NLRP3 inflammatory pathway. Can we unlock depression?

Tabersonine ameliorates depressive-like behavior by inhibiting NLRP3 inflammasome activation in a mouse model

Depression, a common mental disorder, is intimately linked to neuroinflammation. In the central nervous system, microglia, the principal cells involved in immunity, are crucial in neuroinflammation and closely associated with the pathogenesis of depression. Several studies have demonstrated that depressive-like behaviors could be ameliorated by improving brain inflammation. Notably, natural products occupy a critical position in the study of antidepressants. Herein, we explored the antidepressant effects of tabersonine (Tab), a natural inhibitor of NLRP3. Tab significantly improved depressive-like behaviors and anxiety in lipopolysaccharide (LPS)-treated mice. To further elucidate mechanisms underlying the antidepressant actions of Tab, BV2 microglial cells were exposed to LPS and ATP in vitro. Tab effectively inhibited NLRP3 inflammasome activation, subsequent Caspase-1 cleavage, and interleukin-1β secretion both in the hippocampi of mice in vivo and BV2 cells in vitro. Additionally, Tab strongly decreased the concentrations of the proinflammatory cytokines interleukin-1β, tumor necrosis factor, and interleukin-6 in BV2 cell culture supernatants and sera of mice. Further studies indicated that Tab improved LPS-induced neuronal loss, as indicated by a significant rise in the quantity of Nissl-positive cells within the hippocampal regions CA1, CA3, and dentate gyrus. Importantly, Tab counteracted the LPS-induced microglial activation in the hippocampus. Our results indicate that Tab significantly improves LPS-triggered depressive-like behaviors and reverses injuries to hippocampal microglia and neurons, implying its potential as a therapeutic agent for depression.

Mangiferin: A natural neuroprotective polyphenol with anti-inflammatory and anti-oxidant properties for depression

Depression is a severe global health problem accompanied by persistent low mood that harms the physical and mental health of people and places a substantial economic burden on society. Mangiferin (MGF), a natural polyphenol in the traditional Chinese herb Anemarrhena asphodeloides Bge., can improve neuronal damage, memory, and cognitive deficits, implicating the therapeutic potential of MGF for depression. MGF has a unique C-glycosyl and phenolic structure that endows it with multiple biological properties, e.g., anti-oxidant, anti-inflammatory, and anti-mitochondrial dysfunction. However, the pharmacological role of MGF in depression remains unclear. Therefore, this review describes the neuroprotective effects and the antidepressant mechanisms of MGF in preclinical depression studies. MGF ameliorates cognitive deficits in depression and neurodegenerative diseases animal models by reducing amyloid-beta deposition, ameliorating cholinergic dysfunction, and increasing neurotrophic factors. Also, MGF regulates molecular mechanisms in depressed animals mainly through anti-inflammation (by inhibiting NLRP3 inflammasome activation, mitogen-activated protein kinase phosphorylation and its downstream nuclear factor-кB signaling pathway, and indoleamine 2,3-dioxygenase activity), anti-oxidant (by increasing levels of anti-oxidant enzymes and inhibiting lipid peroxidation). Notably, the potential mechanisms of MGF in treating depression by modulating neurotransmission (e.g., glutamate, dopamine, norepinephrine, and serotonin) need to be further explored. It is hoped to explore further the potential molecular mechanisms of MGF's biological activity in depression and provide directions for further clinical applications.

Ginsenoside Re Inhibits NLRP3 Inflammasome Activation in Depressive Mice by Promoting PINK1-Mediated Mitophagy

Ginsenoside Re (Re) was proved effective in improving depressive-like behaviors. However, the potential antidepressant mechanism of Re remains unrevealed. In this study, we investigated whether PINK1-mediated mitophagy and NLRP3 inflammasomes were linked to the antidepressant mechanism of Re in chronic unpredictable mild stress (CUMS) mice and lipopolysaccharide (LPS)-stimulated astrocytes. RNA sequencing and bioinformatics analyses were performed to discover the targets and pathways associated with Re. PTEN-induced putative kinase 1 (PINK1) knockdown was conducted to clarify the role of PINK1-mediated mitophagy in the antidepressant mechanism of Re. The outcomes showed that Re ameliorated depressive-like behaviors, activated PINK1-mediated mitophagy, and inhibited NLRP3 inflammasome activation. PINK1 knockdown attenuated the antidepressant effect of Re. The promotion of mitophagy and the decline of NLRP3 inflammasome activation caused by Re were reversed by PINK1 knockdown. In conclusion, Re inhibited NLRP3 inflammasome activation by promoting PINK1-mediated mitophagy to exert its antidepressant effect.

Immunity in neuromodulation: probing neural and immune pathways in brain disorders

Immunity finely regulates brain function. It is directly involved in the pathological processes of neurodegenerative diseases such as Parkinson's and Alzheimer's disease, post-stroke conditions, multiple sclerosis, traumatic brain injury, and psychiatric disorders (mood disorders, major depressive disorder (MDD), anxiety disorders, psychosis disorders and schizophrenia, and neurodevelopmental disorders (NDD)). Neuromodulation is currently a leading therapeutic strategy for the treatment of these disorders, but little is yet known about its immune impact on neuronal function and its precise beneficial or harmful consequences. We review relevant clinical and preclinical studies and identify several specific immune modifications. These data not only provide insights into how neuromodulation acts to optimize immune-brain interactions, but also pave the way for a better understanding of these interactions in pathological processes.

Downregulation of the HCN1 Channel Alleviates Anxiety- and Depression-Like Behaviors in Mice With Cerebral Ischemia-Reperfusion Injury by Suppressing the NLRP3 Inflammasome

BACKGROUND

Post-stroke depression (PSD) is a prevalent neuropsychiatric complication of stroke. However, the mechanisms underlying PSD are still unclear. Here, we aimed to investigate the role of HCN1 (hyperpolarization-activated cyclic nucleotide-gated cation channel 1) in the pathogenesis of PSD and its underlying mechanisms.

METHODS

The PSD mice model was established by middle cerebral artery occlusion in vivo. Four weeks after middle cerebral artery occlusion, anxiety- and depression-like behaviors of mice were evaluated by various behavioral tests. HCN channels were downregulated by pharmacological inhibitor or neuron-specific adeno-associated virus. The oxygen-glucose deprivation/reoxygenation model in SY5Y cells was used to study the pathogenesis of PSD in vitro.

RESULTS

Mice exhibited anxiety- and depression-like behavior 4 weeks after middle cerebral artery occlusion, along with a significant increase in HCN1 protein expression in the ischemic hippocampus. Furthermore, the Ih current on neurons in the hippocampus was notably enhanced, whereas neuronal excitability was decreased in PSD mice. Treatment with HCN channel selective inhibitor ZD7288 protected SY5Y cells against oxygen-glucose deprivation/reoxygenation injury by suppressing K+ efflux. Additionally, we observed a significant increase in protein expressions of NLRP3 (nucleotide-binding domain-like receptor protein 3) inflammasome pathway-related molecules in the ischemic hippocampus of PSD mice. Knockdown of HCN1 channels via virus injection into the hippocampus resulted in decreased protein expressions of NLRP3 inflammasome-related molecules and improvement in anxiety- and depression-like behaviors in PSD mice.

CONCLUSIONS

Downregulation of HCN1 channels has a beneficial effect on PSD by suppressing the NLRP3 inflammasome pathway, thus offering promise as a strategy for preventing and treating PSD.

Activation of the COX-2/mPGES-1/PGE-2 cascade through the NLRP3 inflammasome contributes to Angiostrongylus cantonensis-induced eosinophilic meningoencephalitis

Prostaglandin E2 (PGE-2) is synthesised by cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase 1 (mPGES-1). PGE-2 exhibits pro-inflammatory properties in inflammatory conditions. However, there remains limited understanding of the COX-2/mPGES-1/PGE-2 pathway in Angiostrongylus cantonensis-induced meningoencephalitis. This study revealed several key findings regarding the activation of the COX-2/mPGES-1/PGE-2 pathway and its correlation with eosinophilic meningoencephalitis induced by A. cantonensis infection. Immunostaining revealed an increase in the expression of COX-2 and mPGES-1 in the subarachnoid space and glial cells compared to control subjects. Inhibition of the NLRP3 inflammasome by small interfering RNA (siRNA) blocked extracellular secretory proteins (ESPs) stimulated COX-2, mPGES-1 and PGE-2 in microglia. MCC950, an NLRP3 inhibitor, inhibited the levels of the COX-2, mPGES-1, and PGE-2 proteins induced by A. cantonensis in mice. Treatment of mice infected with A. cantonensis with the COX-2 inhibitor NS398 significantly reduced the levels of mPGES-1, PGE-2, and matrix metalloproteinase-9 (MMP-9) levels. Similarly, the mPGES-1 inhibitor MF63 significantly reduced PGE-2 and MMP-9 levels in A. cantonensis-infected mice. Administration of MCC950, NS398, or MF63 resulted in marked attenuation of blood-brain barrier (BBB) permeability and eosinophil counts in A. cantonensis-infected mice. These findings highlight the critical role of the COX-2/mPGES-1/PGE-2 pathway and its regulation by the NLRP3 inflammasome in the pathogenesis of eosinophilic meningoencephalitis induced by A. cantonensis infection. Furthermore, pharmacological interventions targeting this pathway, such as MCC950, NS398, and MF63, show promising therapeutic potential in mitigating associated inflammatory responses and disruption of the BBB. The results indicate that blocking NLRP3 using pharmacological (MCC950) and gene silencing (siNLRP3) methods emphasised the crucial involvement of NLRP3 in the COX-2/mPGES-1/PGE-2 pathway. This suggests that the activation of the COX-2/mPGES-1/PGE-2 axis in response to A. cantonensis infection may be mediated through a mechanism involving the NLRP3 inflammasome.

Exploring the potential of drug repurposing for treating depression

Researchers are interested in drug repurposing or drug repositioning of existing pharmaceuticals because of rising costs and slower rates of new medication development. Other investigations that authorized these treatments used data from experimental research and off-label drug use. More research into the causes of depression could lead to more effective pharmaceutical repurposing efforts. In addition to the loss of neurotransmitters like serotonin and adrenaline, inflammation, inadequate blood flow, and neurotoxins are now thought to be plausible mechanisms. Because of these other mechanisms, repurposing drugs has resulted for treatment-resistant depression. This chapter focuses on therapeutic alternatives and their effectiveness in drug repositioning. Atypical antipsychotics, central nervous system stimulants, and neurotransmitter antagonists have investigated for possible repurposing. Nonetheless, extensive research is required to ensure their formulation, effectiveness, and regulatory compliance.

Targeting inflammasome complexes as a novel therapeutic strategy for mood disorders

INTRODUCTION

Inflammasome complexes, especially NLRP3, have gained great attention as a potential therapeutic target in mood disorders. NLRP3 triggers a caspase 1-dependent release of the inflammatory cytokines IL-1β and IL-18, and seems to interact with purinergic and kynurenine pathways, all of which are implicated in mood disorders development and progression.

AREAS COVERED

Emerging evidence supports NLRP3 inflammasome as a promising pharmacological target for mood disorders. We discussed the available evidence from animal models and human studies and provided a reflection on drawbacks and perspectives for this novel target.

EXPERT OPINION

Several studies have supported the involvement of NLRP3 inflammasome in MDD. However, most of the evidence comes from animal models. The role of NLRP3 inflammasome in BD as well as its anti-manic properties is not very clear and requires further exploration. There is evidence of anti-manic effects of P2×R7 antagonists associated with reduction in the brain levels of IL-1β and TNF-α in a murine model of mania. The involvement of other NLRP3 inflammasome expressing cells besides microglia, like astrocytes, and of other inflammasome complexes in mood disorders also deserves further investigation. Preclinical and clinical characterization of NLRP3 and other inflammasomes in mood disorders is needed before considering translational approaches, including clinical trials.

Increasing CB2 Receptor Activity after Early Life Stress Prevents Depressive Behavior in Female Rats

Early adversity, the loss of the inhibitory GABAergic interneuron parvalbumin, and elevated neuroinflammation are associated with depression. Individuals with a maltreatment history initiate medicinal cannabis use earlier in life than non-maltreated individuals, suggesting self-medication. Female rats underwent maternal separation (MS) between 2 and 20 days of age to model early adversity or served as colony controls. The prelimbic cortex and behavior were examined to determine whether MS alters the cannabinoid receptor 2 (CB2), which has anti-inflammatory properties. A reduction in the CB2-associated regulatory enzyme MARCH7 leading to increased NLRP3 was observed with Western immunoblots in MS females. Immunohistochemistry with stereology quantified numbers of parvalbumin-immunoreactive cells and CB2 at 25, 40, and 100 days of age, revealing that the CB2 receptor associated with PV neurons initially increases at P25 and subsequently decreases by P40 in MS animals, with no change in controls. Confocal and triple-label microscopy suggest colocalization of these CB2 receptors to microglia wrapped around the parvalbumin neuron. Depressive-like behavior in MS animals was elevated at P40 and reduced with the CB2 agonist HU-308 or a CB2-overexpressing lentivirus microinjected into the prelimbic cortex. These results suggest that increasing CB2 expression by P40 in the prelimbic cortex prevents depressive behavior in MS female rats.