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The liver has a unique ability to regenerate1,2, however in the setting of acute liver failure (ALF) this regenerative capacity is often overwhelmed and emergency liver transplantation is the only curative option3-5. To advance our understanding of human liver regeneration and to inform design of pro-regenerative therapies, we use paired single-nuclei RNA sequencing (snRNA-seq) combined with spatial profiling of healthy and ALF explant human livers to generate the first single-cell, pan-lineage atlas of human liver regeneration. We uncover a novel ANXA2+migratory hepatocyte subpopulation which emerges during human liver regeneration, and a corollary migratory hepatocyte subpopulation in a mouse model of acetaminophen (APAP)-induced liver regeneration. Importantly, interrogation of necrotic wound closure and hepatocyte proliferation across multiple timepoints following APAP-induced liver injury in mice demonstrates that wound closure precedes hepatocyte proliferation. 4-D intravital imaging of APAP-induced mouse liver injury identifies motile hepatocytes at the edge of the necrotic area, enabling collective migration of the hepatocyte sheet to effect wound closure. Depletion of hepatocyte ANXA2 expression reduces HGF-induced human and mouse hepatocyte migrationin vitro, and abrogates necrotic wound closure following APAP-induced mouse liver injury. Taken together, our work dissects unanticipated aspects of liver regeneration, demonstrating an uncoupling of wound closure and hepatocyte proliferation and uncovering a novel migratory hepatocyte subpopulation which mediates wound closure following liver injury. Therapies designed to promote rapid reconstitution of normal hepatic microarchitecture and reparation of the gut-liver barrier may open up new areas of therapeutic discovery in regenerative medicine.

Intercellular communication between different cell types in solid tumors contributes to tumor growth and metastatic dissemination. The secretome of cancer-associated fibroblasts (CAFs) plays major roles in these processes. Using human mammary CAFs, we unveil a mechanism of cell-cell communication between CAFs with myofibroblast phenotype and endothelial cells (ECs) based on intercellular protein transfer through extracellular vesicles (EVs). CAFs transfer proteins to ECs, including plasma membrane receptors, which we have identified by using mass spectrometry- based proteomics. Using THY1 as an example of transferred plasma membrane-bound protein, we show that CAF-derived proteins can influence how ECs interact with other cell types. Here, we show that CAFs produce high amounts of matrix-bound EVs that have a key role in protein transfer. Hence, our work paves the way for further studies to understand how CAF-derived matrix-bound EVs influence tumor pathology by regulating functions of neighboring cancer, stromal and immune cells.One sentence summaryCAFs with a myofibroblastic-like phenotype transfer proteins to ECs, including plasma membrane receptors, through matrix-bound EVs

Aberrant expansion of KRT5+basal cells in the distal lung accompanies progressive alveolar epithelial cell loss and tissue remodelling during fibrogenesis in idiopathic pulmonary fibrosis (IPF). The mechanisms determining activity of KRT5+cells in IPF have not been delineated. Here, we reveal a potential mechanism by which KRT5+cells migrate within the fibrotic lung, navigating regional differences in collagen topography.In vitro, KRT5+cell migratory characteristics and expression of remodelling genes are modulated by extracellular matrix (ECM) composition and organisation. Mass spectrometry-based proteomics revealed compositional differences in ECM components secreted by primary human lung fibroblasts (HLF) from IPF patients compared to controls. Over-expression of ECM glycoprotein, Secreted Protein Acidic and Cysteine Rich (SPARC) in the IPF HLF matrix restricts KRT5+cell migrationin vitro. Together, our findings demonstrate how changes to the ECM in IPF directly influence KRT5+cell behaviour and function contributing to remodelling events in the fibrotic niche.

Effective anticancer adoptive cellular therapy (ACT) requires sufficient infiltration of injected cytotoxic lymphocytes, but pathophysiology frustrates this. Regulator of G protein signaling 1 limits T cell trafficking to breast tumors and may be targeted to improve ACT.

Genetically encoded probes are widely used to visualize cellular processes in vitro and in vivo. Although effective in cultured cells, fluorescent protein tags and reporters are suboptimal in vivo because of poor tissue penetration and high background signal. Luciferase reporters offer improved signal-to-noise ratios but require injections of luciferin that can lead to variable responses and that limit the number and timing of data points that can be gathered. Such issues in studying the critical transcription factor p53 have limited insight on its activity in vivo during development and tissue injury responses. Here, by linking the expression of the near-infrared fluorescent protein iRFP713 to a synthetic p53-responsive promoter, we generated a knock-in reporter mouse that enabled noninvasive, longitudinal analysis of p53 activity in vivo in response to various stimuli. In the developing embryo, this model revealed the timing and localization of p53 activation. In adult mice, the model monitored p53 activation in response to irradiation and paracetamol- or CCl 4 -induced liver regeneration. After irradiation, we observed potent and sustained activation of p53 in the liver, which limited the production of reactive oxygen species (ROS) and promoted DNA damage resolution. We propose that this new reporter may be used to further advance our understanding of various physiological and pathophysiological p53 responses.

Filarial parasites are tissue dwelling worms transmitted by hematophagous vectors. Understanding the mechanisms regulating microfilariae (the parasite offspring) development is a prerequisite for controlling transmission in filarial infections. Th2 immune responses are key for building efficient anti-parasite responses but have been shown to also lead to detrimental tissue damage in the presence of microfilariae. Litomosoides sigmodontis, a rodent filaria residing in the pleural cavity was therefore used to characterize pleuropulmonary pathology and associated immune responses in wild-type and Th2 deficient mice. Wild-type and Th2-deficient mice (Il-4rα-/-/Il-5-/-) were infected with L. sigmodontis and parasite outcome was analyzed during the patent phase (when microfilariae are in the general circulation). Pleuropulmonary manifestations were investigated and pleural and bronchoalveolar cells were characterized by RNA analysis, imaging and/or flow cytometry focusing on macrophages. Il-4rα-/-/Il-5-/- mice were hypermicrofilaremic and showed an enhanced filarial survival but also displayed a drastic reduction of microfilaria-driven pleural cavity pathologies. In parallel, pleural macrophages from Il-4rα-/-/Il-5-/- mice lacked expression of prototypical alternative activation markers RELMα and Chil3 and showed an altered balance of some markers of the arginine metabolic pathway. In addition, monocytes-derived F4/80intermediate macrophages from infected Il-4rα-/-/Il-5-/- mice failed to mature into resident F4/80high large macrophages. Altogether these data emphasize that the presence of both microfilariae and IL-4R/IL-5 signaling are critical in the development of the pathology and in the phenotype of macrophages. In Il-4rα-/-/Il-5-/- mice, the balance is in favor of parasite development while limiting the pathology associated with the host immune response.

Objective: Hepatocellular carcinoma (HCC) is increasingly associated with non-alcoholic steatohepatitis (NASH). HCC immunotherapy offers great promise; however, recent data suggests NASH-HCC may be less sensitive to conventional immune checkpoint inhibition (ICI). We hypothesised that targeting neutrophils using a CXCR2 small molecule inhibitor may sensitise NASH-HCC to ICI therapy. Design Neutrophil infiltration was characterised in human HCC and mouse models of HCC. Late-stage intervention with anti-PD1 and/or a CXCR2 inhibitor was performed in murine models of NASH-HCC. The tumour immune microenvironment was characterised by imaging mass cytometry, RNA-seq and flow cytometry. Results: neutrophils expressing CXCR2, a receptor crucial to neutrophil recruitment in acute-injury, are highly represented in human NASH-HCC. In models of NASH-HCC lacking response to ICI, the combination of a CXCR2 antagonist with anti-PD1 suppressed tumour burden and extended survival. Combination therapy increased intratumoural XCR1(+) dendritic cell activation and CD8(+) T cell numbers which are associated with anti-tumoural immunity, this was confirmed by loss of therapeutic effect on genetic impairment of myeloid cell recruitment, neutralisation of the XCR1-ligand XCL1 or depletion of CD8(+) T cells. Therapeutic benefit was accompanied by an unexpected increase in tumour-associated neutrophils (TANs) which switched from a protumour to anti-tumour progenitor-like neutrophil phenotype. Reprogrammed TANs were found in direct contact with CD8(+) T cells in clusters that were enriched for the cytotoxic anti-tumoural protease granzyme B. Neutrophil reprogramming was not observed in the circulation indicative of the combination therapy selectively influencing TANs. Conclusion: CXCR2-inhibition induces reprogramming of the tumour immune microenvironment that promotes ICI in NASH-HCC., Cancer Research UK (CRUK); Newcastle Experimental Cancer Medicine Centre; Accelerator Award; Fondazione AIRC; MRC program; AstraZeneca; Wellcome Trust; Newcatle University Faculty of Medical Sciences; WE Harker Foundation; Ministry of Economy and Competitiveness (MINECO) (MICINN); Fundació Universitària Agustí Pedro i Pons; Instituto de Salud Carlos III (ISCIII); European Union (EU); European Social Fund; German Research Foundation (DFG); Fulbright España; National Institutes of Health (NIH); Samuel Waxman Cancer Research Foundation; Spanish National Health Institute; Fundación Científica de la Asociación Española Contra el Cáncer; Generalitat de Catalunya; Sara Borrell Fellowship

Neutrophils have been implicated in poor outcomes in cancer and severe inflammation. We found that neutrophils expressing intermediate levels of Ly6G (Ly6GInt) were present in mouse cancer models and more abundant in those with high rates of spontaneous metastasis. Maturation, age, tissue localization and functional capacity all drive neutrophil heterogeneity. Recent studies have proposed various markers to distinguish between these heterogeneous sub-populations; however, these markers are limited to specific models of inflammation and cancer. Here, we identify and define Ly6G expression level as a robust and reliable marker to distinguish neutrophils at different stages of maturation. Ly6GInt neutrophils were bona fide ‘immature neutrophils’ with reduced immune regulatory and adhesion capacity. Whereas the bone marrow is a more recognised site of granulopoiesis, the spleen also produces neutrophils in homeostasis and cancer. Strikingly, neutrophils matured faster in the spleen than in the bone marrow with unique transcriptional profiles. We propose that developmental origin is critical in neutrophil identity and postulate that neutrophils that develop in the spleen supplement the bone marrow by providing an intermediate more mature reserve before emergency haematopoiesis.

Alveolar macrophages are the most abundant macrophages in the healthy lung where they play key roles in homeostasis and immune surveillance against air-borne pathogens. Tissue-specific differentiation and survival of alveolar macrophages relies on niche-derived factors, such as colony stimulating factor 2 (CSF-2) and transforming growth factor beta (TGF-β). However, the nature of the downstream molecular pathways that regulate the identity and function of alveolar macrophages and their response to injury remains poorly understood. Here, we identify that the transcriptional factor EGR2 is an evolutionarily conserved feature of lung alveolar macrophages and show that cell-intrinsic EGR2 is indispensable for the tissue-specific identity of alveolar macrophages. Mechanistically, we show that EGR2 is driven by TGF-β and CSF-2 in a PPAR-γ-dependent manner to control alveolar macrophage differentiation. Functionally, EGR2 was dispensable for lipid handling, but crucial for the effective elimination of the respiratory pathogen Streptococcus pneumoniae. Finally, we show that EGR2 is required for repopulation of the alveolar niche following sterile, bleomycin-induced lung injury and demonstrate that EGR2-dependent, monocyte-derived alveolar macrophages are vital for effective tissue repair following injury. Collectively, we demonstrate that EGR2 is an indispensable component of the transcriptional network controlling the identity and function of alveolar macrophages in health and disease.One Sentence SummaryEGR2 controls alveolar macrophage function in health and disease

Summary Eosinophils mediate protection against filarial nematodes. Our results demonstrate that eosinophil extracellular traps (EETosis) are induced by microfilariae and infective L3 larvae of Litomosoides sigmodontis. These extracellular DNA traps inhibit microfilariae motility in a DNA- and contact-dependent manner in vitro. Accordingly, microfilariae-injection triggers DNA release in an eosinophil-dependent manner in vivo and microfilariae covered with DNA traps are cleared more rapidly. Using dectin-1, we identify the required receptor for the microfilariae-induced EETosis, whereas signaling via other C-type lectin receptors, prior priming of eosinophils, and presence of antibodies are not required. The DNA released upon microfilariae-induced EETosis is mainly of mitochondrial origin, but acetylated and citrullinated histones are found within the traps. We further demonstrate that the presented DNA-dependent inhibition of microfilariae motility by eosinophils represents a conserved mechanism, as microfilariae from L. sigmodontis and the canine heartworm Dirofilaria immitis induce ETosis in murine and human eosinophils.

Neutrophils are essentially involved in protective immune responses against invading infective larvae of filarial nematodes. The present study investigated the impact of S100A8/S100A9 on protective immune responses against the rodent filarial nematode Litomosoides sigmodontis. S100A9 forms with S100A8 the heterodimer calprotectin, which is expressed by circulating neutrophils and monocytes and mitigates or amplifies tissue damage as well as inflammation depending on the immune environment. Mice deficient for S100A8/A9 had a significantly reduced worm burden in comparison to wildtype (WT) animals 12 days after infection (dpi) with infective L3 larvae, either by the vector or subcutaneous inoculation, the latter suggesting that circumventing natural immune responses within the epidermis and dermis do not alter the phenotype. Nevertheless, upon intradermal injection of L3 larvae, increased total numbers of neutrophils, eosinophils and macrophages were observed within the skin of S100A8/A9-/- mice. Furthermore, upon infection the bronchoalveolar and thoracic cavity lavage of S100A8/A9-/- mice showed increased concentrations of CXCL-1, CXCL-2, CXCL-5, as well as elastase in comparison to the WT controls. Neutrophils from S100A8/A9-/- mice exhibited an increased in vitro activation and reduced L3 larval motility more effectively in vitro compared to WT neutrophils. The depletion of neutrophils from S100A8/A9-/- mice prior to L. sigmodontis infection until 5dpi abrogated the protective effect and led to an increased worm burden, indicating that neutrophils mediate enhanced protective immune responses against invading L3 larvae in S100A8/A9-/- mice. Interestingly, complete circumvention of protective immune responses in the skin and the lymphatics by intravenous injection of L3 larvae reversed the phenotype and resulted in an increased worm burden in S100A8/A9-/- mice. In summary, our results reveal that lack of S100A8/S100A9 triggers L3-induced inflammatory responses, increasing chemokine levels, granulocyte recruitment as well as neutrophil activation and therefore impairs larval migration and susceptibility for filarial infection., Author summary Human pathogenic filariae are responsible for several devastating diseases such as lymphatic filariasis and onchocerciasis. Neutrophils are essentially involved in protective immune responses against invading infective L3 larvae of filarial nematodes. The S100A8/S100A9 heterodimer, also known as calprotectin, is abundantly expressed by neutrophils and markedly increased during infection, tissue damage, neutrophil extracellular trap formation (NETosis) and cellular necrosis. However, calprotectin is also known to have an anti-inflammatory or protective role during infection and inflammation and there is an ongoing controversy on whether S100A8/A9 is pathogenic or rather protective. The present study investigated the impact of calprotectin on protective immune responses against the rodent filarial nematode Litomosoides sigmodontis. Investigations in L. sigmodontis-infected mice deficient in S100A8/S100A9 and wild-type controls demonstrate that the lack of S100A8/S100A9 promotes protective responses that trigger L3-induced inflammation by increasing chemokine production, granulocyte recruitment and neutrophil activation, triggering transient inflammatory responses and therefore impairing larval migration and worm recovery.

Alveolar macrophages are the most abundant macrophages in the healthy lung where they play key roles in homeostasis and immune surveillance against air-borne pathogens. Tissue-specific differentiation and survival of alveolar macrophages relies on niche-derived factors, such as granulocyte-macrophage colony stimulating factor 2 (GM-CSF) and transforming growth factor beta (TGF-). However, the nature of the downstream molecular pathways that regulate the identity and function of alveolar macrophages and their response to injury remains poorly understood. Here, we identify that the transcriptional factor EGR2 is an evolutionarily conserved feature of lung alveolar macrophages and show that cell-intrinsic EGR2 is indispensable for the tissue-specific identity of alveolar macrophages. Mechanistically, we show that EGR2 is driven by TGF- and GM-CSF in a PPAR--dependent manner to control alveolar macrophage differentiation. Functionally, EGR2 was dispensable for regulation of lipids in the airways, but crucial for the effective handling of the respiratory pathogen Streptococcus pneumoniae. Finally, we show that EGR2 is required for repopulation of the alveolar niche following sterile, bleomycin-induced lung injury and demonstrate that EGR2-dependent, monocyte-derived alveolar macrophages are vital for effective tissue repair following injury. Collectively, we demonstrate that EGR2 is an indispensable component of the transcriptional network controlling the identity and function of alveolar macrophages in health and disease.

Our knowledge and control of the pathogenesis induced by the filariae remain limited due to experimental obstacles presented by parasitic nematode biology and the lack of selective prophylactic or curative drugs. Here we thought to investigate the role of neutrophils in the host innate immune response to the infection caused by the Litomosoides sigmodontis murine model of human filariasis using mice harboring a gain-of-function mutation of the chemokine receptor CXCR4 and characterized by a profound blood neutropenia (Cxcr4+/1013). We provided manifold evidence emphasizing the major role of neutrophils in the control of the early stages of infection occurring in the skin. Firstly, we uncovered that the filarial parasitic success was dramatically decreased in Cxcr4+/1013 mice upon subcutaneous delivery of the infective stages of filariae (infective larvae, L3). This protection was linked to a larger number of neutrophils constitutively present in the skin of the mutant mice herein characterized as compared to wild type (wt) mice. Indeed, the parasitic success in Cxcr4+/1013 mice was normalized either upon depleting neutrophils, including the pool in the skin, or bypassing the skin via the intravenous infection of L3. Second, extending these observations to wt mice we found that subcutaneous delivery of L3 elicited an increase of neutrophils in the skin. Finally, living L3 larvae were able to promote in both wt and mutant mice, an oxidative burst response and the release of neutrophil extracellular traps (NET). This response of neutrophils, which is adapted to the large size of the L3 infective stages, likely directly contributes to the anti-parasitic strategies implemented by the host. Collectively, our results are demonstrating the contribution of neutrophils in early anti-filarial host responses through their capacity to undertake different anti-filarial strategies such as oxidative burst, degranulation and NETosis., Author Summary Filariases are chronic debilitating diseases caused by parasitic nematodes affecting more than 150 million people worldwide. None of the current drugs are selective, neither able to eliminate the parasites nor to prevent new infections once the drug pressure has waned. Therefore, blocking the entry and the migration of the infective larvae (L3) could be an efficient way to control the infection. In the present study we investigated the early interaction between the host and the L. sigmodontis murine filariasis with a focus on the neutrophils in the innate host responses. We uncovered a key role of neutrophils in the control of infection provided by the CXCR4-gain-of-function mice (Cxcr4+/1013) that display a blood neutropenia as well as an accumulation of skin-infiltrating neutrophils. Overall, we reveal that in the early phase of filariasis, i.e. after L3 are delivered into the skin and before they reach their site for reproduction, neutrophils are critical elements of the host innate protective response arsenal. A better understanding of their indirect and/or effector role(s) may provide mechanistic clues to host factors implicated in parasitic nematode entry and potentially lead to the identification of new drug targets.