bims-misrem Biomed News
on Mitochondria and sarcoplasmic reticulum in muscle mass
Issue of 2020‒11‒08
ten papers selected by
Rafael Antonio Casuso Pérez
University of Granada


  1. J Mol Cell Cardiol. 2020 Nov 01. pii: S0022-2828(20)30316-3. [Epub ahead of print]
    Boyman L, Greiser M, Lederer WJ.
      Ca2+ flux into the mitochondrial matrix through the MCU holocomplex (MCUcx) has recently been measured quantitatively and with milliseconds resolution for the first time under physiological conditions in both heart and skeletal muscle. Additionally, the dynamic levels of Ca2+ in the mitochondrial matrix ([Ca2+]m) of cardiomyocytes were measured as it was controlled by the balance between influx of Ca2+ into the mitochondrial matrix through MCUcx and efflux through the mitochondrial Na+ / Ca2+ exchanger (NCLX). Under these conditions [Ca2+]m was shown to regulate ATP production by the mitochondria at only a few critical sites. Additional functions attributed to [Ca2+]m continue to be reported in the literature. Here we review the new findings attributed to MCUcx function and provide a framework for understanding and investigating mitochondrial Ca2+ influx features, many of which remain controversial. The properties and functions of the MCUcx subunits that constitute the holocomplex are challenging to tease apart. Such distinct subunits include EMRE, MCUR1, MICUx (i.e. MICU1, MICU2, MICU3), and the pore-forming subunits (MCUpore). Currently, the specific set of functions of each subunit remains non-quantitative and controversial. The more contentious issues are discussed in the context of the newly measured native MCUcx Ca2+ flux from heart and skeletal muscle. These MCUcx Ca2+ flux measurements have been shown to be a highly-regulated, tissue-specific with femto-Siemens Ca2+ conductances and with distinct extramitochondrial Ca2+ ([Ca2+]i) dependencies. These data from cardiac and skeletal muscle mitochondria have been examined quantitatively for their threshold [Ca2+]i levels and for hypothesized gatekeeping function and are discussed in the context of model cell (e.g. HeLa, MEF, HEK293, COS7 cells) measurements. Our new findings on MCUcx dependent matrix [Ca2+]m signaling provide a quantitative basis for on-going and new investigations of the roles of MCUcx in cardiac function ranging from metabolic fuel selection, capillary blood-flow control and the pathological activation of the mitochondrial permeability transition pore (mPTP). Additionally, this review presents the use of advanced new methods that can be readily adapted by any investigator to enable them to carry out quantitative Ca2+ measurements in mitochondria while controlling the inner mitochondrial membrane potential, ΔΨm.
    Keywords:  Heart; Mitochondrial Ca2+ signaling; Mitochondrial Na+/Ca2+ exchanger (NCLX); Mitochondrial calcium uniporter complex (MCUcx); Mitochondrial permeability transition pore (mPTP); Skeletal muscle
    DOI:  https://doi.org/10.1016/j.yjmcc.2020.10.015
  2. Ageing Res Rev. 2020 Oct 29. pii: S1568-1637(20)30335-4. [Epub ahead of print] 101200
    Wiedmer P, Jung T, Castro JP, Pomatto LCD, Sun PY, Davies KJA, Grune T.
      Sarcopenia represents a muscle-wasting syndrome characterized by progressive and generalized degenerative loss of skeletal muscle mass, quality, and strength occurring during normal aging. Sarcopenia patients are mainly suffering from the loss in muscle strength and are faced with mobility disorders reducing their quality of life and are, therefore, at higher risk for morbidity (falls, bone fracture, metabolic diseases) and mortality. Several molecular mechanisms have been described as causes for sarcopenia that refer to very different levels of muscle physiology. These mechanisms cover e. g. function of hormones (e. g. IGF-1 and Insulin), muscle fiber composition and neuromuscular drive, myo-satellite cell potential to differentiate and proliferate, inflammatory pathways as well as intracellular mechanisms in the processes of proteostasis and mitochondrial function. In this review, we describe sarcopenia as a muscle-wasting syndrome distinct from other atrophic diseases and summarize the current view on molecular causes of sarcopenia development as well as open questions provoking further research efforts for establishing efficient lifestyle and therapeutic interventions.
    Keywords:  autophagy; molecular pathways; proteasome; proteostasis
    DOI:  https://doi.org/10.1016/j.arr.2020.101200
  3. Exp Physiol. 2020 Nov 02.
    Hendrickse PW, Krusnauskas R, Hodson-Tole E, Venckunas T, Degens H.
      NEW FINDINGS: What is the central question of this study? Does combining endurance and hypertrophic stimuli blunt the adaptations to both modalities and is this effect greater in muscles with larger baseline fibre cross sectional area? What is the main finding and its importance? Endurance exercise and hypertrophic stimuli can be combined to increase fatigue resistance and fibre size without blunting either adaptation regardless of baseline fibre size.ABSTRACT: Background Previous studies have demonstrated that fibre cross-sectional area (FCSA) is inversely related to oxidative capacity, which is thought to be determined by diffusion limitations of oxygen, ADP and ATP. Consequently, it is hypothesised that 1) when endurance training is combined with a hypertrophic stimulus the response to each will be blunted, and 2) that muscles with a smaller FCSA will show a larger hypertrophic response than those with a large FCSA. Methods To investigate this, we combined overload with endurance exercise in 12-month-old male mice from three different strains with different FCSA: Berlin High (BEH) (large fibres), C57BL/6J (C57) (normal-sized fibres) and Berlin Low (BEL) (small fibres). The right plantaris muscle was subjected to overload through denervation of synergists with the left muscle acting as an internal control. Half the animals trained 30 min per day for 6 weeks. Results The overload-induced hypertrophy was not blunted by endurance exercise, and the exercise-induced increase in fatigue resistance was not impaired by overload. All strains demonstrated similar absolute increases in FCSA, although the BEH mice with more fibres than C57 demonstrated the largest increase in muscle mass and BEL mice with fewer fibres the smallest increase in muscle mass. Conclusions This study suggests that the endurance exercise and hypertrophic stimuli can be combined without attenuating adaptations to either modality, and that increases in FCSA are independent of baseline fibre size. This article is protected by copyright. All rights reserved.
    Keywords:  capillarisation; fibre cross-sectional area; hypertrophy; oxidative capacity; physical activity
    DOI:  https://doi.org/10.1113/EP089096
  4. Int J Mol Sci. 2020 Oct 31. pii: E8157. [Epub ahead of print]21(21):
    Giamogante F, Barazzuol L, Brini M, Calì T.
      Organelle intercommunication represents a wide area of interest. Over the last few decades, increasing evidence has highlighted the importance of organelle contact sites in many biological processes including Ca2+ signaling, lipid biosynthesis, apoptosis, and autophagy but also their involvement in pathological conditions. ER-mitochondria tethering is one of the most investigated inter-organelle communications and it is differently modulated in response to several cellular conditions including, but not limited to, starvation, Endoplasmic Reticulum (ER) stress, and mitochondrial shape modifications. Despite many studies aiming to understand their functions and how they are perturbed under different conditions, approaches to assess organelle proximity are still limited. Indeed, better visualization and characterization of contact sites remain a fascinating challenge. The aim of this review is to summarize strengths and weaknesses of the available methods to detect and quantify contact sites, with a main focus on ER-mitochondria tethering.
    Keywords:  ER–mitochondria tethering; SPLICS; organelle contact sites; split-GFP
    DOI:  https://doi.org/10.3390/ijms21218157
  5. FEBS Open Bio. 2020 Nov 06.
    Shirai T, Obara T, Takemasa T.
      For many ball games, both resistance and endurance training are necessary to improve muscle strength and endurance capacity. Endurance training has been reported to inhibit muscle strength and hypertrophy, but some studies have reported that endurance exercise does not inhibit the effects of resistance exercise. Here, we examined the effect of short or long-duration endurance exercise (EE) on mouse skeletal muscle hypertrophy induced by functional overload at the molecular level. Plantaris muscle hypertrophy was induced by overload (OL) with synergist ablation in mice. Body mass was reduced with endurance training, but EE duration (30 or 90 min) had no effect. The ratio of plantaris muscle weight to body weight was higher in the OL+EE30 and OL+EE90 groups, compared with the OL group. Expression of mTOR signaling proteins, which is related to protein synthesis and hypertrophy, was increased in the OL+EE30 group. Expression of Forkhead box-containing protein O1 (FoxO1), which is related to protein breakdown and atrophy, remained unchanged. However, microtubule- associated protein 1 light chain 3 (LC-3), a known marker of autophagy, and MAFbx which is related to protein breakdown, were significantly increased in the OL+EE90 group. Furthermore, markers of oxidative stress, ubiquitin and (4-hydroxynonenal) 4HNE, were also significantly increased in the OL+EE90 group compared with other groups. In conclusion, EE duration did not affect body- and plantaris mass, and did not interfere with mTOR signaling, but did increase ubiquitinated proteins and oxidative stress. It is therefore necessary to consider training durations for EE when combining endurance and resistance training.
    Keywords:  Endurance training; Exercise duration; Hypertrophy; Protein breakdown; Resistance training; mTOR signaling
    DOI:  https://doi.org/10.1002/2211-5463.13028
  6. Exp Gerontol. 2020 Oct 22. pii: S0531-5565(20)30470-8. [Epub ahead of print]142 111122
    Aas SN, Tømmerbakke D, Godager S, Nordseth M, Armani A, Sandri M, Benestad HB, Raastad T.
      Aging is associated with alterations in skeletal muscle autophagy, potentially affecting both muscle mass and quality in a negative manner. Strength training with protein supplementation has been reported to improve both muscle mass and quality in frail elderly individuals, but whether improvements are accompanied by alterations in protein quality control is not known. To address this issue, we investigated protein degradation markers in skeletal muscle biopsies (m. vastus lateralis) from twenty-four frail elderly men and women (86 ± 7 yr) after acute and chronic (10 weeks) strength training with protein supplementation (ST + PRO) or protein supplementation alone (PRO). Acute increases in mRNA expression of genes related to the ubiquitin proteasome system (MuRF-1, MUSA1), autophagy (ATG7, LC3, p62), and mitochondrial fission (DRP1) were observed after the first, but not after the last training session in ST + PRO. Acute changes in gene expression were accompanied by changes in protein levels of both LC3-I and LC3-II. Hence, the acute training-induced activation of proteasomal degradation and autophagy seems to depend on training status, with activation in the untrained, but not trained state. The ten-week training intervention did not affect basal levels of autophagy mRNAs and proteins, and neither markers of the ubiquitin-proteasome system. This suggests that a relatively short period of strength training may not be sufficient to increase the basal rate of protein degradation in frail elderly.
    Keywords:  Aging; Anabolic resistance; Frailty; Protein breakdown; Resistance exercise
    DOI:  https://doi.org/10.1016/j.exger.2020.111122
  7. Sci Adv. 2020 Nov;pii: eabb7272. [Epub ahead of print]6(45):
    Kong H, Reczek CR, McElroy GS, Steinert EM, Wang T, Sabatini DM, Chandel NS.
      Mitochondria-derived reactive oxygen species (mROS) are required for the survival, proliferation, and metastasis of cancer cells. The mechanism by which mitochondrial metabolism regulates mROS levels to support cancer cells is not fully understood. To address this, we conducted a metabolism-focused CRISPR-Cas9 genetic screen and uncovered that loss of genes encoding subunits of mitochondrial complex I was deleterious in the presence of the mitochondria-targeted antioxidant mito-vitamin E (MVE). Genetic or pharmacologic inhibition of mitochondrial complex I in combination with the mitochondria-targeted antioxidants, MVE or MitoTEMPO, induced a robust integrated stress response (ISR) and markedly diminished cell survival and proliferation in vitro. This was not observed following inhibition of mitochondrial complex III. Administration of MitoTEMPO in combination with the mitochondrial complex I inhibitor phenformin decreased the leukemic burden in a mouse model of T cell acute lymphoblastic leukemia. Thus, mitochondrial complex I is a dominant metabolic determinant of mROS-dependent cellular fitness.
    DOI:  https://doi.org/10.1126/sciadv.abb7272
  8. Biochim Biophys Acta Bioenerg. 2020 Oct 28. pii: S0005-2728(20)30182-1. [Epub ahead of print] 148332
    Cogliati S, Herranz F, Ruiz-Cabello J, Enríquez JA.
      The BlueNative page (BNGE) gel has been the reference technique for studying the electron transport chain organization since it was established 20 years ago. Although the migration of supercomplexes has been demonstrated being real, there are still several concerns about its ability to reveal genuine interactions between respiratory complexes. Moreover, the use of different solubilization conditions generates conflicting interpretations. Here, we thoroughly compare the impact of different digitonin concentrations on the liquid dispersions' physical properties and correlate with the respiratory complexes' migration pattern and supercomplexes. Our results demonstrate that digitonin concentration generates liquid dispersions with specific size and variability critical to distinguish between a real association of complexes from being trapped in the same micelle.
    Keywords:  Bluenative page; detergent,liquid dispersions; digitonin; mitochondria; supercomplexes
    DOI:  https://doi.org/10.1016/j.bbabio.2020.148332
  9. Sci Rep. 2020 Nov 03. 10(1): 18941
    Rohani A, Kashatus JA, Sessions DT, Sharmin S, Kashatus DF.
      Mitochondria are highly dynamic organelles that can exhibit a wide range of morphologies. Mitochondrial morphology can differ significantly across cell types, reflecting different physiological needs, but can also change rapidly in response to stress or the activation of signaling pathways. Understanding both the cause and consequences of these morphological changes is critical to fully understanding how mitochondrial function contributes to both normal and pathological physiology. However, while robust and quantitative analysis of mitochondrial morphology has become increasingly accessible, there is a need for new tools to generate and analyze large data sets of mitochondrial images in high throughput. The generation of such datasets is critical to fully benefit from rapidly evolving methods in data science, such as neural networks, that have shown tremendous value in extracting novel biological insights and generating new hypotheses. Here we describe a set of three computational tools, Cell Catcher, Mito Catcher and MiA, that we have developed to extract extensive mitochondrial network data on a single-cell level from multi-cell fluorescence images. Cell Catcher automatically separates and isolates individual cells from multi-cell images; Mito Catcher uses the statistical distribution of pixel intensities across the mitochondrial network to detect and remove background noise from the cell and segment the mitochondrial network; MiA uses the binarized mitochondrial network to perform more than 100 mitochondria-level and cell-level morphometric measurements. To validate the utility of this set of tools, we generated a database of morphological features for 630 individual cells that encode 0, 1 or 2 alleles of the mitochondrial fission GTPase Drp1 and demonstrate that these mitochondrial data could be used to predict Drp1 genotype with 87% accuracy. Together, this suite of tools enables the high-throughput and automated collection of detailed and quantitative mitochondrial structural information at a single-cell level. Furthermore, the data generated with these tools, when combined with advanced data science approaches, can be used to generate novel biological insights.
    DOI:  https://doi.org/10.1038/s41598-020-75899-5
  10. Mol Cell. 2020 Oct 26. pii: S1097-2765(20)30720-6. [Epub ahead of print]
    Adachi Y, Kato T, Yamada T, Murata D, Arai K, Stahelin RV, Chan DC, Iijima M, Sesaki H.
      Mitochondria are highly dynamic organelles that continuously grow, divide, and fuse. The division of mitochondria is crucial for human health. During mitochondrial division, the mechano-guanosine triphosphatase (GTPase) dynamin-related protein (Drp1) severs mitochondria at endoplasmic reticulum (ER)-mitochondria contact sites, where peripheral ER tubules interact with mitochondria. Here, we report that Drp1 directly shapes peripheral ER tubules in human and mouse cells. This ER-shaping activity is independent of GTP hydrolysis and located in a highly conserved peptide of 18 amino acids (termed D-octadecapeptide), which is predicted to form an amphipathic α helix. Synthetic D-octadecapeptide tubulates liposomes in vitro and the ER in cells. ER tubules formed by Drp1 promote mitochondrial division by facilitating ER-mitochondria interactions. Thus, Drp1 functions as a two-in-one protein during mitochondrial division, with ER tubulation and mechano-GTPase activities.
    Keywords:  Drp1; mitochondria; mitochondrial division; organelle contact sites; phosphaditic acid; the endoplasmic reticulum
    DOI:  https://doi.org/10.1016/j.molcel.2020.10.013