Surveillance of megakaryocytic function by measurement of CD61-exposing microparticles in allogeneic hematopoietic stem cell recipients

Circulating extracellular vesicles as a predictive biomarker for acute graft-versus-host disease

The diagnosis and management of graft-versus-host disease (GVHD) have remained important challenges in allogeneic stem cell transplantation (allo-SCT). Novel diagnostic methods and therapeutic interventions are needed to further improve on patient outcomes. Extracellular vesicles (EV) are microvesicles formed by the inversion of the phospholipid bilayer of different cellular subtypes and have been described as biomarkers of cellular damage, activation, and intercellular signaling in numerous clinical scenarios. We studied the association between the levels of EV and the incidence of acute GVHD (aGVHD). Forty patients undergoing allo-SCT for hematological malignancies had their plasma collected at neutrophil engraftment. Using flow cytometry combined with fluorescent beads, the total circulating EV count (TEV) was established with annexin V positivity; CD61 positivity was used for platelet-derived EV (PEV), and CD235 positivity, for erythrocyte-derived EV (EryEV). TEV counts greater than 516/μL were associated with a higher cumulative incidence (CI) of grade II to IV aGVHD (54% vs. 21%; p = 0.02), as were EryEV counts above 357 /μL (CI of aGVHD: 59% vs. 26%; p = 0.04). In patients who are exposed to reduced intensity conditioning (RIC), stronger associations of both high TEV and EryEV counts with aGVHD were observed (77% vs. 22%; p = 0.003 and 89% vs. 27%; p = 0.002, respectively). PEV levels were not associated with the risk of aGVHD. Our data suggest that the measurement of cell-derived EV at engraftment can be used as a preemptive biomarker for acute GVHD.

Microparticles in systemic sclerosis, targets or tools to control fibrosis: This is the question!

Systemic sclerosis is the main systemic fibrotic disease with unknown etiology characterized by peripheral microvascular injury, activation of immune system, and wide-spread progressive fibrosis. Microparticles can be derived from any cell type during normal cellular differentiation, senescence, and apoptosis, and also upon cellular activation. Carrying along a broad range of surface cytoplasmic and nuclear molecules of originating cells, microparticles are closely implicated in inflammation, thrombosis, angiogenesis, and immunopathogenesis. Recently, microparticles have been proposed as biomarkers of endothelial injury, which is the primary event in the genesis of tissue fibrosis. Microparticles may have a role in fostering endothelial to mesenchymal transition, thus giving a significant contribution to the development of myofibroblasts, the most important final effectors responsible for tissue fibrosis and fibroproliferative vasculopathy. Thanks to potent profibrotic mediators, such as transforming growth factor beta, platelet-derived growth factor, high mobility group box 1 protein, nicotinamide adenine dinucleotide phosphate oxidase 4, and antifibrotic agents, such as matrix metalloproteinases, microparticles may play an opposite role in fibrosis.

Endothelial Microparticles in Uremia: Biomarkers and Potential Therapeutic Targets

Endothelial microparticles (EMPs) are vesicles derived from cell membranes, which contain outsourced phosphatidylserine and express adhesion molecules, such as cadherin, intercellular cell adhesion molecule-1 (ICAM-1), E-selectin, and integrins. EMPs are expressed under physiological conditions and continue circulating in the plasma. However, in pathologic conditions their levels increase, and they assume a pro-inflammatory and pro-coagulant role via interactions with monocytes; these effects are related to the development of atherosclerosis. Chronic kidney dysfunction (CKD) characterizes this dysfunctional scenario through the accumulation of uremic solutes in the circulating plasma, whose toxicity is related to the development of cardiovascular diseases. Therefore, this review aims to discuss the formation of EMPs and their biological effects in the uremic environment. Data from previous research demonstrate that uremic toxins are closely associated with the activation of inflammatory biomarkers, cardiovascular dysfunction processes, and the release of EMPs. The impact of a decrease in circulating EMPs in clinical studies has not yet been evaluated. Thus, whether MPs are biochemical markers and/or therapeutic targets has yet to be established.

Circulating microparticles: challenges and perspectives of flow cytometric assessment

Circulating blood microparticles are likely to play a significant role as messengers of biological information. Their accurate quantification and characterisation is challenging and needs to be carefully designed with preferable usage of fresh minimally-processed blood samples. Utilisation of flow cytometers specifically designed for analysis of small-size particles is likely to provide considerable methodological advantages and should be the preferable option. This viewpoint manuscript provides a critical summary of the key methodological aspects of microparticle analysis.

Note: The review process for this viewpoint article was fully handled by Christian Weber, Editor in Chief.

Role of mTOR1 and mTOR2 complexes in MEG-01 cell physiology

The function of the mammalian target of rapamycin (mTOR) is upregulated in response to cell stimulation with growing and differentiating factors. Active mTOR controls cell proliferation, differentiation and death. Since mTOR associates with different proteins to form two functional macromolecular complexes, we aimed to investigate the role of the mTOR1 and mTOR2 complexes in MEG-01 cell physiology in response to thrombopoietin (TPO). By using mTOR antagonists and overexpressing FKBP38, we have explored the role of both mTOR complexes in proliferation, apoptosis, maturation-like mechanisms, endoplasmic reticulum-stress and the intracellular location of both active mTOR complexes during MEG-01 cell stimulation with TPO. The results demonstrate that mTOR1 and mTOR2 complexes play different roles in the physiology of MEG-01 cells and in the maturation-like mechanisms; hence, these findings might help to understand the mechanism underlying generation of platelets.

Characterization of platelet-monocyte complexes in HIV-1-infected individuals: possible role in HIV-associated neuroinflammation

HIV-1-associated neuroinflammation persists even with effective combined antiretroviral therapy, and it is associated with the presence of activated monocytes/macrophages within the CNS. To infiltrate the CNS, monocytes transmigrate across the selectively permeable blood-brain barrier, which is compromised during HIV-1 infection. Interestingly, platelet-derived excess soluble CD40 ligand found in the plasma and cerebrospinal fluid of HIV-1-infected individuals with cognitive impairment has previously been implicated in increased blood-brain barrier permeability. In this study we show that soluble CD40 ligand also promotes the formation of complexes between inflammatory monocytes and activated platelets (PMCs), which are detected by flow cytometry as monocytes that express excess of CD61, a platelet marker, and that these complexes are increased in individuals with HIV-1 infection. PMCs exhibit an enhanced ability to adhere to human brain microvascular endothelial cells as compared with monocytes alone, and they migrate across the transendothelial barrier. These complexes can be found marginalized in the lumen of postcapillary venules in postmortem brain tissue derived from cases of HIV-1-associated encephalitis. The extravasation of monocytes across the brain endothelium may exacerbate neuroinflammation, indicating that enhancing this event via platelet interaction may be a contributing factor in the development of cognitive impairment. Thus, dampening platelet activation, and in turn PMC formation, with antiplatelet agents may prove beneficial in developing adjunctive therapies for use in combination with combined antiretroviral therapy in an effort to reduce HIV-1-associated neurologic deficit.

Gateway to understanding microparticles: standardized isolation and identification of plasma membrane-derived vesicles

Microparticles (MPs) are small plasma membrane-derived vesicles that can expose molecules originating from their parental cells. As vectors of biological information they are likely to play an active role in both homeostasis and pathogenesis, making them promising biomarkers and nanomedicine tools. Therefore, there is an urgent need for standardization of MP isolation and analysis protocols to propel our understanding of MP biology to the next level. Based on current methodology and recent insights, this review proposes an optimized protocol for the isolation and biochemical characterization of MPs.