Narcolepsy and the Orexin Neuropeptide System
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LESSONS FROM SLEEPY MICE: NARCOLEPSY AND THE OREXIN NEUROPEPTIDE SYSTEM APPROVED BY SUPERVISORY COMMITTEE DEDICATION I would like to thank my mentors and colleagues Masashi Yanagisawa, M.D., Ph.D.; Howard Gershenfeld, M.D.,Ph.D.; Michael Brown, M.D.; Rama Ranganathan, M.D., Ph.D.; Richard Chemelli, M.D.; Christopher Sinton, Ph.D.; Paul Boldt, Ph.D.; Thomas Kodadek, Ph.D.; and Glen R. Willie, M.D. I also thank my program directors and administrators Dennis McKearin, Ph.D.; Rodney Ulane, Ph.D.; Jean Wilson, M.D.; Robin Downing; Stephanie Robertson; Mark Lehrman, Ph.D.; and Carla Childers. I am especially thankful to my wife Abigail, my son Sam, and all my family for their love and support. LESSONS FROM SLEEPY MICE: NARCOLEPSY AND THE OREXIN NEUROPEPTIDE SYSTEM by JON TIMOTHY WILLIE DISSERTATION Presented to the Faculty of the Graduate School of Biomedical Sciences The University of Texas Southwestern Medical Center at Dallas In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY The University of Texas Southwestern Medical Center at Dallas Dallas, Texas June, 2005 Copyright by JON TIMOTHY WILLIE, 2005 All Rights Reserved LESSONS FROM SLEEPY MICE: NARCOLEPSY AND THE OREXIN NEUROPEPTIDE SYSTEM Publication No. JON TIMOTHY WILLIE, M.D., Ph.D. The University of Texas Southwestern Medical Center at Dallas, 2005 Supervising Professor: MASASHI YANAGISAWA, M.D., Ph.D. The hypothalamic orexin neuropeptide system is a neuronal pathway regulating behavioral vigilance states and metabolic functions. Orexins activate the orexin receptors type 1 and type 2 (OX2R). Melanin-concentrating hormone (MCH) is an anatomically- related peptide that may have complementary functions. Orexin null (orexin-/-) mice exhibit a behavioral and electroencephalographic phenotype similar to narcolepsy-cataplexy, a neurological disorder caused by orexin deficiency. Narcolepsy-cataplexy consists of inability to maintain wakefulness, abnormal intrusions of rapid-eye-movement (REM) sleep and related phenomena (i.e. cataplexy) into wakefulness, and poorly characterized metabolic v vi abnormalities. I demonstrate that both OX2R-/- and orexin-/- mice are unable to maintain wakefulness normally. In contrast, OX2R-/- mice are only mildly affected with abnormalities of REM sleep, whereas orexin-/- mice are severely affected. Thus, the profound dysregulation of REM sleep control unique to the narcolepsy-cataplexy syndrome emerges from loss of signaling through both OX2R-dependent and OX2R-independent pathways. Transgenic mice, in which orexin neurons are ablated, fail to respond normally to fasting with increased wakefulness and activity indicating that orexin neurons provide a crucial link between energy balance and arousal. Orexin-/- and MCH-/- mice have increased and decreased adiposity and susceptibility to diet-induced obesity, respectively. While orexin-/- mice exhibit sleepiness and cataplexy, MCH-/- mice are more wakeful than wild-type mice. Orexin-/-;MCH-/- exhibit exacerbation of the narcolepsy phenotype, indicating that orexin and MCH complementarily regulate behavioral stabilty. Mice that ectopically overexpress orexin in the brain exhibit reduced body weight and resistance to diet-induced obesity, inability to maintain sleep, and reduced REM sleep with abnormal myoclonic activity relative to wild-type controls, providing further evidence that orexin alters homeostatic set-points of both energy metabolism and sleep/wakefulnuss. Modafinil, a stimulant used to treat narcoleptics, effectively increases wakefulness but does not suppress cataplexy in orexin-/- mice, indicating that orexin is not required for the wake-promoting action of the drug. By contrast, expression of an orexin transgene in the brain completely prevented cataplectic arrests and other abnormalities of REM sleep in the absence of endogenous orexin neurons. Thus, orexin neuron-ablated mice retain the ability to respond to orexin neuropeptides and orexin receptor agonists would likely contribute to treating human narcolepsy. TABLE OF CONTENTS DEDICATION ....................................................................................................................... ii ABSTRACT ........................................................................................................................... v TABLE OF CONTENTS ..................................................................................................... vii PRIOR PUBLICATIONS ................................................................................................... viii LIST OF FIGURES .............................................................................................................. xi LIST OF TABLES ............................................................................................................. xvii LIST OF APPENDICES ................................................................................................... xviii LIST OF DEFINITIONS .................................................................................................... xix CHAPTER 1 - Introduction and Historical Perspective ......................................................... 1 CHAPTER 2 – Distinct Narcolepsy Syndromes in Orexin Receptor Type 2 (OX2R) and Orexin Knockout Mice: Molecular Genetics of Non-REM and REM Sleep Regulation 26 CHAPTER 3 - Coordinating Energy Balance and Arousal.................................................. 72 CHAPTER 4 - Genetic Interaction of Two Hypothalamic Peptides, Orexin and MCH ...... 91 CHAPTER 5 - Effects of Unregulated Orexin Overexpression ......................................... 133 CHAPTER 6 - Treatment of Narcolepsy – Modafinil........................................................ 154 CHAPTER 7 - Treatment of Narcolepsy - Genetic and Pharmacologic Rescue by Orexin 186 CHAPTER 8 - Conclusion.................................................................................................. 215 APPENDICES .................................................................................................................... 216 BIBLIOGRAPHY............................................................................................................... 255 VITAE ................................................................................................................................ 275 vii PRIOR PUBLICATIONS Original Reports Willie, J. T., Scammell, T. E., Renthal, W., Chemelli, R. M., Miller, M. S., Yanagisawa, M., Sinton, C. M.. Modafinil More Effectively Induces Wakefulness in Orexin Null Mice than in Wild-Type Littermates. Neuroscience. In press. Mieda, M., Willie, J. T., Hara, J., Sakurai, T., Yanagisawa, M. (2004). Orexin Peptides Prevent Cataplexy and Improve Wakefulness in an Orexin Neuron-Ablated Model of Narcolepsy in Mice. PNAS 101: 4649-54. Willie, J. T., Chemelli, R. M., Sinton, C. M., Tokita, S., Williams, S. C., Kisanuki, Y. Y., Marcus, J. N., Lee, C. E., Elmquist, J. K., Kohlmeier, K. A., Leonard, C. S., Richardson, J. A., Hammer, R. E., Yanagisawa, M. (2003). Distinct Narcolepsy Syndromes in Orexin Receptor Type-2 and Orexin Null Mice: Genetic Dissection of Non-REM and REM Sleep Regulatory Processes. Neuron 38: 715-30. Yamanaka, A., Beuckmann, C. T., Willie, J. T., Hara, J., Tsujino, N., Mieda, M., Tominaga, M., Yagami, K., Sugiyama, F., Goto, K., Yanagisawa, M., Sakurai, T. (2003). Hypothalamic Orexin Neurons Regulate Arousal According to Energy Balance in Mice. Neuron 38: 701-13. Georgescu, D., Zachariou, V., Barrot, M., Mieda, M., Willie, J. T., Eisch, A. J., Yanagisawa, M., Nestler, E. J., DiLeone, R. J. (2003). Involvement of the lateral hypothalamic peptide orexin in morphine dependence and withdrawal. Journal of Neuroscience 23: 3106-11. Chou, T. C., Lee, C. E., Lu, J., Elmquist, J. K., Hara, J., Willie, J. T., Beuckmann, C. T., Chemelli, R. M., Sakurai, T., Yanagisawa, M., Saper, C. B., Scammell, T. E. (2001). Orexin (hypocretin) neurons contain dynorphin. Journal of Neuroscience 21: RC168. Hara, J., Beuckmann, C. T., Nambu, T., Willie, J. T., Chemelli, R. M., Sinton, C. M., Sugiyama, F., Yanagi, K., Goto, K., Yanagisawa, M., and Sakurai, T. (2001). Genetic ablation of orexin neurons in mice results in narcolepsy, hypophagia and obesity. Neuron 30: 345-54. Chemelli, R. M., Willie, J. T., Sinton, C. M., Elmquist, J. K., Scammell, T., Richardson, J. A., Williams, S. C., Xiong, Y., Kisanuki, Y., Fitch, T. E., Nakazato, M., Hammer, M., Saper, C. B., and Yanagisawa, M. (1999). Narcolepsy in orexin knockout mice: molecular genetics of sleep regulation. Cell 98: 437-51. viii ix Vashee, S., Willie, J. T., Kodadek, T. (1998). Synergistic activation of transcription by physiologically unrelated transcription factors through cooperative DNA-binding. Biochemical & Biophysical Research Communications 247(2):530-5. Invited Reviews Willie, J. T. and Yanagisawa, M. Lessons from Sleepy Mice. In Narcolepsy and Hypersomnia. Ed. C. Bassetti et al. Marcel Dekker, Inc. In press. Willie, J. T., Chemelli, R. M., Sinton, C. M., and Yanagisawa, M. (2001). To eat or sleep? Orexin in the regulation of feeding and wakefulness. Annual Review of Neuroscience 24:429-58. Peer-Reviewed, Published Abstracts Willie, J. T., Sinton, C. M., Mieda, M., Maratos-Flier, E., Yanagisawa, M. (2003). Orexin and melanin-concentrating hormone (MCH) double knockout mice: Compensatory role for MCH in narcolepsy-cataplexy. Sleep (Abstr). 26:A50. Willie, J. T., Beuckmann, C. T., Hara, J., Sakurai, T., Yanagisawa, M. ( 2002). Ectopic Expression of an Orexin Transgene Rescues