Pain caused by acute pulpitis (AP) is a common symptom in clinical settings. However, its underlying mechanisms have largely remained unknown. Using AP model, we demonstrated that dental injury caused severe pulp inflammation with up-regulated serum IL-1β. Assessment from head-withdrawal reflex thresholds (HWTs) and open-field test demonstrated nociceptive response at 1 day post injury. A consistent up-regulation of Toll-like receptor 4 (TLR4) in the trigeminal ganglion (TG) ipsilateral to the injured pulp was found; and downstream signaling components of TLR4, including MyD88, TRIF and NF-κB and cytokines such as TNF-α and IL-1β, were also increased. Retrograde labeling indicated that most TLR4 positve neuron in the TG innnervated the pulp and TLR4 immunoreactivity was mainly in the medium and small neurons. Double labeling showed that the TLR4 expressing neurons in the ipsilateral TG were TRPV1 and CGRP positive, but IB4 negative. Furthermore, blocking TLR4 by eritoran (TLR4 antagonist) in TGs of the AP model significantly down-regulated MyD88, TRIF, NF-κB, TNF-α and IL-1β production and behavior of nociceptive response. Our findings suggest that TLR4 signaling in TG cells, particularly the peptidergic TRPV1 neurons, plays a key role in AP-induced nociception and indicate that TLR4 signaling could be a potential therapeutic target for orofacial pain.

Proper proliferation and differentiation of neural stem cells or progenitors in hippocampus is critical to learn and memory functions, which might be disturbed by lead toxicity particularly in young individuals. While astroglial and microglial cells are known to play an important role in regulating neurogenesis of hippocampus, their abnormal response and influence on hippocampal neurogenesis remains unclear. In this study, therefore, glial response including microgliosis, astrogliogenesis and mediating involvement of TLR4-MyD88-NFκB signaling cascades were observed in hippocampus of young mice by animal model with lead (plumbum, Pb) exposure. It revealed that (1) significant microglial activation occurred in hippocampus soon following Pb exposure; (2) increased levels of TLR4, MyD88, NFκB expression were concomitantly detected; (3) BrdU-incorporated progenitor cells were observed in dentate gyrus with significantly-increased numbers at d28 in Pb insult group; (4) obvious astrogliogenesis was observed while these doublecortin-labeled differentiated neurons were not significantly changed in hippocampus; (5) administration of MyD88 inhibitory peptide attenuated or relieved above effects; (6) enhanced expression levels of IL-1β, TNFα, p38MAPK and ERK1/2 were also detected in hippocampus, indicating potential implication of inflammatory response and MAPK signaling activation in lead-induced microgliosis and astrogliosis. Data of this study overall have indicated that lead exposure could trigger or induce abnormal microgliosis and astrogliogenesis in the hippocampus of young mice through triggering TLR4-MyD88-NFκB signaling cascades, which might possibly thereafter disturb hippocampal neurogenesis and functional plasticity.

Inflammation is implicated in epileptogenesis. Activated microglia and macrophages (MG/MΦ) are found in the brains of patients with epilepsy-related diseases and animal models of epilepsy. It is not yet known how the MG/MΦ activation phenotype affects pathological changes in the brain after a single seizure. In this study, we had 2 main purposes: first, to characterize post-status epilepticus (SE) inflammation by tracking MG/MΦ polarization, and, second, to explore the role of an innate immune receptor adaptor protein, namely, myeloid differentiation primary response gene 88 (MyD88), in the induction of SE in a mouse model. A lithium–pilocarpine model of seizure conditions was generated in C57BL/6 mice. The intensity and distribution of MG/MΦ polarization were tracked by fluorescent immunohistochemistry and Western blotting for the polarization markers inducible nitrogen oxygenized synthase, arginase-1, CD163, and mannose receptor. We observed steadily increasing M1 MG/MΦ along with MyD88 signal upregulation after SE in the hippocampi of mice, whereas the M2 marker arginase-1 was localized mainly in astrocytes rather than in MG/MΦ. Inhibition or gene knockout of MyD88 reduced M1 MG/MΦ and gliosis although increasing M2 MG/MΦ in the hippocampi of SE mice. MyD88 inhibition also augmented glutamate transporter 1 expression and reduced N-methyl-D-aspartate receptor NR1 subunit expression in the hippocampus to protect pyramidal neurons from apoptosis. These data suggest that MG/MΦ polarization after SE impacts the pathological outcome of the hippocampus via MyD88 signaling and point to MyD88 as a potential neuroprotective target for epilepsy therapy.

Background: Hemorrhage is a direct consequence of traumatic injury to the central nervous system and may cause innate immune reactions including cerebral Toll-like receptor (TLR) 4 upregulation which usually leads to poor outcome in the traumatic brain injury. In spinal cord injury (SCI), however, how hemorrhage induces innate immune reaction in spinal parenchyma remains unknown. The present study aimed to see whether blood component and/or other factor(s) induce TLR4 and microglia/macrophages involved innate immune reactions in the rat spinal cord after traumatic injury.Methods: Using the compressive SCI model of the rat, hemorrhage in the spinal cord was identified by hematoxylin-eosin staining. Microglia/macrophage activation, TLR4 expression, and cell apoptosis were investigated by immunohistochemistry. Nuclear factor (NF)-κB p50 level of the two segments of the cord was detected by western blotting assay. With carbon powder injection, blood origination of the hematoma was explored. The blood-spinal cord barrier (BSCB) states of the lesion site and the hematoma were compared with immunohistochemistry and tannic acid-ferric chloride staining.Results: Histological observation found blood accumulated in the center of compression lesion site (epicenter) and in the hematoma approximately 1.5 cm away from the epicenter. TLR4 expression, microglia//macrophage activation, and subsequent apoptosis in the area of far-away hematoma were late and weak in comparison to that in epicenter. In addition, TLR4 positive microglia/macrophages appeared to be phagocytotic in the far-away hematoma more obviously than that in the epicenter. Injected carbon powder indicated that accumulated blood of the far-away hematoma originated from the bleeding of the lesion epicenter, and the BSCB around the hematoma was not compromised in the early phase. Accordingly, at 3 days post injury, NF-κB p50 was upregulated based on the similar levels of blood component hemoglobin, and cell apoptosis was obvious in the epicenter but not in the far-away hematoma.Conclusion: These data suggest that besides blood component, BSCB compromise and the extent of tissue injury contribute more to TLR4 and microglia/macrophage responses to the spinal cord hemorrhage. Therefore, the innate immune environment is a necessary consideration for the SCI therapy targeting TLR4 and microglia/macrophages.

Ischemic stroke is a neurological disorder caused by vascular stenosis or occlusion, accounting for approximately 87% of strokes. Clinically, the most effective therapy for ischemic stroke is vascular recanalization, which aims to rescue neurons undergoing ischemic insults. Although reperfusion therapy is the most effective treatment for ischemic stroke, it still has limited benefits for many patients, and ischemia-reperfusion (I/R) injury is a widely recognized cause of poor prognosis. Here, we aim to investigate the mechanism of protein phosphatase Mg²⁺/Mn²⁺ dependent 1 K (PPM1K) mediates metabolic disorder of branched-chain amino acids (BCAA) by promoting fatty acid oxidation led to ferroptosis after cerebral I/R injury. We established the I/R model in mice and used BT2, a highly specific BCAA dehydrogenase (BCKD) kinase inhibitor to promote BCAA metabolism. It was further verified by lentivirus knocking down PPM1K in neurons. We found that BCAA levels were elevated after I/R injury due to dysfunctional oxidative degradation caused by phosphorylated BCKD E1α subunit (BCKDHA). Additionally, the level of phosphorylated BCKDHA was determined by decreased PPM1K in neurons. We next demonstrated that BCAA could induce oxidative stress, lipid peroxidation, and ferroptosis in primary cultured cortical neurons in vitro. Our results further showed that BT2 could reduce neuronal ferroptosis by enhancing BCAA oxidation through inhibition of BCKDHA phosphorylation. We further found that defective BCAA catabolism could induce neuronal ferroptosis by PPM1K knockdown. Furthermore, BT2 was found to alleviate neurological behavior disorders after I/R injury in mice, and the effect was similar to ferroptosis inhibitor ferrostatin-1. Our findings reveal a novel role of BCAA in neuronal ferroptosis after cerebral ischemia and provide a new potential target for the treatment of ischemic stroke.

Purpose: Comorbid anxiety and depression in people with epilepsy (PWE) are highly prevalent and contribute to low quality of life (QOL) and may even lead to poor outcomes of epilepsy. Among the various factors that affect these negative emotional comorbidities, possible gender differences remain poorly understood and are often neglected. This research aimed to determine whether there are discrepancies in the incidence and influence factors of anxiety and depression between men and women with epilepsy in a hospital in northwest China. Methods: A total of 158 adult PWE (female: N = 65; 41.1%) completed self-report questionnaires, including the Self-rating Anxiety Scale (SAS), the Self-rating Depression Scale (SDS), the Chinese version of the Quality of Life in Epilepsy-31 (QOLIE-31) inventory and the Pittsburgh Sleep Quality Inventory (PSQI). The comparison between male and female PWE was made by regression analysis. Results: For the prevalence of anxiety and depression in PWE, no gender difference was found in this study. However, the moderating factors of psychiatric comorbidities were significantly different between men and women: male PWE with comorbid anxiety were more likely to be affected by sleep quality, while anxiety symptoms in female PWE were closely associated with the frequency of seizures. Education years and QOL social function were significant indicators of depression in male PWE but not in female PWE. The important and common predictor for anxiety and depressive symptoms in PWE was QOL energy/fatigue, with male patients being more affected. Conclusion: For the PWE included in this study, the incidence of comorbid anxiety and depression in PWE was similar for men and women, but the moderating factors affecting comorbid anxiety and depressive disorders differed between genders: male PWE were more likely to be affected by psychosocial factors, while female PWE were more influenced by epilepsy itself. This exploration suggests that gender-specific health care should be considered in epilepsy therapy to improve the psychiatric condition and QOL of PWE, and different treatments should be conducted for male and female PWE to prevent negative emotional comorbidities.