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Satoru Takase,
Jun-Ichi Osuga,
Hayato Fujita,
Kazuo Hara,
Motohiro Sekiya,
Masaki Igarashi,
Mikio Takanashi, Yoshinori Takeuchi,
Yoshihiko Izumida,
Keisuke Ohta, [......],
Yoko Iizuka,
Ken Ohashi,
Hiroshi Yoshida,
Hidekatsu Yanai,
Norio Tada,
Takanari Gotoda,
Shun Ishibashi,
Takashi Kadowaki,
Hiroaki Okazaki,
Naoya Yahagi
[show abstract]
[hide abstract]
ABSTRACT: Aim: Familial apolipoprotein C-II (apoC-II) deficiency is a rare autosomal recessive disorder with marked hypertriglyceridemia resulting from impaired activation of lipoprotein lipase. In most cases of apoC-II deficiency, causative mutations have been found in the protein-coding region of APOC2; however, several atypical cases of apoC-II deficiency were reported to have markedly reduced, but detectable levels of plasma apoC-II protein (hereafter referred to as hypoapoC-II), which resulted from decreased promoter activity or improper splicing of apoC-II mRNA due to homozygous mutations in APOC2. Here we aim to dissect the molecular bases of a new case of hypoapoC-II.Methods: We performed detailed biochemical/genetic analyses of our new case of hypoapoC-II, manifesting severe hypertriglyceridemia (plasma triglycerides, 3235 mg·dL-1) with markedly reduced levels of plasma apoC-II (0.6 mg·dL-1).Results: We took advantage of a monocyte/macrophage culture system to prove that transcription of apoC-II mRNA was decreased in the patient's cells, which is compatible with the reported features of hypoapoC-II. Concomitantly, transcriptional activity of the minigene reporter construct of the patient's APOC2 gene was decreased; however, no rare variant was detected in the patient's APOC2 gene. Fifty single nucleotide variants were detected in the patient's APOC2, but all were common variants (allele frequencies ＞35%) that are supposedly not causative.Conclusions: A case of apoC-II deficiency was found that is phenotypically identical to hypoapoC-II but with no causative mutations in APOC2, implying that other genes regulate apoC-II levels. The clinical entity of hypoapoC-II is discussed.
Journal of atherosclerosis and thrombosis 03/2013; · 2.69 Impact Factor
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Yoshinori Takeuchi,
Yasuhito Fujino,
Manabu Watanabe,
Masashi Takahashi,
Takayuki Nakagawa,
Ayano Takeuchi,
Makoto Bonkobara,
Tetsuya Kobayashi,
Koichi Ohno,
Kazuyuki Uchida,
Kazushi Asano,
Ryohei Nishimura,
Hiroyuki Nakayama,
Sumio Sugano,
Yasuo Ohashi,
Hajime Tsujimoto
[show abstract]
[hide abstract]
ABSTRACT: The objective of this retrospective cohort study was to validate the prognostic value of histological grading of canine cutaneous mast cell tumours (MCTs) according to the Patnaik (grades I-III) and Kiupel (low, high) grading systems, and to confirm the prognostic significance of internal tandem duplications (ITDs) within exon 11 of the c-kit gene (ITD-Exon11). The baseline characteristics and outcome data from 47 dogs diagnosed with cutaneous MCTs were collected and reviewed. Tumours were graded according to both grading systems and the nucleotide sequence of c-kit was evaluated. Results were analyzed to evaluate predictive factors for overall survival (OS) and progression-free survival (PFS). Log-rank tests indicated that dogs with Patnaik grade III MCTs had significantly reduced OS and PFS compared to those with either grade I or II tumours. However, no significant difference in OS or PFS was observed between grade I and II tumours. The dogs with Kiupel high-grade MCTs had significantly shorter OS and PFS than dogs with low-grade MCTs. The presence of ITD-Exon11 was significantly associated with shorter PFS. The result of Cox regression analysis showed that the Kiupel grading system for OS and PFS, and lymph node metastasis for OS, independently predicted prognosis. Kappa statistics confirmed a significantly higher inter-observer consistency for the Kiupel compared to the Patnaik grading system. These findings demonstrate that the Kiupel grading system is a useful prognostic tool for canine cutaneous MCTs in predicting OS and PFS, while the occurrence of ITD-Exon11 appeared to be a useful predictor for PFS.
The Veterinary Journal 02/2013; · 2.24 Impact Factor
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Ayano Naka,
Kaoruko Tada Iida,
Yoshimi Nakagawa,
Hitoshi Iwasaki, Yoshinori Takeuchi,
Aoi Satoh,
Takashi Matsuzaka,
Kiyo-Aki Ishii,
Kazuto Kobayashi,
Shigeru Yatoh,
Masako Shimada,
Hiroaki Suzuki,
Hirohito Sone,
Nobuhiro Yamada,
Hitoshi Shimano,
Naoya Yahagi
[show abstract]
[hide abstract]
ABSTRACT: Transcription factor E3 (TFE3) belongs to a basic helix-loop-helix family, and is involved in the biology of osteoclasts, melanocytes and their malignancies. We previously reported the metabolic effects of TFE3 on insulin in the liver and skeletal muscles in animal models. In the present study, we explored a novel role for TFE3 in a skeletal muscle cell line. When TFE3 was overexpressed in C2C12 myoblasts by adenovirus before induction of differentiation, myogenic differentiation of C2C12 cells was significantly inhibited. Adenovirus-mediated TFE3 overexpression also suppressed the gene expression of muscle regulatory factors (MRFs), such as MyoD and myogenin, during C2C12 differentiation. In contrast, knockdown of TFE3 using adenovirus encoding short-hairpin RNAi specific for TFE3 dramatically promoted myoblast differentiation associated with significantly increased expression of MRFs. Consistent with these findings, promoter analyses via luciferase reporter assay and electrophoretic mobility shift assay suggested that TFE3 negatively regulated myogenin promoter activity by direct binding to an E-box, E2, in the myogenin promoter. These findings indicated that TFE3 has a regulatory role in myoblast differentiation, and that transcriptional suppression of myogenin expression may be part of the mechanism of action.
Biochemical and Biophysical Research Communications 12/2012; · 2.48 Impact Factor
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[show abstract]
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ABSTRACT: A Japanese domestic long-hair cat of about 8 years of age was presented with vomiting and hematochezia and was found to have significant hypereosinophilia. Bone marrow aspiration revealed moderate increases of eosinophilic lineages. Histopathological examination revealed mild eosinophilic and epitheliotropic T-lymphocytic infiltrations in the duodenum. Although the cat remained asymptomatic with only prednisolone administration, the cat presented with hematemesis, weight loss, and severe anorexia 512 days after the initial presentation. Subsequently, gastrointestinal perforation developed, and the cat died on Day 536. Histopathological examination of autopsy specimens revealed mixed cellular infiltration including eosinophils and neoplastic lymphocytes in the intestinal lymph nodes, intestine, liver, spleen, and pancreas. Immunohistochemical examination supports a diagnosis of intestinal T-cell lymphoma with severe hypereosinophilic syndrome.
Journal of Veterinary Medical Science 03/2012; 74(8):1057-62. · 0.85 Impact Factor
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ABSTRACT: Options of systemic treatment for canine MCT have been still limited and most canine cases with MCTs eventually undergo relapses even after achievement of a remission. Thus additional therapies are required to establish for the tumor. To identify the novel candidate therapeutic targets for canine MCT, the mRNA expression and phosphorylation statuses of several receptor or non-receptor kinases as well as the inhibitory effect of 95 specific inhibitors on the growth were assessed in three canine MCT cell lines (HRMC, VIMC1 and CMMC1). Among the 14 targets, the mRNAs of 11, 7 and 7 kinases were amplified in HRMC, VIMC1 and CMMC1, respectively. The mRNAs of VEGFR3, PDGFRα, SRC, YES, LCK and FYN were detected in all cell lines. The phosphorylation of 12, 8 and 7 kinases was observed by using specific antibody arrays in HRMC, VIMC1 and CMMC1, respectively. DTK, EPHB6, AMPKα1, CREB, STAT5a and STAT5b were phosphorylated in all cell lines. The 10, 9 and 17 inhibitors exhibited the biological activity against the growth of HRMC, VIMC1 and CMMC1, respectively. Only three inhibitors such as SB218078 (for Chk1), PDGF RTK inhibitor IV (for PDGFR) and radicicol (for Hsp90) suppressed the growth of all three cell lines. The present study indicated that several kinases, such as Chk1, PDGFR and Hsp90, could be used as therapeutic targets in the treatment for canine MCT. Further studies and clinical trials are warranted to apply the inhibitors for the treatment of the tumor.
Journal of Veterinary Medical Science 06/2011; 73(10):1295-302. · 0.85 Impact Factor
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Michiyo Amemiya-Kudo,
Junko Oka, Yoshinori Takeuchi,
Hiroaki Okazaki,
Takashi Yamamoto,
Naoya Yahagi,
Kaori Matsuzaka,
Sachiko Okazaki,
Jun-ichi Osuga,
Nobuhiro Yamada,
Toshio Murase,
Hitoshi Shimano
[show abstract]
[hide abstract]
ABSTRACT: Overexpression of sterol regulatory element-binding protein-1c (SREBP-1c) in β cells causes impaired insulin secretion and β cell dysfunction associated with diminished pancreatic duodenal homeodomain transcription factor-1 (PDX-1) expression in vitro and in vivo. To identify the molecular mechanism responsible for this effect, the mouse Pdx-1 gene promoter (2.7 kb) was analyzed in β cell and non-β cell lines. Despite no apparent sterol regulatory element-binding protein-binding sites, the Pdx-1 promoter was suppressed by SREBP-1c in β cells in a dose-dependent manner. PDX-1 activated its own promoter. The E-box (-104/-99 bp) in the proximal region, occupied by ubiquitously expressed upstream stimulatory factors (USFs), was crucial for the PDX-1-positive autoregulatory loop through direct PDX-1·USF binding. This positive feedback activation was a prerequisite for SREBP-1c suppression of the promoter in non-β cells. SREBP-1c and PDX-1 directly interact through basic helix-loop-helix and homeobox domains, respectively. This robust SREBP-1c·PDX-1 complex interferes with PDX-1·USF formation and inhibits the recruitment of PDX-1 coactivators. SREBP-1c also inhibits PDX-1 binding to the previously described PDX-1-binding site (-2721/-2646 bp) in the distal enhancer region of the Pdx-1 promoter. Endogenous up-regulation of SREBP-1c in INS-1 cells through the activation of liver X receptor and retinoid X receptor by 9-cis-retinoic acid and 22-hydroxycholesterol inhibited PDX-1 mRNA and protein expression. Conversely, SREBP-1c RNAi restored Pdx-1 mRNA and protein levels. Through these multiple mechanisms, SREBP-1c, when induced in a lipotoxic state, repressed PDX-1 expression contributing to the inhibition of insulin expression and β cell dysfunction.
Journal of Biological Chemistry 06/2011; 286(32):27902-14. · 4.77 Impact Factor
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Keisuke Ohta,
Motohiro Sekiya,
Hiroshi Uozaki,
Masaki Igarashi,
Satoru Takase,
Masayoshi Kumagai,
Mikio Takanashi, Yoshinori Takeuchi,
Yoshihiko Izumida,
Midori Kubota,
Makiko Nishi,
Hiroaki Okazaki,
Yoko Iizuka,
Naoya Yahagi,
Hiroaki Yagyu,
Masashi Fukayama,
Takashi Kadowaki,
Ken Ohashi,
Shun Ishibashi,
Jun-ichi Osuga
[show abstract]
[hide abstract]
ABSTRACT: We have previously demonstrated that neutral cholesterol ester hydrolase 1 (Nceh1) regulates foam cell formation and atherogenesis through the catalytic activity of cholesterol ester hydrolysis, and that Nceh1 and hormone-sensitive lipase (Lipe) are responsible for the majority of neutral cholesterol ester hydrolase activity in macrophages. There are several cholesterol ester-metabolizing tissues and cells other than macrophages, among which adrenocortical cells are also known to utilize the intracellular cholesterol for steroidogenesis. It has been believed that the mobilization of intracellular cholesterol ester in adrenal glands was facilitated solely by Lipe. We herein demonstrate that Nceh1 is also involved in cholesterol ester hydrolysis in adrenal glands. While Lipe deficiency remarkably reduced the neutral cholesterol ester hydrolase activity in adrenal glands as previously reported, additional inactivation of Nceh1 gene completely abrogated the activity. Adrenal glands were enlarged in proportion to the degree of reduced neutral cholesterol ester hydrolase activity, and the enlargement of adrenal glands and the accumulation of cholesterol esters were most pronounced in the Nceh1/Lipe double-deficient mice. Thus Nceh1 is involved in the adrenal cholesterol metabolism, and the cholesterol ester hydrolytic activity in adrenal glands is associated with the organ enlargement.
Biochemical and Biophysical Research Communications 01/2011; 404(1):254-60. · 2.48 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Several studies indicated that KIT mutation could cause ligand-independent activation of c-Kit receptor in canine mast cell tumor (MCT). The objective of this study was to investigate mechanisms of c-Kit receptor activation in various canine MCT cell lines. Four cell lines, HRMC (derived from cutaneous MCT), VIMC1 (visceral MCT), CoMS1 (visceral MCT) and CMMC1 (cutaneous MCT), were cultured in stem cell factor (SCF, a ligand of c-Kit receptor)-free medium and subjected to analyses of KIT mutation, c-Kit receptor phosphorylation, SCF expression and the effects of SCF stimulation. In addition, the SCF/c-Kit receptor autocrine mechanism was verified in HRMC cells. HRMC cells expressed wild type c-Kit receptor. Both VIMC1 and CoMS1 cells had the same one amino acid (AA) substitution in the extracellular domain of c-Kit receptor. CMMC1 cells had at least three variants of c-Kit receptor such as one AA deletion in the extracellular domain (variant A), one AA substitution in the extracellular domain as well as an internal tandem duplication in the juxtamembrane domain (variant B), and a nonsense mutation (variant C). Both mature and immature forms of c-Kit receptor were observed and the c-Kit receptors were phosphorylated in all cell lines. While both mature and immature forms of c-Kit receptor were substantially phosphorylated in CMMC1 cells, the immature form was slightly phosphorylated in other cell lines. Phosphorylation of c-Kit receptor in HRMC, VIMC1 and CoMS1 cells were enhanced by SCF stimulation whereas no enhancement was observed in CMMC1 cells. There was no effect of SCF stimulation on proliferation of all the cell lines. SCF protein was detectable in only HRMC cells although mRNA expression of SCF was detected in all the cell lines. A tyrosine kinase inhibitor Dasatinib (internal inhibitor) inhibited c-Kit receptor phosphorylation in HRMC cells whereas anti-canine SCF antibody (external inhibitor) had no inhibitory effect. Thus there could be no external SCF/c-Kit receptor autocrine mechanism whereas there could be an internal autocrine mechanism within HRMC cells. The results indicated that consistent c-Kit receptor phosphorylation could be caused by the stimulation with autocrine SCF in HRMC cells while it could be caused by functional mutations of KIT in VIMC1, CoMS1 and CMMC1 cells. As the four canine MCT cell lines had various aberrations associated with c-Kit receptor phosphorylation, KIT mutation and SCF expression, such molecular biological diversity might reflect the different biological behavior in canine MCT.
Veterinary Immunology and Immunopathology 10/2010; 137(3-4):208-16. · 2.08 Impact Factor
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ABSTRACT: A 10-year-old American Shorthair cat with nasal discharge, anorexia, and weight loss was found to have pancytopenia and hyperproteinaemia. Bone marrow aspiration revealed atypical plasma cells that totalled 50% of the nucleated bone marrow cells. The number of atypical plasma cells progressively increased in the peripheral blood during the observation period of 64 days. The cat did not respond to treatments with melphalan, chlorambucil, and prednisolone, and died 71 days after the initial presentation. Clinical, cytological, histopathological, and immunohistochemical findings in this case supported the diagnosis of myeloma-related disorder (MRD) with leukaemic progression.
Journal of feline medicine and surgery. 10/2010; 12(12):982-7.
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ABSTRACT: An 8-year-old miniature dachshund presented with a right femoral muscle mass and anorexia. Cytology of the mass revealed a number of small-sized lymphoid cells containing a pleomorphic-shaped dense nucleus and narrow pale cytoplasm. Histopathology indicated that neoplastic lymphoid cells proliferated in skeletal muscles and replaced the muscular architecture. Immunohistochemical and genetic examinations confirmed the diagnosis of primary skeletal muscle lymphoma classified as the pleomorphic small cell type and T-cell low-grade. Although the dog suffered at least three relapses by combination chemotherapy, the dog survived 713 days after the initial presentation.
Journal of Veterinary Medical Science 05/2010; 72(5):673-7. · 0.85 Impact Factor
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Yoshinori Takeuchi,
Naoya Yahagi,
Yoshihiko Izumida,
Makiko Nishi,
Midori Kubota,
Yuji Teraoka,
Takashi Yamamoto,
Takashi Matsuzaka,
Yoshimi Nakagawa,
Motohiro Sekiya, [......],
Ken Ohashi,
Jun-ichi Osuga,
Takanari Gotoda,
Shun Ishibashi,
Keiji Itaka,
Kazunori Kataoka,
Ryozo Nagai,
Nobuhiro Yamada,
Takashi Kadowaki,
Hitoshi Shimano
[show abstract]
[hide abstract]
ABSTRACT: Sterol regulatory element-binding protein (SREBP)-1 is a key transcription factor for the regulation of lipogenic enzyme genes
in the liver. Polyunsaturated fatty acids (PUFA) selectively suppress hepatic SREBP-1, but molecular mechanisms remain largely
unknown. To gain insight into this regulation, we established in vivo reporter assays to assess the activities of Srebf1c transcription and proteolytic processing. Using these in vivo reporter assays, we showed that the primary mechanism for PUFA suppression of SREBP-1 is at the proteolytic processing level
and that this suppression in turn decreases the mRNA transcription through lowering SREBP-1 binding to the SREBP-binding element
on the promoter (“autoloop regulatory circuit”), although liver X receptor, an activator for Srebf1c transcription, is not involved in this regulation by PUFA. The mechanisms for PUFA suppression of SREBP-1 confirm that the
autoloop regulation for transcription is crucial for the nutritional regulation of triglyceride synthesis.
Journal of Biological Chemistry 04/2010; 285(15):11681-11691. · 4.77 Impact Factor
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Yoshinori Takeuchi,
Naoya Yahagi,
Yoshihiko Izumida,
Makiko Nishi,
Midori Kubota,
Yuji Teraoka,
Takashi Yamamoto,
Takashi Matsuzaka,
Yoshimi Nakagawa,
Motohiro Sekiya, [......],
Ken Ohashi,
Jun-ichi Osuga,
Takanari Gotoda,
Shun Ishibashi,
Keiji Itaka,
Kazunori Kataoka,
Ryozo Nagai,
Nobuhiro Yamada,
Takashi Kadowaki,
Hitoshi Shimano
[show abstract]
[hide abstract]
ABSTRACT: Sterol regulatory element-binding protein (SREBP)-1 is a key transcription factor for the regulation of lipogenic enzyme genes in the liver. Polyunsaturated fatty acids (PUFA) selectively suppress hepatic SREBP-1, but molecular mechanisms remain largely unknown. To gain insight into this regulation, we established in vivo reporter assays to assess the activities of Srebf1c transcription and proteolytic processing. Using these in vivo reporter assays, we showed that the primary mechanism for PUFA suppression of SREBP-1 is at the proteolytic processing level and that this suppression in turn decreases the mRNA transcription through lowering SREBP-1 binding to the SREBP-binding element on the promoter ("autoloop regulatory circuit"), although liver X receptor, an activator for Srebf1c transcription, is not involved in this regulation by PUFA. The mechanisms for PUFA suppression of SREBP-1 confirm that the autoloop regulation for transcription is crucial for the nutritional regulation of triglyceride synthesis.
Journal of Biological Chemistry 02/2010; 285(15):11681-91. · 4.77 Impact Factor
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Takashi Yamamoto,
Kazuhisa Watanabe,
Noriyuki Inoue,
Yoshimi Nakagawa,
Naomi Ishigaki,
Takashi Matsuzaka, Yoshinori Takeuchi,
Kazuto Kobayashi,
Shigeru Yatoh,
Akimitsu Takahashi,
Hiroaki Suzuki,
Naoya Yahagi,
Takanari Gotoda,
Nobuhiro Yamada,
Hitoshi Shimano
[show abstract]
[hide abstract]
ABSTRACT: Sterol-regulatory element binding protein-1c (SREBP-1c) is a transcription factor that controls lipogenesis in the liver. Hepatic SREBP-1c is nutritionally regulated, and its sustained activation causes hepatic steatosis and insulin resistance. Although regulation of SREBP-1c is known to occur at the transcriptional level, the precise mechanism by which insulin signaling activates SREBP-1c promoter remains to be elucidated. Here we show that protein kinase C beta (PKCbeta) is a key mediator of insulin-mediated activation of hepatic SREBP-1c and its target lipogenic genes. Activation of SREBP-1c in the liver of refed mice was suppressed by either adenoviral RNAi-mediated knockdown or dietary administration of a specific inhibitor of protein kinase C beta. The effect of PKCbeta inhibition was cancelled in insulin depletion by streptozotocin (STZ) treatment of mice. Promoter analysis indicated that PKCbeta activates SREBP-1c promoter through replacement of Sp3 by Sp1 for binding to the GC box in the sterol regulatory element (SRE) complex, a key cis-element of SREBP-1c promoter. Knockdown of Sp proteins demonstrated that Sp3 and Sp1 play reciprocally negative and positive roles in nutritional regulation of SREBP-1c, respectively. This new understanding of PKCbeta involvement in nutritional regulation of SREBP-1c activation provides a new aspect of PKCbeta inhibition as a potential therapeutic target for diabetic complications.
The Journal of Lipid Research 02/2010; 51(7):1859-70. · 5.56 Impact Factor
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Motohiro Sekiya,
Naoya Yahagi,
Yoshiaki Tamura,
Hiroaki Okazaki,
Masaki Igarashi,
Keisuke Ohta,
Mikio Takanashi,
Masayoshi Kumagai,
Satoru Takase,
Makiko Nishi, [......],
Ken Ohashi,
Yoko Iizuka,
Hiroaki Yagyu,
Takanari Gotoda,
Ryozo Nagai,
Hitoshi Shimano,
Nobuhiro Yamada,
Takashi Kadowaki,
Shun Ishibashi,
Jun-ichi Osuga
[show abstract]
[hide abstract]
ABSTRACT: It has long been a matter of debate whether the hormone-sensitive lipase (HSL)-mediated lipolysis in pancreatic beta-cells can affect insulin secretion through the alteration of lipotoxicity. We generated mice lacking both leptin and HSL Lep(ob/ob)/HSL(-/-) and explored the role of HSL in pancreatic beta-cells in the setting of obesity. Lep(ob/ob)/HSL(-/-) developed elevated blood glucose levels and reduced plasma insulin levels compared with Lep(ob/ob)/HSL(+/+) in a fed state, while the deficiency of HSL did not affect glucose homeostasis in Lep(+/+) background. The deficiency of HSL exacerbated the accumulation of triglycerides in Lep(ob/ob) islets, leading to reduced glucose-stimulated insulin secretion. The deficiency of HSL also diminished the islet mass in Lep(ob/ob) mice due to decreased cell proliferation. In conclusion, HSL affects insulin secretary capacity especially in the setting of obesity.
Biochemical and Biophysical Research Communications 08/2009; 387(3):511-5. · 2.48 Impact Factor
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Yoshinori Takeuchi,
Shinobu Matsuura,
Yasuhito Fujino,
Mayumi Nakajima,
Masashi Takahashi,
Ko Nakashima,
Yusuke Sakai,
Koji Uetsuka,
Koichi Ohno,
Hiroyuki Nakayama,
Hajime Tsujimoto
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ABSTRACT: Two cats showing chronic vomiting, diarrhea and weight loss were found to have leukocytosis with marked eosinophilia. Both cats were diagnosed with hypereosinophilic syndrome by the findings of increased eosinophils and their precursors in the bone marrow, eosinophilic infiltration into multiple organs, and exclusion of other causes for eosinophilia. Although cytoreductive chemotherapy with hydroxycarbamide and prednisolone was performed, these two cats died 48 days and 91 days after the initial presentation.
Journal of Veterinary Medical Science 11/2008; 70(10):1085-9. · 0.85 Impact Factor
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Noriyuki Inoue,
Naoya Yahagi,
Takashi Yamamoto,
Mayumi Ishikawa,
Kazuhisa Watanabe,
Takashi Matsuzaka,
Yoshimi Nakagawa, Yoshinori Takeuchi,
Kazuto Kobayashi,
Akimitsu Takahashi,
Hiroaki Suzuki,
Alyssa H Hasty,
Hideo Toyoshima,
Nobuhiro Yamada,
Hitoshi Shimano
[show abstract]
[hide abstract]
ABSTRACT: Both adipocyte hyperplasia and hypertrophy are determinant factors for adipocyte differentiation during the development of obesity. p21(WAF1/CIP1), a cyclin-dependent kinase inhibitor, is induced during adipocyte differentiation; however, its precise contribution to this process is unknown. Using both in vitro and in vivo systems, we show that p21 is crucial for maintaining adipocyte hypertrophy and obesity-induced insulin resistance. The absence of p21 in 3T3-L1 fibroblasts by RNA-mediated interference knockdown or in embryonic fibroblasts from p21(-/-) mice impaired adipocyte differentiation, resulting in smaller adipocytes. Despite normal adipose tissue mass on a normal diet, p21(-/-) mice fed high energy diets had reduced adipose tissue mass and adipocyte size accompanied by a marked improvement in insulin sensitivity. Knockdown of p21 in enlarged epididymal fat of diet-induced obese mice and also in fully differentiated 3T3-L1 adipocytes caused vigorous apoptosis by activating p53. Thus, p21 is involved in both adipocyte differentiation and in protecting hypertrophied adipocytes against apoptosis. Via both of these mechanisms, p21 promotes adipose tissue expansion during high fat diet feeding, leading to increased downstream pathophysiological consequences such as insulin resistance.
Journal of Biological Chemistry 08/2008; 283(30):21220-9. · 4.77 Impact Factor
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Toyonori Kato,
Hitoshi Shimano,
Takashi Yamamoto,
Mayumi Ishikawa,
Shin Kumadaki,
Takashi Matsuzaka,
Yoshimi Nakagawa,
Naoya Yahagi,
Masanori Nakakuki,
Alyssa H Hasty, Yoshinori Takeuchi,
Kazuto Kobayashi,
Akimitsu Takahashi,
Shigeru Yatoh,
Hiroaki Suzuki,
Hirohito Sone,
Nobuhiro Yamada
[show abstract]
[hide abstract]
ABSTRACT: Chronic exposure to fatty acids causes beta-cell failure, often referred to as lipotoxicity. We investigated its mechanisms, focusing on contribution of SREBP-1c, a key transcription factor for lipogenesis.
We studied in vitro and in vivo effects of saturated and polyunsaturated acids on insulin secretion, insulin signaling, and expression of genes involved in beta-cell functions. Pancreatic islets isolated from C57BL/6 control and SREBP-1-null mice and adenoviral gene delivery or knockdown systems of related genes were used.
Incubation of C57BL/6 islets with palmitate caused inhibition of both glucose- and potassium-stimulated insulin secretion, but addition of eicosapentaenoate (EPA) restored both inhibitions. Concomitantly, palmitate activated and EPA abolished both mRNA and nuclear protein of SREBP-1c, accompanied by reciprocal changes of SREBP-1c target genes such as insulin receptor substrate-2 (IRS-2) and granuphilin. These palmitate-EPA effects on insulin secretion were abolished in SREBP-1-null islets. Suppression of IRS-2/Akt pathway could be a part of the downstream mechanism for the SREBP-1c-mediated insulin secretion defect because adenoviral constitutively active Akt compensated it. Uncoupling protein-2 (UCP-2) also plays a crucial role in the palmitate inhibition of insulin secretion, as confirmed by knockdown experiments, but SREBP-1c contribution to UCP-2 regulation was partial. The palmitate-EPA regulation of insulin secretion was similarly observed in islets from C57BL/6 mice pretreated with dietary manipulations. Furthermore, administration of EPA to diabetic KK-Ay mice ameliorated impairment of insulin secretion in their islets.
SREBP-1c plays a dominant role in palmitate-mediated insulin secretion defect, and EPA prevents it through SREBP-1c inhibition, implicating a therapeutic potential for treating diabetes related to lipotoxicity.
Diabetes 06/2008; 57(9):2382-92. · 8.29 Impact Factor
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ABSTRACT: A menigioma with polygonal granular cell proliferation in an 11-year and 8-month-old male Chihuahua is described. The tumor was observed under the dura matter of the right cerebrum. Microscopically, the tumor consisted of solid growth foci of small- or large- sized polygonal cells, with pale-stained nuclei, prominent nucleoli, and fine granular to foamy eosinophilic cytoplasm. Some of the proliferating cells contained variable amounts of cytoplasmic PAS-positive granules. Immunohistochemical analysis revealed that neoplastic cells were positive for vimentin and S-100 protein. Ultrastructurally, the neoplastic cells contained vesicular structures with a few small round-shaped bodies in the cytoplasm. We diagnosed the case as canine meningioma with granular cell appearance.
Journal of Veterinary Medical Science 05/2008; 70(5):529-32. · 0.85 Impact Factor
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Yoshinori Takeuchi,
Naoya Yahagi,
Yoshimi Nakagawa,
Takashi Matsuzaka,
Ritsuko Shimizu,
Motohiro Sekiya,
Yoko Iizuka,
Ken Ohashi,
Takanari Gotoda,
Masayuki Yamamoto,
Ryozo Nagai,
Takashi Kadowaki,
Nobuhiro Yamada,
Jun-Ichi Osuga,
Hitoshi Shimano
[show abstract]
[hide abstract]
ABSTRACT: Sterol regulatory element-binding protein (SREBP)-1c is the master regulator of lipogenic gene expression in liver. The mRNA abundance of SREBP-1c is markedly induced when animals are refed after starvation, although the regulatory mechanism is so far unknown. To investigate the mechanism of refeeding response of SREBP-1c gene expression in vivo, we generated a transgenic mouse model that carries 2.2kb promoter region fused to the luciferase reporter gene. These transgenic mice exhibited refeeding responses of the reporter in liver and adipose tissues with extents essentially identical to those of endogenous SREBP-1c mRNA. The same results were obtained from experiments using adenovirus-mediated SREBP-1c-promoter-luciferase fusion gene transduction to liver. These data demonstrate that the regulation of SREBP-1c gene expression is at the transcription level, and that the 2.2kb 5'-flanking region is sufficient for this regulation. Moreover, when these transgenic or adenovirus-infected mice were placed on insulin-depleted state by streptozotocin treatment, the reporter expression was upregulated as strongly as in control mice, demonstrating that this regulation is not dominated by serum insulin level. These mice are the first models to provide the mechanistic insight into the transcriptional regulation of SREBP-1c gene in vivo.
Biochemical and Biophysical Research Communications 12/2007; 363(2):329-35. · 2.48 Impact Factor
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Motohiro Sekiya,
Naoya Yahagi,
Takashi Matsuzaka, Yoshinori Takeuchi,
Yoshimi Nakagawa,
Haruka Takahashi,
Hiroaki Okazaki,
Yoko Iizuka,
Ken Ohashi,
Takanari Gotoda,
Shun Ishibashi,
Ryozo Nagai,
Tsutomu Yamazaki,
Takashi Kadowaki,
Nobuhiro Yamada,
Jun-ichi Osuga,
Hitoshi Shimano
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ABSTRACT: Sterol regulatory element-binding protein (SREBP)-1c is now well established as a key transcription factor for the regulation of lipogenic enzyme genes such as FAS in hepatocytes. Meanwhile, the mechanisms of lipogenic gene regulation in adipocytes remain unclear. Here, we demonstrate that those in adipocytes are independent of SREBP-1c. In adipocytes, unlike in hepatocytes, the stimulation of SREBP-1c expression by liver X receptor agonist does not accompany lipogenic gene upregulation, although nuclear SREBP-1c protein is concomitantly increased, indicating that the activation process of SREBP-1c by the cleavage system is intact in adipocytes. Supportively, transcriptional activity of the mature form of SREBP-1c for the FAS promoter was negligible when measured by reporter analysis. As an underlying mechanism, accessibility of SREBP-1c to the functional elements was involved, because chromatin immunoprecipitation assays revealed that SREBP-1c does not bind to the functional SRE/E-box site on the FAS promoter in adipocytes. Moreover, genetic disruption of SREBP-1 did not cause any changes in lipogenic gene expression in adipose tissue. In summary, in adipocytes, unlike in hepatocytes, increments in nuclear SREBP-1c are not accompanied by transactivation of lipogenic genes; thus, SREBP-1c is not committed to the regulation of lipogenesis.
The Journal of Lipid Research 08/2007; 48(7):1581-91. · 5.56 Impact Factor
