Showing papers by "Leo E. Otterbein published in 2014"

Macrophages sense and kill bacteria through carbon monoxide-dependent inflammasome activation.

Abstract: Microbial clearance by eukaryotes relies on complex and coordinated processes that remain poorly understood. The gasotransmitter carbon monoxide (CO) is generated by the stress-responsive enzyme heme oxygenase-1 (HO-1, encoded by Hmox1), which is highly induced in macrophages in response to bacterial infection. HO-1 deficiency results in inadequate pathogen clearance, exaggerated tissue damage, and increased mortality. Here, we determined that macrophage-generated CO promotes ATP production and release by bacteria, which then activates the Nacht, LRR, and PYD domains-containing protein 3 (NALP3) inflammasome, intensifying bacterial killing. Bacterial killing defects in HO-1–deficient murine macrophages were restored by administration of CO. Moreover, increased CO levels enhanced the bacterial clearance capacity of human macrophages and WT murine macrophages. CO-dependent bacterial clearance required the NALP3 inflammasome, as CO did not increase bacterial killing in macrophages isolated from NALP3-deficient or caspase-1–deficient mice. IL-1β cleavage and secretion were impaired in HO-1–deficient macrophages, and CO-dependent processing of IL-1β required the presence of bacteria-derived ATP. We found that bacteria remained viable to generate and release ATP in response to CO. The ATP then bound to macrophage nucleotide P2 receptors, resulting in activation of the NALP3/IL-1β inflammasome to amplify bacterial phagocytosis by macrophages. Taken together, our results indicate that macrophage-derived CO permits efficient and coordinated regulation of the host innate response to invading microbes.

Heme oxygenase-1: a metabolic nike

Abstract: Significance: Heme degradation, which was described more than 30 years ago, is still very actively explored with many novel discoveries on its role in various disease models every year. Recent Advances: The heme oxygenases (HO) are metabolic enzymes that utilize NADPH and oxygen to break apart the heme moiety liberating biliverdin (BV), carbon monoxide (CO), and iron. Heme that is derived from hemoproteins can be toxic to the cells and if not removed immediately, it causes cell apoptosis and local inflammation. Elimination of heme from the milieu enables generation of three products that influences numerous metabolic changes in the cell. Critical Issues: CO has profound effects on mitochondria and cellular respiration and other hemoproteins to which it can bind and affect their function, while BV and bilirubin (BR), the substrate and product of BV, reductase, respectively, are potent antioxidants. Sequestration of iron into ferritin and its recycling in the tissues is a part of the homeodynamic processes that control oxidation-reduction in cellular metabolism. Further, heme is an important component of a number of metabolic enzymes, and, therefore, HO-1 plays an important role in the modulation of cellular bioenergetics. Future Directions: In this review, we describe the cross-talk between heme oxygenase-1 (HO-1) and its products with other metabolic pathways. HO-1, which we have labeled Nike, the goddess who personified victory, dictates triumph over pathophysiologic conditions, including diabetes, ischemia, and cancer. Antioxid. Redox Signal. 20, 1709–1722.

Bilirubin increases insulin sensitivity in leptin-receptor deficient and diet-induced obese mice through suppression of ER stress and chronic inflammation.

Abstract: Obesity-induced endoplasmic reticulum (ER) stress causes chronic inflammation in adipose tissue and steatosis in the liver, and eventually leads to insulin resistance and type 2 diabetes (T2D). The goal of this study was to understand the mechanisms by which administration of bilirubin, a powerful antioxidant, reduces hyperglycemia and ameliorates obesity in leptin-receptor-deficient (db/db) and diet-induced obese (DIO) mouse models. db/db or DIO mice were injected with bilirubin or vehicle ip. Blood glucose and body weight were measured. Activation of insulin-signaling pathways, expression of inflammatory cytokines, and ER stress markers were measured in skeletal muscle, adipose tissue, and liver of mice. Bilirubin administration significantly reduced hyperglycemia and increased insulin sensitivity in db/db mice. Bilirubin treatment increased protein kinase B (PKB/Akt) phosphorylation in skeletal muscle and suppressed expression of ER stress markers, including the 78-kDa glucose-regulated protein (GRP78), CCAAT/enhancer-binding protein (C/EBP) homologous protein, X box binding protein (XBP-1), and activating transcription factor 4 in db/db mice. In DIO mice, bilirubin treatment significantly reduced body weight and increased insulin sensitivity. Moreover, bilirubin suppressed macrophage infiltration and proinflammatory cytokine expression, including TNF-α, IL-1β, and monocyte chemoattractant protein-1, in adipose tissue. In liver and adipose tissue of DIO mice, bilirubin ameliorated hepatic steatosis and reduced expression of GRP78 and C/EBP homologous protein. These results demonstrate that bilirubin administration improves hyperglycemia and obesity by increasing insulin sensitivity in both genetically engineered and DIO mice models. Bilirubin or bilirubin-increasing drugs might be useful as an insulin sensitizer for the treatment of obesity-induced insulin resistance and type 2 diabetes based on its profound anti-ER stress and antiinflammatory properties.

Heme oxygenase-1 derived carbon monoxide permits maturation of myeloid cells.

Abstract: Critical functions of the immune system are maintained by the ability of myeloid progenitors to differentiate and mature into macrophages. We hypothesized that the cytoprotective gas molecule carbon monoxide (CO), generated endogenously by heme oxygenases (HO), promotes differentiation of progenitors into functional macrophages. Deletion of HO-1, specifically in the myeloid lineage (Lyz-Cre:Hmox1(flfl)), attenuated the ability of myeloid progenitors to differentiate toward macrophages and decreased the expression of macrophage markers, CD14 and macrophage colony-stimulating factor receptor (MCSFR). We showed that HO-1 and CO induced CD14 expression and efficiently increased expansion and differentiation of myeloid cells into macrophages. Further, CO sensitized myeloid cells to treatment with MCSF at low doses by increasing MCSFR expression, mediated partially through a PI3K-Akt-dependent mechanism. Exposure of mice to CO in a model of marginal bone marrow transplantation significantly improved donor myeloid cell engraftment efficiency, expansion and differentiation, which corresponded to increased serum levels of GM-CSF, IL-1α and MCP-1. Collectively, we conclude that HO-1 and CO in part are critical for myeloid cell differentiation. CO may prove to be a novel therapeutic agent to improve functional recovery of bone marrow cells in patients undergoing irradiation, chemotherapy and/or bone marrow transplantation.

Carbon monoxide inhibits sprouting angiogenesis and vascular endothelial growth factor receptor-2 phosphorylation

Abstract: Carbon monoxide (CO) is a gaseous autacoid known to positively regulate vascular tone; however, its role in angiogenesis is unknown. The aim of this study was to investigate the effect of CO on angiogenesis and vascular endothelial growth factor (VEGF) receptor-2 phosphorylation. Human umbilical vein endothelial cells (HUVECs) were cultured on growth factor-reduced Matrigel and treated with a CO-releasing molecule (CORM-2) or exposed to CO gas (250 ppm). Here, we report the surprising finding that exposure to CO inhibits vascular endothelial growth factor (VEGF)-induced endothelial cell actin reorganisation, cell proliferation, migration and capillary-like tube formation. Similarly, CO suppressed VEGF-mediated phosphorylation of VEGFR-2 at tyrosine residue 1175 and 1214 and basic fibroblast growth factor- (FGF-2) and VEGF-mediated Akt phosphorylation. Consistent with these data, mice exposed to 250 ppm CO (1h/day for 14 days) exhibited a marked decrease in FGF-2-induced Matrigel plug angiogenesis (p

Heme oxygenase-1 and carbon monoxide regulate intestinal homeostasis and mucosal immune responses to the enteric microbiota.

Abstract: Heme oxygenase-1 (HO-1) and its enzymatic by-product carbon monoxide (CO) have emerged as important regulators of acute and chronic inflammation Mechanisms underlying their anti-inflammatory effects are only partially understood In this addendum, we summarize current understanding of the role of the HO-1/CO pathway in regulation of intestinal inflammation with a focus on innate immune function In particular, we highlight our recent findings that HO-1 and CO ameliorate intestinal inflammation through promotion of bacterial clearance Our work and that of many others support further investigation of this global homeostatic pathway in the human inflammatory bowel diseases (IBDs)

Circadian Rhythm in Stroke - The Influence of Our Internal Cellular Clock on Cerebrovascular Events

Abstract: The distinct temporal pattern of stroke occurrence in humans has been recognized for decades; yet, the reason underlying the temporal nature of stroke is not completely understood. Several exogenous factors such as seasonal variation, physical activity, diet and sleep/wake cycles can influence stroke occurrence. Furthermore, it has been increasingly recognized that there are several endogenous physiological functions such as blood pressure, autonomic nervous system activity, and coagulation that show temporal variance and ultimately influence susceptibility to stroke. It was long believed that the neurons within the Suprachiasmatic Nucleus (SCN) controlled all of the body’s circadian rhythm cycles serving as the “master clock”. However, circadian gene expression is inherent to almost every cell in the body, controlling cellular metabolism, and ultimately an organ’s susceptibility to injury. These new insights into the molecular mechanisms regulating circadian rhythmicity might help to explain the phenomenon of circadian variation in stroke occurrence.

Autoreactivity to Glucose Regulated Protein 78 Links Emphysema and Osteoporosis in Smokers

Abstract: Rationale: Emphysema and osteoporosis are epidemiologically associated diseases of cigarette smokers. The causal mechanism(s) linking these illnesses is unknown. We hypothesized autoimmune responses may be involved in both disorders. Objectives: To discover an antigen-specific autoimmune response associated with both emphysema and osteoporosis among smokers. Methods: Replicate nonbiased discovery assays indicated that autoimmunity to glucose regulated protein 78 (GRP78), an endoplasmic reticulum chaperone and cell surface signaling receptor, is present in many smokers. Subject assessments included spirometry, chest CT scans, dual x-ray absorptiometry, and immunoblots for anti-GRP78 IgG. Anti-GRP78 autoantibodies were isolated from patient plasma by affinity chromatography, leukocyte functions assessed by flow cytometry, and soluble metabolites and mediators measured by immunoassays. Measurements and Main Results: Circulating anti-GRP78 IgG autoantibodies were detected in plasma specimens from 86 (32%) of the 265 smoking subjects. Anti-GRP78 autoantibodies were singularly prevalent among subjects with radiographic emphysema (OR 3.1, 95%CI 1.7–5.7, p=0.003). Anti-GRP78 autoantibodies were also associated with osteoporosis (OR 4.7, 95%CI 1.7–13.3, p=0.002), and increased circulating bone metabolites (p=0.006). Among emphysematous subjects, GRP78 protein was an autoantigen of CD4 T-cells, stimulating lymphocyte proliferation (p=0.0002) and IFN-gamma production (p=0.03). Patient-derived anti-GRP78 autoantibodies had avidities for osteoclasts and macrophages, and increased macrophage NFkB phosphorylation (p=0.005) and productions of IL-8, CCL-2, and MMP9 (p=0.005, 0.007, 0.03, respectively). Conclusions: Humoral and cellular GRP78 autoimmune responses in smokers have numerous biologically-relevant proinflammatory and other deleterious actions, and are associated with emphysema and osteoporosis. These findings may have relevance for the pathogenesis of smoking-associated diseases, and development of biomarker immunoassays and/or novel treatments for these disorders.

Carbon monoxide induces chromatin remodelling to facilitate endothelial cell migration

Abstract: Vascular injury to vessel endothelial cells (EC), caused by either mechanical damage or chronic inflammation, is still awaiting effective therapies. In the present study we hypothesised that carbon monoxide (CO) acts on the nuclear receptor Rev-erbα to induce chromatin modification and endothelial cell migration. We demonstrate that administration of low, safe doses of exogenous CO enhances endothelial cell (EC) migration, which occurs in part through chromatin remodelling and histone H3 acetylation. Further, we show that the effects of CO are dependent on inhibition of phosphorylation of glycogen synthase kinase-3 β (GSK3β), activation of haem synthesis, and increased expression of Rev-erbα. Rev-erbα is a haem-containing transcription factor which in response to CO binds to target DNA, recruits the Histone Deacetylase/nuclear Receptor Corepressor (HDAC/N-CoR) complex, and regulates transcription of genes responsible for endothelial cell migration and angiogenesis. Decreased levels of Rev-erbα in chimeric mice after bone marrow transplant from Rev-erbα following bone marrow transplantation from rev-erb+/- mice resulted in loss of protective effects of CO against neointima formation after wire injury. Collectively, CO modifies chromatin structure through enhanced acetylation of histone H3 via a GSK3β-Rev-erbα-mediated pathway to increase EC migration. We propose that CO enhances vessel repair following injury in part by regulating EPC/EC motility via Rev-erbα. Thus, inhaled CO may be beneficial in the treatment of vascular syndromes associated with dysregulated thrombosis, wound healing, and angiogenesis.

Eat to Heal: Natural Inducers of the Heme Oxygenase-1 System

Abstract: Heme oxygenase-1 is a widely accepted cytoprotective molecule offering astonishing medical benefits. Products of its activity include carbon monoxide and biliverdin, which have been shown to provide anti-inflammatory, antioxidant, and anti-apoptotic properties. All these factors are important in mediating tissue health, recovery, and protection during the onset of a number of diseases. The use of natural substances as therapeutics has been a universal and distinctive component in the day-to-day existence of mankind since early times, especially in the eastern world, as part of what has come to be termed alternative medicine. In this chapter, we describe the ability of natural substances to increase the level of heme oxygenase, giving special attention to those most studied including curcumin, flavonoids, and isothiocyanates. We provide experimental evidence that such compounds effectively upregulate heme oxygenase-1, which may explain in part the healing aspects of what nature designed over the course of thousands of years. Indeed, HO-1 is highly conserved: found in all species including plants and in nearly all instances offering potent salutary effects.