A Drosophila model of Friedreich ataxia with CRISPR/Cas9 insertion of GAA repeats in the frataxin gene reveals in vivo protection by N-acetyl cysteine

Machine Learning Scoring Reveals Increased Frequency of Falls Proximal to Death in Drosophila melanogaster

Falls are a significant cause of human disability and death. Risk factors include normal aging, neurodegenerative disease, and sarcopenia. Drosophila melanogaster is a powerful model for study of normal aging and for modeling human neurodegenerative disease. Aging-associated defects in Drosophila climbing ability have been observed to be associated with falls, and immobility due to a fall is implicated as one cause of death in old flies. An automated method for quantifying Drosophila falls might facilitate the study of causative factors and possible interventions. Here, machine learning methods were developed to identify Drosophila falls in video recordings of 2D movement trajectories. The study employed existing video of aged flies as they approached death, and young flies subjected to lethal dehydration/starvation stress. Approximately 9 000 frames of video were manually annotated using open-source tools and used as the training set for You Only Look Once (YOLOv4) software. The software was tested on specific hours within a 22 hour video that was originally manually annotated for number of falls per hour and corresponding timestamps. The model predictions were evaluated against the manually-annotated ground truth, revealing a strong correlation between the predicted and actual falls. The frequency of falls per hour increased dramatically 2-4 hours prior to death caused by dehydration/starvation stress, whereas extended periods of increased falls were observed in aged flies prior to death. This automated method effectively quantifies falls in video data without observer bias, providing a robust tool for future studies aimed at understanding causative factors and testing potential interventions.

Network analysis and in vivo experiments reveal the therapeutic mechanisms of total ginsenosides in a Drosophila model of ulcerative colitis

Gut homeostasis is critical for human health, ulcerative colitis (UC) can disrupt gut homeostasis and cause disease. Panax ginseng C.A. Meyer is a widely used traditional herbal medicine known for its anti-inflammatory, antioxidant, and immunomodulatory effects. However, the protective mechanisms of total ginsenosides (TG) in treating UC remain unclear. In this study, we employed Drosophila melanogaster as a model organism to investigate the protective effects of TG on dextran sulfate sodium (DSS)-induced intestinal injury. Our data showed that TG significantly improved survival rates in female flies, restored intestinal length, maintained intestinal barrier integrity, and alleviated oxidative stress. Additionally, TG may protect against intestinal damage by activating the PI3K/Akt signaling pathway and inhibiting the JAK/STAT signaling pathway. These findings suggest that TG alleviates UC symptoms through multi-target regulation, highlighting its potential for developing novel therapeutic strategies for UC.

The impact of cysteine on lifespan in three model organisms: A systematic review and meta-analysis

Cysteine is an amino acid present in thiol proteins and often dictates their secondary structures. Although considered nonessential, cysteine may be essential for patients with certain metabolic diseases and can reduce the requirement for dietary methionine. Cysteine and some of its derivatives, such as N-acetylcysteine, are considered antioxidants and widely used in animal aging studies. To provide insights into the potential anti-aging effects of cysteine, we systematically reviewed and performed a meta-analysis to investigate the impact of cysteine supplementation on lifespan using three model organisms: mice, nematodes, and fruit flies. A total of 13 mouse studies, 13 C. elegans studies, and 5 Drosophila studies were included in the analysis. The findings revealed that cysteine supplementation significantly reduced the risk of mortality in mice and C. elegans. Subgroup analysis showed consistent results across different starting times and administration methods and revealed adverse effects of high doses on worms and a lack of effect in nondisease mouse models. Similar to mice, the effects of cysteine supplementation on Drosophila were not statistically significant, except in transgenic flies. The study identified certain limitations, including the quality of the included studies and the potential for publication bias. We also discussed uncertainties in the underlying molecular mechanisms and the clinical application of dietary cysteine.

Decoding Nucleotide Repeat Expansion Diseases: Novel Insights from Drosophila melanogaster Studies

Drosophila melanogaster usage has provided substantial insights into the pathogenesis of several nucleotide repeat expansion diseases (NREDs), a group of genetic diseases characterized by the abnormal expansion of DNA repeats. Leveraging the genetic simplicity and manipulability of Drosophila, researchers have successfully modeled close to 15 NREDs such as Huntington's disease (HD), several spinocerebellar ataxias (SCA), and myotonic dystrophies type 1 and 2 (DM1/DM2). These models have been instrumental in characterizing the principal associated molecular mechanisms: protein aggregation, RNA toxicity, and protein function loss, thus recapitulating key features of human disease. Used in chemical and genetic screenings, they also enable us to identify promising small molecules and genetic modifiers that mitigate the toxic effects of expanded repeats. This review summarizes the close to 150 studies performed in this area during the last seven years. The relevant highlights are the achievement of the first fly-based models for some NREDs, the incorporation of new technologies such as CRISPR for developing or evaluating transgenic flies containing repeat expanded motifs, and the evaluation of less understood toxic mechanisms in NREDs such as RAN translation. Overall, Drosophila melanogaster remains a powerful platform for research in NREDs.

Animal models of neuropathic pain

Animal models continue to be crucial to developing our understanding of the molecular, cellular, and neurophysiological mechanisms that lead to neuropathic pain. The overwhelming majority of animal studies use rodent models, ranging from surgical and trauma-induced models to those induced by metabolic diseases, genetic mutations, viruses, neurotoxic drugs, and cancer. We discuss the clinical relevance of the available models and the pain behavior tests commonly used as outcome measures. Finally, we summarize the refinements that have been proposed to improve the ability of animal model studies to predict clinical efficacy.

Glial overexpression of Tspo extends lifespan and protects against frataxin deficiency in Drosophila

The translocator protein TSPO is an evolutionary conserved mitochondrial protein overexpressed in various contexts of neurodegeneration. Friedreich Ataxia (FA) is a neurodegenerative disease due to GAA expansions in the FXN gene leading to decreased expression of frataxin, a mitochondrial protein involved in the biosynthesis of iron-sulfur clusters. We previously reported that Tspo was overexpressed in a Drosophila model of this disease generated by CRISPR/Cas9 insertion of approximately 200 GAA in the intron of fh, the fly frataxin gene. Here, we describe a new Drosophila model of FA with 42 GAA repeats, called fh-GAAs. The smaller expansion size allowed to obtain adults exhibiting hallmarks of the FA disease, including short lifespan, locomotory defects and hypersensitivity to oxidative stress. The reduced lifespan was fully rescued by ubiquitous expression of human FXN, confirming that both frataxins share conserved functions. We observed that Tspo was overexpressed in heads and decreased in intestines of these fh-GAAs flies. Then, we further overexpressed Tspo specifically in glial cells and observed improved survival. Finally, we investigated the effects of Tspo overexpression in healthy flies. Increased longevity was conferred by glial-specific overexpression, with opposite effects in neurons. Overall, this study highlights protective effects of glial TSPO in Drosophila both in a neurodegenerative and a healthy context.

Recent Advances in the Elucidation of Frataxin Biochemical Function Open Novel Perspectives for the Treatment of Friedreich’s Ataxia

Friedreich’s ataxia (FRDA) is the most prevalent autosomic recessive ataxia and is associated with a severe cardiac hypertrophy and less frequently diabetes. It is caused by mutations in the gene encoding frataxin (FXN), a small mitochondrial protein. The primary consequence is a defective expression of FXN, with basal protein levels decreased by 70–98%, which foremost affects the cerebellum, dorsal root ganglia, heart and liver. FXN is a mitochondrial protein involved in iron metabolism but its exact function has remained elusive and highly debated since its discovery. At the cellular level, FRDA is characterized by a general deficit in the biosynthesis of iron-sulfur (Fe-S) clusters and heme, iron accumulation and deposition in mitochondria, and sensitivity to oxidative stress. Based on these phenotypes and the proposed ability of FXN to bind iron, a role as an iron storage protein providing iron for Fe-S cluster and heme biosynthesis was initially proposed. However, this model was challenged by several other studies and it is now widely accepted that FXN functions primarily in Fe-S cluster biosynthesis, with iron accumulation, heme deficiency and oxidative stress sensitivity appearing later on as secondary defects. Nonetheless, the biochemical function of FXN in Fe-S cluster biosynthesis is still debated. Several roles have been proposed for FXN: iron chaperone, gate-keeper of detrimental Fe-S cluster biosynthesis, sulfide production stimulator and sulfur transfer accelerator. A picture is now emerging which points toward a unique function of FXN as an accelerator of a key step of sulfur transfer between two components of the Fe-S cluster biosynthetic complex. These findings should foster the development of new strategies for the treatment of FRDA. We will review here the latest discoveries on the biochemical function of frataxin and the implication for a potential therapeutic treatment of FRDA.

Neuroinflammation in the Cerebellum and Brainstem in Friedreich Ataxia: An [18 F]-FEMPA PET Study

BACKGROUND

Neuroinflammation is proposed to accompany, or even contribute to, neuropathology in Friedreich ataxia (FRDA), with implications for disease treatment and tracking.

OBJECTIVES

To examine brain glial activation and systemic immune dysfunction in people with FRDA and quantify their relationship with symptom severity, duration, and onset age.

METHODS

Fifteen individuals with FRDA and 13 healthy controls underwent brain positron emission tomography using the translocator protein (TSPO) radioligand [¹⁸ F]-FEMPA, a marker of glial activation, together with the quantification of blood plasma inflammatory cytokines.

RESULTS

[¹⁸ F]-FEMPA binding was significantly increased in the dentate nuclei (d = 0.67), superior cerebellar peduncles (d = 0.74), and midbrain (d = 0.87), alongside increased plasma interleukin-6 (IL-6) (d = 0.73), in individuals with FRDA compared to controls. Increased [¹⁸ F]-FEMPA binding in the dentate nuclei, brainstem, and cerebellar anterior lobe correlated with earlier age of symptom onset (controlling for the genetic triplet repeat expansion length; all r_part  < -0.6), and in the pons and anterior lobe with shorter disease duration (r = -0.66; -0.73).

CONCLUSIONS

Neuroinflammation is evident in brain regions implicated in FRDA neuropathology. Increased neuroimmune activity may be related to earlier disease onset and attenuate over the course of the illness. © 2021 International Parkinson and Movement Disorder Society.

Molecular Defects in Friedreich's Ataxia: Convergence of Oxidative Stress and Cytoskeletal Abnormalities

Friedreich’s ataxia (FRDA) is a multi-faceted disease characterized by progressive sensory–motor loss, neurodegeneration, brain iron accumulation, and eventual death by hypertrophic cardiomyopathy. FRDA follows loss of frataxin (FXN), a mitochondrial chaperone protein required for incorporation of iron into iron–sulfur cluster and heme precursors. After the discovery of the molecular basis of FRDA in 1996, over two decades of research have been dedicated to understanding the temporal manifestations of disease both at the whole body and molecular level. Early research indicated strong cellular iron dysregulation in both human and yeast models followed by onset of oxidative stress. Since then, the pathophysiology due to dysregulation of intracellular iron chaperoning has become central in FRDA relative to antioxidant defense and run-down in energy metabolism. At the same time, limited consideration has been given to changes in cytoskeletal organization, which was one of the first molecular defects noted. These alterations include both post-translational oxidative glutathionylation of actin monomers and differential DNA processing of a cytoskeletal regulator PIP5K1β. Currently unknown in respect to FRDA but well understood in the context of FXN-deficient cell physiology is the resulting impact on the cytoskeleton; this disassembly of actin filaments has a particularly profound effect on cell–cell junctions characteristic of barrier cells. With respect to a neurodegenerative disorder such as FRDA, this cytoskeletal and tight junction breakdown in the brain microvascular endothelial cells of the blood–brain barrier is likely a component of disease etiology. This review serves to outline a brief history of this research and hones in on pathway dysregulation downstream of iron-related pathology in FRDA related to actin dynamics. The review presented here was not written with the intent of being exhaustive, but to instead urge the reader to consider the essentiality of the cytoskeleton and appreciate the limited knowledge on FRDA-related cytoskeletal dysfunction as a result of oxidative stress. The review examines previous hypotheses of neurodegeneration with brain iron accumulation (NBIA) in FRDA with a specific biochemical focus.