| 1. |
- Correia, Jorge C., et al.
(författare)
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Muscle-secreted neurturin couples myofiber oxidative metabolism and slow motor neuron identity
- 2021
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Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131 .- 1932-7420. ; 33:11, s. 2215-2230
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Tidskriftsartikel (refereegranskat)abstract
- Endurance exercise promotes skeletal muscle vascularization, oxidative metabolism, fiber-type switching, and neuromuscular junction integrity. Importantly, the metabolic and contractile properties of the muscle fiber must be coupled to the identity of the innervating motor neuron (MN). Here, we show that muscle-derived neurturin (NRTN) acts on muscle fibers and MNs to couple their characteristics. Using a muscle-specific NRTN transgenic mouse (HSA-NRTN) and RNA sequencing of MN somas, we observed that retrograde NRTN signaling promotes a shift toward a slow MN identity. In muscle, NRTN increased capillary density and oxidative capacity and induced a transcriptional reprograming favoring fatty acid metabolism over glycolysis. This combination of effects on muscle and MNs makes HSA-NRTN mice lean with remarkable exercise performance and motor coordination. Interestingly, HSA-NRTN mice largely recapitulate the phenotype of mice with muscle-specific expression of its upstream regulator PGC-1a1. This work identifies NRTN as a myokine that couples muscle oxidative capacity to slow MN identity.
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| 2. |
- Lanner, Johanna, et al.
(författare)
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Running reverses tumor-induced muscle weakness in mice with breast cancer
- 2019
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Konferensbidrag (refereegranskat)abstract
- Introduction: Patients with breast cancer experience muscle dysfunction, which is a clinical challenge that is not restricted to advanced stage patients, but also observed in newly diagnosed weight-stable patients with low tumor burden. Recent data indicate that physical activity can reduce breast cancerassociated mortality, suggesting that improved muscle performance per secan have positive impact on survival. Here, the transgenic PyMT mouse model of breast cancer was used to elucidate molecular mechanisms underlying breast cancer-induced muscle impairments.Materials and Methods: PyMT mice and wildtype (WT) littermates w/wo access to an in-cage running wheel for four weeks (week 8-12). Functional readouts included Ca2+imaging; isometric force measurement on single fibers and intact fast-and slow-twitchmuscles. Intramuscular signaling was assessed using immunofluorescence, immunoblotting and enzymatic assays.Results: The specific force (i.e. force/cross-sectional area) was significantly decreased by ~ 35% in slow-twitch soleus muscles from breast cancermice as compared to WT muscles, which was the result of reduced Ca2+release and impaired myofibrillar function. There were no difference in muscle size or fiber type between the two groups. However, higher intramuscular stress (e.g. p38 activation and carbonylation (DNP)) was observed in PyMT than in WT. Intriguingly, voluntary running for four weeks reversed the weakness and PyMT soleus muscles generated similar forces as muscles of exercised WT mice. The running induced higher SOD2 expression and normalized levels of p38 and DNP.Conclusion: Intrinsic contractile dysfunction and higher intramuscular stress was present in mice with breast cancer, which was counteracted with voluntary running.
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| 3. |
- Liu, Zhengye
(författare)
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Mitochondria and its role in metabolic regulation and skeletal muscle function in healthy and disease conditions
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 4. |
- Liu, Zhengye, et al.
(författare)
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Mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force
- 2021
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Ingår i: The FASEB Journal. - : John Wiley & Sons. - 0892-6638 .- 1530-6860. ; 35:12
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Tidskriftsartikel (refereegranskat)abstract
- The hypoxia-inducible nuclear-encoded mitochondrial protein NADH dehydrogenase (ubiquinone) 1 alpha subcomplex, 4-like 2 (NDUFA4L2) has been demonstrated to decrease oxidative phosphorylation and production of reactive oxygen species in neonatal cardiomyocytes, brain tissue and hypoxic domains of cancer cells. Prolonged local hypoxia can negatively affect skeletal muscle size and tissue oxidative capacity. Although skeletal muscle is a mitochondrial rich, oxygen sensitive tissue, the role of NDUFA4L2 in skeletal muscle has not previously been investigated. Here we ectopically expressed NDUFA4L2 in mouse skeletal muscles using adenovirus-mediated expression and in vivo electroporation. Moreover, femoral artery ligation (FAL) was used as a model of peripheral vascular disease to induce hind limb ischemia and muscle damage. Ectopic NDUFA4L2 expression resulted in reduced mitochondrial respiration and reactive oxygen species followed by lowered AMP, ADP, ATP, and NAD(+) levels without affecting the overall protein content of the mitochondrial electron transport chain. Furthermore, ec-topically expressed NDUFA4L2 caused a similar to 20% reduction in muscle mass that resulted in weaker muscles. The loss of muscle mass was associated with increased gene expression of atrogenes MurF1 and Mul1, and apoptotic genes caspase 3 and Bax. Finally, we showed that NDUFA4L2 was induced by FAL and that the Ndufa4l2 mRNA expression correlated with the reduced capacity of the muscle to generate force after the ischemic insult. These results show, for the first time, that mitochondrial NDUFA4L2 is a novel regulator of skeletal muscle mass and force. Specifically, induced NDUFA4L2 reduces mitochondrial activity leading to lower levels of important intramuscular metabolites, including adenine nucleotides and NAD(+), which are hallmarks of mitochondrial dysfunction and hence shows that dysfunctional mitochondrial activity may drive muscle wasting.
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| 5. |
- Mader, Theresa, et al.
(författare)
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Metabolic alteration and muscle dysfunction in mice with breast cancer
- 2018
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Konferensbidrag (refereegranskat)abstract
- Breast cancer accounts for ~25% of diagnosed cancer types in woman [1]. Decreased physical fitness and muscle weakness are common complications in patients with breast cancer. In cancer, muscle weakness has traditionally been linked to muscle wasting and significant weight loss (cachexia) [2]. However, muscle weakness is present in non-cachectic, weight-stable patients with breast cancer [3]. In fact, cancer-induced muscle dysfunction is a broad clinical challenge that is not restricted to palliative or advanced stage patients, but also observed in newly diagnosed patients with low tumor burden [4]. Further, with the breast cancer treatment improving, it is important to take a look on the patients quality of life [5]. However, little is known about the features underlying breast cancer-induced muscle impairments and no drug preventing cancer-induced muscle weakness is clinically proven. Here we aim at characterizing the metabolic status and the muscle function in mice with breast cancer.The breast cancer mouse-model MMTV-PyMT (PyMT) used here, is characterized by an early onset of mammary cancer (from 5 weeks of age) and follows a similar progression pattern as the one observed in human patients [6]. Soleus muscle from PyMT mice exhibited ~30% lower specific force (kN/m2) than soleus muscle from wildtype (WT) mice (n=28-29, p ≤ 0.05, mice were 12 week old at sacrifice). There were no significant differences in muscle mass, fiber size or fiber type distribution between PyMT and WT muscle. Furthermore, there were no differences in glycogen content (μg/g muscle) in soleus muscle from PyMT and WT mice. Simultaneous measurement of numerous parameters (e.g. oxygen consumption (VO2), carbon dioxide production (VCO2), and food and water intake) was carried out using comprehensive lab animal monitoring system (CLAMS) to gain insight into the metabolic status of the mice. The mice were monitored over a week and the average respiratory exchange ratio (RER = CO2production: O2 uptake) were significantly differed between PyMT and WT mice, with mean PyMT RER of 0.95±0.01 and WT RER of 1.0±0.01 (mean data +/-SEM, n=8, p<0.001). Thus, indicative that PyMT have an altered metabolism towards fatty acid utilization.In summary, soleus muscles are weaker and the whole-body metabolism appears altered in mice with breast cancer as compared with healthy control mice. Gene and molecular analysis are currently being performed to further assess mitochondrial and glucose metabolism. Nevertheless, further studies are needed to gain insight into cancer-derived factors that contributes to skeletal muscle dysfunction and altered metabolism.1. Jemal, A., et al., Cancer statistics, 2008. CA Cancer J Clin, 2008. 58(2): p. 71-96.2. Johns, N., N.A. Stephens, and K.C. Fearon, Muscle wasting in cancer. Int J Biochem Cell Biol, 2013. 45(10): p. 2215-29.3. Klassen, O., et al., Muscle strength in breast cancer patients receiving different treatment regimes. Journal of Cachexia, Sarcopenia and Muscle, 2017. 8(2): p. 305-316.4. Villasenor, A., et al., Prevalence and prognostic effect of sarcopenia in breast cancer survivors: the HEAL Study. J Cancer Surviv, 2012. 6(4): p. 398-406.5. Perry, S., T.L. Kowalski, and C.H. Chang, Quality of life assessment in women with breast cancer: benefits, acceptability and utilization. Health Qual Life Outcomes, 2007. 5: p. 24.6. Fantozzi, A. and G. Christofori, Mouse models of breast cancer metastasis. Breast Cancer Res, 2006. 8(4): p. 212.
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