- Title
- Regulation of tyrosine hydroxylase in stress and Parkinson's disease
- Creator
- Guan, Liying
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2015
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of the catecholamines (CAs). In the periphery, CAs function as major hormones and neurotransmitters in the sympatho-adrenomedullary system to facilitate the fight and flight response to stress. In the central nervous system, the CA-containing neurons are located in the locus coeruleus (LC), medial prefrontal cortex (mPFC) and ventral tegmental area (VTA) and are highly activated during the stress response. CA containing neurons are also located in the substantia nigra (SN) and are involved in the control of motor functions, and loss of these neurons are a major feature of Parkinson’s Disease (PD). The rate of CA release is directly coupled to the rate of CA synthesis and this requires the modulation of TH activity. TH activity is primarily regulated by a feedback inhibition by CA and activation by phosphorylation. There are three phosphorylation sites located at the N-terminus of TH, which are known to regulate TH activity, serine 19 (Ser19), serine 31 (Ser31) and serine 40 (Ser40). Whilst there is no direct correlation between Ser19 phosphorylation and TH activity in vivo, Ser31 phosphorylation significantly modulates TH activity in vivo, and Ser40 phosphorylation abolishes the feedback inhibition and can activate TH up to 4 fold in vivo. Alpha-synuclein (αSyn) can also negatively regulate TH activity.The first part of the study presented in this thesis provides a systematic investigation of TH phosphorylation, TH protein levels and TH activity in the short term response to acute footshock stress in the LC, mPFC and VTA and in the adrenal medulla. The in vivo basal stoichiometry of phosphorylation of Ser19, Ser31 and Ser40 in the LC, mPFC and adrenal medulla were determined for the first time. The LC, VTA and adrenal medulla all had higher basal levels of Ser19 phosphorylation and lower basal levels of Ser31 phosphorylation than the mPFC, while the adrenal medulla had the highest basal levels of Ser40 phosphorylation. Analysis of TH activation in vivo over the first 40 minutes after footshock stress showed that there was an increase in Ser31 phosphorylation and a corresponding increase in TH activity in the LC and mPFC. There were no changes detected in the VTA. In the adrenal medulla, there was an early increase in Ser31 phosphorylation and a later increase in Ser40 phosphorylation and a corresponding increase in TH activity. In the adrenal medulla the increased Ser31 and Ser40 phosphorylation was accompanied by increased activation of ERK and PKA. This study has confirmed the important roles of both Ser31 and Ser40 phosphorylation in regulation of TH activity in vivo. It was found that the greatest change of TH activity occurs when both Ser31 and Ser40 are phosphorylated. This study has shown that acute footshock stress leads to activation of TH in the LC, pre-synaptic terminals in the mPFC and adrenal medullary chromaffin cells, as well as changes in activity of the hypothalamic-pituitary-adrenal axis. The second part of the study presented in the thesis examined the interaction between αSyn and TH in vitro. A unique TH/ αSyn interaction was detected in which TH and αSyn formed an SDS-resistant complex and this complex was only found associated with aggregated αSyn. This indicates the capacity of TH and αSyn to form a novel oligomeric species. Analysis of deletion mutants of αSyn and TH indicated the involvement of the NAC region of αSyn and the catalytic domain of TH in the formation of the complex. αSyn mutants associated with familial parkinsonism showed a decreased capacity to generate the TH/αSyn complex. The TH in a midbrain dopaminergic neuron ispredominantly in the DA-bound form. This form of TH shows a dramatically reduced capacity to form the TH/ αSyn complex. Activation of TH by phosphorylation at Ser40 could substantially increase the capacity of the TH to form the complex. This indicates that under normal conditions the formation of the TH/ αSyn complex may be low but when TH is activated the level of the complex can increase. This has the potential functional significance in PD as loss of αSyn may promote the activation of TH which in turn will promote the generation of this unique TH/ αSyn complex and the potential capacity to alter the aggregation of αSyn.
- Subject
- adrenal medulla; brain; footshock stress; serine phosphorylation; tyrosine hydroxylase; serine residues; locus coeruleus; immobilization; Parkinson's disease
- Identifier
- http://hdl.handle.net/1959.13/1310340
- Identifier
- uon:22022
- Rights
- Copyright 2015 Liying Guan
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT02 | Thesis | 3 MB | Adobe Acrobat PDF | View Details Download |