A Novel Genetic Screen Identifies Modifiers of Age-Dependent Amyloid β Toxicity in the Drosophila Brain

Abstract

The accumulation of amyloid β peptide (Aβ) in the brain of Alzheimer’s disease (AD) patients begins many years before clinical onset. Such process has been proposed to be pathogenic through the toxicity of Aβ soluble oligomers leading to synaptic dysfunction, phospho-tau aggregation and neuronal loss. Yet, a massive accumulation of Aβ can be found in approximately 30% of aged individuals with preserved cognitive function. Therefore, within the frame of the “amyloid hypothesis”, compensatory mechanisms and/or additional neurotoxic or protective factors need to be considered and investigated. Here we describe a modifier genetic screen in Drosophila designed to identify genes that modulate toxicity of Aβ42 in the CNS. The expression of Aβ42 led to its accumulation in the brain and a moderate impairment of negative geotaxis at 18 days post-eclosion (d.p.e) as compared with genetic or parental controls. These flies were mated with a collection of lines carrying chromosomal deletions and negative geotaxis was assessed at 5 and 18 d.p.e. Our screen is the first to take into account all of the following features, relevant to sporadic AD: (1) pan-neuronal expression of wild-type Aβ42; (2) a quantifiable complex behavior; (3) Aβ neurotoxicity associated with progressive accumulation of the peptide; and (4) improvement or worsening of climbing ability only evident in aged animals. One hundred and ninety-nine deficiency (Df) lines accounting for ~6300 genes were analyzed. Six lines, including the deletion of 52 Drosophila genes with human orthologs, significantly modified Aβ42 neurotoxicity in 18-day-old flies. So far, we have validated CG11796 and identified CG17249 as a strong candidate (whose human orthologs are HPD and PRCC, respectively) by using RNAi or mutant hemizygous lines. PRCC encodes proline-rich protein PRCC (ppPRCC) of unknown function associated with papillary renal cell carcinoma. HPD encodes 4-hydroxyphenylpyruvate dioxygenase (HPPD), a key enzyme in tyrosine degradation whose Df causes autosomal recessive Tyrosinemia type 3, characterized by mental retardation. Interestingly, lines with a partial Df of HPD ortholog showed increased intraneuronal accumulation of Aβ42 that coincided with geotaxis impairment. These previously undetected modifiers of Aβ42 neurotoxicity in Drosophila warrant further study to validate their possible role and significance in the pathogenesis of sporadic AD.

Predicting and explaining the impact of genetic disruptions and interactions on organismal viability

“…Unlike budding and fission yeast, most human and fruit fly GI datasets were generated using either enhancement or suppression of an overexpressed hyperactive or dominant negative target gene ( Grimm, 2004 ; Jorgensen and Mango, 2002 ; St Johnston, 2002 ). This is typically followed by introduction of gene manipulation strategies that include RNAi, haploinsufficiency (removal of one copy of a gene in a diploid genome) or systematic overexpression of target genes ( Belfiori-Carrasco et al , 2017 ; Boutros and Ahringer, 2008 ; Gregory et al , 2007 ; Raymond et al , 2004 ; Therrien et al , 2000 ). These different manipulations can potentially convert what is classified as a negative GI in certain experimental contexts into a suppressor GI in other contexts ( Fig.…”

Genomic Analysis of miR-21-3p and Expression Pattern with Target Gene in Olive Flounder

“…7). Likewise, PRCC encodes proline-rich protein PRCC‒PPIL2 complex, which acts as protein folding, transport and degradation in the brain of Alzheimer’s disease patients in previous study [33]. Other studies have also shown that PPIL2 interacts with intronic-miRNAs such as miR-130b in host genomes [34, 35].…”

Mitochondria Dysfunction in Frontotemporal Dementia/Amyotrophic Lateral Sclerosis: Lessons From Drosophila Models

“…The ease of access to large libraries of stocks has enabled numerous large-scale enhancer and suppressor screens. This type of screen has been extensively used in neurodegenerative disease models to help identify downstream pathways of toxicity ( Bilen and Bonini, 2007 ; Butzlaff et al, 2015 ; Zhang et al, 2015 ; Belfiori-Carrasco et al, 2017 ). The aim of these screens has been to identify factors that worsen (enhance) or ameliorate (suppress) the phenotype associated with a particular disease model.…”