NLRP3 Inflammasome Activation in the Brain after Global Cerebral Ischemia and Regulation by 17β-Estradiol

Impact of Estrogen on Purinergic Signaling in Microvascular Disease

Microvascular ischemia, especially in the heart and kidneys, is associated with inflammation and metabolic perturbation, resulting in cellular dysfunction and end-organ failure. Heightened production of adenosine from extracellular nucleotides released in response to inflammation results in protective effects, inclusive of adaptations to hypoxia, endothelial cell nitric oxide release with the regulation of vascular tone, and inhibition of platelet aggregation. Purinergic signaling is modulated by ectonucleoside triphosphate diphosphohydrolase-1 (NTPDase1)/CD39, which is the dominant factor dictating vascular metabolism of extracellular ATP to adenosine throughout the cardiovascular tissues. Excess levels of extracellular purine metabolites, however, have been associated with metabolic and cardiovascular diseases. Physiological estrogen signaling is anti-inflammatory with vascular protective effects, but pharmacological replacement use in transgender and postmenopausal individuals is associated with thrombosis and other side effects. Crucially, the loss of this important sex hormone following menopause or with gender reassignment is associated with worsened pro-inflammatory states linked to increased oxidative stress, myocardial fibrosis, and, ultimately, diastolic dysfunction, also known as Yentl syndrome. While there is a growing body of knowledge on distinctive purinergic or estrogen signaling and endothelial health, much less is known about the relationships between the two signaling pathways. Continued studies of the interactions between these pathways will allow further insight into future therapeutic targets to improve the cardiovascular health of aging women without imparting deleterious side effects.

ATR-FTIR spectroscopy to evaluate serum protein expression in a murine cerebral ischemia model

Stroke is a prevalent vascular disease that causes disability and death worldwide. Molecular techniques have been developed to assess serum concentrations of biomarkers associated with this disease, such as some proteins. ATR-FTIR was proposed as an alternative technique to determine protein expression during the early stages of stroke. Serum samples from sham, ischemic, and ischemic treated with estradiol benzoate (EB; as a neuroprotective agent) male rats were evaluated at 0, 2-, 4-, 6-, 12-, and 24-hours post-ischemia. The analysis was developed in the mid-infrared region but mainly focused on the protein region (1500-1700 cm-1), where it was possible to observe the modulation in the absorbance intensity. The peaks at 1545, 1645, 1635, and 1650 cm-1 associated with amide II, amide I, β-sheets, and α-helixes, respectively, were prominent peaks where protein modulation was observed. The results demonstrate that infrared spectroscopy could be a good alternative technique to determine the modulation of protein expression during stroke events.

Gender and sex hormone effects on neonatal innate immune function

OBJECTIVES

Scientific evidence provides a widened view of differences in immune response between male and female neonates. The X-chromosome codes for several genes important in the innate immune response and neonatal innate immune cells express receptors for, and are inhibited by, maternal sex hormones. We hypothesized that sex differences in innate immune responses may be present in the neonatal population which may contribute to the increased susceptibility of premature males to sepsis. We aimed to examine the in vitro effect of pro-inflammatory stimuli and hormones in neutrophils and monocytes of male and female neonates, to examine the expression of X-linked genes involved in innate immunity and the miRNA profiles in these populations.

METHODS

Preterm infants (n = 21) and term control (n = 19) infants were recruited from the Coombe Women and Infants University Hospital Dublin with ethical approval and explicit consent. The preterm neonates (eight female, 13 male) were recruited with a mean gestation at birth (mean ± SD) of 28 ± 2 weeks and corrected gestation at the time of sampling was 30 + 2.6 weeks. The mean birth weight of preterm neonates was 1084 ± 246 g. Peripheral blood samples were used to analyze immune cell phenotypes, miRNA human panel, and RNA profiles for inflammasome and inflammatory genes.

RESULTS

Dividing neutrophil results by sex showed no differences in baseline CD11b between sexes among either term or preterm neonates. Examining monocyte CD11b by sex shows, that at baseline, total and classical monocytes have higher CD11b in preterm females than preterm males. Neutrophil TLR2 did not differ between sexes at baseline or following lipopolysaccharide (LPS) exposure. CD11b expression was higher in preterm male non-classical monocytes following Pam3CSK treatment when compared to females, a finding which is unique to our study. Preterm neonates had higher TLR2 expression at baseline in total monocytes, classical monocytes and non-classical monocytes than term. A sex difference was evident between preterm females and term females in TLR2 expression only. Hormone treatment showed no sex differences and there was no detectable difference between males and females in X-linked gene expression. Two miRNAs, miR-212-3p and miR-218-2-3p had significantly higher expression in preterm female than preterm male neonates.

CONCLUSIONS

This study examined immune cell phenotypes and x-linked gene expression in preterm neonates and stratified according to gender. Our findings suggest that the responses of females mature with advancing gestation, whereas male term and preterm neonates have very similar responses. Female preterm neonates have improved monocyte activation than males, which likely reflects improved innate immune function as reflected clinically by their lower risk of sepsis. Dividing results by sex showed changes in preterm and term infants at baseline and following LPS stimulation, a difference which is reflected clinically by infection susceptibility. The sex difference noted is novel and may be limited to the preterm or early neonatal population as TLR2 expression on monocytes of older children does not differ between males and females. The differences shown in female and male innate immune cells likely reflect a superior innate immune defense system in females with sex differences in immune cell maturation. Existing human studies on sex differences in miRNA expression do not include preterm patients, and most frequently use either adult blood or cord blood. Our findings suggest that miRNA profiles are similar in neonates of opposite sexes at term but require further investigation in the preterm population. Our findings, while novel, provide only very limited insights into sex differences in infection susceptibility in the preterm population leaving many areas that require further study. These represent important areas for ongoing clinical and laboratory study and our findings represent an important contribution to exiting literature.

Sex-specific NLRP3 activation in neutrophils promotes neutrophil recruitment and NETosis in the murine model of diffuse alveolar hemorrhage

Objectives

Diffuse alveolar hemorrhage (DAH) is a life-threatening complication of systemic lupus erythematosus and small vessel vasculitis. We previously showed that neutrophil extracellular traps (NETs) were associated with the pathogenesis of pristane-induced DAH and demonstrated that neutrophil NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome assembly participated in NET generation under sterile stimulation. We investigated whether NLRP3 inflammasome assembly in neutrophils may drive pulmonary NETosis in a mouse model of pristane-induced DAH.

Methods

C57BL/6J mice received a single intraperitoneal injection of 0.5mL of pristane. Neutrophil NLRP3 inflammasome assembly and NETs were characterized by immunofluorescence staining of apoptosis-associated speck-like protein a CARD (ASC), co-staining of DNA, and citrullinated histones, respectively. Clinical status of mice was assessed 11 days after pristane injection by measurement of arterial oxygen saturation and of weight loss; severity of lung injury was determined using a quantification score from hematoxylin-eosin-stained slides.

Results

Pristane induced ASC speck formation in neutrophils and we confirmed that NLRP3 inflammasome was involved in NET generation after pristane stimulation in vitro. NLRP3 deficiency reduced the severity of pristane-induced DAH in female, but not male mice. Interestingly, NLRP3 deficiency reduced the number of neutrophils and NETs in the lungs of females compared to males.

Conclusions

Our results suggest a link between female sex-specific NLRP3 inflammasome activation and subsequent pulmonary NETosis in the development of pristane-induced DAH. Therefore, we identified NLRP3 inflammasome as a potential new therapeutic target in this severe complication of pro-female autoimmune disease for which specific inhibitors of NLRP3 are currently developed.

Intracerebroventricular infusion of secretoneurin inhibits neuronal NLRP3-Apoptosis pathway and preserves learning and memory after cerebral ischemia

Transient global cerebral ischemia (GCI) results in delayed neuronal death, primarily apoptosis, in the hippocampal CA1 subregion, which leads to severe cognitive deficits. While therapeutic hypothermia is an approved treatment for patients following cardiac arrest, it is associated with various adverse effects. Secretoneurin (SN) is an evolutionarily conserved neuropeptide generated in the brain, adrenal medulla and other endocrine tissues. In this study, SN was infused into the rat brain by intracerebroventricular injection 1 day after GCI, and we demonstrated that SN could significantly preserve spatial learning and memory in the Barnes maze tasks examined on days 14-17 after GCI. To further investigate underlying pathways involved, we demonstrated that, on day 5 after GCI, SN could significantly inhibit GCI-induced expression levels of Apoptosis Inducing Factor (AIF) and cleaved-PARP1, as well as neuronal apoptosis and synaptic loss in the hippocampal CA1 region. Additionally, SN could attenuate GCI-induced activation of both caspase-1 and caspase-3, and the levels of pro-inflammatory cytokines IL-1β and IL-18 in the CA1 region. Mechanically, we observed that treatment with SN effectively inhibited NLRP3 protein elevation and the bindings of NLRP3-ASC and ASC-caspase-1 in hippocampal neurons after GCI. In summary, our data indicate that SN could effectively attenuate NLRP3 inflammasome formation, as well as the activation of caspase-1 and -3, the production of pro-inflammatory cytokines, and ultimately the neuronal apoptotic loss induced by GCI. Potential neuronal pyroptosis, or caspase-1-dependent cell death, could also be involved in ischemic neuronal death, which needs further investigation.

Advances in the Study of Etiology and Molecular Mechanisms of Sensorineural Hearing Loss

Sensorineural hearing loss (SNHL), a multifactorial progressive disorder, results from a complex interplay of genetic and environmental factors, with its underlying mechanisms remaining unclear. Several pathological factors are believed to contribute to SNHL, including genetic factors, ion homeostasis, cell apoptosis, immune inflammatory responses, oxidative stress, hormones, metabolic syndrome, human cytomegalovirus infection, mitochondrial damage, and impaired autophagy. These factors collectively interact and play significant roles in the onset and progression of SNHL. The present review offers a comprehensive overview of the various factors that contribute to SNHL, emphasizes recent developments in understanding its etiology, and explores relevant preventive and intervention measures.

From inflammatory signaling to neuronal damage: Exploring NLR inflammasomes in ageing neurological disorders

The persistence of neuronal degeneration and damage is a major obstacle in ageing medicine. Nucleotide-binding oligomerization domain (NOD)-like receptors detect environmental stressors and trigger the maturation and secretion of pro-inflammatory cytokines that can cause neuronal damage and accelerate cell death. NLR (NOD-like receptors) inflammasomes are protein complexes that contain NOD-like receptors. Studying the role of NLR inflammasomes in ageing-related neurological disorders can provide valuable insights into the mechanisms of neurodegeneration. This includes investigating their activation of inflammasomes, transcription, and capacity to promote or inhibit inflammatory signaling, as well as exploring strategies to regulate NLR inflammasomes levels. This review summarizes the use of NLR inflammasomes in guiding neuronal degeneration and injury during the ageing process, covering several neurological disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, stroke, and peripheral neuropathies. To improve the quality of life and slow the progression of neurological damage, NLR-based treatment strategies, including inhibitor-related therapies and physical therapy, are presented. Additionally, important connections between age-related neurological disorders and NLR inflammasomes are highlighted to guide future research and facilitate the development of new treatment options.

Heat shock response during the resolution of inflammation and its progressive suppression in chronic-degenerative inflammatory diseases

The heat shock response (HSR) is a crucial biochemical pathway that orchestrates the resolution of inflammation, primarily under proteotoxic stress conditions. This process hinges on the upregulation of heat shock proteins (HSPs) and other chaperones, notably the 70 kDa family of heat shock proteins, under the command of the heat shock transcription factor-1. However, in the context of chronic degenerative disorders characterized by persistent low-grade inflammation (such as insulin resistance, obesity, type 2 diabetes, nonalcoholic fatty liver disease, and cardiovascular diseases) a gradual suppression of the HSR does occur. This work delves into the mechanisms behind this phenomenon. It explores how the Western diet and sedentary lifestyle, culminating in the endoplasmic reticulum stress within adipose tissue cells, trigger a cascade of events. This cascade includes the unfolded protein response and activation of the NOD-like receptor pyrin domain-containing protein-3 inflammasome, leading to the emergence of the senescence-associated secretory phenotype and the propagation of inflammation throughout the body. Notably, the activation of the NOD-like receptor pyrin domain-containing protein-3 inflammasome not only fuels inflammation but also sabotages the HSR by degrading human antigen R, a crucial mRNA-binding protein responsible for maintaining heat shock transcription factor-1 mRNA expression and stability on heat shock gene promoters. This paper underscores the imperative need to comprehend how chronic inflammation stifles the HSR and the clinical significance of evaluating the HSR using cost-effective and accessible tools. Such understanding is pivotal in the development of innovative strategies aimed at the prevention and treatment of these chronic inflammatory ailments, which continue to take a heavy toll on global health and well-being.

Male versus female inflammatory response after brain death model followed by ex vivo lung perfusion

BACKGROUND

Ex vivo lung perfusion (EVLP) is a useful tool for assessing lung grafts quality before transplantation. Studies indicate that donor sex is as an important factor for transplant outcome, as females present higher inflammatory response to brain death (BD) than males. Here, we investigated sex differences in the lungs of rats subjected to BD followed by EVLP.

METHODS

Male and female Wistar rats were subjected to BD, and as controls sham animals. Arterial blood was sampled for gas analysis. Heart-lung blocks were kept in cold storage (1 h) and normothermic EVLP carried out (4 h), meanwhile ventilation parameters were recorded. Perfusate was sampled for gas analysis and IL-1β levels. Leukocyte infiltration, myeloperoxidase presence, IL-1β gene expression, and long-term release in lung culture (explant) were evaluated.

RESULTS

Brain dead females presented a low lung function after BD, compared to BD-males; however, at the end of the EVLP period oxygenation capacity decreased in all BD groups. Overall, ventilation parameters were maintained in all groups. After EVLP lung infiltrate was higher in brain dead females, with higher neutrophil content, and accompanied by high IL-1β levels, with increased gene expression and concentration in the culture medium (explant) 24 h after EVLP. Female rats presented higher lung inflammation after BD than male rats. Despite maintaining lung function and ventilation mechanics parameters for 4 h, EVLP was not able to alter this profile.

CONCLUSION

In this context, further studies should focus on therapeutic measures to control inflammation in donor or during EVLP to increase lung quality.

Role of NLRP3 Inflammasome in Stroke Pathobiology: Current Therapeutic Avenues and Future Perspective

Neuroinflammation is a key pathophysiological feature of stroke-associated brain injury. A local innate immune response triggers neuroinflammation following a stroke via activating inflammasomes. The nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) inflammasome has been heavily implicated in stroke pathobiology. Following a stroke, several stimuli have been suggested to trigger the assembly of the NLRP3 inflammasome. Recent studies have advanced the understanding and revealed several new players regulating NLRP3 inflammasome-mediated neuroinflammation. This article discussed recent advancements in NLRP3 assembly and highlighted stroke-induced mitochondrial dysfunction as a major checkpoint to regulating NLRP3 activation. The NLRP3 inflammasome activation leads to caspase-1-dependent maturation and release of IL-1β, IL-18, and gasdermin D. In addition, genetic or pharmacological inhibition of the NLRP3 inflammasome activation and downstream signaling has been shown to attenuate brain infarction and improve the neurological outcome in experimental models of stroke. Several drug-like small molecules targeting the NLRP3 inflammasome are in different phases of development as novel therapeutics for various inflammatory conditions, including stroke. Understanding how these molecules interfere with NLRP3 inflammasome assembly is paramount for their better optimization and/or development of newer NLRP3 inhibitors. In this review, we summarized the assembly of the NLRP3 inflammasome and discussed the recent advances in understanding the upstream regulators of NLRP3 inflammasome-mediated neuroinflammation following stroke. Additionally, we critically examined the role of the NLRP3 inflammasome-mediated signaling in stroke pathophysiology and the development of therapeutic modalities to target the NLRP3 inflammasome-related signaling for stroke treatment.

Hua-Feng-Dan Alleviates LPS-induced Neuroinflammation by Inhibiting the TLR4/Myd88/NF-κB Pathway: Integrating Network Pharmacology and Experimental Validation

BACKGROUND

Neuroinflammation is the pathological basis of many neurological diseases, including neurodegenerative diseases and stroke. Hua-Feng-Dan (HFD) is a well-established traditional Chinese medicine that has been used for centuries to treat stroke and various other brain-related ailments.

OBJECTIVE

Our study aims to elucidate the molecular mechanism by which HFD mitigates neuroinflammation by combining network pharmacology and in vitro experiments.

METHODS

TCMSP and SymMap databases were used to extract active compounds and their related targets. The neuroinflammation-related targets were obtained from the GeneCards database. The common targets of HFD and neuroinflammation were used to construct a protein-protein interaction (PPI) network. MCODE plug-in was used to find the hub module genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were used to dissect the hub module genes. The lipopolysaccharide (LPS)-induced BV2 microglial neuroinflammation model was utilized to assess the therapeutic effects of HFD on neuroinflammation. Western blotting analysis was performed to examine the core target proteins in the TLR4/My- D88/NF-κB signaling pathway, potentially implicated in HFD's therapeutic effects on neuroinflammation. Hoechst 33342 staining and JC-1 staining were employed to evaluate neuronal apoptosis.

RESULTS

Through network pharmacology, 73 active compounds were identified, with quercetin, beta-sitosterol, luteolin, and (-)-Epigallocatechin-3-Gallate recognized as important compounds. Meanwhile, 115 common targets of HFD and neuroinflammation were identified, and 61 targets were selected as the hub targets utilizing the MCODE algorithm. The results of in vitro experiments demonstrated that HFD significantly inhibited microglial-mediated neuronal inflammation induced by LPS. Integrating the predictions from network pharmacology with the in vitro experiment results, it was determined that the mechanism of HFD in mitigating neuroinflammation is closely related to the TLR4/MyD88/NF-κB pathway. Furthermore, HFD demonstrated the capacity to shield neurons from apoptosis by curbing the secretion of pro-inflammatory factors subsequent to microglial activation.

CONCLUSION

The findings demonstrated that HFD had an inhibitory effect on LPS-induced neuroinflammation in microglia and elucidated its underlying mechanism. These findings will offer a theoretical foundation for the clinical utilization of HFD in treating neurodegenerative diseases associated with neuroinflammation.

Estrogen plays an important role by influencing the NLRP3 inflammasome

The nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome is an important part of the natural immune system that plays an important role in many diseases. Estrogen is a sex hormone that plays an important role in controlling reproduction and regulates many physiological and pathological processes. Recent studies have indicated that estrogen is associated with disease progression. Estrogen can ameliorate some diseases (e. g, sepsis, mood disturbances, cerebral ischemia, some hepatopathy, Parkinson's disease, amyotrophic lateral sclerosis, inflammatory bowel disease, spinal cord injury, multiple sclerosis, myocardial ischemia/reperfusion injury, osteoarthritis, and renal fibrosis) by inhibiting the NLRP3 inflammasome. Estrogen can also promote the development of diseases (e.g., ovarian endometriosis, dry eye disease, and systemic lupus erythematosus) by upregulating the NLRP3 inflammasome. In addition, estrogen has a dual effect on the development of cancers and asthma. However, the mechanism of these effects is not summarized. This article reviewed the progress in understanding the effects of estrogen on the NLRP3 inflammasome and its mechanisms in recent years to provide a theoretical basis for an in-depth study.

[Photobiomodulation Promotes Hippocampal Neurogenesis and Improves Cognitive Function and Anti-Inflammatory Injury in Rats With Chronic Cerebral Hypoperfusion]

Objective

To investigate the effect of photobiomodulation (PBM) on hippocampal neurogenesis, cognitive function, and inflammatory injury in rats with chronic cerebral hypoperfusion.

Methods

Bilateral ovariectomy (OVX) was performed on female Sprague-Dawley (SD) rats. One week later, the rats were randomly assigned to three groups, Sham surgery (or Sham) group, bilateral common carotid artery occlusion (BCCAO) group, and PBM intervention (or BCCAO+PBM) group. There were 8 rats in each group. In the BCCAO group, chronic cerebral hyporeperfusion was induced by permanent ligation of bilateral common carotid arteries and no PBM was given. Rats in the Sham group underwent the same surgical procedure except for the occlusion of the two carotids arteries and no PBM was given. In addition to the BCCAO surgery, rats in the BCCAO+PBM group received 808 nm laser therapy (5 min each time at a laser dose of 20 mW/cm 2) of the frontal cortex every other day for 1 month. Between 86 and 90 days after BCCAO, Morris water maze (MWM) was used to observe the spatial learning and memory function of the rats. The rats were sacrificed on day 90 and immunofluorescence staining and Western blot were performed thereafter. Immunofluorescence staining was used to determine the expression of 5-bromodeoxyuracil nucleoside (BrdU), a cell proliferation marker, glial fibrillary acidic protein (GFAP), an astrocyte marker, doublecortin (DCX), a specific marker of newborn neuron precursor cells, NeuN, a marker of mature neurons, and Iba1, a microglia marker, in the hippocampal dentate gyrus (DG) region. Western blot was performed to analyze the protein expressions of inflammasome components, NLRP3, ASC, cleaved caspase-1, and Iba1 in the hippocampus.

Results

In the latency trial of MWM test, BCCAO+PBM rats spent shorter periods of time finding the underwater platform than the BCCAO rats did. In the probe trial, after the platform that was original placed in a quadrant was removed, the BCCAO+PBM rats spent longer periods of time exploring the quadrant than the BCCAO animals did ( P<0.05). Compared with BCCAO rats, BCCAO+PBM rats showed significant decrease in the immunofluorescence intensities of GFAP and Iba1 ( P<0.01). PBM intervention significantly increased the number of BrdU-positive cells in the hippocampal DG region compared with those of Sham and BCCAO groups ( P<0.05). Furthermore, the number of NeuN positive cells showed no significant difference among the three groups, while in BCCAO+PBM group, the number of DCX-positive cells was significantly increased ( P<0.001) and the number of DCX +/NeuN + co-located cells was significantly increased compared to that of the BCCAO group ( P<0.001). Compared with those of the BCCAO group, Western blot results showed that the protein expression levels of Iba1, NLRP3, and cleaved caspase-1 in the BCCAO+PBM group were significantly decreased ( P<0.05), while the ASC protein expression level showed no significant difference.

Conclusion

PBM can effectively improve the spatial learning and memory function in rats with chronic cerebral hypoperfusion, inhibit the activation of glial cells, reduce inflammatory damage mediated by NLRP3 inflammasome, and promote the regeneration of endogenous neural stem cells in the hippocampal DG region of rats.

Sexual Dimorphism in the Mechanism of Pain Central Sensitization

It has long been recognized that men and women have different degrees of susceptibility to chronic pain. Greater recognition of the sexual dimorphism in chronic pain has resulted in increasing numbers of both clinical and preclinical studies that have identified factors and mechanisms underlying sex differences in pain sensitization. Here, we review sexually dimorphic pain phenotypes in various research animal models and factors involved in the sex difference in pain phenotypes. We further discuss putative mechanisms for the sexual dimorphism in pain sensitization, which involves sex hormones, spinal cord microglia, and peripheral immune cells. Elucidating the sexually dimorphic mechanism of pain sensitization may provide important clinical implications and aid the development of sex-specific therapeutic strategies to treat chronic pain.

An 8-gene predicting survival model of hepatocellular carcinoma (HCC) related to pyroptosis and cuproptosis

BACKGROUND

The study aimed to establish a prognostic survival model with 8 pyroptosis-and-cuproptosis-related genes to examine the prognostic effect in patients of hepatocellular carcinoma (HCC).

METHODS

We downloaded gene expression data and clinical information of HCC patients from The Cancer Genome Atlas (TCGA), International Cancer Genome Consortium (ICGC) and Gene Expression Omnibus (GEO). The clustering analysis and cox regression with LASSO were used for constructing an 8 PCmRNAs survival model. Using TCGA, ICGC and GEO cohort, the overall survival (OS) between high- and low- risk group was determined. We also evaluated independent prognostic indicators using univariate and multivariate analyses. The relatively bioinformatics analysis, including immune cell infiltration, function enrichment and drug sensitivity analyses, was performed as well. The gene expression of 8 PCmRNAs in vitro were validated in several HCC cell lines by qRT-PCR and Western blot. The relationship between GZMA and Fludarabine were further checked by CCK-8 assay.

RESULTS

The survival prognostic model was constructed with ATP7A, GLS, CDKN2A, BAK1, CHMP4B, NLRP6, NOD1 and GZMA using data from TCGA cohort. The ICGC and GEO cohort were used for model validation. Receiver operating characteristic (ROC) curves showed a good survival prediction by this model. Risk scores had the highest predictable value for survival among Stage, Age, Gender and Grade. Most Immune cells and immune functions were decreased in high-risk group. Besides, function enrichment analyses showed that steroid metabolic process, hormone metabolic process, collagen - containing extracellular matrix, oxidoreductase activity and pyruvate metabolism were enriched. Potential drugs targeted different PCDEGs like Nelarabine, Dexamethasone and Fludarabine were found as well. ATP7A, GLS, CDKN2A, BAK1, CHMP4B, NOD1 were upregulated while NLRP6 and GZMA were downregulated in most HCC cell lines. The potential therapy of Fludarabine was demonstrated when GZMA was low expressed in Huh7 cell line.

CONCLUSION

We constructed a novel 8-gene (ATP7A, GLS, CDKN2A, BAK1, CHMP4B, NLRP6, NOD1 and GZMA) prognostic model and explored potential functional information and microenvironment of HCC, which might be worthy of clinical application. In addition, several potential chemotherapy drugs were screened and Fludarabine might be effective for HCC patients whose GZMA was low expressed.

Chromosomal and gonadal factors regulate microglial sex effects in the aging brain

Biological sex contributes to phenotypic sex effects through genetic (sex chromosomal) and hormonal (gonadal) mechanisms. There are profound sex differences in the prevalence and progression of age-related brain diseases, including neurodegenerative diseases. Inflammation of neural tissue is one of the most consistent age-related phenotypes seen with healthy aging and disease. The pro-inflammatory environment of the aging brain has primarily been attributed to microglial reactivity and adoption of heterogeneous reactive states dependent upon intrinsic (i.e., sex) and extrinsic (i.e., age, disease state) factors. Here, we review sex effects in microglia across the lifespan, explore potential genetic and hormonal molecular mechanisms of microglial sex effects, and discuss currently available models and methods to study sex effects in the aging brain. Despite recent attention to this area, significant further research is needed to mechanistically understand the regulation of microglial sex effects across the lifespan, which may open new avenues for sex informed prevention and treatment strategies.

NLRP3 inflammasome activation increases brain oxidative stress after transient global cerebral ischemia in rats

Pupurpose of the study: Oxidative stress has been reported to be an important mechanism for brain damage following ischemic stroke. Recently, the involvement of cytosolic receptors capable of forming protein complexes called inflammasomes has been demonstrated to perpetuate oxidative stress. Herein, we report the effect of NLRP3 inhibition with MCC950 on brain oxidative stress in an animal model of transient global cerebral ischemia.Materials and methods: Male Wistar rats received an intracerebroventricularly (icv) injection of MCC950 (140 ng/kg) or saline and were subjected to sham procedure or ischemia/reperfusion (I/R). Twenty-four hours after I/R, myeloperoxidase (MPO) activity, nitrite/nitrate (N/N) concentration, lipid peroxidation, protein carbonyls formation, superoxide dismutase (SOD) and catalase (CAT) activity were determined in the prefrontal cortex, hippocampus, cortex, cerebellum and striatum. Results: After I/R, MPO activity increased in the prefrontal cortex, hippocampus, cortex and cerebellum and N/N concentration elevated in the prefrontal cortex, hippocampus and cortex, while MCC950 decreased this level except in hippocampus. After I/R, lipid peroxidation enhanced in the prefrontal cortex and cerebellum and increased the oxidative protein damage in both structures and hippocampus. MCC950 decreased lipid peroxidation in the prefrontal cortex and decreased protein oxidative damage in all brain structures except in the striatum. SOD activity decreased in the cortex after I/R and MCC950 reestablished these levels. CAT activity decreased in the prefrontal cortex, hippocampus and cerebellum after I/R and MCC950 reestablished these levels in the prefrontal cortex.Conclusion: Our data provide novel demonstration that inhibiting NLRP3 activation with MCC950 reduces brain oxidative damage after cerebral I/R in rats.

The Pathological Effects of Circulating Hydrophobic Bile Acids in Alzheimer's Disease

Recent clinical studies have revealed that the serum levels of toxic hydrophobic bile acids (deoxy cholic acid, lithocholic acid [LCA], and glycoursodeoxycholic acid) are significantly higher in patients with Alzheimer's disease (AD) and amnestic mild cognitive impairment (aMCI) when compared to control subjects. The elevated serum bile acids may be the result of hepatic peroxisomal dysfunction. Circulating hydrophobic bile acids are able to disrupt the blood-brain barrier and promote the formation of amyloid-β plaques through enhancing the oxidation of docosahexaenoic acid. Hydrophobic bile acid may find their ways into the neurons via the apical sodium-dependent bile acid transporter. It has been shown that hydrophobic bile acids impose their pathological effects by activating farnesoid X receptor and suppressing bile acid synthesis in the brain, blocking NMDA receptors, lowering brain oxysterol levels, and interfering with 17β-estradiol actions such as LCA by binding to E2 receptors (molecular modelling data exclusive to this paper). Hydrophobic bile acids may interfere with the sonic hedgehog signaling through alteration of cell membrane rafts and reducing brain 24(S)-hydroxycholesterol. This article will 1) analyze the pathological roles of circulating hydrophobic bile acids in the brain, 2) propose therapeutic approaches, and 3) conclude that consideration be given to reducing/monitoring toxic bile acid levels in patients with AD or aMCI, prior/in combination with other treatments.

Estrogen Mediates the Sexual Dimorphism of GT1b-Induced Central Pain Sensitization

We have previously reported that the intrathecal (i.t.) administration of GT1b, a ganglioside, induces spinal cord microglia activation and central pain sensitization as an endogenous agonist of Toll-like receptor 2 on microglia. In this study, we investigated the sexual dimorphism of GT1b-induced central pain sensitization and the underlying mechanisms. GT1b administration induced central pain sensitization only in male but not in female mice. Spinal tissue transcriptomic comparison between male and female mice after GT1b injection suggested the putative involvement of estrogen (E2)-mediated signaling in the sexual dimorphism of GT1b-induced pain sensitization. Upon ovariectomy-reducing systemic E2, female mice became susceptible to GT1b-induced central pain sensitization, which was completely reversed by systemic E2 supplementation. Meanwhile, orchiectomy of male mice did not affect pain sensitization. As an underlying mechanism, we present evidence that E2 inhibits GT1b-induced inflammasome activation and subsequent IL-1β production. Our findings demonstrate that E2 is responsible for sexual dimorphism in GT1b-induced central pain sensitization.

Inflammasomes as biomarkers and therapeutic targets in traumatic brain injury and related-neurodegenerative diseases: A comprehensive overview

Given the ambiguity surrounding traumatic brain injury (TBI) pathophysiology and the lack of any Food and Drug Administration (FDA)-approved neurotherapeutic drugs, there is an increasing need to better understand the mechanisms of TBI. Recently, the roles of inflammasomes have been highlighted as both potential therapeutic targets and diagnostic markers in different neurodegenerative disorders. Indeed, inflammasome activation plays a pivotal function in the central nervous system (CNS) response to many neurological conditions, as well as to several neurodegenerative disorders, specifically, TBI. This comprehensive review summarizes and critically discusses the mechanisms that govern the activation and assembly of inflammasome complexes and the major methods used to study inflammasome activation in TBI and its implication for other neurodegenerative disorders. Also, we will review how inflammasome activation is critical in CNS homeostasis and pathogenesis, and how it can impact chronic TBI sequalae and increase the risk of developing neurodegenerative diseases. Additionally, we discuss the recent updates on inflammasome-related biomarkers and the potential to utilize inflammasomes as putative therapeutic targets that hold the potential to better diagnose and treat subjects with TBI.

Methods to Study Inflammasome Activation in the Central Nervous System: Immunoblotting and Immunohistochemistry

The inflammasome is a multiprotein complex that is responsible for mounting an innate immune response through the activation of caspase-1 and the cleavage of interleukin-1β. This multiprotein complex plays an important role in a variety of central nervous system (CNS) diseases and conditions such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, stroke, and traumatic brain injury, among others. Here we describe methodological procedures to carry out immunoblotting and immunohistochemical techniques used to study inflammasome signaling in CNS tissues (brain and spinal cord).

Cell Death Mechanisms in Cerebral Ischemia-Reperfusion Injury

Ischemic stroke is one of the major causes of morbidity and mortality, affecting millions of people worldwide. Inevitably, the interruption of cerebral blood supply after ischemia may promote a cascade of pathophysiological processes. Moreover, the subsequent restoration of blood flow and reoxygenation may further aggravate brain tissue injury. Although recombinant tissue plasminogen activator (rt-PA) is the only approved therapy for restoring blood perfusion, the reperfusion injury and the narrow therapeutic time window restrict its application for most stroke patients. Increasing evidence indicates that multiple cell death mechanisms are relevant to cerebral ischemia-reperfusion injury, including apoptosis, necrosis, necroptosis, autophagy, pyroptosis, ferroptosis, and so on. Therefore, it is crucial to comprehend various cell death mechanisms and their interactions. In this review, we summarize the various signaling pathways underlying cerebral ischemia-reperfusion injury and elaborate on the crosstalk between the different mechanisms.

Ruscogenin Ameliorated Sjögren's Syndrome by Inhibiting NLRP3 Inflammasome Activation

This article investigated the role and the specific mechanism of Ruscogenin in Sjögren's syndrome (SS). NOD/ShiLtJ mice were treated with Ruscogenin, and acinar cells isolated from submandibular glands were treated with TNF-α, Ruscogenin and transfected with NLRP3 overexpression plasmid. Salivary flow rate (SFR) was measured at weeks 11, 13, 15, 17, and 20. Histological analysis of the submandibular glands was conducted by hematoxylin-eosin staining assay. IL-6, IL-17, TNF-α, and IL-1β mRNA expression was detected through qRT-PCR. AQP 5, AQP 4, P2X7R, NLRP3, caspase 1, IL-1β, Bax, and Bcl-2 protein levels were tested by western blot. Cell apoptosis was assessed through acridine orange and propidium iodide (AO/PI) staining assay and flow cytometry assay. Ruscogenin ameliorated the SFR and submandibular gland inflammation of NOD/ShiLtJ mice. Ruscogenin promoted the preservation of acinar cells and suppressed inflammation-related factors (P2X7R, NLRP3, caspase 1, and IL-1β) in submandibular gland tissues of NOD/ShiLtJ mice. Ruscogenin inhibited acinar cell apoptosis in NOD/ShiLtJ mice and reversed TNF-α-induced apoptosis and inflammation of acinar cells. NLRP3 overexpression reversed the repressive effect of Ruscogenin on TNF-α-induced inflammation and apoptosis of acinar cells. Ruscogenin ameliorated SS by inhibiting NLRP3 inflammasome activation.

Hiding in Plain Sight: Factors Influencing the Neuroinflammatory Response to Sport-Related Concussion

Sport-related concussion (SRC) is a major concern among athletes and clinicians around the world. Research into fluid biomarkers of SRC has made significant progress in understanding the complex underlying pathophysiology of concussion. However, little headway has been made toward clinically validating any biomarkers to improve the clinical management of SRC. A major obstacle toward clinical translation of any fluid biomarker is the heterogeneity of SRC overlapping with multiple physiological systems involved in pathology and recovery. Neuroinflammation post-SRC is one such system that may confound fluid biomarker data on many fronts. Neuroinflammatory processes consist of cell mediators, both within the central nervous system and the periphery, that play vital roles in regulating the response to brain injury. Further, neuroinflammation is influenced by many biopsychosocial variables present in most athletic populations. In this commentary, we propose that future fluid biomarker research should take a systems biology approach in the context of the neuroinflammatory response to SRC. We highlight how biological variables, such as age, sex, immune challenges, and hypothalamic-pituitary-adrenal (HPA)-axis responses to stress, may alter neuroinflammation. Further, we underscore the importance of accounting for health and lifestyle variables, such as diet, exercise, sleep, and pre-morbid medical factors, when measuring inflammatory markers of SRC. To successfully move toward clinical translation, fluid biomarker research should take a more holistic approach in study design and data interpretation, collecting information on hidden variables that may be influencing the neuroinflammatory response to SRC.

Sex-related susceptibility in coronavirus disease 2019 (COVID-19): Proposed mechanisms

The importance of sex differences is increasingly acknowledged in the incidence and treatment of disease. Accumulating clinical evidence demonstrates that sex differences are noticeable in COVID-19, and the prevalence, severity, and mortality rate of COVID-19 are higher among males than females. Sex-related genetic and hormonal factors and immunological responses may underlie the sex bias in COVID-19 patients. Angiotensin-converting enzyme 2 (ACE2) and transmembrane protease/serine subfamily member 2 (TMPRSS2) are essential proteins involved in the cell entry of SARS-CoV-2. Since ACE2 is encoded on the X-chromosome, a double copy of ACE2 in females may compensate for virus-mediated downregulation of ACE2, and thus ACE2-mediated cellular protection is greater in females. The X chromosome also contains the largest immune-related genes leading females to develop more robust immune responses than males. Toll-like receptor-7 (TLR-7), one of the key players in innate immunity, is linked to sex differences in autoimmunity and vaccine efficacy, and its expression is greater in females. Sex steroids also affect immune cell function. Estrogen contributes to higher CD4⁺ and CD8⁺ T cell activation levels, and females have more B cells than males. Sex differences not only affect the severity and progression of the disease, but also alter the efficacy of pharmacological treatment and adverse events related to the drugs/vaccines used against COVID-19. Administration of different drugs/vaccines in different doses or intervals may be useful to eliminate sex differences in efficacy and side/adverse effects. It should be noted that studies should include sex-specific analyses to develop further sex-specific treatments for COVID-19.

How cytosolic compartments play safeguard functions against neuroinflammation and cell death in cerebral ischemia

Ischemic stroke is the second leading cause of mortality and disability globally. Neuronal damage following ischemic stroke is rapid and irreversible, and eventually results in neuronal death. In addition to activation of cell death signaling, neuroinflammation is also considered as another pathogenesis that can occur within hours after cerebral ischemia. Under physiological conditions, subcellular organelles play a substantial role in neuronal functionality and viability. However, their functions can be remarkably perturbed under neurological disorders, particularly cerebral ischemia. Therefore, their biochemical and structural response has a determining role in the sequel of neuronal cells and the progression of disease. However, their effects on cell death and neuroinflammation, as major underlying mechanisms of ischemic stroke, are still not understood. This review aims to provide a comprehensive overview of the contribution of each organelle on these pathological processes after ischemic stroke.

Estrogen receptor β alleviates inflammatory lesions in a rat model of inflammatory bowel disease via down-regulating P2X7R expression in macrophages

Estrogen receptor beta (ERβ) agonists could inhibit inflammation in animal models of inflammatory bowel disease (IBD). However, the mechanism underlying such effect and the potential role of P2 × 7 receptor (P2X7R) remains unclear. In the present study, we examined whether the effect of ERβ activation in IBD rats was related to P2X7R. Overexpression of ERβ using a recombinant lentivirus in IBD rats improved the IBD-like symptoms, including weight loss, disease activity index (DAI) scores, and inflammatory responses. ERβ agonists DPN and ERB-041 attenuated P2X7R expression in macrophages from colitis rats and in a murine macrophage cell line (RAW264.7) in response to either lipopolysaccharide (LPS) or adenosine triphosphate (ATP). DPN and ERB-041 also blocked increased production of TNF-α, IL-6, and IL-1β in the rectocolon of colitis rats. The two ERβ agonists reversed LPS- and ATP-induced up-regulation of P2X7R and its downstream proteins, including NLRP3, ASC, caspase-1, and pro-IL-1β, in RAW264.7 cells. Also, in both the rectocolon of colitis rats and RAW264.7 cells, ERβ agonists reversed the up-regulation of extracellular regulated protein kinases (ERK), the Janus kinase 2 (JAK2), and signal transducer and activator of transcription 3 (STAT3), but not up-regulation of serine threonine kinase or cAMP-response element binding protein (CREB). Blockade of JAK2 or STAT3 phosphorylation significantly reduced the ability of DPN to down-regulate P2X7R expression and the ability of ERB-041 and DPN to inhibit IL-1β release from RAW264.7 cells. We found that ERβ and P2X7R co-localized in the macrophages of rat rectocolon and in RAW264.7 cells. Deletion of macrophages from colitis rats with clodronate abolished the inhibitory effect of DPN. These results suggest that ERβ plays an important anti-inflammatory role in IBD rats by down-regulating P2X7R expression and inhibiting IL-1β release from macrophages through the JAK2/STAT3 signaling pathway.

Sex Differences in Otolaryngology: Focus on the Emerging Role of Estrogens in Inflammatory and Pro-Resolving Responses

Otolaryngology (also known as ear, nose, and throat (ENT)) diseases can be significantly affected by the level of sex hormones, which indicates that sex differences affect the manifestation, pathophysiology, and outcomes of these diseases. Recently, increasing evidence has suggested that proinflammatory responses in ENT diseases are linked to the level of sex hormones. The sex hormone receptors are present on a wide variety of immune cells; therefore, it is evident that they play crucial roles in regulating the immune system and hence affect the disease progression of ENT diseases. In this review, we focus on how sex hormones, particularly estrogens, regulate ENT diseases, such as chronic rhinosinusitis, vocal fold polyps, thyroid cancer, Sjögren’s syndrome, and head and neck cancers, from the perspectives of inflammatory responses and specialized proresolving mediator-driven resolution. This paper aims to clarify why considering sex differences in the field of basic and medical research on otolaryngology is a key component to successful therapy for both males and females in the future.

Sex-Related Overactivation of NLRP3 Inflammasome Increases Lethality of the Male COVID-19 Patients

The COVID-19 pandemic, caused by SARS-CoV-2 infection, remains a dramatic threat to human life and economic well-being worldwide. Significant heterogeneity in the severity of disease was observed for patients infected with SARS-CoV-2 ranging from asymptomatic to severe cases. Moreover, male patients had a higher probability of suffering from high mortality and severe symptoms linked to cytokine storm and excessive inflammation. The NLRP3 inflammasome is presumably critical to this process. Sex differences may directly affect the activation of NLRP3 inflammasome, impacting the severity of observed COVID-19 symptoms. To elucidate the potential mechanisms underlying sex based differences in NLRP3 activation during SARS-CoV-2 infection, this review summarizes the reported mechanisms and identifies potential therapeutic targets.

Simvastatin mitigates depressive-like behavior in ovariectomized rats: Possible role of NLRP3 inflammasome and estrogen receptors' modulation

It is well known that females are more vulnerable than males to stress-related psychiatric disorders, particularly during perimenopausal and postmenopausal periods. Hormone replacement therapy (HRT) has been widely used for the management of postmenopausal depression. However, HRT could be associated with severe adverse effects, including increased risk for coronary heart disease, breast cancer and endometrial cancer. Thus, there is a pressing demand for novel therapeutic options for postmenopausal depression without sacrificing uterine health. Simvastatin (SIM) was proven to have neuroprotective activities besides its hypocholesterolemic effect, the former can be attributed to its, antioxidant, anti-apoptotic and anti-inflammatory activities. Moreover, many reports highlighted that SIM has estrogenic activity and was able to induce the expression of estrogen receptors in rats. The present study showed that SIM (20 mg/kg, p.o.) markedly attenuated depressive-like behavior in ovariectomized (OVX) rats. Moreover, SIM prohibited hippocampal microglial activation, abrogated P2X7 receptor, TLR2 and TLR4 expression, inhibited NLRP3 inflammasome activation, with subsequent reduction in the levels of pro-inflammatory mediators; IL-1β and IL-18. Furthermore, a marked elevation in hippocampal expression of ERα and ERβ was noted in SIM-treated animals, without any significant effect on uterine relative weight or ERα expression. Taken together, SIM could provide a safer alternative for HRT for the management of postmenopausal depression, without any hyperplastic effect on the uterus.

Relevant mediators involved in and therapies targeting the inflammatory response induced by activation of the NLRP3 inflammasome in ischemic stroke

The nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome is a member of the NLR family of inherent immune cell sensors. The NLRP3 inflammasome can detect tissue damage and pathogen invasion through innate immune cell sensor components commonly known as pattern recognition receptors (PRRs). PRRs promote activation of nuclear factor kappa B (NF-κB) pathways and the mitogen-activated protein kinase (MAPK) pathway, thus increasing the transcription of genes encoding proteins related to the NLRP3 inflammasome. The NLRP3 inflammasome is a complex with multiple components, including an NAIP, CIITA, HET-E, and TP1 (NACHT) domain; apoptosis-associated speck-like protein containing a CARD (ASC); and a leucine-rich repeat (LRR) domain. After ischemic stroke, the NLRP3 inflammasome can produce numerous proinflammatory cytokines, mediating nerve cell dysfunction and brain edema and ultimately leading to nerve cell death once activated. Ischemic stroke is a disease with high rates of mortality and disability worldwide and is being observed in increasingly younger populations. To date, there are no clearly effective therapeutic strategies for the clinical treatment of ischemic stroke. Understanding the NLRP3 inflammasome may provide novel ideas and approaches because targeting of upstream and downstream molecules in the NLRP3 pathway shows promise for ischemic stroke therapy. In this manuscript, we summarize the existing evidence regarding the composition and activation of the NLRP3 inflammasome, the molecules involved in inflammatory pathways, and corresponding drugs or molecules that exert effects after cerebral ischemia. This evidence may provide possible targets or new strategies for ischemic stroke therapy.

The Role of NLRP3 Inflammasome in Cerebrovascular Diseases Pathology and Possible Therapeutic Targets

Cerebrovascular diseases are pathological conditions involving impaired blood flow in the brain, primarily including ischaemic stroke, intracranial haemorrhage, and subarachnoid haemorrhage. The nucleotide-binding and oligomerisation (NOD) domain-like receptor (NLR) family pyrin domain (PYD)-containing 3 (NLRP3) inflammasome is a protein complex and a vital component of the immune system. Emerging evidence has indicated that the NLRP3 inflammasome plays an important role in cerebrovascular diseases. The function of the NLRP3 inflammasome in the pathogenesis of cerebrovascular diseases remains an interesting field of research. In this review, we first summarised the pathological mechanism of cerebrovascular diseases and the pathological mechanism of the NLRP3 inflammasome in aggravating atherosclerosis and cerebrovascular diseases. Second, we outlined signalling pathways through which the NLRP3 inflammasome participates in aggravating or mitigating cerebrovascular diseases. Reactive oxygen species (ROS)/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), ROS/thioredoxin-interacting protein (TXNIP) and purinergic receptor-7 (P2X7R) signalling pathways can activate the NLRP3 inflammasome; activation of the NLRP3 inflammasome can aggravate cerebrovascular diseases by mediating apoptosis and pyroptosis. Autophagy/mitochondrial autophagy, nuclear factor E2-related factor-2 (Nrf2), interferon (IFN)-β, sirtuin (SIRT), and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) reportedly alleviate cerebrovascular diseases by inhibiting NLRP3 inflammasome activation. Finally, we explored specific inhibitors of the NLRP3 inflammasome based on the two-step activation of the NLRP3 inflammasome, which can be developed as new drugs to treat cerebrovascular diseases.

17β-Estradiol Reduces Demyelination in Cuprizone-fed Mice by Promoting M2 Microglia Polarity and Regulating NLRP3 Inflammasome

Estrogen produces a beneficial role in animal models of multiple sclerosis (MS). The effect of 17β-estradiol therapy on microglia polarization and neuroinflammation in the corpus callosum of the cuprizone-induced demyelination model has not been elucidated. In this study, mice were given 0.2% cuprizone (CPZ) for 5 weeks to induce demyelination during which they received 50 ng of 17β-estradiol (EST), injected subcutaneously in the neck region, twice weekly. Data revealed that treatment with 17β-estradiol therapy (CPZ+EST) improved neurological behavioral deficits, displayed by a significant reduction in escape latencies, in comparison to untreated CPZ mice. Also, administration of 17β-estradiol caused a decrease in demyelination levels and axonal injury, as demonstrated by staining with Luxol fast blue, immunofluorescence to myelin basic protein, and transmission electron microscopy analysis. In addition, at the transcriptional level in the brain, mice treated with 17β-estradiol (CPZ+EST) showed a decrease in the levels of M1-assosicted microglia markers (CD86, iNOS and MHC-II) whereas M2-associated genes (Arg-1, CD206 and Trem-2) were increased, compared to CPZ mice. Moreover, administration of 17β-estradiol resulted in a significant reduction (∼3-fold) in transcript levels of NLRP3 inflammasome and its downstream product IL-18, compared to controls. In summary, this study demonstrated for the first time that exogenous 17β-estradiol therapy robustly leads to the reduction of M1 phenotype, stimulation of polarized M2 microglia, and repression of NLRP3 inflammasome in the corpus callosum of CPZ demyelination model of MS. The positive effects of 17β-estradiol on microglia and inflammasome seems to facilitate and accelerate the remyelination process.

Nuclear Receptors in the Control of the NLRP3 Inflammasome Pathway

The innate immune system is the first line of defense specialized in the clearing of invaders whether foreign elements like microbes or self-elements that accumulate abnormally including cellular debris. Inflammasomes are master regulators of the innate immune system, especially in macrophages, and are key sensors involved in maintaining cellular health in response to cytolytic pathogens or stress signals. Inflammasomes are cytoplasmic complexes typically composed of a sensor molecule such as NOD-Like Receptors (NLRs), an adaptor protein including ASC and an effector protein such as caspase 1. Upon stimulation, inflammasome complex components associate to promote the cleavage of the pro-caspase 1 into active caspase-1 and the subsequent activation of pro-inflammatory cytokines including IL-18 and IL-1β. Deficiency or overactivation of such important sensors leads to critical diseases including Alzheimer diseases, chronic inflammatory diseases, cancers, acute liver diseases, and cardiometabolic diseases. Inflammasomes are tightly controlled by a two-step activation regulatory process consisting in a priming step, which activates the transcription of inflammasome components, and an activation step which leads to the inflammasome complex formation and the subsequent cleavage of pro-IL1 cytokines. Apart from the NF-κB pathway, nuclear receptors have recently been proposed as additional regulators of this pathway. This review will discuss the role of nuclear receptors in the control of the NLRP3 inflammasome and the putative beneficial effect of new modulators of inflammasomes in the treatment of inflammatory diseases including colitis, fulminant hepatitis, cardiac ischemia-reperfusion and brain diseases.

Therapeutic role of inflammasome inhibitors in neurodegenerative disorders

Neuroinflammation, characterized by the activation of glial cells, is a hallmark in several neurological and neurodegenerative disorders. Inadequate inflammation cannot eliminate the infection of pathogens, while excessive or hyper-reactive inflammation can cause chronic or systemic inflammatory diseases affecting the central nervous system (CNS). In response to a brain injury or pathogen invasion, the pathogen recognition receptors (PRRs) expressed on glial cells are activated via binding to cellular damage-associated molecular patterns (DAMPs) or pathogen-associated molecular patterns (PAMPs). This subsequently leads to the activation of NOD (nucleotide-binding oligomerization domain)-like receptor proteins (NLRs). In neurodegenerative diseases such as HIV-1-associated neurocognitive disorders (HAND), Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS), chronic inflammation is a critical contributing factor for disease manifestation including pathogenesis. Emerging evidence points to the involvement of "inflammasomes", especially the nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain-containing (NLRP) complex in the development of these diseases. The activated NLRP3 results in the proteolytic activation of caspase-1 that facilitates the cleavage of pro-IL-1β and the secretion of IL-1β and IL-18 proinflammatory cytokines. Accordingly, these and other seminal findings have led to the development of NLRP-targeting small-molecule therapeutics as possible treatment options for neurodegenerative disorders. In this review, we will discuss the new advances and evidence-based literature concerning the role of inflammasomes in neurodegenerative diseases, its role in the neurological repercussions of CNS chronic infection, and the examples of preclinical or clinically tested NLRP inhibitors as potential strategies for the treatment of chronic neurological diseases.

Sex disparity in long-term stroke recurrence and mortality in a rural population in the United States

BACKGROUND

Several studies suggest women may be disproportionately affected by poorer stroke outcomes than men. This study aims to investigate whether women have a higher risk of all-cause mortality and recurrence after an ischemic stroke than men in a rural population in central Pennsylvania, United States.

METHODS

We analyzed consecutive ischemic stroke patients captured in the Geisinger NeuroScience Ischemic Stroke research database from 2004 to 2019. Kaplan-Meier (KM) estimator curves stratified by gender and age were used to plot survival probabilities and Cox Proportional Hazards Ratios were used to analyze outcomes of all-cause mortality and the composite outcome of ischemic stroke recurrence or death. Fine-Gray Competing Risk models were used for the outcome of recurrent ischemic stroke, with death as the competing risk. Two models were generated; Model 1 was adjusted by data-driven associated health factors, and Model 2 was adjusted by traditional vascular risk factors.

RESULTS

Among 8900 adult ischemic stroke patients [median age of 71.6 (interquartile range: 61.1-81.2) years and 48% women], women had a higher crude all-cause mortality. The KM curves demonstrated a 63.3% survival in women compared with a 65.7% survival in men (p = 0.003) at 5 years; however, the survival difference was not present after controlling for covariates, including age, atrial fibrillation or flutter, myocardial infarction, diabetes mellitus, dyslipidemia, heart failure, chronic lung diseases, rheumatic disease, chronic kidney disease, neoplasm, peripheral vascular disease, past ischemic stroke, past hemorrhagic stroke, and depression. There was no adjusted or unadjusted sex difference in terms of recurrent ischemic stroke or composite outcome.

CONCLUSION

Sex was not an independent risk factor for all-cause mortality and ischemic stroke recurrence in the rural population in central Pennsylvania.

Brain Selective Estrogen Treatment Protects Dopaminergic Neurons and Preserves Behavioral Function in MPTP-induced Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra and loss of both motor and non-motor features. Several clinical and preclinical studies have provided evidence that estrogen therapy reduces the risk of PD but have limitations in terms of adverse peripheral effects. Therefore, we examined the potential beneficial effects of the brain-selective estrogen prodrug, 10β, 17β-dihydroxyestra-1,4-dien-3-one (DHED) on nigrostriatal dopaminergic neurodegeneration and behavioral abnormalities in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. Wild-type mice were treated with daily subcutaneous injections of DHED (50 and 100 µg/kg) or vehicle for four weeks. To produce PD-like symptoms, mice were injected with MPTP (18 mg/kg in saline; intraperitoneally) four times at 2-hr intervals for one day. After behavioral examination, mice were sacrificed, and the brains were isolated for neurochemical and morphological examinations. MPTP injected mice exhibited loss of dopaminergic neurons and fibers in substantia nigra and striatum respectively, along with impaired motor function at day 7 post MPTP injection. These phenotypes were associated with significantly increased oxidative stress and inflammatory responses in the striatum regions. DHED treatments significantly mitigated behavioral impairments and dopaminergic neurodegeneration induced by MPTP. We further observed that DHED treatment suppressed oxidative stress and inflammation in the striatum of MPTP treated mice when compared to vehicle treated mice. In conclusions, our findings suggest that DHED protects dopaminergic neurons from MPTP toxicity in mouse model of PD and support a beneficial effect of brain-selective estrogen in attenuating neurodegeneration and motor symptoms in PD-related neurological disorders. Graphical Abstract.

Modulatory effect of 17β-estradiol on myeloid cell infiltration into the male rat brain after ischemic stroke

Ischemic stroke is the leading cause of human disability and mortality in the world. Neuroinflammation is the main pathological event following ischemia which contributes to secondary brain tissue damage and is driven by infiltration of circulating immune cells such as macrophages. Because of neuroprotective properties against ischemic brain damage, estrogens have the potential to become of therapeutic interest. However, the exact mechanisms of neuroprotection and signaling pathways is not completely understood. In the current study, 12-week-old male Wistar rats underwent an experimental ischemia by occluding the middle cerebral artery transiently (tMCAO) for 1 h. Male rats subjected to tMCAO were randomly assigned to receive 17β-estradiol or vehicle treatment. The animals were sacrificed 72 h post tMCAO, transcardially perfused and the brains were proceeded either for TTC staining and gene analysis or for flow cytometry (CD45, CD11b, CD11c, CD40). We found that 17β-estradiol substitution significantly reduced the cortical infarct which was paralleled by an improved Garcia test scoring. Flow cytometry revealed that CD45+ cells as well as CD45+CD11b+CD11c+ cells were massively increased in tMCAO animals and numbers were nearly restored to sham levels after 17β-estradiol treatment. Gene expression analysis showed a reperfusion time-dependent upregulation of the markers CD45, CD11b and the activation marker CD40. The reduction in gene expression after 72 h of reperfusion and simultaneous 17β-estradiol substitution did not reach statistical significance. These data indicate that 17β-estradiol alleviated the cerebral ischemia-reperfusion injury and selectively suppressed the activation of the neuroinflammatory cascade via reduction of the number of activated microglia or infiltrated monocyte-derived macrophages in brain.

Progesterone Attenuates Stress-Induced NLRP3 Inflammasome Activation and Enhances Autophagy following Ischemic Brain Injury

NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome inhibition and autophagy induction attenuate inflammation and improve outcome in rodent models of cerebral ischemia. However, the impact of chronic stress on NLRP3 inflammasome and autophagic response to ischemia remains unknown. Progesterone (PROG), a neuroprotective steroid, shows promise in reducing excessive inflammation associated with poor outcome in ischemic brain injury patients with comorbid conditions, including elevated stress. Stress primes microglia, mainly by the release of alarmins such as high-mobility group box-1 (HMGB1). HMGB1 activates the NLRP3 inflammasome, resulting in pro-inflammatory interleukin (IL)-1β production. In experiment 1, adult male Sprague-Dawley rats were exposed to social defeat stress for 8 days and then subjected to global ischemia by the 4-vessel occlusion model, a clinically relevant brain injury associated with cardiac arrest. PROG was administered 2 and 6 h after occlusion and then daily for 7 days. Animals were killed at 7 or 14 days post-ischemia. Here, we show that stress and global ischemia exert a synergistic effect in HMGB1 release, resulting in exacerbation of NLRP3 inflammasome activation and autophagy impairment in the hippocampus of ischemic animals. In experiment 2, an in vitro inflammasome assay, primary microglia isolated from neonatal brain tissue, were primed with lipopolysaccharide (LPS) and stimulated with adenosine triphosphate (ATP), displaying impaired autophagy and increased IL-1β production. In experiment 3, hippocampal microglia isolated from stressed and unstressed animals, were stimulated ex vivo with LPS, exhibiting similar changes than primary microglia. Treatment with PROG reduced HMGB1 release and NLRP3 inflammasome activation, and enhanced autophagy in stressed and unstressed ischemic animals. Pre-treatment with an autophagy inhibitor blocked Progesterone's (PROG's) beneficial effects in microglia. Our data suggest that modulation of microglial priming is one of the molecular mechanisms by which PROG ameliorates ischemic brain injury under stressful conditions.

Sex-Specific Effects of the Nlrp3 Inflammasome on Atherogenesis in LDL Receptor-Deficient Mice

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In this study we observed sex-specific effects of the NLRP3 inflammasome on atherogenesis in LDLR-deficient mice, with NLRP3 inflammasome playing a more prominent role in atherosclerosis in female mice than in males.

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Sex hormones may be involved in NLRP3 inflammasome–mediated atherogenesis and may underlie differential responses to anti-NLRP3 therapy between males and females.

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Testosterone may play an inhibitory role by blocking NLRP3 inflammasome and inflammation in atherogenesis, whereas female sex hormones may promote NLRP3 inflammasome–mediated atherosclerosis.

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The results of the present study may help design future clinical trials, with the objective to personalize cardiovascular care for men and women.

In the Ldlr^-/- mouse model of atherosclerosis, female Nlrp3^-/- bone marrow chimera and Nlrp3^-/- mice developed significantly smaller lesions in the aortic sinus and decreased lipid content in aorta en face, but a similar protection was not observed in males. Ovariectomized female mice lost protection from atherosclerosis in the setting of NLRP3 deficiency, whereas atherosclerosis showed a greater dependency on NLRP3 in castrated males. Thus, castration increased the dependency of atherosclerosis on the NLRP3 inflammasome, suggesting that testosterone may block inflammation in atherogenesis. Conversely, ovariectomy reduced the dependency on NLRP3 inflammasome components for atherogenesis, suggesting that estrogen may promote inflammasome-mediated atherosclerosis.

The NLRP3 inflammasome in traumatic brain injury: potential as a biomarker and therapeutic target

There is a great clinical need to identify the underlying mechanisms, as well as related biomarkers, and treatment targets, for traumatic brain injury (TBI). Neuroinflammation is a central pathophysiological feature of TBI. NLRP3 inflammasome activity is a necessary component of the innate immune response to tissue damage, and dysregulated inflammasome activity has been implicated in a number of neurological conditions. This paper introduces the NLRP3 inflammasome and its implication in the pathogenesis of neuroinflammatory-related conditions, with a particular focus on TBI. Although its role in TBI has only recently been identified, findings suggest that priming and activation of the NLRP3 inflammasome are upregulated following TBI. Moreover, recent studies utilizing specific NLRP3 inhibitors have provided further evidence that this inflammasome is a major driver of neuroinflammation and neurobehavioral disturbances following TBI. In addition, there is emerging evidence that circulating inflammasome-associated proteins may have utility as diagnostic biomarkers of neuroinflammatory conditions, including TBI. Finally, novel and promising areas of research will be highlighted, including the potential involvement of the NLRP3 inflammasome in mild TBI, how factors such as biological sex may affect NLRP3 activity in TBI, and the use of emerging biomarker platforms. Taken together, this review highlights the exciting potential of the NLRP3 inflammasome as a target for treatments and biomarkers that may ultimately be used to improve TBI management.

PELP1 Suppression Inhibits Gastric Cancer Through Downregulation of c-Src-PI3K-ERK Pathway

Background: Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1), a co-activator of estrogen receptors alpha, was confirmed to be directly associated with the oncogenic process of multiple cancers, especially hormone-dependent cancers. The purpose of our research was to explore the biological function, clinical significance, and therapeutic targeted value of PELP1 in gastric cancer (GC).

Methods: The expression status of PELP1 in GC cell lines or tissues was analyzed through bioinformatics data mining. Thirty-six GC tissue chip was applied to demonstrate the results of bioinformatics data mining assayed by immunohistochemical method. The expression status of PELP1 in GC cell lines was also analyzed using western blot. Correlation analysis between PELP1 expression and clinicopathological parameter was performed. Kaplan-Meier survival analysis was applied to analyze the relationship between PELP1 expression and total survival time. Three pairs of siRNA were designed to silence the expression of PELP1 in GC. After PELP1 was silenced by siRNA or activated by saRNA, the growth, plate colony formation, migration and invasion ability of the GC cell or normal gastric epithelium cell line was tested in vitro. Cell cycle was tested by flow cytometry. Nude mice xenograft experiment was performed after PELP1 was silenced. The downstream molecular pathway regulated by PELP1 was explored. Molecular docking tool was applied to combine chlorpromazine with PELP1. The inhibitory effect of chlorpromazine in GC was assayed, then it was tested whether PELP1 was a therapeutic target of chlorpromazine in GC.

Results: PELP1 expression was elevated in GC cell lines and clinical GC tissue samples. PELP1 silence by siRNA compromised the malignant traits of GC. PELP1 expression positively correlated with tumor invasion depth, lymph node metastasis, tissue grade, TNM stage, but had no correlation with patient age, sex, tumor size, and tumor numbers. Kaplan-Meier survival analysis revealed high PELP1 expression had a shorter survival period in GC patients after follow-up. Q-PCR and western blot revealed PELP1 suppression in GC decreased expression of the c-Src-PI3K-ERK pathway. It was also implied that chlorpromazine (CPZ) can inhibit the malignant traits of GC and downregulate the expression of PELP1.

Conclusions: In a word, PELP1 is an oncogene in gastric cancer and c-Src-PI3K-ERK pathway activation may be responsible for its tumorigenesis, PELP1 may be a potential therapeutic target of chlorpromazine in GC.

Auditory function and dysfunction: estrogen makes a difference

Estrogen is the major female hormone involved in reproductive functions, but it also exerts a variety of additional roles in non-reproductive organs. In this review, we highlight the preclinical and clinical studies that have pointed out sex differences and estrogenic influence on audition. We also describe the experimental evidences supporting a protective role of estrogen towards acquired forms of hearing loss. Although a high level of endogenous estrogen is associated with a better hearing function, hormonal treatments at menopause have provided contradictory outcomes. The various factors that are likely to explain these discrepancies include the treatment regimen as well as the hormonal status and responsiveness of the patients. The complexity of estrogen signaling is being untangled and many downstream effectors of its genomic and non-genomic actions have been identified in other systems. Based on these advances and on the common physio-pathological events that underlie age-related, drug or noise-induced hearing loss, we discuss potential mechanisms for their protective actions in the cochlea.

G-protein-coupled estrogen receptor activation upregulates interleukin-1 receptor antagonist in the hippocampus after global cerebral ischemia: implications for neuronal self-defense

BACKGROUND

G-protein-coupled estrogen receptor (GPER/GPR30) is a novel membrane-associated estrogen receptor that can induce rapid kinase signaling in various cells. Activation of GPER can prevent hippocampal neuronal cell death following transient global cerebral ischemia (GCI), although the mechanisms remain unclear. In the current study, we sought to address whether GPER activation exerts potent anti-inflammatory effects in the rat hippocampus after GCI as a potential mechanism to limit neuronal cell death.

METHODS

GCI was induced by four-vessel occlusion in ovariectomized female SD rats. Specific agonist G1 or antagonist G36 of GPER was administrated using minipump, and antisense oligonucleotide (AS) of interleukin-1β receptor antagonist (IL1RA) was administrated using brain infusion kit. Protein expression of IL1RA, NF-κB-P65, phosphorylation of CREB (p-CREB), Bcl2, cleaved caspase 3, and microglial markers Iba1, CD11b, as well as inflammasome components NLRP3, ASC, cleaved caspase 1, and Cle-IL1β in the hippocampal CA1 region were investigated by immunofluorescent staining and Western blot analysis. The Duolink II in situ proximity ligation assay (PLA) was performed to detect the interaction between NLRP3 and ASC. Immunofluorescent staining for NeuN and TUNEL analysis were used to analyze neuronal survival and apoptosis, respectively. We performed Barnes maze and Novel object tests to compare the cognitive function of the rats.

RESULTS

The results showed that G1 attenuated GCI-induced elevation of Iba1 and CD11b in the hippocampal CA1 region at 14 days of reperfusion, and this effect was blocked by G36. G1 treatment also markedly decreased expression of the NLRP3-ASC-caspase 1 inflammasome and IL1β activation, as well as downstream NF-κB signaling, the effects reversed by G36 administration. Intriguingly, G1 caused a robust elevation in neurons of a well-known endogenous anti-inflammatory factor IL1RA, which was reversed by G36 treatment. G1 also enhanced p-CREB level in the hippocampus, a transcription factor known to enhance expression of IL1RA. Finally, in vivo IL1RA-AS abolished the anti-inflammatory, neuroprotective, and anti-apoptotic effects of G1 after GCI and reversed the cognitive-enhancing effects of G1 at 14 days after GCI.

CONCLUSIONS

Taken together, the current results suggest that GPER preserves cognitive function following GCI in part by exerting anti-inflammatory effects and enhancing the defense mechanism of neurons by upregulating IL1RA.

PELP1 signaling contributes to medulloblastoma progression by regulating the NF-κB pathway

Medulloblastoma (MB) is the most common and deadliest brain tumor in children. Proline-, glutamic acid-, and leucine-rich protein 1 (PELP1) is a scaffolding protein and its oncogenic signaling is implicated in the progression of several cancers. However, the role of PELP1 in the progression of MB remains unknown. The objective of this study is to examine the role of PELP1 in the progression of MB. Immunohistochemical analysis of MB tissue microarrays revealed that PELP1 is overexpressed in the MB specimens compared to normal brain. Knockdown of PELP1 reduced cell proliferation, cell survival, and cell invasion of MB cell lines. The RNA-sequencing analysis revealed that PELP1 knockdown significantly downregulated the pathways related to inflammation and extracellular matrix. Gene set enrichment analysis confirmed that the PELP1-regulated genes were negatively correlated with nuclear factor-κB (NF-κB), extracellular matrix, and angiogenesis gene sets. Interestingly, PELP1 knockdown reduced the expression of NF-κB target genes, NF-κB reporter activity, and inhibited the nuclear translocation of p65. Importantly, the knockdown of PELP1 significantly reduced in vivo MB progression in orthotopic models and improved the overall mice survival. Collectively, these results suggest that PELP1 could be a novel target for therapeutic intervention in MB.

Redox status, inflammation, necroptosis and inflammasome as indispensable contributors to high fat diet (HFD)-induced neurodegeneration; Effect of N-acetylcysteine (NAC)

Adequate dietary intake has a crucial effect on brain health. High fat diet (HFD) rich in saturated fatty acids is linked to obesity and its complications as neurodegeneration via inducing oxidative stress and inflammation. The present study aimed to evaluate the effect of HFD on cerebral cortex in addition to shedding the light on the modulatory role of N-acetylcytsteine (NAC) and its possible underlying biochemical and molecular mechanisms. Twenty eight male Wistar rats were equally and randomly divided into four groups. Group III, and group IV were fed on HFD (45% kcal from fat) for 10 weeks. Group II and group IV were treated with NAC in a dose of 150 mg/kg body weight via intraperitoneal route. Body weight, blood glucose, serum insulin, insulin resistance index, cerebral cortex redox and inflammatory status were evaluated. Cerebral cortex receptor-interacting serine/threonine-protein kinase3 (RIPK3), mixed-lineage kinase domain-like protein (MLKL), nod like receptor protein 3 (NLRP3), interleukin (IL)-18 levels were determined by immunoassay. In addition, apoptosis-associated speck-like proteins (ASC) expression by real-time PCR; inducible nitric oxide synthase (iNOS), glial fibrillary activating protein (GFAP) and matrix metalloproteinase-9 (MMP-9) expression by immunohistochemistry were evaluated. NAC supplementation protected against HFD-induced gain of weights, hyperglycemia, and insulin resistance. Furthermore, NAC improved redox and inflammatory status; decreased levels of RIPK3, MLKL, NLRP3, IL-18; down-regulated ASC, iNOS, GFAP and MMP-9 expression; and decreased myeloperoxidase activity in cerebral cortex. NAC could protect against HFD-induced neurodegeneration via improving glycemic status and peripheral insulin resistance, disrupting oxidative stress/neuroinflammation/necroptosis/inflammasome activation axis in cerebral cortex. NAC may represent a promising strategy for conserving brain health against metabolic diseases-induced neurodegeneration.

Mumefural Ameliorates Cognitive Impairment in Chronic Cerebral Hypoperfusion via Regulating the Septohippocampal Cholinergic System and Neuroinflammation

Chronic cerebral hypoperfusion (CCH) causes cognitive impairment and neurogenic inflammation by reducing blood flow. We previously showed that Fructus mume (F. mume) improves cognitive impairment and inhibits neuroinflammation in a CCH rat model. One of the components of F. mume, Mumefural (MF), is known to improve blood flow and inhibit platelet aggregation. Whether MF affects cerebral and cognitive function remains unclear. We investigated the effects of MF on cognitive impairment and neurological function-related protein expression in the rat CCH model, established by bilateral common carotid arterial occlusion (BCCAo). Three weeks after BCCAo, MF (20, 40, or 80 mg/kg) was orally administrated once a day for 42 days. Using Morris water maze assessment, MF treatment significantly improved cognitive impairment. MF treatment also inhibited cholinergic system dysfunction, attenuated choline acetyltransferase-positive cholinergic neuron loss, and regulated cholinergic system-related protein expressions in the basal forebrain and hippocampus. MF also inhibited myelin basic protein degradation and increased the hippocampal expression of synaptic markers and cognition-related proteins. Moreover, MF reduced neuroinflammation, inhibited gliosis, and attenuated the activation of P2X7 receptor, TLR4/MyD88, NLRP3, and NF-κB. This study indicates that MF ameliorates cognitive impairment in BCCAo rats by enhancing neurological function and inhibiting neuroinflammation.

Molecular mechanisms and cellular events involved in the neuroprotective actions of estradiol. Analysis of sex differences

Estradiol, either from peripheral or central origin, activates multiple molecular neuroprotective and neuroreparative responses that, being mediated by estrogen receptors or by estrogen receptor independent mechanisms, are initiated at the membrane, the cytoplasm or the cell nucleus of neural cells. Estrogen-dependent signaling regulates a variety of cellular events, such as intracellular Ca²⁺ levels, mitochondrial respiratory capacity, ATP production, mitochondrial membrane potential, autophagy and apoptosis. In turn, these molecular and cellular actions of estradiol are integrated by neurons and non-neuronal cells to generate different tissue protective responses, decreasing blood-brain barrier permeability, oxidative stress, neuroinflammation and excitotoxicity and promoting synaptic plasticity, axonal growth, neurogenesis, remyelination and neuroregeneration. Recent findings indicate that the neuroprotective and neuroreparative actions of estradiol are different in males and females and further research is necessary to fully elucidate the causes for this sex difference.

Neurosteroids as regulators of neuroinflammation

Neuroinflammation is a physiological protective response in the context of infection and injury. However, neuroinflammation, especially if chronic, may also drive neurodegeneration. Neurodegenerative diseases, such as multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD) and traumatic brain injury (TBI), display inflammatory activation of microglia and astrocytes. Intriguingly, the central nervous system (CNS) is a highly steroidogenic environment synthesizing steroids de novo, as well as metabolizing steroids deriving from the circulation. Neurosteroid synthesis can be substantially affected by neuroinflammation, while, in turn, several steroids, such as 17β-estradiol, dehydroepiandrosterone (DHEA) and allopregnanolone, can regulate neuroinflammatory responses. Here, we review the role of neurosteroids in neuroinflammation in the context of MS, AD, PD and TBI and describe underlying molecular mechanisms. Moreover, we introduce the concept that synthetic neurosteroid analogues could be potentially utilized for the treatment of neurodegenerative diseases in the future.