CCAAT/enhancer-binding protein δ is a critical mediator of lipopolysaccharide-induced acute lung injury

PD-L1 Expression Is Increased in LPS-Induced Acute Respiratory Distress Syndrome by PI3K-AKT-Egr-1/C/EBPδ Signaling Pathway

The role of programmed death ligand 1 (PD-L1) has been extensively investigated in adaptive immune system. However, increasing data show that innate immune responses are also affected by the immune checkpoint molecule. It has been demonstrated that regulation of PD-L1 signaling in macrophages may be a potential therapeutic method for acute respiratory distress syndrome (ARDS). However, the PD-L1 expression pattern in local macrophages and whole lung tissues remains mysterious, hindering optimization of the potential treatment program. Therefore, we aim to determine the PD-L1 expression pattern during ARDS. Our findings show that PD-L1 levels are markedly increased in lipopolysaccharide (LPS)-stimulated lung tissues, which might be attributable to an increase in the gene expression by immune cells, including macrophages and neutrophils. In vitro experiments are performed to explore the mechanism involved in LPS-induced PD-L1 production. We find that PD-L1 generation is controlled by transcription factors early growth response 1 (Egr-1) and CCAAT/enhancer binding protein delta (C/EBPδ). Strikingly, PD-L1 production is enhanced by phosphoinositide-3 kinase (PI3K)-protein kinase B (AKT) signaling pathway via up-regulation of Egr-1 and C/EBPδ expressions. Additionally, we observe that expressions of Egr-1 and C/EBPδ mutually reinforce each other. Moreover, we observe that PD-L1 is protective for ARDS due to its regulatory role in macrophage-associated inflammatory response. In summary, during LPS-induced ARDS, PD-L1 expression, which is beneficial for the disease, is increased via the PI3K-AKT1-Egr-1/C/EBPδ signaling pathway, providing theoretical basis for application of methods controlling PD-L1 signaling in macrophages for ARDS treatment in clinic.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

CEBPD modulates the airway smooth muscle transcriptomic response to glucocorticoids

Background

CCAAT/Enhancer Binding Protein D (CEBPD), a pleiotropic glucocorticoid-responsive transcription factor, modulates inflammatory responses. Of relevance to asthma, expression of CEBPD in airway smooth muscle (ASM) increases with glucocorticoid exposure. We sought to characterize CEBPD-mediated transcriptomic responses to glucocorticoid exposure in ASM by measuring changes observed after knockdown of CEBPD and its impact on asthma-related ASM function.

Methods

Primary ASM cells derived from four donors were transfected with CEBPD or non-targeting (NT) siRNA and exposed to vehicle control, budesonide (100 nM, 18 h), TNFα (10 ng/ml, 18 h), or both budesonide and TNFα. Subsequently, RNA-Seq was used to measure gene expression levels, and pairwise differential expression results were obtained for exposures versus vehicle and knockdown versus control conditions. Weighted gene co-expression analysis was performed to identify groups of genes with similar expression patterns across the various experimental conditions (i.e., CEBPD knockdown status, exposures).

Results

CEBPD knockdown altered expression of 3037 genes under at least one exposure (q-value < 0.05). Co-expression analysis identified sets of 197, 152 and 290 genes that were correlated with CEBPD knockdown status, TNFα exposure status, and both, respectively. JAK-STAT signaling pathway genes, including IL6R and SOCS3, were among those influenced by both TNFα and CEBPD knockdown. Immunoblot assays revealed that budesonide-induced IL-6R protein expression and augmented IL-6-induced STAT3 phosphorylation levels were attenuated by CEBPD knockdown in ASM.

Conclusions

CEBPD modulates glucocorticoid responses in ASM, in part via modulation of IL-6 receptor signaling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02119-1.

C/EBPδ-induced epigenetic changes control the dynamic gene transcription of S100a8 and S100a9

The proinflammatory alarmins S100A8 and S100A9 are among the most abundant proteins in neutrophils and monocytes but are completely silenced after differentiation to macrophages. The molecular mechanisms of the extraordinarily dynamic transcriptional regulation of S100a8 and S100a9 genes, however, are only barely understood. Using an unbiased genome-wide CRISPR/Cas9 knockout (KO)-based screening approach in immortalized murine monocytes, we identified the transcription factor C/EBPδ as a central regulator of S100a8 and S100a9 expression. We showed that S100A8/A9 expression and thereby neutrophil recruitment and cytokine release were decreased in C/EBPδ KO mice in a mouse model of acute lung inflammation. S100a8 and S100a9 expression was further controlled by the C/EBPδ antagonists ATF3 and FBXW7. We confirmed the clinical relevance of this regulatory network in subpopulations of human monocytes in a clinical cohort of cardiovascular patients. Moreover, we identified specific C/EBPδ-binding sites within S100a8 and S100a9 promoter regions, and demonstrated that C/EBPδ-dependent JMJD3-mediated demethylation of H3K27me₃ is indispensable for their expression. Overall, our work uncovered C/EBPδ as a novel regulator of S100a8 and S100a9 expression. Therefore, C/EBPδ represents a promising target for modulation of inflammatory conditions that are characterized by S100a8 and S100a9 overexpression.

CEBPD Potentiates the Macrophage Inflammatory Response but CEBPD Knock-Out Macrophages Fail to Identify CEBPD-Dependent Pro-Inflammatory Transcriptional Programs

CCAAT/enhancer-binding protein delta (C/EBPδ) is a member of the C/EBP family of transcription factors. According to the current paradigm, C/EBPδ potentiates cytokine production and modulates macrophage function thereby enhancing the inflammatory response. Remarkably, however, C/EBPδ deficiency does not consistently lead to a reduction in Lipopolysaccharide (LPS)-induced cytokine production by macrophages. Here, we address this apparent discrepancy and show that the effect of C/EBPδ on cytokine production and macrophage function depends on both the macrophage subtype and the LPS concentration used. Using CRISPR-Cas generated macrophages in which the transactivation domain of C/EBPδ was deleted from the endogenous locus (ΔTAD macrophages), we next show that the context-dependent role of C/EBPδ in macrophage biology relies on compensatory transcriptional activity in the absence of C/EBPδ. We extend these findings by revealing a large discrepancy between transcriptional programs in C/EBPδ knock-out and C/EBPδ transactivation dead (ΔTAD) macrophages implying that compensatory mechanisms do not specifically modify C/EBPδ-dependent inflammatory responses but affect overall macrophage biology. Overall, these data imply that knock-out approaches are not suited for identifying the genuine transcriptional program regulated by C/EBPδ, and we suggest that this phenomenon applies for transcription factor families in general.

High-Throughput Screening for CEBPD-Modulating Compounds in THP-1-Derived Reporter Macrophages Identifies Anti-Inflammatory HDAC and BET Inhibitors

This study aimed to identify alternative anti-inflammatory compounds that modulate the activity of a relevant transcription factor, CCAAT/enhancer binding protein delta (C/EBPδ). C/EBPδ is a master regulator of inflammatory responses in macrophages (Mϕ) and is mainly regulated at the level of CEBPD gene transcription initiation. To screen for CEBPD-modulating compounds, we generated a THP-1-derived reporter cell line stably expressing secreted alkaline phosphatase (SEAP) under control of the defined CEBPD promoter (CEBPD::SEAP). A high-throughput screening of LOPAC^®1280 and ENZO^®774 libraries on LPS- and IFN-γ-activated THP-1 reporter Mϕ identified four epigenetically active hits: two bromodomain and extraterminal domain (BET) inhibitors, I-BET151 and Ro 11-1464, as well as two histone deacetylase (HDAC) inhibitors, SAHA and TSA. All four hits markedly and reproducibly upregulated SEAP secretion and CEBPD::SEAP mRNA expression, confirming screening assay reliability. Whereas BET inhibitors also upregulated the mRNA expression of the endogenous CEBPD, HDAC inhibitors completely abolished it. All hits displayed anti-inflammatory activity through the suppression of IL-6 and CCL2 gene expression. However, I-BET151 and HDAC inhibitors simultaneously upregulated the mRNA expression of pro-inflammatory IL-1ß. The modulation of CEBPD gene expression shown in this study contributes to our understanding of inflammatory responses in Mϕ and may offer an approach to therapy for inflammation-driven disorders.

C/EBPγ is a critical negative regulator of LPS-/IgG immune complex-induced acute lung injury through the downregulation of C/EBPβ-/C/EBPδ-dependent C/EBP transcription activation

Acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome are life-threatening diseases. Despite recent advances in intensive care medicine, the mortality is still as high as 50%, which stems from our insufficient understanding of the underlying mechanisms of the diseases. The roles of C/EBPβ and C/EBPδ have been extensively investigated in LPS- and IgG immune complexes-stimulated acute lung injury. However, the effect of C/EBPγ, belonging to the same family as C/EBPβ and C/EBPδ, on ALI has not been elucidated. Our previous data have shown that during LPS-/IgG immune complexes-induced ALI, the DNA binding activities of C/EBPγ are obviously reduced. In the present study, we determine whether ALI induced by LPS and IgG immune complexes is affected by C/EBPγ. We find that adenovirus-mediated C/EBPγ expression in the lung tissue alleviates LPS-/IgG immune complexes-stimulated acute pulmonary damage through reducing vascular permeability changes and recruitment of neutrophils into alveolar spaces, which might be linked to a decrease in the production of pro-inflammatory mediators, such as TNF-α and IL-6. Moreover, our data obtained from macrophages in vitro are consistent with the in vivo results. In terms of mechanisms, C/EBPγ might inhibit LPS-/IgG immune complexes-mediated inflammation via alleviating C/EBPβ and C/EBPδ transcription activities as reflected by luciferase assays. However, the NF-κB-dependent production of pro-inflammatory mediators is not affected by C/EBPγ. Taken together, C/EBPγ suppresses LPS- and IgG immune complexes-induced pro-inflammatory mediators' production through the downregulation of C/EBP but not NF-κB activation, leading to the subsequent attenuation of ALI. Collectively, our data provide an insight into the critical role of C/EBPγ in acute lung injury.

Low-Intensity Exercise Suppresses CCAAT/Enhancer-Binding Protein δ/Myostatin Pathway Through Androgen Receptor in Muscle Cells

BACKGROUND

Androgen production following exercise has been suggested to contribute anabolic actions of muscle. However, the underlying mechanisms of the androgen receptor (AR) in androgen's action are still unclear.

OBJECTIVE

In the present study, we examined androgen/AR-mediated action in exercise, especially for the suppression of myostatin, a potent negative regulator of muscle mass.

METHODS

To examine the effects of exercise, we employed low-intensity exercise in mice and electric pulse stimulation (EPS) in C2C12 myotubes. Androgen production by C2C12 myotubes was measured by enzyme-linked immunosorbent assay. To block the action of AR, we pretreated C2C12 myotubes with flutamide. Quantitative real-time polymerase chain reaction was used to determine the expression levels of proteolytic genes including CCAAT/enhancer-binding protein delta (C/EBPδ), myostatin and muscle E3 ubiquitin ligases, as well as myogenic genes such as myogenin and PGC1α. The activation of 5'-adenosine-activated protein kinase and STAT3 was determined by Western blot analysis.

RESULTS

Both mRNA and protein levels of AR significantly increased in skeletal muscle of low-intensity exercised mice and C2C12 myotubes exposed to EPS. Production of testosterone and dihydrotestosterone from EPS-treated C2C12 myotubes was markedly increased. Of interest, we found that myostatin was clearly inhibited by EPS, and its inhibition was significantly abrogated when AR was blocked by flutamide. To test how AR suppresses myostatin, we examined the effects of EPS on C/EBPδ because the promoter region of myostatin has several C/EBP recognition sites. C/EBPδ expression was decreased by EPS, and this decrease was negated by flutamide. IL-6 and phospho-STAT3 (pSTAT3) expression, the downstream pathway of myostatin, were decreased by EPS and this was also reversed by flutamide. Similar downregulation of C/EBPδ, myostatin, and IL-6 was seen in skeletal muscle of low-intensity exercised mice.

CONCLUSIONS

Muscle AR expression and androgen production were increased by exercise and EPS treatment. As a mechanistical insight, it is suggested that AR inhibited myostatin expression transcriptionally by C/EBPδ suppression, which negatively influences IL-6/pSTAT3 expression and consequently contributes to the prevention of muscle proteolysis during exercise.

Involvement of multiple transcription factors in regulation of IL-β-induced MCP-1 expression in alveolar type II epithelial cells

During acute lung injury, a large number of monocytes are recruited into the pulmonary tissue, which is mainly mediated by local production of monocyte chemotactic protein 1 (MCP-1). As an essential component of the lung tissues, alveolar type II epithelial cells are one of the major sources of MCP-1. Therefore, uncovering the mechanism whereby MCP-1 production is regulated in the alveolar type II cells will provide a pivotal theoretical basis for clinical intervention in acute lung injury. In the current study, we find that there is a κB binding site in the MCP-1 promoter region, and mutation of the site leads to reduced production of MCP-1 in alveolar type II epithelial cells. In contrast, overexpression of NF-κB p65 significantly increases MCP-1 expression. Furthermore, we elucidate that IKKα/β-NF-κB p65 signaling pathway and phosphorylation of serine 534 in NF-κB p65 are required for the maximal expression of MCP-1. Also, Activator protein 1 (AP-1) site in the promoter region and JNK1/2-c-Jun signaling are required for MCP-1 generation in alveolar type II epithelial cells. Moreover, a CCAAT/enhancer-binding protein (C/EBP) element is identified in the MCP-1 promoter region through the point mutation technique, and further experiments demonstrate that both C/EBPβ and C/EBPδ are involved in basic and IL-1β-mediated MCP-1 expression. Of note, specificity protein 1-Sp1 expression is not changed in alveolar type II epithelial cells incubated with IL-1β, but it still control MCP-1 production by binding to the consensus sequence in the promoter region. More importantly, we find that the results derived from the cell line-MLE-12 cells and primary cells are consistent. Taken together, our data provide insights into the molecular mechanism how MCP-1 expression in inflammatory alveolar type II epithelial cells is regulated at transcription level.

TNF-α induction of IL-6 in alveolar type II epithelial cells: Contributions of JNK/c-Jun/AP-1 element, C/EBPδ/C/EBP binding site and IKK/NF-κB p65/κB site

Although participation of IL-6 in lung inflammation has been widely elucidated, the transcriptional regulation of its generation in alveolar type II cells stimulated by TNF-α remain unclear. Here, we find that TNF-α significantly induces IL-6 production, and TNF-α induction of IL-6 is mainly regulated at transcriptional level. Upon stimulated by TNF-α, Activator Protein-1 (AP-1)-mediated transcriptional activity is apparently increased in alveolar type II epithelial cells, which might be derived from elevated phosphorylation of JNK and subsequent activation of c-Jun. Either down-regulation of c-Jun or the AP-1 site mutation leads to significant reduction of IL-6 expression. In contrast, ectopic expression of c-Jun notably increases IL-6 generation. So, c-Jun, one of the AP-1 family members, plays a pivotal role in TNF-α-induced IL-6 generation. CCAAT/enhancer binding protein δ (C/EBPδ) expression is significantly amplified by TNF-α, which may contribute to the rise of C/EBP activity in alveolar type II cells. C/EBPδ shRNA treatment results in attenuation of IL-6 expression in the cells, which is consistent with data by introduction of mutations into the C/EBP site in the promoter. However, overexpression of C/EBPδ greatly increases the IL-6 promoter activity. In addition, data regarding another transactivator in the family-C/EBPβ show that it does not affect IL-6 production. We also find that the IKK/NF-κB p65 pathway is activated in TNF-α-treated alveolar type II epithelial cells, and plays an essential role in positive regulation of IL-6 expression in TNF-α-treated alveolar type II epithelial cells via knockdown or forced expression of NF-κB p65, or elimination of κB sites in the IL-6 promoter. Notably, IL-6 promoter-driven luciferase production in primary alveolar type II epithelial cells can also be increased by the ectopic expression of c-Jun, C/EBPδ, and NF-κB p65, respectively. Collectively, our data provide insights into molecular mechanism involved in IL-6 expression in alveolar type II epithelial cells on TNF-α treatment, which provides a theoretical basis for specific inhibition of IL-6 production at the transcriptional level.

C/EBPδ drives interactions between human MAIT cells and endothelial cells that are important for extravasation

Many mediators and regulators of extravasation by bona fide human memory-phenotype T cells remain undefined. Mucosal-associated invariant T (MAIT) cells are innate-like, antibacterial cells that we found excelled at crossing inflamed endothelium. They displayed abundant selectin ligands, with high expression of FUT7 and ST3GAL4, and expressed CCR6, CCR5, and CCR2, which played non-redundant roles in trafficking on activated endothelial cells. MAIT cells selectively expressed CCAAT/enhancer-binding protein delta (C/EBPδ). Knockdown of C/EBPδ diminished expression of FUT7, ST3GAL4 and CCR6, decreasing MAIT cell rolling and arrest, and consequently the cells' ability to cross an endothelial monolayer in vitro and extravasate in mice. Nonetheless, knockdown of C/EBPδ did not affect CCR2, which was important for the step of transendothelial migration. Thus, MAIT cells demonstrate a program for extravasastion that includes, in part, C/EBPδ and C/EBPδ-regulated genes, and that could be used to enhance, or targeted to inhibit T cell recruitment into inflamed tissue.

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.

PKCα-LSD1-NF-κB-Signaling Cascade Is Crucial for Epigenetic Control of the Inflammatory Response

The inflammatory response mediated by nuclear factor κB (NF-κB) signaling is essential for host defense against pathogens. Although the regulatory mechanism of NF-κB signaling has been well studied, the molecular basis for epigenetic regulation of the inflammatory response is poorly understood. Here we identify a new signaling axis of PKCα-LSD1-NF-κB, which is critical for activation and amplification of the inflammatory response. In response to excessive inflammatory stimuli, PKCα translocates to the nucleus and phosphorylates LSD1. LSD1 phosphorylation is required for p65 binding and facilitates p65 demethylation, leading to enhanced stability. In vivo genetic analysis using Lsd1^SA/SA mice with ablation of LSD1 phosphorylation and chemical approaches in wild-type mice with inhibition of PKCα or LSD1 activity show attenuated sepsis-induced inflammatory lung injury and mortality. Together, we demonstrate that the PKCα-LSD1-NF-κB signaling cascade is crucial for epigenetic control of the inflammatory response, and targeting this signaling could be a powerful therapeutic strategy for systemic inflammatory diseases, including sepsis.

Central role of myeloid MCPIP1 in protecting against LPS-induced inflammation and lung injury

Although systemic inflammatory responses attributable to infection may lead to significant lung injury, the precise molecular mechanisms leading to lung damage are poorly understood and therapeutic options remain limited. Here, we show that myeloid monocyte chemotactic protein-inducible protein 1 (MCPIP1) plays a central role in protecting against LPS-induced inflammation and lung injury. Myeloid-specific MCPIP1 knockout mice developed spontaneous inflammatory syndromes, but at a late age compared to global MCPIP1 knockout mice. Moreover, mice with a myeloid-specific deletion of MCPIP1 were extremely sensitive to LPS-induced lung injury due to overproduction of proinflammatory cytokines and chemokines. We identified C/EBPβ and C/EBPδ, two critical transcriptional factors that drive cytokine production and lung injury, as targets of MCPIP1 RNase. LPS administration caused MCPIP1 protein degradation in the lungs. Pharmacological inhibition of MALT1, a paracaspase that cleaves MCPIP1, by MI-2 selectively increased the MCPIP1 protein levels in macrophages and in the lungs. Meanwhile, administration of MI-2 protected mice from LPS-induced inflammation, lung injury and death. Collectively, these results indicate that myeloid MCPIP1 is central in controlling LPS-induced inflammation and lung injury. Pharmacological inhibition of MALT1 protease activity may be a good strategy to treat inflammatory diseases by enhancing MCPIP1 expression in myeloid cells.

Gene expression profiling of common signal transduction pathways affected by rBMSCs/F92A-Cav1 in the lungs of rat with pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is associated with sustained vasoconstriction, inflammation and suppressed apoptosis of smooth muscle cells. Our previous studies have found that rat bone marrow-derived mesenchymal stem cells (rBMSCs) transduced with a mutant caveolin-1(F92A-Cav1) could enhance endothelial nitric oxide synthase (eNOS) activity and improve pulmonary vascular remodeling, but the potential mechanism is not yet fully explored. The present study was to investigate the gene expression profile upon rBMSCs/F92A-Cav1delivered to PAH rat to evaluate the role of F92A-Cav1 in its regulation.

METHODS

PAH was induced with monocrotaline (MCT, 60mg/kg) prior to delivery of lentiviral vector transduced rBMSCs expressing Cav1 or F92A-Cav1. Gene expression profiling was performed using Rat Signal Transduction PathwayFinder array. The expression changes of 84 key genes representing 10 signal transduction pathways in rat following rBMSCs/F92A-Cav1 treatment was examined.

RESULTS

Screening with the Rat Signal Transduction PathwayFinder R² PCR Array system and subsequent western blot, immunohistochemistry or real time PCR analysis revealed that F92A-Cav1 modified rBMSCs can inhibit the inflammation factors (TNF-alpha, Icam1 and C/EBPdelta), pro-proliferation genes (c-Myc, Bcl2a1d, Notch1and Hey2), oxidative stress gene (Hmox1) and activate cell cycle arrested gene Cdkn1a, ameliorating inflammation and inhibiting cell proliferation in PAH rat.

CONCLUSION

rBMSCs/F92A-Cav1 inhibits inflammation and cell proliferation by regulating signaling pathways that related to inflammation, proliferation, cell cycle and oxidative stress.

Bigelovii A Protects against Lipopolysaccharide-Induced Acute Lung Injury by Blocking NF-κB and CCAAT/Enhancer-Binding Protein δ Pathways

Optimal methods are applied to acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS), but the mortality rate is still high. Accordingly, further studies dedicated to identify novel therapeutic approaches to ALI are urgently needed. Bigelovii A is a new natural product and may exhibit anti-inflammatory activity. Therefore, we sought to investigate its effect on lipopolysaccharide- (LPS-) induced ALI and the underlying mechanisms. We found that LPS-induced ALI was significantly alleviated by Bigelovii A treatment, characterized by reduction of proinflammatory mediator production, neutrophil infiltration, and lung permeability. Furthermore, Bigelovii A also downregulated LPS-stimulated inflammatory mediator expressions in vitro. Moreover, both NF-κB and CCAAT/enhancer-binding protein δ (C/EBPδ) activation were obviously attenuated by Bigelovii A treatment. Additionally, phosphorylation of both p38 MAPK and ERK1/2 (upstream signals of C/EBPδ activation) in response to LPS challenge was also inhibited by Bigelovii A. Therefore, Bigelovii A could attenuate LPS-induced inflammation by suppression of NF-κB, inflammatory mediators, and p38 MAPK/ERK1/2-C/EBPδ, inflammatory mediators signaling pathways, which provide a novel theoretical basis for the possible application of Bigelovii A in clinic.

Protective Role of Rho Guanosine Diphosphate Dissociation Inhibitor, Ly-GDI, in Pulmonary Alveolitis

Growing evidences indicate that Ly-GDI, an inhibitory protein of Rho GTPases, plays an essential role in regulating actin cytoskeletal alteration which is indispensible for the process such as phagocytosis. However, the role of Ly-GDI in inflammation remains largely unknown. In the current study, we found that Ly-GDI expression was significantly decreased in the IgG immune complex-injured lungs. To determine if Ly-GDI might regulate the lung inflammatory response, we constructed adenovirus vectors that could mediate ectopic expression of Ly-GDI (Adeno-Ly-GDI). In vivo mouse lung expression of Ly-GDI resulted in a significant attenuation of IgG immune complex-induced lung injury, which was due to the decreased pulmonary permeability and lung inflammatory cells, especially neutrophil accumulation. Upon IgG immune complex deposition, mice with Ly-GDI over-expression in the lungs produced significant less inflammatory mediators (TNF-α, IL-6, MCP-1, and MIP-1α) in bronchoalveolar lavage fluid when compared control mice receiving airway injection of Adeno-GFP. Mechanically, IgG immune complex-induced NF-κB activity was markedly suppressed by Ly-GDI in both alveolar macrophages and lungs as measured by luciferase assay and electrophoretic mobility shift assay. These findings suggest that Ly-GDI is a critical regulator of inflammatory injury after deposition of IgG immune complexes and that it negatively regulates the lung NF-κB activity.

Multiple Protein Kinases via Activation of Transcription Factors NF-κB, AP-1 and C/EBP-δ Regulate the IL-6/IL-8 Production by HIV-1 Vpr in Astrocytes

Neurocognitive impairments affect a substantial population of HIV-1 infected individuals despite the success of anti-retroviral therapy in controlling viral replication. Astrocytes are emerging as a crucial cell type that might be playing a very important role in the persistence of neuroinflammation seen in patients suffering from HIV-1 associated neurocognitive disorders. HIV-1 viral proteins including Vpr exert neurotoxicity through direct and indirect mechanisms. Induction of IL-8 in microglial cells has been shown as one of the indirect mechanism through which Vpr reduces neuronal survival. We show that HIV-1 Vpr induces IL-6 and IL-8 in astrocytes in a time-dependent manner. Additional experiments utilizing chemical inhibitors and siRNA revealed that HIV-1 Vpr activates transcription factors NF-κB, AP-1 and C/EBP-δ via upstream protein kinases PI3K/Akt, p38-MAPK and Jnk-MAPK leading to the induction of IL-6 and IL-8 in astrocytes. We demonstrate that one of the mechanism for neuroinflammation seen in HIV-1 infected individuals involves induction of IL-6 and IL-8 by Vpr in astrocytes. Understanding the molecular pathways involved in the HIV-1 neuroinflammation would be helpful in the design of adjunct therapy to ameliorate some of the symptoms associated with HIV-1 neuropathogenesis.

An anti-inflammatory role for C/EBPδ in human brain pericytes

Neuroinflammation contributes to the pathogenesis of several neurological disorders and pericytes are implicated in brain inflammatory processes. Cellular inflammatory responses are orchestrated by transcription factors but information on transcriptional control in pericytes is lacking. Because the transcription factor CCAAT/enhancer binding protein delta (C/EBPδ) is induced in a number of inflammatory brain disorders, we sought to investigate its role in regulating pericyte immune responses. Our results reveal that C/EBPδ is induced in a concentration- and time-dependent fashion in human brain pericytes by interleukin-1β (IL-1β). To investigate the function of the induced C/EBPδ in pericytes we used siRNA to knockdown IL-1β-induced C/EBPδ expression. C/EBPδ knockdown enhanced IL-1β-induced production of intracellular adhesion molecule-1 (ICAM-1), interleukin-8, monocyte chemoattractant protein-1 (MCP-1) and IL-1β, whilst attenuating cyclooxygenase-2 and superoxide dismutase-2 gene expression. Altered ICAM-1 and MCP-1 protein expression were confirmed by cytometric bead array and immunocytochemistry. Our results show that knock-down of C/EBPδ expression in pericytes following immune stimulation increased chemokine and adhesion molecule expression, thus modifying the human brain pericyte inflammatory response. The induction of C/EBPδ following immune stimulation may act to limit infiltration of peripheral immune cells, thereby preventing further inflammatory responses in the brain.

C/EBPβ and C/EBPδ transcription factors: Basic biology and roles in the CNS

CCAAT/enhancer binding protein (C/EBP) β and C/EBPδ are transcription factors of the basic-leucine zipper class which share phylogenetic, structural and functional features. In this review we first describe in depth their basic molecular biology which includes fascinating aspects such as the regulated use of alternative initiation codons in the C/EBPβ mRNA. The physical interactions with multiple transcription factors which greatly opens the number of potentially regulated genes or the presence of at least five different types of post-translational modifications are also remarkable molecular mechanisms that modulate C/EBPβ and C/EBPδ function. In the second part, we review the present knowledge on the localization, expression changes and physiological roles of C/EBPβ and C/EBPδ in neurons, astrocytes and microglia. We conclude that C/EBPβ and C/EBPδ share two unique features related to their role in the CNS: whereas in neurons they participate in memory formation and synaptic plasticity, in glial cells they regulate the pro-inflammatory program. Because of their role in neuroinflammation, C/EBPβ and C/EBPδ in microglia are potential targets for treatment of neurodegenerative disorders. Any strategy to reduce C/EBPβ and C/EBPδ activity in neuroinflammation needs to take into account its potential side-effects in neurons. Therefore, cell-specific treatments will be required for the successful application of this strategy.

CCAAT/enhancer-binding protein δ (C/EBPδ) aggravates inflammation and bacterial dissemination during pneumococcal meningitis

Background

The prognosis of bacterial meningitis largely depends on the severity of the inflammatory response. The transcription factor CAAT/enhancer-binding protein δ (C/EBPδ) plays a key role in the regulation of the inflammatory response during bacterial infections. Consequently, we assessed the role of C/EBPδ during experimental meningitis.

Methods

Wild-type and C/EBPδ-deficient mice (C/EBPδ^−/−) were intracisternally infected with Streptococcus pneumoniae and sacrificed after 6 or 30 h, or followed in a survival study.

Results

In comparison to wild-type mice, C/EBPδ^−/− mice showed decreased bacterial loads at the primary site of infection and decreased bacterial dissemination to lung and spleen 30 h after inoculation. Expression levels of the inflammatory mediators IL-10 and KC were lower in C/EBPδ^−/− brain homogenates, whereas IL-6, TNF-α, IL-1β, and MIP-2 levels were not significantly different between the two genotypes. Moreover, C/EBPδ^−/− mice demonstrated an attenuated systemic response as reflected by lower IL-10, IL-6, KC, and MIP-2 plasma levels. No differences in clinical symptoms or in survival were observed between wild-type and C/EBPδ^−/− mice.

Conclusion

C/EBPδ in the brain drives the inflammatory response and contributes to bacterial dissemination during pneumococcal meningitis. C/EBPδ does, however, not affect clinical parameters of the disease and does not confer a survival benefit.

Biological roles of CCAAT/Enhancer-binding protein delta during inflammation

CCAAT/enhancer-binding protein delta (CEBPD) belongs to the CCAAT/enhancer-binding protein family, and these proteins function as transcription factors in many biological processes, including cell differentiation, motility, growth arrest, proliferation, cell death, metabolism and immune responses. The functional diversity of CEBPD depends, in part, on the cell type and cellular context, which indicates that CEBPD could interpret a variety of cues to adjust cellular responses in specific situations. Here, we review the regulation of the CEBPD gene and its function in response to inflammatory stimuli. We also address its effects in inflammation-related diseases through a discussion of its recently discovered downstream targets. Regarding to the previous discoveries and new insights in inflammation-associated diseases, suggesting CEBPD could also be a central gene in inflammation. Importantly, the results of this study indicate that the investigation of CEBPD could open a new avenue to help better understand the inflammatory response.

Insights into the possible role of IFNG and IFNGR1 in Kala-azar and Post Kala-azar Dermal Leishmaniasis in Sudanese patients

BACKGROUND

Little is known about the parasite/host factors that lead to Post Kala-azar Dermal Leishmaniasis (PKDL) in some visceral leishmaniasis (VL) patients after drug-cure. Studies in Sudan provide evidence for association between polymorphisms in the gene (IFNGR1) encoding the alpha chain of interferon-γ receptor type I and risk of PKDL. This study aimed to identify putative functional polymorphisms in the IFNGR1 gene, and to determine whether differences in expression of interferon-γ (IFNG) and IFNGR1 at the RNA level are associated with pathogenesis of VL and/or PKDL in Sudan.

METHODS

Sanger sequencing was used to re-sequence 841 bp of upstream, exon1 and intron1 of the IFNGR1 gene in DNA from 30 PKDL patients. LAGAN and SYNPLOT bioinformatics tools were used to compare human, chimpanzee and dog sequences to identify conserved noncoding sequences carrying putative regulatory elements. The relative expression of IFNG and IFNGR1 in paired pre- and post-treatment RNA samples from the lymph nodes of 24 VL patients, and in RNA samples from skin biopsies of 19 PKDL patients, was measured using real time PCR. Pre- versus post-treatment expression was evaluated statistically using the nonparametric Wilcoxon matched pairs signed-rank test.

RESULTS

Ten variants were identified in the 841 bp of sequence, four of which are novel polymorphisms at -77A/G, +10 C/T, +18C/T and +91G/T relative to the IFNGR1 initiation site. A cluster of conserved non-coding sequences with putative regulatory variants was identified in the distal promoter of IFNGR1. Variable expression of IFNG was detected in lymph node aspirates of VL patients before treatment, with a marked reduction (P = 0.006) in expression following treatment. IFNGR1 expression was also variable in lymph node aspirates from VL patients, with no significant reduction in expression with treatment. IFNG expression was undetectable in the skin biopsies of PKDL cases, while IFNGR1 expression was also uniformly low.

CONCLUSIONS

Uniformly low expression of IFN and IFNGR1 in PKDL skin biopsies could explain parasite persistence and is consistent with prior demonstration of genetic association with IFNGR1 polymorphisms. Identification of novel potentially functional rare variants at IFNGR1 makes an important general contribution to knowledge of rare variants of potential relevance in this Sudanese population.

CCAAT-enhancer binding protein delta (C/EBPδ) attenuates tubular injury and tubulointerstitial fibrogenesis during chronic obstructive nephropathy

CCAAT-enhancer-binding protein delta (C/EBPδ) is a transcription factor mainly known for its role in inflammation and apoptosis/proliferation. Considering that these are key processes in renal fibrosis, we hypothesized that C/EBPδ would potentiate renal fibrosis. In line with this hypothesis, C/EBPδ has recently been suggested to regulate the fibrotic response during glomerulonephritis. Here we determined the importance of C/EBPδ in the development of renal tubulointerstitial fibrosis by subjecting 8- to 12-week-old C/EBPδ-deficient mice and age- and sex-matched wild-type controls to the unilateral ureteral obstruction model. Mice were killed at 1, 3, or 7 days post surgery, and renal tissues were obtained for RNA, protein, and immunohistochemical analysis. We show that C/EBPδ deficiency resulted in a more profound fibrotic response as evident from enhanced tubular injury, collagen deposition in the interstitial area, and higher expression of transforming growth factor-β. Moreover, we show that the increase in renal fibrosis in C/EBPδ-deficient mice does not depend on an altered proliferation/apoptosis balance or on a differential inflammatory response in the obstructed kidney. In conclusion, our study provides direct evidence that C/EBPδ is a novel mediator of renal fibrosis. Modulating C/EBPδ expression could consequently be a potential antifibrotic strategy in patients with chronic kidney disease.

The many faces of C/EBPδ and their relevance for inflammation and cancer

The CCAAT/enhancer binding protein delta (CEBPD, C/EBPδ) is a transcription factor that modulates many biological processes including cell differentiation, motility, growth arrest, proliferation, and cell death. The diversity of C/EBPδ's functions depends in part on the cell type and cellular context and can have opposing outcomes. For example, C/EBPδ promotes inflammatory signaling, but it can also inhibit pro-inflammatory pathways, and in a mouse model of mammary tumorigenesis, C/EBPδ reduces tumor incidence but promotes tumor metastasis. This review highlights the multifaceted nature of C/EBPδ's functions, with an emphasis on pathways that are relevant for cancer and inflammation, and illustrates how C/EBPδ emerged from the shadow of its family members as a fascinating “jack of all trades.” Our current knowledge on C/EBPδ indicates that, rather than being essential for a specific cellular process, C/EBPδ helps to interpret a variety of cues in a cell-type and context-dependent manner, to adjust cellular functions to specific situations. Therefore, insights into the roles and mechanisms of C/EBPδ signaling can lead to a better understanding of how the integration of different signaling pathways dictates normal and pathological cell functions and physiology.

Transcriptional Regulation of the Group IIA Secretory Phospholipase A2 Gene by C/EBPδ in Rat liver and its Relationship to Hepatic Gluconeogenesis during Sepsis

BACKGROUND

The present study was undertaken to test hypothesis that altered transcription of secretory Phospholipase A2 (sPLA2) gene in rat liver is regulated by CCAAT/enhancer binding protein δ (C/EBPδ), and to assess its relationship to hepatic gluconeogenesis during the progression of sepsis.

METHODS

Sepsis was induced by Cecal Ligation and Puncture (CLP). Experiments were divided into three groups, control, early sepsis (9 h after CLP), and late sepsis (18 h after CLP).

RESULTS

DNA mobility and super shift assays reveal that C/EBP complexes in the liver consisted of at least three isoforms: C/EBPα, C/EBPβ, and C/EBPδ; and various C/EBP isoforms were capable of interacting with each other. Hepatocyte transfection experiments demonstrate that under normal conditions, binding of C/EBPδ to sPLA2 gene enhanced sPLA2 promoter activity and the binding resulted in an increase in hepatic gluconeogenesis. Under pathological conditions such as sepsis, binding of C/EBPδ to sPLA2 promoter increased during early and late phases of sepsis, and the increases in C/EBPδ binding correlated with increases in sPLA2 mRNA abundance and sPLA2 protein levels. Under otherwise the identical experimental conditions, hepatic gluconeogenesis was reduced during early and late phases of sepsis and the sepsis-induced reductions in liver gluconeogenesis were aggravated by binding of C/EBPδ to sPLA2 gene.

CONCLUSIONS

These results link C/EBPδ binding to altered sPLA2 promoter, and to hepatic gluconeogenesis under normal and pathological conditions. It is suggested that C/EBPδ-sPLA2- hepatic gluconeogenesis may function as a signalling axis affecting glucose homeostasis during the progression of sepsis.

Loss of phosphatase and tensin homolog (PTEN) induces leptin-mediated leptin gene expression: feed-forward loop operating in the lung

Elevated levels of systemic and pulmonary leptin are associated with diseases related to lung injury and lung cancer. However, the role of leptin in lung biology and pathology, including the mechanism of leptin gene expression in the pathogenesis of lung diseases, including lung cancer, remains elusive. Here, using conditional deletion of tumor suppressor gene Pten in the lung epithelium in vivo in transgenic mice and human PTEN-null lung epithelial cells, we identify the leptin-driven feed-forward signaling loop in the lung epithelial cells. Leptin-mediated leptin/leptin-receptor gene expression likely amplifies leptin signaling that may contribute to the pathogenesis and severity of lung diseases, resulting in poor clinical outcomes. Loss of Pten in the lung epithelial cells in vivo activated adipokine signaling and induced leptin synthesis as ascertained by genome-wide mRNA profiling and pathway analysis. Leptin gene transcription was mediated by binding of transcription factors NRF-1 and CCAAT/enhancer-binding protein δ (C/EBP) to the proximal promoter regions and STAT3 to the distal promoter regions as revealed by leptin promoter-mutation, chromatin immunoprecipitation, and gain- and loss-of-function studies in lung epithelial cells. Leptin treatment induced expression of the leptin/leptin receptor in the lung epithelial cells via activation of MEK/ERK, PI3K/AKT/mammalian target of rapamycin (mTOR), and JAK2/STAT3 signaling pathways. Expression of constitutively active MEK-1, AKT, and STAT3 proteins increased expression, and treatment with MEK, PI3K, AKT, and mTOR inhibitors decreased LEP expression, indicating that leptin via MAPK/ERK1/2, PI3K/AKT/mTOR, and JAK2/STAT3 pathways, in turn, further induces its own gene expression. Thus, targeted inhibition of the leptin-mediated feed-forward loop provides a novel rationale for pharmacotherapy of disease associated with lung injury and remodeling, including lung cancer.

Myeloid depletion of SOCS3 enhances LPS-induced acute lung injury through CCAAT/enhancer binding protein δ pathway

Although uncontrolled inflammatory response plays a central role in the pathogenesis of acute lung injury (ALI), the precise molecular mechanisms underlying the development of this disorder remain poorly understood. SOCS3 is an important negative regulator of IL-6-type cytokine signaling. SOCS3 is induced in lung during LPS-induced lung injury, suggesting that generation of SOCS3 may represent a regulatory product during ALI. In the current study, we created mice lacking SOCS3 expression in macrophages and neutrophils (LysM-cre SOCS3(fl/fl)). We evaluated the lung inflammatory response to LPS in both LysM-cre SOCS3(fl/fl) mice and the wild-type (WT) mice (SOCS3(fl/fl)). LysM-cre SOCS3(fl/fl) mice displayed significant increase of the lung permeability index (lung vascular leak of albumin), neutrophils, lung neutrophil accumulation (myeloperoxidase activity), and proinflammatory cytokines/chemokines in bronchial alveolar lavage fluids compared to WT mice. These phenotypes were consistent with morphological evaluation of lung, which showed enhanced inflammatory cell influx and intra-alveolar hemorrhage. We further identify the transcription factor, CCAAT/enhancer-binding protein (C/EBP) δ as a critical downstream target of SOCS3 in LPS-induced ALI. These results indicate that SOCS3 has a protective role in LPS-induced ALI by suppressing C/EBPδ activity in the lung. Elucidating the function of SOCS3 would represent prospective targets for a new generation of drugs needed to treat ALI.

CCAAT/enhancer-binding protein δ: multifaceted regulator in respiratory disease

This Correspondence relates to the recently published article by Yan et al (Am J Pathol, 2012:420-430) that demonstrated that CCAAT/enhancer-binding protein δ (C/EBPδ) drives cytokine production, neutrophil accumulation, and lung vascular leakage in a murine model of lipopolysaccharide (LPS)-induced acute lung injury.