Introduction

The molecular mechanisms underlying lipid metabolism in metabolic dysfunction-associated steatotic liver disease (MASLD) regulated by the gut-liver axis remain poorly elucidated. Previous studies have shown that the important effector protein Mas in the RAS non-classical pathway ACE2/Ang(1-7)/Mas axis has multiple target effects such as regulating glucose metabolism and lipid metabolism, but the specific mechanism is unknown.^1-5 This study investigated the role of Mas by examining serum bile acid (BA) profile and fecal microbiota composition.

Aims & Methods

Serum and feces samples from MASLD patients and mouse models were analyzed using metabolomics and 16S rDNA. Mas was in vivo evaluated using mice with systemic (Mas1^-/-) and specific deletion of Mas1 in myeloid cells (LysM^creMas1^f/f), intestinal epithelial cells (Vil1^creMas1^f/f), hepatocytes (Alb^creMas1^f/f), and endothelial cells (Cdh5^creMas1^f/f), after being fed with a methionine/choline-deficient(MCD) diet or high fat diet. Mouse bone marrowderived macrophages and intestinal organoids were prepared for the in vitro experiments.

Results

The relative abundance of serum BA and fecal microbiota showed similar changes in both patients and mouse models with MASLD. In Mas1^-/--MCD mice, the reduced chenodeoxycholic acid (CDCA) levels observed in patients with MASLD were effectively restored, along with an notable increase in beneficial gut microbiota like Akkermansia and Bifidobacterium. These changes were also associated with a significantly improved disease phenotype and enhanced intestinal barrier function. The enriched CDCA inhibits lipid accumulation by activating hepatic and intestinal farnesoid X receptor (FXR) signaling. At the same time, we determined that myeloid cells are the primary effector cells of Mas function through cell-specific knockout of Mas1 in myeloid cells. Considering the metabolic reprogramming of colonic epithelial cells facilitated by polyamines derived from macrophages,⁶ our findings highlight the crucial role of Mas in augmenting monocyte polyamine synthesis and promoting intestinal cell proliferation through the Mas-pS6-Arg1 pathway.

Conclusion

Myeloid-Mas deficiency improves the mouse MASLD phenotype by promoting polyamines synthesis, enhancing gut barrier function, increasing
beneficial gut microbiota, and enriching CDCA to activate hepatic and intestinal FXR signaling, thereby reducing lipid accumulation.

References

1. Santos RAS, Sampaio WO, Alzamora AC, et al. The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7). Physiol Rev 2018;98(1):505-53.
2. Hammer A, Yang G, Friedrich J, et al. Role of the receptor Mas in macrophage-mediated inflammation in vivo. Proc Natl Acad Sci U S A 2016;113(49):14109-14.
3. Feltenberger JD, Andrade JM, Paraíso A, et al. Oral formulation of angiotensin-(1-7) improves lipid metabolism and prevents high-fat diet-induced hepatic steatosis and inflammation in mice. Hypertension 2013;62(2):324-30.
4. Chen S, Lu Z, Jia H, et al. Hepatocyte-specific Mas activation enhances lipophagy and fatty acid oxidation to protect against acetaminophen-induced hepatotoxicity in mice. J Hepatol 2023;78(3):543-57.
5. Kong Y, Zhao X, Qiu M, et al. Tubular Mas receptor mediates lipid-induced kidney injury. Cell Death Dis 2021;12(1):110.
6. Fritsch SD, Sukhbaatar N, Gonzales K, et al. Metabolic support by macrophages sustains colonic epithelial homeostasis. Cell Metabolism 2023;35(11):1931-43.e8.

Introduction

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as nonalcoholic fatty liver disease (NAFLD), has emerged as one of the leading causes of chronic liver disease worldwide. MASLD is closely associated with components of metabolic syndrome, including obesity, insulin resistance, dyslipidemia, and hypertension. The role of gut microbiota dysbiosis in MASLD pathogenesis is increasingly recognized, with microbial imbalance contributing to systemic inflammation and metabolic disturbances.

Aims & Methods

The aim was to determine gut microbiota composition in patients with MASLD and evaluate the impact of probiotic therapy on metabolic, inflammatory, and lipid parameters. The study included 152 patients diagnosed with MASLD. Diagnosis was based on clinical, laboratory, and imaging findings, including ultrasound and steatometry, alongside cardiometabolic risk factors. Gut microbiota composition was evaluated using quantitative real-time PCR (qRT-PCR). Patients received a combined probiotic therapy containing Saccharomyces boulardii CNCM I-745, Lactobacillus acidophilus (LA-5), and Bifidobacterium lactis (BB-12). Changes in biochemical markers, lipid profiles, inflammatory parameters, and gut microbiota composition were assessed before and after therapy.

Results

At baseline, patients with MASLD demonstrated gut microbiota dysbiosis, characterized by an increased proportion of Firmicutes (50.3%) and Actinobacteria (15.34%), and an elevated Firmicutes/Bacteroides (F/B) index (5.02). Following probiotic therapy, significant improvements were observed: the proportions of Firmicutes and Actinobacteria decreased, the F/B index was reduced, and levels of ALT, AST, high-sensitivity C-reactive protein (hsCRP), total cholesterol, and triglycerides declined, while HDL-C levels increased. Positive correlations were identified between elevated Firmicutes and Actinobacteria and markers of cardiometabolic risk, such as hsCRP and triglycerides.

Conclusion

Gut microbiota dysbiosis is strongly associated with metabolic and inflammatory disturbances in MASLD. Combined probiotic therapy effectively corrected microbial imbalance, reduced systemic inflammation, and improved metabolic and lipid parameters. These findings support the role of microbiota-targeted interventions as an adjunctive approach in the comprehensive management of MASLD.

Introduction

Mas is a newly discovered G protein-coupled receptor that plays a critical role in inflammatory responses. The gut-liver axis regulated neutrophilic inflammation is crucial in acute liver failure (ALF); however, the underlying mechanisms remain poorly understood.

Aims & Methods

The aim of this study is to investigate Mas signaling and neutrophilic inflammation in ALF, and to elucidate its underlying mechanisms. The 8-10 week-old male Mas1^-/-, Vil1^creMas1^f/f, and wild-type control mice were subjected to intraperitoneal challenge with D-galactosamine/lipopolysacchari de(D/L) for in vivo analysis of the gut-liver axis-dependent formation of neutrophil extracellular traps (NET), utilizing pharmacological compounds and genetic tools. Age-matched mice received injections of phosphate-buffered saline as vehicle controls.

Results

The hepatic expression of Mas was significantly upregulated in ALF patients and mice models. The knockout of the Mas1 gene in both systemic and intestinal epithelial cells significantly alleviated D/L-induced NETosis and hepatotoxicity in mice. The involvement of gut microbiota in the attenuated hepatotoxicity of Mas1^-/--D/L mice was confirmed through antibiotic experiments. The co-housed experiments between Mas1^-/-and WT mice have demonstrated that Mas1^-/- may confer protection by reducing the intestinal abundance of Eubacterium sp. and inhibiting deoxycholic acid (DCA) production. This was accompanied by hepatic activation of farnesoid X receptor (FXR) signaling and suppression of downstream sphingosine-1-phosphate (S1P)-dependent NETosis. As revealed by single-cell transcriptomics, the downregulation of NETosis in Mas1^-/--D/L mice was found to be dependent on the senescence of Cldn1⁺CD177⁺ neutrophils and the activation of Raf signaling.

Conclusion

Mas1^-/- significantly protects mice from D/L-induced hepatotoxicity by suppressing the FXR/S1P/Raf-dependent NETosis, thereby suggesting Mas as a promising therapeutic target for ALF.

Introduction

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as nonalcoholic fatty liver disease (NAFLD), is a leading cause of chronic liver pathology globally and is closely associated with metabolic syndrome components, including obesity, insulin resistance, dyslipidemia, and hypertension. Recent evidence emphasizes the significant role of gut microbiota dysbiosis in MASLD pathogenesis, with specific bacterial shifts contributing to metabolic disturbances and systemic inflammation.

Aims & Methods

The aim was to evaluate the gut microbiota composition in MASLD patients and assess the impact of probiotic therapy on metabolic, inflammatory, and lipid profile parameters. The study included 152 patients diagnosed with MASLD. Gut microbiota profiling was conducted using quantitative real-time PCR (qRT-PCR), and metabolic parameters were assessed via biochemical analyses. Patients received a combined probiotic regimen containing Saccharomyces boulardii CNCM I-745, Lactobacillus acidophilus (LA-5), and Bifidobacterium lactis (BB-12) for gut microbiota correction. Changes in biochemical markers, lipid profiles, and microbiota composition were evaluated before and after therapy.

Results

At baseline, MASLD patients showed a marked imbalance in gut microbiota, characterized by increased proportions of Firmicutes (50.3%) and Actinobacteria (15.34%), along with an elevated Firmicutes/Bacteroides (F/B) ratio (5.02). Probiotic intervention significantly reduced Firmicutes and Actinobacteria percentages and lowered the F/B ratio. Biochemically, there were significant decreases in ALT, AST, alkaline phosphatase, high-sensitivity C-reactive protein (hsCRP), total cholesterol, triglycerides, and increases in HDL-C levels. Positive correlations were found between elevated Firmicutes and Actinobacteria abundance and markers of cardiometabolic risk, such as hsCRP and triglycerides.

Conclusion

Gut microbiota dysbiosis plays a crucial role in the metabolic and inflammatory disturbances associated with MASLD. Combined probiotic therapy effectively improved gut microbial composition, reduced systemic inflammation, and positively influenced lipid metabolism, supporting its role as an adjunctive treatment strategy for MASLD.

Introduction

Acetaminophen (APAP) overdose is a primary cause of drug-induced liver injury (DILI). Although the inflammatory microenvironment plays a critical role in APAP-induced liver injury (AILI), its cellular interaction network and molecular regulatory mechanisms remain incompletely elucidated. Krüppel-like factor 4 (KLF4), a zinc finger transcription factor, is known to regulate monocyte differentiation, but its functional role in the AILI inflammatory microenvironment remains unclear. This study aims to investigate the regulatory effects of myeloid KLF4 deletion on the AILI microenvironment.

Aims & Methods

By integrating multidimensional omics analysis and a myeloid-specific Klf4 knockout mouse model, we dynamically dissected microenvironmental remodeling during AILI progression. Liver samples were collected for RNA sequencing, combined with single-cell transcriptomics, flow cytometry, and molecular interaction validation to clarify the KLF4-dependent cellular subpopulation interaction network. In vivo liver imaging, histology, biochemical assays, and molecular experiments were performed to validate KLF4-dependent intercellular interactions. Primary hepatocytes and hepatocyte cell lines were used for in vitro verification.

Results

Myeloid-specific KLF4 deletion led to an increase in CXCL2⁺CXCL3⁺CD24⁺ monocytes, which activated the NF-κB signaling pathway to secrete CXCL2/CXCL3 chemokines. These chemokines bound to the CXCR2 receptor on neutrophils, driving neutrophil infiltration and neutrophil extracellular traps (NETs) formation, while amplifying the TNF-α signaling pathway. Concurrently, myeloid KLF4 knockout induced enrichment of CXCL1⁺IL17RA⁺ endothelial cells. Neutrophil-derived NETs promoted endothelial phenotypic switching toward pro-inflammatory polarization, while endothelial-derived CXCL1 further recruited neutrophils, establishing a "monocyte-neutrophil-endothelial" cellular subpopulation interaction that perpetuated microenvironmental inflammation.

Conclusion

This study reveals the molecular mechanism by which KLF4 drives inflammatory cascades in the AILI microenvironment through regulation of the myeloid-endothelial interaction network. We propose therapeutic strategies targeting NETs formation or the CXCL2/CXCL3-CXCR2 axis, providing novel targets for precise intervention in AILI.