The critical role of the MyD88-dependent pathway in non-CNS MPTP-mediated toxicity

A Low-Protein, High-Carbohydrate Diet Exerts a Neuroprotective Effect on Mice with 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-Induced Parkinson's Disease by Regulating the Microbiota-Metabolite-Brain Axis and Fibroblast Growth Factor 21

Parkinson's disease (PD) is closely linked to lifestyle factors, particularly dietary patterns, which have attracted interest as potential disease-modifying factors. Eating a low-protein, high-carbohydrate (LPHC) diet is a promising dietary intervention against brain aging; however, its protective effect on PD remains elusive. Here, we found that an LPHC diet ameliorated 1-methyl-4-phenyl-1,2,3,6-tetrathydropyridine (MPTP)-induced motor deficits, decreased dopaminergic neuronal death, and increased the levels of striatal dopamine, serotonin, and their metabolites in PD mice. Levels of fibroblast growth factor 21 (FGF-21), a member of the fibroblast growth factor family, were elevated in PD mice following LPHC treatment. Furthermore, the administration of FGF-21 exerted a protective effect on MPTP-induced PC12 cells, similar to the effect of an LPHC diet in MPTP-induced mice. Sequencing of the 16S rDNA from fecal microbiota revealed that an LPHC diet normalized the gut bacterial composition imbalance in PD mice, as evidenced by the increased abundance of the genera Bifidobacterium, Ileibacterium, Turicibacter, and Blautia and decreased abundance of Bilophila, Alistipes, and Bacteroides. PICRUSt-predicted fecal microbiome function revealed that an LPHC diet suppressed lipopolysaccharide biosynthesis and the citrate cycle (TCA cycle), biosynthesis of ubiquinone and other terpenoid-quinones, and oxidative phosphorylation pathways caused by MPTP, and enhanced the biosynthesis of amino acids, carbohydrate metabolism, and biosynthesis of other secondary metabolites. A nonmetabolomic analysis of the serum and feces showed that an LPHC diet significantly increased the levels of aromatic amino acids (AAAs), including tryptophan, tyrosine, and phenylalanine. In addition, an LPHC diet elevated the serum concentrations of bile acids (BAs), particularly tauroursodeoxycholic acid (TUDCA) and taurine. Collectively, our current findings point to the potential mechanism of administering an LPHC diet in attenuating movement impairments in MPTP-induced PD mice, with AAAs, microbial metabolites (TUDCA and taurine), and FGF-21 as key mediators along the gut-microbiota-brain axis.

Impact of Sex on Neuroimmune contributions to Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. Inflammation has been observed in both the idiopathic and familial forms of PD. Importantly, PD is reported more often in men than in women, men having at least 1.5- fold higher risk to develop PD than women. This review summarizes the impact of biological sex and sex hormones on the neuroimmune contributions to PD and its investigation in animal models of PD. Innate and peripheral immune systems participate in the brain neuroinflammation of PD patients and is reproduced in neurotoxin, genetic and alpha-synuclein based models of PD. Microglia and astrocytes are the main cells of the innate immune system in the central nervous system and are the first to react to restore homeostasis in the brain. Analysis of serum immunoprofiles in female and male control and PD patients show that a great proportion of these markers differ between male and female. The relationship between CSF inflammatory markers and PD clinical characteristics or PD biomarkers shows sex differences. Conversely, in animal models of PD, sex differences in inflammation are well documented and the beneficial effects of endogenous and exogenous estrogenic modulation in inflammation have been reported. Targeting neuroinflammation in PD is an emerging therapeutic option but gonadal drugs have not yet been investigated in this respect, thus offering new opportunities for sex specific treatments.

Fucosylated Chondroitin Sulfate against Parkinson's Disease through Inhibiting Inflammation Induced by Gut Dysbiosis

Growing evidence for the importance of the gut-brain axis in Parkinson's disease (PD) has attracted researchers' interest in the possible application of microbiota-based treatment approaches. Using a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model, we looked into the prospect of treating PD with fucosylated chondroitin sulfate obtained from sea cucumbers Isostichopus badionotus (fCS-Ib). We showed that giving fCS-Ib polysaccharide orally greatly reduced the motor deficits, dopamine depletion, and alpha-synuclein increase caused by MPTP in the substantia nigra (SN). It appears that the anti-PD action of fCS-Ib polysaccharide could be attained by squelching inflammation. Glial cell hyperactivation in SN and overproduction of proinflammatory substances in serum could both be suppressed by fCS-Ib polysaccharide injection. The bacterial DNA in fresh colonic feces was submitted to 16S rRNA and untargeted metabolic analyses to confirm the participation of the microbiota-gut-brain axis in the aforementioned interpretation. The findings showed that the MPTP treatment-induced decrease in norank_f_Muribaculaceae and the increase in Staphylococcus were reversed by the administration of fCS-Ib polysaccharide. The NF-κB signaling pathway was shown to be involved in the fCS-Ib polysaccharide-induced anti-inflammation. In conclusion, our research demonstrated for the first time how fCS-Ib polysaccharide combats PD by reducing inflammation caused by gut microbial dysbiosis.

Elucidating the Beneficial Effects of Ginger (Zingiber officinale Roscoe) in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease (AD), and its pathogenesis remains obscure. Current treatment approaches mainly including levodopa and dopamine agonists provide symptomatic relief but fail to halt disease progression, and they are often accompanied by severe side effects. In this context, natural phytochemicals have received increasing attention as promising preventive or therapeutic candidates for PD, given their multitarget pharmaceutical mechanisms of actions and good safety profile. Ginger (Zingiber officinale Roscoe, Zingiberaceae) is a very popular spice used as a medicinal herb throughout the world since the ancient years, for a wide range of conditions, including nausea, diabetes, dyslipidemia, and cancer. Emerging in vivo and in vitro evidence supports the neuroprotective effects of ginger and its main pharmaceutically active compounds (zingerone, 6-shogaol, and 6-gingerol) in PD, mainly via the regulation of neuroinflammation, oxidative stress, intestinal permeability, dopamine synaptic transmission, and possibly mitochondrial dysfunction. The regulation of several transcription factors and signaling pathways, including nuclear factor kappa B (NF-κB), p38 mitogen-activated protein kinase (MAPK), phosphatidylinositol-3-kinase (PI3K)/Ak strain transforming (Akt), extracellular signal-regulated kinase (ERK) 1/2, and AMP-activated protein kinase (AMPK)/proliferator-activated receptor gamma coactivator 1 alpha (PGC1α) have been shown to contribute to the protective effects of ginger. Herein, we discuss recent findings on the beneficial role of ginger in PD as a preventive agent or potential supplement to current treatment strategies, focusing on potential underlying molecular mechanisms.

Peripheral Neuroprotective and Immunomodulatory Effects of 5α-Reductase Inhibitors in Parkinson’s Disease Models

Gastrointestinal disorders in Parkinson’s disease (PD) have been associated with neuronal alteration in the plexus of the gut. We previously demonstrated the immunomodulatory effect of female hormones to treat enteric neurodegeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. This study made the hypothesis of obtaining similar neuroprotection as with hormone treatments by affecting steroidogenesis with two 5α-reductase inhibitors, finasteride and dutasteride. These drugs are approved to treat benign prostatic hyperplasia and alopecia and display mitochondrial effects. In MPTP-treated mice, the dopaminergic and vasoactive intestinal peptide (VIP) neurons alteration was prevented by finasteride and dutasteride, while the increase in proinflammatory macrophages density was inhibited by dutasteride treatment but not finasteride. NF-κB response, oxidative stress, and nitric oxide and proinflammatory cytokines production in vitro were only prevented by dutasteride. In addition, mitochondrial production of free radicals, membrane depolarization, decreased basal respiration, and ATP production were inhibited by dutasteride, while finasteride had no effect. In conclusion, the present results indicate that dutasteride treatment prevents enteric neuronal damages in the MPTP mouse model, at least in part through anti-inflammatory and mitochondrial effects. This suggests that drug repurposing of dutasteride might be a promising avenue to treat enteric neuroinflammation in early PD.

DIFFERENTIAL CONTRIBUTION OF ESTROGEN RECEPTORS TO THE INTESTINAL THERAPEUTIC EFFECTS OF 17β-ESTRADIOL IN A MURINE MODEL OF PARKINSON'S DISEASE

Beneficial effects of estrogens have been reported in Parkinson's disease (PD) for many years. We previously reported their neuroprotective and anti-inflammatory potentials in the enteric nervous system of the intestine, a region possibly affected during the early stages of the disease according to Braak's hypothesis. Three different estrogen receptors have been characterized to date: the estrogen receptor alpha (ERα), the estrogen receptor beta (ERβ) and the G protein coupled estrogen receptor 1 (GPER1). The aim of the present study was to decipher the individual contribution of each estrogen receptor to the therapeutic properties of 17β-estradiol (E2) in the myenteric plexus of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. Different agonists, 4,4',4''-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT; ERα), 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN; ERβ), G1 (GPER1), and antagonists, ICI 182,780 (ERα and ERβ), G15 (GPER1), were used to analyze the involvement of each receptor. We confirmed that G1 protects dopamine (DA) neurons to a similar extent as E2. An anti-inflammatory effect on proinflammatory macrophages and cultured human monocytes was also demonstrated with E2 and G1. The effects of PPT and DPN were less potent than G1 with only a partial neuroprotection of DA neurons by PPT and a partial reduction of interleukin (IL)-1β production in monocytes by PPT and DPN. Overall, the present results indicate that the positive outcomes of estrogens are mainly through activation of GPER1. Therefore, this suggests that targeting GPER1 could be a promising approach for future estrogen-based hormone therapies during early PD.

The Pathological Mechanism Between the Intestine and Brain in the Early Stage of Parkinson's Disease

Parkinson's disease (PD) is the second most common chronic progressive neurodegenerative disease. The main pathological features are progressive degeneration of neurons and abnormal accumulation of α-synuclein. At present, the pathogenesis of PD is not completely clear, and many changes in the intestinal tract may be the early pathogenic factors of PD. These changes affect the central nervous system (CNS) through both nervous and humoral pathways. α-Synuclein deposited in the intestinal nerve migrates upward along the vagus nerve to the brain. Inflammation and immune regulation mediated by intestinal immune cells may be involved, affecting the CNS through local blood circulation. In addition, microorganisms and their metabolites may also affect the progression of PD. Therefore, paying attention to the multiple changes in the intestinal tract may provide new insight for the early diagnosis and treatment of PD.

Effect of Docosahexaenoic Acid (DHA) at the Enteric Level in a Synucleinopathy Mouse Model

The aggregation of alpha-synuclein protein (αSyn) is a hallmark of Parkinson’s disease (PD). Considerable evidence suggests that PD involves an early aggregation of αSyn in the enteric nervous system (ENS), spreading to the brain. While it has previously been reported that omega-3 polyunsaturated fatty acids (ω-3 PUFA) acts as neuroprotective agents in the brain in murine models of PD, their effect in the ENS remains undefined. Here, we studied the effect of dietary supplementation with docosahexaenoic acid (DHA, an ω-3 PUFA), on the ENS, with a particular focus on enteric dopaminergic (DAergic) neurons. Thy1-αSyn mice, which overexpress human αSyn, were fed ad libitum with a control diet, a low ω-3 PUFA diet or a diet supplemented with microencapsulated DHA and then compared with wild-type littermates. Our data indicate that Thy1-αSyn mice showed a lower density of enteric dopaminergic neurons compared with non-transgenic animals. This decrease was prevented by dietary DHA. Although we found that DHA reduced microgliosis in the striatum, we did not observe any evidence of peripheral inflammation. However, we showed that dietary intake of DHA promoted a build-up of ω-3 PUFA-derived endocannabinoid (eCB)-like mediators in plasma and an increase in glucagon-like peptide-1 (GLP-1) and the redox regulator, Nrf2 in the ENS. Taken together, our results suggest that DHA exerts neuroprotection of enteric DAergic neurons in the Thy1-αSyn mice, possibly through alterations in eCB-like mediators, GLP-1 and Nrf2.

The Role of Intestinal Macrophages in Gastrointestinal Homeostasis: Heterogeneity and Implications in Disease

Intestinal macrophages play a key role in the gut immune system and the regulation of gastrointestinal physiology, including gut motility and secretion. Their ability to keep the gut from chronic inflammation despite constantly facing foreign antigens has been an important focus in gastrointestinal research. However, the heterogeneity of intestinal macrophages has impeded our understanding of their specific roles. It is now becoming clear that subsets of intestinal macrophages play diverse roles in various gastrointestinal diseases. This occurs through a complex interplay between cytokine production and enteric nervous system activation that differs for each pathologic condition. Key diseases and disorders in which intestinal macrophages play a role include postoperative ileus, inflammatory bowel disease, necrotizing enterocolitis, as well as gastrointestinal disorders associated with human immunodeficiency virus and Parkinson's disease. Here, we review the identification of intestinal macrophage subsets based on their origins and functions, how specific subsets regulate gut physiology, and the potential for these heterogeneous subpopulations to contribute to disease states. Furthermore, we outline the potential for these subpopulations to provide unique targets for the development of novel therapies for these disorders.

Unravelling the role of gut microbiota in Parkinson's disease progression: Pathogenic and therapeutic implications

In recent years, researchers have shown interest in bi-directional interaction between the brain and gut, called "gut-brain axis". Emerging pieces of evidence indicate that disturbances in this axis is found to be associated with the Parkinson's disease (PD). Several clinical investigations revealed the crucial role of gut microbiota in the pathogenesis of PD. It has been suggested that aggregation of misfolded protein α-syn, the neuropathological hallmark of PD, might begin in gut and propagates to the CNS via vagus nerve and olfactory bulb. Emerging evidences also suggest that initiation and progression of PD may be due to inflammation originating from gut. It has been shown that microbial gut dysbiosis causes the production of various pathogenic microbial metabolites which elevates pro-inflammatory environment in the gut that promotes neuroinflammation in the CNS. These observations raise the intriguing question - how gut microbial dysbiosis could contribute to PD progression. In this context, various microbiota-targeted therapies are under consideration that can re-establish the intestinal homeostasis which may have greater promise in the prevention and treatment of PD. This review focuses on the role of the gut microbiota in the initiation, progression of PD and current therapeutic intervention to deplete the severity of the disease.

Ginger and 6-shogaol protect intestinal tight junction and enteric dopaminergic neurons against 1-methyl-4-phenyl 1,2,3,6-tetrahydropyridine in mice

Objective: Ginger and its compound, 6-shogaol, have been known for improving gastrointestinal (GI) function and reducing inflammatory responses in GI tract. Recently, the treatment of GI dysfunction has been recognized as an important part of the management of neurodegenerative diseases, especially for Parkinson's disease (PD). In this study, we investigated whether ginger and 6-shogaol attenuate disruptions induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the intestinal barrier and the enteric dopaminergic neurons.Methods: C57BL/6J mice received MPTP (30 mg/kg) for 5 days to induce GI alterations. Ginger (30, 100, 300 mg/kg) and 6-shogaol (10 mg/kg) were treated by gavage feeding for 15 days including the period of MPTP injection.Results: Ginger and 6-shogaol protected intestinal tight junction proteins disrupted by MPTP in mouse colon. In addition, ginger and 6-shogaol suppressed the increase of inducible nitric oxide synthase, cyclooxygenase-2, TNF-α and IL-1β activated by macrophage. Moreover, ginger and 6-shogaol suppressed the MPTP-induced enteric dopaminergic neuronal damage via increasing the cell survival signaling pathway.Conclusion: These results indicate that ginger and 6-shogaol restore the disruption of intestinal integrity and enteric dopaminergic neurons in an MPTP-injected mouse PD model by inhibiting the processes of inflammation and apoptosis, suggesting that they may attenuate the GI dysfunction in PD patients.

Neuroprotection and immunomodulation of progesterone in the gut of a mouse model of Parkinson's disease

Gastrointestinal symptoms appear in Parkinson's disease patients many years before motor symptoms, suggesting the implication of dopaminergic neurones of the gut myenteric plexus. Inflammation is also known to be increased in PD. We previously reported neuroprotection with progesterone in the brain of mice lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and hypothesised that it also has neuroprotective and immunomodulatory activities in the gut. To test this hypothesis, we investigated progesterone administered to adult male C57BL/6 mice for 10 days and treated with MPTP on day 5. In an additional experiment, progesterone was administered for 5 days following MPTP treatment. Ilea were collected on day 10 of treatment and microdissected to isolate the myenteric plexus. Dopaminergic neurones were reduced by approximately 60% and pro-inflammatory macrophages were increased by approximately 50% in MPTP mice compared to intact controls. These changes were completely prevented by progesterone administered before and after MPTP treatment and were normalised by 8 mg kg^-1 progesterone administered after MPTP. In the brain of MPTP mice, brain-derived neurotrophic peptide (BDNF) and glial fibrillary acidic protein (GFAP) were associated with progesterone neuroprotection. In the myenteric plexus, increased BDNF levels compared to controls were measured in MPTP mice treated with 8 mg kg^-1 progesterone started post MPTP, whereas GFAP levels remained unchanged. In conclusion, the results obtained in the present study show neuroprotective and anti-inflammatory effects of progesterone in the myenteric plexus of MPTP mice that are similar to our previous findings in the brain. Progesterone is non-feminising and could be used for both men and women in the pre-symptomatic stages of the disease.

Toll-like receptors and their therapeutic potential in Parkinson's disease and α-synucleinopathies

Toll-like receptors (TLRs) are pattern recognition receptors which mediate an inflammatory response upon the detection of specific molecular patterns found on foreign organisms and on endogenous damage-related molecules. These receptors play a major role in the activation of microglia, the innate immune cells of the CNS, and are also expressed in peripheral tissues, including blood mononuclear cells and the gut. It is well established that immune activation, in both the brain and periphery, is a feature of Parkinson's disease as well as other α-synucleinopathies. Aggregated forms of α-synuclein can act as ligands for TLRs (particularly TLR2 and TLR4), and hence these receptors may play a critical role in mediating a detrimental immune response to this protein, as well as other inflammatory signals in Parkinson's and related α-synucleinopathies. In this review, the potential role of TLRs in contributing to the progression of these disorders is discussed. Existing evidence comes predominantly from studies in in vitro and in vivo models, as well as analyses of postmortem human brain tissue and pre-clinical studies of TLR inhibitors. This evidence is evaluated in detail, and the potential for therapeutic intervention in α-synucleinopathies through TLR inhibition is discussed.

Gut Inflammation in Association With Pathogenesis of Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disease that is generally thought to be caused by multiple factors, including environmental and genetic factors. Emerging evidence suggests that intestinal disturbances, such as constipation, are common non-motor symptoms of PD. Gut inflammation may be closely associated with pathogenesis in PD. This review aims to discuss the cross-talk between gut inflammation and PD pathology initiation and progression. Firstly, we will highlight the studies demonstrating how gut inflammation is related to PD. Secondly, we will analyze how gut inflammation spreads from the gastro-intestine to the brain. Here, we will mainly discuss the neural pathway of pathologic α-syn and the systemic inflammatory routes. Thereafter, we will address how alterations in the brain subsequently lead to dopaminergic neuron degeneration, in which oxidative stress, glutamate excitotoxicity, T cell driven inflammation and cyclooxygenase-2 (COX-2) are involved. We conclude a model of PD triggered by gut inflammation, which provides a new angle to understand the mechanisms of the disease.

Neuroprotection of Fasting Mimicking Diet on MPTP-Induced Parkinson's Disease Mice via Gut Microbiota and Metabolites

Parkinson's disease (PD) is strongly associated with life style, especially dietary habits, which have gained attention as disease modifiers. Here, we report a fasting mimicking diet (FMD), fasting 3 days followed by 4 days of refeeding for three 1-week cycles, which accelerated the retention of motor function and attenuated the loss of dopaminergic neurons in the substantia nigra in 1-methyl-4-phenyl-1,2,3,6-tetrathydropyridine (MPTP)-induced PD mice. Levels of brain-derived neurotrophic factor (BDNF), known to promote the survival of dopaminergic neurons, were increased in PD mice after FMD, suggesting an involvement of BDNF in FMD-mediated neuroprotection. Furthermore, FMD decreased the number of glial cells as well as the release of TNF-α and IL-1β in PD mice, showing that FMD also inhibited neuro-inflammation. 16S and 18S rRNA sequencing of fecal microbiota showed that FMD treatment modulated the shifts in gut microbiota composition, including higher abundance of Firmicutes, Tenericutes, and Opisthokonta and lower abundance of Proteobacteria at the phylum level in PD mice. Gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry revealed that FMD modulated the MPTP-induced lower propionic acid and isobutyric acid, and higher butyric acid and valeric acid and other metabolites. Transplantation of fecal microbiota, from normal mice with FMD treatment to antibiotic-pretreated PD mice increased dopamine levels in the recipient PD mice, suggesting that gut microbiota contributed to the neuroprotection of FMD for PD. These findings demonstrate that FMD can be a new means of preventing and treating PD through promoting a favorable gut microbiota composition and metabolites.

TLR4 absence reduces neuroinflammation and inflammasome activation in Parkinson's diseases in vivo model

Parkinson's disease (PD) is a progressive, disabling neurodegenerative disorder. It has been shown Toll like receptor (TLR) 4-deficient mice protect against MPTP toxicity, suggesting that dopaminergic cell death is TLR4-dependent. The aim of this study was to demonstrate, in an in vivo model of PD, how TLR4 plays its important role in the pathogenesis of PD by using MPTP neurotoxin model (4 × 20 mg/kg, 2 h apart, i.p). Our experiments have demonstrated that the absence of TLR4 prevented dopamine depletion, increased tyrosine hydroxylase and dopamine transporter activities and reduced the number of α-synuclein-positive neurons. The absence of TLR4 also had an impact on inflammatory processes, modulating the transcription factors NF-κB p65 and AP-1, and reducing astrogliosis. Importantly, we demonstrated that the absence of TLR4 modulated inflammosome pathway. Moreover, it has been shown that TLR4 modulated motor and non-motor symptoms typical of PD. Our results clearly demonstrated that absence of TLR4 reduces the development of neuroinflammation associated with PD through NF-κB, AP-1 and inflammasome pathways modulation; therefore, TLR4 could be considered as an encouraging therapeutic target in neurodegenerative disorders.

Melatonin, a toll-like receptor inhibitor: Current status and future perspectives

Toll-like receptors (TLRs) are crucial activators of inflammatory responses, they are considered immune receptors. TLRs are of fundamental importance in the pathophysiology of disorders related to inflammation including neurodegenerative diseases and cancer. Melatonin is a beneficial agent in the treatment of inflammatory and immune disorders. Melatonin is potent anti-inflammatory hormone that regulates various molecular pathways. Withal, limited studies have evaluated the inhibitory role of melatonin on TLRs. This review summarizes the current knowledge related to the effects of melatonin on TLRs in some common inflammatory and immunity disorders.

Enteric Neurodegeneration is Mediated Through Independent Neuritic and Somal Mechanisms in Rotenone and MPP+ Toxicity

Gut motility malfunction and pathological changes in the enteric nervous system (ENS) are observed in the early stages of Parkinson's disease (PD). In many cases disturbances in the autonomous functions such as gut motility precedes the observed loss of central motor functions in PD. However, the mechanism by which ENS degeneration occurs in PD is unknown. We show that parkinsonian mimetics rotenone and MPP+ induce neurite degeneration that precedes cell death in primary enteric neurons cultured in vitro. If the neuronal death signals originate from degenerating neurites, neuronal death should be prevented by inhibiting neurite degeneration. Our data demonstrate that overexpression of cytNmnat1, an axon protector, maintains healthy neurites in enteric neurons treated with either of the parkinsonian mimetics, but cannot protect the soma. We also demonstrate that neurite protection via cytNmnat1 is independent of mitochondrial dynamics or ATP levels. Overexpression of Bcl-xl, an anti-apoptotic factor, protects both the neuronal cell body and the neurites in both rotenone and MPP+ treated enteric neurons. Our data reveals that Bcl-xl and cytNmnat1 act through separate mechanisms to protect enteric neurites. Our findings suggest that neurite protection alone is not sufficient to inhibit enteric neuronal degeneration in rotenone or MPP+ toxicity, and enteric neurodegeneration in PD may be occurring through independent somatic and neuritic mechanisms. Thus, therapies targeting both axonal and somal protection can be important in finding interventions for enteric symptoms in PD.

Interplay among gut microbiota, intestinal mucosal barrier and enteric neuro-immune system: a common path to neurodegenerative diseases?

Neurological diseases, such as Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis (ALS) and multiple sclerosis, are often associated with functional gastrointestinal disorders. These gastrointestinal disturbances may occur at all stages of the neurodegenerative diseases, to such an extent that they are now considered an integral part of their clinical picture. Several lines of evidence support the contention that, in central neurodegenerative diseases, changes in gut microbiota and enteric neuro-immune system alterations could contribute to gastrointesinal dysfunctions as well as initiation and upward spreading of the neurologic disorder. The present review has been intended to provide a comprehensive overview of the available knowledge on the role played by enteric microbiota, mucosal immune system and enteric nervous system, considered as an integrated network, in the pathophysiology of the main neurological diseases known to be associated with intestinal disturbances. In addition, based on current human and pre-clinical evidence, our intent was to critically discuss whether changes in the dynamic interplay between gut microbiota, intestinal epithelial barrier and enteric neuro-immune system are a consequence of the central neurodegeneration or might represent the starting point of the neurodegenerative process. Special attention has been paid also to discuss whether alterations of the enteric bacterial-neuro-immune network could represent a common path driving the onset of the main neurodegenerative diseases, even though each disease displays its own distinct clinical features.

Intestinal Pathology and Gut Microbiota Alterations in a Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) Mouse Model of Parkinson's Disease

Patients with Parkinson's disease (PD) often have non-motor symptoms related to gastrointestinal (GI) dysfunction, such as constipation and delayed gastric emptying, which manifest prior to the motor symptoms of PD. Increasing evidence indicates that changes in the composition of the gut microbiota may be related to the pathogenesis of PD. However, it is unclear how GI dysfunction occurs and how gut microbial dysbiosis is caused. We investigated whether a neurotoxin model of PD induced by chronic low doses of MPTP is capable of reproducing the clinical intestinal pathology of PD, as well as whether gut microbial dysbiosis accompanies this pathology. C57BL/6 male mice were administered 18 mg/kg MPTP twice per week for 5 weeks via intraperitoneal injection. GI function was assessed by measuring the 1-h stool frequency and fecal water content; motor function was assessed by pole tests; and tyrosine hydroxylase and alpha-synuclein expression were analyzed. Furthermore, the inflammation, intestinal barrier and composition of the gut microbiota were measured. We found that MPTP caused GI dysfunction and intestinal pathology prior to motor dysfunction. The composition of the gut microbiota was changed; in particular, the change in the abundance of Lachnospiraceae, Erysipelotrichaceae, Prevotellaceae, Clostridiales, Erysipelotrichales and Proteobacteria was significant. These results indicate that a chronic low-dose MPTP model can be used to evaluate the progression of intestinal pathology and gut microbiota dysbiosis in the early stage of PD, which may provide new insights into the pathogenesis of PD.

Indomethacin promotes survival of new neurons in the adult murine hippocampus accompanied by anti-inflammatory effects following MPTP-induced dopamine depletion

BACKGROUND

Parkinson's disease (PD) is characterized by dopaminergic cell loss and inflammation in the substantia nigra (SN) leading to motor deficits but also to hippocampus-associated non-motor symptoms such as spatial learning and memory deficits. The cognitive decline is correlated with impaired adult hippocampal neurogenesis resulting from dopamine deficit and inflammation, represented in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP) mouse model of PD. In the inflammatory tissue, cyclooxygenase (COX) is upregulated leading to an ongoing inflammatory process such as prostaglandin-mediated increased cytokine levels. Therefore, inhibition of COX by indomethacin may prevent the inflammatory response and the impairment of adult hippocampal neurogenesis.

METHODS

Wildtype C57Bl/6 and transgenic Nestin-GFP mice were treated with MPTP followed by short-term or long-term indomethacin treatment. Then, aspects of inflammation and neurogenesis were evaluated by cell counts using immunofluorescence and immunohistochemical stainings in the SN and dentate gyrus (DG). Furthermore, hippocampal mRNA expression of neurogenesis-related genes of the Notch, Wnt, and sonic hedgehog signaling pathways and neurogenic factors were assessed, and protein levels of serum cytokines were measured.

RESULTS

Indomethacin restored the reduction of the survival rate of new mature neurons and reduced the amount of amoeboid CD68+ cells in the DG after MPTP treatment. Indomethacin downregulated genes of the Wnt and Notch signaling pathways and increased neuroD6 expression. In the SN, indomethacin reduced the pro-inflammatory cellular response without reversing dopaminergic cell loss.

CONCLUSION

Indomethacin has a pro-neurogenic and thereby restorative effect and an anti-inflammatory effect on the cellular level in the DG following MPTP treatment. Therefore, COX inhibitors such as indomethacin may represent a therapeutic option to restore adult neurogenesis in PD.

Mitotic phosphotyrosine network analysis reveals that tyrosine phosphorylation regulates Polo-like kinase 1 (PLK1)

Tyrosine phosphorylation is closely associated with cell proliferation. During the cell cycle, serine and threonine phosphorylation plays the leading role, and such phosphorylation events are most dynamic during the mitotic phase of the cell cycle. However, mitotic phosphotyrosine is not well characterized. Although a few functionally-relevant mitotic phosphotyrosine sites have been characterized, evidence suggests that this modification may be more prevalent than previously appreciated. Here, we examined tyrosine phosphorylation in mitotic human cells including those on spindle-associated proteins.? Database mining confirmed ~2000 mitotic phosphotyrosine sites, and network analysis revealed a number of subnetworks that were enriched in tyrosine-phosphorylated proteins, including components of the kinetochore or spindle and SRC family kinases. We identified Polo-like kinase 1 (PLK1), a major signaling hub in the spindle subnetwork, as phosphorylated at the conserved Tyr217 in the kinase domain. Substitution of Tyr217 with a phosphomimetic residue eliminated PLK1 activity in vitro and in cells. Further analysis showed that Tyr217 phosphorylation reduced the phosphorylation of Thr210 in the activation loop, a phosphorylation event necessary for PLK1 activity. Our data indicate that mitotic tyrosine phosphorylation regulated a key serine/threonine kinase hub in mitotic cells and suggested that spatially separating tyrosine phosphorylation events can reveal previously unrecognized regulatory events and complexes associated with specific structures of the cell cycle.

Gastrointestinal Dysfunctions in Parkinson's Disease: Symptoms and Treatments

A diagnosis of Parkinson's disease is classically established after the manifestation of motor symptoms such as rigidity, bradykinesia, and tremor. However, a growing body of evidence supports the hypothesis that nonmotor symptoms, especially gastrointestinal dysfunctions, could be considered as early biomarkers since they are ubiquitously found among confirmed patients and occur much earlier than their motor manifestations. According to Braak's hypothesis, the disease is postulated to originate in the intestine and then spread to the brain via the vagus nerve, a phenomenon that would involve other neuronal types than the well-established dopaminergic population. It has therefore been proposed that peripheral nondopaminergic impairments might precede the alteration of dopaminergic neurons in the central nervous system and, ultimately, the emergence of motor symptoms. Considering the growing interest in the gut-brain axis in Parkinson's disease, this review aims at providing a comprehensive picture of the multiple gastrointestinal features of the disease, along with the therapeutic approaches used to reduce their burden. Moreover, we highlight the importance of gastrointestinal symptoms with respect to the patients' responses towards medical treatments and discuss the various possible adverse interactions that can potentially occur, which are still poorly understood.

Restoration of intestinal function in an MPTP model of Parkinson's Disease

Patients with Parkinson’s disease often experience non-motor symptoms including constipation, which manifest prior to the onset of debilitating motor signs. Understanding the causes of these non-motor deficits and developing disease modifying therapeutic strategies has the potential to prevent disease progression. Specific neuronal subpopulations were reduced within the myenteric plexus of mice 21 days after intoxication by the intraperitoneal administration of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and was associated with a reduction in stool frequency, indicative of intestinal dysfunction. Oral administration of the divalent copper complex, Cu^II(atsm), which has been shown to be neuroprotective and restore motor performance to MPTP lesioned mice, improved stool frequency and was correlated with restoration of neuronal subpopulations in the myenteric plexus of MPTP lesioned mice. Restoration of intestinal function was associated with reduced enteric glial cell reactivity and reduction of markers of inflammation. Therapeutics that have been shown to be neuroprotective in the central nervous system, such as Cu^II(atsm), therefore also provide symptom relief and are disease modifying in the intestinal tract, suggesting that there is a common cause of Parkinson’s disease pathogenesis in the enteric nervous system and central nervous system.

Abnormal lipopolysaccharide binding protein as marker of gastrointestinal inflammation in Parkinson disease

Objective: An inflammation-driven model of PD has been proposed based on the endotoxin lipopolysaccaride (LPS), a potential source of inflammation in the gastrointestinal system linked to neurotoxicity. Systemic exposure to bacterial endotoxin (LPS) can be determined by measuring plasma LPS binding protein (LBP). We aimed to evaluate whether lipopolysaccharide binding protein (LBP) can be used to distinguish PD subjects from control subjects and to assess whether LBP levels correlate with PD disease severity.

Methods: We measured plasma LBP (ng/ml) using an ELISA kit in 94 PD subjects of various stages and 97 control subjects. Disease severity was assessed using the UPDRS and Hoehn and Yahr staging. The LBP level between the PD and control groups was compared using analysis of covariance. Spearman correlation was used to explore the relationship between LBP level and disease severity.

Results: The mean LBP level in PD subjects (n = 94) was significantly different from control subjects (n = 95, p = 0.018). In PD subjects, we did not find a correlation between mean LBP level and disease severity.

Conclusions: Our data suggests that LBP is one GI biomarker related to LPS induced neurotoxicity. However, there was significant variability in LBP levels within the PD and control groups, limiting its utility as a stand-alone biomarker. This study supports the role of LPS induced neurotoxicity in PD and further exploration of this pathway may be useful in developing sensitive and specific biomarkers for PD.

Partial depletion of the proinflammatory monocyte population is neuroprotective in the myenteric plexus but not in the basal ganglia in a MPTP mouse model of Parkinson's disease

Parkinson's disease (PD) patients often suffer from gastrointestinal (GI) impairments that are associated with the alteration of dopaminergic (DAergic) neurons in the myenteric nervous system. Growing evidence suggests that inflammation originating from the gut may have a major impact in both the initiation and progression of PD. Here, we investigated the role of the innate immune response in neurodegeneration occurring in central nervous system (CNS) and enteric nervous system (ENS) in response to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin that produces Parkinsonism in both humans and animal models. We found a strong immune response in the gut of mice treated with MPTP, as demonstrated by the prominent presence of macrophages derived from CD115(+) CD11b(+) Ly6C(Hi) monocytes, known as M1 monocytes, and increased production of IL-1β and IL-6. Partial depletion of proinflammatory M1 monocytes through intravenous injections of clodronate-encapsulated liposome protects against MPTP-induced reduction of tyrosine hydroxylase (TH) expression in the ENS. In contrast, loss of striatal TH expression in the CNS after MPTP intoxication occurs regardless of partial monocyte depletion. Examination of brain tissue revealed that microglial activation, comprising the majority of the immune response in the CNS after MPTP injections is unaffected by M1 depletion. In vitro experiments revealed that MPTP and MPP(+) act directly on monocytes to elicit a proinflammatory response that is, in part, dependent on the MyD88/NF-κB signaling pathway resulting in nitrite and proinflammatory cytokine production. Taken together, our results demonstrate a critical role for proinflammatory M1 monocytes/macrophages in DAergic alterations occurring in the GI, but not in the brain, in the MPTP model of PD.

Toll-like receptor expression in the blood and brain of patients and a mouse model of Parkinson's disease

BACKGROUND

Accumulating evidence supports a role for the immune system in the pathogenesis of Parkinson's disease. Importantly, recent preclinical studies are now suggesting a specific contribution of inflammation to the α-synuclein-induced pathology seen in this condition.

METHODS

We used flow cytometry and western blots to detect toll-like receptor 2 and 4 expression in blood and brain samples of Parkinson's disease patients and mice overexpressing human α-synuclein. To further assess the effects of α-synuclein overexpression on the innate immune system, we performed a longitudinal study using Thy1.2-α-synuclein mice that expressed a bicistronic DNA construct (reporter genes luciferase and green fluorescent protein) under the transcriptional control of the murine toll-like receptor 2 promoter.

RESULTS

Here, we report increases in toll-like receptors 2 and 4 expression in circulating monocytes and of toll-like receptor 4 in B cells and in the caudate/putamen of Parkinson's disease patients. Monthly bioluminescence imaging of Thy1.2-α-synuclein mice showed increasing toll-like receptor 2 expression from 10 months of age, although no change in toll-like receptor 2 and 4 expression was observed in the blood and brain of these mice at 12 months of age. Dexamethasone treatment starting at 5 months of age for 1 month significantly decreased the microglial response in the brain of these mice and promoted functional recovery as observed using a wheel-running activity test.

CONCLUSION

Our results show that toll-like receptors 2 and 4 are modulated in the blood and brain of Parkinson's disease patients and that overexpression of α-synuclein leads to a progressive microglial response, the inhibition of which has a beneficial impact on some motor phenotypes of an animal model of α-synucleinopathy.

Multispectral Imaging

The field of anatomic pathology has changed significantly over the last decades and, as a result of the technological developments in molecular pathology and genetics, has had increasing pressures put on it to become quantitative and to provide more information about protein expression on a cellular level in tissue sections. Multispectral imaging (MSI) has a long history as an advanced imaging modality and has been used for over a decade now in pathology to improve quantitative accuracy, enable the analysis of multicolor immunohistochemistry, and drastically reduce the impact of contrast-robbing tissue autofluorescence common in formalin-fixed, paraffin-embedded tissues. When combined with advanced software for the automated segmentation of different tissue morphologies (eg, tumor vs stroma) and cellular and subcellular segmentation, MSI can enable the per-cell quantitation of many markers simultaneously. This article covers the role that MSI has played in anatomic pathology in the analysis of formalin-fixed, paraffin-embedded tissue sections, discusses the technological aspects of why MSI has been adopted, and provides a review of the literature of the application of MSI in anatomic pathology.

Fucosylated but not sialylated milk oligosaccharides diminish colon motor contractions

Human milk oligosaccharides (HMO) are being studied by different groups exploring a broad range of potential beneficial effects to the breastfed infant. Many of these effects have been attributed to a growth promotion effect on certain gut organisms such as bifidobacteria. Additionally, evidence indicates that HMO are able to directly promote positive changes in gut epithelium and immune responses under certain conditions. This study utilizes a standardized ex vivo murine colon preparation to examine the effects of sialylated, fucosylated and other HMO on gut motor contractions. Only the fucosylated molecules, 2’FL and 3’FL, decreased contractility in a concentration dependent fashion. On the basis of IC₅₀ determinations 3’FL was greater than 2 times more effective than 2’FL. The HMO 3’SL and 6’SL, lacto-N-neotetraose (LNnT), and galactooligosaccharides (GOS) elicited no effects. Lactose was used as a negative control. Fucosylation seems to underlie this functional regulation of gut contractility by oligosaccharides, and L-fucose, while it was also capable of reducing contractility, was substantially less effective than 3’FL and 2’FL. These results suggest that specific HMO are unlikely to be having these effects via bifidogenesis, but though direct action on neuronally dependent gut migrating motor complexes is likely and fucosylation is important in providing this function, we cannot conclusively shown that this is not indirectly mediated. Furthermore they support the possibility that fucosylated sugars and fucose might be useful as therapeutic or preventative adjuncts in disorders of gut motility, and possibly also have beneficial central nervous system effects.

Toll like receptor 4 mediates cell death in a mouse MPTP model of Parkinson disease

In mammalians, toll-like receptors (TLR) signal-transduction pathways induce the expression of a variety of immune-response genes, including inflammatory cytokines. It is therefore plausible to assume that TLRs are mediators in glial cells triggering the release of cytokines that ultimately kill DA neurons in the substantia nigra in Parkinson disease (PD). Accordingly, recent data indicate that TLR4 is up-regulated by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment in a mouse model of PD. Here, we wished to evaluate the role of TLR4 in the acute mouse MPTP model of PD: TLR4-deficient mice and wild-type littermates control mice were used for the acute administration way of MPTP or a corresponding volume of saline. We demonstrate that TLR4-deficient mice are less vulnerable to MPTP intoxication than wild-type mice and display a decreased number of Iba1+ and MHC II+ activated microglial cells after MPTP application, suggesting that the TLR4 pathway is involved in experimental PD.

Inflammation and neurodegeneration: the story 'retolled'

Toll-like receptors (TLRs) play a crucial role in innate immunity by recognizing conserved motifs predominantly found in microorganisms. Increasing evidence supports a role for TLRs in sterile inflammation as observed in neurodegenerative disorders. This includes work suggesting a contribution for these receptors to the pathophysiology of Alzheimer's disease (AD), Parkinson's disease (PD), and related disorders. In this review, the potential role of TLRs in the context of protein aggregation, neuronal degeneration, and genetic risk factors is addressed. In particular, we discuss the evidence derived from experimental models of both AD and PD which suggests that activation of TLRs can have beneficial and detrimental effects on pathological features such as protein aggregation and neuronal death. A deeper understanding of these dichotomous observations could be used for therapeutic benefit.

MyD88 deficiency results in both cognitive and motor impairments in mice

The myeloid differentiation primary response gene 88 (MyD88) product is the most common adaptor protein implicated in Toll-like and interleukin receptor (TIR) domain signaling and thus plays an important role in the innate immune system. Despite the fact that the MyD88-dependent pathway has emerged as an important player in cell death processes described in several animal models of neurodegenerative disorders, the contribution of this pathway to specific behavioral phenotypes has been largely ignored. To understand the full implication of this pathway, we tested MyD88(-/-) mice for both motor and cognitive functions in normal conditions. MyD88(-/-) mice displayed impaired spatial and working memory as detected by the Barnes maze, the water T-maze and the passive avoidance tests. Furthermore, MyD88(-/-) mice demonstrated hypolocomotion in the open-field and wheel activity systems, as well as impairments in motor coordination and balance using the pole test and the rotarod. Our findings shed light on behavioral alterations that are associated with the deletion of the MyD88 protein in physiological conditions. These behavioral effects should be taken into consideration when assessing the role of the MyD88-dependent pathway in various infectious and non-infectious conditions.

Cells exposed to sublethal oxidative stress selectively attract monocytes/macrophages via scavenger receptors and MyD88-mediated signaling

The innate immune system responds to endogenous molecules released during cellular stress or those that have undergone modifications normally absent in healthy tissue. These structures are detected by pattern-recognition receptors, alerting the immune system to "danger." In this study, we looked for early signals that direct immune cells to cells undergoing stress before irreversible damage takes place. To avoid detecting signals emanating from apoptotic or necrotic cells we exposed fibroblasts to sublethal oxidative stress. Our results indicate that both nonenzymatic chemical reactions and aldehyde dehydrogenase-2-mediated enzymatic activity released signals from fibroblasts that selectively attracted CD14(+) monocytes but not T, NK, and NKT cells or granulocytes. Splenocytes from MyD88(-/-) mice did not migrate, and treatment with an inhibitory peptide that blocks MyD88 dimerization abrogated human monocyte migration. Monocyte migration was accompanied by downmodulation of CD14 expression and by the phosphorylation of IL-1R-associated kinase 1, a well-known MyD88-dependent signaling molecule. The scavenger receptor inhibitors, dextran sulfate and fucoidan, attenuated monocyte migration toward stressed cells and IL-1R-associated kinase 1 phosphorylation. Surprisingly, although monocyte migration was MyD88 dependent, it was not accompanied by inflammatory cytokine secretion. Taken together, these results establish a novel link between scavenger receptors and MyD88 that together function as sensors of oxidation-associated molecular patterns and induce monocyte motility. Furthermore, the data indicate that MyD88 independently regulates monocyte activation and motility.

Inflammation in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease that is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Inflammatory responses manifested by glial reactions, T cell infiltration, and increased expression of inflammatory cytokines, as well as other toxic mediators derived from activated glial cells, are currently recognized as prominent features of PD. The consistent findings obtained by various animal models of PD suggest that neuroinflammation is an important contributor to the pathogenesis of the disease and may further propel the progressive loss of nigral dopaminergic neurons. Furthermore, although it may not be the primary cause of PD, additional epidemiological, genetic, pharmacological, and imaging evidence support the proposal that inflammatory processes in this specific brain region are crucial for disease progression. Recent in vitro studies, however, have suggested that activation of microglia and subsequently astrocytes via mediators released by injured dopaminergic neurons is involved. However, additional in vivo experiments are needed for a deeper understanding of the mechanisms involved in PD pathogenesis. Further insight on the mechanisms of inflammation in PD will help to further develop alternative therapeutic strategies that will specifically and temporally target inflammatory processes without abrogating the potential benefits derived by neuroinflammation, such as tissue restoration.

The role of the MYD88-dependent pathway in MPTP-induced brain dopaminergic degeneration

Background

Mounting evidence supports a significant role of inflammation in Parkinson's disease (PD) pathophysiology, with several inflammatory pathways being suggested as playing a role in the dopaminergic degeneration seen in humans and animal models of the disease. These include tumor necrosis factor, prostaglandins and oxidative-related stress components. However, the role of innate immunity has not been established in PD.

Methods

Based on the fact that the myeloid differentiation primary response gene (88) (MyD88) is the most common adaptor protein implicated in toll-like receptor (TLR) signaling, critical in the innate immune response, we undertook a study to investigate the potential contribution of this specific pathway to MPTP-induced brain dopaminergic degeneration using MyD88 knock out mice (MyD88-/-), following our observations that the MyD88-dependent pathway was critical for MPTP dopaminergic toxicity in the enteric nervous system. Post-mortem analyses assessing nigrostriatal dopaminergic degeneration and inflammation were performed using HPLC, western blots, autoradiography and immunofluorescence.

Results

Our results demonstrate that MyD88-/- mice are as vulnerable to MPTP-induced dopamine and DOPAC striatal depletion as wild type mice. Furthermore, MyD88-/- mice show similar striatal dopamine transporter and tyrosine hydroxylase loss, as well as dopaminergic cell loss in the substantia nigra pars compacta in response to MPTP. To evaluate the extent of the inflammatory response created by the MPTP regimen utilized, we further performed bioluminescence imaging using TLR2-luc/gfp transgenic mice and microglial density analysis, which revealed a modest brain microglial response following MPTP. This was accompanied by a significant astrocytic reaction in the striatum, which was of similar magnitude both in wild type and MyD88-/- mice.

Conclusions

Our results suggest that subacute MPTP-induced dopaminergic degeneration observed in the central nervous system is MyD88-independent, in contrast to our recent observations that this pathway, in the same cohort of animals, is critical in the loss of dopaminergic neurons in the enteric nervous system.