Sae-Lee, W. et al. (2017) International Worm Meeting "Synergistic patterned neurodegeneration caused by APP and APOE4 in C. elegans model of Alzheimer's disease."

Sae-Lee, W., Encanacion, A.J., Satarasinghe, P., Scott, L.S., Pierce, J.T.

[International Worm Meeting, 2017]

Alzheimer's disease (AD) is a progressive neurodegenerative disease that cannot be prevented, cured, or slowed down. Genetic and epidemiological studies have linked several genes to AD, notably the amyloid precursor protein (APP) and the e4 allele of apoliopoprotein E (APOE4). APOE4 confers the highest risk for developing AD compared to the other isoforms (APOE3 and APOE2) contributing to a 91% life-time chance of developing AD for individuals homozygous for APOE4. Moreover, APOE4 represents the most common genetic risk factor for AD; over 40% of current AD patients carry an APOE4 allele. At present, how APP and APOE4 functionally interact at the cellular and molecular level to trigger neurodegeneration in AD remains elusive. Progress has been slow using common mouse models of AD that do not display neurodegeneration. Here, we show that C. elegans can model important aspects of AD including age-related, patterned neurodegeneration that is modified by APOE. In our worm model of AD, we found that a certain subset of neurons is vulnerable to death, while other neurons survive. This is reminiscent of localized degeneration observed in the hippocampus and entorhinal cortex of brains in AD patients. Furthermore, in our worm model of AD we found that APOE4, but not its neutral risk isoform APOE3, acts synergistically with APP to hasten and expand the pattern of neurodegeneration. By combining genetic, molecular, and cell-specific proteomic approaches, we aim to uncover how these molecules synergize to kill some neurons while leaving others unaffected.

Teo, E. et al. (2015) International Worm Meeting "Characterization of a novel C. elegans Alzheimer's model with constitutive neuronal expression of Abeta1-42."

Ng, L., Gruber, J., Fong, S., Halliwell, B., Chen, C., Tsoi, S., Lakshmanan, L., Teo, E.

[International Worm Meeting, 2015]

Alzheimer's Disease (AD) is a progressive neurological disorder characterized by the deposition of amyloid beta (Abeta) in the brain, predominantly the Abeta1-42 form. While numerous transgenic C. elegans model have been generated to study AD, there is no well characterized model that has constitutive expression of Abeta1-42 in neurons. We therefore generated a novel C. elegans strain that constitutively expresses Abeta1-42 in all neurons and used it to study AD progression. Similar to the age-related onset of sporadic AD in humans, behavioral deficits including executive dysfunction and impaired learning ability were only observed in middle-aged but not in young Abeta worms. Mechanistically, Abeta worms showed altered mitochondrial metabolism, lower maximal and spare respiratory capacity at old age, but surprisingly no significant oxidative stress was observed. Abeta worms also had a decreased health- and lifespan. This novel C. elegans AD model recapitulates the progression of sporadic AD in humans and can be used for identifying potential interventions. .

Benbow, S.J. et al. (2017) International Worm Meeting "Characterization of Alzheimer's disease risk factors in a C. elegans model of tauopathy."

Benbow, S.J., Kraemer, B.C.

[International Worm Meeting, 2017]

Aberrant aggregation, misfolding, and mislocalization of the microtubule-associated protein tau characterize several neurodegenerative diseases, termed tauopathies. Alzheimer's disease (AD) is the most common tauopathy and most prevalent form of dementia within the global aging population. AD is distinguished from related dementias by the presence of two aggregant protein pathologies: intracellular neurofibrillary tangles (NFTs) composed of aggregated tau protein and extracellular amyloid- beta (A beta ) plaques. While heritable mutations in amyloid precursor protein (APP) and presenilins 1 and 2 (PSEN1, PSEN2) have considerably advanced our understanding of AD pathogenesis, they account for only a small portion of total AD cases. The majority of cases are classified as sporadic late-onset Alzheimer's disease and present without known causative mutations. However, human genomic studies have revealed a number of genetic variants contributing significant risk for AD. Genetic analysis by genome wide association studies (GWAS) has led to the identification of several novel genetic risk factors for AD (e.g. ABCA7, PICALM, DSG2, INPP5D, MEF2C, PTK2B, SLC24H4-RIN3, and ABI3). We hypothesize that a subset of these gene variants may modulate the severity of tau pathology, thereby contributing to the risk of developing AD. To test this hypothesis, we will explore whether these genes affect tau pathology in our C. elegans model of tauopathy. In this model, pan-neuronal expression of human tau recapitulates several features of human disease including accumulation of detergent-insoluble phosphorylated tau aggregates, abnormal behavior, neurodegeneration, and shortened lifespan. Tau transgenic C. elegans will be crossed with worms carrying a loss-of-function mutation in one of the homologous genes corresponding to a novel AD risk factor: abt-2, unc-11, hmr-1, unc-26, mef-2, kin-32, rin-1 and abi-1. Using behavioral analysis and biochemical assays to examine tau phosphorylation and aggregation, we will assess the impact of AD genetic risk factor genes on the severity of tau pathology. Identification of the molecular mechanisms underpinning genetic risk for AD remains a key unaddressed area and may provide novel therapeutic targets.

Pho, Kim et al. (2019) International Worm Meeting "Investigating the impact of the human microbiota on Alzheimer's Disease using Caenorhabditis elegans as a model."

Surette, Michael G., Pho, Kim, Tench, Andrea, Lau, Tammy, MacNeil, Lesley T., McArthur, Andrew G.

[International Worm Meeting, 2019]

The risk of developing Alzheimer's Disease (AD) is influenced, not only by genetic factors, but also by environment and lifestyle. The multi-factored pathogenesis that leads to AD development poses a challenge for identifying causal factors that promote neurodegeneration. Two hallmarks of AD are amyloid-? (A?) plaques and neurofibrillary tangles composed of the protein Tau. We use Caenorhabditis elegans as a model of AD to measure the impact of human microbiota species on AD-related phenotypes. Using an A?-overexpressing C. elegans model, we identified several bacterial species that differentially impact paralysis and are characterizing a group of Enterobacteriaceae species that significantly reduce paralysis. Most of these bacteria also decreased neurodegeneration in animals that pan-neuronally express aggregate-prone Tau, providing additional evidence of microbiota-promoted neuroprotection. To explore these effects, we examined global changes in gene expression in animals exposed to neuroprotective bacteria. We identified several biological processes that are differentially regulated in response to the neuroprotective microbiota species, including innate immunity and defense response. Overall, by studying the impact of the human microbiota on models overexpressing A? or aggregate-prone Tau, we gain a greater understanding of conserved pathways involved in gene-environment interactions that influence the development of AD.

Iyer, Sangeetha V. et al. (2013) International Worm Meeting "Innate immune signaling protects against patterned neurodegeneration in Alzheimer's disease."

Pierce-Shimomura, Jon, Crisp, Ashley, Kushwaha, Anushri, Iyer, Sangeetha V.

[International Worm Meeting, 2013]

Alzheimer's disease (AD) affects more than 5 million people in the U.S. At the cellular level, AD is typified by the development of extracellular plaques formed due to aggregation of amyloid precursor protein (APP) fragments. AD can be caused in humans by a single extra copy of the APP gene as observed in Down syndrome. Because APP is widely expressed throughout the brain; it is unclear why this ubiquitously expressed gene leads to a selective pattern of degeneration starting with cholinergic neurons important for memory. To address this question, we generated a novel C. elegans model of AD that expresses a single copy of the human APP gene. Like human AD, our model displays age-dependent degeneration of specific cholinergic neurons. The progressive cholinergic neurodegeneration correlated significantly with the levels of accumulated APP. Identical results were obtained upon over-expression of the orthologous worm gene, apl-1, demonstrating that the basis for this is conserved. Since the initiation of APP accumulation coincided with the onset of immunosenescence, we hypothesized that innate immune signaling may play a role in APP accumulation and degeneration. We found that deletion of any member of a conserved core of ASK1/p38MAPK innate immune pathway led to the selective degeneration of the same cholinergic neurons. Conversely, boosting innate immunity protected against APP accumulation and degeneration cell autonomously. To boost innate immune signaling pharmacologically, we tested a candidate AD drug, the retinoid X receptor agonist bexarotene, on our AD worms. Treatment with bexarotene as well as other nuclear hormone receptor agonists significantly reduced APP accumulation and cholinergic degeneration. Although bexarotene was recently proposed to provide protection via upregulation of the AD-risk gene ApoE in mice, worms do not possess a true homolog of ApoE. Thus, our results imply that bexarotene also protects via pathways independent of ApoE. Together, our data suggest that immunosenescence may unexpectedly sculpt the timing and cellular pattern of neurodegeneration caused by APP, and that the conserved ASK1/p38MAPK innate immune pathway may be harnessed for promising therapeutic outcomes in AD.

Brose, Lotti et al. (2021) International Worm Meeting "Exploring neuron death in a C. elegans model of Alzheimer's disease"

Pierce, Jon, Brose, Lotti

[International Worm Meeting, 2021]

Alzheimer's disease (AD) is the leading cause of dementia worldwide and has been characterized pathologically as gross loss of neurons and neuronal connections in areas of the brain that control memory and executive function. Genetic variations in a number of genes, including amyloid precursor protein (APP) and apolipoprotein E (APOE), have been shown to influence both age of onset and severity of AD. Both an additional copy and gain-of-function mutants in APP can cause earlier onset of AD, while the e4 allele of APOE (APOE4) hastens and exacerbates AD compared to its other alleles (APOE2 and APOE3). How these genes influence neuronal health in AD has yet to be determined. Our lab has developed a C. elegans model of AD that expresses both APP and APOE4. These worms exhibit specific, age-dependent neurodegeneration and cell death that can be readily observed using fluorescent microscopy. Combined with behavioral observations, we determined that expression of APOE4, but not APOE3, leads to death of the command egg laying neuron, HSN, by middle age. Further, genetic manipulation and time-lapse microscopy suggests neurons are not dying via apoptosis. We are currently exploring additional cell death pathways, as discovering the underlying neurodegeneration mechanisms may help identify novel therapeutic targets.

Moloney AM et al. (2009) European Worm Neurobiology Meeting "The Caenorhabditis elegans orthologue of PICALM, UNC-11, helps protects against Beta-amyloid toxicity"

Sattelle DB, Lomas DA, Williams J, Crowther D, Fraboulet S, Link CD, Moloney AM

[European Worm Neurobiology Meeting, 2009]

Authors acknowledge support from MRC and The Alzheimer''s Research Trust. C. elegans has been used in studies of human neurodegenerative diseases (1). Apolioprotein E currently remains the only well confirmed genetic risk factor for sporadic forms of Alzheimer.s disease (AD). However, it is estimated that between 40-70% of AD cases may be caused by genetic variance at additional loci, although much still remains unknown about these. To address this further, this study uses a novel approach to combine an extensive, large-scale, genome-wide association study (GWAS) together with an RNAi screen on a C. elegans transgenic model over-expressing the human amyloid peptide (ABeta1-42) important in AD (2). By applying RNAi approaches to the invertebrate AD model, we can rapidly identify those candidate risk factors which modify Beta-amyloid toxicity and thereby help pinpoint candidate molecular targets and pathways for therapeutic intervention. PICALM (PhosphatidylInositol binding Clathrin Assembly Lymphoid Leukemia Protein) has been identified as an important new AD candidate risk factor (p < 1.92e-08) in the largest GWAS performed to date. The PICALM gene resides on chromosome 11 (p < 1.92e-08) and is essential for clathrin-mediated endocytosis at the synapse. However, very little is known about its precise contribution to synaptic dysfunction in AD. Employing a C. elegans transgenic line CL4176, expressing human ABeta1-42 under a temperature induced system, we have shown that the C.elegans orthologue of PICALM, UNC-11, is necessary to protect against Beta-amyloid toxicity. This application has additionally identified a high frequency of Beta-amyloid modifiers when orthologues of other risk factors, detected in GWAS survey on AD patients, are knocked down using RNAi. Conclusions: This study illustrates the capacity of an invertebrate genetic model of AD to identify novel molecular components or pathways that are implicated in AD pathogenesis as well as prospective targets for therapeutic intervention. References: (1) Culetto E and Sattelle DB. Hum Mol Genet. 2000 9(6):869-77. (2) Link CD., et al., Neurobiol Aging 2003 24(3): 397-413

Pierce-Shimomura, Jonathan T. et al. (2011) International Worm Meeting "Serotonergic blockade prevents age-related neurodegeneration in C. elegans model of Alzheimer's disease."

Pierce-Shimomura, Jonathan T., Crisp, Ashley

[International Worm Meeting, 2011]

Alzheimer's disease (AD) is characterized by the selective degeneration of cholinergic neurons involved in memory. Although the precise etiology of AD remains unclear, the amyloid-precusor protein (APP) appears to be a causal agent for two main reasons. First, overexpression of APP or mutations in APP predict early-onset AD in humans. Second, dying neurons are surrounded by plaques composed of APP peptide fragments. With the simple architecture and ease of molecular manipulation of C. elegans, we explored the mechanisms of neurodegeneration caused by APP. The Li lab has previously found that overexpression of multiple copies of the APP-related gene called apl-1 leads to lethality and vacuolization in C. elegans (Hornsten et al., PNAS 2007). We have now found that, as in human AD, overexpression of a single wild-type copy of apl-1 or human APP result in age-related degeneration of a specific subset of cholinergic neurons in C. elegans. Deficits in two natural behaviors, swimming and egg-laying, correlate with the accumulation of APP protein specifically in these neurons and their eventual death. In addition, through genetic and pharmacological analyses, we have found that serotonergic signaling is both necessary and sufficient for degeneration of these neurons. Our results suggest that therapeutics designed to decrease serotonergic signaling may alleviate the pathology in mouse models of AD and perhaps even in patients with AD.

Lichty, James et al. (2021) International Worm Meeting "Elucidating Alzheimer's Disease related interactions between amyloid beta and the pathogen P. gingivalis in the model organism C. elegans"

Lichty, James, San Miguel, Adriana

[International Worm Meeting, 2021]

Alzheimer's Disease (AD) is a neurodegenerative disease which causes progressive loss of function in patients. AD affects about 5.8 million people in the US and is currently the sixth leading cause of death, with an estimated 122,000 deaths in 2018. AD is characterized by abnormal, widespread aggregation of the proteins amyloid beta (Abeta) and microtubule-associated protein tau (tau), neurodegeneration, immune system activation, inflammation, and oxidative stress. Abeta localization and aggregation have been linked to a number of AD traits but lack a clear causative role in the disease. Recently, infection by several pathogens have been identified as possible initiators for AD. One pathogen in particular, P. gingivalis (PG), has exhibited a number of features capable of inducing AD-like symptoms but its direct interactions with Abeta are poorly understood. We aim to identify and study these Abeta-PG interactions utilizing a novel Abeta expression system in the model organism C. elegans. This approach uses the C99 fragment of the amyloid precursor protein, the endogenous C. elegans gamma-gamma secretase, and a neuron-derived C. elegans signal peptide. Abeta is expressed as a part of C99, which is directed to the neuron membrane and cleaved, releasing Abeta extracellularly. This strain was compared to an intracellular Abeta expression strain to observe localization-dependent effects of Abeta on the organisms. We then infected the strains with PG, observing neuron health and overall health over the worms' lifespan. We seek to further characterize the detrimental effects, connecting them to AD traits seen in humans. Additionally, we will screen for genes relevant to the Abeta-PG interactions, such as C. elegans immunity pathways.

Ai, Ruixue et al. (2021) International Worm Meeting "A combination of artificial intelligence and C. elegans in identifying neuronal mitophagy inducers"

Xie, Chenglong, Fang, Evandro F., Ai, Ruixue

[International Worm Meeting, 2021]

Mitochondrial dysfunction, due to defective mitophagy, triggers the progression of Alzheimer's disease (AD). The identification of potent mitophagy modulators is critical for the development of novel therapeutic intervention strategies. Here, we describe a high-throughput machine-learning approach combined with laboratory validation using a C. elegans model in identifying robust neuronal mitophagy inducers. Lead compounds inhibit memory loss in both C. elegans and mouse models of AD. Collectively, our findings demonstrate a conserved mechanism of memory loss in both Abeta- and Tau- AD models that is mediated by defective mitophagy, while our highly accurate in silico screening platform paves the way for identifying potent mitophagy modulators to promote neuronal health and brain homeostasis during aging.