Emerging roles of angiopoietin-like proteins in inflammation: Mechanisms and potential as pharmacological targets

Hepatokines: unveiling the molecular and cellular mechanisms connecting hepatic tissue to insulin resistance and inflammation

Insulin resistance arising from Non-Alcoholic Fatty Liver Disease (NAFLD) stands as a prevalent global ailment, a manifestation within societies stemming from individuals' suboptimal dietary habits and lifestyles. This form of insulin resistance emerges as a pivotal factor in the development of type 2 diabetes mellitus (T2DM). Emerging evidence underscores the significant role of hepatokines, as hepatic-secreted hormone-like entities, in the genesis of insulin resistance and eventual onset of type 2 diabetes. Hepatokines exert influence over extrahepatic metabolism regulation. Their principal functions encompass impacting adipocytes, pancreatic cells, muscles, and the brain, thereby playing a crucial role in shaping body metabolism through signaling to target tissues. This review explores the most important hepatokines, each with distinct influences. Our review shows that Fetuin-A promotes lipid-induced insulin resistance by acting as an endogenous ligand for Toll-like receptor 4 (TLR-4). FGF21 reduces inflammation in diabetes by blocking the nuclear translocation of nuclear factor-κB (NF-κB) in adipocytes and adipose tissue, while also improving glucose metabolism. ANGPTL6 enhances AMPK and insulin signaling in muscle, and suppresses gluconeogenesis. Follistatin can influence insulin resistance and inflammation by interacting with members of the TGF-β family. Adropin show a positive correlation with phosphoenolpyruvate carboxykinase 1 (PCK1), a key regulator of gluconeogenesis. This article delves into hepatokines' impact on NAFLD, inflammation, and T2DM, with a specific focus on insulin resistance. The aim is to comprehend the influence of these recently identified hormones on disease development and their underlying physiological and pathological mechanisms.

ANGPTL8 deficiency attenuates lipopolysaccharide-induced liver injury by improving lipid metabolic dysregulation

Liver injury is closely related to poor outcomes in sepsis patients. Current studies indicate that sepsis is accompanied by metabolic disorders, especially those related to lipid metabolism. It is highly important to explore the mechanism of abnormal liver lipid metabolism during sepsis. As a key regulator of glucose and lipid metabolism, angiopoietin-like 8 (ANGPTL8) is involved in the regulation of multiple chronic metabolic diseases. In the present study, severe liver lipid deposition and lipid peroxidation were observed in the early stages of lipopolysaccharide (LPS) induced liver injury. LPS promotes the expression of ANGPTL8 both in vivo and in vitro. Knockout of Angptl8 reduced hepatic lipid accumulation and lipid peroxidation, improved fatty acid oxidation and liver function, and increased the survival rate of septic mice by activating the PGC1α/PPARα pathway. We also found that the expression of ANGPTL8 induced by LPS depends on TNF-α, and that inhibiting the TNF-α pathway reduces LPS-induced hepatic lipid deposition and lipid peroxidation. However, knocking out Angptl8 improved the survival rate of septic mice better than inhibiting the TNF-α pathway. Taken together, the results of our study suggest that ANGPTL8 functions as a novel cytokine in LPS-induced liver injury by suppressing the PGC1α/PPARα signaling pathway. Therefore, targeting ANGPTL8 to improve liver lipid metabolism represents an attractive strategy for the management of sepsis patients.

Establishing an oxidative stress mitochondria-related prognostic model in hepatocellular carcinoma based on multi-omics characteristics and machine learning computational framework

Hepatocellular carcinoma (HCC) has high incidence and mortality rates worldwide. Damaged mitochondria are characterized by the overproduction of reactive oxygen species (ROS), which can promote cancer development. The prognostic value of the interplay between mitochondrial function and oxidative stress in HCC requires further investigation. Gene expression data of HCC samples were collected from The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO) and International Cancer Genome Consortium (ICGC). We screened prognostic oxidative stress mitochondria-related (OSMT) genes at the bulk transcriptome level. Based on multiple machine learning algorithms, we constructed a consensus oxidative stress mitochondria-related signature (OSMTS), which contained 26 genes. In addition, we identified six of these genes as having a suitable prognostic value for OSMTS to reduce the difficulty of clinical application. Univariate and multivariate analyses verified the OSMTS as an independent prognostic factor for overall survival (OS) in HCC patients. The OSMTS-related nomogram demonstrated to be a powerful tool for the clinical diagnosis of HCC. We observed differences in biological function and immune cell infiltration in the tumor microenvironment between the high- and low-risk groups. The highest expression of the OSMTS was detected in hepatocytes at the single-cell transcriptome level. Hepatocytes in the high- and low-risk groups differed significantly in terms of biological function and intercellular communication. Moreover, at the spatial transcriptome level, high expression of OSMTS was mainly in regions enriched in hepatocytes and B cells. Potential drugs targeting specific risk subgroups were identified. Our study revealed that the OSMTS can serve as a promising tool for prognosis prediction and precise intervention in HCC patients.

ANGPTL3 negatively regulates IL-1β-induced NF-κB activation by inhibiting the IL1R1-associated signaling complex assembly

Interleukin-1β (IL-1β)-induced signaling is one of the most important pathways in regulating inflammation and immunity. The assembly of the receptor complex, consisting of the ligand IL-1β, the IL-1 receptor (IL-1R) type 1 (IL1R1), and the IL-1R accessory protein (IL1RAP), initiates this signaling. However, how the IL1R1-associated complex is regulated remains elusive. Angiopoietin like 3 (ANGPTL3), a key inhibitor of plasma triglyceride clearance, is mainly expressed in the liver and exists in both intracellular and extracellular secreted forms. Currently, ANGPTL3 has emerged as a highly promising drug target for hypertriglyceridemia and associated cardiovascular diseases. However, most studies have focused on the secreted form of ANGPTL3, while its intracellular role is still largely unknown. Here, we report that intracellular ANGPTL3 acts as a negative regulator of IL-1β-triggered signaling. Overexpression of ANGPTL3 inhibited IL-1β-induced NF-κB activation and the transcription of inflammatory genes in HepG2, THP1, and HEK293T cells, while knockdown or knockout of ANGPTL3 resulted in opposite effects. Mechanistically, ANGPTL3 interacted with IL1R1 and IL1RAP through its intracellular C-terminal fibrinogen-like domain and disrupted the assembly of the IL1R1-associated complex. Taken together, our study reveals a novel role for ANGPTL3 in inflammation, whereby it inhibits the physiological interaction between IL1R1 and IL1RAP to maintain immune tolerance and homeostasis in the liver.

Angiopoietin-Like Proteins: Cardiovascular Biology and Therapeutic Targeting for the Prevention of Cardiovascular Diseases

Despite the best pharmacologic tools available, cardiovascular diseases (CVDs) remain a major cause of morbidity and mortality in developed countries. After 2 decades of research, new therapeutic targets, such as angiopoietin-like proteins (ANGPTLs), are emerging. ANGPTLs belong to a family of 8 members, from ANGPTL1 to ANGPTL8; they have structural homology with angiopoietins and are secreted in the circulation. ANGPTLs display a multitude of physiological and pathologic functions; they contribute to inflammation, angiogenesis, cell death, senescence, hematopoiesis, and play a role in repair, maintenance, and tissue homeostasis. ANGPTLs-particularly the triad ANGPTL3, 4, and 8-have an established role in lipid metabolism through the regulation of triacylglycerol trafficking according to the nutritional status. Some ANGPTLs also contribute to glucose metabolism. Therefore, dysregulation in ANGPTL expression associated with abnormal circulating levels are linked to a plethora of CVD and metabolic disorders including atherosclerosis, heart diseases, diabetes, but also obesity and cancers. Because ANGPTLs bind to different receptors according to the cell type, antagonists are therapeutically inadequate. Recently, direct inhibitors of ANGPTLs, mainly ANGPTL3, have been developed, and specific monoclonal antibodies and antisense oligonucleotides are currently being tested in clinical trials. The aim of the current review is to provide an up-to-date preclinical and clinical overview on the function of the 8 members of the ANGPTL family in the cardiovascular system, their contribution to CVD, and the therapeutic potential of manipulating some of them.

The Proinflammatory Role of ANGPTL8 R59W Variant in Modulating Inflammation through NF-κB Signaling Pathway under TNFα Stimulation

BACKGROUND

Angiopoietin-like protein 8 (ANGPTL8) is known to regulate lipid metabolism and inflammation. It interacts with ANGPTL3 and ANGPTL4 to regulate lipoprotein lipase (LPL) activity and with IKK to modulate NF-κB activity. Further, a single nucleotide polymorphism (SNP) leading to the ANGPTL8 R59W variant associates with reduced low-density lipoprotein/high-density lipoprotein (LDL/HDL) and increased fasting blood glucose (FBG) in Hispanic and Arab individuals, respectively. In this study, we investigate the impact of the R59W variant on the inflammatory activity of ANGPTL8.

METHODS

The ANGPTL8 R59W variant was genotyped in a discovery cohort of 867 Arab individuals from Kuwait. Plasma levels of ANGPTL8 and inflammatory markers were measured and tested for associations with the genotype; the associations were tested for replication in an independent cohort of 278 Arab individuals. Impact of the ANGPTL8 R59W variant on NF-κB activity was examined using approaches including overexpression, luciferase assay, and structural modeling of binding dynamics.

RESULTS

The ANGPTL8 R59W variant was associated with increased circulatory levels of tumor necrosis factor alpha (TNFα) and interleukin 7 (IL7). Our in vitro studies using HepG2 cells revealed an increased phosphorylation of key inflammatory proteins of the NF-κB pathway in individuals with the R59W variant as compared to those with the wild type, and TNFα stimulation further elevated it. This finding was substantiated by increased luciferase activity of NF-κB p65 with the R59W variant. Modeled structural and binding variation due to R59W change in ANGPTL8 agreed with the observed increase in NF-κB activity.

CONCLUSION

ANGPTL8 R59W is associated with increased circulatory TNFα, IL7, and NF-κB p65 activity. Weak transient binding of the ANGPTL8 R59W variant explains its regulatory role on the NF-κB pathway and inflammation.

Effects of In Utero PFOS Exposure on Epigenetics and Metabolism in Mouse Fetal Livers

Prenatal exposure to perfluorooctanesulfonate (PFOS) increases fetus' metabolic risk; however, the investigation of the underlying mechanism is limited. In this study, pregnant mice in the gestational days (GD, 4.5-17.5) were exposed to PFOS (0.3 and 3 μg/g of body weight). At GD 17.5, PFOS perturbed maternal lipid metabolism and upregulated metabolism-regulating hepatokines (Angptl4, Angptl8, and Selenop). Mass-spectrometry imaging and whole-genome bisulfite sequencing revealed, respectively, selective PFOS localization and deregulation of gene methylation in fetal livers, involved in inflammation, glucose, and fatty acid metabolism. PCR and Western blot analysis of lipid-laden fetal livers showed activation of AMPK signaling, accompanied by significant increases in the expression of glucose transporters (Glut2/4), hexose-phosphate sensors (Retsat and ChREBP), and the key glycolytic enzyme, pyruvate kinase (Pk) for glucose catabolism. Additionally, PFOS modulated the expression levels of PPARα and PPARγ downstream target genes, which simultaneously stimulated fatty acid oxidation (Cyp4a14, Acot, and Acox) and lipogenesis (Srebp1c, Acaca, and Fasn). Using human normal hepatocyte (MIHA) cells, the underlying mechanism of PFOS-elicited nuclear translocation of ChREBP, associated with a fatty acid synthesizing pathway, was revealed. Our finding implies that in utero PFOS exposure altered the epigenetic landscape associated with dysregulation of fetal liver metabolism, predisposing postnatal susceptibility to metabolic challenges.

LILRB2/PirB mediates macrophage recruitment in fibrogenesis of nonalcoholic steatohepatitis

Inhibition of immunocyte infiltration and activation has been suggested to effectively ameliorate nonalcoholic steatohepatitis (NASH). Paired immunoglobulin-like receptor B (PirB) and its human ortholog receptor, leukocyte immunoglobulin-like receptor B (LILRB2), are immune-inhibitory receptors. However, their role in NASH pathogenesis is still unclear. Here, we demonstrate that PirB/LILRB2 regulates the migration of macrophages during NASH by binding with its ligand angiopoietin-like protein 8 (ANGPTL8). Hepatocyte-specific ANGPTL8 knockout reduces MDM infiltration and resolves lipid accumulation and fibrosis progression in the livers of NASH mice. In addition, PirB^-/- bone marrow (BM) chimeras abrogate ANGPTL8-induced MDM migration to the liver. And yet, PirB ectodomain protein could ameliorate NASH by sequestering ANGPTL8. Furthermore, LILRB2-ANGPTL8 binding-promoted MDM migration and inflammatory activation are also observed in human peripheral blood monocytes. Taken together, our findings reveal the role of PirB/LILRB2 in NASH pathogenesis and identify PirB/LILRB2-ANGPTL8 signaling as a potential target for the management or treatment of NASH.

Dual role of ANGPTL4 in inflammation

BACKGROUND

Angiopoietin-like 4 (ANGPTL4) belongs to the angiopoietin-like protein family and mediates the inhibition of lipoprotein lipase activity. Emerging evidence suggests that ANGPTL4 has pleiotropic functions with anti- and pro-inflammatory properties.

METHODS

A thorough search on PubMed related to ANGPTL4 and inflammation was performed.

RESULTS

Genetic inactivation of ANGPTL4 can significantly reduce the risk of developing coronary artery disease and diabetes. However, antibodies against ANGPTL4 result in several undesirable effects in mice or monkeys, such as lymphadenopathy and ascites. Based on the research progress on ANGPTL4, we systematically discussed the dual role of ANGPTL4 in inflammation and inflammatory diseases (lung injury, pancreatitis, heart diseases, gastrointestinal diseases, skin diseases, metabolism, periodontitis, and osteolytic diseases). This may be attributed to several factors, including post-translational modification, cleavage and oligomerization, and subcellular localization.

CONCLUSION

Understanding the potential underlying mechanisms of ANGPTL4 in inflammation in different tissues and diseases will aid in drug discovery and treatment development.

Association Between Plasma Levels of ANGPTL3, 4, 8 and the Most Common Additional Cardiovascular Risk Factors in Patients with Hypertension

Background

ANGPTL3, 4 and 8 have been reported to be involved in the regulation of lipid and glucose metabolism. The aim of this study was to investigate the expression of ANGPTL3, 4, 8 in hypertensive patients with or without overweight/obesity, T2D, and hyperlipidemia, and the possible association between their expression and the status of the aforementioned comorbidities.

Methods

Plasma levels of ANGPTL3, 4, and 8 in 87 hospitalized patients with hypertension were measured using ELISA kits. Associations between circulating ANGPTLs levels and the most common additional cardiovascular risk factors were assessed using multivariate linear regression analyses. Pearson's correlation analysis was used to examine the association between ANGPTLs and clinical parameters.

Results

In the context of hypertension, (1) although not statistically significant, circulating ANGPTL3 levels were higher in the overweight/obese group than in the normal weight group; (2) circulating levels of ANGPTL3 and ANGPTL8 were significantly lower in patients with T2D than in non-diabetic patients; (3) circulating ANGPTL3 levels were significantly higher in the hyperlipidemic group than in the non-hyperlipidemic group. ANGPTL3 was associated with T2D and hyperlipidemia status, whereas ANGPTL8 was independently associated with T2D status. In addition, circulating ANGPTL3 levels were positively correlated with TC, TG, LDL-C, HCY, and ANGPTL8, and circulating ANGPTL4 levels were positively correlated with UACR and BNP.

Conclusion

Changes in circulating ANGPTL3 and ANGPTL8 levels have been observed in hypertensive patients with the most common additional cardiovascular risk factors, suggesting a role in the common comorbidities of hypertension and cardiovascular disease. Hypertensive patients with overweight/obesity or hyperlipidemia may benefit from therapies targeting ANGPTL3.

Effects of biomechanical and biochemical stimuli on angio- and vasculogenesis in a complex microvasculature-on-chip

The endothelium of blood vessels is a vital organ that reacts differently to subtle changes in stiffness and mechanical forces exerted on its environment (extracellular matrix (ECM)). Upon alteration of these biomechanical cues, endothelial cells initiate signaling pathways that govern vascular remodeling. The emerging organs-on-chip technologies allow the mimicking of complex microvasculature networks, identifying the combined or singular effects of these biomechanical or biochemical stimuli. Here, we present a microvasculature-on-chip model to investigate the singular effect of ECM stiffness and mechanical cyclic stretch on vascular development. Following two different approaches for vascular growth, the effect of ECM stiffness on sprouting angiogenesis and the effect of cyclic stretch on endothelial vasculogenesis are studied. Our results indicate that ECM hydrogel stiffness controls the size of the patterned vasculature and the density of sprouting angiogenesis. RNA sequencing shows that the cellular response to stretching is characterized by the upregulation of certain genes such as ANGPTL4+5, PDE1A, and PLEC.

The ANGPTL3-4-8 Axis in Normal Gestation and in Gestational Diabetes, and Its Potential Involvement in Fetal Growth

Dyslipidemia in gestational diabetes has been associated with worse perinatal outcomes. The ANGPTL3-4-8 axis regulates lipid metabolism, especially in the transition from fasting to feeding. In this study, we evaluated the response of ANGPTL3, 4, and 8 after the intake of a mixed meal in women with normal glucose tolerance and gestational diabetes, and we assessed their gene expressions in different placental locations. Regarding the circulating levels of ANGPTL3, 4, and 8, we observed an absence of ANGPTL4 response after the intake of the meal in the GDM group compared to its presence in the control group. At the placental level, we observed a glucose tolerance-dependent expression pattern of ANGPTL3 between the two placental sides. When we compared the GDM pregnancies with the control pregnancies, a downregulation of the maternal side ANGPTL3 expression was observed. This suggests a dysregulation of the ANGPTL3-4-8 axis in GDM, both at the circulating level after ingestion and at the level of placental expression. Furthermore, we discerned that the expressions of ANGPTL3, 4, and 8 were related to birth weight and placental weight in the GDM group, but not in the control group, which suggests that they may play a role in regulating the transplacental passage of nutrients.

Pregnancy Toxemia in Ewes: A Review of Molecular Metabolic Mechanisms and Management Strategies

Pregnancy toxemia is a nutritional metabolic disease during late gestation in small ruminants. The condition is characterized by disorders in carbohydrate and fat metabolism. Obese and multiparous ewes are particularly susceptible to pregnancy toxemia, which may lead to maternal death, abortion, or premature birth. Highly productive multiparous meat ewes are major breeding animals, which has led to an increased incidence of the disease. However, the pathogenesis of pregnancy toxemia remains unclear and adequate disease prevention and treatment strategies are absent. Investigating the pathogenesis of pregnancy toxemia, especially the metabolic pathways of hepatic lipids, is key to an improved understanding of the condition. This review provides a snapshot of the genes that are associated with lipid metabolism in the ovine liver, including genes involved in fatty acid oxidation, acetyl coenzyme metabolism, and triglyceride synthesis; describes the interrelationships between these genes; and summarizes the diagnosis, prevention, and treatment of pregnancy toxemia.

Biological Actions, Implications, and Cautions of Statins Therapy in COVID-19

The Coronavirus Disease 2019 (COVID-19) showed worse prognosis and higher mortality in individuals with obesity. Dyslipidemia is a major link between obesity and COVID-19 severity. Statins as the most common lipid regulating drugs have shown favorable effects in various pathophysiological states. Importantly, accumulating observational studies have suggested that statin use is associated with reduced risk of progressing to severe illness and in-hospital death in COVID-19 patients. Possible explanations underlie these protective impacts include their abilities of reducing cholesterol, suppressing viral entry and replication, anti-inflammation and immunomodulatory effects, as well as anti-thrombosis and anti-oxidative properties. Despite these benefits, statin therapies have side effects that should be considered, such as elevated creatinine kinase, liver enzyme and serum glucose levels, which are already elevated in severe COVID-19. Concerns are also raised whether statins interfere with the efficacy of COVID-19 vaccines. Randomized controlled trials are being conducted worldwide to confirm the values of statin use for COVID-19 treatment. Generally, the results suggest no necessity to discontinue statin use, and no evidence suggesting interference between statins and COVID-19 vaccines. However, concomitant administration of statins and COVID-19 antiviral drug Paxlovid may increase statin exposure and the risk of adverse effects, because most statins are metabolized mainly through CYP3A4 which is potently inhibited by ritonavir, a major component of Paxlovid. Therefore, more clinical/preclinical studies are still warranted to understand the benefits, harms and mechanisms of statin use in the context of COVID-19.

Cerebrospinal Fluid in Classical Trigeminal Neuralgia: An Exploratory Study on Candidate Biomarkers

Trigeminal neuralgia (TN) is a severe type of facial pain. A neurovascular conflict between cranial nerve V and a nearby vessel is the main pathophysiological mechanism, but additional factors are likely necessary to elicit TN. In this study, the primary aim was to explore differences in protein expression in the cerebrospinal fluid (CSF) of TN patients in relation to controls. Methods: Sixteen TN patients treated with microvascular decompression and 16 control patients undergoing spinal anesthesia for urological conditions were included. Lumbar CSF was collected preoperatively for the TN patients and before spinal anesthesia for the controls. A multiplexed proximity extension analysis of 91 CSF proteins was conducted using Proseek Multiplex Development 96, including biomarkers of cell communication, cell death, neurogenesis, and inflammation Results: The TN patients and the controls were of similar age, sex, and burden of co-morbidities. The TN patients exhibited higher concentrations of Clec11a, LGMN, MFG-E8, and ANGPTL-4 in CSF than the controls (q < 0.05). Conclusions: TN patients exhibited increased CSF biomarkers indicative of peripheral demyelinating injury (Clec11a), immune tolerance and destruction of myelin (LGMN), neuronal cell death (MFG-E8), and disturbances in myelin clearance (ANGPTL-8). Our findings are hypothesis-generating for candidate biomarkers and pathophysiological processes in classical TN.

ANGPTL8/Betatrophin Improves Glucose Tolerance in Older Mice and Metabolomic Analysis Reveals Its Role in Insulin Resistance in HepG2 Cells

BACKGROUND

Insulin resistance is a determining factor in the pathophysiology of type 2 diabetes mellitus (T2DM). Angiopoietin-like protein 8 (ANGPTL8, also known as betatrophin), associated with glucose homeostasis and lipid metabolism, has attracted attention. But its mechanism in glucose metabolism remains unclear. This study aimed to explore the effect of ANGPTL8/betatrophin on glucose tolerance in Kunming (KM) mice of different ages and metabolic profiles in insulin-resistant HepG2 cells. Our study may provide a new perspective of ANGPTL8/betatrophin in insulin resistance from the metabolic changes.

METHODS

Oral glucose tolerance test was performed in KM mice of different ages. Insulin concentration was measured by using a quantitative enzyme-linked immunosorbent assay (ELISA). ANGPTL8/betatrophin knockouts in HepG2 cells were established with clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) protein 9 (CRISPR/Cas9) system. Cell counting kit-8 (CCK-8) assay was used to determine cell viability after gene knockout. The effect of ANGPTL8/betatrophin on the metabolomic changes was evaluated in high insulin-induced insulin-resistant HepG2 cells by an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method.

RESULTS

ANGPTL8/betatrophin improved glucose tolerance in older mice not by altering the concentration of insulin. Cell growth was affected in ANGPTL8/betatrophin knockout HepG2. Based on UPLC-MS/MS, compared with wild type insulin-resistant HepG2 cells, we identified 83 differential metabolites in ANGPTL8/betatrophin knockout HepG2 cells after high insulin induction. Among the 14 differential up-regulated metabolites, D-mannose had the highest fold change. In insulin-resistant HepG2 cells, ANGPTL8/betatrophin knockout exerted an effect on the amino acid metabolism, carbohydrate metabolism, metabolism of cofactors and vitamins, lipid metabolism, nucleotide metabolism, and genetic information processing pathway.

CONCLUSION

This study identified the effect of ANGPTL8/betatrophin on glucose tolerance in mice of different ages and metabolic profiles in insulin-resistant HepG2 cells. These findings may contribute to a new understanding of its role in glucose metabolism in the context of insulin resistance.