Enhanced insulin signalling ameliorates C9orf72 hexanucleotide repeat expansion toxicity in Drosophila

A multimodal screening platform for endogenous dipeptide repeat proteins in C9orf72 patient iPSC neurons

Repeat expansions in C9orf72 are the most common cause of amyotrophic lateral sclerosis and frontotemporal dementia. Repeat-associated non-AUG (RAN) translation generates neurotoxic dipeptide repeat proteins (DPRs). To study endogenous DPRs, we inserted the minimal HiBiT luciferase reporter downstream of sense repeat derived DPRs polyGA or polyGP in C9orf72 patient iPSCs. We show these "DPReporter" lines sensitively and rapidly report DPR levels in lysed and live cells and optimize screening in iPSC neurons. Small-molecule screening showed the ERK1/2 activator periplocin dose dependently increases DPR levels. Consistent with this, ERK1/2 inhibition reduced DPR levels and prolonged survival in C9orf72 repeat expansion flies. CRISPR knockout screening of all human helicases revealed telomere-associated helicases modulate DPR expression, suggesting common regulation of telomeric and C9orf72 repeats. These DPReporter lines allow investigation of DPRs in their endogenous context and provide a template for studying endogenous RAN-translated proteins, at scale, in other repeat expansion disorders.

Differential neuronal vulnerability to C9orf72 repeat expansion driven by Xbp1-induced endoplasmic reticulum-associated degradation

Neurodegenerative diseases are characterized by the localized loss of neurons. Why cell death is triggered only in specific neuronal populations and whether it is the response to toxic insults or the initial cellular state that determines their vulnerability is unknown. To understand individual cell responses to disease, we profiled their transcriptional signatures throughout disease development in a Drosophila model of C9orf72 (G4C2) repeat expansion (C9), the most common genetic cause of frontotemporal dementia and amyotrophic lateral sclerosis. We identified neuronal populations specifically vulnerable or resistant to C9 expression and found an upregulation of protein homeostasis pathways in resistant neurons at baseline. Overexpression of Xbp1s, a key regulator of the unfolded protein response and a central node in the resistance network, rescues C9 toxicity. This study shows that neuronal vulnerability depends on the intrinsic transcriptional state of neurons and that leveraging resistant neurons' properties can boost resistance in vulnerable neurons.

Dual-targeting CRISPR-CasRx reduces C9orf72 ALS/FTD sense and antisense repeat RNAs in vitro and in vivo

The most common genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) is an intronic G4C2 repeat expansion in C9orf72. The repeats undergo bidirectional transcription to produce sense and antisense repeat RNA species, which are translated into dipeptide repeat proteins (DPRs). As toxicity has been associated with both sense and antisense repeat-derived RNA and DPRs, targeting both strands may provide the most effective therapeutic strategy. CRISPR-Cas13 systems mature their own guide arrays, allowing targeting of multiple RNA species from a single construct. We show CRISPR-Cas13d variant CasRx effectively reduces overexpressed C9orf72 sense and antisense repeat transcripts and DPRs in HEK cells. In C9orf72 patient-derived iPSC-neuron lines, CRISPR-CasRx reduces endogenous sense and antisense repeat RNAs and DPRs and protects against glutamate-induced excitotoxicity. AAV delivery of CRISPR-CasRx to two distinct C9orf72 repeat mouse models significantly reduced both sense and antisense repeat-containing transcripts. This highlights the potential of RNA-targeting CRISPR systems as therapeutics for C9orf72 ALS/FTD.

Metabolic Syndrome and Risk of Amyotrophic Lateral Sclerosis: Insights from a Large-Scale Prospective Study

OBJECTIVE

Although metabolic abnormalities are implicated in the etiology of neurodegenerative diseases, their role in the development of amyotrophic lateral sclerosis (ALS) remains a subject of controversy. We aimed to identify the association between metabolic syndrome (MetS) and the risk of ALS.

METHODS

This study included 395,987 participants from the UK Biobank to investigate the relationship between MetS and ALS. Cox regression model was used to estimate hazard ratios (HR). Stratified analyses were performed based on gender, body mass index (BMI), smoking status, and education level. Mediation analysis was conducted to explore potential mechanisms.

RESULTS

In this study, a total of 539 cases of ALS were recorded after a median follow-up of 13.7 years. Patients with MetS (defined harmonized) had a higher risk of developing ALS after adjusting for confounding factors (HR: 1.50, 95% CI: 1.19-1.89). Specifically, hypertension and high triglycerides were linked to a higher risk of ALS (HR: 1.53, 95% CI: 1.19-1.95; HR: 1.31, 95% CI: 1.06-1.61, respectively). Moreover, the quantity of metabolic abnormalities showed significant results. Stratified analysis revealed that these associations are particularly significant in individuals with a BMI <25. These findings remained stable after sensitivity analysis. Notably, mediation analysis identified potential metabolites and metabolomic mediators, including alkaline phosphatase, cystatin C, γ-glutamyl transferase, saturated fatty acids to total fatty acids percentage, and omega-6 fatty acids to omega-3 fatty acids ratio.

INTERPRETATION

MetS exhibits a robust association with an increased susceptibility to ALS, particularly in individuals with a lower BMI. Furthermore, metabolites and metabolomics, as potential mediators, provide invaluable insights into the intricate biological mechanisms. ANN NEUROL 2024;96:788-801.

Promising animal models for amyotrophic lateral sclerosis drug discovery: a comprehensive update

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motor neurons. Several animal models have been generated to understand ALS pathogenesis. They have provided valuable insight into disease mechanisms and the development of therapeutic strategies.

AREAS COVERED

In this review, the authors provide a concise overview of simple genetic model organisms, including C. elegans, Drosophila, zebrafish, and mouse genetic models that have been generated to study ALS. They emphasize the benefits of each model and their application in translational research for discovering new chemicals, gene therapy approaches, and antibody-based strategies for treating ALS.

EXPERT OPINION

Significant progress is being made in identifying new therapeutic targets for ALS. This progress is being enabled by promising animal models of the disease using increasingly effective genetic and pharmacological strategies. There are still challenges to be overcome in order to achieve improved success rates for translating drugs from animal models to clinics for treating ALS. Several promising future directions include the establishment of novel preclinical protocol standards, as well as the combination of animal models with human induced pluripotent stem cells (iPSCs).

Flight to insight: maximizing the potential of Drosophila models of C9orf72-FTD

Advancements in understanding the pathogenesis of C9orf72-associated frontotemporal dementia (C9orf72-FTD) have highlighted the role of repeat-associated non-ATG (RAN) translation and dipeptide repeat proteins (DPRs), with Drosophila melanogaster models providing valuable insights. While studies have primarily focused on RAN translation and DPR toxicity, emerging areas of investigation in fly models have expanded to neuronal dysfunction, autophagy impairment, and synaptic dysfunction, providing potential directions for new therapeutic targets and mechanisms of neurodegeneration. Despite this progress, there are still significant gaps in Drosophila models of C9orf72-FTD, namely in the areas of metabolism and circadian rhythm. Metabolic dysregulation, particularly lipid metabolism, autophagy, and insulin signaling, has been implicated in disease progression with findings from animal models and human patients with C9orf72 repeat expansions. Moreover, circadian disruptions have been observed in C9of72-FTD, with alterations in rest-activity patterns and cellular circadian machinery, suggesting a potential role in disease pathophysiology. Drosophila models offer unique opportunities to explore these aspects of C9orf72-FTD and identify novel therapeutic targets aimed at mitigating neurodegeneration.

Evidence of mitochondrial dysfunction in ALS and methods for measuring in model systems

Metabolic dysfunction is a hallmark of multiple amyotrophic lateral sclerosis (ALS) models with a majority of ALS patients exhibiting hypermetabolism. The central sites of metabolism in the cell are mitochondria, capable of utilising a multitude of cellular substrates in an array of ATP-generating reactions. With reactive oxygen species (ROS) production occurring during some of these reactions, mitochondria can contribute considerably to oxidative stress. Mitochondria are also very dynamic organelles, interacting with other organelles, undergoing fusion/fission in response to changing metabolic states and being turned over by the cell regularly. Disruptions to many of these mitochondrial functions and processes have been reported in ALS models, largely indicating compromised mitochondrial function, increased ROS production by mitochondria, disrupted interactions with the endoplasmic reticulum and reduced turnover. This chapter summarises methods routinely used to assess mitochondria in ALS models and the alterations that have been reported in these models.

Exploring the Role of Metabolic Hormones in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by progressive loss of motor neurons. Emerging evidence suggests a potential link between metabolic dysregulation and ALS pathogenesis. This study aimed to investigate the relationship between metabolic hormones and disease progression in ALS patients. A cross-sectional study was conducted involving 44 ALS patients recruited from a tertiary care center. Serum levels of insulin, total amylin, C-peptide, active ghrelin, GIP (gastric inhibitory peptide), GLP-1 active (glucagon-like peptide-1), glucagon, PYY (peptide YY), PP (pancreatic polypeptide), leptin, interleukin-6, MCP-1 (monocyte chemoattractant protein-1), and TNFα (tumor necrosis factor alpha) were measured, and correlations with ALSFRS-R, evolution scores, and biomarkers were analyzed using Spearman correlation coefficients. Subgroup analyses based on ALS subtypes, progression pattern of disease, and disease progression rate patterns were performed. Significant correlations were observed between metabolic hormones and ALS evolution scores. Insulin and amylin exhibited strong correlations with disease progression and clinical functional outcomes, with insulin showing particularly robust associations. Other hormones such as C-peptide, leptin, and GLP-1 also showed correlations with ALS progression and functional status. Subgroup analyses revealed differences in hormone levels based on sex and disease evolution patterns, with male patients showing higher amylin and glucagon levels. ALS patients with slower disease progression exhibited elevated levels of amylin and insulin. Our findings suggest a potential role for metabolic hormones in modulating ALS progression and functional outcomes. Further research is needed to elucidate the underlying mechanisms and explore the therapeutic implications of targeting metabolic pathways in ALS management.

ALSUntangled #72: Insulin

ALSUntangled reviews alternative and off-label treatments for people living with amyotrophic lateral sclerosis (PALS). Here we review insulin, which has at least one plausible mechanism for slowing ALS progression. However, pre-clinical studies are limited and there have been no trials in PALS yet. Insulin use in patients without a metabolic need may cause very serious and potentially lethal side effects. While further studies to evaluate potential benefits may be warranted, at this time we cannot endorse insulin treatment to slow ALS progression.

PolyGR and polyPR knock-in mice reveal a conserved neuroprotective extracellular matrix signature in C9orf72 ALS/FTD neurons

Dipeptide repeat proteins are a major pathogenic feature of C9orf72 amyotrophic lateral sclerosis (C9ALS)/frontotemporal dementia (FTD) pathology, but their physiological impact has yet to be fully determined. Here we generated C9orf72 dipeptide repeat knock-in mouse models characterized by expression of 400 codon-optimized polyGR or polyPR repeats, and heterozygous C9orf72 reduction. (GR)400 and (PR)400 knock-in mice recapitulate key features of C9ALS/FTD, including cortical neuronal hyperexcitability, age-dependent spinal motor neuron loss and progressive motor dysfunction. Quantitative proteomics revealed an increase in extracellular matrix (ECM) proteins in (GR)400 and (PR)400 spinal cord, with the collagen COL6A1 the most increased protein. TGF-β1 was one of the top predicted regulators of this ECM signature and polyGR expression in human induced pluripotent stem cell neurons was sufficient to induce TGF-β1 followed by COL6A1. Knockdown of TGF-β1 or COL6A1 orthologues in polyGR model Drosophila exacerbated neurodegeneration, while expression of TGF-β1 or COL6A1 in induced pluripotent stem cell-derived motor neurons of patients with C9ALS/FTD protected against glutamate-induced cell death. Altogether, our findings reveal a neuroprotective and conserved ECM signature in C9ALS/FTD.

C9orf72 proline-arginine dipeptide repeats disrupt the proteasome and perturb proteolytic activities

The hexanucleotide G4C2 repeat expansion in C9orf72 is the most frequent genetic cause of familial amyotrophic lateral sclerosis (ALS). Aberrant translation of this hexanucleotide sequence leads to production of 5 dipeptide repeats (DPRs). One of these DPRs is proline-arginine (polyPR), which is found in C9orf72-expanded ALS (C9ALS) patient brain tissue and is neurotoxic across multiple model systems. PolyPR was previously reported to bind and impair proteasomes in vitro. Nevertheless, the clinical relevance of the polyPR-proteasome interaction and its functional consequences in vivo are yet to be established. Here, we aim to confirm and functionally characterize polyPR-induced impairment of proteolysis in C9ALS patient tissue and an in vivo model system. Confocal microscopy and immunofluorescence studies on both human and Drosophila melanogaster brain tissues revealed sequestration of proteasomes by polyPR into inclusion-like bodies. Co-immunoprecipitation in D. melanogaster showed that polyPR strongly binds to the proteasome. In vivo, functional evidence for proteasome impairment is further shown by the accumulation of ubiquitinated proteins along with lysosomal accumulation and hyper-acidification, which can be rescued by a small-molecule proteasomal enhancer. Together, we provide the first clinical report of polyPR-proteasome interactions and offer in vivo evidence proposing polyPR-induced proteolytic dysfunction as a pathogenic mechanism in C9ALS.

Toxicity of C9orf72-associated dipeptide repeat peptides is modified by commonly used protein tags

Hexanucleotide repeat expansions in the C9orf72 gene are the most prevalent genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. Transcripts of the expansions are translated into toxic dipeptide repeat (DPR) proteins. Most preclinical studies in cell and animal models have used protein-tagged polyDPR constructs to investigate DPR toxicity but the effects of tags on DPR toxicity have not been systematically explored. Here, we used Drosophila to assess the influence of protein tags on DPR toxicity. Tagging of 36 but not 100 arginine-rich DPRs with mCherry increased toxicity, whereas adding mCherry or GFP to GA100 completely abolished toxicity. FLAG tagging also reduced GA100 toxicity but less than the longer fluorescent tags. Expression of untagged but not GFP- or mCherry-tagged GA100 caused DNA damage and increased p62 levels. Fluorescent tags also affected GA100 stability and degradation. In summary, protein tags affect DPR toxicity in a tag- and DPR-dependent manner, and GA toxicity might be underestimated in studies using tagged GA proteins. Thus, including untagged DPRs as controls is important when assessing DPR toxicity in preclinical models.

Repeat length of C9orf72-associated glycine-alanine polypeptides affects their toxicity

G4C2 hexanucleotide repeat expansions in a non-coding region of the C9orf72 gene are the most common cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). G4C2 insertion length is variable, and patients can carry up to several thousand repeats. Dipeptide repeat proteins (DPRs) translated from G4C2 transcripts are thought to be a main driver of toxicity. Experiments in model organisms with relatively short DPRs have shown that arginine-rich DPRs are most toxic, while polyGlycine-Alanine (GA) DPRs cause only mild toxicity. However, GA is the most abundant DPR in patient brains, and experimental work in animals has generally relied on the use of low numbers of repeats, with DPRs often tagged for in vivo tracking. Whether repeat length or tagging affect the toxicity of GA has not been systematically assessed. Therefore, we generated Drosophila fly lines expressing GA100, GA200 or GA400 specifically in adult neurons. Consistent with previous studies, expression of GA100 and GA200 caused only mild toxicity. In contrast, neuronal expression of GA400 drastically reduced climbing ability and survival of flies, indicating that long GA DPRs can be highly toxic in vivo. This toxicity could be abolished by tagging GA400. Proteomics analysis of fly brains showed a repeat-length-dependent modulation of the brain proteome, with GA400 causing earlier and stronger changes than shorter GA proteins. PolyGA expression up-regulated proteins involved in ER to Golgi trafficking, and down-regulated proteins involved in insulin signalling. Experimental down-regulation of Tango1, a highly conserved regulator of ER-to Golgi transport, partially rescued GA400 toxicity, suggesting that misregulation of this process contributes to polyGA toxicity. Experimentally increasing insulin signaling also rescued GA toxicity. In summary, our data show that long polyGA proteins can be highly toxic in vivo, and that they may therefore contribute to ALS/FTD pathogenesis in patients.

Drosophila melanogaster as a model to study autophagy in neurodegenerative diseases induced by proteinopathies

Proteinopathies are a large group of neurodegenerative diseases caused by both genetic and sporadic mutations in particular genes which can lead to alterations of the protein structure and to the formation of aggregates, especially toxic for neurons. Autophagy is a key mechanism for clearing those aggregates and its function has been strongly associated with the ubiquitin-proteasome system (UPS), hence mutations in both pathways have been associated with the onset of neurodegenerative diseases, particularly those induced by protein misfolding and accumulation of aggregates. Many crucial discoveries regarding the molecular and cellular events underlying the role of autophagy in these diseases have come from studies using Drosophila models. Indeed, despite the physiological and morphological differences between the fly and the human brain, most of the biochemical and molecular aspects regulating protein homeostasis, including autophagy, are conserved between the two species.In this review, we will provide an overview of the most common neurodegenerative proteinopathies, which include PolyQ diseases (Huntington's disease, Spinocerebellar ataxia 1, 2, and 3), Amyotrophic Lateral Sclerosis (C9orf72, SOD1, TDP-43, FUS), Alzheimer's disease (APP, Tau) Parkinson's disease (a-syn, parkin and PINK1, LRRK2) and prion diseases, highlighting the studies using Drosophila that have contributed to understanding the conserved mechanisms and elucidating the role of autophagy in these diseases.

Reduced Insulin Signaling Targeted to Serotonergic Neurons but Not Other Neuronal Subtypes Extends Lifespan in Drosophila melanogaster

Reduced Insulin/IGF-like signaling (IIS) plays an evolutionarily conserved role in improving longevity and some measures of health-span in model organisms. Recent studies, however, have found a disconnection between lifespan extension and behavioral health-span. We have previously shown that reduction of IIS in Drosophila neurons extends female lifespan but does not improve negative geotaxis senescence and has a detrimental effect on exploratory walking senescence in both sexes. We hypothesize that individual neuronal subtypes respond differently to IIS changes, thus the behavioral outcomes of pan-neuronal IIS reduction are the balance of positive, negative and neutral functional effects. In order to further understand how reduced IIS in neurons independently modulates lifespan and locomotor behavioral senescence we expressed a dominant negative Insulin receptor transgene selectively in individual neuronal subtypes and measured the effects on lifespan and two measures of locomotor senescence, negative geotaxis and exploratory walking. IIS reduction in cholinergic, GABAergic, dopaminergic, glutamatergic, and octopaminergic neurons was found to have either no affect or a detrimental effect on lifespan and locomotor senescence. However, reduction of IIS selectively in serotonergic neurons resulted in extension of lifespan in females with no effect on locomotor senescence. These data indicate that individual neuronal subtypes respond differently to IIS changes in the modulation of lifespan and locomotor senescence, and identify a specific role for the insulin receptor in serotonergic neurons in the modulation of lifespan.

Altered Bioenergetics and Metabolic Homeostasis in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that primarily affects motor neurons and causes muscle atrophy, paralysis, and death. While a great deal of progress has been made in deciphering the underlying pathogenic mechanisms, no effective treatments for the disease are currently available. This is mainly due to the high degree of complexity and heterogeneity that characterizes the disease. Over the last few decades of research, alterations to bioenergetic and metabolic homeostasis have emerged as a common denominator across many different forms of ALS. These alterations are found at the cellular level (e.g., mitochondrial dysfunction and impaired expression of monocarboxylate transporters) and at the systemic level (e.g., low BMI and hypermetabolism) and tend to be associated with survival or disease outcomes in patients. Furthermore, an increasing amount of preclinical evidence and some promising clinical evidence suggests that targeting energy metabolism could be an effective therapeutic strategy. This review examines the evidence both for and against these ALS-associated metabolic alterations and highlights potential avenues for therapeutic intervention.

Nutrient-Response Pathways in Healthspan and Lifespan Regulation

Cellular, small invertebrate and vertebrate models are a driving force in biogerontology studies. Using various models, such as yeasts, appropriate tissue culture cells, Drosophila, the nematode Caenorhabditis elegans and the mouse, has tremendously increased our knowledge around the relationship between diet, nutrient-response signaling pathways and lifespan regulation. In recent years, combinatorial drug treatments combined with mutagenesis, high-throughput screens, as well as multi-omics approaches, have provided unprecedented insights in cellular metabolism, development, differentiation, and aging. Scientists are, therefore, moving towards characterizing the fine architecture and cross-talks of growth and stress pathways towards identifying possible interventions that could lead to healthy aging and the amelioration of age-related diseases in humans. In this short review, we briefly examine recently uncovered knowledge around nutrient-response pathways, such as the Insulin Growth Factor (IGF) and the mechanistic Target of Rapamycin signaling pathways, as well as specific GWAS and some EWAS studies on lifespan and age-related disease that have enhanced our current understanding within the aging and biogerontology fields. We discuss what is learned from the rich and diverse generated data, as well as challenges and next frontiers in these scientific disciplines.

Frontotemporal Dementia and Glucose Metabolism

Frontotemporal dementia (FTD), hallmarked by antero-temporal degeneration in the human brain, is the second most common early onset dementia. FTD is a diverse disease with three main clinical presentations, four different identified proteinopathies and many disease-associated genes. The exact pathophysiology of FTD remains to be elucidated. One common characteristic all forms of FTD share is the dysregulation of glucose metabolism in patients’ brains. The brain consumes around 20% of the body’s energy supply and predominantly utilizes glucose as a fuel. Glucose metabolism dysregulation could therefore be extremely detrimental for neuronal health. Research into the association between glucose metabolism and dementias has recently gained interest in Alzheimer’s disease. FTD also presents with glucose metabolism dysregulation, however, this remains largely an unexplored area. A better understanding of the link between FTD and glucose metabolism may yield further insight into FTD pathophysiology and aid the development of novel therapeutics. Here we review our current understanding of FTD and glucose metabolism in the brain and discuss the evidence of impaired glucose metabolism in FTD. Lastly, we review research potentially suggesting a causal relationship between FTD proteinopathies and impaired glucose metabolism in FTD.

Modeling C9orf72-Related Frontotemporal Dementia and Amyotrophic Lateral Sclerosis in Drosophila

An intronic hexanucleotide (GGGGCC) expansion in the C9orf72 gene is the most common genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). In the decade following its discovery, much progress has been made in enhancing our understanding of how it precipitates disease. Both loss of function caused by reduced C9orf72 transcript levels, and gain of function mechanisms, triggered by the production of repetitive sense and antisense RNA and dipeptide repeat proteins, are thought to contribute to the toxicity. Drosophila models, with their unrivaled genetic tractability and short lifespan, have played a key role in developing our understanding of C9orf72-related FTD/ALS. There is no C9orf72 homolog in fly, and although this precludes investigations into loss of function toxicity, it is useful for elucidating mechanisms underpinning gain of function toxicity. To date there are a range of Drosophila C9orf72 models, encompassing different aspects of gain of function toxicity. In addition to pure repeat transgenes, which produce both repeat RNA and dipeptide repeat proteins (DPRs), RNA only models and DPR models have been generated to unpick the individual contributions of RNA and each dipeptide repeat protein to C9orf72 toxicity. In this review, we discuss how Drosophila models have shaped our understanding of C9orf72 gain of function toxicity, and address opportunities to utilize these models for further research.

Dysregulation of energy homeostasis in amyotrophic lateral sclerosis

PURPOSE OF REVIEW

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease targeting upper and lower motor neurons, inexorably leading to an early death. Defects in energy metabolism have been associated with ALS, including weight loss, increased energy expenditure, decreased body fat mass and increased use of lipid nutrients at the expense of carbohydrates. We review here recent findings on impaired energy metabolism in ALS, and its clinical importance.

RECENT FINDINGS

Hypothalamic atrophy, as well as alterations in hypothalamic peptides controlling energy metabolism, have been associated with metabolic derangements. Recent studies showed that mutations causing familial ALS impact various metabolic pathways, in particular mitochondrial function, and lipid and carbohydrate metabolism, which could underlie these metabolic defects in patients. Importantly, slowing weight loss, through high caloric diets, is a promising therapeutic strategy, and early clinical trials indicated that it might improve survival in at least a subset of patients. More research is needed to improve these therapeutic strategies, define pharmacological options, and refine the population of ALS patients that would benefit from these approaches.

SUMMARY

Dysfunctional energy homeostasis is a major feature of ALS clinical picture and emerges as a potential therapeutic target.

Amyotrophic lateral sclerosis (ALS) and the endocrine system: Are there any further ties to be explored?

Amyotrophic Lateral Sclerosis (ALS) belongs to the family of neurodegenerative disorders and is classified as fronto-temporal dementia (FTD), progressive muscular atrophy, primary lateral sclerosis, and pseudobulbar palsy. Even though endocrine dysfunction independently impacts the ALS-related survival rate, the complex connection between ALS and the endocrine system has not been studied in depth. Here we review earlier and recent findings on how ALS interacts with hormones a) of the hypothalamus and pituitary gland, b) the thyroid gland, c) the pancreas, d) the adipose tissue, e) the parathyroid glands, f) the bones, g) the adrenal glands, and h) the gonads (ovaries and testes). Of note, endocrine issues should always be explored in patients with ALS, especially those with low skeletal muscle and bone mass, vitamin D deficiency, and decreased insulin sensitivity (diabetes mellitus). Because ALS is a progressively deteriorating disease, addressing any potential endocrine co-morbidities in patients with this malady is quite important for decreasing the overall ALS-associated disease burden. Importantly, as this burden is estimated to increase globally in the decades to follow, in part because of an increasingly aging population, it is high time for future multi-center, multi-ethnic studies to assess the link between ALS and the endocrine system in significantly larger patient populations. Last, the psychosocial stress experienced by patients with ALS and its psycho-neuro-endocrinological sequelae, including hypothalamic-pituitaryadrenal dysregulation, should become an area of intensive study in the future.