Manganese exposure facilitates microglial JAK2-STAT3 signaling and consequent secretion of TNF-a and IL-1β to promote neuronal death

Signal Transduction Associated with Mn-induced Neurological Dysfunction

Manganese (Mn) is a heavy metal that occurs widely in nature and has a vital physiological role in growth and development. However, excessive exposure to Mn can cause neurological damage, especially cognitive dysfunction, such as learning disability and memory loss. Numerous studies on the mechanisms of Mn-induced nervous system damage found that this metal targets a variety of metabolic pathways, for example, endoplasmic reticulum stress, apoptosis, neuroinflammation, cellular signaling pathway changes, and neurotransmitter metabolism interference. This article reviews the latest research progress on multiple signaling pathways related to Mn-induced neurological dysfunction.

Regulatory mechanism of miR-20a-5p in neuronal damage and inflammation in lipopolysaccharide-induced BV2 cells and MPTP-HCl-induced Parkinson's disease mice

BACKGROUND

Parkinson's disease (PD) is a prevailing neurodegenerative disorder increasingly affecting the elderly population. The involvement of microRNAs (miRNAs) in PD has been confirmed. We sought to explore the molecular mechanism of miR-20a-5p in PD.

METHODS

Lipopolysaccharide (LPS)-induced BV2 cell model and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP-HCl)-induced PD mouse model were established. miR-20a-5p, inducible nitric oxide synthase (iNOS), interleukin (IL)-6, tumour necrosis factor (TNF)-α, transforming growth factor (TGF)-β1, and IL-10 expression in BV2 cells was examined by reverse transcription - quantitative polymerase chain reaction. Cell viability was assessed by MTT assay. The apoptotic rate and levels of Bcl-2, Bax, cleaved caspase-3, and signal transducer and activator of transmission (STAT)3 were examined by flow cytometry and Western blot. Bioinformatics software predicted the potential binding sites of miR-20a-5p and STAT3. Dual-luciferase experiment verified the binding relationship. Iba1-positive and tyrosine hydroxylase (TH)-positive cell numbers in substantia nigra pars compacta were detected by immunohistochemistry. The effect of miR-20a-5p on motor function in MPTP-induced PD mice was detected by Rota-rod test, Pole test, Traction test and Beam-crossing task.

RESULTS

miR-20a-5p was under-expressed in LPS-induced BV2 cells. Overexpression of miR-20a-5p increased the viability of LPS-induced BV2 cells and reduced apoptosis rates. Moreover, overexpression of miR-20a-5p reduced cleaved caspase-3, Bax, iNOS, IL-6, and TNF-α and increased Bcl-2 and TGF-β1, and IL-10. miR-20a-5p targeted STAT3. STAT3 overexpression partially reversed miR-20a-5p overexpression-mediated effects on LPS-induced BV2 cell viability, apoptosis, and inflammatory responses. miR-20a-5p overexpression inhibited MPTP-induced STAT3 and α-synuclein levels, microglia activation, and inflammatory response, and reduced the loss of TH-positive cells in mice. miR-20a-5p overexpression ameliorated MPTP-induced dyskinesia in PD model mice.

CONCLUSION

miR-20a-5p alleviates neuronal damage and suppresses inflammation by targeting STAT3 in PD.

Anatomical location of injected microglia in different activation states and time course of injury determines survival of retinal ganglion cells after optic nerve crush

Background: Activated microglia release harmful substances to retinal ganglion cells (RGCs), but may also benefit by removing cellular debris and secreting neurotrophic factors. These paradoxical roles remain controversial because the nature and time-course of the injury that defines their role is unknown. The aim of this study was to determine if pharmacological manipulation of microglia to acquire a pro-inflammatory or pro-survival phenotype will exacerbate or enhance neuronal survival after injury.Material and methods: Treated HAP I (highly aggressively proliferating immortalized) microglia were injected into the vitreous or tail vein (T V) of female Sprague-Dawley rats. Retinas were examined at 4-14 days following optic nerve crush (ONC) and the number of surviving RGCs was determined.Results: Injection of untreated HAP I cells resulted in the greater loss of RGCs early after ONC when injected into the vitreous and later after ONC when injected into the T V. LP S activated HAP I cells injected into the vitreous resulted in greater RGC loss with and without injury. When injected into the T V with ONC there was no loss of RGCs 4 days after ONC but greater loss afterwards. Minocycline treated HAP I cells injected into the vitreous resulted in greater RGC survival than untreated HAP I cells. However, when injected into the T V with ONC there was greater loss of RGCs. These results suggest that optic nerve signals attract extrinsic microglia to the retina, resulting in a proinflammatory response.Conclusion: Neuroprotection or cytotoxicity of microglia depends on the type of activation, time course of the injury, and if they act on the axon or cell body.

Activation of alpha-7 nicotinic acetylcholine receptor by tropisetron mitigates 3-nitropropionic acid-induced Huntington's disease in rats: Role of PI3K/Akt and JAK2/NF-κB signaling pathways

Huntington's disease (HD) is an inheritable autosomal-dominant disorder that targets mainly the striatum. 3-Nitropropionic acid (3-NP) induces obvious deleterious behavioral, neurochemical, and histological effects similar to the symptoms of HD. Our study aimed to examine the neuroprotective activity of tropisetron, an alpha-7 neuronal nicotinic acetylcholine receptor (α-7nAChR) agonist, against neurotoxic events associated with 3-NP-induced HD in rats. Forty-eight rats were randomly allocated into four groups. Group I received normal saline, while Groups II, III and IV received 3-NP for 2 weeks. In addition, Group III and IV were treated with tropisetron 1 h after 3-NP administration. Meanwhile, Group IV received methyllycaconitine (MLA), an α-7nAChR antagonist, 30 min before tropisetron administration. Treatment with tropisetron improved motor deficits as confirmed by the behavioral tests and restored normal histopathological features of the striatum. Moreover, tropisetron showed an anti-oxidant activity via increasing the activities of SDH and HO-1 as well as Nrf2 expression along with reducing MDA level. Tropisetron also markedly upregulated the protein expression of p-PI3K and p-Akt which in turn hampered JAK2/NF-κB inflammatory cascade. In addition, tropisetron showed an anti-apoptotic activity through boosting the expression of Bcl-2 and reducing Bax expression and caspase-3 level. Interestingly, all the aforementioned effects of tropisetron were blocked by pre-administration of MLA, which confirms that such neuroprotective effects are mediated via activating of α-7nAChR. In conclusion, tropisetron showed a neuroprotective activity against 3-NP-induced HD via activating PI3K/Akt signaling and suppressing JAK2/NF-κB inflammatory axis. Thus, repositioning of tropisetron could represent a promising therapeutic strategy in management of HD.

Heavy Metal Mediated Progressive Degeneration and Its Noxious Effects on Brain Microenvironment

Heavy metals, including lead (Pb), cadmium (Cd), arsenic (As), cobalt (Co), copper (Cu), manganese (Mn), zinc (Zn), and others, have a significant impact on the development and progression of neurodegenerative diseases in the human brain. This comprehensive review aims to consolidate the recent research on the harmful effects of different metals on specific brain cells such as neurons, microglia, astrocytes, and oligodendrocytes. Understanding the potential influence of these metals in neurodegeneration is crucial for effectively combating the ongoing advancement of these diseases. Metal-induced neurodegeneration involves molecular mechanisms such as apoptosis induction, dysregulation of metabolic and signaling pathways, metal imbalance, oxidative stress, loss of synaptic transmission, pathogenic peptide aggregation, and neuroinflammation. This review provides valuable insights by compiling the supportive evidence from recent research findings. Additionally, we briefly discuss the modes of action of natural neuroprotective compounds. While this comprehensive review aims to consolidate the recent research on the harmful effects of various metals on specific brain cells, it may not cover all studies and findings related to metal-induced neurodegeneration. Studies that are done using bioinformatics tools, microRNAs, long non-coding RNAs, emerging disease models, and studies based on the modes of exposure to toxic metals are a future prospect to be explored.

Neuroprotective Effect of Lithospermum officinale Callus Extract on Inflamed Primary Microglial Cells

BACKGROUND

Plants that have therapeutic features for humans or animals are commonly referred to as "medicinal plants". They produce secondary metabolites with antioxidant, antimicrobial and/or anti-cancer effects. Lithospermum officinale, known as European stone seed, is a famous medicinal herb. However, due to the pyrrolizidine alkaloids (PzAl) in the root extract of L.officinal, there are therapeutic limitations to this herb.

OBJECTIVE

This research was devoted to the evaluation of the anti-inflammatory capacity of methanolic extracts of L. officinale callus (LoE) (fresh cells) on rat microglial cells, the immune cells of the Central Nervous System, which play an essential role in the responses to neuroinflammation.

METHODS

Primary microglia were obtained from neonatal Wistar rats (1 to 3-days old), and then treated with various concentration of CfA and methanolic extracts of 17 and 31-day-old L. officinale callus before LPS-stimulation. In addition to HPLC analysis of the extracts, viability, nitric oxide production, and evaluation of pro-inflammatory genes and cytokines in the inflamed microglia were investigated by MTT, Griess methos, qrt-PCR, and ELISA.

RESULTS

Methanolic extract of the 17-day-old callus of L. officinale exhibited anti-inflammatory effects on LPS-stimulated microglial cells much higher than observed for CfA. The data were further supported by the decreased expression of Nos2, Tnf-α, and Cox-2 mRNA and the suppression of TNF-α and IL-1β release in the activated microglial cells pretreated with the effective dose of LoE (0.8 mg mL-1).

CONCLUSION

It was assumed that the better anti-neuroinflammatory performance of LoE than CfA in LPS-activated primary microglia could be a result of the synergism of the components of the extract and the lipophilic nature of RsA as the main phenolic acid of LoE. Considering that LoE shows a high antioxidant capacity and lacks PzAl, it is anticipated that LoE extract might be considered a reliable substitute to play a key role in the preparation of neuroprotective pharmaceutical formulas, which require in vivo research and further experiments.

Signaling Pathways Involved in Manganese-Induced Neurotoxicity

Manganese (Mn) is an essential trace element, but insufficient or excessive bodily amounts can induce neurotoxicity. Mn can directly increase neuronal insulin and activate insulin-like growth factor (IGF) receptors. As an important cofactor, Mn regulates signaling pathways involved in various enzymes. The IGF signaling pathway plays a protective role in the neurotoxicity of Mn, reducing apoptosis in neurons and motor deficits by regulating its downstream protein kinase B (Akt), mitogen-activated protein kinase (MAPK), and mammalian target of rapamycin (mTOR). In recent years, some new mechanisms related to neuroinflammation have been shown to also play an important role in Mn-induced neurotoxicity. For example, DNA-sensing receptor cyclic GMP-AMP synthase (cCAS) and its downstream signal efficient interferon gene stimulator (STING), NOD-like receptor family pyrin domain containing 3(NLRP3)-pro-caspase1, cleaves to the active form capase1 (CASP1), nuclear factor κB (NF-κB), sirtuin (SIRT), and Janus kinase (JAK) and signal transducers and activators of the transcription (STAT) signaling pathway. Moreover, autophagy, as an important downstream protein degradation pathway, determines the fate of neurons and is regulated by these upstream signals. Interestingly, the role of autophagy in Mn-induced neurotoxicity is bidirectional. This review summarizes the molecular signaling pathways of Mn-induced neurotoxicity, providing insight for further understanding of the mechanisms of Mn.

Microglia Signaling Pathway Reporters Unveiled Manganese Activation of the Interferon/STAT1 Pathway and Its Mitigation by Flavonoids

Neuroinflammatory responses to neurotoxic manganese (Mn) in CNS have been associated with the Mn-induced Parkinson-like syndromes. However, the framework of molecular mechanisms contributing to manganism is still unclear. Using an in vitro neuroinflammation model based on the insulated signaling pathway reporter transposon constructs stably transfected into a murine BV-2 microglia line, we tested effects of manganese (II) together with a set of 12 metal salts on the transcriptional activities of the NF-κB, activator protein-1 (AP-1), signal transducer and activator of transcription 1 (STAT1), STAT1/STAT2, STAT3, Nrf2, and metal-responsive transcription factor-1 (MTF-1) via luciferase assay, while concatenated destabilized green fluorescent protein expression provided for simultaneous evaluation of cellular viability. This experiment revealed specific and strong responses to manganese (II) in reporters of the type I and type II interferon-induced signaling pathways, while weaker activation of the NF-κB in the microglia was detected upon treatment of cells with Mn(II) and Ba(II). There was a similarity between Mn(II) and interferon-γ in the temporal STAT1 activation profile and in their antagonism to bacterial LPS. Sixty-four natural and synthetic flavonoids differentially affected both cytotoxicity and the pro-inflammatory activity of Mn (II) in the microglia. Whereas flavan-3-ols, flavanones, flavones, and flavonols were cytoprotective, isoflavones enhanced the cytotoxicity of Mn(II). Furthermore, about half of the tested flavonoids at 10-50 μM could attenuate both basal and 100-200 μM Mn(II)-induced activity at the gamma-interferon activated DNA sequence (GAS) in the cells, suggesting no critical roles for the metal chelation or antioxidant activity in the protective potential of flavonoids against manganese in microglia. In summary, results of the study identified Mn as a specific elicitor of the interferon-dependent pathways that can be mitigated by dietary polyphenols.

SIRT1/FOXO3-mediated autophagy signaling involved in manganese-induced neuroinflammation in microglia

Manganese (Mn), as one of the environmental risk factors for Parkinson's disease (PD), has been widely studied. Though autophagy dysfunction and neuroinflammation mainly are responsible for the causative issue of Mn neurotoxicity, the molecular mechanism of parkinsonism caused by Mn has not been explored clearly. The results of in vivo and in vitro experiments showed that overexposure to Mn caused neuroinflammation impairment and autophagy dysfunction, accompanied by the increase of IL-1β, IL-6, and TNF-α mRNA expression, and nerve cell apoptosis, microglia cell activation, NF-κB activation, poor neurobehavior performance. This is due to Mn-induced the downregulation of SIRT1. Upregulation of SIRT1 in vivo and in vitro could alleviate Mn-induced autophagy dysfunction and neuroinflammation, yet these beneficial effects were abolished following 3-MA administration. Furthermore, we found that Mn interfered with the acetylation of FOXO3 by SIRT1 in BV2 cells, leading to a decrease in the nuclear translocation of FOXO3, and its binding of LC3B promoter and transcription activity. This could be antagonized by the upregulation of SIRT1. Finally, it is proved that SIRT1/FOXO3-LC3B autophagy signaling involves in Mn-induced neuroinflammation impairment.

Simultaneous effects of aluminum exposure on the homeostasis of essential metal content in rat brain and perturbation of gut microbiota

The theory of the brain-gut axis has confirmed that gut microbiota and metabolites are involved in the progression of neurodegenerative diseases through multiple pathways. However, few studies have highlighted the role of gut microbiota in cognitive impairment induced by aluminum (Al) exposure and its correlations with the homeostasis of essential metal content in the brain. To explore the relationship between alterations in the content of essential metals in the brain and relative abundance changes in gut microbiota induced by Al exposure, the Al, zinc (Zn), copper (Cu), iron (Fe), chromium (Cr), manganese (Mn), and cobalt (Co) content level in the hippocampus, olfactory bulb, and midbrain tissue were measured by inductively coupled plasma mass spectrometry (ICP-MS) methods after Al maltolate was intraperitoneally injected every other day for exposed groups. Then the unsupervised principal coordinates analysis (PCoA) and linear discriminant analysis effect size (LEfSe) were used to analyze the relative abundance of the gut microbiota community and the structure of the gut microbiome. Finally, the correlations between gut microbiota composition and essential metal content in the different exposure groups were explored by using the Pearson correlation coefficient method. Based on the results, we indicated that the content of Al in the hippocampus, olfactory bulb, and midbrain tissue was increased and then decreased with the increasing exposure duration, with peaks occurring between 14 and 30 days. Concomitantly, Al-exposure decreased the Zn, Fe, and Mn levels in these tissues. 16 S rRNA gene sequencing results indicated that significant differences in the intestinal microbial community structure at the phylum, family, and genus levels were found in the Day 90 exposed group compared with the Day 7 exposed group. Ten enriched species in the exposed group were identified as markers at the three levels. Furthermore, ten bacteria at the genus level were identified to have a significantly strong correlation (r = 0.70-0.90) with Fe, Zn, Mn, and Co.

Preventive treatment with sodium para-aminosalicylic acid inhibits manganese-induced apoptosis and inflammation via the MAPK pathway in rat thalamus

Excessive exposure to manganese (Mn) may lead to neurotoxicity, referred to as manganism. In several studies, sodium para-aminosalicylic acid (PAS-Na) has shown efficacy against Mn-induced neurodegeneration by attenuating the neuroinflammatory response. The present study investigated the effect of Mn on inflammation and apoptosis in the rat thalamus, as well as the underlying mechanism of the PAS-Na protective effect. The study consisted of sub-acute (Mn treatment for 4 weeks) and sub-chronic (Mn and PAS-Na treatment for 8 weeks) experiments. In the sub-chronic experiments, pro-inflammatory cytokines, namely tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and cyclooxygenase 2 (COX-2) were significantly increased in the Mn-exposed group compared to the control II. PAS-Na treatment led to a significant reduction in the Mn-induced neuroinflammation by inhibiting IL-1β and COX-2 mRNA expression and reducing IL-1β secretion and JNK/p38 MAPK pathway activity. Furthermore, immunohistochemical analysis showed that the expression of caspase-3 was significantly increased in both the sub-acute and sub-chronic experimental paradigms concomitant with a significant decrease in B-cell lymphoma 2 (Bcl-2) in the thalamus of Mn-treated rats. PAS-Na also decreased the expression levels of several apoptotic markers downstream of the MAPK pathway, including Bcl-2/Bax and caspase-3, while up-regulating anti-apoptotic Bcl-2 proteins. In conclusion, Mn exposure led to inflammation in the rat thalamus concomitant with apoptosis, which was mediated via the MAPK signaling pathway. PAS-Na treatment antagonized effectively Mn-induced neurotoxicity by inhibiting the MAPK activity in the same brain region.

The cGAS-STING-mediated NLRP3 inflammasome is involved in the neurotoxicity induced by manganese exposure

Heavy metal pollution has become a global health challenge. Exposure to heavy metals represents a major health risk. Manganese (Mn) is an essential trace element but also an environmental pollutant. Mn exposure can induce neurotoxicity and lead to neurodegenerative disease. Inflammation and Tau hyperphosphorylation are prominent hallmarks of neurodegenerative diseases induced by Mn exposure. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway can induce powerful innate immune defense programmes and has emerged as a key mediator of inflammation. In recent years, Mn²⁺ has been found to be the second activator of the cGAS-STING pathway in addition to double-stranded DNA (dsDNA). NLRP3 activation is upstream of Tau pathology, and NLRP3 activation induces Tau hyperphosphorylation and aggregation. Mn exposure-induced neurotoxicity may be associated with excessive activation of the cGAS-STING signaling pathway, leading to inflammation. The cGAS-STING/NLRP3 axis may be a promising option for revealing the mechanisms of neurotoxicity of Mn exposure in the future.

Associations of Heavy Metals with Activities of Daily Living Disability: An Epigenome-Wide View of DNA Methylation and Mediation Analysis

BACKGROUND

Exposure to heavy metals has been reported to be associated with multiple diseases. However, direct associations and potential mechanisms of heavy metals with physical disability remain unclear.

OBJECTIVES

We aimed to quantify associations of heavy metals with physical disability and further explore the potential mechanisms of DNA methylation on the genome scale.

METHODS

A cross-sectional study of 4,391 older adults was conducted and activities of daily living (ADL) disability were identified using a 14-item scale questionnaire including basic and instrumental activities to assess the presence of disability (yes or no) rated on a scale of dependence. Odds ratios (ORs) and 95% confidence intervals (CI) were estimated to quantify associations between heavy metals and ADL disability prevalence using multivariate logistic regression and Bayesian kernel machine regression (BKMR) models. Whole blood-derived DNA methylation was measured using the HumanMethylationEPIC BeadChip array. An ADL disability-related epigenome-wide DNA methylation association study (EWAS) was performed among 212 sex-matched ADL disability cases and controls, and mediation analysis was further applied to explore potential mediators of DNA methylation.

RESULTS

Each 1-standard deviation (SD) higher difference in log10-transformed manganese, copper, arsenic, and cadmium level was significantly associated with a 14% (95% CI: 1.05, 1.24), 16% (95% CI:1.07, 1.26), 22% (95% CI:1.13, 1.33), and 15% (95% CI:1.06, 1.26) higher odds of ADL disability, which remained significant in the multiple-metal and BKMR models. A total of 85 differential DNA methylation sites were identified to be associated with ADL disability prevalence, among which methylation level at cg220000984 and cg23012519 (annotated to IRGM and PKP3) mediated 31.0% and 31.2% of manganese-associated ADL disability prevalence, cg06723863 (annotated to ESRP2) mediated 32.4% of copper-associated ADL disability prevalence, cg24433124 (nearest to IER3) mediated 15.8% of arsenic-associated ADL disability prevalence, and cg07905190 and cg17485717 (annotated to FREM1 and TCP11L1) mediated 21.5% and 30.5% of cadmium-associated ADL disability prevalence (all p<0.05).

DISCUSSION

Our findings suggested that heavy metals contributed to higher prevalence of ADL disability and that locus-specific DNA methylation are partial mediators, providing potential biomarkers for further cellular mechanism studies. https://doi.org/10.1289/EHP10602.

YTHDF1 Negatively Regulates Treponema pallidum-Induced Inflammation in THP-1 Macrophages by Promoting SOCS3 Translation in an m6A-Dependent Manner

Background

Previous studies have confirmed that the bacterium Treponema pallidum (TP) or its proteins provide signals to macrophages that induce an inflammatory response; however, little is known about the negative regulation of this macrophage-mediated inflammatory response during syphilis infection or the underlying mechanism. Recent evidence suggests the role of the RNA modification, N⁶-adenosine methylation (m6A), in regulating the inflammatory response and pathogen-host cell interactions. Therefore, we hypothesized that m6A plays a role in the regulation of the inflammatory response in macrophages exposed to TP.

Methods

We first assessed m6A levels in TP-infected macrophages differentiated from the human monocyte cell line THP-1. The binding and interaction between the m6A "writer" methyltransferase-like 3 (METTL3) or the m6A "reader" YT521-B homology (YTH) domain-containing protein YTHDF1 and the suppressor of cytokine signaling 3 (SOCS3), as a major regulator of the inflammatory response, were explored in differentiated TP-infected THP-1 cells as well as in secondary syphilitic lesions from patients. The mechanisms by which YTHDF1 and SOCS3 regulate the inflammatory response in macrophages were assessed.

Results and Conclusion

After macrophages were stimulated by TP, YTHDF1 was upregulated in the cells. YTHDF1 was also upregulated in the syphilitic lesions compared to adjacent tissue in patients. YTHDF1 recognizes and binds to the m6A methylation site of SOCS3 mRNA, consequently promoting its translation, thereby inhibiting the JAK2/STAT3 pathway, and reducing the secretion of inflammatory factors, which results in anti-inflammatory regulation. This study provides the first demonstration of the role of m6A methylation in the pathological process of syphilis and further offers new insight into the pathogenesis of TP infection.

The α7 nAChR allosteric modulator PNU-120596 amends neuroinflammatory and motor consequences of parkinsonism in rats: Role of JAK2/NF-κB/GSk3β/ TNF-α pathway

Parkinson's disease (PD) is the second most common neurodegenerative disorder and a leading cause of disability. The current gold standard for PD treatment, L-Dopa, has limited clinical efficacy and multiple side effects. Evidence suggests that activation of α7 nicotinic acetylcholine receptors (α7nAChRs) abrogates neuronal and inflammatory insults. Here we tested whether PNU-120596 (PNU), a type II positive allosteric modulator of α7 nAChR, has a critical role in regulating motor dysfunction and neuroinflammation correlated with the associated PD dysfunction. Neuroprotective mechanisms were investigated through neurobehavioral, molecular, histopathological, and immunohistochemical studies. PNU reversed motor incoordination and hypokinesia induced via the intrastriatal injection of 6-hydroxydopamine and manifested by lower falling latency in the rotarod test, short ambulation time and low rearing incidence in open field test. Tyrosine hydroxylase immunostaining showed a significant restoration of dopaminergic neurons following PNU treatment, in addition to histopathological restoration in nigrostriatal tissues. PNU halted striatal neuroinflammation manifested as a suppressed expression of JAK2/NF-κB/GSk3β accompanied by a parallel decline in the protein expression of TNF-α in nigrostriatal tissue denoting the modulator anti-inflammatory capacity. Moreover, the protective effects of PNU were partially reversed by the α7 nAChR antagonist, methyllycaconitine, indicating the role of α7 nAChR modulation in the mechanism of action of PNU. This is the first study to reveal the positive effects of PNU-120596 on motor derangements of PD via JAK2/NF-κB/GSk3β/ TNF-α neuroinflammatory pathways, which could offer a potential therapeutic strategy for PD.

JAK2/STAT3 pathway regulates microglia polarization involved in hippocampal inflammatory damage due to acute paraquat exposure

OBJECTIVE

To explore the effects of acute paraquat (PQ) exposure on the phenotypic polarization of hippocampal microglia and its mechanism.

METHODS

An acute PQ exposure rat model was established. Male SD rats were exposed to 0, 5, 25, and 50 mg/kg PQ, and brain hippocampal tissue was collected after 1, 3, and 7 days of exposure, respectively. Hippocampal pathological changes were examined by H&E staining, and immunohistochemistry (IHC) was used to detect changes in the number of Iba-1-positive cells, the average number of endpoints, and the average process length. The protein expression of Iba-1 was detected by western blotting. BV-2 microglia were treated with 0, 0.01, 0.025, 0.05, or 0.1 μmol/L PQ for 24 h. ELISA and western blotting assays were performed to detect the expression of TNF-α and IL-1β in vivo and in vitro. The M1 microglia marker iNOS, the M2 microglia marker Arg-1, and the p-JAK2 and p-STAT3 protein were detected by western blotting. JAK2/STAT3 pathway activation role in regulating microglia phenotypic polarization was further validated in vivo and in vitro by JAK2-specific inhibitor AG490 administration.

RESULTS

After acute PQ exposure, hippocampal neurons showed pathological changes such as loose arrangement and nuclear pyknosis, the number of Iba-1 positive cells and the expression of Iba-1 protein increased, and the average number of endpoints and average process length of microglia decreased. Histological examination revealed that compared with the control group, in the 50 mg/kg PQ group on the 3rd and 7th day, the expression of TNF-α, IL-1β, and iNOS significantly increased, while that of Arg-1 significantly decreased. p-JAK2 and p-STAT3 expression significantly increased in the 50 mg/kg PQ group on the 1st, 3rd, and 7th day. In vitro, compared with the control group, the expression of TNF-α, IL-1β, iNOS, p-JAK2, and p-STAT3 significantly increased, while Arg-1 expression was significantly reduced in the 0.025, 0.05, and 0.1 μmol/L PQ groups. After AG490 administration, the expression levels of p-JAK2, p-STAT3, iNOS, TNF-α, and IL-1β in the AG490 +PQ group were significantly inhibited in vivo and in vitro compared with the PQ-only group. On the contrary, Arg-1 expression was significantly increased.

CONCLUSION

Our results suggest that acute PQ exposure may induce M1-type polarization of hippocampal microglia by activating the JAK2/STAT3 pathway, which in turn releases pro-inflammatory factors such as TNF-α and IL-1β, leading to hippocampal inflammatory damage.

Echinacoside Protects Dopaminergic Neurons Through Regulating IL-6/JAK2/STAT3 Pathway in Parkinson’s Disease Model

Echinacoside (ECH), the major active constituent of Cistanche deserticola, was found to exert neuroprotection through neurotrophic and anti-inflammatory functions in Parkinson’s disease (PD) models. However, a clear intermediate molecule or pathway that unifies these two effects has to be found. In this study, our results demonstrate that ECH can protect DA neurons in PD mice with Western blot and immunohistochemistry staining. The quantitative real-time polymerase chain reaction was adapted to confirm its anti-inflammatory function with decreased cytokines (interleukin- (IL-) 6, IL-1β, and TNF-α) in PD mice and LPS-induced BV2 cells. Further studies found that ECH inhibited the IL-6/JAK2/STAT3 pathway and decreased phosphorylation of STAT3 on tyr705 by Western blot. It can also increase p-STAT3 (ser727) and brain-derived neurotrophic factor (BDNF) expression in PD mice and LPS-induced BV2 cells. This study revealed that ECH exerts neurotrophic and anti-inflammatory effects by regulating the IL-6/JAK2/STAT3 pathway and the phosphorylation of STAT3, promoting the mutually beneficial influence of the two effects to maximize its neuroprotective function.

Study on the effect of sevoflurane on the cognitive function of aged rats based on the activation of cortical microglia

Postoperative cognitive dysfunction (POCD) is a common clinical manifestation that is a severe complication characterized by decreased learning ability and deterioration of memory following anesthesia and surgery. However, the precise mechanisms of POCD are not completely understood. Rats were divided into blank control group (Con, n = 12) and sevoflurane group (Sev, n = 12). Morris water maze test was performed to evaluate the ability of learning and memory in two groups of rats; immunohistochemical staining was used to detect the expression of ion calcium-binding adaptor molecule-1 (Iba-1) in rat prefrontal cortex (PFC); Western blot analysis was applied respectively to investigate Iba-1, inducible nitric oxide synthase (iNOS), arginase-1 (ARG1), inflammatory cytokines interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) expression; The expression of iNOS, ARG1, IL-1β, and TNF-α in sera of rats was detected by enzyme-linked immunosorbent assay. We found that sevoflurane induced learning and memory impairment assessed by morris water maze test, anesthesia up-regulated the expression of iNOS, IL-1β and TNF-α inflammasome in microglia, as indicated by increased activation of Iba-1 and reduced the level of ARG1 in the PFC. We conclude that the cognitive function of rats after inhaling anesthesia was likely associated with M1/M2 polarization of microglia, which was triggered by sevoflurane.

TRPV4-induced Müller cell gliosis and TNF-α elevation-mediated retinal ganglion cell apoptosis in glaucomatous rats via JAK2/STAT3/NF-κB pathway

Background

Glaucoma, the leading cause of irreversible blindness worldwide, is a type of retinal disease characterized by the selective death of retinal ganglion cells (RGCs). However, the pathogenesis of glaucoma has not been fully elucidated. Transient receptor potential vanilloid 4 (TRPV4) is a pressure-sensitive and calcium-permeable cation channel. TRPV4 is widely distributed in the retina and its sustained activation leads to RGC death; indicating that TRPV4 may be a possible target for glaucoma treatment. Here, we investigated the effects of TRPV4 on RGC apoptosis in a rat model of chronic ocular hypertension (COH), then examined the mechanism underlying these effects.

Methods

The COH model was established by injection of micro-magnetic beads into the anterior chamber of adult male rats. The expression levels of TRPV4, glial fibrillary acidic protein, and inflammatory factors were assessed by immunohistochemistry and immunoblotting. RGC apoptosis and visual dysfunction were evaluated by TUNEL assay and photopic negative response. Functional expression of TRPV4 was examined by electrophysiology and calcium imaging. Real-time polymerase chain reaction and immunoblotting were employed to investigate the molecular mechanism underlying the effects of TRPV4 on tumor necrosis factor-α (TNF-α) release.

Results

We found that TRPV4 played an essential role in glaucoma, such that high levels of TRPV4 expression were associated with elevated intraocular pressure. Furthermore, TRPV4 activation was involved in glaucoma-induced RGC apoptosis and RGC-related reductions in visual function. Mechanistic investigation demonstrated that TRPV4 activation led to enhanced Müller cell gliosis and TNF-α release via the JAK2/STAT3/NF-kB pathway, while TRPV4 inhibition could reverse these effects. Finally, TRPV4 activation could lead to elevated expression of TNF receptor 1 in RGCs, while inhibition of TNF-α could reduce TRPV4-mediated RGC apoptosis.

Conclusions

TRPV4 activation induces Müller cell gliosis and TNF-α elevation via the JAK2/STAT3/NF-κB pathway, which may exacerbate RGC apoptosis in glaucoma; these results suggest that TRPV4 can serve as a therapeutic target in glaucoma treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02315-8.

Manganese exposure causes movement deficit and changes in the protein profile of the external globus pallidus in Sprague Dawley rats

Manganese (Mn) is required for normal brain development and function. Excess Mn may trigger a parkinsonian movement disorder but the underlying mechanisms are incompletely understood. We explored changes in the brain proteomic profile and movement behavior of adult Sprague Dawley (SD) rats systemically treated with or without 1.0 mg/mL MnCl₂ for 3 months. Mn treatment significantly increased the concentration of protein-bound Mn in the external globus pallidus (GP), as demonstrated by inductively coupled plasma mass spectrometry. Behavioral study showed that Mn treatment induced movement deficits, especially of skilled movement. Proteome analysis by two-dimensional fluorescence difference gel electrophoresis coupled with mass spectrometry revealed 13 differentially expressed proteins in the GP of Mn-treated versus Mn-untreated SD rats. The differentially expressed proteins were mostly involved in glycolysis, metabolic pathways, and response to hypoxia. Selected pathway class analysis of differentially expressed GP proteins, which included phosphoglycerate mutase 1 (PGAM1), primarily identified enrichment in glycolytic process and innate immune response. In conclusion, perturbation of brain energy production and innate immune response, in which PGAM1 has key roles, may contribute to the movement disorder associated with Mn neurotoxicity.

Critical Involvement of Glial Cells in Manganese Neurotoxicity

Over the years, most of the research concerning manganese exposure was restricted to the toxicity of neuronal cells. Manganese is an essential trace element that in high doses exerts neurotoxic effects. However, in the last two decades, efforts have shifted toward a more comprehensive approach that takes into account the involvement of glial cells in the development of neurotoxicity as a brain insult. Glial cells provide structural, trophic, and metabolic support to neurons. Nevertheless, these cells play an active role in adult neurogenesis, regulation of synaptogenesis, and synaptic plasticity. Disturbances in glial cell function can lead to neurological disorders, including neurodegenerative diseases. This review highlights the pivotal role that glial cells have in manganese-induced neurotoxicity as well as the most sounding mechanisms involved in the development of this phenomenon.

Does intermittent fasting associated with aerobic training influence parameters related to the gut-brain axis of Wistar rats?

BACKGROUND

Intermittent fasting (IF) and aerobic training have demonstrated beneficial effects on intestinal microbiota composition, but little is known about benefits to the brain through the gut-brain axis. The present study aimed to evaluate gut-brain axis parameters in Wistar rats submitted to IF associated or not with aerobic training.

METHODS

Male rats were evaluated for training performance and then randomized into 4 groups of ten: sedentary control (SC), trained control (TC), sedentary intermittent fasting (SIF), and trained intermittent fasting (TIF), and evaluated during four weeks.

RESULTS

The adiposity index was similar among the TC (2.15±0.43%), SIF (1.98±0.69%) and TIF (1.86±0.51%) groups, and differed from SC (2.98±0.80%). TIF had lower counts of lactic acid bacteria, while SIF had higher counts of Bifidobacterium and Enterococcus. TIF had the highest amount of formic acid in faeces (44.44±2.40 μmol/g) and lowest amount of succinic acid in the gut (0.38±0.00 μmol/g), while SIF had the highest propionic acid amount in the faeces (802.80±00.33 μmol/g) and the lowest amount of lactic acid in the gut (0.85±0.00 μmol/g). TIF demonstrated a tendency towards an anxiolytic effect and SIF showed potential antidepressant effect. IF caused different brain and intestinal injuries. TIF rats presented a diffuse and intense marking of IL-1β in the hippocampus.

CONCLUSION

IF and aerobic exercise, associated or not, can modulate parameters related to the gut-brain axis of Wistar rats, and some benefits may be related to the amounts of organic acids.

Effects of manganese on microglia M1/M2 polarization and SIRT1-mediated transcription of STAT3-dependent genes in mouse

Overexposure to manganese (Mn) can lead to neurological diseases, characterized by behavioral and motor impairments. Microglia-mediated neuroinflammation is involved in the pathogenesis and progression of neurodegenerative diseases. Microglial M1 and M2 phenotypes play pro-inflammatory and anti-inflammatory roles, respectively, in response to microenvironmental disturbances. Silent information regulator (SIRT1) has been demonstrated to play an important role in the neuroinflammatory response by deacetylating various transcription factors, such as proliferator-activated receptor γ coactivator 1α (PGC-1α), nuclear factor kappa B (NF-κB), and signal transducer and activator of transcription 3 (STAT3). In addition, PGC-1α and STAT3 have been implicated in microglial polarization and inflammatory response. In this study, Mn exposure (50, 100, 200 μmol/kg) induced neuroinflammatory injury and interfered with microglial M1/M2 polarization in mice, as indicated by the upregulated expression of M1 polarization marker mRNA (IL-1β, IL-6, TNF-α, and iNOS), whereas changes in M2 polarization markers (IL-4, TGF-β, and Arg1) varied, with some increasing and some decreasing, in response to increasing Mn doses, which was consistent with the flow cytometry results used to detect the percentages of each microglial type. We found that Mn could downregulate SIRT1 expression and activate NF-κB signaling. Following mice in the 200 μmol/kg Mn treatment, STAT3 and PGC-1α levels in the nuclear fraction both significantly decreased, and the interaction between the proteins decreased, affecting the transcription of STAT3-mediated genes. These findings provide new insights regarding the role played by Mn neurotoxicity in the suppression of neuroinflammation through the regulation of microglial polarization.

Sodium P-aminosalicylic Acid Inhibits Manganese-Induced Neuroinflammation in BV2 Microglial Cells via NLRP3-CASP1 Inflammasome Pathway

BACKGROUND

Sodium p-aminosalicylic acid (PAS-Na) was reported to exhibit anti-inflammatory effect in the nervous system. However, the mechanism by which PAS-Na exhibits anti-inflammatory effects on manganese (Mn)-stimulated BV2 microglia cells remains unclear. Thus, this study investigated the role of PAS-Na in Mn-stimulated BV2 microglial cells.

METHODS

Microglia-like BV2 were treated with MnCl₂ with or without the non-steroidal anti-inflammatory drug PAS-Na for 12 or 24 h to examine cell viability using MTT; for 24 or 48 h to examine levels of NLRP3, CASP1, IL-1β, and IL-18 mRNA using Real-Time quantitative PCR; for 48 h to examine levels of NLRP3 and CASP1 inflammasomes, measured by western blot analysis; and for 48 h to examine levels of inflammatory cytokines, measured by enzyme-linked immunosorbent assay.

RESULTS

The MTT assay showed that PAS-Na produced significant neuroprotective effect by preventing Mn-induced inflammation in BV2 microglial cells. PAS-Na significantly concentration and time dependently inhibited Mn-induced production of NLRP3, CASP1, IL-1β, and IL-18.

CONCLUSION

Taken together, our results suggest that PAS-Na exerts anti-inflammatory effects in Mn-stimulated BV2 microglial cells via downregulation of NLRP3, CASP1, IL-1β, and I L-18. Furthermore, a high concentration and prolonged PAS-Na treatment appear necessary for its therapeutic efficacy. Taken together, we conclude that PAS-Na affords therapeutic efficacy in mitigating neurological conditions associated with neuroinflammation.

Revisiting bupropion anti-inflammatory action: involvement of the TLR2/TLR4 and JAK2/STAT3

There are accumulating reports regarding poor response to common antidepressant therapy. Antidepressant resistance is often linked to inflammatory system activation and patients displaying inflammation prior to the treatment are less responsive to antidepressants. We hypothesized that the inefficacy of antidepressant therapy in some patients may be attributable to the drugs' inflammatory mode of action, which has been overlooked because of their substantial therapeutic benefit. Bupropion is a commonly prescribed antidepressant that is often used to treat seasonal affective disorders as well. Nevertheless, research suggests that bupropion causes inflammation and worsens depressive symptoms. Therefore, we investigated the impact of bupropion on cytokines of innate and adaptive immunity, as well as immune signaling pathways. We treated lipopolysaccharide (LPS)-stimulated human peripheral blood mononuclear cells (PBMCs) with different doses of bupropion. Pro-/anti-inflammatory cytokines [tumor necrosis factor alpha (TNFα), interleukin-1β (IL-1β), IL-17, and IL-10] were assessed at both transcriptional and translational levels as well as the involvement of JAK2 /STAT3, TLR2, and TLR4 signaling in this process. Bupropion reduced IL-17A, TNFα, and IL-1β protein levels in the cultures. Nonetheless, bupropion increased IL-1β (P < 0.0001), TNFα (P < 0.0001), and IL-17A (P < 0.05) mRNA levels. Treatment enhanced both IL-10 concentration (P < 0.0001) and gene expression (P < 0.0001). TLR2 (P < 0.0001), TLR4 (P < 0.0001), JAK2 (P < 0.0001), and STAT3 (P < 0.0001) gene expression also rose in response to bupropion. The findings imply that bupropion, particularly 50 μM and 100 μM, has pro-inflammatory effects and should be co-administered with anti-inflammatory medications, at least in patients with inflammatory conditions.

Molecular Targets of Manganese-Induced Neurotoxicity: A Five-Year Update

Understanding of the immediate mechanisms of Mn-induced neurotoxicity is rapidly evolving. We seek to provide a summary of recent findings in the field, with an emphasis to clarify existing gaps and future research directions. We provide, here, a brief review of pertinent discoveries related to Mn-induced neurotoxicity research from the last five years. Significant progress was achieved in understanding the role of Mn transporters, such as SLC39A14, SLC39A8, and SLC30A10, in the regulation of systemic and brain manganese handling. Genetic analysis identified multiple metabolic pathways that could be considered as Mn neurotoxicity targets, including oxidative stress, endoplasmic reticulum stress, apoptosis, neuroinflammation, cell signaling pathways, and interference with neurotransmitter metabolism, to name a few. Recent findings have also demonstrated the impact of Mn exposure on transcriptional regulation of these pathways. There is a significant role of autophagy as a protective mechanism against cytotoxic Mn neurotoxicity, yet also a role for Mn to induce autophagic flux itself and autophagic dysfunction under conditions of decreased Mn bioavailability. This ambivalent role may be at the crossroad of mitochondrial dysfunction, endoplasmic reticulum stress, and apoptosis. Yet very recent evidence suggests Mn can have toxic impacts below the no observed adverse effect of Mn-induced mitochondrial dysfunction. The impact of Mn exposure on supramolecular complexes SNARE and NLRP3 inflammasome greatly contributes to Mn-induced synaptic dysfunction and neuroinflammation, respectively. The aforementioned effects might be at least partially mediated by the impact of Mn on α-synuclein accumulation. In addition to Mn-induced synaptic dysfunction, impaired neurotransmission is shown to be mediated by the effects of Mn on neurotransmitter systems and their complex interplay. Although multiple novel mechanisms have been highlighted, additional studies are required to identify the critical targets of Mn-induced neurotoxicity.

Perinatal Infection: A Major Contributor to Efficacy of Cooling in Newborns Following Birth Asphyxia

Neonatal encephalopathy (NE) is a global burden, as more than 90% of NE occurs in low- and middle-income countries (LMICs). Perinatal infection seems to limit the neuroprotective efficacy of therapeutic hypothermia. Efforts made to use therapeutic hypothermia in LMICs treating NE has led to increased neonatal mortality rates. The heat shock and cold shock protein responses are essential for survival against a wide range of stressors during which organisms raise their core body temperature and temporarily subject themselves to thermal and cold stress in the face of infection. The characteristic increase and decrease in core body temperature activates and utilizes elements of the heat shock and cold shock response pathways to modify cytokine and chemokine gene expression, cellular signaling, and immune cell mobilization to sites of inflammation, infection, and injury. Hypothermia stimulates microglia to secret cold-inducible RNA-binding protein (CIRP), which triggers NF-κB, controlling multiple inflammatory pathways, including nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasomes and cyclooxygenase-2 (COX-2) signaling. Brain responses through changes in heat shock protein and cold shock protein transcription and gene-expression following fever range and hyperthermia may be new promising potential therapeutic targets.

Aging-related modifications to G protein-coupled receptor signaling diversity

Aging is a highly complex molecular process, affecting nearly all tissue systems in humans and is the highest risk factor in developing neurodegenerative disorders such as Alzheimer's and Parkinson's disease, cardiovascular disease and Type 2 diabetes mellitus. The intense complexity of the aging process creates an incentive to develop more specific drugs that attenuate or even reverse some of the features of premature aging. As our current pharmacopeia is dominated by therapeutics that target members of the G protein-coupled receptor (GPCR) superfamily it may be prudent to search for effective anti-aging therapeutics in this fertile domain. Since the first demonstration of GPCR-based β-arrestin signaling, it has become clear that an enhanced appreciation of GPCR signaling diversity may facilitate the creation of therapeutics with selective signaling activities. Such 'biased' ligand signaling profiles can be effectively investigated using both standard molecular biological techniques as well as high-dimensionality data analyses. Through a more nuanced appreciation of the quantitative nature across the multiple dimensions of signaling bias that drugs possess, researchers may be able to further refine the efficacy of GPCR modulators to impact the complex aberrations that constitute the aging process. Identifying novel effector profiles could expand the effective pharmacopeia and assist in the design of precision medicines. This review discusses potential non-G protein effectors, and specifically their potential therapeutic suitability in aging and age-related disorders.

Manganese Exposure Aggravates β-Amyloid Pathology by Microglial Activation

Human epidemiological evidence and animal experimental data suggest that chronic manganese (Mn) exposure increases the risk of Alzheimer’s disease (AD) and amyloid plaques, a hallmark of AD brain pathology, but the underlying mechanisms were not fully understood. Using the transgenic APP/PS1/Tau triple transgenic AD (3×Tg-AD) mouse model and mouse-derived microglia and neuroblastoma cell lines, we found that chronic 5-month Mn treatment increased beta amyloid peptide (Aβ) expression and Aβ plaques in the cerebral cortex and hippocampus in these 3×Tg-AD mice. Furthermore, we found that the β- and γ-secretase cleavage activities were markedly increased, while α-secretase cleavage activity was reduced in the brain of Mn-treated AD mice; these effects increase Aβ production and thus are amyloidogenic. Equally important, Mn treatment alone did not alter β-secretase 1 (BACE1) gene expression or Aβ production in amyloidogenic mutant amyloid precursor protein (APP) gene hAPPsw-transfected N2a cells (APPsw-N2a), but in APPsw-N2a cells either co-cultured with microglia or cultured with microglia-conditioned media, Mn exposure increased BACE1 expression and amyloidogenesis. We further determined that Mn exposure promoted the activation of microglia both in 3×Tg-AD mouse brains and in cultured microglia cells, and increased the secretion of the inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). Taken together, these results suggest that Mn may increase the release of IL-1β and TNF-α from microglia that in turn stimulates the expression of BACE1 gene and protein and consequently Aβ production; this novel molecular mechanism not only advances our understanding about the amyloidogenic effect of chronic Mn exposure reported for special human populations but also indicates Mn dyshomeostasis as a potential contributor to AD pathogenesis.

Emodin Alleviates Hydrogen Peroxide-Induced Inflammation and Oxidative Stress via Mitochondrial Dysfunction by Inhibiting the PI3K/mTOR/GSK3β Pathway in Neuroblastoma SH-SY5Y Cells

Emodin is an active monomer extracted from rhubarb root, which has many biological functions, including anti-inflammation, antioxidation, anticancer, and neuroprotection. However, the protective effect of emodin on nerve injury needs to be further elucidated. The purpose of this study is to investigate the effect of emodin on the neuroprotection and the special molecular mechanism. Here, the protective activity of emodin inhibiting H2O2-induced apoptosis and neuroinflammation as well as its molecular mechanisms was examined using human neuroblastoma cells (SH-SY5Y cells). The results showed that emodin significantly enhanced cell viability, reduced cell apoptosis and LDH release. Simultaneously, emodin downregulated H2O2-induced inflammatory factors, including IL-6, NO, and TNF-α, and alleviated H2O2-induced oxidative stress and mitochondrial dysfunction in SH-SY5Y cells. In addition, emodin inhibited the activation of the PI3K/mTOR/GSK3β signaling pathway. What is more, the PI3K/mTOR/GSK3β pathway participated in the protective mechanism of emodin on H2O2-induced cell damage. Collectively, it suggests that emodin alleviates H2O2-induced apoptosis and neuroinflammation potentially by regulating the PI3K/mTOR/GSK3β signaling pathway.

β-Glucan augments IL-1β production by activating the JAK2/STAT3 pathway in cultured rabbit keratinocytes

Trichophyton mentagrophytes (T. mentagrophytes) is the main cause of rabbit dermatophytosis. As the main pathogen-associated molecular pattern of T. mentagrophytes, the role of β-glucan in the pathogenesis of rabbit dermatophytosis remains elusive. Keratinocytes (KC) are the main cellular component and the first defensive line against fungal pathogens in the skin. Therefore, the present study investigated the effects of β-glucan on rabbit KC from dorsal skin. β-glucan was found to inhibit KC proliferation by 10% at 20 ug/ml and this concentration was thus considered as optimal. Next, 20 ug/ml β-glucan stimulation for 24 h significantly increased CXCL8, CXCL11, and IL-1β secretions in KC. Furthermore, β-glucan exposure induced the expressions of JAK2 mRNA, STAT3 mRNA, and p-STAT3 protein. Silencing JAK2 expression inhibited p-STAT3 protein expression and β-glucan-induced IL-1β secretion. And overexpression of JAK2 further promoted β-glucan-mediated p-STAT3 protein and IL-1β productions. These results suggested that β-glucan-induced CXCL8, CXCL11, and IL-1β secretions in rabbit KC might be involved in the inflammatory response of T. mentagrophytes infected rabbit dorsal skin. However, only IL-1β secretion was promoted by the JAK2/STAT3 signaling pathway. In conclusion, this study is a necessary step toward elucidating the mechanisms that underlie skin immune system injury stimulated by β-glucan.

Muscone relieves inflammatory pain by inhibiting microglial activation-mediated inflammatory response via abrogation of the NOX4/JAK2-STAT3 pathway and NLRP3 inflammasome

Previous studies have shown that muscone, a pharmacologically active ingredient isolated from musk, has excellent effects on anti-inflammation. However, its effect on microglia activation-induced inflammatory pain is not known yet. In the present study, a mouse BV2 microglia cell activation-mediated inflammatory model was developed with LPS induction, and a mouse inflammatory pain model was established with CFA injection. The inhibitory effect of muscone on microglia inflammatory activation was verified by measuring pro-inflammatory cytokines expression (interleukin-6, tumor necrosis factor-α, and interleukin-1β; IL-6, TNF-α and IL-1β). We found that muscone suppressed microglial activation-mediated inflammatory response through the NADPH oxidase 4 (NOX4)/janus kinase 2-signal transducer and activator of transcription 3 (JAK2-STAT3) pathway and pyrin-domain-containing 3 (NLRP3) inflammasome. Notably, muscone mitigated CFA-induced pain hypersensitivity and inflammation, as well as microglia cell activation in vivo. Furthermore, muscone inhibited the CFA-induced NOX4, p-JAK2/p-STAT3, and NLRP3 inflammasome expression in spinal cord of mice. In conclusion, this study uncovered that muscone relieved inflammatory pain by inhibiting microglial activation-mediated inflammatory response via abrogation of the NOX4/JAK2-STAT3 pathway and NLRP3 inflammasome. This finding of muscone is promising for treating inflammatory pain.

Silencing of PTX3 alleviates LPS-induced inflammatory pain by regulating TLR4/NF-κB signaling pathway in mice

Pentraxin 3 (PTX3), an inflammatory marker and a pattern recognition receptor, plays an important role in promoting the progress of tumor and inflammatory diseases. However, the role of PTX3 in the pathogenesis of inflammatory pain diseases is rarely reported. The purpose of the present study is to investigate the effect of PTX3 on the progression of inflammatory pain and the special molecular mechanism. A mouse BV2 microglia cell activation-mediated inflammatory model was developed with Lipopolysaccharide (LPS) induction, and a mouse inflammatory pain model was established with LPS injection. The effect of PTX3 on microglia inflammatory activation was verified by measuring pro-inflammatory cytokines expression. The mechanical hyperalgesia testing, the thermal preference testing and the cold allodynia testing were used to measure the response of mice to mechanical pain, heat stimulation and cold stimulation, respectively. The results revealed that the expression of PTX3 was decreased in the LPS-induced inflammatory pain mice model. Silencing of PTX3 down-regulated LPS-induced inflammatory factors, including IL-6, NO and TNF-α, and alleviated LPS-induced inflammatory pain in BV2 cells. In addition, overexpression of TLR4 reversed the inhibitory effect of si-PTX3 on LPS-induced inflammatory response in BV2 cells. What is more, silencing of PTX3 inhibited TLR4/NF-κB signaling pathway. Collectively, it suggests that silencing of PTX3 alleviates LPS-induced inflammatory response of BV2 cells potentially by regulating the TLR4/NF-κB signaling pathway.

MFG-E8 alleviates oxygen-glucose deprivation-induced neuronal cell apoptosis by STAT3 regulating the selective polarization of microglia

Background: Ischemic stroke is a complex pathological process, involving inflammatory reaction, energy metabolism disorder, free radical injury, cell apoptosis and other aspects. Accumulating evidences have revealed that MFG-E8 had a protective effect on multiple organ injuries. However, the comprehensive function and mechanism of MFG-E8 in ischemic brain remain largely unclear.Methods: BV-2 cells were treated with recombinant murine MFG-E8 (rmMFG-E8) or/and Colivelin TFA after exposing for 4 h with oxygen glucose deprivation (OGD). Cell viability and apoptosis were assessed by MTT assay and Flow cytometry. RT-qPCR and Western blot assays were applied to examine the expression levels of MFG-E8, apoptosis-related proteins and M1/M2 polarization markers.Results: Our results demonstrated that OGD significantly inhibited microglial viability and facilitated apoptosis. In addition, we found that OGD downregulated MFG-E8 expression, and MFG-E8 inhibited OGD-induced microglial apoptosis and promoted microglial M2 polarization. In terms of mechanism, we proved that MFG-E8 regulated OGD-induced microglial M1/M2 polarization by inhibiting p-STAT3 and SOCS3 expressions, which was reversed by STAT3 activator (Colivelin TFA). Finally, we verified MFG-E8 alleviated OGD-induced neuronal cell apoptosis by M2 polarization of BV-2 cells.Conclusions: We demonstrated that MFG-E8 reduced neuronal cell apoptosis by enhancing activation of microglia via STAT3 signaling. Therefore, we suggested that MFG-E8 might provide a novel mechanism for ischemic stroke.

Evidence of the involvement of spinal αB-crystallin in the maintenance of bone cancer pain in rats

BACKGROUND

αB-crystallin (CRYAB) is a small heat shock protein that is able to inhibit neuroinflammatory responses under various pathological conditions. Some studies have proven that neuroinflammatory mechanisms play important roles in bone cancer pain (BCP). However, whether CRYAB participates in the maintenance of BCP has not yet been examined.

METHODS

Walker256 tumour cells were inoculated into the tibia to induce a rat model of BCP. Von Frey hairs were used to measure mechanical allodynia. Immunohistochemistry and western blotting were used to examine the expression level of CRYAB in the spinal dorsal horn.

RESULTS

The gradual development of mechanical allodynia was induced by the injection of Walker256 cells into the tibia. The downregulation of spinal CRYAB expression was found in BCP rats. The intrathecal administration of CRYAB (from days 9 to 15 post-inoculation) dose-dependently alleviated mechanical allodynia in BCP rats. Additionally, there were concomitant increases in spinal CRYAB expression and decreases in TNF-α expression.

CONCLUSIONS

Spinal CRYAB may participate in the maintenance of BCP in rats. The findings will help to identify new drugs for the management of BCP.

Role for calcium signaling in manganese neurotoxicity

BACKGROUND

Calcium is an essential macronutrient that is involved in many cellular processes. Homeostatic control of intracellular levels of calcium ions [Ca²⁺] is vital to maintaining cellular structure and function. Several signaling molecules are involved in regulating Ca²⁺ levels in cells and perturbation of calcium signaling processes is implicated in several neurodegenerative and neurologic conditions. Manganese [Mn] is a metal which is essential for basic physiological functions. However, overexposure to Mn from environmental contamination and workplace hazards is a global concern. Mn overexposure leads to its accumulation in several human organs particularly the brain. Mn accumulation in the brain results in a manganism, a Parkinsonian-like syndrome. Additionally, Mn is a risk factor for several neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. Mn neurotoxicity also affects several neurotransmitter systems including dopaminergic, cholinergic and GABAergic. The mechanisms of Mn neurotoxicity are still being elucidated.

AIM

The review will highlight a potential role for calcium signaling molecules in the mechanisms of Mn neurotoxicity.

CONCLUSION

Ca²⁺ regulation influences the neurodegenerative process and there is possible role for perturbed calcium signaling in Mn neurotoxicity. Mechanisms implicated in Mn-induced neurodegeneration include oxidative stress, generation of free radicals, and apoptosis. These are influenced by mitochondrial integrity which can be dependent on intracellular Ca²⁺ homeostasis. Nevertheless, further elucidation of the direct effects of calcium signaling dysfunction and calcium-binding proteins activities in Mn neurotoxicity is required.

TRPV1 translocated to astrocytic membrane to promote migration and inflammatory infiltration thus promotes epilepsy after hypoxic ischemia in immature brain

BACKGROUND

Neonatal hypoxic-ischemic brain damage (HIBD), a leading cause of neonatal mortality, has intractable sequela such as epilepsy that seriously affected the life quality of HIBD survivors. We have previously shown that ion channel dysfunction in the central nervous system played an important role in the process of HIBD-induced epilepsy. Therefore, we continued to validate the underlying mechanisms of TRPV1 as a potential target for epilepsy.

METHODS

Neonatal hypoxic ischemia and oxygen-glucose deprivation (OGD) were used to simulate HIBD in vivo and in vitro. Primarily cultured astrocytes were used to assess the expression of TRPV1, glial fibrillary acidic protein (GFAP), cytoskeletal rearrangement, and inflammatory cytokines by using Western blot, q-PCR, and immunofluorescence. Furthermore, brain electrical activity in freely moving mice was recorded by electroencephalography (EEG). TRPV1 current and neuronal excitability were detected by whole-cell patch clamp.

RESULTS

Astrocytic TRPV1 translocated to the membrane after OGD. Mechanistically, astrocytic TRPV1 activation increased the inflow of Ca²⁺, which promoted G-actin polymerized to F-actin, thus promoted astrocyte migration after OGD. Moreover, astrocytic TRPV1 deficiency decreased the production and release of pro-inflammatory cytokines (TNF, IL-6, IL-1β, and iNOS) after OGD. It could also dramatically attenuate neuronal excitability after OGD and brain electrical activity in HIBD mice. Behavioral testing for seizures after HIBD revealed that TRPV1 knockout mice demonstrated prolonged onset latency, shortened duration, and decreased seizure severity when compared with wild-type mice.

CONCLUSIONS

Collectively, TRPV1 promoted astrocyte migration thus helped the infiltration of pro-inflammatory cytokines (TNF, IL-1β, IL-6, and iNOS) from astrocytes into the vicinity of neurons to promote epilepsy. Our study provides a strong rationale for astrocytic TRPV1 to be a therapeutic target for anti-epileptogenesis after HIBD.

miR-124 and Parkinson's disease: A biomarker with therapeutic potential

Parkinson's disease (PD) is a multifactorial disorder, attributed to a complex interplay between genetic and epigenetic factors. Although the exact etiology of the disease remains elusive, dysregulation of signaling pathways implicated in cell survival, apoptosis, protein aggregation, mitochondrial dysfunction, autophagy, oxidative damage and neuroinflammation, contributes to its pathogenesis. MicroRNAs (miRs) are endogenous short non-coding RNA molecules that negatively regulate gene expression at a post-transcriptional level. MiR-124 is one of the most abundantly expressed miRs in the brain that participates in neurogenesis, synapse morphology, neurotransmission, inflammation, autophagy and mitochondrial function. Accumulating pre-clinical evidence shows that miR-124 may act through calpain 1/p25/cyclin-dependent kinases 5 (CDK5), nuclear factor-kappa B (NF-κB), signal transducer and activator of transcription 3 (STAT3), Bcl-2-interacting mediator of cell death (Bim), 5' adenosine monophosphate-activated protein kinase (AMPK) and extracellular signal-regulated kinase (ERK)-mediated pathways to regulate cell survival, apoptosis, autophagy, mitochondrial dysfunction, oxidative damage and neuroinflammation in PD. Moreover, clinical evidence indicates that reduced plasma miR-124 levels may serve as a potential diagnostic biomarker in PD. This review provides an update of the pathogenic implication of miR-124 activity in PD and discusses its targeting potential for the development of future therapeutic strategies.

TRPV1 mediates astrocyte activation and interleukin-1β release induced by hypoxic ischemia (HI)

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is a serious birth complication with high incidence in both advanced and developing countries. Children surviving from HIE often have severe long-term sequela including cerebral palsy, epilepsy, and cognitive disabilities. The severity of HIE in infants is tightly associated with increased IL-1β expression and astrocyte activation which was regulated by transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel in the TRP family.

METHODS

Neonatal hypoxic ischemia (HI) and oxygen-glucose deprivation (OGD) were used to simulate HIE in vivo and in vitro. Primarily cultured astrocytes were used for investigating the expression of glial fibrillary acidic protein (GFAP), IL-1β, Janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), and activation of the nucleotide-binding, oligomerization domain (NOD)-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome by using Western blot, q-PCR, and immunofluorescence. Brain atrophy, infarct size, and neurobehavioral disorders were evaluated by Nissl staining, 2,3,5-triphenyltetrazolium chloride monohydrate (TTC) staining and neurobehavioral tests (geotaxis reflex, cliff aversion reaction, and grip test) individually.

RESULTS

Astrocytes were overactivated after neonatal HI and OGD challenge. The number of activated astrocytes, the expression level of IL-1β, brain atrophy, and shrinking infarct size were all downregulated in TRPV1 KO mice. TRPV1 deficiency in astrocytes attenuated the expression of GFAP and IL-1β by reducing phosphorylation of JAK2 and STAT3. Meanwhile, IL-1β release was significantly reduced in TRPV1 deficiency astrocytes by inhibiting activation of NLRP3 inflammasome. Additionally, neonatal HI-induced neurobehavioral disorders were significantly improved in the TRPV1 KO mice.

CONCLUSIONS

TRPV1 promotes activation of astrocytes and release of astrocyte-derived IL-1β mainly via JAK2-STAT3 signaling and activation of the NLRP3 inflammasome. Our findings provide mechanistic insights into TRPV1-mediated brain damage and neurobehavioral disorders caused by neonatal HI and potentially identify astrocytic TRPV1 as a novel therapeutic target for treating HIE in the subacute stages (24 h).

Dehydrocrenatidine Inhibits Voltage-Gated Sodium Channels and Ameliorates Mechanic Allodia in a Rat Model of Neuropathic Pain

Picrasma quassioides (D. Don) Benn, a medical plant, is used in clinic to treat inflammation, pain, sore throat, and eczema. The alkaloids are the main active components in P. quassioides. In this study, we examined the analgesic effect of dehydrocrenatidine (DHCT), a β-carboline alkaloid abundantly found in P. quassioides in a neuropathic pain rat model of a sciatic nerve chronic constriction injury. DHCT dose-dependently attenuated the mechanic allodynia. In acutely isolated dorsal root ganglion, DHCT completely suppressed the action potential firing. Further electrophysiological characterization demonstrated that DHCT suppressed both tetrodotoxin-resistant (TTX-R) and sensitive (TTX-S) voltage-gated sodium channel (VGSC) currents with IC50 values of 12.36 μM and 4.87 µM, respectively. DHCT shifted half-maximal voltage (V1/2) of inactivation to hyperpolarizing direction by ~16.7 mV in TTX-S VGSCs. In TTX-R VGSCs, DHCT shifted V1/2 of inactivation voltage to hyperpolarizing direction and V1/2 of activation voltage to more depolarizing potential by ~23.9 mV and ~12.2 mV, respectively. DHCT preferred to interact with an inactivated state of VGSCs and prolonged the repriming time in both TTX-S and TTX-R VGSCs, transiting the channels into a slow inactivated state from a fast inactivated state. Considered together, these data demonstrated that the analgesic effect of DHCT was likely though the inhibition of neuronal excitability.

PKA- and Ca2+-dependent p38 MAPK/CREB activation protects against manganese-mediated neuronal apoptosis

Although manganese (Mn) is an essential trace element, its excessive consumption may lead to neuronal death and neurodegenerative disorders. Human cells launch adaptive responses to attenuate Mn-induced neurotoxicity. However, the regulation of the responsive proteins and their function during Mn-stimulated neurotoxicity remain largely unknown. We report the role of cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB) in Mn-induced neuronal apoptosis. Mn increased CREB phosphorylation and cellular apoptosis in both PC12 cells and mouse brain tissue. Furthermore, downregulation of CREB with shRNA plasmid transfection significantly worsened the PC12 cell apoptosis by decreasing mRNA and protein expression of brain-derived neurotrophic factor (BDNF). Moreover, Mn enhanced protein kinase A (PKA) activation and activation of the p38 MAPK and JNK pathways. Inhibition of p38 MAPK rather than JNK effectively reduced the CREB phosphorylation. Subsequent analysis showed that a PKA inhibitor blocked p38 MAPK and CREB phosphorylation. Moreover, the intracellular Ca2+ chelator BAPTA-AM decreased the phosphorylation of p38 MAPK and CREB but failed to reduce PKA activation. In summary, p38 MAPK/CREB activation via PKA activation and increased cellular Ca²⁺ helped to alleviate Mn-induced neuronal apoptosis via BDNF regulation. These findings improve our understanding of Mn-induced neurotoxicity and the molecular targets to antagonise it.

Circular RNA circPTK2 regulates oxygen-glucose deprivation-activated microglia-induced hippocampal neuronal apoptosis via miR-29b-SOCS-1-JAK2/STAT3-IL-1β signaling

Oxygen-glucose deprivation (OGD)-activated microglia contribute to neuronal apoptosis via releasing pro-inflammatory cytokines, and some miRNAs have been reported to be involved in this process. Circular RNAs (circRNAs) have been reported to function as miRNA sponges, but it remains unknown whether and how circRNAs contribute to OGD-activated microglia-induced neuronal apoptosis. Here, we investigated the function and relationship of miR-29b and circPTK2 in OGD-activated microglia-induced neuronal apoptosis. We found upregulation of TNF-α and IL-1β, and downregulation of miR-29b in OGD-activated microglia. miR-29b inhibited OGD-activated microglia-induced neuronal apoptosis. Meanwhile, miR-29b promoted SOCS-1 expression, and suppressed JAK2/STAT3 signaling. In addition, inhibition of JAK2/STAT3 signaling downregulated IL-1β expression, while upregulation of miR-29b or SOCS-1 also inhibited IL-1β production. IL-1β was confirmed to be an apoptosis inducer of hippocampal neurons. Moreover, either SOCS-1 upregulation or blockade of JAK2/STAT3 signaling suppressed OGD-activated microglia-induced neuronal apoptosis. These data suggest that miR-29b inhibits OGD-activated microglia-induced neuronal apoptosis via inducing SOCS-1 expression, blocking JNK2/STAT3 signaling, and inhibiting IL-1β production. circPTK2 was confirmed to inhibit miR-29b expression in OGD model by directly binding to miR-29b. Function assay showed that circPTK2 regulated microglia-induced neuronal apoptosis via sponging miR-29b. Collectively, these findings suggest that circPTK2 regulates OGD-activated microglia-induced neuronal apoptosis via miR-29b-SOCS-1-JAK2/STAT3-IL-1β signaling.

SIRT1 downregulation mediated Manganese-induced neuronal apoptosis through activation of FOXO3a-Bim/PUMA axis

Manganese (Mn) is an essential trace element. Excessive exposure to Mn may lead to neuronal death and neurodegenerative disorders. Accumulating evidence has shown that silent mating type information regulation 2 homolog 1 (SIRT1) plays a vital role in brain damage. However, whether aberrant SIRT1 levels contribute to Mn-induced neurotoxicity remains unknown. In this study, we report the important role of SIRT1 downregulation during Mn-induced neuronal apoptosis. Mn was found to downregulate SIRT1 protein levels in the rat pheochromocytoma (PC12) cells and mouse brain tissues. Mn enhanced SIRT1 protein degradation and downregulated its gene expression. Furthermore, Mn induced cell apoptosis in a dose-dependent manner both in vitro and in vivo, and resulted in an increase in forkhead box O (FOXO) 3a expression and acetylation. SIRT1 activation by resveratrol clearly attenuated Mn-triggered apoptosis and FOXO3a activation. Mn markedly increased the expression of Bcl-2 interacting mediator of cell death (Bim) and p53-up-regulated modulator of apoptosis (PUMA), whereas downregulation of FOXO3a significantly inhibited their upregulation and subsequent apoptosis. In summary, we determined that Mn downregulated SIRT1 by multiple mechanisms, thus led to apoptosis via activation of the FOXO3a-Bim/PUMA axis in PC12 cells. These findings on the impact of Mn on SIRT1 may lead to an improved understanding of Mn-induced neurotoxicity and provide a molecular target to antagonise Mn-associated neuronal damage.

Complement protein C5a enhances the β-amyloid-induced neuro-inflammatory response in microglia in Alzheimer’s disease

Objective: The dysregulation of neuro-inflammation is one of the attributes of the pathogenesis of Alzheimer’s disease (AD). Over-expression of complement proteins co-localizes with neurofibrillary tangles, thereby indicating that a complement system may be involved in neuro-inflammation. Here, we report the influence of complement activation on the neuro-inflammation using a microglial cell line.

Methods: first, we performed a cytotoxic assay using the microglial cells BV-2. Second, after treatment of BV-2 cells with Aβ42 and/ or C5a, the anaphylatoxin derived from C5, we determined the expression levels of the pro-inflammatory factors TNF-α, IL-1β, and IL-6. Finally, we explored whether this neuroinflammatory response was mediated by JAK/ STAT3 signaling.

Results: C5a had an enhanced effect on the neural cell viability of BV-2 cells treated with Aβ42. In addition, C5a also increased the Aβ-induced neuro-inflammatory response, and these effects were blocked by the C5aR antagonist, PMX205. Finally, we demonstrated that the neuro-inflammatory responses induced by Aβ and C5a were mediated through JAK/STAT3 signaling. By blocking this pathway with an antagonist, AG490, the expression of TNF-α, IL-1β, and IL-6 was alleviated.

Conclusion: The complement protein C5a could exaggerate the Aβ-induced neuroinflammatory response in microglia, and C5aR may be a potential therapeutic tool for AD treatment.

Inhibitive Effects of FGF2/FGFR1 Pathway on Astrocyte-Mediated Inflammation in vivo and in vitro After Infrasound Exposure

Infrasound, a kind of ambient noise, can cause severe disorders to various human organs, specially to central nervous system (CNS). Our previous studies have shown that infrasound-induced CNS injury was closely related with astrocytes activation and astrocytes-mediated neuroinflammation, but the underlying molecular mechanisms are still largely unclear. FGF2/FGFR1 (Fibroblast growth factor 2/Fibroblast growth factor receptor 1) pathway was reported to play an important role in anti-inflammation in CNS disorders. To further study the possible roles of FGF2/FGFR1 pathway in infrasound-induced CNS injury, here we exposed Sprague-Dawley rats or cultured astrocytes to 16 Hz, 150 dB infrasound, and explored the effects of FGF2 on infrasound-induced astrocytes activation and neuroinflammation. Western blotting, immunofluorescence and liquid chip method were used in this experiment. Our results showed that after 3- or 7-day exposure (2 h/day) of rats as well as 2 h exposure of cultured astrocytes to 16 Hz, 150 dB infrasound, astrocyte-expressed FGFR1 was downregulated in vivo and in vitro. FGF2 pretreatment not only inhibited infrasound-induced astrocyte activation in rat hippocampal CA1 region, but also reduced the levels of pro-inflammatory cytokines, such as TNF-α, IL-1β, IL-18, IL-6, and IFN-γ in vitro and in vivo. However, FGF2 significantly upregulated the expression of FGFR1. Furthermore, we showed that FGF2 could attenuate IκBα phosphorylation, NF-κB p65 translocation, pro-inflammatory cytokines levels, and neuronal loss in the CA1 region induced by infrasound. On the contrary, PD173074, a special antagonist of FGFR1, could reverse the effects above in vitro and in vivo. Taken together, our findings showed that FGF2/FGFR1 pathway may exert inhibitive effects on astrocyte-mediated neuroinflammation in vitro and in vivo after infrasound exposure.