435 research outputs found

    Fine-structural distribution of MMP-2 and MMP-9 activities in the rat skeletal muscle upon training: a study by high-resolution in situ zymography

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    Matrix metalloproteinases (MMPs) are key regulators of extracellular matrix remodeling, but have also important intracellular targets. The purpose of this study was to examine the activity and subcellular localization of the gelatinases MMP-2 and MMP-9 in skeletal muscle of control and physically trained rats. In control hind limb muscle, the activity of the gelatinases was barely detectable. In contrast, after 5 days of intense exercise, in Soleus (Sol), but not Extensor digitorum longus (EDL) muscle, significant upregulation of gelatinolytic activity in myofibers was observed mainly in the nuclei, as assessed by high resolution in situ zymography. The nuclei of quiescent satellite cells did not contain the activity. Within the myonuclei, the gelatinolytic activity colocalized with an activated RNA Polymerase II. Also in Sol, but not in EDL, there were few foci of mononuclear cells with strongly positive cytoplasm, associated with apparent necrotic myofibers. These cells were identified as activated satellite cells/myoblasts. No extracellular gelatinase activity was observed. Gel zymography combined with subcellular fractionation revealed training-related upregulation of active MMP-2 in the nuclear fraction, and increase of active MMP-9 in the cytoplasmic fraction of Sol. Using RT-PCR, selective increase in MMP-9 mRNA was observed. We conclude that training activates nuclear MMP-2, and increases expression and activity of cytoplasmic MMP-9 in Sol, but not in EDL. Our results suggest that the gelatinases are involved in muscle adaptation to training, and that MMP-2 may play a novel role in myonuclear functions

    TRANSCRIPTOMIC AND CELLULAR RESPONSE TO MECHANICAL OVERLOAD AND THE UNDERLYING ROLE OF MACROPHAGES IN EXTRACELLULAR MATRIX REMODELING

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    The extracellular matrix (ECM) in skeletal muscle plays an integral role in tissue development, structural support, and force transmission. Upon mechanical loading, including resistance exercise, which alter muscle fiber contractile activity, size, orientation and connectivity, remodeling processes must occur that involve both ECM deposition and degradation. ECM remodeling involves many cell types in muscle, but the focus of our research was directed towards macrophages, which participate in the early immune response to damage and loading. We have consistently demonstrated a significant increase in skeletal muscle macrophage abundance using pan macrophage markers (CD11b/CD68) and anti-inflammatory markers (CD206/CD163) following exercise training in both middle aged and older adults. We report that with 14-weeks of progressive resistance exercise training (PRT) in older adults (\u3e65 years of age), genes involved in ECM remodeling, including MMP14, a master regulator of ECM turnover, were the most upregulated, differentially expressed genes among those identified by RNA-sequencing in muscle biopsies. Following an acute bout of resistance exercise in humans and mechanical overload in mouse, single cell RNA-sequencing indicated that muscle macrophages accumulate MMP14 mRNA. In vitro, we identified leukemia inhibitory factor (LIF), secreted by electrically-stimulate primary human myotubes, as a contributor to upregulation of MMP14 expression in macrophages. The data presented identify a novel mechanism by which skeletal muscle and macrophages interact to promote ECM remodeling in response to mechanical overload

    Regulation of Exercise Induced Endothelial Sprout Formation

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    Capillary sprouting is known to be guided by Dll4/Notch signaling in mouse retina, while maturation of the endothelium is regulated by Dll1 and Tie2. This study investigates the key molecules involved in endothelial sprouting and maturation, and the gene that orchestrates the expression of these targets in skeletal muscle in response to exercise. In exercised mice, Dll1 and Dll4 proteins were decreased with repeated training. Tie2 mRNA was downregulated with 5 days of exercise. The suppression of these molecules may induce destabilization of the endothelium and allow for sprouting to occur. Moreover, FoxO transcription factors have been shown to be anti-angiogenic and may negatively regulate genes involved in sprouting. Both Dll1 and Dll4 expression were not altered with repeated exercise in mice with endothelial cell directed conditional deletion of FoxO1/3a/4 (FoxO∆). We have provided insight into the mechanisms behind the initiation of capillary growth in skeletal muscle induced by exercise

    Exercise duration-matched interval and continuous sprint cycling induce similar increases in AMPK phosphorylation, PGC-1α and VEGF mRNA expression in trained individuals

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    Purpose: The effects of low-volume interval and continuous ‘all-out’ cycling, matched for total exercise duration, on mitochondrial and angiogenic cell signalling was investigated in trained individuals. Methods: In a repeated measures design, 8 trained males ((Formula presented.), 57 ± 7 ml kg−1 min−1) performed two cycling exercise protocols; interval (INT, 4 × 30 s maximal sprints interspersed by 4 min passive recovery) or continuous (CON, 2 min continuous maximal sprint). Muscle biopsies were obtained before, immediately after and 3 h post-exercise. Results: Total work was 53 % greater (P = 0.01) in INT compared to CON (71.2 ± 7.3 vs. 46.3 ± 2.7 kJ, respectively). Phosphorylation of AMPKThr172 increased by a similar magnitude (P = 0.347) immediately post INT and CON (1.6 ± 0.2 and 1.3 ± 0.3 fold, respectively; P = 0.011), before returning to resting values at 3 h post-exercise. mRNA expression of PGC-1α (7.1 ± 2.1 vs. 5.5 ± 1.8 fold; P = 0.007), VEGF (3.5 ± 1.2 vs. 4.3 ± 1.8 fold; P = 0.02) and HIF-1α (2.0 ± 0.5 vs. 1.5 ± 0.3 fold; P = 0.04) increased at 3 h post-exercise in response to INT and CON, respectively; the magnitude of which were not different between protocols. Conclusions: Despite differences in total work done, low-volume INT and CON ‘all-out’ cycling, matched for exercise duration, provides a similar stimulus for the induction of mitochondrial and angiogenic cell signalling pathways in trained skeletal muscle

    Remodeling the skeletal muscle extracellular matrix in older age—Effects of acute exercise stimuli on gene expression

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    © 2020 by the authors. Licensee MDPI, Basel, Switzerland. With advancing age, the skeletal muscle extracellular matrix (ECM) undergoes fibrotic changes that may lead to increased muscle stiffness, injury susceptibility and strength loss. This study tested the potential of different exercises to counter these changes by stimulating the activity of genes associated with ECM remodeling. Twenty-six healthy men (66.9 ± 3.9 years) were stratified to two of four groups, performing unilateral (i) conventional resistance exercise, (ii) conventional resistance exercise followed by self-myofascial release (CEBR), (iii) eccentric-only exercise (ECC) or (iv) plyometric jumps (PLY). The non-trained leg served as control. Six hours post-exercise, vastus lateralis muscle biopsy samples were analyzed for the expression of genes associated with ECM collagen synthesis (COL1A1), matrix metallopeptidases (collagen degradation; MMPs) and peptidase inhibitors (TIMP1). Significant between-group differences were found for MMP3, MMP15 and TIMP1, with the greatest responses in MMP3 and TIMP1 seen in CEBR and in MMP15 in ECC. MMP9 (3.24–3.81-fold change) and COL1A1 (1.47–2.40-fold change) were increased in CEBR and PLY, although between-group differences were non-significant. The expression of ECM-related genes is exercise-specific, with CEBR and PLY triggering either earlier or stronger remodeling than other stimuli. Training studies will test whether execution of such exercises may help counter age-associated muscle fibrosis

    Temporal Expression of Key Angioregulatory Proteins in Response to Exercise and Detraining

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    Angiogenesis is an important adaptation to exercise, occurring in response to a multitude of different stimuli including: shear stress, mechanical stretch, ischemia, electrical stimulation, and exercise. Current thinking suggests skeletal muscle angiogenesis is a temporal process controlled by a balance between positive and negative angiogenic proteins. But there is limited information on what molecular mediators control skeletal muscle angiogenesis in this time line, creating a critical need to clarify how individual protein responses regulate physiologic skeletal muscle angiogenesis in response to exercise training and/or physical deconditioning. Our objective is to characterize the temporal expression of several key positive (VEGF, MMP-2, MMP-9, nucleolin) and negative (TSP-1, endostatin) angiogenic factors under basal conditions, after acute exercise, in response to training, and after detraining. The central hypothesis is that training and deconditioning will cause temporally coordinated changes in positive and negative angiogenic regulators in response to exercise training, which will be reversed during detraining

    Skeletal muscle matrix metalloproteinase and exercise in humans

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    Skeletal muscle is a highly plastic tissue; it has a great capacity to adapt to environmental demands throughout life. The structural and functional changes that occur in response to exercise training are well characterized whereas much less is known about these adaptive processes at the cellular and molecular levels. A possibly underestimated aspect of skeletal muscle adaptation to exercise is the remodeling of the extracellular matrix (ECM). Degradation and processing of the extracellular matrix are carried out by a specific category of proteases, especially the matrix metalloproteinase family (MMPs). Such remodeling is of crucial importance for successful extravasation of circulating cells and for the migration of cells between the compartments of the tissue. Furthermore, degradation products of ECM components are not always mere debris; several fragments of structural proteins have biological activity after proteolytic processing, and MMP activity may also release growth factors stored in the ECM. Little is known about these enzymes in skeletal muscle of humans and how physiological stimuli such as exercise and exercise training affect their expression and activity. Therefore, the aim of this thesis was to characterize: 1. skeletal muscle MMP activation in response to a single bout of exercise and exercise training with regard to gene expression and enzyme activity, 2. exchange of factors associated with MMP activity between exercising leg and the circulation during exercise, 3. possible cellular sources of MMP in skeletal muscle tissue and blood, 4. the effects of restricted leg blood flow, and thereby reduced oxygen delivery, to the exercising leg on skeletal muscle and circulating levels of MMP and 5. the effects of the myokine interleukin-6 on MMP levels in skeletal muscle and in the circulation. MMP-9 is activated and transcriptionally upregulated in human skeletal muscle after a single bout of exercise. In contrast, MMP-2 is activated and transcriptionally upregulated in human skeletal muscle by exercise training but not after a single bout of exercise. Factors possibly linked to proteolytic processing of MMP-9, such as collagen IV and VEGF-A, are released from the leg to the circulation during a single bout of exercise in humans. Circulating levels of MMP-9 increase during and after a single bout of exercise in humans but do not seem to originate from the skeletal muscle. The myokine interleukin-6 induces an increase in circulating MMP-9 in parity with what is seen after a single bout of exercise in humans, interleukin-6 also induces gene-expression and release of MMP-9 from the human moncyte cell-line THP-1, but not from human myoblasts, myotubes or endothelial cells indicating that monocytes could be the source of the interleukin-6 induced increase in circulating MMP-9. The results from this thesis show that both MMP-2 and MMP-9 are expressed in skeletal muscle and upregulated by a physiological stimulus such as exercise but probably through different mechanisms. Furthermore, it indicates that remodeling of extracellular matrix and release of growth factors in the skeletal muscle occur after only a few minutes of exercise. Overall, the results support MMPs to play a role in the adaptation of the skeletal muscle to physical activity in humans

    The relationship between maximal exercise-induced increases in serum IL-6, MPO and MMP-9 concentrations

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    The aim of this study was to test the hypothesis that exercise would induce inflammatory response characterized by increased pro-inflammatory cytokines - interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α), adhesion molecule, matrix metalloprotease-9 (MMP-9) and myeloperoxidase (MPO) levels. Additional aim was to elucidate the possible source of maximal exercise-induced increase in MMP-9 concentration. To examine our hypothesis, 26 professional male ice hockey players [age 25±1 (mean±SEM) years; BMI 25.8± 0.4kg/m 2] performed an incremental bicycle test until exhaustion, when maximal oxygen consumption was recorded. Venous blood samples were collected 30min before and 2min after exercise. There was an increase in the count of leucocytes (8.7±1.8 versus 5.7±1.3×10 9 cells per l) and IL-6 (1.24±0.17 versus 0.69±0.13pg/ml), MPO (72±7 versus 50±4ng/ml) and MPP-9 (139±9 versus 110±6ng/ml) concentrations (P<0.05) comparing post- and pre-exercise levels. Maximal exercise-induced increase in MPO correlated with the increases in IL-6 (P<0.05, R=0.54) and MMP-9 (P<0.01, R=0.62) concentrations. Furthermore, increase in IL-6 correlated with the increase in MMP-9 concentrations (P<0.05, R=0.60). Maximal exercise induces an inflammatory response characterized by leucocytosis and increased IL-6, MPO and MMP-9 concentrations. Correlations between increased MPO (marker of neutrophils degranulation) and both increased IL-6 and MMP-9 concentrations may suggest that neutrophils could be the main source of these inflammatory biomarkers during maximal exercise. Furthermore, correlation between increases in serum IL-6 and MMP-9 concentrations may suggest that IL-6 could exert modulatory effects on MMP-9 release during maximal exercise.publishersversionPeer reviewe

    The Role of the Skeletal Muscle Secretome in Mediating Endurance and Resistance Training Adaptations

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    Exercise, in the form of endurance or resistance training, leads to specific molecular and cellular adaptions not only in skeletal muscles, but also in many other organs such as the brain, liver, fat or bone. In addition to direct effects of exercise on these organs, the production and release of a plethora of different signaling molecules from skeletal muscle are a centerpiece of systemic plasticity. Most studies have so far focused on the regulation and function of such myokines in acute exercise bouts. In contrast, the secretome of long-term training adaptation remains less well understood, and the contribution of non-myokine factors, including metabolites, enzymes, microRNAs or mitochondrial DNA transported in extracellular vesicles or by other means, is underappreciated. In this review, we therefore provide an overview on the current knowledge of endurance and resistance exercise-induced factors of the skeletal muscle secretome that mediate muscular and systemic adaptations to long-term training. Targeting these factors and leveraging their functions could not only have broad implications for athletic performance, but also for the prevention and therapy in diseased and elderly populations
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