Lipid regulation of NLRP3 inflammasome activity through organelle stress

NLRP3 inflammasome signalling in Alzheimer's disease

Every year, 10 million people develop dementia, the most common of which is Alzheimer's disease (AD). To date, there is no way to prevent cognitive decline and therapies are limited. This review provides a neuroimmunological perspective on the progression of AD, and discusses the immune-targeted therapies that are in preclinical and clinical trials that may impact the development of this disease. Specifically, we look to the role of the NLRP3 inflammasome, its triggers in the brain and how its activation can contribute to the progression of dementia. We summarise the range of inhibitors targeting the NLRP3 inflammasome and its downstream pathways that are under investigation, and discuss future therapeutic perspectives for this devastating condition.

In the Eyes of the Beholder-New Mertk Knockout Mouse and Re-Evaluation of Phagocytosis versus Anti-Inflammatory Functions of MERTK

Greg Lemke's laboratory was one of the pioneers of research into the TAM family of receptor tyrosine kinases (RTKs). Not only was Tyro3 cloned in his laboratory, but his group also extensively studied mice knocked out for individual or various combinations of the TAM RTKs Tyro3, Axl, and Mertk. Here we primarily focus on one of the paralogs-MERTK. We provide a historical perspective on rodent models of loss of Mertk function and their association with retinal degeneration and blindness. We describe later studies employing mouse genetics and the generation of newer knockout models that point out incongruencies with the inference that loss of MERTK-dependent phagocytosis is sufficient for severe, early-onset photoreceptor degeneration in mice. This discussion is meant to raise awareness with regards to the limitations of the original Mertk knockout mouse model generated using 129 derived embryonic stem cells and carrying 129 derived alleles and the role of these alleles in modifying Mertk knockout phenotypes or even displaying Mertk-independent phenotypes. We also suggest molecular approaches that can further Greg Lemke's scintillating legacy of dissecting the molecular functions of MERTK-a protein that has been described to function in phagocytosis as well as in the negative regulation of inflammation.

Cardioprotective Potential of Cymbopogon citratus Essential Oil against Isoproterenol-induced Cardiomyocyte Hypertrophy: Possible Involvement of NLRP3 Inflammasome and Oxidative Phosphorylation Complex Subunits

OBJECTIVE

Cymbopogon citratus (DC.) Stapf is a medicinal and edible herb that is widely used for the treatment of gastric, nervous and hypertensive disorders. In this study, we investigated the cardioprotective effects and mechanisms of the essential oil, the main active ingredient of Cymbopogon citratus, on isoproterenol (ISO)-induced cardiomyocyte hypertrophy.

METHODS

The compositions of Cymbopogon citratus essential oil (CCEO) were determined by gas chromatography-mass spectrometry. Cardiomyocytes were pretreated with 16.9 µg/L CCEO for 1 h followed by 10 µmol/L ISO for 24 h. Cardiac hypertrophy-related indicators and NLRP3 inflammasome expression were evaluated. Subsequently, transcriptome sequencing (RNA-seq) and target verification were used to further explore the underlying mechanism.

RESULTS

Our results showed that the CCEO mainly included citronellal (45.66%), geraniol (23.32%), and citronellol (10.37%). CCEO inhibited ISO-induced increases in cell surface area and protein content, as well as the upregulation of fetal gene expression. Moreover, CCEO inhibited ISO-induced NLRP3 inflammasome expression, as evidenced by decreased lactate dehydrogenase content and downregulated mRNA levels of NLRP3, ASC, CASP1, GSDMD, and IL-1β, as well as reduced protein levels of NLRP3, ASC, pro-caspase-1, caspase-1 (p20), GSDMD-FL, GSDMD-N, and pro-IL-1β. The RNA-seq results showed that CCEO inhibited the increase in the mRNA levels of 26 oxidative phosphorylation complex subunits in ISO-treated cardiomyocytes. Our further experiments confirmed that CCEO suppressed ISO-induced upregulation of mt-Nd1, Sdhd, mt-Cytb, Uqcrq, and mt-Atp6 but had no obvious effects on mt-Col expression.

CONCLUSION

CCEO inhibits ISO-induced cardiomyocyte hypertrophy through the suppression of NLRP3 inflammasome expression and the regulation of several oxidative phosphorylation complex subunits.

Exploring blood lipids-immunity associations following HBV vaccination: evidence from a large cross-sectional study

Introduction

Serological responses following hepatitis B vaccination are crucial for preventing hepatitis B (HBV). However, the potential relationship between serum lipid levels and immunity from HBV vaccination remains poorly understood.

Methods

In this study, we conducted an analysis of the National Health and Nutrition Examination Survey (NHANES) data spanning from 2003 to 2016. Multivariable weighted logistic regression models, generalized linear analysis, stratified models, smooth curve fitting, segmentation effect analysis and sensitivity analysis were utilized to assess the relationships.

Results

After adjusting for relevant covariates, we observed that low levels of high-density lipoprotein cholesterol (HDL) were independently linked to a significantly lower seroprotective rate. Compared to HDL levels of ≥ 60 mg/dL, the odds ratios (ORs) for individuals with borderline levels (40-59 mg/dL for men, 50-59 mg/dL for women) and low levels (< 40 mg/dL for men, < 50 mg/dL for women) were 0.83 (95% CI 0.69-0.99) and 0.65 (95% CI 0.56-0.78), respectively. This association was particularly pronounced in individuals aged 40 or older. Conversely, higher levels of the triglyceride to HDL (TG/HDL) ratio (OR, 0.90; 95% CI, 0.84-0.98), total cholesterol to HDL (Chol/HDL) ratio (OR, 0.77; 95% CI, 0.64-0.92), and low-density lipoprotein to HDL (LDL/HDL) ratio (OR, 0.85; 95% CI, 0.76-0.96) were associated with a decreased likelihood of seroprotection.

Conclusion

This study suggests that lipid levels may play a role in modulating the immune response following HBV vaccination.

Arachidonic acid inhibition of the NLRP3 inflammasome is a mechanism to explain the anti-inflammatory effects of fasting

Elevated interleukin (IL)-1β levels, NLRP3 inflammasome activity, and systemic inflammation are hallmarks of chronic metabolic inflammatory syndromes, but the mechanistic basis for this is unclear. Here, we show that levels of plasma IL-1β are lower in fasting compared to fed subjects, while the lipid arachidonic acid (AA) is elevated. Lipid profiling of NLRP3-stimulated mouse macrophages shows enhanced AA production and an NLRP3-dependent eicosanoid signature. Inhibition of cyclooxygenase by nonsteroidal anti-inflammatory drugs decreases eicosanoid, but not AA, production. It also reduces both IL-1β and IL-18 production in response to NLRP3 activation. AA inhibits NLRP3 inflammasome activity in human and mouse macrophages. Mechanistically, AA inhibits phospholipase C activity to reduce JNK1 stimulation and hence NLRP3 activity. These data show that AA is an important physiological regulator of the NLRP3 inflammasome and explains why fasting reduces systemic inflammation and also suggests a mechanism to explain how nonsteroidal anti-inflammatory drugs work.

C-reactive protein modifies lipoprotein(a)-related risk for coronary heart disease: the BiomarCaRE project

BACKGROUND AND AIMS

Recent investigations have suggested an interdependence of lipoprotein(a) [Lp(a)]-related risk for cardiovascular disease with background inflammatory burden. The aim the present analysis was to investigate whether high-sensitive C-reactive protein (hsCRP) modulates the association between Lp(a) and coronary heart disease (CHD) in the general population.

METHODS

Data from 71 678 participants from 8 European prospective population-based cohort studies were used (65 661 without/6017 with established CHD at baseline; median follow-up 9.8/13.8 years, respectively). Fine and Gray competing risk-adjusted models were calculated according to accompanying hsCRP concentration (<2 and ≥2 mg/L).

RESULTS

Among CHD-free individuals, increased Lp(a) levels were associated with incident CHD irrespective of hsCRP concentration: fully adjusted sub-distribution hazard ratios [sHRs (95% confidence interval)] for the highest vs. lowest fifth of Lp(a) distribution were 1.45 (1.23-1.72) and 1.48 (1.23-1.78) for a hsCRP group of <2 and ≥2 mg/L, respectively, with no interaction found between these two biomarkers on CHD risk (Pinteraction = 0.82). In those with established CHD, similar associations were seen only among individuals with hsCRP ≥ 2 mg/L [1.34 (1.03-1.76)], whereas among participants with a hsCRP concentration <2 mg/L, there was no clear association between Lp(a) and future CHD events [1.29 (0.98-1.71)] (highest vs. lowest fifth, fully adjusted models; Pinteraction = 0.024).

CONCLUSIONS

While among CHD-free individuals Lp(a) was significantly associated with incident CHD regardless of hsCRP, in participants with CHD at baseline, Lp(a) was related to recurrent CHD events only in those with residual inflammatory risk. These findings might guide adequate selection of high-risk patients for forthcoming Lp(a)-targeting compounds.

12/15-lipoxygenase inhibition attenuates neuroinflammation by suppressing inflammasomes

Introduction

Lipoxygenases (LOXs) have essential roles in stroke, atherosclerosis, diabetes, and hypertension. 12/15-LOX inhibition was shown to reduce infarct size and brain edema in the acute phase of experimental stroke. However, the significance of 12/15-LOX on neuroinflammation, which has an essential role in the pathophysiology of stroke, has not been clarified yet.

Methods

In this study, ischemia/recanalization (I/R) was performed by occluding the proximal middle cerebral artery (pMCAo) in mice. Either the 12/15-LOX inhibitor (ML351, 50 mg/kg) or its solvent (DMSO) was injected i.p. at recanalization after 1 h of occlusion. Mice were sacrificed at 6, 24, and 72-h after ischemia induction. Infarct volumes were calculated on Nissl-stained sections. Neurological deficit scoring was used for functional analysis. Lipid peroxidation was determined by the MDA assay, and the inflammatory cytokines IL-6, TNF-alpha, IL-1beta, IL-10, and TGF-beta were quantified by ELISA. The inflammasome proteins NLRP1 and NLRP3, 12/15-LOX, and caspase-1 were detected with immunofluorescence staining.

Results

Infarct volumes, neurological deficit scores, and lipid peroxidation were significantly attenuated in ML351-treated groups at 6, 24, and 72-h. ELISA results revealed that the pro-inflammatory cytokines IL-1beta, IL-6, and TNF-alpha were significantly decreased at 6-h and/or 24-h of I/R, while the anti-inflammatory cytokines IL-10 and TNF-alpha were increased at 24-h or 72-h of ML351 treatment. NLRP1 and NLRP3 immunosignaling were enhanced at three time points after I/R, which were significantly diminished by the ML351 application. Interestingly, NLRP3 immunoreactivity was more pronounced than NLRP1. Hence, we proceeded to study the co-localization of NLRP3 immunoreactivity with 12/15-LOX and caspase-1, which indicated that NLRP3 was co-localized with 12/15-LOX and caspase-1 signaling. Additionally, NLRP3 was found in neurons at all time points but in non-neuronal cells 72 h after I/R.

Discussion

These results suggest that 12/15-LOX inhibition suppresses ischemia-induced inflammation in the acute and subacute phases of stroke via suppressing inflammasome activation. Understanding the mechanisms underlying lipid peroxidation and its associated pathways, like inflammasome activation, may have broader implications for the treatment of stroke and other neurological diseases characterized by neuroinflammation.

The Interplay between Immune and Metabolic Pathways in Kidney Disease

Kidney disease is a significant health problem worldwide, affecting an estimated 10% of the global population. Kidney disease encompasses a diverse group of disorders that vary in their underlying pathophysiology, clinical presentation, and outcomes. These disorders include acute kidney injury (AKI), chronic kidney disease (CKD), glomerulonephritis, nephrotic syndrome, polycystic kidney disease, diabetic kidney disease, and many others. Despite their distinct etiologies, these disorders share a common feature of immune system dysregulation and metabolic disturbances. The immune system and metabolic pathways are intimately connected and interact to modulate the pathogenesis of kidney diseases. The dysregulation of immune responses in kidney diseases includes a complex interplay between various immune cell types, including resident and infiltrating immune cells, cytokines, chemokines, and complement factors. These immune factors can trigger and perpetuate kidney inflammation, causing renal tissue injury and progressive fibrosis. In addition, metabolic pathways play critical roles in the pathogenesis of kidney diseases, including glucose and lipid metabolism, oxidative stress, mitochondrial dysfunction, and altered nutrient sensing. Dysregulation of these metabolic pathways contributes to the progression of kidney disease by inducing renal tubular injury, apoptosis, and fibrosis. Recent studies have provided insights into the intricate interplay between immune and metabolic pathways in kidney diseases, revealing novel therapeutic targets for the prevention and treatment of kidney diseases. Potential therapeutic strategies include modulating immune responses through targeting key immune factors or inhibiting pro-inflammatory signaling pathways, improving mitochondrial function, and targeting nutrient-sensing pathways, such as mTOR, AMPK, and SIRT1. This review highlights the importance of the interplay between immune and metabolic pathways in kidney diseases and the potential therapeutic implications of targeting these pathways.

Mitophagy in atherosclerosis: from mechanism to therapy

Mitophagy is a type of autophagy that can selectively eliminate damaged and depolarized mitochondria to maintain mitochondrial activity and cellular homeostasis. Several pathways have been found to participate in different steps of mitophagy. Mitophagy plays a significant role in the homeostasis and physiological function of vascular endothelial cells, vascular smooth muscle cells, and macrophages, and is involved in the development of atherosclerosis (AS). At present, many medications and natural chemicals have been shown to alter mitophagy and slow the progression of AS. This review serves as an introduction to the field of mitophagy for researchers interested in targeting this pathway as part of a potential AS management strategy.

Role of de novo lipogenesis in inflammation and insulin resistance in alzheimer's disease

Patients with Alzheimer's disease (AD) display both peripheral tissue and brain insulin resistance, the later could be a potential risk factor for cognitive dysfunction. While certain degree of inflammation is required for inducing insulin resistance, underlying mechanism(s) remains unclear. Evidence from diverse research domains suggest that elevated intracellular fatty acids of de novo pathway can induce insulin resistance even without triggering inflammation; however, the effect of saturated fatty acids (SFAs) could be detrimental due the development of proinflammatory cues. In this context, evidence suggest that while lipid/fatty acid accumulation is a characteristic feature of brain pathology in AD, dysregulated de novo lipogenesis could be a potential source for lipid/fatty acid accumulation. Therefore, therapies aimed at regulating de novo lipogenesis could be effective in improving insulin sensitivity and cognitive function in patients with AD.

The neuropeptide CGRP enters the macrophage cytosol to suppress the NLRP3 inflammasome during pulmonary infection

The NLRP3 inflammasome plays an essential role in resistance to bacterial infection. The nervous system secretes multiple neuropeptides affecting the nervous system as well as immune cells. The precise impact of the neuropeptide CGRP on NLRP3 inflammasome activation is still unclear. Here, we show that CGRP negatively regulates the antibacterial process of host cells. CGRP prevents NLRP3 inflammasome activation and reduces mature IL-1β secretion. Following NLRP3 inflammasome stimulation that triggers endosome leakage, CGRP internalized to endosomal compartments is released into the cell cytosol. Cytosolic CGRP binds directly to NLRP3 and dismantles the NLRP3-NEK7 complex, which is crucial for NLRP3 inflammasome activation. CGRP administration exacerbates bacterial infection, while the treatment with a CGRP antagonist has the opposite effect. Our study uncovers a unique role of CGRP in inhibiting inflammasome activation during infections, which might shed new light on antibacterial therapies in the future.

Whole grain benefit: synergistic effect of oat phenolic compounds and β-glucan on hyperlipidemia via gut microbiota in high-fat-diet mice

Increasing evidence has confirmed that whole grain oats are effective in regulating hyperlipidemia. However, which specific ingredient is crucial remains unclear. This study focused on which whole grain components, oat phenolic compounds (OPC) or oat β-glucan (OBG), can regulate lipid metabolism and gut microbiota. The experiment unveiled that OPC and/or OBG not only reduced the body weight and fasting blood glucose (FBG) but also regulated serum and hepatic lipid levels in high-fat-diet (HFD) fed mice. There was no significant difference in the regulatory effects of OPC and OBG (p > 0.05). The combination of OPC and OBG (OPC + OBG) significantly decreased the body weight (p < 0.01) and reduced the blood glucose (p < 0.01) and lipid profile levels (p < 0.01). The real-time quantitative PCR (RT-qPCR) study revealed that OPC + OBG significantly altered mRNA expression related to lipid metabolism. Histopathological analysis showed that OPC + OBG improved liver lipid deposition as well as liver oxidative stress (p < 0.05). In addition, OPC + OBG combination regulated the gut microbiota community phenotype and increased probiotics. OPC + OBG significantly increased the abundance of Bacteroidetes and reduced the abundance of Firmicutes (p < 0.05) compared with the OPC and OBG fed mice. In conclusion, OPC + OBG has a synergistic effect in alleviating hyperlipidemia via lipid metabolism and gut microbiota composition. This finding also provided a potential justification for the advantages of whole grains in preventing hyperlipidemia.

Calciprotein Particles Cause Physiologically Significant Pro-Inflammatory Response in Endothelial Cells and Systemic Circulation

Calciprotein particles (CPPs) represent an inherent mineral buffering system responsible for the scavenging of excessive Ca²⁺ and PO₄^3- ions in order to prevent extraskeletal calcification, although contributing to the development of endothelial dysfunction during the circulation in the bloodstream. Here, we performed label-free proteomic profiling to identify the functional consequences of CPP internalisation by endothelial cells (ECs) and found molecular signatures of significant disturbances in mitochondrial and lysosomal physiology, including oxidative stress, vacuolar acidification, accelerated proteolysis, Ca²⁺ cytosolic elevation, and mitochondrial outer membrane permeabilisation. Incubation of intact ECs with conditioned medium from CPP-treated ECs caused their pro-inflammatory activation manifested by vascular cell adhesion molecule 1 (VCAM1) and intercellular adhesion molecule 1 (ICAM1) upregulation and elevated release of interleukin (IL)-6, IL-8, and monocyte chemoattractant protein-1/ C-C motif ligand 2 (MCP-1/CCL2). Among the blood cells, monocytes were exclusively responsible for CPP internalisation. As compared to the co-incubation of donor blood with CPPs in the flow culture system, intravenous administration of CPPs to Wistar rats caused a considerably higher production of chemokines, indicating the major role of monocytes in CPP-triggered inflammation. Upregulation of sICAM-1 and IL-8 also suggested a notable contribution of endothelial dysfunction to systemic inflammatory response after CPP injections. Collectively, our results demonstrate the pathophysiological significance of CPPs and highlight the need for the development of anti-CPP therapies.

The lipid peroxidation product 4-hydroxynonenal inhibits NLRP3 inflammasome activation and macrophage pyroptosis

Pyroptosis is a form of cell death triggered by the innate immune system that has been implicated in the pathogenesis of sepsis and acute lung injury. At the cellular level, pyroptosis is characterized by cell swelling, membrane rupture, and release of inflammatory cytokines, such as IL-1β. However, the role of endogenous lipids in pyroptosis remains underappreciated. We discovered that 4-hydroxynonenal (HNE), a major endogenous product of lipid peroxidation, inhibited pyroptosis and inflammasome activation. HNE at physiological concentrations (3 µM) blocked nigericin and ATP-induced cell death, as well as secretion of IL-1β, by mouse primary macrophages and human peripheral blood mononuclear cells. Treatment with HNE, or an increase of endogenous HNE by inhibiting glutathione peroxidase 4, reduced inflammasome activation in mouse models of acute lung injury and sepsis. Mechanistically, HNE inhibited the NLRP3 inflammasome activation independently of Nrf2 and NF-κB signaling, and had no effect on the NLRC4 or AIM2 inflammasome. Furthermore, HNE directly bound to NLRP3 and inhibited its interaction with NEK7. Our findings identify HNE as a novel, endogenous inhibitor of the NLRP3 inflammasome.

Salidroside alleviates hepatic ischemia-reperfusion injury during liver transplant in rat through regulating TLR-4/NF-κB/NLRP3 inflammatory pathway

Salidroside has anti-inflammatory, antioxidant and hepatoprotective properties. However, its effect on hepatic ischemia–reperfusion injury (IRI), an unavoidable side effect associated with liver transplantation, remains undefined. Here, we aimed to determine whether salidroside alleviates hepatic IRI and elucidate its potential mechanisms. We used both in vivo and in vitro assays to assess the effect and mechanisms of salidroside on hepatic IRI. Hepatic IRI rat models were pretreated with salidroside (5, 10 or 20 mg/kg/day) for 7 days following liver transplantation while hypoxia/reoxygenation (H/R) model of RAW 264.7 macrophages were pretreated with salidroside (1, 10 or 50 μM). The effect of salidroside on hepatic IRI was assessed using hematoxylin–eosin staining, terminal deoxynucleotidyl transferase dUTP nick-end labeling staining, qRT-PCR, immunosorbent assay and western blotting. Our in vivo assays showed that salidroside significantly reduced pathological liver damage, serum aminotransferase levels and serum levels of IL-1, IL-18 and TNF-α. Besides, salidroside reduced the expression of TLR-4/NF-κB/NLRP3 inflammatory pathway associated proteins (TLR-4, MyD88, p-IKKα, p-IKKβ, p-IKK, p-IκBα, p-P65, NLRP3, ASC, Cleaved caspase-1, IL-1β, IL-18, TNF-α and IL-6) in rats after liver transplantation. On the other hand, data from the in vitro analysis demonstrated that salidroside blocks expression of TLR-4/NF-κB/NLRP3 inflammatory pathway related proteins in the RAW264.7 cells treated with H/R. The salidroside-specific anti-inflammatory effects were partially inhibited by the TLR-4 agonist lipopolysaccharide. Taken together, our study showed that salidroside inhibits hepatic IRI following liver transplantation by modulating the TLR-4/NF-κB/NLRP3 inflammatory pathway.