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Molecular effect of Excercise By Assistant Professor Rasha Ghazala Medical Biochemistry What is the molecular effect of exercise? Exercise produces signaling molecules in response to contraction that influence its own metabolism and the metabolisms of other tissu...

Molecular effect of Excercise By Assistant Professor Rasha Ghazala Medical Biochemistry What is the molecular effect of exercise? Exercise produces signaling molecules in response to contraction that influence its own metabolism and the metabolisms of other tissues and organs. Exercise can induce dynamic remodeling in the cellular composition of tissues and vasculature that will affect data interpretation across multiple omics applications. Types of Exercise Low-Load Endurance Exercise Mechanical stress is low, but depending on the duration. The outcome is characterized by an increase in structures supporting oxygen delivery (capillaries) and consumption (mitochondria). Examples include running, cycling, rowing, swimming, and cross- country skiing. High-Load Strength Exercise Mechanical stressis more Growth of muscle fibers occurs primarily through an increase in the amount of contractile proteins. Mitohormesis Mitochondria are the cellular organelles that provide much of the energy in our cells. Skeletal muscle cells are rich in mitochondria. Increase in intramuscular oxygen consumption accompanies strenuous exercise(Aerobic exercise training )increases the number and volume of mitochondria. Increased mitochondrial metabolism results in increased intracellular levels of free radicals (ROS)that, if unchecked, can damage proteins, DNA, and lipids. How can exercise be beneficial if a direct cellular byproduct is toxic? Mitohormesis Adaptive response of cells to intermittent stress.. Reactive oxygen species—superoxide, hydrogen peroxide, and hydroxyl radicals—that damage DNA, proteins, and lipids are aberrant by-products. The mechanism of senses the accumulation of these damaging reactive oxygen species and reduces them to harmless water. What are the molecules the control mithormesis??? Peroxisome proliferator-activated receptor Gamma Coactivator-1alpha (PGC-1). PGC-1 regulates key genes in skeletal muscles. Endurance training induces elevated levels of PGC- 1. Nuclear factor erythroid 2-related factor 2 (Nrf2). This protein activates various genes that encode antioxidant enzymes. allowing it to enter the nucleus where it increase levels of antioxidant enzymes suchas superoxide dismutase, glutathione synthetase,and heme oxygenase. Thus, Nrf2 activation counterbalances the elevated reactive oxygen species, resulting in net improved overall cellular function during exercise.  Exercise and Angiogenesis Mitochondrial content and capillary content are highly correlated in skeletal muscle. Key to the mechanism by which increased skeletal muscle use drives angiogenesis is Vascular Endothelial Growth Factor (VEGF). Muscle contraction triggers the release of VEGF stored in vesicles into the extracellular space, where it acts through specific cell surface receptors to trigger capillary growth. Exercise induces VEGF expression in skeletal muscle via PGC-1 Acute exercise reduces PiO2 in contracting muscle creating a situation of transient hypoxia which induces release of Hypoxia-inducible factor-1 (HIF-1). It induces transcription of target genes involved in erythropoiesis, angiogenesis, glycolysis and energy metabolism in a manner analogous to exercise.  Myokines and Exercise Skeletal muscle is an endocrine organ. It produces signaling molecules myokines in response to contraction that influence its own metabolism and the metabolisms of other tissues and organs acting through cell surface receptors. The founding member of the myokine family is Interleukin-6: IL-6 that stimulates both glucose and lipid metabolism. Induction of IL-6 in skeletal muscle occurs via a calcium-dependent pathway. IL-6 promotes hypertrophy by stimulating proliferation of muscle stem cells (satellite cells) and by augmenting the rate of protein  Muscle Satellite Cells and Exercise Satellite cells are a heterogeneous population of cells. The majority of cells are committed myogenic cells, which, upon stimulation, undergo symmetric division, and differentiation. Strength training increases skeletal muscle fiber cross- sectional area and satellite cell number. Androgens are steroids promote satellite cell activation and proliferation and further support skeletal muscle hypertrophy suppress myostatin to promote muscle growth. Signal transduction pathways in excercise: The physiological responses prompt the activation of several kinases, including: Adenosine monophosphate (AMP)-activated protein kinase (AMPK) Protein kinase A (PKA) Calcium/calmodulin-dependent protein kinase (CaMK) Mitogen-activated protein kinase (MAPK) Protein kinase C (PKC) Mammalian target of rapamycin (mTOR)  Adenosine monophosphate (AMP)- activated protein kinase The energy-sensing kinase AMPK, which is regulated by cellular energy deficit plays an important role in the beneficial effects of exercise on whole-body metabolic homeostasis. AMPK activation through physical exercise improves mitochondrial biogenesis through the regulation (PGC-1α), which promotes the expression of mitochondrial genes encoded in mitochondrial and nuclear DNA Calcium/calmodulin-dependent protein kinase CaMK-II CaMK-II which is dependent on the intensity of exercise and whose activation promotes the activation of PGC-1α and glucose transporter 4 (GLUT-4). CaMK-II promotes lipid uptake and oxidation and skeletal muscle also triggers regulation of important transcription factors, such as the cyclic AMP response element-binding protein (CREB), MEF2, and HDACs in skeletal muscle  Differences in molecular responses to exercise between endurance and resistance exercise Endurance training activates the AMPK-MAPK-PGC-1α signaling cascades, ultimately leading to increased mitochondrial biogenesis and metabolic adaptations and angiogenesis. Resistance training increases the activation of the phosphoinositide 3- kinases Protein kinase B–mTOR (PI3k-Akt-mTOR) signaling cascade to regulate the rate of protein synthesis and/or degradation and consequently, muscle hypertrophy.  Skeletal muscle wasting Muscle tissue responds to demand by growing. Conversely, it responds to disuse—due to injury, sedentary lifestyle, and age by atrophy: muscle wasting Muscle wasting is accompanied by degradation of myofibrils by the ubiquitin-proteosome pathway (reducing contractile force) and mitochondrial degradation (reducing endurance) In the elderly, this exacerbates the natural progression of age-related sarcopenia. Extreme Sports The “extreme exercise hypothesis” holds that there is a U-shaped curve for the health risk of exercise training, where risks reach a low point at some intensity of training, but then increase when that optimum is exceeded. The most active athletes had mostly calcified plaques, which show a high association with future cardiovascular events, while the least active athletes had a higher prevalence of mixed plaques. EPIGENETICS OF EXCERCISE By Assistant Professor Rasha Ghazala Medical Biochemistry Epigenetics Epigenetics is a concept conceived by Conrad Waddington in 1940,the definition of epigenetics has progressed toward changes in transcriptional expression and/or activity without variation in DNA sequence DNA methylation and histone modifications have been the most studied epigenetic events., other potential epigenetic modifications such as those mediated by microRNAs (miRNAs) may alter gene expression via post- transcriptional modulation and may influence translational events. Interactions between multiple epigenetic modifications and their regulation by metabolism during exercise are complex, and the comprehensive understanding of these adaptations needs to be further investigated. DNA Methylation DNA can be covalently modified by methylation of cytosines present in the 5′CpG3′ dinucleotide sequence(the two nitrogenous bases, cytosine and guanine) This process is catalyzed by a family of DNA methyltransferases (DNMT) transfer a methyl group to cytosine residue to form 5mC (5-methylcytosine) DNMTs are enzymes that establish, recognize, and remove DNA methylation, DNMT writers that catalyze the addition of a methyl group to the cytosine residue DNMT readers, which are enzymes that recognize the methyl group and bind to it to influence gene expression; DNA methyltransferases erasers, enzymes responsible for modifying and removing the 5mC methyl group to reverse DNA methylation DNA Methylation DNA methylation results in the stable silencing of gene expression by repressing transcription DNA Methylation Exercise generally results in DNA hypomethylation in key skeletal muscle genes, representing an early response that mediates skeletal muscle adaptations to exercise to improve metabolic efficiency, oxidative capacity, and contractile activity by altering gene expression profiles and protein levels. One hypothesis explaining how exercise triggers DNA methylation suggests that during muscle contraction this generates reactive oxygen species (ROS) that induce DNA to trigger a genomic response. ROS are modulated by members of carbon metabolism such as S-adenosyl methionine (SAM), which serve as donors of methyl groups used in DNA methylation Modulating the availability of methyl donors is how oxidative stress, along with calcium, could be the triggers that control exercise-induced methylation.  DNA Methylation PGC1-α is a key regulatory gene for mitochondrial biogenesis, fatty acid oxidation, and skeletal muscle sensitivity to insulin. The PGC-1α gene is hypomethylated after an intense exercise session. Hypomethylation levels of PCG-1α correlate with increased mRNA levels three hours after endurance exercise. PDK4 (Pyruvate dehydrogenase kinase 4) is a key gene in skeletal muscle metabolism and its expression is associated with hyperglycemia and is increased after either high- intensity exercise for a short period of time or after prolonged low-intensity exercise, and remains elevated as a consequence of chronic exercise. Histone modification Acetylation Histone acetylation is a transient enzymatic process that is the most common histone post-translational modification. The acetyl group of acetyl-CoA is transferred to a lysine residue of the histone tails. Changes in the positive charges generated a DNA molecule more exposed and accessible to regulatory proteins and associating acetylation with gene activation Histone acetyltransferases (HATs) that add an acetyl group to the histone, and histone deacetylases (HDACs) that remove it. Exercise is associated with the acetylation of several lysine residues in human skeletal muscle histones, so that physical activity correlates with chromatin decompaction and activation of transcription of certain exercise-responsive genes The practice of intense strength exercise produces an increase in histone H3 acetylation Histone modification Methylation Methylation takes place at the lysine and arginine residues of histones H3 and H4, to which a methyl group is added. Histone methyltransferases (HMT) are responsible for catalyzing this reaction, using SAM as a substrate to transfer a methyl group to the lysines Methylated lysines and arginines can activate or repress gene transcription depending on the proteins they recruit to chromatin. H3K4 methylation is highly abundant in promoter regions and transcriptional start sites and increases with physical exercise Phosphorylation Phosphorylation occurs at the serine and tyrosine residues of histones. Exercise causes increased levels of H3 serine phosphorylation in skeletal muscle Thus, certain signaling pathways including AMPK, MAPK, PKA, PKC, and CaMK-II are important for phosphorylation-dependent signaling during exercise in skeletal muscle.Many studies relate these pathways to histone modifications. Histone modification Lactylation Lactate is a cell marker of metabolic state, which results in epigenetics and transcriptomics changes in the cell. Lysine lactylation is an epigenetic modification that occurs in the presence of elevated levels of lactate Lactate inhibits the HDAC activity and thus increases gene expression boosting lactate availability during exercise. Lysine lactylation is involved in the up-regulation of homeostatic genes that play a communication role between cells and tissue inducing adaptive responses during and after exercise  Micro-RNAs Micro-RNAs are small non-coding RNAs that generally repress the expression of several genes (from one hundred to a thousand) at a post-transcriptional level. Micro-RNAs arising from skeletal or cardiac muscle are called myomiRs. MyomiRs related to skeletal muscle have been identified: miR-1, miR-133a, miR- 133b, miR-206 (expressed only in skeletal muscle), miR-208b, miR-486, and miR- 499, and their expression levels depend on the type and length of the exercise MyomiRs’ functions are to control the biogenesis, regeneration, and maintenance of the skeletal muscle tissue miR-1 and miR-206 have been proposed as biomarkers of endurance. Mainly, one unique micro-RNA can interact with many target mRNAs and one unique mRNA can interact with several micro-RNAs at the same time. This fact makes it difficult to understand molecular pathways in which micro-RNAs are implicated Schematic representation of the differentiation stages leading from progenitor muscle cells to terminally differentiated fibers.  Muscle Cellular metabolism is related to exercise and epigenetic control. Metabolites that are directly required to modify the DNA or histones, while other metabolites that have been described to regulate epigenetic mechanisms or epigenetic enzyme functions.