miR-486-5p and miR-22-3p Enable Megakaryocytic Differentiation of Hematopoietic Stem and Progenitor Cells without Thrombopoietin.

Megakaryocytes release submicron size microparticles (MkMPs) in circulation. We have shown that MkMPs target CD34+ hematopoietic stem/progenitor cells (HSPCs) to induce megakaryocytic differentiation, and that small RNAs in MkMPs play an important role in the development of this phenotype. Here, using single-molecule real-time (SMRT) RNA sequencing (RNAseq), we identify the synergetic effect of two microRNAs (miRs), miR-486-5p and miR-22-3p (highly enriched in MkMPs), in driving the Mk differentiation of HSPCs in the absence of thrombopoietin (TPO). Separately, our data suggest that the MkMP-induced Mk differentiation of HSPCs is enabled through JNK and PI3K/Akt/mTOR signaling. The interaction between the two signaling pathways is likely mediated by a direct target of miR-486-5p and a negative regulator of PI3K/Akt signaling, the phosphatase and tensin homologue (PTEN) protein. Our data provide a possible mechanistic explanation of the biological effect of MkMPs in inducing megakaryocytic differentiation of HSPCs, a phenotype of potential physiological significance in stress megakaryopoiesis.

Role of Cytokines and Growth Factors in the Manufacturing of iPSC-Derived Allogeneic Cell Therapy Products.

Cytokines and other growth factors are essential for cell expansion, health, function, and immune stimulation. Stem cells have the additional reliance on these factors to direct differentiation to the appropriate terminal cell type. Successful manufacturing of allogeneic cell therapies from induced pluripotent stem cells (iPSCs) requires close attention to the selection and control of cytokines and factors used throughout the manufacturing process, as well as after administration to the patient. This paper employs iPSC-derived natural killer cell/T cell therapeutics to illustrate the use of cytokines, growth factors, and transcription factors at different stages of the manufacturing process, ranging from the generation of iPSCs to controlling of iPSC differentiation into immune-effector cells through the support of cell therapy after patient administration.

Megakaryocyte membrane-wrapped nanoparticles for targeted cargo delivery to hematopoietic stem and progenitor cells.

Hematopoietic stem and progenitor cells (HSPCs) are desirable targets for gene therapy but are notoriously difficult to target and transfect. Existing viral vector-based delivery methods are not effective in HSPCs due to their cytotoxicity, limited HSPC uptake and lack of target specificity (tropism). Poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) are attractive, nontoxic carriers that can encapsulate various cargo and enable its controlled release. To engineer PLGA NP tropism for HSPCs, megakaryocyte (Mk) membranes, which possess HSPC-targeting moieties, were extracted and wrapped around PLGA NPs, producing MkNPs. In vitro, fluorophore-labeled MkNPs are internalized by HSPCs within 24 h and were selectively taken up by HSPCs versus other physiologically related cell types. Using membranes from megakaryoblastic CHRF-288 cells containing the same HSPC-targeting moieties as Mks, CHRF-wrapped NPs (CHNPs) loaded with small interfering RNA facilitated efficient RNA interference upon delivery to HSPCs in vitro. HSPC targeting was conserved in vivo, as poly(ethylene glycol)-PLGA NPs wrapped in CHRF membranes specifically targeted and were taken up by murine bone marrow HSPCs following intravenous administration. These findings suggest that MkNPs and CHNPs are effective and promising vehicles for targeted cargo delivery to HSPCs.

Human megakaryocytic microparticles induce de novo platelet biogenesis in a wild-type murine model.

Platelet transfusions are used to treat idiopathic or drug-induced thrombocytopenia. Platelets are an expensive product in limited supply, with limited storage and distribution capabilities because they cannot be frozen. We have demonstrated that, in vitro, human megakaryocytic microparticles (huMkMPs) target human CD34+ hematopoietic stem and progenitor cells (huHSPCs) and induce their Mk differentiation and platelet biogenesis in the absence of thrombopoietin. In this study, we showed that, in vitro, huMkMPs can also target murine HSPCs (muHSPCs) to induce them to differentiate into megakaryocytes in the absence of thrombopoietin. Based on that, using wild-type BALB/c mice, we demonstrated that intravenously administering 2 × 106 huMkMPs triggered de novo murine platelet biogenesis to increase platelet levels up to 49% 16 hours after administration. huMkMPs also largely rescued low platelet levels in mice with induced thrombocytopenia 16 hours after administration by increasing platelet counts by 51%, compared with platelet counts in thrombocytopenic mice. Normalized on a tissue-mass basis, biodistribution experiments show that MkMPs localized largely to the bone marrow, lungs, and liver 24 hours after huMkMP administration. Beyond the bone marrow, CD41+ (megakaryocytes and Mk-progenitor) cells were frequent in lungs, spleen, and especially, liver. In the liver, infused huMKMPs colocalized with Mk progenitors and muHSPCs, thus suggesting that huMkMPs interact with muHSPCs in vivo to induce platelet biogenesis. Our data demonstrate the potential of huMkMPs, which can be stored frozen, to treat thrombocytopenias and serve as effective carriers for in vivo, target-specific cargo delivery to HSPCs.

Extracellular vesicles: exosomes, microparticles, their parts, and their targets to enable their biomanufacturing and clinical applications.

Extracellular vesicles (EVs) are membrane vesicles, the submicron-size microparticles and the nanometer-size exosomes, that carry RNAs, proteins and lipids from their parent cells. EV generation takes place under cellular activation or stress. Cells use EVs to communicate with other cells by delivering signals through their content and surface proteins. Beyond diagnostic and discovery applications, EVs are excellent candidates for enabling safe and potent cell and gene therapies, especially those requiring strong target specificity. Here we examine EVs, their engineering and applications by dissecting mechanistic and engineering aspects of their components that endow them with their unique capabilities: their cargo and membranes proteins. Both EV cargo and membranes can be independently engineered and used for various applications. We review early efforts for their biomanufacturing.

Engineering human megakaryocytic microparticles for targeted delivery of nucleic acids to hematopoietic stem and progenitor cells.

Hematopoietic stem and progenitor cells (HSPCs) are important target cells for gene therapy applications. Current genetic modifications of HSPCs rely on viral vectors in vivo or electroporation ex vivo. Here, we developed a nonviral system based on megakaryocytic microparticles (MPs) for targeted delivery of plasmid DNA (pDNA) and small RNAs to HSPCs. We have previously shown that megakaryocytic MPs, the most abundant MPs in blood circulation, target specifically and deliver cargo to HSPCs both in vitro and in vivo. With an optimized electroporation protocol, an average of 4200 plasmid copies per MP were loaded into MP, thus enabling effective delivery of green fluorescent protein (GFP)-encoding pDNA to HSPCs and HSPC nuclei, with up to 81% nuclei containing pDNA. Effective functional small interfering RNA (siRNA) and microRNA (miRNA) delivery were also demonstrated. As patient-specific or generic megakaryocytic MPs can be readily generated and stored frozen, our data suggest that this system has great potential for therapeutic applications targeting HSPCs.

Role of p53 and transcription-independent p53-induced apoptosis in shear-stimulated megakaryocytic maturation, particle generation, and platelet biogenesis.

Megakaryocytes (Mks) derive from hematopoietic stem and progenitor cells (HSPCs) in the bone marrow and develop into large, polyploid cells that eventually give rise to platelets. As Mks mature, they migrate from the bone marrow niche into the vasculature, where they are exposed to shear forces from blood flow, releasing Mk particles (platelet-like particles (PLPs), pro/preplatelets (PPTs), and Mk microparticles (MkMPs)) into circulation. We have previously shown that transcription factor p53 is important in Mk maturation, and that physiological levels of shear promote Mk particle generation and platelet biogenesis. Here we examine the role of p53 in the Mk shear-stress response. We show that p53 is acetylated in response to shear in both immature and mature Mks, and that decreased expression of deacetylase HDAC1, and increased expression of the acetyltransferases p300 and PCAF might be responsible for these changes. We also examined the hypothesis that p53 might be involved in the shear-induced Caspase 3 activation, phosphatidylserine (PS) externalization, and increased biogenesis of PLPs, PPTs, and MkMPs. We show that p53 is involved in all these shear-induced processes. We show that in response to shear, acetyl-p53 binds Bax, cytochrome c is released from mitochondria, and Caspase 9 is activated. We also show that shear-stimulated Caspase 9 activation and Mk particle biogenesis depend on transcription-independent p53-induced apoptosis (TIPA), but PS externalization is not. This is the first report to show that shear flow stimulates TIPA and that Caspase 9 activation and Mk-particle biogenesis are directly modulated by TIPA.

How do megakaryocytic microparticles target and deliver cargo to alter the fate of hematopoietic stem cells?

Megakaryocytic microparticles (MkMPs), the most abundant MPs in circulation, can induce the differentiation of hematopoietic stem and progenitor cells (HSPCs) into functional megakaryocytes. This MkMP capability could be explored for applications in transfusion medicine but also for delivery of nucleic acids and other molecules to HSPCs for targeted molecular therapy. Understanding how MkMPs target, deliver cargo and alter the fate of HSPCs is important for exploring such applications. We show that MkMPs, which are distinct from Mk exosomes (MkExos), target HSPCs with high specificity since they have no effect on other ontologically or physiologically related cells, namely mesenchymal stem cells, endothelial cells or granulocytes. The outcome is also specific: only cells of the megakaryocytic lineage are generated. Observation of intact fluorescently-tagged MkMPs inside HSPCs demonstrates endocytosis as one mechanism of cargo delivery. Fluorescent labeling and scanning electron microscopy (SEM) imaging show that direct fusion of MkMPs into HSPCs is also engaged in cargo delivery. SEM imaging detailed the membrane-fusion process in four stages leading to full adsorption of MkMPs into HSPCs. Furthermore, macropinocytosis and lipid raft-mediated were shown here as mechanisms of MkMP uptake by HSPC. In contrast, the ontologically related platelet-derived MPs (PMPs) cannot be taken up by HSPCs although they bind to and induce HSPC aggregation. We show that platelet-like thrombin activation is apparently responsible for the different biological effects of MkMPs versus PMPs on HSPCs. We show that HSPC uropods are the preferential site for MkMP binding, and that CD54 (ICAM-1), CD11b, CD18 and CD43, localized on HSPC uropods, are involved in MkMP binding to HSPCs. Finally, we show that MkMP RNA is largely responsible for HSPC programming into Mk differentiation.

Electrophoresis of a spherical particle along the axis of a cylindrical pore: effect of electroosmotic flow.

The electrophoresis of a spherical particle along the axis of a cylindrical pore is investigated under conditions of low surface potential and thick double layer. In particular, the effect of electroosmotic flow is taken into account. The results of numerical simulation reveal that if both particle and pore are positively charged, the variation of the mobility of a particle may have a local minimum as the thickness of the double layer varies, which is not reported in the literature. This is mainly due to the charge induced on the particle surface, which arises from the presence of the charged boundary. Depending upon the level of the surface potential of the pore, the presence of the local minima may lead to a reversal in the direction of particle movement as the thickness of the double layer surrounding it varies: if the surface potential is either too low or too high, reversal does not occur; if it has a medium level, reversal occurs twice. This interesting observation can play a role in electrophoresis measurements. Previous analysis predicts that reversal always occurs once, regardless of the level of the surface potential of the pore.

Electrokinetic flow through an elliptical microchannel: effects of aspect ratio and electrical boundary conditions.

The electrokinetic flow of an electrolyte solution through an elliptical microchannel is studied theoretically. The system under consideration simulates the flow of a fluid, for example, in vein. We show that, for a constant cross-sectional area, both the electroosmotic volumetric flow rate and the streaming potential increase monotonically with an increase in the aspect ratio, and both the total electric current and the electroviscous effect may exhibit a local minimum as the aspect ratio varies. Also, for a constant average potential on the channel wall, the difference between the results based on three kinds of boundary conditions, which include constant surface charge, constant surface potential, and charge-regulated surface, is inappreciable if the hydraulic diameter is larger than 1 mum.

Electrophoretic Properties of Latex Particles with Immobilized Bovine Serum Albumin.

In this study, bovine serum albumin (BSA) was covalently immobilized onto the surfaces of methyl methacrylate/methyl acrylic acid core-shell latex particles by the carbodiimide method, and the variation of the zeta potential of the BSA-latex complex as a function of the amount of BSA immobilized was measured. The experimental data revealed that the absolute zeta potential of BSA-latex complex exhibited a local minimum at 0.05 mg/m(2) of immobilized BSA. A two-layer model for the description of the electrophoretic behavior of the BSA-latex complex is proposed which is capable of explaining the behavior of the variation of the zeta potential as a function of the amount of BSA immobilized. Copyright 2001 Academic Press.