Identification of FGFR4 as a regulator of myofibroblast differentiation in Pulmonary Fibrosis.

Introduction IPF is a devastating lung disease with limited therapeutic options. FGFR4 is a known receptor for several paracrine Fibroblast growth factors (FGFs). FGFR4 is also the main receptor for FGF19, an endocrine FGF that was demonstrated by our group to have anti-fibrotic properties in the lung. We aimed to determine whether FGFR4 could modulate pulmonary fibrogenesis. Methods We assessed FGFR4 mRNA and protein levels in IPF and control lungs. In vitro, we determined the effect of TGF-b, Endothelin-1 and PDGF on FGFR4 expression in human lung fibroblasts. We determined the effect FGFR4 inhibition, using a specific pharmacological inhibitor (FGF401), or genetic deletion in murine embryonic fibroblasts (MEFs) on TGF-b-induced myofibroblastic differentiation. In vivo, we evaluated the development of bleomycin-induced lung fibrosis in Fgfr4-deficient (Fgfr4-/-) mice compared to Wild Type littermates (WT), and after FGF401 treatment in WT mice compared to a control group receiving the solvent only. Results FGFR4 was decreased in IPF lungs as compared to control lungs, at mRNA and protein levels. In vitro, FGFR4 was downregulated after treatment by TGF- ß, Endothelin-1 and PDGF. In vitro, FGFR4 inhibition by FGF401 prevented TGF-b1-induced collagen and ACTA2 increase in lung fibroblasts. Similar results were observed in Fgfr4-/- MEFs. In vivo, FGFR4 genetic deficiency or FGFR4 pharmacological inhibition did not modulate bleomycin-induced pulmonary fibrosis. Conclusion Our data suggest that FGFR4 exerts pro-fibrotic properties by enhancing TGF- ß signaling in vitro. However, the inhibition of FGFR4 is not sufficient to prevent the development of pulmonary fibrosis in vivo.

Anti-fibrotic effects of nintedanib on lung fibroblasts derived from patients with Progressive Fibrosing Interstitial Lung Diseases (PF-ILDs).

The tyrosine kinase inhibitor nintedanib has been recently approved for the treatment of Interstitial Lung Diseases (ILDs) that manifest a progressive fibrosis phenotype other than Idiopathic pulmonary Fibrosis (IPF). Nintedanib reduces the development of lung fibrosis in various animal models resembling features of PF-ILD and in vitro, it inhibits the fibrosing phenotype of human lung fibroblasts (HLFs) isolated from patients with IPF. To get insight on the cellular and molecular mechanisms that drive the clinical efficiency of nintedanib in patients with non-IPF PF-ILD, we investigated its effects on the fibrosing functions of HLFs derived from patients with PF-hypersensitivity pneumonitis (PF-HP, n = 7), PF-sarcoidosis (n = 5) and pleuroparenchymal fibroelastosis (PPFE, n = 4). HLFs were treated with nintedanib (10 nM-1 µM) and then stimulated with PDGF-BB (25-50 ng/ml) or TGF-ß1 (1 ng/ml) for 24-72 h to assess proliferation and migration or differentiation. At nanomolar concentrations, nintedanib reduced the levels of PDGF receptor and ERK1/2 phosphorylation, the proliferation and the migration of PF-HP, PF-sarcoidosis and PPFE HLFs stimulated with PDGF-BB. Moreover, nintedanib also attenuates the myofibroblastic differentiation driven by TGF-ß1 but only when it is used at 1 µM. The drug reduced the phosphorylation of SMAD2/3 and decreased the induction of collagen, fibronectin and α-smooth muscle actin expression induced by TGF-ß1. In conclusion, our results demonstrate that nintedanib counteracts fundamental fibrosing functions of lung fibroblasts derived from patients with PF-HP, PF-sarcoidosis and PPFE, at concentrations previously reported to inhibit control and IPF HLFs. Such effects may contribute to its clinical benefit in patients suffering from these irreversible ILDs.

FGF19 Is Downregulated in Idiopathic Pulmonary Fibrosis and Inhibits Lung Fibrosis in Mice.

Idiopathic pulmonary fibrosis (IPF) is a devastating lung disease with limited therapeutic possibilities. FGF19 (fibroblast growth factor 19), an endocrine FGF, was recently shown to decrease liver fibrosis. To ask whether FGF19 had antifibrotic properties in the lung and decipher its effects on common features associated with lung fibrogenesis, we assessed, by ELISA, FGF19 concentrations in plasma and BAL fluids obtained from control subjects and patients with IPF. In vivo, using an intravenously administered adeno11-associated virus, we overexpressed FGF19 at the fibrotic phase of two experimental models of murine lung fibrosis and assessed its effect on lung morphology, lung collagen content, fibrosis markers, and profibrotic mediator expression at mRNA and protein levels. In vitro, we investigated whether FGF19 could modulate the TGF-ß-induced differentiation of primary human lung fibroblasts into myofibroblasts and the apoptosis of murine alveolar type II cells. Although FGF19 was not detected in BAL fluid, FGF19 concentration was decreased in the plasma of patients with IPF compared with control subjects. In vivo, the overexpression of FGF19 was associated with a marked decrease of lung fibrosis and fibrosis markers, with a decrease of profibrotic mediator expression and lung collagen content. In vitro, FGF19 decreased alveolar type 2 epithelial cell apoptosis through the decrease of the proapoptotic BIM protein expression and prevented TGF-ß-induced myofibroblast differentiation through the inhibition of JNK phosphorylation. Altogether, these data identify FGF19 as an antifibrotic molecule with potential therapeutic interest in fibrotic lung disorders.

Blood fibrocytes are associated with severity and prognosis in COVID-19 pneumonia.

Increased blood fibrocytes are associated with a poor prognosis in fibrotic lung diseases. We aimed to determine whether the percentage of circulating fibrocytes could be predictive of severity and prognosis during coronavirus disease 2019 (COVID-19) pneumonia. Blood fibrocytes were quantified by flow cytometry as CD45+/CD15-/CD34+/collagen-1+ cells in patients hospitalized for COVID-19 pneumonia. In a subgroup of patients admitted in an intensive care unit (ICU), fibrocytes were quantified in blood and bronchoalveolar lavage (BAL). Serum amyloid P (SAP), transforming growth factor-ß1 (TGF-ß1), CXCL12, CCL2, and FGF2 concentrations were measured. We included 57 patients in the hospitalized group (median age = 59 yr [23-87]) and 16 individuals as healthy controls. The median percentage of circulating fibrocytes was higher in the patients compared with the controls (3.6% [0.2-9.2] vs. 2.1% [0.9-5.1], P = 0.04). Blood fibrocyte count was lower in the six patients who died compared with the survivors (1.6% [0.2-4.4] vs. 3.7% [0.6-9.2], P = 0.02). Initial fibrocyte count was higher in patients showing a complete lung computed tomography (CT) resolution at 3 mo. Circulating fibrocyte count was decreased in the ICU group (0.8% [0.1-2.0]), whereas BAL fibrocyte count was 6.7% (2.2-15.4). Serum SAP and TGF-ß1 concentrations were increased in hospitalized patients. SAP was also increased in ICU patients. CXCL12 and CCL2 were increased in ICU patients and negatively correlated with circulating fibrocyte count. We conclude that circulating fibrocytes were increased in patients hospitalized for COVID-19 pneumonia, and a lower fibrocyte count was associated with an increased risk of death and a slower resolution of lung CT opacities.

NADPH oxidase DUOX1 sustains TGF-ß1 signalling and promotes lung fibrosis.

Interstitial lung fibroblast activation coupled with extracellular matrix production is a pathological signature of pulmonary fibrosis, and is governed by transforming growth factor (TGF)-ß1/Smad signalling. TGF-ß1 and oxidative stress cooperate to drive fibrosis. Cells can produce reactive oxygen species through activation and/or induction of NADPH oxidases, such as dual oxidase (DUOX1/2). Since DUOX enzymes, as extracellular hydrogen peroxide (H2O2--)-generating systems, are involved in extracellular matrix formation and in wound healing in different experimental models, we hypothesised that DUOX-based NADPH oxidase plays a role in the pathophysiology of pulmonary fibrosis.Our in vivo data (idiopathic pulmonary fibrosis patients and mouse models of lung fibrosis) showed that the NADPH oxidase DUOX1 is induced in response to lung injury. DUOX1-deficient mice (DUOX1+/- and DUOX1-/-) had an attenuated fibrotic phenotype. In addition to being highly expressed at the epithelial surface of airways, DUOX1 appears to be well expressed in the fibroblastic foci of remodelled lungs. By using primary human and mouse lung fibroblasts, we showed that TGF-ß1 upregulates DUOX1 and its maturation factor DUOXA1 and that DUOX1-derived H2O2 promoted the duration of TGF-ß1-activated Smad3 phosphorylation by preventing phospho-Smad3 degradation. Analysis of the mechanism revealed that DUOX1 inhibited the interaction between phospho-Smad3 and the ubiquitin ligase NEDD4L, preventing NEDD4L-mediated ubiquitination of phospho-Smad3 and its targeting for degradation.These findings highlight a role for DUOX1-derived H2O2 in a positive feedback that amplifies the signalling output of the TGF-ß1 pathway and identify DUOX1 as a new therapeutic target in pulmonary fibrosis.

Regulator of telomere length 1 (RTEL1) mutations are associated with heterogeneous pulmonary and extra-pulmonary phenotypes.

Regulator of telomere length 1 (RTEL1) mutations have been evidenced in 5-9% of familial pulmonary fibrosis; however, the phenotype of patients with interstitial lung disease (ILD) and RTEL1 mutations is poorly understood.Whole exome sequencing was performed in 252 probands with ILD and we included all patients with ILD and RTEL1 mutation. RTEL1 expression was evaluated by immunochemistry in the lungs of controls, as well as in RTEL1 and telomerase reverse transcriptase (TERT) mutation carriers.We identified 35 subjects from 17 families. Median age at diagnosis of ILD was 53.1 years (range 28.0-80.6). The most frequent pulmonary diagnoses were idiopathic pulmonary fibrosis (n=20, 57%), secondary ILD (n=7, 20%) and unclassifiable fibrosis or interstitial pneumonia with autoimmune features (n=7, 20%). The median transplant-free and overall survival periods were 39.2 months and 45.3 months, respectively. Forced vital capacity at diagnosis was the only factor associated with decreased transplant-free survival. Extra-pulmonary manifestations were less frequent as compared to other telomere-related gene mutation carriers. A systematic analysis of the literature identified 110 patients with ILD and RTEL1 mutations (including this series) and confirmed the heterogeneity of the pulmonary phenotype, the prevalence of non-idiopathic diseases and the low prevalence of extra-pulmonary manifestations.Immunohistochemistry showed that RTEL1 was expressed by bronchial and alveolar epithelial cells, as well as by alveolar macrophages and lymphocytes, but not by fibroblasts.

Human airway trypsin-like protease exerts potent, antifibrotic action in pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is characterized by the deposition of excessive extracellular matrix and the destruction of lung parenchyma, resulting from an aberrant wound-healing response. Although IPF is often associated with an imbalance in protease activity, the mechanisms underlying the sustained repair mechanisms are not fully understood. Here, we addressed the role of the recently identified, membrane-anchored serine protease human airway trypsin-like protease (HAT). In the present study, we show that both HAT expression and activity were up-regulated in human IPF specimens. Next, adenoviral overexpression of HAT before bleomycin challenge attenuated lung injury as well as extracellular matrix deposition in the bleomycin-induced pulmonary fibrosis model. In vitro, HAT prevented specific fibrosis-associated responses in primary human pulmonary fibroblasts and induced the expression of mediators associated with the prostaglandin E2 pathway. Altogether, our findings suggested that HAT could have a protective role in IPF and other fibrotic lung disorders.-Menou, A., Flajolet, P., Duitmen, J., Justet, A., Moog, S., Jaillet, M., Tabèze, L., Solhonne, B., Garnier, M., Mal, H., Mordant, P., Castier, Y., Cazes, A., Sallenave, J.-M., Mailleux, A. A., Crestani, B. Human airway trypsin-like protease exerts potent, antifibrotic action in pulmonary fibrosis.

FGF9 prevents pleural fibrosis induced by intrapleural adenovirus injection in mice.

Fibroblast growth factor 9 (FGF9) is necessary for fetal lung development and is expressed by epithelium and mesothelium. We evaluated the role of FGF9 overexpression on adenoviral-induced pleural injury in vivo and determined the biological effects of FGF9 on mesothelial cells in vitro. We assessed the expression of FGF9 and FGF receptors by mesothelial cells in both human and mouse lungs. Intrapleural injection of an adenovirus expressing human FGF9 (AdFGF9) or a control adenovirus (AdCont) was performed. Mice were euthanized at days 3, 5, and 14 Expression of FGF9 and markers of inflammation and myofibroblastic differentiation was studied by qPCR and immunohistochemistry. In vitro, rat mesothelial cells were stimulated with FGF9 (20 ng/ml), and we assessed its effect on proliferation, survival, migration, and differentiation. FGF9 was expressed by mesothelial cells in human idiopathic pulmonary fibrosis. FGF receptors, mainly FGFR3, were expressed by mesothelial cells in vivo in humans and mice. AdCont instillation induced diffuse pleural thickening appearing at day 5, maximal at day 14 The altered pleura cells strongly expressed α-smooth muscle actin and collagen. AdFGF9 injection induced maximal FGF9 expression at day 5 that lasted until day 14 FGF9 overexpression prevented pleural thickening, collagen and fibronectin accumulation, and myofibroblastic differentiation of mesothelial cells. In vitro, FGF9 decreased mesothelial cell migration and inhibited the differentiating effect of transforming growth factor-ß1. We conclude that FGF9 has a potential antifibrotic effect on mesothelial cells.

FGF9 and FGF18 in idiopathic pulmonary fibrosis promote survival and migration and inhibit myofibroblast differentiation of human lung fibroblasts in vitro.

Idiopathic pulmonary fibrosis (IPF) is characterized by an accumulation of extracellular matrix proteins and fibroblasts in the distal airways. Key developmental lung signaling pathways are reactivated in IPF. For instance, fibroblast growth factor 9 (FGF9) and FGF18, involved in epithelial-mesenchymal interactions, are critical for lung development. We evaluated the expression of FGF9, FGF18, and FGF receptors (FGFRs) in lung tissue from controls and IPF patients and assessed their effect on proliferation, survival, migration, and differentiation of control and IPF human lung fibroblasts (HLFs). FGF9, FGF18, and all FGFRs were present in the remodeled alveolar epithelium close to the fibroblast foci in IPF lungs. FGFR3 was generally detected in fibroblast foci by immunohistochemistry. In vitro, HLFs mainly expressed mesenchyme-associated FGFR isoforms (FGFR1c and FGFR3c) and FGFR4. FGF9 did not affect fibroblast proliferation, whereas FGF18 inhibited cell growth in control fibroblasts. FGF9 and FGF18 decreased Fas-ligand-induced apoptosis in control but not in IPF fibroblasts. FGF9 prevented transforming growth factor ß1-induced myofibroblast differentiation. FGF9 and FGF18 increased the migratory capacities of HLF, and FGF9 actively modulated matrix metalloproteinase activity. In addition, FGFR3 inhibition by small interfering RNA impacted p-ERK activation by FGF9 and FGF18 and their effects on differentiation and migration. These results identify FGF9 as an antiapoptotic and promigratory growth factor on HLF, maintaining fibroblasts in an undifferentiated state. The biological effects of FGF9 and FGF18 were partially driven by FGFR3. FGF18 was a less potent molecule. Both growth factors likely contribute to the fibrotic process in vivo.

COVID-19 PBMCs are doubly harmful, through LDN-mediated lung epithelial damage and monocytic impaired responsiveness to live Pseudomonas aeruginosa exposure.

Introduction: Although many studies have underscored the importance of T cells, phenotypically and functionally, fewer have studied the functions of myeloid cells in COVID disease. In particular, the potential role of myeloid cells such as monocytes and low-density neutrophils (LDNs) in innate responses and particular in the defense against secondary bacterial infections has been much less documented. Methods: Here, we compared, in a longitudinal study, healthy subjects, idiopathic fibrosis patients, COVID patients who were either hospitalized/moderate (M-) or admitted to ICU (COV-ICU) and patients in ICU hospitalized for other reasons (non-COV-ICU). Results: We show that COVID patients have an increased proportion of low-density neutrophils (LDNs), which produce high levels of proteases (particularly, NE, MMP-8 and MMP-9) (unlike non-COV-ICU patients), which are partly responsible for causing type II alveolar cell damage in co-culture experiments. In addition, we showed that M- and ICU-COVID monocytes had reduced responsiveness towards further live Pseudomonas aeruginosa (PAO1 strain) infection, an important pathogen colonizing COVID patients in ICU, as assessed by an impaired secretion of myeloid cytokines (IL-1, TNF, IL-8,…). By contrast, lymphoid cytokines (in particular type 2/type 3) levels remained high, both basally and post PAO1 infection, as reflected by the unimpaired capacity of T cells to proliferate, when stimulated with anti-CD3/CD28 beads. Discussion: Overall, our results demonstrate that COVID circulatory T cells have a biased type 2/3 phenotype, unconducive to proper anti-viral responses and that myeloid cells have a dual deleterious phenotype, through their LDN-mediated damaging effect on alveolar cells and their impaired responsiveness (monocyte-mediated) towards bacterial pathogens such as P. aeruginosa.

Identification of Paired-related Homeobox Protein 1 as a key mesenchymal transcription factor in pulmonary fibrosis.

Matrix remodeling is a salient feature of idiopathic pulmonary fibrosis (IPF). Targeting cells driving matrix remodeling could be a promising avenue for IPF treatment. Analysis of transcriptomic database identified the mesenchymal transcription factor PRRX1 as upregulated in IPF. PRRX1, strongly expressed by lung fibroblasts, was regulated by a TGF-ß/PGE2 balance in vitro in control and IPF human lung fibroblasts, while IPF fibroblast-derived matrix increased PRRX1 expression in a PDGFR-dependent manner in control ones. PRRX1 inhibition decreased human lung fibroblast proliferation by downregulating the expression of S phase cyclins. PRRX1 inhibition also impacted TGF-ß driven myofibroblastic differentiation by inhibiting SMAD2/3 phosphorylation through phosphatase PPM1A upregulation and TGFBR2 downregulation, leading to TGF-ß response global decrease. Finally, targeted inhibition of Prrx1 attenuated fibrotic remodeling in vivo with intra-tracheal antisense oligonucleotides in bleomycin mouse model of lung fibrosis and ex vivo using human and mouse precision-cut lung slices. Our results identified PRRX1 as a key mesenchymal transcription factor during lung fibrogenesis.

Inhibition of the Arp2/3 complex represses human lung myofibroblast differentiation and attenuates bleomycin-induced pulmonary fibrosis.

BACKGROUND AND PURPOSE: The Arp2/3 multiprotein complex regulates branched polymerisation of the actin cytoskeleton and may contribute to collagen synthesis and fibrogenesis in the lung. EXPERIMENTAL APPROACH: Expression of Arp2/3 components was assessed in human lung fibroblasts and in the bleomycin-induced pulmonary fibrosis model in mice. The Arp2/3 complex was repressed with the allosteric inhibitor CK666 and with interfering RNAs targeting the ARP2, ARP3 and ARPC2 subunits (siARP2, siARP3 and siARPC2) in CCD-16Lu human lung fibroblasts in vitro. Mice received daily intraperitoneal injections of CK666 from the 7th to the 14th day after tracheal bleomycin instillation. KEY RESULTS: Expression of Arp2/3 complex subunits mRNAs was increased in fibroblasts treated with TGF-ß1 and in the lungs of bleomycin-treated mice compared with controls. In vitro, CK666 and siARPC2 inhibited cell growth and TGF-ß1-induced α-smooth muscle actin (ACTA2) and collagen-1 (COL1) expression. CK666 also decreased ACTA2 and COL1 expression in unstimulated cells. CK666 reduced Akt phosphorylation and repressed phospho-GSK3ß, ß-catenin and MRTF-A levels in unstimulated fibroblasts. In vivo, CK666 reduced levels of both procollagen-1 and insoluble collagen in bleomycin-treated mice. CONCLUSION AND IMPLICATIONS: Expression of the Arp2/3 complex was increased in profibrotic environments in vitro and in vivo. Inhibition of the Arp2/3 complex repressed ACTA2 and COL1 expression and repressed an Akt/phospho-GSK3ß/ß-catenin/MRTF-A pathway in lung fibroblasts. CK666 exerted antifibrotic properties in the lung in vivo. Inhibition of the Arp2/3 complex could represent an interesting new therapy for idiopathic pulmonary fibrosis and other fibrotic interstitial lung diseases.

Lung Fibroblasts from Idiopathic Pulmonary Fibrosis Patients Harbor Short and Unstable Telomeres Leading to Chromosomal Instability.

Idiopathic pulmonary fibrosis (IPF) is associated with several hallmarks of aging including telomere shortening, which can result from germline mutations in telomere related genes (TRGs). Here, we assessed the length and stability of telomeres as well as the integrity of chromosomes in primary lung fibroblasts from 13 IPF patients (including seven patients with pathogenic variants in TRGs) and seven controls. Automatized high-throughput detection of telomeric FISH signals highlighted lower signal intensity in lung fibroblasts from IPF patients, suggesting a telomere length defect in these cells. The increased detection of telomere loss and terminal deletion in IPF cells, particularly in TRG-mutated cells (IPF-TRG), supports the notion that these cells have unstable telomeres. Furthermore, fibroblasts from IPF patients with TRGs mutations exhibited dicentric chromosomes and anaphase bridges. Collectively, our study indicates that fibroblasts from IPF patients exhibit telomere and chromosome instability that likely contribute to the physiopathology.

CCAAT/enhancer binding protein delta (C/EBPδ) deficiency does not affect bleomycin-induced pulmonary fibrosis.

BACKGROUND: Idiopathic pulmonary fibrosis is a devastating fibrotic diffuse parenchymal lung disorder that remains refractory to pharmacological therapies. Therefore, novel treatments are urgently required. CCAAT/enhancer binding protein delta (C/EBPδ) is a transcription factor that mediates critical cellular functions in pathophysiology and which was recently suggested to be a key regulatory component in IPF. The purpose of this study was to prove or refute the importance of C/EBPδ in pulmonary fibrosis. METHODS: Pulmonary fibrosis was induced by intranasal instillation of bleomycin into wild-type and C/EBPδ deficient mice. At different time intervals after bleomycin instillation, fibrosis was assessed by hydroxyproline analysis, histochemistry and q-PCR for fibrotic marker expression. RESULTS: C/EBPδ deficient mice developed pulmonary fibrosis to a similar degree as wildtype mice as evident from similar Ashcroft scores, hydroxyproline levels and expression levels of collagen, fibronectin and α-smooth muscle actin at both 14 and 21 days after bleomycin instillation. The resolution of fibrosis, assessed at 48 days after bleomycin instillation, was also similar in wildtype and C/EBPδ deficient mice. In line with the lack of effect of C/EBPδ on fibrosis progression/resolution, macrophage recruitment and/or differentiation were also not different in wildtype or C/EBPδ deficient mice. CONCLUSIONS: Overall, C/EBPδ does not seem to affect bleomycin-induced experimental pulmonary fibrosis and we challenge the importance of C/EBPδ in pulmonary fibrosis. RELEVANCE FOR PATIENTS: This study shows that the transcription factor C/EBPδ does not play a major role in the development of pulmonary fibrosis. Pharmacological targeting of C/EBPδ is therefore not likely to have a beneficial effect for patients suffering from pulmonary fibrosis.

Identification of periplakin as a major regulator of lung injury and repair in mice.

Periplakin is a component of the desmosomes that acts as a cytolinker between intermediate filament scaffolding and the desmosomal plaque. Periplakin is strongly expressed by epithelial cells in the lung and is a target antigen for autoimmunity in idiopathic pulmonary fibrosis. The aim of this study was to determine the role of periplakin during lung injury and remodeling in a mouse model of lung fibrosis induced by bleomycin. We found that periplakin expression was downregulated in the whole lung and in alveolar epithelial cells following bleomycin-induced injury. Deletion of the Ppl gene in mice improved survival and reduced lung fibrosis development after bleomycin-induced injury. Notably, Ppl deletion promoted an antiinflammatory alveolar environment linked to profound changes in type 2 alveolar epithelial cells, including overexpression of antiinflammatory cytokines, decreased expression of profibrotic mediators, and altered cell signaling with a reduced response to TGF-ß1. These results identify periplakin as a previously unidentified regulator of the response to injury in the lung.

The pro-apoptotic BAX protein influences cell growth and differentiation from the nucleus in healthy interphasic cells.

It has become more and more evident that the BCL-2 family proteins mediate a wide range of non-apoptotic functions. The pro-apoptotic BAX protein has been reported in interphasic nuclei. Whether the nuclear form of BAX could be involved in non-apoptotic function is still unknown. Our study showed for the first time that BAX was associated with chromatin in vitro. Next, we used gain and loss of function approaches to decipher the potential role of nuclear BAX in non-apoptotic cells. In vitro, nuclear BAX promoted cell proliferation in lung epithelial cells and primary human lung fibroblasts by modulating CDKN1A expression. Interestingly, BAX occupancy of CDKN1A promoter was specifically enriched close to the transcription-starting site. Nuclear BAX also modulated the basal myofibroblastic differentiation and migration of primary human lung fibroblasts. Finally, BAX nuclear localization was associated in vivo with the remodelling of lung parenchyma during development, tumorigenesis as well as fibrosis compared to control adult human lungs. Hence, our study established for the first time, a strong link between the nuclear localization of the pro-apoptotic BAX protein and key basic cellular functions in the non-apoptotic setting.

Transgenic kallikrein 5 mice reproduce major cutaneous and systemic hallmarks of Netherton syndrome.

Netherton syndrome (NS) is a severe genetic skin disease in which absence of a key protease inhibitor causes congenital exfoliative erythroderma, eczematous-like lesions, and atopic manifestations. Several proteases are overactive in NS, including kallikrein-related peptidase (KLK) 5, KLK7, and elastase-2 (ELA2), which are suggested to be part of a proteolytic cascade initiated by KLK5. To address the role of KLK5 in NS, we have generated a new transgenic murine model expressing human KLK5 in the granular layer of the epidermis (Tg-KLK5). Transgene expression resulted in increased proteolytic activity attributable to KLK5 and its downstream targets KLK7, KLK14, and ELA2. Tg-KLK5 mice developed an exfoliative erythroderma with scaling, growth delay, and hair abnormalities. The skin barrier was defective and the stratum corneum was detached through desmosomal cleavage. Importantly, Tg-KLK5 mice displayed cutaneous and systemic hallmarks of severe inflammation and allergy with pruritus. The skin showed enhanced expression of inflammatory cytokines and chemokines, infiltration of immune cells, and markers of Th2/Th17/Th22 T cell responses. Moreover, serum IgE and Tslp levels were elevated. Our study identifies KLK5 as an important contributor to the NS proteolytic cascade and provides a new and viable model for the evaluation of future targeted therapies for NS or related diseases such as atopic dermatitis.