Deltex family E3 ligases specifically ubiquitinate the terminal ADP-ribose of poly(ADP-ribosyl)ation

Poly(ADP-ribose) polymerases (PARPs) are critical to regulating cellular activities, such as the response to DNA damage and cell death. PARPs catalyze a reversible post-translational modification (PTM) in the form of mono- or poly(ADP-ribosyl)ation. This type of modification is known to form a ubiquitin-ADP-ribose (Ub-ADPR) conjugate that depends on the actions of Deltex family of E3 ubiquitin ligases (DTXs). In particular, DTXs add ubiquitin to the 3'-OH of adenosine ribose' in ADP-ribose, which effectively sequesters ubiquitin and impedes ubiquitin-dependent signaling. Previous work demonstrates DTX function for ubiquitination of protein-free ADPR, mono-ADP-ribosylated peptides, and ADP-ribosylated nucleic acids. However, the dynamics of DTX-mediated ubiquitination of poly(ADP-ribosyl)ation remains to be defined. Here we show that the ADPR ubiquitination function is not found in other PAR-binding E3 ligases and is conserved across DTX family members. Importantly, DTXs specifically target poly(ADP-ribose) chains for ubiquitination that can be cleaved by PARG, the primary eraser of poly(ADP-ribose), leaving the adenosine-terminal ADPR unit conjugated to ubiquitin. Our collective results demonstrate the DTXs' specific ubiquitination of the adenosine terminus of poly(ADP-ribosyl)ation and suggest the unique Ub-ADPR conjugation process as a basis for PARP-DTX control of cellular activities.

MAPK13 controls structural remodeling and disease after epithelial injury

All living organisms are charged with repair after injury particularly at epithelial barrier sites, but in some cases this response leads instead to structural remodeling and long-term disease. Identifying the molecular and cellular control of this divergence is key to disease modification. In that regard, stress kinase control of epithelial stem cells is a rational entry point for study. Here we examine the potential for mitogen-activated protein kinase 13 (MAPK13) regulation of epithelial stem cells using models of respiratory viral injury and post-viral lung disease. We show that Mapk13 gene-knockout mice handle acute infectious illness as expected but are protected against structural remodeling manifest as basal-epithelial stem cell (basal-ESC) hyperplasia-metaplasia, immune activation, and mucinous differentiation. In corresponding cell models, Mapk13-deficiency directly attenuates basal-ESC growth and organoid formation. Extension to human studies shows marked induction/activation of basal-cell MAPK13 in clinical samples of comparable remodeling found in asthma and COPD. Here again, MAPK13 gene-knockdown inhibits human basal-ESC growth in culture. Together, the data identify MAPK13 as a control for structural remodeling and disease after epithelial injury and as a suitable target for down-regulation as a disease-modifying strategy.

The autophagy protein, ATG14 safeguards against unscheduled pyroptosis activation to enable embryo transport during early pregnancy

Recurrent pregnancy loss (RPL), characterized by two or more failed clinical pregnancies, poses a significant challenge to reproductive health. In addition to embryo quality and endometrial function, proper oviduct function is also essential for successful pregnancy establishment. Therefore, structural abnormalities or inflammation resulting from infection in the oviduct may impede the transport of embryos to the endometrium, thereby increasing the risk of miscarriage. However, the precise cellular mechanisms that maintain the structural and functional integrity of the oviduct are not studied yet. Here, we report that autophagy is critical for maintaining the oviduct homeostasis and keeping the inflammation under check to enable embryo transport. Specifically, the loss of the autophagy-related gene, Atg14 in the oviduct causes severe structural abnormalities compromising its cellular plasticity and integrity leading to the retention of embryos. Interestingly, the selective loss of Atg14 in oviduct ciliary epithelial cells did not impact female fertility, highlighting the specificity of ATG14 function in distinct cell types within the oviduct. Mechanistically, loss of Atg14 triggered unscheduled pyroptosis leading to inappropriate embryo retention and impeded embryo transport in the oviduct. Finally, pharmacological activation of pyroptosis in pregnant mice led to an impairment in embryo transport. Together, we found that ATG14 safeguards against unscheduled pyroptosis activation to enable embryo transport from the oviduct to uterus for the successful implantation. Of clinical significance, these findings provide possible insights on the underlying mechanism(s) of early pregnancy loss and might aid in developing novel prevention strategies using autophagy modulators.

IL-33 potentiates histaminergic itch

BACKGROUND

Itch is a common symptom that can greatly diminish quality of life. Histamine is a potent endogenous pruritogen, and while antihistamines are often the first-line treatment for itch, in conditions like chronic spontaneous urticaria (CSU), many patients remain symptomatic while receiving maximal doses. Mechanisms that drive resistance to antihistamines are poorly defined.

OBJECTIVES

Signaling of the alarmin cytokine IL-33 in sensory neurons is postulated to drive chronic itch by inducing neuronal sensitization to pruritogens. Thus, we sought to determine if IL-33 can augment histamine-induced (histaminergic) itch.

METHODS

Itch behavior was assessed in response to histamine after IL-33 or saline administration. Various stimuli and conditional and global knockout mice were utilized to dissect cellular mechanisms. Multiple existing transcriptomic data sets were evaluated, including single-cell RNA sequencing of human and mouse skin, microarrays of isolated mouse mast cells at steady state and after stimulation with IL-33, and microarrays of skin biopsy samples from subjects with CSU and healthy controls.

RESULTS

IL-33 amplifies histaminergic itch independent of IL-33 signaling in sensory neurons. Mast cells are the top expressors of the IL-33 receptor in both human and mouse skin. When stimulated by IL-33, mouse mast cells significantly increase IL-13 levels. Enhancement of histaminergic itch by IL-33 relies on a mast cell- and IL-13-dependent mechanism. IL-33 receptor expression is increased in lesional skin of subjects with CSU compared to healthy controls.

CONCLUSIONS

Our findings suggest that IL-33 signaling may be a key driver of histaminergic itch in mast cell-associated pruritic conditions such as CSU.

Mitogen-activated protein kinase-guided drug discovery for post-viral and related types of lung disease

Respiratory viral infections are a major public health problem, with much of their morbidity and mortality due to post-viral lung diseases that progress and persist after the active infection is cleared. This paradigm is implicated in the most common forms of chronic lung disease, such as asthma and COPD, as well as other virus-linked diseases including progressive and long-term coronavirus disease 2019. Despite the impact of these diseases, there is a lack of small-molecule drugs available that can precisely modify this type of disease process. Here we will review current progress in understanding the pathogenesis of post-viral and related lung disease with characteristic remodelling phenotypes. We will also develop how this data leads to mitogen-activated protein kinase (MAPK) in general and MAPK13 in particular as key druggable targets in this pathway. We will also explore recent advances and predict the future breakthroughs in structure-based drug design that will provide new MAPK inhibitors as drug candidates for clinical applications. Each of these developments point to a more effective approach to treating the distinct epithelial and immune cell based mechanisms, which better account for the morbidity and mortality of post-viral and related types of lung disease. This progress is vital given the growing prevalence of respiratory viruses and other inhaled agents that trigger stereotyped progression to acute illness and chronic disease.

A potent MAPK13-14 inhibitor prevents airway inflammation and mucus production

Common respiratory diseases continue to represent a major public health problem, and much of the morbidity and mortality is due to airway inflammation and mucus production. Previous studies indicated a role for mitogen-activated protein kinase 14 (MAPK14) in this type of disease, but clinical trials are unsuccessful to date. Our previous work identified a related but distinct kinase known as MAPK13 that is activated in respiratory airway diseases and is required for mucus production in human cell-culture models. Support for MAPK13 function in these models came from effectiveness of MAPK13 versus MAPK14 gene-knockdown and from first-generation MAPK13-14 inhibitors. However, these first-generation inhibitors were incompletely optimized for blocking activity and were untested in vivo. Here we report the next generation and selection of a potent MAPK13-14 inhibitor (designated NuP-3) that more effectively downregulates type-2 cytokine-stimulated mucus production in air-liquid interface and organoid cultures of human airway epithelial cells. We also show that NuP-3 treatment prevents respiratory airway inflammation and mucus production in new minipig models of airway disease triggered by type-2 cytokine challenge or respiratory viral infection. The results thereby provide the next advance in developing a small-molecule kinase inhibitor to address key features of respiratory disease.NEW & NOTEWORTHY This study describes the discovery of a potent mitogen-activated protein kinase 13-14 (MAPK13-14) inhibitor and its effectiveness in models of respiratory airway disease. The findings thereby provide a scheme for pathogenesis and therapy of lung diseases [e.g., asthma, chronic obstructive pulmonary disease (COPD), Covid-19, postviral, and allergic respiratory disease] and related conditions that implicate MAPK13-14 function. The findings also refine a hypothesis for epithelial and immune cell functions in respiratory disease that features MAPK13 as a possible component of this disease process.

Classical Estrogen Signaling in Ciliated Epithelial Cells of the Oviduct Is Nonessential for Fertility in Female Mice

Ciliary action performs a critical role in the oviduct (Fallopian tube) during pregnancy establishment through sperm and egg transport. The disruption of normal ciliary function in the oviduct affects oocyte pick-up and is a contributing factor to female infertility. Estrogen is an important regulator of ciliary action in the oviduct and promotes ciliogenesis in several species. Global loss of estrogen receptor α (ESR1) leads to infertility. We have previously shown that ESR1 in the oviductal epithelial cell layer is required for female fertility. Here, we assessed the role of estrogen on transcriptional regulation of ciliated epithelial cells of the oviduct using single-cell RNA-sequencing analysis. We observed minor variations in ciliated cell genes in the proximal region (isthmus and uterotubal junction) of the oviduct. However, 17β-estradiol treatment had little impact on the gene expression profile of ciliated epithelial cells. We also conditionally ablated Esr1 from ciliated epithelial cells of the oviduct (called ciliated Esr1d/d mice). Our studies showed that ciliated Esr1d/d females had fertility rates comparable to control females, did not display any disruptions in preimplantation embryo development or embryo transport to the uterus, and had comparable cilia formation to control females. However, we observed some incomplete deletion of Esr1 in the ciliated epithelial cells, especially in the ampulla region. Nevertheless, our data suggest that ESR1 expression in ciliated cells of the oviduct is dispensable for ciliogenesis and nonessential for female fertility in mice.

A potent MAPK13-14 inhibitor prevents airway inflammation and mucus production

Common respiratory diseases continue to represent a major public health problem, and much of the morbidity and mortality is due to airway inflammation and mucus production. Previous studies indicated a role for mitogen-activated protein kinase 14 (MAPK14) in this type of disease, but clinical trials are unsuccessful to date. Our previous work identified a related but distinct kinase known as MAPK13 that is activated in respiratory airway diseases and is required for mucus production in human cell-culture models. Support for MAPK13 function in these models came from effectiveness of MAPK13 versus MAPK14 gene-knockdown and from first-generation MAPK13-14 inhibitors. However, these first-generation inhibitors were incompletely optimized for blocking activity and were untested in vivo. Here we report the next generation and selection of a potent MAPK13-14 inhibitor (designated NuP-3) that more effectively down-regulates type-2 cytokine-stimulated mucus production in air-liquid interface and organoid cultures of human airway epithelial cells. We also show that NuP-3 treatment prevents respiratory airway inflammation and mucus production in new minipig models of airway disease triggered by type-2 cytokine challenge or respiratory viral infection. The results thereby provide the next advance in developing a small-molecule kinase inhibitor to address key features of respiratory disease.

LRP1 mediates leptin transport by coupling with the short-form leptin receptor in the choroid plexus

Adipocyte-derived leptin enters the brain to exert its anorexigenic action, yet its transport mechanism is poorly understood. Here we report that LRP1 (low-density lipoprotein receptor-related protein-1) mediates the transport of leptin across the blood-CSF barrier in Foxj1 expressing cells highly enriched at the choroid plexus (ChP), coupled with the short-form leptin receptor, and LRP1 deletion from ependymocytes and ChP cells leads to leptin resistance and hyperphagia, causing obesity. Thus, LRP1 in epithelial cells is a principal regulator of leptin transport in the brain.

Defining diurnal fluctuations in mouse choroid plexus and CSF at high molecular, spatial, and temporal resolution

Transmission and secretion of signals via the choroid plexus (ChP) brain barrier can modulate brain states via regulation of cerebrospinal fluid (CSF) composition. Here, we developed a platform to analyze diurnal variations in male mouse ChP and CSF. Ribosome profiling of ChP epithelial cells revealed diurnal translatome differences in metabolic machinery, secreted proteins, and barrier components. Using ChP and CSF metabolomics and blood-CSF barrier analyses, we observed diurnal changes in metabolites and cellular junctions. We then focused on transthyretin (TTR), a diurnally regulated thyroid hormone chaperone secreted by the ChP. Diurnal variation in ChP TTR depended on Bmal1 clock gene expression. We achieved real-time tracking of CSF-TTR in awake TtrmNeonGreen mice via multi-day intracerebroventricular fiber photometry. Diurnal changes in ChP and CSF TTR levels correlated with CSF thyroid hormone levels. These datasets highlight an integrated platform for investigating diurnal control of brain states by the ChP and CSF.

An alternative mechanism for skeletal muscle dysfunction in long-term post-viral lung disease

Chronic lung disease is often accompanied by disabling extrapulmonary symptoms, notably skeletal muscle dysfunction and atrophy. Moreover, the severity of respiratory symptoms correlates with decreased muscle mass and in turn lowered physical activity and survival rates. Previous models of muscle atrophy in chronic lung disease often modeled chronic obstructive pulmonary disease (COPD) and relied on cigarette smoke exposure and LPS stimulation, but these conditions independently affect skeletal muscle even without accompanying lung disease. Moreover, there is an emerging and pressing need to understand the extrapulmonary manifestations of long-term post-viral lung disease (PVLD) as found in COVID-19. Here, we examine the development of skeletal muscle dysfunction in the setting of chronic pulmonary disease caused by infection due to the natural pathogen Sendai virus using a mouse model of PVLD. We identify a significant decrease in myofiber size when PVLD is maximal at 49 days after infection. We find no change in the relative types of myofibers, but the greatest decrease in fiber size is localized to fast-twitch-type IIB myofibers based on myosin heavy chain immunostaining. Remarkably, all biomarkers of myocyte protein synthesis and degradation (total RNA, ribosomal abundance, and ubiquitin-proteasome expression) were stable throughout the acute infectious illness and chronic post-viral disease process. Together, the results demonstrate a distinct pattern of skeletal muscle dysfunction in a mouse model of long-term PVLD. The findings thereby provide new insights into prolonged limitations in exercise capacity in patients with chronic lung disease after viral infections and perhaps other types of lung injury.NEW & NOTEWORTHY Our study used a mouse model of post-viral lung disease to study the impact of chronic lung disease on skeletal muscle. The model reveals a decrease in myofiber size that is selective for specific types of myofibers and an alternative mechanism for muscle atrophy that might be independent of the usual markers of protein synthesis and degradation. The findings provide a basis for new therapeutic strategies to correct skeletal muscle dysfunction in chronic respiratory disease.

Choroid plexus-targeted NKCC1 overexpression to treat post-hemorrhagic hydrocephalus

Post-hemorrhagic hydrocephalus (PHH) refers to a life-threatening accumulation of cerebrospinal fluid (CSF) that occurs following intraventricular hemorrhage (IVH). An incomplete understanding of this variably progressive condition has hampered the development of new therapies beyond serial neurosurgical interventions. Here, we show a key role for the bidirectional Na-K-Cl cotransporter, NKCC1, in the choroid plexus (ChP) to mitigate PHH. Mimicking IVH with intraventricular blood led to increased CSF [K+] and triggered cytosolic calcium activity in ChP epithelial cells, which was followed by NKCC1 activation. ChP-targeted adeno-associated viral (AAV)-NKCC1 prevented blood-induced ventriculomegaly and led to persistently increased CSF clearance capacity. These data demonstrate that intraventricular blood triggered a trans-choroidal, NKCC1-dependent CSF clearance mechanism. Inactive, phosphodeficient AAV-NKCC1-NT51 failed to mitigate ventriculomegaly. Excessive CSF [K+] fluctuations correlated with permanent shunting outcome in humans following hemorrhagic stroke, suggesting targeted gene therapy as a potential treatment to mitigate intracranial fluid accumulation following hemorrhage.

Lung Remodeling Regions in Long-Term Coronavirus Disease 2019 Feature Basal Epithelial Cell Reprogramming

Respiratory viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can trigger chronic lung disease that persists and even progresses after expected clearance of infectious virus. To gain an understanding of this process, we examined a series of consecutive fatal cases of coronavirus disease 2019 (COVID-19) that came to autopsy at 27 to 51 days after hospital admission. In each patient, we identify a stereotyped bronchiolar-alveolar pattern of lung remodeling with basal epithelial cell hyperplasia, immune activation, and mucinous differentiation. Remodeling regions also feature macrophage infiltration and apoptosis and a marked depletion of alveolar type 1 and 2 epithelial cells. This entire pattern closely resembles findings from an experimental model of post-viral lung disease that requires basal-epithelial stem cell growth, immune activation, and differentiation. Together, the results provide evidence of basal epithelial cell reprogramming in long-term COVID-19 and thereby yield a pathway for explaining and correcting lung dysfunction in this type of disease.

Dentate gyrus morphogenesis is regulated by β-catenin function in hem-derived fimbrial glia

The dentate gyrus, a gateway for input to the hippocampal formation, arises from progenitors in the medial telencephalic neuroepithelium adjacent to the cortical hem. Dentate progenitors navigate a complex migratory path guided by two cell populations that arise from the hem, the fimbrial glia and Cajal-Retzius (CR) cells. As the hem expresses multiple Wnt genes, we examined whether β-catenin, which mediates canonical Wnt signaling and also participates in cell adhesion, is necessary for the development of hem-derived lineages. We report that, in mice, the fimbrial glial scaffold is disorganized and CR cells are mispositioned upon hem-specific disruption of β-catenin. Consequently, the dentate migratory stream is severely affected, and the dentate gyrus fails to form. Using selective Cre drivers, we further determined that β-catenin function is required in the fimbrial glial scaffold, but not in the CR cells, for guiding the dentate migration. Our findings highlight a primary requirement for β-catenin for the organization of the fimbrial scaffold and a secondary role for this factor in dentate gyrus morphogenesis.

An alternative mechanism for skeletal muscle dysfunction in long-term post-viral lung disease

Chronic lung disease is often accompanied by disabling extrapulmonary symptoms, notably skeletal muscle dysfunction and atrophy. Moreover, the severity of respiratory symptoms correlates with decreased muscle mass and in turn lowered physical activity and survival rates. Previous models of muscle atrophy in chronic lung disease often modeled COPD and relied on cigarette smoke exposure and LPS-stimulation, but these conditions independently affect skeletal muscle even without accompanying lung disease. Moreover, there is an emerging and pressing need to understand the extrapulmonary manifestations of long-term post-viral lung disease (PVLD) as found in Covid-19. Here, we examine the development of skeletal muscle dysfunction in the setting of chronic pulmonary disease using a mouse model of PVLD caused by infection due to the natural pathogen Sendai virus. We identify a significant decrease in myofiber size when PVLD is maximal at 49 d after infection. We find no change in the relative types of myofibers, but the greatest decrease in fiber size is localized to fast-twitch type IIB myofibers based on myosin heavy chain immunostaining. Remarkably, all biomarkers of myocyte protein synthesis and degradation (total RNA, ribosomal abundance, and ubiquitin-proteasome expression) were stable throughout the acute infectious illness and chronic post-viral disease process. Together, the results demonstrate a distinct pattern of skeletal muscle dysfunction in a mouse model of long-term PVLD. The findings thereby provide new insight into prolonged limitations in exercise capacity in patients with chronic lung disease after viral infections and perhaps other types of lung injury.

Lung remodeling regions in long-term Covid-19 feature basal epithelial cell reprogramming

Respiratory viruses, including SARS-CoV-2, can trigger chronic lung disease that persists and even progresses after expected clearance of infectious virus. To gain an understanding of this process, we examined a series of consecutive fatal cases of Covid-19 that came to autopsy at 27-51 d after hospital admission. In each patient, we identify a stereotyped bronchiolar-alveolar pattern of lung remodeling with basal epithelial cell hyperplasia and mucinous differentiation. Remodeling regions also feature macrophage infiltration and apoptosis and a marked depletion of alveolar type 1 and 2 epithelial cells. This entire pattern closely resembles findings from an experimental model of post-viral lung disease that requires basal-epithelial stem cell growth, immune activation, and differentiation. The present results thereby provide evidence of possible basal epithelial cell reprogramming in long-term Covid-19 as well and thereby a pathway for explaining and correcting lung dysfunction in this type of disease.

Secretory Cells Are the Primary Source of pIgR in Small Airways

Loss of secretory IgA (SIgA) is common in chronic obstructive pulmonary disease (COPD) small airways and likely contributes to disease progression. We hypothesized that loss of SIgA results from reduced expression of pIgR (polymeric immunoglobulin receptor), a chaperone protein needed for SIgA transcytosis, in the COPD small airway epithelium. pIgR-expressing cells were defined and quantified at single-cell resolution in human airways using RNA in situ hybridization, immunostaining, and single-cell RNA sequencing. Complementary studies in mice used immunostaining, primary murine tracheal epithelial cell culture, and transgenic mice with secretory or ciliated cell-specific knockout of pIgR. SIgA degradation by human neutrophil elastase or secreted bacterial proteases from nontypeable Haemophilus influenzae was evaluated in vitro. We found that secretory cells are the predominant cell type responsible for pIgR expression in human and murine airways. Loss of SIgA in small airways was not associated with a reduction in secretory cells but rather a reduction in pIgR protein expression despite intact PIGR mRNA expression. Neutrophil elastase and nontypeable H. influenzae-secreted proteases are both capable of degrading SIgA in vitro and may also contribute to a deficient SIgA immunobarrier in COPD. Loss of the SIgA immunobarrier in small airways of patients with severe COPD is complex and likely results from both pIgR-dependent defects in IgA transcytosis and SIgA degradation.

Chloride channel accessory 1 gene deficiency causes selective loss of mucus production in a new pig model

Morbidity and mortality of respiratory diseases are linked to airway obstruction by mucus but there are still no specific, safe, and effective drugs to correct this phenotype. The need for better treatment requires a new understanding of the basis for mucus production. In that regard, studies of human airway epithelial cells in primary culture show that a mucin granule constituent known as chloride channel accessory 1 (CLCA1) is required for inducible expression of the inflammatory mucin MUC5AC in response to potent type 2 cytokines. However, it remained uncertain whether CLCLA1 is necessary for mucus production in vivo. Conventional approaches to functional biology using targeted gene knockout were difficult due to the functional redundancy of additional Clca genes in mice not found in humans. We reasoned that CLCA1 function might be better addressed in pigs that maintain the same four-member CLCA gene locus and the corresponding mucosal and submucosal populations of mucous cells found in humans. Here we develop to our knowledge the first CLCA1-gene-deficient (CLCA1-/-) pig and show that these animals exhibit loss of MUC5AC+ mucous cells throughout the airway mucosa of the lung without affecting comparable cells in the tracheal mucosa or MUC5B+ mucous cells in submucosal glands. Similarly, CLCA1-/- pigs exhibit loss of MUC5AC+ mucous cells in the intestinal mucosa without affecting MUC2+ mucous cells. These data establish CLCA1 function for controlling MUC5AC expression as a marker of mucus production and provide a new animal model to study mucus production at respiratory and intestinal sites.

Age-Dependent Reduction in Asthmatic Pathology through Reprogramming of Postviral Inflammatory Responses

Asthma is a chronic disease of childhood, but for unknown reasons, disease activity sometimes subsides as children mature. In this study, we present clinical and animal model evidence suggesting that the age dependency of childhood asthma stems from an evolving host response to respiratory viral infection. Using clinical data, we show that societal suppression of respiratory virus transmission during coronavirus disease 2019 lockdown disrupted the traditional age gradient in pediatric asthma exacerbations, connecting the phenomenon of asthma remission to virus exposure. In mice, we show that asthmatic lung pathology triggered by Sendai virus (SeV) or influenza A virus is highly age-sensitive: robust in juvenile mice (4-6 wk old) but attenuated in mature mice (>3 mo old). Interestingly, allergen induction of the same asthmatic traits was less dependent on chronological age than viruses. Age-specific responses to SeV included a juvenile bias toward type 2 airway inflammation that emerged early in infection, whereas mature mice exhibited a more restricted bronchiolar distribution of infection that produced a distinct type 2 low inflammatory cytokine profile. In the basal state, aging produced changes to lung leukocyte burden, including the number and transcriptional landscape of alveolar macrophages (AMs). Importantly, depleting AMs in mature mice restored post-SeV pathology to juvenile levels. Thus, aging influences chronic outcomes of respiratory viral infection through regulation of the AM compartment and type 2 inflammatory responses to viruses. Our data provide insight into how asthma remission might develop in children.

Basal epithelial stem cells cross an alarmin checkpoint for postviral lung disease

Epithelial cells are charged with protection at barrier sites, but whether this normally beneficial response might sometimes become dysfunctional still needs definition. Here, we recognized a pattern of imbalance marked by basal epithelial cell growth and differentiation that replaced normal airspaces in a mouse model of progressive postviral lung disease due to the Sendai virus. Single-cell and lineage-tracing technologies identified a distinct subset of basal epithelial stem cells (basal ESCs) that extended into gas-exchange tissue to form long-term bronchiolar-alveolar remodeling regions. Moreover, this cell subset was selectively expanded by crossing a cell-growth and survival checkpoint linked to the nuclear-localized alarmin IL-33 that was independent of IL-33 receptor signaling and instead connected to autocrine chromatin accessibility. This mechanism creates an activated stem-progenitor cell lineage with potential for physiological or pathological function. Thus, conditional loss of Il33 gene function in basal epithelial cells disrupted the homeostasis of the epithelial barrier at skin and gut sites but also markedly attenuated postviral disease in the lung based on the downregulation of remodeling and inflammation. Thus, we define a basal ESC strategy to deploy innate immune machinery that appears to overshoot the primordial goal of self-defense. Our findings reveal new targets to stratify and correct chronic and often deadly postviral disease.

A single intranasal or intramuscular immunization with chimpanzee adenovirus-vectored SARS-CoV-2 vaccine protects against pneumonia in hamsters

The development of an effective vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiologic agent of coronavirus disease 2019 (COVID-19), is a global priority. Here, we compare the protective capacity of intranasal and intramuscular delivery of a chimpanzee adenovirus-vectored vaccine encoding a prefusion stabilized spike protein (chimpanzee adenovirus [ChAd]-SARS-CoV-2-S) in Golden Syrian hamsters. Although immunization with ChAd-SARS-CoV-2-S induces robust spike-protein-specific antibodies capable of neutralizing the virus, antibody levels in serum are higher in hamsters vaccinated by an intranasal compared to intramuscular route. Accordingly, against challenge with SARS-CoV-2, ChAd-SARS-CoV-2-S-immunized hamsters are protected against less weight loss and have reduced viral infection in nasal swabs and lungs, and reduced pathology and inflammatory gene expression in the lungs, compared to ChAd-control immunized hamsters. Intranasal immunization with ChAd-SARS-CoV-2-S provides superior protection against SARS-CoV-2 infection and inflammation in the upper respiratory tract. These findings support intranasal administration of the ChAd-SARS-CoV-2-S candidate vaccine to prevent SARS-CoV-2 infection, disease, and possibly transmission.

Dysfunction of the proteoglycan Tsukushi causes hydrocephalus through altered neurogenesis in the subventricular zone in mice

The lateral ventricle (LV) is flanked by the subventricular zone (SVZ), a neural stem cell (NSC) niche rich in extrinsic growth factors regulating NSC maintenance, proliferation, and neuronal differentiation. Dysregulation of the SVZ niche causes LV expansion, a condition known as hydrocephalus; however, the underlying pathological mechanisms are unclear. We show that deficiency of the proteoglycan Tsukushi (TSK) in ependymal cells at the LV surface and in the cerebrospinal fluid results in hydrocephalus with neurodevelopmental disorder-like symptoms in mice. These symptoms are accompanied by altered differentiation and survival of the NSC lineage, disrupted ependymal structure, and dysregulated Wnt signaling. Multiple TSK variants found in patients with hydrocephalus exhibit reduced physiological activity in mice in vivo and in vitro. Administration of wild-type TSK protein or Wnt antagonists, but not of hydrocephalus-related TSK variants, in the LV of TSK knockout mice prevented hydrocephalus and preserved SVZ neurogenesis. These observations suggest that TSK plays a crucial role as a niche molecule modulating the fate of SVZ NSCs and point to TSK as a candidate for the diagnosis and therapy of hydrocephalus.

Selective Imaging of Lung Macrophages Using [11C]PBR28-Based Positron Emission Tomography

PURPOSE

We tested whether the translocator protein (TSPO)-targeted positron emission tomography (PET) tracer, N-acetyl-N-(2-[¹¹C]methoxybenzyl)-2-phenoxy-5-pyridinamine ([¹¹C]PBR28), could distinguish macrophage dominant from neutrophilic inflammation better than 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) in mouse models of lung inflammation and assessed TSPO association with macrophages in lung tissue from the mouse models and in patients with chronic obstructive pulmonary disease (COPD).

PROCEDURES

MicroPET imaging quantified [¹¹C]PBR28 and [¹⁸F]FDG lung uptake in wild-type (Wt) C57BL/6J or heterozygous transgenic monocyte-deficient Wt/opT mice at 49 days after Sendai virus (SeV) infection, during macrophage-dominant inflammation, and in Wt mice at 3 days after SeV infection or 24 h after endotoxin instillation during neutrophilic inflammation. Immunohistochemical staining for TSPO in macrophages and neutrophils was performed using Mac3 and Ly6G for cell identification in mouse lung sections and CD68 and neutrophil elastase (NE) in human lung sections taken from explanted lungs from patients with COPD undergoing lung transplantation and donor lungs rejected for transplantation. Differences in tracer uptake among SeV-infected, endotoxin-treated, and uninfected/untreated control mice and in TSPO staining between neutrophils and macrophage populations in human lung sections were tested using analysis of variance.

RESULTS

In Wt mice, [¹¹C]PBR28 uptake (% injected dose/ml lung tissue) increased significantly with macrophage-dominant inflammation at 49 days (D49) after SeV infection compared to controls (p = <0.001) but not at 3 days (D49) after SeV infection (p = 0.167). [¹¹C]PBR28 uptake was unchanged at 24 h after endotoxin instillation (p = 0.958). [¹⁸F]FDG uptake increased to a similar degree in D3 and D49 SeV-infected and endotoxin-treated Wt mice compared to controls with no significant difference in the degree of increase among the tested conditions. [¹¹C]PBR28 but not [¹⁸F]FDG lung uptake at D49 post-SeV infection was attenuated in Wt/opT mice compared to Wt mice. TSPO localized predominantly to macrophages in mouse lung tissue by immunostaining, and TSPO staining intensity was significantly higher in CD68+ cells compared to neutrophils in the human lung sections.

CONCLUSIONS

PET imaging with [¹¹C]PBR28 can specifically detect macrophages versus neutrophils during lung inflammation and may be a useful biomarker of macrophage accumulation in lung disease.

TLR3-Activated Monocyte-Derived Dendritic Cells Trigger Progression from Acute Viral Infection to Chronic Disease in the Lung

Acute infection is implicated as a trigger for chronic inflammatory disease, but the full basis for this switch is uncertain. In this study, we examine this issue using a mouse model of chronic lung disease that develops after respiratory infection with a natural pathogen (Sendai virus). We investigate this model using a combination of TLR3-deficient mice and adoptive transfer of immune cells into these mice versus the comparable responses in wild-type mice. We found that acute and transient expression of TLR3 on monocyte-derived dendritic cells (moDCs) was selectively required to induce long-term expression of IL-33 and consequent type 2 immune-driven lung disease. Unexpectedly, moDC participation was not based on canonical TLR3 signaling and relied instead on a trophic effect to expand the alveolar epithelial type 2 cell population beyond repair of tissue injury and thereby provide an enriched and persistent cell source of IL-33 required for progression to a disease phenotype that includes lung inflammation, hyperreactivity, excess mucus production, and remodeling. The findings thereby provide a framework wherein viral infection activates TLR3 in moDCs as a front-line immune cell niche upstream of lung epithelial cells to drive the type 2 immune response, leading to chronic inflammatory diseases of the lung (such as asthma and chronic obstructive pulmonary disease in humans) and perhaps progressive and long-term postviral disease in general.

Epithelial IL-33 appropriates exosome trafficking for secretion in chronic airway disease

IL-33 is a key mediator of chronic airway disease driven by type 2 immune pathways, yet the nonclassical secretory mechanism for this cytokine remains undefined. We performed a comprehensive analysis in human airway epithelial cells, which revealed that tonic IL-33 secretion is dependent on the ceramide biosynthetic enzyme neutral sphingomyelinase 2 (nSMase2). IL-33 is cosecreted with exosomes by the nSMase2-regulated multivesicular endosome (MVE) pathway as surface-bound cargo. In support of these findings, human chronic obstructive pulmonary disease (COPD) specimens exhibited increased epithelial expression of the abundantly secreted IL33^Δ34 isoform and augmented nSMase2 expression compared with non-COPD specimens. Using an Alternaria-induced airway disease model, we found that the nSMase2 inhibitor GW4869 abrogated both IL-33 and exosome secretion as well as downstream inflammatory pathways. This work elucidates a potentially novel aspect of IL-33 biology that may be targeted for therapeutic benefit in chronic airway diseases driven by type 2 inflammation.