Friday, June 29, 2018

Review of DNA repair, disease, and Drosophila research

Cotterill S. Diseases Associated with Mutation of Replication and Repair Proteins. Adv Exp Med Biol. 2018;1076:215-234. PMID: 29951822.

The abstract: "Alterations in proteins that function in DNA replication and repair have been implicated in the development of human diseases including cancer, premature ageing, skeletal disorders, mental retardation, microcephaly, and neurodegeneration. Drosophila has orthologues of most human replication and repair proteins and high conservation of the relevant cellular pathways, thus providing a versatile system in which to study how these pathways are corrupted leading to the diseased state. In this chapter I will briefly review the diseases associated with defects in replication and repair proteins and discuss how past and future studies on the Drosophila orthologues of such proteins can contribute to the dissection of the mechanisms involved in disease development."

Discussion of Drosophila-based bioassay of prion infectivity

Thackray AM, Andréoletti O, Bujdoso R. The use of PrP transgenic Drosophila to replace and reduce vertebrate hosts in the bioassay of mammalian prion infectivity. F1000Res. 2018 May 15;7:595. PMID: 29946445; PMCID: PMC5998032.

The abstract: "Prion diseases are fatal neurodegenerative conditions of humans and vertebrate species. The transmissible prion agent is a novel infectious particle composed principally of PrP Sc, an abnormal isomer of the normal host protein PrP C. The only reliable method to detect mammalian prion infectivity is by bioassay, invariably in a vertebrate host. The current prion bioassays typically involve intracerebral or peripheral inoculation of test material into the experimental host and subsequent euthanasia when clinical signs of terminal prion disease become evident. It may be months or years before the onset of clinical disease becomes evident and a pre-determined clinical end-point is reached. Consequently, bioassay of prion infectivity in vertebrate species is cumbersome, time consuming, expensive, and increasingly open to ethical debate because these animals are subjected to terminal neurodegenerative disease. Prions are a significant risk to public health through the potential for zoonotic transmission of animal prion diseases. Attention has focussed on the measurement of prion infectivity in different tissues and blood from prion-infected individuals in order to determine the distribution of infectious prions in diseased hosts. New animal models are required in order to replace or reduce, where possible, the dependency on the use of vertebrate species, including the 'gold standard' mouse prion bioassay, to assess prion infectivity levels. Here we highlight the development of a Drosophila-based prion bioassay, a highly sensitive and rapid invertebrate animal system that can efficiently detect mammalian prions. This novel invertebrate model system will be of considerable interest to biologists who perform prion bioassays as it will promote reduction and replacement in the number of sentient animals currently used for this purpose. This article is a composite of previous methods that provides an overview of the methodology of the model and discusses the experimental data to promote its viability for use instead of more sentient hosts."

Monday, June 25, 2018

Fly studies used to gain functional understanding of changes associated with Huntington's disease

Al-Ramahi I, Lu B, Di Paola S, Pang K, de Haro M, Peluso I, Gallego-Flores T, Malik NT, Erikson K, Bleiberg BA, Avalos M, Fan G, Rivers LE, Laitman AM, Diaz-García JR, Hild M, Palacino J, Liu Z, Medina DL, Botas J. High-Throughput Functional Analysis Distinguishes Pathogenic, Nonpathogenic, and Compensatory Transcriptional Changes in Neurodegeneration. Cell Syst. 2018 Jun 6. pii: S2405-4712(18)30228-X. PMID: 29936182.

From the abstract: "Discriminating transcriptional changes that drive disease pathogenesis from nonpathogenic and compensatory responses is a daunting challenge. ... Here we integrate functional testing and network approaches to analyze previously reported transcriptional alterations in the brains of Huntington disease (HD) patients. We selected 312 genes whose expression is dysregulated both in HD patients and in HD mice and then replicated and/or antagonized each alteration in a Drosophila HD model. High-throughput behavioral testing in this model and controls revealed that transcriptional changes in synaptic biology and calcium signaling are compensatory, whereas alterations involving the actin cytoskeleton and inflammation drive disease. Knockdown of disease-driving genes in HD patient-derived cells lowered mutant Huntingtin levels and activated macroautophagy, suggesting a mechanism for mitigating pathogenesis. Our multilayered approach can thus untangle the wealth of information generated by transcriptomics and identify early therapeutic intervention points."

Drosophila study informs understanding of Wolfram syndrome 1

Sakakibara Y, Sekiya M, Fujisaki N, Quan X, Iijima KM. Knockdown of wfs1, a fly homolog of Wolfram syndrome 1, in the nervous system increases susceptibility to age- and stress-induced neuronal dysfunction and degeneration in Drosophila. PLoS Genet. 2018 Jan 22;14(1):e1007196. PMID: 29357349; PMCID: PMC5794194.

From the abstract: "Wolfram syndrome (WS), caused by loss-of-function mutations in the Wolfram syndrome 1 gene (WFS1), is characterized by juvenile-onset diabetes mellitus, bilateral optic atrophy, and a wide spectrum of neurological and psychiatric manifestations. ... the mechanisms underlying neurodegeneration caused by WFS1 deficiency remain elusive. Here, we investigated the role of WFS1 in the maintenance of neuronal integrity in vivo by knocking down the expression of wfs1, the Drosophila homolog of WFS1, in the central nervous system. Neuronal knockdown of wfs1 caused age-dependent behavioral deficits and neurodegeneration in the fly brain. ... This study highlights the protective role of wfs1 against age-associated neurodegeneration and furthers our understanding of potential disease-modifying factors that determine susceptibility and resilience to age-associated neurodegenerative diseases."

Wednesday, June 20, 2018

Genetic modifiers of neurodegeneration

Early online from Genetics:

Genetic Modifiers of Neurodegeneration in a Drosophila Model of Parkinson's Disease
Sierra Lavoy, Vinita G. Chittoor-Vinod, Clement Y. Chow and Ian Martin

From the abstract: "... There is increasing evidence that background genetic variation is a strong driver of disease variability ... To understand the genotype-phenotype relationship ... a large number of backgrounds must be studied. This can be efficiently achieved using model organism collections such as the Drosophila Genetic Reference Panel (DGRP). Here, we used the DGRP to assess the variability of locomotor dysfunction in a LRRK2 G2019S Drosophila melanogaster model of Parkinson's disease. We find substantial variability in the LRRK2 G2019S locomotor phenotype in different DGRP backgrounds. A genome-wide association study for candidate genetic modifiers reveals 177 genes that drive wide phenotypic variation, including 19 top association genes. Genes involved in the outgrowth and regulation of neuronal projections are enriched in these candidate modifiers. RNAi functional testing of the top association and neuronal projection-related genes reveals that pros, pbl, ct and CG33506 significantly modify age-related dopamine neuron loss and associated locomotor dysfunction in the Drosophila LRRK2 G2019S model. These results demonstrate how natural genetic variation can be used as a powerful tool to identify genes that modify disease-related phenotypes. ..."

Monday, June 4, 2018

Fly model contributes to understanding of spinocerebellar ataxia type 1

Bondar VV, Adamski CJ, Onur TS, Tan Q, Wang L, Diaz-Garcia J, Park J, Orr HT, Botas J, Zoghbi HY. PAK1 regulates ATXN1 levels providing an opportunity to modify its toxicity in Spinocerebellar ataxia type 1. Hum Mol Genet. 2018 May 30. PMID: 29860311.

The abstract: "Spinocerebellar ataxia type 1 (SCA1) is caused by the expansion of a trinucleotide repeat that encodes a polyglutamine tract in ataxin-1 (ATXN1). The expanded polygultamine in ATXN1 increases the protein's stability and results in its accumulation and toxicity. Previous studies have demonstrated that decreasing ATXN1 levels ameliorates SCA1 phenotypes and pathology in mouse models. We rationalized that reducing ATXN1 levels through pharmacological inhibition of its modulators could provide a therapeutic avenue for SCA1. Here, through a forward genetic screen in Drosophila we identified, p21-activated kinase 3 (Pak3) as a modulator of ATXN1 levels. Loss-of-function of fly Pak3 and Pak1, whose mammalian homologs are Group I of PAKs, reduces ATXN1 levels, and accordingly, improves disease pathology in a Drosophila model of SCA1. Knockdown of PAK1 potently reduces ATXN1 levels in mammalian cells independent of the well-characterized S776 phosphorylation site (known to stabilize ATXN1) thus revealing a novel molecular pathway that regulates ATXN1 levels. Furthermore, pharmacological inhibition of PAKs decreases ATXN1 levels in a mouse model of SCA1. To explore the potential of using PAK inhibitors in combination therapy, we combined the pharmacological inhibition of PAK with MSK1, a previously identified modulator of ATXN1, and examined their effects on ATXN1 levels. We found that inhibition of both pathways results in an additive decrease in ATXN1 levels. Together, this study identifies PAK signaling as a distinct molecular pathway that regulates ATXN1 levels and presents a promising opportunity to pursue for developing potential therapeutics for SCA1."

Review of fly models of Friedreich's Ataxia

Calap-Quintana P, Navarro JA, González-Fernández J, Martínez-Sebastián MJ, Moltó MD, Llorens JV. Drosophila melanogaster Models of Friedreich's Ataxia. Biomed Res Int. 2018 Apr 5;2018:5065190. PMID: 29850527; PMCID: PMC5907503.

From the abstract: "Friedreich's ataxia (FRDA) is a rare inherited recessive disorder affecting the central and peripheral nervous systems and other extraneural organs such as the heart and pancreas. This incapacitating condition usually manifests in childhood or adolescence, exhibits an irreversible progression that confines the patient to a wheelchair, and leads to early death. FRDA is caused by a reduced level of the nuclear-encoded mitochondrial protein frataxin due to an abnormal GAA triplet repeat expansion in the first intron of the human FXN gene. FXN is evolutionarily conserved, with orthologs in essentially all eukaryotes and some prokaryotes, leading to the development of experimental models of this disease in different organisms. These FRDA models have contributed substantially to our current knowledge of frataxin function and the pathogenesis of the disease, as well as to explorations of suitable treatments. Drosophila melanogaster, an organism that is easy to manipulate genetically, has also become important in FRDA research. This review describes the substantial contribution of Drosophila to FRDA research ..."