bims-mimead Biomed News
on Mitochondrial metabolism in ageing and metabolic disease
Issue of 2024–10–13
eight papers selected by
Rachel M. Handy, University of Guelph
  1. Sensitive fluorescent biosensor reveals differential subcellular regulation of PKC.
  2. Metabolic regulation of mitochondrial morphologies in pancreatic beta cells: coupling of bioenergetics and mitochondrial dynamics.
  3. Decreased mitochondrial creatine kinase 2 impairs skeletal muscle mitochondrial function independently of insulin in type 2 diabetes.
  4. Mitochondrial Extracellular Vesicles (mitoEVs): Emerging mediators of cell-to-cell communication in health, aging and age-related diseases.
  5. Inducible and reversible SOD2 knockdown in mouse skeletal muscle drives impaired pyruvate oxidation and reduced metabolic flexibility.
  6. Mitochondrial apolipoprotein MIC26 is a metabolic rheostat regulating central cellular fuel pathways.
  7. Mitochondrial Function and Dysfunction in White Adipocytes and Therapeutic Implications.
  8. Excessive or sustained endoplasmic reticulum stress: one of the culprits of adipocyte dysfunction in obesity.
  1. Nat Chem Biol. 2024 Oct 11.
    Sensitive fluorescent biosensor reveals differential subcellular regulation of PKC.
    Qi Su, Jing Zhang, Wei Lin, Jin-Fan Zhang, Alexandra C Newton, Sohum Mehta, Jing Yang, Jin Zhang.
      The protein kinase C (PKC) family of serine and threonine kinases, consisting of three distinctly regulated subfamilies, has been established as critical for various cellular functions. However, how PKC enzymes are regulated at different subcellular locations, particularly at emerging signaling hubs, is unclear. Here we present a sensitive excitation ratiometric C kinase activity reporter (ExRai-CKAR2) that enables the detection of minute changes (equivalent to 0.2% of maximum stimulation) in subcellular PKC activity. Using ExRai-CKAR2 with an enhanced diacylglycerol (DAG) biosensor, we uncover that G-protein-coupled receptor stimulation triggers sustained PKC activity at the endoplasmic reticulum and lysosomes, differentially mediated by Ca2+-sensitive conventional PKC and DAG-sensitive novel PKC, respectively. The high sensitivity of ExRai-CKAR2, targeted to either the cytosol or partitioning defective complexes, further enabled us to detect previously inaccessible endogenous atypical PKC activity in three-dimensional organoids. Taken together, ExRai-CKAR2 is a powerful tool for interrogating PKC regulation in response to physiological stimuli.
    DOI:  https://doi.org/10.1038/s41589-024-01758-3
  2. Commun Biol. 2024 Oct 05. 7(1): 1267
    Metabolic regulation of mitochondrial morphologies in pancreatic beta cells: coupling of bioenergetics and mitochondrial dynamics.
    Wen-Wei Tseng, Ching-Hsiang Chu, Yi-Ju Lee, Shirui Zhao, Chen Chang, Yi-Ping Ho, An-Chi Wei.
      Cellular bioenergetics and mitochondrial dynamics are crucial for the secretion of insulin by pancreatic beta cells in response to elevated levels of blood glucose. To elucidate the interactions between energy production and mitochondrial fission/fusion dynamics, we combine live-cell mitochondria imaging with biophysical-based modeling and graph-based network analysis. The aim is to determine the mechanism that regulates mitochondrial morphology and balances metabolic demands in pancreatic beta cells. A minimalistic differential equation-based model for beta cells is constructed that includes glycolysis, oxidative phosphorylation, calcium dynamics, and fission/fusion dynamics, with ATP synthase flux and proton leak flux as main regulators of mitochondrial dynamics. The model shows that mitochondrial fission occurs in response to hyperglycemia, starvation, ATP synthase inhibition, uncoupling, and diabetic conditions, in which the rate of proton leakage exceeds the rate of mitochondrial ATP synthesis. Under these metabolic challenges, the propensities of tip-to-tip fusion events simulated from the microscopy images of the mitochondrial networks are lower than those in the control group and prevent the formation of mitochondrial networks. The study provides a quantitative framework that couples bioenergetic regulation with mitochondrial dynamics, offering insights into how mitochondria adapt to metabolic challenges.
    DOI:  https://doi.org/10.1038/s42003-024-06955-3
  3. Sci Transl Med. 2024 Oct 09. 16(768): eado3022
    Decreased mitochondrial creatine kinase 2 impairs skeletal muscle mitochondrial function independently of insulin in type 2 diabetes.
    David Rizo-Roca, Dimitrius Santiago P S F Guimarães, Logan A Pendergrast, Nicolas Di Leo, Alexander V Chibalin, Salwan Maqdasy, Mikael Rydén, Erik Näslund, Juleen R Zierath, Anna Krook.
      Increased plasma creatine concentrations are associated with the risk of type 2 diabetes, but whether this alteration is associated with or causal for impairments in metabolism remains unexplored. Because skeletal muscle is the main disposal site of both creatine and glucose, we investigated the role of intramuscular creatine metabolism in the pathophysiology of insulin resistance in type 2 diabetes. In men with type 2 diabetes, plasma creatine concentrations were increased, and intramuscular phosphocreatine content was reduced. These alterations were coupled to reduced expression of sarcomeric mitochondrial creatine kinase 2 (CKMT2). In C57BL/6 mice fed a high-fat diet, neither supplementation with creatine for 2 weeks nor treatment with the creatine analog β-GPA for 1 week induced changes in glucose tolerance, suggesting that increased circulating creatine was associated with insulin resistance rather than causing it. In C2C12 myotubes, silencing Ckmt2 using small interfering RNA reduced mitochondrial respiration, membrane potential, and glucose oxidation. Electroporation-mediated overexpression of Ckmt2 in skeletal muscle of high-fat diet-fed male mice increased mitochondrial respiration, independent of creatine availability. Given that overexpression of Ckmt2 improved mitochondrial function, we explored whether exercise regulates CKMT2 expression. Analysis of public data revealed that CKMT2 content was up-regulated by exercise training in both humans and mice. We reveal a previously underappreciated role of CKMT2 in mitochondrial homeostasis beyond its function for creatine phosphorylation, independent of insulin action. Collectively, our data provide functional evidence for how CKMT2 mediates mitochondrial dysfunction associated with type 2 diabetes.
    DOI:  https://doi.org/10.1126/scitranslmed.ado3022
  4. Ageing Res Rev. 2024 Oct 05. pii: S1568-1637(24)00340-4. [Epub ahead of print]101 102522
    Mitochondrial Extracellular Vesicles (mitoEVs): Emerging mediators of cell-to-cell communication in health, aging and age-related diseases.
    Roberto Iorio, Sabrina Petricca, Giovanna Di Emidio, Stefano Falone, Carla Tatone.
      Mitochondria are metabolic and signalling hubs that integrate a plethora of interconnected processes to maintain cell homeostasis. They are also dormant mediators of inflammation and cell death, and with aging damages affecting mitochondria gradually accumulate, resulting in the manifestation of age-associated disorders. In addition to coordinate multiple intracellular functions, mitochondria mediate intercellular and inter-organ cross talk in different physiological and stress conditions. To fulfil this task, mitochondrial signalling has evolved distinct and complex conventional and unconventional routes of horizontal/vertical mitochondrial transfer. In this regard, great interest has been focused on the ability of extracellular vesicles (EVs), such as exosomes and microvesicles, to carry selected mitochondrial cargoes to target cells, in response to internal and external cues. Over the past years, the field of mitochondrial EVs (mitoEVs) has grown exponentially, revealing unexpected heterogeneity of these structures associated with an ever-expanding mitochondrial function, though the full extent of the underlying mechanisms is far from being elucidated. Therefore, emerging subsets of EVs encompass exophers, migrasomes, mitophers, mitovesicles, and mitolysosomes that can act locally or over long-distances to restore mitochondrial homeostasis and cell functionality, or to amplify disease. This review provides a comprehensive overview of our current understanding of the biology and trafficking of MitoEVs in different physiological and pathological conditions. Additionally, a specific focus on the role of mitoEVs in aging and the onset and progression of different age-related diseases is discussed.
    Keywords:  Age-related diseases; Bioenergetic remodelling; Cancer; Intercellular communication; Mitochondria-specific ectocytosis; Mitochondrial derived vesicles (MDVs); Mitochondrial extracellular vesicles (mitoEVs); Mitochondrial quality control (MQC)
    DOI:  https://doi.org/10.1016/j.arr.2024.102522
  5. bioRxiv. 2024 Sep 25. pii: 2024.09.23.614547. [Epub ahead of print]
    Inducible and reversible SOD2 knockdown in mouse skeletal muscle drives impaired pyruvate oxidation and reduced metabolic flexibility.
    Ethan L Ostrom, Rudy Stuppard, Aurora Mattson-Hughes, David J Marcinek.
       Abstract Figure:
    Highlights: SOD2 knockdown and recovery is achieved in skeletal muscle by using a shRNA targeted to SOD2 mRNA controlled by a tetracycline Response Element and reverse tetracycline transactivator proteinSOD2 KD is induced by administering doxycycline in the drinking waterMitochondrial functional decline and recovery follows the time course of SOD2 protein decline and recoverySustained SOD2 KD precipitates reduced metabolic flexibility in skeletal muscle mitochondria characterized by impaired pyruvate respiration in the presence of other substrates.
    Introduction: Skeletal muscle mitochondrial dysfunction is a key characteristic of aging muscle and contributes to age related diseases such as sarcopenia, frailty, and type 2 diabetes. Mitochondrial oxidative distress has been implicated as a driving factor in these age-related diseases, however whether it is a cause, or a consequence of mitochondrial dysfunction remains to be determined. The development of more flexible genetic models is an important tool to test the mechanistic role of mitochondrial oxidative stress on skeletal muscle metabolic dysfunction. We characterize a new model of inducible and reversible mitochondrial redox stress using a tetracycline controlled skeletal muscle specific short hairpin RNA targeted to superoxide dismutase 2 (iSOD2).
    Methods: iSOD2 KD and control (CON) animals were administered doxycycline for 3-or 12-weeks and followed for up to 24 weeks and mitochondrial respiration and muscle contraction were measured to define the time course of SOD2 KD and muscle functional changes and recovery.
    Results: Maximum knockdown of SOD2 protein occurred by 6 weeks and recovered by 24 weeks after DOX treatment. Mitochondrial aconitase activity and maximum mitochondrial respiration declined in KD muscle by 12 weeks and recovered by 24 weeks. There were minimal changes in gene expression between KD and CON muscle. Twelve-week KD showed a small, but significant decrease in muscle fatigue resistance. The primary phenotype was reduced metabolic flexibility characterized by impaired pyruvate driven respiration when other substrates are present. The pyruvate dehydrogenase kinase inhibitor dichloroacetate partially restored pyruvate driven respiration, while the thiol reductant DTT did not.
    Conclusion: We use a model of inducible and reversible skeletal muscle SOD2 knockdown to demonstrate that elevated matrix superoxide reversibly impairs mitochondrial substrate flexibility characterized by impaired pyruvate oxidation. Despite the bioenergetic effect, the limited change in gene expression suggests that the elevated redox stress in this model is confined to the mitochondrial matrix.
    DOI:  https://doi.org/10.1101/2024.09.23.614547
  6. Life Sci Alliance. 2024 Dec;pii: e202403038. [Epub ahead of print]7(12):
    Mitochondrial apolipoprotein MIC26 is a metabolic rheostat regulating central cellular fuel pathways.
    Melissa Damiecki, Ritam Naha, Yulia Schaumkessel, Philipp Westhoff, Nika Atanelov, Anja Stefanski, Patrick Petzsch, Kai Stühler, Karl Köhrer, Andreas Pm Weber, Ruchika Anand, Andreas S Reichert, Arun Kumar Kondadi.
      Mitochondria play central roles in metabolism and metabolic disorders such as type 2 diabetes. MIC26, a mitochondrial contact site and cristae organising system complex subunit, was linked to diabetes and modulation of lipid metabolism. Yet, the functional role of MIC26 in regulating metabolism under hyperglycemia is not understood. We used a multi-omics approach combined with functional assays using WT and MIC26 KO cells cultured in normoglycemia or hyperglycemia, mimicking altered nutrient availability. We show that MIC26 has an inhibitory role in glycolysis and cholesterol/lipid metabolism under normoglycemic conditions. Under hyperglycemia, this inhibitory role is reversed demonstrating that MIC26 is critical for metabolic adaptations. This is partially mediated by alterations of mitochondrial metabolite transporters. Furthermore, MIC26 deletion led to a major metabolic rewiring of glutamine use and oxidative phosphorylation. We propose that MIC26 acts as a metabolic "rheostat," that modulates mitochondrial metabolite exchange via regulating mitochondrial cristae, allowing cells to cope with nutrient overload.
    DOI:  https://doi.org/10.26508/lsa.202403038
  7. Compr Physiol. 2024 Oct 09. 14(4): 5581-5640
    Mitochondrial Function and Dysfunction in White Adipocytes and Therapeutic Implications.
    Fenfen Wang, Phu M Huynh, Yu A An.
      For a long time, white adipocytes were thought to function as lipid storages due to the sizeable unilocular lipid droplet that occupies most of their space. However, recent discoveries have highlighted the critical role of white adipocytes in maintaining energy homeostasis and contributing to obesity and related metabolic diseases. These physiological and pathological functions depend heavily on the mitochondria that reside in white adipocytes. This article aims to provide an up-to-date overview of the recent research on the function and dysfunction of white adipocyte mitochondria. After briefly summarizing the fundamental aspects of mitochondrial biology, the article describes the protective role of functional mitochondria in white adipocyte and white adipose tissue health and various roles of dysfunctional mitochondria in unhealthy white adipocytes and obesity. Finally, the article emphasizes the importance of enhancing mitochondrial quantity and quality as a therapeutic avenue to correct mitochondrial dysfunction, promote white adipocyte browning, and ultimately improve obesity and its associated metabolic diseases. © 2024 American Physiological Society. Compr Physiol 14:5581-5640, 2024.
    DOI:  https://doi.org/10.1002/cphy.c230009
  8. Ther Adv Endocrinol Metab. 2024 ;15 20420188241282707
    Excessive or sustained endoplasmic reticulum stress: one of the culprits of adipocyte dysfunction in obesity.
    Yu Jiang, Jia-Qi Guo, Ya Wu, Peng Zheng, Shao-Fan Wang, Meng-Chen Yang, Gen-Shan Ma, Yu-Yu Yao.
      As the prevalence of obesity continues to rise globally, the research on adipocytes has attracted more and more attention. In the presence of nutrient overload, adipocytes are exposed to pressures such as hypoxia, inflammation, mechanical stress, metabolite, and oxidative stress that can lead to organelle dysfunction. Endoplasmic reticulum (ER) is a vital organelle for sensing cellular pressure, and its homeostasis is essential for maintaining adipocyte function. Under conditions of excess nutrition, ER stress (ERS) will be triggered by the gathering of abnormally folded proteins in the ER lumen, resulting in the activation of a signaling response known as the unfolded protein responses (UPRs), which is a response system to relieve ERS and restore ER homeostasis. However, if the UPRs fail to rescue ER homeostasis, ERS will activate pathways to damage cells. Studies have shown a role for disturbed activation of adipocyte ERS in the pathophysiology of obesity and its complications. Prolonged or excessive ERS in adipocytes can aggravate lipolysis, insulin resistance, and apoptosis and affect the bioactive molecule production. In addition, ERS also impacts the expression of some important genes. In view of the fact that ERS influences adipocyte function through various mechanisms, targeting ERS may be a viable strategy to treat obesity. This article summarizes the effects of ERS on adipocytes during obesity.
    Keywords:  adipocyte; endoplasmic reticulum stress; inflammation; insulin resistance; lipolysis; obesity
    DOI:  https://doi.org/10.1177/20420188241282707
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