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- Mader, Theresa, et al.
(författare)
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Exercise reduces intramuscular stress and counteracts muscle weakness in mice with breast cancer
- 2022
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Ingår i: Journal of Cachexia, Sarcopenia and Muscle. - : John Wiley & Sons. - 2190-5991 .- 2190-6009. ; 13:2, s. 1151-1163
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Patients with breast cancer exhibit muscle weakness, which is associated with increased mortality risk and reduced quality of life. Muscle weakness is experienced even in the absence of loss of muscle mass in breast cancer patients, indicating intrinsic muscle dysfunction. Physical activity is correlated with reduced cancer mortality and disease recurrence. However, the molecular processes underlying breast cancer-induced muscle weakness and the beneficial effect of exercise are largely unknown.METHODS: Eight-week-old breast cancer (MMTV-PyMT, PyMT) and control (WT) mice had access to active or inactive in-cage voluntary running wheels for 4 weeks. Mice were also subjected to a treadmill test. Muscle force was measured ex vivo. Tumour markers were determined with immunohistochemistry. Mitochondrial biogenesis and function were assessed with transcriptional analyses of PGC-1α, the electron transport chain (ETC) and antioxidants superoxide dismutase (Sod) and catalase (Cat), combined with activity measurements of SOD, citrate synthase (CS) and β-hydroxyacyl-CoA-dehydrogenase (βHAD). Serum and intramuscular stress levels were evaluated by enzymatic assays, immunoblotting, and transcriptional analyses of, for example, tumour necrosis factor-α (TNF-α) and p38 mitogen-activated protein kinase (MAPK) signalling.RESULTS: PyMT mice endured shorter time and distance during the treadmill test (~30%, P < 0.05) and ex vivo force measurements revealed ~25% weaker slow-twitch soleus muscle (P < 0.001). This was independent of cancer-induced alteration of muscle size or fibre type. Inflammatory stressors in serum and muscle, including TNF-α and p38 MAPK, were higher in PyMT than in WT mice (P < 0.05). Cancer-induced decreases in ETC (P < 0.05, P < 0.01) and antioxidant gene expression were observed (P < 0.05). The exercise intervention counteracted the cancer-induced muscle weakness and was accompanied by a less aggressive, differentiated tumour phenotype, determined by increased CK8 and reduced CK14 expression (P < 0.05). In PyMT mice, the exercise intervention led to higher CS activity (P = 0.23), enhanced β-HAD and SOD activities (P < 0.05), and reduced levels of intramuscular stressors together with a normalization of the expression signature of TNFα-targets and ETC genes (P < 0.05, P < 0.01). At the same time, the exercise-induced PGC-1α expression, and CS and β-HAD activity was blunted in muscle from the PyMT mice as compared with WT mice, indicative that breast cancer interfere with transcriptional programming of mitochondria and that the molecular adaptation to exercise differs between healthy mice and those afflicted by disease.CONCLUSIONS: Four-week voluntary wheel running counteracted muscle weakness in PyMT mice which was accompanied by reduced intrinsic stress and improved mitochondrial and antioxidant profiles and activities that aligned with muscles of healthy mice.
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| 3. |
- Mader, Theresa
(författare)
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Functional and metabolic alterations in skeletal muscle in response to physiological and pathophysiological stressors
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Skeletal muscle performance is essential for our body’s movement as well as for the wholebody metabolism. In health and disease, skeletal muscle is exposed to various endogenous and exogenous stressors, influencing its physiological functions. In paper I, we showed that exercise performance and muscle force is affected by the stressor breast cancer, in a mouse model of breast cancer (PyMT). Mimicking the experienced muscle weakness of human breast cancer patients, PyMT mice performed poorly in a treadmill exhaustion run and their muscles produced less force than wildtype (WT) mice, although no difference in morphology, fiber type distribution or diameter was found. The muscle weakness was associated with an increase of pro-inflammatory cytokines, such as TNF-α in the skeletal muscle, activating the p38 mitogen-activated protein kinase (MAPK) stress-response pathway and decreasing the expression of mitochondrial electron transport chain (ETC) genes as well as antioxidant genes. After the mice had access to four weeks of voluntary running ad libitum, skeletal muscle force as well as the time and distance of the treadmill exhaustion run improved drastically for PyMT mice. The exercise also reduced the intramuscular stress, improved both the expression of mitochondrial ETC genes and the activity of key mitochondrial enzymes, such as citrate synthase (CS) and especially β-hydroxyacyl-CoA dehydrogenase (β-HAD) and restored the antioxidant defense system including superoxide dismutase (SOD 1,2). Additionally, we could show that the breast cancer blunted the exercise-induced expression of PPARγ coactivator-1α (Pgc-1α) in PyMT mice. Our results showed that breast cancer-induced weakness is linked to increased intramuscular stress signaling and that voluntary, moderate exercise was able to counteract the weakness in PyMT mice. Patients with breast cancer are treated with various systemic anti-cancer treatments, and while aiming to treat cancer, these treatments often cause side-effects. In paper II, we aimed to study the effect of a novel anti-tumorigenic compound (CX-5461) on the whole-body as well skeletal muscle-specific metabolism. Four weeks of CX-5461 treatment effectively reduced the breast cancer tumor in PyMT mice, but also resulted in increased food intake, energy expenditure and a higher respiratory exchange ratio (VCO2/VO2), indicative of a substrate shift towards carbohydrate utilization in both WT and PyMT mice. Moreover, basal blood glucose levels were increased, and we observed a slower glucose clearance from the blood stream in both WT and PyMT mice after CX-5461 treatment. Skeletal muscle is an important tissue involved in maintaining the body’s glucose homeostatic. In WT mice, CX-5461 treatment reduced the basal glucose uptake, whereas in PyMT mice the insulin-stimulated glucose uptake was affected in extensor digitorum longus (EDL) muscles. We found that CX-5461 not only exerts its mechanism of action, the inhibition of the RNA-Polymerase I (Pol I) pre-initiation complex, in breast cancer cells, but also directly in skeletal muscle and through that alters the glucose and fat metabolism in skeletal muscle. The results indicate that the novel drug CX-5461 affects the whole-body metabolism including elevated blood glucose levels and reduced glucose uptake into skeletal muscle, independently of the tumor development. Skeletal muscle is a highly metabolic tissue which functions can also be regulated by oxidative stress, cause by an imbalance in the endogenous oxidative and antioxidative system. In paper III, we investigated the role of the intermuscular redox state on glycogen phosphorylase activity and glycogenolysis, which supply the muscle with energy from glycogen storage during exercise. Glycogen phosphorylase was strongly inhibited by incubation with the reactive nitrogen species (RNS) peroxynitrite (ONOO-), contrary to the reactive oxygen species (ROS) H2O2 in muscle extracts. In intact muscles, ONOOincubation resulted in inhibition of glycogenolysis in resting and contracting as well as a reduction of muscle force in slow-twitch oxidative soleus (SOL) and fast-twitch glycolytic EDL muscles, despite not exerting a direct effect on phosphorylase activity. Moreover, post-translational nitrate modification was observed in EDL muscle after ONOOincubation. Incubation with two antioxidants N-acetylcysteine (NAC) and dithiothreitol (DTT) did not affect phosphorylase activity or glycogenolysis, but reduced the force of EDL and SOL muscle. These results suggest that exogenous ONOOinhibits phosphorylase activity in muscle extracts and glycogenolysis in intact contracted muscles, whereas antioxidants such as DTT and NAC only play a minor role in inducing endogenous ROS and regulate the phosphorylase activity. All results from these three studies in this thesis investigate how the performance and function of skeletal muscle can be affected by different stressors. Taken together, a better understanding of the responsible underlying molecular mechanisms, might lead to targeted therapy approaches for afflicted patients in the future.
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