Microglia polarization of hippocampus is involved in the mechanism of Apelin-13 ameliorating chronic water immersion restraint stress-induced depression-like behavior in rats

The relationship between serum resolvin D1, NLRP3, cytokine levels, and adolescents with first-episode medication-naïve major depressive disorder

BACKGROUND

Inflammation has become a critical pathological mechanism of Major Depressive Disorder (MDD). NLRP3 is a critical inflammatory pathway to maintain the immune balance. Recently, preclinical evidence showed that Resolvin D1 might potentially offer a new option for antidepressant treatment due to its protective effects through the inhibition of neuroinflammation. However, whether they have clinical value in the diagnosis and treatment evaluation of adolescent depression was unclear.

METHODS

Forty-eight untreated first-episode adolescent patients with moderate to severe major depressive disorder, as well as 30 healthy adolescents (HCs, age and gender-matched), were enrolled for this study. Their ages ranged from 13 to 18 (15.75 ± 1.36) years. The patients were treated with fluoxetine for 6-8 weeks. HDRS-17 was used to evaluate the severity of depressive symptoms. Venous blood samples were collected at baseline for the two groups and at the time-point of post-antidepressant treatment for the patients. Serum concentrations of RvD1, NLRP3, IL-1β, IL-18, and IL-4 were measured by enzyme-linked immunosorbent assays (ELISA) pre- and post-fluoxetine treatment.

RESULTS

Serum levels of RvD1 and anti-inflammatory cytokine IL-4 were significantly elevated in adolescents with MDD compared to healthy adolescents, but no significant difference in NLRP3, IL-1β, and IL-18 between the two groups. Meanwhile, RvD1 (positively) and IL-4 (negatively) were correlated with the severity of symptoms (HDRS-17 scores) after adjusting age, gender, and BMI. Interestingly, fluoxetine treatment significantly reduced the serum levels of RvD1, NLRP3, IL-1β, and IL-18 in MDD adolescents but increased the levels of IL-4 relative to baseline. Furthermore, we observed that serum levels of RvD1 might be an excellent distinguishing indicator for depression and healthy adolescents.

CONCLUSIONS

Our study is the first to compare RvD1 and NLRP3 between adolescent MDD and HCs. Our findings of reactive increase of RvD1 in adolescent MDD comprised a novel and critical contribution. Our results showed the presence of inflammation resolution unbalanced in adolescents with MDD and indicated that RvD1 might be an ideal biomarker for diagnosing and treating adolescent MDD.

A review of the pharmacological action and mechanism of natural plant polysaccharides in depression

Depression is a prevalent mental disorder. However, clinical treatment options primarily based on chemical drugs have demonstrated varying degrees of adverse reactions and drug resistance, including somnolence, nausea, and cognitive impairment. Therefore, the development of novel antidepressant medications that effectively reduce suffering and side effects has become a prominent area of research. Polysaccharides are bioactive compounds extracted from natural plants that possess diverse pharmacological activities and medicinal values. It has been discovered that polysaccharides can effectively mitigate depression symptoms. This paper provides an overview of the pharmacological action and mechanisms, intervention approaches, and experimental models regarding the antidepressant effects of polysaccharides derived from various natural sources. Additionally, we summarize the roles and potential mechanisms through which these polysaccharides prevent depression by regulating neurotransmitters, HPA axis, neurotrophic factors, neuroinflammation, oxidative stress, tryptophan metabolism, and gut microbiota. Natural plant polysaccharides hold promise as adjunctive antidepressants for prevention, reduction, and treatment of depression by exerting their therapeutic effects through multiple pathways and targets. Therefore, this review aims to provide scientific evidence for developing polysaccharide resources as effective antidepressant drugs.

The regulatory effects of the apelin/APJ system on depression: A prospective therapeutic target

Depression is a debilitating neuropsychological disorder characterized by high incidence, high recurrence, high suicide, and high disability rates, which poses serious threats to human health and imposes heavy psychological and economic burdens on family and society. The pathogenesis of depression is extremely complex, and its etiology is multifactorial. Mounting evidence suggests that apelin and apelin receptor APJ, which compose the apelin/APJ system, are related to the development of depression. However, the specific mechanism is still unclear, and research in this area in human is still insufficient. Acceleration of research into the regulatory effects and underlying mechanisms of the apelin/APJ system in depression may identify attractive therapeutic targets and contribute to the development of novel intervention strategies against this devastating psychological disorder. In this review, we mainly discuss the regulatory effects of apelin/APJ system on depression and its potential therapeutic applications.

Protective effect of TNIP2 on the inflammatory response of microglia after spinal cord injury in rats

BACKGROUND

Spinal cord injury (SCI) is a devastating disease that can lead to tissue loss and neurological dysfunction. TNIP2 is a negative regulator of NF-κB signaling due to its capacity to bind A20 and suppress inflammatory cytokines-induced NF-κB activation. However, the anti-inflammatory role of TNIP2 in SCI remains unclear. Our study's intention was to evaluate the effect of TNIP2 on the inflammatory response of microglia after spinal cord injury in rats.

METHODS

HE staining and Nissl staining were performed on day 3 following SCI to analyze the histological changes. To further investigate the functional changes of TNIP2 after SCI, we performed immunofluorescence staining experiments. The effect of LPS on TNIP2 expression in BV2 cells was examined by western blot. The levels of TNF-α, IL-1β, and IL-6 in spinal cord tissues of rats with SCI and in BV2 cells with LPS were measured by using qPCR.

RESULTS

TNIP2 expression was closely associated with the pathophysiology of SCI in rats, and TNIP2 was involved in regulating functional changes in microglia. TNIP2 expression was increased during SCI in rats and that overexpression of TNIP2 inhibited M1 polarization and pro-inflammatory cytokine production in microglia, which might ultimately protect against inflammatory responses through the MAPK and NF-κB signaling pathways.

CONCLUSIONS

The present study provides evidence for a role of TNIP2 in the regulation of inflammation in SCI and suggests that induction of TNIP2 expression alleviated the inflammatory response of microglia.

Electroacupuncture relieves chronic pain by promoting microglia M2 polarization in lumbar disc herniation rats

Electroacupuncture has an effective analgesia on chronic pain caused by lumbar disc herniation (LDH) clinically, however, the underlying mechanism is unclear. In this study, we investigated whether electroacupuncture alleviated pain in LDH model rats by inducing spinal microglia M2 polarization. We established a noncompression LDH rat model by implanting autologous caudal nucleus pulposus into L5/L6 nerve root. Electroacupuncture (30 min/day) treatment on the ipsilateral side was started on the 8th postoperative day, once a day for consecutive 7 days. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were tested for pain behavior. Western blotting was used to detect the protein expression in lumbar enlargement (L5/L6). Immunofluorescence was used to detect iNOS+/Iba-1+ and Arg-1+/Iba-1+ and CB2R+/Iba-1+ in lumbar enlargement (L5/L6). We show that PWT and PWL decreased in the LDH group while Iba-1, iNOS, and TNF-α expression increased significantly in lumbar spinal dorsal horn (SDH) after LDH surgery, and revealing that microglia were activated and polarized towards proinflammatory M1 phenotype. Electroacupuncture treatment significantly increased PWT and PWL while reducing Iba-1, iNOS, and TNF-α expression, interestingly, Arg-1 and IL-10 expression were significantly increased. Moreover, electroacupuncture treatment led to CB2 receptors on microglia upregulation, while NF-κB and p-NF-κB expression in lumbar SDH downregulation. Our study indicated that electroacupuncture may reduce nociceptive hyperalgesia by inhibiting microglia activation and microglia M1 polarization and promoting microglia M2 polarization in lumbar SDH of LDH rats, which may be caused by the activation of CB2 receptors on microglia and inhibition of NF-κB pathway in lumbar SDH.

Neuroprotective Roles of Apelin-13 in Neurological Diseases

Apelin is a natural ligand for the G protein-coupled receptor APJ, and the apelin/APJ system is widely distributed in vivo. Among the apelin family, apelin-13 is the major apelin isoform in the central nervous system and cardiovascular system, and is involved in the regulation of various physiopathological mechanisms such as apoptosis, neuroinflammation, angiogenesis, and oxidative stress. Apelin is currently being extensively studied in the nervous system, and apelin-13 has been shown to be associated with the onset and progression of a variety of neurological disorders, including stroke, neurodegenerative diseases, epilepsy, spinal cord injury (SCI), and psychiatric diseases. This study summarizes the pathophysiological roles of apelin-13 in the development and progression of neurological related diseases.

Apelin/APJ system: an emerging therapeutic target for neurological diseases

Apelin, an endogenous ligand for the G protein-coupled receptor APJ, is extensively expressed in various systems, especially the nervous system. This article reviews the role of apelin/APJ system in neurological diseases. In detail, apelin/APJ system can relieve acute brain injury including subarachnoid hemorrhage, traumatic brain injury, and ischemic stroke. Also, apelin/APJ system has therapeutic effects on chronic neurodegenerative disease models, involving the regulation of neurotrophic factors, neuroendocrine, oxidative stress, neuroinflammation, neuronal apoptosis, and autophagy. In addition, through different routes of administration, apelin/APJ system has a biphasic effect on depression, epilepsy, and pain. However, apelin/APJ system exacerbates the proliferation and invasion of glioblastoma. Thus, apelin/APJ system is expected to be a therapeutic target for the treatment of nervous system diseases.

Intranasal interferon-beta alleviates anxiety and depressive-like behaviors by modulating microglia polarization in an Alzheimer's disease model

Alzheimer's disease (AD) patients frequently experience neuropsychiatric symptoms (NPS), which are linked to a lower quality of life and a faster rate of disease progression. A growing body of research indicates that several microglial phenotypes control the inflammatory response and are crucial in the pathophysiology of AD-related NPS. Given the crucial role played by inflammatory mediators produced by microglia in developing of NPS, interferon-beta (IFNβ), a cytokine with anti-inflammatory capabilities, maybe a successful treatment for NPS caused by AD. In this investigation, using a rat model of AD, we examined the impact of intranasal treatment of IFNβ on anxious/depressive-like behavior and microglial M1/M2 polarization. The rat hippocampus was bilaterally injected with lentiviruses harboring mutant human amyloid precursor protein. Rats were given recombinant IFNβ1a (68,000 IU/rat) via the intranasal route, starting on day 23 following viral infection and continuing until day 49. On days 47-49, the elevated plus maze, forced swim, and tail suspension tests were applied to measure anxiety- and depressive-like behavior. Additionally, qPCR was utilized to quantify the expression of M1 markers (CD68, CD86, and CD40) and M2 markers (Ym1, CD206, Arg1, GDNF, BDNF, and SOCS1). Our findings demonstrated that decreased M2 marker expression is accompanied by anxious/depressive-like behavior when the mutant human APP gene is overexpressed in the hippocampus. In the rat model of AD, IFNβ therapy reduces anxious/depressive-like behaviors, at least in part by polarizing microglia towards M2. Therefore, IFNβ may be a viable therapeutic drug for reducing NPS in the context of AD.

Cornel Iridoid Glycoside Alleviates Microglia-Mediated Inflammatory Response via the NLRP3/Calpain Pathway

Vascular dementia (VaD) is associated with cerebral hypoperfusion, which results in long-term cognitive impairment and memory loss. Cornel iridoid glycoside (CIG) is the major active constituent isolated from the ripe fruit of Cornus officinalis. Previous studies have shown that CIG enhances neurological function in VaD rats. In the present research, we attempted to clarify the molecular processes underlying the role of CIG in neuroinflammation in VaD. We created a chronic cerebral ischemia rat model by ligation of the bilateral common carotid arteries (2VO) and then treated rats with different concentrations of CIG. Comprehensive analyses revealed that CIG ameliorated myelin integrity and neuronal loss. Furthermore, we also found that CIG inhibited polarized microglia activation and attenuated inflammasome-mediated production of proinflammatory cytokines in BV2 microglia cells induced by LPS/IFN-γ and in the brains of 2VO rats. To further elucidate the role of CIG in microglia-mediated inflammatory response, we investigated the expression and activity of calpain. CIG inhibited the expression and activity of calpain 1/2, which was characterized by decreased calpastatin and spectrin αII expression. In particular, intra- and extracellular calpain 1 levels were reduced by CIG. However, CIG showed weak interaction with calpain 1. In addition, we found that CG administration significantly repressed the assembly of the NOD-like receptor protein 3 (NLRP3) inflammasome, including NLRP3, ASC, and caspase-1. In conclusion, our knowledge of the mechanisms by which CIG regulates NLRP3/calpain signaling to influence inflammatory responses offers further insights into potential therapeutic strategies to treat VaD.

The beneficial roles of apelin-13/APJ system in cerebral ischemia: Pathogenesis and therapeutic strategies

The incidence of cerebral ischemia has increased in the past decades, and the high fatality and disability rates seriously affect human health. Apelin is a bioactive peptide and the ligand of the G protein-coupled receptor APJ. Both are ubiquitously expressed in the peripheral and central nervous systems, and regulate various physiological and pathological process in the cardiovascular, nervous and endocrine systems. Apelin-13 is one of the subtypes of apelin, and the apelin-13/APJ signaling pathway protects against cerebral ischemia by promoting angiogenesis, inhibiting excitotoxicity and stabilizing atherosclerotic plaques. In this review, we have discussed the role of apelin-13 in the regulation of cerebral ischemia and the underlying mechanisms, along with the therapeutic potential of the apelin-13/APJ signaling pathway in cerebral ischemia.

Microglia in depression: an overview of microglia in the pathogenesis and treatment of depression

Major depressive disorder is a highly debilitating psychiatric disorder involving the dysfunction of different cell types in the brain. Microglia are the predominant resident immune cells in the brain and exhibit a critical role in depression. Recent studies have suggested that depression can be regarded as a microglial disease. Microglia regulate inflammation, synaptic plasticity, and the formation of neural networks, all of which affect depression. In this review, we highlighted the role of microglia in the pathology of depression. First, we described microglial activation in animal models and clinically depressed patients. Second, we emphasized the possible mechanisms by which microglia recognize depression-associated stress and regulate conditions. Third, we described how antidepressants (clinical medicines and natural products) affect microglial activation. Thus, this review aimed to objectively analyze the role of microglia in depression and focus on potential antidepressants. These data suggested that regulation of microglial actions might be a novel therapeutic strategy to counteract the adverse effects of devastating mental disorders.

Acupuncture Ameliorates Depressive Behaviors by Modulating the Expression of Hippocampal Iba-1 and HMGB1 in Rats Exposed to Chronic Restraint Stress

The antidepressant mechanism of acupuncture has not been fully elucidated recently. Thus, the objective of the present study is to investigate the antidepressant mechanism of acupuncture of modulating the neuroinflammation induced by high mobility group box-1 (HMGB1) in rats subjected to chronic restraint stress (CRS). Forty-four male Sprague Dawley rats were randomly divided into control, model, escitalopram, and acupuncture group. Except for rats in the control group, all rats were exposed to CRS for 21 days continuously. Rats in the escitalopram group were subjected to a suspension of escitalopram and saline. One hour before CRS procedures, acupuncture was performed at Baihui (GV20) and Yintang (GV29) for rats in the acupuncture group, 20 min per day for 21 days. All rats in each group were conducted to detect the body weight, sucrose preference test at 0, 7, 14, 21 days to evaluate the depression-like behaviors. The expression of microglial activation and HMGB1 in the hippocampus was detected by immunofluorescence. The expression of hippocampal interleukin-10 (IL-10) was detected by western blot. And the content of serum tumor necrosis factor-α (TNF-α) was detected by the enzyme-linked immunosorbent assay method. CRS-exposed rats showed obviously decreased body weight and sucrose preference when compared with the control group, which was reversed by acupuncture. The results have also shown that acupuncture ameliorated the CRS-induced activation of microglia and HMGB1 in the hippocampus CA1 region. Furthermore, acupuncture reduced the stress-induced upregulation of TNF-α in serum. Collectively, the current study highlights the role of acupuncture in alleviating depressive behavior associated with stress-induced neuroinflammation mediated by HMGB1 in the CRS model of depression.

miR‑146a reduces depressive behavior by inhibiting microglial activation

Depression is one of the major psychiatric diseases affecting the quality of life for individuals worldwide. Numerous reports have investigated depression, although its etiology remains to be elucidated. microRNA (miR)-146a is suggested to regulate innate immune and inflammatory responses. However, it is unclear whether miR-146a is involved in depression. Depression model mice were established using lipopolysaccharide-induced depression and chronic unpredictable mild stress, separately. miR-146a mimic and short interfering RNA were used to treat depressed mice. Depression-like behaviors and levels of pro-inflammatory cytokines were measured, while ionized calcium binding adapter molecule 1 (Iba-1) expression in hippocampus was quantified by immunohistochemistry. Neuroinflammatory factor levels in hippocampus were measured by western blotting. BV-2 cells were used to confirm that miR-146a suppressed microglia activation. Compared with control mice, the two depressed mouse models showed clearly decreased sucrose preference and significantly increased immobility time in the forced swimming test and tail suspension test (P<0.05). miR-146a overexpression significantly increased sucrose preference and reduced immobility time in depressed mice (P<0.05). However, total distance traveled in the locomotor activity test did not differ among groups. Compared with controls, expression levels of Iba-1, inducible nitric oxide, IL-1β, TNF-α, interleukin 1 receptor associated kinase 1 (IRAK1), TNF receptor-associated factor 6 (TRAF6) and phosphorylated NF-κB p65 were significantly increased in depressed mice (P<0.05). miR-146a overexpression effectively inhibited expression of these neuroinflammatory proteins, while miR-146a silencing significantly upregulated their expression (P<0.05). Consistent with these in vivo results, miR-146a mimic treatment inhibited TNF-α, IL-1β, IRAK1 and TRAF6 expression in BV-2 cells. miR-146a improved depressive behaviors in depressed model mice by inhibiting microglial activation and neuroinflammatory factor expression.

The role of microglia in chronic pain and depression: innocent bystander or culprit?

Clinical evidence shows that chronic pain and depression often accompany each other, but the underlying pathogenesis of comorbid chronic pain and depression remains mostly undetermined. Biotechnology is gradually revealing the phenotype and function of microglia, with great progress regarding microglia's role in neurodegeneration, depression, chronic pain, and other conditions. This article summarizes the role of microglia in chronic pain, depression, and comorbidities, which is conducive to finding new targets to treat chronic pain and depression.

Neuroendocrine, neuroinflammatory and pathological outcomes of chronic stress: A story of microglial remodeling

Microglia, the resident macrophage cells of the central nervous system (CNS), are involved in a myriad of processes required to maintain CNS homeostasis. These cells are dynamic and can adapt their phenotype and functions to the physiological needs of the organism. Microglia rapidly respond to changes occurring in their microenvironment, such as the ones taking place during stress. While stress can be beneficial for the organism to adapt to a situation, it can become highly detrimental when it turns chronic. Microglial response to prolonged stress may lead to an alteration of their beneficial physiological functions, becoming either maladaptive or pro-inflammatory. In this review, we aim to summarize the effects of chronic stress exerted on microglia through the neuroendocrine system and inflammation at adulthood. We also discuss how these effects of chronic stress could contribute to microglial involvement in neuropsychiatric and sleep disorders, as well as neurodegenerative diseases.

Apelin-13 Protects Dopaminergic Neurons against Rotenone-Induced Neurotoxicity through the AMPK/mTOR/ULK-1 Mediated Autophagy Activation

Parkinson’s disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Several brain–gut peptides are able to exert neuroprotective effects on the nigrostriatal dopaminergic system. Apelin-13 is a neuropeptide, conveying potential neuroprotective activities. However, whether, and how, apelin-13 could antagonize rotenone-induced neurotoxicity has not yet been elucidated. In the present study, rotenone-treated SH-SY5Y cells and rats were used to clarify whether apelin-13 has protective effects on dopaminergic neurons, both in vivo and in vitro. The results showed that apelin-13 could protect SH-SY5Y cells from rotenone-induced injury and apoptosis. Apelin-13 was able to activate autophagy, and restore rotenone induced autophagy impairment in SH-SY5Y cells, which could be blocked by the autophagy inhibitor 3-Methyladenine. Apelin-13 activated AMPK/mTOR/ULK-1 signaling, AMPKα inhibitor compound C, as well as apelin receptor blockage via siRNA, which could block apelin-13-induced signaling activation, autophagy activation, and protective effects, in rotenone-treated SH-SY5Y cells. These results indicated that apelin-13 exerted neuroprotective properties against rotenone by stimulating AMPK/mTOR/ULK-1 signaling-mediated autophagy via the apelin receptor. We also observed that intracerebroventricular injection of apelin-13 could alleviate nigrostriatal dopaminergic neuron degeneration in rotenone-treated rats. Our findings provide new insights into the mechanism by which apelin-13 might attenuate neurotoxicity in PD.

Metabolomics Deciphers Potential Targets of Xuefu Zhuyu Decoction Against Traumatic Brain Injury in Rat

Xuefu Zhuyu decoction (XFZYD) performs multiple functions for traumatic brain injury (TBI) treatment. However, its clinical application is limited by the incomplete exploration of targets and inadequate discussion of mechanisms. We aimed to investigate the metabolic alterations of XFZYD in acute and chronic stages of TBI. Sprague-Dawley rats were randomly divided into the sham, controlled cortical impact (CCI) and XFZYD group. Behavioral and histopathological tests were used to evaluate the neuroprotective effects. Coagulation assays were performed to assess safety. Moreover, we analyzed the metabolomic profiling of hippocampal samples with different time intervals after CCI by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Differential metabolites were screened by multivariate data analysis. To further uncover the association between candidate metabolites and biological interaction networks, we applied bioinformatics analysis using MetaboAnalyst 4.0, STITCH 5.0 and TCMSP. The potential mechanism was verified by ELISA and Western blot. XFZYD ameliorated neurological deficiencies post-CCI without impairing blood coagulation in the rat’s model. Seventeen and fourteen metabolites were filtered on d 3 and 21, respectively. Eleven of potential metabolites were common at these time points, involving two significant pathways (arginine and proline metabolism, phenylalanine, tyrosine and tryptophan biosynthesis). Gamma-aminobutyric acid (GABA) and the related pathways were specifically affected by XFZYD at the acute phase of TBI, while biosynthesis of amino acids was the major pathway influenced at the chronic phase. This study provides broad insights into the therapeutic effects of XFZYD in treating TBI through the whole phases.