Rescue of early-stage myelodysplastic syndrome-deriving erythroid precursors by the ectopic expression of a dominant-negative form of FADD

Abstract

Myelodysplastic syndromes (MDSs) are characterized by peripheral blood cytopenia including anemia. We have investigated the implication of the extrinsic pathway of apoptosis in MDS-ineffective erythropoiesis by in vitro expansion of erythroid precursors from early stage (low and intermediate-1 International Prognosis Scoring System [IPSS]) MDS, advanced stage (intermediate-2 IPSS) MDS, and control bone marrow samples. We have previously shown that Fas and its ligand were overexpressed in early stage MDS erythroid cells. Here, we show that caspase-8 activity is significantly increased, whereas the expression of death receptors other than Fas, including the type 1 receptor for tumor necrosis factor alpha (TNF-alpha) and the receptors for the TNF-related apoptosis-inducing ligand (TRAIL), DR4 and DR5, was normal. We also observed that the adapter Fas-associated death domain (FADD) was overexpressed in early stage MDS erythroid cells. Transduction of early stage MDS-derived CD34+ progenitors with a FADD-encoding construct increased apoptosis of erythroid cells and dramatically reduced erythroid burst-forming unit (BFU-E) growth. Transduction of a dominant-negative (dn) mutant of FADD inhibited caspase-8 activity and cell death and rescued BFU-E growth without abrogating erythroid differentiation. These results extend the observation that Fas-dependent activation of caspase-8 accounts for apoptosis of early stage MDS erythroid cells and demonstrate for the first time that FADD is a valuable target to correct ineffective erythropoiesis in these syndromes.