bims-misrem Biomed News
on Mitochondria and sarcoplasmic reticulum in muscle mass
Issue of 2021‒08‒29
six papers selected by
Rafael Antonio Casuso Pérez
University of Granada

  1. Physiol Rep. 2021 Aug;9(16): e15016
      This study aimed to examine the effects of voluntary wheel running on cancer cachexia-induced mitochondrial alterations in mouse skeletal muscle. Mice bearing colon 26 adenocarcinoma (C26) were used as a model of cancer cachexia. C26 mice showed a lower gastrocnemius and plantaris muscle weight, but 4 weeks of voluntary exercise rescued these changes. Further, voluntary exercise attenuated observed declines in the levels of oxidative phosphorylation proteins and activities of citrate synthase and cytochrome c oxidase in the skeletal muscle of C26 mice. Among mitochondrial morphology regulatory proteins, mitofusin 2 (Mfn2) and dynamin-related protein 1 (Drp1) were decreased in the skeletal muscle of C26 mice, but exercise resulted in similar improvements as seen in markers of mitochondrial content. In isolated mitochondria, 4-hydroxynonenal and protein carbonyls were elevated in C26 mice, but exercise blunted the increases in these markers of oxidative stress. In addition, electron microscopy revealed that exercise alleviated the observed increase in the percentage of damaged mitochondria in C26 mice. These results suggest that voluntary exercise effectively counteracts mitochondrial dysfunction to mitigate muscle loss in cachexia.
    Keywords:  cancer cachexia; mitochondria; oxidative stress; skeletal muscle; voluntary exercise
  2. Front Cell Dev Biol. 2021 ;9 673618
      Background: Cancer-associated cachexia (CAC) is a syndrome characterized by skeletal muscle atrophy, and the underlying mechanisms are still unclear. Recent research studies have shed light on a noteworthy link between mitochondrial dynamics and muscle physiology. In the present study, we investigate the role of dynamin-related protein 1 (DRP1), a pivotal factor of mitochondrial dynamics, in myotube atrophy during cancer-associated cachexia.Methods: Seventy-six surgical patients, including gastrointestinal tumor and benign disease, were enrolled in the study and divided to three groups: control, non-cachexia, and cancer-associated cachexia. Demographic data were collected. Their rectus abdominis samples were acquired intraoperatively. Muscle fiber size, markers of ubiquitin proteasome system (UPS), mitochondrial ultrastructure, and markers of mitochondrial function and dynamics were assayed. A cachexia model in vitro was established via coculturing a C2C12 myotube with media from C26 colon cancer cells. A specific DRP1 inhibitor, Mdivi-1, and a lentivirus of DRP1 knockdown/overexpression were used to regulate the expression of DRP1. Muscle diameter, mitochondrial morphology, mass, reactive oxygen species (ROS), membrane potential, and markers of UPS, mitochondrial function, and dynamics were determined.
    Results: Patients of cachexia suffered from a conspicuous worsened nutrition status and muscle loss compared to patients of other groups. Severe mitochondrial swelling and enlarged area were observed, and partial alterations in mitochondrial function were found in muscle. Analysis of mitochondrial dynamics indicated an upregulation of phosphorylated DRP1 at the ser616 site. In vitro, cancer media resulted in the atrophy of myotube. This was accompanied with a prominent unbalance of mitochondrial dynamics, as well as enhanced mitochondrial ROS and decreased mitochondrial function and membrane potential. However, certain concentrations of Mdivi-1 and DRP1 knockdown rebalanced the mitochondrial dynamics, mitigating this negative phenotype caused by cachexia. Moreover, overexpression of DRP1 aggravated these phenomena.
    Conclusion: In clinical patients, cachexia induces abnormal mitochondrial changes and possible fission activation for the atrophied muscle. Our cachexia model in vitro further demonstrates that unbalanced mitochondrial dynamics contributes to this atrophy and mitochondrial impairment, and rebuilding the balance by regulating of DRP1 could ameliorate these alterations.
    Keywords:  atrophy; cancer-associated cachexia; dynamin-related protein 1; mitochondria fission; skeletal muscle
  3. FASEB J. 2021 09;35(9): e21864
      Resistance training (RT) dynamically alters the skeletal muscle nuclear DNA methylome. However, no study has examined if RT affects the mitochondrial DNA (mtDNA) methylome. Herein, ten older, Caucasian untrained males (65 ± 7 y.o.) performed six weeks of full-body RT (twice weekly). Body composition and knee extensor torque were assessed prior to and 72 h following the last RT session. Vastus lateralis (VL) biopsies were also obtained. VL DNA was subjected to reduced representation bisulfite sequencing providing excellent coverage across the ~16-kilobase mtDNA methylome (254 CpG sites). Biochemical assays were also performed, and older male data were compared to younger trained males (22 ± 2 y.o., n = 7, n = 6 Caucasian & n = 1 African American). RT increased whole-body lean tissue mass (p = .017), VL thickness (p = .012), and knee extensor torque (p = .029) in older males. RT also affected the mtDNA methylome, as 63% (159/254) of the CpG sites demonstrated reduced methylation (p < .05). Several mtDNA sites presented a more "youthful" signature in older males after RT in comparison to younger males. The 1.12 kilobase mtDNA D-loop/control region, which regulates replication and transcription, possessed enriched hypomethylation in older males following RT. Enhanced expression of mitochondrial H- and L-strand genes and complex III/IV protein levels were also observed (p < .05). While limited to a shorter-term intervention, this is the first evidence showing that RT alters the mtDNA methylome in skeletal muscle. Observed methylome alterations may enhance mitochondrial transcription, and RT evokes mitochondrial methylome profiles to mimic younger men. The significance of these findings relative to broader RT-induced epigenetic changes needs to be elucidated.
    Keywords:  aging; methylation; mitochondrial DNA; resistance training
  4. Front Nutr. 2021 ;8 633987
      Background: Maintaining skeletal muscle mass and function in aging is crucial for preserving the quality of life and health. An experimental bed rest (BR) protocol is a suitable model to explore muscle decline on aging during inactivity. Objective: The purpose of this systematic review and meta-analysis was, therefore, to carry out an up-to-date evaluation of bed rest, with a specific focus on the magnitude of effects on muscle mass, strength, power, and functional capacity changes as well as the mechanisms, molecules, and pathways involved in muscle decay. Design: This was a systematic review and meta-analysis study. Data sources: We used PubMed, Medline; Web of Science, Google Scholar, and the Cochrane library, all of which were searched prior to April 23, 2020. A manual search was performed to cover bed rest experimental protocols using the following key terms, either singly or in combination: "Elderly Bed rest," "Older Bed rest," "Old Bed rest," "Aging Bed rest," "Aging Bed rest," "Bed-rest," and "Bedrest". Eligibility criteria for selecting studies: The inclusion criteria were divided into four sections: type of study, participants, interventions, and outcome measures. The primary outcome measures were: body mass index, fat mass, fat-free mass, leg lean mass, cross-sectional area, knee extension power, cytokine pattern, IGF signaling biomarkers, FOXO signaling biomarkers, mitochondrial modulation biomarkers, and muscle protein kinetics biomarkers. Results: A total of 25 studies were included in the qualitative synthesis, while 17 of them were included in the meta-analysis. In total, 118 healthy elderly volunteers underwent 5-, 7-, 10-, or 14-days of BR and provided a brief sketch on the possible mechanisms involved. In the very early phase of BR, important changes occurred in the skeletal muscle, with significant loss of performance associated with a lesser grade reduction of the total body and muscle mass. Meta-analysis of the effect of bed rest on total body mass was determined to be small but statistically significant (ES = -0.45, 95% CI: -0.72 to -0.19, P < 0.001). Moderate, statistically significant effects were observed for total lean body mass (ES = -0.67, 95% CI: -0.95 to -0.40, P < 0.001) after bed rest intervention. Overall, total lean body mass was decreased by 1.5 kg, while there was no relationship between bed rest duration and outcomes (Z = 0.423, p = 672). The meta-analyzed effect showed that bed rest produced large, statistically significant, effects (ES = -1.06, 95% CI: -1.37 to -0.75, P < 0.001) in terms of the knee extension power. Knee extension power was decreased by 14.65 N/s. In contrast, to other measures, meta-regression showed a significant relationship between bed rest duration and knee extension power (Z = 4.219, p < 0.001). Moderate, statistically significant, effects were observed after bed rest intervention for leg muscle mass in both old (ES = -0.68, 95% CI: -0.96 to -0.40, P < 0.001) and young (ES = -0.51, 95% CI: -0.80 to -0.22, P < 0.001) adults. However, the magnitude of change was higher in older (MD = -0.86 kg) compared to younger (MD = -0.24 kg) adults. Conclusion: Experimental BR is a suitable model to explore the detrimental effects of inactivity in young adults, old adults, and hospitalized people. Changes in muscle mass and function are the two most investigated variables, and they allow for a consistent trend in the BR-induced changes. Mechanisms underlying the greater loss of muscle mass and function in aging, following inactivity, need to be thoroughly investigated.
    Keywords:  aging; bed rest; muscle function; muscle mass; muscle physiopathology
  5. J Cell Biochem. 2021 Aug 25.
      Mitochondria function as an integrated network that moves along the microtubules within cells and changes the morphology through membrane fusion and fission events. Mitofusin (MFN) mediates membrane tethering and subsequent fusion of the mitochondrial outer membrane. Understanding the regulatory mechanisms of MFN function is critical to tackling the pathology related to mitochondrial network imbalance. Here, we reveal a novel inhibitory mechanism of MFN-mediated fusion by mitochondrial Rho GTPase (Miro1) in response to elevated mitochondrial Ca2+ concentration ([Ca2+ ]m ). We showed that elevated [Ca2+ ]m prevents the fusion between mitochondria forming the outer membrane tether by ectopically expressing MFN. Lowering [Ca2+ ]m by treating cells with an inhibitor of mitochondrial calcium uniporter or knocking down Miro1/2 induces more fused networks. Miro1 interacts with MFN as supported by co-immunoprecipitation and protein association identified by proximity labeling proteomics. It suggests that Miro1 functions as a Ca2+ -sensor and inhibits MFN function at elevated [Ca2+ ]m. Miro1 EF-hand mutant has a compromised inhibitory effect, which reiterates Ca2+ -modulated regulation. Dysregulated Ca2+ -handling and mitochondrial network imbalance are highly relevant in the pathology of cancers, cardiovascular, and neurodegenerative diseases. Miro1 functions as a coordinated Ca2+ -responder by pausing mitochondrial transport while reducing network fusion and cooperating with Drp1-mediated fission. It likely prevents the detrimental effect of Ca2+ m overload and facilitates mitophagy. Our finding reveals a novel regulation of mitochondrial network dynamics responding to [Ca2+ ]m through the interplay of Miro1 and MFN. Modulation of Miro1 and MFN interaction is a potential intervention to promote network homeostasis.
    Keywords:  mitochondrial Rho GTPase (Miro); mitochondrial calcium; mitochondrial fusion; mitochondrial network homeostasis; mitofusin (MFN)
  6. Cell Mol Life Sci. 2021 Aug 27.
      Membrane-contact sites are getting more and more credit for their indispensable role in maintenance of cell function and homeostasis. In the last decades, the ER-mitochondrial contact sites in particular received a lot of attention. While our knowledge of ER-mitochondrial contact sites increases steadily, the focus often lies on a static exploration of their functions. However, it is increasingly clear that these contact sites are very dynamic. In this review, we highlight the dynamic nature of ER-mitochondrial contact sites and the role of kinases and phosphatases therein with a focus on recent findings. Phosphorylation events allow for rapid integration of information on the protein level, impacting protein function, localization and interaction at ER-mitochondrial contact sites. To illustrate the importance of these events and to put them in a broader perspective, we connect them to pathologies like diabetes type II, Parkinson's disease and cancer.
    Keywords:  Ca2+ signalling; Insulin signalling; Mitochondria-associated membranes; Mitochondrial dynamics; Mitophagy