Membrane-bound Interleukin-1α mediates leukocyte adhesion during atherogenesis

Introduction

The interleukin-1 (IL-1) family and the NLR family pyrin domain-containing 3 (NLRP3) inflammasome contribute to atherogenesis but the underlying mechanisms are incompletely understood. Unlike IL-1β, IL-1α is not dependent on the NLRP3 inflammasome to exert its pro-inflammatory effects. Here, a non-genetic model was applied to characterize the role of IL-1α, IL-1β, and NLRP3 for the pathogenesis of atherosclerosis.

Methods

Atherogenesis was induced by gain-of-function PCSK9-AAV8 mutant viruses and feeding of a high-fat western diet (WTD) for 12 weeks in C57Bl6/J wildtype mice (WT) and in Il1a-/-, Nlrp3-/-, and Il1b-/- mice.

Results

PCSK9-Il1a-/- mice showed reduced atherosclerotic plaque area in the aortic root with lower lipid accumulation, while no difference was observed between PCSK9-WT, PCSK9-Nlrp3-/- and PCSK9-Il1b-/- mice. Serum proteomic analysis showed a reduction of pro-inflammatory cytokines (e.g., IL-1β, IL-6) in PCSK9-Il1a-/- as well as in PCSK9-Nlrp3-/- and PCSK9-Il1b-/- mice. Bone marrow dendritic cells (BMDC) of PCSK9-WT, PCSK9-Nlrp3-/-, and PCSK9-Il1b-/- mice and primary human monocytes showed translocation of IL-1α to the plasma membrane (csIL-1α) upon stimulation with LPS. The translocation of IL-1α to the cell surface was regulated by myristoylation and increased in mice with hypercholesterolemia. CsIL-1α and IL1R1 protein-protein interaction on endothelial cells induced VCAM1 expression and monocyte adhesion, which was abrogated by the administration of neutralizing antibodies against IL-1α and IL1R1.

Conclusion

The results highlight the importance of IL-1α on the cell surface of circulating leucocytes for the development of atherosclerosis. PCSK9-Il1a-/- mice, but not PCSK9-Nlrp3-/- or PCSK9-Il1b-/- mice, are protected from atherosclerosis after induction of hypercholesterolemia independent of circulating cytokines. Myristoylation and translocation of IL-1α to the cell surface in myeloid cells facilitates leukocyte adhesion and contributes to the development of atherosclerosis.

A novel direct inducible nongenetic murine model of diabetes-aggravated atherosclerosis

Background and aims

Atherosclerosis, the main pathology underlying cardiovascular diseases is accelerated in diabetic patients (1,2). Genetic mouse models require breeding efforts which are time-consuming and costly. Our aim was to establish a new nongenetic model of inducible metabolic risk factors that mimics hyperlipidemia, hyperglycemia, or both and allows the detection of phenotypic differences dependent on the metabolic stressor(s) on any genetic background.

Methods and results

Wild type mice were injected with gain-of-function PCSK9D377Y (proprotein convertase subtilisin/kexin type 9) mutant adeno-associated viral particles (AAV) and streptozotocin (STZ) and fed either a high-fat diet (HFD) or high-cholesterol/high fat-diet (Paigen diet, PD) for 12 and 20 weeks. LDLR KO mice were used as reference control. Combined hyperlipidemic and hyperglycemic mice (HGHCi), but not hyperlipidemia (HCi) alone, displayed characteristic features of aggravated atherosclerosis characterized by larger and less stable plaques (necrotic core area in HGHCi HFD: 24% vs HCi HFD: 13% vs LDLR KO HFD: 18% area, at 20 weeks p<0.05; fibrous cap thickness in HGHCi: 13 μm vs HCi HFD: 23 μm vs LDLR KO HFD: 17 μm, at 20 weeks, p<0.05) which contained more macrophages (MOMA-2 in HGHCi HFD: 27% vs HCi HFD: 19% vs LDLR KO HFD: 46% area/plaque, at 20 weeks, p<0.05) and less smooth muscle cells (α-SMA in HGHCi HFD: 12% vs HCi HFD: 25% vs LDLR KO HFD: 18% area/plaque, at 20 weeks, p<0.05), on both HFD or PD diet. Diabetic atherosclerotic mice (HGHCi) fed a HFD showed 37% plaque area (of total lumen) compared to 16% plaque area in non-diabetic mice (HCi HFD) and 17% in LDLR KO HFD after 12 weeks; and 43% (HGHCi HFD) vs. 29% (HCi HFD) vs 39% plaque area (LDLR KO HFD) after 20 weeks (Figure 1A, B). Differences between the diabetic HGHCi and non-diabetic HCi HFD mice were confirmed using RNA-seq analysis of aortic tissue, revealing that significantly more genes were dysregulated in mice with combined hyperlipidemia and hyperglycemia than in the hyperlipidemia-only group. The HGHCi-associated genes were related to pathways regulating inflammation (increased Cd68, iNos, and Tnfa expression) and extracellular matrix degradation (Adamts4 and Mmp14) (Figure 1C). When comparing HFD with PD, the PD aggravated atherosclerosis to a greater extent in mice and showed plaque formation after 8 weeks (HGHCi PD: 48% plaque area vs. HCi PD: 30% plaque area), therefore, representing a direct inducible hyperglycemic atherosclerosis model compared with HFD-fed mice, in which atherosclerosis is severe by 8 weeks.

Conclusion

We established a nongenetic direct inducible mouse model of diabetes-aggravated atherosclerosis allowing comparative analyses of atherosclerosis in diabetic and non-diabetic conditions and its modification by diet, allowing analyses of multiple metabolic hits in mice.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Deutsche Forschungsgemeinschaft (DFG)

NOD-like receptor protein 3 activation causes spontaneous inflammation and fibrosis that mimics human NASH

BACKGROUND AND AIMS

The NOD-like receptor protein 3 (NLRP3) inflammasome is a central contributor to human acute and chronic liver disease, yet the molecular and cellular mechanisms by which its activation precipitates injury remain incompletely understood. Here, we present single cell transcriptomic profiling of livers from a global transgenic tamoxifen-inducible constitutively activated Nlrp3A350V mutant mouse, and we investigate the changes in parenchymal and nonparenchymal liver cell gene expression that accompany inflammation and fibrosis.

APPROACH AND RESULTS

Our results demonstrate that NLRP3 activation causes chronic extramedullary myelopoiesis marked by myeloid progenitors that differentiate into proinflammatory neutrophils, monocytes, and monocyte-derived macrophages. We observed prominent neutrophil infiltrates with increased Ly6gHI and Ly6gINT cells exhibiting transcriptomic signatures of granulopoiesis typically found in the bone marrow. This was accompanied by a marked increase in Ly6cHI monocytes differentiating into monocyte-derived macrophages that express transcriptional programs similar to macrophages of NASH models. NLRP3 activation also down-regulated metabolic pathways in hepatocytes and shifted hepatic stellate cells toward an activated profibrotic state based on expression of collagen and extracellular matrix regulatory genes.

CONCLUSIONS

These results define the single cell transcriptomes underlying hepatic inflammation and fibrosis precipitated by NLRP3 activation. Clinically, our data support the notion that NLRP3-induced mechanisms should be explored as therapeutic target in NASH-like inflammation.

Reduction of A-to-I RNA editing in the failing human heart regulates formation of circular RNAs

Alterations of RNA editing that affect the secondary structure of RNAs can cause human diseases. We therefore studied RNA editing in failing human hearts. Transcriptome sequencing showed that adenosine-to-inosine (A-to-I) RNA editing was responsible for 80% of the editing events in the myocardium. Failing human hearts were characterized by reduced RNA editing. This was primarily attributable to Alu elements in introns of protein-coding genes. In the failing left ventricle, 166 circRNAs were upregulated and 7 circRNAs were downregulated compared to non-failing controls. Most of the upregulated circRNAs were associated with reduced RNA editing in the host gene. ADAR2, which binds to RNA regions that are edited from A-to-I, was decreased in failing human hearts. In vitro, reduction of ADAR2 increased circRNA levels suggesting a causal effect of reduced ADAR2 levels on increased circRNAs in the failing human heart. To gain mechanistic insight, one of the identified upregulated circRNAs with a high reduction of editing in heart failure, AKAP13, was further characterized. ADAR2 reduced the formation of double-stranded structures in AKAP13 pre-mRNA, thereby reducing the stability of Alu elements and the circularization of the resulting circRNA. Overexpression of circAKAP13 impaired the sarcomere regularity of human induced pluripotent stem cell-derived cardiomyocytes. These data show that ADAR2 mediates A-to-I RNA editing in the human heart. A-to-I RNA editing represses the formation of dsRNA structures of Alu elements favoring canonical linear mRNA splicing and inhibiting the formation of circRNAs. The findings are relevant to diseases with reduced RNA editing and increased circRNA levels and provide insights into the human-specific regulation of circRNA formation.

Extracellular Inflammasome Particles Are Released After Marathon Running and Induce Proinflammatory Effects in Endothelial Cells

Objectives: The intracellular NLRP3 inflammasome is an important regulator of sterile inflammation. Recent data suggest that inflammasome particles can be released into circulation. The effects of exercise on circulating extracellular apoptosis-associated speck-like protein (ASC) particles and their effects on endothelial cells are not known.

Methods: We established a flow cytometric method to quantitate extracellular ASC specks in human serum. ASC specks were quantitated in 52 marathon runners 24–72 h before, immediately after, and again 24–58 h after the run. For mechanistic characterization, NLRP3 inflammasome particles were isolated from a stable mutant NLRP3 (p.D303N)-YFP HEK cell line and used to treat primary human coronary artery endothelial cells.

Results: Athletes showed a significant increase in serum concentration of circulating ASC specks immediately after the marathon (+52% compared with the baseline, p < 0.05) and a decrease during the follow-up after 24–58 h (12% reduction compared with immediately after the run, p < 0.01). Confocal microscopy revealed that human endothelial cells can internalize extracellular NLRP3 inflammasome particles. After internalization, endothelial cells showed an inflammatory response with a higher expression of the cell adhesion molecule ICAM1 (6.9-fold, p < 0.05) and increased adhesion of monocytes (1.5-fold, p < 0.05).

Conclusion: These findings identify extracellular inflammasome particles as novel systemic mediators of cell–cell communication that are transiently increased after acute extensive exercise with a high mechanical muscular load.

Novel Nongenetic Murine Model of Hyperglycemia and Hyperlipidemia-Associated Aggravated Atherosclerosis

Objective

Atherosclerosis, the main pathology underlying cardiovascular diseases is accelerated in diabetic patients. Genetic mouse models require breeding efforts which are time-consuming and costly. Our aim was to establish a new nongenetic model of inducible metabolic risk factors that mimics hyperlipidemia, hyperglycemia, or both and allows the detection of phenotypic differences dependent on the metabolic stressor(s).

Methods and Results

Wild-type mice were injected with gain-of-function PCSK9^D377Y (proprotein convertase subtilisin/kexin type 9) mutant adeno-associated viral particles (AAV) and streptozotocin and fed either a high-fat diet (HFD) for 12 or 20 weeks or a high-cholesterol/high-fat diet (Paigen diet, PD) for 8 weeks. To evaluate atherosclerosis, two different vascular sites (aortic sinus and the truncus of the brachiocephalic artery) were examined in the mice. Combined hyperlipidemic and hyperglycemic (HGHCi) mice fed a HFD or PD displayed characteristic features of aggravated atherosclerosis when compared to hyperlipidemia (HCi HFD or PD) mice alone. Atherosclerotic plaques of HGHCi HFD animals were larger, showed a less stable phenotype (measured by the increased necrotic core area, reduced fibrous cap thickness, and less α-SMA-positive area) and had more inflammation (increased plasma IL-1β level, aortic pro-inflammatory gene expression, and MOMA-2-positive cells in the BCA) after 20 weeks of HFD. Differences between the HGHCi and HCi HFD models were confirmed using RNA-seq analysis of aortic tissue, revealing that significantly more genes were dysregulated in mice with combined hyperlipidemia and hyperglycemia than in the hyperlipidemia-only group. The HGHCi-associated genes were related to pathways regulating inflammation (increased Cd68, iNos, and Tnfa expression) and extracellular matrix degradation (Adamts4 and Mmp14). When comparing HFD with PD, the PD aggravated atherosclerosis to a greater extent in mice and showed plaque formation after 8 weeks. Hyperlipidemic and hyperglycemic mice fed a PD (HGHCi PD) showed less collagen (Sirius red) and increased inflammation (CD68-positive cells) within aortic plaques than hyperlipidemic mice (HCi PD). HGHCi-PD mice represent a directly inducible hyperglycemic atherosclerosis model compared with HFD-fed mice, in which atherosclerosis is severe by 8 weeks.

Conclusion

We established a nongenetically inducible mouse model allowing comparative analyses of atherosclerosis in HCi and HGHCi conditions and its modification by diet, allowing analyses of multiple metabolic hits in mice.

Pediatric percentiles for transient elastography measurements - effects of age, sex, weight status and pubertal stage

BACKGROUND AND AIMS

Transient Elastography is a non-invasive, cost-efficient, non-ionizing, observer-independent and reliable method to detect liver fibrosis using Liver Stiffness Measurement (LSM) and the degree of fat accumulation in the liver using Controlled Attenuation Parameter (CAP). This study aims to derive reference values for both measures from healthy children and adolescents. Further, we aim to assess the potential influence of age, sex, puberty, and BMI-SDS on CAP and LSM.

METHODS

Within the LIFE Child study, amongst others, anthropometric data and pubertal status were assessed. Transient Elastography (TE) was performed using the FibroScan^® device in a population-based cohort at 982 study visits of 482 healthy children aged between 10 and 18 years. Percentiles for LSM and CAP were estimated, and the effects of age, sex, puberty and weight status were assessed through hierarchical regression models.

RESULTS

There was a strong age dependency for LSM with higher values for older children, most pronounced in the upper percentiles in boys. Contrarily, CAP was relatively stable across the age span without considerable difference between boys and girls. We found a significant positive correlation between BMI-SDS and both CAP and LSM for BMI-SDS >1.28. For BMI-SDS < 1.28, the association was also positive but reached statistical significance only for CAP. Further, the association between BMI-SDS and CAP was significantly stronger in younger than in older children. There was no association between pubertal status and CAP. For LSM, we found that children with a high BMI-SDS but not children with normal weight had significantly higher LSM values in Tanner stage 4.

CONCLUSIONS

Age, sex, pubertal status and weight status should be considered when interpreting LSM and CAP in pediatric patients to facilitate and improve early detection of abnormal liver function, which is associated with common pathologies, such as NAFLD.

The long non-coding RNA Heat4 is upregulated in heart failure and decreases the immune response of non-classical monocytes

Background and purpose

Activation of the immune system correlates with the severity and the prognosis of patients with heart failure (HF). This study aims to identify and characterize long non-coding RNAs (lncRNAs) as a potential mechanistic link between the pathophysiology of HF and the activation of the immune system.

Methods and results

Next-generation sequencing (NGS) studies identified a 2.05-fold increase of the lncRNA Heat4 in the blood of patients with HF compared to controls, which was validated in a larger cohort (HF: N=63; Controls: N=38; p&lt;0.05). Interestingly, the lncRNA Heat4 is encoded in the well-known immune receptor locus CD300, together with 8 CD300-receptors which are associated with activation of the immune system. To determine the cellular origin of Heat4 in blood, we performed MACS and identified Heat4 to be enriched in non-classical monocytes compared to classical monocytes (3.37-fold, p&lt;0.05). The expression of Heat4 in non-classical monocytes was further validated by single-cell RNA sequencing. Overexpression of Heat4 in monocytes decreased levels of pro-inflammatory cytokines such as TNFα (38.6% reduction, p&lt;0.05). Conversely, the knockdown of Heat4 resulted in elevated levels of pro-inflammatory cytokines, including IL6 (10.83-fold, p&lt;0.05) and TNFα (4.14-fold, p&lt;0.05). In a larger cohort including patients with HF, Heat4 was able to determine the prevalence of heart failure by AUC=0.734 (p&lt;0.05). Moreover, in a 4-year follow-up of the same cohort, Heat4 predicted mortality by AUC=0.789 (HF: N=63, Dead=32; Controls: N=38, Dead=0; p&lt;0.05).

Conclusion

The long non-coding RNA Heat4 is elevated in the blood of HF patients. Mechanistically, Heat4 limits the extent of the inflammatory response of non-classical monocytes. Therefore, Heat4 may provide a regulatory link between inflammation and HF.

Funding Acknowledgement

Type of funding sources: None.

Reduced RNA editing in the failing human heart mediates alternative circular RNA splicing

Background and purpose

Post-transcriptional RNA editing is an important mechanism in the development of human diseases. RNA editing can affect RNA stability and alternative splicing. The aim of our study was to characterize RNA editing and its impact on alternative RNA splicing in the healthy and failing human heart.

Methods and results

Human heart samples of heart failure (HF) patients (n=20) and controls (n=10) were analyzed using RNA sequencing with subsequent analysis of RNA editing. We identified adenosine-to-inosine (A-to-I) editing as the major form of RNA editing in human hearts, being reduced in HF patients. Consistently, we found the editing enzyme ADAR2 reduced in HF patients. A-to-I RNA editing predominantly occurred in intronic regions of protein-coding genes, specifically in repetitive, primate-specific Alu elements which can affect RNA splicing. Indeed, we found 173 circular RNAs (circRNAs) regulated by alternative mRNA splicing in the failing heart.

Loss of ADAR2 led to reduced RNA editing concomitant with an increase of circRNA, while overexpression reduced circRNA expression and enhanced RNA editing.

Conclusion

A-to-I editing is the major type of RNA editing in the human heart, being reduced in HF. We demonstrate a primate-specific alternative RNA splicing mechanism mediated by RNA editing in human hearts. The findings may be relevant to diseases with reduced RNA editing such as cancer, neurological and cardiac diseases.

Funding Acknowledgement

Type of funding sources: None.

The uptake of trimethylamine N-oxide (TMAO) and its influence on endothelial cell identity and inflammation

Background and purpose

Trimethylamine N-oxide (TMAO) is associated with a higher risk of atherosclerotic diseases. However, the underlying molecular mechanisms are not completely understood. Inflammation and following endothelial-to-mesenchymal transition (EndMT) – a process where endothelial cells (ECs) lose their function and phenotype and gain a mesenchymal character – contribute to the development of atherosclerosis. We therefore aimed to investigate the potential uptake of TMAO into ECs and its potential impact on inflammation and subsequent EndMT.

Methods and results

Tandem mass spectrometry revealed a time-dependent uptake of TMAO into primary human endothelial cells of 0.5 nmol/mg protein within the first 30 minutes and of 5.8 nmol/mg within 24 hours. The uptake of TMAO resulted in a significant increase of inflammation as measured by E-selectin expression (+63.8-fold). A prolonged treatment with TMAO for 3 days resulted in an increase of EndMT indicated by a significant increase of the mesenchymal marker genes Versican (+6.8-fold) and Calponin (+11.9-fold), as well as a concomitant decrease of the endothelial marker LYVE1 (−92%). For identification of a potential TMAO transporter in human endothelial cells, we screened for the expression of Solute Carrier Family member transporters in ECs. Through our research, overexpression of the carrier A5 in ECs resulted in a 36% higher intracellular TMAO concentration as early as 30 minutes. In turn, causing a knockdown of A5 prevented TMAO induced inflammation (−77.8% induction of E-Selectin) and EndMT (−98,3% induction of Versican and −461% induction of Calponin).

Conclusion

Using a large screening approach, we identified A5 as the first TMAO transporter described in ECs. TMAO uptake results in increased inflammation of ECs and induction of EndMT. The data identify a novel mechanism of TMAO uptake into human ECs that may help to better understand lifestyle-mediated effects on atherosclerosis.

Funding Acknowledgement

Type of funding sources: None.

Feeding mice a diet high in oxidized linoleic acid metabolites does not alter liver oxylipin concentrations

The oxidation of dietary linoleic acid (LA) produces oxidized LA metabolites (OXLAMs) known to regulate multiple signaling pathways in vivo. Recently, we reported that feeding OXLAMs to mice resulted in liver inflammation and apoptosis. However, it is not known whether this is due to a direct effect of OXLAMs accumulating in the liver, or to their degradation into bioactive shorter chain molecules (e.g. aldehydes) that can provoke inflammation and related cascades. To address this question, mice were fed a low or high LA diet low in OXLAMs, or a low LA diet supplemented with OXLAMs from heated corn oil (high OXLAM diet). Unesterified oxidized fatty acids (i.e. oxylipins), including OXLAMs, were measured in liver after 8 weeks of dietary intervention using ultra-high pressure liquid chromatography coupled to tandem mass-spectrometry. The high OXLAM diet did not alter liver oxylipin concentrations compared to the low LA diet low in OXLAMs. Significant increases in several omega-6 derived oxylipins and reductions in omega-3 derived oxylipins were observed in the high LA dietary group compared to the low LA group. Our findings suggest that dietary OXLAMs do not accumulate in liver, and likely exert pro-inflammatory and pro-apoptotic effects via downstream secondary metabolites.

Extracellular NLRP3 inflammasome particles are internalized by human coronary artery smooth muscle cells and induce pro-atherogenic effects

Inflammation driven by intracellular activation of the NLRP3 inflammasome is involved in the pathogenesis of a variety of diseases including vascular pathologies. Inflammasome specks are released into the extracellular compartment from disrupting pyroptotic cells. The potential uptake and function of extracellular NLRP3 inflammasomes in human coronary artery smooth muscle cells (HCASMC) are unknown. Fluorescently labeled NLRP3 inflammasome particles were isolated from a mutant NLRP3-YFP cell line and used to treat primary HCASMC for 4 and 24 h. Fluorescent and expressional analyses showed that extracellular NLRP3-YFP particles are internalized into HCASMC, where they remain active and stimulate intracellular caspase-1 (1.9-fold) and IL-1β (1.5-fold) activation without inducing pyroptotic cell death. Transcriptomic analysis revealed increased expression level of pro-inflammatory adhesion molecules (ICAM1, CADM1), NLRP3 and genes involved in cytoskleleton organization. The NLRP3-YFP particle-induced gene expression was not dependent on NLRP3 and caspase-1 activation. Instead, the effects were partly abrogated by blocking NFκB activation. Genes, upregulated by extracellular NLRP3 were validated in human carotid artery atheromatous plaques. Extracellular NLRP3-YFP inflammasome particles promoted the secretion of pro-atherogenic and inflammatory cytokines such as CCL2/MCP1, CXCL1 and IL-17E, and increased HCASMC migration (1.8-fold) and extracellular matrix production, such as fibronectin (5.8-fold) which was dependent on NFκB and NLRP3 activation. Extracellular NLRP3 inflammasome particles are internalized into human coronary artery smooth muscle cells where they induce pro-inflammatory and pro-atherogenic effects representing a novel mechanism of cell-cell communication and perpetuation of inflammation in atherosclerosis. Therefore, extracellular NLRP3 inflammasomes may be useful to improve the diagnosis of inflammatory diseases and the development of novel anti-inflammatory therapeutic strategies.

SLM2 Is A Novel Cardiac Splicing Factor Involved in Heart Failure due to Dilated Cardiomyopathy

Alternative mRNA splicing is a fundamental process to increase the versatility of the genome. In humans, cardiac mRNA splicing is involved in the pathophysiology of heart failure. Mutations in the splicing factor RNA binding motif protein 20 (RBM20) cause severe forms of cardiomyopathy. To identify novel cardiomyopathy-associated splicing factors, RNA-seq and tissue-enrichment analyses were performed, which identified up-regulated expression of Sam68-Like mammalian protein 2 (SLM2) in the left ventricle of dilated cardiomyopathy (DCM) patients. In the human heart, SLM2 binds to important transcripts of sarcomere constituents, such as those encoding myosin light chain 2 (MYL2), troponin I3 (TNNI3), troponin T2 (TNNT2), tropomyosin 1/2 (TPM1/2), and titin (TTN). Mechanistically, SLM2 mediates intron retention, prevents exon exclusion, and thereby mediates alternative splicing of the mRNA regions encoding the variable proline-, glutamate-, valine-, and lysine-rich (PEVK) domain and another part of the I-band region of titin. In summary, SLM2 is a novel cardiac splicing regulator with essential functions for maintaining cardiomyocyte integrity by binding to and processing the mRNAs of essential cardiac constituents such as titin.

Hepatocyte pyroptosis and release of inflammasome particles induce stellate cell activation and liver fibrosis

BACKGROUND & AIMS

Increased hepatocyte death contributes to the pathology of acute and chronic liver diseases. However, the role of hepatocyte pyroptosis and extracellular inflammasome release in liver disease is unknown.

METHODS

We used primary mouse and human hepatocytes, hepatocyte-specific leucine 351 to proline Nlrp3KICreA mice, and GsdmdKO mice to investigate pyroptotic cell death in hepatocytes and its impact on liver inflammation and damage. Extracellular NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasomes were isolated from mutant NLRP3-YFP HEK cells and internalisation was studied in LX2 and primary human hepatic stellate cells. We also examined a cohort of 154 adult patients with biopsy-proven non-alcoholic fatty liver disease (Sir Charles Gairdner Hospital, Nedlands, Western Australia).

RESULTS

We demonstrated that primary mouse and human hepatocytes can undergo pyroptosis upon NLRP3 inflammasome activation with subsequent release of NLRP3 inflammasome proteins that amplify and perpetuate inflammasome-driven fibrogenesis. Pyroptosis was inhibited by blocking caspase-1 and gasdermin D activation. The activated form of caspase-1 was detected in the livers and in serum from patients with non-alcoholic steatohepatitis and correlated with disease severity. Nlrp3KICreA mice showed spontaneous liver fibrosis under normal chow diet, and increased sensitivity to liver damage and inflammation after treatment with low dose lipopolysaccharide. Mechanistically, hepatic stellate cells engulfed extracellular NLRP3 inflammasome particles leading to increased IL-1β secretion and α-smooth muscle actin expression. This effect was abrogated when cells were pre-treated with the endocytosis inhibitor cytochalasin B.

CONCLUSIONS

These results identify hepatocyte pyroptosis and release of inflammasome components as a novel mechanism to propagate liver injury and liver fibrosis development.

LAY SUMMARY

Our findings identify a novel mechanism of inflammation in the liver. Experiments in cell cultures, mice, and human samples show that a specific form of cell death, called pyroptosis, leads to the release of complex inflammatory particles, the NLRP3 inflammasome, from inside hepatocytes into the extracellular space. From there they are taken up by other cells and thereby mediate inflammatory and pro-fibrogenic stress signals. The discovery of this mechanism may lead to novel treatments for chronic liver diseases in the future.

Extracellular inflammasomes as novel endogenous danger signals that exert pro-inflammatory signaling on vascular cells

Background and aims

As part of the innate immune response, NLRP3 inflammasomes are involved in the process of sterile inflammation, IL-1β release and are key mediators of inflammation-related vascular diseases, such as atherosclerosis. Recent data showed the existence of extracellular inflammasomes released from monocytes during pyroptotic cell death. Their biological function in the vascular system is still not known. Here, we established a method to detect extracellular inflammasomes and tested the hypothesis that extracellular NLRP3 inflammasomes can be internalized by vascular cells, such as macrophages, endothelial cells and coronary smooth muscle cells and induce pro-inflammatory signaling.

Methods and result

Stimulation of THP1 monocytes and of isolated primary human monocytes with Lipopolysaccharide and Nigericin activated the NLRP3 inflammasome and induced pyroptosis and the release of inflammasome complexes. Extracellular inflammasomes were isolated from cell-free supernatant and identified as inflammasome complexes (oligomers) by immunoblot. For functional characterization, isolated fluorescent-labeled NLRP3 inflammasome complexes were shown to be internalized by THP1 macrophages (19.7±9.7% pos. cells), primary endothelial cells (HUVEC: 9.0±2.3% pos. cells, coronary artery endothelial cells: 11.0% ± 2.3% pos. cells) and coronary smooth muscle cells (42.8±9.9% pos.cells) using immunofluorescence staining, Z-stacks and imaging flow cytometric analysis. Extracellular NLRP3 inflammasomes (eNLRP3) induced pro-inflammatory signaling in macrophages by increasing IL1b and Tnfa gene expression (3.0- fold) as well as IL-1β release (con: 1.9 pg/ml vs. eNLRP3: 191.0 pg/ml). In coronary smooth muscle cells, treatment with extracellular inflammasomes increased endogenous Nlrp3 and IL1b gene expression as well as upregulation of Cell adhesion molecule 1 (Cadm1). Coronary artery endothelial cells showed also increased protein level of surface adhesion marker Intercellular Adhesion Molecule 1 (ICAM1).

Conclusion

Upon canonical NLRP3 inflammasome activation, mononuclear cells release inflammasome complexes into the extracellular space. Macrophages, endothelial cells and smooth muscle cells are able to internalize these extracellular inflammasome complexes that exert pro-inflammatory effects. These findings support the concept that cell-free NLRP3 inflammasomes act as extracellular signal molecules triggering pro-atherogenic signaling mechanisms in vascular cells.

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Leipzig University, Medical Faculty

Backward walking at three levels of treadmill inclination: an electromyographic and kinematic analysis

Backward walking on a treadmill is a common tool for lower extremity rehabilitation in the clinical setting. The purpose of this study was to evaluate the adaptations in the gait cycle produced by walking backward on a treadmill at 0, 5, and 10% inclination. Sixteen healthy adult subjects (14 females, two males), mean age of 23.19 +/- 3.02, participated. Joint positions for hip, knee, and ankle were measured during a complete gait cycle. Values were time matched with average electromyographic (EMG) activity (surface electrode) of the rectus femoris, hamstrings, gastrocnemius, and anterior tibialis during each subphase of gait (initial contact, midstance, heel-off, and midswing). Values of joint position and average EMG were compared over the three treadmill conditions. Subjects walked for approximately 1 minute at 4.0 km/h. A simple repeated measures analysis of variance (p < .05) with a Duncan post hoc test was used to analyze for changes. Significant changes occurred in the joint positions of the knee and ankle at initial contact (ankle increased from 9.81 +/- 5.06 degrees to 13.08 +/- 3.68 degrees; knee increased from 30.94 +/- 5.25 degrees to 42.42 +/- 4.08 degrees) as the treadmill was raised from 0 to 10%. Significant changes occurred for average EMG activity for each muscle studied over the three treadmill conditions. The greatest changes occurred in the gastrocnemius at initial contact (increase from 189.76 +/- 44.29% to 293.09 +/- 79.16%) between the 0 and 10% conditions. The results of this investigation confirm that backward walking up an incline may place additional muscular demands on an individual.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of blueberry thrips, Frankliniella vaccinii Morgan, with permethrin and effect on yield and residue in fruit

Permethrin at 0.4 kg a.i./ha controlled blueberry thrips Frankliniella vaccinii Morgan. There was no plant damage and crop yield was notably increased. Permethrin was extracted from berries with acetone, partitioned in hexane, cleaned-up on Florisil column and analysed by the electron capture gas chromatography using a 3% OV-210 column. No permethrin residues were found in the berries. The relative retention times of cis-, and trans-permethrins to aldrin were 10.3 and 12.1, respectively. The absence of permethrin from berries was further confirmed by TLC.