Macrophage-derived LTB4 promotes abscess formation and clearance of Staphylococcus aureus skin infection in mice.

The early events that shape the innate immune response to restrain pathogens during skin infections remain elusive. Methicillin-resistant Staphylococcus aureus (MRSA) infection engages phagocyte chemotaxis, abscess formation, and microbial clearance. Upon infection, neutrophils and monocytes find a gradient of chemoattractants that influence both phagocyte direction and microbial clearance. The bioactive lipid leukotriene B4 (LTB4) is quickly (seconds to minutes) produced by 5-lipoxygenase (5-LO) and signals through the G protein-coupled receptors LTB4R1 (BLT1) or BLT2 in phagocytes and structural cells. Although it is known that LTB4 enhances antimicrobial effector functions in vitro, whether prompt LTB4 production is required for bacterial clearance and development of an inflammatory milieu necessary for abscess formation to restrain pathogen dissemination is unknown. We found that LTB4 is produced in areas near the abscess and BLT1 deficient mice are unable to form an abscess, elicit neutrophil chemotaxis, generation of neutrophil and monocyte chemokines, as well as reactive oxygen species-dependent bacterial clearance. We also found that an ointment containing LTB4 synergizes with antibiotics to eliminate MRSA potently. Here, we uncovered a heretofore unknown role of macrophage-derived LTB4 in orchestrating the chemoattractant gradient required for abscess formation, while amplifying antimicrobial effector functions.

Nuclear PTEN enhances the maturation of a microRNA regulon to limit MyD88-dependent susceptibility to sepsis.

Sepsis-induced organ damage is caused by systemic inflammatory response syndrome (SIRS), which results in substantial comorbidities. Therefore, it is of medical importance to identify molecular brakes that can be exploited to dampen inflammation and prevent the development of SIRS. We investigated the role of phosphatase and tensin homolog (PTEN) in suppressing SIRS, increasing microbial clearance, and preventing lung damage. Septic patients and mice with sepsis exhibited increased PTEN expression in leukocytes. Myeloid-specific Pten deletion in an animal model of sepsis increased bacterial loads and cytokine production, which depended on enhanced myeloid differentiation primary response gene 88 (MyD88) abundance and resulted in mortality. PTEN-mediated induction of the microRNAs (miRNAs) miR125b and miR203b reduced the abundance of MyD88. Loss- and gain-of-function assays demonstrated that PTEN induced miRNA production by associating with and facilitating the nuclear localization of Drosha-Dgcr8, part of the miRNA-processing complex. Reconstitution of PTEN-deficient mouse embryonic fibroblasts with a mutant form of PTEN that does not localize to the nucleus resulted in retention of Drosha-Dgcr8 in the cytoplasm and impaired production of mature miRNAs. Thus, we identified a regulatory pathway involving nuclear PTEN-mediated miRNA generation that limits the production of MyD88 and thereby limits sepsis-associated mortality.

The role of host DNA ligases in hepadnavirus covalently closed circular DNA formation.

Hepadnavirus covalently closed circular (ccc) DNA is the bona fide viral transcription template, which plays a pivotal role in viral infection and persistence. Upon infection, the non-replicative cccDNA is converted from the incoming and de novo synthesized viral genomic relaxed circular (rc) DNA, presumably through employment of the host cell's DNA repair mechanisms in the nucleus. The conversion of rcDNA into cccDNA requires preparation of the extremities at the nick/gap regions of rcDNA for strand ligation. After screening 107 cellular DNA repair genes, we herein report that the cellular DNA ligase (LIG) 1 and 3 play a critical role in cccDNA formation. Ligase inhibitors or functional knock down/out of LIG1/3 significantly reduced cccDNA production in an in vitro cccDNA formation assay, and in cccDNA-producing cells without direct effect on viral core DNA replication. In addition, transcomplementation of LIG1/3 in the corresponding knock-out or knock-down cells was able to restore cccDNA formation. Furthermore, LIG4, a component in non-homologous end joining DNA repair apparatus, was found to be responsible for cccDNA formation from the viral double stranded linear (dsl) DNA, but not rcDNA. In conclusion, we demonstrate that hepadnaviruses utilize the whole spectrum of host DNA ligases for cccDNA formation, which sheds light on a coherent molecular pathway of cccDNA biosynthesis, as well as the development of novel antiviral strategies for treatment of hepatitis B.

SOCS1 is a negative regulator of metabolic reprogramming during sepsis.

Sepsis can induce an overwhelming systemic inflammatory response, resulting in organ damage and death. Suppressor of cytokine signaling 1 (SOCS1) negatively regulates signaling by cytokine receptors and Toll-like receptors (TLRs). However, the cellular targets and molecular mechanisms for SOCS1 activity during polymicrobial sepsis are unknown. To address this, we utilized a cecal ligation and puncture (CLP) model for sepsis; C57BL/6 mice subjected to CLP were then treated with a peptide (iKIR) that binds the SOCS1 kinase inhibitory region (KIR) and blocks its activity. Treatment with iKIR increased CLP-induced mortality, bacterial burden, and inflammatory cytokine production. Myeloid cell-specific SOCS1 deletion (Socs1Δmyel) mice were also more susceptible to sepsis, demonstrating increased mortality, higher bacterial loads, and elevated inflammatory cytokines, compared with Socs1fl littermate controls. These effects were accompanied by macrophage metabolic reprograming, as evidenced by increased lactic acid production and elevated expression of the glycolytic enzymes hexokinase, lactate dehydrogenase A, and glucose transporter 1 in septic Socs1Δmyel mice. Upregulation was dependent on the STAT3/HIF-1α/glycolysis axis, and blocking glycolysis ameliorated increased susceptibility to sepsis in iKIR-treated CLP mice. These results reveal a role of SOCS1 as a regulator of metabolic reprograming that prevents overwhelming inflammatory response and organ damage during sepsis.

Sepsis Induces Hematopoietic Stem Cell Exhaustion and Myelosuppression through Distinct Contributions of TRIF and MYD88.

Toll-like receptor 4 (TLR4) plays a central role in host responses to bacterial infection, but the precise mechanism(s) by which its downstream signaling components coordinate the bone marrow response to sepsis is poorly understood. Using mice deficient in TLR4 downstream adapters MYD88 or TRIF, we demonstrate that both cell-autonomous and non-cell-autonomous MYD88 activation are major causes of myelosuppression during sepsis, while having a modest impact on hematopoietic stem cell (HSC) functions. In contrast, cell-intrinsic TRIF activation severely compromises HSC self-renewal without directly affecting myeloid cells. Lipopolysaccharide-induced activation of MYD88 or TRIF contributes to cell-cycle activation of HSC and induces rapid and permanent changes in transcriptional programs, as indicated by persistent downregulation of Spi1 and CebpA expression after transplantation. Thus, distinct mechanisms downstream of TLR4 signaling mediate myelosuppression and HSC exhaustion during sepsis through unique effects of MyD88 and TRIF.

MicroRNA 21 is a homeostatic regulator of macrophage polarization and prevents prostaglandin E2-mediated M2 generation.

Macrophages dictate both initiation and resolution of inflammation. During acute inflammation classically activated macrophages (M1) predominate, and during the resolution phase alternative macrophages (M2) are dominant. The molecular mechanisms involved in macrophage polarization are understudied. MicroRNAs are differentially expressed in M1 and M2 macrophages that influence macrophage polarization. We identified a role of miR-21 in macrophage polarization, and found that cross-talk between miR-21 and the lipid mediator prostaglandin E2 (PGE2) is a determining factor in macrophage polarization. miR-21 inhibition impairs expression of M2 signature genes but not M1 genes. PGE2 and its downstream effectors PKA and Epac inhibit miR-21 expression and enhance expression of M2 genes, and this effect is more pronounced in miR-21-/- cells. Among potential targets involved in macrophage polarization, we found that STAT3 and SOCS1 were enhanced in miR-21-/- cells and further enhanced by PGE2. We found that STAT3 was a direct target of miR-21 in macrophages. Silencing the STAT3 gene abolished PGE2-mediated expression of M2 genes in miR-21-/- macrophages. These data shed light on the molecular brakes involved in homeostatic macrophage polarization and suggest new therapeutic strategies to prevent inflammatory responses.

Leukotriene B4-mediated sterile inflammation promotes susceptibility to sepsis in a mouse model of type 1 diabetes.

Type 1 diabetes mellitus (T1DM) is associated with chronic systemic inflammation and enhanced susceptibility to systemic bacterial infection (sepsis). We hypothesized that low insulin concentrations in T1DM trigger the enzyme 5-lipoxygenase (5-LO) to produce the lipid mediator leukotriene B4 (LTB4), which triggers systemic inflammation that may increase susceptibility to polymicrobial sepsis. Consistent with chronic inflammation, peritoneal macrophages from two mouse models of T1DM had greater abundance of the adaptor MyD88 (myeloid differentiation factor 88) and its direct transcriptional effector STAT-1 (signal transducer and activator of transcription 1) than macrophages from nondiabetic mice. Expression of Alox5, which encodes 5-LO, and the concentration of the proinflammatory cytokine interleukin-1ß (IL-1ß) were also increased in peritoneal macrophages and serum from T1DM mice. Insulin treatment reduced LTB4 concentrations in the circulation and Myd88 and Stat1 expression in the macrophages from T1DM mice. T1DM mice treated with a 5-LO inhibitor had reduced Myd88 mRNA in macrophages and increased abundance of IL-1 receptor antagonist and reduced production of IL-ß in the circulation. T1DM mice lacking 5-LO or the receptor for LTB4 also produced less proinflammatory cytokines. Compared to wild-type or untreated diabetic mice, T1DM mice lacking the receptor for LTB4 or treated with a 5-LO inhibitor survived polymicrobial sepsis, had reduced production of proinflammatory cytokines, and had decreased bacterial counts. These results uncover a role for LTB4 in promoting sterile inflammation in diabetes and the enhanced susceptibility to sepsis in T1DM.

Leukotriene B4 enhances the generation of proinflammatory microRNAs to promote MyD88-dependent macrophage activation.

MicroRNAs are known to control TLR activation in phagocytes. We have shown that leukotriene (LT) B4 (LTB4) positively regulates macrophage MyD88 expression by decreasing suppressor of cytokine signaling-1 (SOCS-1) mRNA stability. In this study, we investigated the possibility that LTB4 control of MyD88 expression involves the generation of microRNAs. Our data show that LTB4, via its receptor B leukotriene receptor 1 (BLT1) and Gαi signaling, increased macrophage expression of inflammatory microRNAs, including miR-155, miR-146b, and miR-125b. LTB4-mediated miR-155 generation was attributable to activating protein-1 activation. Furthermore, macrophage transfection with antagomirs against miR-155 and miR-146b prevented both the LTB4-mediated decrease in SOCS-1 and increase in MyD88. Transfection with miR-155 and miR-146b mimics decreased SOCS-1 levels, increased MyD88 expression, and restored TLR4 responsiveness in both wild type and LT-deficient macrophages. To our knowledge, our data unveil a heretofore unrecognized role for the GPCR BLT1 in controlling expression of microRNAs that regulate MyD88-dependent activation of macrophages.

High levels of protein expression using different mammalian CMV promoters in several cell lines.

With the recent completion of the human genome sequencing project, scientists are faced with the daunting challenge of deciphering the function of these newly found genes quickly and efficiently. Equally as important is to produce milligram quantities of the therapeutically relevant gene products as quickly as possible. Mammalian expression systems provide many advantages to aid in this task. Mammalian cell lines have the capacity for proper post-translational modifications including proper protein folding and glycosylation. In response to the needs described above, we investigated the protein expression levels driven by the human CMV in the presence or absence of intron A, the mouse and rat CMV promoters with intron A, and the MPSV promoter in plasmid expression vectors. We evaluated the different promoters using an in-house plasmid vector backbone. The protein expression levels of four genes of interest driven by these promoters were evaluated in HEK293EBNA and CHO-K1 cells. Stable and transient transfected cells were utilized. In general, the full-length human CMV, in the presence of intron A, gave the highest levels of protein expression in transient transfections in both cell lines. However, the MPSV promoter resulted in the highest levels of stable protein expression in CHO-K1 cells. Using the CMV driven constitutive promoters in the presence of intron A, we have been able to generate >10 microg/ml of recombinant protein using transient transfections.

Transient transfection of CHO-K1-S using serum-free medium in suspension: a rapid mammalian protein expression system.

With the recent completion of the human genome sequencing project, scientists now face the daunting challenge of deciphering the function of these newly found genes quickly and efficiently. For biotechnology, it is equally important to identify the therapeutically relevant genes as quickly as possible. Mammalian expression systems provide many advantages to aid in this task. Mammalian cell lines have the capacity for proper post-translational modifications, including proper protein folding and glycosylation. In response to these needs, a CHO-K1 cell line that grows in suspension and in serum-free media was initially established and designated CHO-K1-S. An antibody gene of interest was chosen as the target for optimization rather than a reporter gene system. A comparison of various lipid transfection reagents was made using recombinant protein expression as the endpoint readout. Various other parameters including lipid:DNA ratios, cell density, and transfections in shaker versus spinner flasks were tested using the CHO-K1-S cell line. As a result, a rapid and reliable transient transfection protocol was developed. Using this procedure, we have produced milligram/per liter quantities of bioactive recombinant proteins from several genes of interest.