Inflammasome activation under high cholesterol load triggers a protective microglial phenotype while promoting neuronal pyroptosis

Microglia and TREM2

TREM2 is a membrane receptor solely expressed on microglia in normal brain. In this review we outline recent advances in TREM2 biology and its implications for microglial function, with particular emphasis on findings from iPSC-derived microglia (iMG) expressing TREM2 loss-of-function mutations. Alterations in receptor proximal and distal signalling underlie TREM2 risk variants linked to neurodegenerative disease, principally NH-linked FTD, and late-onset AD, but emerging data suggest roles for TREM2 in PD, MS and ALS. TREM2 downstream functions include phagocytosis of myelin debris, amyloid beta peptides, and phosphatidylserine-expressing cells (resulting from damage or stress). Microglial survival, migration, DAMP signalling, inflammasome activation, and intercellular signalling including tau spreading via exosomes, as well as roles for sTREM2 in protection and as a biomarker are discussed. The role of TREM2 in metabolic homeostasis, and immunometabolic switching are discussed regarding microglial responses to damage and protection. The use of iPSC models to investigate the role of TREM2 in AD, PD, MS, ALS, and other neurodegenerative diseases could prove invaluable due to their ability to recapitulate human pathology, allowing a full understanding of TREM2 and microglial involvement in the underlying disease mechanisms and progression. This article is part of the Special Issue on "Microglia".

The critical role of P2XR/PGC-1α signalling pathway in hypoxia-mediated pyroptosis and M1/M2 phenotypic differentiation of mouse microglia

Microglia are endogenous immune cells in the brain, and their pyroptosis and phenotype dichotomy are proved to play roles in neurodegenerative diseases. We investigated whether and how hypoxia affected pyroptosis and phenotype polarization in mouse microglia. Primary mouse microglia and BV2 microglia were exposed to hypoxia. Pyroptosis and M1/M2 phenotype were assessed by measuring gasdermin D truncation and M1/M2 surface marker expression. Mechanisms including purinergic ionotropic receptor (P2XR), peroxisome proliferator-activated receptor coactivator-1α (PGC-1α) and NOD-like receptor protein 3 (NLRP3) inflammasome were investigated. We reported hypoxia (90% N2, 5% O2 and 5% CO2) induced pyroptosis and promoted M1 phenotype polarization in primary mouse microglia and BV2 microglia, and the effect appeared after 6 h exposure. Although hypoxia (90% N2, 5% O2 and 5% CO2, 6 h) had no effect on P2X1R and P2X7R expression, it increased P2X4R expression and decreased PGC-1α expression. Interestingly, blockade of P2X4R or P2X7R abolished hypoxia-modulated PGC-1α expression, pyroptosis and M1 polarization. PGC-1α overexpression or overactivation alleviated hypoxia-induced pyroptosis and M1 polarization, while PGC-1α knockdown or deactivation promoted pyroptosis and M1 polarization under normoxic situation. Further, hypoxia induced NLRP3 expression and activated caspase-1 and induced the phosphorylation of NF-κB and reduced the phosphorylation of STAT3/6. NLRP3 inhibitor and caspase-1 inhibitor abolished hypoxia-induced pyroptosis, while NF-κB inhibitor and STAT phosphorylation inducer ameliorated hypoxia-induced M1 polarization. In addition, NF-κB activator and STAT3/6 inhibitor caused microglia M1 polarization under normoxic situation. We concluded in cultured mouse microglia, hypoxia may induce pyroptosis via P2XR/PGC-1α/NLRP3/caspase-1 pathway and trigger M1 polarization through P2XR/PGC-1α/NF-κB/STAT3/6 pathway.

Targeting dysregulated lipid metabolism for the treatment of Alzheimer's disease and Parkinson's disease: Current advancements and future prospects

Alzheimer's and Parkinson's diseases are two of the most frequent neurological diseases. The clinical features of AD are memory decline and cognitive dysfunction, while PD mainly manifests as motor dysfunction such as limb tremors, muscle rigidity abnormalities, and slow gait. Abnormalities in cholesterol, sphingolipid, and glycerophospholipid metabolism have been demonstrated to directly exacerbate the progression of AD by stimulating Aβ deposition and tau protein tangles. Indirectly, abnormal lipids can increase the burden on brain vasculature, induce insulin resistance, and affect the structure of neuronal cell membranes. Abnormal lipid metabolism leads to PD through inducing accumulation of α-syn, dysfunction of mitochondria and endoplasmic reticulum, and ferroptosis. Great progress has been made in targeting lipid metabolism abnormalities for the treatment of AD and PD in recent years, like metformin, insulin, peroxisome proliferator-activated receptors (PPARs) agonists, and monoclonal antibodies targeting apolipoprotein E (ApoE). This review comprehensively summarizes the involvement of dysregulated lipid metabolism in the pathogenesis of AD and PD, the application of Lipid Monitoring, and emerging lipid regulatory drug targets. A better understanding of the lipidological bases of AD and PD may pave the way for developing effective prevention and treatment methods for neurodegenerative disorders.

Chinese medicinal formula Fu Xin decoction against chronic heart failure by inhibiting the NLRP3/caspase-1/GSDMD pyroptotic pathway

BACKGROUND

Various heart diseases ultimately lead to chronic heart failure (CHF). In CHF, the inflammatory response is associated with pyroptosis, which is mediated by the NOD-like receptor protein 3 (NLRP3) inflammasome. Fu Xin decoction (FXD) is commonly used in clinical practice to treat CHF and improve inflammatory conditions. However, the specific pharmacological mechanisms of action for FXD in these processes have yet to be fully understood.

PURPOSE

The objective of this study was to examine the protective mechanism of FXT against CHF, both in H9c2 cells and mice.

METHOD

A CHF mouse model was established, and the effect of FXD was observed via gavage. Cardiac function was evaluated using echocardiography, while serum BNP and LDH levels were analyzed to assess the severity of CHF. Hematoxylin and eosin staining (H&E) and Masson staining were performed to evaluate myocardial pathological changes, and TdT-mediated dUTP Nick-End Labeling staining was used to detect DNA damage. Additionally, doxorubicin was utilized to induce myocardial cell injury in H9c2 cells, establishing a relevant model. CCK8 was used to observe cell viability and detect LDH levels in the cell supernatant. Subsequently, the expression of pyroptosis-related proteins was detected using immunohistochemistry, immunofluorescence, and western blotting. Finally, the pharmacological mechanism of FXD against CHF was further validated by treating H9c2 cells with an NLRP3 activator and inducing NLRP3 overexpression.

RESULT

According to current research findings, echocardiography demonstrated a significant improvement of cardiac function by FXD, accompanied by reduced levels of BNP and LDH, indicating the amelioration of cardiac injury in CHF mice. FXD exhibited the ability to diminish serum CRP and MCP inflammatory markers in CHF mice. The results of HE and Masson staining analyses revealed a significant reduction in pathological damage of the heart tissue following FXD treatment. The CCK8 assay demonstrated the ability of FXD to enhance H9c2 cell viability, improve cell morphology, decrease LDH levels in the cell supernatant, and alleviate cell damage. Immunohistochemistry, Western blotting, and immunofluorescence staining substantiated the inhibitory effect of FXD on the NLRP3/caspase-1/GSDMD pyroptosis signaling pathway in both CHF and H9c2 cell injury models. Ultimately, the administration of the NLRP3 activator (Nigericin) and the overexpression of NLRP3 counteract the effects of FXD on cardiac protection and pyroptosis inhibition in vitro.

CONCLUSION

FXD exhibits a cardioprotective effect, improving CHF and alleviating pyroptosis by inhibiting the NLRP3/caspase-1/GSDMD pathway.

Erjingwan and Alzheimer's disease: research based on network pharmacology and experimental confirmation

Background

Alzheimer's disease (AD), a challenging neurodegenerative condition, has emerged as a significant global public health concern. The Chinese medicine decoction Erjingwan (EJW) has shown promising efficacy in AD treatment, though its mechanism remains unclear.

Objective

This study aims to elucidate the mechanism by which EJW treats AD through network pharmacology analysis and in vivo experiments.

Methods

We identified EJW's components using the Traditional Chinese Medicine Systems Pharmacology (TCMSP) database and determined AD-related targets from various databases. A network comprising herbs-compounds-targets was established, and EJW's core targets were ascertained through protein-protein interaction (PPI) analysis. This study assessed the cognitive abilities of APP/PS1 mice using Morris water mazes and Y mazes, in addition to analyzing blood samples for triglyceride (TG), total cholesterol (TC), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) levels. Brain tissues were examined histologically with HE staining, Nissl staining, and immunohistochemistry (IHC) for amyloid β-protein (Aβ) detection. Superoxide dismutase (SOD), reactive oxygen species (ROS), Interleukin-1β (IL-1β), and Interleukin-6 (IL-6) levels in the hippocampal region were measured by ELISA. mRNA expression of apolipoprotein A-I (APOA-I), apolipoprotein B (APOB), apolipoprotein E4 (APOE4), advanced glycation end products (AGE), the receptor for AGE (RAGE), and nuclear factor kappa-B (NF-κB) was evaluated by quantitative PCR (q-PCR). Western blotting was used to detect the expression of AGE, RAGE, NF-κB, and Tau protein.

Results

Screening identified 57 chemical components and 222 potential targets of EJW. Ten core targets for AD treatment were identified, with enrichment analysis suggesting EJW's effects are related to lipid metabolism and AGEs/RAGE pathways. EJW enhanced learning and memory in APP/PS1 mice, protected neuronal structure in the hippocampal region, reduced Aβ deposition, and altered levels of TG, TC, LDL, IL-1β, and IL-6, and the expression of APOE4, AGEs, RAGE, NF-κB, and Tau protein, while increasing SOD, APOA-I, and APOB mRNA expression.

Conclusion

The study identified four core components of EJW-iosgenin, baicalein, beta-sitosterol, quercetin-and ten core targets including AKT1, IL6, VEGFA, TP53, CASP3, for treating AD. Experimental results demonstrate EJW's capacity to modulate lipid profiles, reduce pathological markers such as Aβ1-42, Tau, IL-6, IL-1β, reactive oxygen species, SOD, and enhance cognitive functions in APP/PS1 mice, potentially through inhibiting the AGEs/RAGE/NF-κB pathway.

Focusing on mitochondria in the brain: from biology to therapeutics

Mitochondria have multiple functions such as supplying energy, regulating the redox status, and producing proteins encoded by an independent genome. They are closely related to the physiology and pathology of many organs and tissues, among which the brain is particularly prominent. The brain demands 20% of the resting metabolic rate and holds highly active mitochondrial activities. Considerable research shows that mitochondria are closely related to brain function, while mitochondrial defects induce or exacerbate pathology in the brain. In this review, we provide comprehensive research advances of mitochondrial biology involved in brain functions, as well as the mitochondria-dependent cellular events in brain physiology and pathology. Furthermore, various perspectives are explored to better identify the mitochondrial roles in neurological diseases and the neurophenotypes of mitochondrial diseases. Finally, mitochondrial therapies are discussed. Mitochondrial-targeting therapeutics are showing great potentials in the treatment of brain diseases.

Cholestane-3β,5α,6β-triol Induces Multiple Cell Death in A549 Cells via ER Stress and Autophagy Activation

Cholestane-3β,5α,6β-triol (CT) and its analogues are abundant in natural sources and are reported to demonstrate cytotoxicity toward different kinds of tumor cells without a deep probe into their mechanism of action. CT is also one of the major metabolic oxysterols of cholesterol in mammals and is found to accumulate in various diseases. An extensive exploration of the biological roles of CT over the past few decades has established its identity as an apoptosis inducer. In this study, the effects of CT on A549 cell death were investigated through cell viability assays. RNA-sequencing analysis and western blot of CT-treated A549 cells revealed the role of CT in inducing endoplasmic reticulum (ER) stress response and enhancing autophagy flux, suggesting a putative mechanism of CT-induced cell-death activation involving reactive oxygen species (ROS)-mediated ER stress and autophagy. It is reported for the first time that the upregulation of autophagy induced by CT can serve as a cellular cytotoxicity response in accelerating CT-induced cell death in A549 cells. This research provides evidence for the effect of CT as an oxysterol in cell response to oxidative damage and allows for a deep understanding of cholesterol in its response in an oxidative stress environment that commonly occurs in the progression of various diseases.

Macrophage pyroptosis induced by Candida albicans

Candida albicans (C. albicans) is a prevalent opportunistic pathogen that causes mucocutaneous and systemic infections, particularly in immunocompromised individuals. Macrophages play a crucial role in eliminating C. albicans in local and bloodstream contexts, while also regulating antifungal immune responses. However, C. albicans can induce macrophage lysis through pyroptosis, a type of regulated cell death. This process can enable C. albicans to escape from immune cells and trigger the release of IL-1β and IL-18, which can impact both the host and the pathogen. Nevertheless, the mechanisms by which C. albicans triggers pyroptosis in macrophages and the key factors involved in this process remain unclear. In this review, we will explore various factors that may influence or trigger pyroptosis in macrophages induced by C. albicans, such as hypha, ergosterol, cell wall remodeling, and other virulence factors. We will also examine the possible immune response following macrophage pyroptosis.

Astaxanthin Inhibits H2O2-Induced Excessive Mitophagy and Apoptosis in SH-SY5Y Cells by Regulation of Akt/mTOR Activation

Oxidative stress, which damages cellular components and causes mitochondrial dysfunction, occurs in a variety of human diseases, including neurological disorders. The clearance of damaged mitochondria via mitophagy maintains the normal function of mitochondria and facilitates cell survival. Astaxanthin is an antioxidant known to have neuroprotective effects, but the underlying mechanisms remain unclear. This study demonstrated that astaxanthin inhibited H2O2-induced apoptosis in SH-SY5Y cells by ameliorating mitochondrial damage and enhancing cell survival. H2O2 treatment significantly reduced the levels of activated Akt and mTOR and induced mitophagy, while pretreatment with astaxanthin prevented H2O2-induced inhibition of Akt and mTOR and attenuated H2O2-induced mitophagy. Moreover, the inhibition of Akt attenuated the protective effect of astaxanthin against H2O2-induced cytotoxicity. Taken together, astaxanthin might inhibit H2O2-induced apoptosis by protecting mitochondrial function and reducing mitophagy. The results also indicate that the Akt/mTOR signaling pathway was critical for the protection of astaxanthin against H2O2-induced cytotoxicity. The results from the present study suggest that astaxanthin can reduce neuronal oxidative injury and may have the potential to be used for preventing neurotoxicity associated with neurodegenerative diseases.

The high-expression programming of SR-B1 mediates adrenal dysfunction in female offspring induced by prenatal caffeine exposure and its cholesterol accumulation mechanism

The cholesterol metabolism and homeostasis of adrenal are important for steroidogenesis. Our previous studies found that prenatal caffeine exposure (PCE) can inhibit adrenal steroidogenesis in offspring, but whether the mechanism is related to local imbalance of cholesterol metabolism remains unknown. Here, we found that PCE inhibited adrenal steroidogenesis and increased the expression of cell pyroptosis and inflammatory-related indicators (NLRP3, caspase-1 and IL-1β) in female adult offspring rats, and at the same time, the cholesterol levels in serum and adrenal gland also significantly increased. In vitro, the high level of cholesterol could inhibit adrenal corticosteroid synthesis through pyroptosis and an inflammatory response. It suggested that the low adrenal steroidogenesis in PCE female adult offspring is related to local cholesterol accumulation-mediated pyroptosis and inflammation. Furthermore, dating back to the intrauterine period, PCE increased the serum CORT level in female fetal rats, and increased the expression of the adrenal cholesterol intake gene SR-B1, which persisted after birth and even into adulthood. At the cellular level, silencing SR-B1 could reverse the increase of intracellular cholesterol content caused by high levels of cortisol in NCI-H295R cells. Finally, we confirmed that high concentrations of glucocorticoids increased the expression and H3K14ac level of the promoter region in SR-B1 by upregulating the GR/SREBP1/p300 pathway in vivo and in vitro. In conclusion, we clarified that the high-expression programming of SR-B1 mediates adrenal dysfunction in PCE female offspring and its cholesterol accumulation mechanism, which provided a favorable basis for finding novel targets to prevent and treat fetal-originated diseases.

Hypertension linked to Alzheimer's disease via stroke: Mendelian randomization

This study aimed to investigate the relationship between hypertension and Alzheimer's disease (AD) and demonstrate the key role of stroke in this relationship using mediating Mendelian randomization. AD, a neurodegenerative disease characterized by memory loss, cognitive impairment, and behavioral abnormalities, severely affects the quality of life of patients. Hypertension is an important risk factor for AD. However, the precise mechanism underlying this relationship is unclear. To investigate the relationship between hypertension and AD, we used a mediated Mendelian randomization method and screened for mediating variables between hypertension and AD by setting instrumental variables. The results of the mediated analysis showed that stroke, as a mediating variable, plays an important role in the causal relationship between hypertension and AD. Specifically, the mediated indirect effect value for stroke obtained using multivariate mediated MR analysis was 54.9%. This implies that approximately 55% of the risk of AD owing to hypertension can be attributed to stroke. The results suggest that the increased risk of AD owing to hypertension is mediated through stroke. The finding not only sheds light on the relationship between hypertension and AD but also indicates novel methods for the prevention and treatment of AD. By identifying the critical role of stroke in the link between hypertension and AD, this study provides insights into potential interventions that could mitigate the impact of hypertension on AD. This could help develop personalized treatments and help improve the quality of life of patients with AD who suffer from hypertension.

Role of trigger receptor 2 expressed on myeloid cells in neuroinflammation－neglected multidimensional regulation of microglia

Neuroinflammation is an inflammatory cascade involved in various neurological disorders, including Alzheimer's disease, multiple sclerosis, and other relevant diseases. The triggering receptor expressed on myeloid cells 2 (TREM2) is a transmembrane immune receptor that is primarily expressed by microglia in the central nervous system (CNS). While TREM2 is initially believed to be an anti-inflammatory factor in the CNS, increasing evidence suggests that TREM2 plays a more complex role in balancing neuroinflammation. However, the exact mechanism remains unclear. Notably, TREM2 directly regulates microglia inflammation through various signaling pathways. Additionally, studies have suggested that TREM2 mediates microglial phagocytosis, autophagy, metabolism, and microglia phenotypes, which may be involved in the modulation of neuroinflammation. In this review, we aim to discuss the critical role of TREM2 in several microglia functions and the underlying molecular mechanism the modulatory which further mediate neuroinflammation, and elaborate. Finally, we discuss the potential of TREM2 as a therapeutic target in neuroinflammatory disorders.

The role of melatonin in amyloid beta-induced inflammation mediated by inflammasome signaling in neuronal cell lines

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder. In addition to amyloid beta (Aβ) and tau, neuroinflammation is a crucial element in the etiology of this disease. However, the relevance of inflammasome-induced pyroptosis to AD is unknown. We aimed to clarify whether the anti-inflammatory effects of melatonin could prevent Aβ-mediated activation of the inflammasome. We demonstrated that Aβ upregulated NOD-like receptor family pyrin domain-containing 3 (NLRP3), apoptosis-associated speck-like protein containing a CARD, and cysteinyl aspartate-specific proteinase caspase (caspase 1) expression in SH-SY5Y neuroblastoma cells, resulting in the release of proinflammatory cytokines, including interleukin-1β (IL-1β), interleukin-18 (IL-18) and tumor necrosis factor (TNF-α). Melatonin prevented inflammasome signaling and excessive cytokine release caused by Aβ. We found that ethyl 2[(2-chlorophenyl)(hydroxy) methyl]acrylate (INF-4E, NLRP3 and caspase 1 inhibitor) significantly abolished Aβ-induced proinflammatory cytokine expression. The increase in cleaved-caspase 1, pro-IL18, and cleaved-IL18 caused by Aβ suggested the occurrence of pyroptosis, which was further confirmed by the increased expression of N-terminal gasdermin D (N-GSDMD). Melatonin plays a protective role against Aβ-induced inflammation via an inflammasome-associated mechanism that is essential in inducing the active forms of cytokines and pyroptosis. The ability of melatonin to inhibit inflammasome may represent a turning point in the treatment of AD progression.