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Background and Aims: Although qualitative and quantitative alterations in liver Polyunsaturated Fatty Acids (PUFAs) are observed in MASH in humans, a causal relationship of PUFAs biosynthetic pathways is yet to be clarified. ELOVL5, an essential enzyme in PUFA elongation regulates hepatic triglyceride metabolism. Nonetheless, the long-term consequences of elongase disruption, particularly in murine models of MASH, have not been evaluated., Approach & Results: In humans, transcriptomic data indicated that PUFAs biosynthesis enzymes and notably ELOVL5 were induced during MASH progression. Moreover, gene module association determination revealed that ELOVL5 expression was associated with mitochondrial function in both humans and mice. WT and Elovl5-deficient mice were fed a high-fat, high-sucrose (HF/HS) diet for four months. Elovl5 deficiency led to limited systemic metabolic alterations but significant hepatic phenotype was observed in Elovl5-/- mice after the HF/HS diet, including hepatomegaly, pronounced macrovesicular and microvesicular steatosis, hepatocyte ballooning, immune cell infiltration, and fibrosis. Lipid analysis confirmed hepatic triglyceride accumulation and a reshaping of FA profile. Transcriptomic analysis indicated significant upregulation of genes involved in immune cell recruitment and fibrosis, and downregulation of genes involved in oxidative phosphorylation in Elovl5-/- mice. Alterations of FA oxidation and energy metabolism were confirmed by non-targeted metabolomic approach. Analysis of mitochondrial function in Elovl5-/- mice showed morphological alterations, qualitative cardiolipin changes with an enrichment in species containing shorter unsaturated FAs, and decreased activity of I and III respiratory chain complexes., Conclusion: Enhanced susceptibility to diet-induced MASH and fibrosis in Elovl5-/- mice is intricately associated with disruptions in mitochondrial homeostasis, stemming from a profound reshaping of mitochondrial lipids, notably cardiolipins., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

The liver macrophage population comprises resident Kupffer cells (KCs) and monocyte-derived macrophages with distinct pro- or anti-inflammatory properties that affect the severity and course of liver diseases. The mechanisms underlying macrophage differentiation and functions in metabolic dysfunction-associated steatotic liver disease and/or steatohepatitis (MASLD/MASH) remain mostly unknown. Using single-cell RNA sequencing (scRNA-seq) and fate mapping of hepatic macrophage subpopulations, we unraveled the temporal and spatial dynamics of distinct monocyte and monocyte-derived macrophage subsets in MASH. We revealed a crucial role for the Notch-Recombination signal binding protein for immunoglobulin kappa J region (RBPJ) signaling pathway in controlling the monocyte-to-macrophage transition, with Rbpj deficiency blunting inflammatory macrophages and monocyte-derived KC differentiation and conversely promoting the emergence of protective Ly6C lo monocytes. Mechanistically, Rbpj deficiency promoted lipid uptake driven by elevated CD36 expression in Ly6C lo monocytes, enhancing their protective interactions with endothelial cells. Our findings uncover the crucial role of Notch-RBPJ signaling in monocyte-to-macrophage transition and will aid in the design of therapeutic strategies for MASH treatment., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

While considerable efforts have been made to develop new therapies, progress in the treatment of pancreatic cancer has so far fallen short of patients' expectations. This is due in part to the lack of predictive in vitro models capable of accounting for the heterogeneity of this tumor and its low immunogenicity. To address this point, we have established and characterized a 3D spheroid model of pancreatic cancer composed of tumor cells, cancer-associated fibroblasts, and blood-derived monocytes. The fate of the latter has been followed from their recruitment into the tumor spheroid to their polarization into a tumor-associated macrophage (TAM)-like population, providing evidence for the formation of an immunosuppressive microenvironment.This 3D model well reproduced the multiple roles of TAMs and their influence on drug sensitivity and cell migration. Furthermore, we observed that lipid-based nanosystems consisting of sphingomyelin and vitamin E could affect the phenotype of macrophages, causing a reduction of characteristic markers of TAMs. Overall, this optimized triple coculture model gives a valuable tool that could find useful application for a more comprehensive understanding of TAM plasticity as well as for more predictive drug screening. This could increase the relevance of preclinical studies and help identify effective treatments., (© 2023. Controlled Release Society.)

Tumor-associated macrophages (TAMs) are a heterogeneous population of cells whose phenotypes and functions are shaped by factors that are incompletely understood. Herein, we asked when and where TAMs arise from blood monocytes and how they evolve during tumor development. We initiated pancreatic ductal adenocarcinoma (PDAC) in inducible monocyte fate-mapping mice and combined single-cell transcriptomics and high-dimensional flow cytometry to profile the monocyte-to-TAM transition. We revealed that monocytes differentiate first into a transient intermediate population of TAMs that generates two longer-lived lineages of terminally differentiated TAMs with distinct gene expression profiles, phenotypes, and intratumoral localization. Transcriptome datasets and tumor samples from patients with PDAC evidenced parallel TAM populations in humans and their prognostic associations. These insights will support the design of new therapeutic strategies targeting TAMs in PDAC.

Cancer is a progressive disease that can develop and evolve over decades, with inflammation playing a central role at each of its stages, from tumor initiation to metastasis. In this context, macrophages represent well-established bridges reciprocally linking inflammation and cancer via an array of diverse functions that have spurred efforts to classify them into subtypes. Here, we discuss the intertwines between macrophages, inflammation, and cancer with an emphasis on temporal dynamics of macrophage diversity and functions in pre-malignancy and cancer. By instilling temporal dynamism into the more static classic view of tumor-associated macrophage biology, we propose a new framework to better contextualize their significance in the inflammatory processes that precede and result from the onset of cancer and shape its evolution., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

High-grade serous carcinoma of the ovary, fallopian tube and peritoneum (HGSC), the most common type of ovarian cancer, ranks among the deadliest malignancies. Many HGSC patients have excess fluid in the peritoneum called ascites. Ascites is a tumour microenvironment (TME) containing various cells, proteins and extracellular vesicles (EVs). We isolated EVs from patients' ascites by orthogonal methods and analyzed them by mass spectrometry. We identified not only a set of 'core ascitic EV-associated proteins' but also defined their subset unique to HGSC ascites. Using single-cell RNA sequencing data, we mapped the origin of HGSC-specific EVs to different types of cells present in ascites. Surprisingly, EVs did not come predominantly from tumour cells but from non-malignant cell types such as macrophages and fibroblasts. Flow cytometry of ascitic cells in combination with analysis of EV protein composition in matched samples showed that analysis of cell type-specific EV markers in HGSC has more substantial prognostic potential than analysis of ascitic cells. To conclude, we provide evidence that proteomic analysis of EVs can define the cellular composition of HGSC TME. This finding opens numerous avenues both for a better understanding of EV's role in tumour promotion/prevention and for improved HGSC diagnostics., (© 2024 The Authors. Journal of Extracellular Vesicles published by Wiley Periodicals LLC on behalf of International Society for Extracellular Vesicles.)

Background: Diabetes is a major risk factor for atherosclerotic cardiovascular diseases with a 2-fold higher risk of cardiovascular events in people with diabetes compared with those without. Circulating monocytes are inflammatory effector cells involved in both type 2 diabetes (T2D) and atherogenesis., Methods: We investigated the relationship between circulating monocytes and cardiovascular risk progression in people with T2D, using phenotypic, transcriptomic, and metabolomic analyses. cardiovascular risk progression was estimated with coronary artery calcium score in a cohort of 672 people with T2D., Results: Coronary artery calcium score was positively correlated with blood monocyte count and frequency of the classical monocyte subtype. Unsupervised k-means clustering based on monocyte subtype profiles revealed 3 main endotypes of people with T2D at varying risk of cardiovascular events. These observations were confirmed in a validation cohort of 279 T2D participants. The predictive association between monocyte count and major adverse cardiovascular events was validated through an independent prospective cohort of 757 patients with T2D. Integration of monocyte transcriptome analyses and plasma metabolomes showed a disruption of mitochondrial pathways (tricarboxylic acid cycle, oxidative phosphorylation pathway) that underlined a proatherogenic phenotype., Conclusions: In this study, we provide evidence that frequency and monocyte phenotypic profile are closely linked to cardiovascular risk in patients with T2D. The assessment of monocyte frequency and count is a valuable predictive marker for risk of cardiovascular events in patients with T2D., Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT04353869., Competing Interests: Disclosures None.

Myeloid cells, including monocytes, macrophages, dendritic cells, and polymorphonuclear cells are key components of homeostasis maintenance and immune response. Among the myeloid lineage, macrophages stand out as highly versatile cells that safeguard tissue functions but also sense and respond to potentially harmful microenvironmental cues. Numerous studies have demonstrated that the nutritional status and macronutrient availability affect macrophage identity and function. However, the exact mechanistic links between macronutrient intake and cellular metabolic shifts are only beginning to be understood. In this chapter, we explore how dietary "macros"-carbohydrates, fats, and amino acids-impact the immunomodulatory activity of macrophages in healthy and inflamed tissues., (© 2024. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

Mast cells (MCs) are tissue-resident immune cells that exhibit homeostatic and neuron-associated functions. Here, we combined whole-tissue imaging and single-cell RNA sequencing datasets to generate a pan-organ analysis of MCs in mice and humans at steady state. In mice, we identify two mutually exclusive MC populations, MrgprB2+ connective tissue-type MCs and MrgprB2neg mucosal-type MCs, with specific transcriptomic core signatures. While MrgprB2+ MCs develop in utero independently of the bone marrow, MrgprB2neg MCs develop after birth and are renewed by bone marrow progenitors. In humans, we unbiasedly identify seven MC subsets (MC1-7) distributed across 12 organs with different transcriptomic core signatures. MC1 are preferentially enriched in the bladder, MC2 in the lungs, and MC4, MC6, and MC7 in the skin. Conversely, MC3 and MC5 are shared by most organs but not skin. This comprehensive analysis offers valuable insights into the natural diversity of MC subtypes in both mice and humans., (© 2023 Tauber et al.)

Macrophages are critical regulators of tissue homeostasis but are also abundant in the tumor microenvironment (TME). In both primary tumors and metastases, such tumor-associated macrophages (TAMs) seem to support tumor development. While we know that TAMs are the dominant immune cells in the TME, their vast heterogeneity and associated functions are only just being unraveled. In this review, we outline the various known TAM populations found thus far and delineate their specialized roles associated with the main stages of cancer progression. We discuss how macrophages may prime the premetastatic niche to enable the growth of a metastasis and then how subsequent metastasis-associated macrophages can support secondary tumor growth. Finally, we speculate on the challenges that remain to be overcome in TAM research., (© 2023. The Author(s).)

Macrophages are involved in immune defense, organogenesis and tissue homeostasis. Macrophages contribute to the different phases of mammary gland remodeling during development, pregnancy and involution postlactation. Less is known about the dynamics of mammary gland macrophages in the lactation stage. Here, we describe a macrophage population present during lactation in mice. By multiparameter flow cytometry and single-cell RNA sequencing, we identified a lactation-induced CD11c + CX3CR1 + Dectin-1 + macrophage population (liMac) that was distinct from the two resident F4/80 hi and F4/80 lo macrophage subsets present pregestationally. LiMacs were predominantly monocyte-derived and expanded by proliferation in situ concomitant with nursing. LiMacs developed independently of IL-34, but required CSF-1 signaling and were partly microbiota-dependent. Locally, they resided adjacent to the basal cells of the alveoli and extravasated into the milk. We found several macrophage subsets in human milk that resembled liMacs. Collectively, these findings reveal the emergence of unique macrophages in the mammary gland and milk during lactation., (© 2023. The Author(s).)

The liver is the site of first pass metabolism, detoxifying and metabolizing blood arriving from the hepatic portal vein and hepatic artery. It is made up of multiple cell types, including macrophages. These are either bona fide tissue-resident Kupffer cells (KC) of embryonic origin, or differentiated from circulating monocytes. KCs are the primary immune cells populating the liver under steady state. Liver macrophages interact with hepatocytes, hepatic stellate cells, and liver sinusoidal endothelial cells to maintain homeostasis, however they are also key contributors to disease progression. Generally tolerogenic, they physiologically phagocytose foreign particles and debris from portal circulation and participate in red blood cell clearance. However as immune cells, they retain the capacity to raise an alarm to recruit other immune cells. Their aberrant function leads to the development of non-alcoholic fatty liver disease (NAFLD). NAFLD refers to a spectrum of conditions ranging from benign steatosis of the liver to steatohepatitis and cirrhosis. In NAFLD, the multiple hit hypothesis proposes that simultaneous influences from the gut and adipose tissue (AT) generate hepatic fat deposition and that inflammation plays a key role in disease progression. KCs initiate the inflammatory response as resident immune effectors, they signal to neighbouring cells and recruit monocytes that differentiated into recruited macrophages in situ . Recruited macrophages are central to amplifying the inflammatory response and causing progression of NAFLD to its fibro-inflammatory stages. Given their phagocytic capacity and their being instrumental in maintaining tissue homeostasis, KCs and recruited macrophages are fast-becoming target cell types for therapeutic intervention. We review the literature in the field on the roles of these cells in the development and progression of NAFLD, the characteristics of patients with NAFLD, animal models used in research, as well as the emerging questions. These include the gut-liver-brain axis, which when disrupted can contribute to decline in function, and a discussion on therapeutic strategies that act on the macrophage-inflammatory axis., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Alabdulaali, Al-rashed, Al-Onaizi, Kandari, Razafiarison, Tonui, Williams, Blériot, Ahmad and Alzaid.)

Type 2 diabetes (T2D) represents a global threat affecting millions of patients worldwide. However, its causes remain incompletely dissected and we lack the tools to predict which individuals will develop T2D. Although there is a clear proven clinical association of T2D with metabolic disorders such as obesity and nonalcoholic fatty liver disease (NAFLD), the existence of a significant number of nondiabetic obese subjects suggests yet-uncovered features of such relationships. Here, we propose that a significant proportion of individuals may harbor an immune profile that renders them susceptible to developing T2D. We note the heterogeneity of circulating monocytes and tissue macrophages in organs that are key to metabolic disorders such as liver, white adipose tissue (WAT), and endocrine pancreas, as well as their contribution to T2D genesis., Competing Interests: Declaration of interests No interests are declared., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Embryonic development is characterized by rapidly dividing cells, cellular plasticity and a highly vascular microenvironment. These features are similar to those of tumour tissue, in that malignant cells are characterized by their ability to proliferate and exhibit cellular plasticity. The tumour microenvironment also often includes immunosuppressive features. Reciprocal communication between various cellular subpopulations enables fetal and tumour tissues to proliferate, migrate and escape immune responses. Fetal-like reprogramming has been demonstrated in the tumour microenvironment, indicating extraordinary cellular plasticity and bringing an additional layer of cellular heterogeneity. More importantly, some of these features are also present during inflammation. This Perspective discusses the similarity between embryogenesis, inflammation and tumorigenesis, and describes the mechanisms of oncofetal reprogramming that enable tumour cells to escape from immune responses, promoting tumour growth and metastasis., (© 2022. Springer Nature Limited.)

The obesity epidemic has led researchers and clinicians to reconsider the etiology of this disease and precisely decipher its molecular mechanisms. The excessive accumulation of fat by cells, most notably adipocytes, which play a key role in this process, has many repercussions in tissue physiology. Herein, we focus on how macrophages, immune cells well known for their tissue gatekeeping functions, assume fundamental, yet ill-defined, roles in the genesis and development of obesity-related metabolic disorders. We first discuss the determinants of the biology of these cells before introducing the specifics of the adipose tissue environment, while highlighting its heterogeneity. Finally, we detail how obesity transforms both adipose tissue and local macrophage populations. Understanding macrophage diversity and their cross talk with the diverse cell types constituting the adipose tissue environment will allow us to frame the therapeutic potential of adipose tissue macrophages in obesity., (© 2022 Chakarov et al.)

Here, we provide detailed protocols for the isolation of mouse Kupffer cells - the liver-resident macrophages - for phenotypic (e.g., via flow cytometry, mass cytometry, or RNA-sequencing) analyses or for functional experiments involving cell culture. The procedures presented can be adapted for the isolation of other hepatic cell populations. For complete details on the use and execution of this protocol, please refer to De Simone et al. (2021)., Competing Interests: M.I. participates in advisory boards/consultancies for Gilead Sciences, Roche, Third Rock Ventures, Amgen, Allovir. M.I. is an inventor on patents filed, owned, and managed by San Raffaele Scientific Institute, Vita-Salute San Raffaele University and Telethon Foundation on technology related to work discussed in this manuscript (WO2020/016434, WO2020/016427, WO2020/030781, WO2020/234483, EU patent applications n. 19211249.8 and n 20156716.1, and UK patent application n. 1907493.9). F.G. is a member of the Immunity advisory board., (© 2021 The Author(s).)

Tissue macrophages are immune cells whose phenotypes and functions are dictated by origin and niches. However, tissues are complex environments, and macrophage heterogeneity within the same organ has been overlooked so far. Here, we used high-dimensional approaches to characterize macrophage populations in the murine liver. We identified two distinct populations among embryonically derived Kupffer cells (KCs) sharing a core signature while differentially expressing numerous genes and proteins: a major CD206 lo ESAM - population (KC1) and a minor CD206 hi ESAM + population (KC2). KC2 expressed genes involved in metabolic processes, including fatty acid metabolism both in steady-state and in diet-induced obesity and hepatic steatosis. Functional characterization by depletion of KC2 or targeted silencing of the fatty acid transporter Cd36 highlighted a crucial contribution of KC2 in the liver oxidative stress associated with obesity. In summary, our study reveals that KCs are more heterogeneous than anticipated, notably describing a subpopulation wired with metabolic functions., Competing Interests: Declaration of interests C.B., M.A., and F.G. are inventors on a patent filed, owned, and managed by A(∗)ccelerate technologies Pte Ltd, A-STAR, Singapore, on technology related to the work presented in this manuscript., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Mononuclear phagocytes (MNPs) encompass dendritic cells, monocytes, and macrophages (MoMac), which exhibit antimicrobial, homeostatic, and immunoregulatory functions. We integrated 178,651 MNPs from 13 tissues across 41 datasets to generate a MNP single-cell RNA compendium (MNP-VERSE), a publicly available tool to map MNPs and define conserved gene signatures of MNP populations. Next, we generated a MoMac-focused compendium that revealed an array of specialized cell subsets widely distributed across multiple tissues. Specific pathological forms were expanded in cancer and inflammation. All neoplastic tissues contained conserved tumor-associated macrophage populations. In particular, we focused on IL4I1 + CD274(PD-L1) + IDO1 + macrophages, which accumulated in the tumor periphery in a T cell-dependent manner via interferon-γ (IFN-γ) and CD40/CD40L-induced maturation from IFN-primed monocytes. IL4I1_Macs exhibited immunosuppressive characteristics through tryptophan degradation and promoted the entry of regulatory T cell into tumors. This integrated analysis provides a robust online-available platform for uniform annotation and dissection of specific macrophage functions in healthy and pathological states., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Macrophages are sessile immune cells with a high functional plasticity. Initially considered as a uniform population of phagocytic scavengers, it is now widely accepted that these cells also assume developmental and metabolic functions specific of their tissue of residence. Hence, the paradigm is shifting while our comprehension of macrophage heterogeneity improves. Accordingly, exploiting this intrinsic versatility appears more and more promising for the establishment of innovative therapeutic strategies. Nevertheless, identifying relevant therapeutic targets remains a considerable challenge. Herein, we discuss various features of macrophage heterogeneity in five main categories of human diseases: infectious, inflammatory, metabolic, age-related, and neoplastic disorders. We summarize the current understanding of how macrophage heterogeneity may impact the pathogenesis of these diseases and propose a comprehensive overview with the aim to help in establishing future macrophage-targeted therapies., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2020 Gessain, Blériot and Ginhoux.)

We employed scRNA sequencing to extensively characterize the cellular landscape of human liver from development to disease. Analysis of ∼212,000 cells representing human fetal, hepatocellular carcinoma (HCC), and mouse liver revealed remarkable fetal-like reprogramming of the tumor microenvironment. Specifically, the HCC ecosystem displayed features reminiscent of fetal development, including re-emergence of fetal-associated endothelial cells (PLVAP/VEGFR2) and fetal-like (FOLR2) tumor-associated macrophages. In a cross-species comparative analysis, we discovered remarkable similarity between mouse embryonic, fetal-liver, and tumor macrophages. Spatial transcriptomics further revealed a shared onco-fetal ecosystem between fetal liver and HCC. Furthermore, gene regulatory analysis, spatial transcriptomics, and in vitro functional assays implicated VEGF and NOTCH signaling in maintaining onco-fetal ecosystem. Taken together, we report a shared immunosuppressive onco-fetal ecosystem in fetal liver and HCC. Our results unravel a previously unexplored onco-fetal reprogramming of the tumor ecosystem, provide novel targets for therapeutic interventions in HCC, and open avenues for identifying similar paradigms in other cancers and disease., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Resident tissue macrophages (RTMs) have a broad spectrum of immune- and non-immune-related tissue-supporting activities. The roots of this heterogeneity and versatility are only beginning to be understood. Here, we propose a conceptual framework for considering the RTM heterogeneity that organizes the factors shaping RTM identity within four cardinal points: (1) ontogeny and the view that adult RTM populations comprise a defined mixture of cells that arise from either embryonic precursors or adult monocytes; (2) local factors unique to the niche of residence, evolving during development and aging; (3) inflammation status; and (4) the cumulative effect of time spent in a specific tissue that contributes to the resilient adaptation of macrophages to their dynamic environment. We review recent findings within this context and discuss the technological advances that are revolutionizing the study of macrophage biology., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Kupffer cells are the liver-resident macrophages lining the sinusoids and are mostly known for their role of scavengers, as crucial keepers of organ integrity. But due to the many fundamental functions of the liver notably linked to detoxication, metabolism, protein synthesis, or immunology, Kupffer cells are exposed to a dynamic environment and constantly adapt themselves by modulating their gene and protein expressions. In this context, the characterization of these cells at steady-state and upon challenges may be limited by the classical microscopy or flow cytometry which allow for the use of only few selected markers. On the other end, transcriptomic approach, although being very powerful, can be costly and time-consuming. So mass cytometry offers a good compromise, allowing for the monitoring of a representative set of markers (up to 40) in a simple experiment. Herein, we describe a straightforward experimental and analysis workflow for Kupffer cell characterization by mass cytometry.

Resident tissue macrophages (RTMs) are cells with a high functional plasticity assuming pleiotropic roles in their tissue of residence, from clearance of dead cells and metabolic sensing in steady state to cytokine production and tissue repair during inflammation. The liver has long been considered as only populated by Kupffer cells (KCs), a macrophage population assumed to be in charge of all of these functions. However, we know now that KCs are not the only macrophage population in the liver, that recently was shown to contain also capsular macrophages, monocyte-derived macrophages as well as recruited peritoneal macrophages inherited from previous inflammatory events. These macrophages exhibit different origins, time of establishing residence and locations in the liver, with both ontogenical and environmental factors shaping their identity and functions. Furthermore, liver macrophages reside in a complex environment with a pronounced metabolic zonation. Here, we briefly discuss how these intrinsic and extrinsic factors influence macrophage biology and liver physiology in general. We notably focus on how the recent advances of single cell transcriptomic approaches are changing our understanding of liver macrophages and diseases., (Copyright © 2019 Blériot and Ginhoux.)

In this issue of Cell, Uderhardt et al. employed intravital two-photon microscopy to examine tissue-resident macrophage responses to sterile cellular injuries of variable size. They observed that while multi-cell "macrolesions" are characteristically pro-inflammatory, resident macrophages can "cloak" single-cell microlesions to prevent excessive neutrophil recruitment and limit subsequent tissue damage., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The foodborne pathogen Listeria monocytogenes ( Lm ) crosses the intestinal villus epithelium via goblet cells (GCs) upon the interaction of Lm surface protein InlA with its receptor E-cadherin. Here, we show that Lm infection accelerates intestinal villus epithelium renewal while decreasing the number of GCs expressing luminally accessible E-cadherin, thereby locking Lm portal of entry. This novel innate immune response to an enteropathogen is triggered by the infection of Peyer's patch CX3CR1 + cells and the ensuing production of IL-23. It requires STAT3 phosphorylation in epithelial cells in response to IL-22 and IL-11 expressed by lamina propria gp38 + stromal cells. Lm -induced IFN-γ signaling and STAT1 phosphorylation in epithelial cells is also critical for Lm -associated intestinal epithelium response. GC depletion also leads to a decrease in colon mucus barrier thickness, thereby increasing host susceptibility to colitis. This study unveils a novel innate immune response to an enteropathogen, which implicates gp38 + stromal cells and locks intestinal villus invasion, but favors colitis., (© 2018 Disson et al.)

Necrosis has long been considered as a passive event resulting from a cell extrinsic stimulus, such as pathogen infection. Recent advances have refined this view and it is now well established that necrosis is tightly regulated at the cell level. Regulated necrosis can occur in the context of host-pathogen interactions, and can either participate in the control of infection or favor it. Here, we review the two main pathways implicated so far in bacteria-associated regulated necrosis: caspase 1-dependent pyroptosis and RIPK1/RIPK3-dependent necroptosis. We present how these pathways are modulated in the context of infection by a series of model bacterial pathogens.

Kupffer cells, the phagocytes of fetal origin that line the liver sinusoids, are key contributors of host defense against enteroinvasive bacteria. Here, we found that infection by Listeria monocytogenes induced the early necroptotic death of Kupffer cells, which was followed by monocyte recruitment and an anti-bacterial type 1 inflammatory response. Kupffer cell death also triggered a type 2 response that involved the hepatocyte-derived alarmin interleukin-33 (IL-33) and basophil-derived interleukin-4 (IL-4). This led to the alternative activation of the monocyte-derived macrophages recruited to the liver, which thereby replaced ablated Kupffer cells and restored liver homeostasis. Kupffer cell death is therefore a key signal orchestrating type 1 microbicidal inflammation and type-2-mediated liver repair upon infection. This indicates that beyond the classical dichotomy of type 1 and type 2 responses, these responses can develop sequentially in the context of a bacterial infection and act interdependently, orchestrating liver immune responses and return to homeostasis, respectively., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Divalent cations play fundamental roles in biological systems where they act as structural and reactive determinants. Their high reactivity with biomolecules has forced living cells to evolve specific pathways for their in vivo handling. For instance the excess of metal can be expelled by dedicated efflux systems. The E. coli RcnA efflux pump expels both Ni and Co. This pump functions together with the periplasmic protein RcnB to maintain metal ion homeostasis. To gain insights into the efflux mechanism, metal binding properties of RcnB were investigated. Initial screening of metal ions by fluorescence quenching revealed Cu as a potential ligand for RcnB. Non-denaturing mass spectrometry and ITC experiments revealed the binding of one Cu ion per monomer with a micromolar affinity. This set of in vitro techniques was broadened by in vivo experiments that showed the accuracy of Cu binding by RcnB. RcnB implication in Cu detoxification was questioned and growth experiments as well as transcriptional analysis excluded a role for RcnB in Cu adaptation. Finally a mutant in a conserved methionine residue (Met86) displayed altered Cu binding. This mutant protein when tested for its Ni and Co resistance capacity was unable to complement an rcn mutant. Taken together these data show that RcnB is a new Cu-binding protein that is strikingly involved in a Ni/Co efflux system.

Nickel and cobalt are both essential trace elements that are toxic when present in excess. The main resistance mechanism that bacteria use to overcome this toxicity is the efflux of these cations out of the cytoplasm. RND (resistance-nodulation-cell division)- and MFS (major facilitator superfamily)-type efflux systems are known to export either nickel or cobalt. The RcnA efflux pump, which belongs to a unique family, is responsible for the detoxification of Ni and Co in Escherichia coli. In this work, the role of the gene yohN, which is located downstream of rcnA, is investigated. yohN is cotranscribed with rcnA, and its expression is induced by Ni and Co. Surprisingly, in contrast to the effect of deleting rcnA, deletion of yohN conferred enhanced resistance to Ni and Co in E. coli, accompanied by decreased metal accumulation. We show that YohN is localized to the periplasm and does not bind Ni or Co ions directly. Physiological and genetic experiments demonstrate that YohN is not involved in Ni import. YohN is conserved among proteobacteria and belongs to a new family of proteins; consequently, yohN has been renamed rcnB. We show that the enhanced resistance of rcnB mutants to Ni and Co and their decreased Ni and Co intracellular accumulation are linked to the greater efflux of these ions in the absence of rcnB. Taken together, these results suggest that RcnB is required to maintain metal ion homeostasis, in conjunction with the efflux pump RcnA, presumably by modulating RcnA-mediated export of Ni and Co to avoid excess efflux of Ni and Co ions via an unknown novel mechanism.

RcnA is an efflux pump responsible for Ni and Co detoxification in Escherichia coli. The expression of rcnA is induced by Ni and Co via the metallo-regulator RcnR. In the present work, the functioning of the promoter-operator region of rcnR and rcnA was investigated using primer extension and DNAse I footprinting experiments. We show that the promoters of rcnR and rcnA are convergent and that apo-RcnR binds on symmetrically located sequences in this intergenic region. Moreover, RcnR DNA binding is specifically modulated by one Ni or Co equivalent and not by other metals. In addition to rcnA, RcnR controls expression of its own gene in response to Ni and Co, but the two genes are differentially expressed., (Copyright © 2010 Elsevier Masson SAS. All rights reserved.)