The myeloid transcription factor KLF2 regulates the host response to polymicrobial infection and endotoxic shock

Apelin/APJ signaling is a critical regulator of statin effects in vascular endothelial cells--brief report

OBJECTIVE

The endothelial response elicited by the G-protein-coupled receptor pathway involving apelin and APJ predicts an overall vasoprotective effect. As a number of downstream endothelial targets of apelin/APJ signaling are also known to be targeted by statins (3-hydroxy-3-methyl-glutaryl [HMG]-CoA reductase inhibitors) as potential mediators of their known pleiotropic effects, we evaluated for the involvement of apelin/APJ signaling in statin endothelial effects.

METHODS AND RESULTS

We found that disruption of apelin/APJ signaling in endothelial cells leads to significantly decreased expression of Krűppel-like factor 2, endothelial nitric oxide synthase, and thrombomodulin. We found that statin-mediated induction of Krűppel-like factor 2, endothelial nitric oxide synthase, and thrombomodulin expression, as well as inhibition of monocyte-endothelial adhesion, was abrogated by concurrent apelin knockdown. Moreover, we found that statins can transcriptionally regulate APJ in a Krűppel-like factor 2-dependent manner, demonstrating the presence of a positive-feedback loop.

CONCLUSIONS

Our findings provide a novel mechanism by which the apelin/APJ pathway serves as a critical intermediary that links statin to its pleiotropic effects in regulating endothelial gene targets and function.

Pseudomonas aeruginosa Alkyl quinolones repress hypoxia-inducible factor 1 (HIF-1) signaling through HIF-1α degradation

The transcription factor hypoxia-inducible factor 1 (HIF-1) has recently emerged to be a crucial regulator of the immune response following pathogen perception, including the response to the important human pathogen Pseudomonas aeruginosa. However, as mechanisms involved in HIF-1 activation by bacterial pathogens are not fully characterized, understanding how bacteria and bacterial compounds impact on HIF-1α stabilization remains a major challenge. In this context, we have focused on the effect of secreted factors of P. aeruginosa on HIF-1 regulation. Surprisingly, we found that P. aeruginosa cell-free supernatant significantly repressed HIF-1α protein levels. Further characterization revealed that HIF-1α downregulation was dependent on a subset of key secreted factors involved in P. aeruginosa pathogenesis, the 2-alkyl-4-quinolone (AQ) quorum sensing (QS) signaling molecules, and in particular the pseudomonas quinolone signal (PQS). Under hypoxic conditions, the AQ-dependent downregulation of HIF-1α was linked to the suppressed induction of the important HIF-1 target gene hexokinase II. Furthermore, we demonstrated that AQ molecules directly target HIF-1α protein degradation through the 26S-proteasome proteolytic pathway but independently of the prolyl hydroxylase domain (PHD). In conclusion, this is the first report showing that bacterial molecules can repress HIF-1α protein levels. Manipulation of HIF-1 signaling by P. aeruginosa AQs could have major consequences for the host response to infection and may facilitate the infective properties of this pathogen.

Kruppel-like factor 2 (KLF2) regulates monocyte differentiation and functions in mBSA and IL-1β-induced arthritis

Kruppel-like factor 2 (KLF2) plays an important role in the regulation of a variety of immune cells, including monocytes. We have previously shown that KLF2 inhibits proinflammatory activation of monocytes. However, the role of KLF2 in arthritis is yet to be investigated. In the current study, we show that recruitment of significantly greater numbers of inflammatory subset of CD11b(+)F4/80(+)Ly6C+ monocytes to the inflammatory sites in KLF2 hemizygous mice compared to the wild type littermate controls. In parallel, inflammatory mediators, MCP-1, Cox-2 and PAI-1 were significantly up-regulated in bone marrow-derived monocytes isolated from KLF2 hemizygous mice, in comparison to wild-type controls. Methylated-BSA and IL-1β-induced arthritis was more severe in KLF2 hemizygous mice as compared to the littermate wild type controls. Consistent with this observation, monocytes isolated from KLF2 hemizygous mice showed an increased number of cells matured and differentiated towards osteoclastic lineage, potentially contributing to the severity of cartilage and bone damage in induced arthritic mice. The severity of arthritis was associated with the higher expression of proteins such as HSP60, HSP90 and MMP13 and attenuated levels of pPTEN, p21, p38 and HSP25/27 molecules in bone marrow cells of arthritic KLF2 hemizygous mice compared to littermate wild type controls. The data provide new insights and evidences of KLF2-mediated transcriptional regulation of arthritis via modulation of monocyte differentiation and function.

Increased hypoxia-inducible factor 1α expression in lung cells of horses with recurrent airway obstruction

Background

Recurrent airway obstruction (RAO, also known as equine heaves) is an inflammatory condition caused by exposure of susceptible horses to organic dusts in hay. The immunological processes responsible for the development and the persistence of airway inflammation are still largely unknown. Hypoxia-inducible factor (Hif) is mainly known as a major regulator of energy homeostasis and cellular adaptation to hypoxia. More recently however, Hif also emerged as an essential regulator of innate immune responses. Here, we aimed at investigating the potential involvement of Hif1-α in myeloid cells in horse with recurrent airway obstruction.

Results

In vitro, we observed that Hif is expressed in equine myeloid cells after hay dust stimulation and regulates genes such as tumor necrosis factor alpha (TNF-α), interleukin-8 (IL-8) and vascular endothelial growth factor A (VEGF-A). We further showed in vivo that airway challenge with hay dust upregulated Hif1-α mRNA expression in myeloid cells from the bronchoalveolar lavage fluid (BALF) of healthy and RAO-affected horses, with a more pronounced effect in cells from RAO-affected horses. Finally, Hif1-α mRNA expression in BALF cells from challenged horses correlated positively with lung dysfunction.

Conclusion

Taken together, our results suggest an important role for Hif1-α in myeloid cells during hay dust-induced inflammation in horses with RAO. We therefore propose that future research aiming at functional inactivation of Hif1 in lung myeloid cells could open new therapeutic perspectives for RAO.

Common patterns and disease-related signatures in tuberculosis and sarcoidosis

In light of the marked global health impact of tuberculosis (TB), strong focus has been on identifying biosignatures. Gene expression profiles in blood cells identified so far are indicative of a persistent activation of the immune system and chronic inflammatory pathology in active TB. Definition of a biosignature with unique specificity for TB demands that identified profiles can differentiate diseases with similar pathology, like sarcoidosis (SARC). Here, we present a detailed comparison between pulmonary TB and SARC, including whole-blood gene expression profiling, microRNA expression, and multiplex serum analytes. Our analysis reveals that previously disclosed gene expression signatures in TB show highly similar patterns in SARC, with a common up-regulation of proinflammatory pathways and IFN signaling and close similarity to TB-related signatures. microRNA expression also presented a highly similar pattern in both diseases, whereas cytokines in the serum of TB patients revealed a slightly elevated proinflammatory pattern compared with SARC and controls. Our results indicate several differences in expression between the two diseases, with increased metabolic activity and significantly higher antimicrobial defense responses in TB. However, matrix metallopeptidase 14 was identified as the most distinctive marker of SARC. Described communalities as well as unique signatures in blood profiles of two distinct inflammatory pulmonary diseases not only have considerable implications for the design of TB biosignatures and future diagnosis, but they also provide insights into biological processes underlying chronic inflammatory disease entities of different etiology.

Macrophage plasticity and polarization: in vivo veritas

Diversity and plasticity are hallmarks of cells of the monocyte-macrophage lineage. In response to IFNs, Toll-like receptor engagement, or IL-4/IL-13 signaling, macrophages undergo M1 (classical) or M2 (alternative) activation, which represent extremes of a continuum in a universe of activation states. Progress has now been made in defining the signaling pathways, transcriptional networks, and epigenetic mechanisms underlying M1-M2 or M2-like polarized activation. Functional skewing of mononuclear phagocytes occurs in vivo under physiological conditions (e.g., ontogenesis and pregnancy) and in pathology (allergic and chronic inflammation, tissue repair, infection, and cancer). However, in selected preclinical and clinical conditions, coexistence of cells in different activation states and unique or mixed phenotypes have been observed, a reflection of dynamic changes and complex tissue-derived signals. The identification of mechanisms and molecules associated with macrophage plasticity and polarized activation provides a basis for macrophage-centered diagnostic and therapeutic strategies.

Krüppel-like factors in lymphocyte biology

The Krüppel-like factor family of transcription factors plays an important role in differentiation, function, and homeostasis of many cell types. While their role in lymphocytes is still being determined, it is clear that these factors influence processes as varied as lymphocyte quiescence, trafficking, differentiation, and function. This review will present an overview of how these factors operate and coordinate with each other in lymphocyte regulation.

A myeloid hypoxia-inducible factor 1α-Krüppel-like factor 2 pathway regulates gram-positive endotoxin-mediated sepsis

Although gram-positive infections account for the majority of cases of sepsis, the molecular mechanisms underlying their effects remains poorly understood. We investigated how cell wall components of gram-positive bacteria contribute to the development of sepsis. Experimental observations derived from cultured primary macrophages and the cell line indicate that gram-positive bacterial endotoxins induce hypoxia-inducible factor 1α (HIF-1α) mRNA and protein expression. Inoculation of live or heat-inactivated gram-positive bacteria with macrophages induced HIF-1 transcriptional activity in macrophages. Concordant with these results, myeloid deficiency of HIF-1α attenuated gram-positive bacterial endotoxin-induced cellular motility and proinflammatory gene expression in macrophages. Conversely, gram-positive bacteria and their endotoxins reduced expression of the myeloid anti-inflammatory transcription factor Krüppel-like transcription factor 2 (KLF2). Sustained expression of KLF2 reduced and deficiency of KLF2 enhanced gram-positive endotoxins induced HIF-1α mRNA and protein expression in macrophages. More importantly, KLF2 attenuated gram-positive endotoxins induced cellular motility and proinflammatory gene expression in myeloid cells. Consistent with these results, mice deficient in myeloid HIF-1α were protected from gram-positive endotoxin-induced sepsis mortality and clinical symptomatology. By contrast, myeloid KLF2-deficient mice were susceptible to gram-positive sepsis induced mortality and clinical symptoms. Collectively, these observations identify HIF-1α and KLF2 as critical regulators of gram-positive endotoxin-mediated sepsis.

Phenotypic and functional plasticity of cells of innate immunity: macrophages, mast cells and neutrophils

Hematopoietic cells, including lymphoid and myeloid cells, can develop into phenotypically distinct 'subpopulations' with different functions. However, evidence indicates that some of these subpopulations can manifest substantial plasticity (that is, undergo changes in their phenotype and function). Here we focus on the occurrence of phenotypically distinct subpopulations in three lineages of myeloid cells with important roles in innate and acquired immunity: macrophages, mast cells and neutrophils. Cytokine signals, epigenetic modifications and other microenvironmental factors can substantially and, in some cases, rapidly and reversibly alter the phenotype of these cells and influence their function. This suggests that regulation of the phenotype and function of differentiated hematopoietic cells by microenvironmental factors, including those generated during immune responses, represents a common mechanism for modulating innate or adaptive immunity.