Leucine-rich repeat kinase 2 and alpha-synuclein: intersecting pathways in the pathogenesis of Parkinson's disease?

Although Parkinson's disease (PD) is generally a sporadic neurological disorder, the discovery of monogenic, hereditable forms of the disease has been crucial in delineating the molecular pathways that lead to this pathology. Genes responsible for familial PD can be ascribed to two categories based both on their mode of inheritance and their suggested biological function. Mutations in parkin, PINK1 and DJ-1 cause of recessive Parkinsonism, with a variable pathology often lacking the characteristic Lewy bodies (LBs) in the surviving neurons. Intriguingly, recent findings highlight a converging role of all these genes in mitochondria function, suggesting a common molecular pathway for recessive Parkinsonism. Mutations in a second group of genes, encoding alpha-synuclein (α-syn) and LRRK2, are transmitted in a dominant fashion and generally lead to LB pathology, with α-syn being the major component of these proteinaceous aggregates. In experimental systems, overexpression of mutant proteins is toxic, as predicted for dominant mutations, but the normal function of both proteins is still elusive. The fact that α-syn is heavily phosphorylated in LBs and that LRRK2 is a protein kinase, suggests that a link, not necessarily direct, exists between the two. What are the experimental data supporting a common molecular pathway for dominant PD genes? Do α-syn and LRRK2 target common molecules? Does LRRK2 act upstream of α-syn? In this review we will try to address these of questions based on the recent findings available in the literature.     

A role for anti-transglutaminase 2 autoantibodies in the pathogenesis of coeliac disease?

Coeliac disease is an autoimmune-mediated disorder with both innate and adaptive immune components. The disease is triggered by dietary gluten, which provokes the development of a massive immune reaction leading to the destruction of the small-intestinal mucosal morphology and intestinal dysfunction. Besides the typical small-bowel symptoms extraintestinal manifestations may also arise in a subset of coeliac disease patients. In addition, gluten evokes the production of antibodies mainly targeting deamidated gluten peptides or transglutaminase 2. Although coeliac disease has traditionally been regarded as a T cell-mediated disorder, this review discusses the role of the gluten-induced disease-specific anti-transglutaminase 2-autoantibodies in the pathogenesis of the disease.     

Reprint of: Revisiting oxidative stress and mitochondrial dysfunction in the pathogenesis of Parkinson disease—resemblance to the effect of amphetamine drugs of abuse

Parkinson disease (PD) is a chronic and progressive neurological disease associated with a loss of dopaminergic neurons. In most cases the disease is sporadic but genetically inherited cases also exist. One of the major pathological features of PD is the presence of aggregates that localize in neuronal cytoplasm as Lewy bodies, mainly composed of α-synuclein (α-syn) and ubiquitin. The selective degeneration of dopaminergic neurons suggests that dopamine itself may contribute to the neurodegenerative process in PD. Furthermore, mitochondrial dysfunction and oxidative stress constitute key pathogenic events of this disorder. Thus, in this review we give an actual perspective to classical pathways involving these two mechanisms of neurodegeneration, including the role of dopamine in sporadic and familial PD, as well as in the case of abuse of amphetamine-type drugs. Mutations in genes related to familial PD causing autosomal dominant or recessive forms may also have crucial effects on mitochondrial morphology, function, and oxidative stress. Environmental factors, such as MPTP and rotenone, have been reported to induce selective degeneration of the nigrostriatal pathways leading to α-syn-positive inclusions, possibly by inhibiting mitochondrial complex I of the respiratory chain and subsequently increasing oxidative stress. Recently, increased risk for PD was found in amphetamine users. Amphetamine drugs have effects similar to those of other environmental factors for PD, because long-term exposure to these drugs leads to dopamine depletion. Moreover, amphetamine neurotoxicity involves α-syn aggregation, mitochondrial dysfunction, and oxidative stress. Therefore, dopamine and related oxidative stress, as well as mitochondrial dysfunction, seem to be common links between PD and amphetamine neurotoxicity.     

Do oxidative stress conditions impairing photosynthesis in the light manifest as photoinhibition?

We compared the effect of photoinhibition by excess photosynthetically active radiation (PAR), UV-B irradiation combined with PAR, low temperature stress and paraquat treatment on photosystem (PS) II. Although the experimental conditions ensured that the four studied stress conditions resulted in approximately the same extent of PS II inactivation, they clearly followed different molecular mechanisms. Our results show that singlet oxygen production in inactivated PS II reaction centres is a unique characteristic of photoinhibition by excess PAR. Neither the accumulation of inactive PS II reaction centres (as in UV-B or chilling stress), nor photo-oxidative damage of PS II (as in paraquat stress) is able to produce the special oxidizing conditions characteristic of acceptor-side-induced photoinhibition.     

Role of mitochondrial dysfunction and oxidative stress in the pathogenesis of selective neuronal loss in Wernicke’s encephalopathy

Thiamine deficiency results in Wernicke’s encephalopathy and is commonly encountered in chronic alcoholism, gastrointestinal diseases, and HIV AIDS. The earliest metabolic consequence of thiamine deficiency is a selective loss in activity of the thiamine diphosphate-dependent enzyme α-ketoglutarate dehydrogenase (α-KGDH), a rate-limiting tricarboxylic acid cycle enzyme. Thiamine deficiency is characterized neuropathologically by selective neuronal cell death in the thalamus, pons, and cerebellum. The cause of this region-selective neuronal loss is unknown, but mechanisms involving cellular energy failure, focal lactic acidosis, and NMDA receptor-mediated excitotoxicity have classically been implicated. More recently, evidence supports a role for oxidative stress. Evidence includes increased endothelial nitric oxide synthase, nitrotyrosine deposition, microglial activation, and lipid peroxidation. Reactive oxygen species production results in decreased expression of astrocytic glutamate transporters and decreased activities of α-KGDH, resulting in an amplification of cell death mechanisms in thiamine deficiency.     

Do the serum oxidative stress biomarkers provide a reasonable index of the general oxidative stress status?

The oxidant status of an individual is assessed by determining a group of markers in noninvasive samples. One limitation when measuring these biomarkers is that they do not give information about tissue localization of oxidative stress. The present study was undertaken to establish whether the serum oxidative stress biomarkers are indicative of oxidative stress in tissues of an individual. To accomplish this, we determined a few generic markers of oxidation in serum and tissues of six groups of rats treated experimentally, to modulate their oxidative stress status. The correlation between serum and tissue levels was calculated for each marker. Also, for each tissue, the correlation between the values of these oxidative stress biomarkers was analysed. Our results show that only lipid peroxides in serum could be useful to predict the oxidative stress in tissues. No correlation was found between any of the oxidative stress markers in serum.     

Is the oxidative stress theory of aging dead?

Currently, the oxidative stress (or free radical) theory of aging is the most popular explanation of how aging occurs at the molecular level. While data from studies in invertebrates (e.g., C. elegans and Drosophila) and rodents show a correlation between increased lifespan and resistance to oxidative stress (and in some cases reduced oxidative damage to macromolecules), direct evidence showing that alterations in oxidative damage/stress play a role in aging are limited to a few studies with transgenic Drosophila that overexpress antioxidant enzymes. Over the past eight years, our laboratory has conducted an exhaustive study on the effect of under- or overexpressing a large number and wide variety of genes coding for antioxidant enzymes. In this review, we present the survival data from these studies together. Because only one (the deletion of the Sod1 gene) of the 18 genetic manipulations we studied had an effect on lifespan, our data calls into serious question the hypothesis that alterations in oxidative damage/stress play a role in the longevity of mice.     

Where in the world do bacteria experience oxidative stress?

Reactive oxygen species – superoxide, hydrogen peroxide and hydroxyl radicals – have long been suspected of constraining bacterial growth in important microbial habitats and indeed of shaping microbial communities. Over recent decades, studies of paradigmatic organisms such as Escherichia coli, Salmonella typhimurium, Bacillus subtilis and Saccharomyces cerevisiae have pinpointed the biomolecules that oxidants can damage and the strategies by which microbes minimize their injuries. What is lacking is a good sense of the circumstances under which oxidative stress actually occurs. In this MiniReview several potential natural sources of oxidative stress are considered: endogenous ROS formation, chemical oxidation of reduced species at oxic–anoxic interfaces, H₂O₂ production by lactic acid bacteria, the oxidative burst of phagocytes and the redox-cycling of secreted small molecules. While all of these phenomena can be reproduced and verified in the lab, the actual quantification of stress in natural habitats remains lacking – and, therefore, we have a fundamental hole in our understanding of the role that oxidative stress actually plays in the biosphere.     

Update on the oxidative stress theory of aging: Does oxidative stress play a role in aging or healthy aging?

The oxidative stress theory of aging predicts that manipulations that alter oxidative stress/damage will alter aging. The gold standard for determining whether aging is altered is life span, i.e., does altering oxidative stress/damage change life span? Mice with genetic manipulations in their antioxidant defense system designed to directly address this prediction have, with few exceptions, shown no change in life span. However, when these transgenic/knockout mice are tested using models that develop various types of age-related pathology, they show alterations in progression and/or severity of pathology as predicted by the oxidative stress theory: increased oxidative stress accelerates pathology and reduced oxidative stress retards pathology. These contradictory observations might mean that (a) oxidative stress plays a very limited, if any, role in aging but a major role in health span and/or (b) the role that oxidative stress plays in aging depends on environment. In environments with minimal stress, as expected under optimal husbandry, oxidative damage plays little role in aging. However, under chronic stress, including pathological phenotypes that diminish optimal health, oxidative stress/damage plays a major role in aging. Under these conditions, enhanced antioxidant defenses exert an “antiaging” action, leading to changes in life span, age-related pathology, and physiological function as predicted by the oxidative stress theory of aging.     

Proteomic analysis of dopamine and α-synuclein interplay in a cellular model of Parkinson's disease pathogenesis

Altered dopamine homeostasis is an accepted mechanism in the pathogenesis of Parkinson's disease. α-Synuclein overexpression and impaired disposal contribute to this mechanism. However, biochemical alterations associated with the interplay of cytosolic dopamine and increased α-synuclein are still unclear. Catecholaminergic SH-SY5Y human neuroblastoma cells are a suitable model for investigating dopamine toxicity. In the present study, we report the proteomic pattern of SH-SY5Y cells overexpressing α-synuclein (1.6-fold induction) after dopamine exposure. Dopamine itself is able to upregulate α-synuclein expression. However, the effect is not observed in cells that already overexpress α-synuclein as a consequence of transfection. The proteomic analysis highlights significant changes in 23 proteins linked to specific cellular processes, such as cytoskeleton structure and regulation, mitochondrial function, energetic metabolism, protein synthesis, and neuronal plasticity. A bioinformatic network enrichment procedure generates a significant model encompassing all proteins and allows us to enrich functional categories associated with the combination of factors analyzed in the present study (i.e. dopamine together with α-synuclein). In particular, the model suggests a potential involvement of the nuclear factor kappa B pathway that is experimentally confirmed. Indeed, α-synuclein significantly reduces nuclear factor kappa B activation, which is completely quenched by dopamine treatment.     

Oxidative/nitrative stress in the pathogenesis of systemic sclerosis: are antioxidants beneficial?

Abstract

Systemic sclerosis (SSc) is a multisystem autoimmune disease: characterised from the clinical side by progressive vasculopathy and fibrosis of the skin and different organs and from the biochemical side by fibroblast deregulation with excessive production of collagen and increased expression of nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4). The latter contributes to an overproduction of reactive oxygen species that through an autocrine loop maintains NOX4 in a state of activation. Reactive oxygen and nitrogen species are implicated in the origin and perpetuation of several clinical manifestations of SSc having vascular damage in common; attempts to dampen oxidative and nitrative stress through different agents with antioxidant properties have not translated into a sustained clinical benefit. Objective of this narrative review is to describe the origin and clinical implications of oxidative and nitrative stress in SSc, with particular focus on the central role of NOX4 and its interactions, to re-evaluate the antioxidant approaches so far used to limit disease progression, to appraise the complexity of antioxidant treatment and to touch on novel pathways elements of which may represent specific treatment targets in the not so distant future.     

Gastrodin prevents motor deficits and oxidative stress in the MPTP mouse model of Parkinson's disease: Involvement of ERK1/2–Nrf2 signaling pathway

Aims

Current no effective therapy is available to halt the progression of Parkinson's disease (PD). Oxidative stress has been implicated in the etiology of PD. The present study evaluates the hypothesis that prevention of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced motor deficits by gastrodin might mainly result from its antioxidant property via interrupting extracellular signal regulated protein kinases (ERK) 1/2-nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway.

Main methods

Pretreatment of mouse model of PD is established by treating C57BL/6 mice with 4 doses of MPTP (30 mg/kg per day, i.p.), with gastrodin (60 mg/kg per day) administered by daily intraperitoneal injection for 2 weeks. Motor behavior of mice was monitored by open-field test and rotarod test. Real-time polymerase chain reaction and Western blotting were used to analyze the expression of genes.

Key findings

MPTP-induced motor deficits were partially and significantly forestalled by gastrodin. Gastrodin treatment prevented MPTP-induced oxidative stress, as measured by malondialdehyde in midbrain. Interestingly, MPTP-intoxicated mice treated with gastrodin robustly increased heme oxygenase 1, superoxide dismutase, glutathione levels, and Nrf2 nuclear translocation in striatum of MPTP-intoxicated mice. Furthermore, results herein suggest that the antioxidant pathway activated by gastrodin involves ERK1/2 phosphorylation.

Significance

Gastrodin protects midbrain of MPTP-intoxicated mice against oxidative stress, in part, through interrupting ERK1/2–Nrf2 pathway mechanism, which will give us an insight into the potential of gastrodin in terms of opening up new therapeutic avenues for PD.     

Time sequence of oxidative stress in the brain from transgenic mouse models of Alzheimer's disease related to the amyloid-β cascade

Alzheimer's disease (AD) is a multifactorial disorder characterized by the presence of amyloid plaques and neurofibrillary tangles (NFTs). Rare early-onset forms of AD are associated with autosomal dominant mutations in the amyloid precursor protein gene, presenilin 1 gene, or presenilin 2 gene. The late-onset form of the disease (LOAD) is the most common form. The causes of LOAD are not yet clarified, but several environmental and genetic risk factors have been identified. Numerous studies have highlighted a role for free radical-mediated injury to brain regions of this illness. In addition, studies from mild cognitive impairment patients suggest that oxidative stress is an early event in the pathogenesis of AD. The associations between these markers of free radical damage and the pathogenic cascades involved in AD are complex. Over the past 2 decades, a number of mouse models have been created to recapitulate the major neuropathological hallmarks of AD, namely amyloid plaques and NFTs. These mice recapitulate many, although not all, of the key features of AD. Some strains of transgenic mice develop amyloid plaques, some accumulate NFTs, and some do both. Here we review the evidence for increased free radical-mediated damage to the brain with particular attention to the stage of the disease in various transgenic models of AD related to the amyloid-β cascade.     

Can mesenchymal stem cells reduce vulnerability of dopaminergic neurons in the substantia nigra to oxidative insult in individuals at risk to Parkinson's disease?

PD (Parkinson's disease) is characterized by the selective loss of DA (dopaminergic) neurons in the substantia nigra of the midbrain region, but not in the ventral tegmental area and other catecholaminergic cell group areas. The aetiology of PD is attributed both to environmental and genetic causes, and certain population of individuals may be classified as at risk of developing PD later in life. However, there are as yet no therapy regimens that can help to delay or prevent the onset of the disease to realize long-term benefits from this early diagnosis. In PD, a vicious cycle gets initiated in the substantia nigra, because of which susceptible neurons continue to degenerate whereas damaged neurons do not get enough support for regeneration. This happens primarily because of the local environment of oxidative damage brought about by the dual presence of dopamine and high levels of iron, decline in cellular detoxification systems and low density of glial cells surrounding the DA neurons in the mesencephalic region. To enhance the defence mechanism of the substantia nigra in this situation, it is necessary to combat the oxidative insult while providing trophic factors for the survival and regeneration of the damaged neurons. In light of in vitro and in vivo studies, MSCs (mesenchymal stem cells) as candidates for cell-based therapies in PD have greater scope than as mere replacement of cell type, since they can be used as a cellular system for the detoxification of ROS (reactive oxygen species) as well as a supplier of neurotrophic factors to modulate the local environment. Building on progress in unravelling the multipronged effect of MSCs, we therefore hypothesize that MSCs could be used as a prophylactic strategy to delay or prevent the onset of PD in at-risk individuals, and to slow down the progression of the disease.     

In vivo oxidative stress in brain of Alzheimer disease transgenic mice: Requirement for methionine 35 in amyloid β-peptide of APP

Numerous studies have demonstrated oxidative damage in the central nervous system in subjects with Alzheimer disease and in animal models of this dementing disorder. In this study, we show that transgenic mice modeling Alzheimer disease—PDAPP mice with Swedish and Indiana mutations in the human amyloid precursor protein (APP)—develop oxidative damage in brain, including elevated levels of protein oxidation (indexed by protein carbonyls and 3-nitrotyrosine) and lipid peroxidation (indexed by protein-bound 4-hydroxy-2-nonenal). This oxidative damage requires the presence of a single methionine residue at position 35 of the amyloid β-peptide (Aβ), because all indices of oxidative damage in brain were completely prevented in genetically and age-matched PDAPP mice with an M631L mutation in APP. No significant differences in the levels of APP, Aβ(1–42), and Aβ(1–40) or in the ratio Aβ(1–42)/Aβ(1–40) were found, suggesting that the loss of oxidative stress in vivo in the brain of PDAPP(M631L) mice results solely from the mutation of the Met35 residue to Leu in the Aβ peptide. However, a marked reduction in Aβ-immunoreactive plaques was observed in the M631L mice, which instead displayed small punctate areas of nonplaque immunoreactivity and a microglial response. In contrast to the requirement for Met at residue 35 of the Aβ sequence (M631 of APP) for oxidative damage, indices of spatial learning and memory were not significantly improved by the M631L substitution. Furthermore, a genetically matched line with a different mutation—PDAPP(D664A)—showed the reverse: no reduction in oxidative damage but marked improvement in memory. This is the first in vivo study to demonstrate the requirement for Aβ residue Met35 for oxidative stress in the brain of a mammalian model of Alzheimer disease. However, in this specific transgenic mouse model of AD, oxidative stress is neither required nor sufficient for memory abnormalities.