The overall goal of my research has been to understand the remarkable mechanisms that account for the control and integration of intermediary metabolism. I have been especially interested in the control of fatty acid metabolism by insulin, adrenaline and other hormones, with a special focus on the enzyme acetyl-CoA carboxylase. This general interest began with an undergraduate project looking at the control of glycogen synthesis in yeast, a project that was followed by my graduate studies of fatty acid metabolism in the heart. My interests in acetyl-CoA carboxylase began with post-doctoral studies and have continued ever since. My specific interests have come full circle with a renewed opportunity to study heart metabolism, especially through collaborative projects with UBC colleagues Michael Allard, Jim Johnson, John McNeill, Kathleen MacLeod and Brian Rodrigues.
Structure, Function and Regulation of Acetyl-CoA Carboxylase (ACC) Isoforms
ACC has a number of crucial roles in fat metabolism and overall body energy metabolism. The study of this enzyme has led to important insights into the structure, function and regulation of the enzyme, particularly in defining important allosteric modulators and the role of phosphorylation in enzyme control. Our work has also lead to the detection of a distinct isoform of acetyl-CoA carboxylase. We first detected this ACC isoform (ACC-2) in liver and it has especially important roles in heart and skeletal muscle. Our current work is aimed at further defining the properties of ACC-1 and ACC-2, including the mechanisms by which ACC undergoes a remarkable allosteric transformation from a low-activity dimeric form into highly active polymers. In this regard, we are investigating the roles of additional proteins that may be important in facilitating ACC polymerization and depolymerization.
Role of Protein Phosphorylation in Insulin Action
Our early studies led to the demonstration that ACC is controlled by reversible phosphorylation within intact fat cells and that the extent of phosphorylation changes rapidly in response to treatment of cells with insulin or adrenaline. These studies led to the early recognition that ACC, as well as other proteins, becomes more highly phosphorylated when cells are stimulated by insulin, probably by activation of protein kinases. Initially, these were controversial findings because prior work on glycogen synthase and pyruvate dehydrogenase indicated that insulin acted through protein dephosphorylation . Over time, it has become apparent that the protein phosphorylation represents a fundamental mechanism of insulin action. Specifically with respect to ACC, phosphorylation is one of several control mechanisms that are integrated in the fine-tuning of ACC function. In this respect, we are continuing to work on the specific sites at which ACC isoforms can be phosphorylated and, importantly, how these sites influence (and are influenced by) the actions of allosteric modulators and regulatory proteins.
A related interest, arising from original work by John McNeill at UBC, is to understand how vanadium salts exert “insulin-like” actions on protein phosphorylation and metabolism. This work has led to the recognition that this transition metal might selectively inhibit adipose tissue lipolysis through an action on cyclic AMP-dependent protein kinase. This underlines the possibility that the anti-lipolytic actions of insulin are especially important.
Energy Metabolism in the Heart
In addition to specific studies of acetyl-CoA carboxylase, our work has led to collaborative projects to study aspects of heart metabolism and how this changes in two clinically significant disease states. One project, with Drs. John McNeill, Brian Rodrigues and Kathleen MacLeod (all in Pharmaceutical Sciences at the University of B.C.) is concerned with metabolic defects in the diabetic heart. In another project, with Dr Michael Allard’s group at the James Hogg Research Centre, St. Paul ‘s Hospital (Department of Pathology and Laboratory Medicine, UBC), we are studying the metabolism of the heart during the development of cardiac hypertrophy. This is of particular interest because of the high risk of sudden heart failure in cardiac hypertrophy and the prevalence of cardiac hypertrophy in diabetes.
Lauzier B, Vaillant F, Bouchard B, Brownsey RW, Gluais P, Roussel J, Thorin E, Tardif J-C, Des Rosiers C. ‘’Ivabridine reduces heart rate while preserving metabolic fluxes and energy status of normoxic working hearts”, American Journal of Physiology, 300(3) H845-H852 (2011).
Chu KY, Lin Y, Hendel A, Kulpa JE, Brownsey RW, Johnson JD. “ATP citrate lyase reduction mediates palmitate-induced apoptosis in pancreatic beta-cells”, Journal of Biological Chemistry, 285(42):32606-32515 (2010).
Lin Y, Brownsey RW, MacLeod KM. “Regulation of mitochondrial aconitase by phosphorylation in diabetic rat heart”. Cellular and Molecular Life Sciences 66(5):919-32 (2009)
Saeedi R, Saran VV, Wu SS, Kume ES, Paulson K, Chan AP, Parsons HL, Wambolt RB, Dyck JR, Brownsey RW, Allard MF. “AMP-activated protein kinase influences metabolic remodeling in H9c2 cells hypertrophied with arginine vasopressin”. American Journal of Physiology 296(6):H1822-1832 (2009)
Sharma V, Dhillon P, Wambolt R, Parsons H, Brownsey RW, Allard MF, McNeill JH. “Metoprolol improves cardiac function and modulates cardiac metabolism in the streptozotocin (STZ) diabetic rat”. American Journal of Physiology 294: H1609-H1620 (2008)
Moien-Afshari F, Ghosh S, Khazaei M, Keiffer T, Brownsey RW, Laher I. “Exercise restores endothelial function independent of weight loss, hyperglycemic status or lipid profile in db/db mice”. Diabetologia, 51: 1327-1337 (2008)
Saeedi R, Parsons HL, Wambolt RB, Paulson K, Sharma V, Dyck JR, Brownsey RW, Allard MF. “Metabolic actions of metformin in the heart can occur by AMPK-independent mechanisms”. American Journal of Physiology 294 :H2497-H2506 (2008)
Allard MF, Parsons HL, Saeedi R, Wambolt RB and Brownsey RW. “AMPK and metabolic adaptation by the heart to pressure overload”. American Journal of Physiology 292::H140-H148 (2007)
Brownsey RW, Boone AN, Elliott JE, Kulpa JE, Lee WM. “Regulation of acetyl-CoA carboxylase”. Biochemical Society Transactions 34(2):223-227 (2006)
Jelveh KA, Zhande R, Brownsey RW. “Inhibition of cyclic AMP-dependent protein kinase by vanadyl sulfate”. Journal of Biological Inorganic Chemistry 11:379-388 (2006)
Brownsey, RW “Introduction to Metabolism”, in: Principles of Biochemistry, by Horton, H.R., Moran, L.A. , Scrimgeour, K.G., Perry, M.D. and Rawn, J.D. (4th edition), Pearson Prentice-Hall, Upper Saddle River, NJ, Chapter 10, pp 296-308 (2006)
Lee WM, Elliott, JE, Brownsey, RW. “Inhibition of acetyl-CoA carboxylase isoforms by pyridoxal phosphate”. Journal of Biological Chemistry 280 (51):41835-41843 (2005)
Qi D, Pulinilkunnil T, An D, Ghosh S, Abrahani A, Pospisilik JA, Brownsey RW, Wambolt R, Allard M, Rodrigues B. Single-dose dexamethasone induces whole-body insulin resistance and alters both cardiac fatty acid and carbohydrate metabolism. Diabetes 53(7):1790-1797 (2004)
Longnus SL, Wambolt RB, Parsons H, Brownsey RW, Allard MF. “5-aminoimidazole-4-carboxamide 1-?-ribofuranoside (AICAR) stimulates myocardial glycogenolysis by allosteric mechanisms”, American Journal of Physiology 284(4):R936-R944 (2003)
Pulinilkunnil T, Qi D, Ghosh S, Cheung C, Yip P, Vargese J, Abrahani A, Brownsey RW, Rodrigues B. “Circulating triglyceride lipolysis facilitates lipoprotein lipase translocation from cardiomyocyte to myocardial endothelial lining”. Cardiovascular Research 59(3):788-797 (2003)
Leong HS, Brownsey RW, Kulpa JE, Allard MF. “Glycolysis and pyruvate oxidation in cardiac hypertrophy – why so unbalanced?”. Comparative Biochemistry and Physiology (A) 135(4): 499-513 (2003)
Pulinilkunnil T, Abrahani A, Varghese J, Chan N, Tang I, Ghosh S, Kulpa JE, Allard MF, Brownsey RW, Rodrigues B. “Evidence for rapid “metabolic switching” through lipoprotein lipase occupation of endothelial binding sites”. Journal of Molecular and Cellular Cardiology 35(9):1093-1103 (2003)
Lydell CP, Chan A, Wambolt RB, Sambandam N, Parsons H, Bondy GP, Rodrigues B, Popov KM, Harris RA, Brownsey RW, Allard MF. “Pyruvate dehydrogenase and the regulation of glucose oxidation in hypertrophied rat hearts”, Cardiovascular Research, 53(4):841-851 (2002)
Leong HS, Grist M, Parsons H, Wambolt RB, Lopaschuk G, Brownsey RW, Allard MF. “Accelerated rates of glycolysis in the hypertrophied heart: are they a methodological artifact?” American Journal of Physiology, 282(5):E1039-E1045 (2002)
Pospisilik JA, Stafford SG, Demuth HU, Brownsey RW, Parkhouse W, Finegood DT, McIntosh CHS, Pederson RA. “Long-term treatment with the DP IV inhibitor P32/98 causes sustained improvements in glucose tolereance, insulin sensitivity, hyperinsulinemia and beta-cell glucose responsiveness in VDF (fa/fa) Zucker rats”, Diabetes, 54(1):943-950 (2002)
Marzban L, Rahimian R, Brownsey RW, McNeill JH. “Mechanisms by which bis(maltolato)oxovanadium (IV) normalizes phosphoenolpyruvate carboxykinase and glucose-6-phosphatase expression in STZ-diabetic rats”, Endocriniology, 143(12):4636-4645 (2002)
Sambandam N, Lopaschuk GD, Brownsey RW, Allard MF. (2002) “Energy metabolism in the hypertrophied heart”. Heart Failure Reviews 7(2): 161-173
Brownsey, R.W. “Introduction to Metabolism”, in: Principles of Biochemistry, by Horton, H.R., Moran, L.A. , Ochs, R.S., Rawn, J.D. and Scrimgeour, K.G. (3rd edition), Prentice-Hall, Upper Saddle River, NJ, Chapter 10, pp 309-318 (2002)
Cam MC, Brownsey RW, Rodrigues B, McNeill JH. “Lack of in vivo effect of vanadium on GLUT4 translocation in white adipose tissue of streptozotocin-diabetic rats”, Metabolism, 50(6):674-80 (2001)
Cam MC, Brownsey RW, McNeill JH. “Mechanisms of vanadium action: insulin-mimetic or insulin enhancing agent?”, Canadian Journal of Physiology and Pharmacology, 78:829-847 (2000)
Wambolt RB, English DR, Lopaschuk GD, Brownsey RW, Allard MF. “Dichloroacetate improves post-ischemic function of hypertrophied rat hearts”, Journal of the American College of Cardiology, 36:1378-1385 (2000)
Boone AN, Chan A, Kulpa JE, Brownsey RW. “Bi-modal activation of acetyl-CoA carboxylase by glutamate”, Journal of Biological Chemistry 275:10819-10825 (2000)