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Biomedical subjects

Yasuhiko Okimura

Publications and source records attributed to Yasuhiko Okimura.

At least 19 recordsLinked to original sources
PubMed2006

Neither intravenous nor intracerebroventricular administration of obestatin affects the secretion of GH, PRL, TSH and ACTH in rats.

To examine the effect of obestatin, a recently identified peptide derived from preproghrelin, on pituitary hormone secretion, obestatin was administered in anesthetized male rats. Intravenous administration of obestatin did not show any effect on plasma GH, PRL, ACTH and TSH levels. Since obestatin has been reported to have opposite effects of ghrelin in regulating food intake, gastric emptying and intestinal contractility, GH suppressive effect, which is opposite effect of ghrelin, was tested. Intravenous administration of GHRH or GHRP-2, a ghrelin receptor ligand, resulted in a marked plasma GH elevation. However obestatin did not show any effect on GHRH- or GHRP-2-induced GH rise. Furthermore intracerebroventricular administration of obestatin also did not influence plasma GH, PRL, ACTH and TSH levels. These findings suggest that obestatin has no effect on pituitary hormone secretions despite the presence of GPR39, a receptor for obestatin, in the pituitary.

Adrenocorticotropic Hormone↗
PubMed2006

The N131S mutation in the von Hippel-Lindau gene in a Japanese family with pheochromocytoma and hemangioblastomas.

von Hippel-Lindau (VHL) disease (VHLD) is a hereditary autosomal dominant syndrome that causes various benign and malignant tumors. VHLD is caused by mutations in the VHL tumor suppressor gene. Here, we report a mutation in the VHL gene in a Japanese family with VHLD type 2A, characterized by pheochromocytoma (PHE), and hemangioblastomas (HAB) in both the retina and thoracic spinal cord but without renal cell carcinoma (RCC). We identified a heterozygous A to G point mutation at the second base of codon 131 of the VHL protein (pVHL). This mutation was predicted to convert codon 131 from asparagine to serine (N131S). Although most mutations in VHLD type 2A have been detected in the alpha domain of pVHL, the present mutated amino acid was located at the region encoding the beta domain of pVHL. Previous patients with the N131K or N131T mutation in pVHL developed VHLD type 2B with RCC or VHLD type 1 without PHE, respectively. We also identified somatic loss of heterozygosity (LOH) at chromosome 3p25-26 in the adrenal tumor of the patient. The results of our study suggest that not only the location of mutation but also the altered amino acid may be critical for determining the clinical phenotype of VHLD. LOH was associated with the development of PHE in a patient with the N131S mutation in pVHL.

Adrenal Gland Neoplasms↗
PubMed2006

A novel mutation in the von Hippel-Lindau tumor suppressor gene identified in a Japanese family with pheochromocytoma and hepatic hemangioma.

Von Hippel-Lindau (VHL) syndrome is a neoplastic syndrome caused by a mutation in the VHL gene. There is a discrepancy between the phenotypes of human VHL syndrome and VHL gene-disrupted mouse models. A heterozygous VHL gene-disrupted model (vhl +/-) developed hepatic vascular lesions; in contrast, hepatic hemangioma is a rare manifestation of human VHL syndrome. We identified a novel mutation (P154S) in the VHL gene in a Japanese family with pheochromocytoma. One of the members demonstrated hepatic hemangiomas, suggesting that there may be a relationship between the mutation of the VHL gene and hepatic vascular lesions, even in humans.

Adrenal Gland Neoplasms↗
PubMed2006

Gene expression profile in the heart of spontaneous dwarf rat: in vivo effects of growth hormone.

Excess and deficit of growth hormone (GH) both affect cardiac architecture as well as its function. To date, experimental and clinical studies have reported that GH has an inotropic effect on animal and human heart, however, it remains controversial whether GH is applicable to the treatment for the patients with chronic heart failure. Also, the mechanism by which GH exerts these biological effects on the heart is not well understood. In this study, we attempted to specify the genes regulated by GH in the heart of spontaneous dwarf rat using a microarray analysis. We found that soluble forms of guanylate cyclase, cofilin1, and thymosin beta4 mRNA were up-regulated in the heart by GH treatment. On the other hand, acyl-CoA synthetase, aldosterone receptor, myosin regulatory light chain, troponin T, laminA, and beta-actin mRNA were down-regulated. These results suggest GH regulates essential molecules that regulate structural, contractile, remodeling, and regenerative functions. Collectively, our data indicate a new integrative understanding for the biological effects of GH on cardiac function.

Animals↗
PubMed2004

Up-regulation of mitochondrial transcription factor 1 mRNA levels by GH in VSMC.

It is well known that growth hormone (GH) is involved in the development of arteriosclerosis in which vascular smooth muscle cells (VSMC) play an important role. In this study, we attempted to specify the genes up- or down-regulated by recombinant human GH (rhGH) in VSMC using a differential display method. We found that rhGH increased cytochrome oxidase subunit II/III mRNA in VSMC. Furthermore, the mRNA for mitochondrial transcription factor 1 (mtTF1), which stimulates the expression of cytochrome oxidase subunit II/III, was found to be up-regulated by rhGH in a dose dependent manner using a quantitative PCR method. On the other hand, IGF-I alone did not change mtTF1 mRNA levels. In rat L6 myoblasts and rat H4-II-E hepatocytes, rhGH did not change mtTF1 mRNA levels. Pretreatment with a JAK2 inhibitor AG490 (10 nM) and a MEK inhibitor PD98059 (10 microM) suppressed rhGH-induced rise in mtTF1 mRNA levels of VSMC to the control levels. Pretreatment with a PI-3kinase inhibitor wortomannin (1 nM) did not suppress rhGH-induced rise in mtTF1 mRNA levels. These findings suggest that GH up-regulates mtTF1 mRNA levels through JAK2 and MEK signaling in VSMC.

Androstadienes↗
PubMed2004

Intravenous administration of ghrelin stimulates growth hormone secretion in vagotomized patients as well as normal subjects.

OBJECTIVE: Ghrelin is a potent peptide stimulating GH secretion. Besides its direct action on the pituitary, ghrelin has been reported to stimulate GH release via the vagal afferent nerve in rats. To examine the involvement of vagal nerve in ghrelin-induced GH secretion in humans, GH responses to ghrelin were compared between vagotomized patients with gastrectomy and normal subjects. METHODS: Ghrelin (0.2 microg/kg) or GHRH (1 microg/kg) was administered intravenously in vagotomized patients and normal subjects on separate days, and plasma GH responses to the stimuli were examined. RESULTS: Ghrelin caused a significant plasma GH rise in both vagotomized patients and normal subjects. Peak GH levels in vagotomized patients (37.5+/-16.9 ng/ml) were not different from those in normal subjects (29.9+/-23.1 ng/ml). The areas under the curve of GH response to ghrelin did not differ between the two groups. GHRH also increased GH levels, and peak GH levels and areas under the curve after GHRH stimulation were also comparable between vagotomized patients and normal subjects. CONCLUSIONS: In the present study, the involvement of the afferent vagal nerve in ghrelin-induced GH secretion was not confirmed in humans.

Adult↗
PubMed2004

A variety of phenotype with R161Q germline mutation of the von Hippel-Lindau tumor suppressor gene in Japanese kindred.

Von Hippel-Lindau (VHL) syndrome is an autosomal dominant neoplastic disorder characterized by hemangioblastomas of the central nervous system and retina, renal cell carcinomas, pheochromocytoma, and islet cell tumors. This syndrome is closely related with the VHL, a tumor suppressor gene, implying that loss of function or inactivating mutations of both alleles or copies of this gene cause tumor formation. The product of the VHL gene, pVHL, is known to be a component of ubiquitin ligase which targets the transcription factor such as hypoxia-inducible factor (HIF) for degradation in the presence of oxygen. Different VHL mutations confer different site-specific risks of cancer. However, the precise role of pVHL to develop only some specified tumors, especially pheochromocytoma, is not fully understood. We identified a missense mutation of VHL gene, 695 G --> A (R161Q), in a Japanese kindred with type 2A VHL syndrome. We analysed 16 members of this family and detected the same mutation in 8 individuals. All 5 members with tumors possessed the same mutation. Interestingly, one of the identical twins, who had the same R161Q germline mutation, did not show any visible tumors throughout the body, while another of the twins developed a huge pheochromocytoma and retinal angioma. Moreover, one of the affected members in the kindred developed pancreatic neuro-endocrine tumors without pheochromocytoma in spite of possessing the identical germline mutation of the VHL gene. These findings suggest that there are some other additional factors including environmental exposures to initiate and develop tumor formation in the VHL syndrome although abnormalities of VHL gene might be involved.

Base Sequence↗
PubMed2003

Diverse regulation of full-length and truncated growth hormone receptor expression in 3T3-L1 adipocytes.

Two truncated forms of growth hormone (GH) receptor (GHR), 1-277 and 1-279, were reported to be normally produced in human tissues by alternative splicing in exon 9 and its boundary. We found previously that GHR-277 exerts a dominant-negative effect on full-length GHR (GHR-fl)-mediated GH signaling causing short stature. The existence of truncated GHRs (hGHR-tr) in normal tissues suggests that hGHR-tr may play a physiological role in regulation of GH action at the cellular level. To clarify the physiological significance of GHR-tr and the regulation mechanism of GHR-tr expression, we examined the expression of mouse GHR-tr (mGHR-tr) mRNA in mouse adipocyte 3T3-L1 cells, comparing with that of mouse GHR-fl (mGHR-fl). The mRNAs of two mGHR-tr, mGHR-282 and mGHR-280, were detected by RT-PCR methods using specific primers. Although the mGHR-282 and mGHR-280 mRNA levels were approximately 100 times lower than that of mGHR-fl in mature 3T3-L1 cells, quantitative analysis by competitive RT-PCR methods revealed that the mRNA levels of mGHR-280 in 3T3-L1 cells were transiently reduced and thereafter increased during differentiation from preadipocyte to adipocyte. In contrast, the mRNA levels of mGHR-fl were increased in parallel with the progress of differentiation. Stimulation by GH of differentiated 3T3-L1 mature adipocytes resulted in dose-dependent increases of the mRNA of both mGHR-fl and mGHR-282, whereas it caused a paradoxical decrease of the mRNA of mGHR-280 stimulated by high concentration of GH. These findings suggest that the expressions of truncated mGHRs were regulated in a different manner from that of mGHR-fl, thereby modulating GH action in murine adipocytes.

3T3 Cells↗
PubMed2003

Cloning of a protein binding to the most proximal Pit-1 binding element of prolactin gene from human pituitary cDNA library.

A human pituitary cDNA library was screened using a yeast one-hybrid system to find a factor binding Pit-1 binding elements in the PRL gene other than Pit-1. Beside colonies containing Pit-1 or Oct-1 cDNA, three colonies contained mPOU cDNA, a member of the POU protein family. Immunohistochemical analysis showed mPOU-like immunoreactivity was present in human PRL-producing pituitary tumors but not in non-functioning pituitary tumors. Mobility shift analysis revealed that mPOU bound to Pit-1 binding elements of the PRL gene, 1P and 3P. mPOU activated the expression of 0.6 k PRL and 7x1P reporter genes in the presence of Pit-1 and cAMP, although it did not enhance Pit-1-induced expression of 7x3P reporter gene. These findings suggest that mPOU is involved in the activation of the PRL gene by cAMP through 1P in the presence of Pit-1.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed2003

Cloning and characterization of the 5(')-flanking region of the human ghrelin gene.

Ghrelin, a novel growth hormone releasing peptide, was recently isolated from stomach. We have cloned and characterized the 5(')-flanking region, containing from -2000 to -1 upstream from the translation start site of the human ghrelin gene. There was neither typical GC nor CAAT box but there were a TATATAA element and putative binding sites for several transcription factors. Ghrelin promoter was activated only in human stomach derived ECC10 cells among several cell lines examined. Functional analysis showed that promoter activity was increased by deletion of nucleotides from -2000 to -605 whereas it was decreased by further deletion and that the TATATAA element is not functioning. Glucagon and its second messenger cAMP enhanced the promoter activity, suggesting that stimulated transcription of ghrelin gene by glucagon might be responsible for increased ghrelin production during fasting at least in part. These initial characterizations will facilitate further studies of the regulatory mechanisms for ghrelin gene expression.

5' Flanking Region↗
PubMed2003

The role of circulating ghrelin in growth hormone (GH) secretion in freely moving male rats.

To examine the physiological significance of plasma ghrelin in generating pulsatile growth hormone (GH) secretion in rats, plasma GH and ghrelin levels were determined in freely moving male rats. Plasma GH was pulsatilely secreted as reported previously. Plasma ghrelin levels were measured by both N-RIA recognizing the active form of ghrelin and C-RIA determining total amount of ghrelin. Mean +/- SE plasma ghrelin levels determined by N-RIA and C-RIA were 21.6 +/- 8.5 and 315.5 +/- 67.5 pM, respectively, during peak periods when plasma GH levels were greater than 100 ng / ml. During trough periods when plasma GH levels were less than 10 ng / ml, they were 16.5 +/- 4.5 and 342.1 +/- 29.8 pM, respectively. There were no significant differences in plasma ghrelin levels between two periods. Next, effect of a GH secretagogue antagonist, [D-Lys-3]-GHRP-6, on plasma GH profiles was examined. There were no significant differences in both peak GH levels and area under the curves of GH (AUCs) between [D-Lys-3]-GHRP-6-treated and control rats. These findings suggest circulating ghrelin in peripheral blood does not play a role in generating pulsatile GH secretion in freely moving male rats.

Animals↗
PubMed2003

A study of carotid intima-media thickness in GH-deficient Japanese adults during onset among adults and children.

OBJECTIVES: Increased carotid intima-media thickness (IMT) has been reported among Caucasian adult GH-deficient (AGHD) patients, but not Japanese. Also, it is known that the clinical and biochemical characteristics of AGHD patients are somewhat different based on the onset of the disease in either childhood or adult life. Nevertheless, there has been no study comparing the magnitude of the deviation of their IMT from normal subjects between child-onset (CO) and adult-onset (AO) patients in terms of Z score. The aim of this study, therefore, was first to examine whether Japanese AGHD patients have a risk of early development of atherosclerosis similar to Caucasian patients and secondly to assess the difference in the onset and in progression of atherosclerosis. DESIGN AND SUBJECTS: Thirty-four patients (17 CO-AGHD, age 29+/-7 Years, body mass index (BMI) 24+/-3.8 kg/m(2) and 17 AO-AGHD, age 48+/-12 Years, BMI 23+/-3.6 kg/m(2)) and 34 age- and sex-matched healthy controls (17 CO controls and 17 AO controls) were enrolled in the present study. Blood samples were taken for measurements of lipids, lipoproteins and IGF-I. Subsequently, patients underwent IMT assessment. RESULTS: CO patients were significantly younger than AO patients. The duration of GH-deficiency in CO patients was significantly longer than that in AO patients. Serum triglyceride (TG) was significantly higher in CO patients than in CO controls (P<0.05). Serum total cholesterol and TG were significantly higher in AO patients than in AO controls (P<0.01). The IMT was significantly greater in CO and AO patients (0.82+/-0.08 and 0.79+/-0.03 mm) than in CO and AO controls (0.59+/-0.02 and 0.68+/-0.03 mm, P<0.01 and P<0.01 respectively). There was no significant difference in raw values of IMT between CO and AO patients. However, the Z score of IMT calculated using normal Japanese IMT values was significantly higher in CO than in AO patients (2.07+/-0.68 vs 0.35+/-0.48, P<0.05). CONCLUSIONS: These findings suggest that GH deficiency appears to increase an atherosclerotic risk in Japanese AGHD patients, as with Caucasians, and to cause more extensive IMT thickening in CO-AGHD than AO-AGHD patients.

Adult↗
PubMed2003

The R271W mutant form of Pit-1 does not act as a dominant inhibitor of Pit-1 action to activate the promoters of GH and prolactin genes.

OBJECTIVE: Genetic abnormalities of the pituitary specific transcription factor, Pit-1, have been reported in several patients with GH, prolactin (PRL) and TSH deficiencies. The most common is a mutation altering an arginine to a tryptophan in codon 271 (R271W) in one allele of the Pit-1 gene. According to the previous in vitro expression study, R271W acted as a dominant negative inhibitor of the wild type to activate the GH promoter. However, healthy carriers with this mutation, who should be affected by the dominant negative effect of R271W, have also been reported. The aim of this study was to clarify in more detail the function of this mutant form of Pit-1. METHODS: Transcriptional activity of R271W for the expression of Pit-1-associated genes was investigated in COS7 cells with the aid of transient transfection assays. The 1.8 kb rat GH, 0.6 kb rat PRL or 1.9 kb rat PRL 5'-flanking regions were inserted upstream of the luciferase reporter gene and were used for functional analysis of R271W. Another reporter gene containing seven Pit-1 responsive elements was also used. The same experiments were also performed using JEG3 and CHO cells. RESULTS: We could not confirm the dominant negative effect of R271W on wild type Pit-1. Furthermore, our expression study revealed that R271W could activate the promoters of GH and PRL genes to levels similar to the wild type. CONCLUSION: Taken together with the evidence that phenotypically normal cases have been reported with this mutation, our results deny the relationship between R271W and combined pituitary hormone deficiency.

Animals↗
PubMed2003

Expression of mPOU protein in the human pituitary adenomas.

OBJECTIVE: mPOU is a POU protein classified as class VI. It is present in the pituitary gland as well as the brain, heart muscle, skeletal muscle, lung, and lymphocytes. In our previous investigation, mPOU bound to the Pit-1-binding DNA elements of the rat PRL gene, and promoted transcription of the GH and PRL genes. In this study, we immunohistologically investigated the expression of mPOU in pituitary adenomas. METHODS: 17 patients with pituitary adenoma underwent tumor excision by transsphenoidal approach at our hospital (PRL: 5, GH: 4, FSH: 1, non-functioning: 7). The expression in the tissue sections was investigated using immunostaining (ABC method). RESULTS: In all GH-producing and PRL-producing adenomas, mPOU protein was specifically expressed, particularly in the nuclei. DISCUSSION: Pit-1 has been considered to be a factor determining the expression of GH and PRL genes, but mPOU may also be involved in the expression.

Adenoma↗