Increased peripheral platelet destruction and caspase-3–independent programmed cell death of bone marrow megakaryocytes in myelodysplastic patients

Abstract

To investigate underlying mechanisms of thrombocytopenia in myelodysplastic syndrome (MDS), radiolabeled platelet studies were performed in 30 MDS patients with platelet counts less than 100 ؋ 10 9 /L. Furthermore, plasma thrombopoietin and glycocalicin index (a parameter of platelet or megakaryocyte destruction) were determined. Mean platelet life (MPL), corrected for the degree of thrombocytopenia, was reduced in 15 of 30 patients (4.3 ؎ 0.9 days [mean ؎ SD] vs 6.0 ؎ 1.3, P ‫؍‬ .0003). Platelet production rate (PPR) was reduced in 25 of 30 patients (68 ؎ 34 ؋ 10 9 /d vs 220 ؎ 65, P < .0001). Thrombopoietin levels were not significantly correlated with the PPR. However, the glycocalicin index was significantly higher compared with controls (15 ؎ 16 vs 0.7 ؎ 0.2, P ‫؍‬ .001) and significantly correlated with the PPR (P ‫؍‬ .02, r ‫؍‬ ؊0.5), but not with the MPL (P ‫؍‬ 1 IntroductionMyelodysplastic syndromes (MDSs) are clonal hematologic disorders characterized by ineffective hematopoiesis resulting in one or more cytopenias in the peripheral blood, despite a normo-or hypercellular bone marrow. Anemia is the most common cytopenia, however thrombocytopenia occurs frequently whereby bleeding complications are often noticed. 1,2 Thrombocytopenia in MDS is caused mainly by ineffective platelet production due to a disturbed proliferation and differentiation process of megakaryocytes or their precursors. The cause of the altered megakaryocytopoiesis in MDS has not been elucidated, but recent studies indicate that an increased apoptosis of early progenitors and inhibitory effects of cytokines might contribute to this process. [3][4][5][6][7] However, thrombocytopenia in MDS might also be related to other causes such as concurrent bone marrow fibrosis 8 and immune-mediated mechanisms. [9][10][11] This notion is supported by findings that immunomodulatory agents, such as danazol, antithymocyte globulin (ATG), and cyclosporin A, are effective in some patients with MDS with thrombocytopenia. [12][13][14][15] Furthermore, a reduced platelet life span, measured with radiolabeled platelets, has been found in about 15% of MDS patients with thrombocytopenia. Some of these patients had a recovery of their platelet count after splenectomy. 16 To discriminate further between an increased destruction of platelets in the peripheral blood and an impaired production by the bone marrow megakaryocytes, plasma levels of glycocalicin (GC) and thrombopoietin (TPO) and ultrastructural study of megakaryocytes may be of relevance.GC is a fragment of the platelet membrane glycoprotein Ib. The glycocalicin index (GCI), the plasma GC level corrected for the platelet count, is considered to be a parameter of peripheral platelet turnover. 17 Recently, it was demonstrated in a subgroup of patients with idiopathic thrombocytopenic purpura (ITP) that a decreased platelet production rate, determined with platelet kinetic studies, was associated with an elevated GCI, reflecting an increased destruction of platelets or megakaryocytes in the bone marro...

Megakaryocytic dysfunction in myelodysplastic syndromes and idiopathic thrombocytopenic purpura is in part due to different forms of cell death

“…Similarly, a recent study 34 using ISEL demonstrated apoptosis in only 4% of megakaryocytes, which were predominantly micromegakaryocytes. These findings are largely consistent with results from our own study, 19 in which MDS megakaryocytes were negative for activated caspase-3 and showed no ultrastructural features of apoptosis. The megakaryocytes demonstrated ultrastructural changes resembling necrosislike cell death, including clumping and random degradation of nuclear chromatin and cytoplasmic vacuoles ( Figure 2c and 35 Apart from inducing apoptosis, stimulation of Fas and other death receptors (i.e.…”

“…Up to 50% of patients have a decreased platelet lifespan, suggesting that increased peripheral platelet destruction mediated by (non-)immune mechanisms might contribute to thrombocytopenia in MDS. 19 Findings that several immunomodulatory agents and splenectomy lead to an increase in platelet counts in some MDS patients may support this notion. 20,21 Decreased platelet production.…”

“…Ultrastructure Nuclear changes Nucleus in periphery of cell Chromatin condensation: Some MKs: crescent-shaped (apoptosis) Majority of MKs: without margination (compatible with para-apoptosis) 19 Nucleus centrally in the MK Non-condensed chromatin, partly lying in spherical speckles/small clumps; no nucleoli; smooth non-lobulated outlines 43 Cytoplasmic changes Vacuoles, swelling of endoplasmic reticulum, mitochondria with disrupted cristae and distended DMS; enlarged peripheral zone (para-apoptosis) 19 Cytoplasmic vacuoles; mitochondrial disruption reduced numbers of granules, disordered DMS 43 DNA fragmentation TUNEL/ISEL Normal in children with acute and chronic ITP (bone marrow aspirates) 48 Conflicting results (see text)…”

Mitochondria in hematopoiesis and hematological diseases

“…On the other hand, the thrombopenia observed in myelodysplastic patients was recently shown to be related to a necrosis-like, caspase-3-independent death of megakaryocytes (Houwerzijl et al, 2005).…”

Erythroid precursors from patients with low-risk myelodysplasia demonstrate ultrastructural features of enhanced autophagy of mitochondria

“…To identify activated caspase-3 in erythroblasts from bone marrow biopsy samples, immunostaining with a rabbit polyclonal antibody (1:100; New England Biolabs, Beverly, MA, USA) was used as previously described. 8 Samples were scored as negative (that is, absence of detectable cytoplasmic staining) or positive. A total of 100 erythroblasts per sample were examined.…”