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CVRI Scientists
Metabolism, obesity and metabolic diseases
Kaveh Ashrafi, Ph.D.
Assistant Professor
Research Interests:
Genetics of fat regulation and neurobiology of feeding behavior
Summary:
Obesity is a major risk factor associated with many diseases including diabetes, cardiovascular and gastrointestinal diseases, arthritis, and certain forms of cancers. Obesity is a global epidemic common to all socio-economic and age groups. The prevalence of obesity reflects the combination of high calorie diets with sedentary lifestyles. However, genetic predispositions play profound roles in determination of an individual's body fat and the progression of obesity related disorders. Fat regulation is under tight control of a complex network of checks and balances between the feeding regulatory centers in the brain and fat storage and energy utilizing sites in the body. How genetic and environmental factor interact to impact body fat content and how excess fat accumulation causes disease processes are poorly understood.
To identify genes that underlie fat regulation we use the genetically tractable worm C. elegans. This microscopic worm has been used extensively to study animal development, aging, and pathways implicated in human diseases. This is because it many of its 20,000 genes have significant similarity to human genes. Using genetic and genomic techniques, we have identified over 400 genes that, when inactivated, impact fat regulation in these animals. These include genes whose mammalian counterparts were previously shown to be important in fat regulation as well as many genes previously unassociated with fat content. The shared ancestry of known mammalian and C. elegans fat regulatory genes suggests that many of the newly identified genes similarly impact fat regulation in mammals. Our efforts are now aimed at elucidating the modes of function and regulation of the newly identified genes. We have already shown that some of these genes function in the C. elegans nervous system to centrally regulate fat and feeding pathways while other genes function at the sites of fat storage to regulate metabolism. Based on our findings we have initiated collaborative studies to identify mammalian obesity genes.
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Robert V. Farese, Jr., M.D.
Senior Scientist, J. David Gladstone Institutes, Professor of Medicine and of Biochemistry & Biophysics
Research Interests:
Cell Biology of Energy Metabolism
Summary:
"The ability of cells to store and utilize energy in a regulated manner is fundamental to life, and abnormalities in energy metabolism play a central role in diseases such as obesity, type two diabetes, neurodegeneration, and aging. Our laboratory is interested in cellular energy homeostasis, focusing on three interrelated areas of research: the cell biology of lipid storage, the enzymes of neutral lipid synthesis, and energy metabolism in neurons. Our approaches are basic, emphasizing biochemistry and cellular biology, with specific hypothesis testing in model organisms such as flies and mice. Our group has two new areas of investigation: 1) the cell biology of lipid droplet formation and utilization, and 2) neuron cell biology and neurodegeneration, with a focus on frontotemporal dementia. For more information on our laboratory, please visit our laboratory web site (www.gladstone.ucsf.edu/gladstone/files/farese/HomePage/index.html)."
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Christopher J. Fielding, Ph.D.
Professor of Physiology
Research Interests:
Structure-function analysis of cholesterol-binding proteins
Summary:
The research in our laboratory deals with the formation, activity and turnover of high density lipoprotein (HDL), the Ògood cholesterolÓ component of plasma lipoproteins. HDL lowers peripheral cell cholesterol levels by promoting cholesterol transport to the liver. It regulates signaling across cell membranes by controlling the cholesterol content of lipid rafts and caveolae, cell surface complexes of signaling proteins. Finally, HDL opposes inflammation when it acts as a scaffold for enzymes that bind and break down oxidized lipids to harmless by-products. Low HDL is a strong indicator of increased risk for human atherosclerotic heart disease. The development of HDL-raising drugs has recently accelerated. Our ability to raise plasma HDL levels will depend on defining the molecular mechanisms by which HDL is formed and recycled.
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Phoebe Fielding, Ph.D.
Adjunct Professor of Medicine
Research Interests:
Caveolin and caveolae: Roles in cholesterol transport and signaling
Summary:
The research in our laboratory deals with the formation, activity and turnover of high density lipoprotein (HDL), the Ògood cholesterolÓ component of plasma lipoproteins. HDL lowers peripheral cell cholesterol levels by promoting cholesterol transport to the liver. It regulates signaling across cell membranes by controlling the cholesterol content of lipid rafts and caveolae, cell surface complexes of signaling proteins. Finally, HDL opposes inflammation when it acts as a scaffold for enzymes that bind and break down oxidized lipids to harmless by-products. Low HDL is a strong indicator of increased risk for human atherosclerotic heart disease. The development of HDL-raising drugs has recently accelerated. Our ability to raise plasma HDL levels will depend on defining the molecular mechanisms by which HDL is formed and recycled.
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John P. Kane, M.S., M.D., Ph.D.
Professor of Medicine and Biochemistry & Biophysics
Research Interests:
Structure and function of lipoproteins; genetic determinants of arteriosclerosis
Summary:
Because it has been found that faulty transport of cholesterol and other lipids is an underlying element in the development of arteriosclerosis, elucidation of molecular mechanisms involved in cholesterol transport has been a major goal of this group. This has led to the identification of previously unidentified proteins that participate in the process. Certain complexes of cholesterol and other fatty substances with proteins (lipoproteins) are known to convey cholesterol to the artery wall to initiate the formation of diseased areas (plaques) that can eventually lead to occlusion of arteries serving the heart or brain. Others (High Density Lipoproteins, HDL) have the task of removing cholesterol to protect the arteries. Understanding how HDL accomplish this task requires the discovery and characterization of previously unknown molecular complexes. Whereas it was thought that there were two species of HDL, work by this group has identified sixteen to date, detecting the different proteins that comprise each species using the technique of mass spectrometry. Studies are conducted in parallel to discover the biochemical pathways by which they are assembled, and the processes they mediate. This has led to the discovery of species that have antioxidant and anti-inflammatory activities, and another that protects humans against the organism that causes Trypanosomiasis, better known as African sleeping sickness. It has also been found that the removal of chemically injurious fatty substances from the retina involves HDL, leading to important new insights that can be applied to understanding macular degeneration, the leading cause of blindness in people over fifty years of age in the U.S.
Another goal in this laboratory is the discovery of genes related to the development of heart attacks and stroke. To accomplish this, a very large collection of human DNA, approaching 30,000 individual samples, has been assembled by the group. Each sample is accompanied by an extensive clinical history. Over twelve thousand genes have been studied thus far. Variations in twenty-one genes have now been found to be associated with heart attack and four genes have been linked to stroke. Because risk genes may interact with one another, the group is collaborating with the Los Alamos National Laboratory, using its supercomputers to develop new mathematical formulas for accomplishing this challenging task. Discovery of the genes that are linked to heart attack and stroke is expected to lead to new strategies for prevention and treatment of those diseases. Other targets of the genetic research by this group that are related to heart disease are diabetes, HDL deficiency states, other lipoprotein disorders, and macular degeneration. Six previously unrecognized diseases caused by defective genes have been discovered in this effort.
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Robert E. Pitas, Ph.D.
Professor of Pathology; Senior Investigator, Gladstone Institute of Cardiovascular Disease, Gladstone Institute of Neurological Disease
Research Interests:
Lipoprotein metabolism in vivo and in vitro; role of lipoproteins in the development of atherosclerosis; lipoprotein receptors and atherosclerosis
Summary:
Elevated low density lipoprotein (LDL) cholesterol is the best-known, but not the only, risk factor for heart disease. High levels of lipoprotein(a) [Lp(a)] are also atherogenic. Plasma Lp(a) levels in excess of 30 mg/dl are associated with atherosclerosis and an increased risk of heart attack and stroke. Research into the role of Lp(a) in these pathologies has been hampered by the lack of a suitable animal model with high-level Lp(a) expression.
To address this problem, we developed transgenic mice with high-level expression of Lp(a). In Lp(a), apolipoprotein(a) [apo(a)], a plasminogen-like glycoprotein, is covalently linked to apoB-100, the protein component of LDL. First, we produced mice expressing apo(a) and crossed them with mice expressing human apoB-100. Using an antibody that detects oxidized phospholipids and oxidized phospholipid protein adducts, we made the interesting discovery that Lp(a) in plasma of these mice contained oxidized phospholipids, whereas LDL did not.
Oxidized LDL is thought to contribute to the development of atherosclerosis. LDL that is retained in the artery wall undergoes oxidative modification with resultant detrimental effects. This oxidized LDL apparently is not released or does not accumulate in plasma. Oxidized phospholipids in LDL are partially responsible for the uptake of lipoproteins by cells, which leads to foam-cell formation and the release of cytokines from cells, resulting in monocyte recruitment to the artery wall and in the proliferation of smooth muscle cells.
Our work is focusing on determining if oxidized phospholipids contribute to the atherogenicity of the Lp(a). Our preliminary data suggest that the Lp(a) in these mice are more atherogenic than similar levels of plasma LDL. However, it is not at all clear why plasma Lp(a) contains oxidized phospholipid and LDL does not. What is the source of the oxidized phospholipid? How does it affect the properties of Lp(a)? These new mouse models are currently being used to study these and other questions related to Lp(a), oxidized phospholipid, and atherogenesis.
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Karl H. Weisgraber, Ph.D.
Senior Investigator, Gladstone Institute of Cardiovascular Disease and Gladstone Institute of Neurological Disease
Research Interests:
Structure-function of apolipoprotein E
Summary:
The current focus of our research is on the structure and function relationships of plasma apolipoprotein (apo) E in both lipoprotein metabolism and Alzheimer's disease. ApoE is a 299 residue, single chain protein that contains two structural domains, an amino- and carboxyl-terminal domain that also defines functional domains. The amino-terminal domain (residues 1Ð191) contains the LDL receptor binding region of apoE and the carboxyl-terminal domain contains the major lipid binding elements. Previous studies have established that the three common isoforms of apoE, apoE2, apoE3, and apoE4, which differ by cysteine and arginine contents at two positions in the molecule, have very different metabolic properties with a dramatic impact on two diseases. For example, apoE3 (Cys-112, Arg-158) binds normally to the low density lipoprotein (LDL) receptors and is associated with normal metabolism, whereas apoE2 (Cys-112, Cys-258) binds defectively and is associated with the genetic lipoprotein disorder, type III hyperlipoproteinemia. The apoE4 allele is a major risk factor for Alzheimer's disease and other neurodegenerative diseases; apoE4 is also associated with elevated cholesterol levels and an increased risk for heart disease, although it binds normally to LDL receptors.
In our research, physical-chemical techniques, including x-ray crystallography, are combined with site-directed mutagenesis to probe structure and function questions. We have identified two unique properties of apoE4 compared to apoE3 and apoE2: domain interaction and low stability to unfolding. It is our working hypothesis that either or both of these properties account for the association of apoE4 with disease. To distinguish between the relative contribution of domain interaction and stability to the known effects of apoE4, we have taken advantage of the fact that mouse apoE does not display either property. By identifying the key residues in apoE4 that contribute to domain interaction and stability, we have introduced each property selectively into a mouse model by gene targeting. Our overall goal is to determine how structural changes in apoE influence its known metabolic properties and contribute to the isoform-specific effects in lipoprotein metabolism, heart disease, and Alzheimer's disease.
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