Cell Signalling and Movement - Brunel University London 2024 PDF

Introduction to Medical Sciences 1 Cell Signalling and Movement Cell Signalling Copyright © Brunel University London v.3 2024. All rights reserved. Cell Signalling and Movement – Cell Signalling Professor Mike Ferenczi Version 3 2024 [email protected]...

Introduction to Medical Sciences 1 Cell Signalling and Movement Cell Signalling Copyright © Brunel University London v.3 2024. All rights reserved. Cell Signalling and Movement – Cell Signalling Professor Mike Ferenczi Version 3 2024 [email protected] Copyright © Brunel University London V.3 2024. All rights reserved. Cell Signalling Billions of cells work together to create our body. By working together, the cells ensure our health as well as our physical, intellectual and emotional performance are maintained. The processes involved in keeping a steady internal environment in spite of varying external conditions and varying demands on the body at various times is called homeostasis. For this to be achieved, cells need to communicate. Communication between cells ensures coordination of actions, of responses and also our ability to think, react, create, feel sadness and fear, love and enjoyment. Copyright © Brunel University London V.3 2024. All rights reserved. Cell Signalling When cell signalling goes wrong You have disease Copyright © Brunel University London V.3 2024. All rights reserved. Cell Signalling So how does cell signalling work? We can divide cell signalling into two parts: Nerve signalling and chemical signalling But nerve conduction is really a mechanism to bring signals quickly to distant parts of the body, or back to the central nervous system. Even nerve signalling involves chemical signalling Copyright © Brunel University London V.3 2024. All rights reserved. So how does cell signalling work? Chemical signalling: Endocrine signalling through hormones travelling in the blood stream Paracrine signalling between neighbouring cells, for example at the nerve synapse, junction between two nerve cells or a nerve cell and another excitable cell such as a muscle cell. Autocrine signalling where chemical signals act on the cell itself Cell-cell direct contact, usually through gap junctions and molecules travelling between cells Copyright © Brunel University London V.3 2024. All rights reserved. So how does cell signalling work? What are the chemical signals? These are molecules synthesized inside cells and released in the extracellular space, either to diffuse to neighbouring cells, or to travel to distant parts in the blood stream. Why do I need to know about these? Because defects of secretion and signalling may lead to disease Because drugs often are designed to act as chemical mimics, functioning as agonists or antagonists of chemical signals Copyright © Brunel University London V.3 2024. All rights reserved. Chemical signals NEUROTRANSMITTERS: cells of the CNS or PNS Amino acids: γ-aminobutyric acid (GABA), glutamine, glycine Acetylcholine Small molecules: Biogenic amines, made from amino acid precursors: serotonin, histamine, dopamine Catecholamines: noradrenaline, adrenaline from tyrosine Purinergic neurotransmitters: ATP and adenosine (nucleotide or nucleoside) Copyright © Brunel University London V.3 2024. All rights reserved. Chemical signals Neuropeptides: endorphin, enkephalins, substance P (pain), neuropeptide Y (eating) Many neurotransmitters are also involved in other ways. HORMONES: long-distance signals Lipid-soluble hormones, usually derived from cholesterol and are called steroid hormones. They can diffuse across the plasma membrane or the nuclear envelope. Oestradiol, testosterone, aldosterone, cortisol. Bound to proteins for transport in the blood stream. Quite long half-life in the blood : 60 – 90 minutes Copyright © Brunel University London V.3 2024. All rights reserved. Chemical signals HORMONES: long-distance signals 2. Amino-acid derived hormones: Adrenaline and noradrenaline (derived from tyrosine in the medulla of adrenal gland) with a half-life of ~ a minute. Thyroxine (produced in thyroid gland) from tyrosine plus iodine Melatonin (pineal gland) from tryptophan. Copyright © Brunel University London V.3 2024. All rights reserved. Chemical signals HORMONES: long-distance signals 3. Peptide hormones: Antidiuretic hormone (ADH) and oxytocin are short peptides produced in the brain and released in the circulation by the posterior pituitary gland (9 AAs). Small proteins such as growth hormone (191 AAs) Glycoproteins such as follicle stimulating hormone, FSH (96 AAs) Copyright © Brunel University London V.3 2024. All rights reserved. Chemical signals HORMONES: long-distance signals 3. Peptide hormones (continued): Insulin: α-chain (21 AAs) and β-chain 30 (AAs). Linked via disulphide bonds at cysteine residues. Produced by β-cells of pancreatic islets (Islets of Langerhans) Glucagon: 29 AAs Produced by α-cells of pancreatic islets (Islets of Langerhans) Copyright © Brunel University London V.3 2024. All rights reserved. Chemical signals Glucagon: Islet of Langerhans stained for glucagon showing α- cells Image is public domain courtesy of Wikimedia Commons https://en.wikipedia.org/wiki/File:Glucagon_rednblue.png#filelinks Copyright © Brunel University London V.3 2024. All rights reserved. What do chemical signals do? Chemical signals trigger responses in target cells: These responses are varied, and cell-type specific Examples are: Muscle contraction Signal amplification Mitosis Cell differentiation Copyright © Brunel University London V.3 2024. All rights reserved. What do chemical signals do? Cell apoptosis or cell death Secretion Synthesis of proteins: transcription of specific genes Storage of chemicals Adrenaline causes breakdown of glycogen to release glucose in muscle cells to prepare for activity Copyright © Brunel University London V.3 2024. All rights reserved. What do chemical signals do? They trigger signal transduction Lets consider the case of the neuromuscular junction Copyright © Brunel University London V.3 2024. All rights reserved. The neuromuscular junction or motor end plate A motor nerve fibre divides into many branches in the muscle. Each branch will innervate a single muscle cell at the neuromuscular junction. These connection points are called buttons. Each button contains a synapse. http://stevegallik.org/sites/histologyolm.stevegallik.org/htmlpages/HOLM_Chapte r07_Page06.html Copyright © Brunel University London V.3 2024. All rights reserved. The synapse at the motor end plate Schwann cell Mitochondria Presynaptic terminal Intracellular vesicles (granules) Synaptic cleft Muscle cell myofilaments https://upload.wikimedia.org/wikipedia/commons/3/30/HeuserNeuro.jpg Copyright © Brunel University London V.3 2024. All rights reserved. The motor end plate When a nerve impulse reaches the motor end plate, vesicles which are filled with acetylcholine fuse with the pre-synaptic membrane and open up. Acetylcholine diffuses into the synaptic cleft (extracellular space) and binds to Acetylcholine receptors (AchR) on the postsynaptic membrane (the plasma membrane of the muscle cell). https://upload.wikimedia.org/wikipedia/commons/3/30/Heuser Neuro.jpg Copyright © Brunel University London V.3 2024. All rights reserved.  Post-synaptic events Acetylcholinesterase in the synaptic cleft breaks down acetylcholine, making sure it is only present for a short while. Some ACh is also taken back up by the presynaptic membrane. Some neurotoxins and insecticides inhibit acetylcholinesterase, causing paralysis. Nerve agents, treatment of myasthenia gravis, dementia; eg neostigmine https://upload.wikimedia.org/wikipedia/commons/3/30/Heuser Neuro.jpg Presynaptic vesicles release more than one bioactive substance Copyright © Brunel University London V.3 2024. All rights reserved. Post-synaptic events The neurotransmitter binds to a receptor on the post- synaptic membrane of the target cell (muscle cell) The receptor is the nicotinic acetylcholine receptor (AChR) which consists of 5 subunits spanning the plasma membrane, with acetylcholine binding site in Transmembrane view and top view from the extracellular space. the extracellular space. Unwin, 2013 https://doi.org/10.1017/s0033583513000061 Copyright © Brunel University London V.3 2024. All rights reserved.  Post-synaptic events Acetylcholine binding causes a subtle reorganisation of the subunits resulting in the opening of a channel of 0.65nm diameter through the structure through which Na+ and K+ ions can flow. Acetylcholine binds and Open and closed conformation of the nicotinic AChR comes off the active site every Unwin, 2013 https://doi.org/10.1017/s0033583513000061 millisecond. Drugs can block the channel: curare is a muscle relaxant. Ivermectin? Copyright © Brunel University London V.3 2024. All rights reserved. Post-synaptic events The membrane potential across the postsynaptic membrane in the resting state is about -90 mV, with the intracellular cytoplasm at a negative potential compared to the extracellular space. This is caused by the negative charge of the non-diffusible intracellular proteins and phosphates, and the non- equilibrium ionic distribution of Na+ and K+ maintained by active pumps, in particular the Na-K pump. Outside: [Na+] = 150 mM/L; [K+] = 5 mM/L; [Cl-] = 110mM/L Inside: [Na+] = 10 mM/L; [K+] = 150 mM/L; [Cl-] = 5 mM/L Copyright © Brunel University London V.3 2024. All rights reserved. Post-synaptic events The action potential: When the nicotinic AChR opens, Na+ rushes into the cell causing a temporary loss of membrane potential, and its reversal, the action potential. Voltage-gated Na+ channels are activated in the postsynaptic membrane to propagate the action potential Time course of the action potential along the fibre HowMed, 2010 http://howmed.net/physiology/action-potential/. Copyright © Brunel University London V.3 2024. All rights reserved. Post-synaptic events In striated muscle, the action potential causes the release of calcium from internal stores which activate muscle contraction In cardiac muscle, the action potential propagates from cell to cell through gap junctions. Voltage-gated calcium channels cause influx of calcium ions to activate contraction In nerve cells, dendritic depolarisations add-up at the axon hillock, and an action potential travelling down the axon is triggered if voltage summation reaches a threshold. Copyright © Brunel University London V.3 2024. All rights reserved. Slower signalling Ion channel activation and propagated action potentials produce the fastest types of signalling and transduction Other mechanisms are slower, but allow more subtle response than the all-or-none response characteristics of nerve and muscle transduction. Integration of several signals are important for optimal adaptation of the response to the needs of the organism Copyright © Brunel University London V.3 2024. All rights reserved. Muscarinic Acetylcholine receptor To illustrate more complex signalling pathway, we shall stay with acetylcholine, but consider a different postsynaptic response: Muscarinic receptors are G-protein-coupled receptors that mediate the response to acetylcholine released http://chemistry.elmhurst.edu/vchembook/662cholin ergic.html from parasympathetic nerves. They do not contain an ion channel, so even though they are sensitive to the same agonist, the response is completely different, and the pharmacology is also different, viz. nicotine and muscarine Copyright © Brunel University London V.3 2024. All rights reserved. Muscarinic receptor Acetylcholine binds to the extracellular side of M-type receptor causing a structural change on the inner side of the protein. This changes the interaction with the G-protein complex. G-protein is a GTP-coupled protein complex Maeda et al., 2019 https://doi.org/10.1126/science.aaw5188 Copyright © Brunel University London V.3 2024. All rights reserved. Muscarinic receptors G-protein is GTP-coupled protein complex. Many cell functions are dependent on G-protein-coupled receptors and subject of much research, e.g. nonselective muscarinic receptor Englen, Choppin and Watson, 2001 antagonist tolterodine for use in https://www.cell.com/trends/pharmacological- urinary incontinence. sciences/fulltext/S0165-6147(00)01737-5. M1 to M5 subtypes are coded by different genes. M2 and M4 receptors are linked to Gi/o protein, whereas M1, M3, M5 are linked to Gq proteins. Copyright © Brunel University London V.3 2024. All rights reserved. Muscarinic receptors The cellular effects caused by mAChR stimulation are mediated by both activated G-protein α-subunits as well as free βγ complexes generated following receptor- mediated G-protein activation. GIRK, G-protein-activated inwardly rectifying potassium channel; MAPK, mitogen activated protein https://www.nature.com/articles/nrd2379 kinase; J. Wess, R. M. Eglen and D. Gautam 2007 PLCβ, phospholipase Cβ Copyright © Brunel University London V.3 2024. All rights reserved. Muscarinic receptors Because of the wide range of effects, muscarinic receptors are subject to extensive research, both for agonists and antagonists, e.g. Mental health: Alzheimer, schizophrenia, addiction, Parkinson’s. Also COPD, asthma (airways smooth muscle), chronic bowel https://www.nature.com/articles/nrd2379 disease, obesity etc. Jürgen Wess, Richard M. Eglen and Dinesh Gautam 2007 Copyright © Brunel University London V.3 2024. All rights reserved. The signalling cascade Signalling cascades are illustrated in diagrams such as in the picture. Often they involve the activation of a nuclear transcription factor which regulates protein synthesis and cellular activity. https://www.researchgate.net/publication/261408128_Non- Neuronal_Functions_of_the_M2_Muscarinic_Acetylcholine_Receptor Ockenga et al, 2013 Copyright © Brunel University London V.3 2024. All rights reserved. Cell signalling – the insulin receptor Extracellular glucose needs to be kept low Insulin triggers glucose uptake in cardiac and skeletal muscle and in adipose tissue, and liver Once in muscle, glucose is phosphorylated, then either polymerises to glycogen or enters glycolysis to generate ATP. In fats, it is turned into triglycerides. Glucose enter muscle and fat cells through the glucose transporter (GLUT4, one of about 14 distinct transporters) which is a facilitated transporter by exchange of Na+ ions. GLUT4 is activated by the insulin receptor. Copyright © Brunel University London V.3 2024. All rights reserved. Cell signalling – the insulin receptor Metabolomics of Type 1 and Type 2 Diabetes (2019) Arneth B., Arneth R., Shams M. Int. J. Mol. Sci. GLUT4 is activated by the insulin receptor which has tyrosine-protein kinase activity. IRS is the insulin receptor substrate. Intracellular Glut4 relocates to plasma membrane. Copyright © Brunel University London V.3 2024. All rights reserved. Cell signalling - summary We have had an overview of cell signalling, focusing on the acetyl choline receptor AChR. AChR is one of hundreds of different types of receptors which cause changes in cellular function. Some changes are very fast and involve ionic flow Others are slower and involve complex signalling cascades inside cells, and sometimes inside the nuclei for altering gene expression and protein synthesis Involved in cell division, immunology and autoimmune diseases, cancer, ageing, learning and behaviour Copyright © Brunel University London V.3 2024. All rights reserved. Cell signalling - summary The complexity of cell signalling pathways allows for the integration of signals from different sources, the gradation of the response, and controlling the time scale of the responses. Copyright © Brunel University London V.3 2024. All rights reserved. Please feel free to contact me using the following address: [email protected] Copyright © Brunel University London V.3 2024. All rights reserved.