STAT3-dependent CXC chemokine formation and neutrophil migration in streptococcal M1 protein-induced acute lung inflammation

Stat3 Regulates Developmental Hematopoiesis and Impacts Myeloid Cell Function via Canonical and Non-Canonical Modalities

INTRODUCTION

Signal transducer and activator of transcription (STAT) 3 is extensively involved in the development, homeostasis, and function of immune cells, with STAT3 disruption associated with human immune-related disorders. The roles ascribed to STAT3 have been assumed to be due to its canonical mode of action as an inducible transcription factor downstream of multiple cytokines, although alternative noncanonical functional modalities have also been identified. The relative involvement of each mode was further explored in relevant zebrafish models.

METHODS

Genome editing with CRISPR/Cas9 was used to generate mutants of the conserved zebrafish Stat3 protein: a loss of function knockout (KO) mutant and a mutant lacking C-terminal sequences including the transactivation domain (ΔTAD). Lines harboring these mutations were analyzed with respect to blood and immune cell development and function in comparison to wild-type zebrafish.

RESULTS

The Stat3 KO mutant showed perturbation of hematopoietic lineages throughout primitive and early definitive hematopoiesis. Neutrophil numbers did not increase in response to lipopolysaccharide (LPS) or granulocyte colony-stimulating factor (G-CSF) and their migration was significantly diminished, the latter correlating with abrogation of the Cxcl8b/Cxcr2 pathway, with macrophage responses perturbed. Intriguingly, many of these phenotypes were not shared by the Stat3 ΔTAD mutant. Indeed, only neutrophil and macrophage development were disrupted in these mutants with responsiveness to LPS and G-CSF maintained, and neutrophil migration actually increased.

CONCLUSION

This study has identified roles for zebrafish Stat3 within hematopoietic stem cells impacting multiple lineages throughout primitive and early definitive hematopoiesis, myeloid cell responses to G-CSF and LPS and neutrophil migration. Many of these roles showed conservation, but notably several involved noncanonical modalities, providing additional insights for relevant diseases.

Signaling through the IL-6-STAT3 Pathway Promotes Proteolytically-Active Macrophage Accumulation Necessary for Development of Small AAA

INTRODUCTION

Elevated interleukin-6 (IL-6) plasma levels have been associated with abdominal aortic aneurysm (AAA), but whether this cytokine plays a causative role in the degenerative remodeling or represents an effect from the inflammatory cascades initiated by infiltrating leukocytes remained unclear. This project aims to demonstrate that within the aortic wall, signaling from IL-6 through the STAT3 transcription factor is necessary for infiltration of proteolytically-active macrophages and development of small AAA.

METHODS

Following measurement of baseline infrarenal aortic diameter (AoD, digital microscopy), C57Bl/6 and IL-6 knockout (IL-6KO) mice underwent AAA induction by application of peri-adventitial CaCl2 (0.5 M) +/- implantation of an osmotic mini-pump delivering IL-6 (4.36 µg/kg/day over 21 days). At the terminal procedure, AoDs were measured by digital microscopy and aortas harvested for immunoblot (pSTAT3/STAT3), matrix metalloproteinase (MMP) quantification, or flow cytometric analysis of macrophage content. Plasma was collected for cytokine analysis.

RESULTS

IL-6 infusion significantly increased the plasma IL-6 levels in C57Bl/6 and IL-6KO animals. The C57Bl/6 + CaCl2 group developed AAA (AoD >50% above baseline) but IL-6KO + CaCl2 did not. In the IL-6KO + IL-6+CaCl2 group, AAA developed to match that of C57Bl/6 + CaCl2 mice. STAT3 activity was significantly increased in animals with advanced stages of dilation (>40% from baseline), compared to those with ectasia (≤25%). Although cytokine profiles did not support T-cells or neutrophils as being active contributors in this stage of aortic remodeling, changes in the profile of elaborated MMPs suggested macrophage activity with a trend toward alternatively activated pathways. Flow cytometry confirmed significantly increased macrophage abundance specifically in animals with upregulated STAT3 activity and advanced aortic dilation.

CONCLUSION

In this murine model of AAA, progressive dilation to development of true AAA was only accomplished when IL-6 signaling upregulated STAT3 activity to effect accumulation of proteolytically-active macrophages. This pathway warrants further investigation to identify potential therapeutic avenues to abrogate growth of small AAA.

microRNA-193-3p attenuates myocardial injury of mice with sepsis via STAT3/HMGB1 axis

Objective

Little is known regarding the functional role of microRNA-193-3p (miR-193-3p) in sepsis. Hence, the aim of the present study was to investigate the effect of miR-193-3p on myocardial injury in mice with sepsis and its mechanism through the regulation of signal transducers and activators of transcription 3 (STAT3).

Methods

The mice model of sepsis was established by cecal ligation and puncture (CLP), septic mice were injected with miR-193-3p agomir, miR-193-3p antagomir or siRNA-STAT3. The expression of miR-193-3p, STAT3 and HMGB1 in the myocardial tissue of septic mice were detected. Cardiac ultrasound, hemodynamics, myocardial injury markers, inflammatory factors and cardiomyocyte apoptosis in septic mice were measured.

Results

MiR-193-3p expression was reduced while STAT3 expression was increased in septic mice. Down-regulated STAT3 or up-regulated miR-193-3p improved cardiac function, attenuated myocardial injury, inflammation and cardiomyocyte apoptosis in septic mice. Knockdown STAT3 reversed the role of inhibited miR-193-3p for mice with sepsis. miR-193-3p targeted STAT3, thereby inhibiting HMGB1 expression.

Conclusion

This study provides evidence that miR-193-3p targets STAT3 expression to reduce HMGB1 expression, thereby reducing septic myocardial damage. MiR-193-3p might be a potential candidate marker and therapeutic target for sepsis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03022-x.

STAT3-activated lncRNA XIST accelerates the inflammatory response and apoptosis of LPS-induced acute lung injury

Acute lung injury (ALI) is a severe lung respiratory failure characterized by high morbidity and mortality. Novel findings demonstrated the critical roles of long non-coding RNA (lncRNA) in ALI. Here, we tried to investigate the roles and potential mechanism of lncRNA X-inactive specific transcript (XIST) in ALI. Results illustrated that lncRNA XIST was up-regulated in the lipopolysaccharide (LPS)-induced ALI mice models and pulmonary endothelial cells. Biofunctional assays unveiled that knockdown of XIST repressed the inflammatory response and apoptosis in LPS-induced endothelial cells. Mechanistically, XIST acted as the miR-146a-5p sponge to positively regulate STAT3. Moreover, STAT3 combined the promoter region of XIST to accelerate the transcription, constituting the positive feedback loop of XIST/miR-146a-5p/STAT3 in ALI. Collectively, these findings suggested that XIST knockdown attenuates the LPS-induced ALI, providing a potential therapeutic target.

STAT3 Activation Correlates with Adventitial Neutrophil Infiltration in Human Aortic Dissection

Objective: Aortic dissection (AD) is a fatal disease that is caused by the rapid destruction of the aortic wall. Although recent studies in animal models indicate an important relationship between inflammation and tissue destruction, activation status of inflammatory signaling and its relation to the inflammatory cell infiltration are poorly characterized in human AD.

Materials and Methods: We examined the activation of inflammatory signaling molecules NFκB and STAT3, and neutrophil infiltration in AD tissue samples that were obtained during the surgical repair within 24 h after AD onset.

Results: Activation of NFκB was observed mainly in the intima both in AD samples and in aortic samples without AD. Activation of STAT3 was observed in AD samples, but not in the aortic sample without AD. Neutrophil infiltration was observed predominantly in the adventitial layer of AD samples. Histological analysis revealed that STAT3 was activated in cells other than neutrophils. Notably, STAT3 activation and neutrophil infiltration showed positive correlation in adventitial layer of AD tissue.

Conclusion: These findings demonstrated that adventitial STAT3 activation was associated with neutrophil infiltration, suggesting their importance in AD pathogenesis.

Organic dust induces inflammatory gene expression in lung epithelial cells via ROS-dependent STAT-3 activation

Exposure to dust in agricultural and animal environments, known as organic dust, is associated with the development of respiratory symptoms and respiratory diseases. Inflammation is a key feature of lung pathologies associated with organic dust exposure, and exposure to organic dust induces the expression of several immune and inflammatory mediators. However, information on transcription factors and cellular and molecular mechanisms controlling the production of immune and inflammatory mediators induced by organic dust is limited. In this study, we have identified STAT-3 as an important transcription factor controlling the induction of expression of immune and inflammatory mediators by poultry dust extracts in airway epithelial cells and in mouse lungs and delineated the cellular pathway for STAT-3 activation. Poultry dust extract activated STAT-3 phosphorylation in Beas2B and normal human bronchial epithelial cells and in mouse lungs. Chemical inhibition and siRNA knockdown of STAT-3 suppressed induction of immune and inflammatory mediator expression. Antioxidants suppressed the increase of STAT-3 phosphorylation induced by poultry dust extract indicating that oxidative stress [elevated reactive oxygen species (ROS) levels] is important for the activation. Chemical inhibition and siRNA knockdown experiments demonstrated that STAT-3 activation is dependent on the activation of nonreceptor tyrosine-protein kinase 2 (TYK2) and epidermal growth factor receptor (EGFR) tyrosine kinases. Our studies show that poultry dust extract controls the induction of immune and inflammatory mediator expression via a cellular pathway involving oxidative stress-mediated STAT-3 activation by TYK2 and EGFR tyrosine kinases.

IFNAR2 Is Required for Anti-influenza Immunity and Alters Susceptibility to Post-influenza Bacterial Superinfections

Influenza virus infections particularly when followed by bacterial superinfections (BSI) result in significant morbidities and mortalities especially during influenza pandemics. Type I interferons (IFNs) regulate both anti-influenza immunity and host susceptibility to subsequent BSIs. These type I IFNs consisting of, among others, 14 IFN-α's and a single IFN-β, are recognized by and signal through the heterodimeric type I IFN receptor (IFNAR) comprised of IFNAR1 and IFNAR2. However, the individual receptor subunits can bind IFN-β or IFN-α's independently of each other and induce distinct signaling. The role of type I IFN signaling in regulating host susceptibility to both viral infections and BSI has been only examined with respect to IFNAR1 deficiency. Here, we demonstrate that despite some redundancies, IFNAR1 and IFNAR2 have distinct roles in regulating both anti-influenza A virus (IAV) immunity and in shaping host susceptibility to subsequent BSI caused by S. aureus. We found IFNAR2 to be critical for anti-viral immunity. In contrast to Ifnar1^−/− mice, IAV-infected Ifnar2^−/− mice displayed both increased and accelerated morbidity and mortality compared to WT mice. Furthermore, unlike IFNAR1, IFNAR2 was sufficient to generate protection from lethal IAV infection when stimulated with IFN-β. With regards to BSI, unlike what we found previously in Ifnar1^−/− mice, Ifnar2^−/− mice were not susceptible to BSI induced on day 3 post-IAV, even though absence of IFNAR2 resulted in increased viral burden and an increased inflammatory environment. The Ifnar2^−/− mice similar to what we previously found in Ifnar1^−/− mice were less susceptible than WT mice to BSI induced on day 7 post-IAV, indicating that signaling through a complete receptor increases BSI susceptibility late during clinical IAV infection. Thus, our results support a role for IFNAR2 in induction of anti-IAV immune responses that are involved in altering host susceptibility to BSI and are essential for decreasing the morbidity and mortality associated with IAV infection. These results begin to elucidate some of the mechanisms involved in how the individual IFNAR subunits shape the anti-viral immune response. Moreover, our results highlight the importance of examining the contributions of entire receptors, as individual subunits can induce distinct outcomes as shown here.

Genetic rescue of lineage-balanced blood cell production reveals a crucial role for STAT3 antiinflammatory activity in hematopoiesis

Blood cell formation must be appropriately maintained throughout life to provide robust immune function, hemostasis, and oxygen delivery to tissues, and to prevent disorders that result from over- or underproduction of critical lineages. Persistent inflammation deregulates hematopoiesis by damaging hematopoietic stem and progenitor cells (HSPCs), leading to elevated myeloid cell output and eventual bone marrow failure. Nonetheless, antiinflammatory mechanisms that protect the hematopoietic system are understudied. The transcriptional regulator STAT3 has myriad roles in HSPC-derived populations and nonhematopoietic tissues, including a potent antiinflammatory function in differentiated myeloid cells. STAT3 antiinflammatory activity is facilitated by STAT3-mediated transcriptional repression of Ube2n, which encodes the E2 ubiquitin-conjugating enzyme Ubc13 involved in proinflammatory signaling. Here we demonstrate a crucial role for STAT3 antiinflammatory activity in preservation of HSPCs and lineage-balanced hematopoiesis. Conditional Stat3 removal from the hematopoietic system led to depletion of the bone marrow lineage- Sca-1+ c-Kit+ CD150+ CD48- HSPC subset (LSK CD150+ CD48- cells), myeloid-skewed hematopoiesis, and accrual of DNA damage in HSPCs. These responses were accompanied by intrinsic transcriptional alterations in HSPCs, including deregulation of inflammatory, survival and developmental pathways. Concomitant Ube2n/Ubc13 deletion from Stat3-deficient hematopoietic cells enabled lineage-balanced hematopoiesis, mitigated depletion of bone marrow LSK CD150+ CD48- cells, alleviated HSPC DNA damage, and corrected a majority of aberrant transcriptional responses. These results indicate an intrinsic protective role for STAT3 in the hematopoietic system, and suggest that this is mediated by STAT3-dependent restraint of excessive proinflammatory signaling via Ubc13 modulation.

Recent advances in our understanding of the mechanisms of late lung development and bronchopulmonary dysplasia

The objective of lung development is to generate an organ of gas exchange that provides both a thin gas diffusion barrier and a large gas diffusion surface area, which concomitantly generates a steep gas diffusion concentration gradient. As such, the lung is perfectly structured to undertake the function of gas exchange: a large number of small alveoli provide extensive surface area within the limited volume of the lung, and a delicate alveolo-capillary barrier brings circulating blood into close proximity to the inspired air. Efficient movement of inspired air and circulating blood through the conducting airways and conducting vessels, respectively, generates steep oxygen and carbon dioxide concentration gradients across the alveolo-capillary barrier, providing ideal conditions for effective diffusion of both gases during breathing. The development of the gas exchange apparatus of the lung occurs during the second phase of lung development-namely, late lung development-which includes the canalicular, saccular, and alveolar stages of lung development. It is during these stages of lung development that preterm-born infants are delivered, when the lung is not yet competent for effective gas exchange. These infants may develop bronchopulmonary dysplasia (BPD), a syndrome complicated by disturbances to the development of the alveoli and the pulmonary vasculature. It is the objective of this review to update the reader about recent developments that further our understanding of the mechanisms of lung alveolarization and vascularization and the pathogenesis of BPD and other neonatal lung diseases that feature lung hypoplasia.

Endothelial fibrosis induced by suppressed STAT3 expression mediated by signaling involving the TGF-β1/ALK5/Smad pathway

During systemic inflammatory pathologies, mediators of inflammation circulate in the bloodstream and interact with endothelial cells (ECs), resulting in endothelial dysfunction that maintains and enhances the pathological condition. Inflammatory mediators change the protein expression profile of ECs, which become activated fibroblasts via endothelial-to-mesenchymal transition. This process is characterized by downregulated endothelial proteins and strongly upregulated fibrotic-specific genes and extracellular matrix-forming proteins. The main inductor of endothelial fibrosis is transforming growth factor-β1 (TGF-β1), which acts through the TGF-β1/activin receptor-like kinase 5 (ALK5)/Smads intracellular signaling pathway. The signal transducer and activator of transcription 3 (STAT3) is also involved in fibrosis in several tissues (e.g. heart and vascular system), where STAT3 signaling decreases TGF-β1-induced responses by directly interacting with Smad proteins, suggesting that decreased STAT3 could induce TGF-β1-mediated fibrosis. However, it is unknown if suppressed STAT3 expression induces EC fibrosis through a mechanism involving the TGF-β signaling pathway. The present study evaluated the fibrotic actions of STAT3 suppression in ECs and investigated TGF-β1/ALK5/Smad4 signaling pathway participation. Suppressed STAT3 expression stimulated fibrotic conversion in ECs, as mediated by protein expression reprograming that decreased endothelial marker expression and increased fibrotic and extracellular matrix protein levels. The potential mechanism underlying these changes was dependent on TGF-β1 secretion, the ALK5 activation pathway, and Smad4 translocation into the nucleus. We conclude that suppressed STAT3 expression converts ECs into activated fibroblasts via TGF-β1/ALK5/Smad4 signaling pathway involvement.

Extravillous Trophoblast and Endothelial Cell Crosstalk Mediates Leukocyte Infiltration to the Early Remodeling Decidual Spiral Arteriole Wall

Decidual spiral arteriole (SpA) remodeling is essential to ensure optimal uteroplacental blood flow during human pregnancy, yet very little is known about the regulatory mechanisms. Uterine decidual NK (dNK) cells and macrophages infiltrate the SpAs and are proposed to initiate remodeling before colonization by extravillous trophoblasts (EVTs); however, the trigger for their infiltration is unknown. Using human first trimester placenta, decidua, primary dNK cells, and macrophages, we tested the hypothesis that EVTs activate SpA endothelial cells to secrete chemokines that have the potential to recruit maternal immune cells into SpAs. Gene array, real-time PCR, and ELISA analyses showed that treatment of endothelial cells with EVT conditioned medium significantly increased production of two chemokines, CCL14 and CXCL6. CCL14 induced chemotaxis of both dNK cells and decidual macrophages, whereas CXCL6 also induced dNK cell migration. Analysis of the decidua basalis from early pregnancy demonstrated expression of CCL14 and CXCL6 by endothelial cells in remodeling SpAs, and their cognate receptors are present in both dNK cells and macrophages. Neutralization studies identified IL-6 and CXCL8 as factors secreted by EVTs that induce endothelial cell CCL14 and CXCL6 expression. This study has identified intricate crosstalk between EVTs, SpA cells, and decidual immune cells that governs their recruitment to SpAs in the early stages of remodeling and has identified potential key candidate factors involved. This provides a new understanding of the interactions between maternal and fetal cells during early placentation and highlights novel avenues for research to understand defective SpA remodeling and consequent pregnancy pathology.