Macrophage Subsets in Obesity, Aligning the Liver and Adipose Tissue

Adropin regulates macrophage phenotype via PPARγ signalling: A preliminary study of adropin and Crohn's disease

Macrophage polarization is increasingly recognized as a vital pathogenetic factor in Crohn's disease (CD). Adropin is a secreted protein implicated in energy homeostasis, chiefly linked to glucose and lipid metabolism. However, the significance of adropin in CD is not clear. The objective of this study was to detect the expression of adropin in CD patients and investigate the effect of adropin on macrophage polarization induced by lipopolysaccharide (LPS) and its potential mechanism. Our study showed that serum adropin levels were markedly lower in patients with CD in active (CDA) than patients with CD in remission (CDR) and control groups (p < 0.01), however, there was no significant difference between in remission CD and healthy controls (p > 0.05). The colon mucous adropin levels in CDA were distinctly higher than CDR and controls (p < 0.01), while a significant difference between in remission CD and in healthy controls was not observed (p > 0.05). Exploration of the specific mechanism of action indicated that adropin promoted LPS-induced RAW264.7 macrophage polarization to M2 phenotype by modulating the expression and nuclear translocation of peroxisome proliferator receptor gamma (PPARγ), which may help weaken the intestinal inflammatory response. PPARγ inhibitor GW9662 reversed adropin-induced M2 macrophage polarization. Knockdown of GPR19, an adropin receptor, abrogated the M2 macrophage polarization caused by PPARγ. These findings suggest that adropin in colonic mucosa is a protective response in patients with active Crohn's disease.

Identification of conserved and tissue-restricted transcriptional profiles for lipid associated macrophages (LAMs)

Macrophages are essential immune cells present in all tissues, and are vital for maintaining tissue homeostasis, immune surveillance, and immune responses. Considerable efforts have identified shared and tissue-specific gene programs for macrophages across organs during homeostasis. This information has dramatically enhanced our understanding of tissue-restricted macrophage programming and function. However, few studies have addressed the overlapping and tissue-specific responses of macrophage subsets following inflammatory responses. One subset of macrophages that has been observed across several studies, lipid-associated macrophages (LAMs), have gained interest due to their unique role in lipid metabolism and potential as a therapeutic target. LAMs have been associated with regulating disease outcomes in metabolically related disorders including atherosclerosis, obesity, and nonalcoholic fatty liver disease (NAFLD). In this study, we utilized single-cell RNA sequencing (scRNAseq) data to profile LAMs across multiple tissues and sterile inflammatory conditions in mice and humans. Integration of data from various disease models revealed that LAMs share a set of conserved transcriptional profiles, including Trem2 and Lpl, but also identified key sets of tissue-specific LAM gene programs. Importantly, the shared LAM markers were highly conserved with human LAM populations that also emerge in chronic inflammatory settings. Overall, this analysis provides a detailed transcriptional landscape of tissue-restricted and shared LAM gene programs and offers insights into their roles in metabolic and chronic inflammatory diseases. These data may help instruct appropriate targets for broad or tissue-restricted therapeutic interventions to modulate LAM populations in disease.

Enrichment of novel CD3+F4/80+ cells in brown adipose tissue following adrenergic stimulation

Macrophages play a multifaceted role in maintaining tissue homeostasis, fighting infections, and regulating cold-induced thermogenesis. The brown adipose tissue (BAT) is crucial for maintaining body temperature during cold exposure. Cold stress triggers the sympathetic nervous system to release norepinephrine (NE), which activates BAT via β3-adrenergic receptors, initiating lipolysis and glycolysis. BAT-infiltrating macrophages can either hinder or enhance thermogenesis by controlling the interplay between BAT cells and sympathetic nerves. In this study we report on a unique population of CD3+F4/80+ dual lineage co-expressing (DE) cells within the interscapular BAT (iBAT), that increased following chronic adrenergic stimulation. In forward scatter/side scatter plots, they formed a cluster distinct from lymphocytes, appearing larger and more complex. These CD3+F4/80+ DE cells demonstrated the lack of T cell markers CD62L and TCRβ and expressed higher levels of Ly6C, F4/80, and CD11b markers compared to T cells and CD3- macrophages. Furthermore, analysis revealed two subpopulations within the CD3+F4/80+ DE population based on MHCII expression, with the proportion of MHCII-low subset increasing with adrenergic stimulation. This novel DE population within iBAT, unequivocally identified by the its unique surface marker profile, warrants further investigation into the intricate mechanisms governing adaptive thermogenesis regulation.

Adrenal gland macrophages regulate glucocorticoid production through Trem2 and TGF-β

Glucocorticoid synthesis by adrenal glands (AGs) is regulated by the hypothalamic-pituitary-adrenal axis to facilitate stress responses when the host is exposed to stimuli. Recent studies implicate macrophages as potential steroidogenic regulators, but the molecular mechanisms by which AG macrophages exert such influence remain unclear. In this study, we investigated the role of AG macrophages in response to cold challenge or atherosclerotic inflammation as physiologic models of acute or chronic stress. Using single-cell RNA sequencing, we observed dynamic AG macrophage polarization toward classical activation and lipid-associated phenotypes following acute or chronic stimulation. Among transcriptional alterations induced in macrophages, triggering receptor expressed on myeloid cells 2 (Trem2) was highlighted because of its upregulation following stress. Conditional deletion of macrophage Trem2 revealed a protective role in stress responses. Mechanistically, Trem2 deletion led to increased AG macrophage death, abolished the TGF-β-producing capacity of AG macrophages, and resulted in enhanced glucocorticoid production. In addition, enhanced glucocorticoid production was replicated by blockade of TGF-β signaling. Together, these observations suggest that AG macrophages restrict steroidogenesis through Trem2 and TGF-β, which opens potential avenues for immunotherapeutic interventions to resolve stress-related disorders.

Comprehensive study of the interplay between immunological and metabolic factors in hepatic steatosis

The pathophysiology of hepatic steatosis is thoroughly reviewed in this comprehensive report, with particular attention to the complex interactions between inflammatory pathways, insulin resistance, lipid metabolism, metabolic dysregulation, and immunological responses in the liver including non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and hepatocellular carcinoma (HCC). The study highlights the role of immune cell regulation in disease progression and explores the potential of immune cell-specific treatments for treating hepatic disorders. The development of liver disorders is significantly influenced by immune cells, including dendritic cells, T cells, and natural killer cells. Clinical investigations show that immune cell-specific treatments can effectively reduce liver fibrosis and inflammation. Future research should focus on finding new immunological targets for therapeutic interventions, as well as addressing the management challenges associated with NAFLD/NASH. Hepatic immune microorganisms also impact liver homeostasis and disorders. Improvements in immune cell regulation and liver transplantation methods give patients hope for better prognoses. Important phases include optimizing the selection of donors for malignancy of the liver, using machine perfusion for organ preservation, and fine-tuning immunosuppressive strategies. For focused treatments in hepatic steatosis, it is imperative to understand the intricate interactions between immune and metabolic variables. Understanding the liver's heterogeneous immune profile, encompassing a range of immune cell subpopulations, is crucial for formulating focused therapeutic interventions. To improve patient care and outcomes in hepatic illnesses, there is an urgent need for further research and innovation. Therefore, to effectively treat hepatic steatosis, it is important to enhance therapeutic techniques and maximize liver transplantation strategies.

Facile adipocyte uptake and liver/adipose tissue delivery of conjugated linoleic acid-loaded tocol nanocarriers for a synergistic anti-adipogenesis effect

Obesity is a major risk to human health. Adipogenesis is blocked by α-tocopherol and conjugated linoleic acid (CLA). However, their effect at preventing obesity is uncertain. The effectiveness of the bioactive agents is associated with their delivery method. Herein, we designed CLA-loaded tocol nanostructured lipid carriers (NLCs) for enhancing the anti-adipogenic activity of α-tocopherol and CLA. Adipogenesis inhibition by the nanocarriers was examined using an in vitro adipocyte model and an in vivo rat model fed a high fat diet (HFD). The targeting of the tocol NLCs into adipocytes and adipose tissues were also investigated. A synergistic anti-adipogenesis effect was observed for the combination of free α-tocopherol and CLA. Nanoparticles with different amounts of solid lipid were developed with an average size of 121‒151 nm. The NLCs with the smallest size (121 nm) showed greater adipocyte internalization and differentiation prevention than the larger size. The small-sized NLCs promoted CLA delivery into adipocytes by 5.5-fold as compared to free control. The nanocarriers reduced fat accumulation in adipocytes by counteracting the expression of the adipogenic transcription factors peroxisome proliferator activated receptor (PPAR)γ and CCAAT/enhancer-binding protein (C/EBP)α, and lipogenic enzymes acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS). Localized administration of CLA-loaded tocol NLCs significantly reduced body weight, total cholesterol, and liver damage indicators in obese rats. The biodistribution study demonstrated that the nanoparticles mainly accumulated in liver and adipose tissues. The NLCs decreased adipocyte hypertrophy and cytokine overexpression in the groin and epididymis to a greater degree than the combination of free α-tocopherol and CLA. In conclusion, the lipid-based nanocarriers were verified to inhibit adipogenesis in an efficient and safe way.

Steatosis drives monocyte-derived macrophage accumulation in human metabolic dysfunction-associated fatty liver disease

Background & Aims

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a common complication of obesity with a hallmark feature of hepatic steatosis. Recent data from animal models of MAFLD have demonstrated substantial changes in macrophage composition in the fatty liver. In humans, the relationship between liver macrophage heterogeneity and liver steatosis is less clear.

Methods

Liver tissue from 21 participants was collected at time of bariatric surgery and analysed using flow cytometry, immunofluorescence, and H&E microscopy. Single-cell RNA sequencing was also conducted on a subset of samples (n = 3). Intrahepatic triglyceride content was assessed via MRI and tissue histology. Mouse models of hepatic steatosis were used to investigate observations made from human liver tissue.

Results

We observed variable degrees of liver steatosis with minimal fibrosis in our participants. Single-cell RNA sequencing revealed four macrophage clusters that exist in the human fatty liver encompassing Kupffer cells and monocyte-derived macrophages (MdMs). The genes expressed in these macrophage subsets were similar to those observed in mouse models of MAFLD. Hepatic CD14+ monocyte/macrophage number correlated with the degree of steatosis. Using mouse models of early liver steatosis, we demonstrate that recruitment of MdMs precedes Kupffer cell loss and liver damage. Electron microscopy of isolated macrophages revealed increased lipid accumulation in MdMs, and ex vivo lipid transfer experiments suggested that MdMs may serve a distinct role in lipid uptake during MAFLD.

Conclusions

The human liver in MAFLD contains macrophage subsets that align well with those that appear in mouse models of fatty liver disease. Recruited myeloid cells correlate well with the degree of liver steatosis in humans. MdMs appear to participate in lipid uptake during early stages of MALFD.

Impact and implications

Metabolic dysfunction associated fatty liver disease (MAFLD) is extremely common; however, the early inflammatory responses that occur in human disease are not well understood. In this study, we investigated macrophage heterogeneity in human livers during early MAFLD and demonstrated that similar shifts in macrophage subsets occur in human disease that are similar to those seen in preclinical models. These findings are important as they establish a translational link between mouse and human models of disease, which is important for the development and testing of new therapeutic approaches for MAFLD.

Peripheral and central macrophages in obesity

Obesity is associated with chronic, low-grade inflammation. Excessive nutrient intake causes adipose tissue expansion, which may in turn cause cellular stress that triggers infiltration of pro-inflammatory immune cells from the circulation as well as activation of cells that are residing in the adipose tissue. In particular, the adipose tissue macrophages (ATMs) are important in the pathogenesis of obesity. A pro-inflammatory activation is also found in other organs which are important for energy metabolism, such as the liver, muscle and the pancreas, which may stimulate the development of obesity-related co-morbidities, including insulin resistance, type 2 diabetes (T2D), cardiovascular disease (CVD) and non-alcoholic fatty liver disease (NAFLD). Interestingly, it is now clear that obesity-induced pro-inflammatory signaling also occurs in the central nervous system (CNS), and that pro-inflammatory activation of immune cells in the brain may be involved in appetite dysregulation and metabolic disturbances in obesity. More recently, it has become evident that microglia, the resident macrophages of the CNS that drive neuroinflammation, may also be activated in obesity and can be relevant for regulation of hypothalamic feeding circuits. In this review, we focus on the action of peripheral and central macrophages and their potential roles in metabolic disease, and how macrophages interact with other immune cells to promote inflammation during obesity.

From Reductionistic Approach to Systems Immunology Approach for the Understanding of Tumor Microenvironment

The tumor microenvironment (TME) is a complex and dynamic ecosystem that includes a variety of immune cells mutually interacting with tumor cells, structural/stromal cells, and each other. The immune cells in the TME can have dual functions as pro-tumorigenic and anti-tumorigenic. To understand such paradoxical functions, the reductionistic approach classifies the immune cells into pro- and anti-tumor cells and suggests the therapeutic blockade of the pro-tumor and induction of the anti-tumor immune cells. This strategy has proven to be partially effective in prolonging patients' survival only in a fraction of patients without offering a cancer cure. Recent advances in multi-omics allow taking systems immunology approach. This essay discusses how a systems immunology approach could revolutionize our understanding of the TME by suggesting that internetwork interactions of the immune cell types create distinct collective functions independent of the function of each cellular constituent. Such collective function can be understood by the discovery of the immunological patterns in the TME and may be modulated as a therapeutic means for immunotherapy of cancer.

Effects of Bacillus Calmette-Guérin on immunometabolism, microbiome and liver diseases⋆

Metabolic diseases have overtaken infectious diseases as the most serious public health issue and economic burden in most countries. Moreover, metabolic diseases increase the risk of having infectious diseases. The treatment of metabolic disease may require a long-term strategy of taking multiple medications, which can be costly and have side effects. Attempts to expand the therapeutic use of vaccination to prevent or treat metabolic diseases have attracted significant interest. A growing body of evidence indicates that Bacillus Calmette-Guérin (BCG) offers protection against non-infectious diseases. The non-specific effects of BCG occur likely due to the induction of trained immunity. In this regard, understanding how BCG influences the development of chronic metabolic health including liver diseases would be important. This review focuses on research on BCG, the constellation of disorders associated with metabolic health issues including liver diseases and diabetes as well as how BCG affects the gut microbiome, immunity, and metabolism.

Hepatic TREM2+ macrophages express matrix metalloproteinases to control fibrotic scar formation

Liver cirrhosis is characterized by the extensive deposition of extracellular matrix such as fibril collagen, causing dysfunction and failure of the liver. Hepatic macrophages play pivotal roles in the transition from inflammatory to restorative properties upon hepatic injury. In particular, scar-associated macrophages (SAMacs) control liver fibrosis with the representative expression of matrix metalloproteinase (MMP). However, the heterogenic SAMac population has not been well characterized yet. This study profiled heterogeneous liver macrophages using public databases of single-cell transcriptomics and found T-cell immunoglobulin and mucin containing (TIM)4^- macrophages exhibited elevated expression of MMPs. Scar-associated triggering receptor expressed on myeloid cells (TREM)2 was positively correlated with MMP expression, suggesting that TREM2⁺ subsets exert their fibrotic role via MMPs. During the progression of diet-induced nonalcoholic steatohepatitis and drug-induced liver cirrhosis, monocyte-derived TREM2⁺ macrophages accumulate in the liver with the distinct expression of MMPs. A noticeable expansion of MMP- and TREM2- double positive macrophages was observed in fibrotic scar regions. Consistently, the analysis of single-cell transcriptomics for human cirrhotic livers supported the theory that TREM2⁺ SAMacs are strongly associated with MMPs. The results could expand the understanding of liver fibrosis and SAMac, offering potential therapeutic approaches for liver cirrhosis.

Adipose Tissue Dysfunction: Impact on Metabolic Changes?

Adipose tissue is a metabolically dynamic organ that is the primary site of storage for excess energy, but it serves as an endocrine organ capable of synthesizing a number of biologically active compounds that regulate metabolic homeostasis. However, when the capacity of expansion of this tissue exceeds, dysfunction occurs, favoring ectopic accumulation of fat in the visceral, which has been implicated in several disease states, most notably obesity. This review highlights the mechanisms involved in the structure of adipose tissue, tissue expandability, adipocyte dysfunction, as well as the impact of these events on the manifestation of important metabolic disorders associated with adipose tissue dysfunction. A literature search using Pubmed, Web of Science, Scopus, and Cochrane databases were used to identify relevant studies, using clinical trials, experimental studies in animals and humans, case-control studies, case series, letters to the editor, and review articles published in English, without restrictions on year of publication. The excessive ectopic lipid accumulation leads to local inflammation and insulin resistance. Indeed, overnutrition triggers uncontrolled inflammatory responses white adipose tissue, leading to chronic low-grade inflammation, therefore fostering the progression of important metabolic disorders. Thus, it is essential to advance the understanding of the molecular mechanisms involved in adipose tissue dysfunction in order to mitigate the negative metabolic consequences of obesity.

Liver macrophages in health and disease

Single-cell and spatial transcriptomic technologies have revealed an underappreciated heterogeneity of liver macrophages. This has led us to rethink the involvement of macrophages in liver homeostasis and disease. Identification of conserved gene signatures within these cells across species and diseases is enabling the correct identification of specific macrophage subsets and the generation of more specific tools to track and study the functions of these cells. Here, we discuss what is currently known about the definitions of these different macrophage populations, the markers that can be used to identify them, how they are wired within the liver, and their functional specializations in health and disease.

Targeted therapeutics and novel signaling pathways in non-alcohol-associated fatty liver/steatohepatitis (NAFL/NASH)

Non-alcohol-associated fatty liver/steatohepatitis (NAFL/NASH) has become the leading cause of liver disease worldwide. NASH, an advanced form of NAFL, can be progressive and more susceptible to developing cirrhosis and hepatocellular carcinoma. Currently, lifestyle interventions are the most essential and effective strategies for preventing and controlling NAFL without the development of fibrosis. While there are still limited appropriate drugs specifically to treat NAFL/NASH, growing progress is being seen in elucidating the pathogenesis and identifying therapeutic targets. In this review, we discussed recent developments in etiology and prospective therapeutic targets, as well as pharmacological candidates in pre/clinical trials and patents, with a focus on diabetes, hepatic lipid metabolism, inflammation, and fibrosis. Importantly, growing evidence elucidates that the disruption of the gut-liver axis and microbe-derived metabolites drive the pathogenesis of NAFL/NASH. Extracellular vesicles (EVs) act as a signaling mediator, resulting in lipid accumulation, macrophage and hepatic stellate cell activation, further promoting inflammation and liver fibrosis progression during the development of NAFL/NASH. Targeting gut microbiota or EVs may serve as new strategies for the treatment of NAFL/NASH. Finally, other mechanisms, such as cell therapy and genetic approaches, also have enormous therapeutic potential. Incorporating drugs with different mechanisms and personalized medicine may improve the efficacy to better benefit patients with NAFL/NASH.

Modulating hepatic macrophages with annexin A1 in non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) and associated end-stage liver disease is a growing cause of concern throughout the Western world. It constitutes a significant clinical burden for which therapeutic approaches are very limited. Over the last years, considerable attention has therefore been paid to identifying potential therapeutic strategies to reduce this burden. Annexin A1 (AnxA1), a calcium-phospholipid binding protein, has been proposed to be a negative regulator of inflammation in the context of NASH. In a recent publication, Gadipudi, Ramavath, Provera et al. investigated the therapeutic potential of Annexin A1 treatment in preventing the progression of NASH. They demonstrate that treatment of mice with NASH with recombinant human AnxA1 can reduce inflammation and fibrosis without affecting steatosis or metabolic syndrome. This was proposed to be achieved through the modulation of the macrophage populations present in the liver. Here, we discuss the main findings of this work and raise some outstanding questions regarding the possible mechanisms involved and the functions of distinct macrophage populations in NASH.

Endoplasmic reticulum stress in innate immune cells - a significant contribution to non-alcoholic fatty liver disease

Liver disease and its complications affect millions of people worldwide. NAFLD (non-alcoholic fatty liver disease) is the liver disease associated with metabolic dysfunction and consists of four stages: steatosis with or without mild inflammation (NAFLD), non-alcoholic steatohepatitis (NASH), fibrosis, and cirrhosis. With increased necroinflammation and progression of liver fibrosis, NAFLD may progress to cirrhosis or even hepatocellular carcinoma. Although the underlying mechanisms have not been clearly elucidated in detail, what is clear is that complex immune responses are involved in the pathogenesis of NASH, activation of the innate immune system is critically involved in triggering and amplifying hepatic inflammation and fibrosis in NAFLD/NASH. Additionally, disruption of endoplasmic reticulum (ER) homeostasis in cells, also known as ER stress, triggers the unfolded protein response (UPR) which has been shown to be involved to inflammation and apoptosis. To further develop the prevention and treatment of NAFLD/NASH, it is imperative to clarify the relationship between NAFLD/NASH and innate immune cells and ER stress. As such, this review focuses on innate immune cells and their ER stress in the occurrence of NAFLD and the progression of cirrhosis.

Plasticity of monocytes and macrophages in cirrhosis of the liver

Cirrhosis of the liver is a systemic condition with raising prevalence worldwide. Patients with cirrhosis are highly susceptible to develop bacterial infections leading to acute decompensation and acute-on-chronic liver failure both associated with a high morbidity and mortality and sparse therapeutic options other than transplantation. Mononuclear phagocytes play a central role in innate immune responses and represent a first line of defence against pathogens. Their function includes phagocytosis, killing of bacteria, antigen presentation, cytokine production as well as recruitment and activation of immune effector cells. Liver injury and development of cirrhosis induces activation of liver resident Kupffer cells and recruitment of monocytes to the liver. Damage- and pathogen-associated molecular patterns promote systemic inflammation which involves multiple compartments besides the liver, such as the circulation, gut, peritoneal cavity and others. The function of circulating monocytes and tissue macrophages is severely impaired and worsens along with cirrhosis progression. The underlying mechanisms are complex and incompletely understood. Recent 'omics' technologies help to transform our understanding of cellular diversity and function in health and disease. In this review we point out the current state of knowledge on phenotypical and functional changes of monocytes and macrophages during cirrhosis evolution in different compartments and their role in disease progression. We also discuss the value of potential prognostic markers for cirrhosis-associated immuneparesis, and future immunotherapeutic strategies that may reduce the need for transplantation and death.

SerpinB3 as a Pro-Inflammatory Mediator in the Progression of Experimental Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is becoming the most common chronic liver disease worldwide. In 20-30% of patients, NAFLD can progress into non-alcoholic steatohepatitis (NASH), eventually leading to fibrosis, cirrhosis and hepatocellular carcinoma development. SerpinB3 (SB3), a hypoxia-inducible factor-2α dependent cysteine protease inhibitor, is up-regulated in hepatocytes during progressive NAFLD and proposed to contribute to disease progression. In this study we investigated the pro-inflammatory role of SB3 by employing phorbol-myristate acetate-differentiated human THP-1 macrophages exposed in vitro to human recombinant SB3 (hrSB3) along with mice overexpressing SB3 in hepatocytes (TG/SB3) or knockout for SB3 (KO/SB3) in which NASH was induced by feeding methionine/choline deficient (MCD) or a choline-deficient, L-amino acid defined (CDAA) diets. In vivo experiments showed that the induction of NASH in TG/SB3 mice was characterized by an impressive increase of liver infiltrating macrophages that formed crown-like aggregates and by an up-regulation of hepatic transcript levels of pro-inflammatory cytokines. All these parameters and the extent of liver damage were significantly blunted in KO/SB3 mice. In vitro experiments confirmed that hrSB3 stimulated macrophage production of M1-cytokines such as TNFα and IL-1β and reactive oxygen species along with that of TGFβ and VEGF through the activation of the NF-kB transcription factor. The opposite changes in liver macrophage activation observed in TG/SB3 or KO/SB3 mice with NASH were associated with a parallel modulation in the expression of triggering receptor expressed on myeloid cells-2 (TREM2), CD9 and galectin-3 markers, recently detected in NASH-associated macrophages. From these results we propose that SB3, produced by activated/injured hepatocytes, may operate as a pro-inflammatory mediator in NASH contributing to the disease progression.

TREM2 in the pathogenesis of AD: a lipid metabolism regulator and potential metabolic therapeutic target

Triggering receptor expressed on myeloid cells 2 (TREM2) is a single-pass transmembrane immune receptor that is mainly expressed on microglia in the brain and macrophages in the periphery. Recent studies have identified TREM2 as a risk factor for Alzheimer’s disease (AD). Increasing evidence has shown that TREM2 can affect lipid metabolism both in the central nervous system (CNS) and in the periphery. In the CNS, TREM2 affects the metabolism of cholesterol, myelin, and phospholipids and promotes the transition of microglia into a disease-associated phenotype. In the periphery, TREM2 influences lipid metabolism by regulating the onset and progression of obesity and its complications, such as hypercholesterolemia, atherosclerosis, and nonalcoholic fatty liver disease. All these altered lipid metabolism processes could influence the pathogenesis of AD through several means, including affecting inflammation, insulin resistance, and AD pathologies. Herein, we will discuss a potential pathway that TREM2 mediates lipid metabolism to influence the pathogenesis of AD in both the CNS and periphery. Moreover, we discuss the possibility that TREM2 may be a key factor that links central and peripheral lipid metabolism under disease conditions, including AD. This link may be due to impacts on the integrity of the blood–brain barrier, and we introduce potential pathways by which TREM2 affects the blood–brain barrier. Moreover, we discuss the role of lipids in TREM2-associated treatments for AD. We propose some potential therapies targeting TREM2 and discuss the prospect and limitations of these therapies.

Cell-Type Resolved Insights into the Cis-Regulatory Genome of NAFLD

The prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing rapidly, and unmet treatment can result in the development of hepatitis, fibrosis, and liver failure. There are difficulties involved in diagnosing NAFLD early and for this reason there are challenges involved in its treatment. Furthermore, no drugs are currently approved to alleviate complications, a fact which highlights the need for further insight into disease mechanisms. NAFLD pathogenesis is associated with complex cellular changes, including hepatocyte steatosis, immune cell infiltration, endothelial dysfunction, hepatic stellate cell activation, and epithelial ductular reaction. Many of these cellular changes are controlled by dramatic changes in gene expression orchestrated by the cis-regulatory genome and associated transcription factors. Thus, to understand disease mechanisms, we need extensive insights into the gene regulatory mechanisms associated with tissue remodeling. Mapping cis-regulatory regions genome-wide is a step towards this objective and several current and emerging technologies allow detection of accessible chromatin and specific histone modifications in enriched cell populations of the liver, as well as in single cells. Here, we discuss recent insights into the cis-regulatory genome in NAFLD both at the organ-level and in specific cell populations of the liver. Moreover, we highlight emerging technologies that enable single-cell resolved analysis of the cis-regulatory genome of the liver.

The National Consensus statement on the management of adult patients with non-alcoholic fatty liver disease and main comorbidities

The National Consensus was prepared with the participation of the National Medical Association for the Study of the Multimorbidity, Russian Scientific Liver Society, Russian Association of Endocrinologists, Russian Association of Gerontologists and Geriatricians, National Society for Preventive Cardiology, Professional Foundation for the Promotion of Medicine Fund PROFMEDFORUM. The aim of the multidisciplinary consensus is a detailed analysis of the course of non-alcoholic fatty liver disease (NAFLD) and the main associated conditions. The definition of NAFLD is given, its prevalence is described, methods for diagnosing its components such as steatosis, inflammation and fibrosis are described. The association of NAFLD with a number of cardio-metabolic diseases (arterial hypertension, atherosclerosis, thrombotic complications, type 2 diabetes mellitus (T2DM), obesity, dyslipidemia, etc.), chronic kidney disease (CKD) and the risk of developing hepatocellular cancer (HCC) were analyzed. The review of non-drug methods of treatment of NAFLD and modern opportunities of pharmacotherapy are presented. The possibilities of new molecules in the treatment of NAFLD are considered: agonists of nuclear receptors, antagonists of pro-inflammatory molecules, etc. The positive properties and disadvantages of currently used drugs (vitamin E, thiazolidinediones, etc.) are described. Special attention is paid to the multi-target ursodeoxycholic acid (UDCA) molecule in the complex treatment of NAFLD as a multifactorial disease. Its anti-inflammatory, anti-oxidant and cytoprotective properties, the ability to reduce steatosis an independent risk factor for the development of cardiovascular pathology, reduce inflammation and hepatic fibrosis through the modulation of autophagy are considered. The ability of UDCA to influence glucose and lipid homeostasis and to have an anticarcinogenic effect has been demonstrated. The Consensus statement has advanced provisions for practitioners to optimize the diagnosis and treatment of NAFLD and related common pathogenetic links of cardio-metabolic diseases.

Hepatic sexual dimorphism - implications for non-alcoholic fatty liver disease

The liver is often thought of as a single functional unit, but both its structural and functional architecture make it highly multivalent and adaptable. In any given physiological situation, the liver can maintain metabolic homeostasis, conduct appropriate inflammatory responses, carry out endobiotic and xenobiotic transformation and synthesis reactions, as well as store and release multiple bioactive molecules. Moreover, the liver is a very resilient organ. This resilience means that chronic liver diseases can go unnoticed for decades, yet culminate in life-threatening clinical complications once the adaptive capacity of the liver is overwhelmed. Non-alcoholic fatty liver disease (NAFLD) predisposes individuals to cirrhosis and increases liver-related and cardiovascular disease-related mortality. This Review discusses the accumulating evidence of sexual dimorphism in NAFLD, which is currently rarely considered in preclinical and clinical studies. Increased awareness of the mechanistic causes of hepatic sexual dimorphism could lead to improved understanding of the biological processes that are dysregulated in NAFLD, to the identification of relevant therapeutic targets and to improved risk stratification of patients with NAFLD undergoing therapeutic intervention.

Welcoming c-MAF to the macrophage transcription factor VAM-ily

[Figure: see text].

The Role of Innate Immune Cells in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a very common hepatic pathology featuring steatosis and is linked to obesity and related conditions, such as the metabolic syndrome. When hepatic steatosis is accompanied by inflammation, the disorder is defined as nonalcoholic steatohepatitis (NASH), which in turn can progress toward fibrosis development that can ultimately result in cirrhosis. Cells of innate immunity, such as neutrophils or macrophages, are central regulators of NASH-related inflammation. Recent studies utilizing new experimental technologies, such as single-cell RNA sequencing, have revealed substantial heterogeneity within the macrophage populations of the liver, suggesting distinct functions of liver-resident Kupffer cells and recruited monocyte-derived macrophages with regards to regulation of liver inflammation and progression of NASH pathogenesis. Herein, we discuss recent developments concerning the function of innate immune cell subsets in NAFLD and NASH.

Hepatic Macrophage Responses in Inflammation, a Function of Plasticity, Heterogeneity or Both?

With the increasing availability and accessibility of single cell technologies, much attention has been given to delineating the specific populations of cells present in any given tissue. In recent years, hepatic macrophage heterogeneity has also begun to be examined using these strategies. While previously any macrophage in the liver was considered to be a Kupffer cell (KC), several studies have recently revealed the presence of distinct subsets of hepatic macrophages, including those distinct from KCs both under homeostatic and non-homeostatic conditions. This heterogeneity has brought the concept of macrophage plasticity into question. Are KCs really as plastic as once thought, being capable of responding efficiently and specifically to any given stimuli? Or are the differential responses observed from hepatic macrophages in distinct settings due to the presence of multiple subsets of these cells? With these questions in mind, here we examine what is currently understood regarding hepatic macrophage heterogeneity in mouse and human and examine the role of heterogeneity vs plasticity in regards to hepatic macrophage responses in settings of both pathogen-induced and sterile inflammation.

Metformin Actions on the Liver: Protection Mechanisms Emerging in Hepatocytes and Immune Cells against NASH-Related HCC

Nonalcoholic fatty liver disease (NAFLD) is strongly linked to the global epidemic of obesity and type 2 diabetes mellitus (T2DM). Notably, NAFLD can progress from the mildest form of simple steatosis to nonalcoholic steatohepatitis (NASH) that increases the risk for hepatocellular carcinoma (HCC), which is a malignancy with a dismal prognosis and rising incidence in the United States and other developed counties, possibly due to the epidemic of NAFLD. Metformin, the first-line drug for T2DM, has been suggested to reduce risks for several types of cancers including HCC and protect against NASH-related HCC, as revealed by epidemical studies on humans and preclinical studies on animal models. This review focuses on the pathogenesis of NASH-related HCC and the mechanisms by which metformin inhibits the initiation and progression of NASH-related HCC. Since the functional role of immune cells in liver homeostasis and pathogenesis is increasingly appreciated in developing anti-cancer therapies on liver malignancies, we discuss both the traditional targets of metformin in hepatocytes and the recently defined effects of metformin on immune cells.

Hepatic transcriptional profile reveals the role of diet and genetic backgrounds on metabolic traits in female progenitor strains of the Collaborative Cross

Mice have provided critical mechanistic understandings of clinical traits underlying metabolic syndrome (MetSyn) and susceptibility to MetSyn in mice is known to vary among inbred strains. We investigated the diet- and strain-dependent effects on metabolic traits in the eight Collaborative Cross (CC) founder strains (A/J, C57BL/6J, 129S1/SvImJ, NOD/ShiLtJ, NZO/HILtJ, CAST/EiJ, PWK/PhJ, and WSB/EiJ). Liver transcriptomics analysis showed that both atherogenic diet and host genetics have profound effects on the liver transcriptome, which may be related to differences in metabolic traits observed between strains. We found strain differences in circulating trimethylamine N-oxide (TMAO) concentration and liver triglyceride content, both of which are traits associated with metabolic diseases. Using a network approach, we identified a module of transcripts associated with TMAO and liver triglyceride content, which was enriched in functional pathways. Interrogation of the module related to metabolic traits identified NADPH oxidase 4 (Nox4), a gene for a key enzyme in the production of reactive oxygen species, which showed a strong association with plasma TMAO and liver triglyceride. Interestingly, Nox4 was identified as the highest expressed in the C57BL/6J and NZO/HILtJ strains and the lowest expressed in the CAST/EiJ strain. Based on these results, we suggest that there may be genetic variation in the contribution of Nox4 to the regulation of plasma TMAO and liver triglyceride content. In summary, we show that liver transcriptomic analysis identified diet- or strain-specific pathways for metabolic traits in the Collaborative Cross (CC) founder strains.

Liver macrophages and inflammation in physiology and physiopathology of non-alcoholic fatty liver disease

Non‐alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of metabolic syndrome, being a common comorbidity of type 2 diabetes and with important links to inflammation and insulin resistance. NAFLD represents a spectrum of liver conditions ranging from steatosis in the form of ectopic lipid storage, to inflammation and fibrosis in nonalcoholic steatohepatitis (NASH). Macrophages that populate the liver play important roles in maintaining liver homeostasis under normal physiology and in promoting inflammation and mediating fibrosis in the progression of NAFLD toward to NASH. Liver macrophages are a heterogenous group of innate immune cells, originating from the yolk sac or from circulating monocytes, that are required to maintain immune tolerance while being exposed portal and pancreatic blood flow rich in nutrients and hormones. Yet, liver macrophages retain a limited capacity to raise the alarm in response to danger signals. We now know that macrophages in the liver play both inflammatory and noninflammatory roles throughout the progression of NAFLD. Macrophage responses are mediated first at the level of cell surface receptors that integrate environmental stimuli, signals are transduced through multiple levels of regulation in the cell, and specific transcriptional programmes dictate effector functions. These effector functions play paramount roles in determining the course of disease in NAFLD and even more so in the progression towards NASH. The current review covers recent reports in the physiological and pathophysiological roles of liver macrophages in NAFLD. We emphasise the responses of liver macrophages to insulin resistance and the transcriptional machinery that dictates liver macrophage function.

Macrophages in Chronic Liver Failure: Diversity, Plasticity and Therapeutic Targeting

Chronic liver injury results in immune-driven progressive fibrosis, with risk of cirrhosis development and impact on morbidity and mortality. Persistent liver cell damage and death causes immune cell activation and inflammation. Patients with advanced cirrhosis additionally experience pathological bacterial translocation, exposure to microbial products and chronic engagement of the immune system. Bacterial infections have a high incidence in cirrhosis, with spontaneous bacterial peritonitis being the most common, while the subsequent systemic inflammation, organ failure and immune dysregulation increase the mortality risk. Tissue-resident and recruited macrophages play a central part in the development of inflammation and fibrosis progression. In the liver, adipose tissue, peritoneum and intestines, diverse macrophage populations exhibit great phenotypic and functional plasticity determined by their ontogeny, epigenetic programming and local microenvironment. These changes can, at different times, promote or ameliorate disease states and therefore represent potential targets for macrophage-directed therapies. In this review, we discuss the evidence for macrophage phenotypic and functional alterations in tissue compartments during the development and progression of chronic liver failure in different aetiologies and highlight the potential of macrophage modulation as a therapeutic strategy for liver disease.

MAFLD vs. NAFLD: shared features and potential changes in epidemiology, pathophysiology, diagnosis, and pharmacotherapy

ABSTRACT

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide, placing an increasing burden on human health. NAFLD is a complex multifactorial disease involving genetic, metabolic, and environmental factors. It is closely associated with metabolic syndrome, obesity, and type 2 diabetes, of which insulin resistance is the main pathophysiological mechanism. Over the past few decades, investigation of the pathogenesis, diagnosis, and treatments has revealed different aspects of NAFLD, challenging the accuracy of definition and therapeutic strategy for the clinical practice. Recently, experts reach a consensus that NAFLD does not reflect the current knowledge, and metabolic (dysfunction) associated fatty liver disease (MAFLD) is suggested as a more appropriate term. The new definition puts increased emphasis on the important role of metabolic dysfunction in it. Herein, the shared features and potential changes in epidemiology, pathophysiology, diagnosis, and pharmacotherapy of the newly defined MAFLD, as compared with the formerly defined NAFLD, are reviewed for updating our understanding.

Pro-inflammatory effect of obesity on rats with burn wounds

Objective

A burn is an inflammatory injury to the skin or other tissue due to contact with thermal, radioactive, electric, or chemical agents. Burn injury is an important cause of disability and death worldwide. Obesity is a significant public health problem, often causing underlying systemic inflammation. Studying the combined impact of burn injuries on obese patients has become critical to the successful treatment of these patients. The aim of this paper is to highlight the effect of inflammation associated with burn injuries on several body weight group in a rat study.

Materials and methods

Different degrees of obesity and burns were established in rats and divided into a normal weight group, overweight group, obese group, second-degree burn group, third-degree burn group, over-weight second-degree burn group, over-weight third-degree burn group, obese second-degree burn group, and obese third-degree burn group (20 rats per group). Changes in inflammatory factors and growth factor were measured on the 1st, 3rd, 7th and 14th days after burns were inflicted.

Results

The ELISA test showed that in the unburned control group, MCP-1, IL-1β and TNF-α protein expressions in the obese and over-weight groups were higher than the normal-weight group (P < 0.05). RT-PCR test showed that the expressions of MCP-1, IL-1β and TNF-α genes in the obese group were higher compared to the overweight and normal weight groups (P < 0.05). Three and 7 days after burns were inflicted, the level of VEGF in the normal weight group was higher than the obese group (P < 0.05), however increased VEGF was not observed on days 1 and 14.

Conclusion

Burn injury and obesity have a mutually synergistic effect on the body’s inflammatory response.

Lysosomotropic Features and Autophagy Modulators among Medical Drugs: Evaluation of Their Role in Pathologies

The concept of lysosomotropic agents significantly changed numerous aspects of cellular biochemistry, biochemical pharmacology, and clinical medicine. In the present review, we focused on numerous low-molecular and high-molecular lipophilic basic compounds and on the role of lipophagy and autophagy in experimental and clinical medicine. Attention was primarily focused on the most promising agents acting as autophagy inducers, which offer a new window for treatment and/or prophylaxis of various diseases, including type 2 diabetes mellitus, Parkinson's disease, and atherosclerosis. The present review summarizes current knowledge on the lysosomotropic features of medical drugs, as well as autophagy inducers, and their role in pathological processes.

Osteopontin Expression Identifies a Subset of Recruited Macrophages Distinct from Kupffer Cells in the Fatty Liver

Metabolic-associated fatty liver disease (MAFLD) represents a spectrum of disease states ranging from simple steatosis to non-alcoholic steatohepatitis (NASH). Hepatic macrophages, specifically Kupffer cells (KCs), are suggested to play important roles in the pathogenesis of MAFLD through their activation, although the exact roles played by these cells remain unclear. Here, we demonstrated that KCs were reduced in MAFLD being replaced by macrophages originating from the bone marrow. Recruited macrophages existed in two subsets with distinct activation states, either closely resembling homeostatic KCs or lipid-associated macrophages (LAMs) from obese adipose tissue. Hepatic LAMs expressed Osteopontin, a biomarker for patients with NASH, linked with the development of fibrosis. Fitting with this, LAMs were found in regions of the liver with reduced numbers of KCs, characterized by increased Desmin expression. Together, our data highlight considerable heterogeneity within the macrophage pool and suggest a need for more specific macrophage targeting strategies in MAFLD.

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Resident KCs are lost with time in MAFLD

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Resident KCs are replaced by distinct subsets of bone marrow derived macrophages

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One subset of recruited macrophages termed hepatic LAMs, express Osteopontin

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Hepatic LAMs are found in zones characterized by increased Desmin expression

Chronic Inflammation in Non-Alcoholic Steatohepatitis: Molecular Mechanisms and Therapeutic Strategies

Non-Alcoholic Steatohepatitis (NASH) is the progressive form of Non-Alcoholic Fatty Liver Disease (NAFLD), the main cause of chronic liver complications. The development of NASH is the consequence of aberrant activation of hepatic conventional immune, parenchymal, and endothelial cells in response to inflammatory mediators from the liver, adipose tissue, and gut. Hepatocytes, Kupffer cells and liver sinusoidal endothelial cells contribute to the significant accumulation of bone-marrow derived-macrophages and neutrophils in the liver, a hallmark of NASH. The aberrant activation of these immune cells elicits harmful inflammation and liver injury, leading to NASH progression. In this review, we highlight the processes triggering the recruitment and/or activation of hepatic innate immune cells, with a focus on macrophages, neutrophils, and innate lymphoid cells as well as the contribution of hepatocytes and endothelial cells in driving liver inflammation/fibrosis. On-going studies and preliminary results from global and specific therapeutic strategies to manage this NASH-related inflammation will also be discussed.