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.

Decreased affinity of recombinant human tumor necrosis factor-related apoptosis-inducing ligand (rhTRAIL) D269H/E195R to osteoprotegerin (OPG) overcomes TRAIL resistance mediated by the bone microenvironment.

The bone marrow microenvironment provides important signals for the survival and proliferation of hematopoietic and malignant cells. In multiple myeloma, plasma cells are surrounded by stromal cells including osteoblasts. These stromal cells protect multiple myeloma cells from apoptosis induced by chemotherapeutic agents. Osteoprotegerin (OPG), a soluble receptor of the cytokine TNF-related apoptosis-inducing ligand (TRAIL), is secreted by osteoblasts and has been implicated in the prevention of cell death induced by TRAIL in malignant cells. Previously, we have designed death receptor-specific TRAIL variants that induce apoptosis exclusively via one of its death receptors. Here, we have studied in detail the interaction between recombinant human (rhTRAIL) variants and OPG. We show that a DR5-specific variant (rhTRAIL D269H/E195R) displays a significantly decreased affinity to OPG. Furthermore, this rhTRAIL variant shows a much higher activity when compared with rhTRAIL WT and retains its effectiveness in inducing cell death in multiple myeloma cell lines, in the presence of OPG secreted by stromal cells. We also demonstrate that stromal cells are largely insensitive to high concentrations of this rhTRAIL variant. In conclusion, rhTRAIL D269H/E195R is a potential therapy for multiple myeloma due to its high effectiveness and diminished binding to OPG.

Bone marrow dysfunction in chronic heart failure patients.

AIMS: To investigate whether chronic heart failure (CHF) is associated with a general dysfunction of the haematopoietic compartment. METHODS AND RESULTS: Bone marrow was obtained during coronary artery bypass graft surgery from 20 patients with CHF (age 67 +/- 6 years, 75% NYHA class >or= III, LVEF 32 +/- 6%), and 20 age- and gender-matched control patients with normal cardiac function. CD34(+) haematopoietic progenitor cells were isolated and cultured with increasing doses of erythropoietin (0.02-10 IU/mL, EPO), myeloid growth factors or a mix of both. After 14 days, burst forming units erythroid (BFU-E), and granulocyte or monocyte colony forming units (CFU-G, CFU-M, respectively) were counted. Apoptosis and erythropoietin-receptor (EPO-R) density were quantified by flow cytometry. Throughout the EPO dose range, the CD34(+) cells from CHF patients produced a two-fold lower number of BFU-E colonies compared with controls (P = 0.02). The resistance to EPO was associated with markedly increased apoptosis during erythroid differentiation in CHF patients compared with controls [5.3% (2.9-8.1%) vs. 1.5% (0.8-3.4%), P = 0.01]. Erythropoietin-receptor expression was, however, comparable between CHF patients and controls and the anti-apoptotic cytokine interleukin-3 did not rescue erythropoiesis. In the myeloid cultures, the number of CFU-G and CFU-M colonies was also two-fold lower in CHF patients compared with controls (both P < 0.01). In the mixed-culture assay, myelopoiesis and erythropoiesis were reduced to a similar magnitude in CHF patients. The impaired clonogenic potential was independently associated with clinical and biochemical severity of CHF, but not with the presence of anaemia. CONCLUSION: Chronic heart failure is associated with profound and general bone marrow dysfunction, simultaneously affecting multiple haematopoietic lineages.

Role of the polycomb group gene BMI1 in normal and leukemic hematopoietic stem and progenitor cells.

PURPOSE OF REVIEW: The polycomb group gene BMI1 fulfills essential roles in both normal and leukemic stem cells. The underlying molecular mechanisms are beginning to become unraveled and an overview of the current knowledge on BMI1 signaling in normal and leukemic stem cells will be presented here. RECENT FINDINGS: In addition to a role in bypassing senescence and the orchestration of the symmetry of hematopoietic stem cell divisions, it has recently become clear that BMI1 also functions in the protection against oxidative stress. In the absence of BMI1, reactive oxygen species accumulate, associating with activation of DNA damage response pathways and increased apoptosis. BMI1-mediated control over reactive oxygen species levels might occur independently of the INK4a/ARF pathway, but rather involves impaired mitochondrial functions. In human hematopoietic malignancies, BMI1 is frequently overexpressed, which associates with poor prognosis. Down modulation of BMI1 impairs self-renewal and long-term expansion of leukemic stem cells. SUMMARY: Understanding molecular mechanisms by which BMI1 affects stem cell fate will increase our insights into the biology of hematopoietic stem cells and will also aid in understanding the process of leukemic transformation and ultimately in the identification of drugable targets that might facilitate the eradication of leukemic stem cells.