Profiling deacetylase activities in cell lysates with peptide arrays and SAMDI mass spectrometry

The development of arrays that can profile molecular activities in cells is important to understanding signaling pathways in normal and pathological settings. While oligonucleotide arrays are now routinely used to profile global gene expression, there is still a lack of tools for profiling enzyme activities in cell lysates. This paper describes the combination of peptide arrays formed on self-assembled monolayers and mass spectrometry to provide a label-free approach for identifying patterns of enzyme activities in cell lysates. The approach is demonstrated by profiling lysine deacetylase (KDAC) activities in cell lysates of the CHRF megakaryocytic (Mk) cell line. Class-specific deacetylase inhibitors were used to show that terminal Mk differentiation of CHRF cells is marked by a pronounced decrease in sirtuin activity and by little change in activity of KDACs 1-11. This work establishes a platform that can be used to identify changes in global activity profiles of cell lysates for a wide variety of enzymatic activities.

Bioreactor design for perfusion-based, highly-vascularized organ regeneration

Bioartificial or laboratory-grown organs is a growing field centered on developing replacement organs and tissues to restore body function and providing a potential solution to the shortage of donor organs for transplantation. With the entry of engineered planar tissues, such as bladder and trachea, into clinical studies, an increasing focus is being given to designing complex, three-dimensional solid organs. As tissues become larger, thicker and more complex, the vascular network becomes crucial for supplying nutrients and maintaining viability and growth of the neo-organ. Perfusion decellularization, the process of removing cells from an entire organ, leaves the matrix of the vascular network intact. Organ engineering requires a delicate process of decellularization, sterilization, reseeding with appropriate cells, and organ maturation and stimulation to ensure optimal development. The design of bioreactors to facilitate this sequence of events has been refined to the extent that some bioartificial organs grown in these systems have been transplanted into recipient animals with sustained, though limited, function. This review focuses on the state-of-art in bioreactor development for perfusion-based bioartificial organs and highlights specific design components in need of further refinement.

Three-stage ex vivo expansion of high-ploidy megakaryocytic cells: toward large-scale platelet production

Hematopoietic stem and progenitor cells (HSPCs) have been cultured using a wide variety of cytokines to promote differentiation into megakaryocytic cells (Mks), the precursors to platelets. Greater Mk DNA content, or ploidy, has been correlated with increased platelet release. Gradients of pH, pO2, and signaling factors regulate megakaryopoiesis in the bone marrow niche. In this study, we demonstrate that a 3-phase culture process with increasing pH and pO2 and different cytokine cocktails greatly increases megakaryocyte production. CD34(+) HSPCs were first cultured at 5% O2 and pH 7.2 with a cytokine cocktail previously shown to promote Mk progenitor production. At day 5, cells were shifted to 20% O2 and pH 7.4 and maintained in 1 of 17 cytokine cocktails identified using a 2(4) factorial design of experiments method to evaluate the effects of interleukin (IL)-3, IL-6, IL-9, and high- or low-dose stem cell factor (SCF), in conjunction with thrombopoietin (Tpo) and IL-11, on expansion of mature Mks from progenitors. The combination of Tpo, high-dose SCF, IL-3, IL-9, and IL-11 best promoted Mk expansion. IL-3 greatly increased total cell fold expansion, but this was partially offset by lower Mk purity. IL-9 promoted CD41 and CD42b expression. High-dose (100 ng/mL) SCF increased Mk production and ploidy. Different commercial media and IL-3 sources substantially impacted differentiation, and X-VIVO 10 serum-free media best supported mature Mk expansion. Shifting from pH 7.4 to pH 7.6 at day 7 increased Mk production by 30%. Treatment with nicotinamide at day 7 or day 8 more than doubled the fraction of high-ploidy (>4N) Mks. Ultimately, the 3-phase culture system gave rise to 44.5±8.1 Mks and 8.5±3.1 high-ploidy Mks per input HSPC. Further optimization was required to improve platelet production. Using Iscove's modified Dulbecco's medium (IMDM)+20% BSA, insulin and transferin (BIT) 9500 Serum Substitute greatly improved the frequency and quality of Mk proplatelet extensions without affecting Mk expansion, commitment, or polyploidization in the 3-phase process. Mks cultured in IMDM+20% BIT 9500 gave rise to platelets with functional activity similar to that of fresh platelets from normal donors, as evidenced by basal tubulin distribution and the expression of surface markers and spreading in response to platelet agonists.

Administration of nicotinamide does not increase platelet levels in mice

Elucidating ways to enhance megakaryopoiesis in vivo would have therapeutic applications for thrombocytopenia and transfusion medicine. Nicotinamide has been shown to enhance endomitosis in megakaryocytes cultured in vitro, suggesting that it may be beneficial for the production of platelets in culture. We hypothesized that regular injections of nicotinamide in mice would also increase platelets in vivo. However, we found that platelet counts were reduced by about 25% with daily injections of nicotinamide. Altering the schedule, duration, or nicotinamide dose did not improve platelet production. Consistent with lower platelet levels, nicotinamide also tended to decrease megakaryocyte frequency in sternum and spleen sections, as well as colony formation in vitro by bone marrow progenitor cells. However, there was no effect on the fraction or ploidy of CD41(+) cells harvested from bone marrow. Together, our results suggest that, although nicotinamide increases polyploidization of megakaryocytes in culture, it does not have translatable effects in vivo.

Energy, water and fish: biodiversity impacts of energy-sector water demand in the United States depend on efficiency and policy measures

Rising energy consumption in coming decades, combined with a changing energy mix, have the potential to increase the impact of energy sector water use on freshwater biodiversity. We forecast changes in future water use based on various energy scenarios and examine implications for freshwater ecosystems. Annual water withdrawn/manipulated would increase by 18-24%, going from 1,993,000-2,628,000 Mm(3) in 2010 to 2,359,000-3,271,000 Mm(3) in 2035 under the Reference Case of the Energy Information Administration (EIA). Water consumption would more rapidly increase by 26% due to increased biofuel production, going from 16,700-46,400 Mm(3) consumption in 2010 to 21,000-58,400 Mm(3) consumption in 2035. Regionally, water use in the Southwest and Southeast may increase, with anticipated decreases in water use in some areas of the Midwest and Northeast. Policies that promote energy efficiency or conservation in the electric sector would reduce water withdrawn/manipulated by 27-36 m(3)GJ(-1) (0.1-0.5 m(3)GJ(-1) consumption), while such policies in the liquid fuel sector would reduce withdrawal/manipulation by 0.4-0.7 m(3)GJ(-1) (0.2-0.3 m(3)GJ(-1) consumption). The greatest energy sector withdrawal/manipulation are for hydropower and thermoelectric cooling, although potential new EPA rules that would require recirculating cooling for thermoelectric plants would reduce withdrawal/manipulation by 441,000 Mm(3) (20,300 Mm(3) consumption). The greatest consumptive energy sector use is evaporation from hydroelectric reservoirs, followed by irrigation water for biofuel feedstocks and water used for electricity generation from coal. Historical water use by the energy sector is related to patterns of fish species endangerment, where water resource regions with a greater fraction of available surface water withdrawn by hydropower or consumed by the energy sector correlated with higher probabilities of imperilment. Since future increases in energy-sector surface water use will occur in areas of high fish endemism (e.g., Southeast), additional management and policy actions will be needed to minimize further species imperilment.

Development of novel perfusion chamber to retain nonadherent cells and its use for comparison of human "mobilized" peripheral blood mononuclear cell cultures with and without irradiated bone marrow stroma

Perfusion and static cultures of peripheral blood (PB) mononuclear cells (MNCs), obtained from patients following stem cell mobilization, were supplemented with interleukin-3 (IL-3), IL-6, granulocyte colony-stimulating factor (G-CSF), and stem cell factor (SCF) and compared with and without a preformed irradiated allogeneic bone marrow stromal layer. Perfusion cultures without a stromal layer effectively retained nonadherent cells through the use of a novel "grooved" perfusion chamber, which was designed with minimal mass transfer barriers in order to achieve a well-defined culture environment. The grooved chamber allowed easy and efficient culture inoculation and cell recovery. Average maximum expansion of CFU-GM (colony-forming unit granulocyte-macrophage) cells was observed on day 10 for all cultures. Perfusion cultures had a maximum CFU-GM expansion of 17- and 19-fold with and without a stromal layer, respectively. In contrast, static cultures had a maximum CFU-GM expansion of 18- and 13-fold with and without a stromal layer, respectively. Average long-term-culture initiating cell (LTC-IC) numbers on day 15 were 34% and 64% of input in stroma-containing and stroma-free perfusion cultures and 12% and 11% of input in stroma-containing and stroma-free static cultures, respectively. Thus, perfusion enhanced CFU-GM expansion and LTC-IC maintenance more for the stroma-free cultures than for stroma-containing cultures. This was surprising because analysis of medium supernatants indicated that the stroma-containing cultures were metabolically more active than the stroma-free cultures. In view of their equivalent, if not superior, performance compared to stroma-containing cultures, stroma-free perfusion cultures may offer significant advantages for potential clinical applications.

A kinetic analysis of hybridoma growth and metabolism in batch and continuous suspension culture: effect of nutrient concentration, dilution rate, and pH

Hybridomas are finding increased use for the production of a wide variety of monoclonal antibodies. Understanding the roles of physiological and environmental factors on the growth and metabolism of mammalian cells is a prerequisite for the development of rational scale-up procedures. An SP2/0-derived mouse hybridoma has been employed in the present work as a model system for hybridoma suspension culture. In preliminary shake flask studies to determine the effect of glucose and glutamine, it was found that the specific growth rate, the glucose and glutamine metabolic quotients, and the cumulative specific antibody production rate were independent of glucose concentration over the range commonly employed in cell cultures. Only the specific rate of glutamine uptake was found to depend on glutamine concentration. The cells were grown in continuous culture at constant pH and oxygen concentration at a variety of dilution rates. Specific substrate consumption rates and product formation rates were determined from the steady state concentrations. The specific glucose uptake rate deviated from the maintenance energy model(1) at low specific growth rates, probably due to changes in the metabolic pathways of the cells. Antibody production was not growth-associated; and higher specific antibody production rates were obtained at lower specific growth rates. The effect of pH on the metabolic quotients was also determined. An optimum in viable cell concentration was obtained between pH 7.1 and 7.4. The viable cell number and viability decreased dramatically at pH 6.8. At pH 7.7 the viable cell concentration initially decreased, but then recovered to values typical of pH 7.1-7.4. Higher specific nutrient consumption rates were found at the extreme pH values; however, glucose consumption was inhibited at low pH. The pH history also influenced the behavior at a given pH. Higher antibody metabolic quotients were obtained at the extreme pH values. Together with the effect of specific growth rate, this suggests higher antibody production under environmental or nutritional stress.

Declining sexually transmitted infections among female sex workers: the results of an HIV and sexually transmitted infection prevention strategy in Honduras, 2006-08

In 2006, we implemented an HIV and sexually transmitted infection (STI) prevention programme for female sex workers (FSWs) in three Honduran cities. All FSW attending STI clinics underwent regular examinations and STI testing. Information on condom use with different partners was collected at each visit. After three years, we detected a significant decline in the prevalence of syphilis from 2.3% at the first screening to 0.0% at the third screening (P = 0.05), and of chlamydia, from 6.1% to 3.3% (P = 0.01). No changes were observed in the prevalence of gonorrhoea or trichomoniasis. The cumulative HIV prevalence remained constant (P = 0.44). Reports of condom use with clients increased from 93.8% to 98.9% (P < 0.001). The implementation of an HIV/STI prevention programme in FSW has contributed to increases in condom use with clients and the reduction in syphilis and chlamydia prevalence. The intervention should be strengthened and considered as part of a national health policy strategy.

Proposed megakaryocytic regulon of p53: the genes engaged to control cell cycle and apoptosis during megakaryocytic differentiation

During endomitosis, megakaryocytes undergo several rounds of DNA synthesis without division leading to polyploidization. In primary megakaryocytes and in the megakaryocytic cell line CHRF, loss or knock-down of p53 enhances cell cycling and inhibits apoptosis, leading to increased polyploidization. To support the hypothesis that p53 suppresses megakaryocytic polyploidization, we show that stable expression of wild-type p53 in K562 cells (a p53-null cell line) attenuates the cells' ability to undergo polyploidization during megakaryocytic differentiation due to diminished DNA synthesis and greater apoptosis. This suggested that p53's effects during megakaryopoiesis are mediated through cell cycle- and apoptosis-related target genes, possibly by arresting DNA synthesis and promoting apoptosis. To identify candidate genes through which p53 mediates these effects, gene expression was compared between p53 knock-down (p53-KD) and control CHRF cells induced to undergo terminal megakaryocytic differentiation using microarray analysis. Among substantially downregulated p53 targets in p53-KD megakaryocytes were cell cycle regulators CDKN1A (p21) and PLK2, proapoptotic FAS, TNFRSF10B, CASP8, NOTCH1, TP53INP1, TP53I3, DRAM1, ZMAT3 and PHLDA3, DNA-damage-related RRM2B and SESN1, and actin component ACTA2, while antiapoptotic CKS1B, BCL2, GTSE1, and p53 family member TP63 were upregulated in p53-KD cells. Additionally, a number of cell cycle-related, proapoptotic, and cytoskeleton-related genes with known functions in megakaryocytes but not known to carry p53-responsive elements were differentially expressed between p53-KD and control CHRF cells. Our data support a model whereby p53 expression during megakaryopoiesis serves to control polyploidization and the transition from endomitosis to apoptosis by impeding cell cycling and promoting apoptosis. Furthermore, we identify a putative p53 regulon that is proposed to orchestrate these effects.

Effects of CO2 and osmolality on hybridoma cells: growth, metabolism and monoclonal antibody production

CO2 partial pressure (pCO2) in industrial cell culture reactors may reach 150-200 mm Hg, which can significantly inhibit cell growth and recombinant protein production. Due to equilibrium with bicarbonate, increased pCO2 at constant pH results in a proportional increase in osmolality. Hybridoma AB2-143.2 cell growth rate decreased with increasing pCO2 in well-plate culture, with a 45% decrease at 195 mm Hg with partial osmolality compensation (to 361 mOsm kg- 1). Inhibition was more extensive without osmolality compensation, with a 63% decrease in growth rate at 195 mm Hg and 415 mOsm kg-1. Also, the hybridoma death rate increased with increasing pCO2, with 31- and 64-fold increases at 250 mm Hg pCO2 for 401 and 469 mOsm kg- 1, respectively. The specific glucose consumption and lactate production rates were 40-50% lower at 140 mm Hg pCO2. However, there was little further inhibition of glycolysis at higher pCO2. The specific antibody production rate was not significantly affected by pCO2 or osmolality within the range tested. Hybridomas were also exposed to elevated pCO2 in continuous culture. The viable cell density decreased by 25-40% at 140 mm Hg. In contrast to the well-plate cultures, the death rate was lower at the new steady state at 140 mm Hg. This was probably due to higher residual nutrient and lower byproduct levels at the lower cell density (at the same dilution rate), and was associated with increased cell-specific glucose and oxygen uptake. Thus, the apparent effects of pCO2 may vary with the culture system.

Bone marrow niche-inspired, multiphase expansion of megakaryocytic progenitors with high polyploidization potential

BACKGROUND AIMS

Megakaryopoiesis encompasses hematopoietic stem and progenitor cell (HSPC) commitment to the megakaryocytic cell (Mk) lineage, expansion of Mk progenitors and mature Mks, polyploidization and platelet release. pH and pO2 increase from the endosteum to sinuses, and different cytokines are important for various stages of differentiation. We hypothesized that mimicking the changing conditions during Mk differentiation in the bone marrow would facilitate expansion of progenitors that could generate many high-ploidy Mks.

METHODS

CD34+ HSPCs were cultured at pH 7.2 and 5% O2 with stem cell factor (SCF), thrombopoietin (Tpo) and all combinations of Interleukin (IL)-3, IL-6, IL-11 and Flt-3 ligand to promote Mk progenitor expansion. Cells cultured with selected cytokines were shifted to pH 7.4 and 20% O2 to generate mature Mks, and treated with nicotinamide (NIC) to enhance polyploidization.

RESULTS

Using Tpo + SCF + IL-3 + IL-11, we obtained 3.5 CD34+ CD41+ Mk progenitors per input HSPC, while increasing purity from 1% to 17%. Cytokine cocktails with IL-3 yielded more progenitors and mature Mks, although the purities were lower. Mk production was much greater at higher pH and pO2. Although fewer progenitors were present, shifting to 20% O2 /pH 7.4 at day 5 (versus days 7 or 9) yielded the greatest mature Mk production, 14 per input HSPC. NIC more than doubled the percentage of high-ploidy Mks to 40%.

CONCLUSIONS

We obtained extensive Mk progenitor expansion, while ensuring that the progenitors could produce high-ploidy Mks. We anticipate that subsequent optimization of cytokines for mature Mk production and delayed NIC addition will greatly increase high-ploidy Mk production.

Jarisch-Herxheimer reaction among syphilis patients in Rio de Janeiro, Brazil

The Jarisch-Herxheimer reaction (JHR) is a syndrome observed after antimicrobial treatment of some infectious diseases. The syndrome has clinical characteristics of an inflammatory reaction to antibiotic treatment. A prospective study of patients with a clinical and laboratory diagnosis of syphilis was conducted at a sexually transmitted diseases clinic in Rio de Janeiro, Brazil. Patients were treated with benzathine penicillin and observed for the JHR. A total of 115 patients were included in this study. Fifty-one patients (44%) had secondary syphilis; 37 (32%), primary; 26 (23%), latent; and one (1%), tertiary syphilis. Ten patients (9%) developed the JHR. All JHRs occurred in patients with secondary and latent syphilis. No patients experienced an allergic reaction to penicillin. The JHR occurred less frequently than in previous studies. It is important that health-care professionals recognize the clinical characteristics of the JHR so that it is not misinterpreted as an allergic reaction to penicillin.

(2E)-3-{4-[(1H-1,3-Benzimidazol-2-yl)meth-oxy]-3-eth-oxy-phen-yl}-1-(4-bromo-phen-yl)prop-2-en-1-one monohydrate

In the title compound, C(25)H(21)BrN(2)O(3)·H(2)O, the benzimidazole fragment and the water mol-ecule of crystallization are each disordered over two sets of sites of equal occupancy. The dihedral angles between the least-squares planes of the benzimidazole and the 3-eth-oxy- and 4-bromo-benzene rings are 86.9 (6) and 85.1 (1)°, respectively in one disorder component. The crystal packing is stabilized by inter-molecular O-H⋯O, O-H⋯N and N-H⋯N hydrogen bonds, which link the mol-ecules into chains along the a axis.

The transient responses of hybridoma cells to nutrient additions in continuous culture: II. Glutamine pulse and step changes

The transient and steady-state responses of hybridoma growth and metabolism to glutamine pulse and step changes have been examined. Metabolic quotients are reported for oxygen, glucose, lactate, ammonia, glutamine, alanine, and other amino acids. The specific glutamine consumption rate increased rapidly after all glutamine additions, but the responses of the glucose and oxygen consumption rates and the cell concentration were found to depend on the intial feed glutamine concentration. The glucose consumption rate was 1.4-10.9 times that of glutamine, and serine and branched-chain amino acids were consumed in larger amounts at the higher glucose: glutamine uptake ratios. It was estimated that maintenance accounted for ca. 60% of the cellular ATP requirements at specific growth rates ranging from 0.57 to 0.68 day(-1).

Ex-vivo expansion of CFU-GM and BFU-E in unselected PBMC cultures with Flt3L is enhanced by autologous plasma

BACKGROUND

Previous ex-vivo expansion studies in our laboratory, comparing unselected and CD34(+)-selected PBMC, have shown no advantage for CD34(+) cell selection, in terms of the expansion achieved. Our goal was to develop procedures for consistent generation of large numbers of hematopoietic progenitor and post-progenitor cells from unselected PBMC.

METHODS

Unselected PBMC, collected from cancer patients undergoing apheresis prior to high-dose chemotherapy and autologous stem cell rescue, were expanded ex vivo in static cultures, without a stromal layer, in the presence of Flt3 ligand (Flt3L), a recombinant GM-CSF/IL-3 fusion protein (PIXY321), G-CSF and GM-CSF for 10 days.

RESULTS

The addition of 2% autologous plasma to this cytokine combination enhanced expansion of total cell numbers (3.2 fold versus 1.9 fold; p < 0.01), colony-forming units granulocyte-macrophage (CFU-GM) (22.0 fold versus 8.1 fold, p < 0.01) and burst-forming units erythroid (BFU-E) (17.6 fold versus 7.0 fold, 0.01 < p < 0.02). The optimal seeding density for a given specimen was inversely related to the frequency of CD34(+) cells in the sample. CFU-GM expansion with the Flt3L-containing cytokine cocktail was equivalent to that obtained with IL-3, IL-6, G-CSF and SCF, whether or not the cultures were supplemented with autologous plasma. In plasma-free cultures, BFU-E expansion was significantly higher with IL-3, IL-6, G-CSF and SCF than with Flt3L, PIXY321, G-CSF and GM-CSF. In the presence of autologous plasma, however BFU-E expansion was higher in the Flt3L-containing media. In comparison studies, autologous plasma suppressed BFU-E expansion in SCF-containing cultures. Consistent with our colony assay results, dual-parameter flow cytometric analysis of the expanded cell population revealed that supplementation with autologous plasma yielded a significant increase in the numbers of myeloid progenitors in Flt3L-containing cultures.

DISCUSSION

Unselected PBMC from cancer patients can be effectively expanded ex vivo in Flt3L, PIXY321, G-CSF and GM-CSF, supplemented with autologous plasma, yielding high numbers of myeloid and erythroid progenitors.

Mechanistic studies on the effects of nicotinamide on megakaryocytic polyploidization and the roles of NAD+ levels and SIRT inhibition

OBJECTIVE

Megakaryocytic cells (Mks) undergo endomitosis and become polyploid. Mk ploidy correlates with platelet production. We previously showed that nicotinamide (NIC) greatly increases Mk ploidy in cultures of human mobilized peripheral blood CD34(+) cells. This study aims to examine the generality of NIC effects, NIC's impact on Mk ultrastructure, and potential mechanisms for the increased ploidy.

MATERIALS AND METHODS

We used electron microscopy to examine Mk ultrastructure and flow cytometry to evaluate NIC effects on Mk differentiation and ploidy in mobilized peripheral blood CD34(+) cell cultures under diverse megakaryopoietic conditions. Mk ploidy and NAD(H) content were evaluated for NIC and other NAD(+) precursors. We tested additional inhibitors of the sirtuin (or SIRT) 1 and SIRT2 histone/protein deacetylases and, after treatment with NIC, evaluated changes in the acetylation of SIRT1/2 targets.

RESULTS

NIC increased ploidy under diverse culture conditions and did not alter Mk ultrastructure; 6.25 mM NIC increased NAD(+) levels fivefold. Quinolinic acid increased NAD(+) similar to that for 1 mM NIC, but yielded a much smaller ploidy increase. Similar increases in Mk ploidy were obtained using NIC or the SIRT1/2 inhibitor cambinol, while the SIRT2 inhibitor AGK2 moderately increased ploidy. SIRT1/2 inhibition in cells treated with NIC was evidenced by increased acetylation of nucleosomes and p53. Greater p53 acetylation with NIC was associated with increased binding of p53 to its consensus DNA binding sequence.

CONCLUSION

NIC greatly increases Mk ploidy under a wide range of conditions without altering Mk morphology. Inhibition of SIRT1 and/or SIRT2 is primarily responsible for NIC effects on Mk maturation.

Effects of supported lipid monolayer fluidity on the adhesion of hematopoietic progenitor cell lines to fibronectin-derived peptide ligands for alpha5beta1 and alpha4beta1 integrins

Mimicking the in vivo stem cell niche to increase stem cell expansion will likely require the presentation of multiple ligands. Presenting ligands in fluid-supported lipid monolayers (SLMs) or bilayers (SLBs) allows for ligand diffusion to complement the arrangement of cell receptors as well as cell-mediated ligand rearrangement and clustering. Cells in tissues interact with ligands presented by other cells and the extracellular matrix (ECM), so it will likely be beneficial to present both cell-associated and ECM-derived ligands. A number of investigators have incorporated cell-membrane-associated ligands within fluid surfaces, and several groups have shown that these ligands cluster beneath the cells. However, few studies have investigated cell adhesion to ECM-derived ligands in fluid surfaces. Fibronectin is an important ECM component in many tissues, including the hematopoietic stem cell niche. We examined the adhesion of the M07e and THP-1 hematopoietic progenitor cell lines to fibronectin-derived peptide ligands for the alpha5beta1 (cyclic and linear RGD) and alpha4beta1 (cyclic LDV) integrins as well as the heparin-binding domain (HBD) presented as lipopeptides in fluid and gel SLMs. M07e cells adhered more avidly than THP-1 cells to all of the lipopeptides in fluid and gel surfaces. The adhesion of both cell lines to all peptides was less avid in fluid versus gel SLMs. Adhesion to cyclic LDV (cLDV) and cRGD was similar on gel SLMs for both cell lines. In contrast, adhesion to cLDV was less extensive than to cRGD in fluid SLMs, especially for M07e cells. Adhesion to linear RGD was less avid than to cRGD or cLDV and decreased to a greater extent in fluid SLMs. Human aortic endothelial cells adhered to cRGD in fluid SLMs and remained viable for at least 24 h but did not spread. We also showed additive THP-1 cell adhesion to cLDV and linear RGD lipopeptides presented in a fluid SLM. Although DOPC (dioleoyl phosphatidyl choline) SLMs are not sufficiently stable for long-term cell culture studies, our results and those of others suggest that fluid SLMs are likely to be useful for presenting multiple ligands and for mimicking short-term interactions in the stem cell niche.

Mimicking stem cell niches to increase stem cell expansion

Niches regulate lineage-specific stem cell self-renewal versus differentiation in vivo and are composed of supportive cells and extracellular matrix components arranged in a three-dimensional topography of controlled stiffness in the presence of oxygen and growth factor gradients. Mimicking stem cell niches in a defined manner will facilitate production of the large numbers of stem cells needed to realize the promise of regenerative medicine and gene therapy. Progress has been made in mimicking components of the niche. Immobilizing cell-associated Notch ligands increased the self-renewal of hematopoietic (blood) stem cells. Culture on a fibrous scaffold that mimics basement membrane texture increased the expansion of hematopoietic and embryonic stem cells. Finally, researchers have created intricate patterns of cell-binding domains and complex oxygen gradients.

Tumor suppressor protein p53 regulates megakaryocytic polyploidization and apoptosis

The molecular mechanisms underlying differentiation of hematopoietic stem cells into megakaryocytes are poorly understood. Tumor suppressor protein p53 can act as a transcription factor affecting both cell cycle control and apoptosis, and we have previously shown that p53 is activated during terminal megakaryocytic (Mk) differentiation of the CHRF-288-11 (CHRF) cell line. Here, we use RNA interference to reduce p53 expression in CHRF cells and show that reduced p53 activity leads to a greater fraction of polyploid cells, higher mean and maximum ploidy, accelerated DNA synthesis, and delayed apoptosis and cell death upon phorbol 12-myristate 13-acetate-induced Mk differentiation. In contrast, reduced p53 expression did not affect the ploidy or DNA synthesis of CHRF cells in the absence of phorbol 12-myristate 13-acetate stimulation. Furthermore, primary Mk cells from cultures initiated with p53-null mouse bone marrow mononuclear cells displayed higher ploidy compared with wild-type controls. Quantitative reverse transcription-PCR analysis of p53-knockdown CHRF cells, compared with the "scrambled" control CHRF cells, revealed that six known transcriptional targets of p53 (BBC3, BAX, TP53I3, TP53INP1, MDM2, and P21) were down-regulated, whereas BCL2 expression, which is known to be negatively affected by p53, was up-regulated. These studies show that the functional role of the intrinsic activation of p53 during Mk differentiation is to control polyploidization and the transition to endomitosis by impeding cell cycling and promoting apoptosis.

Gene Ontology-driven transcriptional analysis of CD34+ cell-initiated megakaryocytic cultures identifies new transcriptional regulators of megakaryopoiesis

Differentiation of hematopoietic stem and progenitor cells is an intricate process controlled in large part at the level of transcription. While some key megakaryocytic transcription factors have been identified, the complete network of megakaryocytic transcriptional control is poorly understood. Using global gene expression microarray analysis, Gene Ontology-based functional annotations, and a novel interlineage comparison with parallel, isogenic granulocytic cultures as a negative control, we closely examined the mRNA level of transcriptional regulators in megakaryocytes derived from human mobilized peripheral blood CD34(+) hematopoietic cells. This approach identified 199 differentially expressed transcription factors or transcriptional regulators. We identified and detailed the transcriptional kinetics of most known megakaryocytic transcription factors including GATA1, FLI1, and MAFG. Furthermore, many genes with transcription factor activity or transcription factor binding activity were identified in megakaryocytes that had not previously been associated with that lineage, including BTEB1, NR4A2, FOXO1A, MEF2C, HDAC5, VDR, and several genes associated with the tumor suppressor p53 (HIPK2, FHL2, and TADA3L). Protein expression and nuclear localization were confirmed in megakaryocytic cells for four of the novel candidate megakaryocytic transcription factors: FHL2, MXD1, E2F3, and RFX5. In light of the hypothesis that transcription factors expressed in a particular differentiation program are important contributors to such a program, these data substantially expand our understanding of transcriptional regulation in megakaryocytic differentiation of stem and progenitor cells.

Comparative, genome-scale transcriptional analysis of CHRF-288-11 and primary human megakaryocytic cell cultures provides novel insights into lineage-specific differentiation

OBJECTIVES

Little is known about the transcriptional events underlying megakaryocytic (Mk) differentiation. We sought to identify genes and pathways previously unassociated with megakaryopoiesis and to evaluate the CHRF-288-11 (CHRF) megakaryoblastic cell line as a model system for investigating megakaryopoiesis.

METHODS

Using DNA microarrays, Q-RT-PCR, and protein-level assays, we compared the dynamic gene expression pattern of phorbol ester-induced differentiation of CHRF cells to cytokine-induced Mk differentiation of human mobilized peripheral blood CD34(+) cells.

RESULTS

Transcriptional patterns of well-known Mk genes were similar between the two systems. CHRF cells constitutively express some early Mk genes including GATA-1. Expression patterns of apoptosis-related genes suggested that increased p53 activity is involved in Mk apoptosis, and this was confirmed by p53-DNA-binding activity data and flow-cytometric analysis of the p53 target gene BBC3. Certain Rho and G-protein-coupled-receptor signaling pathway components were upregulated, including genes not previously associated with Mk cells. Ontological analysis revealed upregulation of defense-response genes, including both known and candidate platelet-derived contributors to inflammation. Upregulation of interferon-responsive genes occurred in the cell line, but not in the primary cells, likely due to a known genetic mutation in the JAK2/STAT5 signaling pathway.

CONCLUSIONS

This analysis of megakaryopoiesis, which integrates dynamic gene expression data with protein abundance and activity assays, has identified a number of genes and pathways that may help govern megakaryopoiesis. Furthermore, the transcriptional data support the hypothesis that CHRF cells resemble an early Mk phenotype and, with certain limitations, exhibit genuine transcriptional features of Mk differentiation upon treatment with phorbol esters.