Δ-aminolevulinic Acid Synthase Research Articles

FLVCR1a Controls Cellular Cholesterol Levels through the Regulation of Heme Biosynthesis and Tricarboxylic Acid Cycle Flux in Endothelial Cells.

Feline leukemia virus C receptor 1a (FLVCR1a), initially identified as a retroviral receptor and localized on the plasma membrane, has emerged as a crucial regulator of heme homeostasis. Functioning as a positive regulator of δ-aminolevulinic acid synthase 1 (ALAS1), the rate-limiting enzyme in the heme biosynthetic pathway, FLVCR1a influences TCA cycle cataplerosis, thus impacting TCA flux and interconnected metabolic pathways. This study reveals an unexplored link between FLVCR1a, heme synthesis, and cholesterol production in endothelial cells. Using cellular models with manipulated FLVCR1a expression and inducible endothelial-specific Flvcr1a-null mice, we demonstrate that FLVCR1a-mediated control of heme synthesis regulates citrate availability for cholesterol synthesis, thereby influencing cellular cholesterol levels. Moreover, alterations in FLVCR1a expression affect membrane cholesterol content and fluidity, supporting a role for FLVCR1a in the intricate regulation of processes crucial for vascular development and endothelial function. Our results underscore FLVCR1a as a positive regulator of heme synthesis, emphasizing its integration with metabolic pathways involved in cellular energy metabolism. Furthermore, this study suggests that the dysregulation of heme metabolism may have implications for modulating lipid metabolism. We discuss these findings in the context of FLVCR1a's potential heme-independent function as a choline importer, introducing additional complexity to the interplay between heme and lipid metabolism.

Illuminating Dersimelagon: A Novel Agent in the Treatment of Erythropoietic Protoporphyria and X-Linked Protoporphyria.

Erythropoietic protoporphyria (EPP) is a genetic disorder stemming from reduced ferrochelatase expression, the final enzyme in the pathway of heme biosynthesis. A closely related condition, X-linked protoporphyria (XLP), bears similar clinical features although it arises from the heightened activity of δ-aminolevulinic acid synthase 2 (ALAS2), the first and normally rate-controlling enzyme in heme biosynthesis in developing red blood cells. Both of these abnormalities result in the buildup of protoporphyrin IX, leading to excruciating light sensitivity and, in a minority of cases, potentially fatal liver complications. Traditionally, managing EPP and XLP involved sun avoidance. However, the emergence of innovative therapies, such as dersimelagon, is reshaping the therapeutic landscape for these conditions. In this review, we summarize salient features of the properties of dersimelagon, shedding light on its potential role in advancing our understanding of treatment options for EPP and XLP.

Solution phase refinement of active site structure using 2D NMR and judiciously 13C-labeled cytochrome P450

The Cytochrome P450 (CYP450) superfamily has been the subject of intense research for over six decades. Here the HU227 strain of E. coli, lacking the δ-aminolevulinic acid (δ-ALA) synthase gene, was employed, along with [5-13C] δ-ALA, in the heterologous expression of P450cam harboring a prosthetic group labeled with 13C at the four methine carbons (Cm) and pyrrole Cα positions. The product was utilized as a proof of principle strategy for defining and refining solution phase active site structure in cytochrome P450cam, providing proton-to-proton distances from 13CmH to protons on bound substrate or nearby amino acid residues, using short mixing time 2D or 3D NOESY-HMQC methods. The results reveal the interesting finding that 2D 13C-filtered NOESY-HMQC can be used to obtain distances between protons on labeled 13C to positions of protons nearby in the active site, confirming the utility of this NMR-based approach to probing active site structure under physiological conditions. Such 13C-heme-filtered NOE data complement X-ray crystallographic and T1-based NMR measurements; and, may also be of potentially significant utility in furnishing experimental distance constraints in validations of docking routines commonly employed for determining the relative affinities and binding orientations of drug candidates with CYP450s.

Cimetidine for erythropoietic protoporphyria

BackgroundErythropoietic protoporphyria (EPP) is caused by deficiency of the enzyme converting protoporphyrin IX (PpIX) into heme resulting in accumulation of PpIX; leading to photosensitivity and liver toxicity. Cimetidine might inhibit δ-aminolevulinic acid synthase influencing the heme biosynthesis. We present cases with EPP treated with cimetidine at our department, and a literature review. MethodsSystematic searches were performed to identify literature describing EPP patients treated with cimetidine. On that ground we treated EPP patients with cimetidine through spring and summer in 2020 and 2021 at our department. Their erythrocyte PpIX level and standard blood and liver parameters were collected before and during 4 months of treatment. Using a questionnaire, patients were asked about change in photosensitivity, side effects, and whether they would like to resume treatment in the spring of 2022. ResultsLiterature searches identified 9 patients treated with cimetidine. Four were outpatients reporting decreased photosensitivity. At our department 18 outpatients started treatment. Fifteen used oral cimetidine daily for 4 months or more providing a significant decrease in erythrocyte PpIX with a median of 20% (range: -18% to 53%) after 4 months. Eleven of the 15 patients reported a decrease in photosensitivity during treatment, 3 patients were unsure, and 1 patient experienced unchanged photosensitivity. Only mild side effects were reported. Fourteen patients requested to resume treatment in the spring of 2022. ConclusionsThese cases suggest that cimetidine can lower erythrocyte PpIX in patients with EPP.

Azacitidine is a potential therapeutic drug for pyridoxine-refractory female X-linked sideroblastic anemia

AbstractX-linked sideroblastic anemia (XLSA) is associated with mutations in the erythroid-specific δ-aminolevulinic acid synthase (ALAS2) gene. Treatment of XLSA is mainly supportive, except in patients who are pyridoxine responsive. Female XLSA often represents a late onset of severe anemia, mostly related to the acquired skewing of X chromosome inactivation. In this study, we successfully generated active wild-type and mutant ALAS2-induced pluripotent stem cell (iPSC) lines from the peripheral blood cells of an affected mother and 2 daughters in a family with pyridoxine-resistant XLSA related to a heterozygous ALAS2 missense mutation (R227C). The erythroid differentiation potential was severely impaired in active mutant iPSC lines compared with that in active wild-type iPSC lines. Most of the active mutant iPSC-derived erythroblasts revealed an immature morphological phenotype, and some showed dysplasia and perinuclear iron deposits. In addition, globin and HO-1 expression and heme biosynthesis in active mutant erythroblasts were severely impaired compared with that in active wild-type erythroblasts. Furthermore, genes associated with erythroblast maturation and karyopyknosis showed significantly reduced expression in active mutant erythroblasts, recapitulating the maturation defects. Notably, the erythroid differentiation ability and hemoglobin expression of active mutant iPSC-derived hematopoietic progenitor cells (HPCs) were improved by the administration of δ-aminolevulinic acid, verifying the suitability of the cells for drug testing. Administration of a DNA demethylating agent, azacitidine, reactivated the silent, wild-type ALAS2 allele in active mutant HPCs and ameliorated the erythroid differentiation defects, suggesting that azacitidine is a potential novel therapeutic drug for female XLSA. Our patient-specific iPSC platform provides novel biological and therapeutic insights for XLSA.

Givosiran: A Review in Acute Hepatic Porphyria.

Givosiran (Givlaari®) is an δ-aminolevulinic acid synthase 1 (ALAS1)-directed small interfering RNA (siRNA) approved for the treatment of acute hepatic porphyria (AHP). In the phase 3 ENVISION trial, givosiran significantly reduced the annualized rate of composite porphyria attacks (i.e. attacks requiring hospitalization, urgent healthcare visit or intravenous hemin administration at home) compared with placebo in patients with recurrent acute intermittent porphyria (the most common type of AHP) attacks. Givosiran also improved several other outcomes, including hemin use and pain (the cardinal symptom of AHP). While generally well tolerated with an acceptable safety profile, the drug may increase the risk of hepatic and kidney adverse events. Givosiran offers the convenience of once-monthly subcutaneous administration. Available evidence indicates that givosiran is an important newer therapeutic option for patients with AHP and severe recurrent attacks.

Recurrent attacks of acute hepatic porphyria: major role of the chronic inflammatory response in the liver.

Acute intermittent porphyria (AIP) is an inherited disorder of haem metabolism characterized by life-threatening acute neurovisceral attacks due to the induction of hepatic δ-aminolevulinic acid synthase 1 (ALAS1) associated with hydroxymethylbilane synthase (HMBS) deficiency. So far, the treatment of choice is hemin which represses ALAS1. The main issue in the medical care of AIP patients is the occurrence of debilitating recurrent attacks. The aim of this study was to determine whether chronic hemin administration contributes to the recurrence of acute attacks. A follow-up study was conducted between 1974 and 2015 and included 602 French AIP patients, of whom 46 had recurrent AIP. Moreover, we studied the hepatic transcriptome, serum proteome, liver macrophage polarization and oxidative and inflammatory profiles of Hmbs-/- mice chronically treated by hemin and extended the investigations to five explanted livers from recurrent AIP patients. The introduction of hemin into the pharmacopeia has coincided with a 4.4-fold increase in the prevalence of chronic patients. Moreover, we showed that both in animal model and in human liver, frequent hemin infusions generate a chronic inflammatory hepatic disease which induces HO1 remotely to hemin treatment and maintains a high ALAS1 level responsible for recurrence. Altogether, this study has important impacts on AIP care underlying that hemin needs to be restricted to severe neurovisceral crisis and suggests that alternative treatment targeting the liver such as ALAS1 and HO1 inhibitors, and anti-inflammatory therapies should be considered in patients with recurrent AIP.

An Inducible Promoter Responsive to Different Porphyrinogenic Stimuli Improves Gene Therapy Vectors for Acute Intermittent Porphyria.

Porphobilinogen deaminase (PBGD) gene therapy represents a promising therapeutic option for acute intermittent porphyria (AIP) patients suffering recurrent acute attacks. A first-in-human Phase I clinical trial confirmed the safety and tolerability of adeno-associated virus (AAV)-AAT-PBGD gene therapy, but higher doses and/or more efficient vectors are needed to achieve therapeutic expression of the transgene. This study assayed the insertion into the promoter of a short enhancer element able to induce transgene expression during exposure to endogenous and exogenous stimuli related to the pathology of the disease. The inclusion in tandem of two elements of the minimal functional sequence of human δ-aminolevulinic acid synthase drug-responsive enhancing sequence (ADRES) positioned upstream of the promoter strongly induced transgene expression in the presence of estrogens, starvation, and certain drugs known to trigger attacks in porphyria patients. The inclusion of two ADRES motives in an AAV vector improved therapeutic efficacy, reducing 10-fold the effective dose in AIP mice. In conclusion, the inclusion of specific enhancer elements in the promoter of gene therapy vectors for AIP was able to overexpress the therapeutic transgene when it is most needed, at the time when porphyrinogenic factors increase the demand for hepatic heme and precipitate acute porphyria attacks.

Generation of Patient-Derived Human Induced Pluripotent Stem Cells in X-Linked Sideroblastic Anemia and Novel Therapeutic Strategies

Sideroblastic anemias consist of a heterogeneous group of inherited and acquired disorders. The most common hereditary type is X-linked sideroblastic anemia (XLSA), which is associated with mutations in the erythroid-specific δ-aminolevulinic acid synthase (ALAS2) gene. Heme synthesis starts with the polymerization of glycine and succinyl CoA polymerization and synthesis of δ-aminolevulinic acid (ALA) in the mitochondria. ALAS2 encodes the enzyme that catalyzes these first steps in the heme synthetic pathway in erythroid cells, steps that require pyridoxal 5'-phosphate (PLP) as a cofactor. It has been found that treatment with PLP is effective for a small fraction of XLSA patients, but there are no effective treatments for the other fraction. The aim of this study is to explore the molecular mechanisms of XLSA and to develop new effective therapies.We used episomal methods to generate induced pluripotent stem cells (iPSCs) from peripheral blood mononuclear cells (PBMCs) of three late-onset XLSA female patients in one family. The cells harbored the heterozygous mutation (R227C) in the ALAS2 gene. Because ALAS2 is located in the X-chromosome, either wild-type or mutant ALAS2 gene is inactivated in the erythroid cells of female heterozygotes. All three patients showed severe anemia and their PBMCs showed skewed X-chromosome inactivation with preferential inactivation of the X chromosome carrying wild-type ALAS2, indicating a condition associated with unbalanced lyonization. From each patient, we successfully established iPSC lines with the active mutant ALAS2 allele and with the active wild-type ALAS2 allele.We assessed the hematopoietic differentiation potential of these two types of iPSC lines derived from the same patient. Differentiation into hematopoietic progenitor cells (HPCs) using embryoid body formation was comparable in the two groups. However, further differentiation in erythroid culture was significantly impaired in iPSC lines harboring the active mutant ALAS2 allele compared with those harboring the active wild-type ALAS2 allele (CD235a+ cells: 59.20±12.16% with the active wild-type ALAS2 allele vs. 3.95±4.71% with the active mutant ALAS2 allele, p<0.01). Only mutant ALAS2 expression was observed in erythroid cells differentiated from iPS cells harboring the active mutant ALAS2 allele, and only wild-type ALAS2 expression was observed in erythroid cells differentiated from iPS cells harboring the active wild-type ALAS2 allele. Hematopoietic maturation capacity was assessed by performing colony-forming unit (CFU) assays of HPCs (CD34+CD38-CD43+lineage marker-) from iPSC lines derived from the same XLSA patient. Erythroid colony count was significantly less in HPCs from iPSC lines with the active mutant ALAS2 allele, but there was no difference in total colony count between the two types of iPSC lines (erythroid colony numbers: 9.66±10.69 vs. 0±0 per 7,500 HPCs, p<0.01; mixed erythroid colony numbers: 15.00±11.26 vs. 0.66±0.57 per 7,500 HPCs, p<0.01; HPCs with the active wild-type ALAS2 allele vs. HPCs with the active mutant ALAS2 allele).We examined the effect of ALA on the erythroid differentiation of the HPCs. The CD235a-positive erythroid cell ratio of HPCs with the active wild-type ALAS2 allele did not increase following administration of ALA. By contrast, the ratio reached normal levels for HPCs with the active mutant ALAS2 allele (CD235a+ cells: 6.10± 5.61% vs. 85.34± 11.05%, p<0.01; without vs. with administration of ALA).Our data suggest that our iPSC-based system could be useful for studying the precise molecular mechanisms of XLSA and drug testing. [Display omitted] DisclosuresMorimoto:Grant-in-Aid for JSPS Research Fellow: Research Funding. Takaori-Kondo:celgene: Honoraria, Research Funding; Bristol-Myers Squibb, Novartis, Janssen pharma, Pfizer: Honoraria.

Deep sequencing of the prothoracic gland transcriptome reveals new players in insect ecdysteroidogenesis.

Ecdysteroids are steroid hormones that induce molting and determine developmental timing in arthropods. In insect larva, the prothoracic gland (PG) is a major organ for ecdysone synthesis and release. Released ecdysone is converted into the active form, 20-hydroxyecdysone (20E) in the peripheral tissues. All processes from ecdysone synthesis and release from the PG to its conversion to 20E are called ecdysteroidogenesis and are under the regulation of numerous factors expressed in the PG and peripheral tissues. Classical genetic approaches and recent transcriptomic screening in the PG identified several genes responsible for ecdysone synthesis and release, whereas the regulatory mechanism remains largely unknown. We analyzed RNA-seq data of the silkworm Bombyx mori PG and employed the fruit fly Drosophila melanogaster GAL4/UAS binary RNAi system to comprehensively screen for genes involved in ecdysone synthesis and/or release. We found that the genes encoding δ-aminolevulinic acid synthase (CG3017/alas) and putative NAD kinase (CG33156) were highly expressed in the PG of both B. mori and D. melanogaster. Neither alas nor CG33156 RNAi-induced larvae could enter into the pupal stage, and they had a lower abundance of the active form ecdysteroids in their prolonged larval stage. These results demonstrated that alas and CG33156 are indispensable for ecdysteroidogenesis.

A Japanese family with X-linked sideroblastic anemia affecting females and manifesting as macrocytic anemia

X-linked sideroblastic anemia (XLSA) is a rare hereditary disorder that typically manifests in males as microcytic anemia. Here, we report a family with XLSA that affects females and manifests as macrocytic anemia. The proband was a Japanese woman harboring a heterozygous mutation c.679C>T in the ALAS2 gene. This mutation causes the amino acid substitution R227C, which disrupts the enzymatic activity of erythroid-specific δ-aminolevulinic acid synthase. The mutation was not detected in the ALAS2 complementary DNA from peripheral blood red blood cells of the proband, indicating that the cells were mostly derived from erythroblasts expressing wild-type ALAS2. The proband's mother, who had been diagnosed with myelodysplastic syndrome, also had XLSA with the same mutation. Clinicians should be aware that XLSA can occur not only in males but also in females, in whom it manifests as macrocytic anemia.

Abstract 15796: Increased Cardiac Heme Levels Through Cardiac Overexpression of Delta-aminolevulinic Acid Synthase 2 (ALAS2) Lead to Exacerbated Ischemic Injury

Introduction: Heme is an essential iron-containing molecule for cardiovascular physiology, but in excess it may increase oxidative stress. Failing human hearts have increased heme levels, with upregulation of the rate-limiting enzyme in heme synthesis, δ-aminolevulinic acid synthase 2 (ALAS2), which is normally not expressed in cardiomyocytes. Hypothesis: We hypothesized that increased heme accumulation (through cardiac overexpression of ALAS2) leads to increased oxidative stress and cell death in the heart. Results: We first showed that ALAS2 and heme levels are increased in the hearts of mice subjected to coronary ligation. To determine the causative role of increased heme in the development of heart failure, we generated transgenic mice with cardiac-specific overexpression of ALAS2. While ALAS2 transgenic mice have normal cardiac function at baseline, their hearts display increased heme content, higher oxidative stress, exacerbated cell death, and worsened cardiac function after coronary ligation compared to non-transgenic littermates. We confirmed in cultured cardiomyoblasts that the increased oxidative stress and cell death by ALAS2 overexpression is mediated by increased heme accumulation. Furthermore, knockdown of ALAS2 in cultured cardiomyoblasts exposed to hypoxia reversed the increases in heme content and cell death. Administration of the mitochondrial antioxidant MitoTempo to ALAS2-overexpressing cardiomyoblasts normalized the elevated oxidative stress and cell death levels to baseline, indicating that the effects of increased ALAS2 and heme are through elevated mitochondrial oxidative stress. The clinical relevance of these findings was supported by the finding of increased ALAS2 induction and heme accumulation in failing human hearts from patients with ischemic cardiomyopathy compared to non-ischemic cardiomyopathy. Conclusions: Heme accumulation is detrimental to cardiac function under ischemic conditions, and reducing heme in the heart may be a novel approach for protection against the development of heart failure.

A method for determining δ-aminolevulinic acid synthase activity in homogenized cells and tissues

ObjectiveIn mammalian cells the rate-limiting step in heme biosynthesis is the formation of δ-aminolevulinic acid (ALA). The reaction intermediates, porphyrins and iron and the final product, heme can be highly cytotoxic if allowed to accumulate. The importance of maintaining the levels of metabolic intermediates and heme within a narrow range is apparent based on the complex homeostatic system(s) that have developed. Ultimately, determining the enzymatic activity of ALA synthase (ALAS) present in the mitochondria is highly beneficial to confirm the effects of the transcriptional, translational and post-translational events. The aim of this study was to develop a highly sensitive assay for ALAS that could be used on whole tissue or cellular homogenates. Design and methodsA systematic approach was used to optimize steps in formation of ALA by ALAS. Reducing the signal to noise ratio for the assay was achieved by derivatizing the ALA formed into a fluorescent product that could be efficiently separated by ultra performance liquid chromatography (UPLC) from other derivatized primary amines. The stability of ALAS activity in whole tissue homogenate and cellular homogenate was determined after extended storage at −80°C. ConclusionsA method for assaying ALAS has been developed that can be used with tissue homogenates or cellular lysates. There is no need to purify mitochondria and radiolabeled substrates are not needed for this assay. General laboratory reagents can be used to prepare the samples. Standard UPLC chromatography will resolve the derivatized ALA peak. Samples of tissue homogenate can be stored for approximately one year without significant loss of enzymatic activity.

Toxic Effects of Lead Exposure in Rats: Involvement of Oxidative Stress, Genotoxic Effect, and the Beneficial Role of N-Acetylcysteine Supplemented with Selenium

This study was carried out to investigate the in vivo protective role of N-acetylcysteine (NAC) per se, along with selenium (Se), against lead-induced hepatic, nephritic-oxidative, and neuronal-oxidative damage in rats. Lead acetate at a dose of 50 mg/kg body weight administered intraperitoneally for 3 days was preferred as the source of lead. Various oxidative stress markers such as reduced glutathione content, lipid peroxidation, superoxide dismutase, and catalase were measured to determine the degree of oxidative damage and healing due to NAC (50 mg/kg body weight administered orally) and Se (0.5 mg/kg body weight administered orally) and were studied along with the activities of enzymes such as transaminases (aspartate aminotransferase/alanine aminotransferase), δ-aminolevulinic acid dehydratase, δ-aminolevulinic acid synthase, and acetyl cholinesterase activity. The genotoxic effect of lead also was studied in terms of DNA damage using comet assay. The effect of lead was studied in blood biochemical variables such as cholesterol, triglycerides, urea, uric acid, and creatinine. Our data suggest that supplementation of Se with NAC can improve the lead-induced biochemical oxidative stress in blood and tissue, the burden of lead on the body, and molecular alterations by recoupment in mean DNA damage.

ATP-Binding Cassette B10 Regulates Early Steps of Heme Synthesis

Heme plays a critical role in gas exchange, mitochondrial energy production, and antioxidant defense in cardiovascular system. The mitochondrial transporter ATP-binding cassette (ABC) B10 has been suggested to export heme out of the mitochondria and is required for normal hemoglobinization of erythropoietic cells and protection against ischemia-reperfusion injury in the heart; however, its primary function has not been established. The aim of this study was to identify the function of ABCB10 in heme synthesis in cardiac cells. Knockdown of ABCB10 in cardiac myoblasts significantly reduced heme levels and the activities of heme-containing proteins, whereas supplementation with δ-aminolevulinic acid reversed these defects. Overexpression of mitochondrial δ-aminolevulinic acid synthase 2, the rate-limiting enzyme upstream of δ-aminolevulinic acid export, failed to restore heme levels in cells with ABCB10 downregulation. ABCB10 and heme levels were increased by hypoxia, and reversal of ABCB10 upregulation caused oxidative stress and cell death. Furthermore, ABCB10 knockdown in neonatal rat cardiomyocytes resulted in a significant delay of calcium removal from the cytoplasm, suggesting a relaxation defect. Finally, ABCB10 expression and heme levels were altered in failing human hearts and mice with ischemic cardiomyopathy. ABCB10 plays a critical role in heme synthesis pathway by facilitating δ-aminolevulinic acid production or export from the mitochondria. In contrast to previous reports, we show that ABCB10 is not a heme exporter and instead is required for the early mitochondrial steps of heme biosynthesis.

Abstract 29: Heme Levels Are Increased in the Hearts of Patients with End-Stage Heart Failure

Introduction: Diseases of iron imbalance can cause cardiomyopathy, as observed in hereditary hemochromatosis or Friedreich’s ataxia. However, the iron status of a failing heart has not been systematically examined. Results: The iron levels were quantified in ten hearts from human patients with end-stage cardiomyopathy and ten unmatched healthy control hearts. Total cellular and cytosolic non-heme iron levels were significantly reduced in failing hearts; however, there was a 2-fold increase in cytosolic heme levels in heart failure, as measured by the total protoporphyrin IX (PPIX) content. The amount of iron-free PPIX was low and did not differ between the two groups, suggesting that the majority of PPIX is complexed with iron to form heme, and thus our assay accurately estimates heme levels in the heart. To study the mechanism for the increased heme content in failing hearts, we examined the expression of genes involved in heme and iron homeostasis. Consistent with elevated heme, there was a decrease in the levels of the cellular iron importer (transferrin receptor 1 orTfR1) and the first enzyme in heme synthesis (δ-aminolevulinic acid synthase 1 or ALAS1), both of which are negatively regulated by heme. Other genes involved in heme synthesis, iron incorporation into PPIX, and heme degradation were not affected. However, we noted a significant increase in the mRNA and protein levels of ALAS2 in the failing hearts. ALAS2 is normally expressed in hemoatopoietic cells and displays very low expression in the heart. Its induction in the setting of heart failure provides a possible explanation for increased heme levels. We then assessed whether increase in ALA and heme in failing hearts is associated with generation of reactive oxygen species (ROS). Addition of exogenous ALA led to a four-fold increase in ROS, while incubation with hemin have doubled ROS levels in these cells, suggesting that augmentation of heme synthesis may exacerbate heart failure by increasing the oxidative stress. Conclusions: Our results suggest that heme levels are increased in human hearts with end-stage cardiomyopathy, possibly through the induction of ALAS2 expression. The elevated heme levels may exacerbate heart failure by increased production of ROS.

Egr-1 regulates the transcriptional repression of mouse δ-aminolevulinic acid synthase 1 by heme

δ-Aminolevulinic acid synthase 1 (ALAS1) is the first and rate-limiting enzyme in the heme biosynthesis. It has been well known that heme exerts a negative feedback control over the transcription of ALAS1 gene to maintain intracellular heme at appropriate level. To clarify the mechanisms by which heme regulates the expression of ALAS1, we examined the promoter activity of the gene and identified the heme-responsive element (HRE) located in the proximal promoter of the mouse ALAS1 gene. Reporter and EMSA assays revealed the sequence (GCGGGGGCG), as the site of repression by heme, at − 301/− 293 bp of the ALAS1 promoter. Subsequently, EMSA and ChIP assays showed that a transcription factor, early growth response 1 (Egr-1) and its major corepressors, NAB1 and NAB2 were found to bind to the ALAS1-HRE, and these bindings increased dependent on the level of intracellular heme. When Egr-1 and NAB1 in combination were expressed in the cells, decreases of the level of ALAS1 mRNA and intracellular level of heme were observed. These results suggest that Egr-1–NABs complex is involved in the regulation of the transcription of ALAS1 by heme, leading to the regulation of the heme biosynthesis.

The lack of plastidal transit sequence cannot override the targeting capacity of Bradyrhizobium japonicum δ-aminolevulinic acid synthase in transgenic rice

The δ-aminolevulinic acid synthase (ALA-S) is an enzyme which catalyzes the synthesis of δ-aminolevulinic acid (ALA). The Bradyrhizobium japonicum ALA-S coding sequence lacking plastidal transit sequence was introduced into the rice genome (C line). The transgenic lines, C4 and C5, were compared with the transgenic lines expressing TALA-S gene with plastidal transit sequence (P line) to investigate whether the plastidal sequence affects the targeting capacity of B. japonicum ALA-S gene and the ALA-synthesizing capacity in rice plants. The B. japonicum ALA-S mRNA was expressed efficiently in C lines and the protein was localized in the stroma of chloroplasts regardless of the transit sequence as in P lines. The resulting transgenic plants, C line, had similar levels of ALA-S activity, ALA, protoporphyrin IX and chlorophylls, compared to those of P lines. In response to irradiance of 350 μmol m-2 s-1, transgenic lines C4 and C5 displayed the characteristic phenotypes of photodynamic damage, i.e., decreases in photosynthetic parameter Fv/Fm, as in P5 and P14 lines, whereas wild type did not. These results indicate that the lack of the plastidal transit sequence influences neither chloroplast translocation of B. japonicum ALA-S nor ALA-synthesizing capacity in the transgenic rice.

Relevant expression of Drosophila heme oxygenase is necessary for the normal development of insect tissues

Heme oxygenase (HO) is a rate-limiting step of heme degradation, which catalyzes the conversion of heme into biliverdin, iron, and CO. HO has been characterized in micro-organisms, insects, plants, and mammals. The mammalian enzyme participates in adaptive and protective responses to oxidative stress and various inflammatory stimuli. The present study reports the use of RNA-interference (RNAi) to suppress HO in the multicellular eukaryote Drosophila. Eye imaginal disc-specific suppression of the Drosophila HO homolog (dHO) conferred serious abnormal eye morphology in adults. Deficiency of the dHO protein resulted in increased levels of iron and heme in larvae. The accumulation of iron was also observed in the compound eyes of dHO-knockdown adult flies. In parallel with the decrease of dHO, the expression of δ-aminolevulinic acid synthase, the first enzyme of the heme-biosynthetic pathway, in larvae was decreased markedly, suggesting that heme biosynthesis was totally suppressed by dHO-deficiency. The activation of caspase-3 occurred in eye imaginal discs of dHO-knockdown flies, indicating the occurrence of apoptosis in the discs. On the other hand, the overexpression of dHO resulted in a weak but significant rough eye phenotype in adults. Taken together, considering that dHO is not a stress-inducible protein, the expression of dHO can be tightly regulated at developmental stages and the relevant expression is necessary for the normal development of tissues in Drosophila.

Zinc Transporters ZnT1 (Slc30a1), Zip8 (Slc39a8), and Zip10 (Slc39a10) in Mouse Red Blood Cells Are Differentially Regulated during Erythroid Development and by Dietary Zinc Deficiency

Zinc is essential for normal erythroid cell functions and therefore intracellular zinc homeostasis during erythroid differentiation is tightly regulated. However, a characterization of zinc transporters in erythrocytes has not been conducted. The membrane fraction of mature mouse RBC was screened for zinc transporter expression using western analysis as a first step in the characterization process. ZnT1, Zip8, and Zip10 were detected among the 12 transporter proteins tested. We examined expression of these zinc transporters during erythropoietin (EPO)-induced differentiation of splenic erythroid progenitor cells into reticulocytes. Both Zip8 and Zip10 mRNA increased by 2–6 h after addition of EPO to the cells. In contrast, maximal RNA levels for the zinc transporter ZnT1 and erythroid δ-aminolevulinic acid synthase were only produced by 24 h after EPO. We confirmed these changes in transcript abundance by western analysis. Dietary zinc status influences zinc-dependent functions of RBC. To determine whether the identified zinc transporters respond to dietary zinc status, mice were fed a zinc-deficient or control diet. Incorporation of 65Zn into erythrocytes in vitro was significantly increased in cells from the zinc-deficient mice. Western analysis and densitometry revealed that erythrocyte Zip10 was upregulated and ZnT1 was downregulated in the zinc-depleted mice. Zip8 was not affected by restricted zinc intake. Collectively, these data suggest that the zinc transporters ZnT1, Zip8, and Zip10 are important for zinc homeostasis in erythrocytes and that ZnT1 and Zip10 respond to the dietary zinc supply.