Rv0100: An essential acyl carrier protein from M. tuberculosis important in dormancy.

We have identified an acyl-carrier protein, Rv0100, that is up-regulated in a dormancy model. This protein plays a critical role in the fatty acid biosynthesis pathway, which is important for energy storage and cell wall synthesis in Mycobacterium tuberculosis (MTB). Knocking out the Rv0100 gene resulted in a significant reduction of growth compared to wild-type MTB in the Wayne model of non-replicating persistence. We have also shown that Rv0100 is essential for the growth and survival of this pathogen during infection in mice and a macrophage model. Furthermore, knocking out Rv0100 disrupted the synthesis of phthiocerol dimycocerosates, the virulence-enhancing lipids produced by MTB and Mycobacterium bovis. We hypothesize that this essential gene contributes to MTB virulence in the state of latent infection. Therefore, inhibitors targeting this gene could prove to be potent antibacterial agents against this pathogen.

Risk of type III secretion systems in burn patients with Pseudomonas aeruginosa wound infection: A systematic review and meta-analysis.

PURPOSE: The pathogenesis of Pseudomonas aeruginosa is multifactorial and attributed to the production of several cell-associated and extracellular virulence factors including those implicated in adherence, iron uptake, exoenzymes (Exo) and exotoxins. The present study aimed to determine the prevalence of type III secretion systems (T3SS) effectors in Iranian burn patients with P. aeruginosa wound infection. METHODS: A systematic search was conducted to identify papers published by Iranian authors in the Web of Science, PubMed, Scopus, Embase, and Google Scholar electronic databases during the period of January, 2000 to December, 2018. Publications which met our inclusion criteria were selected for data extraction and analysis by Comprehensive Meta-Analysis Software. The inclusion criteria were articles that include burn patients with a wound infection caused by P. aeruginosa, and reported the prevalence of aimed exoenzymes. RESULTS: Ten publications were selected out of 15 full-text reviewed articles with the inclusion criteria. Of ten studies, the pooled prevalence of ExoS producing isolates was estimated at 57.1% (95% CI: 40.3-72.5%). Five studies reported the prevalence of ExoU and ExoT, from which, the pooled prevalence of ExoU and ExoT producing isolates was estimated at 51.4% (95% CI: 31.4-70.9%) and 86.4% (95% CI: 48.1-97.8%), respectively. Four studies reported the prevalence of ExoY, from which, the pooled prevalence of ExoY producing isolates was estimated at 79.0% (95% CI: 48.6-93.8%). CONCLUSION: Our results showed a remarkable prevalence of T3SS-positive genotype in patients with burn injuries. These findings provided attractive targets for new therapeutic strategies for burn patients who were infected with cytotoxin-producing P. aeruginosa.

Inositol Monophosphatase: A Bifunctional Enzyme in Mycobacterium smegmatis.

Inositol monophosphatase (IMPase) is a crucial enzyme for the biosynthesis of phosphatidylinositol, an essential component in mycobacterial cell walls. IMPase A (ImpA) from Mycobacterium smegmatis is a bifunctional enzyme that also functions as a fructose-1,6-bisphosphatase (FBPase). To better understand the bifunctional nature of this enzyme, point mutagenesis was conducted on several key residues and their enzyme activity was tested. Our results along with active site models support the fact that ImpA is a bifunctional enzyme with residues Gly94, Thr95 hypothesized to be contributing to the FBPase activity and residues Trp220, Asp221 hypothesized to be contributing to the IMPase activity. Double mutants, W220A + D221A reduced both FBPase and IMPase activity drastically while the double mutant G94A + T95A surprisingly partially restored the IMPase activity compared to the single mutants. This study establishes the foundation toward obtaining a better understanding of the bifunctional nature of this enzyme.

Cross-immunoreactivity between bacterial aquaporin-Z and human aquaporin-4: potential relevance to neuromyelitis optica.

Neuromyelitis optica (NMO) is a chronic inflammatory disease of the CNS that is mediated, in part, by a self-reactive Ab against the astrocyte aquaporin-4 protein. In the current study, we examined the possibility and the biological significance of cross-immunoreactivity between bacterial aquaporin-Z and human aquaporin-4 proteins. Sequence-alignment analysis of these proteins revealed several regions of significant structural homology. Some of the homologous regions were also found to overlap with important immune and disease-relevant epitopes. Cross-immunoreactivity between aquaporin-Z and aquaporin-4 was investigated and ascertained in multiple immune-based assays using sera from patients with neuromyelitis optica, immune mouse serum, and Abs raised against aquaporin-Z. The biological significance of this phenomenon was established in series of experiments demonstrating that induction of an immune response against aquaporin-Z or its homologous regions can also trigger an autoimmune reaction against aquaporin-4 and inflammation of the CNS. Our study indicates that the autoimmune response against aquaporin-4 in neuromyelitis optica may be triggered by infection-induced cross-immunoreactivity and presents a new perspective on the pathogenesis of this disease.

Overexpression of the dominant-negative form of interferon regulatory factor 1 in oligodendrocytes protects against experimental autoimmune encephalomyelitis.

Interferon regulatory factor 1 (IRF-1) is a transcription factor that has been implicated in the pathogenesis of the human autoimmune demyelinating disease multiple sclerosis (MS) and in its animal model, experimental autoimmune encephalomyelitis (EAE). The goal of the present study was to directly examine the role of IRF-1 in oligodendrocyte injury and inflammatory demyelination. For the purpose of this study, we generated a transgenic mouse line (CNP/dnIRF-1) that overexpresses the dominant-negative form of IRF-1 (dnIRF1) specifically in oligodendrocytes. CNP/dnIRF-1 mice exhibited no phenotypic abnormalities but displayed suppressed IRF-1 signaling in oligodendrocytes. The major finding of our study was that the CNP/dnIRF-1 mice, compared with the wild-type mice, were protected against EAE, a phenomenon associated with significant reduction of inflammatory demyelination and with oligodendrocyte and axonal preservation. The observed protection was related to suppressed IRF-1 signaling and impaired expression of immune and proapoptotic genes in oligodendrocytes. No significant differences in the peripheral immune responses between the wild-type and the CNP/dnIRF-1 mice were identified throughout the experiments. This study indicates that IRF-1 plays a critical role in the pathogenesis of EAE by mediating oligodendrocyte response to inflammation and injury. It also suggests that oligodendrocytes are actively involved in the neuroimmune network, and that exploring oligodendrocyte-related pathogenic mechanisms, in addition to the conventional immune-based ones, may have important therapeutic implications in MS.

IRF-1 signaling in central nervous system glial cells regulates inflammatory demyelination.

The present study provides evidence that interferon regulatory factor 1 (IRF-1) signaling in glial cells is involved in the pathogenesis of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). Using a bone marrow chimera model of EAE, we demonstrated that CNS IRF-1 regulates inflammatory demyelination and disease severity independently of the peripheral immune cells. In addition, we identified Caspase 1, a pro-inflammatory and pro-apoptotic molecule, as an important transcriptional target of IRF-1. The findings of our study indicate that IRF-1 signaling in glial cells serves as a final common pathway of inflammatory demyelination and may have important clinical implications in MS.

Central nervous system expression of interferon regulatory factor 1 regulates experimental autoimmune encephalomyelitis.

Interferon regulatory factor 1 (IRF-1) is a transcription factor that has been implicated in the disease mechanisms of experimental autoimmune encephalomyelitis (EAE). In this study, we examined the role of central nervous system (CNS) expression of IRF-1 in the natural course of EAE. In an effort to dissect the CNS effects from the peripheral immune effects of IRF-1, we generated bone marrow chimera mice that differentially expressed IRF-1 in the CNS and in the immune system. We found that mice lacking IRF-1 in the CNS developed significantly milder clinical symptoms and shorter disease duration compared to those with wild-type background. Based on these results, we concluded that the CNS expression of IRF-1 regulates the disease process in EAE. Our findings are relevant to the inflammatory mechanisms involved in multiple sclerosis and may provide a basis for development of novel therapeutic targets of the disease.

STAT1/IRF-1 signaling pathway mediates the injurious effect of interferon-gamma on oligodendrocyte progenitor cells.

Interferon-gamma (IFN-gamma) is a pleiotropic cytokine that is critically involved in the pathogenesis of inflammatory demyelinating diseases. There is strong evidence that IFN-gamma can function as a distinct and independent injurious factor to oligodendrocyte progenitor cells (OPCs). The intracellular signaling pathways leading to OPC death, however, remain poorly understood. In this study, we examined IFN-gamma signaling in OPCs in relation to cell death in vitro. Using expression knock-down and forced overexpression methods, we directly demonstrated the role of signal transducer and transcription activator 1 (STAT1) and interferon-regulated factor 1 (IRF-1) in IFN-gamma- induced OPC death. In addition, our study identified two proapoptotic genes, caspase 1 and double-stranded RNA-dependent protein kinase (PKR), whose expression was upregulated by IFN-gamma and transcriptionally controlled by IRF-1. The conclusion of this study is that STAT1 and IRF-1 function as components of the signaling pathway that mediates IFN-gamma-induced OPC death.

Differential regulation of sphingomyelin synthesis and catabolism in oligodendrocytes and neurons.

Neurons (both primary cultures of 3-day rat hippocampal neurons and embryonic chick neurons) rapidly converted exogenous NBD-sphingomyelin (SM) to NBD-Cer but only slowly converted NBD-Cer to NBD-SM. This was confirmed by demonstrating low in vitro sphingomyelin synthase (SMS) and high sphingomyelinase (SMase) activity in neurons. Similar results were observed in a human neuroblastoma cell line (LA-N-5). In contrast, primary cultures of 3-day-old rat oligodendrocytes only slowly converted NBD-SM to NBD-Cer but rapidly converted NBD-Cer to NBD-SM. This difference was confirmed by high in vitro SMS and low SMase activity in neonatal rat oligodendrocytes. Similar results were observed in a human oligodendroglioma cell line. Mass-Spectrometric analyses confirmed that neurons had a low SM/Cer ratio of (1.5 : 1) whereas oligodendroglia had a high SM/Cer ratio (9 : 1). Differences were also confirmed by [(3)H]palmitate-labeling of ceramide, which was higher in neurons compared with oligodendrocytes. Stable transfection of human oligodendroglioma cells with neutral SMase, which enhanced the conversion of NBD-SM to NBD-Cer and increased cell death, whereas transfection with SMS1 or SMS2 enhanced conversion of NBD-Cer to NBD-SM and was somewhat protective against cell death. Thus, SMS rather than SMases may be more important for sphingolipid homeostasis in oligodendrocytes, whereas the reverse may be true for neurons.

Expression of the receptor for advanced glycation end products in oligodendrocytes in response to oxidative stress.

Demyelination is a common result of oxidative stress in the nervous system, and we report here that the response of oligodendrocytes to oxidative stress involves the receptor for advanced glycation end products (RAGE). RAGE has not previously been reported in neonatal rat oligodendrocytes (NRO), but, by using primers specific for rat RAGE, we were able to show expression of messenger RNA (mRNA) for RAGE in NRO, and a 55-kDa protein was detected by Western blotting with antibodies to RAGE. Neonatal rat oligodendrocytes stained strongly for RAGE, suggesting membrane localization of RAGE. Addition of low concentrations of hydrogen peroxide (100 microM) initiated 55-kDa RAGE shedding from the cell membrane and the appearance of "soluble" 45-kDa RAGE in the culture medium, followed by restoration of RAGE expression to normal levels. Increasing hydrogen peroxide concentration (>200 microM) resulted in no restoration of RAGE, and the cells underwent apoptosis and necrosis. We further confirmed the observation in a human oligodendroglioma-derived (HOG) cell line. Both the antioxidant N-acetyl-L-cysteine and the broad-spectrum metalloproteases inhibitor TAPI0 were able partially to inhibit shedding of RAGE, suggesting involvement of metalloproteases in cleavage to produce soluble RAGE. The level of 55-kDa RAGE in autopsy brain of patients undergoing neurodegeneration with accompanying inflammation [multiple sclerosis and neuronal ceroid-lipofuscinosis (Batten's disease)] was much lower than that in age-matched controls, suggesting that shedding of RAGE might occur as reactive oxygen species accumulate in brain cells and be part of the process of neurodegeneration.

Interferon-gamma-oligodendrocyte interactions in the regulation of experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is an animal model of the human demyelinating disorder multiple sclerosis (MS). The immune cytokine interferon-gamma (IFN-gamma) is believed to participate in disease pathogenesis in both EAE and MS. In the present study, we examined the significance of IFN-gamma-oligodendrocyte interactions in the course of EAE. For the purpose of our study, we used the previously described [proteolipid protein/suppressor of cytokine signaling 1 (PLP/SOCS1)] transgenic mouse line that displays suppressed oligodendrocyte responsiveness to IFN-gamma. PLP/SOCS1 mice developed EAE with an accelerated onset associated with enhanced early inflammation and markedly increased oligodendrocyte apoptosis. Moreover, we found that IFN-gamma pretreatment of mature oligodendrocytes in vitro had a protective effect against oxidative stress and the inhibition of proteasome activity and resulted in upregulation in expression of a number of chemokines, including CXCL10 (IP10), CCL2 (MCP-1), CCL3 (MCP-1alpha), and CCL5 (RANTES). These results suggest that IFN-gamma-oligodendrocyte interactions are of significance to the clinical and pathological aspects of EAE. In addition, the present study suggests that oligodendrocytes are not simply targets of inflammatory injury but active participants of the neuroimmune network operating during the course of EAE.

Ceramide in rafts (detergent-insoluble fraction) mediates cell death in neurotumor cell lines.

Detergent-resistant lipid microdomains (Rafts) were isolated from human oligodendroglioma (HOG), human neuroblastoma (LA-N-5), and immortalized dorsal root ganglion (F-11) cell lines by sucrose-density gradient ultracentrifugation and shown to be enriched in cholesterol, sphingomyelin, and ceramide. [(3)H]palmitate labeling allowed the Raft fraction to be easily identified as a sharp peak of (3)H radioactivity in the 5-30% sucrose interphase. Treatment of [(3)H]palmitate-labeled cells with staurosporine (to activate caspase 8 and induce apoptosis) or exogenous sphingomyelinase specifically increased the [(3)H]ceramide content of the Raft fraction. Depletion of cholesterol with beta-methylcyclodextran decreased Raft formation and partially blocked staurosporine-induced apoptosis. Similarly, treatment of cells with Fumonisin B1 to inhibit de novo sphingolipid synthesis by 50% reduced the labeling of the Raft fraction and partially blocked staurosporine-induced apoptosis. Staurosporine treatment activated neutral sphingomyelinase but had no effect on acid sphingomyelinase activity or on other lysosomal hydrolases, such as alpha-L-fucosidase. Most of the neutral sphingomyelinase activity is in the Raft fraction, suggesting that the conversion of sphingomyelin to ceramide in Rafts is an important event in neural cell apoptosis.