Images in clinical medicine. Apoptosis in myelodysplastic syndromes

Ubiquitin-proteasome-rich cytoplasmic structures in neutrophils of patients with Shwachman-Diamond syndrome

BACKGROUND

Shwachman-Diamond syndrome is an autosomal recessive disorder in which severe bone marrow dysfunction causes neutropenia and an increased risk of leukemia. Recently, novel particulate cytoplasmic structures, rich in ubiquitinated and proteasomal proteins, have been detected in epithelial cells and neutrophils from patients with Helicobacter pylori gastritis and several epithelial neoplasms.

DESIGN AND METHODS

Blood neutrophils from 13 cases of Shwachman-Diamond syndrome - ten with and three without SBDS gene mutation - and ten controls were investigated by confocal microscopy and ultrastructural immunocytochemistry using antibodies against ubiquitinated proteins, proteasomes, p62 protein, and Helicobacter pylori VacA, urease and outer membrane proteins.

RESULTS

Many extensively disseminated particulate cytoplasmic structures, accounting for 22.78 ± 5.57% (mean ± standard deviation) of the total cytoplasm, were found in blood neutrophils from mutated Shwachman-Diamond syndrome patients. The particulate cytoplasmic structures showed immunoreactivity for polyubiquitinated proteins and proteasomes, but no reactivity for Helicobacter pylori products, which are present in particulate cytoplasmic structures of Helicobacter pylori-positive gastritis. Neutrophils from patients with Shwachman-Diamond syndrome frequently showed p62-positive autophagic vacuoles and apoptotic changes in 5% of cells. No particulate cytoplasmic structures were observed in most control neutrophils; however, in a few cells from two cases we noted focal development of minute particulate cytoplasmic structures, accounting for 0.74 ± 0.56% of the total cytoplasm (P<0.001 versus particulate cytoplasmic structures from mutated Shwachman-Diamond syndrome patients). Neutrophils from non-mutated Shwachman-Diamond-syndrome-like patients resembled controls in two cases, and a third case showed particulate cytoplasmic structure patterns intermediate between those in controls and those in mutated Shwachman-Diamond syndrome patients.

CONCLUSIONS

Particulate cytoplasmic structures are a prominent feature of neutrophils from patients with Shwachman-Diamond syndrome. They may help us to understand the mechanism of granulocyte dysfunction and the neoplastic risk of the disease.

Apoptosis: biochemical aspects and clinical implications

Apoptosis and necrosis represent two distinct types of cell death. Apoptosis possesses unique morphologic and biochemical features which distinguish this mechanism of programmed cell death from necrosis. Extrinsic apoptotic cell death is receptor-linked and initiates apoptosis by activating caspase 8. Intrinsic apoptotic cell death is mediated by the release of cytochrome c from mitochondrial and initiates apoptosis by activating caspase 3. Cancer chemotherapy utilizes apoptosis to eliminate tumor cells. Agents which bind to the minor groove of DNA, like camptothecin and Hoechst 33342, inhibit topoisomerase I, RNA polymerase II, DNA polymerase and initiate intrinsic apoptotic cell death. Hoechst 33342-induced apoptosis is associated with disruption of TATA box binding protein/TATA box complexes, replication protein A/single-stranded DNA complexes, topoisomerase I/DNA cleavable complexes and with an increased intracellular concentration of E2F-1 transcription factor and nitric oxide concentration. Nitric oxide and transcription factor activation or respression also regulate the two apoptotic pathways. Some human diseases are associated with excess or deficient rates of apoptosis, and therapeutic strategies to regulate the rate of apoptosis include inhibition or activation of caspases, mRNA antisense to reduce anti-apoptotic factors like Bcl-2 and survivin and recombinant TRAIL to activate pro-apoptotic receptors, DR4 and DR5.