The 5'-untranslated region of Parkinson's disease alpha-synuclein messengerRNA contains a predicted iron responsive element

Untangling Tau and Iron: Exploring the Interaction Between Iron and Tau in Neurodegeneration

There is an emerging link between the accumulation of iron in the brain and abnormal tau pathology in a number of neurodegenerative disorders, such as Alzheimer’s disease (AD). Studies have demonstrated that iron can regulate tau phosphorylation by inducing the activity of multiple kinases that promote tau hyperphosphorylation and potentially also by impacting protein phosphatase 2A activity. Iron is also reported to induce the aggregation of hyperphosphorylated tau, possibly through a direct interaction via a putative iron binding motif in the tau protein, facilitating the formation of neurofibrillary tangles (NFTs). Furthermore, in human studies high levels of iron have been reported to co-localize with tau in NFT-bearing neurons. These data, together with our own work showing that tau has a role in mediating cellular iron efflux, provide evidence supporting a critical tau:iron interaction that may impact both the symptomatic presentation and the progression of disease. Importantly, this may also have relevance for therapeutic directions, and indeed, the use of iron chelators such as deferiprone and deferoxamine have been reported to alleviate the phenotypes, reduce phosphorylated tau levels and stabilize iron regulation in various animal models. As these compounds are also moving towards clinical translation, then it is imperative that we understand the intersection between iron and tau in neurodegeneration. In this article, we provide an overview of the key pathological and biochemical interactions between tau and iron. We also review the role of iron and tau in disease pathology and the potential of metal-based therapies for tauopathies.

High Dietary Iron Supplement Induces the Nigrostriatal Dopaminergic Neurons Lesion in Transgenic Mice Expressing Mutant A53T Human Alpha-Synuclein

Both alpha-synuclein aggregation and iron deposits are neuropathological hallmarks of Parkinson’s disease (PD). We are particularly interested in whether iron could synergize with alpha-synuclein pathology in vivo, especially in the nigrostriatal system. In the present study, we reported transgenic mice with overexpressing human A53T alpha-synuclein, as well as WT mice with high dietary iron displayed hyperactive motor coordination and impaired colonic motility, compared with those with basal dietary iron. Only A53T mice, but not WT mice with high dietary iron exhibited nigral dopaminergic neuronal loss, lower levels of tyrosine hydroxylase (TH) in the substantia nigra (SN) and decreased dopamine contents in the striatum. Although there was no obvious elevation of iron contents in the SN in WT mice with high dietary iron, we observed iron contents in the SN were especially higher than the other brain regions in 12-month aged mice with either high or basal dietary iron. These results suggested high dietary iron supplement could induce nigral dopaminergic neurons lesion in A53T mice, which might be due to the vulnerability of SN to accumulate iron.

The Aging of Iron Man

Brain iron is tightly regulated by a multitude of proteins to ensure homeostasis. Iron dyshomeostasis has become a molecular signature associated with aging which is accompanied by progressive decline in cognitive processes. A common theme in neurodegenerative diseases where age is the major risk factor, iron dyshomeostasis coincides with neuroinflammation, abnormal protein aggregation, neurodegeneration, and neurobehavioral deficits. There is a great need to determine the mechanisms governing perturbations in iron metabolism, in particular to distinguish between physiological and pathological aging to generate fruitful therapeutic targets for neurodegenerative diseases. The aim of the present review is to focus on the age-related alterations in brain iron metabolism from a cellular and molecular biology perspective, alongside genetics, and neuroimaging aspects in man and rodent models, with respect to normal aging and neurodegeneration. In particular, the relationship between iron dyshomeostasis and neuroinflammation will be evaluated, as well as the effects of systemic iron overload on the brain. Based on the evidence discussed here, we suggest a synergistic use of iron-chelators and anti-inflammatories as putative anti-brain aging therapies to counteract pathological aging in neurodegenerative diseases.

Iron in neurodegenerative disorders: being in the wrong place at the wrong time?

Brain iron deposits have been reported consistently in imaging and histologic examinations of patients with neurodegenerative disorders. While the origins of this finding have not been clarified yet, it is speculated that impaired iron homeostasis or deficient transport mechanisms result in the accumulation of this highly toxic metal ultimately leading to formation of reactive oxygen species and cell death. On the other hand, there are also those who support that iron is just an incidental finding, a by product of neuronal loss. A literature review has been performed in order to present the key findings in support of the iron hypothesis of neurodegeneration, as well as to identify conditions causing or resulting from iron overload and compare and contrast their features with the most prominent neurodegenerative disorders. There is an abundance of experimental and observational findings in support of the hypothesis in question; however, as neurodegeneration is a rare incident of commonly encountered iron-associated disorders of the nervous system, and this metal is found in non-neurodegenerative disorders as well, it is possible that iron is the result or even an incidental finding in neurodegeneration. Understanding the underlying processes of iron metabolism in the brain and particularly its release during cell damage is expected to provide a deeper understanding of the origins of neurodegeneration in the years to come.

Astroglial and microglial contributions to iron metabolism disturbance in Parkinson's disease

Understandings of the disturbed iron metabolism in Parkinson's disease (PD) are largely from the perspectives of neurons. Neurodegenerative processes in PD trigger universal and conserved astroglial dysfunction and microglial activation. In this review, we start with astroglia and microglia in PD with an emphasis on their roles in spreading α-synuclein pathology, and then focus on their contributions in iron metabolism under normal conditions and the diseased state of PD. Elevated iron in the brain regions affects glial features, meanwhile, glial effects on neuronal iron metabolism are largely dependent on their releasing factors. These advances might be valuable for better understanding and modulating iron metabolism disturbance in PD.

The Relevance of Iron in the Pathogenesis of Multiple System Atrophy: A Viewpoint

Iron is essential for cellular development and maintenance of multiple physiological processes in the central nervous system. The disturbance of its homeostasis leads to abnormal iron deposition in the brain and causes neurotoxicity via generation of free radicals and oxidative stress. Iron toxicity has been established in the pathogenesis of Parkinson's disease; however, its contribution to multiple system atrophy (MSA) remains elusive. MSA is characterized by cytoplasmic inclusions of misfolded α-synuclein (α-SYN) in oligodendrocytes referred to as glial cytoplasmic inclusions (GCIs). Remarkably, the oligodendrocytes possess high amounts of iron, which together with GCI pathology make a contribution toward MSA pathogenesis likely. Consistent with this observation, the GCI density is associated with neurodegeneration in central autonomic networks as well as olivopontocerebellar and striatonigral pathways. Iron converts native α-SYN into a β-sheet conformation and promotes its aggregation either directly or via increasing levels of oxidative stress. Interestingly, α-SYN possesses ferrireductase activity and α-SYN expression underlies iron mediated translational control via RNA stem loop structures. Despite a correlation between progressive putaminal atrophy and iron accumulation as well as clinical decline, it remains unclear whether pathologic iron accumulation in MSA is a secondary event in the cascade of neuronal degeneration rather than a primary cause. This review summarizes the current knowledge of iron in MSA and gives evidence for perturbed iron homeostasis as a potential pathogenic factor in MSA-associated neurodegeneration.

The impact of obesity on brain iron levels and α-synuclein expression is regionally dependent

BACKGROUND

The importance of iron homeostasis is particularly apparent in the brain, where iron deficiency results in impaired cognition and iron accumulation is associated with neurodegenerative diseases. Obesity is linked to iron deficiency systemically, but the effects of obesity on brain iron and its associated consequences, including neurodegenerative processes remain unexplored. This preliminary study examined the effect of dietary-induced obesity on brain regional iron, α-synuclein expression, and F2-isoprostane (oxidative stress marker) concentrations in selected brain regions.

OBJECTIVE

The objective of the study was to elucidate the vulnerability of selected brain regions (e.g. midbrain, hippocampus) to the possible process of neurodegeneration due to the altered iron content associated with obesity.

METHODS

Twenty-one-day-old male C57BL/6J mice were fed with a high-fat diet (60% kcal from fat) or a control-fat diet (10% kcal from fat) for 20 weeks. Brain samples were collected and dissected into hippocampus, midbrain, striatum, and thalamus regions. Iron content, ferritin H (FtH) and α-synuclein protein and mRNA expressions, and F₂-isoprostane were measured in selected regions.

RESULTS

The results indicated that obesity caused significant differences in iron levels in the midbrain and thalamus, but not in the hippocampus or striatum, compared to control mice. Furthermore, markers of neurodegeneration (α-synuclein mRNA expression and F₂-isoprostanes) were increased in the midbrain.

DISCUSSION

These results support previous findings that brain iron metabolism responds to environmental stress in a regionally distinct manner and suggests that alterations in brain iron metabolism due to obesity may be relevant in neurodegeneration.

A panel of clinical and neuropathological features of cerebrovascular disease through the novel neuroimaging methods

The last decade has witnessed substantial progress in acquiring diagnostic biomarkers for the diagnostic workup of cerebrovascular disease (CVD). Advanced neuroimaging methods not only provide a strategic contribution for the differential diagnosis of vascular dementia (VaD) and vascular cognitive impairment (VCI), but also help elucidate the pathophysiological mechanisms ultimately leading to small vessel disease (SVD) throughout its course.

OBJECTIVE

In this review, the novel imaging methods, both structural and metabolic, were summarized and their impact on the diagnostic workup of age-related CVD was analysed. Methods: An electronic search between January 2010 and 2017 was carried out on PubMed/MEDLINE, Institute for Scientific Information Web of Knowledge and EMBASE.

RESULTS

The use of full functional multimodality in simultaneous Magnetic Resonance (MR)/Positron emission tomography (PET) may potentially improve the clinical characterization of VCI-VaD; for structural imaging, MRI at 3.0 T enables higher-resolution scanning with greater imaging matrices, thinner slices and more detail on the anatomical structure of vascular lesions.

CONCLUSION

Although the importance of most of these techniques in the clinical setting has yet to be recognized, there is great expectancy in achieving earlier and more refined therapeutic interventions for the effective management of VCI-VaD.

Repositioning drugs for traumatic brain injury - N-acetyl cysteine and Phenserine

Traumatic brain injury (TBI) is one of the most common causes of morbidity and mortality of both young adults of less than 45 years of age and the elderly, and contributes to about 30% of all injury deaths in the United States of America. Whereas there has been a significant improvement in our understanding of the mechanism that underpin the primary and secondary stages of damage associated with a TBI incident, to date however, this knowledge has not translated into the development of effective new pharmacological TBI treatment strategies. Prior experimental and clinical studies of drugs working via a single mechanism only may have failed to address the full range of pathologies that lead to the neuronal loss and cognitive impairment evident in TBI and other disorders. The present review focuses on two drugs with the potential to benefit multiple pathways considered important in TBI. Notably, both agents have already been developed into human studies for other conditions, and thus have the potential to be rapidly repositioned as TBI therapies. The first is N-acetyl cysteine (NAC) that is currently used in over the counter medications for its anti-inflammatory properties. The second is (-)-phenserine ((-)-Phen) that was originally developed as an experimental Alzheimer's disease (AD) drug. We briefly review background information about TBI and subsequently review literature suggesting that NAC and (-)-Phen may be useful therapeutic approaches for TBI, for which there are no currently approved drugs.

Metal chelator EGCG attenuates Fe(III)-induced conformational transition of α-synuclein and protects AS-PC12 cells against Fe(III)-induced death

The fibrillation and aggregation of α-synuclein (AS), along with the conformational transition from random coil to β-sheet, are the critical steps in the development of Parkinson's disease (PD). It is acknowledged that iron accumulation in the brain may lead to the fibrillation of AS. However, (-)-epigallocatechin gallate (EGCG) can penetrate the blood-brain barrier, chelate metal ions, and inhibit the fibrillation of amyloid proteins. Therefore, EGCG is warranted to be investigated for its potential to cure amyloid-related diseases. In the present work, we sought to study the effects of EGCG on Fe(III)-induced fibrillation of AS on both molecular and cellular levels. We demonstrate that Fe(III) interacts with the amino residue of Tyr and Ala of AS, then accelerates the fibrillation of AS, and increases intracellular reactive oxygen species (ROS) in the AS transduced-PC12 cells (AS-PC12 cells). However, EGCG significantly inhibits this process by chelating Fe(III) and protects AS-PC12 cells against the toxicity induced by ROS and β-sheet-enriched AS fibrils. These findings yield useful information that EGCG might be a promising drug to prevent and treat the neurodegenerative diseases.

Iron Metabolism in Parkinson’s Disease

In the central nervous system, iron is involved in many biologically important processes such as oxygen transport and storage, electron transport, energy metabolism, and antioxidant and DNA synthesis. Parkinson’s disease (PD) is a common neurodegenerative disease characterized by loss of dopaminergic neurons in the substantia nigra. Extensive research has reported that iron is heavily accumulated in the dopaminergic neurons in substantia nigra (SN) of PD patients. Changes in the expression of key iron transporters have also been observed in PD patients. Excessive iron accumulation can induce neuronal damage through reactive oxygen species production, which can cause oxidative stress increased membrane lipid peroxidation, DNA damage and protein oxidation and misfolding. This chapter provides a review about brain iron metabolism in PD, the role of iron transporters expression and function on brain iron homeostasis and distribution of intracellular iron. This knowledge will be of benefit to novel therapeutic targets for PD.

Blood Transcriptomic Meta-analysis Identifies Dysregulation of Hemoglobin and Iron Metabolism in Parkinson' Disease

Disrupted iron metabolism has been implicated in the pathogenesis of Parkinson’s disease (PD), a progressive neurodegenerative disorder that severely affects movement and coordination, yet the molecular mechanisms underlying this association remain unknown. To this end, we performed a transcriptomic meta-analysis of four blood microarrays in PD. We observed a significant downregulation of genes related to hemoglobin including, hemoglobin delta (HBD), alpha hemoglobin stabilizing protein (ASHP), genes implicated in iron metabolism including, solute carrier family 11 member 2 (SLC11A2), ferrochelatase (FECH), and erythrocyte-specific genes including erythrocyte membrane protein (EPB42), and 5′-aminolevulinate synthase 2 (ALAS2). Pathway and network analysis identified enrichment in processes related to mitochondrial membrane, oxygen transport, oxygen and heme binding, hemoglobin complex, erythrocyte development, tetrapyrrole metabolism and the spliceosome. Collectively, we identified a subnetwork of genes in blood that may provide a molecular explanation for the disrupted hemoglobin and iron metabolism in the pathogenesis of PD.

Overview of iron metabolism in health and disease

Iron is an essential element for numerous fundamental biologic processes, but excess iron is toxic. Abnormalities in systemic iron balance are common in patients with chronic kidney disease and iron administration is a mainstay of anemia management in many patients. This review provides an overview of the essential role of iron in biology, the regulation of systemic and cellular iron homeostasis, how imbalances in iron homeostasis contribute to disease, and the implications for chronic kidney disease patients.

Mitochondrial ferritin protects SH-SY5Y cells against H2O2-induced oxidative stress and modulates α-synuclein expression

Mitochondrial ferritin (FtMt) is a type of ferritin that sequesters iron. Previous studies have shown that FtMt is expressed by dopaminergic neurons in the substantia nigra and that it may be involved in the pathology of Parkinson's disease. However, the functional roles of FtMt in dopaminergic neurons remain unclear. In this study, we investigated the function of FtMt in α-synuclein regulation and its antioxidant roles in dopaminergic cells using human dopaminergic neuroblastoma cells, SH-SY5Y. In physiological conditions, FtMt knockdown increased α-synuclein expression at the protein level but not at the mRNA level. By contrast, FtMt overexpression reduced α-synuclein expression at the protein level but not at the mRNA level. FtMt enhanced the iron levels in mitochondria but decreased the iron levels in the intracellular labile iron pool. We found that FeCl₂ could abolish the effects of FtMt overexpression on α-synuclein expression. Under oxidative stress conditions induced by H₂O₂, we found that H₂O₂ treatment induced FtMt and α-synuclein expression at both the mRNA and protein levels in a dose-dependent manner. FtMt overexpression protected cells against oxidative stress and alleviated the enhanced α-synuclein expression induced by H₂O₂ at the posttranscriptional level. Our results indicate that FtMt modulates α-synuclein expression at the posttranscriptional level via iron regulation in physiological conditions. FtMt expression is enhanced under oxidative stress conditions, where FtMt protects cells against the oxidative stress as well as plays an important role in maintaining α-synuclein levels.

Patterns of Brain Iron Accumulation in Vascular Dementia and Alzheimer's Dementia Using Quantitative Susceptibility Mapping Imaging

BACKGROUND

Emerging evidence suggests that the excessive accumulation of iron in subcortical and deep gray matter has been related to dementia. However, the presence and pattern of iron accumulation in vascular dementia (VaD) and Alzheimer's disease (AD) are rarely investigated.

OBJECTIVE

To examine and compare the pattern and presence of brain iron accumulation of VaD and AD using quantitative susceptibility mapping (QSM).

MATERIALS AND METHODS

Twelve patients with VaD, 27 patients with AD, and 18 control subjects were recruited in this institutional review-board approved study. Susceptibility maps were reconstructed from a three-dimensional multiecho spoiled gradient-echo sequence. Four regions of interest were drawn manually on QSM images, namely the globus pallidus, putamen, caudate nucleus, and pulvinar nucleus of the thalamus. Comparisons of patient demographics, and iron concentrations among the VaD, AD, and control subjects were assessed using analysis of variance and post-hoc analyses. The relationships of age and cognitive state with susceptibility values were assessed using partial correlation analysis.

RESULTS

In VaD and AD, overall susceptibility values were higher than those of control subjects. A significant difference in susceptibility values was found in the putamen and caudate nucleus (p <  0.001 and p = 0.002, respectively). However, susceptibility values did not differ between VaD and AD. Age and cognitive deficit severity were not related to susceptibility values in the VaD and AD groups.

CONCLUSION

Increased iron deposition in the putamen and caudate nucleus in VaD and AD patients was not associated with age or the severity of cognitive deficits. Further evaluations are needed to determine the temporal changes in iron load and their diagnostic role in dementia pathology.

Iron chelation in the treatment of neurodegenerative diseases

Disturbance of cerebral iron regulation is almost universal in neurodegenerative disorders. There is a growing body of evidence that increased iron deposits may contribute to degenerative changes. Thus, the effect of iron chelation therapy has been investigated in many neurological disorders including rare genetic syndromes with neurodegeneration with brain iron accumulation as well as common sporadic disorders such as Parkinson's disease, Alzheimer's disease, and multiple sclerosis. This review summarizes recent advances in understanding the role of iron in the etiology of neurodegeneration. Outcomes of studies investigating the effect of iron chelation therapy in neurodegenerative disorders are systematically presented in tables. Iron chelators, particularly the blood brain barrier-crossing compound deferiprone, are capable of decreasing cerebral iron in areas with abnormally high concentrations as documented by MRI. Yet, currently, there is no compelling evidence of the clinical effect of iron removal therapy on any neurological disorder. However, several studies indicate that it may prevent or slow down disease progression of several disorders such as aceruloplasminemia, pantothenate kinase-associated neurodegeneration or Parkinson's disease.

Does any drug to treat cancer target mTOR and iron hemostasis in neurodegenerative disorders?

The prevalence of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and Huntington's disease are increased by age. Alleviation of their symptoms and protection of normal neurons against degeneration are the main aspects of the research to establish novel therapeutic strategies. Iron as the one of most important cation not only play important role in the structure of electron transport chain proteins but also has pivotal duties in cellular activities. But disruption in iron hemostasis can make it toxin to neurons which causes lipid peroxidation, DNA damage and etc. In patients with Alzheimer and Parkinson misbalancing in iron homeostasis accelerate neurodegeneration and cause neuroinflmmation. mTOR as the common signaling pathway between cancer and neurodegenerative disorders controls iron uptake and it is in active form in both diseases. Anti-cancer drugs which target mTOR causes iron deficiency and dual effects of mTOR inhibitors can candidate them as a therapeutic strategy to alleviate neurodegeneration/inflammation because of iron overloading.

The neurotoxicity of iron, copper and cobalt in Parkinson's disease through ROS-mediated mechanisms

Parkinson's disease (PD) is the second most common neurodegenerative disease with gradual loss of dopaminergic neurons. Despite extensive research in the past decades, the etiology of PD remains elusive. Nevertheless, multiple lines of evidence suggest that oxidative stress is one of the common causes in the pathogenesis of PD. It has also been suggested that heavy metal-associated oxidative stress may be implicated in the etiology and pathogenesis of PD. Here we review the roles of redox metals, including iron, copper and cobalt, in PD. Iron is a highly reactive element and deregulation of iron homeostasis is accompanied by concomitant oxidation processes in PD. Copper is a key metal in cell division process, and it has been shown to have an important role in neurodegenerative diseases such as PD. Cobalt induces the generation of reactive oxygen species (ROS) and DNA damage in brain tissues.

Constitutive translation of human α-synuclein is mediated by the 5'-untranslated region

Genetic and biochemical studies have established a central role for α-synuclein (SNCA) accumulation in the pathogenesis of Parkinson's disease. Uncovering and subsequently interfering with physiological mechanisms that control SNCA expression is one approach to limit disease progression. To this end, the long and GC-rich 5'-untranslated region (UTR) of SNCA, which is predicted to fold into stable hairpin and G-quadruplex RNA motifs, was investigated for its role in mRNA translation. Inclusion of SNCA 5'-UTR significantly induced expression of both SNCA and luciferase ORF constructs. This effect was not associated with a change in mRNA levels or differential nucleocytoplasmic shuttling. Further, the presence of the 5'-UTR enhanced SNCA synthesis when cap-dependent translation was attenuated with rapamycin treatment. Analysis using multiple methodologies revealed that the 5'-UTR harbours an internal ribosome entry site (IRES) element that spans most of its nucleotide sequence. Signals such as plasma-membrane depolarization, serum starvation and oxidative stress stimulated SNCA protein translation via its 5'-UTR as well as enhanced its IRES activity. Taken together, these data support the idea that the 5'-UTR is an important positive regulator of SNCA synthesis under diverse physiological and pathological conditions, explaining in part the abundance of SNCA in healthy neurons and its accumulation in degenerative cells.

Brain Iron Metabolism Dysfunction in Parkinson's Disease

Dysfunction of iron metabolism, which includes its uptake, storage, and release, plays a key role in neurodegenerative disorders, including Parkinson's disease (PD), Alzheimer's disease, and Huntington's disease. Understanding how iron accumulates in the substantia nigra (SN) and why it specifically targets dopaminergic (DAergic) neurons is particularly warranted for PD, as this knowledge may provide new therapeutic avenues for a more targeted neurotherapeutic strategy for this disease. In this review, we begin with a brief introduction describing brain iron metabolism and its regulation. We then provide a detailed description of how iron accumulates specifically in the SN and why DAergic neurons are especially vulnerable to iron in PD. Furthermore, we focus on the possible mechanisms involved in iron-induced cell death of DAergic neurons in the SN. Finally, we present evidence in support that iron chelation represents a plausable therapeutic strategy for PD.

Alpha-Synuclein Oligomers Interact with Metal Ions to Induce Oxidative Stress and Neuronal Death in Parkinson's Disease

AIMS

Protein aggregation and oxidative stress are both key pathogenic processes in Parkinson's disease, although the mechanism by which misfolded proteins induce oxidative stress and neuronal death remains unknown. In this study, we describe how aggregation of alpha-synuclein (α-S) from its monomeric form to its soluble oligomeric state results in aberrant free radical production and neuronal toxicity.

RESULTS

We first demonstrate excessive free radical production in a human induced pluripotent stem-derived α-S triplication model at basal levels and on application of picomolar doses of β-sheet-rich α-S oligomers. We probed the effects of different structural species of α-S in wild-type rat neuronal cultures and show that both oligomeric and fibrillar forms of α-S are capable of generating free radical production, but that only the oligomeric form results in reduction of endogenous glutathione and subsequent neuronal toxicity. We dissected the mechanism of oligomer-induced free radical production and found that it was interestingly independent of several known cellular enzymatic sources.

INNOVATION

The oligomer-induced reactive oxygen species (ROS) production was entirely dependent on the presence of free metal ions as addition of metal chelators was able to block oligomer-induced ROS production and prevent oligomer-induced neuronal death.

CONCLUSION

Our findings further support the causative role of soluble amyloid oligomers in triggering neurodegeneration and shed light into the mechanisms by which these species cause neuronal damage, which, we show here, can be amenable to modulation through the use of metal chelation.

Clioquinol Improves Cognitive, Motor Function, and Microanatomy of the Alpha-Synuclein hA53T Transgenic Mice

The abnormal accumulation of alpha-synuclein (α-syn) has been linked to a number of neurodegenerative disorders, the most noteworthy of which is Parkinson's disease. Alpha-synuclein itself is not toxic and fulfills various physiological roles in the central nervous system. However, specific types of aggregates have been shown to be toxic, and metals have been linked to the assembly of these toxic aggregates. In this paper, we have characterized a transgenic mouse that overexpresses the A53T mutation of human α-syn, specifically assessing cognition, motor performance, and subtle anatomical markers that have all been observed in synucleinopathies in humans. We hypothesized that treatment with the moderate-affinity metal chelator, clioquinol (CQ), would reduce the interaction between metals and α-syn to subsequently improve the phenotype of the A53T animal model. We showed that CQ prevents an iron-synuclein interaction, the formation of urea-soluble α-syn aggregates, α-syn-related substantia nigra pars compacta cell loss, reduction in dendritic spine density of hippocampal and caudate putamen medium spiny neurons, and the decline in motor and cognitive function. In conclusion, our data suggests that CQ is capable of mitigating the pathological metal/α-syn interactions, suggesting that the modulation of metal ions warrants further study as a therapeutic approach for the synucleinopathies.

Differential interaction between iron and mutant alpha-synuclein causes distinctive Parkinsonian phenotypes in Drosophila

Alpha-synuclein aggregation is the central hallmark of both sporadic and familial Parkinson's disease (PD). Patients with different PD-causing genetic defects of alpha-synuclein usually show distinctive clinical features that are atypical to sporadic PD. Iron accumulation is invariably found in PD. Recent studies showed that mutant and wild-type alpha-synuclein may have differential interaction with iron and mutant alpha-synuclein toxicity could be preferentially exacerbated by iron. We hence hypothesized that iron overload could selectively influence mutant alpha-synuclein toxicity and disease phenotypes. To test the hypothesis, we investigated if Drosophila melanogaster over-expressing A53T, A30P, and wild-type (WT) alpha-synuclein have different responses to iron treatment. We showed that iron treatment induced similar reduction of survival rate in all flies but induced a more severe motor decline in A53T and A30P mutant alpha-synuclein expressing flies, suggesting interaction between mutant alpha-synuclein and iron. Although no significant difference in total head iron content was found among these flies, we demonstrated that iron treatment induced selective DA neuron loss in motor-related PPM3 cluster only in the flies that express A53T and A30P mutant alpha-synuclein. We provided the first in vivo evidence that iron overload could induce distinctive neuropathology and disease phenotypes in mutant but not WT alpha-synuclein expressing flies, providing insights to the cause of clinical features selectively exhibited by mutant alpha-synuclein carriers.

RNA Structures as Mediators of Neurological Diseases and as Drug Targets

RNAs adopt diverse folded structures that are essential for function and thus play critical roles in cellular biology. A striking example of this is the ribosome, a complex, three-dimensionally folded macromolecular machine that orchestrates protein synthesis. Advances in RNA biochemistry, structural and molecular biology, and bioinformatics have revealed other non-coding RNAs whose functions are dictated by their structure. It is not surprising that aberrantly folded RNA structures contribute to disease. In this Review, we provide a brief introduction into RNA structural biology and then describe how RNA structures function in cells and cause or contribute to neurological disease. Finally, we highlight successful applications of rational design principles to provide chemical probes and lead compounds targeting structured RNAs. Based on several examples of well-characterized RNA-driven neurological disorders, we demonstrate how designed small molecules can facilitate the study of RNA dysfunction, elucidating previously unknown roles for RNA in disease, and provide lead therapeutics.

The association between the C282Y and H63D polymorphisms of HFE gene and the risk of Parkinson's disease: A meta-analysis

Impaired brain iron homeostasis has been considered as an important mechanism in Parkinson's diseases (PD). There are indications that C282Y and H63D polymorphisms of HFE genes involved in iron metabolism might contribute to the pathogenesis of PD in some cases. However, the investigation of the relationship between PD and the two polymorphisms had produced contradictory results. We performed a meta-analysis to assess the C282Y and H63D polymorphisms of HFE in PD susceptibility. PubMed, EMBASE and Web of Science were systematically searched to identify relevant researches. The strict selection criteria and exclusion standard were applied. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of associations. A fixed-effect or random-effect model was selected, depending on the results of the heterogeneity test. Fifteen studies were included in the meta-analysis (eight studies with 1631 cases and 4548 controls for C282Y; seven studies with 1192 cases and 4065 controls for H63D). For the C282Y polymorphism, significant associations were observed in the Recessive model (YY vs CY+CC: OR=0.22, 95% CI=0.09-0.57, P=0.002). This indicated that the C282Y polymorphism in HFE might be a potential protective factor for PD. However, no significant associations were found for any genetic model for the H63D polymorphism, suggesting that the H63D polymorphism might not be associated with PD.

Review: iron metabolism and the role of iron in neurodegenerative disorders

Iron plays a role for the biogenesis of two important redox-reactive prosthetic groups of enzymes, iron sulphur clusters (ISC) and heme. A part of these biosynthetic pathways takes plays in the mitochondria. While several important proteins of cellular iron uptake and storage and of mitochondrial iron metabolism are well-characterized, limited knowledge exists regarding the mitochondrial iron importers (mitoferrins). A disturbed distribution of iron, hampered Fe-dependent biosynthetic pathways and eventually oxidative stress resulting from an increased labile iron pool are suggested to play a role in several neurodegenerative diseases. Friedreich's ataxia is associated with mitochondrial iron accumulation and hampered ISC/heme biogenesis due to reduced frataxin expression, thus representing a monogenic mitochondrial disorder, which is clearly elicited solely by a disturbed iron metabolism. Less clear are the controversially discussed impacts of iron dysregulation and iron-dependent oxidative stress in the most common neurodegenerative disorders, i.e. Alzheimer's disease (AD) and Parkinson's disease (PD). Amyotrophic lateral sclerosis (ALS) may be viewed as a disease offering a better support for a direct link between iron, oxidative stress and regional neurodegeneration. Altogether, despite significant progress in molecular knowledge, the true impact of iron on the sporadic forms of AD, PD and ALS is still uncertain. Here we summarize the current knowledge of iron metabolism disturbances in neurodegenerative disorders.

Iron in neurodegenerative disorders of protein misfolding: a case of prion disorders and Parkinson's disease

SIGNIFICANCE

Intracellular and extracellular aggregation of a specific protein or protein fragments is the principal pathological event in several neurodegenerative conditions. We describe two such conditions: sporadic Creutzfeldt-Jakob disease (sCJD), a rare but potentially infectious and invariably fatal human prion disorder, and Parkinson's disease (PD), a common neurodegenerative condition second only to Alzheimer's disease in prevalence. In sCJD, a cell surface glycoprotein known as the prion protein (PrP(C)) undergoes a conformational change to PrP-scrapie, a pathogenic and infectious isoform that accumulates in the brain parenchyma as insoluble aggregates. In PD, α-synuclein, a cytosolic protein, forms insoluble aggregates that accumulate in neurons of the substantia nigra and cause neurotoxicity.

RECENT ADVANCES

Although distinct processes are involved in the pathogenesis of sCJD and PD, both share brain iron dyshomeostasis as a common associated feature that is reflected in the cerebrospinal fluid in a disease-specific manner.

CRITICAL ISSUES

Since PrP(C) and α-synuclein play a significant role in maintaining cellular iron homeostasis, it is important to understand whether the aggregation of these proteins and iron dyshomeostasis are causally related. Here, we discuss recent information on the normal function of PrP(C) and α-synuclein in cellular iron metabolism and the cellular and biochemical processes that contribute to iron imbalance in sCJD and PD.

FUTURE DIRECTIONS

Improved understanding of the relationship between brain iron imbalance and protein aggregation is likely to help in the development of therapeutic strategies that can restore brain iron homeostasis and mitigate neurotoxicity.

The iron regulatory capability of the major protein participants in prevalent neurodegenerative disorders

As with most bioavailable transition metals, iron is essential for many metabolic processes required by the cell but when left unregulated is implicated as a potent source of reactive oxygen species. It is uncertain whether the brain’s evident vulnerability to reactive species-induced oxidative stress is caused by a reduced capability in cellular response or an increased metabolic activity. Either way, dys-regulated iron levels appear to be involved in oxidative stress provoked neurodegeneration. As in peripheral iron management, cells within the central nervous system tightly regulate iron homeostasis via responsive expression of select proteins required for iron flux, transport and storage. Recently proteins directly implicated in the most prevalent neurodegenerative diseases, such as amyloid-β precursor protein, tau, α-synuclein, prion protein and huntingtin, have been connected to neuronal iron homeostatic control. This suggests that disrupted expression, processing, or location of these proteins may result in a failure of their cellular iron homeostatic roles and augment the common underlying susceptibility to neuronal oxidative damage that is triggered in neurodegenerative disease.

Phenotypic screens for compounds that target the cellular pathologies underlying Parkinson's disease

Parkinson's disease (PD) is a devastating neurodegenerative disease that affects over one million patients in the US. Yet, no disease modifying drugs exist, only those that temporarily alleviate symptoms. Because of its poorly defined and highly complex disease etiology, it is essential to embrace unbiased and innovative approaches for identifying new chemical entities that target the underlying toxicities associated with PD. Traditional target-based drug discovery paradigm can suffer from a bias toward a small number of potential targets. Phenotypic screening of both genetic and pharmacological PD models offers an alternative approach to discover compounds that target the initiating causes and effectors of cellular toxicity. The relative paucity of reported phenotypic screens illustrates the intrinsic difficulty in establishing model systems that are both biologically meaningful and adaptable to high-throughput screening. Parallel advances in PD models and in vivo screening technologies will help create opportunities for identifying new therapeutic leads with unanticipated, breakthrough mechanisms of action.

Brain iron homeostasis: from molecular mechanisms to clinical significance and therapeutic opportunities

Iron has emerged as a significant cause of neurotoxicity in several neurodegenerative conditions, including Alzheimer's disease (AD), Parkinson's disease (PD), sporadic Creutzfeldt-Jakob disease (sCJD), and others. In some cases, the underlying cause of iron mis-metabolism is known, while in others, our understanding is, at best, incomplete. Recent evidence implicating key proteins involved in the pathogenesis of AD, PD, and sCJD in cellular iron metabolism suggests that imbalance of brain iron homeostasis associated with these disorders is a direct consequence of disease pathogenesis. A complete understanding of the molecular events leading to this phenotype is lacking partly because of the complex regulation of iron homeostasis within the brain. Since systemic organs and the brain share several iron regulatory mechanisms and iron-modulating proteins, dysfunction of a specific pathway or selective absence of iron-modulating protein(s) in systemic organs has provided important insights into the maintenance of iron homeostasis within the brain. Here, we review recent information on the regulation of iron uptake and utilization in systemic organs and within the complex environment of the brain, with particular emphasis on the underlying mechanisms leading to brain iron mis-metabolism in specific neurodegenerative conditions. Mouse models that have been instrumental in understanding systemic and brain disorders associated with iron mis-metabolism are also described, followed by current therapeutic strategies which are aimed at restoring brain iron homeostasis in different neurodegenerative conditions. We conclude by highlighting important gaps in our understanding of brain iron metabolism and mis-metabolism, particularly in the context of neurodegenerative disorders.

Alzheimer's disease therapeutics targeted to the control of amyloid precursor protein translation: maintenance of brain iron homeostasis

The neurotoxicity of amyloid beta (Aβ), a major cleavage product of the amyloid precursor protein (APP), is enhanced by iron, as found in the amyloid plaques of Alzheimer's disease (AD) patients. By contrast, the long-known neuroprotective activity of APP is evident after α-secretase cleavage of the precursor to release sAPPα, and depends on the iron export actions of APP itself. The latter underlie its neurotrophic and protective effects in facilitating the homeostatic actions of ferroportin mediated-iron export. Thus APP-dependent iron export may alleviate oxidative stress by minimizing labile iron thus protecting neurons from iron overload during stroke and hemorrhage. Consistent with this, altered phosphorylation of iron-regulatory protein-1 (IRP1) and its signaling processes play a critical role in modulating APP translation via the 5' untranslated region (5'UTR) of its transcript. The APP 5'UTR region encodes a functional iron-responsive element (IRE) RNA stem loop that represents a potential target for modulating APP production. Targeted regulation of APP gene expression via the modulation of 5'UTR sequence function represents a novel approach for the potential treatment of AD since altering APP translation can be used to improve both the protective brain iron balance and provide anti-amyloid efficacy. Approved drugs including paroxetine and desferrioxamine and several novel compounds have been identified that suppress abnormal metal-promoted Aβ accumulation with a subset of these acting via APP 5'UTR-dependent mechanisms to modulate APP translation and cleavage to generate the non-toxic sAPPα.

A low-molecular-weight ferroxidase is increased in the CSF of sCJD cases: CSF ferroxidase and transferrin as diagnostic biomarkers for sCJD

AIMS

Most biomarkers used for the premortem diagnosis of sporadic Creutzfeldt-Jakob disease (CJD) are surrogate in nature, and provide suboptimal sensitivity and specificity.

RESULTS

We report that CJD-associated brain iron dyshomeostasis is reflected in the cerebrospinal fluid (CSF), providing disease-specific diagnostic biomarkers. Analysis of 290 premortem CSF samples from confirmed cases of CJD, Alzheimer's disease, and other dementias (DMs), and 52 non-DM (ND) controls revealed a significant difference in ferroxidase (Frx) activity and transferrin (Tf) levels in sporadic Creutzfeldt-Jakob disease (sCJD) relative to other DM and ND controls. A combination of CSF Frx and Tf discriminated sCJD from other DMs with a sensitivity of 86.8%, specificity of 92.5%, accuracy of 88.9%, and area-under-the receiver-operating-characteristic (ROC) curve of 0.94. This combination provided a similar diagnostic accuracy in discriminating CJD from rapidly progressing cases who died within 6 months of sample collection. Surprisingly, ceruloplasmin and amyloid precursor protein, the major brain Frxs, displayed minimal activity in the CSF. Most of the Frx activity was concentrated in the <3-kDa fraction in normal and diseased CSF, and resisted heat and proteinase-K treatment.

INNOVATION

(i) A combination of CSF Frx and Tf provides disease-specific premortem diagnostic biomarkers for sCJD. (ii) A novel, nonenzymatic, nonprotein Frx predominates in human CSF that is distinct from the currently known CSF Frxs.

CONCLUSION

The underlying cause of iron imbalance is distinct in sCJD relative to other DMs associated with the brain iron imbalance. Thus, change in the CSF levels of iron-management proteins can provide disease-specific biomarkers and insight into the cause of iron imbalance in neurodegenerative conditions.

Targeting dysregulation of brain iron homeostasis in Parkinson's disease by iron chelators

Brain iron accumulation has been implicated in a host of chronic neurological diseases, including Parkinson's disease (PD). The elevated iron levels observed in the substantia nigra of PD subjects have been suggested to incite the generation of reactive oxygen species and intracellular α-synuclein aggregation, terminating in the oxidative neuronal destruction of this brain area. Thus, elucidation of the molecular mechanisms involved in iron dysregulation and oxidative stress-induced neurodegeneration is a crucial step in deciphering PD pathology and in developing novel iron-complexing compounds aimed at restoring brain iron homeostasis and attenuating neurodegeneration. This review discusses the involvement of dysregulation of brain iron homeostasis in PD pathology, with an emphasis on the potential effectiveness of naturally occurring compounds and novel iron-chelating/antioxidant therapeutic hybrid molecules, exerting a spectrum of neuroprotective interrelated activities: antioxidant/monoamine oxidase inhibition, activation of the hypoxia-inducible factor (HIF)-1 signaling pathway, induction of HIF-1 target iron-regulatory and antioxidative genes, and inhibition of α-synuclein accumulation and aggregation.

Metallostasis in Alzheimer's disease

2012 has been another year in which multiple large-scale clinical trials for Alzheimer's disease (AD) have failed to meet their clinical endpoints. With the social and financial burden of this disease increasing every year, the onus is now on the field of AD researchers to investigate alternative ideas to deliver outcomes for patients. Although several major clinical trials targeting Aβ have failed, three smaller clinical trials targeting metal interactions with Aβ have all shown benefit for patients. Here we review the genetic, pathological, biochemical, and pharmacological evidence that underlies the metal hypothesis of AD. The AD-affected brain suffers from metallostasis, or fatigue of metal trafficking, resulting in redistribution of metals into inappropriate compartments. The metal hypothesis is built upon a triad of transition elements: iron, copper, and zinc. The hypothesis has matured from early investigations showing amyloidogenic and oxidative stress consequences of these metals; recently, disease-related proteins, APP, tau, and presenilin, have been shown to have major roles in metal regulation, which provides insight into the pathway of neurodegeneration in AD and illuminates potential new therapeutic avenues.

Novel 5' untranslated region directed blockers of iron-regulatory protein-1 dependent amyloid precursor protein translation: implications for down syndrome and Alzheimer's disease

We reported that iron influx drives the translational expression of the neuronal amyloid precursor protein (APP), which has a role in iron efflux. This is via a classic release of repressor interaction of APP mRNA with iron-regulatory protein-1 (IRP1) whereas IRP2 controls the mRNAs encoding the L- and H-subunits of the iron storage protein, ferritin. Here, we identified thirteen potent APP translation blockers that acted selectively towards the uniquely configured iron-responsive element (IRE) RNA stem loop in the 5' untranslated region (UTR) of APP mRNA. These agents were 10-fold less inhibitory of 5'UTR sequences of the related prion protein (PrP) mRNA. Western blotting confirmed that the 'ninth' small molecule in the series selectively reduced neural APP production in SH-SY5Y cells at picomolar concentrations without affecting viability or the expression of α-synuclein and ferritin. APP blocker-9 (JTR-009), a benzimidazole, reduced the production of toxic Aβ in SH-SY5Y neuronal cells to a greater extent than other well tolerated APP 5'UTR-directed translation blockers, including posiphen, that were shown to limit amyloid burden in mouse models of Alzheimer's disease (AD). RNA binding assays demonstrated that JTR-009 operated by preventing IRP1 from binding to the IRE in APP mRNA, while maintaining IRP1 interaction with the H-ferritin IRE RNA stem loop. Thus, JTR-009 constitutively repressed translation driven by APP 5'UTR sequences. Calcein staining showed that JTR-009 did not indirectly change iron uptake in neuronal cells suggesting a direct interaction with the APP 5'UTR. These studies provide key data to develop small molecules that selectively reduce neural APP and Aβ production at 10-fold lower concentrations than related previously characterized translation blockers. Our data evidenced a novel therapeutic strategy of potential impact for people with trisomy of the APP gene on chromosome 21, which is a phenotype long associated with Down syndrome (DS) that can also cause familial Alzheimer's disease.

A delicate balance: Iron metabolism and diseases of the brain

Iron is the most abundant transition metal within the brain, and is vital for a number of cellular processes including neurotransmitter synthesis, myelination of neurons, and mitochondrial function. Redox cycling between ferrous and ferric iron is utilized in biology for various electron transfer reactions essential to life, yet this same chemistry mediates deleterious reactions with oxygen that induce oxidative stress. Consequently, there is a precise and tightly controlled mechanism to regulate iron in the brain. When iron is dysregulated, both conditions of iron overload and iron deficiencies are harmful to the brain. This review focuses on how iron metabolism is maintained in the brain, and how an alteration to iron and iron metabolism adversely affects neurological function.

Applying transcriptomic and proteomic knowledge to Parkinson's disease drug discovery

It is recognised that in both genetic and sporadic cases of Parkinson's disease (PD), the basis of its etiopathology resides in the particular vulnerability of the dopaminergic neurons of the substantia nigra pars compacta (SNpc) to oxidative stress and in the failure to adequately remove abnormal proteins. These observations have been confirmed recently by microarray transcriptomic studies in human SN from PD brains and have extended understanding of the molecular pathways underlying the PD pathology. This article reviews recent gene expression profiling studies in sporadic PD postmortem SN and highlights gene candidates as putative molecular signatures for early disease diagnosis. In addition, the application of transcriptomics and proteomics in the quest for multifunctional neuroprotective-neurorescue drugs that might possess disease-modifying action is discussed.

Mammalian iron homeostasis in health and disease: uptake, storage, transport, and molecular mechanisms of action

Iron is a crucial factor for life. However, it also has the potential to cause the formation of noxious free radicals. These double-edged sword characteristics demand a tight regulation of cellular iron metabolism. In this review, we discuss the various pathways of cellular iron uptake, cellular iron storage, and transport. Recent advances in understanding the reduction and uptake of non-transferrin-bound iron are discussed. We also discuss the recent progress in the understanding of transcriptional and translational regulation by iron. Furthermore, we discuss recent advances in the understanding of the regulation of cellular and systemic iron homeostasis and several key diseases resulting from iron deficiency and overload. We also discuss the knockout mice available for studying iron metabolism and the related human conditions.

Chronic intranasal deferoxamine ameliorates motor defects and pathology in the α-synuclein rAAV Parkinson's model

Parkinson's disease is characterized by neuronal death in the substantia nigra and the presence of intracellular inclusions of α-synuclein in the Lewy bodies. Several lines of data support a role for iron in Parkinson's disease: iron is present in Lewy bodies, iron accumulates in the dopaminergic neurons in the substantia nigra, and Parkinson's disease is correlated with polymorphisms of several genes implicated in iron metabolism. Furthermore, iron can compromise the solubility of α-synuclein through direct interaction and can induce neurotoxicity in vitro. Here, we investigate the possible neuroprotective effect of the iron chelator deferoxamine in vivo to elucidate whether iron chelation can provide meaningful therapy for Parkinson's disease. Hence, we used a Parkinson's disease animal model based on unilateral injection of a recombinant adeno-associated viral vector encoding α-synuclein in the rat midbrain. Rats were treated with a novel deferoxamine delivery approach: 6 mg of the compound was administered intranasally three times a week for 3 or 7 weeks. The behavior of the animals and histopathological changes in the brain were analyzed. Our data show that although intranasal administration of deferoxamine in rats did not protect them from dopaminergic cell death, it did decrease the number of the pathological α-synuclein formations at the terminal level. In addition, this treatment resulted in changes in the immune response and an overall partial improvement in motor behavior. Taken together, our data show that in vivo iron chelation can modulate α-synuclein-induced pathology in the central nervous system. Our data suggest that chronic administration of intranasal deferoxamine may be a valid approach to limiting the mishandling of α-synuclein in the central nervous system observed in Parkinson's disease and slowing disease progression.

Role of α-synuclein aggregation and the nuclear factor E2-related factor 2/heme oxygenase-1 pathway in iron-induced neurotoxicity

Abnormal aggregation of α-synuclein (α-syn) plays a critical role in the pathogenesis of Parkinson's disease (PD). Iron is also believed to serve as a major contributor by inducing oxidative stress and α-syn aggregation. Here, we report that down-regulation of nuclear factor E2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) may contribute to iron-induced α-syn aggregation. In this study, we show that ferrous iron down-regulates Nrf2 and HO-1 in a time-dependent manner in SK-N-SH neuroblastoma cells. Levels of both Nrf2 and HO-1 are decreased even more by ferrous iron in SK-N-SH cells that overexpress α-syn and results in greater cell toxicity. Consistent with these results, knockdown of α-syn expression prevents reduction of Nrf2 and HO-1 by ferrous iron, eliminates α-syn aggregates, and protects SK-N-SH cells against ferrous iron-induced cell damage. Furthermore, increased HO-1 expression exerts a protective role against ferrous iron. These results support a new hypothesis of synergistic α-syn/iron cytotoxicity, whereby ferrous iron induces α-syn aggregation and neurotoxicity by inhibiting Nrf2/HO-1. Inhibition of Nrf2/HO-1 leads to more α-syn aggregation and greater toxicity induced by iron, creating a vicious cycle of iron accumulation, α-syn aggregation and HO-1 disruption in PD.

Cellular strategies for regulating functional and nonfunctional protein aggregation

Growing evidence suggests that aggregation-prone proteins are both harmful and functional for a cell. How do cellular systems balance the detrimental and beneficial effect of protein aggregation? We reveal that aggregation-prone proteins are subject to differential transcriptional, translational, and degradation control compared to nonaggregation-prone proteins, which leads to their decreased synthesis, low abundance, and high turnover. Genetic modulators that enhance the aggregation phenotype are enriched in genes that influence expression homeostasis. Moreover, genes encoding aggregation-prone proteins are more likely to be harmful when overexpressed. The trends are evolutionarily conserved and suggest a strategy whereby cellular mechanisms specifically modulate the availability of aggregation-prone proteins to (1) keep concentrations below the critical ones required for aggregation and (2) shift the equilibrium between the monomeric and oligomeric/aggregate form, as explained by Le Chatelier’s principle. This strategy may prevent formation of undesirable aggregates and keep functional assemblies/aggregates under control.

A synopsis on the role of tyrosine hydroxylase in Parkinson's disease

Parkinson's disease (PD) is a common chronic progressive neurodegenerative disorder in elderly people. A consistent neurochemical abnormality in PD is degeneration of dopaminergic neurons in substantia nigra pars compacta, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-dihydroxyphenylalanine (L-DOPA), the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Problems related to PD usually build up when vesicular storage of DA is altered by the presence of either α-synuclein protofibrils or oxidative stress. Phosphorylation of three physiologically-regulated specific sites of N-terminal domain of TH is vital in regulating its kinetic and protein interaction. The concept of physiological significance of TH isoforms is another interesting aspect to be explored further for a comprehensive understanding of its role in PD. Thus, a logical and efficient strategy for PD treatment is based on correcting or bypassing the enzyme deficiency by the treatment with L-DOPA, DA agonists, inhibitors of DA metabolism or brain grafts with cells expressing a high level of TH. Neurotrophic factors are also attracting the attention of neuroscientists because they provide the essential neuroprotective and neurorestorative properties to the nigrostriatal DA system. PPAR-γ, a key regulator of immune responses, is likewise a promising target for the treatment of PD, which can be achieved by the use of agonists with the potential to impact the expression of pro- and anti-inflammatory cytokines at the transcriptional level in immune cells via expression of TH. Herein, we review the primary biochemical and pathological features of PD, and describe both classical and developing approaches aimed to ameliorate disease symptoms and its progression.