Biochemical characterization of biliverdins IXβ/δ generated by a selective heme oxygenase

Engineering Escherichia coli Nissle 1917 as a microbial chassis for therapeutic and industrial applications

Genetically engineered microbes, especially Escherichia coli, have been widely used in the biosynthesis of proteins and metabolites for medical and industrial applications. As a traditional probiotic with a well-established safety record, E. coli Nissle 1917 (EcN) has recently emerged as a microbial chassis for generating living therapeutics, drug delivery vehicles, and microbial platforms for industrial production. Despite the availability of genetic tools for engineering laboratory E. coli K-12 and B strains, new genetic engineering systems are still greatly needed to expand the application range of EcN. In this review, we have summarized the latest progress in the development of genetic engineering systems in EcN, as well as their applications in the biosynthesis and delivery of valuable small molecules and biomacromolecules of medical and/or industrial interest, followed by a glimpse of how this rapidly growing field will evolve in the future.

Biliverdin modulates the Nrf2/A20/eEF1A2 axis to alleviate cerebral ischemia-reperfusion injury by inhibiting pyroptosis

This study aimed to examine whether Biliverdin, which is a common metabolite of haem, can alleviate cerebral ischemia reperfusion injury (CIRI) by inhibiting pyroptosis. Here, CIRI was induced by middle cerebral artery occlusion-reperfusion (MCAO/R) in C57BL/6 J mice and modelled by oxygen and glucose deprivation/reoxygenation (OGD/R) in HT22 cells, it was treated with or without Biliverdin. The spatiotemporal expression of GSDMD-N and infarction volumes were assessed by immunofluorescence staining and triphenyltetrazolium chloride (TTC), respectively. The NLRP3/Caspase-1/GSDMD pathway, which is central to the pyroptosis process, as well as the expression of Nrf2, A20, and eEF1A2 were determined by Western-blots. Nrf2, A20, and eEF1A2 interactions were verified using dual-luciferase reporter assays, chromatin immunoprecipitation, or co-immunoprecipitation. Additionally, the role of Nrf2/A20/eEF1A2 axis in modulating the neuroprotective properties of Biliverdin was investigated using A20 or eEF1A2 gene interference (overexpression and/or silencing). 40 mg/kg of Biliverdin could significantly alleviate CIRI both in vivo and in vitro, promoted the activation of Nrf2, elevated A20 expression, but decreased eEF1A2 expression. Nrf2 can bind to the promoter of A20, thereby transcriptionally regulating the expression of A20. A20 can furthermore interacted with eEF1A2 through its ZnF4 domain to ubiquitinate and degrade it, leading to the downregulation of eEF1A2. Our studies have also demonstrated that either the knock-down of A20 or over-expression of eEF1A2 blunted the protective effect of Biliverdin. Rescue experiments further confirmed that Biliverdin could regulate the NF-κB pathway via the Nrf2/A20/eEF1A2 axis. In summary, our study demonstrates that Biliverdin ameliorates CIRI by inhibiting the NF-κB pathway via the Nrf2/A20/eEF1A2 axis. Our findings can help identify novel therapeutic targets for the treatment of CIRI.

Metabolic Functions of Biliverdin IXβ Reductase in Redox-Regulated Hematopoietic Cell Fate

Cytoprotective heme oxygenases derivatize heme to generate carbon monoxide, ferrous iron, and isomeric biliverdins, followed by rapid NAD(P)H-dependent biliverdin reduction to the antioxidant bilirubin. Recent studies have implicated biliverdin IXβ reductase (BLVRB) in a redox-regulated mechanism of hematopoietic lineage fate restricted to megakaryocyte and erythroid development, a function distinct and non-overlapping from the BLVRA (biliverdin IXα reductase) homologue. In this review, we focus on recent progress in BLVRB biochemistry and genetics, highlighting human, murine, and cell-based studies that position BLVRB-regulated redox function (or ROS accumulation) as a developmentally tuned trigger that governs megakaryocyte/erythroid lineage fate arising from hematopoietic stem cells. BLVRB crystallographic and thermodynamic studies have elucidated critical determinants of substrate utilization, redox coupling and cytoprotection, and have established that inhibitors and substrates bind within the single-Rossmann fold. These advances provide unique opportunities for the development of BLVRB-selective redox inhibitors as novel cellular targets that retain potential for therapeutic applicability in hematopoietic (and other) disorders.

Recombinant Production of Biliverdin IXβ and δ Isomers in the T7 Promoter Compatible Escherichia coli Nissle

The ability to obtain purified biliverdin IX (BVIX) isomers other than the commercially available BVIXα is limited due to the low yields obtained by the chemical coupled oxidation of heme. Chemical oxidation requires toxic chemicals, has very poor BVIX yields (<0.05%), and is not conducive to scalable production. Alternative approaches utilizing recombinant E. coli BL21 expressing a cyanobacterial heme oxygenase have been employed for the production BVIXα, but yields are limited by the rate of endogenous heme biosynthesis. Furthermore, the emerging roles of BVIXβ and BVIXδ in biology and their lack of commercial availability has led to a need for an efficient and scalable method with the flexibility to produce all three physiologically relevant BVIX isomers. Herein, we have taken advantage of an optimized non-pathogenic E. coli Nissle (EcN(T7)) strain that encodes an endogenous heme transporter and an integrated T7 polymerase gene. Protein production of the Pseudomonas aeruginosa BVIXβ and BVIXδ selective heme oxygenase (HemO) or its BVIXα producing mutant (HemOα) in the EcN(T7) strain provides a scalable method to obtain all three isomers, that is not limited by the rate of endogenous heme biosynthesis, due to the natural ability of EcN(T7) to transport extracellular heme. Additionally, we have optimized our previous LC-MS/MS protocol for semi-preparative separation and validation of the BVIX isomers. Utilizing this new methodology for scalable production and separation we have increased the yields of the BVIXβ and -δ isomers >300-fold when compared to the chemical oxidation of heme.

Divergent erythroid megakaryocyte fates in Blvrb-deficient mice establish non-overlapping cytoprotective functions during stress hematopoiesis

Cytoprotective mechanisms of heme oxygenases function by derivatizing heme to generate carbon monoxide, ferrous iron, and isomeric biliverdins, followed by rapid NAD(P)H-dependent biliverdin reduction to the antioxidant bilirubin using two non-overlapping biliverdin reductases that display biliverdin isomer-restricted redox activity. Although cytoprotective functions of heme oxygenases are widely recognized, concomitant effects of downstream biliverdin reductases remain incomplete. A computational model predicated on murine hematopoietic single-cell transcriptomic data identified Blvrb as a biological driver linked to the tumor necrosis factor stress pathway as a predominant source of variation defining hematopoietic cell heterogeneity. In vivo studies using Blvrb-deficient mice established the dispensable role of Blvrb in steady-state hematopoiesis, although model validation using aged Blvrb-deficient mice established an important cytoprotective function in stress hematopoiesis with dichotomous megakaryocyte-biased hematopoietic recovery. Defective stress erythropoiesis was evident in Blvrb^-/- spleens and in bone marrow erythroid development, occurring in conjunction with defective lipid peroxidation as a marker of oxidant mishandling. Cell autonomous effects on megakaryocyte lineage bias were documented using multipotential progenitor assays. These data provide the first physiological function of murine Blvrb in a non-redundant pathway of stress cytoprotection. Divergent effects on erythroid/megakaryocyte lineage speciation impute a novel redox-regulated mechanism for lineage partitioning.