Lipopolysaccharide-Induced Microglia Activation Promotes the Survival of Midbrain Dopaminergic Neurons In Vitro

2,4-Dichlorophenoxyacetic Acid Induces Degeneration of mDA Neurons In Vitro

Background: Parkinson's disease (PD) affects 1-2% of the population over the age of 60 and the majority of PD cases are sporadic, without any family history of the disease. Neuroinflammation driven by microglia has been shown to promote the progression of midbrain dopaminergic (mDA) neuron loss through the release of neurotoxic factors. Interestingly, the risk of developing PD is significantly higher in distinct occupations, such as farming and agriculture, and is linked to the use of pesticides and herbicides. Methods: The neurotoxic features of 2,4-Dichlorophenoxyacetic acid (2,4D) at concentrations of 10 µM and 1 mM were analyzed in two distinct E14 midbrain neuron culture systems and in primary microglia. Results: The application of 1 mM 2,4D resulted in mDA neuron loss in neuron-enriched cultures. Notably, 2,4D-induced neurotoxicity significantly increased in the presence of microglia in neuron-glia cultures, suggesting that microglia-mediated neurotoxicity could be one mechanism for progressive neuron loss in this in vitro setup. However, 2,4D alone was unable to trigger microglia reactivity. Conclusions: Taken together, we demonstrate that 2,4D is neurotoxic for mDA neurons and that the presence of glia cells enhances 2,4D-induced neuron death. These data support the role of 2,4D as a risk factor for the development and progression of PD and further suggest the involvement of microglia during 2,4D-induced mDA neuron loss.

Ursolic Acid Ameliorated Neuronal Damage by Restoring Microglia-Activated MMP/TIMP Imbalance in vitro

Purpose

The oxygen and glucose deprivation-reoxygenation (OGDR) model is widely used to evaluate ischemic stroke and cerebral ischemia-reperfusion (I/R) injury in vitro. Excessively activated microglia produce pro-inflammatory mediators such as matrix metalloproteinases [MMPs] and their specific inhibitors, tissue inhibitors of metalloproteinases [TIMPs], causing neuronal damage. Ursolic acid (UA) acts as a neuroprotective agent in the rat middle cerebral artery occlusion/reperfusion (MCAO/R) model keeping the MMP/TIMP balance with underlying mechanisms unclear. Our study used OGDR model to determine whether and how UA reduces neuronal damage by reversing MMP/TIMP imbalance caused by microglia in I/R injury in vitro.

Methods

SH-SY5Y cells were first cultured with 95% N2 and 5% CO2 and then cultivated regularly for OGDR model. Cell viability was tested for a proper UA dose. We established a co-culture system with SH-SY5Y cells and microglia-conditioned medium (MCM) stimulated by lipopolysaccharide (LPS) and interferon-gamma (IFNγ). MMP9 and TIMP1 levels were measured with ELISA assay to confirm the UA effect. We added recombinant MMP9 (rMMP9) and TIMP1 neutralizing antibody (anti-TIMP1) for reconfirmation. Transmission electron microscopy was used to observe cell morphology, and flow cytometry and Annexin V-FITC and PI labeling for apoptotic conditions. We further measured the calcium fluorescence intensity in SH-SY5Y cells.

Results

The MCM significantly reduced cell viability of SH-SY5Y cells after OGDR (p<0.01), which was restored by UA (0.25 µM) (p<0.05), whereas lactate dehydrogenase activity, intraneuronal Ca2+ concentration, and apoptosis-related indexes were showed significant improvement after UA treatment (p<0.01). UA corrected the MMP/TIMP imbalance by decreasing MMP9 expression and increasing TIMP1 expression in the co-culture system (p<0.01) and the effects of UA on SH-SY5Y cells were mitigated by the administration of rMMP9 and anti-TIMP1 (p<0.01).

Conclusion

We demonstrated that UA inhibited microglia-induced neuronal cell death in an OGDR model of ischemic reperfusion injury by stabilizing the MMP9/TIMP1 imbalance.

Gut-derived bacterial LPS attenuates incubation of methamphetamine craving via modulating microglia

BACKGROUND

The microbiota-gut-brain axis plays a critical role in the pathophysiology of neuropsychiatric disorders, and the compositions of gut microbiota are altered by addictive drugs. However, the role of gut microbiota in the incubation of methamphetamine (METH) craving remains poorly understood.

METHODS

16S rRNA gene sequencing was performed to assess the richness and diversity of gut microbiota in METH self-administration model. Hematoxylin and eosin staining was performed to evaluate the integrity of intestinal barrier. Immunofluorescence and three-dimensional reconstruction were performed to assess the morphologic changes of microglia. Serum levels of lipopolysaccharide (LPS) were determined using the rat enzyme-linked immunosorbent assay kits. Quantitative real-time PCR was performed to assess transcript levels of dopamine receptor, glutamate ionotropic AMPA receptor 3 and brain-derived neurotrophic factor.

RESULTS

METH self-administration induced gut microbiota dysbiosis, intestinal barrier damage and microglia activation in the nucleus accumbens core (NAcc), which was partially recovered after prolonged withdrawal. Microbiota depletion via antibiotic treatment increased LPS levels and induced a marked change in the microglial morphology in the NAcc, as indicated by the decreases in the lengths and numbers of microglial branches. Depleting the gut microbiota also prevented the incubation of METH craving and increased the population of Klebsiella oxytoca. Furthermore, Klebsiella oxytoca treatment or exogenous administration of the gram-negative bacterial cell wall component LPS increased serum and central LPS levels, induced microglial morphological changes and reduced the dopamine receptor transcription in the NAcc. Both treatments and NAcc microinjections of gut-derived bacterial LPS significantly decreased METH craving after prolonged withdrawal.

CONCLUSIONS

These data suggest that LPS from gut gram-negative bacteria may enter circulating blood, activate microglia in the brain and consequently decrease METH craving after withdrawal, which may have important implications for novel strategies to prevent METH addiction and relapse.

LPS-Activated Microglial Cell-Derived Conditioned Medium Protects HT22 Neuronal Cells against Glutamate-Induced Ferroptosis

Neuron-glia interactions are essential for the central nervous system's homeostasis. Microglial cells are one of the key support cells in the brain that respond to disruptions in such homeostasis. Although their participation in neuroinflammation is well known, studies investigating their role in ferroptosis, an iron-dependent form of nonapoptotic cell death, are lacking. To address this issue, we explored whether microglial (BV-2 cells) activation products can intensify, mitigate or block oxidative and/or ferroptotic damage in neuronal cells (HT22 cell line). Cultured BV-2 microglial cells were stimulated with 5-100 ng/mL lipopolysaccharide (LPS) for 24 h and, after confirmation of microglial activation, their culture medium (conditioned media; CM) was transferred to neuronal cells, which was subsequently (6 h later) exposed to glutamate or tert-butyl hydroperoxide (t-BuOOH). As a major finding, HT22 cells pretreated for 6 h with CM exhibited a significant ferroptosis-resistant phenotype characterized by decreased sensitivity to glutamate (15 mM)-induced cytotoxicity. However, no significant protective effects of LPS-activated microglial cell-derived CM were observed in t-BuOOH (30 µM)-challenged cells. In summary, activated microglia-derived molecules may protect neuronal cells against ferroptosis. The phenomenon observed in this work highlights the beneficial relationship between microglia and neurons, highlighting new possibilities for the control of ferroptosis.

Regulation of N6-methyladenosine (m6A) RNA methylation in microglia-mediated inflammation and ischemic stroke

N6-methyladenosine (m6A) is the most abundant post-transcription modification, widely occurring in eukaryotic mRNA and non-coding RNA. m6A modification is highly enriched in the mammalian brain and is associated with neurological diseases like Alzheimer’s disease (AD) and Parkinson’s disease (PD). Ischemic stroke (IS) was discovered to alter the cerebral m6A epi-transcriptome, which might have functional implications in post-stroke pathophysiology. Moreover, it is observed that m6A modification could regulate microglia’s pro-inflammatory and anti-inflammatory responses. Given the critical regulatory role of microglia in the inflammatory processes in the central nervous system (CNS), we speculate that m6A modification could modulate the post-stroke microglial inflammatory responses. This review summarizes the vital regulatory roles of m6A modification in microglia-mediated inflammation and IS. Stroke is associated with a high recurrence rate, understanding the relationship between m6A modification and stroke may help stroke rehabilitation and develop novel therapies in the future.

Hyodeoxycholic acid inhibits lipopolysaccharide-induced microglia inflammatory responses through regulating TGR5/AKT/NF-κB signaling pathway

BACKGROUND

Hyodeoxycholic acid (HDCA) is a natural secondary bile acid with enormous pharmacological effects, such as modulating inflammation in neuron. However, whether HDCA could suppress microglial inflammation has not been elucidated yet.

AIMS

To determine the anti-microglial inflammatory effect of HDCA in lipopolysaccharide (LPS) models and its mechanisms.

METHODS

The effect of HDCA was evaluated in LPS-stimulated BV2 microglial cells in vitro and the cortex of LPS-treated mice in vivo. Immunohistochemistry and immunofluorescence were used to visualize the localization of nuclear factor kappa light-chain enhancer of activated B cells (NF-κB) and ionized calcium-binding adaptor protein-1 (Iba-1), respectively. The mRNA expression of inflammatory cytokines was measured by RT-qPCR. The protein expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), takeda G-coupled protein receptor 5 (TGR5), and the phosphorylation of protein kinase B (AKT), NF-κB, and inhibitor of NF-κB protein α (IκBα) was examined by Western blot.

RESULTS

HDCA inhibited the inflammatory responses in LPS-treated BV2 cells and in the cortex of LPS-treated mice, evidenced by decreased production of inflammatory mediators such as iNOS, COX-2, tumor necrosis factor (TNF-α), interleukin (IL)-6, and IL-1β. Further study demonstrated that HDCA repressed the phosphorylation, nuclear translocation, and transcriptional activity of NF-κB and inhibited the activation of AKT in BV-2 cells induced by LPS. Meanwhile, addition of TGR5 inhibitor, triamterene, abolished the effects of HDCA on TGR5, AKT, and NF-κB.

CONCLUSION

The present study demonstrated that HDCA prevents LPS-induced microglial inflammation in vitro and in vivo, the action of which is via regulating TGR5/AKT/NF-κB signaling pathway.

The impact of early life stress and immune challenge on behavior and glia cells alteration in late adolescent rats

Maternal deprivation (MD) is known to be related to long-term changes that could influence the onset of psychiatric disorders. Studies have demonstrated that early life stress makes the cells in the brain more susceptible to subsequent stressors. To test it, we used an animal model of MD conducted from postnatal day (PND) 1 to 10. Deprived and non-deprived rats (control) were randomized to receive or not lipopolysaccharide (LPS) at 5 mg/kg on PND 50. The behavior and glial cells activation were evaluated in all groups from 51 to 53 PND. There was an increase in the immobility time in the MD and MD+LPS groups. The spontaneous locomotor activity was not changed between groups. We found elevated ionized calcium-binding adapter molecule 1 (Iba-1)-positive cells levels in the control+LPS and MD+LPS groups. In the MD+LPS group, it was found an increase in Iba-positive cells compared to the MD+sal group. The glial fibrillary acidic protein (GFAP)-positive cells were also increased in the MD+LPS, compared to control+sal, control+LPS, and MD+sal groups. Immune challenge by LPS in late adolescence, which was subjected to MD, did not influence the depressive-like behavior but exerted a pronounced effect in the microglial activation and astrocyte atrophy.

The impact of trophic and immunomodulatory factors on oligodendrocyte maturation: Potential treatments for encephalopathy of prematurity

Encephalopathy of prematurity (EoP) is a major cause of morbidity in preterm neonates, causing neurodevelopmental adversities that can lead to lifelong impairments. Preterm birth-related insults, such as cerebral oxygen fluctuations and perinatal inflammation, are believed to negatively impact brain development, leading to a range of brain abnormalities. Diffuse white matter injury is a major hallmark of EoP and characterized by widespread hypomyelination, the result of disturbances in oligodendrocyte lineage development. At present, there are no treatment options available, despite the enormous burden of EoP on patients, their families, and society. Over the years, research in the field of neonatal brain injury and other white matter pathologies has led to the identification of several promising trophic factors and cytokines that contribute to the survival and maturation of oligodendrocytes, and/or dampening neuroinflammation. In this review, we discuss the current literature on selected factors and their therapeutic potential to combat EoP, covering a wide range of in vitro, preclinical and clinical studies. Furthermore, we offer a future perspective on the translatability of these factors into clinical practice.

Melatonin alleviates intestinal injury, neuroinflammation and cognitive dysfunction caused by intestinal ischemia/reperfusion

Intestinal ischemia/reperfusion (I/R) can cause multiple organ damage with extremely high morbidity and mortality. Melatonin has anti-inflammatory, anti-oxidative and anti-apoptotic effects against various diseases. This study aimed to explore whether melatonin had a protective effect against intestinal I/R-induced neuroinflammation and cognitive dysfunction, and investigate its potential mechanisms. In this study, melatonin was administered to the rats with intestinal I/R, then histological changes in intestine and brain (frontal cortex and hippocampal CA1 area) tissues and cognitive function were detected, respectively. The encephaledema and blood-brain barrier (BBB) permeability were observed. Moreover, the alterations of proinflammatory factors (tumor necrosis factor-α, interleukin-6 and interleukin-1β), oxidative response (malondialdehyde, superoxide dismutase, and reactive oxygen species), apoptosis and proteins associated with inflammation,including Toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (Myd88) and phosphorylated nuclear factor kappa beta (NF-κB), and apoptosis (cleaved caspase-3) in brain tissues were examined. Furthermore, the expressions of TLR4, Myd88, and microglial activity were observed by multiple immunofluorescence staining. The results showed that intestinal I/R-induced abnormal neurobehavior and cerebral damage were ameliorated after melatonin treatment, which were demonstrated by improved cognitive dysfunction and aggravated histology. Furthermore, melatonin decreased the levels of proinflammatory factors and oxidative stress in plasma, intestine and brain tissues, attenuated apoptotic cell, and inhibited the expressions of related proteins and the immunoreactivity of TLR4 or Myd88 in microglia in brain tissues. These findings showed that melatonin might relieve neuroinflammation and cognitive dysfunction caused by intestinal I/R, which could be, at least partially, related to the inhibition of the TLR4/Myd88 signaling in microglia.