Mitochondrial Dysfunction As a Potential Source of Reactive Oxygen Species in Cellular Models of Shwachman-Diamond Syndrome

Abstract 1343

Shwachman-Diamond Syndrome (SDS) is an inherited bone marrow failure syndrome linked to defects in ribosome synthesis. The heterogeneous array of clinical findings associated with this disease state most commonly includes exocrine pancreas insufficiency, neutropenia, and metaphyseal chondroplasia. Patients also show a predisposition for progression to myelodysplastic syndromes and acute myelogenous leukemia. Mutations in the gene SBDS are known to be responsible for most cases of SDS. Initial studies of the yeast ortholog of SBDS, Sdo1, revealed that this family of proteins is involved in the maturation of 60S subunits. Other studies have suggested that SBDS is a multifunctional protein affecting processes other than ribosome synthesis. Most recently it has been shown that reactive oxygen species are dysregulated in TF-1 erythroleukemic cells depleted of SBDS leading to increased cell death (Pediatr Blood Cancer. 2010 Dec 1;55(6): 1138–44). In an effort to elucidate potential sources of increased reactive oxygen species we investigated mitochondrial function in yeast and human models of SDS. Yeast cells lacking Sdo1 fail to grow on media containing only respiratory carbon sources, indicative of a defect in mitochondrial energy metabolism. Related studies in human TF-1 cells revealed that cells depleted of SBDS exhibit reduced oxygen consumption relative to controls. Given that the largest producer of reactive oxygen species is the mitochondrial electron transport chain, perturbation of respiratory function in cells depleted of SBDS family members could be a potential source of elevated reactive oxygen species. To investigate the potential molecular mechanisms underlying these respiratory deficient phenotypes we carried out a proteomic analysis comparing yeast cells depleted of Sdo1 with controls. Our data reveal that cells lacking Sdo1 overexpress Por1, an ortholog of human VDAC1. VDAC1 is a voltage dependent anion channel of the mitochondrial outer membrane that is thought to be an essential component of the mitochondrial permeability pore. Both over and under expression of VDAC1 have been shown to disrupt mitochondrial function and lead to enhanced apoptosis. Current efforts are focused on possible changes in VDAC1 expression and the role they play in the respiratory deficient phenotype in human SDS models. These studies continue to shed further insight into the molecular mechanisms underlying SDS pathophysiology.