Epigenetic memory of coronavirus infection in innate immune cells and their progenitors.

Inflammation can trigger lasting phenotypes in immune and non-immune cells. Whether and how human infections and associated inflammation can form innate immune memory in hematopoietic stem and progenitor cells (HSPC) has remained unclear. We found that circulating HSPC, enriched from peripheral blood, captured the diversity of bone marrow HSPC, enabling investigation of their epigenomic reprogramming following coronavirus disease 2019 (COVID-19). Alterations in innate immune phenotypes and epigenetic programs of HSPC persisted for months to 1 year following severe COVID-19 and were associated with distinct transcription factor (TF) activities, altered regulation of inflammatory programs, and durable increases in myelopoiesis. HSPC epigenomic alterations were conveyed, through differentiation, to progeny innate immune cells. Early activity of IL-6 contributed to these persistent phenotypes in human COVID-19 and a mouse coronavirus infection model. Epigenetic reprogramming of HSPC may underlie altered immune function following infection and be broadly relevant, especially for millions of COVID-19 survivors.

Gut-innervating nociceptors regulate the intestinal microbiota to promote tissue protection.

Nociceptive pain is a hallmark of many chronic inflammatory conditions including inflammatory bowel diseases (IBDs); however, whether pain-sensing neurons influence intestinal inflammation remains poorly defined. Employing chemogenetic silencing, adenoviral-mediated colon-specific silencing, and pharmacological ablation of TRPV1+ nociceptors, we observed more severe inflammation and defective tissue-protective reparative processes in a murine model of intestinal damage and inflammation. Disrupted nociception led to significant alterations in the intestinal microbiota and a transmissible dysbiosis, while mono-colonization of germ-free mice with Gram+Clostridium spp. promoted intestinal tissue protection through a nociceptor-dependent pathway. Mechanistically, disruption of nociception resulted in decreased levels of substance P, and therapeutic delivery of substance P promoted tissue-protective effects exerted by TRPV1+ nociceptors in a microbiota-dependent manner. Finally, dysregulated nociceptor gene expression was observed in intestinal biopsies from IBD patients. Collectively, these findings indicate an evolutionarily conserved functional link between nociception, the intestinal microbiota, and the restoration of intestinal homeostasis.

Fungal microbiota sustains lasting immune activation of neutrophils and their progenitors in severe COVID-19.

Gastrointestinal fungal dysbiosis is a hallmark of several diseases marked by systemic immune activation. Whether persistent pathobiont colonization during immune alterations and impaired gut barrier function has a durable impact on host immunity is unknown. We found that elevated levels of Candida albicans immunoglobulin G (IgG) antibodies marked patients with severe COVID-19 (sCOVID-19) who had intestinal Candida overgrowth, mycobiota dysbiosis and systemic neutrophilia. Analysis of hematopoietic stem cell progenitors in sCOVID-19 revealed transcriptional changes in antifungal immunity pathways and reprogramming of granulocyte myeloid progenitors (GMPs) for up to a year. Mice colonized with C. albicans patient isolates experienced increased lung neutrophilia and pulmonary NETosis during severe acute respiratory syndrome coronavirus-2 infection, which were partially resolved with antifungal treatment or by interleukin-6 receptor blockade. sCOVID-19 patients treated with tocilizumab experienced sustained reductions in C. albicans IgG antibodies titers and GMP transcriptional changes. These findings suggest that gut fungal pathobionts may contribute to immune activation during inflammatory diseases, offering potential mycobiota-immune therapeutic strategies for sCOVID-19 with prolonged symptoms.

Microglia promote learning-dependent synapse formation through brain-derived neurotrophic factor.

Microglia are the resident macrophages of the CNS, and their functions have been extensively studied in various brain pathologies. The physiological roles of microglia in brain plasticity and function, however, remain unclear. To address this question, we generated CX3CR1(CreER) mice expressing tamoxifen-inducible Cre recombinase that allow for specific manipulation of gene function in microglia. Using CX3CR1(CreER) to drive diphtheria toxin receptor expression in microglia, we found that microglia could be specifically depleted from the brain upon diphtheria toxin administration. Mice depleted of microglia showed deficits in multiple learning tasks and a significant reduction in motor-learning-dependent synapse formation. Furthermore, Cre-dependent removal of brain-derived neurotrophic factor (BDNF) from microglia largely recapitulated the effects of microglia depletion. Microglial BDNF increases neuronal tropomyosin-related kinase receptor B phosphorylation, a key mediator of synaptic plasticity. Together, our findings reveal that microglia serve important physiological functions in learning and memory by promoting learning-related synapse formation through BDNF signaling.

Inulin fibre promotes microbiota-derived bile acids and type 2 inflammation.

Dietary fibres can exert beneficial anti-inflammatory effects through microbially fermented short-chain fatty acid metabolites^1,2, although the immunoregulatory roles of most fibre diets and their microbiota-derived metabolites remain poorly defined. Here, using microbial sequencing and untargeted metabolomics, we show that a diet of inulin fibre alters the composition of the mouse microbiota and the levels of microbiota-derived metabolites, notably bile acids. This metabolomic shift is associated with type 2 inflammation in the intestine and lungs, characterized by IL-33 production, activation of group 2 innate lymphoid cells and eosinophilia. Delivery of cholic acid mimics inulin-induced type 2 inflammation, whereas deletion of the bile acid receptor farnesoid X receptor diminishes the effects of inulin. The effects of inulin are microbiota dependent and were reproduced in mice colonized with human-derived microbiota. Furthermore, genetic deletion of a bile-acid-metabolizing enzyme in one bacterial species abolishes the ability of inulin to trigger type 2 inflammation. Finally, we demonstrate that inulin enhances allergen- and helminth-induced type 2 inflammation. Taken together, these data reveal that dietary inulin fibre triggers microbiota-derived cholic acid and type 2 inflammation at barrier surfaces with implications for understanding the pathophysiology of allergic inflammation, tissue protection and host defence.

Neuropeptide regulation of non-redundant ILC2 responses at barrier surfaces.

Emerging studies indicate that cooperation between neurons and immune cells regulates antimicrobial immunity, inflammation and tissue homeostasis. For example, a neuronal rheostat provides excitatory or inhibitory signals that control the functions of tissue-resident group 2 innate lymphoid cells (ILC2s) at mucosal barrier surfaces1-4. ILC2s express NMUR1, a receptor for neuromedin U (NMU), which is a prominent cholinergic neuropeptide that promotes ILC2 responses5-7. However, many functions of ILC2s are shared with adaptive lymphocytes, including the production of type 2 cytokines8,9 and the release of tissue-protective amphiregulin (AREG)10-12. Consequently, there is controversy regarding whether innate lymphoid cells and adaptive lymphocytes perform redundant or non-redundant functions13-15. Here we generate a new genetic tool to target ILC2s for depletion or gene deletion in the presence of an intact adaptive immune system. Transgenic expression of iCre recombinase under the control of the mouse Nmur1 promoter enabled ILC2-specific deletion of AREG. This revealed that ILC2-derived AREG promotes non-redundant functions in the context of antiparasite immunity and tissue protection following intestinal damage and inflammation. Notably, NMU expression levels increased in inflamed intestinal tissues from both mice and humans, and NMU induced AREG production in mouse and human ILC2s. These results indicate that neuropeptide-mediated regulation of non-redundant functions of ILC2s is an evolutionarily conserved mechanism that integrates immunity and tissue protection.

A validated regulatory network for Th17 cell specification.

Th17 cells have critical roles in mucosal defense and are major contributors to inflammatory disease. Their differentiation requires the nuclear hormone receptor RORγt working with multiple other essential transcription factors (TFs). We have used an iterative systems approach, combining genome-wide TF occupancy, expression profiling of TF mutants, and expression time series to delineate the Th17 global transcriptional regulatory network. We find that cooperatively bound BATF and IRF4 contribute to initial chromatin accessibility and, with STAT3, initiate a transcriptional program that is then globally tuned by the lineage-specifying TF RORγt, which plays a focal deterministic role at key loci. Integration of multiple data sets allowed inference of an accurate predictive model that we computationally and experimentally validated, identifying multiple new Th17 regulators, including Fosl2, a key determinant of cellular plasticity. This interconnected network can be used to investigate new therapeutic approaches to manipulate Th17 functions in the setting of inflammatory disease.

Antigen-presenting innate lymphoid cells orchestrate neuroinflammation.

Pro-inflammatory T cells in the central nervous system (CNS) are causally associated with multiple demyelinating and neurodegenerative diseases1-6, but the pathways that control these responses remain unclear. Here we define a population of inflammatory group 3 innate lymphoid cells (ILC3s) that infiltrate the CNS in a mouse model of multiple sclerosis. These ILC3s are derived from the circulation, localize in proximity to infiltrating T cells in the CNS, function as antigen-presenting cells that restimulate myelin-specific T cells, and are increased in individuals with multiple sclerosis. Notably, antigen presentation by inflammatory ILC3s is required to promote T cell responses in the CNS and the development of multiple-sclerosis-like disease in mouse models. By contrast, conventional and tissue-resident ILC3s in the periphery do not appear to contribute to disease induction, but instead limit autoimmune T cell responses and prevent multiple-sclerosis-like disease when experimentally targeted to present myelin antigen. Collectively, our data define a population of inflammatory ILC3s that is essential for directly promoting T-cell-dependent neuroinflammation in the CNS and reveal the potential of harnessing peripheral tissue-resident ILC3s for the prevention of autoimmune disease.

The microbiota regulate neuronal function and fear extinction learning.

Multicellular organisms have co-evolved with complex consortia of viruses, bacteria, fungi and parasites, collectively referred to as the microbiota1. In mammals, changes in the composition of the microbiota can influence many physiologic processes (including development, metabolism and immune cell function) and are associated with susceptibility to multiple diseases2. Alterations in the microbiota can also modulate host behaviours-such as social activity, stress, and anxiety-related responses-that are linked to diverse neuropsychiatric disorders3. However, the mechanisms by which the microbiota influence neuronal activity and host behaviour remain poorly defined. Here we show that manipulation of the microbiota in antibiotic-treated or germ-free adult mice results in significant deficits in fear extinction learning. Single-nucleus RNA sequencing of the medial prefrontal cortex of the brain revealed significant alterations in gene expression in excitatory neurons, glia and other cell types. Transcranial two-photon imaging showed that deficits in extinction learning after manipulation of the microbiota in adult mice were associated with defective learning-related remodelling of postsynaptic dendritic spines and reduced activity in cue-encoding neurons in the medial prefrontal cortex. In addition, selective re-establishment of the microbiota revealed a limited neonatal developmental window in which microbiota-derived signals can restore normal extinction learning in adulthood. Finally, unbiased metabolomic analysis identified four metabolites that were significantly downregulated in germ-free mice and have been reported to be related to neuropsychiatric disorders in humans and mouse models, suggesting that microbiota-derived compounds may directly affect brain function and behaviour. Together, these data indicate that fear extinction learning requires microbiota-derived signals both during early postnatal neurodevelopment and in adult mice, with implications for our understanding of how diet, infection, and lifestyle influence brain health and subsequent susceptibility to neuropsychiatric disorders.

Joint single-cell measurements of nuclear proteins and RNA in vivo.

Identifying gene-regulatory targets of nuclear proteins in tissues is a challenge. Here we describe intranuclear cellular indexing of transcriptomes and epitopes (inCITE-seq), a scalable method that measures multiplexed intranuclear protein levels and the transcriptome in parallel across thousands of nuclei, enabling joint analysis of transcription factor (TF) levels and gene expression in vivo. We apply inCITE-seq to characterize cell state-related changes upon pharmacological induction of neuronal activity in the mouse brain. Modeling gene expression as a linear combination of quantitative protein levels revealed genome-wide associations of each TF and recovered known gene targets. TF-associated genes were coexpressed as distinct modules that each reflected positive or negative TF levels, showing that our approach can disentangle relative putative contributions of TFs to gene expression and add interpretability to inferred gene networks. inCITE-seq can illuminate how combinations of nuclear proteins shape gene expression in native tissue contexts, with direct applications to solid or frozen tissues and clinical specimens.

Angiopoietin 2 Is Associated with Vascular Necroptosis Induction in Coronavirus Disease 2019 Acute Respiratory Distress Syndrome.

Vascular injury is a well-established, disease-modifying factor in acute respiratory distress syndrome (ARDS) pathogenesis. Recently, coronavirus disease 2019 (COVID-19)-induced injury to the vascular compartment has been linked to complement activation, microvascular thrombosis, and dysregulated immune responses. This study sought to assess whether aberrant vascular activation in this prothrombotic context was associated with the induction of necroptotic vascular cell death. To achieve this, proteomic analysis was performed on blood samples from COVID-19 subjects at distinct time points during ARDS pathogenesis (hospitalized at risk, N = 59; ARDS, N = 31; and recovery, N = 12). Assessment of circulating vascular markers in the at-risk cohort revealed a signature of low vascular protein abundance that tracked with low platelet levels and increased mortality. This signature was replicated in the ARDS cohort and correlated with increased plasma angiopoietin 2 levels. COVID-19 ARDS lung autopsy immunostaining confirmed a link between vascular injury (angiopoietin 2) and platelet-rich microthrombi (CD61) and induction of necrotic cell death [phosphorylated mixed lineage kinase domain-like (pMLKL)]. Among recovery subjects, the vascular signature identified patients with poor functional outcomes. Taken together, this vascular injury signature was associated with low platelet levels and increased mortality and can be used to identify ARDS patients most likely to benefit from vascular targeted therapies.

The serotonin 2B receptor is required in neonatal microglia to limit neuroinflammation and sickness behavior in adulthood.

Severe peripheral infections induce an adaptive sickness behavior and an innate immune reaction in various organs including the brain. On the long term, persistent alteration of microglia, the brain innate immune cells, is associated with an increased risk of psychiatric disorders. It is thus critical to identify genes and mechanisms controlling the intensity and duration of the neuroinflammation induced by peripheral immune challenges. We tested the hypothesis that the 5-HT2B receptor, the main serotonin receptor expressed by microglia, might represent a valuable candidate. First, we observed that Htr2b-/- mice, knock-out for the 5-HT2B receptor gene, developed, when exposed to a peripheral lipopolysaccharide (LPS) challenge, a stronger weight loss compared to wild-type mice; in addition, comparison of inflammatory markers in brain, 4 and 24 hr after LPS injection, showed that Htr2b deficiency leads to a prolonged neuroinflammation. Second, to assess the specific contribution of the microglial 5-HT2B receptor, we investigated the response to LPS of conditional knock-out mice invalidated for Htr2b in microglia only. We found that deletion of Htr2b in microglia since birth is sufficient to cause enhanced weight loss and increased neuroinflammatory response upon LPS injection at adult stage. In contrast, mice deleted for microglial Htr2b in adulthood responded normally to LPS, revealing a neonatal developmental effect. These results highlight the role of microglia in the response to a peripheral immune challenge and suggest the existence of a developmental, neonatal period, during which instruction of microglia through 5-HT2B receptors is necessary to prevent microglia overreactivity in adulthood.

Microglial NFκB-TNFα hyperactivation induces obsessive-compulsive behavior in mouse models of progranulin-deficient frontotemporal dementia.

Frontotemporal dementia (FTD) is the second most common dementia before 65 years of age. Haploinsufficiency in the progranulin (GRN) gene accounts for 10% of all cases of familial FTD. GRN mutation carriers have an increased risk of autoimmune disorders, accompanied by elevated levels of tissue necrosis factor (TNF) α. We examined behavioral alterations related to obsessive-compulsive disorder (OCD) and the role of TNFα and related signaling pathways in FTD patients with GRN mutations and in mice lacking progranulin (PGRN). We found that patients and mice with GRN mutations displayed OCD and self-grooming (an OCD-like behavior in mice), respectively. Furthermore, medium spiny neurons in the nucleus accumbens, an area implicated in development of OCD, display hyperexcitability in PGRN knockout mice. Reducing levels of TNFα in PGRN knockout mice abolished excessive self-grooming and the associated hyperexcitability of medium spiny neurons of the nucleus accumbens. In the brain, PGRN is highly expressed in microglia, which are a major source of TNFα. We therefore deleted PGRN specifically in microglia and found that it was sufficient to induce excessive grooming. Importantly, excessive grooming in these mice was prevented by inactivating nuclear factor κB (NF-κB) in microglia/myeloid cells. Our findings suggest that PGRN deficiency leads to excessive NF-κB activation in microglia and elevated TNFα signaling, which in turn lead to hyperexcitability of medium spiny neurons and OCD-like behavior.

Peripheral elevation of TNF-α leads to early synaptic abnormalities in the mouse somatosensory cortex in experimental autoimmune encephalomyelitis.

Sensory abnormalities such as numbness and paresthesias are often the earliest symptoms in neuroinflammatory diseases including multiple sclerosis. The increased production of various cytokines occurs in the early stages of neuroinflammation and could have detrimental effects on the central nervous system, thereby contributing to sensory and cognitive deficits. However, it remains unknown whether and when elevation of cytokines causes changes in brain structure and function under inflammatory conditions. To address this question, we used a mouse model for experimental autoimmune encephalomyelitis (EAE) to examine the effect of inflammation and cytokine elevation on synaptic connections in the primary somatosensory cortex. Using in vivo two-photon microscopy, we found that the elimination and formation rates of dendritic spines and axonal boutons increased within 7 d of EAE induction--several days before the onset of paralysis--and continued to rise during the course of the disease. This synaptic instability occurred before T-cell infiltration and microglial activation in the central nervous system and was in conjunction with peripheral, but not central, production of TNF-α. Peripheral administration of a soluble TNF inhibitor prevented abnormal turnover of dendritic spines and axonal boutons in presymptomatic EAE mice. These findings indicate that peripheral production of TNF-α is a key mediator of synaptic instability in the primary somatosensory cortex and may contribute to sensory and cognitive deficits seen in autoimmune diseases.

WNK1 enforces macrophage lineage fidelity.

The appropriate development of macrophages, the body's professional phagocyte, is essential for organismal development, especially in mammals. This dependence is exemplified by the observation that loss-of-function mutations in colony stimulating factor 1 receptor (CSF1R) results in multiple tissue abnormalities owing to an absence of macrophages. Despite this importance, little is known about the molecular and cell biological regulation of macrophage development. Here, we report the surprising finding that the chloride-sensing kinase With-no-lysine 1 (WNK1) is required for development of tissue-resident macrophages (TRMs). Myeloid-specific deletion of Wnk1 resulted in a dramatic loss of TRMs, disrupted organ development, systemic neutrophilia, and mortality between 3 and 4 weeks of age. Strikingly, we found that myeloid progenitors or precursors lacking WNK1 not only failed to differentiate into macrophages, but instead differentiated into neutrophils. Mechanistically, the cognate CSF1R cytokine macrophage-colony stimulating factor (M-CSF) stimulates macropinocytosis by both mouse and human myeloid progenitors and precursor cells. Macropinocytosis, in turn, induces chloride flux and WNK1 phosphorylation. Importantly, blocking macropinocytosis, perturbing chloride flux during macropinocytosis, and inhibiting WNK1 chloride-sensing activity each skewed myeloid progenitor differentiation from macrophages into neutrophils. Thus, we have elucidated a role for WNK1 during macropinocytosis and discovered a novel function of macropinocytosis in myeloid progenitors and precursor cells to ensure macrophage lineage fidelity. Highlights: Myeloid-specific WNK1 loss causes failed macrophage development and premature deathM-CSF-stimulated myeloid progenitors and precursors become neutrophils instead of macrophagesM-CSF induces macropinocytosis by myeloid progenitors, which depends on WNK1Macropinocytosis enforces macrophage lineage commitment.

Early life high fructose exposure disrupts microglia function and impedes neurodevelopment.

Despite the success of fructose as a low-cost food additive, recent epidemiological evidence suggests that high fructose consumption by pregnant mothers or during adolescence is associated with disrupted neurodevelopment 1-7 . An essential step in appropriate mammalian neurodevelopment is the synaptic pruning and elimination of newly-formed neurons by microglia, the central nervous system's (CNS) resident professional phagocyte 8-10 . Whether early life high fructose consumption affects microglia function and if this directly impacts neurodevelopment remains unknown. Here, we show that both offspring born to dams fed a high fructose diet and neonates exposed to high fructose exhibit decreased microglial density, increased uncleared apoptotic cells, and decreased synaptic pruning in vivo . Importantly, deletion of the high affinity fructose transporter SLC2A5 (GLUT5) in neonates completely reversed microglia dysfunction, suggesting that high fructose directly affects neonatal development. Mechanistically, we found that high fructose treatment of both mouse and human microglia suppresses synaptic pruning and phagocytosis capacity which is fully reversed in GLUT5-deficient microglia. Using a combination of in vivo and in vitro nuclear magnetic resonance- and mass spectrometry-based fructose tracing, we found that high fructose drives significant GLUT5-dependent fructose uptake and catabolism, rewiring microglia metabolism towards a hypo-phagocytic state. Importantly, mice exposed to high fructose as neonates exhibited cognitive defects and developed anxiety-like behavior which were rescued in GLUT5-deficient animals. Our findings provide a mechanistic explanation for the epidemiological observation that early life high fructose exposure is associated with increased prevalence of adolescent anxiety disorders.

Target genes of the largest human SWI/SNF complex subunit control cell growth.

The largest subunit of the mammalian SWI/SNF-A or BAF (BRG1-associated factor) chromatin-remodelling complex is encoded by two related cDNAs hOsa1/BAF250a and hOsa2/BAF250b that are unique to the BAF complex and absent in the related PBAF (Polybromo BAF). hOsa/BAF250 has been shown to interact with transcriptional activators and bind to DNA suggesting that it acts to target the remodelling complex to chromatin. To better understand the functions of hOsa2, we established inducible stable HeLa cell lines over-expressing FLAG-hOsa2 or a derivative lacking the ARID (AT-rich interactive domain) DNA-binding domain. Immunopurification of complexes containing hOsa2 that was followed by mass spectrometry and immunoblotting demonstrated the presence of BRG1 and known BAFs, but not hOsa1 or hBRM. Deletion of the ARID did not compromise the integrity of the complex. Induction of hOsa2 expression caused impaired cell growth and accumulation of cells in the G0/G1 cell cycle phase. Elevated levels of the p53 and p21 proteins were detected in these cells while c-Myc mRNA and protein levels were found to decrease. Chromatin immunoprecipitation and reporter assays suggested that hOsa2 had a direct effect on c-myc and p21 promoter activity. Thus hOsa2 plays an important role in controlling genes regulating the cell cycle.

Post-Intensive Care Unit Syndrome in a Cohort of COVID-19 Survivors in New York City.

Rationale: The coronavirus disease (COVID-19) pandemic has led to a dramatic increase in the number of survivors of critical illness. These survivors are at increased risk for physical, psychological, and cognitive impairments known collectively as post-intensive care syndrome (PICS). Little is known about the prevalence of PICS in COVID-19 survivors. Objectives: To report the prevalence of physical, psychological, and cognitive impairment among COVID-19 intensive care unit (ICU) survivors receiving follow-up care in an ICU recovery clinic, to assess for associations between PICS and ICU-related factors, and to compare the cohort of ICU survivors who attended a post-ICU clinic with a cohort of ICU survivors who did not. Methods: We performed a retrospective cohort study of COVID-19 ICU survivors admitted from March to May 2020 who were subsequently seen in a post-ICU recovery clinic in New York City. We abstracted medical chart data on available clinical screening instruments for physical, psychological, and cognitive impairment. Associations between these outcomes and care-related variables were tested. Baseline characteristics and in-hospital treatments of the post-ICU clinic cohort were compared with those of COVID-19 ICU survivors from the same institution who were not seen in the post-ICU clinic. Results: Eighty-seven COVID-19 ICU survivors were seen in our post-ICU recovery clinic. The median age was 62 years, and 74% were male. The median length of hospitalization was 51 days, and the median length of ICU stay was 22 days. At the post-ICU follow-up visit, 29%, 21%, and 13% of patients reported clinically significant levels of depressive symptoms, anxiety, and post-traumatic stress disorder symptoms, respectively. Twenty-five percent had cognitive impairment. The overall prevalence of PICS was 90%. There were no associations between length of ICU stay, delirium, and exposure to benzodiazepines, steroids, or systemic paralytics with positive screening results for physical, psychological, or cognitive impairment. Baseline characteristics and ICU-related factors were similar in the cohort of COVID-19 ICU survivors who attended the ICU recovery clinic and those who did not. Conclusions: PICS is common in COVID-19 survivors. We did not find any association with length of ICU stay or the use of benzodiazepines, steroids, or paralytics.

Neutrophil heterogeneity in complement C1q expression associated with sepsis mortality.

Sepsis is a life-threatening systemic inflammatory condition causing approximately 11 million annual deaths worldwide. Although key hyperinflammation-based organ dysfunctions that drive disease pathology have been recognized, our understanding of the factors that predispose patients to septic mortality is limited. Due to the lack of reliable prognostic measures, the development of appropriate clinical management that improves patient survival remains challenging. Here, we discovered that a subpopulation of CD49chigh neutrophils with dramatic upregulation of the complement component 1q (C1q) gene expression arises during severe sepsis. We further found that deceased septic patients failed to maintain C1q protein expression in their neutrophils, whereas septic survivors expressed higher levels of C1q. In mouse sepsis models, blocking C1q with neutralizing antibodies or conditionally knocking out C1q in neutrophils led to a significant increase in septic mortality. Apoptotic neutrophils release C1q to control their own clearance in critically injured organs during sepsis; thus, treatment of septic mice with C1q drastically increased survival. These results suggest that neutrophil C1q is a reliable prognostic biomarker of septic mortality and a potential novel therapeutic target for the treatment of sepsis.

Nuclear localization of the p75 neurotrophin receptor intracellular domain.

The p75 neurotrophin receptor, a member of the tumor necrosis factor superfamily of receptors, undergoes an alpha-secretase-mediated release of its extracellular domain, followed by a gamma-secretase-mediated intramembrane cleavage. Like amyloid precursor protein and Notch, gamma-secretase cleavage of the p75 receptor releases an intracellular domain (ICD). However, it has been experimentally challenging to determine the precise subcellular localization and functional consequences of the p75 ICD. Here, we utilized a nuclear translocation assay and biochemical fractionation approaches to follow the fate of the ICD. We found that the p75 ICD can translocate to the nucleus to activate a green fluorescent protein reporter gene. Furthermore, the p75 ICD was localized in nuclear fractions. Chromatin immunoprecipitation experiments indicated that nerve growth factor induced the association of endogenous p75 with the cyclin E(1) promoter. Expression of the p75 ICD resulted in modulation of gene expression from this locus. These results suggest that the p75 ICD generated by gamma-secretase cleavage is capable of modulating transcriptional events in the nucleus.