Alteration of nuclear factor-kappaB pathway promote neuroinflammation depending on the functions of estrogen receptors in substantia nigra after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment

Neuroactive steroids and Parkinson's disease: Review of human and animal studies

The greater prevalence and incidence of Parkinson's disease (PD) in men suggest a beneficial effect of sex hormones. Neuroactive steroids have neuroprotective activities thus offering interesting option for disease-modifying therapy for PD. Neuroactive steroids are also neuromodulators of neurotransmitter systems and may thus help to control PD symptoms and side effect of dopamine medication. Here, we review the effect on sex hormones (estrogen, androgen, progesterone and its metabolites) as well as androstenediol, pregnenolone and dehydroepiandrosterone) in human studies and in animal models of PD. The effect of neuroactive steroids is reviewed by considering sex and hormonal status to help identify specifically for women and men with PD what might be a preventive approach or a symptomatic treatment. PD is a complex disease and the pathogenesis likely involves multiple cellular processes. Thus it might be useful to target different cellular mechanisms that contribute to neuronal loss and neuroactive steroids provide therapeutics options as they have multiple mechanisms of action.

Systems level analysis of sex-dependent gene expression changes in Parkinson's disease

Parkinson's disease (PD) is a heterogeneous disorder, and among the factors which influence the symptom profile, biological sex has been reported to play a significant role. While males have a higher age-adjusted disease incidence and are more frequently affected by muscle rigidity, females present more often with disabling tremors. The molecular mechanisms involved in these differences are still largely unknown, and an improved understanding of the relevant factors may open new avenues for pharmacological disease modification. To help address this challenge, we conducted a meta-analysis of disease-associated molecular sex differences in brain transcriptomics data from case/control studies. Both sex-specific (alteration in only one sex) and sex-dimorphic changes (changes in both sexes, but with opposite direction) were identified. Using further systems level pathway and network analyses, coordinated sex-related alterations were studied. These analyses revealed significant disease-associated sex differences in mitochondrial pathways and highlight specific regulatory factors whose activity changes can explain downstream network alterations, propagated through gene regulatory cascades. Single-cell expression data analyses confirmed the main pathway-level changes observed in bulk transcriptomics data. Overall, our analyses revealed significant sex disparities in PD-associated transcriptomic changes, resulting in coordinated modulations of molecular processes. Among the regulatory factors involved, NR4A2 has already been reported to harbor rare mutations in familial PD and its pharmacological activation confers neuroprotective effects in toxin-induced models of Parkinsonism. Our observations suggest that NR4A2 may warrant further research as a potential adjuvant therapeutic target to address a subset of pathological molecular features of PD that display sex-associated profiles.

Inhibition of BET Protein Function Suppressed the Overactivation of the Canonical NF-κB Signaling Pathway in 6-OHDA-Lesioned Rat Model of Levodopa-Induced Dyskinesia

Background

Neuroinflammation is involved in the mechanisms of levodopa-induced dyskinesia (LID). The canonical NF-κB activation signaling pathway plays a critical role in the neuroinflammation development and BET protein-induced NF-κB-mediated neuroinflammation. The inhibition of the BET protein function has been reported to alleviate LID; however, its association with the canonical NF-κB signaling pathway in the 6-OHDA-lesioned striatum of the LID rat model remains unknown. Accordingly, we identified the status of the canonical NF-κB signaling pathway in the 6-OHDA-lesioned striatum of the LID rat model and whether the anti-dyskinetic effect of the BET inhibitor JQ1 was associated with its suppression on NF-κB-mediated neuroinflammation.

Methods

6-OHDA PD rat models were treated with either L-dopa plus JQ1 or L-dopa alone. L-dopa treatment was given for 2 weeks, and the JQ1 treatment was given for 3 weeks and was initiated a week prior to L-dopa treatment. As a control, the sham rats were treated with JQ1 or Veh for 3 weeks. The ALO AIM assessment and cylinder test were performed during the treatment. Glial activation markers, pro-inflammatory substances, and critical proteins in the canonical NF-κB signaling pathway were tested in the lesioned striatum after the final treatment.

Results

JQ1 effectively alleviated LID without influencing motor improvement. In the lesioned striatum, L-dopa triggered an overactivation of the canonical NF-κB signaling pathway, with an increase in the phospho-IKKα/β, phospho-IκBα, and NF-κB nuclear translocation and its phosphorylation at Ser 536 and Ser 276 sites (p < 0.01 vs. sham group). L-dopa induced an overexpression of the pro-inflammatory substances of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and inducible nitric oxide synthase (iNOS), and the glial activation markers CD68 and GFAP. All the molecular changes were greatly inhibited by JQ1.

Conclusion

L-dopa triggered an overactivation of the canonical NF-κB signaling pathway, leading to an enhanced neuroinflammation response in the 6-OHDA-lesioned striatum of LID rat models. The inhibition of the BET protein function significantly suppressed the activation of the canonical NF-κB signaling pathway in the striatum, alleviating the neuroinflammation response and the severity of LID.

RelB and Neuroinflammation

Neuroinflammation within the central nervous system involves multiple cell types that coordinate their responses by secreting and responding to a plethora of inflammatory mediators. These factors activate multiple signaling cascades to orchestrate initial inflammatory response and subsequent resolution. Activation of NF-κB pathways in several cell types is critical during neuroinflammation. In contrast to the well-studied role of p65 NF-κB during neuroinflammation, the mechanisms of RelB activation in specific cell types and its roles during neuroinflammatory response are less understood. In this review, we summarize the mechanisms of RelB activation in specific cell types of the CNS and the specialized effects this transcription factor exerts during neuroinflammation.

Nuclear factor-kappa B (NF-κB) in pathophysiology of Parkinson disease: Diverse patterns and mechanisms contributing to neurodegeneration

Parkinson's disease (PD), the most common movement disorder, comprises several pathophysiologic mechanisms including misfolded alpha-synuclein aggregation, inflammation, mitochondrial dysfunction, and synaptic loss. Nuclear Factor-Kappa B (NF-κB), as a key regulator of a myriad of cellular reactions, is shown to be involved in such mechanisms associated with PD, and the changes in NF-κB expression is implicated in PD. Alpha-synuclein accumulation, the characteristic feature of PD pathology, is known to trigger NF-κB activation in neurons, thereby propagating apoptosis through several mechanisms. Furthermore, misfolded alpha-synuclein released from degenerated neurons, activates several signaling pathways in glial cells which culminate in activation of NF-κB and production of pro-inflammatory cytokines, thereby aggravating neurodegenerative processes. On the other hand, NF-κB activation, acting as a double-edged sword, can be necessary for survival of neurons. For instance, NF-κB activation is necessary for competent mitochondrial function and deficiency in c-Rel, one of the NF-κB proteins, is known to propagate DA neuron loss via several mechanisms. Despite the dual role of NF-κB in PD, several agents by selectively modifying the mechanisms and pathways associated with NF-κB, can be effective in attenuating DA neuron loss and PD, as reviewed in this paper.

Genetic targeting of astrocytes to combat neurodegenerative disease

Astrocytes, glial cells that interact extensively with neurons and other support cells throughout the central nervous system, have recently come under the spotlight for their potential contribution to, or potential regenerative role in a host of neurodegenerative disorders. It is becoming increasingly clear that astrocytes, in concert with microglial cells, activate intrinsic immunological pathways in the setting of neurodegenerative injury, although the direct and indirect consequences of such activation are still largely unknown. We review the current literature on the astrocyte’s role in several neurodegenerative diseases, as well as highlighting recent advances in genetic manipulation of astrocytes that may prove critical to modulating their response to neurological injury, potentially combatting neurodegenerative damage.

Shaping the Nrf2-ARE-related pathways in Alzheimer's and Parkinson's diseases

A failure in redox homeostasis is a common hallmark of Alzheimer's Disease (AD) and Parkinson's Disease (PD), two age-dependent neurodegenerative disorders (NDD), causing increased oxidative stress, oxidized/damaged biomolecules, altered neuronal function and consequent cell death. Activation of nuclear factor erythroid 2-related factor 2 (Nrf2), a redox-regulated transcription factor, results in upregulation of cytoprotective and antioxidant enzymes/proteins, protecting against oxidative stress. Nrf2 regulation is achieved by various proteins and pathways, at both cytoplasmatic and nuclear level; however, the elaborate network of mechanisms involved in Nrf2 regulation may restrain Nrf2 pathway normal activity. Indeed, altered Nrf2 activity is involved in aging and NDD, such as AD and PD. Therefore, understanding the diversity of Nrf2 control mechanisms and regulatory proteins is of high interest, since more effective NDD therapeutics can be identified. In this review, we first introduce Keap1-Nrf2-ARE structure, function and regulation, with a special focus on the several pathways involved in Nrf2 positive and negative modulation, namely p62, PKC, PI3K/Akt/GSK-3β, NF-kB and p38 MAPK. We then briefly describe the evidences for oxidative stress and Nrf2 pathway deregulation in different stages of NDDs. Finally, we discuss the potential of Nrf2-related pathways as potential therapeutic targets to possibly prevent or slowdown NDD progression.

Acute Neuroinflammatory Response in the Substantia Nigra Pars Compacta of Rats after a Local Injection of Lipopolysaccharide

Models of Parkinson's disease with neurotoxins have shown that microglial activation does not evoke a typical inflammatory response in the substantia nigra, questioning whether neuroinflammation leads to neurodegeneration. To address this issue, the archetypal inflammatory stimulus, lipopolysaccharide (LPS), was injected into the rat substantia nigra. LPS induced fever, sickness behavior, and microglial activation (OX42 immunoreactivity), followed by astrocyte activation and leukocyte infiltration (GFAP and CD45 immunoreactivities). During the acute phase of neuroinflammation, pro- and anti-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-4, and IL-10) responded differentially at mRNA and protein level. Increased NO production and lipid peroxidation occurred at 168 h after LPS injection. At this time, evidence of neurodegeneration could be seen, entailing decreased tyrosine hydroxylase (TH) immunoreactivity, irregular body contour, and prolongation discontinuity of TH⁺ cells, as well as apparent phagocytosis of TH⁺ cells by OX42⁺ cells. Altogether, these results show that LPS evokes a typical inflammatory response in the substantia nigra that is followed by dopaminergic neurodegeneration.

TNFR2 mediated TNF-α signaling and NF-κB activation in hippocampus of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice

1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine (MPTP) -induced neuroinflammation and its impact in hippocampus remain elusive till date. Our present study includes the time dependent changes of inflammatory molecules in mouse hippocampus during MPTP treatment. MPTP treatment increased level of TNF-α, enhanced expression of TNFR2 along with PI3 kinase (PI3K) induced phosphorylation of Akt resulting in persistent nuclear factor-κB (NF-κB) activation. The expressions gradually increased from Day1 post-MPTP treatment, maximally at Day3 post-treatment. MPTP induced translocation of p65 and p52, two subunits of NF-κB family, to nucleus where they had been found to dimerize. Therefore, MPTP induced TNF-α signaling through TNFR2 mediated pathway and recruited p65-p52 dimer in hippocampal nucleus which is reported to have protective effect on hippocampal neurons indicated by unchanged neuronal count in hippocampus in treated groups with respect to control. Our finding suggests that this unique NF-κB dimer plays some role in providing inherent protection to hippocampus during MPTP-treatment.

Neuroprotective Effects of Temsirolimus in Animal Models of Parkinson's Disease

Parkinson's disease (PD) is a disorder caused by degeneration of dopaminergic neurons. At the moment, there is no cure. Recent studies have shown that autophagy may have a protective function against the advance of a number of neurodegenerative diseases. Temsirolimus is an analogue of rapamycin that induces autophagy by inhibiting mammalian target of rapamycin complex 1. For this purpose, in the present study we investigated the neuroprotective effects of temsirolimus (5 mg/kg intraperitoneal) on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced (MPTP) neurotoxicity in in vivo model of PD. At the end of the experiment, brain tissues were processed for histological, immunohistochemical, Western blot, and immunofluorescent analysis. Treatment with temsirolimus significantly ameliorated behavioral deficits, increased the expression of specific markers of PD such as tyrosine hydroxylase, dopamine transporter, as well as decreased the upregulation of α-synuclein in the substantia nigra after MPTP induction. Furthermore, Western blot and immunohistochemistry analysis showed that temsirolimus administration significantly increased autophagy process. In fact, treatment with temsirolimus maintained high Beclin-1, p62, and microtubule-associated protein 1A/1B-light chain 3 expression and inhibited the p70S6K expression. In addition, we showed that temsirolimus has also anti-inflammatory properties as assessed by the significant inhibition of the expression of mitogen-activated protein kinases such as p-JNK, p-p38, and p-ERK, and the restored levels of neurotrophic factor expression such as BDNF and NT-3. On the basis of this evidence, we clearly demonstrate that temsirolimus is able to modulate both the autophagic process and the neuroinflammatory pathway involved in PD, actions which may underlie its neuroprotective effect.

Neuroprotective Effects of Echinacoside on Regulating the Stress-Active p38MAPK and NF-κB p52 Signals in the Mice Model of Parkinson's Disease

Herbal medicines have long been used to treat Parkinson's disease (PD). To systematically analyze the anti-parkinsonian activity of echinacoside (ECH) in a neurotoxic model of PD and provide a future basis for basic and clinical investigations, male C57BL/6 mice were randomized into blank control, PD model and ECH-administration groups. ECH significantly suppressed the dopaminergic neuron loss (P < 0.01) caused by MPTP and maintained dopamine content (P < 0.01) and dopamine metabolite content (P < 0.05) compared with that measured in mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced damage. Additionally, ECH inhibited the activation of microglia and astrocytes in the substantia nigra, which suggested the involvement of neuroinflammation. The relevant cytokines were detected with a Proteome Profiler Array, which confirmed that ECH participated in the regulation of seven cytokines. Given that p38 mitogen-activated protein kinase (p38MAPK) and NF-kappaB (NF-κB) signals are considered to be closely related to neuroninflammation, the gene expression levels of p38MAPK and six NF-κB DNA-binding subunits were assessed. Western blotting analysis showed that both p38MAPK and the NF-κB p52 subunit were upregulated in the MPTP group and that ECH downregulated their expressions. Minocycline was administered as the positive control to inhibit neuroinflammation, and no differences were detected between the minocycline- and ECH-mediated inhibition of the p38MAPK and NF-κB p52 signals. In conclusion, echinacoside is a potential novel orally active compound for regulating neuroinflammation and related signals in Parkinson's disease and may provide a new prospect for clinical treatment.

HNO suppresses LPS-induced inflammation in BV-2 microglial cells via inhibition of NF-κB and p38 MAPK pathways

Both hydrogen sulfide (H2S) and nitric oxide (NO) are important gaseous mediators. We and others previously reported that these two gases react with each other to generate a new mediator, nitroxyl (HNO), and regulate cardiovascular functions. In this study, we demonstrated for the first time that the interaction between the two gases also existed in microglia. The biological functions of HNO in microglial cells were further studied with Angeli's salt (AS), an HNO donor. We found that AS attenuated lipopolysaccharide (LPS)-evoked production of reactive oxygen species (ROS) and pro-inflammatory cytokines (e.g. IL-1β and TNFα) through downregulating the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). HNO significantly reduced the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and the activation of nuclear factor-κB (NF-κB) through suppression of phosphorylation p65 and IκBα. The above effects were abolished by l-cysteine, an HNO scavenger, but were not mimicked by nitrite, another product of AS during generating HNO. A Cys-179-to-Ala mutation in inhibitory κB kinase β (IKKβ) mimicked the effect of HNO on LPS-induced NF-κB activation. Interestingly, AS abolished the inflammation in cells overexpressing WT-IKKβ, but had no significant effect in cells overexpressing C179A-IKKβ. These data suggest that HNO may act on C179 to prevent IKKβ-dependent inflammation. Taken together, our data demonstrated for the first time that H2S interacts with NO to generate HNO in microglial cells. HNO produces anti-inflammatory effects through suppressing the IKKβ dependent NF-κB activation and p38 MAPK pathways.