Cell-cell signalling in the regulation of blood cell formation and function

Formulation and In Vitro Characterization of PLGA/PLGA-PEG Nanoparticles Loaded with Murine Granulocyte-Macrophage Colony-Stimulating Factor

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has demonstrated notable clinical activity in cancer immunotherapy, but it is limited by systemic toxicities, poor bioavailability, rapid clearance, and instability in vivo. Nanoparticles (NPs) may overcome these limitations and provide a mechanism for passive targeting of tumors. This study aimed to develop GM-CSF-loaded PLGA/PLGA-PEG NPs and evaluate them in vitro as a potential candidate for in vivo administration. NPs were created by a phase-separation technique that did not require toxic/protein-denaturing solvents or harsh agitation techniques and encapsulated GM-CSF in a more stable precipitated form. NP sizes were within 200 nm for enhanced permeability and retention (EPR) effect with negative zeta potentials, spherical morphology, and high entrapment efficiencies. The optimal formulation was identified by sustained release of approximately 70% of loaded GM-CSF over 24 h, alongside an average size of 143 ± 35 nm and entrapment efficiency of 84 ± 5%. These NPs were successfully freeze-dried in 5% (w/v) hydroxypropyl-β-cyclodextrin for long-term storage and further characterized. Bioactivity of released GM-CSF was determined by observing GM-CSF receptor activation on murine monocytes and remained fully intact. NPs were not cytotoxic to murine bone marrow-derived macrophages (BMDMs) at concentrations up to 1 mg/mL as determined by MTT and trypan blue exclusion assays. Lastly, NP components generated no significant transcription of inflammation-regulating genes from BMDMs compared to IFNγ+LPS "M1" controls. This report lays the preliminary groundwork to validate in vivo studies with GM-CSF-loaded PLGA/PEG-PLGA NPs for tumor immunomodulation. Overall, these data suggest that in vivo delivery will be well tolerated.

A Metabolic Roadmap for Somatic Stem Cell Fate

While metabolism was initially thought to play a passive role in cell biology by generating ATP to meet bioenergetic demands, recent studies have identified critical roles for metabolism in the generation of new biomass and provision of obligate substrates for the epigenetic modification of histones and DNA. This review details how metabolites generated through glycolysis and the tricarboxylic acid cycle are utilized by somatic stem cells to support cell proliferation and lineage commitment. Importantly, we also discuss the evolving hypothesis that histones can act as an energy reservoir during times of energy stress. Finally, we discuss how cells integrate both extrinsic metabolic cues and intrinsic metabolic machinery to regulate cell fate.

Nonequilibrium population dynamics of phenotype conversion of cancer cells

Tumorigenesis is a dynamic biological process that involves distinct cancer cell subpopulations proliferating at different rates and interconverting between them. In this paper we proposed a mathematical framework of population dynamics that considers both distinctive growth rates and intercellular transitions between cancer cell populations. Our mathematical framework showed that both growth and transition influence the ratio of cancer cell subpopulations but the latter is more significant. We derived the condition that different cancer cell types can maintain distinctive subpopulations and we also explain why there always exists a stable fixed ratio after cell sorting based on putative surface markers. The cell fraction ratio can be shifted by changing either the growth rates of the subpopulations (Darwinism selection) or by environment-instructed transitions (Lamarckism induction). This insight can help us to understand the dynamics of the heterogeneity of cancer cells and lead us to new strategies to overcome cancer drug resistance.

A PML–PPAR-δ pathway for fatty acid oxidation regulates hematopoietic stem cell maintenance

Stem-cell function is an exquisitely regulated process. Thus far, the contribution of metabolic cues to stem-cell function has not been well understood. Here we identify a previously unknown promyelocytic leukemia (PML)–peroxisome proliferator-activated receptor δ (PPAR-δ)–fatty-acid oxidation (FAO) pathway for the maintenance of hematopoietic stem cells (HSCs). We have found that loss of PPAR-δ or inhibition of mitochondrial FAO induces loss of HSC maintenance, whereas treatment with PPAR-δ agonists improved HSC maintenance. PML exerts its essential role in HSC maintenance through regulation of PPAR signaling and FAO. Mechanistically, the PML–PPAR-δ–FAO pathway controls the asymmetric division of HSCs. Deletion of Ppard or Pml as well as inhibition of FAO results in the symmetric commitment of HSC daughter cells, whereas PPAR-δ activation increased asymmetric cell division. Thus, our findings identify a metabolic switch for the control of HSC cell fate with potential therapeutic implications.

Clinical uses of GM-CSF, a critical appraisal and update

The role of granulocyte-macrophage-colony-stimulating factor (GM-CSF) in the supportive care of cancer patients has been evaluated with promising results. More recently, GM-CSF has been added to regimens for the mobilization of hematopoietic progenitor cells. An expanding role for GM-CSF in regulating immune responses has been recognized based upon its activity on the development and maturation of antigen presenting cells and its capability for skewing the immune system toward Th1-type responses. GM-CSF has been shown to preferentially enhance both the numbers and activity of type 1 dendritic cells (DC1), the subsets of dendritic cells responsible for initiating cytotoxic immune responses. The increase in DC1 content and activity following local and systemic GM-CSF administration support a role for GM-CSF as an immune stimulant and vaccine adjuvant in cancer patients. GM-CSF has shown clinical activity as an immune stimulant in tumor cell and dendritic cell vaccines, and may increase antibody-dependent cellular cytotoxicity. The successful use of myeloid acting cytokines to enhance anti-tumor responses will likely require the utilization of GM-CSF in combination with cytotoxic or other targeted therapies.

Inflammation triggers emergency granulopoiesis through a density-dependent feedback mechanism

Normally, neutrophil pools are maintained by homeostatic mechanisms that require the transcription factor C/EBPα. Inflammation, however, induces neutrophilia through a distinct pathway of “emergency” granulopoiesis that is dependent on C/EBPβ. Here, we show in mice that alum triggers emergency granulopoiesis through the IL-1RI-dependent induction of G-CSF. G-CSF/G-CSF-R neutralization impairs proliferative responses of hematopoietic stem and progenitor cells (HSPC) to alum, but also abrogates the acute mobilization of BM neutrophils, raising the possibility that HSPC responses to inflammation are an indirect result of the exhaustion of BM neutrophil stores. The induction of neutropenia, via depletion with Gr-1 mAb or myeloid-specific ablation of Mcl-1, elicits G-CSF via an IL-1RI-independent pathway, stimulating granulopoietic responses indistinguishable from those induced by adjuvant. Notably, C/EBPβ, thought to be necessary for enhanced generative capacity of BM, is dispensable for increased proliferation of HSPC to alum or neutropenia, but plays a role in terminal neutrophil differentiation during granulopoietic recovery. We conclude that alum elicits a transient increase in G-CSF production via IL-1RI for the mobilization of BM neutrophils, but density-dependent feedback sustains G-CSF for accelerated granulopoiesis.

Pharmacokinetic/pharmacodynamic modeling of pegfilgrastim in healthy subjects

This analysis was conducted to characterize the pharmacokinetics and pharmacodynamics of pegfilgrastim and to develop a pharmacokinetic-pharmacodynamic model to describe the granulopoietic effects of pegfilgrastim and the homeostatic regulation of pegfilgrastim clearance in healthy subjects. Pegfilgrastim serum concentration data and differential white cell counts were obtained from an open-label, single-dose, dose escalation study. Healthy subjects (8 subjects/dose group) received a single subcutaneous dose of 30, 60, 100, or 300 microg/kg pegfilgrastim. Pegfilgrastim exhibited nonlinear pharmacokinetics; clearance decreased with increasing dose. A dose-dependent increase in absolute neutrophil count with an increase in the percentage of band cells was observed. A pharmacokinetic-pharmacodynamic model was developed that adequately described the nonlinear pharmacokinetics of pegfilgrastim, feedback regulation of pegfilgrastim clearance by neutrophils, and the differential effects of pegfilgrastim on neutrophil populations in blood.

PK1/EG-VEGF induces monocyte differentiation and activation

Macrophages exist as sentinels in innate immune response and react by expressing proinflammatory cytokines and up-regulating antigen-presenting and costimulatory molecules. We report a novel function for prokineticin-1 (PK1)/endocrine gland-derived vascular endothelial growth factor. Screening of murine tissue sections and cells for specific binding site leads to the identification of macrophages as an in vivo cellular target for PK1. We demonstrate PK1 induces differentiation of murine and human bone marrow cells into the monocyte/macrophage lineage. Human peripheral blood monocytes respond to PK1 by morphological changes and down-regulation of B7-1, CD14, CC chemokine receptor 5, and CXC chemokine receptor 4. Monocytes treated with PK1 have elevated interleukin (IL)-12 and tumor necrosis factor alpha and down-regulated IL-10 production in response to lipopolysaccharide. PK1 induces a distinct monocyte-derived cell population, which is primed for release of proinflammatory cytokines that favor a T helper cell type 1 response.

Site-matched papillary and reticular human dermal fibroblasts differ in their release of specific growth factors/cytokines and in their interaction with keratinocytes

The interfollicular dermis of adult human skin is partitioned into histologically and physiologically distinct papillary and reticular zones. Each of these zones contains a unique population of fibroblasts that differ in respect to their proliferation kinetics, rates at which they contract type I collagen gels, and in their relative production of decorin and versican. Here, site-matched papillary and reticular dermal fibroblasts couples were compared to determine whether each population interacted with keratinocytes in an equivalent or different manner. Papillary and reticular fibroblasts grown in monolayer culture differed significantly from each other in their release of keratinocyte growth factor (KGF) and granulocyte-macrophage colony stimulating factor (GM-CSF) into culture medium. Some matched fibroblast couples also differed in their constitutive release of interleukin-6 (IL-6). Papillary fibroblasts produced a higher ratio of GM-CSF to KGF than did corresponding reticular fibroblasts. Interactions between site-matched papillary and reticular couples were also assayed in a three-dimensional culture system where fibroblasts and keratinocytes were randomly mixed, incorporated into type I collagen gels, and allowed to sort. Keratinocytes formed distinctive cellular masses in which the keratinocytes were organized such that the exterior most layer of cells exhibited characteristics of basal keratinocytes and the interior most cells exhibited characteristics of terminally differentiated keratinocytes. In the presence of papillary dermal fibroblasts, keratinocyte masses were highly symmetrical and cells expressed all levels of differentiation markers. In contrast, keratinocyte masses that formed in the presence of reticular fibroblasts tended to have irregular shapes, and terminal differentiation was suppressed. Furthermore, basement membrane formation was retarded in the presence of reticular cells. These studies indicate that site-matched papillary and reticular dermal fibroblasts qualitatively differ in their support of epidermal cells, with papillary cells interacting more effectively than corresponding reticular cells.

Inhibition of hematopoietic progenitor cell growth by Tyr-MIF, an endogenous opiate modulator, and its degradation products

There is increasing evidence that neuronal factors can affect hematopoietic cell proliferation. Endogenous opioids with specificity for several opioid receptor classes were tested for their ability to inhibit murine and human hematopoietic progenitor cell proliferation. Tyr-MIF, an opioid tetrapeptide (H-Tyr-Pro-Leu-Gly-NH2), demonstrated a dose-dependent inhibition of colony formation at concentrations < 10 uM, inhibiting M-CSF and G-CSF-responsive progenitor cells equally. Tyr-MIF did not inhibit the number of colonies responsive to recombinant interleukin 3 (rmIL-3) or recombinant murine granulocyte-macrophage colony stimulating factor (rmGM-CSF), but significantly reduced colony size of GM-CSF responsive colonies. Colony formation by human low density and CD34+ marrow cells in response to G-CSF was also inhibited by Tyr-MIF and was more sensitive to inhibition than murine progenitor cells. Colony formation by single CD34+ cells was also inhibited by Tyr-MIF, indicating an effect directly on progenitor cells. Incubation of marrow cells in liquid culture and removal of Tyr-MIF prior to quantitating progenitor cell proliferation demonstrated that opioid-induced inhibition was reversible. The inhibitory effect of Tyr-MIF was not blocked by naloxone, a mu receptor specific antagonist, or diminished in mu opioid receptor deficient mice. HPLC analysis of cell-free culture medium containing Tyr-MIF showed no presence of the parent peptide after 24 h while progenitor cell inhibitory activity was retained. Analysis of potential degradation products of Tyr-MIF indicated that only H-Gly-NH9 or H-Gly-NH2 containing peptides inhibited colony forming unit (CFU) proliferation. These results indicate that Tyr-MIF is a reversible inhibitor of mature hematopoietic progenitor cell proliferation, and that this effect is most likely mediated by the degradation product H-Gly-NH2. Potential applications including protection of myeloid cells after cytosuppresive therapy are discussed.

Transcription factors that regulate growth and differentiation of myeloid cells

Recently much progress has been made in our understanding of how myeloid progenitor cells undergo commitment and become mature granulocytes or monocytes/macrophages. Studies of normal and leukemic myeloid cells as well as those of cells derived from mice with targeted disruption showed that a series of transcription factors play a major role in both commitment and maturation of myeloid cells. This is primarily because these transcription factors direct an ordered pattern of gene expression according to a well-defined developmental program. PU.1, an Ets family member, is one of the master transcription factors identified to regulate development of both granulocytes and monocytes/macrophages. Further, C/EBPalpha and C/EBPvarepsilon of the bZip family have important roles in directing granulocytic maturation. A number of additional transcription factors such as AML1, RARalpha, MZF-1, Hox and STAT families of transcription factors, Egr-1 and c-myb etc are shown to play roles in myeloid cell differentiation. Our laboratory has recently obtained evidence that ICSBP, a member of the IRF family, is involved in lineage commitment during myeloid cell differentiation and stimulates maturation of functional macrophages. Future elucidation of pathways and networks through which these transcription factors act in various stages of development would provide a more definitive picture of myeloid cell commitment and maturation.

c-Jun and JunB antagonistically control cytokine-regulated mesenchymal-epidermal interaction in skin

Interactions between mesenchymal and epithelial cells are responsible for organogenesis and tissue homeostasis. This mutual cross-talk involves cell surface proteins and soluble factors, which are mostly the result of regulated transcription. To elucidate dimer-specific functions of the AP-1 family of transcription factors, we reconstituted skin by combining primary human keratinocytes and mouse wild-type, c-jun(-/-), and junB(-/-) fibroblasts. We have discovered an antagonistic function of these AP-1 subunits in the fibroblast-mediated paracrine control of keratinocyte proliferation and differentiation, and traced this effect to the IL-1-dependent regulation of KGF and GM-CSF. These data suggest that the relative activation state of these AP-1 subunits in a non-cell-autonomous, transregulatory fashion directs regeneration of the epidermis and maintenance of tissue homeostasis in skin.