Publications

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.

Abstract:

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.

Abstract:

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.

Abstract:

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

Abstract:

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

Highlights

  • 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

Summary

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.

ABSTRACT:
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

Abstract:

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.


Restoration of mitophagy ameliorates cardiomyopathy in Barth syndrome
Jun Zhang, Xueling Liu, Jia Nie, Yuguang Shi
Autophagy. 2022 Jan 5;1-16. doi: 10.1080/15548627.2021.2020979. Online ahead of print.

Abstract:

Barth syndrome (BTHS) is an X-linked genetic disorder caused by mutations in the TAFAZZIN/Taz gene which encodes a transacylase required for cardiolipin remodeling. Cardiolipin is a mitochondrial signature phospholipid that plays a pivotal role in maintaining mitochondrial membrane structure, respiration, mtDNA biogenesis, and mitophagy. Mutations in the TAFAZZIN gene deplete mature cardiolipin, leading to mitochondrial dysfunction, dilated cardiomyopathy, and premature death in BTHS patients. Currently, there is no effective treatment for this debilitating condition. In this study, we showed that TAFAZZIN deficiency caused hyperactivation of MTORC1 signaling and defective mitophagy, leading to accumulation of autophagic vacuoles and dysfunctional mitochondria in the heart of Tafazzin knockdown mice, a rodent model of BTHS. Consequently, treatment of TAFAZZIN knockdown mice with rapamycin, a potent inhibitor of MTORC1, not only restored mitophagy, but also mitigated mitochondrial dysfunction and dilated cardiomyopathy. Taken together, these findings identify MTORC1 as a novel therapeutic target for BTHS, suggesting that pharmacological restoration of mitophagy may provide a novel treatment for BTHS.


LRG1 is an adipokine that mediates obesity-induced hepatosteatosis and insulin resistance
Sijia He, Jiyoon Ryu, Juanhong Liu, Hairong Luo, Ying Lv, Paul R Langlais, Jie Wen, Feng Dong, Zhe Sun, Wenjuan Xia, Jane L Lynch, Ravindranath Duggirala, Bruce J Nicholson, Mengwei Zang, Yuguang Shi, Fang Zhang, Feng Liu, Juli Bai, Lily Q Dong.
J Clin Invest. 2021;131(24):e148545. https://doi.org/10.1172/JCI148545

Abstract:

Dysregulation in adipokine biosynthesis and function contributes to obesity-induced metabolic diseases. However, the identities and functions of many of the obesity-induced secretory molecules remain unknown. Here, we report the identification of leucine-rich alpha-2-glycoprotein 1 (LRG1) as an obesity-associated adipokine that exacerbates high fat diet–induced hepatosteatosis and insulin resistance. Serum levels of LRG1 were markedly elevated in obese humans and mice compared with their respective controls. LRG1 deficiency in mice greatly alleviated diet-induced hepatosteatosis, obesity, and insulin resistance. Mechanistically, LRG1 bound with high selectivity to the liver and promoted hepatosteatosis by increasing de novo lipogenesis and suppressing fatty acid β-oxidation. LRG1 also inhibited hepatic insulin signaling by downregulating insulin receptor substrates 1 and 2. Our study identified LRG1 as a key molecule that mediates the crosstalk between adipocytes and hepatocytes in diet-induced hepatosteatosis and insulin resistance. Suppressing LRG1 expression and function may be a promising strategy for the treatment of obesity-related metabolic diseases.


The Insulin-Sensitizer Pioglitazone Remodels Adipose Tissue Phospholipids in Humans
Juan P. Palavicini, Alberto Chavez-Velazquez, Marcel Fourcaudot, Devjit Tripathy, Meixia Pan, Luke Norton, Ralph A. DeFronzo and Christopher E. Shannon
Frontiers in Physiology, 02 December 2021 | DOI: doi.org/10.3389/fphys.2021.784391

Abstract:

The insulin-sensitizer pioglitazone exerts its cardiometabolic benefits in type 2 diabetes (T2D) through a redistribution of body fat, from ectopic and visceral areas to subcutaneous adipose depots. Whereas excessive weight gain and lipid storage in obesity promotes insulin resistance and chronic inflammation, the expansion of subcutaneous adipose by pioglitazone is associated with a reversal of these immunometabolic deficits. The precise events driving this beneficial remodeling of adipose tissue with pioglitazone remain unclear, and whether insulin-sensitizers alter the lipidomic composition of human adipose has not previously been investigated. Using shotgun lipidomics, we explored the molecular lipid responses in subcutaneous adipose tissue following 6months of pioglitazone treatment (45mg/day) in obese humans with T2D. Despite an expected increase in body weight following pioglitazone treatment, no robust effects were observed on the composition of storage lipids (i.e., triglycerides) or the content of lipotoxic lipid species (e.g., ceramides and diacylglycerides) in adipose tissue. Instead, pioglitazone caused a selective remodeling of the glycerophospholipid pool, characterized by a decrease in lipids enriched for arachidonic acid, such as plasmanylethanolamines and phosphatidylinositols. This contributed to a greater overall saturation and shortened chain length of fatty acyl groups within cell membrane lipids, changes that are consistent with the purported induction of adipogenesis by pioglitazone. The mechanism through which pioglitazone lowered adipose tissue arachidonic acid, a major modulator of inflammatory pathways, did not involve alterations in phospholipase gene expression but was associated with a reduction in its precursor linoleic acid, an effect that was also observed in skeletal muscle samples from the same subjects. These findings offer important insights into the biological mechanisms through which pioglitazone protects the immunometabolic health of adipocytes in the face of increased lipid storage.


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