Peripheral immune tolerance alleviates the intracranial lipopolysaccharide injection-induced neuroinflammation and protects the dopaminergic neurons from neuroinflammation-related neurotoxicity

Pharmaceutical-mediated neuroimmune modulation in psychiatric/psychological adverse events

The therapeutic use of many pharmaceuticals, including small molecules and biological therapies, has been associated with the onset of psychiatric and psychological adverse events (PPAEs), posing substantial concerns to patients' health and safety. These events, which encompass mood (e.g., depression, schizophrenia, suicidal ideation) and cognitive changes (e.g., learning and memory impairment, dementia) often remain undetected until advanced stages of clinical trials or pharmacovigilance, mostly because the mechanisms underlying the onset of PPAEs remain poorly understood. In recent years, the role of neuroimmune modulation (comprising an intricate interplay between various cell types and signaling pathways) in PPAEs has garnered substantial interest. Indeed, understanding these complex interactions would substantially contribute to increase the ability to predict the potential onset of PPAEs during preclinical stages of a new drug's R&D. This review provides a comprehensive summary of the most recent advances in neuroimmune modulation-related mechanisms contributing to the onset of PPAEs and their association with specific pharmaceuticals. Reported data strongly support an association between neuroimmune modulation and the onset of PPAEs. Pharmaceuticals may target specific molecular pathways and pathway elements (e.g., cholinergic and serotonergic systems), which in turn may directly or indirectly impact the inflammatory status and the homeostasis of the brain, regulating inflammation and neuronal function. Also, modulation of the peripheral immune system by pharmaceuticals that do not permeate the blood-brain barrier (e.g., monoclonal antibodies) may alter the neuroimmunomodulatory status of the brain, leading to PPAEs. In summary, this review underscores the diverse pathways through which drugs can influence brain inflammation, shedding light on potential targeted interventions.

Endotoxin tolerance ameliorates lipopolysaccharide/D-galactosamine-induced acute liver failure by negative regulation of the NF-κB/NLRP3 and activation of Nrf2/HO-1 via Sitr1

Acute liver failure (ALF) is a potentially fatal disorder characterized by extensive hepatocyte necrosis and rapid decline in liver function. Numerous factors, including oxidative stress, cell death, and inflammatory responses, are associated with its pathogenesis. Endotoxin tolerance (ET) refers to the phenomenon in which the body or cells exhibit low or no response to high-dose lipopolysaccharide (LPS) stimulation after pre-stimulation with low-dose LPS. However, the specific mechanism through which ET regulates LPS/D-galactosamine (D-GalN)-induced ALF remains unclear. An ALF mouse model was established by intraperitoneal injection of D-GalN (400 mg/kg) and LPS (10 mg/kg). A low dose of LPS (0.1 mg/kg/d) was continuously administered to mice for 5 d before modeling to assess the protective effect of ET. The data from this study showed that ET alleviated the inflammatory response in mice with LPS/D-GalN-induced ALF. ET inhibited LPS-induced oxidative damage and pyroptosis in macrophages in vitro. RNA sequencing analysis showed that the NF-κB/NLRP3 pathway was linked to the anti-inflammatory and antioxidative effects of ET. Furthermore, using western blot, RT-qPCR, and immunofluorescence, we verified that ET inhibited the NF-κB/NLRP3 pathway and triggered the Nrf2/HO-1 signaling pathway to attenuate oxidative stress and cell pyroptosis. Sirt1 knockdown reversed this protective effect. In summary, our research elucidates that ET prevents ALF advancement by upregulating Sirt1 levels, triggering the Nrf2/HO-1 signaling axis, and suppressing the NF-κB/NLRP3 signaling cascade to inhibit oxidative stress and cell pyroptosis. Our results provide a mechanistic explanation for the protective effect of ET against ALF.

Lipopolysaccharide-Induced Delirium-like Behaviour in a Rat Model of Chronic Cerebral Hypoperfusion Is Associated with Increased Indoleamine 2,3-Dioxygenase Expression and Endotoxin Tolerance

Indoleamine 2,3-dioxygenase (IDO) and the tryptophan-kynurenine pathway (TRP-KP) are upregulated in ageing and could be implicated in the pathogenesis of delirium. This study evaluated the role of IDO/KP in lipopolysaccharide (LPS)-induced delirium in an animal model of chronic cerebral hypoperfusion (CCH), a proposed model for delirium. CCH was induced by a permanent bilateral common carotid artery ligation (BCCAL) in Sprague Dawley rats to trigger chronic neuroinflammation-induced neurodegeneration. Eight weeks after permanent BCCAL, the rats were treated with a single systemic LPS. The rats were divided into three groups: (1) post-BCCAL rats treated with intraperitoneal (i.p.) saline, (2) post-BCCAL rats treated with i.p. LPS 100 μg/kg, and (3) sham-operated rats treated with i.p. LPS 100 μg/kg. Each group consisted of 10 male rats. To elucidate the LPS-induced delirium-like behaviour, natural and learned behaviour changes were assessed by a buried food test (BFT), open field test (OFT), and Y-maze test at 0, 24-, 48-, and 72 h after LPS treatment. Serum was collected after each session of behavioural assessment. The rats were euthanised after the last serum collection, and the hippocampi and cerebral cortex were collected. The TRP-KP neuroactive metabolites were measured in both serum and brain tissues using ELISA. Our data show that LPS treatment in CCH rats was associated with acute, transient, and fluctuated deficits in natural and learned behaviour, consistent with features of delirium. These behaviour deficits were mild compared to the sham-operated rats, which exhibited robust behaviour impairments. Additionally, heightened hippocampal IDO expression in the LPS-treated CCH rats was associated with reduced serum KP activity together with a decrease in the hippocampal quinolinic acid (QA) expression compared to the sham-operated rats, suggested for the presence of endotoxin tolerance through the immunomodulatory activity of IDO in the brain. These data provide new insight into the underlying mechanisms of delirium, and future studies should further explore the role of IDO modulation and its therapeutic potential in delirium.

α-Synuclein induces prodromal symptoms of Parkinson's disease via activating TLR2/MyD88/NF-κB pathway in Schwann cells of vagus nerve in a rat model

BACKGROUND

Increasing evidence suggests that patients with Parkinson's disease (PD) present with peripheral autonomic dysfunction (AutD) that even precedes motor deficits, through which α-synuclein can spread to the central nervous system. However, the pathological mechanisms underlying AutD in prodromal PD remain unclear. Here, we investigated the role of α-synuclein and its interplay with the activation of Schwann cells (SCs) of the vagus nerve in AutD.

METHODS

Rats were subjected to injection with adeno-associated viruses containing the human mutated A53T gene (AAV-A53T) or an empty vector into the left cervical vagus nerve and evaluated for gastrointestinal symptoms, locomotor functions, intestinal blood flow, and nerve electrophysiology. Further, we examined the impact of α-synucleinopathy on vagus nerves, SCs, and central nervous system neurons using electron microscopy, immunofluorescence, immunohistochemistry, and western blot. Finally, the role of Toll-like receptor 2 (TLR2) in regulating the neuroinflammation in the vagus nerve via MyD88 and NF-κB pathway was determined using genetic knockdown.

RESULTS

We found that rats injected with AAV-A53T in the vagus nerve exhibited prominent signs of AutD, preceding the onset of motor deficits and central dopaminergic abnormalities by at least 3 months, which could serve as a model for prodromal PD. In addition, reduced intestinal blood flow and decreased nerve conduction velocity were identified in AAV-A53T-injected rats, accompanied by disrupted myelin sheaths and swollen SCs in the vagus nerve. Furthermore, our data demonstrated that p-α-synuclein was deposited in SCs but not in axons, activating the TLR2/MyD88/NF-κB signaling pathway and leading to neuroinflammatory responses. In contrast, silencing the TLR2 gene not only reduced inflammatory cytokine expression but also ameliorated vagal demyelination and secondary axonal loss, consequently improving autonomic function in rats.

CONCLUSIONS

These observations suggest that overexpression of α-synuclein in the vagus nerve can induce symptoms of AutD in prodromal PD, and provide support for a deeper understanding of the pathological mechanisms underlying AutD and the emergence of effective therapeutic strategies for PD.

Identification of an immune-related gene prognostic index for predicting prognosis, immunotherapeutic efficacy, and candidate drugs in amyotrophic lateral sclerosis

Rationale and objectives

Considering the great insufficiency in the survival prediction and therapy of amyotrophic lateral sclerosis (ALS), it is fundamental to determine an accurate survival prediction for both the clinical practices and the design of treatment trials. Therefore, there is a need for more accurate biomarkers that can be used to identify the subtype of ALS which carries a high risk of progression to guide further treatment.

Methods

The transcriptome profiles and clinical parameters of a total of 561 ALS patients in this study were analyzed retrospectively by analysis of four public microarray datasets. Based on the results from a series of analyses using bioinformatics and machine learning, immune signatures are able to be used to predict overall survival (OS) and immunotherapeutic response in ALS patients. Apart from other comprehensive analyses, the decision tree and the nomogram, based on the immune signatures, were applied to guide individual risk stratification. In addition, molecular docking methodology was employed to screen potential small molecular to which the immune signatures might response.

Results

Immune was determined as a major risk factor contributing to OS among various biomarkers of ALS patients. As compared with traditional clinical features, the immune-related gene prognostic index (IRGPI) had a significantly higher capacity for survival prediction. The determination of risk stratification and assessment was optimized by integrating the decision tree and the nomogram. Moreover, the IRGPI may be used to guide preventative immunotherapy for patients at high risks for mortality. The administration of 2MIU IL2 injection in the short-term was likely to be beneficial for the prolongment of survival time, whose dosage should be reduced to 1MIU if the long-term therapy was required. Besides, a useful clinical application for the IRGPI was to screen potential compounds by the structure-based molecular docking methodology.

Conclusion

Ultimately, the immune-derived signatures in ALS patients were favorable biomarkers for the prediction of survival probabilities and immunotherapeutic responses, and the promotion of drug development.

Inflammatory Animal Models of Parkinson’s Disease

Accumulating evidence suggests that microglia and peripheral immune cells may play determinant roles in the pathogenesis of Parkinson’s disease (PD). Consequently, there is a need to take advantage of immune-related models of PD to study the potential contribution of microglia and peripheral immune cells to the degeneration of the nigrostriatal system and help develop potential therapies for PD. In this review, we have summarised the main PD immune models. From a historical perspective, we highlight first the main features of intranigral injections of different pro-inflammogens, including lipopolysaccharide (LPS), thrombin, neuromelanin, etc. The use of adenoviral vectors to promote microglia-specific overexpression of different molecules in the ventral mesencephalon, including α-synuclein, IL-1β, and TNF, are also presented and briefly discussed. Finally, we summarise different models associated with peripheral inflammation whose contribution to the pathogenesis of neurodegenerative diseases is now an outstanding question. Illustrative examples included systemic LPS administration and dextran sulfate sodium-induced colitis in rodents.

Effects of intraperitoneal injection of lipopolysaccharide-induced peripheral inflammation on dopamine neuron damage in rat midbrain

Introduction

Current studies have documented neuroinflammation is implicated in Parkinson's disease. Recently, growing evidence indicated peripheral inflammation plays an important role in regulation of neuroinflammation and thus conferring protection against dopamine (DA) neuronal damage. However, the underlying mechanisms are not clearly illuminated.

Methods

The effects of intraperitoneal injection of LPS (LPS_[i.p.])‐induced peripheral inflammation on substantia nigra (SN) injection of LPS (LPS_[SN])‐elicited DA neuronal damage in rat midbrain were investigated. Rats were intraperitoneally injected with LPS (0.5 mg/kg) daily for 4 consecutive days and then given single injection of LPS (8 μg) into SN with an interval of 0 (LPS_(i.p.) 0 day ± LPS_(SN)), 30 (LPS_(i.p.) 30 days ± LPS_(SN)), and 90 (LPS_(i.p.) 90 days ± LPS_(SN)) days after LPS_(i.p.) administration.

Results

LPS_(i.p.) increased the levels of inflammatory factors in peripheral blood in (LPS_(i.p.) 0 day ± LPS_(SN)). Importantly, in (LPS_(i.p.) 0 day ± LPS_(SN)) and (LPS_(i.p.) 30 days ± LPS_(SN)), LPS_(i.p.) attenuated LPS_(SN)‐induced DA neuronal loss in SN. Besides, LPS_(i.p.) reduced LPS_(SN)‐induced microglia and astrocytes activation in SN. Furtherly, LPS_(i.p.) reduced pro‐inflammatory M1 microglia markers mRNA levels and increased anti‐inflammatory M2 microglia markers mRNA levels. In addition, the increased T‐cell marker expression and the decreased M1 microglia marker expression and more DA neuronal survival were discerned at the same area of rat midbrain in LPS_(SN)‐induced DA neuronal damage 30 days after LPS_(i.p.) application.

Conclusion

This study suggested LPS_(i.p.)‐induced peripheral inflammation might cause T cells to infiltrate the brain to regulate microglia‐mediated neuroinflammation, thereby protecting DA neurons.

Protective effects of endotoxin tolerance on peripheral lipopolysaccharide-induced neuroinflammation and dopaminergic neuronal injury

CONTEXT

Parkinson's disease is a common chronic neurodegenerative disease characterized by massive loss of dopaminergic neurons in the substantia nigra. Neuroinflammation has been shown to play an important role in the pathogenesis of neurodegenerative diseases such as Parkinson's disease. The role of immune tolerance in neuroinflammation and neurodegenerative diseases induced by peripheral factors is unclear.

OBJECTIVE

This study established a model of endotoxin tolerance to explore the protective effect of endotoxin tolerance on Parkinson-like changes induced by repeated peripheral injections of high-dose LPS, and to explore its inflammatory mechanism.

MATERIALS AND METHODS

In this study, mice were injected intraperitoneally with low dose (0.5 mg/kg) LPS for 4 days to induce endotoxin tolerance (ET). Then, high-dose (1 mg/kg) LPS was injected continuously intraperitoneally for 4 days to induce Parkinson-like changes. Cytokines were detected by enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR). Activation of microglial cells was detected by protein expression of CD68 and ionized calcium binding adapter molecule 1(Iba-1) by Western blotting and immunofluorescence. Hematoxylin and eosin staining and expression of tyrosine hydroxylase (TH) and dopamine (DA) were used to assess dopaminergic neuronal injury. The open field test and muscle tension test were used to assess behavioral disorders.

RESULTS

As expected, compared with non-ET animals, ET preconditioning significantly reduced the production of inflammatory cytokines in the substantia nigra, inhibited microglial activation, and alleviated the pathological changes of dopaminergic neurons.

CONCLUSIONS

ET may be a promising intervention method for neurodegenerative diseases.HighlightsET was successfully induced by continuous low-dose intraperitoneal LPS injection in mice.ET pretreatment inhibited neuroinflammation in the SN induced by continuous peripheral high doses of LPS.ET pretreatment inhibited continuous peripheral high-dose LPS injection-induced microglial activation in the SN.ET pretreatment decreased LPS-induced functional impairment of dopaminergic neurons.ET reversed the morphological changes of dopaminergic neurons induced by peripheral high-dose LPS.ET pretreatment improved continuous peripheral high-dose LPS injection-induced behavioral impairment.

Prenatal LPS exposure increases hippocampus IL-10 and prevents short-term memory loss in the male adolescent offspring of high-fat diet fed dams

Lipopolysaccharide (LPS) tolerance can reduce the neuroinflammation caused by high fat maternal diets; however, there are no reports that have evaluated the effects of prenatal LPS exposure on the memories of the offspring of high-fat diet fed dams. This study evaluated the effects of prenatal LPS exposure on the inflammatory parameters and redox status in the brain, as well as the object recognition memory of adolescent offspring of Wistar rat dams that were treated with a high-fat diet during gestation and lactation. Female pregnant Wistar rats randomly received a standard diet (17.5% fat) or a high-fat diet (45.0% fat) during gestation and lactation. On gestation days 8, 10, and 12, half of the females in each group were intraperitoneally treated with LPS (0.1 mg.kg-1). After weaning, the male offspring were placed in cages in standard conditions, and at 6 weeks old, animals underwent the novel object recognition test (for short- and long-term memory). The offspring of the high-fat diet fed dams showed increased hippocampus IL-6 levels (21-days-old) and impaired short-term memories. These effects were avoided in the offspring of high-fat diet fed dams submitted to prenatal LPS exposure, which showed greater hippocampus IL-10 levels (at 21- and 50-days-old), increased antioxidant activity (50-days-old) in the hippocampus and prefrontal cortex, without memory impairments (short- and long-term memory). IL-6 has been consistently implicated in memory deficits and as an endogenous mechanism for limiting plasticity, while IL-10 regulates glial activation and has a strong association with improvements in cognitive function. Prenatal LPS exposure preventing the increase of IL-6 in the hippocampus and the impairment to short-term object recognition memory caused by the high-fat maternal diet.

Developmental Stressors Induce Innate Immune Memory in Microglia and Contribute to Disease Risk

Many types of stressors have an impact on brain development, function, and disease susceptibility including immune stressors, psychosocial stressors, and exposure to drugs of abuse. We propose that these diverse developmental stressors may utilize a common mechanism that underlies impaired cognitive function and neurodevelopmental disorders such as schizophrenia, autism, and mood disorders that can develop in later life as a result of developmental stressors. While these stressors are directed at critical developmental windows, their impacts are long-lasting. Immune activation is a shared pathophysiology across several different developmental stressors and may thus be a targetable treatment to mitigate the later behavioral deficits. In this review, we explore different types of prenatal and perinatal stressors and their contribution to disease risk and underlying molecular mechanisms. We highlight the impact of developmental stressors on microglia biology because of their early infiltration into the brain, their critical role in brain development and function, and their long-lived status in the brain throughout life. Furthermore, we introduce innate immune memory as a potential underlying mechanism for developmental stressors' impact on disease. Finally, we highlight the molecular and epigenetic reprogramming that is known to underlie innate immune memory and explain how similar molecular mechanisms may be at work for cells to retain a long-term perturbation after exposure to developmental stressors.

Neuroinflammation in Parkinson's Disease: Triggers, Mechanisms, and Immunotherapies

Parkinson's disease (PD) is a heterogeneous neurodegenerative disease involving multiple etiologies and pathogenesis, in which neuroinflammation is a common factor. Both preclinical experiments and clinical studies provide evidence for the involvement of neuroinflammation in the pathophysiology of PD, although there are a number of key issues related to neuroinflammatory processes in PD that remain to be addressed. In this review, we highlight the relationship between the common pathological mechanisms of PD and neuroinflammation, including aggregation of α-synuclein, genetic factors, mitochondrial dysfunction, and gut microbiome dysbiosis. We also describe the two positive feedback loops initiated in PD after the immune system is activated, and their role in the pathogenesis of PD. In addition, the interconnections and differences between the central and peripheral immune systems are discussed. Finally, we review the latest progress in immunotherapy research for PD patients, and propose future directions for clinical research.

Role of Peripheral Immune Cells-Mediated Inflammation on the Process of Neurodegenerative Diseases

Neurodegenerative diseases are characterized by progressive loss of selectively vulnerable neuronal populations, which contrasts with selectively static loss of neurons due to toxic or metabolic disorders. The mechanisms underlying their progressive nature remain unknown. To date, a timely and well-controlled peripheral inflammatory reaction is verified to be essential for neurodegenerative diseases remission. The influence of peripheral inflammation on the central nervous system is closely related to immune cells activation in peripheral blood. The immune cells activation participated in the uncontrolled and prolonged inflammation that drives the chronic progression of neurodegenerative diseases. Thus, the dynamic modulation of this peripheral inflammatory reaction by interrupting the vicious cycle might become a disease-modifying therapeutic strategy for neurodegenerative diseases. This review focused on the role of peripheral immune cells on the pathological progression of neurodegenerative diseases.

Ellagic Acid Inhibits Neuroinflammation and Cognitive Impairment Induced by Lipopolysaccharides

Neuroinflammation is a predisposing factor for the development of cognitive impairment and dementia. Among the new molecules that are currently being studied, ellagic acid (EA) has stood out for its neuroprotective properties. The present study investigated the effects of ellagic acid in the object recognition test, oxidative stress, cholinergic neurotransmission, glial cell expression, and phosphorylated Tau protein expression. For this, 32 male Wistar rats received an intraperitoneal (IP) application of lipopolysaccharides (LPS) at a dose of 250 µg/kg or 0.9% saline solution (SAL) for 8 days. Two hours after the IP injections, the animals received 100 mg/kg of EA or SAL via intragastric gavage. Behavioral parameters (open field test and object recognition) were performed on days 5, 6, and 7 of the experimental periods. The results showed that the treatment with EA in the LPS group was able to inhibit cognitive impairment, modulate the immune system response by significantly reducing glial cell expression, attenuating phosphorylated Tau and oxidative damage with consequent improvement in the antioxidant system, as well as preventing the increase of acetylcholinesterase activity. Thus, the neuroprotective effects of EA and its therapeutic potential in cognitive disorders secondary to neuroinflammation were demonstrated.

Parkinson disease and the immune system - associations, mechanisms and therapeutics

Multiple lines of evidence indicate that immune system dysfunction has a role in Parkinson disease (PD); this evidence includes clinical and genetic associations between autoimmune disease and PD, impaired cellular and humoral immune responses in PD, imaging evidence of inflammatory cell activation and evidence of immune dysregulation in experimental models of PD. However, the mechanisms that link the immune system with PD remain unclear, and the temporal relationships of innate and adaptive immune responses with neurodegeneration are unknown. Despite these challenges, our current knowledge provides opportunities to develop immune-targeted therapeutic strategies for testing in PD, and clinical studies of some approaches are under way. In this Review, we provide an overview of the clinical observations, preclinical experiments and clinical studies that provide evidence for involvement of the immune system in PD and that help to define the nature of this association. We consider autoimmune mechanisms, central and peripheral inflammatory mechanisms and immunogenetic factors. We also discuss the use of this knowledge to develop immune-based therapeutic approaches, including immunotherapy that targets α-synuclein and the targeting of immune mediators such as inflammasomes. We also consider future research and clinical trials necessary to maximize the potential of targeting the immune system.

Chronic Systemic Inflammation Exacerbates Neurotoxicity in a Parkinson's Disease Model

Systemic inflammation is a crucial factor for microglial activation and neuroinflammation in neurodegeneration. This work is aimed at assessing whether previous exposure to systemic inflammation potentiates neurotoxic damage by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and how chronic systemic inflammation participates in the physiopathological mechanisms of Parkinson's disease. Two different models of systemic inflammation were employed to explore this hypothesis: a single administration of lipopolysaccharide (sLPS; 5 mg/kg) and chronic exposure to low doses (mLPS; 100 μg/kg twice a week for three months). After three months, both groups were challenged with MPTP. With the sLPS administration, Iba1 staining increased in the striatum and substantia nigra, and the cell viability lowered in the striatum of these mice. mLPS alone had more impact on the proinflammatory profile of the brain, steadily increasing TNFα levels, activating microglia, reducing BDNF, cell viability, and dopamine levels, leading to a damage profile similar to the MPTP model per se. Interestingly, mLPS increased MAO-B activity possibly conferring susceptibility to MPTP damage. mLPS, along with MPTP administration, exacerbated the neurotoxic effect. This effect seemed to be coordinated by microglia since minocycline administration prevented brain TNFα increase. Coadministration of sLPS with MPTP only facilitated damage induced by MPTP without significant change in the inflammatory profile. These results indicate that chronic systemic inflammation increased susceptibility to MPTP toxic effect and is an adequate model for studying the impact of systemic inflammation in Parkinson's disease.

Critical Role of Monocyte Recruitment in Optic Nerve Damage Induced by Experimental Optic Neuritis

Neuroinflammatory diseases are characterized by blood-brain barrier disruption (BBB) and leukocyte infiltration. We investigated the involvement of monocyte recruitment in visual pathway damage provoked by primary optic neuritis (ON) induced by a microinjection of bacterial lipopolysaccharide (LPS) into the optic nerve from male Wistar rats. Increased Evans blue extravasation and cellularity were observed at 6 h post-LPS injection. In WT-GFPþ/WT chimeric rat optic nerves, the presence of GFP(+) neutrophils and GFP(+) monocytes, and in wild-type rat optic nerves, an increase in CD11b⁺CD45^low and CD11b⁺CD45^high cell number, were observed at 24 h post-LPS. Gamma-irradiation did not affect the increase in BBB permeability, but significantly lessened the decrease in pupil light reflex (PLR), and retinal ganglion cell (RGC) number induced by LPS. At 6 h post-LPS, an increase in chemokine (C-C motif) ligand 2 (CCL2) immunoreactivity co-localized with neutrophils (but not microglia/macrophages or astrocytes) was observed, while at 24 h post-injection, an increase in Iba-1-immunoreactivity and its co-localization with CCL2 became evident. The co-injection of LPS with bindarit (a CCL2 synthesis inhibitor) lessened the effect of LPS on PLR, and RGC loss. The treatment with etoposide or gadolinium chloride that significantly decreased peripheral monocyte (but not neutrophil or lymphocyte) percentage decreased the effect of LPS on PLR, and RGC number. Moreover, a negative correlation between PRL and monocyte (but not lymphocyte or neutrophil) percentage was observed at 7 days post-LPS. Taken together, these results support that monocytes are key players in the initial events that take place during primary ON.

The maintenance of an oral epithelial barrier

Oral epithelial barrier consists of closely controlled structure of the stratified squamous epithelium, which is the gateway to human bodies and encounters a huge burden of microbial, airborne and dietary antigens, as well as masticatory damage. Once this barrier is destroyed, it will trigger bone loss, tissue damage and microbial dysbiosis and lead to diseases, such as periodontitis, oral mucosal diseases and oral cancer. Recently, increasing evidences showed that different factors including microorganism, saliva, proteins and immune components have been considered to play a critical role in the disruption of oral epithelial barrier. Herein, we discussed mechanisms governing the maintenance of oral epithelial barrier. Besides, the role of oral epithelial barrier failure in oral carcinogenesis will also be talked about.

Retinoic Acid-Induced Protein 14 (RAI14) Promotes mTOR-Mediated Inflammation Under Inflammatory Stress and Chemical Hypoxia in a U87 Glioblastoma Cell Line

Retinoic acid-induced 14 is a developmentally regulated gene induced by retinoic acid and is closely associated with NIK/NF-κB signaling. In the present study, we examined the effect of RAI14 on mTOR-mediated glial inflammation in response to inflammatory factors and chemical ischemia. A U87 cell model of LPS- and TNF-α-induced inflammation was used to investigate the role of RAI14 in glial inflammation. U87 cells were treated with siR-RAI14 or everolimus to detect the correlation between mTOR, RAI14, and NF-κB. CoCl₂-stimulated U87 cells were used to analyze the effect of RAI14 on mTOR-mediated NF-κB inflammatory signaling under chemical hypoxia. LPS and TNF-α stimulation resulted in the upregulation of RAI14 mRNA and protein levels in a dose- and time-dependent manner. RAI14 knockdown significantly attenuated the level of pro-inflammatory cytokine via inhibiting the IKK/NF-κB pathway. Treatment with an mTOR inhibitor (everolimus) ameliorated NF-κB activity and IKKα/β phosphorylation via RAI14 signaling. Notably, RAI14 also enhanced mTOR-mediated NF-κB activation under conditions of chemical hypoxia. These findings provide significant insight into the role of RAI14 in mTOR-induced glial inflammation, which is closely associated with infection and ischemia stimuli. Thus, RAI14 may be a potential drug target for the treatment of inflammatory diseases.

Inhibition of the hepatic Nlrp3 protects dopaminergic neurons via attenuating systemic inflammation in a MPTP/p mouse model of Parkinson's disease

Background

Parkinson’s disease (PD) is a neurodegenerative disorder with progressive loss of dopaminergic (DA) neurons. Systemic inflammation is shown to initiate and exacerbate DA neuronal degeneration in the substantia nigra. The infiltration and transformation of immune cells from the peripheral tissues are detected in and around the affected brain regions of PD patients. Our previous studies demonstrated the crucial role that microglial Nod-like receptor protein (NLRP) 3 inflammasome plays in the pathogenesis of PD. Nevertheless, the direct linkage between peripheral inflammation and DA neuron death remains obscure.

Methods

In the present study, we detected the NLRP3 expressions in the midbrain, liver, and bone marrow-derived macrophages in response to 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) acute and chronic challenge. We then used a tail vein injection of Nlrp3-siRNA wrapped with lentivirus to explore the potential influence of hepatic NLRP3 inflammasome-mediated inflammation on neuronal injury in a mouse model of PD via immunohistochemistry, ELISA, and Western blotting analysis.

Results

We showed that siNlrp3 downregulated the NLRP3 protein expression and inhibited the activation of NLRP3 inflammasomes in mice livers. The tail vein injection of LV3-siNlrp3 reduced the liver pro-inflammatory cytokine production, which subsequently alleviated MPTP-triggered microglial activation and DA neuron loss in the midbrain. These findings indicated that inhibition of hepatic NLRP3 inflammasome weakens inflammatory cytokines spreading into the brain and delays the progress of neuroinflammation and DA neuronal degeneration.

Conclusion

This study gives us an insight into the direct linkage between liver inflammation and DA neuron damage in the pathogenesis of PD and provides the potential target of NLRP3 for developing novel drugs for PD therapy.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1236-z) contains supplementary material, which is available to authorized users.

Conditioning Against the Pathology of Parkinson's disease

Parkinson's disease is delayed in clinical onset, asymmetric in initial appearance, and slow in progression. One explanation for these characteristics may be a boost in natural defenses after early exposure to mild cellular stress. As the patient ages and resilience recedes, however, stress levels may become sufficiently high that toxic cellular responses can no longer be curbed, culminating in inverted U-shaped stress-response curves as a function of disease duration. If dopaminergic systems are indeed capable of responding to mild stress with effective natural defenses, experimental models of Parkinson's disease should adhere to the principles of preconditioning, whereby stress exposure fortifies cells and tempers the toxic sequelae of subsequent stressors. Here, I review evidence favoring the efficacy of preconditioning in dopaminergic systems. Recent animal work also raises the possibility that cross-hemispheric preconditioning may arrest the spread of asymmetric Parkinson's pathology to the other side of the brain. Indeed, compensatory homeostatic systems have long been hypothesized to maintain neurological function until a threshold of cell loss is exceeded and are often displayed as inverted U-shaped curves. However, some stress responses assume an exponential or sigmoidal profile as a function of disease severity, suggesting end-stage deceleration of disease processes. Thus, surviving dopaminergic neurons may become progressively harder to kill, with the dorsal nigral tier dying slower due to superior baseline defenses, inducible conditioning capacity, or delayed dorsomedial nigral spread of disease. In addition, compensatory processes may be useful as biomarkers to distinguish "responder patients" from "nonresponders" before clinical trials. However, another possibility is that defenses are already maximally conditioned in most patients and no further boost is possible. A third alternative is that genuinely diseased human cells cannot be conditioned, in contrast to preclinical models, none of which faithfully recapitulate age-related human conditions. Disease-related "conditioning deficiencies" would then explain how Parkinson's pathology takes root, progressively shrinks defenses, and eventually kills the patient.