Palmitoyl-Protein Thioesterase 1 Deficiency in Drosophila melanogaster Causes Accumulation of Abnormal Storage Material and Reduced Life Span

Abstract

Human neuronal ceroid lipofuscinoses (NCLs) are a group of genetic neurodegenerative diseases characterized by progressive death of neurons in the central nervous system (CNS) and accumulation of abnormal lysosomal storage material. Infantile NCL (INCL), the most severe form of NCL, is caused by mutations in the Ppt1 gene, which encodes the lysosomal enzyme palmitoyl-protein thioesterase 1 (Ppt1). We generated mutations in the Ppt1 ortholog of Drosophila melanogaster to characterize phenotypes caused by Ppt1 deficiency in flies. Ppt1-deficient flies accumulate abnormal autofluorescent storage material predominantly in the adult CNS and have a life span 30% shorter than wild type, phenotypes that generally recapitulate disease-associated phenotypes common to all forms of NCL. In contrast, some phenotypes of Ppt1-deficient flies differed from those observed in human INCL. Storage material in flies appeared as highly laminar spherical deposits in cells of the brain and as curvilinear profiles in cells of the thoracic ganglion. This contrasts with the granular deposits characteristic of human INCL. In addition, the reduced life span of Ppt1-deficient flies is not caused by progressive death of CNS neurons. No changes in brain morphology or increases in apoptotic cell death of CNS neurons were detected in Ppt1-deficient flies, even at advanced ages. Thus, Ppt1-deficient flies accumulate abnormal storage material and have a shortened life span without evidence of concomitant neurodegeneration.

Mutations in palmitoyl-protein thioesterase 1 alter exocytosis and endocytosis at synapses inDrosophilalarvae

“…Whereas the locomotor defects in PPT1 -/-mice coincide with cerebellar neuronal loss, however, the locomotor defects observed in Drosophila larvae occur before intracellular inclusions are observed in the nervous system. 17 It is unclear whether the motor dysfunction in human INCL patients precedes or requires neuronal loss, although some synaptic phenotypes are observed in the absence of typical NCL pathology in cultured mouse cortical neurons, indicating that important neuronal processes are disrupted early in the disease process. 25 This is consistent with the work presented here, suggesting that the larval synaptic phenotypes we describe in the fly are very relevant to NCL disease etiology.…”

“…The deficiency completely removes the coding region of Ppt1 and thus represents the complete loss of Ppt1 function in the fly. 17 The Alanine to Threonine mutation (Ppt1 A179 ) is analogous to position 171 in the human protein and is located at the distal end of the substrate binding pocket. Human INCL mutations, V181M and E184K, are also located in this region and result in an almost complete loss (< 2%) of wild-type function.…”

“…[12][13][14]. This has also been the case for lysosomal storage disorders where both gain-of-function and loss-of-function genetic models have been produced for Congenital NCL (Ctsd), 15,16 INCL 17,18 and Juvenile NCL (Cln3). 19,20 Mutations in Drosophila that mimic the Ppt1 loss-of-function seen in human INCL produce cytoplasmic inclusions and autoflourescent storage material.…”

“…19,20 Mutations in Drosophila that mimic the Ppt1 loss-of-function seen in human INCL produce cytoplasmic inclusions and autoflourescent storage material. 17 Embryological characterization of these mutations in the fly demonstrates a role for Ppt1 in early neuronal specification and axon guidance. 21 Gain-of-function genetic screens in the fly have implicated Ppt1 function in the regulation of several neuronal processes, including synaptic growth/homeostasis and synaptic vesicle endo/exocytosis.…”

Autophagy-Dependent Rhodopsin Degradation Prevents Retinal Degeneration inDrosophila

“…The suppression of Ppt1 causes retinal degeneration in Drosophila and this defect is enhanced synergistically by Psd knockdown Since it is known that Psd interacts genetically with the Drosophila ortholog of human PPT1, a gene that is mutated in the pediatric neurodegenerative disease known as infantile neuronal ceroid lipofuscinosis (INCL) (Glaser et al, 2003;Hickey et al, 2006), we expected that palmitoyl-protein thioesterase 1 (Ppt1) in Drosophila would be essential for the viability of photoreceptor cells. Therefore, we analyzed the phenotype of the Ppt1 knockdown.…”