Granulocyte colony-stimulating factor inhibits spontaneous cytochrome c release and mitochondria-dependent apoptosis of myelodysplastic syndrome hematopoietic progenitors

Abstract

Low-risk myelodysplastic syndromes (MDS), including refractory anemia and sideroblastic anemia, are characterized by increased apoptotic death of erythroid progenitors. The signaling pathways that elicit this pathologic cell death in MDS have, however, remained unclear. Treatment with erythropoietin in combination with granulocyte colony-stimulating factor (G-CSF) may synergistically improve the anemia in patients with MDS, with a concomitant decrease in the number of apoptotic bone marrow precursors. Moreover, we have previously reported that G-CSF inhibits Fas-induced caspase activation in sideroblastic anemia (RARS). The present data demonstrate that almost 50% of erythroid progenitor cells derived from patients with MDS exhibit spontaneous release of cytochrome c from mitochondria with ensuing activation of caspase-9, whereas normal erythroid progenitors display neither of these features. G-CSF significantly inhibited cytochrome c release and suppressed apoptosis, most noticeably in cells from patients with sideroblastic anemia. Furthermore, inhibition of caspase-9 suppressed both spontaneous and Fas-mediated apoptosis of erythroid progenitors in all low-risk MDS cases studied. We propose that the increased sensitivity of MDS progenitor cells to death receptor stimulation is due to a constitutive activation of the mitochondrial axis of the apoptotic signaling pathway in these cells. These studies yield a mechanistic explanation for the beneficial clinical effects of growth factor administration in patients with MDS, and provide a model for the study of growth factor-mediated suppression of apoptosis in other bone marrow disorders. IntroductionThe myelodysplastic syndromes (MDS) constitute a heterogeneous group of clonal stem cell disorders characterized by ineffective hematopoiesis, various degrees of pancytopenia, and a risk of progression to acute myeloid leukemia. 1 Low-risk myelodysplastic syndromes, including refractory anemia (RA) and RA with ringed sideroblasts (RARS), are defined as MDS with a low probability of progression to leukemia and with a relatively favorable outcome. 2 Anemia and transfusion dependency are the main clinical problems for these patients.Increased apoptosis of bone marrow precursors is a hallmark of MDS, [3][4][5] and is thought to underlie the ineffective hematopoiesis evidenced in individuals with MDS. Indeed, apoptosis mediated via the death receptor, Fas, and its ligand has been suggested to serve as an important pathogenic mechanism in MDS. [6][7][8][9] However, a clear-cut correlation between the level of expression of these apoptosis regulators and the degree of bone marrow apoptosis, or cytopenia, has not been demonstrated. In addition to extrinsic, death receptor-mediated induction of apoptosis, intrinsic signaling pathways that depend on mitochondrial events, including the release of apoptogenic factors such as cytochrome c, also exist. 10,11 Interestingly, signs of mitochondrial pathology are commonly seen in MDS, including the characteristic accumulation of iron in...

Mitochondria in hematopoiesis and hematological diseases

“…Similarly, caspase-3 is clearly much more activated in myelodysplastic precursors as compared to their normal counterparts (Bouscary et al, 2000;Claessens et al, 2002;Matthes et al, 2002). Cytochrome c-mediated activation of caspase-9 and downstream caspase-3 was further suggested by the protective effects of cell permeant peptide inhibitors (Tehranchi et al, 2003).…”

“…At early stages of acquired myelodysplastic syndromes, exacerbation of the physiological pathway to caspase activation in erythroid cells, even in the presence of elevated Epo concentrations, is responsible for a high rate of apoptosis, ineffective erythropoiesis and increased phagocytosis (Raza et al, 1995;Bouscary et al, 1997;Hellstrom-Lindberg et al, 2001;Shetty et al, 2002;Tehranchi et al, 2003;Testa, 2004). Several observations argue for a role of the Fas-L/Fas pathway in this pathogenic event.…”

“…This decrease is associated with the mitochondrial release of cytochrome c to the cytosol (Tehranchi et al, 2003). The consequences of cytochrome c release are caspase-9 overactivation as compared to normal erythroid cells undergoing differentiation (Zermati et al, 2001).…”

Early mitochondrial alterations in ATRA-induced cell death

“…[19][20][21] We have earlier shown that G-CSF decreases cytochrome c release from mitochondria to cytosol, thereby reducing caspase activation and premature death of cultured MDS erythroblasts. 22,23 However, the precise mode of the antiapoptotic action of G-CSF is still unclear.…”

Revisiting Use of Growth Factors in Myelodysplastic Syndromes

“…It also promotes erythroid colony growth and differentiation of stem cells from RARS patients (Schmidt-Mende et al, 2001;Molineau 2011).There is evidence that G-CSF changes the survival abilities of the mobilized CD34+ cells and it was found that peripheral blood stem cell mobilization with G-CSF results in a significant reduction in the number of apoptotic CD34+ cells in comparison with a more apoptotic CD34+ cells collected form an unstimulated mobilization (Philpott et al, 1997). Additionally it has been shown by in vitro experiments that G-CSF blocks spontaneous cytochrome c release and mitochondria-dependent apoptosis in hematopoietic progenitor cells of RARS patients and improves erythropoiesis in MDS (Tehranchi et al, 2003;Sung 2007;Molineau 2011).…”