Research Projects: Lukas-Whiteaker Lab
Science of Medicine, Spirit of Discovery
Turning back again to fundamental laboratory science, there are many lines of investigation in the laboratory. First and foremost, because there is not just one type of nicotinic acetylcholine receptor, fundamental work involves identification and classification of the diverse family of nicotinic receptors, each of which is defined by the building blocks or subunits that constitute them. These studies identify subunits and receptor subtypes in different tissues and organ systems, exploit tumor cell lines as factories naturally making nicotinic receptors like those found in normal tissue, or involve creation of genetically engineered cell lines fashioned to examine features of nicotinic receptors suspected or known to exist. Research tools are critical to advances, and we have created or exploited many, including natural products from frogs, snakes, harpoon-wielding sea snails, or mushrooms, and their synthetic analogues.
Molecular and cellular biology, immunology, protein chemistry, pharmacology, and electrophysiology converge in these studies to provide the most comprehensive description of nicotinic receptors under study that is possible. For example, identification of differences in the ability of different nicotinic receptor subtypes to interact with specific drugs is used not only to discriminate receptor subtypes, but also to discover new drugs that are selective or specific in their preference for a given receptor subtype. This creates the opportunity to find a nicotine-like drug that could elevate mood by acting at one receptor subtype without causing nicotine dependence through interactions with receptors in the pleasure-reward center of the brain.
Work is continuing to define which of the 17 subunits identified to date combine to make unique receptor subtypes, and features of every subtype identified then need to be characterized. Studies of the effects of chronic nicotine exposure on receptor numbers and function are being done to define how the brain changes in response. Fundamental features of nicotinic receptors in pleasure-reward, emotional, and attention centers are being studied, as well as in neurological and other medical conditions.
Studies extend beyond muscle and nerve cells. For example, there is evidence that nicotinic receptors are in blood vessels in many organs including the brain, where they contribute to formation of the blood-brain barrier and influence cytotoxic and vasogenic phases of edema during stroke. Other studies concern roles nicotinic receptors play in nervous system/immune system interactions and in lung or lung tumor growth. Bone formation and reproductive organ function also seem to be influenced by nicotine exposure, implying that nicotinic receptors are found on the relevant cell types.
Nicotinic receptors also can be used as models to test new techniques and to push back biotechnological horizons. For example, we are evaluating nicotinic receptors as models for the development of sophisticated tools for proteomics research. Genetically engineered cells and site-directed mutagenesis studies are being used not only to define structure-function relationships for the many interesting domains in nicotinic receptors, but also as models of genetically based neurological diseases and for studies to define the functional consequences of such mutations.
Our work has revealed nicotinic receptor subunit gene polymorphisms, which may prove to be indicators—assessable through gene array techniques—of susceptibility to neurological or psychiatric disease or to nicotine dependence and likelihood of success in smoking cessation therapy. Conversely, other studies have revealed changes in gene activity induced by nicotine exposure, possibly revealing how some effects of nicotine exposure can be long-lasting but also revealing important targets for normal signaling through nicotinic receptors.
Naturally, many factors can influence nicotinic receptor levels and function, from the cytoskeleton and extracellular matrix, gene expression regulators, other types of receptors engaging in cross-talk, and cytoplasmic entities and the signaling cascades they trigger. Reciprocally, nicotinic receptor activity can affect all of those. Hormones and small peptides are among the other agents that have such effects. Some of our most exciting work concerns another large family of molecules initially revealed by studies of the immune system and that resemble in some ways natural product toxins that target nicotinic receptors. These molecules can have a wide range of effects, and combinations of them and receptor subtypes challenge us with a huge matrix of possible interactions of biological relevance. Indications are that genetic variation in some of these molecules can predispose individuals to disorders such as anxiety and can affect how the maturing brain is constructed.
We take great pride in our studies and contributions we have made. We are even more excited when we make new discoveries that overturn accepted science and dogma, even if we had a hand in formulating those initial but still-immature perspectives and interpretations. We invite inquiries about this, but now we are creeping deeply into esoteric matters. For example, it once was thought that one receptor subtype that is a major target of nicotine action at human smoker levels had one structure. We and others then did studies showing that that subtype actually existed in two “isoforms” that differed in the ratio of the two building blocks constituting the subtype. These isoforms responded differently to markedly different levels of acetylcholine or nicotine. We then developed tools to modify the receptors very subtly but by keeping control of ratios and arrangements of the building blocks. That led us to discover critical differences between interfaces between building blocks that influenced sensitivity to acetylcholine and nicotine. Further studies, even more esoteric, showed that activity dictated by what building blocks made up interfaces is further influenced by the next-door building blocks!
Picture this – nicotinic acetylcholine receptors at the atomic level are in constant motion, wiggling like leaves in the wind. Each leaf has a little different structure and wiggles differently in the same wind. These are the receptor subtypes. If a bug lands on a leaf, the leaf’s response to the wind changes, just as the receptor’s does when it encounters nicotine or acetylcholine. That is how delicate these entities are, and the likelihood that they are in the closed or open channel state is influenced by interactions with acetylcholine or nicotine. Just as a dry leaf or a water-soaked one will behave differently in the wind, other elements in and around cells where nicotinic receptors are found can loosen or restrict these movements. Just as an infestation can decimate a tree of its leaves, or hearty winds shaking the leaves can cause branches to crash to the earth, harmful processes can lead to loss of receptors, and receptor hyperactivity can be harmful to the cells that make them, in either case, perhaps setting disease wheels in motion.
- Demonstrating recognition for our work nationally and internationally, past or current funded studies or studies leading to published contributions involve dozens of collaborating scientists at the University of Arizona, Arizona State University, Banner Sun Health Research Institute, several biotechnology companies in the state, nationally, or internationally, and at many institutions in the country and worldwide. Co-workers are in Arizona cities including Phoenix, Tempe, Tucson, Scottsdale, and Sun City; other U.S. cities including Baltimore, Bethesda, Boston, Denver, Durham, Gainesville, Houston, Ithaca, Kalamazoo, Lubbock, Los Angeles, Memphis, Palo Alto, Philadelphia, Raleigh, Richmond, Salt Lake City, San Diego, San Juan, St. Louis, Tampa, and Winston-Salem; and non-US cities including Bahia Blanca, Bath, Edinburgh, Edmonton, Geneva, Heidelberg, Montpellier, Oxford, and Paris.
- Visiting foreign national scientists, faculty doing sabbatical work, and educators doing summer research projects have been active in our laboratory.
- Contributed to demonstration of nicotinic acetylcholine receptor diversity
- Identified or created natural or genetically engineered cell models for nicotinic receptor research
- Contributed to basic pharmacological and structural characterization of nicotinic receptors
- Definition, at the molecular level, of effects that occur with smoking and of chronic nicotine exposure on nicotinic receptor function
- Insights into medical conditions as diverse as Alzheimer’s, epilepsy, and multiple sclerosis