Oxidative phosphorylation selectively orchestrates tissue macrophage homeostasis

SLAMF7 is a key molecule that promotes M1 polarization in lung tissue macrophages of high-fat diet-fed asthma mice model

OBJECTIVE

Investigating the regulatory role of Signaling lymphocyte activation molecule family 7 (SLAMF7) in the pathogenesis of asthma in a high fat-fed (HFD) mouse model, providing targets for treating obese asthma.

METHODS

We constructed a mouse model of obese asthma, and Quantitative real-time RT-PCR (qPCR) for the detection of mRNA levels of SLAMF7 and M1 polarization markers of macrophages. Lung tissue levels of SLAMF7 protein, macrophage M1 polarization markers, and neutrophil markers were measured by Western blotting. The proportions of SLAMF7+ macrophages and neutrophils in bronchoalveolar lavage fluid (BALF) were determined by flow cytometry. Neutrophil inflammatory cytokine levels were determined by Enzyme-linked immunosorbent assay (ELISA). Immunofluorescence performed the colocalization of SLAMF7 and inducible nitric oxide synthase (iNOS). The regulation of SLAMF7 on M1 polarization of macrophages was verified by cell experiments.

RESULTS

The group of HFD asthmatic mice had more severe airway inflammation and mucus secretion. They also had higher SLAMF7 levels, airway neutrophil inflammation and M1 polarization of macrophages in lung tissue. SLAMF7 overexpression increased M1 polarization, and SLAMF7 knockdown decreased M1 polarization. The expression change of SLAMF7 affects the expression of NR4A1 and RUNX3, inhibiting NR4A1 and promoting RUNX3.

CONCLUSION

SLAMF7 expression is increased in obese asthma mice, accompanied by neutrophil infiltration and enhanced M1 polarization. SLAMF7 promotes M1 polarization may be through the NR4A1-RUNX3 axis, suppressing NR4A1, and promoting RUNX3.

TREM2 modulates macrophage pyroptosis and inflammatory responses to ameliorate aortic valve calcification

BACKGROUND

Calcific aortic valve disease (CAVD) leads to valve thickening and calcification. Valvular interstitial cells (VICs) play a crucial role in valve homeostasis and their differentiation into osteoblast-like cells is influenced by macrophages. Triggering receptor expressed on myeloid cells 2 (TREM2) is involved in lipid metabolism and inflammation, but its role in CAVD remains unclear.

METHODS

We evaluated TREM2 expression in CAVD using public datasets and clinical aortic valve samples. To investigate the impact and underlying mechanisms of macrophage TREM2 on VIC osteogenic differentiation, we utilized a high-fat diet (HFD)-induced ApoE-/- mouse model and a THP-1-VIC transwell co-culture system.

RESULTS

TREM2 expression was significantly elevated in macrophages within calcified aortic valve tissues from CAVD patients, as determined by bioinformatics, flow cytometry, qRT-PCR, western blot, and immunofluorescence. Inhibition of TREM2 in ApoE-/- mice on an HFD exacerbated aortic valve calcification. Mechanistically, TREM2 inhibition activated the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, promoting pyroptosis and the release of inflammatory cytokines. Additionally, TREM2 downregulation led to reduced phosphorylation of Syk/PI3K/AKT, decreased activity of respiratory chain complexes, impaired oxidative phosphorylation (OXPHOS), diminished ATP production, and increased reactive oxygen species (ROS) levels.

CONCLUSION

TREM2 regulates macrophage oxidative phosphorylation, NLRP3 inflammasome activation, pyroptosis, and inflammatory responses through the PI3K/AKT pathway. This underscores TREM2 as a potential therapeutic target for mitigating aortic valve calcification and slowing the progression of CAVD.

Immunometabolic shifts in autoimmune disease: Mechanisms and pathophysiological implications

Autoimmune diseases occur when the immune system abnormally attacks the body's normal tissues, causing inflammation and damage. Each disease has unique immune and metabolic dysfunctions during pathogenesis. In rheumatoid arthritis (RA), immune cells have different metabolic patterns and mitochondrial/lysosomal dysfunctions at different disease stages. In systemic lupus erythematosus (SLE), type I interferon (IFN) causes immune cell metabolic dysregulation, linking activation to metabolic shifts that may worsen the disease. In systemic sclerosis (SSc), mitochondrial changes affect fibroblast metabolism and the immune response. Idiopathic inflammatory myopathies (IIMs) patients have mitochondrial and metabolic issues. In primary Sjögren's syndrome (pSS), immune cell metabolism is imbalanced and mitochondrial damage can lead to cell/tissue damage. Metabolic reprogramming links cellular energy needs and immune dysfunctions, causing inflammation, damage, and symptoms in these diseases. It also affects immune cell functions like differentiation, proliferation, and secretion. This review discusses the potential of targeting metabolic pathways to restore immune balance, offering directions for future autoimmune disease research and treatment.

MSCs-EVs harboring OA immune memory reprogram macrophage phenotype via modulation of the mt-ND3/NADH-CoQ axis for OA treatment

BACKGROUND

Osteoarthritis (OA) is a prevalent degenerative joint disease and current therapies are insufficient to halt its progression. Mesenchymal stem cells-derived extracellular vesicles (MSCs-EVs) offer promising therapeutic potential for OA treatment, and their efficacy can be enhanced through strategic engineering approaches.

METHODS

Inspired by the immune memory of the adaptive immune system, we developed an engineered strategy to impart OA-specific immune memory to MSCs-EVs. Using Luminex technology, inflammatory factors (IFN-γ, IL-6, and TNF-α), which mimic the OA inflammatory microenvironment, were identified and used to prime MSCs, generating immune memory-bearing MSCs-EVs (iEVs). Proteomic analysis and complementary experiments were conducted to evaluate iEVs' effects on macrophage phenotypic reprogramming.

RESULTS

iEVs, particularly IL-6-EV, exhibited potent immunoregulatory functions along with the ability to modulate mitochondrial metabolism. Both in vitro and in vivo, IL-6-EV significantly reprogrammed macrophages towards the M2 subtype, effectively suppressing articular inflammation and OA progression. Mechanistic studies revealed that IL-6-EV facilitated M2 polarization by regulating mitochondrial oxidative phosphorylation via the mt-ND3/NADH-CoQ axis.

CONCLUSION

This study introduces a strategy to enhance MSCs-EVs' therapeutic efficacy in OA. Multi-omics analysis and biological validation demonstrate its potential, providing new insights for MSCs-EVs' future application in OA and other clinical conditions.

An sp2 Carbon-Conjugated Covalent Organic Framework for Fusing Lipid Droplets and Engineered Macrophage Therapy

Engineered immune cell therapy has proven to be a transformative cancer treatment despite the challenges of its prohibitive costs and manufacturing complexity. In this study, we propose a concise "lipid droplet fusion" strategy for engineering macrophages. Because of the integration of hydrophobic alkyl chains and π-conjugated structures, the mildly synthesized sp2C-conjugated covalent organic framework (COF) UM-101 induced lipid droplet fusion and metabolic reprogramming of macrophages, thus promoting their antitumor classical activation. Intravenous injection of UM-101-engineered macrophages effectively inhibited tumor progression. These results represent the first report of room-temperature synthesis of sp2C-conjugated COFs for engineered immune cell therapy, providing a new perspective for the development of therapeutic immune cells via organelle manipulation.

Nucleotide-binding domain, leucine-rich repeat, and pyrin domain-containing protein 3 inflammasome: From action mechanism to therapeutic target in clinical trials

The nucleotide-binding domain, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) inflammasome is a critical modulator in inflammatory disease. Activation and mutation of NLRP3 can cause severe inflammation in diseases such as chronic infantile neurologic cutaneous and articular syndrome, Muckle-Wells syndrome, and familial cold autoinflammatory syndrome 1. To date, a great effort has been made to decode the underlying mechanisms of NLRP3 activation. The priming and activation of NLRP3 drive the maturation and release of active interleukin (IL)-18 and IL-1β to cause inflammation and pyroptosis, which can significantly trigger many diseases including inflammatory diseases, immune disorders, metabolic diseases, and neurodegenerative diseases. The investigation of NLRP3 as a therapeutic target for disease treatment is a hot topic in both preclinical studies and clinical trials. Developing potent NLRP3 inhibitors and downstream IL-1 inhibitors attracts wide-spectrum attention in both research and pharmaceutical fields. In this minireview, we first updated the molecular mechanisms involved in NLRP3 inflammasome activation and the associated downstream signaling pathways. We then reviewed the molecular and cellular pathways of NLRP3 in many diseases, including obesity, diabetes, and other metabolic diseases. In addition, we briefly reviewed the roles of NLRP3 in cancer growth and relative immune checkpoint therapy. Finally, clinical trials with treatments targeting NLRP3 and its downstream signaling pathways were summarized.

Epidermal maintenance of Langerhans cells relies on autophagy-regulated lipid metabolism

Macroautophagy (often-named autophagy), a catabolic process involving autophagy-related (Atg) genes, prevents the accumulation of harmful cytoplasmic components and mobilizes energy reserves in long-lived and self-renewing cells. Autophagy deficiency affects antigen presentation in conventional dendritic cells (DCs) without impacting their survival. However, previous studies did not address epidermal Langerhans cells (LCs). Here, we demonstrate that deletion of either Atg5 or Atg7 in LCs leads to their gradual depletion. ATG5-deficient LCs showed metabolic dysregulation and accumulated neutral lipids. Despite increased mitochondrial respiratory capacity, they were unable to process lipids, eventually leading them to ferroptosis. Finally, metabolically impaired LCs upregulated proinflammatory transcripts and showed decreased expression of neuronal interaction receptors. Altogether, autophagy represents a critical regulator of lipid storage and metabolism in LCs, allowing their maintenance in the epidermis.

α-Ketoglutaric Acid Reprograms Macrophages by Altering Energy Metabolism to Promote the Regeneration of Small-Diameter Vascular Grafts

Small-diameter vascular grafts still cannot clinically replace autologous blood vessels due to high restenosis rates caused by long-term inflammatory infiltration. Foreign body reactions to vascular grafts induce macrophages to adopt the pro-inflammatory M1 phenotype, releasing inflammatory factors such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). This induces a phenotypic switch in smooth muscle cells, eventually leading to intimal hyperplasia. Herein, we constructed small-diameter artificial vascular grafts capable of modulating immune responses through the controlled release of α-ketoglutaric acid (α-KG). Our findings verify that the delivery of α-KG reprograms the macrophage phenotype from a pro-inflammatory M1 to an anti-inflammatory and pro-repair M2 phenotype by regulating the energy metabolism of the tricarboxylic acid cycle (TAC). More interestingly, the delivery of α-KG positively influences the behavior of vascular cells by enhancing the proliferation of human umbilical vein endothelial cells (HUVECs) and inhibiting the expansion of mouse aortic vascular smooth muscle cells (MOVAS), thereby reducing vascular restenosis. In vivo evaluation in rabbit carotid artery replacement confirms the optimal performance of α-KG-doped vascular grafts in terms of endothelial coverage and long-term patency. Collectively, our work presents a promising approach for creating artificial vascular grafts with inflammatory regulation to ensure rapid endothelialization and sustained patency.

Reductive stress: The key pathway in metabolic disorders induced by overnutrition

BACKGROUND

The balance of redox states is crucial for maintaining physiological homeostasis. For decades, the focus has been mainly on the concept of oxidative stress, which is involved in the mechanism of almost all diseases. However, robust evidence has highlighted that reductive stress, the other side of the redox spectrum, plays a pivotal role in the development of various diseases, particularly those related to metabolism and cardiovascular health.

AIM OF REVIEW

In this review, we present an extensive array of evidence for the occurrence of reductive stress and its significant implications mainly in metabolic and cardiovascular diseases.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Reductive stress is defined as a shift in the cellular redox balance towards a more reduced state, characterized by an excess of endogenous reductants (such as NADH, NADPH, and GSH) over their oxidized counterparts (NAD+, NADP+, and GSSG). While oxidative stress has been the predominant mechanism studied in obesity, metabolic disorders, and cardiovascular diseases, growing evidence underscores the critical role of reductive stress. This review discusses how reductive stress contributes to metabolic and cardiovascular pathologies, emphasizing its effects on key cellular processes. For example, excessive NADH accumulation can disrupt mitochondrial function by impairing the electron transport chain, leading to decreased ATP production and increased production of reactive oxygen species. In the endoplasmic reticulum (ER), an excess of reductive equivalents hampers protein folding, triggering ER stress and activating the unfolded protein response, which can lead to insulin resistance and compromised cellular homeostasis. Furthermore, we explore how excessive antioxidant supplementation can exacerbate reductive stress by further shifting the redox balance, potentially undermining the beneficial effects of exercise, impairing cardiovascular health, and aggravating metabolic disorders, particularly in obese individuals. This growing body of evidence calls for a reevaluation of the role of reductive stress in disease pathogenesis and therapeutic interventions.

Muscle Tissue Transcriptome of Idiopathic Inflammatory Myopathy Reflects the Muscle Damage Process by Monocytes and Presence of Skin Lesions

OBJECTIVE

We aim to investigate transcriptomic and immunophenotypic features of muscle specimens from patients with idiopathic inflammatory myopathy (IIM).

METHODS

Bulk RNA-sequencing was performed on muscle biopsy samples from 16 patients with dermatomyositis (DM) and 9 patients with polymyositis (PM). Seven tested positive for anti-aminoacyl transfer RNA synthetase antibodies in the patients with DM (ARS-DM). We conducted weighted gene coexpression network analysis (WGCNA), differentially expressed gene (DEG) analysis, and gene set variation analysis to assess contributions of specific pathways. Cell proportions in muscle specimens were estimated using a deconvolution approach.

RESULTS

WGCNA revealed significant positive correlations between serum creatine kinase (CK) levels and gene modules involved in cellular respiration, phagocytosis, and oxidative phosphorylation (OXPHOS). Significant positive correlations were also observed between CK levels and proportions of CD16-positive and negative monocytes and myeloid dendritic cells. Notably, patients with DM demonstrated enrichment of complement and interferon-α and γ pathway genes compared with those with PM. Furthermore, ARS-DM demonstrated a higher proportion of Th1 cells and DEGs related to OXPHOS. Additionally, serum Krebs von den Lungen-6 levels correlated with gene modules associated with extracellular matrix and the transforming growth factor-β signaling pathway.

CONCLUSION

Our study highlights a significant involvement of monocytes in muscle damage and delineates pathologic differences among IIM subtypes. DM was characterized by complement and interferon-α and γ signaling, whereas ARS-DM was associated with OXPHOS. Distinctive gene expression variations in muscle specimens suggest that different pathologic mechanisms underlie muscle damage in each IIM phenotype.

Engineered Magneto-Piezoelectric Nanoparticles-Enhanced Scaffolds Disrupt Biofilms and Activate Oxidative Phosphorylation in Icam1+ Macrophages for Infectious Bone Defect Regeneration

Infectious bone defects pose significant clinical challenges due to persistent infection and impaired bone healing. Icam1+ macrophages were identified as crucial and previously unrecognized regulators in the repair of bone defects, where impaired oxidative phosphorylation within this macrophage subset represents a significant barrier to effective bone regeneration. To address this challenge, dual-responsive iron-doped barium titanate (BFTO) nanoparticles were synthesized with magnetic and ultrasonic properties. These nanoparticles were further loaded with the anti-inflammatory agent curcumin and coated with engineered mesenchymal stem cell membranes (EMM) modified with γ3 peptide, creating BFTO-Cur@EMM nanoparticles specifically designed to target Icam1+ macrophages. These nanoparticles were shown to disrupt bacterial biofilms under alternating magnetic fields (AMF) and to activate oxidative phosphorylation and osteogenic immune responses in Icam1+ macrophages via low-intensity pulsed ultrasound (LIPUS). Transcriptomic sequencing and validation experiments demonstrated that this approach activates oxidative phosphorylation (OXPHOS) by stimulating the JAK2-STAT3 pathway and inhibiting the MAPK-JNK pathway, thereby promoting the polarization of Icam1+ macrophages toward a pro-reparative phenotype and enhancing the secretion of pro-angiogenic and osteogenic cytokines. These nanoparticles were subsequently integrated into quaternized chitosan (QCS) and tricalcium phosphate (TCP) to create a bioink for three-dimensional (3D) printing anti-infection QT/BFTO-Cur@EMM bone repair scaffolds. In vivo studies indicated that these scaffolds significantly improved the healing of infectious bone defects without causing thermal damage to surrounding tissues. This work highlights the potential of this material and the targeting of Icam1+ macrophages as an effective strategy for simultaneously controlling infection and promoting bone regeneration.

ABCG1 orchestrates adipose tissue macrophage plasticity and insulin resistance in obesity by rewiring saturated fatty acid pools

The mechanisms governing adipose tissue macrophage (ATM) metabolic adaptation during diet-induced obesity (DIO) are poorly understood. In obese adipose tissue, ATMs are exposed to lipid fluxes, which can influence the activation of specific inflammatory and metabolic programs and contribute to the development of obesity-associated insulin resistance and other metabolic disorders. In the present study, we demonstrate that the membrane ATP-binding cassette g1 (Abcg1) transporter controls the ATM functional response to fatty acids (FAs) carried by triglyceride-rich lipoproteins, which are abundant in high-energy diets. Mice genetically lacking Abcg1 in the myeloid lineage presented an ameliorated inflammatory status in adipose tissue and reduced insulin resistance. Abcg1-deficient ATMs exhibited a less inflammatory phenotype accompanied by a low bioenergetic profile and modified FA metabolism. A closer look at the ATM lipidome revealed a shift in the handling of FA pools, including a redirection of saturated FAs from membrane phospholipids to lipid droplets, leading to a reduction in membrane rigidity and neutralization of proinflammatory FAs. ATMs from human individuals with obesity presented the same reciprocal relationship between ABCG1 expression and this inflammatory and metabolic status. Abolition of this protective, anti-inflammatory phenotype in Abcg1-deficient ATMs was achieved through restoration of lipoprotein lipase (Lpl) activity, thus delineating the importance of the Abcg1/Lpl axis in controlling ATM metabolic inflammation. Overall, our study identifies the rewiring of FA pools by Abcg1 as a major pathway orchestrating ATM plasticity and insulin resistance in DIO.

Innate immunity champions: The diverse functions of macrophages

Macrophages are instrumental in maintaining tissue homeostasis, modulating inflammation, and driving regeneration. The advent of omics techniques has led to the identification of numerous tissue-specific macrophage subtypes, thereby introducing the concept of the "macrophage niche". This paradigm underscores the ability of macrophages to adapt their functions based on environmental cues, such as tissue-specific signals. This adaptability is closely linked to their metabolic states, which are crucial for their function and role in health and disease. Macrophage metabolism is central to their ability to switch between proinflammatory and anti-inflammatory states. In this regard, environmental factors, including the extracellular matrix, cellular interactions, and microbial metabolites, profoundly influence macrophage behavior. Moreover, diet and gut microbiota significantly impact macrophage function, with nutrients and microbial metabolites influencing their activity and contributing to conditions like inflammatory bowel disease. Targeting specific macrophage functions and their metabolic processes is leading to the development of novel treatments for a range of chronic inflammatory conditions. The exploration of macrophage biology enriches our understanding of immune regulation and holds the promise of innovative approaches to managing diseases marked by inflammation and immune dysfunction, offering a frontier for scientific and clinical advancement.

Exosomes from human bone marrow MSCs alleviate PD-1/PD-L1 inhibitor-induced myocardial injury in melanoma mice by regulating macrophage polarization and pyroptosis

Myocarditis, which can be triggered by immune checkpoint inhibitor (ICI) treatment, represents a critical and severe adverse effect observed in cancer therapy. Thus, elucidating the underlying mechanism and developing effective strategies to mitigate its harmful impact is of utmost importance. The objective of this study is to investigate the potential role and regulatory mechanism of exosomes derived from human bone marrow mesenchymal stem cells (hBMSC-Exos) in providing protection against myocardial injury induced by ICIs. We observed that the administration of programmed death 1/programmed death-ligand 1 (PD-1/PD-L1) inhibitor BMS-1 in tumor-bearing mice led to evident cardiac dysfunction and myocardial injury, which were closely associated with M1 macrophage polarization and cardiac pyroptosis. Remarkably, these adverse effects were significantly alleviated through tail-vein injection of hBMSC-Exos. Moreover, either BMS-1 or hBMSC-Exos alone demonstrated the ability to reduce tumor size, while the combination of hBMSC-Exos with BMS-1 treatment not only effectively improved the probability of tumor inhibition but also alleviated cardiac anomalies induced by BMS-1.

Optimized full-spectrum flow cytometry panel for deep immunophenotyping of murine lungs

The lung immune system consists of both resident and circulating immune cells that communicate intricately. The immune system is activated by exposure to bacteria and viruses, when cancer initiates in the lung (primary lung cancer), or when metastases of other cancer types, including breast cancer, spread to and develop in the lung (secondary lung cancer). Thus, in these pathological situations, a comprehensive and quantitative assessment of changes in the lung immune system is of paramount importance for understanding mechanisms of infectious diseases, lung cancer, and metastasis but also for developing efficacious treatments. Unfortunately, lung tissue exhibits high autofluorescence, and this high background signal makes high-parameter flow cytometry analysis complicated. Here, we provide an optimized 30-parameter antibody panel for the analysis of all major immune cell types and states in normal and metastatic murine lungs using spectral flow cytometry.

Hexokinase 2 senses fructose in tumor-associated macrophages to promote colorectal cancer growth

Fructose is associated with colorectal cancer tumorigenesis and metastasis through ketohexokinase-mediated metabolism in the colorectal epithelium, yet its role in the tumor immune microenvironment remains largely unknown. Here, we show that a modest amount of fructose, without affecting obesity and associated complications, promotes colorectal cancer tumorigenesis and growth by suppressing the polarization of M1-like macrophages. Fructose inhibits M1-like macrophage polarization independently of fructose-mediated metabolism. Instead, it serves as a signal molecule to promote the interaction between hexokinase 2 and inositol 1,4,5-trisphophate receptor type 3, the predominant Ca2+ channel on the endoplasmic reticulum. The interaction reduces Ca2+ levels in cytosol and mitochondria, thereby suppressing the activation of mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 1 (STAT1) as well as NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome activation. Consequently, this impedes M1-like macrophage polarization. Our study highlights the critical role of fructose as a signaling molecule that impairs the polarization of M1-like macrophages for tumor growth.

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.

Synergistic rheumatoid arthritis therapy by interrupting the detrimental feedback loop to orchestrate hypoxia M1 macrophage polarization using an enzyme-catalyzed nanoplatform

A detrimental feedback loop between hypoxia and oxidative stress consistently drives macrophage polarization toward a pro-inflammatory M1 phenotype, thus persistently aggravating rheumatoid arthritis (RA) progression. Herein, an enzyme-catalyzed nanoplatform with synergistic hypoxia-relieving and reactive oxygen species (ROS)-scavenging properties was developed using bovine serum albumin-bilirubin-platinum nanoparticles (BSA-BR-Pt NPs). Bilirubin was employed to eliminate ROS, while platinum exhibited a synergistic effect in scavenging ROS and simultaneously generated oxygen. In mice RA model, BSA-BR-Pt NPs treatment exhibited superior effects, resulting in significant improvements in joint inflammation, cartilage damage, and bone erosion, compared to methotrexate, the most widely used antirheumatic drug. Mechanistically, RNA-sequencing data and experimental results elucidated that BSA-BR-Pt NPs induced a re-polarization of hypoxic M1 macrophages to M2 macrophages via switching glycolysis to oxidative phosphorylation through the inhibition of HIF-1α pathway. Collectively, this research for the first time elaborated the underlying mechanism of enzyme-catalyzed nanoplatform in orchestrating macrophage polarization, and identified a novel therapeutic strategy for RA and other inflammatory disorders.

Selenoprotein o as a regulator of macrophage metabolism in selenium deficiency-induced lung inflammation

Selenium (Se) deficiency induces an inflammatory response in the lungs, but the underlying mechanisms are unknown. Selenoprotein O (SelO) is the largest selenoprotein in terms of molecular weight, yet its potential biological functions have yet to be characterized. Our study revealed that Se deficiency leads to an imbalance in the expression of pro-inflammatory "M1" macrophages and anti-inflammatory "M2" macrophages in alveolar macrophages (AMs) and interstitial macrophages (IMs) and contributed to the development of lung inflammation. Through the analysis of differentially expressed selenoproteins, we identified SelO as a potential regulator of the imbalance in pulmonary macrophage polarization caused by Se deficiency. In vitro experiments showed that SelO knockdown enhanced the polarization of M1 macrophages while suppressing that of M2 macrophages. In addition, SelO knockdown reprogrammed macrophage metabolism to glycolysis, disrupting oxidative phosphorylation (OXPHOS). Mechanistically, SelO primarily targets mitochondrial transcription factor A (TFAM), which plays a crucial role in the transcription and replication of mitochondrial DNA (mtDNA) and is essential for mitochondrial biogenesis and energy metabolism. The deficiency of SelO affects TFAM, resulting in its uncontrolled degradation, which compromises mitochondrial function and energy metabolism. In summary, the findings presented here offer significant theoretical insights into the physiological functions of SelO.

Polyamine metabolism in macrophage-adipose tissue function and homeostasis

Intracellular metabolism is a crucial regulator of macrophage function. Recent evidence revealed that the polyamine pathway and subsequent hypusination of eukaryotic initiation factor 5A (eIF5A) are master regulators of immune cell functions. In brown adipose tissue (BAT), macrophages show an impressive degree of heterogenicity, with specific subsets supporting adaptive thermogenesis during cold exposure. In this review, we discuss the impact of polyamine metabolism on macrophage diversity and function, with a particular focus on their role in adipose tissue homeostasis. Thus, we highlight the exploration of how polyamine metabolism in macrophages contributes to BAT homeostasis as an attractive and exciting new field of research.

Immunometabolic rewiring in macrophages for periodontitis treatment via nanoquercetin-mediated leverage of glycolysis and OXPHOS

Periodontitis is a chronic inflammatory disease marked by a dysregulated immune microenvironment, posing formidable challenges for effective treatment. The disease is characterized by an altered glucose metabolism in macrophages, specifically an increase in aerobic glycolysis, which is linked to heightened inflammatory responses. This suggests that targeting macrophage metabolism could offer a new therapeutic avenue. In this study, we developed an immunometabolic intervention using quercetin (Q) encapsulated in bioadhesive mesoporous polydopamine (Q@MPDA) to treat periodontitis. Our results demonstrated that Q@MPDA could reprogram inflammatory macrophages to an anti-inflammatory phenotype (i.e., from-M1-to-M2 repolarization). In a murine periodontitis model, locally administered Q@MPDA reduced the presence of inflammatory macrophages, and decreased the levels of inflammatory cytokines (IL-1β and TNF-α) and reactive oxygen species (ROS) in the periodontium. Consequently, it alleviated periodontitis symptoms, reduced alveolar bone loss, and promoted tissue repair. Furthermore, our study revealed that Q@MPDA could inhibit the glycolysis of inflammatory macrophages while enhancing oxidative phosphorylation (OXPHOS), facilitating the shift from M1 to M2 macrophage subtype. Our findings suggest that Q@MPDA is a promising treatment for periodontitis via immunometabolic rewiring.

Engineered Enucleated Mesenchymal Stem Cells Regulating Immune Microenvironment and Promoting Wound Healing

Persistent excessive inflammation caused by neutrophil and macrophage dysfunction in the wound bed leads to refractory response during wound healing. However, previous studies using cytokines or drugs often suffer from short half-lives and limited targeting, resulting in unsatisfactory therapeutic effects. Herein, the enucleated mesenchymal stem cell is engineered by aptamer bioorthogonal chemistry to modify the cell membrane and mRNA loading in the cell cytoplasm as a novel delivery vector (Cargocyte) with accurate targeting and sustained cytokine secretion. Cargocytes can successfully reduce NETosis by targeting the nuclear chromatin protein DEK protein with aptamers and sustaining interleukin (IL)-4 expression to overcome the challenges associated with the high cost and short half-life of IL-4 protein and significantly prevent the transition of macrophages into the M1 phenotype. Therapeutic effects have been demonstrated in murine and porcine wound models and have powerful potential to improve wound immune microenvironments effectively. Overall, the use of engineered enucleated mesenchymal stem cells as a delivery system may be a promising approach for wound healing.

Exploring macrophage heterogeneity in IgA nephropathy: Mechanisms of renal impairment and current therapeutic targets

The lack of understanding of the mechanism of renal injury in IgA nephropathy (IgAN) hinders the development of personalized treatment plans and targeted therapies. Improved insight into the cause of renal dysfunction in IgAN is necessary to enhance the effectiveness of strategies for slowing the progression of the disease. This study examined single cell RNA sequencing (scRNA seq) and bulk-RNA seq data and found that the gene expression of renal intrinsic cells (RIC) was significantly changed in patients with renal impairment, with a primary focus on energy metabolism. We discovered a clear metabolic reprogramming of RIC during renal function impairment (RF) using the 'scMetabolism' package, which manifested as a weakening of oxidative phosphorylation, alterations in fatty acid metabolism, and changes in glycolysis. Cellular communication analysis revealed that communication between macrophages (Ma) and RIC became more active and impacted cell function through the ligand-receptor-transcription factor (L-R-TF) axis in patients with RF. Our studies showed a notable upsurge in the expression of gene CLU and the infiltration of CLU+ Ma in patients with RF. CLU is a multifunctional protein, extensively involved in processes such as cell apoptosis and immune responses. Data obtained from the Nephroseq V5 database and multiplex immunohistochemistry (mIHC) were used to validate the findings, which were found to be robustly correlated with estimated glomerular filtration rate (eGFR) of the IgAN patients, as demonstrated by linear regression (LR). This study provides new insights into the cellular and molecular changes that occur in IgAN during renal impairment, revealing that elevated expression of CLU and CLU+ Ma percolation are common features in patients with RF. These findings offer potential targets and strategies for personalized management and targeted therapy of IgAN.

CENCAT enables immunometabolic profiling by measuring protein synthesis via bioorthogonal noncanonical amino acid tagging

Cellular energy metabolism significantly contributes to immune cell function. To further advance immunometabolic research, novel methods to study the metabolism of immune cells in complex samples are required. Here, we introduce CENCAT (cellular energetics through noncanonical amino acid tagging). This technique utilizes click labeling of alkyne-bearing noncanonical amino acids to measure protein synthesis inhibition as a proxy for metabolic activity. CENCAT successfully reproduced known metabolic signatures of lipopolysaccharide (LPS)/interferon (IFN)γ and interleukin (IL)-4 activation in human primary macrophages. Application of CENCAT in peripheral blood mononuclear cells revealed diverse metabolic rewiring upon stimulation with different activators. Finally, CENCAT was used to analyze the cellular metabolism of murine tissue-resident immune cells from various organs. Tissue-specific clustering was observed based on metabolic profiles, likely driven by microenvironmental priming. In conclusion, CENCAT offers valuable insights into immune cell metabolic responses, presenting a powerful platform for studying cellular metabolism in complex samples and tissues in both humans and mice.

Identification and validation of efferocytosis-related biomarkers for the diagnosis of metabolic dysfunction-associated steatohepatitis based on bioinformatics analysis and machine learning

Background

Metabolic dysfunction-associated steatohepatitis (MASH) is a highly prevalent liver disease globally, with a significant risk of progressing to cirrhosis and even liver cancer. Efferocytosis, a process implicated in a broad spectrum of chronic inflammatory disorders, has been reported to be associated with the pathogenesis of MASH; however, its precise role remains obscure. Thus, we aimed to identify and validate efferocytosis linked signatures for detection of MASH.

Methods

We retrieved gene expression patterns of MASH from the GEO database and then focused on assessing the differential expression of efferocytosis-related genes (EFRGs) between MASH and control groups. This analysis was followed by a series of in-depth investigations, including protein-protein interaction (PPI), correlation analysis, and functional enrichment analysis, to uncover the molecular interactions and pathways at play. To screen for biomarkers for diagnosis, we applied machine learning algorithm to identify hub genes and constructed a clinical predictive model. Additionally, we conducted immune infiltration and single-cell transcriptome analyses in both MASH and control samples, providing insights into the immune cell landscape and cellular heterogeneity in these conditions.

Results

This research pinpointed 39 genes exhibiting a robust correlation with efferocytosis in MASH. Among these, five potential diagnostic biomarkers-TREM2, TIMD4, STAB1, C1QC, and DYNLT1-were screened using two distinct machine learning models. Subsequent external validation and animal experimentation validated the upregulation of TREM2 and downregulation of TIMD4 in MASH samples. Notably, both TREM2 and TIMD4 demonstrated area under the curve (AUC) values exceeding 0.9, underscoring their significant potential in facilitating the diagnosis of MASH.

Conclusion

Our study comprehensively elucidated the relationship between MASH and efferocytosis, constructing a favorable diagnostic model. Furthermore, we identified potential therapeutic targets for MASH treatment and offered novel insights into unraveling the underlying mechanisms of this disease.

Sex-specific phenotypical, functional and metabolic profiles of human term placenta macrophages

BACKGROUND

Placental macrophages, Hofbauer cells (HBC) are the only fetal immune cell population within the stroma of healthy placenta along pregnancy. They are central players in maintaining immune tolerance during pregnancy. Immunometabolism emerged a few years ago as a new field that integrates cellular metabolism with immune responses, however, the immunometabolism of HBC has not been explored yet. Here we studied the sex-specific differences in the phenotypic, functional and immunometabolic profile of HBC.

METHODS

HBC were isolated from human term placentas (N = 31, 16 from male and 15 female neonates). Ex vivo assays were carried out to assess active metabolic and endoplasmic reticulum stress pathways by flow cytometry, confocal microscopy, gene expression and in silico approaches.

RESULTS

HBC from female placentas displayed a stronger M2 phenotype accompanied by high rates of efferocytosis majorly sustained on lipid metabolism. On the other hand, male HBC expressed a weaker M2 phenotype with higher glycolytic metabolism. LPS stimulation reinforced the glycolytic metabolism in male but not in female HBC. Physiological endoplasmic reticulum stress activates IRE-1 differently, since its pharmacological inhibition increased lipid mobilization, accumulation and efferocytosis only in female HBC. Moreover, differential sex-associated pathways accompanying the phenotypic and functional profiles of HBC appeared related to the placental villi environment.

CONCLUSIONS

These results support sex-associated effects on the immunometabolism of the HBC and adds another layer of complexity to the intricate maternal-fetal immune interaction.

Metabolic regulation of the immune system in health and diseases: mechanisms and interventions

Metabolism, including glycolysis, oxidative phosphorylation, fatty acid oxidation, and other metabolic pathways, impacts the phenotypes and functions of immune cells. The metabolic regulation of the immune system is important in the pathogenesis and progression of numerous diseases, such as cancers, autoimmune diseases and metabolic diseases. The concept of immunometabolism was introduced over a decade ago to elucidate the intricate interplay between metabolism and immunity. The definition of immunometabolism has expanded from chronic low-grade inflammation in metabolic diseases to metabolic reprogramming of immune cells in various diseases. With immunometabolism being proposed and developed, the metabolic regulation of the immune system can be gradually summarized and becomes more and more clearer. In the context of many diseases including cancer, autoimmune diseases, metabolic diseases, and many other disease, metabolic reprogramming occurs in immune cells inducing proinflammatory or anti-inflammatory effects. The phenotypic and functional changes of immune cells caused by metabolic regulation further affect and development of diseases. Based on experimental results, targeting cellular metabolism of immune cells becomes a promising therapy. In this review, we focus on immune cells to introduce their metabolic pathways and metabolic reprogramming, and summarize how these metabolic pathways affect immune effects in the context of diseases. We thoroughly explore targets and treatments based on immunometabolism in existing studies. The challenges of translating experimental results into clinical applications in the field of immunometabolism are also summarized. We believe that a better understanding of immune regulation in health and diseases will improve the management of most diseases.

Targeting Macrophage Phenotypes and Metabolism as Novel Therapeutic Approaches in Atherosclerosis and Related Cardiovascular Diseases

PURPOSE OF THE REVIEW

Macrophage accumulation and activation function as hallmarks of atherosclerosis and have complex and intricate dynamics throughout all components and stages of atherosclerotic plaques. In this review, we focus on the regulatory roles and underlying mechanisms of macrophage phenotypes and metabolism in atherosclerosis. We highlight the diverse range of macrophage phenotypes present in atherosclerosis and their potential roles in progression and regression of atherosclerotic plaque. Furthermore, we discuss the challenges and opportunities in developing therapeutic strategies for preventing and treating atherosclerotic cardiovascular disease.

RECENT FINDINGS

Dysregulation of macrophage polarization between the proinflammatory M1 and anti-inflammatory M2 phenotypealters the immuno-inflammatory response during atherosclerosis progression, leading to plaque initiation, growth, and ultimately rupture. Altered metabolism of macrophage is a key feature for their function and the subsequent progression of atherosclerotic cardiovascular disease. The immunometabolism of macrophage has been implicated to macrophage activation and metabolic rewiring of macrophages within atherosclerotic lesions, thereby shifting altered macrophage immune-effector and tissue-reparative function. Targeting macrophage phenotypes and metabolism are potential therapeutic strategies in the prevention and treatment of atherosclerosis and atherosclerotic cardiovascular diseases. Understanding the precise function and metabolism of specific macrophage subsets and their contributions to the composition and growth of atherosclerotic plaques could reveal novel strategies to delay or halt development of atherosclerotic cardiovascular diseases and their associated pathophysiological consequences. Identifying biological stimuli capable of modulating macrophage phenotypes and metabolism may lead to the development of innovative therapeutic approaches for treating patients with atherosclerosis and coronary artery diseases.

Catching the Big Fish in Big Data: A Meta-Analysis of Zebrafish Kidney scRNA-Seq Datasets Highlights Conserved Molecular Profiles of Macrophages and Neutrophils in Vertebrates

The innate immune system (IIS) is an ancient and essential defense mechanism that protects animals against a wide range of pathogens and diseases. Although extensively studied in mammals, our understanding of the IIS in other taxa remains limited. The zebrafish (Danio rerio) serves as a promising model organism for investigating IIS-related processes, yet the immunogenetics of fish are not fully elucidated. To address this gap, we conducted a meta-analysis of single-cell RNA sequencing (scRNA-seq) datasets from zebrafish kidney marrow, encompassing approximately 250,000 immune cells. Our analysis confirms the presence of key genetic pathways in zebrafish innate immune cells that are similar to those identified in mammals. Zebrafish macrophages specifically express genes encoding cathepsins, major histocompatibility complex class II proteins, integral membrane proteins, and the V-ATPase complex and demonstrate the enrichment of oxidative phosphorylation ferroptosis processes. Neutrophils are characterized by the significant expression of genes encoding actins, cytoskeleton organizing proteins, the Arp2/3 complex, and glycolysis enzymes and have demonstrated their involvement in GnRH and CLR signaling pathways, adherents, and tight junctions. Both macrophages and neutrophils highly express genes of NOD-like receptors, phagosomes, and lysosome pathways and genes involved in apoptosis. Our findings reinforce the idea about the existence of a wide spectrum of immune cell phenotypes in fish since we found only a small number of cells with clear pro- or anti-inflammatory signatures.

Convergent evolution of monocyte differentiation in adult skin instructs Langerhans cell identity

Langerhans cells (LCs) are distinct among phagocytes, functioning both as embryo-derived, tissue-resident macrophages in skin innervation and repair and as migrating professional antigen-presenting cells, a function classically assigned to dendritic cells (DCs). Here, we demonstrate that both intrinsic and extrinsic factors imprint this dual identity. Using ablation of embryo-derived LCs in the murine adult skin and tracking differentiation of incoming monocyte-derived replacements, we found intrinsic intraepidermal heterogeneity. We observed that ontogenically distinct monocytes give rise to LCs. Within the epidermis, Jagged-dependent activation of Notch signaling, likely within the hair follicle niche, provided an initial site of LC commitment before metabolic adaptation and survival of monocyte-derived LCs. In the human skin, embryo-derived LCs in newborns retained transcriptional evidence of their macrophage origin, but this was superseded by DC-like immune modules after postnatal expansion. Thus, adaptation to adult skin niches replicates conditioning of LC at birth, permitting repair of the embryo-derived LC network.

Activation of G Protein-Coupled Estrogen Receptor 1 (GPER) Attenuates Obesity-Induced Asthma by Switching M1 Macrophages to M2 Macrophages

The prevalence of obesity-induced asthma increases in women after menopause. We hypothesized that the increase in obese asthma in middle-aged women results from estrogen loss. In particular, we focused on the acute action of estrogen through the G protein-coupled estrogen receptor 1 (GPER), previously known as GPR30. We investigated whether GPER activation ameliorates obesity-induced asthma with a high-fat diet (HFD) using G-1, the GPER agonist, and G-36, the GPER antagonist. Administration of G-1 (0.5 mg/kg) suppressed HFD-induced airway hypersensitivity (AHR), and increased immune cell infiltration, whereas G-36 co-treatment blocked it. Histological analysis showed that G-1 treatment inhibited HFD-induced inflammation, fibrosis, and mucus hypersecretion in a GPER-dependent manner. G-1 inhibited the HFD-induced rise in the mRNA levels of pro-inflammatory cytokines in the gonadal white adipose tissue and lungs, whereas G-36 co-treatment reversed this effect. G-1 increased anti-inflammatory M2 macrophages and inhibited the HFD-induced rise in pro-inflammatory M1 macrophages in the lungs. In addition, G-1 treatment reversed the HFD-induced increase in leptin expression and decrease in adiponectin expression in the lungs and gonadal white adipose tissue. The results suggest that activation of GPER could be a therapeutic option for obesity-induced asthma.

Not just sugar: metabolic control of neutrophil development and effector functions

The mammalian immune system is constantly surveying our tissues to clear pathogens and maintain tissue homeostasis. In order to fulfill these tasks, immune cells take up nutrients to supply energy for survival and for directly regulating effector functions via their cellular metabolism, a process now known as immunometabolism. Neutrophilic granulocytes, the most abundant leukocytes in the human body, have a short half-life and are permanently needed in the defense against pathogens. According to a long-standing view, neutrophils were thought to primarily fuel their metabolic demands via glycolysis. Yet, this view has been challenged, as other metabolic pathways recently emerged to contribute to neutrophil homeostasis and effector functions. In particular during neutrophilic development, the pentose phosphate pathway, glycogen synthesis, oxidative phosphorylation, and fatty acid oxidation crucially promote neutrophil maturation. At steady state, both glucose and lipid metabolism sustain neutrophil survival and maintain the intracellular redox balance. This review aims to comprehensively discuss how neutrophilic metabolism adapts during development, which metabolic pathways fuel their functionality, and how these processes are reconfigured in case of various diseases. We provide several examples of hereditary diseases, in which mutations in metabolic enzymes validate their critical role for neutrophil function.

Injectable Thermosensitive Gel CH-BPNs-NBP for Effective Periodontitis Treatment through ROS-Scavenging and Jaw Vascular Unit Protection

Periodontitis, a prevalent inflammatory condition in the oral cavity, is closely associated with oxidative stress-induced tissue damage mediated by excessive reactive oxygen species (ROS) production. The jaw vascular unit (JVU), encompassing both vascular and lymphatic vessels, plays a crucial role in maintaining tissue fluid homeostasis and contributes to the pathological process in inflammatory diseases of the jaw. This study presents a novel approach for treating periodontitis through the development of an injectable thermosensitive gel (CH-BPNs-NBP). The gel formulation incorporates black phosphorus nanosheets (BPNs), which are notable for their ROS-scavenging properties, and dl-3-n-butylphthalide (NBP), a vasodilator that promotes lymphatic vessel function within the JVU. These results demonstrate that the designed thermosensitive gel serve as a controlled release system, delivering BPNs and NBP to the site of inflammation. CH-BPNs-NBP not only protects macrophages and human lymphatic endothelial cells from ROS attack but also promotes M2 polarization and lymphatic function. In in vivo studies, this work observes a significant reduction in inflammation and tissue damage, accompanied by a notable promotion of alveolar bone regeneration. This research introduces a promising therapeutic strategy for periodontitis, leveraging the unique properties of BPNs and NBP within an injectable thermosensitive gel.

Role of sex as a biological variable in neonatal alveolar macrophages

The lung macrophages play a crucial role in health and disease. Sexual dimorphism significantly impacts the phenotype and function of tissue-resident macrophages. The primary mechanisms responsible for sexually dimorphic outcomes in bronchopulmonary dysplasia (BPD) remain unidentified. We tested the hypothesis that biological sex plays a crucial role in the transcriptional state of alveolar macrophages, using neonatal murine hyperoxia-induced lung injury as a relevant model for human BPD. The effects of neonatal hyperoxia exposure (95 % FiO2, PND1-5: saccular stage) on the lung myeloid cells acutely after injury and during normoxic recovery were measured. Alveolar macrophages (AM) from room air- and hyperoxia exposed from male and female neonatal murine lungs were subjected to bulk-RNA Sequencing. AMs are significantly depleted in the hyperoxia-exposed lung acutely after injury, with subsequent recovery in both sexes. The transcriptome of the alveolar macrophages is impacted by neonatal hyperoxia exposure and by sex as a biological variable. Pathways related to DNA damage and interferon-signaling were positively enriched in female AMs. Metabolic pathways related to glucose and carbohydrate metabolism were positively enriched in the male AMs, while oxidative phosphorylation was negatively enriched. These pathways were shared with monocytes and airway macrophages from intubated male and female human premature neonates.

Metabolic homeostasis of tissue macrophages across the lifespan

Macrophages are present in almost all organs. Apart from being immune sentinels, tissue-resident macrophages (TRMs) have organ-specific functions that require a specialized cellular metabolism to maintain homeostasis. In addition, organ-dependent metabolic adaptations of TRMs appear to be fundamentally distinct in homeostasis and in response to a challenge, such as infection or injury. Moreover, TRM function becomes aberrant with advancing age, contributing to inflammaging and organ deterioration, and a metabolic imbalance may underlie TRM immunosenescence. Here, we outline current understanding of the particular metabolic states of TRMs across organs and the relevance for their function. Moreover, we discuss the concomitant aging-related decline in metabolic plasticity and functions of TRMs, highlighting potential novel therapeutic avenues to promote healthy aging.

Metabolism and bioenergetics in the pathophysiology of organ fibrosis

Fibrosis is the tissue scarring characterized by excess deposition of extracellular matrix (ECM) proteins, mainly collagens. A fibrotic response can take place in any tissue of the body and is the result of an imbalanced reaction to inflammation and wound healing. Metabolism has emerged as a major driver of fibrotic diseases. While glycolytic shifts appear to be a key metabolic switch in activated stromal ECM-producing cells, several other cell types such as immune cells, whose functions are intricately connected to their metabolic characteristics, form a complex network of pro-fibrotic cellular crosstalk. This review purports to clarify shared and particular cellular responses and mechanisms across organs and etiologies. We discuss the impact of the cell-type specific metabolic reprogramming in fibrotic diseases in both experimental and human pathology settings, providing a rationale for new therapeutic interventions based on metabolism-targeted antifibrotic agents.

Role of oxidative phosphorylation in the antidepressant effects of arketamine via the vagus nerve-dependent spleen-brain axis

Arketamine, the (R)-enantiomer of ketamine, exhibits antidepressant-like effects in mice, though the precise molecular mechanisms remain elusive. It has been shown to reduce splenomegaly and depression-like behaviors in the chronic social defeat stress (CSDS) model of depression. This study investigated whether the spleen contributes to the antidepressant-like effects of arketamine in the CSDS model. We found that splenectomy significantly inhibited arketamine's antidepressant-like effects in CSDS-susceptible mice. RNA-sequencing analysis identified the oxidative phosphorylation (OXPHOS) pathway in the prefrontal cortex (PFC) as a key mediator of splenectomy's impact on arketamine's effects. Furthermore, oligomycin A, an inhibitor of the OXPHOS pathway, reversed the suppressive effects of splenectomy on arketamine's antidepressant-like effects. Specific genes within the OXPHOS pathways, such as COX11, UQCR11 and ATP5e, may contribute to these inhibitory effects. Notably, transforming growth factor (TGF)-β1, along with COX11, appears to modulate the suppressive effects of splenectomy and contribute to arketamine's antidepressant-like effects. Additionally, SRI-01138, an agonist of the TGF-β1 receptor, alleviated the inhibitory effects of splenectomy on arketamine's antidepressant-like effects. Subdiaphragmatic vagotomy also counteracted the inhibitory effects of splenectomy on arketamine's antidepressant-like effects in CSDS-susceptible mice. These findings suggest that the OXPHOS pathway and TGF-β1 in the PFC play significant roles in the antidepressant-like effects of arketamine, mediated through the spleen-brain axis via the vagus nerve.

Mitochondrial control of lymphocyte homeostasis

Mitochondria play a multitude of essential roles within mammalian cells, and understanding how they control immunity is an emerging area of study. Lymphocytes, as integral cellular components of the adaptive immune system, rely on mitochondria for their function, and mitochondria can dynamically instruct their differentiation and activation by undergoing rapid and profound remodelling. Energy homeostasis and ATP production are often considered the primary functions of mitochondria in immune cells; however, their importance extends across a spectrum of other molecular processes, including regulation of redox balance, signalling pathways, and biosynthesis. In this review, we explore the dynamic landscape of mitochondrial homeostasis in T and B cells, and discuss how mitochondrial disorders compromise adaptive immunity.

Nucleophosmin 1 promotes mucosal immunity by supporting mitochondrial oxidative phosphorylation and ILC3 activity

Nucleophosmin 1 (NPM1) is commonly mutated in myelodysplastic syndrome (MDS) and acute myeloid leukemia. Concurrent inflammatory bowel diseases (IBD) and MDS are common, indicating a close relationship between IBD and MDS. Here we examined the function of NPM1 in IBD and colitis-associated colorectal cancer (CAC). NPM1 expression was reduced in patients with IBD. Npm1+/- mice were more susceptible to acute colitis and experimentally induced CAC than littermate controls. Npm1 deficiency impaired the function of interleukin-22 (IL-22)-producing group three innate lymphoid cells (ILC3s). Mice lacking Npm1 in ILC3s exhibited decreased IL-22 production and accelerated development of colitis. NPM1 was important for mitochondrial biogenesis and metabolism by oxidative phosphorylation in ILC3s. Further experiments revealed that NPM1 cooperates with p65 to promote mitochondrial transcription factor A (TFAM) transcription in ILC3s. Overexpression of Npm1 in mice enhanced ILC3 function and reduced the severity of dextran sulfate sodium-induced colitis. Thus, our findings indicate that NPM1 in ILC3s protects against IBD by regulating mitochondrial metabolism through a p65-TFAM axis.

Lipid synthesis, triggered by PPARγ T166 dephosphorylation, sustains reparative function of macrophages during tissue repair

Macrophages may acquire a reparative phenotype that supports tissue repair and remodeling in response to tissue injury. However, the metabolic requirements underpinning this process are incompletely understood. Here, we show that posttranslational modification (PTM) of PPARγ regulates lipid synthesis in response to wound microenvironmental cues and that metabolic rewiring orchestrates function of reparative macrophages. In injured tissues, repair signaling leads to decreased macrophage PPARγ threonine 166 (T166) phosphorylation, which results in a partially active PPARγ transcriptional program comprised of increased binding activity to the regulator regions of lipid synthesis-associated genes, thereby increased lipogenesis. The accumulated lipids serve as signaling molecules, triggering STAT3-mediated growth factor expression, and supporting the synthesis of phospholipids for the expansion of the endoplasmic reticulum (ER), which is required for protein secretion. Genetic or pharmacological inhibition of PPARγ T166 phosphorylation promotes the reparative function of macrophages and facilitates tissue regeneration. In summary, our work identifies PPARγ T166-regulated lipid biosynthesis as an essential pathway for meeting the anabolic demands of the activation and function of macrophages and provides a rationale for potential therapeutic targeting of tissue repair.

Rethinking the role of microglia in obesity

Microglia are the macrophages of the central nervous system (CNS), implying their role in maintaining brain homeostasis. To achieve this, these cells are sensitive to a plethora of endogenous and exogenous signals, such as neuronal activity, cellular debris, hormones, and pathological patterns, among many others. More recent research suggests that microglia are highly responsive to nutrients and dietary variations. In this context, numerous studies have demonstrated their significant role in the development of obesity under calorie surfeit. Because many reviews already exist on this topic, we have chosen to present the state of our reflections on various concepts put forth in the literature, bringing a new perspective whenever possible. Our literature review focuses on studies conducted in the arcuate nucleus of the hypothalamus, a key structure in the control of food intake. Specifically, we present the recent data available on the modifications of microglial energy metabolism following the consumption of an obesogenic diet and their consequences on hypothalamic neuron activity. We also highlight the studies unraveling the mechanisms underlying obesity-related sexual dimorphism. The review concludes with a list of questions that remain to be addressed in the field to achieve a comprehensive understanding of the role of microglia in the regulation of body energy metabolism. This article is part of the Special Issue on "Microglia".

Microglia mitochondrial complex I deficiency during development induces glial dysfunction and early lethality

Primary mitochondrial diseases (PMDs) are associated with pediatric neurological disorders and are traditionally related to oxidative phosphorylation system (OXPHOS) defects in neurons. Interestingly, both PMD mouse models and patients with PMD show gliosis, and pharmacological depletion of microglia, the innate immune cells of the brain, ameliorates multiple symptoms in a mouse model. Given that microglia activation correlates with the expression of OXPHOS genes, we studied whether OXPHOS deficits in microglia may contribute to PMDs. We first observed that the metabolic rewiring associated with microglia stimulation in vitro (via IL-33 or TAU treatment) was partially changed by complex I (CI) inhibition (via rotenone treatment). In vivo, we generated a mouse model deficient for CI activity in microglia (MGcCI). MGcCI microglia showed metabolic rewiring and gradual transcriptional activation, which led to hypertrophy and dysfunction in juvenile (1-month-old) and adult (3-month-old) stages, respectively. MGcCI mice presented widespread reactive astrocytes, a decrease of synaptic markers accompanied by an increased number of parvalbumin neurons, a behavioral deficit characterized by prolonged periods of immobility, loss of weight and premature death that was partially rescued by pharmacologic depletion of microglia. Our data demonstrate that microglia development depends on mitochondrial CI and suggest a direct microglial contribution to PMDs.

A single-cell pan-cancer analysis to show the variability of tumor-infiltrating myeloid cells in immune checkpoint blockade

Myeloid cells are vital components of the immune system and have pivotal functions in orchestrating immune responses. Understanding their functions within the tumor microenvironment and their interactions with tumor-infiltrating lymphocytes presents formidable challenges across diverse cancer types, particularly with regards to cancer immunotherapies. Here, we explore tumor-infiltrating myeloid cells (TIMs) by conducting a pan-cancer analysis using single-cell transcriptomics across eight distinct cancer types, encompassing a total of 192 tumor samples from 129 patients. By examining gene expression patterns and transcriptional activities of TIMs in different cancer types, we discern notable alterations in abundance of TIMs and kinetic behaviors prior to and following immunotherapy. We also identify specific cell-cell interaction targets in immunotherapy; unique and shared regulatory profiles critical for treatment response; and TIMs associated with survival outcomes. Overall, our study illuminates the heterogeneity of TIMs and improves our understanding of tissue-specific and cancer-specific myeloid subsets within the context of tumor immunotherapies.

Differential cell type-specific function of the aryl hydrocarbon receptor and its repressor in diet-induced obesity and fibrosis

OBJECTIVE

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor regulating xenobiotic responses as well as physiological metabolism. Dietary AhR ligands activate the AhR signaling axis, whereas AhR activation is negatively regulated by the AhR repressor (AhRR). While AhR-deficient mice are known to be resistant to diet-induced obesity (DIO), the influence of the AhRR on DIO has not been assessed so far.

METHODS

In this study, we analyzed AhRR-/- mice and mice with a conditional deletion of either AhRR or AhR in myeloid cells under conditions of DIO and after supplementation of dietary AhR ligands. Moreover, macrophage metabolism was assessed using Seahorse Mito Stress Test and ROS assays as well as transcriptomic analysis.

RESULTS

We demonstrate that global AhRR deficiency leads to a robust, but not as profound protection from DIO and hepatosteatosis as AhR deficiency. Under conditions of DIO, AhRR-/- mice did not accumulate TCA cycle intermediates in the circulation in contrast to wild-type (WT) mice, indicating protection from metabolic dysfunction. This effect could be mimicked by dietary supplementation of AhR ligands in WT mice. Because of the predominant expression of the AhRR in myeloid cells, AhRR-deficient macrophages were analyzed for changes in metabolism and showed major metabolic alterations regarding oxidative phosphorylation and mitochondrial activity. Unbiased transcriptomic analysis revealed increased expression of genes involved in de novo lipogenesis and mitochondrial biogenesis. Mice with a genetic deficiency of the AhRR in myeloid cells did not show alterations in weight gain after high fat diet (HFD) but demonstrated ameliorated liver damage compared to control mice. Further, deficiency of the AhR in myeloid cells also did not affect weight gain but led to enhanced liver damage and adipose tissue fibrosis compared to controls.

CONCLUSIONS

AhRR-deficient mice are resistant to diet-induced metabolic syndrome. Although conditional ablation of either the AhR or AhRR in myeloid cells did not recapitulate the phenotype of the global knockout, our findings suggest that enhanced AhR signaling in myeloid cells deficient for AhRR protects from diet-induced liver damage and fibrosis, whereas myeloid cell-specific AhR deficiency is detrimental.

Compartmentalization of the inflammatory response during bacterial sepsis and severe COVID-19

Acute infections cause local and systemic disorders which can lead in the most severe forms to multi-organ failure and eventually to death. The host response to infection encompasses a large spectrum of reactions with a concomitant activation of the so-called inflammatory response aimed at fighting the infectious agent and removing damaged tissues or cells, and the anti-inflammatory response aimed at controlling inflammation and initiating the healing process. Fine-tuning at the local and systemic levels is key to preventing local and remote injury due to immune system activation. Thus, during bacterial sepsis and Coronavirus disease 2019 (COVID-19), concomitant systemic and compartmentalized pro-inflammatory and compensatory anti-inflammatory responses are occurring. Immune cells (e.g., macrophages, neutrophils, natural killer cells, and T-lymphocytes), as well as endothelial cells, differ from one compartment to another and contribute to specific organ responses to sterile and microbial insult. Furthermore, tissue-specific microbiota influences the local and systemic response. A better understanding of the tissue-specific immune status, the organ immunity crosstalk, and the role of specific mediators during sepsis and COVID-19 can foster the development of more accurate biomarkers for better diagnosis and prognosis and help to define appropriate host-targeted treatments and vaccines in the context of precision medicine.

Immunometabolic Signatures of Circulating Monocytes in Humans With Obesity and Insulin Resistance

Obesity is associated with chronic inflammation and metabolic complications, including insulin resistance (IR). Immune cells drive inflammation through the rewiring of intracellular metabolism. However, the impact of obesity-related IR on the metabolism and functionality of circulating immune cells, like monocytes, remains poorly understood. To increase insight into the interindividual variation of immunometabolic signatures among individuals and their role in the development of IR, we assessed systemic and tissue-specific IR and circulating immune markers, and we characterized metabolic signatures and cytokine secretion of circulating monocytes from 194 individuals with a BMI ≥25 kg/m2. Monocyte metabolic signatures were defined using extracellular acidification rates (ECARs) to estimate glycolysis and oxygen consumption rates (OCRs) for oxidative metabolism. Although monocyte metabolic signatures and function based on cytokine secretion varied greatly among study participants, they were strongly associated with each other. The ECAR-to-OCR ratio, representing the balance between glycolysis and oxidative metabolism, was negatively associated with fasting insulin levels, systemic IR, and liver-specific IR. These results indicate that monocytes from individuals with IR were relatively more dependent on oxidative metabolism, whereas monocytes from more insulin-sensitive individuals were more dependent on glycolysis. Additionally, circulating CXCL11 was negatively associated with the degree of systemic IR and positively with the ECAR-to-OCR ratio in monocytes, suggesting that individuals with high IR and a monocyte metabolic dependence on oxidative metabolism also have lower levels of circulating CXCL11. Our findings suggest that monocyte metabolism is related to obesity-associated IR progression and deepen insights into the interplay between innate immune cell metabolism and IR development in humans.

ARTICLE HIGHLIGHTS

Trem2 Agonist Reprograms Foamy Macrophages to Promote Atherosclerotic Plaque Stability-Brief Report

BACKGROUND

Trem2 (triggering receptor on myeloid cells 2), a surface lipid receptor, is expressed on foamy macrophages within atherosclerotic lesions and regulates cell survival, proliferation, and anti-inflammatory responses. Studies examining the role of Trem2 in atherosclerosis have shown that deletion of Trem2 leads to impaired foamy macrophage lipid uptake, proliferation, survival, and cholesterol efflux. Thus, we tested the hypothesis that administration of a Trem2 agonist antibody (AL002a) to atherogenic mice would enhance macrophage survival and decrease necrotic core formation to improve plaque stability.

METHODS

To model a therapeutic intervention approach, atherosclerosis-prone mice (Ldlr [low-density lipoprotein receptor]-/-) were fed a high-fat diet for 8 weeks, then transitioned to treatment with AL002a or isotype control for an additional 8 weeks while continuing on a high-fat diet.

RESULTS

AL002a-treated mice had increased lesion size in both the aortic root and whole mount aorta, which correlated with an expansion of plaque macrophage area. This expansion was due to increased macrophage survival and proliferation in plaques. Importantly, plaques from AL002a-treated mice showed improved features of plaque stability, including smaller necrotic cores, increased fibrous caps, and greater collagen deposition. Single-cell RNA sequencing of whole aorta suspensions from isotype- and AL002a-treated atherosclerotic mice revealed that Trem2 agonism dramatically altered foamy macrophage transcriptome. This included upregulation of oxidative phosphorylation and increased expression of collagen genes. In vitro studies validated that Trem2 agonism with AL002a promoted foamy macrophage oxidized low-density lipoprotein uptake, survival, and cholesterol efflux.

CONCLUSIONS

Trem2 agonism expands atherosclerotic plaque macrophages by promoting cell survival and proliferation but improves features of plaque stability by rewiring foamy macrophage function to enhance cholesterol efflux and collagen deposition.

Research progresses on mitochondrial-targeted biomaterials for bone defect repair

In recent years, the regulation of the cell microenvironment has opened up new avenues for bone defect repair. Researchers have developed novel biomaterials to influence the behavior of osteoblasts and immune cells by regulating the microenvironment, aiming to achieve efficient bone repair. Mitochondria, as crucial organelles involved in energy conversion, biosynthesis and signal transduction, play a vital role in maintaining bone integrity. Dysfunction of mitochondria can have detrimental effects on the transformation of the immune microenvironment and the differentiation of stem cells, thereby hindering bone tissue regeneration. Consequently, targeted therapy strategies focusing on mitochondria have emerged. This approach offers a wide range of applications and reliable therapeutic effects, thereby providing a new treatment option for complex and refractory bone defect diseases. In recent studies, more biomaterials have been used to restore mitochondrial function and promote positive cell differentiation. The main directions are mitochondrial energy metabolism, mitochondrial biogenesis and mitochondrial quality control. In this review, we investigated the biomaterials used for mitochondria-targeted treatment of bone defect repair in recent years from the perspective of progress and strategies. We also summarized the micro-molecular mechanisms affected by them. Through discussions on energy metabolism, oxidative stress regulation and autophagy regulation, we emphasized the opportunities and challenges faced by mitochondria-targeted biomaterials, providing vital clues for developing a new generation of bone repair materials.

Anandamide modulation of monocyte-derived Langerhans cells: implications for immune homeostasis and skin inflammation

Introduction

The endocannabinoid system (ECS), named after the chemical compounds found in the cannabis plant, is a regulatory network of neurotransmitters, receptors, and enzymes that plays crucial roles in skin health and disease. Endogenous ligands of the ECS, called endocannabinoids, have proven to be important regulators of immune responses. One of the most prevalent endocannabinoids, arachidonoylethanolamide (also known as anandamide), is known for its anti-inflammatory effects. Langerhans cells (LCs) are the sole antigen-presenting cells present in the human epidermis. They serve as the first line of defense against pathogens and are essential for the skin's specific immune responses and play a critical role in maintaining tissue homeostasis; however, little is known about the effect of endocannabinoids on these cells. Our research aimed to provide the connection between monocyte-derived Langerhans cells (moLCs) and the ECS, shedding light on their collaborative roles in immune homeostasis and inflammation.

Methods

Human monocytes were differentiated into moLCs using established protocols. Anandamide was applied during the differentiation process to test its effect on the viability, marker expression, and cytokine production of the cells, as well as in short term treatments for intracellular calcium measurement. TLR ligands applied after the differentiation protocol were used to activate moLCs. The impact of anandamide on the functionality of moLCs was further assessed using differential gene expression analysis of bulk RNA-Seq data, moLC-T cell cocultures, while ELISpot was employed to determine polarization of T cells activated in the aforementioned cocultures.

Results

Anandamide did not significantly affect the viability of moLCs up to 10 µM. When applied during the differentiation process it had only a negligible effect on CD207 expression, the prototypic marker of LCs; however, there was an observed reduction in CD1a expression by moLCs. Anandamide had no significant effects on the maturation status of moLCs, nor did it affect the maturation induced by TLR3 and TLR7/8 agonists. MoLCs differentiated in the presence of anandamide did however show decreased production of CXCL8, IL-6, IL-10 and IL-12 cytokines induced by TLR3 and TLR7/8 activation. Anandamide-treated moLCs showed an increased capability to activate naïve T cells; however, not to the level seen with combined TLR agonism. RNA sequencing analysis of moLCs differentiated with anandamide showed modest changes compared to control cells but did reveal an inhibitory effect on oxidative phosphorylation specifically in activated moLCs. Anandamide also promoted the polarization of naïve T cells towards a Th1 phenotype.

Discussion

Our results show that anandamide has nuanced effects on the differentiation, maturation, cytokine secretion, metabolism and function of activated moLCs. Among these changes the decrease in CD1a expression on moLCs holds promise to selectively dampen inflammation induced by CD1a restricted T cells, which have been implicated as drivers of inflammation in common inflammatory skin conditions such as psoriasis, atopic dermatitis and contact dermatitis.