UK-5099, a mitochondrial pyruvate carrier inhibitor, recovers impaired neutrophil maturation caused by AK2 deficiency in human pluripotent stem cell models.

Reticular dysgenesis (RD) is a rare genetic disease caused by gene mutations in the ATP:AMP phosphotransferase, adenylate kinase 2 (AK2). Patients with RD suffer from severe combined immunodeficiency with neutrophil maturation arrest. Although hematopoietic stem cell transplantation can be a curative option, it is invasive, and complications of agranulocytosis-induced infection worsen the prognosis. Here, we report that the use of UK-5099, an inhibitor of the mitochondrial pyruvate carrier (MPC), on hemo-angiogenic progenitor cells (HAPCs) derived from AK2-deficient induced pluripotent stem cells improved neutrophil maturation. Reactive oxygen species (ROS) levels in AK2-deficient HAPCs remained unchanged throughout all experiments, implying that UK-5099 improved the phenotype without affecting ROS levels. Overall, our results suggest that the MPC is a potential therapeutic target for the treatment of neutrophil maturation defects in RD.

The Effect of Heterozygous Mutation of Adenylate Kinase 2 Gene on Neutrophil Differentiation.

Mitochondrial ATP production plays an important role in most cellular activities, including growth and differentiation. Previously we reported that Adenylate kinase 2 (AK2) is the main ADP supplier in the mitochondrial intermembrane space in hematopoietic cells, especially in the bone marrow. AK2 is crucial for the production of neutrophils and T cells, and its deficiency causes reticular dysgenesis. However, the relationship between ADP supply by AK2 and neutrophil differentiation remains unclear. In this study, we used CRISPR/Cas9 technology to establish two heterozygous AK2 knock-out HL-60 clones as models for reticular dysgenesis. Their AK2 activities were about half that in the wild-type (WT). Furthermore, neutrophil differentiation was impaired in one of the clones. In silico analysis predicted that the obtained mutations might cause a structural change in AK2. Time course microarray analysis of the WT and mutants revealed that similar gene clusters responded to all-trans retinoic acid treatment, but their expression was lower in the mutants than in WT. Application of fructose partially restored neutrophil differentiation in the heterozygous knock-out HL-60 clone after all-trans retinoic acid treatment. Collectively, our study suggests that the mutation of N-terminal region in AK2 might play a role in AK2-dependent neutrophil differentiation and fructose could be used to treat AK2 deficiency.

Mitochondrial Activity and Unfolded Protein Response are Required for Neutrophil Differentiation.

BACKGROUND/AIMS: Endoplasmic reticulum (ER) stress and unfolded protein response (UPR) are involved in hematopoietic differentiation. However, the mechanistic linkage between ER stress/UPR and hematopoietic differentiation remains unclear. METHODS: We used bipotent HL-60 cells as an in vitro hematopoietic differentiation system to investigate the role of ER stress and UPR activity in neutrophil and macrophage differentiation. RESULTS: The in vitro differentiation analysis revealed that ER stress decreased during both neutrophil and macrophage differentiations, and the activities of PERK and ATF6 were decreased and that of IRE1α was increased during neutrophil differentiation in a stage-specific manner. By contrast, the activities of ATF6 and ATF4 decreased during macrophage differentiation. When the cells were treated with oligomycin, the expression of CD11b, a myelocytic differentiation marker, and morphological differentiation were suppressed, and XBP-1 activation was inhibited during neutrophil differentiation, whereas CD11b expression was maintained, and morphological differentiation was not obviously affected during macrophage differentiation. CONCLUSION: In this study, we demonstrated that neutrophil differentiation is regulated by ER stress/UPR that is supported by mitochondrial ATP supply, in which IRE1α-XBP1 activation is essential. Our findings provide the evidence that mitochondrial energy metabolism may play a critical role in neutrophil differentiation.

Human AK2 links intracellular bioenergetic redistribution to the fate of hematopoietic progenitors.

AK2 is an adenylate phosphotransferase that localizes at the intermembrane spaces of the mitochondria, and its mutations cause a severe combined immunodeficiency with neutrophil maturation arrest named reticular dysgenesis (RD). Although the dysfunction of hematopoietic stem cells (HSCs) has been implicated, earlier developmental events that affect the fate of HSCs and/or hematopoietic progenitors have not been reported. Here, we used RD-patient-derived induced pluripotent stem cells (iPSCs) as a model of AK2-deficient human cells. Hematopoietic differentiation from RD-iPSCs was profoundly impaired. RD-iPSC-derived hemoangiogenic progenitor cells (HAPCs) showed decreased ATP distribution in the nucleus and altered global transcriptional profiles. Thus, AK2 has a stage-specific role in maintaining the ATP supply to the nucleus during hematopoietic differentiation, which affects the transcriptional profiles necessary for controlling the fate of multipotential HAPCs. Our data suggest that maintaining the appropriate energy level of each organelle by the intracellular redistribution of ATP is important for controlling the fate of progenitor cells.

Deciphering defective amelogenesis using in vitro culture systems.

The conventional two-dimensional (2D) in vitro culture system is frequently used to analyze the gene expression with or without extracellular signals. However, the cells derived from primary culture and cell lines frequently deviate the gene expression profile compared to the corresponding in vivo samples, which sometimes misleads the actual gene regulation in vivo. To overcome this gap, we developed the comparative 2D and 3D in vitro culture systems and applied them to the genetic study of amelogenesis imperfecta (AI) as a model. Recently, we found specificity protein 6 (Sp6) mutation in an autosomal-recessive AI rat that was previously named AMI. We constructed 3D structure of ARE-B30 cells (AMI-derived rat dental epithelial cells) or G5 (control wild type cells) combined with RPC-C2A cells (rat pulp cell line) separated by the collagen membrane, while in 2D structure, ARE-B30 or G5 was cultured with or without the collagen membrane. Comparative analysis of amelogenesis-related gene expression in ARE-B30 and G5 using our 2D and 3D in vitro systems revealed distinct expression profiles, showing the causative outcomes. Bone morphogenetic protein 2 and follistatin were reciprocally expressed in G5, but not in ARE-B30 cells. All-or-none expression of amelotin, kallikrein-related peptidase 4, and nerve growth factor receptor was observed in both cell types. In conclusion, our in vitro culture systems detected the phenotypical differences in the expression of the stage-specific amelogenesis-related genes. Parallel analysis with 2D and 3D culture systems may provide a platform to understand the molecular basis for defective amelogenesis caused by Sp6 mutation.

Sp6 regulation of Rock1 promoter activity in dental epithelial cells.

Sp6 is a transcription factor of the SP/KLF family and an indispensable regulator of the morphological dynamics of ameloblast differentiation during tooth development. However, the underlying molecular mechanisms remain unclear. We have previously identified one of the Sp6 downstream genes, Rock1, which is involved in ameloblast polarization. In this study, we investigated the transcriptional regulatory mechanisms of Rock1 by Sp6. First, we identified the transcription start sites (TSS) and cloned the 5'-flanking region of Rock1. Serial deletion analyses identified a critical region for Rock1 promoter activity within the 249-bp upstream region of TSS, and chromatin immunoprecipitation assays revealed Sp6-binding to this region. Subsequent transient transfection experiments showed that Rock1 promoter activity is enhanced by Sp6, but reduced by Sp1. Treatment of dental epithelial cells with the GC-selective DNA binding inhibitor, mithramycin A, affected Rock1 promoter activity in loss of enhancement by Sp6, but not repression by Sp1. Further site-directed mutagenesis indicated that the region from -206 to -150 contains responsive elements for Sp6. Taken together, we conclude that Sp6 positively regulates Rock1 transcription by direct binding to the Rock1 promoter region from -206 to -150, which functionally distinct from Sp1.

Adenylate kinase 2 deficiency limits survival and regulates various genes during larval stages of Drosophila melanogaster.

Adenylate kinase isozyme 2 (AK2) is located in mitochondrial intermembrane space and regulates energy metabolism by reversibly converting ATP and AMP to 2 ADPs. We previously demonstrated that disruption of the Drosophila melanogaster AK2 gene (Dak2) resulted in growth arrest during the larval stage and subsequent death. Two other groups found that human AK2 mutations cause reticular dysgenesis, a form of severe combined immunodeficiency (SCID) that is associated with severe hematopoietic defects and sensorineural deafness. However, the mechanisms underlying differential outcomes of AK2 deficiency in Drosophila and human systems remain unknown. In this study, effects of tissue-specific inactivation of the Dak2 gene on Drosophila development were analyzed using RNAi-mediated gene knockdown. In addition, to investigate the roles of AK2 in the regulation of gene expression during development, microarray analysis was performed using RNA from first and second instar larvae of Dak2-deficient mutant and wild-type D. melanogaster. Knockdown of Dak2 in all germ layers caused cessation of growth and subsequent death of flies. Microarray analysis revealed that Dak2 deficiency downregulates various genes, particularly those involved in the proteasomal function and in mitochondrial translation machinery. These data indicate that adenine nucleotide interconversion by Dak2 is crucial for developmental processes of Drosophila melanogaster.

Ctip2-mediated Sp6 transcriptional regulation in dental epithelium-derived cells.

Tooth development relies on the interaction between the oral ectoderm and underlying mesenchyme, and is regulated by a complex genetic cascade. This transcriptional cascade is regulated by the spatiotemporal activation and deactivation of transcription factors. The specificity proteins 6 (Sp6) and chicken ovalbumin upstream promoter transcription factor-interacting protein 2 (Ctip2) were identified in loss-of-function studies as key transcription factors required for tooth development. Ctip2 binds to the Sp6 promoter in vivo; however, its role in Sp6 expression remains unclear. In this study, we investigated Sp6 transcriptional regulation by Ctip2. Immunohistochemical analysis revealed that Sp6 and Ctip2 colocalize in the rat incisor during tooth development. We examined whether Ctip2 regulates Sp6 promoter activity in dental epithelial cells. Cotransfection experiments using serial Sp6 promoter-luciferase constructs and Ctip2 expression plasmids showed that Ctip2 significantly suppressed the Sp6 second promoter activity, although the Sp6 first promoter activity was unaffected. Ctip2 was able to bind to the proximal region of the Sp6 first promoter, as previously demonstrated, and also to the novel distal region of the first, and second promoter regions. Our findings indicate that Ctip2 regulates Sp6 gene expression through direct binding to the Sp6 second promoter region. J. Med. Invest. 61: 126-136, February, 2014.

Differential expression of adenine nucleotide converting enzymes in mitochondrial intermembrane space: a potential role of adenylate kinase isozyme 2 in neutrophil differentiation.

Adenine nucleotide dynamics in the mitochondrial intermembrane space (IMS) play a key role in oxidative phosphorylation. In a previous study, Drosophila adenylate kinase isozyme 2 (Dak2) knockout was reported to cause developmental lethality at the larval stage in Drosophila melanogaster. In addition, two other studies reported that AK2 is a responsible gene for reticular dysgenesis (RD), a human disease that is characterized by severe combined immunodeficiency and deafness. Therefore, mitochondrial AK2 may play an important role in hematopoietic differentiation and ontogenesis. Three additional adenine nucleotide metabolizing enzymes, including mitochondrial creatine kinases (CKMT1 and CKMT2) and nucleoside diphosphate kinase isoform D (NDPK-D), have been found in IMS. Although these kinases generate ADP for ATP synthesis, their involvement in RD remains unclear and still an open question. In this study, mRNA and protein expressions of these mitochondrial kinases were firstly examined in mouse ES cells, day 8 embryos, and 7-week-old adult mice. It was found that their expressions are spatiotemporally regulated, and Ak2 is exclusively expressed in bone marrow, which is a major hematopoietic tissue in adults. In subsequent experiments, we identified increased expression of both AK2 and CKMT1 during macrophage differentiation and exclusive production of AK2 during neutrophil differentiation using HL-60 cells as an in vitro model of hematopoietic differentiation. Furthermore, AK2 knockdown specifically inhibited neutrophil differentiation without affecting macrophage differentiation. These data suggest that AK2 is indispensable for neutrophil differentiation and indicate a possible causative link between AK2 deficiency and neutropenia in RD.

Role of serine 249 of ezrin in the regulation of sodium-dependent phosphate transporter NaPi-IIa activity in renal proximal tubular cells.

Type IIa sodium-dependent phosphate transporter (NaPi-IIa) is responsible for renal phosphate reabsorption and maintenance of systemic phosphate homeostasis in mammals. Macromolecular complex formation of NaPi-IIa with sodium-proton exchanger related factor-1 (NHERF-1) and ezrin is important for apical membrane localization in the proximal tubular cells. Here, we investigated the interactions of the ezrin phosphomimetic mutation of serine to aspartic acid at 249 with NHERF-1 and the inhibition of apical membrane localization of NaPi-IIa. In vitro phosphorylation analysis revealed that serine 249 of human ezrin serves as a phosphorylation site for protein kinase A. The N-terminal half of ezrin had a dominant negative effect on the phosphate transport activity and inhibited the apical localization of NaPi-IIa in renal proximal tubular cells. We found that the phosphomimetic S249D mutant interfered with the inhibitory effects of the dominant negative mutant on the transport and localization of NaPi-IIa. The S249D mutant also inhibited the interaction with NHERF-1. Therefore, serine 249 of ezrin can play important roles in the regulation of the complex formation and membrane localization of NaPi-IIa.

Evaluation of anti-stress nutrients in the endothelial cells with fluorescence indicator.

Oxidative stress has emerged as an important pathogenic factor in the development of long-term complications, such as hypertension, atherosclerosis, nephropathy, and cancer. Taking many antioxidants from natural food may be effective to prevent us from those diseases. We have attempted to evaluate the effect of improvement by dietary antioxidants on the endothelial dysfunction induced by hyperglycemia. Fluorescence indicators for reactive oxygen species and nitric oxide were employed to the evaluation. The combination of those fluorescence indicators could be powerful tool to evaluate the effect of anti-stress nutrients on both oxidative stress and endothelial dysfunction.