UCP2 modulates cell proliferation through the MAPK/ERK pathway during erythropoiesis and has no effect on heme biosynthesis

Cerium Oxide Nanoparticle Administration to Skeletal Muscle Cells under Different Gravity and Radiation Conditions

For their remarkable biomimetic properties implying strong modulation of the intracellular and extracellular redox state, cerium oxide nanoparticles (also termed "nanoceria") were hypothesized to exert a protective role against oxidative stress associated with the harsh environmental conditions of spaceflight, characterized by microgravity and highly energetic radiations. Nanoparticles were supplied to proliferating C2C12 mouse skeletal muscle cells under different gravity and radiation levels. Biological responses were thus investigated at a transcriptional level by RNA next-generation sequencing. Lists of differentially expressed genes (DEGs) were generated and intersected by taking into consideration relevant comparisons, which led to the observation of prevailing effects of the space environment over those induced by nanoceria. In space, upregulation of transcription was slightly preponderant over downregulation, implying involvement of intracellular compartments, with the majority of DEGs consistently over- or under-expressed whenever present. Cosmic radiations regulated a higher number of DEGs than microgravity and seemed to promote increased cellular catabolism. By taking into consideration space physical stressors alone, microgravity and cosmic radiations appeared to have opposite effects at transcriptional levels despite partial sharing of molecular pathways. Interestingly, gene ontology denoted some enrichment in terms related to vision, when only effects of radiations were assessed. The transcriptional regulation of mitochondrial uncoupling protein 2 in space-relevant samples suggests perturbation of the intracellular redox homeostasis, and leaves open opportunities for antioxidant treatment for oxidative stress reduction in harsh environments.

Molecular Pathways Involved in the Development of Congenital Erythrocytosis

Patients with idiopathic erythrocytosis are directed to targeted genetic testing including nine genes involved in oxygen sensing pathway in kidneys, erythropoietin signal transduction in pre-erythrocytes and hemoglobin-oxygen affinity regulation in mature erythrocytes. However, in more than 60% of cases the genetic cause remains undiagnosed, suggesting that other genes and mechanisms must be involved in the disease development. This review aims to explore additional molecular mechanisms in recognized erythrocytosis pathways and propose new pathways associated with this rare hematological disorder. For this purpose, a comprehensive review of the literature was performed and different in silico tools were used. We identified genes involved in several mechanisms and molecular pathways, including mRNA transcriptional regulation, post-translational modifications, membrane transport, regulation of signal transduction, glucose metabolism and iron homeostasis, which have the potential to influence the main erythrocytosis-associated pathways. We provide valuable theoretical information for deeper insight into possible mechanisms of disease development. This information can be also helpful to improve the current diagnostic solutions for patients with idiopathic erythrocytosis.

Copper deficiency-induced anemia is caused by a mitochondrial metabolic reprograming in erythropoietic cells

The lack of copper has been associated with anemia, myelodysplastic syndromes and leukemia as well as with a loss in complex IV activity and an enlarged mitochondrial morphology. Mitochondria play a key role during the differentiation of hematopoietic stem cells by regulating the passage from a glycolytic to oxidative metabolism. The former is associated with cell proliferation and the latter with cell differentiation. Oxidative metabolism, which occurs inside mitochondria, is sustained by the respiratory chain, where complex IV is copper-dependent. We have hypothesized that a copper deficiency induces a mitochondrial metabolic reprogramming, favoring cell expansion over cell differentiation in erythropoiesis. Erythroid progression analysis of the bone marrow of mice fed with a copper deficient diet and of the in vitro erythropoiesis of human CD34+ cells treated with a bathocuproine - a copper chelator - showed a major expansion of progenitor cells and a decreased differentiation. Under copper deficiency, mitochondria switched to a higher membrane potential, lower oxygen consumption rate and lower ROS levels as compared with control cells. In addition, mitochondrial biomass was increased and an up-regulation of the mitochondrial fusion protein mitofusin 2 was observed. Most copper-deficient phenotypes were mimicked by the pharmacological inhibition of complex IV with azide. We concluded that copper deficiency induced a mitochondrial metabolic reprogramming, making hematopoietic stem cells favor progenitor cell expansion over cell differentiation.

Lifestyle mediates the role of nutrient-sensing pathways in cognitive aging: cellular and epidemiological evidence

Aging induces cellular and molecular changes including modification of stem cell pools. In particular, alterations in aging neural stem cells (NSCs) are linked to age-related cognitive decline which can be modulated by lifestyle. Nutrient-sensing pathways provide a molecular basis for the link between lifestyle and cognitive decline. Adopting a back-translation strategy using stem cell biology to inform epidemiological analyses, here we show associations between cellular readouts of NSC maintenance and expression levels of nutrient-sensing genes following NSC exposure to aging human serum as well as morphological and gene expression alterations following repeated passaging. Epidemiological analyses on the identified genes showed associations between polymorphisms in SIRT1 and ABTB1 and cognitive performance as well as interactions between SIRT1 genotype and physical activity and between GRB10 genotype and adherence to a Mediterranean diet. Our study contributes to the understanding of neural stem cell molecular mechanisms underlying human cognitive aging and hints at lifestyle modifiable factors.

Uncoupling protein 2 is upregulated in melanoma cells and contributes to the activation of Akt/mTOR and ERK signaling

The aim of the present study was to characterize the expression of uncoupling protein 2 (UCP2) in melanoma and to study the potential mechanisms underlying the involvement of UCP2 in melanomagenesis using human melanoma cell lines. The expression of UCP2 was evaluated in specimens from normal control subjects, patients with compound nevus, and patients with cutaneous and mucosal melanoma. Stable knockdown of UCP2 was achieved in human melanoma cell lines, which were used to examine whether UCP2 knockdown affects the mitochondrial membrane potential and intracellular levels of ATP, reactive oxygen species and lactate. Cell proliferation, invasion, spheroid formation and cisplatin sensitivity were also evaluated in the UCP2 knockdown cells. Finally, the effects of UCP2 knockdown on the Akt/mammalian target of rapamycin (mTOR) and extracellular signal‑regulated kinase (ERK) pathways, which are important oncogenic pathways during melanomagenesis, were evaluated. Relatively high expression of UCP2 was detected in human melanoma specimens, which was correlated with Clark level and Breslow thickness. Knockdown of UCP2 suppressed cell proliferation, invasion and spheroid formation, and increased the sensitivity of melanoma cells to cisplatin. Furthermore, the UCP2 knockdown cells exhibited inhibition of Akt/mTOR signaling and ERK activation. Therefore, human melanoma tissues exhibit relatively high UCP2 expression, which may be implicated in the mechanisms underlying tumor progression. The potential role of UCP2 in melanomagenesis may involve enhancing the Akt/mTOR and mitogen‑activated protein kinase/ERK pathways.

Mitochondrial Iron in Human Health and Disease

Mitochondria are an iconic distinguishing feature of eukaryotic cells. Mitochondria encompass an active organellar network that fuses, divides, and directs a myriad of vital biological functions, including energy metabolism, cell death regulation, and innate immune signaling in different tissues. Another crucial and often underappreciated function of these dynamic organelles is their central role in the metabolism of the most abundant and biologically versatile transition metals in mammalian cells, iron. In recent years, cellular and animal models of mitochondrial iron dysfunction have provided vital information in identifying new proteins that have elucidated the pathways involved in mitochondrial homeostasis and iron metabolism. Specific signatures of mitochondrial iron dysregulation that are associated with disease pathogenesis and/or progression are becoming increasingly important. Understanding the molecular mechanisms regulating mitochondrial iron pathways will help better define the role of this important metal in mitochondrial function and in human health and disease.

Mitochondrial Uncoupling Proteins: Subtle Regulators of Cellular Redox Signaling

SIGNIFICANCE

Mitochondria are the energetic, metabolic, redox, and information signaling centers of the cell. Substrate pressure, mitochondrial network dynamics, and cristae morphology state are integrated by the protonmotive force Δp or its potential component, ΔΨ, which are attenuated by proton backflux into the matrix, termed uncoupling. The mitochondrial uncoupling proteins (UCP1-5) play an eminent role in the regulation of each of the mentioned aspects, being involved in numerous physiological events including redox signaling. Recent Advances: UCP2 structure, including purine nucleotide and fatty acid (FA) binding sites, strongly support the FA cycling mechanism: UCP2 expels FA anions, whereas uncoupling is achieved by the membrane backflux of protonated FA. Nascent FAs, cleaved by phospholipases, are preferential. The resulting Δp dissipation decreases superoxide formation dependent on Δp. UCP-mediated antioxidant protection and its impairment are expected to play a major role in cell physiology and pathology. Moreover, UCP2-mediated aspartate, oxaloacetate, and malate antiport with phosphate is expected to alter metabolism of cancer cells.

CRITICAL ISSUES

A wide range of UCP antioxidant effects and participations in redox signaling have been reported; however, mechanisms of UCP activation are still debated. Switching off/on the UCP2 protonophoretic function might serve as redox signaling either by employing/releasing the extra capacity of cell antioxidant systems or by directly increasing/decreasing mitochondrial superoxide sources. Rapid UCP2 degradation, FA levels, elevation of purine nucleotides, decreased Mg²⁺, or increased pyruvate accumulation may initiate UCP-mediated redox signaling.

FUTURE DIRECTIONS

Issues such as UCP2 participation in glucose sensing, neuronal (synaptic) function, and immune cell activation should be elucidated. Antioxid. Redox Signal. 29, 667-714.

Uncoupling protein 2 deficiency results in higher neutrophil counts and lower B-cell counts during aging in mice

Progress of age-related hematopoietic diseases such as myelodysplastic syndrome has previously been linked to enhanced levels of reactive oxygen species (ROS). Uncoupling protein 2 (UCP2) was found to reduce mitochondrial ROS production through uncoupling of the respiratory chain. The impact of UCP2 loss and elevated ROS on hematopoiesis during aging has not yet been investigated. In this study, UCP2 knockout mice were analyzed at aging stages of 3, 12, and 24 months with respect to oxidative and energy status of bone marrow cells. Further, the cellular bone marrow subpopulation composition was characterized, as were the differential blood counts at all time points. UCP2 knockout mice revealed enhanced levels of mitochondrial superoxide in elderly animals. Following oxidative stress, adenosine triphosphate (ATP) levels decreased more in the knockout mice than in the wild type. Investigation of bone marrow and blood counts of the knockout mice revealed an enhanced amount of monocytes and neutrophils, as well as a decreased amount of B cells and impaired erythropoiesis throughout aging. In summary, UCP2 induces protective effects on ROS and ATP levels during aging. Additionally, the results suggest an imbalance in hematopoiesis because of the lack of UCP2.

Non-cytotoxic copper overload boosts mitochondrial energy metabolism to modulate cell proliferation and differentiation in the human erythroleukemic cell line K562

Copper is integral to the mitochondrial respiratory complex IV and contributes to proliferation and differentiation, metabolic reprogramming and mitochondrial function. The K562 cell line was exposed to a non-cytotoxic copper overload to evaluate mitochondrial dynamics, function and cell fate. This induced higher rates of mitochondrial turnover given by an increase in mitochondrial fusion and fission events and in the autophagic flux. The appearance of smaller and condensed mitochondria was also observed. Bioenergetics activity included more respiratory complexes, higher oxygen consumption rate, superoxide production and ATP synthesis, with no decrease in membrane potential. Increased cell proliferation and inhibited differentiation also occurred. Non-cytotoxic copper levels can modify mitochondrial metabolism and cell fate, which could be used in cancer biology and regenerative medicine.

Alteration of UCP2 and ZO-1 expression in trabecular meshwork of neovascular glaucoma patients

PURPOSE

The aim of this study was to investigate the expression of uncoupling protein 2 (UCP2) and zonula occludens-1 (ZO-1) in the trabecular meshwork (TM) of neovascular glaucoma (NVG) patients treated with trabeculectomy.

MATERIALS AND METHODS

Six eyes with NVG underwent trabeculectomy for therapeutic purposes. The data consisted of patient demographics, presurgical and postsurgical visual acuity, intraocular pressure, gonioscopy, and neovascularization of iris and/or the anterior chamber angle. TM samples were obtained from the NVG eyes that had undergone surgery. Immunofluorescence and confocal laser scanning microscopy were carried out to determine the expression of UCP2 and ZO-1 in the TM cells.

RESULTS

The baseline median visual acuity was light perception, and the mean intraocular pressure (standard error) was 52.5 (8.3) mm Hg. All eyes displayed neovascularization of the iris and the anterior chamber angle. The expression of UCP2 was significantly decreased in TM cells of NVG compared with the control (P=0.000), whereas increase in ZO-1 expression was detected in staining cells with NVG in comparison with the control (P=0.000). The necrotic cells in the TM were increased (P=0.000), whereas the viable cells were reduced (P=0.000) in comparison with the control.

CONCLUSIONS

The decreased UCP2 expression and increased ZO-1 expression suggest that the oxidative stress-induced mitochondrial dysfunction and tight junction formation may play pivotal roles in the progress of NVG.

Quercetin Affects Erythropoiesis and Heart Mitochondrial Function in Mice

Quercetin, a dietary flavonoid used as a food supplement, showed powerful antioxidant effects in different cellular models. However, recent in vitro and in vivo studies in mammals have suggested a prooxidant effect of quercetin and described an interaction with mitochondria causing an increase in O₂^∙− production, a decrease in ATP levels, and impairment of respiratory chain in liver tissue. Therefore, because of its dual actions, we studied the effect of quercetin in vivo to analyze heart mitochondrial function and erythropoiesis. Mice were injected with 50 mg/kg of quercetin for 15 days. Treatment with quercetin decreased body weight, serum insulin, and ceruloplasmin levels as compared with untreated mice. Along with an impaired antioxidant capacity in plasma, quercetin-treated mice showed a significant delay on erythropoiesis progression. Heart mitochondrial function was also impaired displaying more protein oxidation and less activity for IV, respectively, than no-treated mice. In addition, a significant reduction in the protein expression levels of Mitofusin 2 and Voltage-Dependent Anion Carrier was observed. All these results suggest that quercetin affects erythropoiesis and mitochondrial function and then its potential use as a dietary supplement should be reexamined.

Stem cells, mitochondria and aging

Decline in metabolism and regenerative potential of tissues are common characteristics of aging. Regeneration is maintained by somatic stem cells (SSCs), which require tightly controlled energy metabolism and genomic integrity for their homeostasis. Recent data indicate that mitochondrial dysfunction may compromise this homeostasis, and thereby contribute to tissue degeneration and aging. Progeroid Mutator mouse, accumulating random mtDNA point mutations in their SSCs, showed disturbed SSC homeostasis, emphasizing the importance of mtDNA integrity for stem cells. The mechanism involved changes in cellular redox-environment, including subtle increase in reactive oxygen species (H₂O₂and superoxide anion), which did not cause oxidative damage, but disrupted SSC function. Mitochondrial metabolism appears therefore to be an important regulator of SSC fate determination, and defects in it in SSCs may underlie premature aging. Here we review the current knowledge of mitochondrial contribution to SSC dysfunction and aging. This article is part of a Special Issue entitled: Mitochondrial Dysfunction in Aging.

Adaptive responses of mitochondria to mild copper deprivation involve changes in morphology, OXPHOS remodeling and bioenergetics

Copper is an essential cofactor of complex IV of the electron transfer chain, and it is directly involved in the generation of mitochondrial membrane potential. Its deficiency induces the formation of ROS, large mitochondria and anemia. Thus, there is a connection between copper metabolism and bioenergetics, mitochondrial dynamics and erythropoiesis. Copper depletion might end in cellular apoptosis or necrosis. However, before entering into those irreversible processes, mitochondria may execute a series of adaptive responses. Mitochondrial adaptive responses (MAR) may involve multiple and diverse mechanisms for preserving cell life, such as mitochondrial dynamics, OXPHOS remodeling and bioenergetics output. In this study, a mild copper deficiency was produced in an animal model through intraperitoneal injections of bathocuproine disulfonate in order to study the MAR. Under these conditions, a new type of mitochondrial morphology was discovered in the liver. Termed the "butternut squash" mitochondria, it coexisted with normal and swollen mitochondria. Western blot analyses of mitochondrial dynamics proteins showed an up-regulation of MFN-2 and OPA1 fusion proteins. Furthermore, isolated liver mitochondria displayed OXPHOS remodeling through a decrease in supercomplex activity with a concomitant increase at an individual level of complexes I and IV, higher respiratory rates at complex I and II levels, higher oligomycin-insensitive respiration, and lower respiratory control ratio values when compared to the control group. As expected, total ATP and ATP/ADP values were not significantly different, since animal's health was not compromised. As a whole, these results describe a compensatory and adaptive response of metabolism and bioenergetics under copper deprivation.

Inhibition of high glucose-induced apoptosis by uncoupling protein 2 in human umbilical vein endothelial cells

Studies have shown that an overproduction of mitochondrial reactive oxygen species (ROS) is an initiating cause in the pathogenesis of diabetic complications. However, uncoupling protein 2 (UCP2) can protect retinal vascular endothelial cells from damage by inhibiting the overproduction of mitochondrial ROS, although the protective mechanism involved is not completely clear. This study aimed to assess the effect and mechanism of UCP2 on the apoptosis of human umbilical vein endothelial cells (HUVECs). HUVECs were cultured in normal glucose (NG, 5.5 mmol/l) or high glucose (HG, 30 mmol/l) medium in the presence or absence of UCP2(+/+) lentiviral transfection. Lentivirus-mediated UCP2 overexpression inhibited the apoptosis of HUVECs induced by HG. Treatment with HG resulted in the upregulation of caspase-3 and cytochrome c and the downregulation of Bcl-2 in vitro. Furthermore, compared with the NG group, the rate of apoptosis was significantly increased in the HG group. On day two post-infection, NG cells showed significantly greater HUVEC cell proliferation than HG cells. Notably, UCP2 overexpression inhibited these processes. Taken together, these results suggest that UCP2 promotes cell proliferation and inhibits HG-induced apoptosis in HUVECs via the Bcl-2 up‑ and downregulation of caspase-3 and cytochrome c in vitro. This may provide experimental evidence for the application of UCP2 as a new protective factor for diabetic complications, such as diabetic retinopathy.

Uncoupling protein 2 and 4 expression pattern during stem cell differentiation provides new insight into their putative function

Apart from the first family member, uncoupling protein 1 (UCP1), the functions of other UCPs (UCP2-UCP5) are still unknown. In analyzing our own results and those previously published by others, we have assumed that UCP's cellular expression pattern coincides with a specific cell metabolism and changes if the latter is altered. To verify this hypothesis, we analyzed the expression of UCP1-5 in mouse embryonic stem cells before and after their differentiation to neurons. We have shown that only UCP2 is present in undifferentiated stem cells and it disappears simultaneously with the initiation of neuronal differentiation. In contrast, UCP4 is simultaneously up-regulated together with typical neuronal marker proteins TUJ-1 and NeuN during mESC differentiation in vitro as well as during murine brain development in vivo. Notably, several tested cell lines express UCP2, but not UCP4. In line with this finding, neuroblastoma cells that display metabolic features of tumor cells express UCP2, but not UCP4. UCP2's occurrence in cancer, immunological and stem cells indicates that UCP2 is present in cells with highly proliferative potential, which have a glycolytic type of metabolism as a common feature, whereas UCP4 is strongly associated with non-proliferative highly differentiated neuronal cells.

Transcription factor SCL/TAL1 mediates the phosphorylation of MEK/ERK pathway in umbilical cord blood CD34⁺ stem cells during hematopoietic differentiation

Transcription factor stem cell leukemia (SCL), also known as the T-cell acute lymphocytic leukemia 1 (TAL1), plays a key role in the regulation of hematopoiesis, but the molecular mechanisms are not well understood. The aim of the present study is to elucidate the effects of the epidermal growth factor receptor (EGFR) signal pathways underlying the biologic activity of SCL/TAL1 on normal hematopoietic development. Lentiviral vectors with up or down-regulation of SCL/TAL1 were transfected into umbilical cord blood CD34 stem cells. EGFR signaling pathways (including MEK/ERK and Akt/mTOR) and surface hematopoietic markers were analyzed in the process of hematopoietic differentiation. The data revealed that up or down-regulation of SCL/TAL1 gene was accompanied positively by the expressions of p-MEK and p-ERK1/2 protein, but the changes of Akt/mTOR were unobvious. MEK/ERK inhibitor U0126 and SCL/TAL1 down-regulation showed similar inhibitory effects on erythroid, myeloid, and megakaryoid differentiation. However, Akt/mTOR pathway altered insignificantly. MEK/ERK inhibitor U0126 could not affect the expression of SCL/TAL1 mRNA or protein. Taken together, these findings fully illustrated that SCL/TAL1 is located in the up-stream of MEK/ERK pathway and partially regulates hematopoiesis by modulating the phosphorylation level of the key proteins in MEK/ERK pathway.

Akt- and Erk-mediated regulation of proliferation and differentiation during PDGFRβ-induced MSC self-renewal

Understanding the mechanisms that direct mesenchymal stem cell (MSC) self-renewal fate decisions is a key to most tissue regenerative approaches. The aim of this study here was to investigate the mechanisms of action of platelet-derived growth factor receptor β (PDGFRβ) signalling on MSC proliferation and differentiation. MSC were cultured and stimulated with PDGF-BB together with inhibitors of second messenger pathways. Cell proliferation was assessed using ethynyl-2′-deoxyuridine and phosphorylation status of signalling molecules assessed by Western Blots. To assess differentiation potentials, cells were transferred to adipogenic or osteogenic media, and differentiation assessed by expression of differentiation association genes by qRT-PCR, and by long-term culture assays. Our results showed that distinct pathways with opposing actions were activated by PDGF. PI3K/Akt signalling was the main contributor to MSC proliferation in response to activation of PDGFRβ. We also demonstrate a negative feedback mechanism between PI3K/Akt and PDGFR-β expression. In addition, PI3K/Akt downstream signal cascades, mTOR and its associated proteins p70S6K and 4E-BP1 were involved. These pathways induced the expression of cyclin D1, cyclin D3 and CDK6 to promote cell cycle progression and MSC proliferation. In contrast, activation of Erk by PDGFRβ signalling potently inhibited the adipocytic differentiation of MSCs by blocking PPARγ and CEBPα expression. The data suggest that PDGFRβ-induced Akt and Erk pathways regulate opposing fate decisions of proliferation and differentiation to promote MSC self-renewal. Thus, activation of multiple intracellular cascades is required for successful and sustainable MSC self-renewal strategies.

Quantification of uncoupling protein 2 reveals its main expression in immune cells and selective up-regulation during T-cell proliferation

Uncoupling protein 2 (UCP2) is an inner mitochondrial membrane protein. Although the protein was discovered in 1997, its function and even its tissue distribution are still under debate. Here we present a quantitative analysis of mRNA and protein expression in various mice tissues, revealing that UCP2 is mainly expressed in organs and cells associated with the immune system. Although the UCP2 gene is present in the brain, as demonstrated using quantitative RT-PCR, the protein was not detectable in neurons under physiological conditions. Instead, we could detect UCP2 in microglia, which act in the immune defense of the central nervous system. In lymphocytes, activation led to a ten-fold increase of UCP2 protein expression simultaneously to the increase in levels of other mitochondrial proteins, whereas lymphocyte re-stimulation resulted in the selective increase of UCP2. The highest detected level of UCP2 expression in stimulated T-cells (0.54 ng/(µg total cellular protein)) was approximately 200 times lower than the level of UCP1 in brown adipose tissue from room temperature acclimated mice. Both the UCP2 expression pattern and the time course of up-regulation in stimulated T-cells imply UCP2’s involvement in the immune response, probably by controlling the metabolism during cell proliferation.

The mitochondrial transporter ABC-me (ABCB10), a downstream target of GATA-1, is essential for erythropoiesis in vivo

The mitochondrial transporter ATP binding cassette mitochondrial erythroid (ABC-me/ABCB10) is highly induced during erythroid differentiation by GATA-1 and its overexpression increases hemoglobin production rates in vitro. However, the role of ABC-me in erythropoiesis in vivo is unknown. Here we report for the first time that erythrocyte development in mice requires ABC-me. ABC-me-/- mice die at day 12.5 of gestation, showing nearly complete eradication of primitive erythropoiesis and lack of hemoglobinized cells at day 10.5. ABC-me-/- erythroid cells fail to differentiate because they exhibit a marked increase in apoptosis, both in vivo and ex vivo. Erythroid precursors are particularly sensitive to oxidative stress and ABC-me in the heart and its yeast ortholog multidrug resistance-like 1 have been shown to protect against oxidative stress. Thus, we hypothesized that increased apoptosis in ABC-me-/- erythroid precursors was caused by oxidative stress. Within this context, ABC-me deletion causes an increase in mitochondrial superoxide production and protein carbonylation in erythroid precursors. Furthermore, treatment of ABC-me-/- erythroid progenitors with the mitochondrial antioxidant MnTBAP (superoxide dismutase 2 mimetic) supports survival, ex vivo differentiation and increased hemoglobin production. Altogether, our findings demonstrate that ABC-me is essential for erythropoiesis in vivo.

ErbB1/2 tyrosine kinase inhibitor mediates oxidative stress-induced apoptosis in inflammatory breast cancer cells

Overexpression of epidermal growth factor receptors (ErbB) is frequently seen in inflammatory breast cancer (IBC). Treatment with ErbB1/2-targeting agents (lapatinib) mediates tumor apoptosis by downregulating ErbB1/2 phosphorylation and downstream survival signaling. In this study, using carboxy-H(2)DCFDA, DHE, and MitoSOX Red to examine changes in hydrogen peroxide radicals, cytoplasmic and mitochondrial superoxide, respectively, we observed that GW583340 (a lapatinib-analog) increases reactive oxygen species (ROS) in two models of IBC (SUM149, SUM190) that are sensitive to ErbB1/2 blockade. This significant increase in ROS levels was similar to those generated by classical oxidative agents H(2)O(2) and paraquat. In contrast, minimal to basal levels of ROS were measured in a clonal population of GW583340-resistant IBC cells (rSUM149 and rSUM190). The GW583340-resistant IBC cells displayed increased SOD1, SOD2, and glutathione expression, which correlated with decreased sensitivity to the apoptotic-inducing effects of GW583340, H(2)O(2), and paraquat. The ROS increase and cell death in the GW583340-sensitive cells was reversed by simultaneous treatment with a superoxide dismutase (SOD) mimic. Additionally, overcoming the high levels of antioxidants using redox modulators induced apoptosis in the GW583340-resistant cells. Taken together, these data demonstrate a novel mechanism of lapatinib-analog-induced apoptosis and indicate that resistant cells have increased antioxidant potential, which can be overcome by treatment with SOD modulators.

Induction of erythroid differentiation in human erythroleukemia cells by depletion of malic enzyme 2

Malic enzyme 2 (ME2) is a mitochondrial enzyme that catalyzes the conversion of malate to pyruvate and CO2 and uses NAD as a cofactor. Higher expression of this enzyme correlates with the degree of cell de-differentiation. We found that ME2 is expressed in K562 erythroleukemia cells, in which a number of agents have been found to induce differentiation either along the erythroid or the myeloid lineage. We found that knockdown of ME2 led to diminished proliferation of tumor cells and increased apoptosis in vitro. These findings were accompanied by differentiation of K562 cells along the erythroid lineage, as confirmed by staining for glycophorin A and hemoglobin production. ME2 knockdown also totally abolished growth of K562 cells in nude mice. Increased ROS levels, likely reflecting increased mitochondrial production, and a decreased NADPH/NADP+ ratio were noted but use of a free radical scavenger to decrease inhibition of ROS levels did not reverse the differentiation or apoptotic phenotype, suggesting that ROS production is not causally involved in the resultant phenotype. As might be expected, depletion of ME2 induced an increase in the NAD+/NADH ratio and ATP levels fell significantly. Inhibition of the malate-aspartate shuttle was insufficient to induce K562 differentiation. We also examined several intracellular signaling pathways and expression of transcription factors and intermediate filament proteins whose expression is known to be modulated during erythroid differentiation in K562 cells. We found that silencing of ME2 leads to phospho-ERK1/2 inhibition, phospho-AKT activation, increased GATA-1 expression and diminished vimentin expression. Metabolomic analysis, conducted to gain insight into intermediary metabolic pathways that ME2 knockdown might affect, showed that ME2 depletion resulted in high orotate levels, suggesting potential impairment of pyrimidine metabolism. Collectively our data point to ME2 as a potentially novel metabolic target for leukemia therapy.

Do UCP2 and mild uncoupling improve longevity?

Mild uncoupling of mitochondrial respiration is considered to prolong life span of organisms by reducing the production of reactive oxygen species (ROS). Experimental evidence against this hypothesis has been brought forward by premature senescence in cell cultures treated with uncouplers. Exposing HUVEC to a mixture of nutritionally important fatty acids (oil extract of chicken yolk) mild uncoupling with "naturally acting substances" was performed. This treatment also resulted in premature senescence although ROS production did not increase. Fatty acids activate uncoupling proteins (UCP) in the inner mitochondrial membrane. UCP2 expression proved to be sensitive to the presence of fatty acids but remains unchanged during the ageing process. UCP3 expression in senescent HUVEC and avUCP expression in senescent CEF were considerably less than in young cultures. No indication for protonophoric reduction of mitochondrial membrane potential was found in UCP2 overexpressing HeLa cells and only little in HUVEC. ROS levels increased instead of being reduced in these cells. Stable transfection with UCP2-GFP was possible only in chick embryo fibroblasts and HeLa cells and resulted in decreased proliferation. Stable transfection of HUVEC with UCP2-GFP resulted in death of cultures within one or two weeks. The reason for this behaviour most probably is apoptosis preceded by mitochondrial fragmentation and loss of membrane potential.

Pro-inflammatory cytokine-mediated anemia: regarding molecular mechanisms of erythropoiesis

Anemia of cancer and chronic inflammatory diseases is a frequent complication affecting quality of life. For cancer patients it represents a particularly bad prognostic. Low level of erythropoietin is considered as one of the causes of anemia in these pathologies. The deficiency in erythropoietin production results from pro-inflammatory cytokines effect. However, few data is available concerning molecular mechanisms involved in cytokine-mediated anemia. Some recent publications have demonstrated the direct effect of pro-inflammatory cytokines on cell differentiation towards erythroid pathway, without erythropoietin defect. This suggested that pro-inflammatory cytokine-mediated signaling pathways affect erythropoietin activity. They could interfere with erythropoietin-mediated signaling pathways, inducing early apoptosis and perturbing the expression and regulation of specific transcription factors involved in the control of erythroid differentiation. In this review we summarize the effect of tumor necrosis factor (TNF)α, TNF-related apoptosis-inducing ligand (TRAIL), and interferon (IFN)-γ on erythropoiesis with a particular interest for molecular feature.

Erythropoiesis: model systems, molecular regulators, and developmental programs

Human erythropoiesis is a complex multistep developmental process that begins at the level of pluripotent hematopoietic stem cells (HSCs) at bone marrow microenvironment (HSCs niche) and terminates with the production of erythrocytes (RBCs). This review covers the basic and contemporary aspects of erythropoiesis. These include the: (a) cell-lineage restricted pathways of differentiation originated from HSCs and going downward toward the blood cell development; (b) model systems employed to study erythropoiesis in culture (erythroleukemia cell lines and embryonic stem cells) and in vivo (knockout animals: avian, mice, zebrafish, and xenopus); (c) key regulators of erythropoiesis (iron, hypoxia, stress, and growth factors); (d) signaling pathways operating at hematopoietic stem cell niche for homeostatic regulation of self renewal (SCF/c-kit receptor, Wnt, Notch, and Hox) and for erythroid differentiation (HIF and EpoR). Furthermore, this review presents the mechanisms through which transcriptional factors (GATA-1, FOG-1, TAL-1/SCL/MO2/Ldb1/E2A, EKLF, Gfi-1b, and BCL11A) and miRNAs regulate gene pattern expression during erythroid differentiation. New insights regarding the transcriptional regulation of alpha- and beta-globin gene clusters were also presented. Emphasis was also given on (i) the developmental program of erythropoiesis, which consists of commitment to terminal erythroid maturation and hemoglobin production, (two closely coordinated events of erythropoieis) and (ii) the capacity of human embryonic and umbilical cord blood (UCB) stem cells to differentiate and produce RBCs in culture with highly selective media. These most recent developments will eventually permit customized red blood cell production needed for transfusion.

MAPK signaling pathways in the regulation of hematopoiesis

The MAPKs are a family of serine/threonine kinases that play an essential role in connecting cell-surface receptors to changes in transcriptional programs. MAPKs are part of a three-component kinase module consisting of a MAPK, an upstream MEK, and a MEKK that couples the signals from cell-surface receptors to trigger downstream pathways. Three major groups of MAPKs have been characterized in mammals, including ERKs, JNKs, and p38MAPKs. Over the last decade, extensive work has established that these proteins play critical roles in the regulation of a wide variety of cellular processes including cell growth, migration, proliferation, differentiation, and survival. It has been demonstrated that ERK, JNK, and p38MAPK activity can be regulated in response to a plethora of hematopoietic cytokines and growth factors that play critical roles in hematopoiesis. In this review, we summarize the current understanding of MAPK function in the regulation of hematopoiesis in general and myelopoiesis in particular. In addition, the consequences of aberrant MAPK activation in the pathogenesis of various myeloid malignancies will be discussed.