Noriko Yamano

AKT signaling promotes derivation of embryonic germ cells from primordial germ cells

Primordial germ cells (PGCs) are embryonic germ cell precursors. Although the developmental potency of PGCs is restricted to the germ lineage, PGCs can acquire pluripotency, as verified by the in vitro establishment of embryonic germ (EG) cells and the in vivo production of testicular teratomas. PGC-specific inactivation of PTEN, which is a lipid phosphatase antagonizing phosphoinositide-3 kinase (PI3K), enhances both EG cell production and testicular teratoma formation. Here, we analyzed the effect of the serine/threonine kinase AKT, one of the major downstream effectors of PI3K, on the developmental potency of PGCs. We used transgenic mice that expressed an AKT-MER fusion protein, the kinase activity of which could be regulated by the ligand of modified estrogen receptor (MER), 4-hydroxytamoxifen. We found that hyperactivation of AKT signaling in PGCs at the proliferative phase dramatically augmented the efficiency of EG cell establishment. Furthermore, AKT signaling activation substituted to some extent for the effects of bFGF, an essential growth factor for EG cell establishment. By contrast, AKT activation had no effect on germ cells that were in mitotic arrest or that began meiosis at a later embryonic stage. In the transgenic PGCs, AKT activation induced phosphorylation of GSK3, which inhibits its kinase activity; enhanced the stability and nuclear localization of MDM2; and suppressed p53 phosphorylation, which is required for its activation. The p53 deficiency, but not GSK3 inhibition, recapitulated the effects of AKT hyperactivation on EG cell derivation, suggesting that p53 is one of the crucial downstream targets of the PI3K/AKT signal and that GSK3 is not.

Deferoxamine promotes angiogenesis via the activation of vascular endothelial cell function

BACKGROUND Deferoxamine (DFO), an iron chelator for disorders of excess iron, upregulates the expression of angiogenic factors, such as vascular endothelial growth factor (VEGF) and cyclooxygenase-2 (COX-2), indicating that it affects angiogenesis. Herein, we clarify the effect and mechanism of action of DFO on angiogenesis. METHODS AND RESULTS In an in vitro study, DFO increased endothelial nitric oxide synthesis (eNOS) phosphorylation in human aortic endothelial cells (HAECs), which were inhibited by the phosphatidylinositol 3-kinase inhibitor LY294002. Tube formation, cell proliferation, and cell migration in HAECs were promoted by DFO, which were significantly reduced by LY294002. In an in vivo study, DFO promoted blood flow recovery in response to the hindlimb ischemia in mice with unilateral hindlimb surgery. The density of capillaries and arterioles in ischemic muscle was higher in DFO-treated mice compared to vehicle-treated mice. Endothelial cell proliferation increased and oxidative stress and apoptosis decreased in ischemic muscles of DFO-treated mice. The phosphorylation of Akt and eNOS on the ischemic side was elevated and urinary nitric oxide/nitric dioxide (NOx) excretion was higher in DFO-treated mice compared to vehicle-treated mice. The effect of DFO on angiogenesis was abolished in eNOS-deficient mice with hindlimb ischemia. CONCLUSION These findings indicate that DFO promotes revascularization via the activation of vascular endothelial cell function by an Akt-eNOS-dependent mechanism.

Smooth muscle cell-specific Hif-1α deficiency suppresses angiotensin II-induced vascular remodelling in mice

AIM Vascular remodelling is mediated by vascular smooth muscle cell (VSMC) proliferation and hypertrophy, both processes of which are linked to medial thickening and fibrosis. Here, we show that hypoxia-inducible factor-1α (Hif-1α) expressed in smooth muscle cells (SMCs) is involved in angiotensin II (Ang II)-induced vascular remodelling in an in vivo model. METHODS AND RESULTS To clarify the role of Hif-1α in vascular remodelling, we created mice lacking the Hif-1α gene in SMCs (SMKO mice). Ang II infusion induced medial thickening and vascular fibrosis, accompanied by Hif-1α up-regulation, in the aortae of control mice, but not in those of SMKO mice. In accordance with those results, our in vitro studies showed that the deletion of SMC-derived Hif-1α suppressed the Ang II-induced hypertrophy of VSMCs, and our in vivo studies showed that the Ang II-induced expression of fibrosis-related genes in aortae was suppressed by SMC-specific Hif-1α deficiency. In addition, the SMC-specific Hif-1α deficiency suppressed Ang II-induced macrophage infiltration and Ang II-induced expression of inflammation-related genes in aortae. The superoxide production observed in the aortae of control mice with Ang II was suppressed in those of SMKO mice with Ang II, and this finding was consistent with the results of little Ang II-induced c-Src phosphorylation in SMKO mouse aortae. Loss- and gain-of-function analysis in in vitro experiments confirmed that VSMC-derived Hif-1α functions as an intrinsic modulator of vascular remodelling-related gene expression. CONCLUSION Our results revealed that SMC-derived Hif-1α is a crucial mediator of Ang II-induced vascular remodelling.

Basic fibroblast growth factor regulates glucose metabolism through glucose transporter 1 induced by hypoxia-inducible factor-1α in adipocytes.

Hypoxia-inducible factor-1α (HIF-1α), which is a transcription factor that enhances glycolysis in cells in response to hypoxia, is induced in hypertrophied adipocytes in obesity. Recent studies have shown that growth factors are able to induce HIF-1α by mechanisms independent of hypoxia. Since basic fibroblast growth factor (bFGF), an angiogenic factor, is concentrated in expanding adipose tissue, the possible effects of bFGF on regulation of HIF-1α in adipocytes were investigated. Treatment of differentiated 3T3-L1 adipocytes with bFGF induced HIF-1α. Concomitantly, glucose transporter 1 (GLUT1), which is a target gene of HIF-1α, was induced at both mRNA and protein levels and was translocated to the plasma membrane. A chromatin immunoprecipitation assay and an RNA interference study indicated that bFGF-induced HIF-1α directly upregulates GLUT1. In addition, it was observed that bFGF increases lactate production of adipocytes. This result indicates that bFGF reprograms the metabolism toward glycolysis. Intraperitoneal injection of bFGF into mice upregulated HIF-1α and GLUT1 in adipose tissues, suggesting that bFGF regulates the metabolism of adipocytes via HIF-1α-GLUT1 regulation in vivo. We also found that bFGF inhibits insulin-induced phosphorylation of insulin receptor substrate-1 and Akt, suggesting that bFGF attenuates the insulin signal in adipocytes. Taken together, the findings suggest that bFGF has a harmful effect on the development of type 2 diabetes through metabolism reprogramming and attenuation of the insulin signal.

Deletion of Hypoxia-Inducible Factor-1α in Adipocytes Enhances Glucagon-Like Peptide-1 Secretion and Reduces Adipose Tissue Inflammation

It is known that obese adipose tissues are hypoxic and express hypoxia-inducible factor (HIF)-1α. Although some studies have shown that the expression of HIF-1α in adipocytes induces glucose intolerance, the mechanisms are still not clear. In this study, we examined its effects on the development of type 2 diabetes by using adipocyte-specific HIF-1α knockout (ahKO) mice. ahKO mice showed improved glucose tolerance compared with wild type (WT) mice. Macrophage infiltration and mRNA levels of monocyte chemotactic protein-1 (MCP-1) and tumor necrosis factor α (TNFα) were decreased in the epididymal adipose tissues of high fat diet induced obese ahKO mice. The results indicated that the obesity-induced adipose tissue inflammation was suppressed in ahKO mice. In addition, in the ahKO mice, serum insulin levels were increased under the free-feeding but not the fasting condition, indicating that postprandial insulin secretion was enhanced. Serum glucagon-like peptide-1 (GLP-1) levels were also increased in the ahKO mice. Interestingly, adiponectin, whose serum levels were increased in the obese ahKO mice compared with the obese WT mice, stimulated GLP-1 secretion from cultured intestinal L cells. Therefore, insulin secretion may have been enhanced through the adiponectin-GLP-1 pathway in the ahKO mice. Our results suggest that the deletion of HIF-1α in adipocytes improves glucose tolerance by enhancing insulin secretion through the GLP-1 pathway and by reducing macrophage infiltration and inflammation in adipose tissue.

Metastable primordial germ cell-like state induced from mouse embryonic stem cells by Akt activation.

Specification to primordial germ cells (PGCs) is mediated by mesoderm-induction signals during gastrulation. We found that Akt activation during in vitro mesodermal differentiation of embryonic stem cells (ESCs) generated self-renewing spheres with differentiation states between those of ESCs and PGCs. Essential regulators for PGC specification and their downstream germ cell-specific genes were expressed in the spheres, indicating that the sphere cells had commenced differentiation to the germ lineage. However, the spheres did not proceed to spermatogenesis after transplantation into testes. Sphere cell transfer to the original feeder-free ESC cultures resulted in chaotic differentiation. In contrast, when the spheres were cultured on mouse embryonic fibroblasts or in the presence of ERK-cascade and GSK3 inhibitors, reversion to the ESC-like state was observed. These results indicate that Akt signaling promotes a novel metastable and pluripotent state that is intermediate to those of ESCs and PGCs.

Nitrosonifedipine ameliorates the progression of type 2 diabetic nephropathy by exerting antioxidative effects.

Diabetic nephropathy (DN) is the major cause of end-stage renal failure. Oxidative stress is implicated in the pathogenesis of DN. Nitrosonifedipine (NO-NIF) is a weak calcium channel blocker that is converted from nifedipine under light exposure. Recently, we reported that NO-NIF has potential as a novel antioxidant with radical scavenging abilities and has the capacity to treat vascular dysfunction by exerting an endothelial protective effect. In the present study, we extended these findings by evaluating the efficacy of NO-NIF against DN and by clarifying the mechanisms of its antioxidative effect. In a model of type 2 DN (established in KKAy mice), NO-NIF administration reduced albuminuria and proteinuria as well as glomerular expansion without affecting glucose metabolism or systolic blood pressure. NO-NIF also suppressed renal and systemic oxidative stress and decreased the expression of intercellular adhesion molecule (ICAM)-1, a marker of endothelial cell injury, in the glomeruli of the KKAy mice. Similarly, NO-NIF reduced albuminuria, oxidative stress, and ICAM-1 expression in endothelial nitric oxide synthase (eNOS) knockout mice. Moreover, NO-NIF suppressed urinary angiotensinogen (AGT) excretion and intrarenal AGT protein expression in proximal tubular cells in the KKAy mice. On the other hand, hyperglycemia-induced mitochondrial superoxide production was not attenuated by NO-NIF in cultured endothelial cells. These findings suggest that NO-NIF prevents the progression of type 2 DN associated with endothelial dysfunction through selective antioxidative effects.

Induction of Primordial Germ Cell-Like Cells From Mouse Embryonic Stem Cells by ERK Signal Inhibition

Primordial germ cells (PGCs) are embryonic germ cell precursors. Specification of PGCs occurs under the influence of mesodermal induction signaling during in vivo gastrulation. Although bone morphogenetic proteins and Wnt signaling play pivotal roles in both mesodermal and PGC specification, the signal regulating PGC specification remains unknown. Coculture of mouse embryonic stem cells (ESCs) with OP9 feeder cells induces mesodermal differentiation in vitro. Using this mesodermal differentiation system, we demonstrated that PGC‐like cells were efficiently induced from mouse ESCs by extracellular signal‐regulated kinase (ERK) signaling inhibition. Inhibition of ERK signaling by a MAPK/ERK kinase (MEK) inhibitor upregulated germ cell marker genes but downregulated mesodermal genes. In addition, the PGC‐like cells showed downregulation of DNA methylation and formed pluripotent stem cell colonies upon treatment with retinoic acid. These results show that inhibition of ERK signaling suppresses mesodermal differentiation but activates germline differentiation program in this mesodermal differentiation system. Our findings provide a new insight into the signaling networks regulating PGC specification. Stem Cells 2014;32:2668–2678

A Long-Term High-Fat Diet Changes Iron Distribution in the Body, Increasing Iron Accumulation Specifically in the Mouse Spleen

Although iron is an essential trace metal, its presence in excess causes oxidative stress in the human body. Recent studies have indicated that iron storage is a risk factor for type 2 diabetes mellitus. Dietary iron restriction or iron chelation ameliorates symptoms of type 2 diabetes in mouse models. However, whether iron content in the body changes with the development of diabetes is unknown. Here, we investigated the dynamics of iron accumulation and changes in iron absorption-related genes in mice that developed obesity and diabetes by consuming a high-fat diet (HFD-fed mice). HFD-fed mice (18-20 wk) were compared with control mice for hematologic features, serum ferritin levels, and iron contents in the gastrocnemius muscle, heart, epididymal fat, testis, liver, duodenum, and spleen. In addition, the spleen was examined histologically. Iron absorption-related gene expression in the liver and duodenum was also examined. Hemoglobin and serum ferritin levels were increased in HFD-fed mice. The HFD-fed mice showed iron accumulation in the spleen, but not in the heart or liver. Increased percentages of the splenic red pulp and macrophages were observed in HFD-fed mice and iron accumulation in the spleen was found mainly in the splenic red pulp. The HFD-fed mice also showed decreased iron content in the duodenum. The mRNA expression of divalent metal transporter-1 (DMT-1), an iron absorption-related gene, was elevated in the duodenum of HFD-fed mice. These results indicate that iron accumulation (specifically accumulation in the spleen) is enhanced by the development of type 2 diabetes induced by HFD.

Construction of a gene knockout CHO cell line using a simple gene targeting method

Background Therapeutic antibodies have become an important focus of the biopharmaceutical industry. The Chinese hamster ovary (CHO) cell line is a major host for therapeutic antibody production. To construct productive CHO cell lines, two major transfection methods are commonly used, i.e., random integration and gene targeting. Random integration is a common method in which randomly integrated transgenes cause variation in antibody productivity because they are located in various chromosomal regions that affect transgene expression levels. Recently, gene-targeting methods, in which exogenous genes are inserted into a specific chromosomal region, have improved remarkably. Gene targeting is based on homologous recombination using sequences targeting a specific genomic region of the host cell. Homologous sequences located on both sides of the exogenous gene are used. We used the recently developed clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated proteins (Cas9) system as a gene-targeting method. The CRISPR-Cas9 system induces double-strand breaks (DSBs) via guide RNA and Cas9, which increases the efficiency of homologous recombination [1]. Guide RNA hybridizes to a target integration site and induces Cas9 protein expression, leading to DSB. Finally, the Cas9 protein cuts genomic DNA. In this study, we constructed a simple genetargeting method in CHO cells using the CRISPR-Cas9 system in which CRISPR vectors induce DSBs and genetargeting vectors are inserted at the DSB site. In the conventional method, gene-targeting vectors should contain homology arms for effective recombination. In this study, we used the CRISPER system without homology arms for gene-targeted recombination. Materials and methods We constructed a CRISPR-Cas9 vector that expresses a guide RNA sequence targeting a region on chromosome O. Chromosome O was selected based on a previous classification of gene-amplified CHO cell chromosomes in order of decreasing size and assigned letters from A to T by fluorescence in situ hybridization (FISH) [2]. The CRISPR targeting sequence was determined from the BAC clone Cg0031N14, which contained the chromosome O sequence. Gene targeting vectors (pcDNA-GFP-DHFR) with or without target site homology arms were constructed from BAC clone Cg0031N14. The percentage of exogenous gene integration into chromosome O was determined by a FISH analysis. Total RNA extracted from E14Tg2a (mouse ES cells) was kindly provided by Dr. Tohru Kimura, Kitasato University, Kanagawa, Japan.