Innate immune cell activation causes lung fibrosis in a humanized model of long COVID.

COVID-19 remains a global pandemic of an unprecedented magnitude with millions of people now developing "COVID lung fibrosis." Single-cell transcriptomics of lungs of patients with long COVID revealed a unique immune signature demonstrating the upregulation of key proinflammatory and innate immune effector genes CD47, IL-6, and JUN. We modeled the transition to lung fibrosis after COVID and profiled the immune response with single-cell mass cytometry in JUN mice. These studies revealed that COVID mediated chronic immune activation reminiscent to long COVID in humans. It was characterized by increased CD47, IL-6, and phospho-JUN (pJUN) expression which correlated with disease severity and pathogenic fibroblast populations. When we subsequently treated a humanized COVID lung fibrosis model by combined blockade of inflammation and fibrosis, we not only ameliorated fibrosis but also restored innate immune equilibrium indicating possible implications for clinical management of COVID lung fibrosis in patients.

JUN promotes hypertrophic skin scarring via CD36 in preclinical in vitro and in vivo models.

Pathologic skin scarring presents a vast economic and medical burden. Unfortunately, the molecular mechanisms underlying scar formation remain to be elucidated. We used a hypertrophic scarring (HTS) mouse model in which Jun is overexpressed globally or specifically in α-smooth muscle or collagen type I­expressing cells to cause excessive extracellular matrix deposition by skin fibroblasts in the skin after wounding. Jun overexpression triggered dermal fibrosis by modulating distinct fibroblast subpopulations within the wound, enhancing reticular fibroblast numbers, and decreasing lipofibroblasts. Analysis of human scars further revealed that JUN is highly expressed across the wide spectrum of scars, including HTS and keloids. CRISPR-Cas9­mediated JUN deletion in human HTS fibroblasts combined with epigenomic and transcriptomic analysis of both human and mouse HTS fibroblasts revealed that JUN initiates fibrosis by regulating CD36. Blocking CD36 with salvianolic acid B or CD36 knockout model counteracted JUN-mediated fibrosis efficacy in both human fibroblasts and mouse wounds. In summary, JUN is a critical regulator of pathological skin scarring, and targeting its downstream effector CD36 may represent a therapeutic strategy against scarring.

Tuning MPL signaling to influence hematopoietic stem cell differentiation and inhibit essential thrombocythemia progenitors.

Thrombopoietin (TPO) and the TPO-receptor (TPO-R, or c-MPL) are essential for hematopoietic stem cell (HSC) maintenance and megakaryocyte differentiation. Agents that can modulate TPO-R signaling are highly desirable for both basic research and clinical utility. We developed a series of surrogate protein ligands for TPO-R, in the form of diabodies (DBs), that homodimerize TPO-R on the cell surface in geometries that are dictated by the DB receptor binding epitope, in effect "tuning" downstream signaling responses. These surrogate ligands exhibit diverse pharmacological properties, inducing graded signaling outputs, from full to partial TPO agonism, thus decoupling the dual functions of TPO/TPO-R. Using single-cell RNA sequencing and HSC self-renewal assays we find that partial agonistic diabodies preserved the stem-like properties of cultured HSCs, but also blocked oncogenic colony formation in essential thrombocythemia (ET) through inverse agonism. Our data suggest that dampening downstream TPO signaling is a powerful approach not only for HSC preservation in culture, but also for inhibiting oncogenic signaling through the TPO-R.

Elucidating the fundamental fibrotic processes driving abdominal adhesion formation.

Adhesions are fibrotic scars that form between abdominal organs following surgery or infection, and may cause bowel obstruction, chronic pain, or infertility. Our understanding of adhesion biology is limited, which explains the paucity of anti-adhesion treatments. Here we present a systematic analysis of mouse and human adhesion tissues. First, we show that adhesions derive primarily from the visceral peritoneum, consistent with our clinical experience that adhesions form primarily following laparotomy rather than laparoscopy. Second, adhesions are formed by poly-clonal proliferating tissue-resident fibroblasts. Third, using single cell RNA-sequencing, we identify heterogeneity among adhesion fibroblasts, which is more pronounced at early timepoints. Fourth, JUN promotes adhesion formation and results in upregulation of PDGFRA expression. With JUN suppression, adhesion formation is diminished. Our findings support JUN as a therapeutic target to prevent adhesions. An anti-JUN therapy that could be applied intra-operatively to prevent adhesion formation could dramatically improve the lives of surgical patients.

CD47 prevents the elimination of diseased fibroblasts in scleroderma.

Scleroderma is a devastating fibrotic autoimmune disease. Current treatments are partly effective in preventing disease progression but do not remove fibrotic tissue. Here, we evaluated whether scleroderma fibroblasts take advantage of the "don't-eat-me-signal" CD47 and whether blocking CD47 enables the body's immune system to get rid of diseased fibroblasts. To test this approach, we used a Jun-inducible scleroderma model. We first demonstrated in patient samples that scleroderma upregulated transcription factor JUN and increased promoter accessibilities of both JUN and CD47. Next, we established our scleroderma model, demonstrating that Jun mediated skin fibrosis through the hedgehog-dependent expansion of CD26+Sca1- fibroblasts in mice. In a niche-independent adaptive transfer model, JUN steered graft survival and conferred increased self-renewal to fibroblasts. In vivo, JUN enhanced the expression of CD47, and inhibiting CD47 eliminated an ectopic fibroblast graft and increased in vitro phagocytosis. In the syngeneic mouse, depleting macrophages ameliorated skin fibrosis. Therapeutically, combined CD47 and IL-6 blockade reversed skin fibrosis in mice and led to the rapid elimination of ectopically transplanted scleroderma cells. Altogether, our study demonstrates the efficiency of combining different immunotherapies in treating scleroderma and provides a rationale for combining CD47 and IL-6 inhibition in clinical trials.

Activation of JUN in fibroblasts promotes pro-fibrotic programme and modulates protective immunity.

The transcription factor JUN is highly expressed in pulmonary fibrosis. Its induction in mice drives lung fibrosis, which is abrogated by administration of anti-CD47. Here, we use high-dimensional mass cytometry to profile protein expression and secretome of cells from patients with pulmonary fibrosis. We show that JUN is activated in fibrotic fibroblasts that expressed increased CD47 and PD-L1. Using ATAC-seq and ChIP-seq, we found that activation of JUN rendered promoters and enhancers of CD47 and PD-L1 accessible. We further detect increased IL-6 that amplified JUN-mediated CD47 enhancer activity and protein expression. Using an in vivo mouse model of fibrosis, we found two distinct mechanisms by which blocking IL-6, CD47 and PD-L1 reversed fibrosis, by increasing phagocytosis of profibrotic fibroblasts and by eliminating suppressive effects on adaptive immunity. Our results identify specific immune mechanisms that promote fibrosis and suggest a therapeutic approach that could be used alongside conventional anti-fibrotics for pulmonary fibrosis.

Expansion of Bone Precursors through Jun as a Novel Treatment for Osteoporosis-Associated Fractures.

Osteoporosis and osteoporotic fractures lead to decreased life quality and high healthcare costs. Current treatments prevent losses in bone mass and fractures to some extent but have side effects. Therefore, better therapies are needed. This study investigated whether the transcription factor Jun has a specific pro-osteogenic potency and whether modulating Jun could serve as a novel treatment for osteoporosis-associated fractures. We demonstrate that ectopically transplanted whole bones and distinct osteoprogenitors increase bone formation. Perinatal Jun induction disturbs growth plate architecture, causing a striking phenotype with shortened and thickened bones. Molecularly, Jun induces hedgehog signaling in skeletal stem cells. Therapeutically, Jun accelerates bone growth and healing in a drilling-defect model. Altogether, these results demonstrate that Jun drives bone formation by expanding osteoprogenitor populations and forcing them into the bone fate, providing a rationale for future clinical applications.

Inhibition of Six1 affects tumour invasion and the expression of cancer stem cell markers in pancreatic cancer.

BACKGROUND: Epithelial-to-mesenchymal transition (EMT) and cancer stem cells (CSC) contribute to tumour progression and metastasis. Assessment of transcription factors involved in these two mechanisms can help to identify new targets for an oncological therapy. In this study, we focused on the evaluation of the transcription factor Six1 (Sine oculis 1). This protein is involved in embryologic development and its contribution to carcinogenesis has been described in several studies. METHODS: Immunohistochemistry against Six1 was performed on a tissue microarray containing specimens of primary pancreatic ductal adenocarcinomas (PDAC) of 139 patients. Nuclear and cytoplasmic expression was evaluated and correlated to histopathological parameters. Expression of Six1 was inhibited transiently by siRNA in Panc1 and BxPc3 cells and stably by shRNA in Panc1 cells. Expression analysis of CDH1 and Vimentin mRNA was performed and cell motility was tested in a migration assay. Panc1 cells transfected with Six1 shRNA or scrambled shRNA were injected subcutaneously into nude mice. Tumour growth was observed for four weeks. Afterwards, tumours were stained against Six1, CD24 and CD44. RESULTS: Six1 was overexpressed in the cytoplasm and cellular nuclei in malignant tissues (p < 0.0001). No correlation to histopathological parameters could be detected. Six1 down-regulation decreased pancreatic cancer cell motility in vitro. CDH1 and vimentin expression was decreased after inhibition of the expression of Six1. Pancreatic tumours with impaired expression of Six1 showed significantly delayed growth and displayed loss of the CD24+/CD44+ phenotype. CONCLUSION: We show that Six1 is overexpressed in human PDAC and that its inhibition results in a decreased tumour progression in vitro and in vivo. Therefore, targeting Six1 might be a novel therapeutic approach in patients with pancreatic cancer.

Overexpression of SIX1 is an independent prognostic marker in stage I-III colorectal cancer.

Epithelial-to-mesenchymal transition (EMT) contributes significantly to tumor progression and metastasis. The assessment of EMT-associated transcription factors could be a promising approach to identify biomarkers and potential therapeutic targets in colorectal cancer. In our study, we focused on the transcription factor "Sine oculis homeobox" (SIX) 1, which is a member of the superfamily of the homeobox genes and has been described to promote EMT in different types of tumors. Immunohistochemistry against SIX1 was performed on colorectal mucosa, adenomas, carcinomas-in situ and primary adenocarcinomas. An expression score was developed and subsequently assessed for its prognostic value in two independent cohorts. Cohort 1 consisted of 128 patients with stage I-III colorectal cancer; cohort 2 included 817 patients with stage I-III colorectal cancer who had participated in the DACHS study. HCT-116 cells were transfected with SIX1 plasmids and subjected to migration and colony formation assays. The expression of SIX1 increases gradually from mucosa to colorectal adenocarcinomas (p > 0.0001). Univariate and multivariate analyses reveal that high expression of SIX1 is associated with decreased overall survival (cohort 1: HR: 4.01, CI: 1.20-14.07, p = 0.025; cohort 2: HR: 1.43, CI: 1.014-2.02, p = 0.047). Overexpression of SIX1 induces a more mesenchymal-like phenotype in HCT-116 cells and enhances tumor migration. High expression of SIX1 is an independent prognostic marker in colorectal cancer. It might be a promising biomarker to stratify patients into different risk groups. Moreover, targeting SIX1 might be a novel therapeutic approach in patients with colorectal cancer.