Drosophila Model of Human Inherited Triosephosphate Isomerase Deficiency Glycolytic Enzymopathy

Abstract

Heritable mutations, known as inborn errors of metabolism, cause numerous devastating human diseases, typically as a result of a deficiency in essential metabolic products or the accumulation of toxic intermediates. We have isolated a missense mutation in the Drosophila sugarkill (sgk) gene that causes phenotypes analogous to symptoms of triosephosphate isomerase (TPI) deficiency, a human familial disease, characterized by anaerobic metabolic dysfunction resulting from pathological missense mutations affecting the encoded TPI protein. In Drosophila, the sgk gene encodes the glycolytic enzyme TPI. Our analysis of sgk mutants revealed TPI impairment associated with reduced longevity, progressive locomotor deficiency, and neural degeneration. Biochemical studies demonstrate that mutation of this glycolytic enzyme gene does not result in a bioenergetic deficit, suggesting an alternate cause of enzymopathy associated with TPI impairment.

Degradation of Functional Triose Phosphate Isomerase Protein UnderliessugarkillPathology

“…Our model allows us to directly test the role of these mechanisms in pathogenesis resulting from a specific pathogenic missense mutation affecting TPI. Previously we have shown TPI sugarkill markedly reduces glycolytic flux, but this does not result in a bioenergetic crisis, suggesting a compensatory mechanism and an alternative cause of pathogenesis (Celotto et al 2006). Our data utilizing the TPI sugarkill model of TPI deficiency reveal that the mutant protein is capable of forming a dimer and retains function; however, pathogenesis results when the protein is targeted for proteasome degradation.…”

“…The mutation was positionally cloned and found to be a missense mutation in the TPI (triose phosphate isomerase) gene (Celotto et al 2006). TPI sugarkill (sgk) animals have progressive stress-sensitive locomotor impairment and reduced longevity.…”

“…This numbering uses the established nomenclature for TPI mutations, where the start methionine is assumed to be removed following translation (see the recent review by Orosz et al 2006). TPI transgenic strains were previously published (Celotto et al 2006). All other strains used were obtained from the Bloomington Stock Center.…”

“…We have previously identified a recessive, hypomorphic, missense (M80T) mutation (sugarkill or sgk) in the TPI gene of Drosophila featuring reduced longevity, neurodegenration, and locomotor impairment (Celotto et al 2006). These mutants, referred to as TPI sugarkill , serve as an amendable genetic model for elucidating the mechanism of TPI deficiency in vivo (Celotto et al 1 These authors contributed equally to this work.…”

“…The mutation was originally identified as a temperaturesensitive paralytic mutant (Palladino et al 2002). Each phenotype examined-including onset of neuropathology, locomotor impairment, and reduced longevity-is significantly worsened by modest elevations in temperature between 20°and 29° (Celotto et al 2006). This suggests that TPI sugarkill animals may serve as a useful model of TPI impairment where varying temperatures can be utilized to study a series of hypomorphic conditions from mild to severe.…”