Landscape of Intercellular Crosstalk in Healthy and NASH Liver Revealed by Single-Cell Secretome Gene Analysis

GPNMB regulates the differentiation and transformation of monocyte-derived macrophages during MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) is an increasingly concerning global health issue characterized by pronounced hepatic steatosis and liver fibrosis. Hepatic monocyte-derived macrophages (MDMs) are crucial in the pathogenesis of liver fibrosis under MASLD. Nevertheless, the precise functions of MDMs and the underlying mechanisms governing their differentiation remain inadequately elucidated. In this study, we revealed an orchestrator of this process: Glycoprotein Non-Metastatic Melanoma Protein B (GPNMB), one of the characteristic genes of MDMs. Notably, myeloid-specific Gpnmb-knockout contributed to the retention of resident Kupffer cells (KCs) and rerouted monocyte differentiation towards a monocyte-derived macrophage subset that occupies the Kupffer cell niche (MoKC subset, resembling resident KCs), thereby impeding the formation of hepatic lipid-associated macrophages (LAMs). This transition has a profound impact, manifested in significantly reduced steatosis and modestly decreased liver fibrosis in myeloid-specific Gpnmb-knockout mice. In conclusion, our research clarifies the complex interactions between Gpnmb and MDMs and underscores the therapeutic potential of targeting Gpnmb within MDMs to manage MASLD.

Liver lipid droplet cholesterol content is a key determinant of metabolic dysfunction-associated steatohepatitis

Metabolic dysfunction-associated steatohepatitis (MASH) represents a progressive form of steatotic liver disease which increases the risk for fibrosis and advanced liver disease. The accumulation of discrete species of bioactive lipids has been postulated to activate signaling pathways that promote inflammation and fibrosis. However, the key pathogenic lipid species is a matter of debate. We explored candidates using various dietary, molecular, and genetic models. Mice fed a choline-deficient L-amino acid-defined high-fat diet (CDAHFD) developed steatohepatitis and manifested early markers of liver fibrosis associated with increased cholesterol content in liver lipid droplets within 5 d without any changes in total liver cholesterol content. Treating mice with antisense oligonucleotides against Coenzyme A synthase (Coasy) or treatment with bempedoic acid or atorvastatin decreased liver lipid droplet cholesterol content and prevented CDAHFD-induced MASH and the fibrotic response. All these salutary effects were abrogated with dietary cholesterol supplementation. Analysis of human liver samples demonstrated that cholesterol in liver lipid droplets was increased in humans with MASH and liver fibrosis and was higher in PNPLA3 I148M (variants rs738409) than in HSD17B13 variants (rs72613567). Together, these data identify cholesterol in liver lipid droplets as a critical mediator of MASH and demonstrate that Coenzyme A synthase knockdown and bempedoic acid are therapeutic approaches to reduce liver lipid droplet cholesterol content and thereby prevent the development of MASH and liver fibrosis.

Netrin 4 is a novel cytokine associated with oxidative stress and insulin resistance in obese individuals

BACKGROUND

Netrin 4 (NTN4) has been reported to be involved in a variety of pathophysiological processes, such as the occurrence and development of tumors, viral replication and infection, and diabetic retinopathy. However, the relationships between NTN4 and metabolic diseases have not been reported.

METHODS

The PhenoScanner tool and R language were used for bioinformatics analysis. Serum NTN4 was measured by ELISA in 211 healthy women and 193 overweight/obesity (OW/OB) women. Alterations in the serum NTN4 level were examined during the cold-exposure tests, acute exercise, lipid infusion, OGTT and EHC.

RESULTS

GWAS and Bioinformatics analysis revealed that NTN4 was closely related to energy metabolism and OS. In a population-based cohort study, we observed that individuals with OW/OB and IR exhibited significantly elevated levels of circulating NTN4. In addition, the serum NTN4 concentration was found to be significantly correlated with indicators of obesity, IR, sex hormone and glucose/lipid metabolism.

CONCLUSIONS

NTN4 is associated with obesity-related IR.

TRIAL REGISTRATION

All research plans were approved by the Human Research Ethics Committee of Chongqing Medical University (No. (74)2012, No. (72)2014 and No. (74)2015).

Cellular communication networks in fibrosis: Insights from the MASLD pig model

BACKGROUND

This research aims to reveal the cellular cross talk in fibrosis liver using transgenic pigs (TG) expressing humanized risk genes (PNPLA3I148M-GIPRdn-hIAPP) as a metabolic dysfunction-associated steatotic liver disease (MASLD) model.

METHODS AND RESULTS

The study uses single-nucleus sequencing to reveal the differentiation and interaction characteristics of various cell populations in the liver during the development of MASLD. After 6 months of high-fat, high-sucrose diet induction, the model pigs exhibited obvious liver pathological features, including fat deposition, inflammatory cell aggregation, fibrosis, and blocked insulin signaling pathways, similar to PNPLA3 rs738409 C>G carriers. Single-nucleus RNA sequencing showed that pigs share a high correlation with human hepatic cell types and zonation. HSCs in TG pigs are more activated, showing enhancing fibrosis-related pathways and declining retinol metabolism. Pseudo-trajectory analysis revealed that over 90% of macrophages in TG liver differentiated to Fate 1 (CD68hi) with higher expression of major histocompatibility complex-II molecules, proinflammatory cytokines, phagosomes, and lysosomal-related genes. Active cell interactions were found between HSCs, endothelial cells, and Fate1 macrophages. Ligand and receptor interactions, including FGF23-FGFR, PDGFs-PDGFRs, EFNA1-EPHRs, and CXCL12-CXCR4/CXCR7, were predicted to involve in hepatic fibrosis in model pigs.

CONCLUSIONS

The transgenic pig model of MASLD exhibits liver pathological features consistent with patients with MASLD. Our data supplemented the mechanism by which PNPLA3 mutations lead to hepatic steatosis, depicted a detailed atlas of hepatic profibrosis cellular network, and provided a reliable large animal model and data reference for MASLD drug development and precision treatment.

A robust diagnostic model for high-risk MASH: integrating clinical parameters and circulating biomarkers through a multi-omics approach

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a critical health concern, with metabolic dysfunction-associated steatohepatitis (MASH) representing a severe subtype that poses significant risks. This study aims to develop a robust diagnostic model for high-risk MASH utilizing a multi-omics approach.

METHODS

We initiated proteomic analysis to select differential proteins, followed by liver transcriptional profiling to localize these proteins. An intersection of differential proteins and liver-expressed genes facilitated the identification of candidate biomarkers. Subsequently, scRNA-seq data helped ascertain the subcellular localization of these biomarkers in kupffer cells. We then established two MASLD models to investigate the co-localization of F4/80 and the target proteins in Kupffer cells using immunofluorescence dual-labeling. Correlation analyses were performed using blood samples from a discovery cohort of 144 individuals with liver pathology to validate the relationships between candidate biomarkers and MASLD phenotypes. Using LASSO regression, we established the ABD-LTyG predictive model for high-risk MASH (NAS ≥ 4 + F ≥ 2) and validated its efficacy in an independent cohort of 171 individuals. Finally, we compared this model against three classic non-invasive liver fibrosis diagnostic methods.

RESULTS

A proteo-transcriptomic comparison identified 58 consistent biomarkers in plasma and liver, with 25 closely associated with MASLD phenotype. Utilizing single-cell data and the HPA database, we delineated the localization of these biomarkers in liver cells, identifying TREM2, IL18BP, and LGALS3BP predominantly in the Kupffer cell subpopulation. Validation in animal models confirmed elevated expression and cellular localization of TREM2, IL18BP, and LGALS3BP in MASLD. To enhance diagnostic capability, we integrated clinical characteristics using LASSO regression to develop the ABD-LTyG model, comprising AST, BMI, total bilirubin (TB), vitamin D, TyG, and the biomarkers LGALS3BP and TREM2. This model demonstrated an AUC of 0.832 (95% CI 0.753-0.911) in the discovery cohort and 0.807 (95% CI 0.742-0.872) in the validation cohort for diagnosing high-risk MASH, outperforming traditional assessments such as FIB-4, NFS, and APRI.

CONCLUSION

The integration of circulating biomarkers and clinical parameters into the ABD-LTyG model offers a promising approach for diagnosing high-risk MASH. This study underscores the importance of multi-omics strategies in enhancing diagnostic accuracy and guiding clinical decision-making.

Soluble TREM2 reflects liver fibrosis status and predicts postoperative liver dysfunction after liver surgery

Background & Aims

Triggering receptor expressed on myeloid cells 2 (TREM2)-expressing macrophages and systemic levels of soluble TREM2 (sTREM2) appear critical in the development of chronic liver disease (CLD) and seem relevant in its detection. The aim of this study was to examine sTREM2 as a marker for early CLD and its potential to predict posthepatectomy liver failure (PHLF) in patients undergoing partial hepatectomy.

Methods

sTREM2 was assessed in the plasma of 108 patients undergoing liver resection. Blood was drawn prior to surgery (preop) and on the first and fifth postoperative day.

Results

Preop sTREM2 levels were similar across different indications for resection (p = 0.091). Higher preop sTREM2 levels were associated with advanced hepatic fibrosis (p = 0.030) and PHLF (p = 0.007). Fibrosis-4 index (FIB-4) (p = 0.619) and model for end-stage liver disease (MELD) (p = 0.590) did not show a difference between patients grouped by their CLD. Comparing the AUC from receiver-operating characteristic analysis, sTREM2 (AUC = 0.708) outperformed FIB-4 (AUC = 0.529), MELD (AUC = 0.587), Child-Pugh grading (AUC = 0.570) and LiMAx (liver maximum capacity test) (AUC = 0.516) in predicting PHLF. Similarly, in uni- and multivariate analysis, only sTREM2 proved predictive for PHLF (p = 0.023). High-risk (p = 0.003) and low-risk (p = 0.011) cut-offs for systemic sTREM2 levels could identify patients at risk for adverse outcomes after surgery. Finally, high sTREM2 was associated with decreased overall survival after liver surgery (p <0.001).

Conclusions

Circulating sTREM2 shows sensitivity for early-stage, asymptomatic liver disease, irrespective of the underlying indication for liver surgery. Assessment of CLD via sTREM2 monitoring could improve early detection of CLD and improve outcomes after liver surgery.

Impact and implications

Soluble TREM2 (sTREM2) has previously been shown to correlate with the degree of chronic liver disease. We found that even in patients undergoing liver resection, who generally do not suffer from end-stage liver disease, sTREM2 reflects liver fibrosis status and predicts postoperative development of liver dysfunction. This is especially relevant for liver surgeons and patients, as postoperative liver dysfunction is the main reason for postoperative mortality. Our findings are also important for hepatologists, as early detection of liver fibrosis and cirrhosis is paramount for overall patient survival and we can show that even in a cohort with a median model for end-stage liver disease score of 6, sTREM2 is able to distinguish patients based on their liver fibrosis status.

Molecular Landscape and Diagnostic Model of MASH: Transcriptomic, Proteomic, Metabolomic, and Lipidomic Perspectives

Metabolic dysfunction-associated steatohepatitis (MASH), a progressive form of fatty liver disease, presents a significant global health challenge. Despite extensive research, fully elucidating its complex pathogenesis and developing accurate non-invasive diagnostic tools remain key goals. Multi-omics approaches, integrating data from transcriptomics, proteomics, metabolomics, and lipidomics, offer a powerful strategy to achieve these aims. This review summarizes key findings from multi-omics studies in MASH, highlighting their contributions to our understanding of disease mechanisms and the development of improved diagnostic models. Transcriptomic studies have revealed widespread gene dysregulation affecting lipid metabolism, inflammation, and fibrosis, while proteomics has identified altered protein expression patterns and potential biomarkers. Metabolomic and lipidomic analyses have further uncovered significant changes in various metabolites and lipid species, including ceramides, sphingomyelins, phospholipids, and bile acids, underscoring the central role of lipid dysregulation in MASH. These multi-omics findings have been leveraged to develop novel diagnostic models, some incorporating machine learning algorithms, with improved accuracy compared to traditional methods. Further research is needed to validate these findings, explore the complex interplay between different omics layers, and translate these discoveries into clinically useful tools for improved MASH diagnosis and prognosis.

Single-cell RNA sequencing advances in revealing the development and progression of MASH: the identifications and interactions of non-parenchymal cells

Developing drugs for the treatment of Metabolic Associated Steatohepatitis (MASH) has always been a significant challenge. Researchers have been dedicated to exploring drugs and therapeutic strategies to alleviate disease progression, but treatments remain limited. This is partly due to the complexity of the pathophysiological processes, and inadequate knowledge of the cellular and molecular mechanisms in MASH. Especially, the liver non-parenchymal cells (NPCs) like Kupffer cells, hepatic stellate cells and sinusoidal endothelial cells which play critical roles in live function, immune responses, fibrosis and disease progression. Deciphering how these cells function in MASH, would help understand the pathophysiological processes and find potential drug targets. In recent years, new technologies have been developed for single-cell transcriptomic sequencing, making cell-specific transcriptome profiling a reality in healthy and diseased livers. In this review, we discussed how the use of single-cell transcriptomic sequencing provided us with an in-depth understanding of the heterogeneous, cellular interactions among non-parenchymal cells and tried to highlight recent discoveries in MASH by this technology. It is hoped that the summarized features and markers of various subclusters in this review could provide a technical reference for further experiments and a theoretical basis for clinical applications.

Myeloid cell path to malignancy: insights into liver cancer

Clinically approved treatments for advanced liver cancer often lack potency because of the heterogeneous characteristics of hepatocellular carcinoma (HCC). This complexity is largely driven by context-dependent inflammatory responses brought on by diverse etiologies, such as metabolic dysfunction-associated steatohepatitis (MASH), the genetic makeup of cancer cells, and the versatile adaptability of immune cells, such as myeloid cells. In this review, we discuss the evolutionary dynamics of the immune landscape, particularly that of liver-resident Kupffer cells (KCs), TREM2+, and SPP1+ macrophages with an active role during liver disease progression, which eventually fuels hepatocarcinogenesis. We highlight exploitable immunomodulatory avenues amenable to mitigate both the inherent pathological characteristics of liver cancers and the associated external factors that favor malignancy, paving a roadmap toward improving the management and therapeutic outcome for patients with HCC.

Regulation of Hepatic Stellate Cell Phenotypes in Metabolic Dysfunction-Associated Steatohepatitis

Hepatic stellate cells (HSCs) play a crucial role in the pathogenesis of liver fibrosis in metabolic dysfunction-associated steatohepatitis (MASH), a condition characterized by excessive fat accumulation in the hepatocytes, unrelated to alcohol consumption. In a healthy liver, HSCs are quiescent, store vitamin A, and function as pericytes. However, in response to liver injury and inflammation, HSCs become activated. In MASH, HSC activation is driven by metabolic stress, lipotoxicity, and chronic inflammation. Injured hepatocytes, recruited macrophage, capillarized sinusoidal endothelial cells, and permeable intestinal epithelium may each contribute to activating HSCS. This leads to a unique inflammatory environment that promotes fibrosis. MASH HSCs change their metabolism to favor glycolysis, glutaminolysis, and lactate generation. Activated HSCs transform into myofibroblast-like cells, producing excessive extracellular matrix components that result in fibrosis. In addition, HSCs in MASH have inflammatory and intermediate activated phenotypes. This fibrotic process is a key feature of MASH, which can lead to cirrhosis and liver cancer. Understanding the mechanisms of HSC activation and their role in MASH progression is essential for developing targeted therapies to treat and prevent liver fibrosis in affected individuals.

IL-33-Induced TREM2+ Macrophages Promote Pathological New Bone Formation Through CREG1-IGF2R Axis in Ankylosing Spondylitis

Pathological new bone formation is the main cause of disability in ankylosing spondylitis (AS), and so far, it lacks a targeted therapy. Macrophages are central orchestrators of inflammation progression and tissue remodeling, but their contribution to pathological new bone formation has largely not been explored. Here, it is identified that TREM2+ macrophages predominated within the sites of new bone formation and adjacent to osteogenic precursor cells. In vivo, both depletion of macrophages and knockout of Trem2 significantly reduced pathological new bone formation in a collagen antibody-induced arthritis (CAIA) model. Specifically, TREM2+ macrophages promoted osteogenic differentiation of ligament-derived progenitor cells (LDPCs) by secreting CREG1, a secretory glycoprotein involved in cell differentiation and normal physiology. CREG1-IGF2R-PI3K-AKT signaling pathway is involved in TREM2+ macrophage-mediated pathological new bone formation. In addition, it is found that IL-33 promoted TREM2+ macrophage differentiation through phosphorylation of STAT6. Targeting the above signalings alleviated new bone formation in the CAIA model. The findings highlight the critical role of IL-33-induced TREM2+ macrophages in pathological new bone formation and provide potential therapeutic targets for halting spinal ankylosis in AS.

ATF4 drives regulatory T cell functional specification in homeostasis and obesity

Regulatory T cells (Tregs) have diverse functional specification in homeostasis and disease. However, how liver Tregs function and are transcriptionally regulated in obesity is not well understood. Here, we identified that effector Tregs expressing activating transcription factor 4 (ATF4) were enriched in the livers of obese mice. ATF4 was critical for driving an effector Treg transcriptional program, and ATF4-expressing Tregs promoted the development of obesity-induced liver fibrosis by enhancing transforming growth factor-β activation via integrin αvβ8. Treg-specific deletion of Atf4 resulted in reduced liver Tregs and attenuation of obesity-induced liver abnormalities. Furthermore, ATF4 was required to promote the differentiation of nonlymphoid tissue Treg precursors under steady state. These findings demonstrate that ATF4 is important for regulating Treg functional specification in homeostasis and obesity.

A dataset of single-cell transcriptomic atlas of Bama pig and potential marker genes across seven tissues

The use of single-cell sequencing technology for single-cell transcriptomics studies in pigs is expanding progressively. However, the comprehensive classification of cell types across different anatomical tissues and organs of pig in multiple datasets remains relatively limited. This study employs single-cell and single-nucleus sequencing technologies in Bama pig to identify unique marker genes and their corresponding transcriptomic profiles across diverse cell types in various anatomical tissues and organs, including subcutaneous fat, visceral fat, psoas major muscle, liver, spleen, lung, and kidney. Through detailed data analyses, we observed widespread cellular diversity across various anatomical tissues and organs of Bama pig. This work contributes a comprehensive dataset that supports physiological studies and aids in the identification and prediction of potential marker genes through single-cell transcriptomics of these tissues. The methodologies and data employed in this study are designed to improve the accuracy of cell type identification and ensure consistent cell type allocation.

Microbiota-derived H2S induces c-kit+ cDC1 autophagic cell death and liver inflammation in metabolic dysfunction-associated steatohepatitis

Immune dysregulation-induced inflammation serves as a driving force in the progression of metabolic dysfunction-associated steatohepatitis (MASH), while the underlying cellular and molecular mechanisms remain largely uncharted. A Western diet (WD) is employed to construct mouse models of metabolic dysfunction associated steatotic liver disease (MASLD) or MASH. Mass cytometry identifies a c-kit+ cDC1 subset whose frequency is reduced in the livers of mice and patients with MASH compared with healthy controls. Adoptive cell transfer of c-kit+ cDC1 protects the progression of MASH. Moreover, analysis of gut microbe sequence shows that WD-fed mice and MASLD/MASH patients exhibit gut microbiota dysbiosis, with an elevated abundance of H2S-producing Desulfovibrio_sp. Transplanting of MASH-derived fecal flora, Desulfovibrio_sp., or injecting H2S intraperitoneally into MASLD mice decreases the c-kit+cDC1 population and exacerbates liver inflammation. Mechanistically, H2S induces autophagic cell death of cDC1 in a c-kit-dependent manner in cDC-specific c-kit-/- and Atg5-/- mice. We thus uncover that microbiota-derived H2S triggers the autophagic cell death of c-kit+ cDC1 and ignites the liver inflammatory cascade in MASH.

Chenodeoxycholic acid modulates cholestatic niche through FXR/Myc/P-selectin axis in liver endothelial cells

Cholestatic liver diseases are characterized by excessive bile acid accumulation in the liver. Endothelial cells (ECs) shape the local microenvironment in both normal conditions and liver injury, yet their role in cholestasis is unclear. Through a comparative analysis of single-cell RNA sequencing data from various murine models of liver injury, we identify distinctive Myc activation within ECs during obstructive cholestasis resulting from bile duct ligation (BDL). Myc overexpression in ECs significantly upregulates P-selectin, increasing neutrophil infiltration and worsening cholestatic liver injury. This process occurs through the FXR, activated by chenodeoxycholic acid (CDCA) and its conjugate TCDCA. Inhibiting P-selectin with PSI-697 reduces neutrophil recruitment and alleviates injury. Cholestatic patient liver samples also show elevated Myc and P-selectin in ECs, along with increased neutrophils. The findings identify ECs as key drivers of cholestatic liver injury through a Myc-driven program and suggest that targeting the CDCA/FXR/Myc/P-selectin axis may offer a therapeutic approach.

Impaired mitochondrial degradation of CHCHD2 promotes metabolic dysfunction-associated steatohepatitis-related hepatocellular carcinoma by upregulating VEGFA

Metabolic dysfunction-associated steatohepatitis (MASH) is the fastest-growing cause of liver cancer. The liver microenvironment of patients with MASH supports the development of hepatocellular carcinoma (HCC). Coiled-coil-helix-coiled-coil-helix domain-containing 2 (CHCHD2), which is located in both the mitochondria and nucleus, is increased in MASH liver. Its role in the development of MASH-HCC remain unknown. In this study, we found CHCHD2 protein levels were elevated in both tumor and para-tumor tissues of patients with MASH-HCC and diethylnitrosamine- and high-fat diet-induced MASH-HCC mice. Chchd2-knockout mice were generated. CHCHD2 was overexpressed in hepatocytes using AAV with TBG promoter. Chchd2 knockout inhibited the progression of MASH-HCC in mice. CHCHD2 protein-targeted ChIP-sequencing data revealed that CHCHD2 target genes encoding secretory proteins were enriched in cancer pathways. Among these genes, vascular endothelial growth factor A (VEGFA) level increased in CHCHD2-overexpressing livers and hepatocytes. Chchd2 knockdown reduced palmitate-induced VEGFA expression. Palmitate-treated hepatocyte increased the angiogenic activity of endothelial cells in a paracrine manner, and this was suppressed by Chchd2 knockdown in hepatocytes. CHCHD2-overexpressing hepatocytes promoted the angiogenic activity of endothelial cells. We futher employed an orthotopic murine model of HCC to demonstrate that elevated CHCHD2 protein levels in para-tumor tissues support HCC growth. In addition, we found that the degradation of CHCHD2 was primarily mediated by mitochondrial protease ClpXP, which was repressed in the MASH liver. In conclusion, the mitochondrial degradation of CHCHD2 is impaired in MASH, and elevated CHCHD2 levels in hepatocytes promote VEGFA transcription and support the growth of HCC.

C/EBPβ transcription factor promotes alcohol-induced liver fibrosis in males via HDL remodeling

BACKGROUND

Alcohol-associated liver disease (ALD) is the main cause of alcohol-associated mortality. However, the mechanism of ALD development is poorly understood. Epigenetic changes are thought to play an important role in ALD. We aimed to define the epigenetic changes induced by alcohol and predict drivers of these changes.

METHODS

Mice were fed high-fat diet with or without 20% of alcohol in the drinking water for 20 weeks (WDA model). scATAC-seq data set was analyzed using Signac R package. To test the role of C/EBPβ, Cebpb-floxed mice were treated with AAV8-TBG-Cre or AAV8-control.

RESULTS

We analyzed differentially accessible regions in livers from control and alcohol-fed mice and found that activity of C/EBPβ transcription factor was associated with alcohol-induced epigenetic changes in hepatocytes. C/EBPβ protein levels were significantly upregulated in multiple models of ALD and human ALD samples. Using hepatocyte-specific Cebpb knockout mice we found that Cebpb loss protected male mice from alcohol-induced fibrosis development. We found no protection in female mice, suggesting that this mechanism is specific to male ALD. In vitro studies suggested that the protective effect of Cebpb loss was mediated by altered hepatocyte-macrophage cross talk. Cebpb knockout in hepatocytes reduced a profibrotic and promoted a pro-resolving phenotype in macrophages, thus modulating ALD development. We further identified the mediators of the cross talk. Cebpb knockout altered the expression of several HDL protein components, increasing APOA1 and apolipoprotein M and reducing apolipoprotein E and SAA levels in male mice. HDL secreted by Cebpb knockout hepatocytes was sufficient to confer anti-inflammatory and antifibrotic changes to macrophages.

CONCLUSIONS

Taken together, alcohol-induced C/EBPβ activation is a key driver of ALD fibrosis in males via C/EBPβ-dependent HDL remodeling.

Liver lipid droplet cholesterol content is a key determinant of metabolic dysfunction-associated steatohepatitis

Metabolic dysfunction-associated steatohepatitis (MASH) represents a progressive form of steatotic liver disease which increases the risk for fibrosis and advanced liver disease. The accumulation of discrete species of bioactive lipids has been postulated to activate signaling pathways that promote inflammation and fibrosis. However, the key pathogenic lipid species is a matter of debate. We explored candidates using various dietary, molecular, and genetic models. Mice fed a choline-deficient L-amino acid-defined high-fat diet (CDAHFD) developed steatohepatitis and manifested early markers of liver fibrosis associated with increased cholesterol content in liver lipid droplets within 5 days without any changes in total liver cholesterol content. Treating mice with antisense oligonucleotides (ASOs) against Coenzyme A synthase (Cosay) or treatment with bempedoic acid or atorvastatin decreased liver lipid droplet cholesterol content and prevented CDAHFD-induced MASH and the fibrotic response. All these salutary effects were abrogated with dietary cholesterol supplementation. Analysis of human liver samples demonstrated that cholesterol in liver lipid droplets was increased in humans with MASH and liver fibrosis and was higher in PNPLA3 I148M (variants rs738409) than in HSD17B13 variants (rs72613567). Together, these data identify cholesterol in liver lipid droplets as a critical mediator of MASH and demonstrate that COASY knockdown and bempedoic acid are novel therapeutic approaches to reduce liver lipid droplet cholesterol content and thereby prevent the development of MASH and liver fibrosis.

Significance Statement

Metabolic dysfunction-associated steatohepatitis (MASH) is a progressive liver disease linked to fibrosis. The role of specific lipid species in its pathogenesis remains debated. Using dietary, molecular, and genetic models, we found that mice on a choline-deficient, high-fat diet (CDAHFD) developed steatohepatitis and early fibrosis, marked by increased cholesterol in liver lipid droplets within five days. Targeting COASY with antisense oligonucleotides or treating with bempedoic acid or atorvastatin reduced lipid droplet cholesterol and prevented MASH. However, dietary cholesterol supplementation negated these effects. Human liver samples confirmed elevated lipid droplet cholesterol in MASH and fibrosis, especially in PNPLA3 I148M carriers. These findings highlight cholesterol reduction as a potential MASH therapy.

Role of triggering receptor expressed on myeloid cells 2 in the pathogenesis of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a progressive disease. Without effective interventions, NAFLD can gradually develop to non-alcoholic steatohepatitis, fatty liver fibrosis, liver cirrhosis and even hepatocellular carcinoma. It is still to investigate the precise molecular mechanism behind the pathophysiology of NAFLD. Triggering receptor expressed on myeloid cells 2 (TREM2) can sense tissue injury and mediate immune remodeling, thereby inducing phagocytosis, lipid metabolism, and metabolic transfer, promoting cell survival and combating inflammatory activation. NAFLD might develop as a result of TREM2's regulatory role. We here briefly summarize the biological characteristics of TREM2 and its functions in the disease progression of NAFLD. Moreover, we propose to broaden the therapeutic strategy for NAFLD by targeting TREM2.

Overview of the hazardous impacts of metabolism-disrupting chemicals on the progression of fatty liver diseases

Background

Given the global increase in obesity, metabolic dysfunction-associated steatotic liver disease (MASLD) is a major health concern. Because the liver is the primary organ for xenobiotic metabolism, the impact of environmental stressors on liver homeostasis and MASLD has garnered significant interest over the past few decades. The concept of metabolism-disrupting chemicals (MDCs) has been introduced to underscore the importance of environmental factors in metabolic homeostasis. Recent epidemiological and biological studies suggest a causal link between exposure to MDCs and prevalence and progression of MASLD.

Objective

This review aims to introduce the emerging concept of MDCs and their representative toxic mechanisms. In particular, this review focuses on broadening the understanding of their impacts on MASLD or metabolic dysfunction-associated steatohepatitis (MASH) progression.

Result

Recent research has highlighted the environmental contaminants, such as heavy metals, microplastics, and pesticides, have the potential to influence hepatic metabolism and aggravate MASLD/MASH progression. These MDCs not only directly affect lipid metabolism in hepatocytes but also affect other cell types, such as immune cells and stellate cells, as well as the gut-liver axis.

Conclusion

Collectively, these findings contribute to establishing a well-defined adverse outcome pathway and identify novel therapeutic options for liver diseases associated with pollutants.

Lipid droplet efferocytosis attenuates proinflammatory signaling in macrophages via TREM2- and MS4A7-dependent mechanisms

Metabolic dysfunction-associated steatohepatitis (MASH) is characterized by injury to steatotic hepatocytes that triggers the release of endogenous danger-associated molecular patterns. Recent work demonstrated that exposed lipid droplets (LDs) serve as a pathogenic signal that promotes monocyte infiltration and its maturation into triggering receptor expressed in myeloid cells 2 (TREM2+) macrophages in MASH liver. Here we explore the role of LD exposure in modulating inflammatory signaling in macrophages. We found that LD efferocytosis triggers a global transcriptional response and dampens pro-inflammatory signaling in macrophages. LD treatment attenuated NLRP3 inflammasome activation via mechanisms independent of lysosomal LD hydrolysis. While TREM2 was dispensable for LD efferocytosis by macrophages, it was required for the attenuation of proinflammatory signaling upon LD exposure. Additionally, MS4A7 downregulation contributes to LD efferocytosis-mediated dampening of inflammatory response. These results underscore the dual role of LD exposure in MASH liver by promoting monocyte infiltration and TREM2+ macrophage induction, while restraining proinflammatory response in macrophages.

Hepatic sphingomyelin phosphodiesterase 3 promotes steatohepatitis by disrupting membrane sphingolipid metabolism

Metabolic-dysfunction-associated steatohepatitis (MASH) remains a major health challenge. Herein, we identify sphingomyelin phosphodiesterase 3 (SMPD3) as a key driver of hepatic ceramide accumulation through increasing sphingomyelin hydrolysis at the cell membrane. Hepatocyte-specific Smpd3 gene disruption or pharmacological inhibition of SMPD3 alleviates MASH, whereas reintroducing SMPD3 reverses the resolution of MASH. Although healthy livers express low-level SMPD3, lipotoxicity-induced DNA damage suppresses sirtuin 1 (SIRT1), triggering an upregulation of SMPD3 during MASH. This disrupts membrane sphingomyelin-ceramide balance and promotes disease progression by enhancing caveolae-dependent lipid uptake and extracellular vesicle secretion from steatotic hepatocytes to exacerbate inflammation and fibrosis. Consequently, SMPD3 acts as a central hub integrating key MASH hallmarks. Notably, we discovered a bifunctional agent that simultaneously activates SIRT1 and inhibits SMPD3, which shows significant therapeutic potential in MASH treatment. These findings suggest that inhibition of hepatic SMPD3 restores membrane sphingolipid metabolism and holds great promise for developing novel MASH therapies.

The Intersection between Immune System and Idiopathic Pulmonary Fibrosis-A Concise Review

Idiopathic pulmonary fibrosis (IPF) is marked by progressive alveolar destruction, impaired tissue regeneration, and relentless fibrogenesis, culminating in respiratory failure and death. A diverse array of resident and non-resident cells within the lung contribute to disease pathogenesis. Notably, immune cells, both resident and recruited, respond to cues from sites of lung injury by undergoing phenotypic transitions and producing a wide range of mediators that influence, initiate, or dictate the function, or dysfunction, of key effector cells in IPF pathology, such as alveolar epithelial cells, lung fibroblasts, and capillary endothelial cells. The role of the immune system in IPF has undergone an interesting evolution, oscillating from initial enthusiasm to skepticism, and now to a renewed focus. This shift reflects both the past failures of immune-targeting therapies for IPF and the unprecedented insights into immune cell heterogeneity provided by emerging technologies. In this article, we review the historical evolution of perspectives on the immune system's role in IPF pathogenesis and examine the lessons learned from previous therapeutic failures targeting immune responses. We discuss the major immune cell types implicated in IPF progression, highlighting their phenotypic transitions and mechanisms of action. Finally, we identify key knowledge gaps and propose future directions for research on the immune system in IPF.

Spatially restricted and ontogenically distinct hepatic macrophages are required for tissue repair

Our understanding of the functional heterogeneity of resident versus recruited macrophages in the diseased liver is limited. A population of recruited lipid-associated macrophages (LAMs) has been reported to populate the diseased liver alongside resident Kupffer cells (KCs). However, the precise roles of these distinct macrophage subsets remain elusive. Here, using proteogenomics, we have identified LAMs in multiple models of liver injury. Moreover, we found that this phenotype is not specific to recruited macrophages, as a subset of resident KCs can also adopt a LAM-like phenotype in the mouse and human liver. By combining genetic mouse models targeting the distinct populations, we determined that both recruited LAMs and resident LAM-like KCs play crucial roles in tissue repair. Specifically, triggering receptor expressed on myeloid cells 2 (TREM2) expression on either resident or recruited macrophages is required for the efficient clearance of dying cells, enhancing repair and preventing exacerbated fibrosis.

Liver diseases: epidemiology, causes, trends and predictions

As a highly complex organ with digestive, endocrine, and immune-regulatory functions, the liver is pivotal in maintaining physiological homeostasis through its roles in metabolism, detoxification, and immune response. Various factors including viruses, alcohol, metabolites, toxins, and other pathogenic agents can compromise liver function, leading to acute or chronic injury that may progress to end-stage liver diseases. While sharing common features, liver diseases exhibit distinct pathophysiological, clinical, and therapeutic profiles. Currently, liver diseases contribute to approximately 2 million deaths globally each year, imposing significant economic and social burdens worldwide. However, there is no cure for many kinds of liver diseases, partly due to a lack of thorough understanding of the development of these liver diseases. Therefore, this review provides a comprehensive examination of the epidemiology and characteristics of liver diseases, covering a spectrum from acute and chronic conditions to end-stage manifestations. We also highlight the multifaceted mechanisms underlying the initiation and progression of liver diseases, spanning molecular and cellular levels to organ networks. Additionally, this review offers updates on innovative diagnostic techniques, current treatments, and potential therapeutic targets presently under clinical evaluation. Recent advances in understanding the pathogenesis of liver diseases hold critical implications and translational value for the development of novel therapeutic strategies.

Spatial‒temporal heterogeneities of liver cancer and the discovery of the invasive zone

Solid tumours are intricate and highly heterogeneous ecosystems, which grow in and invade normal organs. Their progression is mediated by cancer cells' interaction with different cell types, such as immune cells, stromal cells and endothelial cells, and with the extracellular matrix. Owing to its high incidence, aggressive growth and resistance to local and systemic treatments, liver cancer has particularly high mortality rates worldwide. In recent decades, spatial heterogeneity has garnered significant attention as an unfavourable biological characteristic of the tumour microenvironment, prompting extensive research into its role in liver tumour development. Advances in spatial omics have facilitated the detailed spatial analysis of cell types, states and cell‒cell interactions, allowing a thorough understanding of the spatial and temporal heterogeneities of tumour microenvironment and informing the development of novel therapeutic approaches. This review illustrates the latest discovery of the invasive zone, and systematically introduced specific macroscopic spatial heterogeneities, pathological spatial heterogeneities and tumour microenvironment heterogeneities of liver cancer.

Diverse Functions of Macrophages in Obesity and Metabolic Dysfunction-Associated Steatotic Liver Disease: Bridging Inflammation and Metabolism

Macrophages play crucial roles in immune response and tissue homeostasis, with their functions becoming increasingly complex in obesity-mediated metabolic disorders. This review explores the extensive range of macrophage activities within adipose and liver tissues, emphasizing their contribution to the pathogenesis and progression of obesity and its related metabolic dysfunction-associated steatotic liver disease (MASLD). In the context of obesity, macrophages respond adaptively to lipid overloads and inflammatory cues in adipose tissue, profoundly influencing insulin resistance and metabolic homeostasis. Concurrently, their role in the liver extends to moderating inflammation and orchestrating fibrotic responses, integral to the development of MASLD. Highlighting the spectrum of macrophage phenotypes across these metabolic landscapes, we summarize their diverse roles in linking inflammatory processes with metabolic functions. This review advocates for a deeper understanding of macrophage subsets in metabolic tissues, proposing targeted research to harness their therapeutic potential in mitigating MASLD and other metabolic disorders.

Single-Cell RNA Sequencing Reveals Macrophage Dynamics During MASH in Leptin-Deficient Rats

Macrophages play important roles in metabolic dysfunction-associated steatohepatitis (MASH), an advanced and inflammatory stage of metabolic dysfunction-associated steatotic liver disease (MASLD). In humans and mice, the cellular heterogeneity and diverse function of hepatic macrophages in MASH have been investigated by single cell RNA sequencing (scRNA-seq). However, little is known about their roles in rats. Here, we collected liver tissues at the postnatal week 16, when our previously characterized Lep∆I14/∆I14 rats developed MASH phenotypes. By scRNA-seq, we found an increase in the number of macrophages and endothelial cells and a decrease in that of NK and B cells. Hepatic macrophages in rats underwent a unique M1 to M2 transition without expression of the classical markers such as Arg1 and Nos2, except for Cd163. Lipid-associated macrophages (LAMs) were increased, which could be detected by the antibody against Cd63. In the microenvironment, macrophages had an increased number of interactions with hepatocytes, myofibroblasts, T cells, neutrophils, and dendritic cells, while their interaction strengths remained unchanged. Finally, the macrophage migration inhibitory factor (MIF) pathway was identified as the top upregulated cell-communication pathway in MASH. In conclusion, we dissected hepatic macrophage dynamics during MASH at single cell resolution and provided fundamental tools for the investigation of MASH in rat models.

Targeting immune cellular populations and transcription factors: unraveling the therapeutic potential of JQF for NAFLD

Background

Non-alcoholic fatty liver disease (NAFLD) constitutes the most prevalent chronic liver disease worldwide. Progression to non-alcoholic steatohepatitis (NASH), the immune cell reservoir within the liver undergoes remodeling, exacerbating liver inflammation and potentially leading to liver fibrosis. Jiangtang Qingre Formula (JQF) is an effective prescription for the clinical treatment of NAFLD. However, its underlying mechanism of action remains unclear.

Methods

Using a high-fat diet-induced NAFLD mouse model, we evaluated JQF's effects with biochemical tests and histopathology. Single-cell RNA sequencing and spatial transcriptomics furthered our understanding of NAFLD pathophysiology and JQF's treatment mechanisms.

Results

Our findings initially revealed significant improvements in JQF on hepatic steatosis, inflammation, fibrosis and glucose tolerance in NAFLD mice. Furthermore, significant changes were observed in the immune cells including monocytes, macrophages, and T cells in the livers of NAFLD mice. Notably, regions infiltrated by T cells presented the most severe liver inflammation and fibrosis. Importantly, JQF effectively modulated these immune cells. Advanced subcluster and cell communication analyses identified key macrophage (KCs, MoMFs) and T cell (Tc, Th2) subpopulations in JQF's therapeutic actions. Further SCENIC analysis additionally uncovered the essential transcription factors that regulate these cell subclusters, such as Stat2, Mta3, Eomes, and Etv5.

Conclusion

Overall, our research suggests a promising potential therapeutic agent and identifies critical cell populations and transcription factors that contribute to its therapeutic effects, thereby revealing potential therapeutic targets for NAFLD.

Innate immune cells link dietary cues to normal and abnormal metabolic regulation

A slew of common metabolic disorders, including type 2 diabetes, metabolic dysfunction-associated steatotic liver disease and steatohepatitis, are exponentially increasing in our sedentary and overfed society. While macronutrients directly impact metabolism and bioenergetics, new evidence implicates immune cells as critical sensors of nutritional cues and important regulators of metabolic homeostasis. A deeper interrogation of the intricate and multipartite interactions between dietary components, immune cells and metabolically active tissues is needed for a better understanding of metabolic regulation and development of new treatments for common metabolic diseases. Responding to macronutrients and micronutrients, immune cells play pivotal roles in interorgan communication between the microbiota, small intestine, metabolically active cells including hepatocytes and adipocytes, and the brain, which controls feeding behavior and energy expenditure. This Review focuses on the response of myeloid cells and innate lymphocytes to dietary cues, their cross-regulatory interactions and roles in normal and aberrant metabolic control.

Characterisation of macrophages in healthy and diseased livers in mice: identification of necrotic lesion-associated macrophages

Background

Healthy livers contain a large number of resident macrophages named Kupffer cells (KCs), which are partially replaced by infiltrating monocyte-derived macrophages (MoMFs) during acute or chronic liver injury. Despite extensive research, understanding macrophage heterogeneity, spatial distribution and interactions with other cells within the liver remains challenging.

Methods

This study employs sequential multiplex immunofluorescence staining, advanced image analysis and single-cell RNA sequencing (scRNA-seq) analysis to characterise macrophages in both healthy and diseased livers in mice.

Results

Our data revealed that liver KCs made up more than 80% of total immune cells in healthy mouse livers, while massive amounts of MoMFs infiltrated into the livers after acute and chronic liver injury. KCs were more abundant and larger in Zones 1 and 2 compared with Zone 3 in healthy livers. Zone 1 KCs exhibited higher phagocytic activity than Zone 2/3 KCs and MoMFs. We simultaneously evaluated cell proliferation and apoptosis on one slide and found that proliferation and apoptosis of KCs and MoMFs significantly increased in acutely injured livers. We also performed scRNA-seq to investigate liver macrophage gene expression in naïve and concanavalin A (ConA)-treated mice. MoMF clusters expanded following ConA treatment, while KCs remained stable. Macrophages were divided into distinct subtypes, including C1q+ MoMFs, with differential expression of genes like Trem2, Spp1, Fabp5 and Gpnmb. Newly recruited C1q- MoMFs expressed high levels of Lyz and Ccr2, while Itgax (Cd11c)+ MoMFs expressed endothelin converting enzyme 1 (Ece1), a gene encoding ECE1 enzyme that activates endothelin to promote hepatic stellate cell contraction and necrotic lesion resolution. By immunostaining analysis of the proteins encoded by these signature genes, we identified several populations of MoMFs that were mainly located surrounding the necrotic lesion area and expressed various proteins that are involved in dead cell debris clearance.

Conclusion

We developed a robust framework for studying liver macrophages in vivo, offering insights into their roles in host defence and liver injury/repair. We identified several populations of MoMFs that surround necrotic lesion areas and express proteins that promote dead cell debris clearance. These necrotic lesion-associated macrophages likely play key roles in promoting necrotic lesion resolution.

PPARα agonist ameliorates cholestatic liver injury by regulating hepatic macrophage homeostasis

Inflammatory response plays an essential role in the pathogenesis of cholestatic liver injury. PPARα agonists have been shown to regulate bile acid homeostasis and hepatic inflammation. However, the immunoregulatory mechanisms through which PPARα agonists ameliorate cholestatic liver injury remain unclear. In this study, surgical bile duct ligation was performed to establish a mouse model of cholestasis. Our study revealed that PPARα agonist alleviated cholestatic liver injury in mice by suppressing inflammatory response, reducing neutrophil infiltration, and promoting M2-like macrophage polarization. CyTOF analysis showed that PPARα agonist increased the proportion of anti-inflammatory F4/80hiCD44+MHCII- M2-like macrophages while decreasing the proportion of pro-inflammatory CD64+CX3CR1+CCR2hiVISTAhiCD172a+CD44hi M1-like MoMFs. Additionally, scRNA-seq indicated that PPARα agonist regulated the developmental trajectory and homeostasis of hepatic macrophages. Mechanistically, PPARα agonist may influence the expression of immune regulators in heterogeneous macrophages to exert protective effects against cholestasis. In addition, the CCL and MIF signaling pathways may participate in the communication among hepatic immune cells, including macrophages, neutrophils, natural killer cells, and dendritic cells, in response to the PPARα agonist. In conclusions, PPARα agonist alleviated cholestatic liver injury by attenuating the inflammatory response and restoring hepatic macrophage homeostasis. This study might enhance the understanding of the immunoregulatory mechanisms of PPARα agonists, providing promising therapeutic targets for cholestatic liver diseases.

MicroRNA-206-3p suppresses hepatic lipogenesis and cholesterol synthesis while driving cholesterol efflux

BACKGROUND AND AIMS

Hepatosteatosis, hypertriglyceridemia, and hypercholesterolemia are interconnected metabolic disorders. This study is designed to characterize how microRNA-206-3p (miR-206) simultaneously prevents de novo lipogenesis (DNL), cholesterol synthesis, and VLDL production in hepatocytes while promoting cholesterol efflux in macrophages.

APPROACH AND RESULTS

MiR-206 levels were reduced in hepatocytes and macrophages of mice subjected to a high-fat, high-cholesterol diet. A negative feedback between LXRα (liver X receptor alpha) and miR-206 is formed to maintain high LXRα and low miR-206 in hepatocytes. Systemic administration of miR-206 alleviated hepatosteatosis, hypertriglyceridemia, and hypercholesterolemia in mice. A significant reduction in LDL cholesterol and VLDL cholesterol but unaltered HDL cholesterol was observed in miR-206-treated mice. Mirroring these findings, miR-206 reprogrammed the transcriptome of hepatocytes towards the inhibition of DNL, cholesterol synthesis, and assembly and secretion of VLDL. In macrophages, miR-206 activated the expression of genes regulating cholesterol efflux. Hepatocyte-specific expression of miR-206 reduced hepatic and circulating triglycerides and cholesterol, as well as VLDL production, while transplantation of macrophages bearing miR-206 facilitated cholesterol efflux. Mechanistically, miR-206 directly targeted Lxrα and Hmgcr in hepatocytes but facilitated expression of Lxrα in macrophages by targeting macrophage-specific tricho-rhino-phalangeal syndrome 1 (TRPS1), a transcription repressor of Lxrα . By targeting Hmgc r and Lxrα , miR-206 inhibited DNL, VLDL production, and cholesterol synthesis in hepatocytes, whereas it drove cholesterol efflux by activating the TRPS1-LXRα axis.

CONCLUSIONS

MiR-206, through differentially modulating LXRα signaling in hepatocytes and macrophages, inhibits DNL, promotes cholesterol efflux, and concurrently hinders cholesterol synthesis and VLDL production. MiR-206 simulates the functions of lipid-lowering medications, statins, and LXRα agonists.

LIX1L aggravates MASH-HCC progression by reprogramming of hepatic metabolism and microenvironment via CD36

Limb expression 1-like protein (LIX1L) is an essential player in liver disorders, but its function in metabolic dysfunction-associated steatohepatitis (MASH) and associated hepatocellular carcinoma (HCC) progression remains obscure. Here, we identify LIX1L as a key integrative regulator linking lipid metabolism and inflammation, adipose tissue and hepatic microenvironment, which promotes MASH progression. LIX1L significantly upregulates in MASH patients, mouse models, and palmitic acid-stimulated hepatocytes. Lix1l deletion inhibits hepatic lipid accumulation, inflammation, and fibrosis as well as adipocyte differentiation by downregulating CD36, alleviating MASH and associated HCC progression in mice. Mechanistically, metabolic stress promotes PARP1-mediated poly-ADP-ribosylation of LIX1L to increase stability and RNA binding ability of LIX1L. Subsequently, LIX1L binds to AU-rich element in the 3'UTR and CDS of CD36 mRNA, thus mitigating CD36 mRNA decay. Furthermore, LIX1L deficiency-mediated downregulation of CD36 reprograms the tumor-prone liver microenvironment with increased cytotoxic T lymphocytes and reduced immunosuppressive cell proportions. These data indicate a systematic function of LIX1L in the pathogenesis of MASH and underscore targeting PARP1/LIX1L/CD36 axis as a feasible strategy for treatment of MASH and associated HCC.

Single-cell transcriptome analysis of stem cells from human exfoliated deciduous teeth investigating functional heterogeneity in immunomodulation

Mesenchymal stem cells (MSCs) have been widely used in the treatment of various inflammatory diseases. The inadequate understanding of MSCs and their heterogeneity can impact the immune environment, which may be the cause of the good outcomes of MSCs-based therapy that cannot always be achieved. Recently, stem cells from human exfoliated deciduous teeth (SHED) showed great potential in inflammatory and autoimmune diseases due to their immature properties compared with MSCs. In our study, single-cell RNA sequencing (scRNA-seq) revealed that SHED in a low differentiation state (S7) exhibited the powerful ability to recruit multiple immune cells. In contrast, SHED in a relatively high differentiation state (S1) may hold a solid ability to secret many factors with paracrine signaling capacity. The analysis result shows that SHED has more robust immunomodulatory properties than human bone marrow-derived mesenchymal stem cells (hBMSCs) or human umbilical cord-derived mesenchymal stem cells (hUCMSCs). When co-cultured with PBMCs, SHED can enhance the proliferation of Treg and down-regulate TNF-α in vitro. SHED may have some advantages in the treatment of inflammatory and autoimmune diseases.

A prognostic molecular signature of hepatic steatosis is spatially heterogeneous and dynamic in human liver

Hepatic steatosis is a central phenotype in multi-system metabolic dysfunction and is increasing in parallel with the obesity pandemic. We use a translational approach integrating clinical phenotyping and outcomes, circulating proteomics, and tissue transcriptomics to identify dynamic, functional biomarkers of hepatic steatosis. Using multi-modality imaging and broad proteomic profiling, we identify proteins implicated in the progression of hepatic steatosis that are largely encoded by genes enriched at the transcriptional level in the human liver. These transcripts are differentially expressed across areas of steatosis in spatial transcriptomics, and several are dynamic during stages of steatosis. Circulating multi-protein signatures of steatosis strongly associate with fatty liver disease and multi-system metabolic outcomes. Using a humanized "liver-on-a-chip" model, we induce hepatic steatosis, confirming cell-specific expression of prioritized targets. These results underscore the utility of this approach to identify a prognostic, functional, dynamic "liquid biopsy" of human liver, relevant to biomarker discovery and mechanistic research applications.

Essentiality of SLC7A11-mediated nonessential amino acids in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) remains a rapidly growing global health burden. Here, we report that the nonessential amino acid (NEAA) transporter SLC7A11 plays a key role in MASLD. In patients with MASLD, we found high expression levels of SLC7A11 that were correlated directly with clinical grade. Using both loss-of-function and gain-of-function genetic models, we found that Slc7a11 deficiency accelerated MASLD progression via classic cystine/cysteine deficiency-induced ferroptosis, while serine deficiency and a resulting impairment in de novo cysteine production were attributed to ferroptosis-induced MASLD progression in mice overexpressing hepatic Slc7a11. Consistent with these findings, we found that both serine supplementation and blocking ferroptosis significantly alleviated MASLD, and the serum serine/glutamate ratio was significantly lower in these preclinical disease models, suggesting that it might serve as a prognostic biomarker for MASLD in patients. These findings indicate that defects in NEAA metabolism are involved in the progression of MASLD and that serine deficiency-triggered ferroptosis may provide a therapeutic target for its treatment.

Multi-omics in exploring the pathophysiology of diabetic retinopathy

Diabetic retinopathy (DR) is a leading global cause of vision impairment, with its prevalence increasing alongside the rising rates of diabetes mellitus (DM). Despite the retina's complex structure, the underlying pathology of DR remains incompletely understood. Single-cell RNA sequencing (scRNA-seq) and recent advancements in multi-omics analyses have revolutionized molecular profiling, enabling high-throughput analysis and comprehensive characterization of complex biological systems. This review highlights the significant contributions of scRNA-seq, in conjunction with other multi-omics technologies, to DR research. Integrated scRNA-seq and transcriptomic analyses have revealed novel insights into DR pathogenesis, including alternative transcription start site events, fluctuations in cell populations, altered gene expression profiles, and critical signaling pathways within retinal cells. Furthermore, by integrating scRNA-seq with genetic association studies and multi-omics analyses, researchers have identified novel biomarkers, susceptibility genes, and potential therapeutic targets for DR, emphasizing the importance of specific retinal cell types in disease progression. The integration of scRNA-seq with metabolomics has also been instrumental in identifying specific metabolites and dysregulated pathways associated with DR. It is highly conceivable that the continued synergy between scRNA-seq and other multi-omics approaches will accelerate the discovery of underlying mechanisms and the development of novel therapeutic interventions for DR.

Impact of heterogeneity in liver matrix and intrahepatic cells on the progression of hepatic fibrosis

Liver fibrosis is a disease with a high prevalence worldwide. The development of hepatic fibrosis results from a combination of factors within the liver, such as extracellular matrix (ECM) deposition, hepatic stellate cells (HSCs) activation, collagen cross-linking, and inflammatory response. Heterogeneity in fibrotic liver is the result of a combination of heterogeneity in the intrahepatic microenvironment as well as heterogeneous expression of fibrosis-associated enzymes and cells, complicating the study of the mechanisms underlying the progression of liver fibrosis. The role of this heterogeneity on the crosstalk between cells and matrix and on the fibrotic process is worth exploring. In this paper, we will describe the phenomenon and mechanism of heterogeneity of liver matrix and intrahepatic cells in the process of hepatic fibrosis and discuss the crosstalk between heterogeneous factors on the development of fibrosis. The elucidation of heterogeneity is important for a deeper understanding of the pathological mechanisms of liver fibrosis as well as for clinical diagnosis and targeted therapies.

Aberrant basement membrane production by HSCs in MASLD is attenuated by the bile acid analog INT-767

BACKGROUND

The farnesoid X receptor (FXR) is a leading therapeutic target for metabolic dysfunction-associated steatohepatitis (MASH)-related fibrosis. INT-767, a potent FXR agonist, has shown promise in preclinical models. We aimed to define the mechanisms of INT-767 activity in experimental MASH and dissect cellular and molecular targets of FXR agonism in human disease.

METHODS

Leptin-deficient ob/ob mice were fed a MASH-inducing diet for 15 weeks before the study started. After baseline liver biopsy and stratification, mice were allocated to INT-767 (10 mg/kg/d) or vehicle treatment for 8 weeks, either alongside an ongoing MASH diet (progression) or following conversion to normal chow (reversal). Effects on extracellular matrix remodeling were analyzed histologically and by RNA-sequencing. Serum fibrosis biomarkers were measured longitudinally. Human liver samples were investigated using bulk and single-cell RNA-sequencing, histology, and cell culture assays.

RESULTS

INT-767 treatment was antifibrotic during MASH progression but not reversal, attenuating the accumulation of type I collagen and basement membrane proteins (type IV collagen and laminin). Circulating levels of PRO-C4, a type IV collagen formation marker, were reduced by INT-767 treatment and correlated with fibrosis. Expression of basement membrane constituents also correlated with fibrosis severity and adverse clinical outcomes in human MASH. Single-cell RNA-sequencing analysis of mouse and human livers, and immunofluorescence staining colocalized FXR and basement membrane expression to myofibroblasts within the fibrotic niche. Treatment of culture-activated primary human HSCs with INT-767 decreased expression of basement membrane components.

CONCLUSIONS

These findings highlight the importance of basement membrane remodeling in MASH pathobiology and as a source of circulating biomarkers. Basement membrane deposition by activated HSCs is abrogated by INT-767 treatment and measurement of basement membrane molecules should be included when determining the therapeutic efficacy of FXR agonists.

LiverSCA: A comprehensive and user-friendly cell atlas in human hepatocellular carcinoma

We developed a cell atlas named LiverSCA on human liver cancer single-cell RNA sequencing data. It has a user-friendly web interface and comprehensive functionalities aiming to help researchers to make easy access to cellular and molecular landscapes of the tumor microenvironment in liver cancer. LiverSCA includes a complete analytical pipeline that allow mechanistic exploration on a wide variety of functionalities, such as cell clustering, cell annotation, identification of differentially expressed genes, functional enrichment analysis, analysis of cellular crosstalk, and pseudo-time trajectory analysis. Notably, our intuitive web interface allows users, particularly wet-lab researchers, to easily explore and undertake data discovery, without the need to handle any of the raw data.

Biological and clinical role of TREM2 in liver diseases

Liver diseases constitute a major health burden worldwide, accounting for more than 4% of all disease-related mortalities. While the incidence of viral hepatitis is expected to decrease, metabolic liver disorders are increasingly diagnosed. Liver pathology is diverse, with functional and molecular alterations in both parenchymal and mesenchymal cells, including immune cells. Triggering receptor expressed on myeloid cells 2 (TREM2) is a transmembrane receptor of the immunoglobulin superfamily and mainly expressed on myeloid cells. Several studies have demonstrated that TREM2 plays a critical role in tissue physiology and various pathological conditions. TREM2 is recognized as being associated with the development of liver diseases by regulating tissue homeostasis and the immune microenvironment. The biological and clinical impact of TREM2 is complex, given its diverse context-dependent functions. This review aims to summarize recent progress in understanding the association between TREM2 and different liver disorders and shed light on the clinical significance of targeting TREM2.

Gut-liver axis: Recent concepts in pathophysiology in alcohol-associated liver disease

The growing recognition of the role of the gut microbiome's impact on alcohol-associated diseases, especially in alcohol-associated liver disease, emphasizes the need to understand molecular mechanisms involved in governing organ-organ communication to identify novel avenues to combat alcohol-associated diseases. The gut-liver axis refers to the bidirectional communication and interaction between the gut and the liver. Intestinal microbiota plays a pivotal role in maintaining homeostasis within the gut-liver axis, and this axis plays a significant role in alcohol-associated liver disease. The intricate communication between intestine and liver involves communication between multiple cellular components in each organ that enable them to carry out their physiological functions. In this review, we focus on novel approaches to understanding how chronic alcohol exposure impacts the microbiome and individual cells within the liver and intestine, as well as the impact of ethanol on the molecular machinery required for intraorgan and interorgan communication.

Exosomal miR-146a-5p Derived from HSCs Accelerates Sepsis-induced Liver Injury by Suppressing KLF-4

This study aimed to investigate whether and how lipopolysaccharide (LPS) activated hepatic stellate cells (HSCs) regulate macrophage activity and to explore the impact of microRNAs (miRNAs) in exosomes from HSCs on this process. Mice subjected to LPS or cecal ligation and puncture (CLP) were used to explore sepsis-induced liver injury. Liver injury was evaluated using HE staining, and alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were measured. LPS-Exo or N-LPS-Exo from HSCs were added to hepatic macrophages, and iNOS, IL-1β, and TNF-α expression was detected via Western blotting. miRNA microarray analysis and PCR were used to evaluate differentially expressed miRNAs between LPS-Exo and N-LPS-Exo. Target genes were screened using the TargetScan database and verified with luciferase assays and WB. Inflammation and macrophage activity were observed in vivo using HE and CD86 staining in mice injected with PKH67-labeled LPS-Exo or N-LPS-Exo. Sepsis-related liver injury activates hepatic stellate cells, which regulate macrophage activity through exosomes. Specifically, exosomal miR-146a-5p secreted by hepatic stellate cells targets KLF-4, regulating the macrophage inflammatory response through the JNK signaling pathway. Exosomes containing miRNA-146a-5p released from HSCs following LPS treatment may increase macrophage sensitivity to LPS and trigger an inflammatory response. Exosomal miR-146a-5p derived from HSCs accelerates sepsis-induced liver injury by suppressing KLF-4 expression.

Kaempferol Remodels Liver Monocyte Populations and Treats Hepatic Fibrosis in Mice by Modulating Intestinal Flora and Metabolic Reprogramming

Changes in gut flora are associated with liver fibrosis. The interactions of host with intestinal flora are still unknown, with little research investigating such interactions with comprehensive multi-omics data. The present work analyzed and integrated large-scale multi-omics transcriptomics, microbiome, metabolome, and single-cell RNA-sequencing datasets from Kaempferol-treated and untreated control groups by advanced bioinformatics methods. This study concludes that kaempferol dose-dependently improved serum markers (like AST, ALT, TBil, Alb, and PT) and suppressed fibrosis markers (including HA, PC III, LN, α-SMA, and Collagen I), while kaempferol also increased body weight. Mechanistically, kaempferol improved the metabolic levels of intestinal flora dysbiosis and associated lipids. This was achieved by increasing the abundance of g__Robinsoniella, g__Erysipelotrichaceae_UCG-003, g__Coriobacteriaceae_UCG-002, and 5-Methylcytidine, all-trans-5,6- Epoxyretinoic acid, LPI (18:0), LPI (20:4), etc. to achieve this. Kaemferol exerts anti-inflammatory and immune-enhancing effects by down-regulating the Th17/IL-17 signaling pathway in PDGF-induced LX2 cells. In addition, kaempferol administration remarkably elevated CD4 + T and CD8 + T cellular proportions, thereby activating immune cells for protecting the body and controlling inflammatory conditions. The combined interaction of multiple data may explain how Kaempferol modulates the intestinal flora thereby remodeling the hepatocyte population and alleviating liver fibrosis.

The double-edged role and therapeutic potential of TREM2 in atherosclerosis

Atherosclerosis is a chronic lipid-driven inflammatory disease characterized by infiltration of large numbers of macrophages. The progression of the disease is closely related to the status of macrophages in atherosclerotic plaques. Recent advances in plaque analysis have revealed a subpopulation of macrophages that express high levels of triggering receptor expressed on myeloid cells 2 (TREM2). Although TREM2 is known to play a critical role in inflammation, lipid metabolism, and tissue repair, its role in atherosclerosis is still not fully understood. Recent studies have shown that TREM2 promotes macrophage cholesterol uptake and efflux, enhances efferocytosis function, regulates inflammation and metabolism, and promotes cell survival, all of which are significant functions in atherosclerosis. In early plaques TREM2 promotes lipid uptake and increases lesion size. In advanced plaques TREM2 promotes macrophage survival and increases plaque stability. The dualistic nature of TREM2 in atherosclerosis, where it can exert both protective effect and a side effect of increased lesion size, presents a complex but crucial area of study. Understanding these dual roles could help in the development of new therapeutic strategies to modulate TREM2 activity and utilize its atheroprotective function while mitigating its deleterious effects. In this review, we discuss the roles and mechanisms of TREM2 during different stages of atherosclerotic plaques, as well as the potential applications of TREM2 in the diagnosis and treatment of atherosclerosis.

Understanding the complex macrophage landscape in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) represents a spectrum of disease states ranging from simple steatosis to metabolic dysfunction-associated steatohepatitis (MASH), which can eventually lead to the development of cirrhosis and hepatocellular carcinoma. Macrophages have long been implicated in driving the progression from steatosis to end-stage disease, yet we still know relatively little about the precise involvement of these cells in MASLD progression and/or regression. Rather, there are a considerable number of conflicting reports regarding the precise roles of these cells. This confusion stems from the fact that, until recently, macrophages in the liver were considered a homogenous population. However, thanks to recent technological advances including multi-parameter flow cytometry, single-cell RNA sequencing and spatial proteogenomics, we now know that this is not the case. Rather hepatic macrophages, even in the healthy liver, are heterogenous, existing in multiple subsets with distinct transcriptional profiles and hence likely functions. This heterogeneity is even more prominent in MASLD, where the macrophage pool consists of multiple different subsets of resident and recruited cells. To probe the unique functions of these cells and determine if targeting macrophages may be a viable therapeutic strategy in MASLD, we first need to unravel this complexity and decipher which populations and/or activation states are present and what functions each of these may play in driving MASLD progression. In this review, we summarise recent advances in the field, highlighting what is currently known about the hepatic macrophage landscape in MASLD and the questions that remain to be tackled.

Unveiling the impact of TREM-2+ Macrophages in metabolic disorders

The Triggering Receptor Expressed on Myeloid cells 2 (TREM-2) has been widely known by its anti-inflammatory activity. It can be activated in response to microbes and tissue damage, leading to phagocytosis, autophagy, cell polarization and migration, counter inflammation, and tissue repair. So far, the receptor has been largely explored in neurodegenerative disorders, however, a growing number of studies have been investigating its contribution in different pathological conditions, including metabolic diseases, in which (resident) macrophages play a crucial role. In this regard, TREM-2 + macrophages have been implicated in the onset and development of obesity, atherosclerosis, and fibrotic liver disease. These macrophages can be detected in the brain, white adipose tissue, liver, and vascular endothelium. In this review we discuss how different murine models have been demonstrating the ability of such cells to contribute to tissue and body homeostasis by phagocytosing cellular debris and lipid structures, besides contributing to lipid homeostasis in metabolic diseases. Therefore, understanding the role of TREM-2 in metabolic disorders is crucial to expand our current knowledge concerning their immunopathology as well as to foster the development of more targeted therapies to treat such conditions.

TET3-overexpressing macrophages promote endometriosis

Endometriosis is a debilitating, chronic inflammatory disease affecting approximately 10% of reproductive-age women worldwide with no cure. While macrophages have been intrinsically linked to the pathophysiology of endometriosis, targeting them therapeutically has been extremely challenging due to their high heterogeneity and because these disease-associated macrophages (DAMs) can be either pathogenic or protective. Here, we report identification of pathogenic macrophages characterized by TET3 overexpression in human endometriosis lesions. We show that factors from the disease microenvironment upregulated TET3 expression, transforming macrophages into pathogenic DAMs. TET3 overexpression stimulated proinflammatory cytokine production via a feedback mechanism involving inhibition of let-7 miRNA expression. Remarkably, these cells relied on TET3 overexpression for survival and hence were vulnerable to TET3 knockdown. We demonstrated that Bobcat339, a synthetic cytosine derivative, triggered TET3 degradation in both human and mouse macrophages. This degradation was dependent on a von Hippel-Lindau (VHL) E3 ubiquitin ligase whose expression was also upregulated in TET3-overexpressing macrophages. Furthermore, depleting TET3-overexpressing macrophages either through myeloid-specific Tet3 ablation or using Bobcat339 strongly inhibited endometriosis progression in mice. Our results defined TET3-overexpressing macrophages as key pathogenic contributors to and attractive therapeutic targets for endometriosis. Our findings may also be applicable to other chronic inflammatory diseases where DAMs have important roles.

Dissection of molecular mechanisms of liver injury induced by microcystin-leucine arginine via single-cell RNA-sequencing

The occurrence of poisoning incidents caused by cyanobacterial blooms has aroused wide public concern. Microcystin-leucine arginine (MC-LR) is a well-established toxin produced by cyanobacterial blooms, which is widely distributed in eutrophic waters. MC-LR is not only hazardous to the water environment but also exerts multiple toxic effects including liver toxicity in both humans and animals. However, the underlying mechanisms of MC-LR-induced liver toxicity are unclear. Herein, we used advanced single-cell RNA sequencing technology to characterize MC-LR-induced liver injury in mice. We established the first single-cell atlas of mouse livers in response to MC-LR. Our results showed that the differentially expressed genes and pathways in diverse cell types of liver tissues of mice treated with MC-LR are highly heterogeneous. Deep analysis showed that MC-LR induced an increase in a subpopulation of hepatocytes that highly express Gstm3, which potentially contributed to hepatocyte apoptosis in response to MC-LR. Moreover, MC-LR increased the proportion and multiple subtypes of Kupffer cells with M1 phenotypes and highly expressed proinflammatory genes. Furthermore, the MC-LR increased several subtypes of CD8+ T cells with highly expressed multiple cytokines and chemokines. Overall, apart from directly inducing hepatocytes apoptosis, MC-LR activated proinflammatory Kupffer cell and CD8+ T cells, and their interaction may constitute a hostile microenvironment that contributes to liver injury. Our findings not only present novel insight into underlying molecular mechanisms but also provide a valuable resource and foundation for additional discovery of MC-LR-induced liver toxicity.