In this review, we summarize the major cells that are closely associated with platelets and discuss the essential role of the interaction between platelets with these cells in tumorigenesis and tumor development.

Platelet depletion does not alter long-term functional outcome after cerebral ischaemia in mice

Platelets are key mediators of thrombus formation and inflammation during the acute phase of ischaemic stroke. Particularly, the platelet glycoprotein (GP) receptors GPIbα and GPVI have been shown to mediate platelet adhesion and activation in the ischaemic brain. GPIbα and GPVI blockade could reduce infarct volumes and improve functional outcome in mouse models of acute ischaemic stroke, without concomitantly increasing intracerebral haemorrhage. However, the functional role of platelets during long-term stroke recovery has not been elucidated so far.

Thus, we here examined the impact of platelet depletion on post-stroke recovery after transient middle cerebral artery occlusion (tMCAO) in adult male mice. Platelet depleting antibodies or isotype control were applied from day 3–28 after tMCAO in mice matched for infarct size. Long-term functional recovery was assessed over the course of 28 days by behavioural testing encompassing motor and sensorimotorical functions, as well as anxiety-like or spontaneous behaviour. Whole brain flow cytometry and light sheet fluorescent microscopy were used to identify resident and infiltrated immune cell types, and to determine the effects of platelet depletion on the cerebral vascular architecture, respectively.

We found that delayed platelet depletion does not improve long-term functional outcome in the tMCAO stroke model. Immune cell abundance, the extent of thrombosis and the organisation of the cerebral vasculature were also comparable between platelet-depleted and control mice. Our study demonstrates that, despite their critical role in the acute stroke setting, platelets appear to contribute only marginally to tissue reorganisation and functional recovery at later stroke stages.

•

Stable and safe global platelet depletion can be achieved for a prolonged period.

•

Platelets only play a minor role in neurological recovery during the chronic phase.

•

Platelet depletion after infarct maturation does not alter inflammatory response.

•

Cerebral architecture after stroke is not influenced by delayed platelet depletion.

Regulation of Atherosclerosis by Toll-Like Receptor 4 Induced by Serum Amyloid 1: A Systematic In Vitro Study

The objective of this study was to investigate the effects of serum amyloid 1 (SAA1) on activation of endothelial cells, formation of foam cells, platelet aggregation, and monocyte/platelet adhesion to endothelial cells. The effect of SAA1 on the inflammatory activation of endothelial cells was investigated by detecting the expression of inflammatory factors and adhesion molecules. The role of SAA1 in formation of foam cells was verified by detecting lipid deposition and expression of molecules related to the formation of foam cells. After platelets were stimulated by SAA1, the aggregation rate was evaluated to determine the effect of SAA1 on platelet aggregation. Monocytes/platelets were cocultured with human umbilical vein endothelial cells (HUVECs) pretreated with or without SAA1 to determine whether SAA1 affected monocyte/platelet adhesion to endothelial cells. By inhibiting toll-like receptor 4 (TLR4) function, we further identified the role of TLR4 signaling in SAA1-mediated endothelial inflammatory activation, foam-cell formation, and monocyte/platelet adhesion to HUVECs. SAA1 significantly increased the expression of adhesion molecules and inflammatory factors in HUVECs. Moreover, SAA1 also promoted lipid deposition and the expression of inflammatory factors and low-density lipoprotein receptor-1 (LOX-1) in THP-1-derived macrophages. In addition, SAA1 induced platelet aggregation and enhanced monocyte/platelet adhesion to HUVECs. However, the TLR4 antagonist significantly inhibited SAA1-induced endothelial cell activation, foam-cell formation, and monocyte/platelet adhesion to HUVECs and downregulated the expression of myeloid differentiation factor 88 (MyD88), phosphor-inhibitor of nuclear factor κB kinase subunit α/β (P-IKKα/β), phospho-inhibitor of nuclear factor κB subunit α (P-IKBα), and phosphorylation of nuclear transcription factor-κB p65 (P-p65) in SAA1-induced HUVECs and THP-1 cells. Conclusively, it is speculated that SAA1 promotes atherosclerosis through enhancing endothelial cell activation, platelet aggregation, foam-cell formation, and monocyte/platelet adhesion to endothelial cells. These biological functions of SAA1 may depend on the activation of TLR4-related nuclear factor-kappa B (NF-κB) signaling pathway.