Mitochondria and its role in metabolic regulation and skeletal muscle function in healthy and disease conditions

Skeletal muscle function is critical for our overall health and to be able to perform daily activities. Skeletal muscle has the ability to adapt to various stimuli and mitochondria are known to play an important role in these adaptation processes. Healthy mitochondria are essential for providing skeletal muscle with energy, which are used for various biochemical reactions including generating force and maintaining muscle mass, whereas dysfunctional mitochondria have been associated with loss of skeletal muscle mass and function. In study I, we investigated the role of nuclear-encoded mitochondrial protein NDUFA4L2 in skeletal muscle. NDUFA4L2 has been shown to decrease oxidative phosphorylation and the production of reactive oxygen species in various tissues and cell lines. We ectopically expressed NDUFA4L2 in mouse skeletal muscles with adenovirus-mediated expression and in vivo electroporation. We found that ectopic NDUFA4L2 expression in skeletal muscle reduced mitochondrial respiration and reactive oxygen species production, together with lowered levels of AMP, ADP, ATP, and NAD+, while the overall protein content of mitochondrial remained unchanged. Furthermore, ectopic expression of NDUFA4L2 resulted in smaller muscle mass and hence weaker muscles. The loss of muscle mass was associated with the activation of atrogenes MurF1 and Mul1, and apoptotic genes caspase 3. We used unilateral femoral artery ligation (FAL) as a mouse model of peripheral vascular disease (PVD) to induce muscle ischemia. Our results showed that NDUFA4L2 was induced in skeletal muscle after FAL. The gene expression of Ndufa4l2 correlated with the reduced capacity of the muscle to produce force. In study II, we aim to study the role of mitochondria in PVD-induced muscle dysfunction. PVD lowers blood flow to the lower limbs, causing debilitating skeletal muscle myopathy. Interventions that improve distal arterial pressures (i.e., bypass surgery) generally fail to normalize the functional performance of muscle indicating pathophysiological mechanisms inside the skeletal myofibers that reduce overall muscle function. We performed FAL surgery on mice that were fed either a normal chow diet (ND) or a high-fat diet (HFD) for eight weeks. Our results showed that the muscle weakness induced by FAL was exacerbated in mice fed HFD, together with more serious fibrosis and ectopic fat accumulation in these muscles. Our RNA-sequencing results showed that mitochondrial gene expressions had synchronized reduction in ND-FAL legs, while the reduction was attenuated in HFD-FAL legs. Mitochondrial assembly and cellular respiration were identified as the top suppressed pathway in ND-FAL legs, but not in HFD mice. Fibrosis, fat metabolism, and myosin heavy chain isotypes were amongst the top variable genes in control and FAL muscle from normal and obese mice. Inference of proportions of different cell types with ImmuCC found that HFD has already induced an inflammatory response in skeletal muscle without FAL. Our results suggested that mitochondria content and function may be potential targets to improve muscle function in PVD associated with T2D. Insulin resistance and defects in mitochondrial oxidative phosphorylation (OXPHOS) have been suggested to play an important role in the metabolic dysfunction and muscle impairments caused by T2D. However, we are currently lacking effective treatment against muscle dysfunction in T2D. In study III, we manipulated the mitochondrial electron transport chain (ETC) with our novel NDUFA4L2 genetically knocked-out mouse model. Skeletal muscle lacking NDUFA4L2 appeared stronger, more fatigue resistant, and exhibited higher capillary density and whole-body glucose clearance. NDUFA4L2 knockout mice showed a different metabolic status compared with wild-type litters. Our results indicated that NDUFA4L2 influences skeletal muscle function and hence may be a novel target for T2D-associated muscle dysfunction. The coactivator PGC-1α1 is pivotal to the regulation of mitochondrial function and content in skeletal muscle. In skeletal muscle after exercise, PGC-1α1 enhanced the expression of kynurenine aminotransferases (Kats), an enzyme that catalyzes the conversion from kynurenine to kynurenic acid. In study IV, we observed that PGC-1α1 increased the expression of genes associated with glycolysis and malate-aspartate shuttle (MAS), together with an elevation in aspartate and glutamate levels. These processes promote energy utilization and facilitate the transfer of electrons from the donors to mitochondrial respiration. Thus, trained skeletal muscle can use kynurenine metabolism to increase the bioenergetic efficiency of glucose oxidation through this PGC-1α1-dependent mechanism. Inhibition of Kat with carbidopa resulted in impairments in aspartate biosynthesis, mitochondrial respiration, and skeletal muscle function. After all, the activate MAS and kynurenine catabolism in skeletal muscle after exercise by PGC-1α1 is important for the muscle’s adaptation to endurance training. Taken together, these four studies presented in this thesis highlighted the important role of mitochondria in skeletal muscle and the feasibility of targeting mitochondria for the improvement of skeletal muscle function in both healthy and diseased conditions

Quantitative security analysis of three-level unitary operations in quantum secret sharing without entanglement

Quantum secret sharing (QSS) protocols without entanglement have showed high security by virtue of the characteristics of quantum mechanics. However, it is still a challenge to compare the security of such protocols depending on quantitative security analysis. Based on our previous security analysis work on protocols using single qubits and two-level unitary operations, QSS protocols with single qutrits and three-level unitary operations are considered in this paper. Under the Bell-state attack we propose, the quantitative security analyses according to different three-level unitary operations are provided respectively in the one-step and two-step situations. Finally, important conclusions are drawn for designing and implementing such QSS protocols. The method and results may also contribute to analyze the security of other high-level quantum cryptography schemes based on unitary operations

Multi-transcriptome analysis following an acute skeletal muscle growth stimulus yields tools for discerning global and MYC regulatory networks

Myc is a powerful transcription factor implicated in epigenetic reprogramming, cellular plasticity, and rapid growth as well as tumorigenesis. Cancer in skeletal muscle is extremely rare despite marked and sustained Myc induction during loading-induced hypertrophy. Here, we investigated global, actively transcribed, stable, and myonucleus-specific transcriptomes following an acute hypertrophic stimulus in mouse plantaris. With these datasets, we define global and Myc-specific dynamics at the onset of mechanical overload-induced muscle fiber growth. Data collation across analyses reveals an under-appreciated role for the muscle fiber in extracellular matrix remodeling during adaptation, along with the contribution of mRNA stability to epigenetic-related transcript levels in muscle. We also identify Runx1 and Ankrd1 (Marp1) as abundant myonucleus-enriched loading-induced genes. We observed that a strong induction of cell cycle regulators including Myc occurs with mechanical overload in myonuclei. Additionally, in vivo Myc-controlled gene expression in the plantaris was defined using a genetic muscle fiber-specific doxycycline-inducible Myc-overexpression model. We determined Myc is implicated in numerous aspects of gene expression during early-phase muscle fiber growth. Specifically, brief induction of Myc protein in muscle represses Reverbα, Reverbβ, and Myh2 while increasing Rpl3, recapitulating gene expression in myonuclei during acute overload. Experimental, comparative, and in silico analyses place Myc at the center of a stable and actively transcribed, loading-responsive, muscle fiber–localized regulatory hub. Collectively, our experiments are a roadmap for understanding global and Myc-mediated transcriptional networks that regulate rapid remodeling in postmitotic cells. We provide open webtools for exploring the five RNA-seq datasets as a resource to the field

Disrupted circadian oscillations in type 2 diabetes are linked to altered rhythmic mitochondrial metabolism in skeletal muscle

Funding: The authors are supported by grants from the AstraZeneca SciLifeLab Research Programme, Novo Nordisk Foundation (NNF14OC0011493, and NNF17OC0030088), Swedish Diabetes Foundation (DIA2018-357), Swedish Research Council (2015-00165 and 2018-02389), the Knut and Alice Wallenberg Foundation (2018-0094), the Strategic Research Programme in Diabetes at Karolinska Institutet (2009-1068), the Stockholm County Council (SLL20170159), and the Swedish Research Council for Sport Science (P2019-0140). B.M.G. was supported by fellowships from the Novo Nordisk Foundation (NNF19OC0055072), the Wenner-Gren Foundation, an Albert Renold Travel Fellowship from the European Foundation for the Study of Diabetes, and an Eric Reid Fund for Methodology from the Biochemical Society. N.J.P. and L.S.-P. were supported by an Individual Fellowship from the Marie Skłodowska-Curie Actions (European Commission: 704978 and 675610). X.Z. and K.A.E. were supported by NIH R01AR066082. N.J.P. was supported by grants from the Sigurd och Elsa Goljes Minne and Lars Hierta Memorial Foundations (Sweden). We acknowledge the Beta Cell in-vivo Imaging/Extracellular Flux Analysis core facility supported by the Strategic Research Program in Diabetes for the usage of the Seahorse flux analyzer. Additional support was received from the Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen (NNF18CC0034900). The Novo Nordisk Foundation Center for Basic Metabolic Research is an independent research center at the University of Copenhagen, partially funded by an unrestricted donation from the Novo Nordisk Foundation. We acknowledge the Single-Cell Omics platform at the Novo Nordisk Foundation Center for Basic Metabolic Research for technical and computational expertise and support. Schematics are created with BioRender.com.Peer reviewedPublisher PD

Skeletal muscle PGC-1α1 reroutes kynurenine metabolism to increase energy efficiency and fatigue-resistance

The coactivator PGC-1α1 is activated by exercise training in skeletal muscle and promotes fatigue-resistance. In exercised muscle, PGC-1α1 enhances the expression of kynurenine aminotransferases (Kats), which convert kynurenine into kynurenic acid. This reduces kynurenine-associated neurotoxicity and generates glutamate as a byproduct. Here, we show that PGC-1α1 elevates aspartate and glutamate levels and increases the expression of glycolysis and malate-aspartate shuttle (MAS) genes. These interconnected processes improve energy utilization and transfer fuel-derived electrons to mitochondrial respiration. This PGC-1α1-dependent mechanism allows trained muscle to use kynurenine metabolism to increase the bioenergetic efficiency of glucose oxidation. Kat inhibition with carbidopa impairs aspartate biosynthesis, mitochondrial respiration, and reduces exercise performance and muscle force in mice. Our findings show that PGC-1α1 activates the MAS in skeletal muscle, supported by kynurenine catabolism, as part of the adaptations to endurance exercise. This crosstalk between kynurenine metabolism and the MAS may have important physiological and clinical implications

A Study of Racket Weight Adaptation in Advanced and Beginner Badminton Players

The jump smash is the most aggressive manoeuvre in badminton. Racket parameters may be the key factor affecting the performance of jump smash. Previous studies have focused only on the biomechanical characteristics of athletes or on racket parameters in isolation, with less observation of the overall performance of the human-racket system. This study aims to explore the effects of different racket weights on neuromuscular control strategies in advanced and beginner players. Nonnegative matrix factorisation (NMF) was used to extract the muscle synergies of players when jumping smash using different rackets (3U, 5U), and K-means clustering was used to obtain the fundamental synergies. Uncontrolled manifold (UCM) analyses were used to establish links between synergy and motor performance, and surface electromyography (sEMG) was mapped to each spinal cord segment. The study found significant differences (P <0.05) in the postural muscles of skilled players and significant differences (P <0.001) in the upper-limb muscles of beginners when the racket weight was increased. Advanced players adapt to the increase in racket weight primarily by adjusting the timing of the activation of the third synergy. Combined synergy in advanced players is mainly focused on the backswing, while that in beginners is mainly focused on the frontswing. This suggests that advanced players may be more adept at utilising the postural muscles and their coordination with the upper-limb muscles to adapt to different rackets. In addition, the motor experience can help athletes adapt more quickly to heavier rackets, and this adaptation occurs primarily by adjusting the temporal phase and covariation characteristics of the synergies rather than by increasing the number of synergies