Reduced vesicular storage of catecholamines in the pathogenesis of Parkinson's Disease Open Access
Taylor, Tonya (2010)
Published
Abstract
Parkinson's disease (PD) is a neurodegenerative disorder which
affects millions of people
worldwide. Although the cause of PD is unknown, it is thought to be
due to a combination of
genetic and environmental factors; many therapies aim to restore
dopamine (DA) within the
brain. Animal models, both chemical and transgenic, have been used
to uncover potential
mechanisms of PD, but none have successfully recapitulated the
symptoms of PD on an
appropriate timescale. Genetic perturbation of the vesicular
monoamine transporter (VMAT2)
yielded the VMAT2-deficient mice, which display many of the motor
and non-motor symptoms
associated with PD. With a 95% reduction in VMAT2 expression,
VMAT2-deficient animals
have decreased novelty-induced locomotor activity and a shortened
stride length at older ages.
VMAT2-deficient animals also displayed progressive deficits in
olfactory discrimination without
changes in other sensory systems, which appear to be possibly
correlated with previously seen
age-dependent reduction in dopamine transporter expression.
Moreover, VMAT2-deficient mice
have a shorter latency to behavioral signs of sleep, delayed
gastric emptying, anxiety-like
behaviors at younger ages, and a progressive depressive-like
phenotype. Taken together, these
data suggest that reduced storage of monoamines may contribute to
the development of many
features of Parkinson's disease. Progressive neurodegeneration in
the substantia nigra (SNpc),
locus coeruleus (LC), and dorsal raphe (DR) has been observed,
accompanied by α-synuclein
accumulation. Moreover, primary cultures from the SNpc, LC, and DR
of postnatal mice
exposed to physiological concentrations of monoamines were found to
undergo increased
oxidative stress via formation of H2O2 and other oxidative species;
whereas, cultures from
wildtype mice were unaffected. These studies demonstrate that
reduced vesicular storage may
play a role in the pathogenesis of parkinsonian symptoms and
neurodegeneration. Perturbing the
catecholaminergic cytosolic environment may ultimately lead to the
development of several
behavioral phenotypes and neuronal death. Using the VMAT2-deficient
mice as a new model of
PD, could potentially lead to new therapeutic strategies beyond DA
replacement therapy.
Table of Contents
CONTENTS
CHAPTER 1: INTRODUCTION AND BACKGROUND
Parkinson's Disease……………………………………………………………………...2
Dopamine and PD……………………………………………………………..…………3
Non-motor symptoms of PD…………………………………………………………..…5
Norepinephrine in PD………………………………………………………………..…..6
Serotonergic involvement in PD…………………………………………………..…….8
Hypotheses of PD……………………………………………………………………….10
Vesicular Monoamine Transporter……………………………………………………13
Introduction to Specific Aims………………………………………………...………..15
CHAPTER 2: BEHAVIORAL PHENOTYPING OF MOUSE MODELS OF PD
Abstract…………………………………………………………………………………18
Introduction……………………………………………………………………………..19
General Health………………………………………………………………………….20
Motor phenotype of PD……………………………………………………………..….22
Olfactory deficits in PD……………………………………………………………..….23
Sleep abnormalities in PD…………………………………………………………...…25
Gastrointestinal dysfunction in PD……………………………………………………27
Anxiety and depression…………………………………………………………...……30
Cognitive deficits in PD……………………………………………………………..….34
Conclusion………………………………………………………………………………35
CHAPTER 3: NON-MOTOR SYMPTOMS OF PD REVEALED IN MICE WITH REDUCED VESICULAR MONOAMINE STORAGE
Abstract………………………………………………………………………………….40
Introduction………………………………………………………..…………..………..41
Materials and Methods…………………………………………………………………42
Results…………………………………………………………………………………...48
Discussion……………………………………………………………………………….53
Acknowledgments………………………………………………………………………58
CHAPTER 4: PROGRESSIVE NORADRENERGIC DEGENERATION PRECEDES NIGRAL CELL LOSS IN A MOUSE MODEL OF PD
Abstract………………………………………………………………………………….76
Introduction……………………………………………………………………………..77
Materials and Methods……………………………………………………………..…..78
Results………………………………………………………………………………...…82
Discussion…………………………………………………………………………….....87
Acknowledgments……………………………………………………………………....90
CHAPTER 5: SEROTONERGIC DYSFUNCTION IN A MOUSE MODEL OF PARKINSON'S DISEASE
Abstract……………………………………………………………………..………….106
Introduction…………………………………………………………………..………..107
Materials and Methods………………………………………………………..………108
Results………………………………………………………………………………….111
Discussion……………………………………………………………………...………113
Acknowledgments……………………………………………………………………..116
CHAPTER 6: SUMMARY AND CONCLUSIONS
Introduction……………………………………………………………………..……..125
Genetic Manipulation of VMAT2…………………………………………………….127
The VMAT2 Hypomorph Mouse……………………………………………….……129
Perfected Perturbation: VMAT2-deficient mice………………………………...…..132
Conclusions………………………………………………………………………...…..136
Future Directions…………………………………………………………………...…137
Final Thoughts….……………………………………………………………………..139
APPENDIX A: THE EFFECT OF INCREASED CYTOSOLIC CATECHOLAMINES ON CELL TOXICITY
Summary……………………………………………………………………………….145
REFERENCES…………………………………………………………………………..……..153
LIST OF FIGURES
CHAPTER 3: NON-MOTOR SYMPTOMS OF PD REVEALED IN MICE WITH REDUCED VESICULAR MONOAMINE STORAGE
Figure 3-1. VMAT2-deficient mice display widespread reductions in monoamines at 12-15 months of age……………………………………………………..…………59
Figure 3-2. VMAT2-deficient animals display progressive deficits in olfactory discrimination…………………………………………………………..……...61
Figure 3-3. VMAT2-deficient mice display age-dependent deficits in non-social olfactory acuity……………………………………………………………………………63
Figure 3-4. VMAT2-deficient mice do not display deficits in general sensory behavioral tests……………………………………………………………………….……..65
Figure 3-5. VMAT2-deficient animals display normal circadian activity but a premature shortened latency to behavioral signs of sleep…………………………..……67
Figure 3-6. VMAT2-deficient animals have delayed gastric emptying……………...…..69
Figure 3-7. VMAT2-deficient animals display an anxiety-like and a progressive depressive-like phenotype…………………………………………….……….71
Figure 3-8. VMAT2-deficient mice have decreased retinal DA but normal vision…..…73
CHAPTER 4: PROGRESSIVE NORADRENERGIC DEGENERATION PRECEDES NIGRAL CELL LOSS IN A MOUSE MODEL OF PD
Figure 4-1. Immunohistochemical analysis of tyrosine hydroxylase in substantia nigra of aged VMAT2-deficient mice……………………………………..……………91
Figure 4-2. Immunohistochemical analysis of tyrosine hydroxylase in locus coeruleus of aged VMAT2-deficient mice……………………………………..……………93
Figure 4-3. VMAT2-deficient mice show evidence of catecholaminergic degeneration at 24 months of age……………………………………………………..…………95
Figure 4-4 . TH and hematoxylin cell counts in the SNpc and LC of 18, 24, and 30 month wildtype andVMAT2-deficient mice………………………………………….97
Figure 4-5 . Evidence of dopaminergic-induced oxidative stress in VMAT2-deficient SNpc primary neurons…………………………………………………..…….97
Figure 4-6 . Evidence of noradrenergic-induced oxidative stress in VMAT2-deficient LC primary neurons…………………………………………………………...…101
Figure 4-7. Immunohistochemical analysis of α -synuclein in substantia nigra and locus coeruleus of aged VMAT2-deficient mice…………………………..……….103
CHAPTER 5: SEROTONERGIC DYSFUNCTION IN A MOUSE MODEL OF PARKINSON'S DISEASE
Figure 5-1. Evidence of serotonergic-induced oxidative stress in VMAT2-deficient DR primary neurons………………………………………………...……………116
Figure 5-2. VMAT2-deficient mice show evidence of monoaminergic degeneration at 24 months of age…………………………………………………….……………118
Figure 5-3. VMAT2-deficient mice show evidence of monoaminergic degeneration at 24 months of age…………………………………………………….……………120
Figure 5-4. VMAT2-deficient animals display a progressive depressive-like phenotype that is sensitive to fluoxetine…………………………………………………122
CHAPTER 6: SUMMARY AND CONCLUSIONS
Figure 6-1. VMAT2-deficient animals display impaired stride length at older ages….141
Figure 6-2. Timeline of parkinsonian features observed in the VMAT2-deficient mice……………………………………………………………………………143
APPENDIX A: THE EFFECT OF INCREASED CYTOSOLIC CATECHOLAMINES ON CELL TOXICITY
Figure A-1. Manipulation of DAT and VMAT2 do not enhance intracellular oxidative damage after exposure to exogenous catecholamines in vitro………..…….147
Figure A-2. Toxicity of catecholamines and their precursors to SN4741 cells…………149
Figure A-3. SN4741 cells exposed to various concentrations of catecholamines do not exhibit increased oxidative stress as measured by DCF……………………151
LIST OF TABLES
CHAPTER 2: BEHAVIORAL PHENOTYPING OF MOUSE MODELS OF PD
Table 2-1: L-DOPA responsive motor phenotypes in parkinsonian mouse model…….36
Table 2-2: Behavioral phenotypes in mouse models of Parkinson's disease…………..37
Table 2-3: Summary of parkinsonian behavioral analyses……………………...………38
CHAPTER 6: SUMMARY AND CONCLUSIONS
Table 6-1: Summary of L-DOPA responsive parkinsonian symptoms………..………140
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