Discovering selective antiferroptotic inhibitors of the 15LOX/PEBP1 complex noninterfering with biosynthesis of lipid mediators.

Programmed ferroptotic death eliminates cells in all major organs and tissues with imbalanced redox metabolism due to overwhelming iron-catalyzed lipid peroxidation under insufficient control by thiols (Glutathione (GSH)). Ferroptosis has been associated with the pathogenesis of major chronic degenerative diseases and acute injuries of the brain, cardiovascular system, liver, kidneys, and other organs, and its manipulation offers a promising new strategy for anticancer therapy. This explains the high interest in designing new small-molecule-specific inhibitors against ferroptosis. Given the role of 15-lipoxygenase (15LOX) association with phosphatidylethanolamine (PE)-binding protein 1 (PEBP1) in initiating ferroptosis-specific peroxidation of polyunsaturated PE, we propose a strategy of discovering antiferroptotic agents as inhibitors of the 15LOX/PEBP1 catalytic complex rather than 15LOX alone. Here we designed, synthesized, and tested a customized library of 26 compounds using biochemical, molecular, and cell biology models along with redox lipidomic and computational analyses. We selected two lead compounds, FerroLOXIN-1 and 2, which effectively suppressed ferroptosis in vitro and in vivo without affecting the biosynthesis of pro-/anti-inflammatory lipid mediators in vivo. The effectiveness of these lead compounds is not due to radical scavenging or iron-chelation but results from their specific mechanisms of interaction with the 15LOX-2/PEBP1 complex, which either alters the binding pose of the substrate [eicosatetraenoyl-PE (ETE-PE)] in a nonproductive way or blocks the predominant oxygen channel thus preventing the catalysis of ETE-PE peroxidation. Our successful strategy may be adapted to the design of additional chemical libraries to reveal new ferroptosis-targeting therapeutic modalities.

Kinetic and structural investigations of novel inhibitors of human epithelial 15-lipoxygenase-2.

Human epithelial 15-lipoxygenase-2 (h15-LOX-2, ALOX15B) is expressed in many tissues and has been implicated in atherosclerosis, cystic fibrosis and ferroptosis. However, there are few reported potent/selective inhibitors that are active ex vivo. In the current work, we report newly discovered molecules that are more potent and structurally distinct from our previous inhibitors, MLS000545091 and MLS000536924 (Jameson et al, PLoS One, 2014, 9, e104094), in that they contain a central imidazole ring, which is substituted at the 1-position with a phenyl moiety and with a benzylthio moiety at the 2-position. The initial three molecules were mixed-type, non-reductive inhibitors, with IC50 values of 0.34 ±â€¯0.05 µM for MLS000327069, 0.53 ±â€¯0.04 µM for MLS000327186 and 0.87 ±â€¯0.06 µM for MLS000327206 and greater than 50-fold selectivity versus h5-LOX, h12-LOX, h15-LOX-1, COX-1 and COX-2. A small set of focused analogs was synthesized to demonstrate the validity of the hits. In addition, a binding model was developed for the three imidazole inhibitors based on computational docking and a co-structure of h15-LOX-2 with MLS000536924. Hydrogen/deuterium exchange (HDX) results indicate a similar binding mode between MLS000536924 and MLS000327069, however, the latter restricts protein motion of helix-α2 more, consistent with its greater potency. Given these results, we designed, docked, and synthesized novel inhibitors of the imidazole scaffold and confirmed our binding mode hypothesis. Importantly, four of the five inhibitors mentioned above are active in an h15-LOX-2/HEK293 cell assay and thus they could be important tool compounds in gaining a better understanding of h15-LOX-2's role in human biology. As such, a suite of similar pharmacophores that target h15-LOX-2 both in vitro and ex vivo are presented in the hope of developing them as therapeutic agents.

Genetic control of ColE1 plasmid stability that is independent of plasmid copy number regulation.

ColE1-like plasmid vectors are widely used for expression of recombinant genes in E. coli. For these vectors, segregation of individual plasmids into daughter cells during cell division appears to be random, making them susceptible to loss over time when no mechanisms ensuring their maintenance are present. Here we use the plasmid pGFPuv in a recA relA strain as a sensitized model to study factors affecting plasmid stability in the context of recombinant gene expression. We find that in this model, plasmid stability can be restored by two types of genetic modifications to the plasmid origin of replication (ori) sequence: point mutations and a novel 269 nt duplication at the 5' end of the plasmid ori, which we named DAS (duplicated anti-sense) ori. Combinations of these modifications produce a range of copy numbers and of levels of recombinant expression. In direct contradiction with the classic random distribution model, we find no correlation between increased plasmid copy number and increased plasmid stability. Increased stability cannot be explained by reduced levels of recombinant gene expression either. Our observations would be more compatible with a hybrid clustered and free-distribution model, which has been recently proposed based on detection of individual plasmids in vivo using super-resolution fluorescence microscopy. This work suggests a role for the plasmid ori in the control of segregation of ColE1 plasmids that is distinct from replication initiation, opening the door for the genetic regulation of plasmid stability as a strategy aimed at enhancing large-scale recombinant gene expression or bioremediation.

Experimental and In Silico Analysis of TEM ß-Lactamase Adaptive Evolution.

Multiple mutations often have non-additive (epistatic) phenotypic effects. Epistasis is of fundamental biological relevance but is not well understood mechanistically. Adaptive evolution, i.e., the evolution of new biochemical activities, is rich in epistatic interactions. To better understand the principles underlying epistasis during genetic adaptation, we studied the evolution of TEM-1 ß-lactamase variants exhibiting cefotaxime resistance. We report the collection of a library of 487 observed evolutionary trajectories for TEM-1 and determine the epistasis status based on cefotaxime resistance phenotype for 206 combinations of 2-3 TEM-1 mutations involving 17 positions under adaptive selective pressure. Gain-of-function (GOF) mutations are gatekeepers for adaptation. To see if GOF phenotypes can be inferred based solely on sequence data, we calculated the enrichment of GOF mutations in the different categories of epistatic pairs. Our results suggest that this is possible because GOF mutations are particularly enriched in sign and reciprocal sign epistasis, which leave a major imprint on the sequence space accessible to evolution. We also used FoldX to explore the relationship between thermodynamic stability and epistasis. We found that mutations in observed evolutionary trajectories tend to destabilize the folded structure of the protein, albeit their cumulative effects are consistently below the protein's free energy of folding. The destabilizing effect is stronger for epistatic pairs, suggesting that modest or local alterations in folding stability can modulate catalysis. Finally, we report a significant relationship between epistasis and the degree to which two protein positions are structurally and dynamically coupled, even in the absence of ligand.

Mycobacterium smegmatis RoxY is a repressor of oxyS and contributes to resistance to oxidative stress and bactericidal ubiquitin-derived peptides.

The mycobactericidal properties of macrophages include the generation of reactive oxygen intermediates and the delivery of bacteria to a hydrolytic lysosome enriched in bactericidal ubiquitin-derived peptides (Ub-peptides). To better understand the interactions of ubiquitin-derived peptides with mycobacteria and identify putative mycobacterial intrinsic resistance mechanisms, we screened for transposon mutants with increased susceptibility to the bactericidal Ub-peptide Ub2. We isolated 27 Mycobacterium smegmatis mutants that were hypersusceptible to Ub2. Two mutants were isolated that possessed mutations in the msmeg_0166 gene, which encodes a transcriptional regulator. The msmeg_0166 mutants were also hypersusceptible to other host antimicrobial peptides and oxidative stress. In characterizing msmeg_0166, we found that it encodes a repressor of oxyS, and therefore we have renamed the gene roxY. We demonstrate that RoxY and OxyS contribute to M. smegmatis resistance to oxidative stress. An ahpD transposon mutant was also isolated in our screen for Ub-peptide hypersusceptibility. Overexpression of oxyS in M. smegmatis reduced transcription of the ahpCD genes, which encode a peroxide detoxification system. Our data indicate that RoxY, OxyS, and AhpD play a role in the mycobacterial oxidative stress response and are important for resistance to host antimicrobial peptides.

DHA 12-LOX-derived oxylipins regulate platelet activation and thrombus formation through a PKA-dependent signaling pathway.

BACKGROUND: The effects of docosahexaenoic acid (DHA) on cardiovascular disease are controversial and a mechanistic understanding of how this omega-3 polyunsaturated fatty acid (ω-3 PUFA) regulates platelet reactivity and the subsequent risk of a thrombotic event is warranted. In platelets, DHA is oxidized by 12-lipoxygenase (12-LOX) producing the oxidized lipids (oxylipins) 11-HDHA and 14-HDHA. We hypothesized that 12-LOX DHA-oxylipins may be involved in the beneficial effects observed in dietary supplemental treatment with ω-3 PUFAs or DHA itself. OBJECTIVES: To determine the effects of DHA, 11-HDHA, and 14-HDHA on platelet function and thrombus formation, and to elucidate the mechanism by which these ω-3 PUFAs regulate platelet activation. METHODS AND RESULTS: DHA, 11-HDHA, and 14-HDHA attenuated collagen-induced human platelet aggregation, but only the oxylipins inhibited ⍺IIbß3 activation and decreased ⍺-granule secretion. Furthermore, treatment of whole blood with DHA and its oxylipins impaired platelet adhesion and accumulation to a collagen-coated surface. Interestingly, thrombus formation was only diminished in mice treated with 11-HDHA or 14-HDHA, and mouse platelet activation was inhibited following acute treatment with these oxylipins or chronic treatment with DHA, suggesting that under physiologic conditions, the effects of DHA are mediated through its oxylipins. Finally, the protective mechanism of DHA oxylipins was shown to be mediated via activation of protein kinase A. CONCLUSIONS: This study provides the first mechanistic evidence of how DHA and its 12-LOX oxylipins inhibit platelet activity and thrombus formation. These findings support the beneficial effects of DHA as therapeutic intervention in atherothrombotic diseases.

Comprehensive maternal serum proteomic profiles of preclinical and clinical preeclampsia.

We systematically characterized maternal serum proteome in women with clinical preeclampsia (PE) and asymptomatic women in early pregnancy that subsequently developed PE. Clinical PE cohort comprised 30 patients with mild PE, 30 with severe PE, and 58 normotensive women. Preclinical PE cohort included 149 women whose serum samples were collected at 8-14 gestational weeks and in whom 30 women later developed mild and 40 severe PE. Serum proteome was analyzed and enzyme-linked immunosorbent assays were used for protein quantification. In Clinical PE, fibronectin, pappalysin-2, choriogonadotropin-beta, apolipoprotein C-III, cystatin-C, vascular endothelial growth factor receptor-1, and endoglin were more abundant compared to normotensive women. In preclinical PE, differently expressed proteins included placental, vascular, transport, matrix, and acute phase proteins. Angiogenic and antiangiogenic proteins were not significant. We conclude that placental and antiangiogenic proteins are abundant in clinical PE. In preclinical PE, proteomic profile is distinct and different from that in clinical PE.

Fluorescence-Based Reporters for Detection of Mutagenesis in E. coli.

Mutagenesis in model organisms following exposure to chemicals is used as an indicator of genotoxicity. Mutagenesis assays are also used to study mechanisms of DNA homeostasis. This chapter focuses on detection of mutagenesis in prokaryotes, which boils down to two approaches: reporter inactivation (forward mutation assay) and reversion of an inactivating mutation (reversion mutation assay). Both methods are labor intensive, involving visual screening, quantification of colonies on solid media, or determining a Poisson distribution in liquid culture. Here, we present two reversion reporters for in vivo mutagenesis that produce a quantitative output, and thus have the potential to greatly reduce the amount of test chemical and labor involved in these assays. This output is obtained by coupling a TEM ß lactamase-based reversion assay with GFP fluorescence, either by placing the two genes on the same plasmid or by fusing them translationally and interrupting the N-terminus of the chimeric ORF with a stop codon. We also describe a reporter aimed at facilitating the monitoring of continuous mutagenesis in mutator strains. This reporter couples two reversion markers, allowing the temporal separation of mutation events in time, thus providing information about the dynamics of mutagenesis in mutator strains. Here, we describe these reporter systems, provide protocols for use, and demonstrate their key functional features using error-prone Pol I mutagenesis as a source of mutations.

Genotoxicants target distinct molecular networks in neonatal neurons.

BACKGROUND: Exposure of the brain to environmental agents during critical periods of neuronal development is considered a key factor underlying many neurologic disorders. OBJECTIVES: In this study we examined the influence of genotoxicants on cerebellar function during early development by measuring global gene expression changes. METHODS: We measured global gene expression in immature cerebellar neurons (i.e., granule cells) after treatment with two distinct alkylating agents, methylazoxymethanol (MAM) and nitrogen mustard (HN2). Granule cell cultures were treated for 24 hr with MAM (10-1,000 microM) or HN2 (0.1-20 microM) and examined for cell viability, DNA damage, and markers of apoptosis. RESULTS: Neuronal viability was significantly reduced (p < 0.01) at concentrations > 500 microM for MAM and > 1.0 microM for HN2; this correlated with an increase in both DNA damage and markers of apoptosis. Neuronal cultures treated with sublethal concentrations of MAM (100 microM) or HN2 (1.0 microM) were then examined for gene expression using large-scale mouse cDNA microarrays (27,648). Gene expression results revealed that a) global gene expression was predominantly up-regulated by both genotoxicants; b) the number of down-regulated genes was approximately 3-fold greater for HN2 than for MAM; and c) distinct classes of molecules were influenced by MAM (i.e, neuronal differentiation, the stress and immune response, and signal transduction) and HN2 (i.e, protein synthesis and apoptosis). CONCLUSIONS: These studies demonstrate that individual genotoxicants induce distinct gene expression signatures. Further study of these molecular networks may explain the variable response of the developing brain to different types of environmental genotoxicants.

Proteomic profiling of mature CD10+ B-cell lymphomas.

Proteomic profiling with protein-chip technology has been used successfully to discover biomarkers with potential clinical usefulness in several cancer types. Little proteomic study has been done in B-cell lymphomas. We determined whether the expression of a set of proteins by protein-chip technology coupled with new informatics tools could be used to build a model to molecularly classify B-cell lymphoma subgroups. We used surface-enhanced laser desorption/ionization time-of-flight mass spectrometry to analyze 18 CD10+ B-cell lymphomas, including 6 grade 1 (G1) follicular lymphomas (FLs), 7 grade 3 (G3) FLs, and 5 Burkitt lymphomas. We used 7 reactive follicular hyperplasia cases as a control group. By using SAX2 ProteinChip arrays (Ciphergen Biosystems, Fremont, CA), we found a unique protein expression profile for each type of lesion. Two-way hierarchical clustering analysis of these protein expression profiles differentiated reactive follicular hyperplasia, FL, and Burkitt lymphoma, with 5 major clusters of differentially expressed protein peaks. In addition, we identified histone H4 as a potential differentially expressed protein marker that seems to distinguish G1 from G3 FL. To our knowledge, this is the first proteomic study using protein-chip technology for molecular classification of B-cell lymphoma subtypes with clinical samples.

Proteomic identification of urinary biomarkers of diabetic nephropathy.

OBJECTIVE: Diabetic nephropathy is a serious complication of both type 1 and type 2 diabetes, and, unless arrested, leads to end-stage renal disease. Current diagnosis consists of urine assays of microalbuminuria, which have inadequate specificity and sensitivity. RESEARCH DESIGN AND METHODS: We used proteomic analyses to identify novel biomarkers of nephropathy in urine from type 2 diabetic patients with demonstrated normo-, micro-, or macroalbuminuria. Samples were analyzed by fluorescence two-dimensional (2-D) differential in-gel electrophoresis (DIGE), and protein identification was performed by liquid chromatography-tandem mass spectrometry. RESULTS: 2-D DIGE analysis of the urinary proteome in diabetes with nephropathy identified 195 protein spots representing 62 unique proteins. These proteins belonged to several functional groups, i.e., cell development, cell organization, defense response, metabolism, and signal transduction. Comparisons between control and diabetic subjects with different stages of renal dysfunction revealed the differential expression of several proteins. Spot volume quantification identified 7 proteins that were progressively upregulated with increasing albuminuria and 4 proteins that exhibited progressive downregulation. The majority of these potential candidate biomarkers were glycoproteins. CONCLUSIONS: These data demonstrate the ability of proteomic analyses to reveal potential biomarkers for diabetic nephropathy in urine, an important step forward in advancing accurate diagnosis and our understanding of disease mechanisms.

Expression of Pseudomonas stutzeri Zobell cytochrome c-551 and its H47A variant in Escherichia coli.

The nirM gene encoding cytochrome c-551 from Pseudomonas stutzeri Zobell (PZ) has been expressed in Escherichia coli at levels higher than those previously reported but only under strict anaerobic growth conditions. Expression yields for wild-type cytochrome in this study typically reached 0.6 micromol per liter of saturated E. coli culture (5.5mg/L). Culture conditions investigated are compared to obtained c-551 expression levels; the results may lead to a greater understanding of the challenges encountered when expressing c-type hemoproteins in E. coli. The nirM gene was mutated to produce a histidine-47-alanine mutation of c-551 that been heterologously expressed in E. coli using optimum culture conditions and had its physiochemical properties compared to those of the wild-type protein. In PZ, the histidine-47 residue is part of a conserved hydrogen-bonding network located at the bottom of the heme crevice that also involves tryptophan-56 and a heme propionate. Ionization events within this network are experimentally demonstrated to modulate c-551 oxidation-reduction potential and its observed dependence on pH around neutrality. The redox potential of the mutant cytochrome still displays pH-dependence; however, the midpoint potential is approximately 25mV lower with respect to wild-type c-551 at neutral pH while the pK at which the heme propionate (HP-17) ionizes is lowered by 1.3 pH units. Temperature and chemical denaturant studies also show that loss of the hydrogen-bond-donating imidazole leads to a large decrease in c-551 tertiary stability.