Biofilm formation and antioxidation were responsible for the increased resistance of N. eutropha to chloramination for drinking water treatment.

Chloramination is an effective strategy for eliminating pathogens from drinking water and repressing their regrowth in water distribution systems. However, the inevitable release of NH4+ potentially promotes nitrification and associated ammonia-oxidizing bacteria (AOB) contamination. In this study, AOB (Nitrosomona eutropha) were isolated from environmental water and treated with two disinfection stages (chloramine disinfection and chloramine residues) to investigate the occurrence mechanisms of AOB in chloramination. The results showed that N. eutropha had considerable resistance to monochloramine compared to Escherichia coli, whose inactivation rate constant was 19.4-fold lower. The higher resistance was attributed to high levels of extracellular polymer substances (EPS) in AOB, which contribute to AOB surviving disinfection and entering the distribution system. In AOB response to the chloramine residues stage, the respiratory activity of N. eutropha remained at a high level after three days of continuous exposure to high chloramine residue concentrations (0.5-1.5 mg/L). Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) suggested that the mechanism of N. eutropha tolerance involved a significantly high expression of the intracellular oxidative stress-regulating (sodB, txrA) and protein-related (NE1545, NE1546) genes. Additionally, this process enhanced EPS secretion and promoted biofilm formation. Adhesion predictions based on the XDLVO theory corroborated the trend of biofilm formation. Overall, the naturally higher resistance contributed to the survival of AOB in primary disinfection; the enhanced antioxidant response of surviving N. eutropha accompanied by biofilm formation was responsible for their increased resistance to the residual chloramines.

N-MYC regulates cell survival via eIF4G1 in inv(16) acute myeloid leukemia.

N-MYC (encoded by MYCN) is a critical regulator of hematopoietic stem cell function. While the role of N-MYC deregulation is well established in neuroblastoma, the importance of N-MYC deregulation in leukemogenesis remains elusive. Here, we demonstrate that N-MYC is overexpressed in acute myeloid leukemia (AML) cells with chromosome inversion inv(16) and contributes to the survival and maintenance of inv(16) leukemia. We identified a previously unknown MYCN enhancer, active in multiple AML subtypes, essential for MYCN mRNA levels and survival in inv(16) AML cells. We also identified eukaryotic translation initiation factor 4 gamma 1 (eIF4G1) as a key N-MYC target that sustains leukemic survival in inv(16) AML cells. The oncogenic role of eIF4G1 in AML has not been reported before. Our results reveal a mechanism whereby N-MYC drives a leukemic transcriptional program and provides a rationale for the therapeutic targeting of the N-MYC/eIF4G1 axis in myeloid leukemia.

Microbiological risks increased by ammonia-oxidizing bacteria under global warming: The neglected issue in chloraminated drinking water distribution system.

A rising outbreak of waterborne diseases caused by global warming requires higher microbial stability in the drinking water distribution system (DWDS). Chloramine disinfection is gaining popularity in this context due to its good persistent stability and fewer disinfection byproducts. However, the microbiological risks may be significantly magnified by ammonia-oxidizing bacteria (AOB) in distribution systems during global warming, which is rarely noticed. Hence, this work mainly focuses on AOB to explore its impact on water quality biosafety in the context of global warming. Research indicates that global warming-induced high temperatures can directly or indirectly promote the growth of AOB, thus leading to nitrification. Further, its metabolites or cellular residues can be used as substrates for the growth of heterotrophic bacteria (e.g., waterborne pathogens). Thus, biofilm may be more persistent in the pipelines due to the presence of AOB. Breakpoint chlorination is usually applied to control such situations. However, switching between this strategy and chloramine disinfection would result in even more severe nitrification and other adverse effects. Based on the elevated microbiological risks in DWDS, the following aspects should be paid attention to in future research: (1) to understand the response of nitrifying bacteria to high temperatures and the possible association between AOB and pathogenic growth, (2) to reveal the mechanisms of AOB-mediated biofilm formation under high-temperature stress, and (3) to develop new technologies to prevent and control the occurrence of nitrification in drinking water distribution system.

Endothelial Rap1B mediates T-cell exclusion to promote tumor growth: a novel mechanism underlying vascular immunosuppression.

Overcoming vascular immunosuppression: lack of endothelial cell (EC) responsiveness to inflammatory stimuli in the proangiogenic environment of tumors, is essential for successful cancer immunotherapy. The mechanisms through which Vascular Endothelial Growth Factor A(VEGF-A) modulates tumor EC response to exclude T-cells are not well understood. Here, we demonstrate that EC-specific deletion of small GTPase Rap1B, previously implicated in normal angiogenesis, restricts tumor growth in endothelial-specific Rap1B-knockout (Rap1BiΔEC) mice. EC-specific Rap1B deletion inhibits angiogenesis, but also leads to an altered tumor microenvironment with increased recruitment of leukocytes and increased activity of tumor CD8+ T-cells. Depletion of CD8+ T-cells restored tumor growth in Rap1BiΔEC mice. Mechanistically, global transcriptome and functional analyses indicated upregulation of signaling by a tumor cytokine, TNF-α, and increased NF-κB transcription in Rap1B-deficient ECs. Rap1B-deficiency led to elevated proinflammatory chemokine and Cell Adhesion Molecules (CAMs) expression in TNF-α stimulated ECs. Importantly, CAM expression was elevated in tumor ECs from Rap1BiΔEC mice. Significantly, Rap1B deletion prevented VEGF-A-induced immunosuppressive downregulation of CAM expression, demonstrating that Rap1B is essential for VEGF-A-suppressive signaling. Thus, our studies identify a novel endothelial-endogenous mechanism underlying VEGF-A-dependent desensitization of EC to proinflammatory stimuli. Significantly, they identify EC Rap1B as a potential novel vascular target in cancer immunotherapy.

Group 3 innate lymphoid cells require BATF to regulate gut homeostasis in mice.

Group 3 innate lymphoid cells (ILC3s) are crucial for the maintenance of host-microbiota homeostasis in gastrointestinal mucosal tissues. The mechanisms that maintain lineage identity of intestinal ILC3s and ILC3-mediated orchestration of microbiota and mucosal T cell immunity are elusive. Here, we identified BATF as a gatekeeper of ILC3 homeostasis in the gut. Depletion of BATF in ILC3s resulted in excessive interferon-γ production, dysbiosis, aberrant T cell immune responses, and spontaneous inflammatory bowel disease (IBD), which was considerably ameliorated by the removal of adaptive immunity, interferon-γ blockade, or antibiotic treatment. Mechanistically, BATF directly binds to the cis-regulatory elements of type 1 effector genes, restrains their chromatin accessibility, and inhibits their expression. Conversely, BATF promotes chromatin accessibility of genes involved in MHCII antigen processing and presentation pathways, which in turn directly promotes the transition of precursor ILC3s to MHCII+ ILC3s. Collectively, our findings reveal that BATF is a key transcription factor for maintaining ILC3 stability and coordinating ILC3-mediated control of intestinal homeostasis.

Endocytosis of the thrombopoietin receptor Mpl regulates megakaryocyte and erythroid maturation in mice.

Dnm2fl/fl Pf4-Cre (Dnm2Plt-/- ) mice lacking the endocytic GTPase dynamin 2 (DNM2) in platelets and megakaryocytes (MKs) develop hallmarks of myelofibrosis. At the cellular level, the tyrosine kinase JAK2 is constitutively active but decreased in expression in Dnm2Plt-/- platelets. Additionally, Dnm2Plt-/- platelets cannot endocytose the thrombopoietin (TPO) receptor Mpl, leading to elevated circulating TPO levels. Here, we assessed whether the hyperproliferative phenotype of Dnm2Plt-/- mice was due to JAK2 constitutive activation or to elevated circulating TPO levels. In unstimulated Dnm2Plt-/- platelets, STAT3 and, to a lower extent, STAT5 were phosphorylated, but their phosphorylation was slowed and diminished upon TPO stimulation. We further crossed Dnm2Plt-/- mice in the Mpl-/- background to generate Mpl-/-Dnm2Plt-/- mice lacking Mpl ubiquitously and DNM2 in platelets and MKs. Mpl-/- Dnm2Plt-/- platelets had severely reduced JAK2 and STAT3 but normal STAT5 expression. Mpl-/- Dnm2Plt-/- mice had severely reduced bone marrow MK and hematopoietic stem and progenitor cell numbers. Additionally, Mpl-/- Dnm2Plt-/- mice had severe erythroblast (EB) maturation defects, decreased expression of hemoglobin and heme homeostasis genes and increased expression of ribosome biogenesis and protein translation genes in spleen EBs, and developed anemia with grossly elevated plasma erythropoietin (EPO) levels, leading to early fatality by postnatal day 25. Mpl-/- Dnm2Plt+/+ mice had impaired EB development at three weeks of age, which normalized with adulthood. Together, the data shows that DNM2-dependent Mpl-mediated endocytosis in platelets and MKs is required for steady-state hematopoiesis and provides novel insights into a developmentally controlled role for Mpl in normal erythropoiesis, regulating hemoglobin and heme production.

Tfh-cell-derived interleukin 21 sustains effector CD8+ T cell responses during chronic viral infection.

CD4+ T cell-derived interleukin 21 (IL-21) sustains CD8+ T cell responses during chronic viral infection, but the helper subset that confers this protection remains unclear. Here, we applied scRNA and ATAC-seq approaches to determine the heterogeneity of IL-21+CD4+ T cells during LCMV clone 13 infection. CD4+ T cells were comprised of three transcriptionally and epigenetically distinct populations: Cxcr6+ Th1 cells, Cxcr5+ Tfh cells, and a previously unrecognized Slamf6+ memory-like (Tml) subset. T cell differentiation was specifically redirected toward the Tml subset during chronic, but not acute, LCMV infection. Although this subset displayed an enhanced capacity to accumulate and some developmental plasticity, it remained largely quiescent, which may hinder its helper potential. Conversely, mixed bone marrow chimera experiments revealed that Tfh cell-derived IL-21 was critical to sustain CD8+ T cell responses and viral control. Thus, strategies that bolster IL-21+Tfh cell responses may prove effective in enhancing CD8+ T cell-mediated immunity.

BATF promotes group 2 innate lymphoid cell-mediated lung tissue protection during acute respiratory virus infection.

Activated group 2 innate lymphoid cells (ILC2s) accumulate and promote inflammatory resolution and tissue repair in host defense against acute respiratory viral infections. However, the heterogeneity of ILC2s in the lung and the mechanisms by which ILC2 cells contribute to tissue repair remain elusive. Using single-cell RNA sequencing, we identify a transcriptionally distinct ILC2 subset that showed enrichment for wound healing signature genes and the transcription factor BATF. BATF promotes the proliferation and function of ILC2s and restricts their plasticity during infection with influenza virus. In the absence of BATF, ILC2s lose their immune protective properties and acquire pathogenic ILC3-like functions, leading to persistent neutrophil infiltration, tissue damage, and respiratory failure. Mechanistically, BATF directly binds to the cis-regulatory elements of wound healing genes, maintains their chromatin accessibility, and promotes their expression. Last, BATF plays an important role in an IL-33­ST2 feed-forward loop that supports ILC2 cell identity and function. Collectively, our findings shed light on a BATF-dependent ILC2 program, thereby providing a potential therapeutic target for terminating detrimental inflammation during acute viral infection.

Differential roles of BAF and PBAF subunits, Arid1b and Arid2, in MLL-AF9 leukemogenesis.

The Switch/Sugar Non-Fermenting (SWI/SNF) nucleosome remodeling complexes play important roles in normal development and in the development of various cancers. Core subunits of the SWI/SNF complexes have been shown to have oncogenic roles in acute myeloid leukemia. However, the roles of the unique targeting subunits, including that of Arid2 and Arid1b, in AML leukemogenesis are not well understood. Here, we used conditional knockout mouse models to elucidate their role in MLL-AF9 leukemogenesis. We uncovered that Arid2 has dual roles; enhancing leukemogenesis when deleted during leukemia initiation and yet is required during leukemia maintenance. Whereas, deleting Arid1b in either phase promotes leukemogenesis. Our integrated analyses of transcriptomics and genomic binding data showed that, globally, Arid2 and Arid1b regulate largely distinct sets of genes at different disease stages, respectively, and in comparison, to each other. Amongst the most highly dysregulated transcription factors upon their loss, Arid2 and Arid1b converged on the regulation of Etv4/Etv5, albeit in an opposing manner while also regulating distinct TFs including Gata2,Tcf4, Six4, Irf4 and Hmgn3. Our data demonstrate the differential roles of SWI/SNF subunits in AML leukemogenesis and emphasize that cellular context and disease stage are key in determining their functions during this process.

Ancient Oriental Wisdom still Works: Removing ARGs in Drinking Water by Boiling as compared to Chlorination.

Antibiotic resistance genes (ARGs) in municipal drinking water may not be effectively removed during centralized treatment. To reduce potential health risks, water disinfection at the point-of-use scale is warranted. This study investigated the performance of boiling, a prevalent household water disinfection means, in response to ARGs contamination. We found that boiling was more efficient in inactivating both Escherichia coli and environmental bacteria compared to chlorination and pasteurization. Boiling of environmental bacteria suspension removed a much broader spectrum of ARGs and mobile genetic elements (up to 141 genes) than chlorination (up to 13 genes), such better performance was largely attributed to a stronger inactivation of chlorine-tolerant bacteria including Acinetobacter and Bacillus. Accumulation of extracellular ARGs was found during low-temperature heating (≤ 80°C) and in the initial stage of chlorination (first 3 min when initial chlorine was 5 mg/L and first 12 min when initial chlorine was 1 mg/L). These extracellular ARGs as well as the intracellular ARGs got removed as the heating temperature increased or the chlorination time prolonged. Under the same treatment time (30 min), high-temperature heating (≥ 90.1°C) damaged the DNA structure more thoroughly than chlorination (5 mg/L). Taking into account the low transferability of ARGs after DNA melting, boiling may provide an effective point-of-use approach to attenuating bacterial ARGs in drinking water and is still worth promoting in the future.

BATF regulates progenitor to cytolytic effector CD8+ T cell transition during chronic viral infection.

During chronic viral infection, CD8+ T cells develop into three major phenotypically and functionally distinct subsets: Ly108+TCF-1+ progenitors, Ly108-CX3CR1- terminally exhausted cells and the recently identified CX3CR1+ cytotoxic effector cells. Nevertheless, how CX3CR1+ effector cell differentiation is transcriptionally and epigenetically regulated remains elusive. Here, we identify distinct gene regulatory networks and epigenetic landscapes underpinning the formation of these subsets. Notably, our data demonstrate that CX3CR1+ effector cells bear a striking similarity to short-lived effector cells during acute infection. Genetic deletion of Tbx21 significantly diminished formation of the CX3CR1+ subset. Importantly, we further identify a previously unappreciated role for the transcription factor BATF in maintaining a permissive chromatin structure that allows the transition from TCF-1+ progenitors to CX3CR1+ effector cells. BATF directly bound to regulatory regions near Tbx21 and Klf2, modulating their enhancer accessibility to facilitate the transition. These mechanistic insights can potentially be harnessed to overcome T cell exhaustion during chronic infection and cancer.

Harnessing the IL-21-BATF Pathway in the CD8+ T Cell Anti-Tumor Response.

In cancer, CD8+ T cells enter a dysfunctional state which prevents them from effectively targeting and killing tumor cells. Tumor-infiltrating CD8+ T cells consist of a heterogeneous population of memory-like progenitor, effector, and terminally exhausted cells that exhibit differing functional and self-renewal capacities. Our recently published work has shown that interleukin (IL)-21-producing CD4+ T cells help to generate effector CD8+ T cells within the tumor, which results in enhanced tumor control. However, the molecular mechanisms by which CD4+ helper T cells regulate the differentiation of effector CD8+ T cells are not well understood. In this study, we found that Basic Leucine Zipper ATF-Like Transcription Factor (BATF), a transcription factor downstream of IL-21 signaling, is critical to maintain CD8+ T cell effector function within the tumor. Using mixed bone marrow chimeras, we demonstrated that CD8+ T cell-specific deletion of BATF resulted in impaired tumor control. In contrast, overexpressing BATF in CD8+ T cells enhanced effector function and resulted in improved tumor control, bypassing the need for CD4+ helper T cells. Transcriptomic analyses revealed that BATF-overexpressing CD8+ T cells had increased expression of costimulatory receptors, effector molecules, and transcriptional regulators, which may contribute to their enhanced activation and effector function. Taken together, our study unravels a previously unappreciated CD4+ T cell-derived IL-21-BATF axis that could provide therapeutic insights to enhance effector CD8+ T cell function to fight cancer.

Arid2 regulates hematopoietic stem cell differentiation in normal hematopoiesis.

The switch/sugar nonfermenting (SWI/SNF) family of chromatin remodeling complexes have been implicated in normal hematopoiesis. The ARID2 protein is a component of the polybromo-associated BAF (PBAF), one of the two main SWI/SNF complexes. In the current study, we used a conditional Arid2 knockout mouse model to determine its role in normal hematopoiesis. We found that the loss of Arid2 has no discernable effects on steady-state hematopoiesis, with the exception of a modest effect on erythropoiesis. On bone marrow transplantation, however, the loss of Arid2 affects HSC differentiation in a cell-autonomous manner, resulting in significant decreases in the ability to reconstitute the lymphoid lineage. Gene expression analysis of Arid2 knockout cells revealed enrichment of myeloid-biased multipotent progenitor (MPP) cell signatures, while the lymphoid-biased MPPs are enriched in the wild type, consistent with the observed phenotype. Moreover, Arid2 knockout cells revealed enrichment of inflammatory pathways with upregulation of TLR receptors, as well as downstream signaling cascade genes. Furthermore, under lymphocyte-biased growth conditions in vitro, Arid2 null bone marrow cells have significantly impaired proliferation, which decreased further on lipopolysaccharide stimulation. Overall, these data suggest that the loss of Arid2 impairs HSC differentiation ability, and this effect may be mediated through upregulation of inflammatory pathways.

Effects of hydrodynamic shear stress on sludge properties, N2O generation, and microbial community structure during activated sludge process.

Sludge properties are critical to the treatment performance and potentially correlate with nitrous oxide (N2O) generation during activated sludge processes. The hydrodynamic shear stress induced by aeration has a significant influence on sludge properties and is inevitable for wastewater treatment plants (WWTPs). In this study, the effects of aerobic induced hydrodynamic shear stress on sludge properties, N2O generation, and microbial community structure were investigated using three parallel sequencing batch reactors (SBRs) with identical dissolved oxygen (DO) concentrations. Results showed that with a shear stress increase from 1.5 × 10-2 N/m2 to 5.0 × 10-2 N/m2, the COD and NH4+-N removal rates were enhanced from 89.4% to 94.0% and from 93.9% to 98.0%, respectively, while the TN removal rate decreased from 66.0% to 56.5%. Settleability of the activated sludge flocs (ASFs) also increased with the enhancement of shear stress, due to variation in sludge properties including particle size, regularity, compactibility, and EPS (extracellular polymeric substances) composition. The increase in shear stress promoted oxygen diffusion within the ASFs and mitigated NO2--N accumulation, leading to a decrease in the N2O-N conversion rate from (4.8 ± 0.3)% to (2.2 ± 0.6)% (based on TN removal). Microbial analysis results showed that the functional bacteria involved in the biological nitrogen removal was closely related with shear stress. The increase in shear stress favored the enrichment of nitrite oxidizing bacteria (NOB) while suppressed the accumulation of ammonia-oxidizing bacteria (AOB) and denitrifying bacteria (DNB).

Effects of exogenous N-acyl-homoserine lactones on nutrient removal, sludge properties and microbial community structures during activated sludge process.

This study investigated the effects of exogenous N-acyl-homoserine lactone (AHL) signal molecules, N-hexanoyl-l-homoserine lactone (C6-HSL) and N-octanoyl-l-homoserine lactone (C8-HSL), on treatment performance, sludge properties and microbial community structures in activated sludge systems. Results showed that the nitrification and denitrification efficiencies were enhanced with the addition of signal molecules. The particle size, irregularity, and internal mass transfer resistance of activated sludge flocs (ASFs) increased, primarily because dosing AHLs led to a content increase and chemical composition variation of extracellular polymeric substances (EPS) in sludge. Microbial analysis indicated an increase in both the bacterial richness and diversity of the systems. The relative abundances of the key functional groups, including bacteria related to C and N removal and EPS production, varied correspondingly. This study presents an insight into the comprehensive understanding of the effects of AHL-based quorum sensing on activated sludge treatment process.

Distribution characteristics and noncarcinogenic risk assessment of culturable airborne bacteria and fungi during winter in Xinxiang, China.

Bioaerosols are an important component of particulate matter in the atmosphere and are harmful to human health. In this study, the concentration, size distribution, and factors influencing culturable airborne bacteria and fungi in the atmosphere were investigated using a six-stage impactor device in the city of Xinxiang, China, during the winter season. The results revealed that the concentration of culturable airborne bacteria and fungi varied significantly during the sampling period: 4595 ± 3410 and 6358 ± 5032 CFU/m3, respectively. The particle sizes of the bioaerosols were mainly within stage V (1.1-2.1 µm), and fine particulate matter accounted for 45.9% ± 18.9% of airborne bacteria and 52.0% ± 18.5% of airborne fungi, respectively. With the deterioration of air quality, the concentration of airborne fungi gradually increased, and that of airborne bacteria increased when the air quality index was lower than 200 and decreased when it was higher than 200. With respect to the diurnal variation pattern of bioaerosol concentration, the highest and lowest concentrations were registered at night and noon, respectively, probably because of changes in ultraviolet radiation intensity. Bioaerosol concentration positively correlated with humidity, concentration of PM2.5, PM10, SO2, and NO2 and negatively correlated with O3 concentration. The risk of exposure of humans to the airborne bacteria was primarily associated with the respiratory inhalation pathway, and the risk of skin exposure was negligible. These results should improve our understanding of the threat of bioaerosols to public health.

Characteristics of N2O generation within the internal micro-environment of activated sludge flocs under different dissolved oxygen concentrations.

Nitrous oxide (N2O) is a strong greenhouse gas that is produced in significant quantities through biological nitrogen removal processes in wastewater treatment plants; however, N2O generation within the internal micro-environment of activated sludge flocs (ASFs) is poorly understood. In this study, microelectrodes and molecular techniques were employed to investigate the concentrations of N2O and other chemicals and the composition and distribution of microbes within ASFs, respectively. The results showed that N2O generation was correlated with the ASF micro-environment, and was significantly influenced by the dissolved oxygen (DO) concentration of the bulk wastewater. Equal N2O, DO, NH4+-N, and NO3--N concentrations were found in small flocs (<100 µm). By contrast, higher N2O generation rates and lower DO, NH4+-N, and NO3--N concentrations were detected in the center of large flocs (>200 µm) compared with those at their surfaces. Microbial structures of varying particle sizes were distinct and depended on the micro-environmental characteristics.

[Emission Inventory of Greenhouse Gas from Urban Wastewater Treatment Plants and Its Temporal and Spatial Distribution in China].

Urban wastewater treatment plants are considered important greenhouse gas resources with massive emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) during operation. Based on the emission factor approach of pollutant reduction, the 2014 emission inventory of greenhouse gases (CO2, CH4, and N2O) from urban wastewater treatment plants in China was established. In addition, the temporal and spatial distribution and influencing factors of greenhouse gas emissions were analyzed in this study. The results showed that total emissions of greenhouse gas from urban wastewater treatment plants in China was 7348.60 Gg (CO2-eq) in 2014, which included CO2, CH4, and N2O emissions of 6054.57 Gg, 27.47 Gg (769.08 Gg, CO2-eq), and 1.98 Gg (524.95 Gg, CO2-eq), respectively. The difference in greenhouse gas emissions among provinces was significant:high emissions appeared in the eastern areas of China, low emissions were observed in the northwest, and hardly any emissions were found in Xizang. From 2005 to 2014, annual greenhouse gas emissions from urban sewage treatment plants in China increased by 229.4%, and the rates of CO2, CH4, and N2O increased by 217.9%, 217.9%, and 520.3%, respectively. The regional economic development level and number of wastewater treatment plants were correlated the most with the emissions of greenhouse gasses, and the per-capita protein supply was closely related with the N2O emission.

Inhibition of Myeloperoxidase by N-Acetyl Lysyltyrosylcysteine Amide Reduces Oxidative Stress-Mediated Inflammation, Neuronal Damage, and Neural Stem Cell Injury in a Murine Model of Stroke.

Recent studies suggest that myeloperoxidase (MPO)-dependent oxidative stress plays a significant role in brain injury in stroke patients. We previously showed that N-acetyl lysyltyrosylcysteine amide (KYC), a novel MPO inhibitor, significantly decreased infarct size, blood-brain barrier leakage, infiltration of myeloid cells, loss of neurons, and apoptosis in the brains of middle cerebral artery occlusion (MCAO) mice. Inhibition of MPO also noticeably reduced neurologic severity scores of MCAO mice. Thus, our data support the idea that MPO-dependent oxidative stress plays a detrimental role in tissue injury in ischemic stroke. However, the mechanisms of MPO-induced injury in stroke are still largely unknown. Here, we present new evidence showing that KYC treatment greatly reduced inflammation by decreasing the number of proinflammatory M1 microglial cells and N1 neutrophils in the brains of MCAO mice. KYC also markedly reduced the expression of high-mobility group box 1, receptor for advanced glycation end products, and nuclear factor-κB in the brains of MCAO mice. Both neurons and neural stem cells (NSCs) were oxidatively injured by MPO-dependent oxidative stress in MCAO mice. Inhibiting MPO-dependent oxidative stress with KYC significantly reduced oxidative injury and apoptosis in neurons and NSCs. KYC treatment also protected transplanted exogenous NSCs in the brains of MCAO mice. Thus, our studies suggest that MPO-dependent oxidative stress directly injures brain tissues by oxidizing neurons and NSCs and increasing inflammation during stroke. Inhibition of MPO activity with KYC preserves neuronal function and helps the brain recover from injury after stroke.

Inhibition of myeloperoxidase by N-acetyl lysyltyrosylcysteine amide reduces experimental autoimmune encephalomyelitis-induced injury and promotes oligodendrocyte regeneration and neurogenesis in a murine model of progressive multiple sclerosis.

It is known that oxidative stress produced by proinflammatory myeloid cells plays an important role in demyelination and neuronal injury in progressive multiple sclerosis (MS). Myeloperoxidase (MPO) is a pro-oxidative enzyme released from myeloid cells during inflammation. It has been shown that MPO-dependent oxidative stress plays important roles in inducing tissue injury in many inflammatory diseases. In this report, we treated NOD experimental autoimmune encephalomyelitis (EAE) mice, a murine model of progressive MS, with N-acetyl lysyltyrosylcysteine amide (KYC), a novel specific MPO inhibitor. Our data showed that KYC treatment not only attenuated MPO-mediated oxidative stress but also reduced demyelination and axonal injury in NOD EAE mice. More importantly, we found that KYC treatment increased oligodendrocyte regeneration and neurogenesis in NOD EAE mice. Taken together, our data suggests that targeting MPO should be a good therapeutic approach for reducing oxidative injury and preserving neuronal function in progressive MS patients.