Integrase (IN) enzymes are found in all retroviruses and are crucial in the retroviral integration process. Many studies have revealed how exogenous IN enzymes, such as the human immunodeficiency virus (HIV) IN, contribute to altered cellular function. However, the same consideration has not been given to viral IN originating from symbionts within our own DNA. Endogenous retrovirus-K (ERVK) is pathologically associated with neurological and inflammatory diseases along with several cancers. The ERVK IN interactome is unknown, and the question of how conserved the ERVK IN protein–protein interaction motifs are as compared to other retroviral integrases is addressed in this paper. The ERVK IN protein sequence was analyzed using the Eukaryotic Linear Motif (ELM) database, and the results are compared to ELMs of other betaretroviral INs and similar eukaryotic INs. A list of putative ERVK IN cellular protein interactors was curated from the ELM list and submitted for STRING analysis to generate an ERVK IN interactome. KEGG analysis was used to identify key pathways potentially influenced by ERVK IN. It was determined that the ERVK IN potentially interacts with cellular proteins involved in the DNA damage response (DDR), cell cycle, immunity, inflammation, cell signaling, selective autophagy, and intracellular trafficking. The most prominent pathway identified was viral carcinogenesis, in addition to select cancers, neurological diseases, and diabetic complications. This potentiates the role of ERVK IN in these pathologies via protein–protein interactions facilitating alterations in key disease pathways.

The study of human neurological infection faces many technical and ethical challenges. While not as common as mammalian models, the use of Drosophila (fruit fly) in the investigation of virus–host dynamics is a powerful research tool. In this review, we focus on the benefits and caveats of using Drosophila as a model for neurological infections and neuroimmunity. Through the examination of in vitro, in vivo and transgenic systems, we highlight select examples to illustrate the use of flies for the study of exogenous and endogenous viruses associated with neurological disease. In each case, phenotypes in Drosophila are compared to those in human conditions. In addition, we discuss antiviral drug screening in flies and how investigating virus–host interactions may lead to novel antiviral drug targets. Together, we highlight standardized and reproducible readouts of fly behaviour, motor function and neurodegeneration that permit an accurate assessment of neurological outcomes for the study of viral infection in fly models. Adoption of Drosophila as a valuable model system for neurological infections has and will continue to guide the discovery of many novel virus–host interactions.

Amyotrophic Lateral Sclerosis (ALS) is an incurable neurodegenerative disease characterized by the loss of cortical and spinal motor neurons. Endogenous retrovirus K (ERVK) is a genomic viral symbiont that has been associated with motor neuron loss in ALS. The ERVK integrase (IN) is an enzyme with a role in driving neuropathology and motor deficit. The primary role of the viral IN enzyme is to insert viral DNA into the host cell genome. Accumulating evidence also points to ERVK IN activity causing DNA damage and genomic instability in the host. In Drosophila, retroelement activity contributes to deregulation of the ALS risk gene TARDBP (TDP-43, TBPH in Drosophila) via DNA damage-mediated cell toxicity. This suggests a dynamic interaction between TDP-43 biology, DNA damage and retroelements. I have determined that motor disability in ERVK IN expressing Drosophila correlates with neuropathological evidence of DNA damage, inflammation, and TDP-43 aggregation. Viability and behavioral assays and the Trikinetics DAM5H monitor were used to assess motor impairment in ERVK IN expressing flies. Two FDA approved HIV integrase inhibitors were administered to determine if the progression of motor impairments could be limited. Western blot analysis was used to monitor changes in ERVK IN, ãH2AV (DNA damage marker), TDP-43, PARP1 and other related proteins over time. Pathological molecular markers were correlated with behavioural assays for motor function, to identify potential biomarkers. Establishment of this model allowed me to assess the association between ERVK IN-driven motor impairment and neuropathological outcomes. Determining the effect of integrase inhibitors in ERVK IN expressing Drosophila is a crucial step towards evaluating antivirals as a novel therapeutic strategy for the reversal of motor neuron damage and motor deficit in ALS.