TLR4/AP-1-Targeted Anti-Inflammatory Intervention Attenuates Insulin Sensitivity and Liver Steatosis

Mechanisms and Therapeutic Strategies for MAFLD Targeting TLR4 Signaling Pathways

BACKGROUND

Metabolic-associated fatty liver disease (MAFLD) is one of the most common chronic liver diseases. The underlying pathophysiological mechanisms are intricate and involve various factors. Unfortunately, there is currently a lack of available effective treatment options. Toll-like receptors (TLRs) are a group of pattern-recognition receptors that are responsible for activating the innate immune system. Research has demonstrated that TLR4 plays a pivotal role in the progression of MAFLD by facilitating the pathophysiological mechanisms.

SUMMARY

Lipid peroxidation, pro-inflammatory factors, insulin resistance (IR), and dysbiosis of intestinal microbiota are considered as the pathogenic mechanisms of MAFLD. This review summarizes the impact of TLR4 signaling pathways on the progression of MAFLD, specifically in relation to lipid metabolic disorders, IR, oxidative stress, and gut microbiota disorders. Additionally, we emphasize the potential therapeutic approaches for MAFLD that target TLR4 signaling pathways, including the use of plant extracts, traditional Chinese medicines, probiotics, pharmaceuticals such as peroxisome proliferator-activated receptor antagonists and farnesol X agonists, and lifestyle modifications such as dietary changes and exercise also considered. Furthermore, TLR4 signaling pathways have also been linked to the lean MAFLD.

KEY MESSAGES

TLR4 plays a crucial role in MAFLD by triggering IR, buildup of lipids, imbalance in gut microbiota, oxidative stress, and initiation of immune responses. The mitigation of MAFLD can be accomplished by suppressing the TLR4 signaling pathway. In the future, it could potentially emerge as a therapeutic target for the condition.

Rotundic acid improves nonalcoholic steatohepatitis in mice by regulating glycolysis and the TLR4/AP1 signaling pathway

BACKGROUND

Steatosis and inflammation are the hallmarks of nonalcoholic steatohepatitis (NASH). Rotundic acid (RA) is among the key triterpenes of Ilicis Rotundae Cortex and has exhibited multipronged effects in terms of lowering the lipid content and alleviating inflammation. The study objective is to systematically evaluate the potential mechanisms through which RA affects the development and progression of NASH.

METHODS

Transcriptomic and proteomic analyses of primary hepatocytes isolated from the control, high-fat diet-induced NASH, and RA treatment groups were performed through Gene Ontology analysis and pathway enrichment. Hub genes were identified through network analysis. Integrative analysis revealed key RA-regulated pathways, which were verified by gene and protein expression studies and cell assays.

RESULTS

Hub genes were identified and enriched in the Toll-like receptor 4 (TLR4)/activator protein-1 (AP1) signaling pathway and glycolysis pathway. RA reversed glycolysis and attenuated the TLR4/AP1 pathway, thereby reducing lipid accumulation and inflammation. Additionally, lactate release in L-02 cells increased with NaAsO2-treated and significantly decreased with RA treatment, thus revealing that RA had a major impact on glycolysis.

CONCLUSIONS

RA is effective in lowering the lipid content and reducing inflammation in mice with NASH by ameliorating glycolysis and TLR4/AP1 pathways, which contributes to the existing knowledge and potentially sheds light on the development of therapeutic interventions for patients with NASH.

Unraveling the Mechanism of Immunity and Inflammation Related to Molecular Signatures Crosstalk Among Obesity, T2D, and AD: Insights From Bioinformatics Approaches

Individuals with type 2 diabetes (T2D) and obesity have a higher risk of developing Alzheimer disease (AD), and increasing evidence indicates a link between impaired immune signaling pathways and the development of AD. However, the shared cellular mechanisms and molecular signatures among these 3 diseases remain unknown. The purpose of this study was to uncover similar molecular markers and pathways involved in obesity, T2D, and AD using bioinformatics and a network biology approach. First, we investigated the 3 RNA sequencing (RNA-seq) gene expression data sets and determined 224 commonly shared differentially expressed genes (DEGs) from obesity, T2D, and AD diseases. Gene ontology and pathway enrichment analyses revealed that mutual DEGs were mainly enriched with immune and inflammatory signaling pathways. In addition, we constructed a protein-protein interactions network for finding hub genes, which have not previously been identified as playing a critical role in these 3 diseases. Furthermore, the transcriptional factors and protein kinases regulating commonly shared DEGs among obesity, T2D, and AD were also identified. Finally, we suggested potential drug candidates as possible therapeutic interventions for 3 diseases. The results of this bioinformatics analysis provided a new understanding of the potential links between obesity, T2D, and AD pathologies.

Immune system modulation in aging: Molecular mechanisms and therapeutic targets

The function of the immune system declines during aging, compromising its response against pathogens, a phenomenon termed as "immunosenescence." Alterations of the immune system undergone by aged individuals include thymic involution, defective memory T cells, impaired activation of naïve T cells, and weak memory response. Age-linked alterations of the innate immunity comprise perturbed chemotactic, phagocytic, and natural killing functions, as well as impaired antigen presentation. Overall, these alterations result in chronic low-grade inflammation (inflammaging) that negatively impacts health of elderly people. In this review, we address the most relevant molecules and mechanisms that regulate the relationship between immunosenescence and inflammaging and provide an updated description of the therapeutic strategies aimed to improve immunity in aged individuals.

Vitamin D and Swimming Exercise Prevent Obesity in Rats under a High-Fat Diet via Targeting FATP4 and TLR4 in the Liver and Adipose Tissue

The prevalence of obesity has risen in the last decades, and it has caused massive health burdens on people's health, especially metabolic and cardiovascular issues. The risk of vitamin D insufficiency is increased by obesity, because adipose tissue alters both the requirements for and bioavailability of vitamin D. Exercise training is acknowledged as having a significant and long-term influence on body weight control; the favorable impact of exercise on obesity and obesity-related co-morbidities has been demonstrated via various mechanisms. The current work illustrated the effects of vitamin D supplementation and exercise on obesity induced by a high-fat diet (HFD) and hepatic steatosis in rats and explored how fatty acid transport protein-4 (FATP4) and Toll-like receptor-4 antibodies (TLR4) might be contributing factors to obesity and related hepatic steatosis. Thirty male albino rats were divided into five groups: group 1 was fed a normal-fat diet, group 2 was fed an HFD, group 3 was fed an HFD and given vitamin D supplementation, group 4 was fed an HFD and kept on exercise, and group 5 was fed an HFD, given vitamin D, and kept on exercise. The serum lipid profile adipokines, interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) were analyzed, and the pathological changes in adipose and liver tissues were examined. In addition, the messenger-ribonucleic acid (mRNA) expression of FATP4 and immunohistochemical expression of TLR4 in adipose and liver tissues were evaluated. Vitamin D supplementation and exercise improved HFD-induced weight gain and attenuated hepatic steatosis, along with improving the serum lipid profile, degree of inflammation, and serum adipokine levels. The expression of FATP4 and TLR4 in both adipose tissue and the liver was downregulated; it was noteworthy that the group that received vitamin D and was kept on exercise showed also improvement in the histopathological picture of this group. According to the findings of this research, the protective effect of vitamin D and exercise against obesity and HFD-induced hepatic steatosis is associated with the downregulation of FATP4 and TLR4, as well as a reduction in inflammation.

Catch-up fat in male adults induces low testosterone and consequently promotes metabolic abnormalities and cognitive impairment

BACKGROUND

Catch-up fat in adult (CUFA) caused by rapid nutrition promotion after undernutrition plays an important role in the epidemic of insulin resistance-related diseases in developing societies. Insulin resistance is considered to be closely associated with reduced testosterone levels and cognitive function. However, the effects of CUFA on testosterone levels and cognitive function are unclear in males.

OBJECTIVES

To investigate the changes of testosterone levels and cognitive function in CUFA in male humans and rats, and explore their probable relationship and mechanisms in rats.

MATERIALS AND METHODS

The blood testosterone levels, fasting glucose, and blood insulin (FINS) were measured in subpopulation 1 (27 CUFA individuals, 61 controls without CUFA) aged 40-50 years to show the characteristics of sex hormone levels and the metabolic status in CUFA men. Cognitive Flexibility Inventory was conducted in subpopulation 2 (54 CUFA individuals, 214 controls) over 20 years to investigate the associations between sex hormone levels, cognitive function, and CUFA. Male rats (n = 27) were randomly allocated to NC group (normal chow controls), RN group (CUFA, refeeding after caloric restriction), and RT group (RN with testosterone intramuscular injected while refeeding). The blood testosterone levels, intraperitoneal insulin tolerance test (IPITT), and FINS were measured, and the attentional set-shifting task test (ASST) for the assessment of cognitive function was performed in these animals. Insulin signaling pathway, N-methyl-d-aspartate receptors subtype 2A (NR2A) and 2B (NR2B) expression levels were determined in the rat cerebral cortex.

RESULTS

The total testosterone levels decreased (medium [IQRs], 13.43[9.87-18.96] vs 15.58[13.37-24.96], P = 0.036), and HOMA-IR (Homeostatic Model Assessment for Insulin Resistance) elevated (1.61[1.08-2.33] vs 1.24[0.87-1.87], P = 0.037) in CUFA men in subpopulation 1. Additionally, cognitive impairment was observed in CUFA men in subpopulation 2. Moreover, our results indicated decreases in total and free testosterone levels, elevations in visceral lipid accumulation, FINS, HOMA-IR, blood glucose and the area under the curve (AUC) after IPITT, increases in the number of trials required to achieve the criterion of the first reversal of discrimination (R1) in ASST, and downregulation of IRS-1 mRNA expression, AKT phosphorylation, and the NR2A and NR2B expression in brain tissue in male CUFA rats. Notably, testosterone supplementation improved visceral lipid accumulation and insulin resistance-related metabolic disorders, cognitive dysfunction, decreases in IRS-1 mRNA expression, Akt phosphorylation, and NR2A and NR2B expression in brain tissue in male CUFA rodents.

DISCUSSION AND CONCLUSION

CUFA was characterized by reduced testosterone levels, metabolic abnormalities, and cognitive dysfunction in males, and testosterone supplementation attenuated these changes, as well as the alteration in insulin signaling and NR2A and NR2B expression in male CUFA rodents. Herein, we tentatively put forward that CUFA in males induces low testosterone, consequently promoting metabolic abnormalities and cognitive impairment probably mediated by defects in insulin signaling and NR2A, NR2B pathway in brain tissue. This article is protected by copyright. All rights reserved.

Saturated fat ingestion stimulates proatherogenic inflammation in polycystic ovary syndrome

Inflammation and dyslipidemia are often present in polycystic ovary syndrome (PCOS). We determined the effect of saturated fat ingestion on circulating heat shock protein-70 (HSP-70) and mononuclear cell (MNC) toll-like receptor-2 (TLR2) gene expression, activator protein-1 (AP-1) activation, and matrix matalloproteinase-2 (MMP-2) protein in women with PCOS. Twenty reproductive-age women with PCOS (10 lean, 10 with obesity) and 20 ovulatory controls (10 lean, 10 with obesity) participated in the study. HSP-70 was measured in serum and TLR2 mRNA and protein, AP-1 activation, and MMP-2 protein were quantified in MNC from blood drawn while fasting and 2, 3, and 5 h after saturated fat ingestion. Insulin sensitivity was derived from an oral glucose tolerance test (IS_OGTT). Androgen secretion was assessed from blood drawn while fasting and 24, 48, and 72 h after human chorionic gonadotropin (HCG) administration. In response to saturated fat ingestion, serum HSP-70, TLR2 gene expression, activated AP-1, and MMP-2 protein were greater in lean women with PCOS compared with lean controls and in women with PCOS and obesity compared with controls with obesity. Both PCOS groups exhibited lower IS_OGTT and greater HCG-stimulated androgen secretion compared with control subjects of their respective weight classes. Lipid-stimulated proatherogenic inflammation marker responses were negatively correlated with IS_OGTT and positively correlated with abdominal adiposity and HCG-stimulated androgen secretion. In PCOS, saturated fat ingestion stimulates proatherogenic inflammation independent of obesity. This effect is greater when PCOS is combined with obesity compared with obesity alone. Abdominal adiposity and hyperandrogenism may perpetuate proatherogenic inflammation.NEW & NOTEWORTHY This paper demonstrates that in polycystic ovary syndrome (PCOS), ingestion of saturated fat triggers a molecular pathway of inflammation known to drive atherogenesis. This effect is independent of obesity as it occurs in lean women with PCOS and not in lean ovulatory control subjects. Furthermore, the combined effects of PCOS and obesity are greater compared with obesity alone.

Immune-Enhancing Effects of a Novel Glucan from Purple Sweet Potato Ipomoea batatas (L.) Lam on RAW264.7 Macrophage Cells via TLR2- and TLR4-Mediated Pathways

PSPP-1 was obtained from purple sweet potato, and the effects of PSPP-1 on the immune modulation on macrophage cells were investigated for the first time. PSPP-1 promoted RAW264.7 proliferation and increased the total cell percentage in DNA synthesis and mitosis phases, and the cell morphology changed in volume and appearance. Additionally, the RAW264.7 immune functions of phagocytic activity and nitric oxide, reactive oxygen species, and cytokine production were improved by PSPP-1. The western blot experiment showed that PSPP-1 could activate toll-like receptor 2 and toll-like receptor 4-mediated pathways, and the expressions of proteins in MyD88-dependent, mitogen-activated protein kinase (MAPK)-signaling, NF-κB-signaling, AP-1 signaling, and TRIF-dependent pathways were improved markedly. Molecular docking and Biolayer Interferometry study further indicated that PSPP-1 could recognize and bind TLR2 and TLR4 by targeting the binding sites with a strong affinity. It suggested that PSPP-1 could enhance immunity via TLR2- and TLR4-mediated pathways, and it could be explored as an immunomodulatory agent.

Long Chain Fatty Acids as Modulators of Immune Cells Function: Contribution of FFA1 and FFA4 Receptors

Long-chain fatty acids are molecules that act as metabolic intermediates and constituents of membranes; however, their novel role as signaling molecules in immune function has also been demonstrated. The presence of free fatty acid (FFA) receptors on immune cells has contributed to the understanding of this new role of long-chain fatty acids (LCFAs) in immune function, showing their role as anti-inflammatory or pro-inflammatory molecules and elucidating their intracellular mechanisms. The FFA1 and FFA4 receptors, also known as GPR40 and GPR120, respectively, have been described in macrophages and neutrophils, two key cells mediating innate immune response. Ligands of the FFA1 and FFA4 receptors induce the release of a myriad of cytokines through well-defined intracellular signaling pathways. In this review, we discuss the cellular responses and intracellular mechanisms activated by LCFAs, such as oleic acid, linoleic acid, palmitic acid, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), in T-cells, macrophages, and neutrophils, as well as the role of the FFA1 and FFA4 receptors in immune cells.

Andrographolide, an Anti-Inflammatory Multitarget Drug: All Roads Lead to Cellular Metabolism

Andrographolide is a labdane diterpene and the main active ingredient isolated from the herb Andrographis paniculata. Andrographolide possesses diverse biological effects including anti-inflammatory, antioxidant, and antineoplastic properties. Clinical studies have demonstrated that andrographolide could be useful in therapy for a wide range of diseases such as osteoarthritis, upper respiratory diseases, and multiple sclerosis. Several targets are described for andrographolide, including the interference of transcription factors NF-κB, AP-1, and HIF-1 and signaling pathways such as PI3K/Akt, MAPK, and JAK/STAT. In addition, an increase in the Nrf2 (nuclear factor erythroid 2–related factor 2) signaling pathway also supports its antioxidant and anti-inflammatory properties. However, this scenario could be more complex since recent evidence suggests that andrographolide targets can modulate glucose metabolism. The metabolic effect of andrographolide might be the key to explaining the diverse therapeutic effects described in preclinical and clinical studies. This review discusses some of the most recent evidence about the anti-inflammatory and metabolic effects of andrographolide.