Pathogenic tau–induced transposable element–derived dsRNA drives neuroinflammation
Elizabeth Ochoa, Paulino Ramirez, Elias Gonzalez, Jasmine De Mange, William J. Ray, Kevin F. Bieniek, and Bess Frost.
Science Advances. 6 Jan 2023. Vol 9, Issue 1. DOI: 10.1126/sciadv.abq5423
Deposition of tau protein aggregates in the brain of affected individuals is a defining feature of “tauopathies,” including Alzheimer’s disease. Studies of human brain tissue and various model systems of tauopathy report that toxic forms of tau negatively affect nuclear and genomic architecture, identifying pathogenic tau–induced heterochromatin decondensation and consequent retrotransposon activation as a causal mediator of neurodegeneration. On the basis of their similarity to retroviruses, retrotransposons drive neuroinflammation via toxic intermediates, including double-stranded RNA (dsRNA). We find that dsRNA and dsRNA sensing machinery are elevated in astrocytes of postmortem brain tissue from patients with Alzheimer’s disease and progressive supranuclear palsy and in brains of tau transgenic mice. Using a Drosophila model of tauopathy, we identify specific tau-induced retrotransposons that form dsRNA and find that pathogenic tau and heterochromatin decondensation causally drive dsRNA-mediated neurodegeneration and neuroinflammation. Our study suggests that pathogenic tau–induced heterochromatin decondensation and retrotransposon activation cause elevation of inflammatory, transposable element–derived dsRNA in the adult brain.
Sulfatide Deficiency, an Early Alzheimer’s Lipidomic Signature, Causes Brain Ventricular Enlargement in the Absence of Classical Neuropathological Hallmarks
Juan Pablo Palavicini, Lin Ding, Meixia Pan, Shulan Qiu, Hu Wang, Qiang Shen, Jeffrey L. Dupree, and Xianlin Han
International Journal of Molecular Sciences, 2023, 24(1), 233; https://doi.org/10.3390/ijms24010233
Alzheimer’s disease (AD) is a neurodegenerative disease characterized by progressive memory loss and a decline in activities of daily life. Ventricular enlargement has been associated with worse performance on global cognitive tests and AD. Our previous studies demonstrated that brain sulfatides, myelin-enriched lipids, are dramatically reduced in subjects at the earliest clinically recognizable AD stages via an apolipoprotein E (APOE)-dependent and isoform-specific process. Herein, we provided pre-clinical evidence that sulfatide deficiency is causally associated with brain ventricular enlargement. Specifically, taking advantage of genetic mouse models of global and adult-onset sulfatide deficiency, we demonstrated that sulfatide losses cause ventricular enlargement without significantly affecting hippocampal or whole brain volumes using histological and magnetic resonance imaging approaches. Mild decreases in sulfatide content and mild increases in ventricular areas were also observed in human APOE4 compared to APOE2 knock-in mice. Finally, we provided Western blot and immunofluorescence evidence that aquaporin-4, the most prevalent aquaporin channel in the central nervous system (CNS) that provides fast water transportation and regulates cerebrospinal fluid in the ventricles, is significantly increased under sulfatide-deficient conditions, while other major brain aquaporins (e.g., aquaporin-1) are not altered. In short, we unraveled a novel and causal association between sulfatide deficiency and ventricular enlargement. Finally, we propose putative mechanisms by which sulfatide deficiency may induce ventricular enlargement.
Keywords: sulfatide; cerebroside sulfotransferase; ventricular enlargement; Alzheimer’s disease; brain MRI; aquaporins
Effect of acute TLR4 inhibition on insulin resistance in human subjects
Hanyu Liang, Nattapol Sathavarodom, Claudia Colmenares, Jonathan Gelfond, Sara E Espinoza, Vinutha Ganapathy, Nicolas Musi.
J Clin Invest. 2022 Sep 6;e162291. doi: 10.1172/JCI162291. Online ahead of print.
Background: Studies in cell cultures and rodents suggest that toll-like receptor (TLR)4 is involved in the pathogenesis of insulin resistance, but direct data in humans are limited. We tested the hypothesis that pharmacologic blockade of TLR4 with the competitive inhibitor eritoran would improve insulin resistance in humans.
Methods: In Protocol I, 10 lean, healthy subjects received the following 72-h intravenous (I.V.) infusions in a randomized crossover design: saline (30 ml/h)+vehicle; Intralipid® (30 ml/h)+vehicle; or Intralipid® (30 ml/h)+eritoran (12 mg I.V. every 12 h). In Protocol II, 9 obese, non-diabetic subjects received eritoran (12 mg I.V. every 12 h) or vehicle for 72 h, also in a randomized crossover design. The effects of eritoran were assessed with a euglycemic, hyperinsulinemic clamp.
Results: In Protocol I, lipid infusion significantly decreased peripheral insulin sensitivity (M value) by 14% and increased fasting plasma glucose (FPG), fasting plasma insulin (FPI) and HOMA insulin resistance index (HOMA-IR) by 7%, 22%, and 26%, respectively. Eritoran did not prevent lipid-induced alterations in these metabolic parameters. Eritoran also failed to improve any baseline metabolic parameters (M, FPG, FPI, HOMA-IR) in obese, insulin-resistant subjects (Protocol II).
Conclusions: Acute TLR4 inhibition with eritoran did not protect against lipid-induced insulin resistance. Short-term eritoran administration also failed to improve obesity-associated insulin resistance. These data do not support a role for TLR4 in insulin resistance. Future studies with a different class of TLR4 inhibitors, longer drug exposure, and/or lipid-enhancing interventions richer in saturated fats may be needed to further clarify the role of TLR4 on metabolic dysfunction in humans.
Clinicaltrials: gov NCT02321111, NCT02267317FUNDING. NIH grants R01DK080157, P30AG044271, P30AG013319 and UL1TR002645.
Keywords: Diabetes; Endocrinology; Metabolism; Obesity.
Pharmacological inhibition of ALCAT1 mitigates amyotrophic lateral sclerosis by attenuating SOD1 protein aggregation
Xueling Liu, Jun Zhang, Jie Li, Chengjie Song, and Yuguang Shi
Molecular Metabolism. 2022 Sep;63:101536. doi: 10.1016/j.molmet.2022.101536. Epub 2022 Jun 28.
Objective: Mutations in the copper-zinc superoxide dismutase (SOD1) gene cause familial amyotrophic lateral sclerosis (ALS), a progressive fatal neuromuscular disease characterized by motor neurons death and severe skeletal muscle degeneration. However, there is no effective treatment for this debilitating disease, since the underlying cause for the pathogenesis remains poorly understood. Here, we investigated a role of acyl-CoA:lysocardiolipin acyltransferase 1 (ALCAT1), an acyltransferase that promotes mitochondrial dysfunction in age-related diseases by catalyzing pathological remodeling of cardiolipin, in promoting the development of ALS in the SOD1G93A transgenic mice.
Methods: Using SOD1G93A transgenic mice with targeted deletion of the ALCAT1 gene and treated with Dafaglitapin (Dafa), a very potent and highly selective ALCAT1 inhibitor, we determined whether ablation or pharmaceutical inhibition of ALCAT1 by Dafa would mitigate ALS and the underlying pathogenesis by preventing pathological remodeling of cardiolipin, oxidative stress, and mitochondrial dysfunction by multiple approaches, including lifespan analysis, behavioral tests, morphological and functional analysis of skeletal muscle, electron microscopic and Seahorse analysis of mitochondrial morphology and respiration, western blot analysis of the SOD1G93A protein aggregation, and lipidomic analysis of cardiolipin content and acyl composition in mice spinal cord.
Results: ALCAT1 protein expression is potently upregulated in the skeletal muscle of the SOD1G93A mice. Consequently, ablation or pharmacological inhibition of ALCAT1 by Dafa attenuates motor neuron dysfunction, neuronal inflammation, and skeletal muscle atrophy in SOD1G93A mice by preventing SOD1G93A protein aggregation, mitochondrial dysfunction, and pathological CL remodeling, leading to moderate extension of lifespan in the SOD1G93A transgenic mice.
Conclusions: ALCAT1 promotes the development of ALS by linking SOD1G93A protein aggregation to mitochondrial dysfunction, implicating Dafa as a potential treatment for this debilitating disorder.
Keywords: ALS; Cardiolipin; Mitochondrial dysfunction; Neuronal inflammation; SOD1 aggregation.
De novo labeling and trafficking of individual lipid species in live cells
Jun Zhang, Jia Nie, Haoran Sun, Jie Li, John-Paul Andersen, and Yuguang Shi
Molecular metabolism. 2022 Jul;61:101511. doi: 10.1016/j.molmet.2022.101511.
Objective: Lipids exert dynamic biological functions which are determined both by their fatty acyl compositions and spatiotemporal distributions inside the cell. However, it remains a daunting task to investigate any of these features for each of the more than 1000 lipid species due to a lack of a universal labeling method for individual lipid moieties in live cells. Here we report a de novo lipid labeling method for individual lipid species with precise acyl compositions in live cells. The method is based on the principle of de novo lipid remodeling of exogenously added lysolipids with fluorescent acyl-CoA, leading to the re-synthesis of fluorescence-labeled lipids which can be imaged by confocal microscopy.
Methods: The cells were incubated with lysolipids and a nitro-benzoxadiazolyl (NBD) labeled acyl-CoA. The newly remodeled NBD-labeled lipids and their subcellular localization were analyzed by confocal imaging in live cells. Thin layer chromatography was carried out to verify the synthesis of NBD-labeled lipids. The mitochondrial trafficking of NBD-labeled lipids was validated in live cells with targeted deletion of phospholipids transporters, including TRIAP1/PRELI protein complex and StarD7.
Results: Incubation cells with lysolipids and NBD-acyl-CoA successfully labeled major lipid species with precise acyl compositions, including phospholipids, cholesterol esters, and neutral lipids, which can be analyzed by confocal imaging in live cells. In contrast to exogenously labeled lipids, the de novo labeled lipids retained full biological properties of their endogenous counterparts, including subcellular localization, trafficking, and recognition by lipid transporters. This method also uncovered some unexpected features of newly remodeled lipids and their transporters.
Conclusions: The de novo lipid labeling method not only provides a powerful tool for functional analysis of individual lipid species and lipid transporters, but also calls for re-evaluation of previously published results using exogenously labeled lipids.
Keywords: Lipid remodeling; Lipid trafficking; NBD; Phospholipid transporters.
In Search of the Holy Grail: Toward a Unified Hypothesis on Mitochondrial Dysfunction in Age-related Diseases
Jun Zhang and Yuguang Shi
Cells. 2022 Jun 12;11(12):1906. doi: 10.3390/cells11121906.
Cardiolipin (CL) is a mitochondrial signature phospholipid that plays a pivotal role in mitochondrial dynamics, membrane structure, oxidative phosphorylation, mtDNA bioenergetics, and mitophagy. The depletion or abnormal acyl composition of CL causes mitochondrial dysfunction, which is implicated in the pathogenesis of aging and age-related disorders. However, the molecular mechanisms by which mitochondrial dysfunction causes age-related diseases remain poorly understood. Recent development in the field has identified acyl-CoA:lysocardiolipin acyltransferase 1 (ALCAT1), an acyltransferase upregulated by oxidative stress, as a key enzyme that promotes mitochondrial dysfunction in age-related diseases. ALCAT1 catalyzes CL remodeling with very-long-chain polyunsaturated fatty acids, such as docosahexaenoic acid (DHA). Enrichment of DHA renders CL highly sensitive to oxidative damage by reactive oxygen species (ROS). Oxidized CL becomes a new source of ROS in the form of lipid peroxides, leading to a vicious cycle of oxidative stress, CL depletion, and mitochondrial dysfunction. Consequently, ablation or the pharmacological inhibition of ALCAT1 have been shown to mitigate obesity, type 2 diabetes, heart failure, cardiomyopathy, fatty liver diseases, neurodegenerative diseases, and cancer. The findings suggest that age-related disorders are one disease (aging) manifested by different mitochondrion-sensitive tissues, and therefore should be treated as one disease. This review will discuss a unified hypothesis on CL remodeling by ALCAT1 as the common denominator of mitochondrial dysfunction, linking mitochondrial dysfunction to the development of age-related diseases.
Keywords: ALCAT1; age-related diseases; aging; cardiolipin; mitochondrial dysfunction.
Tau-induced deficits in nonsense-mediated mRNA decay contribute to neurodegeneration
Gabrielle Zuniga, Simon Levy, Paulino Ramirez, Jasmine De Mange, Elias Gonzalez, Maria Gamez, Bess Frost.
Alzheimer’s & Dementia. 2022 Apr 13;1-16. https://doi.org/10.1002/alz.12653
Introduction: While brains of patients with Alzheimer’s disease and related tauopathies have evidence of altered RNA processing, we lack a mechanistic understanding of how altered RNA processing arises in these disorders and if such changes are causally linked to neurodegeneration.
Methods: Using Drosophila melanogaster models of tauopathy, we find that overall activity of nonsense-mediated mRNA decay (NMD), a key RNA quality-control mechanism, is reduced. Genetic manipulation of NMD machinery significantly modifies tau-induced neurotoxicity, suggesting that deficits in NMD are causally linked to neurodegeneration. Mechanistically, we find that deficits in NMD are a consequence of aberrant RNA export and RNA accumulation within nuclear envelope invaginations in tauopathy. We identify a pharmacological activator of NMD that suppresses neurodegeneration in tau transgenic Drosophila, indicating that tau-induced deficits in RNA quality control are druggable.
Discussion: Our studies suggest that NMD activators should be explored for their potential therapeutic value to patients with tauopathies.
Keywords: Alzheimer’s disease, Drosophila, neurodegeneration, nonsense-mediated mRNA decay, nucleus, tauopathy
Deadenylase-dependent mRNA decay of GDF15 and FGF21 orchestrates food intake and energy expenditure
Sakie Katsumura, Nadeem Siddiqui, Michael Rock Goldsmith, Jaime H. Cheah, Teppei Fujikawa, Genki Minegishi, Atsushi Yamagata, Yukako Yabuki, Kaoru Kobayashi, Mikako Shirouzu, Takeshi Inagaki, Tim H.-M. Huang, Nicolas Musi, Ivan Topisirovic, Ola Larsson, Masahiro Morita.
Cell Metabolism. 34, 564–580, 5 April 2022. https://doi.org/10.1016/j.cmet.2022.03.005
- Hepatic CNOT6L controls food intake, energy expenditure, and fat utilization
- Gdf15 and Fgf21 mRNAs are degraded by CNOT6L deadenylase in response to stimuli
- GDF15 and FGF21 mediate the CNOT6L effects on food intake and energy expenditure
- Targeting CNOT6L has a therapeutic potential to treat diet-induced metabolic disorders
Hepatokines, secretory proteins from the liver, mediate inter-organ communication to maintain a metabolic balance between food intake and energy expenditure. However, molecular mechanisms by which hepatokine levels are rapidly adjusted following stimuli are largely unknown. Here, we unravel how CNOT6L deadenylase switches off hepatokine expression after responding to stimuli (e.g., exercise and food) to orchestrate energy intake and expenditure. Mechanistically, CNOT6L inhibition stabilizes hepatic Gdf15 and Fgf21 mRNAs, increasing corresponding serum protein levels. The resulting upregulation of GDF15 stimulates the hindbrain to suppress appetite, while increased FGF21 affects the liver and adipose tissues to induce energy expenditure and lipid consumption. Despite the potential of hepatokines to treat metabolic disorders, their administration therapies have been challenging. Using small-molecule screening, we identified a CNOT6L inhibitor enhancing GDF15 and FGF21 hepatokine levels, which dramatically improves diet-induced metabolic syndrome. Our discovery, therefore, lays the foundation for an unprecedented strategy to treat metabolic syndrome.
Keywords: hepatokine; GDF15; FGF21; mRNA degradation; CCR4-NOT deadenylase complex; inter-organ communication; food intake; energy expenditure; metabolic syndrome
Metabolic benefits of methionine restriction in adult mice do not require functional methionine sulfoxide reductase A (MsrA)
Kevin M. Thyne, Adam B. Salmon
Scientific Reports. 2022 Mar 24;12(1):5073. doi: 10.1038/s41598-022-08978-4.
Methionine restriction (MR) extends lifespan and improves several markers of health in rodents. However, the proximate mechanisms of MR on these physiological benefits have not been fully elucidated. The essential amino acid methionine plays numerous biological roles and limiting its availability in the diet directly modulates methionine metabolism. There is growing evidence that redox regulation of methionine has regulatory control on some aspects of cellular function but interactions with MR remain largely unexplored. We tested the functional role of the ubiquitously expressed methionine repair enzyme methionine sulfoxide reductase A (MsrA) on the metabolic benefits of MR in mice. MsrA catalytically reduces both free and protein-bound oxidized methionine, thus playing a key role in its redox state. We tested the extent to which MsrA is required for metabolic effects of MR in adult mice using mice lacking MsrA. As expected, MR in control mice reduced body weight, altered body composition, and improved glucose metabolism. Interestingly, lack of MsrA did not impair the metabolic effects of MR on these outcomes. Moreover, females had blunted MR responses regardless of MsrA status compared to males. Overall, our data suggests that MsrA is not required for the metabolic benefits of MR in adult mice.
Redox regulation of age-associated defects in generation and maintenance of T cell self-tolerance and immunity to foreign antigens
Allison K. Hester, Manpreet K. Semwal, Sergio Cepeda, Yangming Xiao, Meghan Rueda, Kymberly Wimberly, Thomas Venables, Thamotharampillai Dileepan, Ellen Kraig, Ann V. Griffith.
Cell Reports. 2022 Feb 15;38(7):110363. https://doi.org/10.1016/j.celrep.2022.110363
Thymic atrophy reduces naive T cell production and contributes to increased susceptibility to viral infection with age. Expression of tissue-restricted antigen (TRA) genes also declines with age and has been thought to increase autoimmune disease susceptibility. We find that diminished expression of a model TRA gene in aged thymic stromal cells correlates with impaired clonal deletion of cognate T cells recognizing an autoantigen involved in atherosclerosis. Clonal deletion in the polyclonal thymocyte population is also perturbed. Distinct age-associated defects in the generation of antigen-specific T cells include a conspicuous decline in generation of T cells recognizing an immunodominant influenza epitope. Increased catalase activity delays thymic atrophy, and here, we show that it mitigates declining production of influenza-specific T cells and their frequency in lung after infection, but does not reverse declines in TRA expression or efficient negative selection. These results reveal important considerations for strategies to restore thymic function.
Keywords: autoimmunity; central tolerance; immunosenescence; thymus.