The role of bone marrow microenvironment in platelet production and their implications for the treatment of thrombocytopenic diseases

The hematopoietic microenvironment: a network of niches for the development of all blood cell lineages

Blood cell formation (hematopoiesis) takes place mainly in the bone marrow, within the hematopoietic microenvironment, composed of a number of different cell types and their molecular products that together shape spatially organized and highly specialized microstructures called hematopoietic niches. From the earliest developmental stages and throughout the myeloid and lymphoid lineage differentiation pathways, hematopoietic niches play a crucial role in the preservation of cellular integrity and the regulation of proliferation and differentiation rates. Current evidence suggests that each blood cell lineage develops under specific, discrete niches that support committed progenitor and precursor cells and potentially cooperate with transcriptional programs determining the gradual lineage commitment and specification. This review aims to discuss recent advances on the cellular identity and structural organization of lymphoid, granulocytic, monocytic, megakaryocytic, and erythroid niches throughout the hematopoietic microenvironment and the mechanisms by which they interconnect and regulate viability, maintenance, maturation, and function of the developing blood cells.

Recent lessons learned for ex-vivo platelet production

PURPOSE OF REVIEW

Platelet transfusion can be life-saving but carries a risk of infection or alloimmunization and is limited by insufficient donor sources and restricted unit shelf life. Generating sufficient platelets in vitro to replace a unit of collected blood remains a challenge. Here, we examine the latest advances in the regulation of megakaryocyte maturation and expansion along with platelet formation and survival. We also discuss alternative therapies investigated to induce platelet production.

RECENT FINDINGS

Recent studies examined candidate niche cells in the bone marrow microenvironment for promoting platelet formation and developed an explant-based bioreactor to enhance platelet production ex vivo. Chemical inhibitors were examined for their ability to promote megakaryocyte maturation and expansion. Microparticles from megakaryocytes or platelets were found to improve megakaryocyte maturation and platelet formation. Membrane budding was identified as a novel mode of platelet formation. Lastly, a chemical inhibitor to improve cold-stored platelets was identified.

SUMMARY

Recent advances in the regulation of megakaryocyte expansion and platelet production provide exciting promise for the development of improved approaches to generate platelets in vitro. These findings bring the field one step closer to achieving the ultimate goal of creating a unit of platelets without the need for donation.

In vitro facilitating role of polygonatum sibiricum polysaccharide in osteogenic differentiation of bone marrow mesenchymal stem cells from patients with multiple myeloma

BACKGROUND

Bone marrow mesenchymal stem cells (BMMSCs) were proved to play a vital role in multiple myeloma (MM). Polygonatum sibiricum polysaccharide (PSP) was found to have anti-tumor pharmacological effects, yet its interaction with BMMSCs remained poorly understood. Therefore, we explore the effect of PSP on osteogenic differentiation of BMMSCs.

METHODS

BMMSCs were isolated by density gradient centrifugation. CD90 and CD34 were detected by flow cytometry (FCM). Osteogenic marks were detected by quantitative real-time PCR (qRT-PCR) and Western blotting (WB). The vitality of cells treated with different concentrations of PSP was observed by Cell Counting Kit-8 (CCK-8). ALP staining kit was used to detect the activity of alkaline phosphatase (ALP). Alizarin red staining detected the formation of mineralized nodules. Osteoblast-associated genes were evaluated by qRT-PCR and WB. The phosphoinositide 3-kinase (PI3K), protein kinase B (AKT), and mammalian target of rapamycin (mTOR) signaling pathways were tested by WB.

RESULTS

The BMMSCs showed good growth under an inverted microscope. FCM showed that CD34 and CD45 was low-expressed, whereas CD44, CD90 and CD105 was highly expressed. Compared with the Control group, the expressions of Runx2 and ALP in cells were significantly increased. CCK-8 showed that different concentrations of PSP had no significant effect on the viability of BMMSCs. BMMSCs treated with 25 mg/l PSP were stained the most deeply by ALP. Mineralized nodules in PSP groups dramatically increased, and hit a peak under the action of 25 mg/l PSP. PSP up-regulated p-PI3K, p-AKT, and p-mTOR, but had no significant effect on PI3K, AKT, and mTOR.

CONCLUSION

PSP induced osteogenic differentiation of BMMSCs from MM patients.

Insights on chronic immune thrombocytopenia pathogenesis: A bench to bedside update

Immune thrombocytopenia (ITP) is a heterogeneous disease with an unpredictable course. Chronicity can develop in up to two-thirds of adults and 20-25% of children, representing a significant burden on patients' quality of life. Despite acceptable responses to treatment, precise etiology and pathophysiology phenomena driving evolution to chronicity remain undefined. We analyzed reported risk factors for chronic ITP and associated them with proposed underlying mechanisms in its pathogenesis, including bone marrow (BM) microenvironment disturbances, clinical features, and immunological markers. Their understanding has diagnostic implications, such as screening for the presence of specific antibodies or BM examination employing molecular tools, which could help predict prognosis and recognize main pathogenic pathways in each patient. Identifying these underlying mechanisms could guide the use of personalized therapies such as all-trans retinoic acid, mTor inhibitors, FcRn inhibitors, oseltamivir, and others. Further research should lead to tailored treatments and chronic course prevention, improving patients' quality of life.

Platelet disturbances correlate with endothelial cell activation in uncomplicated Plasmodium vivax malaria

Platelets drive endothelial cell activation in many diseases. However, if this occurs in Plasmodium vivax malaria is unclear. As platelets have been reported to be activated and to play a role in inflammatory response during malaria, we hypothesized that this would correlate with endothelial alterations during acute illness. We performed platelet flow cytometry of PAC-1 and P-selectin. We measured platelet markers (CXCL4, CD40L, P-selectin, Thrombopoietin, IL-11) and endothelial activation markers (ICAM-1, von Willebrand Factor and E-selectin) in plasma with a multiplex-based assay. The values of each mediator were used to generate heatmaps, K-means clustering and Principal Component analysis. In addition, we determined pair-wise Pearson’s correlation coefficients to generate correlation networks. Platelet counts were reduced, and mean platelet volume increased in malaria patients. The activation of circulating platelets in flow cytometry did not differ between patients and controls. CD40L levels (Median [IQ]: 517 [406–651] vs. 1029 [732–1267] pg/mL, P = 0.0001) were significantly higher in patients, while P-selectin and CXCL4 showed a nonsignificant trend towards higher levels in patients. The network correlation approach demonstrated the correlation between markers of platelet and endothelial activation, and the heatmaps revealed a distinct pattern of activation in two subsets of P. vivax patients when compared to controls. Although absolute platelet activation was not strong in uncomplicated vivax malaria, markers of platelet activity and production were correlated with higher endothelial cell activation, especially in a specific subset of patients.

Endothelial cell activation is a key process in the pathogenesis of Plasmodium vivax malaria. Platelets are classically involved in endothelial cell activation in several diseases, but their role in the context of vivax malaria remains unclear. Thrombocytopenia is the most common hematological disturbance in P. vivax-infected patients, and platelets have been implicated in parasitemia control. In this work, we studied the activation of platelets in association with endothelial cell activation in vivax malaria. Platelets retrieved from infected peripheral blood were non-activated when analyzed by flow cytometry; however, they displayed higher mean volume and significantly reduced counts. We also found higher levels of circulating factors associated with platelet activation (especially soluble CD40L), thrombopoiesis and endothelial cell activation in infected patients. Further, through pair-wise correlation and clustering analysis, we found a subgroup of patients showing significant associations between markers of platelet and endothelial activation in a pattern different from that of endemic controls. Collectively, our findings indicate a role of platelets in endothelial cell activation in vivax malaria and indicate a heterogeneous host response in the setting of uncomplicated disease, a finding to be further explored in future studies.