Disruption of Monoamine Homeostasis in Models of Neurological and Neuroendocrine Diseases Öffentlichkeit
Dean, Erika Danielle (2011)
Published
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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