bims-celmim 2023-07-30 papers

bims-celmim

Biomed News

on Cellular and mitochondrial metabolism

Issue of 2023–07–30
twenty-two papers selected by
Marc Segarra Mondejar, University of Cologne

A transient increase of HIF-1α during the G1 phase (G1-HIF) ensures cell survival under nutritional stress.
Alkaline intracellular pH (pHi) increases PI3K kinase activity to promote mTORC1 and mTORC2 signaling and function during growth factor limitation.
A GSTP1-mediated lactic acid signaling promotes tumorigenesis through the PPP oxidative branch.
Glucose Transporter-2 Regulation of Male versus Female Hypothalamic Astrocyte MAPK Expression and Activation: Impact of Glucose.
ENO1 promotes liver carcinogenesis through YAP1-dependent arachidonic acid metabolism.
AMPKγ3 controls muscle glucose uptake in recovery from exercise to recapture energy stores.
CD38 Inhibition Protects Fructose-Induced Toxicity in Primary Hepatocytes.
Linking ROS Levels to Autophagy: The Key Role of AMPK.
PGAM5 is an MFN2 phosphatase that plays an essential role in the regulation of mitochondrial dynamics.
The Role of Mitochondrial Dynamics and Mitotic Fission in Regulating the Cell Cycle in Cancer and Pulmonary Arterial Hypertension: Implications for Dynamin-Related Protein 1 and Mitofusin2 in Hyperproliferative Diseases.
Metformin Alleviates Sepsis-associated Myocardial Injury by Enhancing AMPK/mTOR Signaling Pathway-mediated Autophagy.
The Metabolic Basis for Nervous System Dysfunction in Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease.
Glucose Inhibits Yeast AMPK (Snf1) by Three Independent Mechanisms.
Impaired Insulin Signaling Mediated by the Small GTPase Rac1 in Skeletal Muscle of the Leptin-Deficient Obese Mouse.
Regulation of mTOR Signaling: Emerging Role of Cyclic Nucleotide-Dependent Protein Kinases and Implications for Cardiometabolic Disease.
Matrix metalloproteinase-2 proteolyzes mitofusin-2 and impairs mitochondrial function during myocardial ischemia-reperfusion injury.
A Medium Chain Fatty Acid, 6-hydroxyhexanoic acid (6-HHA), Protects Against Obesity and Insulin Resistance.
SIRT3 ameliorates diabetes-associated cognitive dysfunction via regulating mitochondria-associated ER membranes.
TRPV4-mediated mitochondrial dysfunction induces pyroptosis and cartilage degradation in osteoarthritis via the Drp1-HK2 axis.
Ketogenic diet and β-Hydroxybutyrate alleviate ischemic brain injury in mice via an IRAKM-dependent pathway.
Glucocorticoid enhances presenilin1-dependent Aβ production at ER's mitochondrial-associated membrane by downregulating Rer1 in neuronal cells.
Nutritional stress-induced regulation of microtubule organization and mRNP transport by HDAC1 controlled α-tubulin acetylation.

Cell Death Dis. 2023 Jul 27. 14(7): 477

A transient increase of HIF-1α during the G1 phase (G1-HIF) ensures cell survival under nutritional stress.

Ratnal Belapurkar, Maximilian Pfisterer, Jan Dreute, Sebastian Werner, Sven Zukunft, Ingrid Fleming, Michael Kracht, M Lienhard Schmitz.

The family of hypoxia-inducible transcription factors (HIF) is activated to adapt cells to low oxygen conditions, but is also known to regulate some biological processes under normoxic conditions. Here we show that HIF-1α protein levels transiently increase during the G1 phase of the cell cycle (designated as G1-HIF) in an AMP-activated protein kinase (AMPK)-dependent manner. The transient elimination of G1-HIF by a degron system revealed its contribution to cell survival under unfavorable metabolic conditions. Indeed, G1-HIF plays a key role in the cell cycle-dependent expression of genes encoding metabolic regulators and the maintenance of mTOR activity under conditions of nutrient deprivation. Accordingly, transient elimination of G1-HIF led to a significant reduction in the concentration of key proteinogenic amino acids and carbohydrates. These data indicate that G1-HIF acts as a cell cycle-dependent surveillance factor that prevents the onset of starvation-induced apoptosis.

DOI: https://doi.org/10.1038/s41419-023-06012-7
J Biol Chem. 2023 Jul 26. pii: S0021-9258(23)02125-7. [Epub ahead of print] 105097

Alkaline intracellular pH (pHi) increases PI3K kinase activity to promote mTORC1 and mTORC2 signaling and function during growth factor limitation.

Dubek Kazyken, Stephen I Lentz, Maxwell Wadley, Diane C Fingar.

  The conserved protein kinase mTOR (mechanistic target of rapamycin) responds to diverse environmental cues to control cell metabolism and promote cell growth, proliferation, and survival as part of two multiprotein complexes, mTOR complex 1 (mTORC1) and mTORC2. Our prior work demonstrated that an alkaline intracellular pH (pHi) increases mTORC2 activity and cell survival in complete media in part by activating AMPK, a kinase best known to sense energetic stress. It is important to note that an alkaline pHi represents an under-appreciated hallmark of cancer cells that promotes their oncogenic behaviors. In addition, mechanisms that control mTORC1 and mTORC2 signaling and function remain incompletely defined, particularly in response to stress conditions. Here, we demonstrate that an alkaline pHi increases PI3K activity to promote mTORC1 and mTORC2 signaling in the absence of serum growth factors. Alkaline pHi increases mTORC1 activity through PI3K-Akt signaling, which mediates inhibitory phosphorylation of the upstream proteins TSC2 and PRAS40 and dissociates TSC2 from lysosomal membranes, thus enabling Rheb-mediated activation of mTORC1. Thus, we show that an alkaline pHi mimics growth factor-PI3K signaling. Functionally, we also demonstrate that an alkaline pHi increases cap-dependent protein synthesis through inhibitory phosphorylation of 4EBP1 and suppresses apoptosis in a PI3K- and mTOR-dependent manner. We speculate that an alkaline pHi promotes a low, basal level of cell metabolism (e.g., protein synthesis) that enables cancer cells within growing tumors to proliferate and survive despite limiting growth factors and nutrients, in part through elevated PI3K-mTORC1 and/or PI3K-mTORC2 signaling.

Keywords:  Akt PKB; S6 kinase; apoptosis; cell signaling; eukaryotic translation initiation factor 4E (eIF4E); eukaryotic translation initiation factor 4E-binding protein (eIF4EBP1); pH regulation; phosphatidylinositide 3-kinase (PI 3-kinase); protein synthesis; target of rapamycin (TOR)

DOI:  https://doi.org/10.1016/j.jbc.2023.105097
Cell Death Dis. 2023 07 25. 14(7): 463

A GSTP1-mediated lactic acid signaling promotes tumorigenesis through the PPP oxidative branch.

Yandi Sun, Qian He, Jingjia Li, Ze Yang, Mashaal Ahmad, Yindan Lin, Di Wu, Lei Zheng, Jiangtao Li, Ben Wang, Chitty Chen, Yue Hu, Heng Luo, Yan Luo.

Lactic acidosis is a feature of solid tumors and plays fundamental role(s) rendering cancer cells to adapt to diverse metabolic stresses, but the mechanism underlying its roles in redox homeostasis remains elusive. Here we show that G6PD is phosphorylated at tyrosine 249/322 by the SRC through the formation of a GSTP1-G6PD-SRC complex. Lactic acid attenuates this formation and the phosphorylation of G6PD by non-covalently binding with GSTP1. Furthermore, lactic acid increases the activity of G6PD and facilitates the PPP (NADPH production) through its sensor GSTP1, thereby exhibiting resistance to reactive oxygen species when glucose is scarce. Abrogating a GSTP1-mediated lactic acid signaling showed attenuated tumor growth and reduced resistance to ROS in breast cancer cells. Importantly, positive correlations between immuno-enriched SRC protein and G6PD Y249/322 phosphorylation specifically manifest in ER/PR positive or HER negative types of breast cancer. Taken together, these results suggest that GSTP1 plays a key role in tumor development by functioning as a novel lactate sensor.

DOI: https://doi.org/10.1038/s41419-023-05998-4
Neuroglia. 2023 Sep;4(3): 158-171

Glucose Transporter-2 Regulation of Male versus Female Hypothalamic Astrocyte MAPK Expression and Activation: Impact of Glucose.

MadhuBabu Pasula, Sagor C Roy, Khaggeswar Bheemanapally, Paul W Sylvester, Karen P Briski.

  The plasma membrane glucose transporter (GLUT)-2 is unique among GLUT family proteins in that it also functions as a glucose sensor. GLUT2 imposes sex-dimorphic control of hypothalamic astrocyte glucose storage and catabolism by unknown mechanisms. Mitogen-activated protein kinase (MAPK) signaling cascades operate within stress-sensitive signal transduction pathways. Current research employed an established primary astrocyte culture model and gene knockdown tools to investigate whether one or more of the three primary MAP kinase families are regulated by GLUT2. GLUT2 gene knockdown caused opposing adjustments in total ERK1/2 proteins in glucose-supplied male versus female astrocytes, augmenting or reducing the mean phosphorylated/total protein ratio for 44 and 42 kDa variants in these sexes. Glucose deprivation amplified this ratio for both ERK1/2 variants, albeit by a larger magnitude in male; GLUT2 siRNA exacerbated this stimulatory response in males only. Phosphorylated/total p38 MAPK protein ratios were up-regulated by GLUT2 knockdown in male, but not female astrocytes. Glucose-deprived astrocytes exhibited no change (male) or reduction (female) in this ratio after GLUT2 gene silencing. GLUT2 siRNA increased the phosphorylated/total protein ratio for 54 and 46 kDa SAPK/JNK proteins in each sex when glucose was present. However, glucose withdrawal suppressed (male) or amplified (female) these ratios, while GLUT2 knockdown attenuated these inverse responses. Results show that GLUT2 inhibits ERK1/2, p38, and SAPK/JNK MAPK activity in male, but differentially stimulates and inhibits activity of these signaling pathways in female hypothalamic astrocytes. Glucoprivation induces divergent adjustments in astrocyte p38 MAPK and SAPK/JNK activities. The findings demonstrate a stimulatory role for GLUT2 in p38 MAPK activation in glucose-starved female astrocytes, but can act as either an inhibitor or inducer of SAPK/JNK activation in glucose-deprived male versus female glial cells, respectively.

Keywords:  ERK1/2; GLUT2; SAPK/JNK; p38 MAPK; primary astrocyte cultures; sex differences

DOI:  https://doi.org/10.3390/neuroglia4030011
Nat Chem Biol. 2023 Jul 27.

ENO1 promotes liver carcinogenesis through YAP1-dependent arachidonic acid metabolism.

Linchong Sun, Caixia Suo, Tong Zhang, Shengqi Shen, Xuemei Gu, Shiqiao Qiu, Pinggen Zhang, Haoran Wei, Wenhao Ma, Ronghui Yan, Rui Chen, Weidong Jia, Jie Cao, Huafeng Zhang, Ping Gao.

Enolase 1 (ENO1) is a glycolytic enzyme that plays essential roles in various pathological activities including cancer development. However, the mechanisms underlying ENO1-contributed tumorigenesis are not well explained. Here, we uncover that ENO1, as an RNA-binding protein, binds to the cytosine-uracil-guanine-rich elements of YAP1 messenger RNA to promote its translation. ENO1 and YAP1 positively regulate alternative arachidonic acid (AA) metabolism by inverse regulation of PLCB1 and HPGD (15-hydroxyprostaglandin dehydrogenase). The YAP1/PLCB1/HPGD axis-mediated activation of AA metabolism and subsequent accumulation of prostaglandin E2 (PGE2) are responsible for ENO1-mediated cancer progression, which can be retarded by aspirin. Finally, aberrant activation of ENO1/YAP1/PLCB1 and decreased HPGD expression in clinical hepatocellular carcinoma samples indicate a potential correlation between ENO1-regulated AA metabolism and cancer development. These findings underline a new function of ENO1 in regulating AA metabolism and tumorigenesis, suggesting a therapeutic potential for aspirin in patients with liver cancer with aberrant expression of ENO1 or YAP1.

DOI: https://doi.org/10.1038/s41589-023-01391-6
Diabetes. 2023 Jul 28. pii: db230358. [Epub ahead of print]

AMPKγ3 controls muscle glucose uptake in recovery from exercise to recapture energy stores.

Kohei Kido, Nicolas O Eskesen, Nicolai S Henriksen, Johan Onslev, Jonas M Kristensen, Magnus R Larsen, Janne R Hingst, Jonas R Knudsen, Jesper B Birk, Nicoline R Andersen, Thomas E Jensen, Christian Pehmøller, Jørgen F P Wojtaszewski, Rasmus Kjøbsted.

Exercise increases muscle glucose uptake independently of insulin signaling and represents a cornerstone for the prevention of metabolic disorders. Pharmacological activation of the exerciseresponsive AMPK in skeletal muscle has been proven successful as a therapeutic approach to treat metabolic disorders by improving glucose homeostasis through the regulation of muscle glucose uptake. However, conflicting observations cloud the proposed role of AMPK as a necessary regulator of muscle glucose uptake during exercise. We show that glucose uptake increases in human skeletal muscle in the absence of AMPK activation during exercise and that exercisestimulated AMPKγ3 activity strongly correlates to muscle glucose uptake in the post-exercise period. In AMPKγ3-deficient mice, muscle glucose uptake is normally regulated during exercise and contractions but impaired in the recovery period from these stimuli. Impaired glucose uptake in recovery from exercise and contractions is associated to a lower glucose extraction, which can be explained by a diminished permeability to glucose and abundance of glucose transporter 4 (GLUT4) at the muscle plasma membrane. As a result, AMPKγ3-deficiency impairs muscle glycogen resynthesis following exercise. These results identify a physiological function of the AMPKγ3 complex in human and rodent skeletal muscle that serves to regulate glucose uptake in recovery from exercise to recapture muscle energy stores.

DOI: https://doi.org/10.2337/db23-0358
Mol Cells. 2023 Jul 27.

CD38 Inhibition Protects Fructose-Induced Toxicity in Primary Hepatocytes.

Soo-Jin Lee, Sung-E Choi, Seokho Park, Yoonjung Hwang, Youngho Son, Yup Kang.

  A fructose-enriched diet is thought to contribute to hepatic injury in developing non-alcoholic steatohepatitis (NASH). However, the cellular mechanism of fructose-induced hepatic damage remains poorly understood. This study aimed to determine whether fructose induces cell death in primary hepatocytes, and if so, to establish the underlying cellular mechanisms. Our results revealed that treatment with high fructose concentrations for 48 h induced mitochondria-mediated apoptotic death in mouse primary hepatocytes (MPHs). Endoplasmic reticulum stress responses were involved in fructose-induced death as the levels of phosho-eIF2α, phospho-C-Jun-N-terminal kinase (JNK), and C/EBP homologous protein (CHOP) increased, and a chemical chaperone tauroursodeoxycholic acid (TUDCA) prevented cell death. The impaired oxidation metabolism of fatty acids was also possibly involved in the fructose-induced toxicity as treatment with an AMP-activated kinase (AMPK) activator and a PPAR-α agonist significantly protected against fructose-induced death, while carnitine palmitoyl transferase I inhibitor exacerbated the toxicity. However, uric acid-mediated toxicity was not involved in fructose-induced death as uric acid was not toxic to MPHs, and the inhibition of xanthine oxidase (a key enzyme in uric acid synthesis) did not affect cell death. On the other hand, treatment with inhibitors of the nicotinamide adenine dinucleotide (NAD)+-consuming enzyme CD38 or CD38 gene knockdown significantly protected against fructose-induced toxicity in MPHs, and fructose treatment increased CD38 levels. These data suggest that CD38 upregulation plays a role in hepatic injury in the fructose-enriched diet-mediated NASH. Thus, CD38 inhibition may be a promising therapeutic strategy to prevent fructose-enriched diet-mediated NASH.

Keywords:  CD38; apoptosis; endoplasmic reticulum stress; fructose; hepatocyte; non-alcoholic steatohepatitis

DOI:  https://doi.org/10.14348/molcells.2023.0045
Antioxidants (Basel). 2023 Jul 10. pii: 1406. [Epub ahead of print]12(7):

Linking ROS Levels to Autophagy: The Key Role of AMPK.

Francesco Agostini, Marco Bisaglia, Nicoletta Plotegher.

  Oxygen reactive species (ROS) are a group of molecules generated from the incomplete reduction of oxygen. Due to their high reactivity, ROS can interact with and influence the function of multiple targets, which include DNA, lipids, and proteins. Among the proteins affected by ROS, AMP-activated protein kinase (AMPK) is considered a major sensor of the intracellular energetic status and a crucial hub involved in the regulation of key cellular processes, like autophagy and lysosomal function. Thanks to these features, AMPK has been recently demonstrated to be able to perceive signals related to the variation of mitochondrial dynamics and to transduce them to the lysosomes, influencing the autophagic flux. Since ROS production is largely dependent on mitochondrial activity, through the modulation of AMPK these molecules may represent important signaling agents which participate in the crosstalk between mitochondria and lysosomes, allowing the coordination of these organelles' functions. In this review, we will describe the mechanisms through which ROS activate AMPK and the signaling pathways that allow this protein to affect the autophagic process. The picture that emerges from the literature is that AMPK regulation is highly tissue-specific and that different pools of AMPK can be localized at specific intracellular compartments, thus differentially responding to altered ROS levels. For this reason, future studies will be highly advisable to discriminate the specific contribution of the activation of different AMPK subpopulations to the autophagic pathway.

Keywords:  AMPK; ROS; autophagy; lysosomes; mitochondria

DOI:  https://doi.org/10.3390/antiox12071406
Cell Rep. 2023 Jul 26. pii: S2211-1247(23)00906-3. [Epub ahead of print]42(8): 112895

PGAM5 is an MFN2 phosphatase that plays an essential role in the regulation of mitochondrial dynamics.

Sudeshna Nag, Kaitlin Szederkenyi, Olena Gorbenko, Hannah Tyrrell, Christopher M Yip, G Angus McQuibban.

  Mitochondrial morphology is regulated by the post-translational modifications of the dynamin family GTPase proteins including mitofusin 1 (MFN1), MFN2, and dynamin-related protein 1 (DRP1). Mitochondrial phosphatase phosphoglycerate mutase 5 (PGAM5) is emerging as a regulator of these post-translational modifications; however, its precise role in the regulation of mitochondrial morphology is unknown. We show that PGAM5 interacts with MFN2 and DRP1 in a stress-sensitive manner. PGAM5 regulates MFN2 phosphorylation and consequently protects it from ubiquitination and degradation. Further, phosphorylation and dephosphorylation modification of MFN2 regulates its fusion ability. Phosphorylation enhances fission and degradation, whereas dephosphorylation enhances fusion. PGAM5 dephosphorylates MFN2 to promote mitochondrial network formation. Further, using a Drosophila genetic model, we demonstrate that the MFN2 homolog Marf and dPGAM5 are in the same biological pathway. Our results identify MFN2 dephosphorylation as a regulator of mitochondrial fusion and PGAM5 as an MFN2 phosphatase.

Keywords:  CP: Molecular biology; DRP1; MFN2; PGAM5; mitochondrial morphology

DOI:  https://doi.org/10.1016/j.celrep.2023.112895
Cells. 2023 Jul 20. pii: 1897. [Epub ahead of print]12(14):

The Role of Mitochondrial Dynamics and Mitotic Fission in Regulating the Cell Cycle in Cancer and Pulmonary Arterial Hypertension: Implications for Dynamin-Related Protein 1 and Mitofusin2 in Hyperproliferative Diseases.

Pierce Colpman, Asish Dasgupta, Stephen L Archer.

  Mitochondria, which generate ATP through aerobic respiration, also have important noncanonical functions. Mitochondria are dynamic organelles, that engage in fission (division), fusion (joining) and translocation. They also regulate intracellular calcium homeostasis, serve as oxygen-sensors, regulate inflammation, participate in cellular and organellar quality control and regulate the cell cycle. Mitochondrial fission is mediated by the large GTPase, dynamin-related protein 1 (Drp1) which, when activated, translocates to the outer mitochondrial membrane (OMM) where it interacts with binding proteins (Fis1, MFF, MiD49 and MiD51). At a site demarcated by the endoplasmic reticulum, fission proteins create a macromolecular ring that divides the organelle. The functional consequence of fission is contextual. Physiological fission in healthy, nonproliferating cells mediates organellar quality control, eliminating dysfunctional portions of the mitochondria via mitophagy. Pathological fission in somatic cells generates reactive oxygen species and triggers cell death. In dividing cells, Drp1-mediated mitotic fission is critical to cell cycle progression, ensuring that daughter cells receive equitable distribution of mitochondria. Mitochondrial fusion is regulated by the large GTPases mitofusin-1 (Mfn1) and mitofusin-2 (Mfn2), which fuse the OMM, and optic atrophy 1 (OPA-1), which fuses the inner mitochondrial membrane. Mitochondrial fusion mediates complementation, an important mitochondrial quality control mechanism. Fusion also favors oxidative metabolism, intracellular calcium homeostasis and inhibits cell proliferation. Mitochondrial lipids, cardiolipin and phosphatidic acid, also regulate fission and fusion, respectively. Here we review the role of mitochondrial dynamics in health and disease and discuss emerging concepts in the field, such as the role of central versus peripheral fission and the potential role of dynamin 2 (DNM2) as a fission mediator. In hyperproliferative diseases, such as pulmonary arterial hypertension and cancer, Drp1 and its binding partners are upregulated and activated, positing mitochondrial fission as an emerging therapeutic target.

Keywords:  apoptosis; cancer; cardiolipin (CL); dynamin 2 (DNM2); dynamin-related protein 1 (Drp1); mitochondrial dynamics protein of 49 kDa (MiD49); mitochondrial dynamics protein of 51 kDa (MiD51); mitochondrial fission factor (MFF); mitochondrial fission protein 1 (Fis1); mitophagy; mitotic fission; phosphatidic acid (PA); pulmonary arterial hypertension

DOI:  https://doi.org/10.3390/cells12141897
J Cardiovasc Pharmacol. 2023 Jul 27.

Metformin Alleviates Sepsis-associated Myocardial Injury by Enhancing AMPK/mTOR Signaling Pathway-mediated Autophagy.

Yu Gao, Jiao Liu, Kemin Li, Tian Li, Ruihan Li, Wenlong Zhang, Xuanping Zhang, Yan Wang, Min Chen, Ruizan Shi, Jing Cao.

ABSTRACT: Sepsis-associated myocardial injury is one of the main causes of death in intensive care units, and current clinical treatments have not been satisfactory. Therefore, finding an effective intervention is an urgent requirement. Metformin, an anti-type 2 diabetes drug, has been reported to be an autophagic activator agent that confers protection in some diseases. However, it is unclear whether it can provide defense against sepsis-associated myocardial injury. In this study, we investigated the cardioprotective effects of metformin pretreatment against lipopolysaccharide (LPS)-induced myocardial injury in C57BL/6J mice or H9c2 cells and the possible underlying mechanisms. Metformin was administered at a dose of 100 mg/kg for a week prior to LPS intraperitoneal injection. Twenty-four hours after LPS intervention, echocardiographic evaluation, reactive oxygen species measurement, Hoechst staining, western blotting, hematoxylin and eosin staining, and enzyme-linked immunosorbent assay were performed. Inhibitors of autophagy and AMP-activated protein kinase (AMPK) were used to further clarify the mechanisms involved. Metformin pretreatment effectively attenuated cardiac dysfunction, reduced the levels of myocardial enzymes, and alleviated cardiac hydroncus in LPS-treated mice. Additionally, metformin restored the LPS-disrupted antioxidant defense and activated LPS-reduced autophagy by modulating the AMPK/mammalian target of rapamycin (AMPK/mTOR) pathway both in vivo and in vitro. The antioxidant effects of metformin on cardiomyocytes were abolished by the autophagy inhibitor 3-methyladenine (3-MA). Treatment with compound C, an AMPK inhibitor, reversed the metformin-induced autophagy in LPS-treated H9c2 cells. In conclusion, metformin pretreatment alleviates LPS-induced myocardial injury by activating AMPK/mTOR pathway-mediated autophagy.

DOI: https://doi.org/10.1097/FJC.0000000000001463
Curr Neurovasc Res. 2023 Jul 21.

The Metabolic Basis for Nervous System Dysfunction in Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease.

Kenneth Maiese.

  Disorders of metabolism affect multiple systems throughout the body but may have the greatest impact on both central and peripheral nervous systems. Currently available treatments and behavior changes for disorders that include diabetes mellitus (DM) and nervous system diseases are limited and cannot reverse the disease burden. Greater access to healthcare and a longer lifespan have led to an increased prevalence of metabolic and neurodegenerative disorders. In light of these challenges, innovative studies into the underlying disease pathways offer new treatment perspectives for Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease. Metabolic disorders are intimately tied to neurodegenerative diseases and can lead to debilitating outcomes, such as multi-nervous system disease, susceptibility to viral pathogens, and long-term cognitive disability. Novel strategies that can robustly address metabolic disease and neurodegenerative disorders involve a careful consideration of cellular metabolism, programmed cell death pathways, the mechanistic target of rapamycin (mTOR) and its associated pathways of mTOR Complex 1 (mTORC1), mTOR Complex 2 (mTORC2), AMP-activated protein kinase (AMPK), growth factor signaling, and underlying risk factors such as the apolipoprotein E (APOE-4) gene. Yet, these complex pathways necessitate comprehensive understanding to achieve clinical outcomes that target disease susceptibility, onset, and progression.

Keywords:  Alzheimer’s disease; COVID-19; Huntington’s disease; Parkinson’s disease; apoptosis; autophagy; diabetes mellitus; erythropoietin; mTOR; pyroptosis

DOI:  https://doi.org/10.2174/1567202620666230721122957
Biology (Basel). 2023 Jul 14. pii: 1007. [Epub ahead of print]12(7):

Glucose Inhibits Yeast AMPK (Snf1) by Three Independent Mechanisms.

Kobi Simpson-Lavy, Martin Kupiec.

  Snf1, the fungal homologue of mammalian AMP-dependent kinase (AMPK), is a key protein kinase coordinating the response of cells to a shortage of glucose. In fungi, the response is to activate respiratory gene expression and metabolism. The major regulation of Snf1 activity has been extensively investigated: In the absence of glucose, it becomes activated by phosphorylation of its threonine at position 210. This modification can be erased by phosphatases when glucose is restored. In the past decade, two additional independent mechanisms of Snf1 regulation have been elucidated. In response to glucose (or, surprisingly, also to DNA damage), Snf1 is SUMOylated by Mms21 at lysine 549. This inactivates Snf1 and leads to Snf1 degradation. More recently, glucose-induced proton export has been found to result in Snf1 inhibition via a polyhistidine tract (13 consecutive histidine residues) at the N-terminus of the Snf1 protein. Interestingly, the polyhistidine tract plays also a central role in the response to iron scarcity. This review will present some of the glucose-sensing mechanisms of S. cerevisiae, how they interact, and how their interplay results in Snf1 inhibition by three different, and independent, mechanisms.

Keywords:  AMPK; Saccharomyces cerevisiae; Snf1; fermentation; glucose metabolism; hexose; respiration; yeast

DOI:  https://doi.org/10.3390/biology12071007
Int J Mol Sci. 2023 Jul 16. pii: 11531. [Epub ahead of print]24(14):

Impaired Insulin Signaling Mediated by the Small GTPase Rac1 in Skeletal Muscle of the Leptin-Deficient Obese Mouse.

Man Piu Chan, Nobuyuki Takenaka, Takaya Satoh.

  Insulin-stimulated glucose uptake in skeletal muscle is mediated by the glucose transporter GLUT4. The small GTPase Rac1 acts as a switch of signal transduction that regulates GLUT4 translocation to the plasma membrane following insulin stimulation. However, it remains obscure whether signaling cascades upstream and downstream of Rac1 in skeletal muscle are impaired by obesity that causes insulin resistance and type 2 diabetes. In an attempt to clarify this point, we investigated Rac1 signaling in the leptin-deficient (Lepob/ob) mouse model. Here, we show that insulin-stimulated GLUT4 translocation and Rac1 activation are almost completely abolished in Lepob/ob mouse skeletal muscle. Phosphorylation of the protein kinase Akt2 and plasma membrane translocation of the guanine nucleotide exchange factor FLJ00068 following insulin stimulation were also diminished in Lepob/ob mice. On the other hand, the activation of another small GTPase RalA, which acts downstream of Rac1, by the constitutively activated form of Akt2, FLJ00068, or Rac1, was partially abrogated in Lepob/ob mice. Taken together, we conclude that insulin-stimulated glucose uptake is impaired by two mechanisms in Lepob/ob mouse skeletal muscle: one is the complete inhibition of Akt2-mediated activation of Rac1, and the other is the partial inhibition of RalA activation downstream of Rac1.

Keywords:  Akt2; GLUT4; GTPase; Rac1; RalA; glucose uptake; insulin; obesity; skeletal muscle

DOI:  https://doi.org/10.3390/ijms241411531
Int J Mol Sci. 2023 Jul 15. pii: 11497. [Epub ahead of print]24(14):

Regulation of mTOR Signaling: Emerging Role of Cyclic Nucleotide-Dependent Protein Kinases and Implications for Cardiometabolic Disease.

Fubiao Shi, Sheila Collins.

  The mechanistic target of rapamycin (mTOR) kinase is a central regulator of cell growth and metabolism. It is the catalytic subunit of two distinct large protein complexes, mTOR complex 1 (mTORC1) and mTORC2. mTOR activity is subjected to tight regulation in response to external nutrition and growth factor stimulation. As an important mechanism of signaling transduction, the 'second messenger' cyclic nucleotides including cAMP and cGMP and their associated cyclic nucleotide-dependent kinases, including protein kinase A (PKA) and protein kinase G (PKG), play essential roles in mediating the intracellular action of a variety of hormones and neurotransmitters. They have also emerged as important regulators of mTOR signaling in various physiological and disease conditions. However, the mechanism by which cAMP and cGMP regulate mTOR activity is not completely understood. In this review, we will summarize the earlier work establishing the ability of cAMP to dampen mTORC1 activation in response to insulin and growth factors and then discuss our recent findings demonstrating the regulation of mTOR signaling by the PKA- and PKG-dependent signaling pathways. This signaling framework represents a new non-canonical regulation of mTOR activity that is independent of AKT and could be a novel mechanism underpinning the action of a variety of G protein-coupled receptors that are linked to the mTOR signaling network. We will further review the implications of these signaling events in the context of cardiometabolic disease, such as obesity, non-alcoholic fatty liver disease, and cardiac remodeling. The metabolic and cardiac phenotypes of mouse models with targeted deletion of Raptor and Rictor, the two essential components for mTORC1 and mTORC2, will be summarized and discussed.

Keywords:  PKA; PKG; Raptor; Rictor; cAMP; cGMP; cardiac hypertrophy; fatty liver disease; mTOR; obesity

DOI:  https://doi.org/10.3390/ijms241411497
Basic Res Cardiol. 2023 Jul 26. 118(1): 29

Matrix metalloproteinase-2 proteolyzes mitofusin-2 and impairs mitochondrial function during myocardial ischemia-reperfusion injury.

Wesam Bassiouni, Robert Valencia, Zabed Mahmud, John M Seubert, Richard Schulz.

  During myocardial ischemia and reperfusion (IR) injury matrix metalloproteinase-2 (MMP-2) is rapidly activated in response to oxidative stress. MMP-2 is a multifunctional protease that cleaves both extracellular and intracellular proteins. Oxidative stress also impairs mitochondrial function which is regulated by different proteins, including mitofusin-2 (Mfn-2), which is lost in IR injury. Oxidative stress and mitochondrial dysfunction trigger the NLRP3 inflammasome and the innate immune response which invokes the de novo expression of an N-terminal truncated isoform of MMP-2 (NTT-MMP-2) at or near mitochondria. We hypothesized that MMP-2 proteolyzes Mfn-2 during myocardial IR injury, impairing mitochondrial function and enhancing the inflammasome response. Isolated hearts from mice subjected to IR injury (30 min ischemia/40 min reperfusion) showed a significant reduction in left ventricular developed pressure (LVDP) compared to aerobically perfused hearts. IR injury increased MMP-2 activity as observed by gelatin zymography and increased degradation of troponin I, an intracellular MMP-2 target. MMP-2 preferring inhibitors, ARP-100 or ONO-4817, improved post-ischemic recovery of LVDP compared to vehicle perfused IR hearts. In muscle fibers isolated from IR hearts the rates of mitochondrial oxygen consumption and ATP production were impaired compared to those from aerobic hearts, whereas ARP-100 or ONO-4817 attenuated these reductions. IR hearts showed higher levels of NLRP3, cleaved caspase-1 and interleukin-1β in the cytosolic fraction, while the mitochondria-enriched fraction showed reduced levels of Mfn-2, compared to aerobic hearts. ARP-100 or ONO-4817 attenuated these changes. Co-immunoprecipitation showed that MMP-2 is associated with Mfn-2 in aerobic and IR hearts. ARP-100 or ONO-4817 also reduced infarct size and cell death in hearts subjected to 45 min ischemia/120 min reperfusion. Following myocardial IR injury, impaired contractile function and mitochondrial respiration and elevated inflammasome response could be attributed, at least in part, to MMP-2 activation, which targets and cleaves mitochondrial Mfn-2. Inhibition of MMP-2 activity protects against cardiac contractile dysfunction in IR injury in part by preserving Mfn-2 and suppressing inflammation.

Keywords:  Inflammasomes; Ischemia–reperfusion injury; Matrix metalloproteinase-2; Mitochondria; Mitofusin-2

DOI:  https://doi.org/10.1007/s00395-023-00999-y
bioRxiv. 2023 Jul 20. pii: 2023.07.19.549684. [Epub ahead of print]

A Medium Chain Fatty Acid, 6-hydroxyhexanoic acid (6-HHA), Protects Against Obesity and Insulin Resistance.

Sara C Sebag, Qingwen Qian, Chawin Upara, Qiong Ding, Huojun Cao, Liu Hong, Ling Yang.

Obesity, a worldwide health problem, increases the risk for developing metabolic diseases such as insulin resistance and diabetes. It is well recognized that obesity-associated chronic inflammation plays a key role in the pathogenesis of systemic metabolic dysfunction. Previously, we revealed an anti-inflammatory role for spent culture supernatants isolated from the oral commensal bacterial species Streptococcus gordonii (Sg-SCS). Here, we identified that 6-hydroxyhexanoic acid (6-HHA), a medium chain fatty acid (MCFA), is the one of the key components of Sg-SCS . We found that treatment of 6-HHA in mice fed a high-fat diet (HFD) significantly reduced HFD-mediated weight gain which was largely attributed to a decrease in fat mass. Systemically, 6-HHA improves obesity-associated glucose intolerance and insulin resistance. Furthermore, administration of 6-HHA suppressed obesity-associated systemic inflammation and dyslipidemia. At the cellular level, treatment of 6-HHA ameliorated aberrant inflammatory and metabolic transcriptomic signatures in white adipose tissue of mice with diet-induced obesity (HFD). Mechanistically, we found that 6-HHA suppressed adipocyte-proinflammatory cytokine production and lipolysis, the latter through Gαi-mediated signaling. This work provides direct evidence for the anti-obesity effects of a novel MCFA, which could be a new therapeutic treatment for combating obesity.
KEY POINTS: Hydroxyhexanoic medium chain fatty acids (MCFAs) are dietary and bacterial-derived energy sources, however, the outcomes of using MCFAs in treating metabolic disorders are diverse and complex. The MCFA 6-hydroxyhexanoic acid (6-HHA) is a metabolite secreted by the oral bacterial commensal species Streptococcus gordonii; here we investigated its role in modulating high-fat diet (HFD)-induced metabolic dysfunction. In a murine model of obesity, we found 6-HHA-mediated improvement of diet-mediated adiposity, insulin resistance and inflammation were in part due to actions on white adipose tissue (WAT).6-HHA suppressed proinflammatory cytokine production and lipolysis through Gi-mediated signaling in differentiated white adipocytes.

DOI: https://doi.org/10.1101/2023.07.19.549684
J Transl Med. 2023 07 22. 21(1): 494

SIRT3 ameliorates diabetes-associated cognitive dysfunction via regulating mitochondria-associated ER membranes.

Yanmin Chang, Cailin Wang, Jiahui Zhu, Siyi Zheng, Shangqi Sun, Yanqing Wu, Xingjun Jiang, Lulu Li, Rong Ma, Gang Li.

   BACKGROUND: Diabetes is associated with an increased risk of cognitive decline and dementia. These diseases are linked with mitochondrial dysfunction, most likely as a consequence of excessive formation of mitochondria-associated membranes (MAMs). Sirtuin3 (SIRT3), a key mitochondrial NAD+-dependent deacetylase, is critical responsible for mitochondrial functional homeostasis and is highly associated with neuropathology. However, the role of SIRT3 in regulating MAM coupling remains unknown.
METHODS: Streptozotocin-injected diabetic mice and high glucose-treated SH-SY5Y cells were established as the animal and cellular models, respectively. SIRT3 expression was up-regulated in vivo using an adeno-associated virus in mouse hippocampus and in vitro using a recombinant lentivirus vector. Cognitive function was evaluated using behavioural tests. Hippocampus injury was assessed using Golgi and Nissl staining. Apoptosis was analysed using western blotting and TUNEL assay. Mitochondrial function was detected using flow cytometry and confocal fluorescence microscopy. The mechanisms were investigated using co-immunoprecipitation of VDAC1-GRP75-IP3R complex, fluorescence imaging of ER and mitochondrial co-localisation and transmission electron microscopy of structural analysis of MAMs.
RESULTS: Our results demonstrated that SIRT3 expression was significantly reduced in high glucose-treated SH-SY5Y cells and hippocampal tissues from diabetic mice. Further, up-regulating SIRT3 alleviated hippocampus injuries and cognitive impairment in diabetic mice and mitigated mitochondrial Ca2+ overload-induced mitochondrial dysfunction and apoptosis. Mechanistically, MAM formation was enhanced under high glucose conditions, which was reversed by genetic up-regulation of SIRT3 via reduced interaction of the VDAC1-GRP75-IP3R complex in vitro and in vivo. Furthermore, we investigated the therapeutic effects of pharmacological activation of SIRT3 in diabetic mice via honokiol treatment, which exhibited similar effects to our genetic interventions.
CONCLUSIONS: In summary, our findings suggest that SIRT3 ameliorates cognitive impairment in diabetic mice by limiting aberrant MAM formation. Furthermore, targeting the activation of SIRT3 by honokiol provides a promising therapeutic candidate for diabetes-associated cognitive dysfunction. Overall, our study suggests a novel role of SIRT3 in regulating MAM coupling and indicates that SIRT3-targeted therapies are promising for diabetic dementia patients.

Keywords:  Diabetes-associated cognitive dysfunction; Honokiol; Mitochondria-associated ER membranes; Sirtuin3; VDAC1–GRP75–IP3R complex

DOI:  https://doi.org/10.1186/s12967-023-04246-9
Int Immunopharmacol. 2023 Jul 26. pii: S1567-5769(23)00976-1. [Epub ahead of print]123 110651

TRPV4-mediated mitochondrial dysfunction induces pyroptosis and cartilage degradation in osteoarthritis via the Drp1-HK2 axis.

Zijian Yan, Zili He, Hongyi Jiang, Yu Zhang, Yitie Xu, Yingze Zhang.

  Osteoarthritis (OA) is an age-related chronic degenerative disease with complex pathophysiological mechanisms. Accumulating evidence indicates that nod-like receptor pyrin domain 3 (NLRP3) inflammasome-mediated pyroptosis of chondrocytes plays a crucial role in the OA progression. Transient Receptor Potential Vanilloid 4 (TRPV4), described as a calcium-permeable cation channel, isassociated with proinflammatory factors and pyroptosis. In this study, we studied the potential functions of TRPV4 in chondrocyte pyroptosis and cartilage degradation. We found that lipopolysaccharides(LPS)-induced mitochondrial reactive oxygen species (mtROS) accumulation aggravated chondrocyte pyroptosis and cartilage degeneration. TRPV4 induces dynamin-related protein 1 (Drp1) mitochondrial translocation through the Ca2+-calmodulin-dependent protein kinase II (CaMKII) signaling pathway, which subsequently caused the mitochondrial dysfunction (e.g., mPTP over opening; Δψm depolarization; ATP production decreased; mtROS accumulation), pyroptosis and extracellular matrix (ECM) degradation through hexokinase 2 (HK2) dissociation from mitochondrial membrane. Moreover, TRPV4 inhibition reversed Drp1-involved chondrocyte pyroptosis and cartilage degeneration in the anterior cruciate ligament transection (ACLT) mouse model. Our findings revealed the internal mechanisms underlying TRPV4 regulation in chondrocytes and its intrinsic therapeutic efficacy for OA.

Keywords:  Cartilage degeneration; Drp1; HK2; Osteoarthritis; Pyroptosis; TRPV4

DOI:  https://doi.org/10.1016/j.intimp.2023.110651
Eur J Pharmacol. 2023 Jul 20. pii: S0014-2999(23)00445-4. [Epub ahead of print]955 175933

Ketogenic diet and β-Hydroxybutyrate alleviate ischemic brain injury in mice via an IRAKM-dependent pathway.

Chuman Lin, Shengnan Wang, Jiaxin Xie, Juan Zhu, Jiawei Xu, Kewei Liu, Jiancong Chen, Mingjia Yu, Hengren Zhong, Kaibin Huang, Suyue Pan.

  Ketogenic diet (KD) is a classical nonpharmacological therapy that has recently been shown to benefit cerebral ischemia, but the mechanism remains unclear. This study investigated the neuroprotective effects of KD pretreatment and β-hydroxybutyrate (BHB, bioactive product of KD) post-treatment in a mouse model of temporary middle cerebral artery occlusion (tMCAO). Neurological function, infarct volume, as well as inflammatory reactions are evaluated 24 h after ischemia. Results showed that both KD pretreatment or BHB post-treatment improved the Bederson score and Grip test score, reduced infarct volume and the extravasation of IgG, suppressed the over-activation of microglia, and modulated the expression of cytokines. Mechanically, we found that both KD pretreatment or BHB post-treatment significantly stimulated the expression of interleukin-1 receptor-associated kinase M (IRAKM) and then inhibited the nuclear translocation of NF-κB. IRAKM deletion (Irakm-/-) exacerbated tMCAO-induced neurovascular injuries, and aggravated neuroinflammatory response. Moreover, KD pretreatment or BHB post-treatment lost their neuroprotection in the tMCAO-treated Irakm-/- mice. Our results support that KD pretreatment and BHB post-treatment alleviate ischemic brain injury in mice, possibly via an IRAKM-dependent way.

Keywords:  IRAKM; Ischemic brain injury; Ketogenic diet; Proinflammatory cytokines; β-Hydroxybutyrate

DOI:  https://doi.org/10.1016/j.ejphar.2023.175933
Redox Biol. 2023 Jul 20. pii: S2213-2317(23)00222-7. [Epub ahead of print]65 102821

Glucocorticoid enhances presenilin1-dependent Aβ production at ER's mitochondrial-associated membrane by downregulating Rer1 in neuronal cells.

Gee Euhn Choi, Ji Yong Park, Mo Ran Park, Jee Hyeon Yoon, Ho Jae Han.

  Stress-induced release of glucocorticoid is an important amyloidogenic factor that upregulates amyloid precursor protein (APP) and β secretase 1 (BACE1) levels. Glucocorticoid also contributes to the pathogenesis of Alzheimer's disease (AD) by increasing ER-mitochondria connectivity, in which amyloid β (Aβ) processing occurs rigorously because of its lipid raft-rich characteristics. However, the mechanism by which glucocorticoid enhances γ-secretase activity in the mitochondrial-associated membrane of ER (MAM) and subsequent accumulation of mitochondrial Aβ is unclear. In this study, we determined how glucocorticoid enhances Aβ production in MAM using SH-SY5Y cells and ICR mice. First, we observed that cortisol-induced Aβ accumulation in mitochondria preceded its extracellular apposition by enhancing γ-secretase activity, which was the result of increased presenilin 1 (PSEN1) localization in MAM. Screening data revealed that cortisol selectively downregulated the ER retrieval protein Rer1, which triggered its maturation and subsequent entry into the endocytic secretory pathway of PSEN1. Accordingly, overexpression of RER1 reversed the deleterious effects of mitochondrial Aβ on mitochondrial respiratory function and neuronal cell viability. Notably, we found that cortisol guided the glucocorticoid receptor (GR) to bind directly to the RER1 promoter, thus trans-repressing its expression. Inhibiting GR function reduced Aβ accumulation at mitochondria and improved the outcome of a spatial memory task in mice exposed to corticosterone. Taken together, glucocorticoid enhances PSEN1-mediated Aβ generation at MAM by downregulating Rer1, which is a potential target at early stages of AD pathogenesis.

Keywords:  Alzheimer’s disease; Aβ; Glucocorticoid; MAM; Presenilin; Rer1

DOI:  https://doi.org/10.1016/j.redox.2023.102821
Commun Biol. 2023 Jul 25. 6(1): 776

Nutritional stress-induced regulation of microtubule organization and mRNP transport by HDAC1 controlled α-tubulin acetylation.

Frank Wippich, Vaishali, Marco L Hennrich, Anne Ephrussi.

In response to nutritional stress, microtubules in cells of the Drosophila female germline are depleted from the cytoplasm and accumulate cortically. This triggers aggregation of mRNPs into large processing bodies (P-bodies) and oogenesis arrest. Here, we show that hyperacetylation of α-tubulin at lysine 40 (K40) alters microtubule dynamics and P-body formation. We found that depletion of histone deacetylase 1 (HDAC1) by RNAi phenocopies the nutritional stress response, causing α-tubulin hyperacetylation and accumulation of maternally deposited mRNPs in P-bodies. Through in vitro and in vivo studies, we identify HDAC1 as a direct regulator of α-tubulin K40 acetylation status. In well-fed flies, HDAC1 maintains low levels of α-tubulin acetylation, enabling the microtubule dynamics required for mRNP transport. Using quantitative phosphoproteomics we identify nutritional stress-induced changes in protein phosphorylation that act upstream of α-tubulin acetylation, including phosphorylation of HDAC1 at S391, which reduces its ability to deacetylate α-tubulin. These results reveal that Drosophila HDAC1 senses and relays the nutritional status, which regulates germline development through modulation of cytoskeleton dynamics.

DOI: https://doi.org/10.1038/s42003-023-05138-w