4. Disturbed neutrophil functioning, autophagy and signal transduction in MDS

The Myelodysplastic syndromes are a group of clonal hematopoietic disorders that are characterised by a disturbed differentiation of the erythroid, megakaryocytic and myeloid lineages. The major cause of death of these patients is a direct result of a high susceptibility to bacterial infections, due to ineffective myelopoiesis. One of the most important defense mechanisms of granulocytes is the production of reactive oxygen species (ROS) which can be stimulated by bacterial peptides such as fMLP. Furthermore, cytokines like granulocyte-macrophage colony stimulating factor (GM-CSF) significantly enhance the fMLP mediated ROS production. However, in MDS neutrophils this ‘priming’ is severely decreased. Of great importance in ROS production is the lipid phosphatidylinositol 3,4,5-trisphosphate (PIP3), which is produced by PI3-kinase, and can be converted into other lipids by phosphatases such as SHIP. We have previously shown a decreased accumulation of PIP3 in MDS neutrophils, implying a disturbed regulation of PIP3 formation. Enhanced SHIP protein expression found in MDS neutrophils indicates a possible role of this phosphatase in the pathology of this disease. In addition , the formation of ‘signalosomes’ at specific sites at the plasma membrane, the so-called lipid rafts, has been shown to be essential for PIP3 formation. Indeed, disruption of these lipid rafts has been shown to inhibit ROS production in healthy granulocytes. Furthermore, SHIP has been show to translocate to lipid rafts.

The goals of our studies are to (1) investigate effect of fMLP stimulation of GM-CSF and unprimed neutrophils on lipid raft formation (2) to assess the effect of GM-CSF and fMLP stimulation on the translocation of SHIP to lipid rafts (3)To compare the activation and translocation of SHIP, and the involvement of lipid rafts in these, between neutrophils from MDS patients and healthy donors, in order to find a possible explanation for the disturbed neutrophil functioning in MDS patients.

Besides the described defects in the myeloid lineage, distinct defects have been observed in the megaryocytic lineage in MDS patients. Electron microscopy revealed programmed cell death (PCD) with characteristic of necrosis-like PCD without signs of apoptosis. This was confirmed by negative staining for caspase 3 on bone marrow biopsies of MDS patients.

for further information on this project please contact: e.vellenga int.azg.nl