Regulation of Nutrient Metabolism PDF

Regulation of Nutrient Metabolism • Metabolism • Components? • describes all chemical reactions involved in maintaining the living state of the cells and the organism http://www.nature.com/scitable/topicpage/cell-metabolism-14026182 Rapamycin the Molecule Rapamycin  Derived from Streptomyce...

Regulation of Nutrient Metabolism • Metabolism • Components? • describes all chemical reactions involved in maintaining the living state of the cells and the organism http://www.nature.com/scitable/topicpage/cell-metabolism-14026182 Rapamycin the Molecule Rapamycin  Derived from Streptomyces hygroscopicus (bacterium)  Rapamycin properties  Antibiotic – Antifungal – Immunosuppresant – coat stents  Inhibits mTORC1 master regulator have developed drugs that are  Pharmaceutical companies – also Sirolimus, Rapamune® similar  Modifications to C40 hydroxyl group Nature Reviews Drug Discovery 5, 671-688 (August 2006) doi:10.1038/nrd2062 Discovery and Development a not very short story •Canadian research team goes to Easter Island •Soil samples shared with Ayerst's research laboratories •1964 Dr. Suren Shigal (1932 -2003) 1972 1983 1987 1998 •Suren identified and isolated Rapamycin •Anti-fungal and Immunosupresant properties noted •Sent to the National Cancer Institute •Ayerst closes Montreal R&D facility •Suren moved to Princeton NJ with the company •Secretly made a large-scale batch to bring with him to Princeton •Wyeth and Ayerst merged •Suren resurrected his research •Michael Hall cloned TOR in yeasts TOR conserved in all organisms •Development of Rapamune as an immunosuppressant and anticancer drug • clinical studies on rapamycin neared completion • FDA approved in 1999 Fires on Rapa Nui in 2022 Rapamycin Today • Studies in C elegans, yeast, Drosophila, • Extends lifespan, mimics effects of calorie restriction • NOW - Clinical Trials in Dogs • https://www.technologyreview.com/2022/08/15/1 057697/scientists-extend-lifespan-pet-dogsowners/ • https://vet.tufts.edu/clinical-trials/dog-agingproject-test-rapamycin-aging-dogs-triad What is the target of this drug? key to regulation • mTOR = mechanistic Target of Rapamycin controls function at a cellular level • Meaning of life? We could argue it is Survival and Replication promote survival and • Cellular level: maintain function and/or replace itself replication at a longer term We always want to keep metabolism to maintain homeostasis —> don’t want disregulation that causes stress and potentially cell death mTOR is an important part of the cascade for intra and extra cell signals to remain homeostasis and cell growth • Metabolism is dependent on nutrient availability • Energy excess or deficiency causes cellular metabolic dysregulation • mTOR integrates important extra and intra cellular signals involved in cell growth: • NUTRIENTS, ENERGY and GROWTH FACTORS • *Nutrients are involved in all aspects of cellular function* • mTOR regulates cellular metabolism • the balance between intracellular anabolism and catabolism • mTOR is central in the regulation of cell growth • And therefore, proliferation in response to integrating those extra and intra cell signals Concerted regulation of protein and lipid biosynthesis (Dr Agellon’s slide) AMPK senses energy status mTOR complex 1 (several proteins that binds with it to create this complex that will response to nutrient availability, growth factors, cellular energy status) requires a lot of ATP if cell energy status is low = low ATP = inhibition of mTORC1 and downstream processes Source: Biochemical Society Transactions (2009) 37, 278-283 mTOR Complex 1: central regulator of cell growth and metabolism promotes anabolism and decreases catabolism GLUT4: stored in vesicles in the cell increase GLUT4 to increase glucose transport, which stimulates aa transporter to important more aa mTOR: GLUT4 vesicles —> PM mTOR (Inhibits) Autophagy form of cell death Porth’s Pathophysiology 7th Edition Key Regulators • PI3K-Akt-mTOR Pathway • • • • PI3K = phosphatidylinositol 3- kinase Akt = Protein Kinase B (or PKB) mTOR = mechanistic Target of Rapamycin Intracellular signal transduction pathway Upstream regulators between insulin and mTOR • • • • • downstream effects Metabolism Proliferation Cell survival Growth blood vessels Angiogenesis angio: genesis: making new making blood vessels —> key for growth and cancer Example of integration of metabolic processes (From Dr Agellon) Source: Biochemical Society Transactions (2009) 37, 278-283 Posttranslational modification of proteins: Phosphorylation HMG-CoA reductase (HMGR) catalyzes the rate-limiting step in the biosynthesis of cholesterol. Image source: Proteins. In: Panini S, ed. Medical Biochemistry: An Essential Textbook. 2nd Edition. New York: Thieme; 2021. doi:10.1055/b000000285 mTOR stimulates mRNA translation eIF: eukaryotic initiation factor binds to binding protein 4E-BP1 mTOR phosphorylates binding protein, which release eIF4E Fig. (2). Schematics of the mTOR/4E-BP1/eIF4E signalling pathway. PI3K, Akt, and mTOR are activated as a consequence of extracellular stimuli. mTOR forms two distinct complexes: mTORC1 and mTORC2. mTORC2 activation leads to actin regulation and cytoskeleton organization, while mTORC1 activates the capdependent translation via phosphorylation of 4E-BPs.The cap-binding protein eIF4E is released by 4E-BPs upon phosphorylation, allowing eIF4F complex formation. In cancerouscells, eIF4E is, in turn, phosphorylated by the MNK1/2 kinases. Maracci, Cristina et al. “The mTOR/4E-BP1/eIF4E Signalling Pathway as a Source of Cancer Drug Targets.” Current medicinal chemistry vol. 29,20 (2022): 3501-3529. doi:10.2174/0929867329666220224112042 Prof. Sonenberg’s discovery of eIF4E, the protein that binds mRNA and recruits it to the ribosome to commence translation was a landmark event helping unravel the mechanisms controlling the rate of protein synthesis, the foundation of the modern field of translational control. Dr. Sonenberg has said, “What attracted me to the field was that the nature of proteins and everything that follows—our behaviour, our wellbeing, everything—is dictated by genes.” Muscle Hypertrophy Atrophy • Growth • Anabolic • Activation of PI3K-Akt mTOR pathway • Wasting • Catabolic • Activation of ubiquitinproteasome pathway Contributors to protein synthesis 10 10 30 Special Products minimal quantitatively, but really important 50 muscle visceral plasma proteins blood cells Body Protein Synthesis emphasis the role of protein post translational modification like kinase phosphorylation Energy Expensive 4 ATP per peptide bond Protein degradation = Proteolysis • Helps to determine protein levels within cells • Wide variation in half-lives of proteins • Two major intracellular pathways • Ubiquitin-proteasome pathway • Lysosomal proteolysis • Extracellular proteolysis • Where does this occur? pancreatic juice: a lot of proteolyase The Ubiquitin-Proteasome Pathway • Major pathway for selective protein degradation • Ubiquitin: 76 AA protein • Attached by ligases E1,E2, E3 to amino group of lysine side chain •  Polyubiquitinated protein  recognized by proteasome 3 different units • Proteasome: large multi-subunit complex hollow • Degrades protein • ATP required 1 ATP/peptide bond Less energy dense than requirement for protein synthesis The Ubiquitin-Proteasome Pathway protein specifically targeted to be broken down protein will be chewed up, ubiquitin will be recycled Mitch and Goldberg, NEJM 1996; 335:1897-1905 Control of Proteolysis. In: Panini S, ed. Medical Biochemistry: An Essential Textbook. 2nd Edition. New York: Thieme; 2021. doi:10.1055/b000000285 Lysosomal Proteolysis acid pH in the interior of the lysosome don’t function at normal cytosolic pH —> protective mechanism If the membrane ruptures, we don’t want active enzyme to spill in the cytosol and degrade macronutrients where protein are chewed up Pepsinogen: synthesize in the cell as an inactive precuorsor and hydrolyze in the stomach to make pepsin, which activates it —> for protection Mitch and Goldberg, NEJM 1996; 335:1897-1905 Lysosomal Proteolysis • Hydrolases are active at acidic pH in the lysosome, but not at neutral cytoplasmic pH • Why is this important? • Not all lysosomal protein uptake is non-selective! • Cellular starvation  selective uptake/degradation of particular proteins • Proteins with specific AA sequences • Sacrificed to produce AAs for other uses