Manganese superoxide dismutase depletion in murine hematopoietic stem cells perturbs iron homeostasis, globin switching, and epigenetic control in erythrocyte precursor cells

Impacts of organic manganese supplementation on blood mineral, biochemical, and hematology in Afshari Ewes and their newborn lambs in the transition period

OBJECTIVE

Maternal mineral status, including manganese (Mn), is critical for fetal growth as well as the health of the newborn lamb. Consequently, it is essential to supply minerals at sufficient levels for the pregnant animal to achieve the development of the embryo and fetus during gestation.

METHODS

The current research was conducted to investigate the impact of organic Mn supplementation on blood biochemical, other mineral and, hematology in Afshari ewes and their newborn lambs in the transition period. Twenty-four ewes were randomly divided into three groups with eight replications. The control group was fed with a diet without organic Mn. The other groups were fed a diet supplemented with 40 (recommended by the NRC) and 80 (twice-recommended by the NRC) mg/kg of DM organic Mn.

RESULTS

In this study, the consumption of organic Mn caused a significant increase in ewes and lambs plasma Mn concentration. Moreover, in the groups mentioned, levels of glucose, insulin, and superoxide dismutase were significantly increased in both ewes and lambs. Concentrations of total protein and albumin were higher in ewes fed whit organic Mn. In both ewes and newborn lambs, the levels of red blood cells, hemoglobin, hematocrit, mean corpuscular hemoglobin, and mean corpuscular concentration in groups fed with organic Mn raised.

CONCLUSION

In general, the nutrition of organic Mn, improved factors of blood biochemical and hematology in ewes and their newborn lambs, and since the twice-recommended NRC level did not cause poisoning, it was recommended to supplement the diet with 80 mg of organic Mn per kg of DM.

Emerging mitochondrial signaling mechanisms in cardio-oncology: beyond oxidative stress

Many anticancer therapies (CTx) have cardiotoxic side effects that limit their therapeutic potential and cause long-term cardiovascular complications in cancer survivors. This has given rise to the field of cardio-oncology, which recognizes the need for basic, translational, and clinical research focused on understanding the complex signaling events that drive CTx-induced cardiovascular toxicity. Several CTx agents cause mitochondrial damage in the form of mitochondrial DNA deletions, mutations, and suppression of respiratory function and ATP production. In this review, we provide a brief overview of the cardiovascular complications of clinically used CTx agents and discuss current knowledge of local and systemic secondary signaling events that arise in response to mitochondrial stress/damage. Mitochondrial oxidative stress has long been recognized as a contributor to CTx-induced cardiotoxicity; thus, we focus on emerging roles for mitochondria in epigenetic regulation, innate immunity, and signaling via noncoding RNAs and mitochondrial hormones. Because data exploring mitochondrial secondary signaling in the context of cardio-oncology are limited, we also draw upon clinical and preclinical studies, which have examined these pathways in other relevant pathologies.

Association between the blood manganese (Mn) and hemoglobin in patients undergoing maintenance hemodialysis

BACKGROUND AND AIMS

Manganese (Mn) and iron metabolism are closely related. Iron metabolism disorders often lead to anemia in patients undergoing maintenance hemodialysis (MHD). Here, we aimed to investigate the relationship between blood Mn and hemoglobin (Hb) in patients undergoing MHD.

METHODS

Patients undergoing MHD in September 2019 were included in a cross-sectional study. Clinical and demographic data and blood samples were collected before hemodialysis sessions, and blood levels of Mn were measured by inductively coupled plasma mass spectrometry. Both multivariable linear and binary logistic regression analyses were performed to study the relationship between the blood Mn and Hb.

RESULTS

A total of 144 patients undergoing MHD were enrolled in the study. The patients had a mean age of 64.33 ± 13.39 years, median vintage of 33.50 (16.25-57.50) months. Among them, 66 were females (45.8%). The median blood Mn level was 13.55 µg/L (IQR:9.92-17.48). Ninety-nine patients were anemic (68.8%). The mean Hb level was 99.83 ± 19.68 g/L. The patient group with high blood Mn had a high proportion of females, and these patients had high levels of RBC, hemoglobin, Hct, UIBC, serum TCHOL, and serum LDL, yet short dialysis vintage, low prevalence of anemia, low levels of serum ferritin, serum iron, and TSAT. Following adjustment for confounding factors, we found that low blood Mn level was independently associated with lower Hb level and anemia in patients undergoing MHD by multivariate linear and multivariate binary logistic regression, respectively, in different models.

CONCLUSION

Whilst our study showed that high levels of blood Mn were independently associated with high hemoglobin in patients undergoing MHD, further multicenter studies with large sample sizes are still required.

Mitochondria signaling to the epigenome: A novel role for an old organelle

Epigenetic modifications influence gene expression programs ultimately dictating physiological outcomes. In the past decades, an increasing body of work has demonstrated that the enzymes that deposit and/or remove epigenetic marks on DNA or histones use metabolites as substrates or co-factors, rendering the epigenome sensitive to metabolic changes. In this context, acetyl-CoA and α-ketoglutarate have been recognized as critical for epigenetics, impinging on histone marks and nuclear DNA methylation patterns. Given that these metabolites are primarily generated in the mitochondria through the tricarboxylic acid cycle (TCA), the requirement of proper mitochondrial function for maintenance of the epigenetic landscape seems obvious. Nevertheless, it was not until recently when the epigenomic outcomes of mitochondrial dysfunction were tested, revealing mitochondria's far-reaching impact on epigenetics. This review will focus on data that directly tested the role of mitochondria on the epigenetic landscape, the mechanisms by which mitochondrial dysfunction may dysregulate the epigenome and gene expression, and their potential implications to health and disease.

The epigenetic and morphogenetic effects of molecular oxygen and its derived reactive species in development

The development of multicellular organisms involves the unpacking of a complex genetic program. Extensive characterization of discrete developmental steps has revealed the genetic program is controlled by an epigenetic state. Shifting the epigenome is a group of epigenetic enzymes that modify DNA and proteins to regulate cell type specific gene expression. While the role of these modifications in development has been established, the input(s) responsible for electing changes in the epigenetic state remains unknown. Development is also associated with dynamic changes in cellular metabolism, redox, free radical production, and oxygen availability. It has previously been postulated that these changes are causal in development by affecting gene expression. This suggests that oxygen is a morphogenic compound that impacts the removal of epigenetic marks. Likewise, metabolism and reactive oxygen species influence redox signaling through iron and glutathione to limit the availability of key epigenetic cofactors such as α-ketoglutarate, ascorbate, NAD⁺ and S-adenosylmethionine. Given the close relationship between these cofactors and epigenetic marks it seems likely that the two are linked. Here we describe how changing these inputs might affect the epigenetic state during development to drive gene expression. Combined, these cofactors and reactive oxygen species constitute the epigenetic landscape guiding cells along differing developmental paths.

An IDH1-vitamin C crosstalk drives human erythroid development by inhibiting pro-oxidant mitochondrial metabolism

The metabolic changes controlling the stepwise differentiation of hematopoietic stem and progenitor cells (HSPCs) to mature erythrocytes are poorly understood. Here, we show that HSPC development to an erythroid-committed proerythroblast results in augmented glutaminolysis, generating alpha-ketoglutarate (αKG) and driving mitochondrial oxidative phosphorylation (OXPHOS). However, sequential late-stage erythropoiesis is dependent on decreasing αKG-driven OXPHOS, and we find that isocitrate dehydrogenase 1 (IDH1) plays a central role in this process. IDH1 downregulation augments mitochondrial oxidation of αKG and inhibits reticulocyte generation. Furthermore, IDH1 knockdown results in the generation of multinucleated erythroblasts, a morphological abnormality characteristic of myelodysplastic syndrome and congenital dyserythropoietic anemia. We identify vitamin C homeostasis as a critical regulator of ineffective erythropoiesis; oxidized ascorbate increases mitochondrial superoxide and significantly exacerbates the abnormal erythroblast phenotype of IDH1-downregulated progenitors, whereas vitamin C, scavenging reactive oxygen species (ROS) and reprogramming mitochondrial metabolism, rescues erythropoiesis. Thus, an IDH1-vitamin C crosstalk controls terminal steps of human erythroid differentiation.

Serum trace metal association with response to erythropoiesis stimulating agents in incident and prevalent hemodialysis patients

Alterations in hemodialysis patients' serum trace metals have been documented. Early studies addressing associations levels of serum trace metals with erythropoietic responses and/or hematocrit generated mixed results. These studies were conducted prior to current approaches for erythropoiesis stimulating agent (ESA) drug dosing guidelines or without consideration of inflammation markers (e.g. hepcidin) important for regulation of iron availability. This study sought to determine if the serum trace metal concentrations of incident or chronic hemodialysis patients associated with the observed ESA response variability and with consideration to ESA dose response, hepcidin, and high sensitivity C-reactive protein levels. Inductively-coupled plasma-mass spectrometry was used to measure 14 serum trace metals in 29 incident and 79 prevalent dialysis patients recruited prospectively. We compared these data to three measures of ESA dose response, sex, and dialysis incidence versus dialysis prevalence. Hemoglobin was negatively associated with ESA dose and cadmium while positively associated with antimony, arsenic and lead. ESA dose was negatively associated with achieved hemoglobin and vanadium while positively associated with arsenic. ESA response was positively associated with arsenic. Vanadium, nickel, cadmium, and tin were increased in prevalent patients. Manganese was increased in incident patients. Vanadium, nickel, and arsenic increased with time on dialysis while manganese decreased. Changes in vanadium and manganese were largest and appeared to have some effect on anemia. Incident and prevalent patients' chromium and antimony levels exceeded established accepted upper limits of normal.

Oxidation and erythropoiesis

PURPOSE OF REVIEW

Erythropoiesis is a complex multistep process going from committed erythroid progenitors to mature red cells. Although recent advances allow the characterization of some components of erythropoiesis, much still remains to be investigated particularly on stress erythropoiesis. This review summarizes recent progresses made to understand the impact of oxidative stress on normal and pathologic erythropoiesis.

RECENT FINDINGS

During erythroid maturation, reactive oxygen species might function as second messenger through either transient oxidation of cysteine residues on signaling targets or modulation of intracellular signaling pathways. Thus, in erythropoiesis, efficient cytoprotective systems are required to limit possible reactive oxygen species-related toxic effects especially in stress erythropoiesis characterized by severe oxidation such as β-thalassemia. In addition, prolonged or severe oxidative stress impairs autophagy, which might contribute to the block of erythroid maturation in stress erythropoiesis. Understanding the functional role of cytoprotective systems such as peroxiredoxin-2 or classical molecular chaperones such as the heat shock proteins will contribute to develop innovative therapeutic strategies for ineffective erythropoiesis.

SUMMARY

We provide an update on cytoprotective mechanisms against oxidation in normal and stress erythropoiesis. We discuss the role of oxidative sensors involved in modulation of intracellular signaling during erythroid maturation process in normal and stress erythropoiesis.

MnSOD Val16Ala gene polymorphism is associated with REDOX biomarkers in the elderly of primary health care in the city of Porto Alegre

Studies suggest that redox imbalance may be closely associated with pathological aging, contributing effectively to the genesis of several chronic diseases. One of the major defence enzymes against oxidation is Manganese-dependent superoxide dismutase (MnSOD) that acts within the mitochondria. The gene encoding this enzyme is polymorphic and Val16Ala variant is one of its most investigated polymorphisms regarding aging and oxidative stress. This study aimed to verify the occurrence of the MnSOD Val16Ala gene polymorphism association with markers of REDOX metabolism in the elderly of primary health care. A cross-sectional study was performed. The sample consisted of 270 elderly individuals from Family Health Strategy in the city of Porto Alegre, Rio Grande do Sul, Brazil (EMISUS). The following variables were investigated in all subjects: sociodemographic: gender, age, marital status, schooling and income; Anthropometric: weight, height, body mass index (BMI); REDOX markers: advanced oxidation protein products (AOPP), ischemia-modified albumin (IMA), nitric oxide metabolites (NOx), ferric reducing ability of plasma (FRAP) and malondialdehyde (MDA), MnSOD Val16Ala gene polymorphism. Val16Ala gene polymorphism was evaluated by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP). Statistically significant associations were observed in the elderly with AA genotype compared to those with VV genotype, concerning AOPP (p = 0.023) and FRAP (p = 0.027) quartile frequencies, respectively. No statistically significant differences were observed between MnSOD genotypes with MDA, NOx and IMA oxidative markers. Val16Ala gene polymorphism is associated with AOPP and FRAP quartiles frequencies in the elderly of primary health care.

Succinate Accumulation Links Mitochondrial MnSOD Depletion to Aberrant Nuclear DNA Methylation and Altered Cell Fate

Previous studies showed that human cell line HEK293 lacking mitochondrial superoxide dismutase (MnSOD) exhibited decreased succinate dehydrogenase (SDH) activity, and mice lacking MnSOD displayed significant reductions in SDH and aconitase activities. Since MnSOD has significant effects on SDH activity, and succinate is a key regulator of TET enzymes needed for proper differentiation, we hypothesized that SOD2 loss would lead to succinate accumulation, inhibition of TET activity, and impaired erythroid precursor differentiation. To test this hypothesis, we genetically disrupted the SOD2 gene using the CRISPR/Cas9 genetic strategy in a human erythroleukemia cell line (HEL 92.1.7) capable of induced differentiation toward an erythroid phenotype. Cells obtained in this manner displayed significant inhibition of SDH activity and ~10-fold increases in cellular succinate levels compared to their parent cell controls. Furthermore, SOD2 ^-/- cells exhibited significantly reduced TET enzyme activity concomitant with decreases in genomic 5-hmC and corresponding increases in 5-mC. Finally, when stimulated with δ-aminolevulonic acid (δ-ALA), SOD2 ^-/- HEL cells failed to properly differentiate toward an erythroid phenotype, likely due to failure to complete the necessary global DNA demethylation program required for erythroid maturation. Together, our findings support the model of an SDH/succinate/TET axis and a role for succinate as a retrograde signaling molecule of mitochondrial origin that significantly perturbs nuclear epigenetic reprogramming and introduce MnSOD as a governor of the SDH/succinate/TET axis.

Enrichment of superoxide dismutase 2 in glioblastoma confers to acquisition of temozolomide resistance that is associated with tumor-initiating cell subsets

Background

Intratumor subsets with tumor-initiating features in glioblastoma are likely to survive treatment. Our goal is to identify the key factor in the process by which cells develop temozolomide (TMZ) resistance.

Methods

Resistant cell lines derived from U87MG and A172 were established through long-term co-incubation of TMZ. Primary tumors obtained from patients were maintained as patient-derived xenograft for studies of tumor-initating cell (TIC) features. The cell manifestations were assessed in the gene modulated cells for relevance to drug resistance.

Results

Among the mitochondria-related genes in the gene expression databases, superoxide dismutase 2 (SOD2) was a significant factor in resistance and patient survival. SOD2 in the resistant cells functionally determined the cell fate by limiting TMZ-stimulated superoxide reaction and cleavage of caspase-3. Genetic inhibition of the protein led to retrieval of drug effect in mouse study. SOD2 was also associated with the TIC features, which enriched in the resistant cells. The CD133⁺ specific subsets in the resistant cells exhibited superior superoxide regulation and the SOD2-related caspase-3 reaction. Experiments applying SOD2 modulation showed a positive correlation between the TIC features and the protein expression. Finally, co-treatment with TMZ and the SOD inhibitor sodium diethyldithiocarbamate trihydrate in xenograft mouse models with the TMZ-resistant primary tumor resulted in lower tumor proliferation, longer survival, and less CD133, Bmi-1, and SOD2 expression.

Conclusion

SOD2 plays crucial roles in the tumor-initiating features that are related to TMZ resistance. Inhibition of the protein is a potential therapeutic strategy that can be used to enhance the effects of chemotherapy.

Graphical abstract

A case-control study of trace-element status and lung cancer in Appalachian Kentucky

Appalachian Kentucky (App KY) leads the nation in lung cancer incidence and mortality. Trace elements, such as As, have been associated with lung cancers in other regions of the country and we hypothesized that a population-based study would reveal higher trace element concentrations in App KY individuals with cancer compared to controls. Using toenail and drinking water trace element concentrations, this study investigated a possible association between lung cancer incidence and trace-element exposure in residents of this region. This population-based case-control study had 520 subjects, and 367 subjects provided toenail samples. Additionally, we explored the relationship between toenail and fingernail trace-element concentrations to determine if fingernails could be used as a surrogate for toenails when patients are unable to provide toenail samples. We found that, contrary to our initial hypothesis, trace element concentrations (Al, As, Cr, Mn, Co, Fe, Ni, Cu, Se, and Pb) were not higher in cancer cases than controls with the exception of Zn where concentrations were slightly higher in cases. In fact, univariate logistic regression models showed that individuals with lower concentrations of several elements (Al, Mn, Cr, and Se) were more likely to have lung cancer, although only Mn was significant in multivariate models which controlled for confounding factors. While drinking water concentrations of Al, Cr and Co were positively related to cancer incidence in univariate models, only Co remained significant in multivariate models. However, since the drinking water concentrations were extremely low and not reflected in the toenail concentrations, the significance of this finding is unclear. We also found that fingernail concentrations were not consistently predictive of toenail concentrations, indicating that fingernails should not be used as surrogates for toenails in future studies.

Mitochondrial superoxide disrupts the metabolic and epigenetic landscape of CD4+ and CD8+ T-lymphocytes

While the role of mitochondrial metabolism in controlling T-lymphocyte activation and function is becoming more clear, the specifics of how mitochondrial redox signaling contributes to T-lymphocyte regulation remains elusive. Here, we examined the global effects of elevated mitochondrial superoxide (O₂^-) on T-lymphocyte activation using a novel model of inducible manganese superoxide dismutase (MnSOD) knock-out. Loss of MnSOD led to specific increases in mitochondrial O₂^- with no evident changes in hydrogen peroxide (H₂O₂), peroxynitrite (ONOO^-), or copper/zinc superoxide dismutase (CuZnSOD) levels. Unexpectedly, both mitochondrial and glycolytic metabolism showed significant reductions in baseline, maximal capacities, and ATP production with increased mitochondrial O₂^- levels. MnSOD knock-out T-lymphocytes demonstrated aberrant activation including widespread dysregulation in cytokine production and increased cellular apoptosis. Interestingly, an elevated proliferative signature defined by significant upregulation of cell cycle regulatory genes was also evident in MnSOD knock-out T-lymphocytes, but these cells did not show accelerated proliferative rates. Global disruption in T-lymphocyte DNA methylation and hydroxymethylation was also observed with increased mitochondrial O₂^-, which was correlated to alterations in intracellular metabolite pools linked to the methionine cycle. Together, these results demonstrate a mitochondrial redox and metabolic couple that when disrupted may alter cellular processes necessary for proper T-lymphocyte activation.

Inhibition of ferrochelatase impairs vascular eNOS/NO and sGC/cGMP signaling

Ferrochelatase (FECH) is an enzyme necessary for heme synthesis, which is essential for maintaining normal functions of endothelial nitric oxide synthase (eNOS) and soluble guanylyl cyclase (sGC). We tested the hypothesis that inhibition of vascular FECH to attenuate heme synthesis downregulates eNOS and sGC expression, resulting in impaired NO/cGMP-dependent relaxation. To this end, isolated bovine coronary arteries (BCAs) were in vitro incubated without (as controls) or with N-methyl protoporphyrin (NMPP; 10⁻⁵–10^-7M; a selective FECH antagonist) for 24 and 72 hours respectively. Tissue FECH activity, heme, nitrite/NO and superoxide levels were sequentially measured. Protein expression of FECH, eNOS and sGC was detected by western blot analysis. Vascular responses to various vasoactive agents were evaluated via isometric tension studies. Treatment of BCAs with NMPP initiated a time- and dose-dependent attenuation of FECH activity without changes in its protein expression, followed by significant reduction in the heme level. Moreover, ACh-induced relaxation and ACh-stimulated release of NO were significant reduced, associated with suppression of eNOS protein expression in NMPP-treated groups. Decreased relaxation to NO donor spermine-NONOate reached the statistical significance in BCAs incubated with NMPP for 72 hours, concomitantly with downregulation of sGCβ1 expression that was independent of heat shock protein 90 (HSP90), nor did it significantly affect BCA relaxation caused by BAY 58–2667 that activates sGC in the heme-deficiency. Neither vascular responses to non-NO/sGC-mediators nor production of superoxide was affected by NMPP-treatment. In conclusion, deletion of vascular heme production via inhibiting FECH elicits downregulation of eNOS and sGC expression, leading to an impaired NO-mediated relaxation in an oxidative stress-independent manner.

A review of select minerals influencing the haematopoietic process

Micronutrients are indispensable for adequate metabolism, such as biochemical function and cell production. The production of blood cells is named haematopoiesis and this process is highly consuming due to the rapid turnover of the haematopoietic system and consequent demand for nutrients. It is well established that micronutrients are relevant to blood cell production, although some of the mechanisms of how micronutrients modulate haematopoiesis remain unknown. The aim of the present review is to summarise the effect of Fe, Mn, Ca, Mg, Na, K, Co, iodine, P, Se, Cu, Li and Zn on haematopoiesis. This review deals specifically with the physiological requirements of selected micronutrients to haematopoiesis, showing various studies related to the physiological requirements, deficiency or excess of these minerals on haematopoiesis. The literature selected includes studies in animal models and human subjects. In circumstances where these minerals have not been studied for a given condition, no information was used. All the selected minerals have an important role in haematopoiesis by influencing the quality and quantity of blood cell production. In addition, it is highly recommended that the established nutrition recommendations for these minerals be followed, because cases of excess or deficient mineral intake can affect the haematopoiesis process.

Mouse Models of Erythropoiesis and Associated Diseases

Animal models of erythropoiesis have been, and will continue to be, important tools for understanding molecular mechanisms underlying the development of this cell lineage and the pathophysiology associated with various human erythropoietic diseases. In this regard, the mouse is probably the most valuable animal model available to investigators. The physiology and short gestational period of mice make them ideal for studying developmental processes and modeling human diseases. These attributes, coupled with cutting-edge genetic tools such as transgenesis, gene knockouts, conditional gene knockouts, and genome editing, provide a significant resource to the research community to test a plethora of hypotheses. This review summarizes the mouse models available for studying a wide variety of erythroid-related questions, as well as the properties inherent in each one.

Excess iron: considerations related to development and early growth

What effects might arise from early life exposures to high iron? This review considers the specific effects of high iron on the brain, stem cells, and the process of erythropoiesis and identifies gaps in our knowledge of what molecular damage may be incurred by oxidative stress that is imparted by high iron status in early life. Specific areas to enhance research on this topic include the following: longitudinal behavioral studies of children to test associations between iron exposures and mood, emotion, cognition, and memory; animal studies to determine epigenetic changes that reprogram brain development and metabolic changes in early life that could be followed through the life course; and the establishment of human epigenetic markers of iron exposures and oxidative stress that could be monitored for early origins of adult chronic diseases. In addition, efforts to understand how iron exposure influences stem cell biology could be enhanced by establishing platforms to collect biological specimens, including umbilical cord blood and amniotic fluid, to be made available to the research community. At the molecular level, there is a need to better understand stress erythropoiesis and changes in iron metabolism during pregnancy and development, especially with respect to regulatory control under high iron conditions that might promote ineffective erythropoiesis and iron-loading anemia. These investigations should focus not only on factors such as hepcidin and erythroferrone but should also include newly identified interactions between transferrin receptor-2 and the erythropoietin receptor. Finally, despite our understanding that several key micronutrients (e.g., vitamin A, copper, manganese, and zinc) support iron's function in erythropoiesis, how these nutrients interact remains, to our knowledge, unknown. It is necessary to consider many factors when formulating recommendations on iron supplementation.

On the Origin of Superoxide Dismutase: An Evolutionary Perspective of Superoxide-Mediated Redox Signaling

The field of free radical biology originated with the discovery of superoxide dismutase (SOD) in 1969. Over the last 5 decades, a plethora of research has been performed in species ranging from bacteria to mammals that has elucidated the molecular reaction, subcellular location, and specific isoforms of SOD. However, while humans have only begun to study this class of enzymes over the past 50 years, it has been estimated that these enzymes have existed for billions of years, and may be some of the original enzymes found in primitive life. As life evolved over this expanse of time, these enzymes have taken on new and different functional roles potentially in contrast to how they were originally derived. Herein, examination of the evolutionary history of these enzymes provides both an explanation and further inquiries into the modern-day role of SOD in physiology and disease.

Redox regulation of cardiovascular inflammation - Immunomodulatory function of mitochondrial and Nox-derived reactive oxygen and nitrogen species

Oxidative stress is a major hallmark of cardiovascular diseases although a causal link was so far not proven by large clinical trials. However, there is a close association between oxidative stress and inflammation and increasing evidence for a causal role of (low-grade) inflammation for the onset and progression of cardiovascular diseases, which may serve as the missing link between oxidative stress and cardiovascular morbidity and mortality. With the present review we would like to highlight the multiple redox regulated pathways in inflammation, discuss the sources of reactive oxygen and nitrogen species that are of interest for these processes and finally discuss the importance of angiotensin II (AT-II) as a trigger of cardiovascular inflammation and the initiation and progression of cardiovascular diseases.

Mitochondrial Superoxide Signaling Contributes to Norepinephrine-Mediated T-Lymphocyte Cytokine Profiles

Norepinephrine (NE) produces multifaceted regulatory patterns in T-lymphocytes. Recently, we have shown that NE utilizes redox signaling as evidenced by increased superoxide (O2●-) causally linked to the observed changes in these cells; however, the source of this reactive oxygen species (ROS) remains elusive. Herein, we hypothesized that the source of increased O2●- in NE-stimulated T-lymphocytes is due to disruption of mitochondrial bioenergetics. To address this hypothesis, we utilized purified mouse splenic CD4+ and CD8+ T-lymphocytes stimulated with NE and assessed O2●- levels, mitochondrial metabolism, cellular proliferation, and cytokine profiles. We demonstrate that the increase in O2●- levels in response to NE is time-dependent and occurs at later points of T-lymphocyte activation. Moreover, the source of O2●- was indeed the mitochondria as evidenced by enhanced MitoSOX Red oxidation as well as abrogation of this signal by the addition of the mitochondrial-targeted O2●--scavenging antioxidant MitoTempol. NE-stimulated T-lymphocytes also demonstrated decreased mitochondrial respiratory capacity, which suggests disruption of mitochondrial metabolism and the potential source of increased mitochondrial O2●-. The effects of NE in regards to redox signaling appear to be adrenergic receptor-dependent as specific receptor antagonists could reverse the increase in O2●-; however, differential receptors regulating these processes were observed in CD4+ versus CD8+ T-lymphocytes. Finally, mitochondrial O2●- was shown to be mechanistic to the NE-mediated T-lymphocyte phenotype as supplementation of MitoTempol could reverse specific changes in cytokine expression observed with NE treatment. Overall, these studies indicate that mitochondrial metabolism and O2●--mediated redox signaling play a regulatory role in the T-lymphocyte response to NE.

Mitochondrial aerobic respiration is activated during hair follicle stem cell differentiation, and its dysfunction retards hair regeneration

Background. Emerging research revealed the essential role of mitochondria in regulating stem/progenitor cell differentiation of neural progenitor cells, mesenchymal stem cells and other stem cells through reactive oxygen species (ROS), Notch or other signaling pathway. Inhibition of mitochondrial protein synthesis results in hair loss upon injury. However, alteration of mitochondrial morphology and metabolic function during hair follicle stem cells (HFSCs) differentiation and how they affect hair regeneration has not been elaborated upon.

Methods. We compared the difference in mitochondrial morphology and activity between telogen bulge cells and anagen matrix cells. Expression levels of mitochondrial ROS and superoxide dismutase 2 (SOD2) were measured to evaluate redox balance. In addition, the level of pyruvate dehydrogenase kinase (PDK) and pyruvate dehydrogenase (PDH) were estimated to present the change in energetic metabolism during differentiation. To explore the effect of the mitochondrial metabolism on regulating hair regeneration, hair growth was observed after application of a mitochondrial respiratory inhibitor upon hair plucking.

Results. During HFSCs differentiation, mitochondria became elongated with more abundant organized cristae and showed higher activity in differentiated cells. SOD2 was enhanced for redox balance with relatively stable ROS levels in differentiated cells. PDK increased in HFSCs while differentiated cells showed enhanced PDH, indicating that respiration switched from glycolysis to oxidative phosphorylation during differentiation. Inhibiting mitochondrial respiration in differentiated hair follicle cells upon hair plucking repressed hair regeneration in vivo.

Conclusions. Upon HFSCs differentiation, mitochondria are elongated with more abundant cristae and show higher activity, accompanying with activated aerobic respiration in differentiated cells for higher energy supply. Also, dysfunction of mitochondrial respiration delays hair regeneration upon injury.

Potential role of mitochondrial superoxide decreasing ferrochelatase and heme in coronary artery soluble guanylate cyclase depletion by angiotensin II

Oxidation of the soluble guanylate cyclase (sGC) heme promotes loss of regulation by nitric oxide (NO) and depletion of sGC. We hypothesized that angiotensin II (ANG II) stimulation of mitochondrial superoxide by its type 1 receptor could function as a potential inhibitor of heme biosynthesis by ferrochelatase, and this could decrease vascular responsiveness to NO by depleting sGC. These processes were investigated in a 24-h organoid culture model of bovine coronary arteries (BCA) with 0.1 μM ANG II. Treatment of BCA with ANG II increased mitochondrial superoxide, depleted mitochondrial superoxide dismutase (SOD2), ferrochelatase, and cytochrome oxidase subunit 4, and sGC, associated with impairment of relaxation to NO. These processes were attenuated by organoid culture with 8-bromo-cGMP and/or δ-aminolevulinic acid (a stimulator of sGC by protoporphyrin IX generation and heme biosynthesis). Organoid culture with Mito-TEMPOL, a scavenger of mitochondrial matrix superoxide, also attenuated ANG II-elicited ferrochelatase depletion and loss of relaxation to NO, whereas organoid culture with Tempol, an extramitochondrial scavenger of superoxide, attenuated the loss of relaxation to NO by ANG II, but not ferrochelatase depletion, suggesting cytosolic superoxide could be an initiating factor in the loss of sGC regulation by NO. The depletion of cytochrome oxidase subunit 4 and sGC (but not catalase) suggests that sGC expression may be very sensitive to depletion of heme caused by ANG II disrupting ferrochelatase activity by increasing mitochondrial superoxide. In addition, cGMP-dependent activation of protein kinase G appears to attenuate these ANG II-stimulated processes through both preventing SOD2 depletion and increases in mitochondrial and extramitochondrial superoxide.

SOD2 targeted gene editing by CRISPR/Cas9 yields Human cells devoid of MnSOD

To date no models exist to study MnSOD deficiency in human cells. To address this deficiency, we created a SOD2-null human cell line that is completely devoid of detectable MnSOD protein expression and enzyme activity. We utilized the CRISPR/Cas9 system to generate biallelic SOD2 disruption in HEK293T cells. These SOD2-null cells exhibit impaired clonogenic activity, which was rescued by either treatment with GC4419, a pharmacological small-molecule mimic of SOD, or growth in hypoxia. The phenotype of these cells is primarily characterized by impaired mitochondrial bioenergetics. The SOD2-null cells displayed perturbations in their mitochondrial ultrastructure and preferred glycolysis as opposed to oxidative phosphorylation to generate ATP. The activities of mitochondrial complex I and II were both significantly impaired by the absence of MnSOD activity, presumably from disruption of the Fe/S centers in NADH dehydrogenase and succinate dehydrogenase subunit B by the aberrant redox state in the mitochondrial matrix of SOD2-null cells. By creating this model we provide a novel tool with which to study the consequences of lack of MnSOD activity in human cells.

Redox regulation of genome stability by effects on gene expression, epigenetic pathways and DNA damage/repair

Reactive oxygen and nitrogen species (e.g. H2O2, nitric oxide) confer redox regulation of essential cellular signaling pathways such as cell differentiation, proliferation, migration and apoptosis. In addition, classical regulation of gene expression or activity, including gene transcription to RNA followed by translation to the protein level, by transcription factors (e.g. NF-κB, HIF-1α) and mRNA binding proteins (e.g. GAPDH, HuR) is subject to redox regulation. This review will give an update of recent discoveries in this field, and specifically highlight the impact of reactive oxygen and nitrogen species on DNA repair systems that contribute to genomic stability. Emphasis will be placed on the emerging role of redox mechanisms regulating epigenetic pathways (e.g. miRNA, DNA methylation and histone modifications). By providing clinical correlations we discuss how oxidative stress can impact on gene regulation/activity and vise versa, how epigenetic processes, other gene regulatory mechanisms and DNA repair can influence the cellular redox state and contribute or prevent development or progression of disease.

Lead, Arsenic, and Manganese Metal Mixture Exposures: Focus on Biomarkers of Effect

The increasing exposure of human populations to excessive levels of metals continues to represent a matter of public health concern. Several biomarkers have been studied and proposed for the detection of adverse health effects induced by lead (Pb), arsenic (As), and manganese (Mn); however, these studies have relied on exposures to each single metal, which fails to replicate real-life exposure scenarios. These three metals are commonly detected in different environmental, occupational, and food contexts and they share common neurotoxic effects, which are progressive and once clinically apparent may be irreversible. Thus, chronic exposure to low levels of a mixture of these metals may represent an additive risk of toxicity. Building upon their shared mechanisms of toxicity, such as oxidative stress, interference with neurotransmitters, and effects on the hematopoietic system, we address putative biomarkers, which may assist in assessing the onset of neurological diseases associated with exposure to this metal mixture.

Insights into the diverse effects of nitric oxide on tumor biology

Among its many roles in cellular biology, nitric oxide (·NO) has long been associated with cancers both as a protumorigenic and as an antitumorigenic agent. The dual nature of this signaling molecule in varied settings is attributable to its temporal and concentration-dependent effects that produce different phenotypes. The steady-state ·NO concentration within the cell is a balance between its rate of enzymatic synthesis from the three nitric oxide synthase (NOS) isoforms and consumption via numerous metabolic pathways and demonstrates strong dependence on the tissue oxygen concentration. NOS expression and ·NO production are often deregulated and associated with numerous types of cancers with dissimilar prognostic outcomes. ·NO influences several facets of tumor initiation and progression including DNA damage, chronic inflammation, angiogenesis, epithelial-mesenchymal transition, and metastasis, to name a few. The role of ·NO as an epigenetic modulator has also recently emerged and has potentially important mechanistic implications in regulating transcription of oncogenes and tumor-suppressor genes. ·NO-derived cellular adducts such as dinitrosyliron complexes and the formation of higher nitrogen oxides further alter its cellular behavior. Among anticancer strategies, the use of NOS as a prognostic biomarker and modulation of ·NO production for therapeutic benefit have gained importance over the past decade. Numerous ·NO-releasing drugs and NOS inhibitors have been evaluated in preclinical and clinical settings to arrest tumor growth. Taken together, ·NO affects various arms of cancer signaling networks. An overview of this complex interplay is provided in this chapter.

Heme biosynthesis modulation via δ-aminolevulinic acid administration attenuates chronic hypoxia-induced pulmonary hypertension

This study examines how heme biosynthesis modulation with δ-aminolevulinic acid (ALA) potentially functions to prevent 21-day hypoxia (10% oxygen)-induced pulmonary hypertension in mice and the effects of 24-h organoid culture with bovine pulmonary arteries (BPA) with the hypoxia and pulmonary hypertension mediator endothelin-1 (ET-1), with a focus on changes in superoxide and regulation of micro-RNA 204 (miR204) expression by src kinase phosphorylation of signal transducer and activator of transcription-3 (STAT3). The treatment of mice with ALA attenuated pulmonary hypertension (assessed through echo Doppler flow of the pulmonary valve, and direct measurements of right ventricular systolic pressure and right ventricular hypertrophy), increases in pulmonary arterial superoxide (detected by lucigenin), and decreases in lung miR204 and mitochondrial superoxide dismutase (SOD2) expression. ALA treatment of BPA attenuated ET-1-induced increases in mitochondrial superoxide (detected by MitoSox), STAT3 phosphorylation, and decreases in miR204 and SOD2 expression. Because ALA increases BPA protoporphyrin IX (a stimulator of guanylate cyclase) and cGMP-mediated protein kinase G (PKG) activity, the effects of the PKG activator 8-bromo-cGMP were examined and found to also attenuate the ET-1-induced increase in superoxide. ET-1 increased superoxide production and the detection of protoporphyrin IX fluorescence, suggesting oxidant conditions might impair heme biosynthesis by ferrochelatase. However, chronic hypoxia actually increased ferrochelatase activity in mouse pulmonary arteries. Thus, a reversal of factors increasing mitochondrial superoxide and oxidant effects that potentially influence remodeling signaling related to miR204 expression and perhaps iron availability needed for the biosynthesis of heme by the ferrochelatase reaction could be factors in the beneficial actions of ALA in pulmonary hypertension.

Absence of manganese superoxide dismutase delays p53-induced tumor formation

Background

Manganese superoxide dismutase (MnSOD) is a mitochondrial antioxidant enzyme that is down-regulated in a majority of cancers. Due to this observation, as well as MnSOD's potent antioxidant enzymatic activity, MnSOD has been suggested as a tumor suppressor for over 30 years. However, testing this postulate has proven difficult due to the early post-natal lethality of the MnSOD constitutive knock-out mouse. We have previously used a conditional tissue-specific MnSOD knock-out mouse to study the effects of MnSOD loss on the development of various cell types, but long-term cancer development studies have not been performed. We hypothesized the complete loss of MnSOD would significantly increase the rate of tumor formation in a tissue-specific manner.

Results

Utilizing a hematopoietic stem cell specific Cre-recombinase mouse model, we created pan-hematopoietic cell MnSOD knock-out mice. Additionally, we combined this MnSOD knock-out with two well established models of lymphoma development: B-lymphocyte specific Myc over-expression and conditional pan-hematopoietic cell p53 knock-out. Mice were allowed to age unchallenged until illness or death had occurred. Contrary to our initial hypothesis, the loss of MnSOD alone was insufficient in causing an increase in tumor formation, but did cause significant life-shortening skin pathology in a strain-dependent manner. Moreover, the loss of MnSOD in conjunction with either Myc overexpression or p53 knock-out did not accelerate tumor formation, and in fact delayed lymphomagenesis in the p53 knock-out model.

Conclusions

Our findings strongly suggest that MnSOD does not act as a classical tumor suppressor in hematological tissues. Additionally, the complete loss of MnSOD may actually protect from tumor development by the creation of an unfavorable redox environment for tumor progression. In summary, these results in combination with our previous work suggest that MnSOD needs to be tightly regulated for proper cellular homeostasis, and altering the activity in either direction may lead to cellular dysfunction, oncogenesis, or death.

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The free radical theory of cancer postulates that loss of MnSOD promotes cancer.

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We created mouse models of malignancy with and without conditional loss of MnSOD.

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We show that MnSOD loss delays the onset of p53-dependent tumor development.

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Our data suggest that inhibition of MnSOD in tumor cells may slow tumor progression.