A Transcriptomic Meta-Analysis Shows Lipid Metabolism Dysregulation as an Early Pathological Mechanism in the Spinal Cord of SOD1 Mice

Elevation of inositol pyrophosphate IP7 in the mammalian spinal cord of amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder associated with progressive impairment of spinal motor neurons. Continuous research endeavor is underway to fully understand the molecular mechanisms associating with this disorder. Although several studies have implied the involvement of inositol pyrophosphate IP7 in ALS, there is no direct experimental evidence proving this notion. In this study, we analyzed inositol pyrophosphate IP7 and its precursor IP6 in the mouse and human ALS biological samples to directly assess whether IP7 level and/or its metabolism are altered in ALS disease state.

Methods

We used a liquid chromatography-mass spectrometry (LC-MS) protocol originally-designed for mammalian IP6 and IP7 analysis. We measured the abundance of these molecules in the central nervous system (CNS) of ALS mouse model SOD1(G93A) transgenic (TG) mice as well as postmortem spinal cord of ALS patients. Cerebrospinal fluid (CSF) and peripheral blood mononuclear cells (PBMCs) from ALS patients were also analyzed to assess if IP7 status in these biofluids is associated with ALS disease state.

Results

SOD1(G93A) TG mice showed significant increase of IP7 level in the spinal cord compared with control mice at the late stage of disease progression, while its level in cerebrum and cerebellum remains constant. We also observed significantly elevated IP7 level and its product-to-precursor ratio (IP7/IP6) in the postmortem spinal cord of ALS patients, suggesting enhanced enzymatic activity of IP7-synthesizing kinases in the human ALS spinal cord. In contrast, human CSF did not contain detectable level of IP6 and IP7, and neither the IP7 level nor the IP7/IP6 ratio in human PBMCs differentiated ALS patients from age-matched healthy individuals.

Conclusion

By directly analyzing IP7 in the CNS of ALS mice and humans, the findings of this study provide direct evidence that IP7 level and/or the enzymatic activity of IP7-generating kinases IP6Ks are elevated in ALS spinal cord. On the other hand, this study also showed that IP7 is not suitable for biofluid-based ALS diagnosis. Further investigation is required to elucidate a role of IP7 in ALS pathology and utilize IP7 metabolism on the diagnostic application of ALS.

Regulation of cortical hyperexcitability in amyotrophic lateral sclerosis: focusing on glial mechanisms

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by the loss of both upper and lower motor neurons, resulting in muscle weakness, atrophy, paralysis, and eventually death. Motor cortical hyperexcitability is a common phenomenon observed at the presymptomatic stage of ALS. Both cell-autonomous (the intrinsic properties of motor neurons) and non-cell-autonomous mechanisms (cells other than motor neurons) are believed to contribute to cortical hyperexcitability. Decoding the pathological relevance of these dynamic changes in motor neurons and glial cells has remained a major challenge. This review summarizes the evidence of cortical hyperexcitability from both clinical and preclinical research, as well as the underlying mechanisms. We discuss the potential role of glial cells, particularly microglia, in regulating abnormal neuronal activity during the disease progression. Identifying early changes such as neuronal hyperexcitability in the motor system may provide new insights for earlier diagnosis of ALS and reveal novel targets to halt the disease progression.

Early Alterations in Structural and Functional Properties in the Neuromuscular Junctions of Mutant FUS Mice

Amyotrophic lateral sclerosis (ALS) is manifested as skeletal muscle denervation, loss of motor neurons and finally severe respiratory failure. Mutations of RNA-binding protein FUS are one of the common genetic reasons of ALS accompanied by a 'dying back' type of degeneration. Using fluorescent approaches and microelectrode recordings, the early structural and functional alterations in diaphragm neuromuscular junctions (NMJs) were studied in mutant FUS mice at the pre-onset stage. Lipid peroxidation and decreased staining with a lipid raft marker were found in the mutant mice. Despite the preservation of the end-plate structure, immunolabeling revealed an increase in levels of presynaptic proteins, SNAP-25 and synapsin 1. The latter can restrain Ca2+-dependent synaptic vesicle mobilization. Indeed, neurotransmitter release upon intense nerve stimulation and its recovery after tetanus and compensatory synaptic vesicle endocytosis were markedly depressed in FUS mice. There was a trend to attenuation of axonal [Ca2+]in increase upon nerve stimulation at 20 Hz. However, no changes in neurotransmitter release and the intraterminal Ca2+ transient in response to low frequency stimulation or in quantal content and the synchrony of neurotransmitter release at low levels of external Ca2+ were detected. At a later stage, shrinking and fragmentation of end plates together with a decrease in presynaptic protein expression and disturbance of the neurotransmitter release timing occurred. Overall, suppression of synaptic vesicle exo-endocytosis upon intense activity probably due to alterations in membrane properties, synapsin 1 levels and Ca2+ kinetics could be an early sign of nascent NMJ pathology, which leads to neuromuscular contact disorganization.

Recent Insight into the Role of Sphingosine-1-Phosphate Lyase in Neurodegeneration

Sphingosine-1-phosphate lyase (SPL) is a pyridoxal 5'-phosphate-dependent enzyme involved in the irreversible degradation of sphingosine-1-phosphate (S1P)-a bioactive sphingolipid that modulates a broad range of biological processes (cell proliferation, migration, differentiation and survival; mitochondrial functioning; and gene expression). Although SPL activity leads to a decrease in the available pool of S1P in the cell, at the same time, hexadecenal and phosphoethanolamine, compounds with potential biological activity, are generated. The increased expression and/or activity of SPL, and hence the imbalance between S1P and the end products of its cleavage, were demonstrated in several pathological states. On the other hand, loss-of-function mutations in the SPL encoding gene are a cause of severe developmental impairments. Recently, special attention has been paid to neurodegenerative diseases as the most common pathologies of the nervous system. This review summarizes the current findings concerning the role of SPL in the nervous system with an emphasis on neurodegeneration. Moreover, it briefly discusses pharmacological compounds directed to inhibit its activity.

Involvement of Lipids in the Pathogenesis of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive degeneration of upper and lower motor neurons. To study its underlying mechanisms, a variety of models are currently used at the cellular level and in animals with mutations in multiple ALS associated genes, including SOD1, C9ORF72, TDP-43, and FUS. Key mechanisms involved in the disease include excitotoxicity, oxidative stress, mitochondrial dysfunction, neuroinflammatory, and immune reactions. In addition, significant metabolism alterations of various lipids classes, including phospholipids, fatty acids, sphingolipids, and others have been increasingly recognized. Recently, the mechanisms of programmed cell death (apoptosis), which may be responsible for the degeneration of motor neurons observed in the disease, have been intensively studied. In this context, sphingolipids, which are the most important sources of secondary messengers transmitting signals for cell proliferation, differentiation, and apoptosis, are gaining increasing attention in the context of ALS pathogenesis given their role in the development of neuroinflammatory and immune responses. This review describes changes in lipids content and activity of enzymes involved in their metabolism in ALS, both summarizing current evidence from animal models and clinical studies and discussing the potential of new drugs among modulators of lipid metabolism enzymes.

Fatty acids derived from the probiotic Lacticaseibacillus rhamnosus HA-114 suppress age-dependent neurodegeneration

The human microbiota is believed to influence health. Microbiome dysbiosis may be linked to neurological conditions like Alzheimer's disease, amyotrophic lateral sclerosis, and Huntington's disease. We report the ability of a probiotic bacterial strain in halting neurodegeneration phenotypes. We show that Lacticaseibacillus rhamnosus HA-114 is neuroprotective in C. elegans models of amyotrophic lateral sclerosis and Huntington's disease. Our results show that neuroprotection from L. rhamnosus HA-114 is unique from other L. rhamnosus strains and resides in its fatty acid content. Neuroprotection by L. rhamnosus HA-114 requires acdh-1/ACADSB, kat-1/ACAT1 and elo-6/ELOVL3/6, which are associated with fatty acid metabolism and mitochondrial β-oxidation. Our data suggest that disrupted lipid metabolism contributes to neurodegeneration and that dietary intervention with L. rhamnosus HA-114 restores lipid homeostasis and energy balance through mitochondrial β-oxidation. Our findings encourage the exploration of L. rhamnosus HA-114 derived interventions to modify the progression of neurodegenerative diseases.

Deciphering lipid dysregulation in ALS: from mechanisms to translational medicine

Lipids, defined by low solubility in water and high solubility in nonpolar solvents, can be classified into fatty acids, glycerolipids, glycerophospholipids, sphingolipids, and sterols. Lipids not only regulate integrity and fluidity of biological membranes, but also serve as energy storage and bioactive molecules for signaling. Causal mutations in SPTLC1 (serine palmitoyltransferase long chain subunit 1) gene within the lipogenic pathway have been identified in amyotrophic lateral sclerosis (ALS), a paralytic and fatal motor neuron disease. Furthermore, lipid dysmetabolism within the central nervous system and circulation is associated with ALS. Here, we aim to delineate the diverse roles of different lipid classes and understand how lipid dysmetabolism may contribute to ALS pathogenesis. Among the different lipids, accumulation of ceramides, arachidonic acid, and lysophosphatidylcholine is commonly emerging  as detrimental to motor neurons. We end with exploring the potential ALS therapeutics by reducing these toxic lipids.

Singling out motor neurons in the age of single-cell transcriptomics

Motor neurons are a remarkably powerful cell type in the central nervous system. They innervate and control the contraction of virtually every muscle in the body and their dysfunction underlies numerous neuromuscular diseases. Some motor neurons seem resistant to degeneration whereas others are vulnerable. The intrinsic heterogeneity of motor neurons in adult organisms has remained elusive. The development of high-throughput single-cell transcriptomics has changed the paradigm, empowering rapid isolation and profiling of motor neuron nuclei, revealing remarkable transcriptional diversity within the skeletal and autonomic nervous systems. Here, we discuss emerging technologies for defining motor neuron heterogeneity in the adult motor system as well as implications for disease and spinal cord injury. We establish a roadmap for future applications of emerging techniques - such as epigenetic profiling, spatial RNA sequencing, and single-cell somatic mutational profiling to adult motor neurons, which will revolutionize our understanding of the healthy and degenerating adult motor system.

The Role of Sphingomyelin and Ceramide in Motor Neuron Diseases

Amyotrophic Lateral Sclerosis (ALS), Spinal Bulbar Muscular Atrophy (SBMA), and Spinal Muscular Atrophy (SMA) are motor neuron diseases (MNDs) characterised by progressive motor neuron degeneration, weakness and muscular atrophy. Lipid dysregulation is well recognised in each of these conditions and occurs prior to neurodegeneration. Several lipid markers have been shown to predict prognosis in ALS. Sphingolipids are complex lipids enriched in the central nervous system and are integral to key cellular functions including membrane stability and signalling pathways, as well as being mediators of neuroinflammation and neurodegeneration. This review highlights the metabolism of sphingomyelin (SM), the most abundant sphingolipid, and of its metabolite ceramide, and its role in the pathophysiology of neurodegeneration, focusing on MNDs. We also review published lipidomic studies in MNDs. In the 13 studies of patients with ALS, 12 demonstrated upregulation of multiple SM species and 6 demonstrated upregulation of ceramides. SM species also correlated with markers of clinical progression in five of six studies. These data highlight the potential use of SM and ceramide as biomarkers in ALS. Finally, we review potential therapeutic strategies for targeting sphingolipid metabolism in neurodegeneration.

Downstream Effects of Mutations in SOD1 and TARDBP Converge on Gene Expression Impairment in Patient-Derived Motor Neurons

Amyotrophic Lateral Sclerosis (ALS) is a progressive and fatal neurodegenerative disease marked by death of motor neurons (MNs) present in the spinal cord, brain stem and motor cortex. Despite extensive research, the reason for neurodegeneration is still not understood. To generate novel hypotheses of putative underlying molecular mechanisms, we used human induced pluripotent stem cell (hiPSCs)-derived motor neurons (MNs) from SOD1- and TARDBP (TDP-43 protein)-mutant-ALS patients and healthy controls to perform high-throughput RNA-sequencing (RNA-Seq). An integrated bioinformatics approach was employed to identify differentially expressed genes (DEGs) and key pathways underlying these familial forms of the disease (fALS). In TDP43-ALS, we found dysregulation of transcripts encoding components of the transcriptional machinery and transcripts involved in splicing regulation were particularly affected. In contrast, less is known about the role of SOD1 in RNA metabolism in motor neurons. Here, we found that many transcripts relevant for mitochondrial function were specifically altered in SOD1-ALS, indicating that transcriptional signatures and expression patterns can vary significantly depending on the causal gene that is mutated. Surprisingly, however, we identified a clear downregulation of genes involved in protein translation in SOD1-ALS suggesting that ALS-causing SOD1 mutations shift cellular RNA abundance profiles to cause neural dysfunction. Altogether, we provided here an extensive profiling of mRNA expression in two ALS models at the cellular level, corroborating the major role of RNA metabolism and gene expression as a common pathomechanism in ALS.

Apolipoprotein A1 Enhances Endothelial Cell Survival in an In Vitro Model of ALS

Altered lipoprotein metabolism is considered a pathogenic component of amyotrophic lateral sclerosis (ALS). Apolipoprotein A1 (ApoA1), a major high-density lipoprotein (HDL) protein, is associated with prevention of vascular damage. However, ApoA1's effects on damaged endothelium in ALS are unknown. This study aimed to determine therapeutic potential of ApoA1 for endothelial cell (EC) repair under a pathologic condition reminiscent of ALS. We performed in vitro studies using mouse brain ECs (mBECs) exposed to plasma from symptomatic G93A SOD1 mice. Dosage effects of ApoA1, including inhibition of the phosphoinoside 3-kinase (PI3K)/Akt signaling pathway and integration of ApoA1 into mBECs were examined. Also, human bone marrow-derived endothelial progenitor cells (hBM-EPCs) and mBECs were co-cultured without cell contact to establish therapeutic mechanism of hBM-EPC transplantation. Results showed that ApoA1 significantly reduced mBEC death via the PI3K/Akt downstream signaling pathway. Also, ApoA1 was incorporated into mBECs as confirmed by blocked ApoA1 cellular integration. Co-culture system provided evidence that ApoA1 was secreted by hBM-EPCs and incorporated into injured mBECs. Thus, our study findings provide important evidence for ApoA1 as a potential novel therapeutic for endothelium protection in ALS. This in vitro study lays the groundwork for further in vivo research to fully determine therapeutic effects of ApoA1 in ALS.

Lipid Metabolic Alterations in the ALS-FTD Spectrum of Disorders

There is an increasing interest in the study of the relation between alterations in systemic lipid metabolism and neurodegenerative disorders, in particular in Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD). In ALS these alterations are well described and evident not only with the progression of the disease but also years before diagnosis. Still, there are some discrepancies in findings relating to the causal nature of lipid metabolic alterations, partly due to the great clinical heterogeneity in ALS. ALS presentation is within a disorder spectrum with Frontotemporal Dementia (FTD), and many patients present mixed forms of ALS and FTD, thus increasing the variability. Lipid metabolic and other systemic metabolic alterations have not been well studied in FTD, or in ALS-FTD mixed forms, as has been in pure ALS. With the recent development in lipidomics and the integration with other -omics platforms, there is now emerging data that not only facilitates the identification of biomarkers but also enables understanding of the underlying pathological mechanisms. Here, we reviewed the recent literature to compile lipid metabolic alterations in ALS, FTD, and intermediate mixed forms, with a view to appraising key commonalities or differences within the spectrum.

Body Complexion and Circulating Lipids in the Risk of TDP-43 Related Disorders

Objective

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are two distinct degenerative disorders with overlapping genetics, clinical manifestations, and pathology, including the presence of TDP-43 aggregates in nearly 50% of patients with FTD and 98% of all patients with ALS. Here, we evaluate whether different genetically predicted body lipid metabolic traits are causally associated with the risk of FTD with TDP-43 aggregates, compare it to their causal role in the risk of ALS, and identify genetic variants shared between these two TDP43 related disorders in relation to lipid metabolic traits.

Methods

We conducted two-sample Mendelian randomization analyses (2SMR) to evaluate the causal association of 9 body complexion and 9 circulating lipids traits with the risk of FTD with TDP-43 aggregates and the risk of ALS. The inverse-variance weighted method was the primary analysis, followed by secondary sensitive analyses. We then looked for common genetic variants between FTD and ALS in relation to lipid metabolic traits.

Results

Genetically increased trunk-predicted mass, fat-free mass, and higher circulating triglycerides levels were suggestively associated with a higher risk of FTD with TDP-43 aggregates. Circulating lipids, mainly LDL cholesterol, were causally associated with a higher risk of ALS. We identified two genetic variants, EIF4ENIF1 and HNRNPK, in relation to body complexion and circulating lipids shared between FTD with TDP-43 aggregates and ALS.

Conclusion

This work provides evidence that body complexion and circulating lipids traits impact differentially on the risk of FTD and ALS, suggesting new and specific interventional approaches in the control of body lipid metabolism for FTD and ALS, and identified HNRNPK as a potential link between circulating lipids levels and these disorders.

Key Disease Mechanisms Linked to Amyotrophic Lateral Sclerosis in Spinal Cord Motor Neurons

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with no modifying treatments available. The molecular mechanisms underpinning disease pathogenesis are not fully understood. Recent studies have employed co-expression networks to identify key genes, known as “switch genes”, responsible for dramatic transcriptional changes in the blood of ALS patients. In this study, we directly investigate the root cause of ALS by examining the changes in gene expression in motor neurons that degenerate in patients. Co-expression networks identified in ALS patients’ spinal cord motor neurons revealed 610 switch genes in seven independent microarrays. Switch genes were enriched in several pathways, including viral carcinogenesis, PI3K-Akt, focal adhesion, proteoglycans in cancer, colorectal cancer, and thyroid hormone signaling. Transcription factors ELK1 and GATA2 were identified as key master regulators of the switch genes. Protein-chemical network analysis identified valproic acid, cyclosporine, estradiol, acetaminophen, quercetin, and carbamazepine as potential therapeutics for ALS. Furthermore, the chemical analysis identified metals and organic compounds including, arsenic, copper, nickel, and benzo(a)pyrene as possible mediators of neurodegeneration. The identification of switch genes provides insights into previously unknown biological pathways associated with ALS.

The impact of chronic stress on the PFC transcriptome: a bioinformatic meta-analysis of publicly available RNA-sequencing datasets

The prefrontal cortex (PFC) is one of several brain structures that are sensitive to chronic stress exposure. There have been several studies which have examined the effects on chronic stress, using various protocols such as chronic unpredictable stress and chronic social defeat stress, on the PFC transcriptome. In this report, a bioinformatic meta-analysis of publicly available RNA sequencing datasets (101 samples) from seven chronic stress studies was carried out to identify core PFC transcriptional signatures that underpin behavioral phenotypes including resilience and susceptibility. The results showed 160 differentially expressed genes in chronic stress mice compared to controls with significant enrichment in mechanisms associated with translation and localization of membrane-bound proteins with a putative effect on synaptic plasticity in glutamatergic neurons. Moreover, the meta-analysis revealed no differentially expressed genes in resilient mice but 144 in susceptible mice compared to controls, of which 44 were not identified in the individual studies. Enrichment analysis revealed that susceptibility genes were most affected in oligodendrocytes and linked to mechanisms which mediate biochemical, bidirectional communication between this cell-type and myelinated axons. These results provide new avenues for further research into the neurobiology and treatment of chronic stress-induced disorders.

Histone Deacetylase Inhibition Regulates Lipid Homeostasis in a Mouse Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is an incurable and fatal neurodegenerative disorder of the motor system. While the etiology is still incompletely understood, defects in metabolism act as a major contributor to the disease progression. Recently, histone deacetylase (HDAC) inhibition using ACY-738 has been shown to restore metabolic alterations in the spinal cord of a FUS mouse model of ALS, which was accompanied by a beneficial effect on the motor phenotype and survival. In this study, we investigated the specific effects of HDAC inhibition on lipid metabolism using untargeted lipidomic analysis combined with transcriptomic analysis in the spinal cord of FUS mice. We discovered that symptomatic FUS mice recapitulate lipid alterations found in ALS patients and in the SOD1 mouse model. Glycerophospholipids, sphingolipids, and cholesterol esters were most affected. Strikingly, HDAC inhibition mitigated lipid homeostasis defects by selectively targeting glycerophospholipid metabolism and reducing cholesteryl esters accumulation. Therefore, our data suggest that HDAC inhibition is a potential new therapeutic strategy to modulate lipid metabolism defects in ALS and potentially other neurodegenerative diseases.