Ayako Tanimura

Paradoxical Regulation of Human FGF21 by Both Fasting and Feeding Signals: Is FGF21 a Nutritional Adaptation Factor?

Fibroblast growth factor 21 (FGF21) has recently emerged as a metabolic hormone involved in regulating glucose and lipid metabolism in mouse, but the regulatory mechanisms and actions of FGF21 in humans remain unclear. Here we have investigated the regulatory mechanisms of the human FGF21 gene at the transcriptional level. A deletion study of the human FGF21 promoter (−1672 to +230 bp) revealed two fasting signals, including peroxisome proliferator-activated receptor α (PPARα) and glucagon signals, that independently induced human FGF21 gene transcription in mouse primary hepatocytes. In addition, two feeding signals, glucose and xylitol, also dose-dependently induced human FGF21 gene transcription and mRNA expression in both human HepG2 cells and mouse primary hepatocytes. FGF21 protein expression and secretion were also induced by high glucose stimulation. The human FGF21 promoter (−1672 to +230 bp) was found to have a carbohydrate-responsive element at −380 to −366 bp, which is distinct from the PPAR response element (PPRE). Knock-down of the carbohydrate response element binding protein by RNAi diminished glucose-induced human FGF21 transcription. Moreover, we found that a region from −555 to −443 bp of the human FGF21 promoter region exerts an important role in the activation of basic transcription. In conclusion, human FGF21 gene expression is paradoxically and independently regulated by both fasting and feeding signals. These regulatory mechanisms suggest that human FGF21 is increased with nutritional crisis, including starvation and overfeeding.

Dietary phosphate restriction ameliorates endothelial dysfunction in adenine-induced kidney disease rats

Hyperphosphatemia causes endothelial dysfunction as well as vascular calcification. Management of serum phosphate level by dietary phosphate restriction or phosphate binders is considered to be beneficial to prevent chronic kidney disease patients from cardiovascular disease, but it has been unclear whether keeping lower serum phosphate level can ameliorate endothelial dysfunction. In this study we investigated whether low-phosphate diet can ameliorate endothelial dysfunction in adenine-induced kidney disease rats, one of useful animal model of chronic kidney disease. Administration of 0.75% adenine-containing diet for 21 days induced renal failure with hyperphosphatemia, and impaired acetylcholine-dependent vasodilation of thoracic aortic ring in rats. Then adenine-induced kidney disease rats were treated with either control diet (1% phosphate) or low-phosphate diet (0.2% phosphate) for 16 days. Low-phosphate diet ameliorated not only hyperphosphatemia but also the impaired vasodilation of aorta. In addition, the activatory phosphorylation of endothelial nitric oxide synthase at serine 1177 and Akt at serine 473 in the aorta were inhibited by in adenine-induced kidney disease rats. The inhibited phosphorylations were improved by the low-phosphate diet treatment. Thus, dietary phosphate restriction can improve aortic endothelial dysfunction in chronic kidney disease with hyperphosphatemia by increase in the activatory phosphorylations of endothelial nitric oxide synthase and Akt.

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.

Gene Signature of Human Oral Mucosa Fibroblasts: Comparison with Dermal Fibroblasts and Induced Pluripotent Stem Cells

Oral mucosa is a useful material for regeneration therapy with the advantages of its accessibility and versatility regardless of age and gender. However, little is known about the molecular characteristics of oral mucosa. Here we report the first comparative profiles of the gene signatures of human oral mucosa fibroblasts (hOFs), human dermal fibroblasts (hDFs), and hOF-derived induced pluripotent stem cells (hOF-iPSCs), linking these with biological roles by functional annotation and pathway analyses. As a common feature of fibroblasts, both hOFs and hDFs expressed glycolipid metabolism-related genes at higher levels compared with hOF-iPSCs. Distinct characteristics of hOFs compared with hDFs included a high expression of glycoprotein genes, involved in signaling, extracellular matrix, membrane, and receptor proteins, besides a low expression of HOX genes, the hDFs-markers. The results of the pathway analyses indicated that tissue-reconstructive, proliferative, and signaling pathways are active, whereas senescence-related genes in p53 pathway are inactive in hOFs. Furthermore, more than half of hOF-specific genes were similarly expressed to those of hOF-iPSC genes and might be controlled by WNT signaling. Our findings demonstrated that hOFs have unique cellular characteristics in specificity and plasticity. These data may provide useful insight into application of oral fibroblasts for direct reprograming.

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.

Isolation and characterization of dental epithelial cells derived from amelogenesis imperfecta rat.

OBJECTIVE Disruption of the third zinc finger domain of specificity protein 6 (SP6) presents an enamel-specific defect in a rat model of amelogenesis imperfecta (AMI rats). To understand the molecular basis of amelogenesis imperfecta caused by the Sp6 mutation, we established and characterized AMI-derived rat dental epithelial (ARE) cells. MATERIALS AND METHODS ARE cell clones were isolated from the mandibular incisors of AMI rats, and amelogenesis-related gene expression was analyzed by reverse transcription polymerase chain reaction (RT-PCR). Localization of wild-type SP6 (SP6WT) and mutant-type SP6 (SP6AMI) was analyzed by immunocytochemistry. SP6 transcriptional activity was monitored by rho-associated protein kinase 1 (Rock1) promoter activity with its specific binding to the promoter region in dental (G5 and ARE) and non-dental (COS-7) epithelial cells. RESULTS Isolated ARE cells were varied in morphology and gene expression. Both SP6WT and SP6AMI were mainly detected in nuclei. The promoter analysis revealed that SP6WT and SP6AMI enhanced Rock1 promoter activity in G5 cells but that enhancement by SP6AMI was weaker, whereas no enhancement was observed in the ARE and COS-7 cells, even though SP6WT and SP6AMI bound to the promoter in all instances. CONCLUSION ARE cell clones can provide a useful in vitro model to study the mechanism of SP6-mediated amelogenesis imperfecta.

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.