Characterization of Drosophila saposin-related mutants as a model for lysosomal sphingolipid storage diseases

Abstract

Sphingolipidoses are inherited diseases belonging to the class of lysosomal storage diseases (LSDs), which are characterized by the accumulation of indigestible material in the lysosome caused by specific defects in the lysosomal degradation machinery. While some LSDs can be efficiently treated by enzyme replacement therapy (ERT), this is not possible if the nervous system is affected due to the presence of the blood-brain barrier. Sphingolipidoses in particular often present as severe, untreatable forms of LSDs with massive sphingolipid and membrane accumulation in lysosomes, neurodegeneration and very short life expectancy. The digestion of intralumenal membranes within lysosomes is facilitated by lysosomal sphingolipid activator proteins (saposins), which are cleaved from a prosaposin precursor. Prosaposin mutations cause some of the severest forms of sphingolipidoses, and are associated with perinatal lethality in mice, hampering studies on disease progression. We identify the Drosophila prosaposin orthologue Saposin-related (Sap-r) as a key regulator of lysosomal lipid homeostasis in the fly. Its mutation leads to a typical spingolipidosis phenotype with an enlarged endolysosomal compartment and sphingolipid accumulation as shown by mass spectrometry and thin layer chromatography. Sap-r mutants show reduced viability with ∼50% survival to adulthood, allowing us to study progressive neurodegeneration and analyze their lipid profile in young and aged flies. Additionally, we observe a defect in sterol homeostasis with local sterol depletion at the plasma membrane. Furthermore, we find that autophagy is increased, resulting in the accumulation of mitochondria in lysosomes, concomitant with increased oxidative stress. Together, we establish Drosophila Sap-r mutants as a lysosomal storage disease model suitable for studying the age-dependent progression of lysosomal dysfunction associated with lipid accumulation and the resulting pathological signaling events.

Unbalanced lipolysis results in lipotoxicity and mitochondrial damage in peroxisome-deficient Pex19 mutants

“…For metabolic labeling, third instar w- and Pex19− / − larvae were fed with [1– 14 C] sodium acetate (61 Ci/mol; Amersham, Braunschweig, Germany) in heat-inactivated yeast (10 µCi/agar dish containing 150 larvae) for 6 h. Afterward, larvae were homogenized and extracted as described for adult Drosophila in Sellin et al. (2017) .…”

A single-cell atlas of adult Drosophila ovary identifies transcriptional programs and somatic cell lineage regulating oogenesis

“…The newly identified genes in the SC cluster fall into 6 general categories of activity: endocytosis/vesicle mediated transport (Syx1A, RabX1, AnxB9, and shrb), antibacterial/immune response (CecA1 and LRR), morphogenesis (Mob2, CG44325, RhoGAP71E, and RhoL), catalytic/metabolic (CG12065, Cip4, and Nmda1), lipid binding (Cip4 and Gdap2), and metal ion transport, especially zinc and magnesium (spict, Swip-1, ZnT63C, and Zip99C). In addition, we validated 3 new SC genes (Fig 6F), which are also expressed in hemocytes: a proteolytic enzyme, Cp1, involved in cellular catabolism, an oxidation-reduction enzyme, GILT1, involved in bacterial response, and Sap-r, a lysosomal lipid storage homeostasis gene with known expression in embryonic hemocytes [96][97][98]. Together, these findings suggest that SCs and hemocytes share transcriptomic signatures required for apoptotic cell clearance, reinforcing their role as "amateur" phagocytes at this stage of development [99].…”

Exploiting the Potential of Drosophila Models in Lysosomal Storage Disorders: Pathological Mechanisms and Drug Discovery

“…Sphingolipidoses are a group of inherited lysosomal storage diseases characterized by a massive sphingolipid and membrane accumulation in lysosomes, neurodegeneration and short life expectancy [ 103 ].…”