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

Myelodysplastic syndromes (MDS) are a group of hematopoietic disorders char acterized by the concomitant presence of peripheral cytopenias and normocel lular to hypercellular BM. This paradox has been proposed to be due to the presence of excessive proliferation matched by excessive intramedullary apo ptosis of hematopoietic cells. When cultured in vitro MDS BM mononuclear ce lls (BMMC) undergo apoptosis within 4 h. We measured caspase-1-like and cas pase-3-like activity in 22 MDS and 4 normal BM immediately following cell s eparation or after 4 h culture. When cultured in vitro, MDS BMMC demonstrat ed an increased apoptotic index within 4 h as measured by in situ end-label ing of fragmented DNA that was matched by a concurrent increase in caspase- 3-like specific activity, and the two were significantly correlated. During the 4 h culture, a sequential activation of caspase-1-like and caspase-3-l ike activities was detected. Caspase-1-like specific activity was detected early and transiently at approximately 15 min, followed by a gradual increa se in caspase-3-like-specific activity peaking at 2 h. When the broad-spect rum caspase inhibitor, Z-VAD.FMK, was included in the MDS BM aspirate 4 h c ulture, apoptosis was attenuated. We conclude that sequential activation of caspase-1-like and caspase-3-like activities may form the central biochemi cal pathway of apoptosis in BMMC from some MDS patients, and prevention of this process by caspase inhibitors may be of significant therapeutic value for these patients, in whom supportive care continues to be the mainstay of therapy.