IL-1R-IRAKM-Slc25a1 signaling axis reprograms lipogenesis in adipocytes to promote diet-induced obesity in mice

Total saponins from Panax japonicus regulated the intestinal microbiota to alleviate lipid metabolism disorders in aging mice

Total saponins from Panax japonicus (TSPJ) have many beneficial physiological activities, particularly in alleviating the damages of aging and abnormal lipid metabolism. This work used mice models to investigate if TSPJ reduced obesity and regulated metabolic functions via the intestinal microbiota, the disturbance of which has been shown to cause aging-related diseases. The results showed that TSPJ significantly reduced the weight and blood lipid level of aging mice. Further analyses showed that TSPJ significantly inhibited adipogenesis, changed the composition of the intestinal flora, and protected the integrity of the intestinal barrier. It was inferred from the accumulated experimental data that TSPJ helped to combat obesity in aging mice by regulating the intestinal microbiota and promoting microbial metabolism.

IL-1β promotes adipogenesis by directly targeting adipocyte precursors

Postprandial IL-1β surges are predominant in the white adipose tissue (WAT), but its consequences are unknown. Here, we investigate the role of IL-1β in WAT energy storage and show that adipocyte-specific deletion of IL-1 receptor 1 (IL1R1) has no metabolic consequences, whereas ubiquitous lack of IL1R1 reduces body weight, WAT mass, and adipocyte formation in mice. Among all major WAT-resident cell types, progenitors express the highest IL1R1 levels. In vitro, IL-1β potently promotes adipogenesis in murine and human adipose-derived stem cells. This effect is exclusive to early-differentiation-stage cells, in which the adipogenic transcription factors C/EBPδ and C/EBPβ are rapidly upregulated by IL-1β and enriched near important adipogenic genes. The pro-adipogenic, but not pro-inflammatory effect of IL-1β is potentiated by acute treatment and blocked by chronic exposure. Thus, we propose that transient postprandial IL-1β surges regulate WAT remodeling by promoting adipogenesis, whereas chronically elevated IL-1β levels in obesity blunts this physiological function.

Cell-cell crosstalk between fat cells and immune cells

Obesity is a metabolic disorder with pandemic-like implications, lacking viable pharmaceutical treatments currently. Thermogenic adipose tissues, including brown and beige adipose tissues, play an essential role in regulating systemic energy homeostasis and have emerged as appealing therapeutic targets for the treatment of obesity and obesity-related diseases. The function of adipocytes is subject to complex regulation by a cellular network of immune signaling pathways in response to environmental signals. However, the specific regulatory roles of immune cells in thermogenesis and relevant involving mechanisms are still not well understood. Here, we concentrate on our present knowledge of the interaction between thermogenic adipocytes and immune cells and present an overview of cellular and molecular mechanisms underlying immunometabolism in adipose tissues. We discuss cytokines, especially interleukins, which originate from widely variable sources, and their impacts on the development and function of thermogenic adipocytes. Moreover, we summarize the neuroimmune regulation in heat production and expand a new mode of intercellular communication mediated by mitochondrial transfer. The crosstalk between immune cells and adipocytes achieves adipose tissue homeostasis and systemic energy balance. A deep understanding of this intricate interaction would provide evidence for improving thermogenic efficiency by remodeling the immune microenvironment. Interventions based on these factors show a high potential to prevent adverse metabolic outcomes in patients with obesity.

Inhibition of mitochondrial citrate shuttle alleviates metabolic syndromes induced by high-fat diet

The mitochondrial citrate shuttle, which relies on the solute carrier family 25 member 1 (SLC25A1), plays a pivotal role in transporting citrate from the mitochondria to the cytoplasm. This shuttle supports glycolysis, lipid biosynthesis, and protein acetylation. Previous research has primarily focused on SLC25A1 in pathological models, particularly high-fat diet (HFD)-induced obesity. However, the impact of SLC25A1 inhibition on nutrient metabolism under HFD remains unclear. To address this gap, we used zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus) to evaluate the effects of inhibiting Slc25a1. In zebrafish, we administered Slc25a1-specific inhibitors (CTPI-2) for 4 wk, whereas Nile tilapia received intraperitoneal injections of dsRNA to knock down slc25a1b for 7 days. Inhibition of the mitochondrial citrate shuttle effectively protected zebrafish from HFD-induced obesity, hepatic steatosis, and insulin resistance. Of note, glucose tolerance was unaffected. Inhibition of Slc25a1 altered hepatic protein acetylation patterns, with decreased cytoplasmic acetylation and increased mitochondrial acetylation. Under HFD conditions, Slc25a1 inhibition promoted fatty acid oxidation and reduced hepatic triglyceride (TAG) accumulation by deacetylating carnitine palmitoyltransferase 1a (Cpt1a). In addition, Slc25a1 inhibition triggered acetylation-induced inactivation of Pdhe1α, leading to a reduction in glucose oxidative catabolism. This was accompanied by enhanced glucose uptake and storage in zebrafish livers. Furthermore, Slc25a1 inhibition under HFD conditions activated the SIRT1/PGC1α pathway, promoting mitochondrial proliferation and enhancing oxidative phosphorylation for energy production. Our findings provide new insights into the role of nonhistone protein acetylation via the mitochondrial citrate shuttle in the development of hepatic lipid deposition and hyperglycemia caused by HFD.NEW & NOTEWORTHY The mitochondrial citrate shuttle is a crucial physiological process for maintaining metabolic homeostasis. In the present study, we found that inhibition of mitochondrial citrate shuttle (Slc25a1) could alleviate metabolic syndromes induced by high-fat diet (HFD) through remodeling hepatic protein acetylation modification. Briefly, Slc25a1 inhibition reduces hepatic triglyceride deposition by deacetylating Cpt1a and reduces glucose oxidative catabolism by acetylating Pdhe1α. Our study provides new insights into the treatment of diet-induced metabolic syndromes.

Inhibiting mitochondrial citrate shuttling induces hepatic triglyceride deposition in Nile tilapia (Oreochromis niloticus) through lipid anabolic remodeling

The solute carrier family 25 member 1 (Slc25a1)-dependent mitochondrial citrate shuttle is responsible for exporting citrate from the mitochondria to the cytoplasm for supporting lipid biosynthesis and protein acetylation. Previous studies on Slc25a1 concentrated on pathological models. However, the importance of Slc25a1 in maintaining metabolic homeostasis under normal nutritional conditions remains poorly understood. Here, we investigated the mechanism of mitochondrial citrate shuttle in maintaining lipid metabolism homeostasis in male Nile tilapia (Oreochromis niloticus). To achieve the objective, we blocked the mitochondrial citrate shuttle by inhibiting Slc25a1 under normal nutritional conditions. Slc25a1 inhibition was established by feeding Nile tilapia with 250 mg/kg 1,2,3-benzenetricarboxylic acid hydrate for 6 weeks or intraperitoneal injecting them with dsRNA to knockdown slc25a1b for 7 days. The Nile tilapia with Slc25a1 inhibition exhibited an obesity-like phenotype accompanied by fat deposition, liver damage and hyperglycemia. Moreover, Slc25a1 inhibition decreased hepatic citrate-derived acetyl-CoA, but increased hepatic triglyceride levels. Furthermore, Slc25a1 inhibition replenished cytoplasmic acetyl-CoA through enhanced acetate pathway, which led to hepatic triglycerides accumulation. However, acetate-derived acetyl-CoA caused by hepatic Slc25a1 inhibition did not activate de novo lipogenesis, but rather modified protein acetylation. In addition, hepatic Slc25a1 inhibition enhanced fatty acids esterification through acetate-derived acetyl-CoA, which increased Lipin1 acetylation and its protein stability. Collectively, our results illustrate that inhibiting mitochondrial citrate shuttle triggers lipid anabolic remodeling and results in lipid accumulation, indicating the importance of mitochondrial citrate shuttle in maintaining lipid metabolism homeostasis.

Association between protein-to-energy ratio and overweight/obesity in children and adolescents in the United States: a cross-sectional study based on NHANES

Background

The dietary protein proportion may be crucial in triggering overweight and obesity among children and adolescents.

Methods

Cross-sectional data from 4,336 children and adolescents who participated in the National Health and Nutrition Survey (NHANES) between 2011 and March 2020 were analyzed. Multivariate logistic regression was used to calculate odds ratio (OR) and 95% confidence interval (CI). Restricted cubic splines assessed the nonlinear relationships between dietary protein intake and the prevalence of overweight and obesity.

Results

Adjusted logistic regression models showed that each 1% increase in dietary protein proportion was associated with a 4% higher risk of overweight and obesity (OR = 1.04, 95% CI: 1.01-1.07). A nonlinear relationship was noted in children aged 6-11 years (P < 0.05), as demonstrated by restricted cubic spline analysis. After dividing dietary protein intake into quartiles, the highest quartile had an adjusted OR of 2.07 (95% CI: 1.35, 3.16, P = 0.001) compared to the lowest, among children aged 6-11 years.

Conclusion

Dietary protein intake is positively linked to overweight and obesity in American children, irrespective of individual characteristics and total energy consumption.

Piperine alleviates nonalcoholic steatohepatitis by inhibiting NF-κB-mediated hepatocyte pyroptosis

PURPOSE

Nonalcoholic steatohepatitis (NASH) is the progressive form of nonalcoholic fatty liver disease (NAFLD), which has a high risk of cirrhosis, liver failure, and hepatocellular carcinoma. Piperine (Pip) is an extract of plants with powerful anti-inflammatory effects, however, the function of Pip in NASH remains elusive. Here, we aim to explore the role of Pip in NASH and to find the possible mechanisms.

METHODS

Methionine and choline-deficient (MCD) diets were used to induce steatohepatitis, methionine- and choline-sufficient (MCS) diets were used as the control. After Pip treatment, H&E staining, Oil Red O staining, hepatic triglyceride (TG) content and F4/80 expression were performed to analysis liver steatosis and inflammation; Masson's staining, COL1A1 and α-SMA were detected liver fibrosis. Lipopolysaccharide (LPS) -treated AML12 cells were used to as the cell model to induce pyroptosis. Then, pyroptosis-related proteins, IL-1β and LDH release were detected in vivo and in vitro. Finally, NF-κB inhibitor, BAY11-7082, was used to further demonstrate the mechanism of Pip in NASH.

RESULTS

The study found that Pip alleviated liver steatosis, inflammation, hepatocyte injury, and fibrosis in mice fed with MCD diets. Moreover, the pyroptosis markers (NLRP3, ASC, caspase-1 p20, and GSDMD), IL-1β and LDH release were decreased by Pip treatment. NF-κB activation was suppressed by Pip treatment and pyroptosis-related proteins were down regulated by BAY11-7082.

CONCLUSION

Pip ameliorates NASH progression, and the therapeutical effect was associated with inhibition of hepatocyte pyroptosis induced by NF-κB.

Bempedoic Acid Unveils Therapeutic Potential in Non-Alcoholic Fatty Liver Disease: Suppression of the Hepatic PXR-SLC13A5/ACLY Signaling Axis

The hepatic SLC13A5/SLC25A1-ATP-dependent citrate lyase (ACLY) signaling pathway, responsible for maintaining the citrate homeostasis, plays a crucial role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Bempedoic acid (BA), an ACLY inhibitor commonly used for managing hypercholesterolemia, has shown promising results in addressing hepatic steatosis. This study aimed to elucidate the intricate relationships in processes of hepatic lipogenesis among SLC13A5, SLC25A1, and ACLY and to examine the therapeutic potential of BA in NAFLD, providing insights into its underlying mechanism. In murine primary hepatocytes and HepG2 cells, the silencing or pharmacological inhibition of SLC25A1/ACLY resulted in significant upregulation of SLC13A5 transcription and activity. This increase in SLC13A5 activity subsequently led to enhanced lipogenesis, indicating a compensatory role of SLC13A5 when the SLC25A1/ACLY pathway was inhibited. However, BA effectively counteracted this upregulation, reduced lipid accumulation, and ameliorated various biomarkers of NAFLD. The disease-modifying effects of BA were further confirmed in NAFLD mice. Mechanistic investigations revealed that BA could reverse the elevated transcription levels of SLC13A5 and ACLY, and the subsequent lipogenesis induced by PXR activation in vitro and in vivo. Importantly, this effect was diminished when PXR was knocked down, suggesting the involvement of the hepatic PXR-SLC13A5/ACLY signaling axis in the mechanism of BA action. In conclusion, SLC13A5-mediated extracellular citrate influx emerges as an alternative pathway to SLC25A1/ACLY in the regulation of lipogenesis in hepatocytes, BA exhibits therapeutic potential in NAFLD by suppressing the hepatic PXR-SLC13A5/ACLY signaling axis, while PXR, a key regulator in drug metabolism may be involved in the pathogenesis of NAFLD. SIGNIFICANCE STATEMENT: This work describes that bempedoic acid, an ATP-dependent citrate lyase (ACLY) inhibitor, ameliorates hepatic lipid accumulation and various hallmarks of non-alcoholic fatty liver disease. Suppression of hepatic SLC25A1-ACLY pathway upregulates SLC13A5 transcription, which in turn activates extracellular citrate influx and the subsequent DNL. Whereas in hepatocytes or the liver tissue challenged with high energy intake, bempedoic acid reverses compensatory activation of SLC13A5 via modulating the hepatic PXR-SLC13A5/ACLY axis, thereby simultaneously downregulating SLC13A5 and ACLY.

Mutations in the Vicinity of the IRAK3 Guanylate Cyclase Center Impact Its Subcellular Localization and Ability to Modulate Inflammatory Signaling in Immortalized Cell Lines

Interleukin-1 receptor-associated kinase 3 (IRAK3) modulates the magnitude of cellular responses to ligands perceived by interleukin-1 receptors (IL-1Rs) and Toll-like receptors (TLRs), leading to decreases in pro-inflammatory cytokines and suppressed inflammation. The molecular mechanism of IRAK3's action remains unknown. IRAK3 functions as a guanylate cyclase, and its cGMP product suppresses lipopolysaccharide (LPS)-induced nuclear factor kappa-light-chain-enhancer of activated B cell (NFκB) activity. To understand the implications of this phenomenon, we expanded the structure-function analyses of IRAK3 through site-directed mutagenesis of amino acids known or predicted to impact different activities of IRAK3. We verified the capacity of the mutated IRAK3 variants to generate cGMP in vitro and revealed residues in and in the vicinity of its GC catalytic center that impact the LPS-induced NFκB activity in immortalized cell lines in the absence or presence of an exogenous membrane-permeable cGMP analog. Mutant IRAK3 variants with reduced cGMP generating capacity and differential regulation of NFκB activity influence subcellular localization of IRAK3 in HEK293T cells and fail to rescue IRAK3 function in IRAK3 knock-out THP-1 monocytes stimulated with LPS unless the cGMP analog is present. Together, our results shed new light on the mechanism by which IRAK3 and its enzymatic product control the downstream signaling, affecting inflammatory responses in immortalized cell lines.

Si-Ni-SAN ameliorates obesity through AKT/AMPK/HSL pathway-mediated lipolysis: Network pharmacology and experimental validation

ETHNOPHARMACOLOGICAL RELEVANCE

Si-Ni-San (SNS) is a famous Chinese herbal formula used in China for thousands of years. It has clinical effects on a variety of lipid metabolism disorders, but the ameliorating effects of SNS on obesity and underlying mechanisms remained poorly elucidated.

AIM OF THE STUDY

This study aims to explore the therapeutic effect and mechanism of SNS on obesity from multiple perspectives in vitro and in vivo.

MATERIALS AND METHODS

The high-fat diet (HFD)-induced obesity mouse model was established to evaluate the effect of SNS. Then network pharmacologic methods were performed to predict underlying mechanisms, and the core pathways were verified in animal and cell studies.

RESULTS

Our results demonstrated that SNS significantly reduced body weight, body fat content, white adipose tissue (WAT) expansion in obese mice, and lipid accumulation in primary mouse embryonic fibroblasts (MEFs) cells. Network pharmacologic analysis identified 66 potential therapeutic targets, and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of these genes revealed that the most important signaling pathway includes AMP-activated protein kinase (AMPK) signaling pathway, regulation of lipolysis in adipocytes, lipid and atherosclerosis. Western blot assay confirmed that SNS activated hormone-sensitive triglyceride lipase (HSL) and adipose triglyceride lipase (ATGL) activity and promoted lipolysis through AMPK signaling pathway.

CONCLUSION

The results confirmed that SNS improves lipid accumulation through AKT/AMPK/HSL axis mediated lipolysis, which opens a new option for clinical treatment of obesity and associated complications.

From Beneath the Skin to the Airway Wall: Understanding the Pathological Role of Adipose Tissue in Comorbid Asthma-Obesity

This article provides a contemporary report on the role of adipose tissue in respiratory dysfunction. Adipose tissue is distributed throughout the body, accumulating beneath the skin (subcutaneous), around organs (visceral), and importantly in the context of respiratory disease, has recently been shown to accumulate within the airway wall: "airway-associated adipose tissue." Excessive adipose tissue deposition compromises respiratory function and increases the severity of diseases such as asthma. The mechanisms of respiratory impairment are inflammatory, structural, and mechanical in nature, vary depending on the anatomical site of deposition and adipose tissue subtype, and likely contribute to different phenotypes of comorbid asthma-obesity. An understanding of adipose tissue-driven pathophysiology provides an opportunity for diagnostic advancement and patient-specific treatment. As an exemplar, the potential impact of airway-associated adipose tissue is highlighted, and how this may change the management of a patient with asthma who is also obese. © 2023 American Physiological Society. Compr Physiol 13:4321-4353, 2023.