Cell shape sensing licenses dendritic cells for homeostatic migration to lymph nodes.

Immune cells experience large cell shape changes during environmental patrolling because of the physical constraints that they encounter while migrating through tissues. These cells can adapt to such deformation events using dedicated shape-sensing pathways. However, how shape sensing affects immune cell function is mostly unknown. Here, we identify a shape-sensing mechanism that increases the expression of the chemokine receptor CCR7 and guides dendritic cell migration from peripheral tissues to lymph nodes at steady state. This mechanism relies on the lipid metabolism enzyme cPLA2, requires nuclear envelope tensioning and is finely tuned by the ARP2/3 actin nucleation complex. We also show that this shape-sensing axis reprograms dendritic cell transcription by activating an IKKß-NF-κB-dependent pathway known to control their tolerogenic potential. These results indicate that cell shape changes experienced by immune cells can define their migratory behavior and immunoregulatory properties and reveal a contribution of the physical properties of tissues to adaptive immunity.

Elevated Calprotectin and Abnormal Myeloid Cell Subsets Discriminate Severe from Mild COVID-19.

Blood myeloid cells are known to be dysregulated in coronavirus disease 2019 (COVID-19), caused by SARS-CoV-2. It is unknown whether the innate myeloid response differs with disease severity and whether markers of innate immunity discriminate high-risk patients. Thus, we performed high-dimensional flow cytometry and single-cell RNA sequencing of COVID-19 patient peripheral blood cells and detected disappearance of non-classical CD14LowCD16High monocytes, accumulation of HLA-DRLow classical monocytes (Human Leukocyte Antigen - DR isotype), and release of massive amounts of calprotectin (S100A8/S100A9) in severe cases. Immature CD10LowCD101-CXCR4+/- neutrophils with an immunosuppressive profile accumulated in the blood and lungs, suggesting emergency myelopoiesis. Finally, we show that calprotectin plasma level and a routine flow cytometry assay detecting decreased frequencies of non-classical monocytes could discriminate patients who develop a severe form of COVID-19, suggesting a predictive value that deserves prospective evaluation.

Dual ontogeny of disease-associated microglia and disease inflammatory macrophages in aging and neurodegeneration.

Brain macrophage populations include parenchymal microglia, border-associated macrophages, and recruited monocyte-derived cells; together, they control brain development and homeostasis but are also implicated in aging pathogenesis and neurodegeneration. The phenotypes, localization, and functions of each population in different contexts have yet to be resolved. We generated a murine brain myeloid scRNA-seq integration to systematically delineate brain macrophage populations. We show that the previously identified disease-associated microglia (DAM) population detected in murine Alzheimer's disease models actually comprises two ontogenetically and functionally distinct cell lineages: embryonically derived triggering receptor expressed on myeloid cells 2 (TREM2)-dependent DAM expressing a neuroprotective signature and monocyte-derived TREM2-expressing disease inflammatory macrophages (DIMs) accumulating in the brain during aging. These two distinct populations appear to also be conserved in the human brain. Herein, we generate an ontogeny-resolved model of brain myeloid cell heterogeneity in development, homeostasis, and disease and identify cellular targets for the treatment of neurodegeneration.

Cross-tissue single-cell landscape of human monocytes and macrophages in health and disease.

Mononuclear phagocytes (MNPs) encompass dendritic cells, monocytes, and macrophages (MoMac), which exhibit antimicrobial, homeostatic, and immunoregulatory functions. We integrated 178,651 MNPs from 13 tissues across 41 datasets to generate a MNP single-cell RNA compendium (MNP-VERSE), a publicly available tool to map MNPs and define conserved gene signatures of MNP populations. Next, we generated a MoMac-focused compendium that revealed an array of specialized cell subsets widely distributed across multiple tissues. Specific pathological forms were expanded in cancer and inflammation. All neoplastic tissues contained conserved tumor-associated macrophage populations. In particular, we focused on IL4I1+CD274(PD-L1)+IDO1+ macrophages, which accumulated in the tumor periphery in a T cell-dependent manner via interferon-γ (IFN-γ) and CD40/CD40L-induced maturation from IFN-primed monocytes. IL4I1_Macs exhibited immunosuppressive characteristics through tryptophan degradation and promoted the entry of regulatory T cell into tumors. This integrated analysis provides a robust online-available platform for uniform annotation and dissection of specific macrophage functions in healthy and pathological states.

A subset of Kupffer cells regulates metabolism through the expression of CD36.

Tissue macrophages are immune cells whose phenotypes and functions are dictated by origin and niches. However, tissues are complex environments, and macrophage heterogeneity within the same organ has been overlooked so far. Here, we used high-dimensional approaches to characterize macrophage populations in the murine liver. We identified two distinct populations among embryonically derived Kupffer cells (KCs) sharing a core signature while differentially expressing numerous genes and proteins: a major CD206loESAM- population (KC1) and a minor CD206hiESAM+ population (KC2). KC2 expressed genes involved in metabolic processes, including fatty acid metabolism both in steady-state and in diet-induced obesity and hepatic steatosis. Functional characterization by depletion of KC2 or targeted silencing of the fatty acid transporter Cd36 highlighted a crucial contribution of KC2 in the liver oxidative stress associated with obesity. In summary, our study reveals that KCs are more heterogeneous than anticipated, notably describing a subpopulation wired with metabolic functions.

IL-1ß+ macrophages fuel pathogenic inflammation in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with high resistance to therapies1. Inflammatory and immunomodulatory signals co-exist in the pancreatic tumour microenvironment, leading to dysregulated repair and cytotoxic responses. Tumour-associated macrophages (TAMs) have key roles in PDAC2, but their diversity has prevented therapeutic exploitation. Here we combined single-cell and spatial genomics with functional experiments to unravel macrophage functions in pancreatic cancer. We uncovered an inflammatory loop between tumour cells and interleukin-1ß (IL-1ß)-expressing TAMs, a subset of macrophages elicited by a local synergy between prostaglandin E2 (PGE2) and tumour necrosis factor (TNF). Physical proximity with IL-1ß+ TAMs was associated with inflammatory reprogramming and acquisition of pathogenic properties by a subset of PDAC cells. This occurrence was an early event in pancreatic tumorigenesis and led to persistent transcriptional changes associated with disease progression and poor outcomes for patients. Blocking PGE2 or IL-1ß activity elicited TAM reprogramming and antagonized tumour cell-intrinsic and -extrinsic inflammation, leading to PDAC control in vivo. Targeting the PGE2-IL-1ß axis may enable preventive or therapeutic strategies for reprogramming of immune dynamics in pancreatic cancer.

iPS-cell-derived microglia promote brain organoid maturation via cholesterol transfer.

Microglia are specialized brain-resident macrophages that arise from primitive macrophages colonizing the embryonic brain1. Microglia contribute to multiple aspects of brain development, but their precise roles in the early human brain remain poorly understood owing to limited access to relevant tissues2-6. The generation of brain organoids from human induced pluripotent stem cells recapitulates some key features of human embryonic brain development7-10. However, current approaches do not incorporate microglia or address their role in organoid maturation11-21. Here we generated microglia-sufficient brain organoids by coculturing brain organoids with primitive-like macrophages generated from the same human induced pluripotent stem cells (iMac)22. In organoid cocultures, iMac differentiated into cells with microglia-like phenotypes and functions (iMicro) and modulated neuronal progenitor cell (NPC) differentiation, limiting NPC proliferation and promoting axonogenesis. Mechanistically, iMicro contained high levels of PLIN2+ lipid droplets that exported cholesterol and its esters, which were taken up by NPCs in the organoids. We also detected PLIN2+ lipid droplet-loaded microglia in mouse and human embryonic brains. Overall, our approach substantially advances current human brain organoid approaches by incorporating microglial cells, as illustrated by the discovery of a key pathway of lipid-mediated crosstalk between microglia and NPCs that leads to improved neurogenesis.

Neutrophils promote T-cell activation through the regulated release of CD44-bound Galectin-9 from the cell surface during HIV infection.

The interaction of neutrophils with T cells has been the subject of debate and controversies. Previous studies have suggested that neutrophils may suppress or activate T cells. Despite these studies, the interaction between neutrophils and T cells has remained a largely unexplored field. Here, based on our RNA sequencing (RNA-seq) analysis, we found that neutrophils have differential transcriptional and functional profiling depending on the CD4 T-cell count of the HIV-infected individual. In particular, we identified that neutrophils in healthy individuals express surface Galectin-9 (Gal-9), which is down-regulated upon activation, and is consistently down-regulated in HIV-infected individuals. However, down-regulation of Gal-9 was associated with CD4 T-cell count of patients. Unstimulated neutrophils express high levels of surface Gal-9 that is bound to CD44, and, upon stimulation, neutrophils depalmitoylate CD44 and induce its movement out of the lipid raft. This process causes the release of Gal-9 from the surface of neutrophils. In addition, we found that neutrophil-derived exogenous Gal-9 binds to cell surface CD44 on T cells, which promotes LCK activation and subsequently enhances T-cell activation. Furthermore, this process was regulated by glycolysis and can be inhibited by interleukin (IL)-10. Together, our data reveal a novel mechanism of Gal-9 shedding from the surface of neutrophils. This could explain elevated plasma Gal-9 levels in HIV-infected individuals as an underlying mechanism of the well-characterized chronic immune activation in HIV infection. This study provides a novel role for the Gal-9 shedding from neutrophils. We anticipate that our results will spark renewed investigation into the role of neutrophils in T-cell activation in other acute and chronic conditions, as well as improved strategies for modulating Gal-9 shedding.

Infection of lung megakaryocytes and platelets by SARS-CoV-2 anticipate fatal COVID-19.

SARS-CoV-2, although not being a circulatory virus, spread from the respiratory tract resulting in multiorgan failures and thrombotic complications, the hallmarks of fatal COVID-19. A convergent contributor could be platelets that beyond hemostatic functions can carry infectious viruses. Here, we profiled 52 patients with severe COVID-19 and demonstrated that circulating platelets of 19 out 20 non-survivor patients contain SARS-CoV-2 in robust correlation with fatal outcome. Platelets containing SARS-CoV-2 might originate from bone marrow and lung megakaryocytes (MKs), the platelet precursors, which were found infected by SARS-CoV-2 in COVID-19 autopsies. Accordingly, MKs undergoing shortened differentiation and expressing anti-viral IFITM1 and IFITM3 RNA as a sign of viral sensing were enriched in the circulation of deadly COVID-19. Infected MKs reach the lung concomitant with a specific MK-related cytokine storm rich in VEGF, PDGF and inflammatory molecules, anticipating fatal outcome. Lung macrophages capture SARS-CoV-2-containing platelets in vivo. The virus contained by platelets is infectious as capture of platelets carrying SARS-CoV-2 propagates infection to macrophages in vitro, in a process blocked by an anti-GPIIbIIIa drug. Altogether, platelets containing infectious SARS-CoV-2  alter COVID-19 pathogenesis and provide a powerful fatality marker. Clinical targeting of platelets might prevent viral spread, thrombus formation and exacerbated inflammation at once and increase survival in COVID-19.

Galectin-9 and VISTA Expression Define Terminally Exhausted T Cells in HIV-1 Infection.

We report significant upregulation of Galectin-9 (Gal-9) and VISTA on both CD4+ and CD8+ T cells in HIV-infected human patients. Gal-9 and VISTA expression was associated with impaired T cells effector functions. Although Gal-9 was coexpressed with other coinhibitory receptors such as TIGIT, CD160, CD39, and VISTA, it was simultaneously coexpressed with PD-1. Coexpression of Gal-9 with PD-1 was associated with a more terminally exhausted T cell phenotype in HIV-1 patients. This was marked by higher expression of EOMES, blimp1, and Glut1 in Gal-9+ versus Gal-9- T cells, which is consistent with an exhausted T cell phenotype. Gal-9+ T cells exhibited the phenotype characteristics of effector T cells (CD45RA+, CD45RO-/lo, CD62L-, CD27lo) with higher T-bet expression. A positive correlation between the plasma viral load with the plasma Gal-9 levels in treatment-naive HIV patients and an inverse correlation between CD4 count with the frequency of CD4+Gal-9+ T cells were observed. Increased percentages of Gal-9+ T cells was evident in HIV-treated patients. Enhanced expression of Gal-9 on T cells following PMA stimulation via protein kinase C suggests persistent TCR stimulation as a potential contributing factor in Gal-9 upregulation in HIV patients. This was supported by the constant degranulation of Gal-9+ T cells. Moreover, CD44 clustering by Gal-9 may influence cytoskeleton rearrangement and coclustering of CD3, which likely impact initiation of signal transduction via TCR. Our preliminary data also confirm upregulation of Gal-9 on T cells in hepatitis B virus and HPV infections. These results demonstrate a novel role for Gal-9 and VISTA in HIV pathogenesis.

Post-neonatal Outcomes of Infants Born to Women with Active Trimester One Inflammatory Bowel Disease: A Pilot Study.

BACKGROUND: Ulcerative colitis (UC) and Crohn's disease (CD) are chronic inflammatory bowel diseases (IBD) that affect women in their childbearing years. Early pregnancy flare-up negatively impacts obstetrical and perinatal outcomes, but the impact on infants is unclear. AIM: To determine whether active IBD disease activity is associated with adverse post-neonatal outcomes post-partum. METHODS: This is a single-center cohort study of women with IBD who underwent serial monitoring of post-neonatal outcomes post-partum. Infant outcomes were collected via self-filled questionnaires, including perinatal outcomes, APGAR scores, infant weights, heights, feeding habits and comorbidities within the first year of life. RESULTS: There was a total of 98 women with IBD and 78 live births throughout the study: 50 women were enrolled during trimester one alone and 49 were included into the current study. Among the 49 analyzed, 32 were in remission and 17 were in relapse during trimester one. Trimester one disease activity was associated with more adverse obstetrical outcomes including emergency C-sections and reduced 1-min APGAR scores. At follow-up, infants born to women with T1-flare had reduced weight-for-age Z scores and length-for-age Z scores up to 6 months of age. CONCLUSIONS: Active IBD during trimester one is correlated with adverse post-neonatal outcomes, particularly decreased infant weight and height up to 6 months of age. This suggests disease control in first trimester is essential for optimizing infant growth and post-neonatal outcomes.

Elevated IL-6 and IL-22 in Early Pregnancy Are Associated with Worse Disease Course in Women with Inflammatory Bowel Disease.

Inflammatory bowel diseases (IBD), including Ulcerative Colitis (UC) and Crohn's disease (CD), are inflammatory conditions of the intestinal tract that affect women in their reproductive years. Pregnancy affects Th1- and Th2-cytokines, but how these changes occur during pregnancy in IBD is unclear. We performed a longitudinal profiling of serum cytokines in a cohort of 11 healthy pregnant women and 76 pregnant women with IBD from the first trimester of pregnancy to the first 12 months post-partum. Participants were monitored for biochemical disease activity (C-reactive protein [CRP] and fecal calprotectin [FCP]) and clinical activities. Maternal cytokines were measured using ELISA. We identified changes in Th1 and Th17 cytokines throughout pregnancy in healthy pregnant women. During pregnancy, maternal serum cytokine expressions were influenced by IBD, disease activity, and medications. Active UC was associated with an elevation in IL-21, whereas active CD was associated with elevated IFN-γ, IL-6, and IL-21. Interestingly, T1 serum cytokine levels of IL-22 (>0.624 pg/mL) and IL-6 (>0.648 pg/mL) were associated with worse IBD disease activity throughout pregnancy in women with UC and CD, respectively. This shows serum cytokines in pregnancy differ by IBD, disease activity, and medications. We show for the first time that T1 IL-22 and IL-6 correlate with IBD disease course throughout pregnancy.

CD71+ Erythroid Suppressor Cells Promote Fetomaternal Tolerance through Arginase-2 and PDL-1.

Survival of the allogeneic pregnancy depends on the maintenance of immune tolerance to paternal alloantigens at the fetomaternal interface. Multiple localized mechanisms contribute to the fetal evasion from the mother's immune rejection as the fetus is exposed to a wide range of stimulatory substances such as maternal alloantigens, microbes and amniotic fluids. In this article, we demonstrate that CD71+ erythroid cells are expanded at the fetomaternal interface and in the periphery during pregnancy in both humans and mice. These cells exhibit immunosuppressive properties, and their abundance is associated with a Th2 skewed immune response, as their depletion results in a proinflammatory immune response at the fetomaternal interface. In addition to their function in suppressing proinflammatory responses in vitro, maternal CD71+ erythroid cells inhibit an aggressive allogeneic response directed against the fetus such as reduction in TNF-α and IFN-γ production through arginase-2 activity and PD-1/programmed death ligand-1 (PDL-1) interactions. Their depletion leads to the failure of gestation due to the immunological rejection of the fetus. Similarly, fetal liver CD71+ erythroid cells exhibit immunosuppressive activity. Therefore, immunosuppression mediated by CD71+ erythroid cells on both sides (mother/fetus) is crucial for fetomaternal tolerance. Thus, our results reveal a previously unappreciated role for CD71+ erythroid cells in pregnancy and indicate that these cells mediate homeostatic immunosuppressive/immunoregulatory responses during pregnancy.

Erythroid Suppressor Cells Compromise Neonatal Immune Response against Bordetella pertussis.

Newborns are highly susceptible to infection. The underlying mechanism of neonatal infection susceptibility has generally been associated with neonatal immune cell immaturity. In this study, we challenged this notion and built upon our recent discovery that neonates are physiologically enriched with erythroid TER119+CD71+ cells (Elahi et al. 2013. Nature 504: 158-162). We have used Bordetella pertussis, a common neonatal respiratory tract infection, as a proof of concept to investigate the role of these cells in newborns. We found that CD71+ cells have distinctive immune-suppressive properties and suppress innate immune responses against B. pertussis infection. CD71+ cell ablation unleashed innate immune response and restored resistance to B. pertussis infection. In contrast, adoptive transfer of neonatal CD71+ cells into adult recipients impaired their innate immune response to B. pertussis infection. Enhanced innate immune response to B. pertussis was characterized by increased production of protective cytokines IFN-γ, TNF-α, and IL-12, as well as recruitment of NK cells, CD11b+, and CD11c+ cells in the lung. Neonatal and human cord blood CD71+ cells express arginase II, and this enzymatic activity inhibits phagocytosis of B. pertussis in vitro. Thus, our study challenges the notion that neonatal infection susceptibility is due to immune cell-intrinsic defects and instead highlights active immune suppression mediated by abundant CD71+ cells in the newborn. Our findings provide additional support for the novel theme in neonatal immunology that immunosuppression is essential to dampen robust immune responses in the neonate. We anticipate that our results will spark renewed investigation in modulating the function of these cells and developing novel strategies for enhancing host defense to infections in newborns.

A temporal perspective for tumor-associated macrophage identities and functions.

Cancer is a progressive disease that can develop and evolve over decades, with inflammation playing a central role at each of its stages, from tumor initiation to metastasis. In this context, macrophages represent well-established bridges reciprocally linking inflammation and cancer via an array of diverse functions that have spurred efforts to classify them into subtypes. Here, we discuss the intertwines between macrophages, inflammation, and cancer with an emphasis on temporal dynamics of macrophage diversity and functions in pre-malignancy and cancer. By instilling temporal dynamism into the more static classic view of tumor-associated macrophage biology, we propose a new framework to better contextualize their significance in the inflammatory processes that precede and result from the onset of cancer and shape its evolution.

Proteomic analysis of ascitic extracellular vesicles describes tumour microenvironment and predicts patient survival in ovarian cancer.

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

Multicellular tumor spheroid model to study the multifaceted role of tumor-associated macrophages in PDAC.

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

Immune system and intestinal microbiota determine efficacy of androgen deprivation therapy against prostate cancer.

BACKGROUND: Prostate cancer (PC) responds to androgen deprivation therapy (ADT) usually in a transient fashion, progressing from hormone-sensitive PC (HSPC) to castration-resistant PC (CRPC). We investigated a mouse model of PC as well as specimens from PC patients to unravel an unsuspected contribution of thymus-derived T lymphocytes and the intestinal microbiota in the efficacy of ADT. METHODS: Preclinical experiments were performed in PC-bearing mice, immunocompetent or immunodeficient. In parallel, we prospectively included 65 HSPC and CRPC patients (Oncobiotic trial) to analyze their feces and blood specimens. RESULTS: In PC-bearing mice, ADT increased thymic cellularity and output. PC implanted in T lymphocyte-depleted or athymic mice responded less efficiently to ADT than in immunocompetent mice. Moreover, depletion of the intestinal microbiota by oral antibiotics reduced the efficacy of ADT. PC reduced the relative abundance of Akkermansia muciniphila in the gut, and this effect was reversed by ADT. Moreover, cohousing of PC-bearing mice with tumor-free mice or oral gavage with Akkermansia improved the efficacy of ADT. This appears to be applicable to PC patients because long-term ADT resulted in an increase of thymic output, as demonstrated by an increase in circulating recent thymic emigrant cells (sjTRECs). Moreover, as compared with HSPC controls, CRPC patients demonstrated a shift in their intestinal microbiota that significantly correlated with sjTRECs. While feces from healthy volunteers restored ADT efficacy, feces from PC patients failed to do so. CONCLUSIONS: These findings suggest the potential clinical utility of reversing intestinal dysbiosis and repairing acquired immune defects in PC patients.

Escherichia coli-Specific CXCL13-Producing TFH Are Associated with Clinical Efficacy of Neoadjuvant PD-1 Blockade against Muscle-Invasive Bladder Cancer.

Biomarkers guiding the neoadjuvant use of immune-checkpoint blockers (ICB) are needed for patients with localized muscle-invasive bladder cancers (MIBC). Profiling tumor and blood samples, we found that follicular helper CD4+ T cells (TFH) are among the best therapeutic targets of pembrolizumab correlating with progression-free survival. TFH were associated with tumoral CD8 and PD-L1 expression at baseline and the induction of tertiary lymphoid structures after pembrolizumab. Blood central memory TFH accumulated in tumors where they produce CXCL13, a chemokine found in the plasma of responders only. IgG4+CD38+ TFH residing in bladder tissues correlated with clinical benefit. Finally, TFH and IgG directed against urothelium-invasive Escherichia coli dictated clinical responses to pembrolizumab in three independent cohorts. The links between tumor infection and success of ICB immunomodulation should be prospectively assessed at a larger scale. SIGNIFICANCE: In patients with bladder cancer treated with neoadjuvant pembrolizumab, E. coli-specific CXCL13 producing TFH and IgG constitute biomarkers that predict clinical benefit. Beyond its role as a biomarker, such immune responses against E. coli might be harnessed for future therapeutic strategies. This article is highlighted in the In This Issue feature, p. 2221.

Nasal Septum Deviation as the Consequence of BMP-Controlled Changes to Cartilage Properties.

The nasal septum cartilage is a specialized hyaline cartilage important for normal midfacial growth. Abnormal midfacial growth is associated with midfacial hypoplasia and nasal septum deviation (NSD). However, the underlying genetics and associated functional consequences of these two anomalies are poorly understood. We have previously shown that loss of Bone Morphogenetic Protein 7 (BMP7) from neural crest (BMP7 ncko ) leads to midfacial hypoplasia and subsequent septum deviation. In this study we elucidate the cellular and molecular abnormalities underlying NSD using comparative gene expression, quantitative proteomics, and immunofluorescence analysis. We show that reduced cartilage growth and septum deviation are associated with acquisition of elastic cartilage markers and share similarities with osteoarthritis (OA) of the knee. The genetic reduction of BMP2 in BMP7 ncko mice was sufficient to rescue NSD and suppress elastic cartilage markers. To our knowledge this investigation provides the first genetic example of an in vivo cartilage fate switch showing that this is controlled by the relative balance of BMP2 and BMP7. Cellular and molecular changes similar between NSD and knee OA suggest a related etiology underlying these cartilage abnormalities.