The epigenetic state of IL-4-polarized macrophages enables inflammatory cistromic expansion and extended synergistic response to TLR ligands

Prior exposure to microenvironmental signals could fundamentally change the response of macrophages to subsequent stimuli. It is believed that T helper-2 (Th2)-cell-type cytokine interleukin-4 (IL-4) and Toll-like receptor (TLR) ligand-activated transcriptional programs mutually antagonize each other, and no remarkable convergence has been identified between them. In contrast, here, we show that IL-4-polarized macrophages established a hyperinflammatory gene expression program upon lipopolysaccharide (LPS) exposure. This phenomenon, which we termed extended synergy, was supported by IL-4-directed epigenomic remodeling, LPS-activated NF-κB-p65 cistrome expansion, and increased enhancer activity. The EGR2 transcription factor contributed to the extended synergy in a macrophage-subtype-specific manner. Consequently, the previously alternatively polarized macrophages produced increased amounts of immune-modulatory factors both in vitro and in vivo in a murine Th2 cell-type airway inflammation model upon LPS exposure. Our findings establish that IL-4-induced epigenetic reprogramming is responsible for the development of inflammatory hyperresponsiveness to TLR activation and contributes to lung pathologies.

The transcription factor EGR2 is the molecular linchpin connecting STAT6 activation to the late, stable epigenomic program of alternative macrophage polarization

In this study, Daniel et al. examined the mechanisms of macrophage polarization in general and alternative polarization in particular. Using unbiased epigenomic, molecular biology, and genetic GOF and LOF approaches, the authors show that the zinc finger transcription factor EGR2 acts as an essential and evolutionarily conserved broad-acting factor, linking transient polarization signals to stable epigenomic and transcriptional changes in macrophages.

Macrophages polarize into functionally distinct subtypes while responding to microenvironmental cues. The identity of proximal transcription factors (TFs) downstream from the polarization signals are known, but their activity is typically transient, failing to explain the long-term, stable epigenomic programs developed. Here, we mapped the early and late epigenomic changes of interleukin-4 (IL-4)-induced alternative macrophage polarization. We identified the TF, early growth response 2 (EGR2), bridging the early transient and late stable gene expression program of polarization. EGR2 is a direct target of IL-4-activated STAT6, having broad action indispensable for 77% of the induced gene signature of alternative polarization, including its autoregulation and a robust, downstream TF cascade involving PPARG. Mechanistically, EGR2 binding results in chromatin opening and the recruitment of chromatin remodelers and RNA polymerase II. Egr2 induction is evolutionarily conserved during alternative polarization of mouse and human macrophages. In the context of tissue resident macrophages, Egr2 expression is most prominent in the lung of a variety of species. Thus, EGR2 is an example of an essential and evolutionarily conserved broad acting factor, linking transient polarization signals to stable epigenomic and transcriptional changes in macrophages.

Effect of soil/contaminant interactions on the biodegradation of naphthalene in flooded soil under denitrifying conditions

The mineralization of 14C-labelled naphthalene was studied in pristine and oil-contaminated soil slurry (30% solids) under denitrifying conditions using a range of concentrations from below to above the aqueous phase saturation level. Results from sorption-desorption experiments indicated that naphthalene desorption was highly irreversible and decreased with an increase in the soil organic content, thus influencing the availability for microbial consumption. Under denitrifying conditions, the mineralization of naphthalene to CO2 occurred in parallel with the consumption of nitrate and an increase in pH from 7.0 to 8.6. When the initial substrate concentration was 50 ppm (i.e. close to the aqueous phase saturation level), about 90% of the total naphthalene was mineralized within 50 days, and a maximum mineralization rate of 1.3 ppm day-1 was achieved after a lag period of approx. 18 days. When added at concentrations higher than the aqueous phase saturation level (200 and 500 ppm), similar mineralization rates (1.8 ppm day-1) occurred until about 50 ppm of the naphthalene was mineralized. After that the mineralization rates decreased logarithmically to a minimum of 0.24 ppm day-1 for the rest of the 160 days of the experiments. For both of these higher concentrations, the reaction kinetics were independent of the concentration, indicating that desorption of the substrate governs the mineralization rate. Other results indicated that pre-exposure of soil to oil contamination did not improve the degradation rates nor reduce the lag periods. This study clearly shows the potential of denitrifying conditions for the biodegradation of low molecular weight PAHs.

Adsorption-Desorption Characteristics of Polychlorinated Biphenyls on Various Polymers Commonly Found in Laboratories

Adsorption and desorption of Aroclor 1254 (a mixture of polychlorinated biphenyls [PCBs]) from 0.25% (wt/vol) aqueous solutions of Triton X-100 on polymeric materials common in laboratories (red vacuum rubber, latex, Tygon, Norprene, manosil, polyethylene, polypropylene, phenoxy resin, nylon, and Teflon) is described. Teflon, nylon, and phenoxy resins showed the lowest adsorptions, with efficiencies of 3.4, 22.9, and 33.0%, respectively. The other polymers adsorbed more than 90% of Aroclor 1254 under similar conditions. Adsorption of PCBs was found to increase with the lipophilicity of the polymer and to be irreversible on soft polymers. The variation in the adsorption efficiencies of these polymers toward PCBs is apparently related to variations in the chemical composition, electronic properties, and degree of softness of these polymers. The present study showed that Teflon, with less than 4% adsorption and more than 99% desorption of Aroclor 1254, is the best candidate for use in biological laboratory work.