Loss of swiss cheese in Neurons Contributes to Neurodegeneration with Mitochondria Abnormalities, Reactive Oxygen Species Acceleration and Accumulation of Lipid Droplets in Drosophila Brain

Unraveling the link between neuropathy target esterase NTE/SWS, lysosomal storage diseases, inflammation, abnormal fatty acid metabolism, and leaky brain barrier

Mutations in Drosophila Swiss cheese (SWS) gene or its vertebrate orthologue neuropathy target esterase (NTE) lead to progressive neuronal degeneration in flies and humans. Despite its enzymatic function as a phospholipase is well established, the molecular mechanism responsible for maintaining nervous system integrity remains unclear. In this study, we found that NTE/SWS is present in surface glia that forms the blood-brain barrier (BBB) and that NTE/SWS is important to maintain its structure and permeability. Importantly, BBB glia-specific expression of Drosophila NTE/SWS or human NTE in the sws mutant background fully rescues surface glial organization and partially restores BBB integrity, suggesting a conserved function of NTE/SWS. Interestingly, sws mutant glia showed abnormal organization of plasma membrane domains and tight junction rafts accompanied by the accumulation of lipid droplets, lysosomes, and multilamellar bodies. Since the observed cellular phenotypes closely resemble the characteristics described in a group of metabolic disorders known as lysosomal storage diseases (LSDs), our data established a novel connection between NTE/SWS and these conditions. We found that mutants with defective BBB exhibit elevated levels of fatty acids, which are precursors of eicosanoids and are involved in the inflammatory response. Also, as a consequence of a permeable BBB, several innate immunity factors are upregulated in an age-dependent manner, while BBB glia-specific expression of NTE/SWS normalizes inflammatory response. Treatment with anti-inflammatory agents prevents the abnormal architecture of the BBB, suggesting that inflammation contributes to the maintenance of a healthy brain barrier. Considering the link between a malfunctioning BBB and various neurodegenerative diseases, gaining a deeper understanding of the molecular mechanisms causing inflammation due to a defective BBB could help to promote the use of anti-inflammatory therapies for age-related neurodegeneration.

The phospholipase A2 superfamily as a central hub of bioactive lipids and beyond

In essence, "phospholipase A₂" (PLA₂) means a group of enzymes that release fatty acids and lysophospholipids by hydrolyzing the sn-2 position of glycerophospholipids. To date, more than 50 enzymes possessing PLA₂ or related lipid-metabolizing activities have been identified in mammals, and these are subdivided into several families in terms of their structures, catalytic mechanisms, tissue/cellular localizations, and evolutionary relationships. From a general viewpoint, the PLA₂ superfamily has mainly been implicated in signal transduction, driving the production of a wide variety of bioactive lipid mediators. However, a growing body of evidence indicates that PLA₂s also contribute to phospholipid remodeling or recycling for membrane homeostasis, fatty acid β-oxidation for energy production, and barrier lipid formation on the body surface. Accordingly, PLA₂ enzymes are considered one of the key regulators of a broad range of lipid metabolism, and perturbation of specific PLA₂-driven lipid pathways often disrupts tissue and cellular homeostasis and may be associated with a variety of diseases. This review covers current understanding of the physiological functions of the PLA₂ superfamily, focusing particularly on the two major intracellular PLA₂ families (Ca²⁺-dependent cytosolic PLA₂s and Ca²⁺-independent patatin-like PLA₂s) as well as other PLA₂ families, based on studies using gene-manipulated mice and human diseases in combination with comprehensive lipidomics.

The Drosophila blood-brain barrier emerges as a model for understanding human brain diseases

The accurate regulation of the microenvironment within the nervous system is one of the key features characterizing complex organisms. To this end, neural tissue has to be physically separated from circulation, but at the same time, mechanisms must be in place to allow controlled transport of nutrients and macromolecules into and out of the brain. These roles are executed by cells of the blood-brain barrier (BBB) found at the interface of circulation and neural tissue. BBB dysfunction is observed in several neurological diseases in human. Although this can be considered as a consequence of diseases, strong evidence supports the notion that BBB dysfunction can promote the progression of brain disorders. In this review, we compile the recent evidence describing the contribution of the Drosophila BBB to the further understanding of brain disease features in human patients. We discuss the function of the Drosophila BBB during infection and inflammation, drug clearance and addictions, sleep, chronic neurodegenerative disorders and epilepsy. In summary, this evidence suggests that the fruit fly, Drosophila melanogaster, can be successfully employed as a model to disentangle mechanisms underlying human diseases.

'Fly-ing' from rare to common neurodegenerative disease mechanisms

Advances in genome sequencing have enabled researchers and clinicians to probe vast numbers of human variants to distinguish pathogenic from benign variants. Model organisms have been crucial in variant assessment and in delineating the molecular mechanisms of some of the diseases caused by these variants. The fruit fly, Drosophila melanogaster, has played a valuable role in this endeavor, taking advantage of its genetic technologies and established biological knowledge. We highlight the utility of the fly in studying the function of genes associated with rare neurological diseases that have led to a better understanding of common disease mechanisms. We emphasize that shared themes emerge among disease mechanisms, including the importance of lipids, in two prominent neurodegenerative diseases: Alzheimer's disease (AD) and Parkinson's disease (PD).

The Catalytic Domain of Neuropathy Target Esterase Influences Lipid Droplet Biogenesis and Lipid Metabolism in Human Neuroblastoma Cells

As an endoplasmic reticulum (ER)-anchored phospholipase, neuropathy target esterase (NTE) catalyzes the deacylation of lysophosphatidylcholine (LPC) and phosphatidylcholine (PC). The catalytic domain of NTE (NEST) exhibits comparable activity to NTE and binds to lipid droplets (LD). In the current study, the nucleotide monophosphate (cNMP)-binding domains (CBDs) were firstly demonstrated not to be essential for the ER-targeting of NTE, but to be involved in the normal ER distribution and localization to LD. NEST was associated with LD surface and influenced LD formation in human neuroblastoma cells. Overexpression of NEST enhances triacylglycerol (TG) accumulation upon oleic acid loading. Quantitative targeted lipidomic analysis shows that overexpression of NEST does not alter diacylglycerol levels but reduces free fatty acids content. NEST not only lowered levels of LPC and acyl-LPC, but not PC or alkyl-PC, but also widely altered levels of other lipid metabolites. Qualitative PCR indicates that the increase in levels of TG is due to the expression of diacylglycerol acyltransferase 1 gene by NEST overexpression. Thus, NTE may broadly regulate lipid metabolism to play roles in LD biogenesis in cells.

PNPLA6/NTE, an Evolutionary Conserved Phospholipase Linked to a Group of Complex Human Diseases

Patatin-like phospholipase domain-containing protein 6 (PNPLA6), originally called Neuropathy Target Esterase (NTE), belongs to a family of hydrolases with at least eight members in mammals. PNPLA6/NTE was first identified as a key factor in Organophosphate-induced delayed neuropathy, a degenerative syndrome that occurs after exposure to organophosphates found in pesticides and nerve agents. More recently, mutations in PNPLA6/NTE have been linked with a number of inherited diseases with diverse clinical symptoms that include spastic paraplegia, ataxia, and chorioretinal dystrophy. A conditional knockout of PNPLA6/NTE in the mouse brain results in age-related neurodegeneration, whereas a complete knockout causes lethality during embryogenesis due to defects in the development of the placenta. PNPLA6/NTE is an evolutionarily conserved protein that in Drosophila is called Swiss-Cheese (SWS). Loss of SWS in the fly also leads to locomotory defects and neuronal degeneration that progressively worsen with age. This review will describe the identification of PNPLA6/NTE, its expression pattern, and normal role in lipid homeostasis, as well as the consequences of altered NPLA6/NTE function in both model systems and patients.

Drosophila Lysophospholipase Gene swiss cheese Is Required for Survival and Reproduction

Simple Summary

Biological evolution implies fitness of newly evolved organisms that have inherent adaptive traits because of mutations in genes. However, most mutations are detrimental, and they spoil the organism’s life, its survival and its ability to leave progeny. Some genes are extremely vital for an organism, and therefore, they tend to save their structure and do not mutate or do it very composedly. That is the case of the gene encoding PNPLA6 lysophospholipase domain that evolved in bacteria, and evolution obliged it to save its function in higher animals. In mammals, complete dysfunction of such a gene is lethal because of its high importance in placenta for early embryo development. Why is it conserved in other species, for instance insects, that have no placenta? Here we studied the role of the PNPLA6-encoding gene named swiss cheese in Drosophila melanogaster fitness. We have found that its dysfunction results in premature death of specimens and their inability to leave enough progeny. Thus, we provide the first evidence for significance of the gene that encodes the lysophospholipase enzyme in fitness of insects.

Abstract

Drosophila melanogaster is one of the most famous insects in biological research. It is widely used to analyse functions of different genes. The phosphatidylcholine lysophospholipase gene swiss cheese was initially shown to be important in the fruit fly nervous system. However, the role of this gene in non-nervous cell types has not been elucidated yet, and the evolutional explanation for the conservation of its function remains elusive. In this study, we analyse expression pattern and some aspects of the role of the swiss cheese gene in the fitness of Drosophila melanogaster. We describe the spatiotemporal expression of swiss cheese throughout the fly development and analyse the survival and productivity of swiss cheese mutants. We found swiss cheese to be expressed in salivary glands, midgut, Malpighian tubes, adipocytes, and male reproductive system. Dysfunction of swiss cheese results in severe pupae and imago lethality and decline of fertility, which is impressive in males. The latter is accompanied with abnormalities of male locomotor activity and courtship behaviour, accumulation of lipid droplets in testis cyst cells and decrease in spermatozoa motility. These results suggest that normal swiss cheese is important for Drosophila melanogaster fitness due to its necessity for both specimen survival and their reproductive success.

Tissue-specific regulation of translational readthrough tunes functions of the traffic jam transcription factor

Translational readthrough (TR) occurs when the ribosome decodes a stop codon as a sense codon, resulting in two protein isoforms synthesized from the same mRNA. TR has been identified in several eukaryotic organisms; however, its biological significance and mechanism remain unclear. Here, we quantify TR of several candidate genes in Drosophila melanogaster and characterize the regulation of TR in the large Maf transcription factor Traffic jam (Tj). Using CRISPR/Cas9-generated mutant flies, we show that the TR-generated Tj isoform is expressed in a subset of neural cells of the central nervous system and is excluded from the somatic cells of gonads. Control of TR in Tj is critical for preservation of neuronal integrity and maintenance of reproductive health. The tissue-specific distribution of a release factor splice variant, eRF1H, plays a critical role in modulating differential TR of leaky stop codon contexts. Fine-tuning of gene regulatory functions of transcription factors by TR provides a potential mechanism for cell-specific regulation of gene expression.