Disruption of Monoamine Homeostasis in Models of Neurological and Neuroendocrine Diseases Open Access

Dean, Erika Danielle (2011)

Permanent URL: https://etd.library.emory.edu/concern/etds/3t945r48t?locale=en
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Abstract


Abstract
Disruption of Monoamine Homeostasis in Models of Neurological and Neuroendocrine Diseases
By Erika Danielle Dean
While glucose intolerance has been associated with Parkinson's disease (PD), a
link between PD and diabetes has been demonstrated in epidemiological studies
only recently. Additionally, numerous
studies have shown that polychlorinated biphenyls (PCBs) increase the risk of developing both
PD and diabetes suggesting that common molecular pathways targeted by PCBs
may be involved in both diseases. Disruption of dopamine homeostasis is
is linked to PCBs in PD; however, disruption of dopamine
homeostasis with relation to glucose homeostasis is unknown. Since the pancreas is
dopaminergic, the effects of PCBs on glucose homeostasis were
investigated.
Female mice treated with PCBs gain weight, develop impaired glucose tolerance, and
have reduced adiponectin serum levels. PCB-treated female mice have a 36% reduction in
pancreatic dopamine levels and increased glucose-sensitive secretion of insulin. PCBs inhibit the
vesicular monoamine transporter 2 (VMAT2) that packages dopamine into vesicles in neurons
and beta cells at low micromolar concentrations. Unlike PCB-treated females, female mice
expressing low levels of VMAT2 (VMAT2 LO) do not develop age-associated changes in
glucose homeostasis that wild-type mice develop. VMAT2 LO mice have low fasting glucose
and improved glucose tolerance at 24 months of age when wild-type littermates have
begun to develop impaired fasting glucose and glucose tolerance. Like PCB-treated
female mice, VMAT2 LO female mice have a 70% reduction in pancreatic dopamine levels and
secrete more insulin in response to rising blood glucose levels than wild-type mice. Intriguingly,
glucose tolerance in male mice treated with PCBs is improved as it is in VMAT2 LO
mice. Thus, loss of dopamine is sufficient to affect glucose-stimulated insulin release, but does
not promote insulin resistance in mice.


Disruption of Monoamine Homeostasis in Models of Neurological and Neuroendocrine Diseases
By
Erika Danielle Dean
M.S., University of Tennessee, Knoxville, 2002
Advisor: Gary W. Miller, Ph.D.
A dissertation submitted to the Faculty of the
James T. Laney School of Graduate Studies of Emory University
in partial fulfillment of the requirements for the degree of
Doctor of Philosophy
in Graduate Division of Biological and Biomedical Science
Molecular Systems Pharmacology
2011.

Table of Contents

Chapter 1: Introduction and Background
Monoaminergic Neurotransmission………………………….…………….……………………....2
Introduction to Parkinson's Disease…………………………….…………….….………….…….8
Polychlorinated Biphenyls in Parkinson's Disease ………………………………….…………...11
Polychlorinated Biphenyls in Diabetes Mellitus………………………………….………………15
Is There a Link Between Parkinson's Disease and Diabetes Mellitus?..........................................18
VMAT2 as a Critical Regulator of Monoaminergic Signaling………….……...…….……..……21
VMAT2 in Aging and Neurodegenerative Disease…………………..………….........………….24
Effect of VMAT2 Inhibition…………………………………..………….….…………...…...….27
Genetic Mouse Models of VMAT2 Inhibition ……………………….…………..……..…….....28
Regulation of VMAT2 Protein Function…………………………………….…………..…...…..29
PCBs as Environmental Targets of VMAT2………………………………………………..……30
Monoaminergic Signaling in the Regulation of Glucose Homeostasis…………………..………31
Potential Role of VMAT2 in Glucose Homeostasis and Beta Cell Imaging...…..………...……..39
α-Synuclein in the Beta Cell and Neuron…………………….………….………………..……...40
α-Synuclein Regulation of Monoamine Homeostasis…………………………..………..………42 Introduction to Specific Aims…………………….……………………………………...……….44
Chapter 2: Polychlorinated Biphenyl Mixtures Reduce Dopamine Levels in the Pancreas and Impair Glucose Tolerance and Insulin Release
Abstract……………………….………………………………………………..………...……….56
Introduction…………………………………..………………………..………………...………..57
Materials and Methods………………………...…………………………………………...……..59
Results………………………………………….………………………………………...……….63
Discussion………………………………………………………………………………...………68
Chapter 3: Reduced Vesicular Monoamine Transporter 2 Protein expression Prevents Age-Associated Glucose Intolerance
Abstract………………………….…………………………………..………………...………….92
Introduction…………………………..………………………………………………...…………93
Materials and Methods………………...……………………………………………...…………..94
Results………………………………………………………………………………...…………..98
Discussion……………………………………………………………………………...………..102
Chapter 4: The Parkinson Disease Associated Protein α-synuclein Interacts with the Vesicular Monoamine Transporter 2 and Facilitates Packaging of Monoamines
Abstract……………………….…………………………………………………………...…….121
Introduction…………………………..……………………………………………...…………..122 Materials and Methods…………………...……………………………………...……...……….124
Results…………………………..……………………………………………………...….…….130
Discussion……………………………………………………………………………...………..132
Chapter 5: Summary and Conclusions
Summary and Discussion ……..………………………………………..……………...….…….153
Final Thoughts……………………………………………………..…………………..………..163
Appendix: Vitamin D Depletion Does Not Exacerbate MPTP-Induced Dopamine Neuron Damage in Mice
Abstract……………………………………………………….……………………...………….172
Introduction………………………………………………………..………………...…………..173
Materials and Methods………………………………………………...…………...…………....174
Results…………………………………………………………………………...………………178
Discussion………………………………………………………………………...……………..180
References…...…………………………………………………………………...……………..202 LIST OF FIGURES
Chapter 1: Introduction and Background
Figure 1.1 Monoamine Metabolism …………………………………….……...…...……..………4
Figure 1.2 Monoamine Homeostasis ……………………...……………...………...……………..6
Figure 1.3 Structure of PCB.………………………………………..…..….……...…..….………13
Figure 1.4 Vesicular Monoamine Transporter 2 Topography…………………...………...……..22
Figure 1.5 Vesicular Packaging of Monoamines………………….…………….........…………..25
Figure 1.6 Pancreatic Islet Organization ………………………………………...….…..………..32
Figure 1.7 Monoamine Regulation of Glucose-Stimulated Insulin Release ……...….….……….35
Figure 1.8 Proposed Model of the Interaction Between Parkinson's Disease and Diabetes Mellitus…...………………………………………………………………………..……………..46
Figure 1.9 Proposed Effect of PCB-mediated VMAT2 Inhibition on Glucose-Stimulated Insulin Release..……………………………………….………………………………….……..………..48
Figure 1.10 Proposed Effect of VMAT2 Inhibition on Glucose-Stimulated Insulin Release…………………………………………………………………………..…………...…...50
Chapter 2: Polychlorinated Biphenyl Mixtures Reduce Dopamine Levels in the Pancreas and Impair Glucose Tolerance and Insulin Release
Table 2.1 VMAT2 IC50 Values of Various PCB Congeners and Commercial Mixtures…….......73
Figure 2.1 PCB Exposure Promotes Increased Body Mass Over Time in Female Mice……...…75
Figure 2.2 PCB Exposure Impairs Glucose Tolerance in Female Mice……..……………..…….77 Figure 2.3 PCB Exposure Promotes Wasting and Loss of Body Mass Over Time in Male Mice………………………………………………………………………………………..……..79
Figure 2.4 PCB Exposure Does Not Impair Glucose Tolerance in Male Mice…………...……...81
Figure 2.5 PCB Exposure Increases Glucose-Stimulated Insulin Release in Female Mice…...…83
Figure 2.6 PCB Exposure Decreases Serum Adiponectin Levels in Female Mice…………..…..85
Figure 2.7 PCB exposure Increases Serum Cholesterol Levels, but Not Triglycerides in Female Mice. …………………….………………………………………………………….....................87
Figure 2.8 PCB Exposure Decreases Dopamine Levels in the Pancreas…...........................…….89
Chapter 3: Reduced Vesicular Monoamine Transporter 2 Protein expression Prevents Age-Associated Glucose Intolerance
Figure 3.1 VMAT2 LO Mice Have Normal Islet Morphology ……………...………..………..108
Figure 3.2 VMAT2 LO Mice Have Reduced VMAT2 Levels in the Pancreas …………..…....110
Figure 3.3 VMAT2 LO Mice Have Reduced Monoamine Levels in the Pancreas ………..…...112
Figure 3.4 VMAT2 LO Mice Show Improved Fasting Glucose Levels as They Age ……........114
Figure 3.5 VMAT2 LO Mice Do Not Develop Impaired Glucose Tolerance as They Age…….116
Figure 3.6 VMAT2 LO Mice Have Higher Glucose-Stimulated Insulin Release as Compared to Their WT Littermates ……………………………………………………....……………..……118
Chapter 4: The Parkinson Disease Associated Protein α-synuclein Interacts with the Vesicular Monoamine Transporter 2 and Facilitates Packaging of Monoamines
Table 4.1 Analyses of VMAT2 Kinetic Parameters…………………………….………..….….136 Figure 4.1 Colocalization of VMAT2 and α-Syn in Human Substantia Nigra Pars Compacta (SNpC) Neurons ……….…………………………………………………………………..…...138
Figure 4.2 Expression of Dopaminergic Neuronal Markers in Mouse Primary Cultured Neuron………………………………………………………………………………..…………140
Figure 4.3 VMAT2 and α-Syn Expression from Subcellular Fractionation of Mouse Striatum………………………………………………………………………………...………..142
Figure 4.4 Confocal Microscopy Images of α-Syn and VMAT2 in Cultured SHSY5Y Cells…………………………………………………………………………………..…………144
Figure 4.5 Effect of α-Syn Expression on Dopamine Uptake in Immortalized Dopaminergic Cells...………………………………………………………………………………..………….146
Figure 4.6 Effect of α-Syn on VMAT2 Expression…………….………………...………….….148
Figure 4.7 VMAT2 Interacts with α-Syn………………………………...……...………...….…150
Chapter 5: Summary and Conclusions
Figure 5.1 PCBs and Monoaminergic Dysfunction as Related to Parkinson's Disease and Diabetes Mellitus……………………………………………………………..…………....……165
Figure 5.2 Proposed Mechanism of PCB-mediated Effects on Glucose Homeostasis……….…167
Figure 5.3 Proposed Mecanism of VMAT2 Inhibiton-Mediated Effects on Glucose Homeostasis…………………………………………………………………………..…………169
Appendix: Vitamin D Depletion Does Not Exacerbate MPTP-Induced Dopamine Neuron Damage in Mice
Figure A.1 Diagram of Experimental Procedure…...……...……………………..……………..184 Figure A.2 Vitamin D Depletion Has No Effect on Body Mass………………….....………….186
Figure A.3 Short Term Vitamin D Depletion Has No Observable Effect on Mouse Behavior……………………………………………………………………………...………….188
Figure A.4 Behavioral and Neurochemical Effects of Vitamin D Depletion on MPTP Susceptibility in Mice………………………………………………………………..….………190
Figure A.5 Effects of Vitamin D Depletion on TH and DAT Expression in MPTP-Lesioned Mice……...…………………………………………………………………………..………….192
Figure A.6 Vitamin D Depletion Does Not the Exacerbate Loss of Tyrosine Hydroxylase Staining in the Striatum and Nigra after MPTP Lesion………………….………………………….……194
Figure A.7 MPP+ Levels Are Not Altered by Vitamin D Depletion……………………………196
Figure A.8 MPTP Lesioning Does Not Affect Serum 25-hydroxyvitamin D Levels .............…198
Figure A.9 Serum 25-hydroxyvitamin D Levels Are Not Changed in VMAT2 LO Mice.......…200

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