Sequential activation of caspase-1 and caspase-3-like proteases during apoptosis in myelodysplastic syndromes

TNFα induces Caspase-3 activity in hematopoietic progenitor cells CD34+, CD33+, and CD41 + of myelodysplastic syndromes

BACKGROUND

Cytopenia is the primary feature of Myelodysplastic Syndrome, even in the presence of hypercellular bone marrow. TNFα is recognized as both a proinflammatory, and proapoptotic cytokine with a well established role in promoting apoptosis in MDS. Therefore, TNFα has the potential to be a valuable biomarker for predicting the progression of cytopenia in MDS. This study aims to establish the role of TNFα exposure in triggering apoptosis through caspase-3 activity in CD34+, CD33+, and CD41 + cells in MDS.

METHODS

This study is an in vitro comparative experimental research. Bone marrow mononuclear cells were isolated as the source of hematopoietic progenitor cells. Subsequently, CD34+, CD33+, and CD41 + cells were exposed to rhTNFα, and the caspase-3 activity was measured using flowcytometry.

RESULTS

In MDS CD33 + and CD41 + caspase-3 activity of rhTNFα exposed cells was significantly higher than without exposed cells. The opposite result was found in CD34 + cells, where the caspase-3 activity without rhTNFα exposed cells was significantly higher than rhTNFα exposed cells.

CONCLUSION

rhTNFα exposure led to an elevation in caspase-3 activity in MDS progenitor cells, especially in those that had differentiated into myeloid cell CD33 + and megakaryocyte cell CD41+, as opposed to the early progenitor cells CD34+.

The NLRP3 inflammasome functions as a driver of the myelodysplastic syndrome phenotype

Despite genetic heterogeneity, myelodysplastic syndromes (MDSs) share features of cytological dysplasia and ineffective hematopoiesis. We report that a hallmark of MDSs is activation of the NLRP3 inflammasome, which drives clonal expansion and pyroptotic cell death. Independent of genotype, MDS hematopoietic stem and progenitor cells (HSPCs) overexpress inflammasome proteins and manifest activated NLRP3 complexes that direct activation of caspase-1, generation of interleukin-1β (IL-1β) and IL-18, and pyroptotic cell death. Mechanistically, pyroptosis is triggered by the alarmin S100A9 that is found in excess in MDS HSPCs and bone marrow plasma. Further, like somatic gene mutations, S100A9-induced signaling activates NADPH oxidase (NOX), increasing levels of reactive oxygen species (ROS) that initiate cation influx, cell swelling, and β-catenin activation. Notably, knockdown of NLRP3 or caspase-1, neutralization of S100A9, and pharmacologic inhibition of NLRP3 or NOX suppress pyroptosis, ROS generation, and nuclear β-catenin in MDSs and are sufficient to restore effective hematopoiesis. Thus, alarmins and founder gene mutations in MDSs license a common redox-sensitive inflammasome circuit, which suggests new avenues for therapeutic intervention.

The genetic basis of phenotypic heterogeneity in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are malignant clonal disorders of haematopoietic stem cells and their microenvironment, affecting older individuals (median age ∼70 years). Unique features that are associated with MDS - but which are not necessarily present in every patient with MDS - include excessive apoptosis in maturing clonal cells, a pro-inflammatory bone marrow microenvironment, specific chromosomal abnormalities, abnormal ribosomal protein biogenesis, the presence of uniparental disomy, and mutations affecting genes involved in proliferation, methylation and epigenetic modifications. Although emerging insights establish an association between molecular abnormalities and the phenotypic heterogeneity of MDS, their origin and progression remain enigmatic.

Emerging immunosuppressive drugs in myelodysplastic syndromes

INTRODUCTION

Myelodysplastic syndromes (MDS) are characterized by dysplastic morphologic features and ineffective hematopoiesis. Pathophysiological characteristics change over time making therapeutic development a major challenge. In early MDS, cytopenias arise or are exacerbated by humoral and cellular immune-mediators that suppress hematopoietic progenitor survival and alter the bone marrow microenvironment.

AREAS COVERED

In this review, current immunosuppressive regimens are described. To identify new therapies that may enhance immunosuppressive therapy (IST) response and identify pharmacodynamic biomarkers for patient selection, the inflammasome, cytokines, metabolic pathways and signaling events are described.

EXPERT OPINION

Agents with the potential to induce early, durable hematologic remissions are needed and many new immunosuppressive agents are available for investigation. An immune-mediated mechanism is likely to contribute to MDS early after diagnosis. New approaches that interfere with inflammatory pathways in the bone marrow microenvironment may move closer toward sustained disease control in MDS.

Infliximab chimeric antitumor necrosis factor-α monoclonal antibody as potential treatment for myelodysplastic syndromes

Accumulating evidence indicates tumor necrosis factor-a (TNF-a) as a key cytokine in the pathogenesis of the myelodysplastic syndromes (MDS). The identification of TNF-a as a regulator of apoptosis and the increased susceptibility of MDS cells to this cytokine provided the basis for several clinical trials of TNF inhibitors. Infliximab is an IgG1 chimeric anti-TNF-a monoclonal antibody composed of human constant and murine variable regions that bind specifically to both soluble and membrane-bound TNF-a. To date, only 2 studies have investigated the use of infliximab in patients with low-risk MDS. In both reports the drug showed a limited but significant activity and a favorable side-effect profile. In some patients, hematopoietic response was associated with decreased apoptosis as well as a decrease in abnormal metaphases by 50%. Further studies are currently underway and should provide useful information to define the more responsive subtypes of MDS, the patient characteristics, and the proper dosing regimen.

Myelodysplastic syndromes and acute myeloid leukemia in cats infected with feline leukemia virus clone33 containing a unique long terminal repeat

Feline leukemia virus (FeLV) clone33 was obtained from a domestic cat with acute myeloid leukemia (AML). The long terminal repeat (LTR) of this virus, like the LTRs present in FeLV from other cats with AML, differs from the LTRs of other known FeLV in that it has 3 tandem direct 47-bp repeats in the upstream region of the enhancer (URE). Here, we injected cats with FeLV clone33 and found 41% developed myelodysplastic syndromes (MDS) characterized by peripheral blood cytopenias and dysplastic changes in the bone marrow. Some of the cats with MDS eventually developed AML. The bone marrow of the majority of cats with FeLV clone33 induced MDS produced fewer erythroid and myeloid colonies upon being cultured with erythropoietin or granulocyte-macrophage colony-stimulating factor (GM-SCF) than bone marrow from normal control cats. Furthermore, the bone marrow of some of the cats expressed high-levels of the apoptosis-related genes TNF-alpha and survivin. Analysis of the proviral sequences obtained from 13 cats with naturally occurring MDS reveal they also bear the characteristic URE repeats seen in the LTR of FeLV clone33 and other proviruses from cats with AML. Deletions and mutations within the enhancer elements are frequently observed in naturally occurring MDS as well as AML. These results suggest that FeLV variants that bear URE repeats in their LTR strongly associate with the induction of both MDS and AML in cats.

Non-canonical effects of anthrax toxins on haematopoiesis: implications for vaccine development

Anthrax receptor (ATR) shares similarities with molecules relevant to haematopoiesis. This suggests that anthrax proteins might bind to these mimicking molecules and exert non-specific haematopoietic effects. The haematopoietic system is the site of immune cell development in the adult. As such, ATR ligand, protective antigen (PA) and the other anthrax proteins, lethal factor, edema factor, could be significant to haematopoietic responses against Bacillus anthracis infection. Because haematopoiesis is the process of immune cell development, effects by anthrax proteins could be relevant to vaccine development. Here, we report on effects of anthrax proteins and toxins on early and late haematopoiesis. Flow cytometry shows binding of PA to haematopoietic cells. This binding might be partly specific because flow cytometry and Western blots demonstrate the presence of ATR1 on haematopoietic cell subsets and the supporting stromal cells. Functional studies with long-term initiating cell and clonogenic assays determined haematopoietic suppression by anthrax toxins and stimulation by monomeric proteins. The suppressive effects were not attributed to cell death, but partly through the induction of haematopoietic suppressors, interleukin (IL)-10 and CCL3 (MIP-1alpha). In summary, anthrax proteins affect immune cell development by effects on haematopoiesis. The type of effect, stimulation or suppression, depend on whether the stimulator is a toxin or monomeric protein. The studies show effects of anthrax proteins beginning at the early stage of haematopoiesis, and also show secondary mediators such as IL-10 and CCL3. The roles of other cytokines and additional ATR are yet to be investigated.

Analysis of apoptosis regulatory genes expression in the bone marrow (BM) of adult de novo Myelodysplastic Syndromes (MDS)

The aim of the present study was to examine caspases, granzyme B and bcl-2 family mRNA expression and the degree of apoptosis in the bone marrow (BM) of 46 Myelodysplastic Syndromes (MDS) and to correlate our findings with clinical parameters. The degree of apoptosis was determined by Annexin V, whereas expression of genes was determined using a multiprobe RNase Protection System. A positive correlation was found between caspases 8, 5, 3, 2, 1 and the level of apoptosis. bfl1 and mcl1 levels were significantly higher in patients with BM blasts >5%. Cases with ratio of bid expression >1 compared to normal pool were associated with IPSS values < or =1.

Interleukin-1beta and caspase-1: players in the regulation of age-related cognitive dysfunction

Scientific research on the unprecedented and growing number of older adults in the United States and other industrialized countries has focused much attention on the health consequences of aging. Over the last few decades, inflammation in the brain and its implication in the progression of aging and age-related cognitive dysfunction has been an area of increasing importance to neuroscientists and is now considered as one of the most interesting and promising topics for aging research. One of the critical aspects of inflammatory processes is that the activation of one upstream inflammatory molecule initiates a cascade of self-sustaining inflammatory events which leads to the activation of a number of different downstream functions. Recently, a great deal of attention has been given to the interplay between inflammatory and apoptotic processes and the regulation of these processes by the caspases. The caspase family of proteases can be divided into proapoptotic and pro-inflammatory members. The present review summarizes recent observations of the interactions between the inflammatory cytokine interleuldn-1 (IL-1) beta and the inflammatory/apoptotic caspase-1 and their involvement in age-related impairments in cognition. A comprehensive understanding of these mechanisms could potentially lead to the development of preventive or protective therapies that reduce or inhibit the cognitive decline associated with aging and age-related neurodegenerative disease.

Impact of growth factors in the regulation of apoptosis in low-risk myelodysplastic syndromes

Increased apoptosis of hematopoietic progenitors is a hallmark of myelodysplastic syndromes (MDS) and results in ineffective hematopoiesis. Erythroid apoptosis is thought to be the main mechanism underlying the severe anemia observed in the low-risk subgroups, refractory anemia (RA) and RA with ringed sideroblasts (RARS). Treatment with erythropoietin (Epo) alone or in combination with granulocyte colony-stimulating factor (G-CSF) may significantly improve anemia and reduce bone marrow apoptosis. A synergistic effect between Epo and G-CSF has been observed in the clinic, in particular in RARS. However, the molecular mechanisms beyond the anti-apoptotic effect of these growth factors have not been fully understood. This paper outlines the potential mechanisms underlying the augmented apoptosis during the erythroid differentiation in low-risk MDS as well as the anti-apoptotic effect of the growth factors.

Potential new strategies to prevent the development of diabetic retinopathy

Recent studies have demonstrated that diabetic retinopathy has several characteristics of a chronic inflammatory disease, such as increased nitric oxide production, intracellular adhesion molecule-1 upregulation, leukostasis and increased vascular permeability. In addition, diabetes leads to the activation of caspase-1, the enzyme responsible for the production of the pro-inflammatory cytokines IL-1beta and IL-18 in the retinae of diabetic animals and diabetic patients. Minocycline, a second-generation tetracycline derivative, was able to prevent the activation of capase-1 in the retinae of diabetic mice. Therefore, this review is focused on discussing the role of caspase-1 as a mediator of chronic inflammation and/or apoptosis inducer in the development of diabetic retinopathy and the suitability of caspase-1 as a new potential therapeutic target.

Targeted therapies in myeloid leukemia

Targeted therapies for hematological malignancies have come of age since the advent of all trans retinoic acid (ATRA) for treating APL and STI571/Imatinib Mesylate/Gleevec for CML. There are good molecular targets for other malignancies and several new drugs are in clinical trials. In this review, we will concentrate on individual abnormalities that exist in the myelodysplastic syndromes (MDS) and myeloid leukemias that are targets for small molecule therapies (summarised in Fig. 1). We will cover fusion proteins that are produced as a result of translocations, including BCR-ABL, the FLT3 tyrosine kinase receptor and RAS. Progression of diseases such as MDS to secondary AML occur as a result of changes in the balance between cell proliferation and apoptosis and we will review targets in both these areas, including reversal of epigenetic silencing of genes such as p15(INK4B).

Expression of FLIP(Long) and FLIP(Short) in bone marrow mononuclear and CD34+ cells in patients with myelodysplastic syndrome: correlation with apoptosis

Several apoptosis-inducing systems, including Fas/Fas ligand and TNF-related apoptosis-inducing ligand (TRAIL) and its receptors, are upregulated in myelodysplastic syndrome (MDS). FLIP (FLICE (FAS-associated death-domain-like IL-1beta-converting enzyme)-inhibitory protein)) was identified as an inhibitor of FAS and TRAIL signals. Here, we characterized FLIP(Long) (FLIP(L)) and FLIP(Short) (FLIP(S)) expression in bone marrow mononuclear cells (BMMNCs) and in CD34+ cells of 29 MDS patients, and in 17 normal volunteers. The expression was correlated with apoptotic indices. In CD34+ cells, FLIP(L) levels were higher among normal individuals than in MDS patients (P=0.04). Among total BMMNC, FLIP(L) levels also tended to be higher in normal subjects than in MDS patients, although this difference was not significant (P=0.71). FLIP(L) levels in CD34+ cells were negatively correlated with apoptosis in both normal and MDS marrows (P=0.03). FLIP(Short) RNA expression was higher in MDS patients than in normal controls in both BMMNC (P=0.03) and CD34+ cells (P=0.08). In contrast to FLIP(L), FLIP(St) levels were positively correlated with apoptosis. At the protein level FLIP was most readily detectable in patients with high blast counts. The data suggest that FLIP(L) and FLIP(S) are differentially regulated, and that the relative levels of both isoforms play a role in the regulation of apoptosis in MDS.

The myelodysplastic syndromes: a matter of life or death

Apoptosis is upregulated in early myelodysplastic syndromes (MDS) and may contribute to the peripheral cytopenias commonly observed. Conversely, leukemic progression is associated with abrogation of programmed cell death (PCD). The stage of hematopoietic cell maturation at which defects in PCD arise and the underlying causes of apoptosis dysregulation remain unknown. This paper outlines the apoptotic process in normal hematopoietic cells and summarizes current data regarding the role, potential causes and clinical implications of altered apoptosis in MDS.

Lingering biologic dilemmas about the status of the progenitor cells in myelodysplasia

Myelodysplastic syndromes (MDS) are considered to be stem cell disorders. High incidence of intramedullary apoptosis has been associated with the peripheral cytopenia and refractory anemia in these disorders. The investigations on the cell of origin in the bone marrow have invariably been hampered by a poor yield of CD34+ cells from these marrows. Interestingly, even though limited in number, these studies raised more questions and dilemmas than providing answers. While the enigma surrounding the clonality of these marrows continues, the controversies regarding incidence of apoptosis, proliferation, and potential of clonogenic expansion may be closer to a settlement. The present review proposes a model depicting interplay between extraneous apoptogenic factors and intracellular apoptosis-susceptibility determinants that contributes significantly toward the progression of MDS and how a shift in dynamics of this interplay may provide grounds to accumulate additional mutations with a probable block in differentiation eventually leading to a leukemic transformation.

Expression and prognostic significance of Bcl-2 family proteins in myelodysplastic syndromes

Excessive apoptosis is implicated in the pathogenesis of myelodysplastic syndromes (MDS). We assessed by flow cytometry the expression of several members of the Bcl-2 family in bone marrow mononuclear cells (BMMNC) of 168 MDS samples at diagnosis. The proteins studied were Bcl-2, Bcl-xL (anti-apoptotic), Bax, Bad, Bak, and Bcl-xS (pro-apoptotic). The percentage of BMMNC expressing Bcl-2 and Bcl-xL was higher in refractory anemia with excess of blasts (RAEB), RAEB in transformation (RAEB-T), and chronic myelomonocytic leukemia (CMML) than in refractory anemia (RA) and RA with ringed sideroblasts (RAS). Conversely pro-apoptotic proteins Bad, Bak, and Bcl-xS were detected in a higher percentage of cells in RA and RAS. RA and RAS were associated with an increased Bcl-xS/Bcl-xL ratio. The expression of anti-apoptotic proteins was also correlated with that of CD34 and P170 and with the percentage of blast cells. Two-color analyses demonstrated that CD34 and Bcl-2 were usually expressed in the same cells. No significant correlation was found with cytogenetic abnormalities. Higher expression of pro-apoptotic Bcl-2-family proteins (Bak, Bad, Bcl-xS) and higher Bcl-xS/Bcl-xL ratio were associated with longer survival and decreased risk of leukemic transformation in univariate analysis, whereas expression of anti-apoptotic proteins was associated with decreased survival. Consequently Bcl-2 proteins expression was well correlated with the International Prognostic Scoring System (IPSS). Our data confirm that the control of apoptosis is deregulated in MDS cells. Moreover, the study of markers such as CD34 (or Bcl-2), Bcl-xL, and Bcl-xS provides additional prognostic information.

Molecular, cytogenetic and genetic abnormalities in MDS and secondary AML

Myelodysplasia (MDS) is a clonal disease, which increases with age, suggesting that multiple steps are required for the evolution of the condition. Approximately 30% of MDS evolve into acute myelogenous leukemia (AML). In this review, we intend to delineate the genetic events, which may drive this sequence and therefore we will focus primarily on cytogenetic abnormalities where the genes have been identified and oncogenes and suppressor genes that have been implicated. In terms of the biological mechanisms, which characterise this process, it is generally thought that the MDS cell has impaired differentiation, and has increased apoptosis. As the disease progresses in addition, the cells have increased proliferation. As the disease evolves, the population of cells, which predominate remain immature, have decreased apoptosis and in many cases, upregulate anti-apoptotic genes and have deregulated proliferation as the number of blast cells increase. Etiological factors, which contribute to the development of leukemia, include therapeutic agents administered for a primary malignancy. The cytogenetic abnormalities, predisposition factors and genes involved in secondary leukemia will also be reviewed.

Caspase activation in retinas of diabetic and galactosemic mice and diabetic patients

Apoptosis of retinal capillary cells begins early in diabetes and likely contributes to the capillary obliteration that is an important feature of diabetic retinopathy. Caspases are proteolytic enzymes that are closely involved in the induction and execution phases of apoptosis, but their role in the development of diabetic retinopathy has not been studied previously. Our study focused on the measurement of activities of multiple caspases in retinas of mice at different durations of diabetes. Several caspases (including caspases-1, -2, -6, -8, and -9) were activated as early as 2 months of diabetes. The caspases activity pattern changed with increasing duration of disease, suggesting a slowly developing caspases cascade. Activities of executioner caspases (e.g., cas-6 and -3) became elevated after longer duration of diabetes, and the induction of cas-3 activity was associated with the duration of diabetes at which capillary cells begin to show evidence of undergoing apoptosis. Retinas from patients with type 2 diabetes likewise showed a significant increase in activities of cas-1, -3, -4, and -6. For comparison, retinal caspases were also measured in experimental galactosemia, another model that develops a diabetic-like retinopathy. The pattern of caspases activation differed between diabetes and galactosemia, but cas-1 activity became elevated soon after elevation of blood hexose concentration in both. Caspases offer new therapeutic targets to test the role of apoptosis in the development of diabetic retinopathy.

The end is just the beginning: megakaryocyte apoptosis and platelet release

Under influence of hematopoietic growth factors, particularly thrombopoietin (TPO), hematopoietic stem cells in the bone marrow go through a process of commitment, proliferation, differentiation, and maturation and become mature megakaryocytes. At this critical point, terminally differentiated megakaryocytes face a new fate: ending the old life as mature megakaryocytes by induction of apoptosis and beginning a new life as platelets by fragmentation of the large megakaryocyte cytoplasm. These events are as important as megakaryocyte commitment, proliferation, differentiation, and maturation, but the molecular mechanisms regulating these events are not well established. Although TPO drives megakaryocyte proliferation and differentiation and protects hematopoietic progenitor cells from death, it does not appear to promote platelet release from terminally differentiated megakaryocytes. Although mature megakaryocyte apoptosis is temporally associated with platelet formation, premature megakaryocyte death directly causes thrombocytopenia in cancer therapy and in diseases such as mvelodysplastic syndromes and human immunodeficiency virus infection. Also, genetic studies have shown that accumulation of megakaryocytes in bone marrow is not necessarily sufficient to produce platelets. All of these findings suggest that platelet release from megakaryocytes is an important and regulated aspect of platelet production, in which megakaryocyte apoptosis may also play a role. This review summarizes recent research progress on megakaryocyte apoptosis and platelet release.

Treatment of myelodysplastic syndrome with agents interfering with inhibitory cytokines

Results of these trials provide evidence for biological activity and some clinical efficacy of agents potentially blocking inhibitory cytokines in patients with MDS. However, given the limited responses, it appears that factors additional to TNFalpha inhibitory activity contribute to the development of cytopenias in these patients. Further studies are warranted using anti-TNFalpha/anti-inhibitory cytokine approaches, either alone or in combination with other agents, capable of abrogating the effects of additional inhibitory mechanisms in MDS.

Granulocyte colony-stimulating factor inhibits Fas-triggered apoptosis in bone marrow cells isolated from patients with refractory anemia with ringed sideroblasts

Treatment with granulocyte colony-stimulating factor (G-CSF) plus erythropoietin may synergistically improve hemoglobin levels and reduce bone marrow apoptosis in patients with refractory anemia with ringed sideroblasts (RARS). Fas-induced caspase activity is increased in RARS bone marrow cells. We showed that G-CSF significantly reduced Fas-mediated caspase-8 and caspase-3-like activity and the degree of nuclear apoptotic changes in bone marrow from nine RARS patients. A decrease in mitochondrial membrane potential and an increase in intracellular reactive oxygen species occurred in Fas-treated cells, but became significant only 24 h after changes in caspase activity and decrease in proliferation. G-CSF also reduced the magnitude of these late apoptotic changes. In CD34-selected normal cells, G-CSF induced myeloid colony growth, and an overall small decrease in the number of erythroid colonies. By contrast, G-CSF induced a 33-263% increase of erythroid colony formation in CD34+ cells from four of five RARS patients with severely reduced erythroid growth, while the normal or slightly reduced erythroid growth of three other patients was not influenced by G-CSF. This study suggests that G-CSF may reduce the pathologically increased caspase activity and concomitant apoptotic changes, and promote erythroid growth and differentiation of stem cells from RARS patients. Our data support the clinical benefit of G-CSF in this subgroup of myelodysplastic syndromes.

The role of apoptosis in the pathogenesis of the myelodysplastic syndromes

The paradoxical occurrence of peripheral cytopenias despite a normo/hypercellular marrow in myelodysplastic syndromes (MDS) has been attributed to excessive intramedullary hematopoietic cell apoptosis. It has also been postulated that abrogation of programmed cell death (PCD) may underlie MDS transformation to acute myeloid leukemia (AML). Despite overwhelming evidence for a role of aberrant apoptosis in myelodysplasia, the molecular mechanisms responsible for such changes have not been elucidated. This paper summarizes current evidence implicating a role for altered PCD in MDS and outlines potential cellular mechanisms whereby hematopoietic progenitor cell apoptosis may be dysregulated.

Functional role of caspase-1 and caspase-3 in an ALS transgenic mouse model

Mutations in the copper/zinc superoxide dismutase (SOD1) gene produce an animal model of familial amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder. To test a new therapeutic strategy for ALS, we examined the effect of caspase inhibition in transgenic mice expressing mutant human SOD1 with a substitution of glycine to alanine in position 93 (mSOD1(G93A)). Intracerebroventricular administration of zVAD-fmk, a broad caspase inhibitor, delays disease onset and mortality. Moreover, zVAD-fmk inhibits caspase-1 activity as well as caspase-1 and caspase-3 mRNA up-regulation, providing evidence for a non-cell-autonomous pathway regulating caspase expression. Caspases play an instrumental role in neurodegeneration in transgenic mSOD1(G93A) mice, which suggests that caspase inhibition may have a protective role in ALS.