Stress-induced neuroinflammation is mediated by GSK3-dependent TLR4 signaling that promotes susceptibility to depression-like behavior

AdipoRon exerts an antidepressant effect by inhibiting NLRP3 inflammasome activation in microglia via promoting mitophagy

Depression is a serious mental disorder that threatens patients' physical and mental health worldwide. The activation of the NLR family pyrin domain-containing 3 (NLRP3) inflammasome is essential for microglia-mediated neuroinflammation and neuronal damage in depression. Numerous pathophysiological factors, such as mitochondrial dysfunction and impaired mitophagy, have an essential role in activating the NLRP3 inflammasome. AdipoRon is a potent adiponectin receptor agonist; however, its antidepressant effects have not been thoroughly investigated. In this study, we found that AdipoRon ameliorated depression-like behavior and neuronal damage induced by chronic unpredictable mild stress (CUMS). Further research demonstrated that AdipoRon inhibited the activation of the NLRP3 inflammasome and protected hippocampal neurons from microglial cytotoxicity by promoting mitophagy, increasing the clearance of damaged mitochondria, and reducing mtROS accumulation. Importantly, inhibition of mitophagy attenuated the antidepressant and neuroprotective effects of AdipoRon. Overall, these findings indicate that AdipoRon alleviates depression by inhibiting NLRP3 inflammasome activation in microglia via improving mitophagy.

Nociplastic pain mechanisms and toll-like receptors as promising targets for its management

ABSTRACT

Nociplastic pain, characterized by abnormal pain processing without an identifiable organic cause, affects a significant portion of the global population. Unfortunately, current pharmacological treatments for this condition often prove ineffective, prompting the need to explore new potential targets for inducing analgesic effects in patients with nociplastic pain. In this context, toll-like receptors (TLRs), known for their role in the immune response to infections, represent promising opportunities for pharmacological intervention because they play a relevant role in both the development and maintenance of pain. Although TLRs have been extensively studied in neuropathic and inflammatory pain, their specific contributions to nociplastic pain remain less clear, demanding further investigation. This review consolidates current evidence on the connection between TLRs and nociplastic pain, with a specific focus on prevalent conditions like fibromyalgia, stress-induced pain, sleep deprivation-related pain, and irritable bowel syndrome. In addition, we explore the association between nociplastic pain and psychiatric comorbidities, proposing that modulating TLRs can potentially alleviate both pain syndromes and related psychiatric disorders. Finally, we discuss the potential sex differences in TLR signaling, considering the higher prevalence of nociplastic pain among women. Altogether, this review aims to shed light on nociplastic pain, its underlying mechanisms, and its intriguing relationship with TLR signaling pathways, ultimately framing the potential therapeutic role of TLRs in addressing this challenging condition.

Du-moxibustion ameliorates depression-like behavior and neuroinflammation in chronic unpredictable mild stress-induced mice

BACKGROUND

Neuroinflammation is involved in the advancement of depression. Du-moxibustion can treat depression. Here, we explored whether Du-moxibustion could alleviate neuroglia-associated neuro-inflammatory process in chronic unpredictable mild stress (CUMS) mice.

METHODS

C57BL/6J mice were distributed into five groups. Except for the CON group, other four groups underwent CUMS for four consecutive weeks, and Du-moxibustion was given simultaneously after modeling. Behavioral tests were then carried out. Additionally, Western blot was conducted to measure the relative expression levels of high-mobility group box 1 (HMGB1), toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88), and nuclear factor-kappa B (NF-κB). Immunofluorescence was employed to evaluate the positive cells of ionized calcium binding adapter molecule 1 (Iba-1) and glial fibrillary acidic protein (GFAP). Furthermore, interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) were analyzed using an ELISA assay.

RESULTS

We found that CUMS induced depression-like behaviors, such as reduced sucrose preference ratio, decreased locomotor and exploratory activity, decreased the time in open arms and prolonged immobility. Furthermore, versus the CON group, the expression of HMGB1, TLR4, MyD88, NF-κB, positive cells of Iba-1, IL-1β and TNF-α were increased but positive cells of GFAP were decreased in CUMS group. However, the detrimental effects were ameliorated by treatment with CUMS+FLU and CUMS+DM.

LIMITATIONS

A shortage of this study is that only CUMS model of depression were used, while other depression model were not included.

CONCLUSIONS

Du-moxibustion alleviates depression-like behaviors in CUMS mice mainly by reducing neuroinflammation, which offers novel insights into the potential treatment of depression.

Exploring the interplay between stress mediators and skin microbiota in shaping age-related hallmarks: A review

Psychological stress is a major contributing factor to several health problems (e.g., depression, cardiovascular disease). Around 35 % of the world's population suffers from it, including younger generations. Physiologically, stress manifests through neuroendocrine pathways (Hypothalamic-Pituitary-Adrenal (HPA) axis and Sympathetic-Adrenal-Medullary (SAM) system) which culminate in the production of stress mediators like cortisol, epinephrine and norepinephrine. Stress and its mediators have been associated to body aging, through molecular mechanisms such as telomere attrition, mitochondrial dysfunction, cellular senescence, chronic inflammation, and dysbiosis, among others. Regarding its impact in the skin, stress impacts its structural integrity and physiological function. Despite this review focusing on several hallmarks of aging, emphasis was placed on skin microbiota dysbiosis. In this line, several studies, comprising different age groups, demographic contexts and body sites, have reported skin microbiota alterations associated with aging, and some effects of stress mediators on skin microbiota have also been reviewed in this paper. From a different perspective, since it is not a "traditional" stress mediator, oxytocin, a cortisol antagonist, has been related to glucorticoids inhibition and to display positive effects on cellular aging. This hormone dysregulation has been associated to psychological issues such as depression, whereas its upregulation has been linked to positive social interaction.

I-C-F-6 attenuates chronic cerebral hypoperfusion-induced neurological injury in mice by modulating microglia polarization

Chronic cerebral hypoperfusion (CCH) is the leading cause of chronic cerebral dysfunction syndrome with its complex pathological mechanisms involving cortical and hippocampal neuronal loss, white matter lesions, and neuroinflammation. I-C-F-6 is a septapeptide, which has anti-inflammatory and anti-fibrotic effects. This study aimed to evaluate the neuroprotective effect of I-C-F-6 in chronic cerebral hypoperfusion (CCH)-induced neurological injury. C57BL/6 J mice were subjected to bilateral common carotid artery stenosis (BCAS), and BV2 microglia cells were induced with oxygen-glucose deprivation (OGD). In vivo, mice were divided randomly into four groups: Sham, BCAS, GBE (30 mg/kg), and I-C-F-6 (0.5 mg/kg). In vitro, microglia were divided randomly into four groups: control, OGD, I-C-F-6 (25 μg/mL), and Shikonin (800 nmol/L). Through LFB, TUNEL, and NeuN staining, we found that I-C-F-6 was able to mitigate myelin pathology and reduce the number of apoptotic neurons. Furthermore, immunofluorescence staining revealed that I-C-F-6 was able to reduce microglia clustering and downregulate NF-κB p65. We also observed a significant downregulation of M1 phenotype microglia signature genes, such as TNF-α, iNOS, and upregulation of anti-inflammatory cytokines, such as Arg-1 and IL-10, indicating that I-C-F-6 may mainly reduce polarization towards the M1 phenotype in microglia. Notably, I-C-F-6 downregulated the expression of NF-κB signaling pathway-related proteins IKK-β and NF-κB p65, as well as pro-inflammatory cytokines IL-1β and iNOS. In conclusion, I-C-F-6 can improve neurological damage, alleviate neuroinflammation, and inhibit microglia polarization to the M1 phenotype via the NF-κB signaling pathway.

Molecular signatures of astrocytes and microglia maladaptive responses to acute stress are rescued by a single administration of ketamine in a rodent model of PTSD

Stress affects the brain and alters its neuroarchitecture and function; these changes can be severe and lead to psychiatric disorders. Recent evidence suggests that astrocytes and microglia play an essential role in the stress response by contributing to the maintenance of cerebral homeostasis. These cells respond rapidly to all stimuli that reach the brain, including stressors. Here, we used a recently validated rodent model of post-traumatic stress disorder in which rats can be categorized as resilient or vulnerable after acute inescapable footshock stress. We then investigated the functional, molecular, and morphological determinants of stress resilience and vulnerability in the prefrontal cortex, focusing on glial and neuronal cells. In addition, we examined the effects of a single subanesthetic dose of ketamine, a fast-acting antidepressant recently approved for the treatment of resistant depression and proposed for other stress-related psychiatric disorders. The present results suggest a prompt glial cell response and activation of the NF-κB pathway after acute stress, leading to an increase in specific cytokines such as IL-18 and TNF-α. This response persists in vulnerable individuals and is accompanied by a significant change in the levels of critical glial proteins such as S100B, CD11b, and CX43, brain trophic factors such as BDNF and FGF2, and proteins related to dendritic arborization and synaptic architecture such as MAP2 and PSD95. Administration of ketamine 24 h after the acute stress event rescued many of the changes observed in vulnerable rats, possibly contributing to support brain homeostasis. Overall, our results suggest that pivotal events, including reactive astrogliosis, changes in brain trophic factors, and neuronal damage are critical determinants of vulnerability to acute traumatic stress and confirm the therapeutic effect of acute ketamine against the development of stress-related psychiatric disorders.

The Emerging Role of Human Gut Bacteria Extracellular Vesicles in Mental Disorders and Developing New Pharmaceuticals

In recent years, further evidence has emerged regarding the involvement of extracellular vesicles in various human physiopathological conditions such as Alzheimer's disease, Parkinson's disease, irritable bowel syndrome, and mental disorders. The biogenesis and cargo of such vesicles may reveal their impact on human health nd disease and set the underpinnings for the development of novel chemical compounds and pharmaceuticals. In this review, we examine the link between bacteria-derived exosomes in the gastrointestinal tract and mental disorders, such as depression and anxiety disorders. Crucially, we focus on whether changes in the gut environment affect the human mental state or the other way around. Furthermore, the possibility of handling bacteria-derived exosomes as vectors of chemicals to treat such conditions is examined.

New Advances in the Pharmacology and Toxicology of Lithium: A Neurobiologically Oriented Overview

Over the last six decades, lithium has been considered the gold standard treatment for the long-term management of bipolar disorder due to its efficacy in preventing both manic and depressive episodes as well as suicidal behaviors. Nevertheless, despite numerous observed effects on various cellular pathways and biologic systems, the precise mechanism through which lithium stabilizes mood remains elusive. Furthermore, there is recent support for the therapeutic potential of lithium in other brain diseases. This review offers a comprehensive examination of contemporary understanding and predominant theories concerning the diverse mechanisms underlying lithium's effects. These findings are based on investigations utilizing cellular and animal models of neurodegenerative and psychiatric disorders. Recent studies have provided additional support for the significance of glycogen synthase kinase-3 (GSK3) inhibition as a crucial mechanism. Furthermore, research has shed more light on the interconnections between GSK3-mediated neuroprotective, antioxidant, and neuroplasticity processes. Moreover, recent advancements in animal and human models have provided valuable insights into how lithium-induced modifications at the homeostatic synaptic plasticity level may play a pivotal role in its clinical effectiveness. We focused on findings from translational studies suggesting that lithium may interface with microRNA expression. Finally, we are exploring the repurposing potential of lithium beyond bipolar disorder. These recent findings on the therapeutic mechanisms of lithium have provided important clues toward developing predictive models of response to lithium treatment and identifying new biologic targets. SIGNIFICANCE STATEMENT: Lithium is the drug of choice for the treatment of bipolar disorder, but its mechanism of action in stabilizing mood remains elusive. This review presents the latest evidence on lithium's various mechanisms of action. Recent evidence has strengthened glycogen synthase kinase-3 (GSK3) inhibition, changes at the level of homeostatic synaptic plasticity, and regulation of microRNA expression as key mechanisms, providing an intriguing perspective that may help bridge the mechanistic gap between molecular functions and its clinical efficacy as a mood stabilizer.

Immunotherapy for depression: Recent insights and future targets

Depression stands as a prominent contributor to global disability, entailing an elevated risk of suicide. Substantial evidence supports the notion that immune dysregulation may play a role in the development of depression and impede responses to antidepressant treatments. Immune dysregulation may cause depression in susceptible individuals through raising inflammatory responses. Differences in immune cell types and the release of pro-inflammatory mediators are observed in the blood and cerebrospinal fluid of patients with major depressive disorder, which is associated with neuroimmune dysfunction. Therefore, the interaction of peripheral and central immune targets in depression needs to be understood. Urgent attention is required for the development of innovative therapeutics directed at modulating immune responses for the treatment of depression. This review delineates the immune mechanisms involved in the pathogenesis of depression, assesses the therapeutic potential of immune system targeting for depression treatment, and deliberates on the merits and constraints of employing immunotherapy in the management of depression.

Research on the mechanism of antidepressive effect of Suanzaoren Decoction through TLR4/MyD88/NF-κB pathway and Wnt/β-catenin pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Increased inflammatory response and disruption of neuroplasticity are important mechanisms in the hypothesis of the pathogenesis of depression. Thus, these two aspects are conducive to the development of treatments for depression. Suanzaoren Decoction (SZRD) is a classic traditional Chinese medicine compound for the treatment of insomnia, which can clinically relieve depression symptoms, but its antidepressant pharmacological mechanism remains to be elucidated.

AIM OF THIS STUDY

Based on the hypothesis of inflammation and neuroplasticity in depression, this study aimed to investigate the antidepressant effect of SZRD and its specific molecular mechanism through chronic unpredictable mild stress (CUMS) induced SD rat model and lipopolysaccharide (LPS) induced BV2 cell neuroinflammation model.

MATERIALS AND METHODS

The body weight and behavioral indexes of CUMS model rats treated with orally or without oral SZRD for 4 weeks were detected. Hematoxylin and eosin staining was used to observe brain pathological damage. Terminal-deoxynucleoitidyl Transferase Mediated Nick End Labeling (TUNEL) staining was used to observe neuronal apoptosis. Immunofluorescence, ELISA kit and Western blotting were used to detect the inflammatory index Iba-1 and inflammatory factors, as well as the important inflammatory pathway TLR4/MyD88/NF-κB. Enzyme linked immunosorbent assay (ELISA) and western blotting were used to detect neuroplasticity indexes proteins-brain-derived neurotrophic factor (BDNF), presynaptic membrane protein-synaptophysin (SYP), and postsynaptic protein- 95(PSD95), and the key pathway Wnt/β-catenin. The possible mechanism of SZRD antidepressant was further explored in LPS-induced BV2 cells.

RESULTS

In vivo and in vitro experiments showed that SZRD treatment significantly reversed the depression-like behaviors in rats, decreased the levels of inflammatory factors and increased the expression levels of BDNF, SYP, PSD95 in depression model rats. Furthermore, SZRD treatment inhibited the activation of TLR4/MyD88/NF-κB and Wnt/β-catenin pathways and reduced the massive nuclear translocation of NF-κB and β-catenin. The addition of NF-κB pathway agonists could partially offset the inhibitory effect of SZRD on the Wnt pathway, and the addition of Wnt pathway agonists could also partially offset the inhibitory effect of SZRD on the TLR4 pathway.

CONCLUSION

This study suggestted that SZRD may exert its antidepressant effect by regulating TLR4/MyD88/NF-κB pathway and Wnt/β-catenin pathway in combination.

Exploring the role of inflammation in major depressive disorder: beyond the monoamine hypothesis

Major depressive disorder affects approximately 8.4% of the United States population. The World Health Organization estimates that 280 million adults worldwide are suffering from depression. They have estimated that by 2030 it will be the second most serious condition. Current treatment relies on the monoamine hypothesis, however, one-third of patients with MDD do not respond to monoamine-based antidepressants. For years, it was hypothesized that the primary pathway of MDD involved serotonin as the main neurotransmitter. The monoamine hypothesis, a widely accepted theory, sought to explain the biological basis of MDD as being caused by the depletion of monoamine neurotransmitters, namely norepinephrine and serotonin. This hypothesis regarding monoamines as the pathophysiological basis of MDD led to the design and widespread use of selective serotonin reuptake inhibitors. However, given that only one-third of patients improve with SSRI it is reasonable to infer that the pathway involved is more complex than once hypothesized and there are more neurotransmitters, receptors, and molecules involved. The monoamine hypothesis does not explain why there is a delay in the onset of effect and action of SSRIs. Several studies have demonstrated that chronic stress is a risk factor for the development of MDD. Thus the monoamine hypothesis alone is not enough to fully account for the pathophysiology of MDD highlighting the need for further research involving the pathways of MDD. In this paper, we review the role of inflammation and cytokines on MDD and discuss other pathways involved in the development and persistence of depressive symptoms.

Fluoxetine attenuates stress-induced depression-like behavior due to decrease in pro-inflammatory cytokines in male rats

Background: Pro-inflammatory cytokines are implicated in depression caused by both environmental- and alcohol-induced stress. The purpose of the study was to investigate the cytokine levels in serum and hippocampus following induction of depression-like behaviors (DLB) by either forced swimming test (FST) or ethanol-induced DLB (EID). We also investigated the effect of prior administration of antidepressant drug fluoxetine on cytokines in animals exposed to both models of DLB. Methods: Animals were pretreated with fluoxetine before inducing DLB, while DLB was induced in some animals using FST and ethanol in different groups of rats without fluoxetine pretreatment. The ELISA was used to detect changes in cytokine (IL-1β, IL-6, and TNF-α) levels in serum and hippocampus. Results: The mean levels of IL-1β and IL-6 measured in serum and hippocampus were significantly higher in FST and EID models when compared to the control group. The serum concentrations of IL-1β and IL-6 were significantly reduced in animals pre-treated with 5 mg/kg and 10 mg/kg of fluoxetine in both FST and EID models when compared to the untreated FST and EID groups respectively. Conclusions: In conclusion, both environment and alcohol can induce stress and DLB in rats with similar intensity, and their mechanisms of DLB induction involve activation of pro-inflammatory cytokines. Moreover, fluoxetine can prevent stress-induced inflammation in models of DLB.

The role of the Toll like receptor 4 signaling in sex-specific persistency of depression-like behavior in response to chronic stress

Chronic stress is a major risk factor for Major Depressive Disorder (MDD), and it has been shown to impact the immune system and cause microglia activation in the medial prefrontal cortex (mPFC) involved in the pathogenesis of depression. The aim of this study is to further investigate cellular and molecular mechanisms underlying persistent depression behavior in sex specific manner, which is observed clinically. Here, we report that both male and female mice exhibited depression-like behavior following exposure to chronic stress. However, only female mice showed persistent depression-like behavior, which was associated with microglia activation in mPFC, characterized by distinctive alterations in the phenotype of microglia. Given these findings, to further investigate the underlying molecular mechanisms associated with persistent depression-like behavior and microglia activation in female mice, we used translating-ribosome affinity purification (TRAP). We find that Toll like receptor 4 (TLR4) signaling is casually related to persistent depression-like behavior in female mice. This is supported by the evidence that the fact that genetic ablation of TLR4 expression in microglia significantly reduced the persistent depression-like behavior to baseline levels in female mice. This study tentatively supports the hypothesis that the TLR4 signaling in microglia may be responsible for the sex differences in persistent depression-like behavior in female.

Cool the Inflamed Brain: A Novel Anti-inflammatory Strategy for the Treatment of Major Depressive Disorder

BACKGROUND

Abundant evidence suggests that inflammatory cytokines contribute to the symptoms of major depressive disorder (MDD) by altering neurotransmission, neuroplasticity, and neuroendocrine processes. Given the unsatisfactory response and remission of monoaminergic antidepressants, anti-inflammatory therapy is proposed as a feasible way to augment the antidepressant effect. Recently, there have been emerging studies investigating the efficiency and efficacy of anti-inflammatory agents in the treatment of MDD and depressive symptoms comorbid with somatic diseases.

METHODS

In this narrative review, prospective clinical trials focusing on anti-inflammatory treatment for depression have been comprehensively searched and screened. Based on the included studies, we summarize the rationale for the anti-inflammatory therapy of depression and discuss the utilities and confusions regarding the anti-inflammatory strategy for MDD.

RESULTS

This review included over 45 eligible trials. For ease of discussion, we have grouped them into six categories based on their mechanism of action, and added some other anti-inflammatory modalities, including Chinese herbal medicine and non-drug therapy. Pooled results suggest that anti-inflammatory therapy is effective in improving depressive symptoms, whether used as monotherapy or add-on therapy. However, there remain confusions in the application of anti-inflammatory therapy for MDD.

CONCLUSION

Based on current clinical evidence, anti-inflammatory therapy is a promisingly effective treatment for depression. This study proposes a novel strategy for clinical diagnosis, disease classification, personalized treatment, and prognostic prediction of depression. Inflammatory biomarkers are recommended to be assessed at the first admission of MDD patients, and anti-inflammatory therapy are recommended to be included in the clinical practice guidelines for diagnosis and treatment. Those patients with high levels of baseline inflammation (e.g., CRP > 3 mg/L) may benefit from adjunctive anti-inflammatory therapy.

New insights into the role of GSK-3β in the brain: from neurodegenerative disease to tumorigenesis

Glycogen synthase kinase 3 (GSK-3) is a serine/threonine kinase widely expressed in various tissues and organs. Unlike other kinases, GSK-3 is active under resting conditions and is inactivated upon stimulation. In mammals, GSK-3 includes GSK-3 α and GSK-3β isoforms encoded by two homologous genes, namely, GSK3A and GSK3B. GSK-3β is essential for the control of glucose metabolism, signal transduction, and tissue homeostasis. As more than 100 known proteins have been identified as GSK-3β substrates, it is sometimes referred to as a moonlighting kinase. Previous studies have elucidated the regulation modes of GSK-3β. GSK-3β is involved in almost all aspects of brain functions, such as neuronal morphology, synapse formation, neuroinflammation, and neurological disorders. Recently, several comparatively specific small molecules have facilitated the chemical manipulation of this enzyme within cellular systems, leading to the discovery of novel inhibitors for GSK-3β. Despite these advancements, the therapeutic significance of GSK-3β as a drug target is still complicated by uncertainties surrounding the potential of inhibitors to stimulate tumorigenesis. This review provides a comprehensive overview of the intricate mechanisms of this enzyme and evaluates the existing evidence regarding the therapeutic potential of GSK-3β in brain diseases, including Alzheimer's disease, Parkinson's disease, mood disorders, and glioblastoma.

Therapeutic potential for KCC2-targeted neurological diseases

Patients with neurological diseases, such as schizophrenia, tend to show low K+-Cl- co-transporter 2 (KCC2) levels in the brain. The cause of these diseases has been associated with stress and neuroinflammation. However, since the pathogenesis of these diseases is not yet fully investigated, drug therapy is still limited to symptomatic therapy. Targeting KCC2, which is mainly expressed in the brain, seems to be an appropriate approach in the treatment of these diseases. In this review, we aimed to discuss about stress and inflammation, KCC2 and Gamma-aminobutyric acid (GABA) function, diseases which decrease the KCC2 levels in the brain, factors that regulate KCC2 activity, and the possibility to overcome neuronal dysfunction targeting KCC2. We also aimed to discuss the relationships between neurological diseases and LPS caused by Porphyromonas gingivalis (P. g), which is a type of oral bacterium. Clinical trials on oxytocin, sirtuin 1 (SIRT1) activator, and transient receptor potential cation channel subfamily V Member 1 activator have been conducted to develop effective treatment methods. We believe that KCC2 modulators that regulate mitochondria, such as oxytocin, glycogen synthase kinase 3β (GSK3β), and SIRT1, can be potential targets for neurological diseases.

Circulating Toll-Like Receptor 4, Nucleotide-Binding Oligomerization Domain-Like Receptor Protein 3, and Cytokines in Patients with Bipolar Depression: A Case-Control Study

Objective

The etiology of bipolar disorder (BD), a complex psychiatric condition, remains uncertain. Previous research has suggested a potential involvement of the host immune system in the development of BD. This study aims to investigate plasma levels of cytokines, circulating toll-like receptor 4 (TLR4), and nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) in patients with bipolar depression.

Methods

This study recruited patients with a depressive episode of BD and healthy controls (HCs). Inflammatory cytokines were quantified using enzyme linked immunosorbent assay (ELISA) analysis.

Results

A total of 26 BD patients with a depressive episode and 14 HCs were enrolled in the study. The findings revealed that individuals with BD with a depressive episode exhibited elevated serum levels of NLRP3 and interleukin-18 compared to HCs. Correlation analyses indicated a favorable association between the frequency of episodes, duration of illness, and TLR4 levels.

Conclusion

The results suggest a connection between cytokines associated with the activation of NLRP3 and their potential impact on the pathogenesis of BD.

CaMKK2 as an emerging treatment target for bipolar disorder

Current pharmacological treatments for bipolar disorder are inadequate and based on serendipitously discovered drugs often with limited efficacy, burdensome side-effects, and unclear mechanisms of action. Advances in drug development for the treatment of bipolar disorder remain incremental and have come largely from repurposing drugs used for other psychiatric conditions, a strategy that has failed to find truly revolutionary therapies, as it does not target the mood instability that characterises the condition. The lack of therapeutic innovation in the bipolar disorder field is largely due to a poor understanding of the underlying disease mechanisms and the consequent absence of validated drug targets. A compelling new treatment target is the Ca2+-calmodulin dependent protein kinase kinase-2 (CaMKK2) enzyme. CaMKK2 is highly enriched in brain neurons and regulates energy metabolism and neuronal processes that underpin higher order functions such as long-term memory, mood, and other affective functions. Loss-of-function polymorphisms and a rare missense mutation in human CAMKK2 are associated with bipolar disorder, and genetic deletion of Camkk2 in mice causes bipolar-like behaviours similar to those in patients. Furthermore, these behaviours are ameliorated by lithium, which increases CaMKK2 activity. In this review, we discuss multiple convergent lines of evidence that support targeting of CaMKK2 as a new treatment strategy for bipolar disorder.

Cranial venous-outflow obstruction promotes neuroinflammation via ADAM17/solTNF-α/NF-κB pathway following experimental TBI

Traumatic brain injury (TBI) is a global public health problem. As an important cause of secondary injury, cerebrovascular reaction can cause secondary bleeding, venous sinus thrombosis, and malignant brain swelling. Recent clinical studies have confirmed that intracranial venous return disorder is closely related to the prognosis of patients, yet the specific molecular mechanism involved in this process is still unclear. This study used an acute subdural hematoma (ASDH) model with cranial venous outflow obstruction (CVO) to explore how CVO aggravates the pathological process after TBI, especially for inflammation and tissue damage. The results suggest that intracranial venous return disorder exacerbates neurological deficits and brain edema in rats with ASDH by aggravating the destruction of endothelial cell tight junctions (TJs) proteins and promoting the expression of inflammatory factors, the activation of microglia and expression of recombinant A disintegrin and metalloprotease 17 (ADAM17) as well as the secretion of solTNF-α, a soluble form of tumor necrosis factor-alpha (TNFα), which in turn increase IκB-α ((inhibitor of the transcription factor nuclear factor-κB) and NF-κB p65. Our study revealed a molecular basis of how CVO aggravates inflammation and tissue damage.

Stress-activated brain-gut circuits disrupt intestinal barrier integrity and social behaviour

Chronic stress underlies the etiology of both major depressive disorder (MDD) and irritable bowel syndrome (IBS), two highly prevalent and debilitating conditions with high rates of co-morbidity. However, it is not fully understood how the brain and gut bi-directionally communicate during stress to impact intestinal homeostasis and stress-relevant behaviours. Using the chronic social defeat stress (CSDS) model, we find that stressed mice display greater intestinal permeability and circulating levels of the endotoxin lipopolysaccharide (LPS) compared to unstressed control (CON) mice. Interestingly, the microbiota in the colon also exhibit elevated LPS biosynthesis gene expression following CSDS. Additionally, CSDS triggers an increase in pro-inflammatory colonic IFNγ+ Th1 cells and a decrease in IL4+ Th2 cells compared to CON mice, and this gut inflammation contributes to stress-induced intestinal barrier permeability and social avoidance behaviour. We next investigated the role of enteric neurons and identified that noradrenergic dopamine beta-hydroxylase (DBH)+ neurons in the colon are activated by CSDS, and that their ablation protects against gut pathophysiology and disturbances in social behaviour. Retrograde tracing from the colon identified a population of corticotropin-releasing hormone-expressing (CRH+) neurons in the paraventricular nucleus of the hypothalamus (PVH) that innervate the colon and are activated by stress. Chemogenetically activating these PVH CRH+ neurons is sufficient to induce gut inflammation, barrier permeability, and social avoidance behaviour, while inhibiting these cells prevents these effects following exposure to CSDS. Thus, we define a stress-activated brain-to-gut circuit that confers colonic inflammation, leading to impaired intestinal barrier function, and consequent behavioural deficits.

Serum levels of high mobility group box-1 protein (HMGB1) and soluble receptors of advanced glycation end-products (RAGE) in depressed patients treated with electroconvulsive therapy

AIMS

High mobility group box-1 (HMGB1) is one of the damage-associated molecular patterns produced by stress and induces inflammatory responses mediated by receptors of advanced glycation end-products (RAGE) on the cell surface. Meanwhile, soluble RAGE (sRAGE) exhibits an anti-inflammatory effect by capturing HMGB1. Animal models have shown upregulation of HMGB1 and RAGE in the brain or blood, suggesting the involvement of these proteins in depression pathophysiology. However, there have been no reports using blood from depressed patients, nor ones focusing on HMGB1 and sRAGE changes associated with treatment and their relationship to depressive symptoms.

METHODS

Serum HMGB1 and sRAGE concentrations were measured by enzyme-linked immunosorbent assay in a group of patients with severe major depressive disorder (MDD) (11 males and 14 females) who required treatment with electroconvulsive therapy (ECT), and also in a group of 25 age- and gender-matched healthy subjects. HMGB1 and sRAGE concentrations were also measured before and after a course of ECT. Depressive symptoms were assessed using the Hamilton Rating Scale for Depression (HAMD).

RESULTS

There was no significant difference in HMGB1 and sRAGE concentrations in the MDD group compared to healthy subjects. Although ECT significantly improved depressive symptoms, there was no significant change in HMGB1 and sRAGE concentrations before and after treatment. There was also no significant correlation between HMGB1 and sRAGE concentrations and the HAMD total score or subitem scores.

CONCLUSION

There were no changes in HMGB1 and sRAGE in the peripheral blood of severely depressed patients, and concentrations had no relationship with symptoms or ECT.

HMGB1 in depression: An overview of microglial HMBG1 in the pathogenesis of depression

Depression is a prevalent psychiatric disorder with elusive pathogenesis. Studies have proposed that enhancement and persistence of aseptic inflammation in the central nervous system (CNS) may be closely associated with the development of depressive disorder. High mobility group box 1 (HMGB1) has obtained significant attention as an evoking and regulating factor in various inflammation-related diseases. It is a non-histone DNA-binding protein that can be released as a pro-inflammatory cytokine by glial cells and neurons in the CNS. Microglia, as the immune cell of the brain, interacts with HMGB1 and induces neuroinflammation and neurodegeneration in the CNS. Therefore, in the current review, we aim to investigate the role of microglial HMGB1 in the pathogenetic process of depression.

Stress promotes the infiltration of peripheral immune cells to the brain

Immune cells and the brain have a privileged interaction. Here, we report changes in the hippocampal immune microenvironment at the single cell level after stress, uncovering the tight orchestration of immune cell infiltration into the hippocampus after stress to maintain homeostasis. We show the distribution of several immune cell types in the hippocampus associated with their susceptibility or resilience to the learned helplessness paradigm in a sex- and microbiota-dependent manner using single-cell RNA sequencing and bioinformatic tools, flow cytometry, and immunofluorescence. We uncovered the presence of tissue-resident memory T cells that accumulate over time in the hippocampus of learned helpless mice, and the presence of CD74-expressing myeloid cells. These cells were found by a knockdown approach to be critical to induce resilience to learned helplessness. Altogether, these findings provide a novel overview of the neuro-immune repertoire and its impact on the landscape of the hippocampus after learned helplessness.

Microglial Responses to Stress-Induced Depression: Causes and Consequences

Chronic stress is a major risk factor for various psychiatric diseases, including depression; it triggers various cellular and structural changes, resulting in the alteration of neurocircuitry and subsequent development of depression. Accumulating evidence suggests that microglial cells orchestrate stress-induced depression. Preclinical studies of stress-induced depression revealed microglial inflammatory activation in regions of the brain that regulate mood. Although studies have identified several molecules that trigger inflammatory responses in microglia, the pathways that regulate stress-induced microglial activation remain unclear. Understanding the exact triggers that induce microglial inflammatory activation can help find therapeutic targets in order to treat depression. In the current review, we summarize the recent literature on possible sources of microglial inflammatory activation in animal models of chronic stress-induced depression. In addition, we describe how microglial inflammatory signaling affects neuronal health and causes depressive-like behavior in animal models. Finally, we propose ways to target the microglial inflammatory cascade to treat depressive disorders.

Spinal alarmin HMGB1 and the activation of TLR4 lead to chronic stress-induced nociceptive hypersensitivity in rodents

Chronic stress affects millions of people around the world, and it can trigger different behavioral disorders like nociceptive hypersensitivity and anxiety, among others. However, the mechanisms underlaying these chronic stress-induced behavioral disorders have not been yet elucidated. This study was designed to understand the role of high-mobility group box-1 (HMGB1) and toll-like receptor 4 (TLR4) in chronic stress-induced nociceptive hypersensitivity. Chronic restraint stress induced bilateral tactile allodynia, anxiety-like behaviors, phosphorylation of ERK and p38MAPK and activation of spinal microglia. Moreover, chronic stress enhanced HMGB1 and TLR4 protein expression at the dorsal root ganglion, but not at the spinal cord. Intrathecal injection of HMGB1 or TLR4 antagonists reduced tactile allodynia and anxiety-like behaviors induced by chronic stress. Additionally, deletion of TLR4 diminished the establishment of chronic stress-induced tactile allodynia in male and female mice. Lastly, the antiallodynic effect of HMGB1 and TLR4 antagonists were similar in stressed male and female rats and mice. Our results suggest that chronic restraint stress induces nociceptive hypersensitivity, anxiety-like behaviors, and up-regulation of spinal HMGB1 and TLR4 expression. Blockade of HMGB1 and TLR4 reverses chronic restraint stress-induced nociceptive hypersensitivity and anxiety-like behaviors and restores altered HMGB1 and TLR4 expression. The antiallodynic effects of HMGB1 and TLR4 blockers in this model are sex independent. TLR4 could be a potential pharmacological target for the treatment of the nociceptive hypersensitivity associated with widespread chronic pain.

GSK-3β: An exuberating neuroinflammatory mediator in Parkinson's disease

Neuroinflammation is a critical degradative condition affecting neurons in the brain. Progressive neurodegenerative conditions such as Alzheimer's disease and Parkinson's disease (PD) have been strongly linked to neuroinflammation. The trigger point for inflammatory conditions in the cells and body is the physiological immune system. The immune response mediated by glial cells and astrocytes can rectify the physiological alterations occurring in the cell for the time being but prolonged activation leads to pathological progression. The proteins mediating such an inflammatory response, as per the available literature, are undoubtedly GSK-3β, NLRP3, TNF, PPARγ, and NF-κB, along with a few other mediatory proteins. NLRP3 inflammasome is undeniably a principal instigator of the neuroinflammatory response, but the regulatory pathways controlling its activation are still unclear, besides less clarity for the interplay between different inflammatory proteins. Recent reports have suggested the involvement of GSK-3β in regulating NLRP3 activation, but the exact mechanistic pathway remains vague. In the current review, we attempt to provide an elaborate description of crosstalk between inflammatory markers and GSK-3β mediated neuroinflammation progression, linking it to regulatory transcription factors and posttranslational modification of proteins. The recent clinical therapeutic advances targeting these proteins are also discussed in parallel to provide a comprehensive view of the progress made in PD management and lacunas still existing in the field.

The Missing Piece? A Case for Microglia's Prominent Role in the Therapeutic Action of Anesthetics, Ketamine, and Psychedelics

There is much excitement surrounding recent research of promising, mechanistically novel psychotherapeutics - psychedelic, anesthetic, and dissociative agents - as they have demonstrated surprising efficacy in treating central nervous system (CNS) disorders, such as mood disorders and addiction. However, the mechanisms by which these drugs provide such profound psychological benefits are still to be fully elucidated. Microglia, the CNS's resident innate immune cells, are emerging as a cellular target for psychiatric disorders because of their critical role in regulating neuroplasticity and the inflammatory environment of the brain. The following paper is a review of recent literature surrounding these neuropharmacological therapies and their demonstrated or hypothesized interactions with microglia. Through investigating the mechanism of action of psychedelics, such as psilocybin and lysergic acid diethylamide, ketamine, and propofol, we demonstrate a largely under-investigated role for microglia in much of the emerging research surrounding these pharmacological agents. Among others, we detail sigma-1 receptors, serotonergic and γ-aminobutyric acid signalling, and tryptophan metabolism as pathways through which these agents modulate microglial phagocytic activity and inflammatory mediator release, inducing their therapeutic effects. The current review includes a discussion on future directions in the field of microglial pharmacology and covers bidirectional implications of microglia and these novel pharmacological agents in aging and age-related disease, glial cell heterogeneity, and state-of-the-art methodologies in microglial research.

Inhibition of Microglial GSK3β Activity Is Common to Different Kinds of Antidepressants: A Proposal for an In Vitro Screen to Detect Novel Antidepressant Principles

Depression is a major public health concern. Unfortunately, the present antidepressants often are insufficiently effective, whilst the discovery of more effective antidepressants has been extremely sluggish. The objective of this review was to combine the literature on depression with the pharmacology of antidepressant compounds, in order to formulate a conceivable pathophysiological process, allowing proposals how to accelerate the discovery process. Risk factors for depression initiate an infection-like inflammation in the brain that involves activation microglial Toll-like receptors and glycogen synthase kinase-3β (GSK3β). GSK3β activity alters the balance between two competing transcription factors, the pro-inflammatory/pro-oxidative transcription factor NFκB and the neuroprotective, anti-inflammatory and anti-oxidative transcription factor NRF2. The antidepressant activity of tricyclic antidepressants is assumed to involve activation of GS-coupled microglial receptors, raising intracellular cAMP levels and activation of protein kinase A (PKA). PKA and similar kinases inhibit the enzyme activity of GSK3β. Experimental antidepressant principles, including cannabinoid receptor-2 activation, opioid μ receptor agonists, 5HT2 agonists, valproate, ketamine and electrical stimulation of the Vagus nerve, all activate microglial pathways that result in GSK3β-inhibition. An in vitro screen for NRF2-activation in microglial cells with TLR-activated GSK3β activity, might therefore lead to the detection of totally novel antidepressant principles with, hopefully, an improved therapeutic efficacy.

Acupuncture exerts preventive effects in rats of chronic unpredictable mild stress: The involvement of inflammation in amygdala and brain-spleen axis

BACKGROUND

Acupuncture has shown the preventive effects on depression in rats with chronic unpredictable mild stress (CUMS). However, the mechanisms of acupuncture for preventing depression still need to be explored. In the study, acupuncture was applied to a rat depression model of CUMS, high-mobility group box 1(HMGB1)/toll-like receptor 4 (TLR4) and brain-spleen axis were assessed.

METHODS

Male Sprague Dawley (SD) rats were exposed to CUMS with two stressors per day for 28 days. In the meantime, manual acupuncture (at GV16 and GV23 acupoints, once every other day) and fluoxetine gavage (2.1 mg/kg, 0.21 mg/mL) were administered daily post CUMS stressors. Behavioral tests and biological detection methods were conducted in sequence to evaluate depression-like phenotypes in rats.

RESULTS

The results showed CUMS induced depression-like behaviors, hyper-activation of HMGB1/TLR4 signaling pathway, elevated inflammation in amygdala and peripheral blood, and hyperactivation of hypothalamic-pituitary-adrenal (HPA) axis. These changes could be prevented and reversed by acupuncture to varying extents.

CONCLUSION

Acupuncture prevented and ameliorated depression-like symptoms induced by CUMS, possibly via regulating inflammation through brain-spleen axis mediated by HMGB1/TLR4 signaling pathway and HPA axis regulation.

NLRP3 inflammasome in depression: A review

The present article provides a detailed concept of the role of NLRP3 inflammasome in the pathophysiology of depression-like chronic diseases where inflammation and release of various cytokines plays a pivotal role in exaggerating the condition. The various pathways involved in NLRP3 activation are the main target of NLRP3 inhibitors for the therapeutic management of depression as per the recent clinical and research studies conducted so far. Further various drug inhibitors for NLRP3 available in preclinical and clinical trials have been discussed in detail. Hence, blockage of the action of NLRP3 inflammasome is crucial to anticipate the inflammatory cytokine release from the mediators that contributes to cause depression.

Adaptor protein MyD88 confers the susceptibility to stress via amplifying immune danger signals

Increasing evidence supports the pathogenic role of neuroinflammation in psychiatric diseases, including major depressive disorder (MDD) and neuropsychiatric symptoms of Coronavirus disease 2019 (COVID-19); however, the precise mechanism and therapeutic strategy are poorly understood. Here, we report that myeloid differentiation factor 88 (MyD88), a pivotal adaptor that bridges toll-like receptors to their downstream signaling by recruiting the signaling complex called 'myddosome', was up-regulated in the medial prefrontal cortex (mPFC) after exposure to chronic social defeat stress (CSDS) or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. The inducible expression of MyD88 in the mPFC primed neuroinflammation and conferred stress susceptibility via amplifying immune danger signals, such as high-mobility group box 1 and SARS-CoV-2 spike protein. Overexpression of MyD88 aggravated, whereas knockout or pharmacological inhibition of MyD88 ameliorated CSDS-induced depressive-like behavior. Notably, TJ-M2010-5, a novel synthesized targeting inhibitor of MyD88 dimerization, alleviated both CSDS- and SARS-CoV-2 spike protein-induced depressive-like behavior. Taken together, our findings indicate that inhibiting MyD88 signaling represents a promising therapeutic strategy for stress-related mental disorders, such as MDD and COVID-19-related neuropsychiatric symptoms.

Chronic restraint stress-induced depression-like behavior is mediated by upregulation of melanopsin expression in C57BL/6 mice retina

BACKGROUND

Depression is associated with circadian disturbances in which melanopsin was a key mechanism. Further studies have demonstrated that melanopsin gene variations are associated with some depressive disorders and aberrant light can impair mood through melanopsin-expressing retinal ganglion cells (mRGCs). The goal of this study was to explore the direct relationship between depression and melanopsin.

METHODS

Adult C57BL/6 male mice were physically restrained for 16 h in a 50-ml polypropylene centrifuge tube and all behavioral tests were performed after CRS treatment. Western blot analysis and immunofluorescence were used to detect melanopsin expression in the retina of C57BL/6 mice. And we observed the change of the electrophysiological function and release of glutamate of mRGCs.

RESULTS

The melanopsin expression upregulate in mRGCs of chronic restraint stress (CRS)-treating mice which exhibit depression-like behavior. The frequency of blue light-induced action potentials and light-induced glutamate release mediated by melanopsin also increase significantly. This change of melanopsin is mediated by the CRS-induced glucocorticoid.

CONCLUSIONS

CRS may induce the depression-like behavior in mice via glucocorticoid-melanopsin pathway. Our findings provide a novel mechanistic link between CRS-induced depression and melanopsin in mice.

The hippocampus in stress susceptibility and resilience: Reviewing molecular and functional markers

Understanding the individual variability that comes with the likelihood of developing stress-related psychopathologies is of paramount importance when addressing mechanisms of their neurobiology. This article focuses on the hippocampus as a region that is highly influenced by chronic stress exposure and that has strong ties to the development of related disorders, such as depression and post-traumatic stress disorder. We first outline three commonly used animal models that have been used to separate animals into susceptible and resilient cohorts. Next, we review molecular and functional hippocampal markers of susceptibility and resilience. We propose that the hippocampus plays a crucial role in the differences in the processing and storage of stress-related information in animals with different stress susceptibilities. These hippocampal markers not only help us attain a more comprehensive understanding of the various facets of stress-related pathophysiology, but also could be targeted for the development of new treatments.

Inhibition of glycogen synthase kinase 3 by lithium, a mechanism in search of specificity

Inhibition of Glycogen synthase kinase 3 (GSK3) is a popular explanation for the effects of lithium ions on mood regulation in bipolar disorder and other mental illnesses, including major depression, cyclothymia, and schizophrenia. Contribution of GSK3 is supported by evidence obtained from animal and patient derived model systems. However, the two GSK3 enzymes, GSK3α and GSK3β, have more than 100 validated substrates. They are thus central hubs for major biological functions, such as dopamine-glutamate neurotransmission, synaptic plasticity (Hebbian and homeostatic), inflammation, circadian regulation, protein synthesis, metabolism, inflammation, and mitochondrial functions. The intricate contributions of GSK3 to several biological processes make it difficult to identify specific mechanisms of mood stabilization for therapeutic development. Identification of GSK3 substrates involved in lithium therapeutic action is thus critical. We provide an overview of GSK3 biological functions and substrates for which there is evidence for a contribution to lithium effects. A particular focus is given to four of these: the transcription factor cAMP response element-binding protein (CREB), the RNA-binding protein FXR1, kinesin subunits, and the cytoskeletal regulator CRMP2. An overview of how co-regulation of these substrates may result in shared outcomes is also presented. Better understanding of how inhibition of GSK3 contributes to the therapeutic effects of lithium should allow for identification of more specific targets for future drug development. It may also provide a framework for the understanding of how lithium effects overlap with those of other drugs such as ketamine and antipsychotics, which also inhibit brain GSK3.

Comparison of inflammatory and behavioral responses to chronic stress in female and male mice

Major depressive disorder (MDD) is a debilitating disease with a high worldwide prevalence. Despite its greater prevalence in women, male animals are used in most preclinical studies of depression even though there are many sex differences in key components of depression, such as stress responses and immune system functions. In the present study, we found that chronic restraint stress-induced depressive-like behaviors are quite similar in male and female mice, with both sexes displaying increased immobility time in the tail suspension test and reduced social interactions, and both sexes exhibited deficits in working and spatial memories. However, in contrast to the similar depressive-like behaviors developed by male and female mice in response to stress, they displayed different patterns of pro-inflammatory cytokine increases in the periphery and the brain, different changes in microglia, and different changes in the expression of Toll-like receptor 4 in response to stress. Treatment with (+)-naloxone, a Toll-like receptor 4 antagonist that previously demonstrated anti-depressant-like effects in male mice, was more efficacious in male than female mice in reducing the deleterious effects of stress, and its effects were not microbiome-mediated. Altogether, these results suggest differential mechanisms to consider in potential sex-specific treatments of depression.

n-3 polyunsaturated fatty acids improve depression-like behavior by inhibiting hippocampal neuroinflammation in mice via reducing TLR4 expression

INTRODUCTION

n-3 polyunsaturated fatty acids (PUFAs) are believed to be implicated in the pathogenesis of many inflammation-related diseases, including depression.

METHODS

The mouse model of depression was established through chronic unpredictable mild stress (CUMS), the mice were intervened with n-3 PUFAs, and then the expression of toll-like receptor 4 (TLR4) was stimulated with lipopolysaccharides (LPS). Tail suspension test (TST), forced swimming test (FST) and sucrose preference test were performed to monitor the depression behavior of mice. Microglia activation was detected by Iba1 immunofluorescence, and neuronal injury was detected by Nissl staining. Concentrations of tumor necrosis factor (TNF)-α, Interleukin (IL)-6 and IL-1β in the hippocampus were assessed via enzyme linked immunosorbent assay (ELISA). Quantitative real time polymerase chain reaction was used to detect IL-6, IL-1β and TNF-α messenger RNA levels. Western blot was utilized for detection of TLR4 protein expression.

RESULTS

CUMS significantly reduced the sucrose preference in mice, while increased the immobility time in FST and TST. Moreover, CUMS significantly aggravated microglia activation and neuronal damage in mice and increased the levels of IL-6, IL-1β and TNF-α in hippocampal tissues, however, intervention with n-3 PUFAs could improve the above effects. Further, the increased TLR4 induced by LPS partially reversed the inhibition of n-3 PUFAs on depression-like behaviors, microglial activation and inflammatory injury of hippocampal neurons.

CONCLUSION

n-3 PUFAs may ameliorate depression-like behaviors via reducing hippocampal neuroinflammation in CUMS-induced mice by regulating TLR4 expression, suggesting that n-3 PUFAs may be an effective antidepressant, which provides evidence for future treatment of depression.

Selective serotonin reuptake inhibitors and inflammatory bowel disease; Beneficial or malpractice

IBD, a chronic inflammatory disease, has been manifested as a growing health problem. No Crohn's and Colitis councils have officially ratified anti-depressants as a routine regimen for IBD patients. However, some physicians empirically prescribe them to rectify functional bowel consequences such as pain and alleviate psychiatric comorbidities. On the other side, SSRIs' prescription is accompanied by adverse effects such as sleep disturbances. Prolonged intermittent hypoxia throughout sleep disturbance such as sleep apnea provokes periodic reductions in the partial oxygen pressure gradient in the gut lumen. It promotes gut microbiota to dysbiosis, which induces intestinal inflammation. This phenomenon and evidence representing the higher amount of serotonin associated with Crohn's disease challenged our previous knowledge. Can SSRIs worsen the IBD course? Evidence answered the question with the claim on anti-inflammatory properties (central and peripheral) of SSRIs and illuminated the other substantial elements (compared to serotonin elevation) responsible for IBD pathogenesis. However, later clinical evidence was not all in favor of the benefits of SSRIs. Hence, in this review, the molecular mechanisms and clinical evidence are scrutinized and integrated to clarify the interfering molecular mechanism justifying both supporting and disproving clinical evidence. Biphasic dose-dependent serotonin behavior accompanying SSRI shifting function when used up for the long-term can be assumed as the parameters leading to IBD patients' adverse outcomes. Despite more research being needed to elucidate the effect of SSRI consumption in IBD patients, periodic prescriptions of SSRIs at monthly intervals can be recommended.

Alzheimer’s Disease and Inflammaging

Alzheimer’s disease is one of the most common age-related neurodegenerative disorders. The main theory of Alzheimer’s disease progress is the amyloid-β cascade hypothesis. However, the initial mechanisms of insoluble forms of amyloid-β formation and hyperphosphorylated tau protein in neurons remain unclear. One of the factors, which might play a key role in senile plaques and tau fibrils generation due to Alzheimer’s disease, is inflammaging, i.e., systemic chronic low-grade age-related inflammation. The activation of the proinflammatory cell phenotype is observed during aging, which might be one of the pivotal mechanisms for the development of chronic inflammatory diseases, e.g., atherosclerosis, metabolic syndrome, type 2 diabetes mellitus, and Alzheimer’s disease. This review discusses the role of the inflammatory processes in developing neurodegeneration, activated during physiological aging and due to various diseases such as atherosclerosis, obesity, type 2 diabetes mellitus, and depressive disorders.

The role of damage associated molecular pattern molecules (DAMPs) and permeability of the blood-brain barrier in depression and neuroinflammation

Depression is a heterogeneous mental disorder characterized by feelings of sadness and loss of interest that render the subject unable to handle basic daily activities such as sleeping, eating, or working. Neurobiological traits leading to depression include genetic background, early life abuse, life stressors, and systemic and central inflammatory profiles. Several clinical and preclinical reports documented that depression shows an increase in pro-inflammatory markers such as interleukin (IL-)1β, IL-6, IL-12, tumor necrosis factor (TNF), and interferon (IFN)-γ; and a decrease in anti-inflammatory IL-4, IL-10, and transforming growth factor (TGF)-β species. Inflammatory activation may trigger and maintain depression. Dynamic crosstalk between the peripheral immune system and the central nervous system (CNS) such as activated endothelial cells, monocytes, monocyte-derived dendritic cells, macrophages, T cells, and microglia has been proposed as a leading cause of neuroinflammation. Notably, pro-inflammatory cytokines disrupt the hypothalamic-pituitary-adrenal (HPA) axis and serotonergic, noradrenergic, dopaminergic, and glutamatergic neurotransmission. While still under investigation, peripheral cytokines can engage brain pathways and affect the central synthesis of HPA hormones and neurotransmitters through several mechanisms such as activation of the vagus nerve, increasing the permeability of the blood-brain barrier (BBB), altered cytokines transport systems, and engaging toll-like receptors (TLRs) by pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs). However, physiological mechanisms that favor time-dependent central inflammation before or during illness are not totally understood. This review will provide preclinical and clinical evidence of DAMPs and the BBB permeability as contributors to depression and neuroinflammation. We will also discuss pharmacologic approaches that could potentially modulate DAMPs and BBB permeability for future interventions against major depression.

Stress-induced biological aging: A review and guide for research priorities

Exposure to chronic adverse conditions, and the resultant activation of the neurobiological response cascade, has been associated with an increased risk of early onset of age-related disease and, recently, with an older biological age. This body of research has led to the hypothesis that exposure to stressful life experiences, when occurring repeatedly or over a prolonged period, may accelerate the rate at which the body ages. The mechanisms through which chronic psychosocial stress influences distinct biological aging pathways to alter rates of aging likely involve multiple layers in the physiological-molecular network. In this review, we integrate research using animal, human, and in vitro models to begin to delineate the distinct pathways through which chronic psychosocial stress may impact biological aging, as well as the neuroendocrine mediators (i.e., norepinephrine, epinephrine, and glucocorticoids) that may drive these effects. Findings highlight key connections between stress and aging, namely cellular metabolic activity, DNA damage, telomere length, cellular senescence, and inflammatory response patterns. We conclude with a guiding framework and conceptual model that outlines the most promising biological pathways by which chronic adverse conditions could accelerate aging and point to key missing gaps in knowledge where future research could best answer these pressing questions.

Role of high mobility group box protein 1 in depression: A mechanistic and therapeutic perspective

As a common and serious psychiatric disorder, depression significantly affects psychosocial functioning and quality of life. However, the mechanism of depression is still enigmatic and perplexing, which limits its precise and effective therapeutic methods. Recent studies demonstrated that neuroinflammation activation plays an important role in the pathophysiology of depression. In this respect, high mobility group box 1 (HMGB1) may be a possible signaling inducer of neuroinflammation and can be a potential mechanistic and therapeutic target for depression. Herein, we review recent studies on the mechanistic and therapeutic targets of HMGB1 in depression and propose potential perspectives on this topic.

Oxytocin ameliorates KCC2 decrease induced by oral bacteria-derived LPS that affect rat primary cultured cells and PC-12 cells

Inflammation, especially neuroinflammation, which is caused by stress, leads to central nervous system (CNS) dysfunction. Because lipopolysaccharides (LPSs) cause neuroinflammation, we investigated the effect of LPSs to CNS. In PC-12 cells, LPSs derived from oral bacteria reduced the expression of KCC2, a Cl^- transporter. LPS derived from P. gingivalis (P. g) administered to rat primary cultured cells also reduced the KCC2 expression. However, LPSs derived from E. coli did not reduce the KCC2 expression. LPS treatment activated TLR4, IL-1β, and REST gene expressions, which led to KCC2 inactivation in PC-12 cells. The mechanism of KCC2 has been shown to play an important role in brain maturation, function (such as the GABA switch), and behavioral problems, we investigated the GABA function. We found that the GABA function was changed from inhibitory to excitatory by the LPS derived from P. g treatment. We demonstrated that the GSK3β also involved in the KCC2 reduction by LPS treatment. We show that oxytocin rescued the reduction in KCC2 expression caused by LPSs by inhibiting GSK3β signaling but vasopressin could not. Considered together, our results indicate that the LPSs from oral bacteria but not the LPS from E. coli increase the risk for brain disorders and oxytocin might be a candidate to overcome the abnormal behavior caused by brain disorders such as psychiatric disorders.

Anti-Neuroinflammatory Effects of a Semi-Synthetic Isoorientin-Based Glycogen Synthase Kinase-3β Inhibitor in Lipopolysaccharide-Activated Microglial Cells

Neuroinflammation contributes to the pathogenesis of several neurodegenerative disorders. Glycogen synthase kinase-3β (GSK-3β) regulates the release of proinflammatory cytokines and promotes inflammatory responses in immune cells. Microglia are the resident mononuclear immune cells of the central nervous system. Here, we investigated the anti-neuroinflammatory effects of (2S,3S,4R,5R,6S)-6-(2-(3,4-dimethoxyphenyl)-5,7-dimethoxy-4-oxo-4H-chromen-6-yl)-3,4,5-trihydroxy-N-((S)-1,1,1-trifluoropropan-2-yl)tetrahydro-2H-pyran-2-carboxamide (TFGF-18), a semisynthetic GSK-3β inhibitor, in lipopolysaccharide (LPS) activation of spontaneously immortalized SIM-A9 microglial cells and of mouse cortical microglia. TFGF-18 at 2.5 μM concentration inhibited LPS-induced production of nitric oxide by 56.3% and the proinflammatory cytokines TNF-α and IL-1β by 28.3 and 59.2% in SIM-A9 cells, respectively, relative to the LPS treatment control group. Pretreatment of mouse primary microglial cells with TFGF-18 at 2.5 μM concentration led to a reduction of 58.7% in TNF-α+ microglial cells at 24 h post-LPS stimulation. The migration of LPS-activated SIM-A9 cells was also reduced by 26.7% with pretreatment of TFGF-18 in a scratch assay. Analyses of signaling pathways demonstrated that TFGF-18 led to the suppression of LPS-induced GSK-3β activation and p65/NF-κB activity. Furthermore, the co-culture of SIM-A9 with SH-SY5Y neuroblastoma cells showed the suppression of TFGF-18 to microglia-mediated neurotoxicity in vitro. The findings indicate strong inhibitory effects of TFGF-18 on LPS-induced microglia activation via regulation of GSK-3β and downstream p65/NF-κB signaling. The results suggest a potential role of TFGF-18 in neuroprotection via its anti-neuroinflammatory effect.

Puerarin Alleviates Depression-Like Behavior Induced by High-Fat Diet Combined With Chronic Unpredictable Mild Stress via Repairing TLR4-Induced Inflammatory Damages and Phospholipid Metabolism Disorders

Puerarin has been reported as a potential agent for neuro-inflammatory disorders. However, there have been no reports of using puerarin for the treatment of depression based on Toll-like receptor 4 (TLR4)–mediated inflammatory injury. In this study, we evaluated the protective effects of puerarin on depression-like rats induced by a high-fat diet (HFD) combined with chronic unpredictable mild stress (CUMS). The mechanism was screened by lipidomics and molecular docking and confirmed by in vivo tests. Puerarin treatment significantly improved 1% sucrose preference and ameliorated depression-like behavior in the open-field test. The antidepressive effects of puerarin were associated with decreased pro-inflammatory cytokine production, including interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), and increased anti-inflammatory cytokine levels (IL-10) in rat hippocampal tissues and plasma. Hematoxylin–eosin (H&E), immunofluorescence staining, and Western blotting results displayed that puerarin alleviated inflammatory injury by suppressing TLR4 expression and by repairing the intestine mucus barrier via enhancing the expression of claudin-1 and occludin. Non-targeted lipidomics analysis showed that the most significantly different metabolites modified by puerarin were phospholipids. Puerarin treatment–altered biomarkers were identified as PC (15:1/20:1), PE (15:1/16:1), and PI (18:2/20:1) in comparison with the HFD/CUMS group. Molecular docking modeling revealed that puerarin could bind with cytosolic phospholipase A2 (cPLA2) and cyclooxygenase-2 (COX-2), which play central roles in TLR4-mediated phospholipid metabolism. In vivo, puerarin treatment decreased the enzyme activities of cPLA2 and COX-2, resulting in lower production of prostaglandin E₂ (PGE₂) in hippocampal and intestinal tissues. In conclusion, puerarin treatment reverses HFD/CUMS-induced depression-like behavior by inhibiting TLR4-mediated intestine mucus barrier dysfunction and neuro-inflammatory damages via the TLR4/cPLA2/COX-2 pathway.

Microglial glutaminase 1 deficiency mitigates neuroinflammation associated depression

Glutaminase 1 (GLS1) has recently been reported to be expressed in microglia and plays a crucial role in neuroinflamation. Significantly increased level of GLS1 mRNA expression together with neuroinflammation pathway were observed in postmortem prefrontal cortex from depressed patients. To find out the function of microglial GLS1 in depression and neuroinflammation, we generated transgenic mice (GLS1 cKO), postnatally losing GLS1 in microglia, to detect changes in the lipopolysaccharide (LPS)-induced depression model. LPS-induced anxiety/depression-like behavior was attenuated in GLS1 cKO mice, paralleled by a significant reduction in pro-inflammatory cytokines and an abnormal microglia morphological phenotype in the prefrontal cortex. Reduced neuroinflammation by GLS1 deficient microglia was a result of less reactive astrocytes, as GLS1 deficiency enhanced miR-666-3p and miR-7115-3p levels in extracellular vesicles released from microglia, thus suppressing astrocyte activation via inhibiting Serpina3n expression. Together, our data reveal a novel mechanism of GLS1 in neuroinflammation and targeting GLS1 in microglia may be a novel strategy to alleviate neuroinflammation-related depression and other disease.

Underlying mechanisms of glucocorticoid-induced β-cell death and dysfunction: a new role for glycogen synthase kinase 3

Glucocorticoids (GCs) are widely prescribed for their anti-inflammatory and immunosuppressive properties as a treatment for a variety of diseases. The use of GCs is associated with important side effects, including diabetogenic effects. However, the underlying mechanisms of GC-mediated diabetogenic effects in β-cells are not well understood. In this study we investigated the role of glycogen synthase kinase 3 (GSK3) in the mediation of β-cell death and dysfunction induced by GCs. Using genetic and pharmacological approaches we showed that GSK3 is involved in GC-induced β-cell death and impaired insulin secretion. Further, we unraveled the underlying mechanisms of GC-GSK3 crosstalk. We showed that GSK3 is marginally implicated in the nuclear localization of GC receptor (GR) upon ligand binding. Furthermore, we showed that GSK3 regulates the expression of GR at mRNA and protein levels. Finally, we dissected the proper contribution of each GSK3 isoform and showed that GSK3β isoform is sufficient to mediate the pro-apoptotic effects of GCs in β-cells. Collectively, in this work we identified GSK3 as a viable target to mitigate GC deleterious effects in pancreatic β-cells.

Glycogen synthesis and beyond, a comprehensive review of GSK3 as a key regulator of metabolic pathways and a therapeutic target for treating metabolic diseases

Glycogen synthase kinase‐3 (GSK3) is a highly evolutionarily conserved serine/threonine protein kinase first identified as an enzyme that regulates glycogen synthase (GS) in response to insulin stimulation, which involves GSK3 regulation of glucose metabolism and energy homeostasis. Both isoforms of GSK3, GSK3α, and GSK3β, have been implicated in many biological and pathophysiological processes. The various functions of GSK3 are indicated by its widespread distribution in multiple cell types and tissues. The studies of GSK3 activity using animal models and the observed effects of GSK3‐specific inhibitors provide more insights into the roles of GSK3 in regulating energy metabolism and homeostasis. The cross‐talk between GSK3 and some important energy regulators and sensors and the regulation of GSK3 in mitochondrial activity and component function further highlight the molecular mechanisms in which GSK3 is involved to regulate the metabolic activity, beyond its classical regulatory effect on GS. In this review, we summarize the specific roles of GSK3 in energy metabolism regulation in tissues that are tightly associated with energy metabolism and the functions of GSK3 in the development of metabolic disorders. We also address the impacts of GSK3 on the regulation of mitochondrial function, activity and associated metabolic regulation. The application of GSK3 inhibitors in clinical tests will be highlighted too. Interactions between GSK3 and important energy regulators and GSK3‐mediated responses to different stresses that are related to metabolism are described to provide a brief overview of previously less‐appreciated biological functions of GSK3 in energy metabolism and associated diseases through its regulation of GS and other functions.

Effects of Toll-like receptor 4 inhibition on spatial memory and cell proliferation in male and female adult and aged mice

Toll-like receptors (TLRs) participate in the response to infection, stress, and injury by initiating an innate immune response. In addition, these receptors are expressed in many neural cell types and under physiological conditions are implicated in modulating cognitive function and neural plasticity in the adult and aged brain. Knockout of the Toll-like receptor 4 (TLR4) subtype enhances spatial memory and adult hippocampal neurogenesis through increasing proliferation and neuronal differentiation. Currently unknown is whether pharmacological inhibition of TLR4 produces similar enhancements in cognitive function and cell proliferation. The present study evaluated water maze performance, cytokine expression, and cell proliferation in the hippocampus of young and aged male and female C57BL6/J mice following treatment with the TLR4 antagonist, TAK-242. Further, alterations in the response to an acute stressor were evaluated in TAK-242-treated mice. Results showed that TAK-242 selectively enhanced spatial learning and memory in young females. Additionally, TAK-242 treatment reduced thigmotaxis in the water maze and lowered corticosterone levels following acute stress in females. TAK-242 decreased hippocampal interleukin (IL)-1β expression but had no effect on IL-6 or tumor necrosis factor-α (TNFα). Aged mice showed decreased cell proliferation compared to young mice, but TAK-242 administration had minimal effects on estimated Ki67 positive cell numbers. Findings indicate that pharmacological inhibition of TLR4 improves cognitive function in young females likely through attenuating stress reactivity.

Glycogen Synthase Kinase-3: A Focal Point for Advancing Pathogenic Inflammation in Depression

Increasing evidence indicates that the host immune response has a monumental role in the etiology of major depressive disorder (MDD), motivating the development of the inflammatory hypothesis of depression. Central to the involvement of chronic inflammation in MDD is a wide range of signaling deficits induced by the excessive secretion of pro-inflammatory cytokines and imbalanced T cell differentiation. Such signaling deficits include the glutamatergic, cholinergic, insulin, and neurotrophin systems, which work in concert to initiate and advance the neuropathology. Fundamental to the communication between such systems is the protein kinase glycogen synthase kinase-3 (GSK-3), a multifaceted protein critically linked to the etiology of MDD and an emerging target to treat pathogenic inflammation. Here, a consolidated overview of the widespread multi-system involvement of GSK-3 in contributing to the neuropathology of MDD will be discussed, with the feed-forward mechanistic links between all major neuronal signaling pathways highlighted.