Cloning of cDNA and the gene encoding human hepatocyte nuclear factor (HNF)-3 beta and mutation screening in Japanese subjects with maturity-onset diabetes of the young

AIMS/HYPOTHESIS

Molecular defects of the genes for transcription factors, hepatocyte nuclear factor (HNF)-4 alpha, HNF-1 alpha, HNF-1 beta and insulin promoter factor-1 cause maturity-onset diabetes of the young (MODY1, 3, 5, and 4, respectively). This suggests the HNF-related transcription cascade is important in insulin secretion which is induced by glucose. These genes and the gene encoding glycolytic enzyme glucokinase (MODY2) are, however, responsible for only 15-20% of cases of MODY in the Japanese. Searching for a novel form of MODY in this population, we cloned a new candidate gene encoding human HNF-3 beta, a winged helix transcription factor, which also belongs to the same HNF-transcription cascade.

METHODS

The cDNA clone for human HNF-3 beta was isolated from a liver cDNA library. The gene was also cloned from a genomic library and its organization and chromosomal localization were determined. We screened 68 Japanese subjects with MODY/early-onset diabetes for mutations in this gene.

RESULTS

Human HNF-3 beta is composed of 457 amino acids. The human gene, which was mapped to the segment 30 cR from SHGC-37039 on chromosome 20p by radiation hybrid mapping, spans approximately 4.5 kb and consists of three exons. Direct sequencing of the exons and flanking regions identified one missense mutation A328 V and seven polymorphisms, although the functional significance of the mutation in the pathogenesis of diabetes is not known.

CONCLUSION/INTERPRETATION

The characterization of the structure of the HNF-3 beta gene and its mapping in the framework of markers will be helpful in genetic studies of the various forms of diabetes mellitus.

Activation of locomotor and grasping spine muscle fibres in chaetognaths: a curious paradox

Chaetognath muscle fibres resemble vertebrate muscle fibres in having an abundant sarcoplasmic reticulum (SR) and analogues of the transverse (T) tubular system. but contraction is regulated differently. In intact chaetognaths electrically-evoked contractions of the striated locomotor muscles were largely or totally blocked by d-tubocurarine, by surgical removal of the ventral ganglion and by Co2 +. Contractions of single cells enzymatically dissociated from locomotor muscles were likewise blocked by Co2+, they twitched once only after calciseptine, showed neither contractures nor elevated intracellular Ca2+ with caffeine, and ryanodine did not block contractions. Whole cell voltage-clamped locomotor muscle cells displayed a typical inward rectified Ca2 + current that was sensitive to the Ca2+ channel blockers nifedipine and calciseptine and showed voltage-dependent activation with a threshold at approximately-25 mV and a peak inward current at approximately + 10 mV. In contrast, whole cell voltage-clamped cells from the muscles operating the grasping spines of the head showed an initial very rapid and rapidly-inactivating inward current abolished by tetrodotoxin (TTX), followed by a slower and slowly-inactivating inward current blocked by calciseptine. The relation between these observations and the unusual 'vertebrate-like' structure of the muscle cells is discussed.

Functional analysis of a mutation occurring between the two in-frame AUG codons of human angiotensinogen

Angiotensinogen (ANG) is the specific substrate of the renin-angiotensin system, a major participant in blood pressure control. We have identified a natural mutation at the -30 amino acid position of the angiotensinogen signal peptide, in which an arginine is replaced by a proline (R-30P). Heterozygous individuals with R-30P showed a tendency to lowered plasma angiotensinogen level (1563 ng of ANG I/ml (range 1129-1941)) compared with normal individuals in the family (1892 ng of ANG I/ml (range 1603-2072)). Human angiotensinogen mRNA has two in-phase translation initiation codons (AUG) starting upstream 39 and 66 nucleotides from the cap site. R-30P occurs in a cluster of basic residues adjacent to the first AUG codon that may affect intracellular sorting of the nascent protein. Pulse-chase experiments in transiently transfected cultured cells revealed that the R-30P mutation was associated with reduced amounts of both intra- and extracellular protein. In a cell-free system, we found that two forms of native angiotensinogen were generated by alternative initiation of translation at either AUG codon. Alteration of either the first or second AUG codons abolished the synthesis of the longer and the shorter form of native angiotensinogen, respectively. Furthermore, the rate of secretion of the shorter form was lower than that of the longer form. By transplanting angiotensinogen signal peptide onto green fluorescence protein, however, we found that both forms of the signal peptide could target green fluorescence protein, normally localized in the cytoplasm, to the secretory pathway. Although the R-30P mutation may not affect intracellular sorting of angiotensinogen in a qualitative manner, it leads to a quantitative reduction in the net secretion of mature angiotensinogen through decreased translocation or increased residence time in the endoplasmic reticulum.

Identification of genes differentially expressed in canine vasospastic cerebral arteries after subarachnoid hemorrhage

To understand the molecular processes of continuous vasospasm of cerebral arteries after subarachnoid hemorrhage, mRNA differential display and screening of cDNA expression array were performed to identify genes that are differentially expressed in vasospastic arteries of canine two-hemorrhage models. The expression levels of 18 genes were found to be upregulated, and those of two genes to be downregulated. Of these, 12 represent known genes or homologues of genes characterized previously, and the other eight genes are not related to any sequences in the databases. The known genes include five upregulated inflammation-related genes encoding monocyte chemotactic protein-1, cystatin B, inter-alpha-trypsin inhibitor family heavy chain-related protein, serum amyloid A protein, and glycoprotein 130, suggesting that inflammatory reaction may be involved in the development of cerebral vasospasm. The upregulation of three known genes encoding stress-related proteins of vascular endothelial growth factor, BiP protein, and growth-arrest and DNA-damage-inducible protein may be involved in possible cell survival in the damaged arteries. A full-length cDNA for the unknown clone DVS 27, whose expression was most highly upregulated, was isolated from the cerebral artery cDNA library by hybridization. Characterization of these genes should help to clarify the molecular mechanism of continuous cerebral vasospasm after subarachnoid hemorrhage.

Reactive oxygen species as a risk factor in verotoxin-1-exposed rats

It has been suggested the the interaction of Escherichia coli O157-derived verotoxins (VTs) with the vascular endothelium plays a central role in the pathogenesis of the thrombotic microangiopathy and ischemic lesions characteristic of hemolytic uremic syndrome (HUS) and E. coli O157-associated hemorrhagic colitis. Intravenous administration of both E. coli O157-derived VT1 and lipopolysaccharide (LPS) in the rat induced a synergistic increase in thiobarbituric acid (TBA) values in those animal's plasma, as compared with that injected with VT1 or LPS alone. We then hypothesized that an increase in lipid peroxidation in the rat plasma was due to an enhanced production of endothelial cell-derived reactive oxidant. Based on determination of rat sera and cultured human aortic endothelial cells (HAECs), VT1 had little if any effect on LPS-stimulated increase of nitric oxide and the resultant peroxynitrite generations. Both RT-PCR and Western blot studies of reactive oxygen species-related enzymes showed that VT1 markedly decreased the expression of catalase mRNA and protein in HAECs, but caused less alteration in the levels of Cu, Zn-superoxide dismutase, and NADPH oxidase mRNA. Further studies by spin trapping analysis using 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) revealed a time-dependent increase in hydroxyl radicals by VT1 in HAECs. The accumulated data thus suggest that bacterial VT1 reduces mainly catalase levels in endothelial cells, which is synergistically potentiated by LPS, and that the resulting hydroxyl radical participates in endothelium injury through a marked enhancement of lipid peroxidation, leading to HUS.

Loss-of-function and dominant-negative mechanisms associated with hepatocyte nuclear factor-1beta mutations in familial type 2 diabetes mellitus

Hepatocyte nuclear factor (HNF)-1beta, a homeodomain-containing transcription factor, regulates gene expression in a dimerized form in pancreas, liver, and some other tissues. Recent genetic studies have identified two HNF-1beta mutations, R177X and A263fsinsGG, in subjects with a monogenic form of type 2 diabetes. Despite the defects being in the same gene, diverse severities of disease are observed in the affected subjects. To investigate the molecular mechanism by which mutations might cause various phenotypic features, wild type and mutant proteins were transiently expressed in insulin-producing (MIN6) and hepatic (HepG2) cells. Luciferase reporter assay showed that both mutations resulted in a marked reduction of transactivation activity. Because their dimerization activity was found to be intact by the yeast two-hybrid system, it was possible that they were dominant-negative to wild type activity. When co-expressed with wild type, both of the mutants significantly decreased wild type activity in HepG2 cells. In contrast, although A263fsinsGG functioned similarly in MIN6 cells, R177X failed to affect wild type activity in this cell line. Immunohistochemical analysis of the mutants suggests that this functional divergence might be generated by the modification of nuclear localization. These results suggest that HNF-1beta mutations may impair pancreatic beta-cell function by loss-of-function and dominant-negative mechanisms.

Human retinoic X receptor beta: complete genomic sequence and mutation search for ossification of posterior longitudinal ligament of the spine

Ossification of the posterior longitudinal ligament of the spine (OPLL) is characterized by ectopic bone formation in the ligament. OPLL is a very common disorder, in fact it constitutes the leading cause of myelopathy among Japanese. In the previous report, we provided the genetic linkage evidence that the genetic susceptibility of OPLL mapped to HLA complex of chromosome 6. As a candidate gene approach, retinoic X receptor beta (RXR beta), assigned to chromosome 6p21.3 adjacent to HLA class II, was analyzed for a possible causality. To start screening for the molecular variants of RXR beta in OPLL subjects, we first obtained P1 phage genomic clones containing the entire human RXR beta and elucidated the genomic organization of the gene. The human RXR beta is composed of 10 exons spanning over 6.2 kb of genomic DNA. Sequence analysis of the promoter region revealed a GC-rich sequence without TATA motif. We have identified three distinct molecular variants, one was in exon 10 and two were in the intergenic region between RXR beta and collagen 11A2 (COL11A2). Two variants in the intergenic region, 3' end + 140 and 3' end + 561, exhibit statistically significant associations with OPLL in case-control study (p = 0.0028 for 3' end + 140 and p = 0.034 for 3' end + 561). These results indicate that the genetic causality of OPLL lies within or close to the RXR beta/COL11A2 locus.

Reduced alkaline phosphatase activity in diabetic rat bone: a re-evaluation

We found previously that human bone alkaline phosphatase (AP) was glycated by aseptic incubation with glucose, and partially broken down by reactive oxygen species. In this study, we examined whether selective in vivo glycation of AP molecules occurred in bone tissue, using experimental diabetic rats induced by streptozotocin and spontaneously diabetic rats. Additionally, the effects of hyperlipidemia on bone AP activity were examined. Serum AP activity was significantly elevated after incipient onset of diabetes, and the increased activity originated from the intestinal isozyme. High levels of intestinal AP activity were also observed in rats with hyperlipidemia induced by feeding high-fat or high-fructose chow, but the AP activity in bone tissues was maintained at a constant level. AP activity in bone was reduced after the onset of diabetes. The resulting bone AP molecule bound to an aminophenylboronic acid column, which had affinity for glycated proteins, and contained smaller molecular sizes than the native bone AP. These results suggest that elevated levels of serum AP activity originated from the intestinal isozyme accompanied with hyperlipidemia induced by diabetes. In contrast, the reduced serum levels of AP activity in diabetic rats might be dependent on inactivation of bone AP, which was glycated, followed by partial breakdown of bone AP molecules, possibly due to reactive oxygen species.

Behavioural characterization and amounts of brain monoamines and their metabolites in mice lacking histamine H1 receptors

Behavioural assessments were made of mutant mice lacking histamine H1 receptors to reveal the function of H1 receptors in the behaviour of mice. Exploratory behaviour of mice in a new environment was examined to discover whether the absence of H1 receptors in mice affects actions relating to their emotions. The H1 receptor-deficient mice showed a significant decrease in ambulation in an open field and on an activity wheel. Cognitive functions and anxiety were examined using passive avoidance response test and the elevated plus-maze test, respectively. The passive avoidance test did not show any change in latency. The elevated plus-maze test revealed that the transfer latency of the mutant mice was significantly prolonged, indicating that H1 receptors are partly associated with the control of anxiety. Aggressive behaviour was examined by a resident-intruder aggression test. When confronted with an intruder, the mutant mice attacked the intruder significantly slower and less frequently than did wild-type mice after a six-month isolation period. A formalin test and a forced swimming test were used to evaluate the nociceptive response and depressive or despairing state, respectively, of both groups. The mutant mice showed a significant decrease of nociceptive response in the late phase without affecting the early phase. There was no significant difference in the forced swimming test between the two groups. The brain content of monoamines and their metabolites was measured in the H1 receptor null and wild-type mice. The turnover rate of 5-hydroxytryptamine defined by the ratio of 5-hydroxyindoleacetic acid and 5-hydroxytryptamine was significantly increased in the cerebral cortex and hippocampus of H1 receptor null mice. These results support the previous pharmacological findings that histamine modulates various neurophysiological functions such as locomotor activity, emotion, memory and learning, nociception and aggressive behaviour through H1 receptors.

Genetic mapping of ossification of the posterior longitudinal ligament of the spine

Ossification of the posterior longitudinal ligament of the spine (OPLL) is recognized as a common disorder among Japanese and throughout Asia. Estimates of its prevalence are in the range of 1. 9%-4.3%. Although its etiology is thought to involve a multiplicity of factors, epidemiological and family studies strongly implicate genetic susceptibility in the pathogenesis of OPLL. In this study we report an identification of a predisposing locus for OPLL, on chromosome 6p, close to the HLA complex. The evidence for this localization is provided by a genetic-linkage study of 91 affected sib pairs from 53 Japanese families. In this sib-pair study, D6S276, a marker lying close to the HLA complex, gives evidence for strongly significant linkage (P = .000006) to the OPLL locus. A candidate gene in the region, that for collagen 11A2, was analyzed for the presence of molecular variants in affected probands. Of 19 distinct variants identified, 4 showed strong statistical associations with OPLL (highest P = .0004). These observations of linkage and association, taken together, show that a genetic locus for OPLL lies close to the HLA region, on chromosome 6p.

Expression of peroxisome proliferator-activated receptor alpha (PPAR alpha) in primary cultures of human vascular endothelial cells

The peroxisome proliferator-activated receptor (PPAR) is a member of the steroid nuclear receptor superfamily. Three types of PPARs have been described in humans: PPAR alpha, PPAR beta, and PPAR gamma. Here we investigated the levels of PPAR alpha mRNA in primary cultures of human umbilical venous endothelial cells (HUVEC), human umbilical arterial endothelial cells (HUAEC), human coronary arterial endothelial cells (HCAEC), and human aortic endothelial cells (HAEC), using the reverse transcriptase-polymerase chain reaction (RT-PCR). The HUVEC, HAEC, and HCAEC, but not the HUAEC, showed relatively low expression of PPAR alpha in comparison with liver, which was used as a positive control. Moreover, the partial sequences of the PCR-amplified products from HUVEC, HAEC, and HCAEC were similar to that of the PPAR alpha from human liver. The expression of PPAR alpha in cultured HAEC, which were induced by dexamethasone, was inhibited by insulin. In addition, PPAR alpha expression was also increased by benzafibrate or eicosapentaenoic acid with the physiological concentration. These results suggest that the PPAR alpha in endothelial cells may have the same physiological role as the expression of PPAR alpha in the liver.

Living with a person who has Parkinson's disease: the spouse's perspective by stage of disease. Parkinson's Study Group

The objective of this study was to examine the experience of spouses caregiving for their spouse with Parkinson's disease (PD) and to determine whether their experiences differed by stage of disease. By using a cross-sectional design and mail questionnaire data from 380 spouse caregivers across 23 sites of the Parkinson Study Group, key caregiver variables were examined by stage of PD. Three categories of variables--caregiver role strain (10 measures), caregiver situation (four measures), and caregiver characteristics (four measures)--were analyzed by using t tests with Bonferroni correction. Specific types and amounts of role strain accumulated as the disease progressed, and they differed significantly between stages (p < 0.05). In the caregiving situation, the mean number of caregiving tasks tripled by stage 4/5. Negative changes in lifestyle plus decreases in predictability in caregivers' lives increased significantly in late-stage disease (p < 0.05). Caregiver characteristics of physical health and preparedness did not significantly differ across stages of disease. Depression was significantly higher by stage 4/5. Mutuality, the positive quality of the relationship as perceived by the caregiving spouse, declined beginning at stage 2. Caregiver strain is experienced across all stages of PD and accumulates significantly as the disease progresses. This study defines types and amounts of strain by stage of disease, which will be helpful in designing formal intervention trials to provide more effective help for spouse caregivers.

Bezafibrate has an antioxidant effect: peroxisome proliferator-activated receptor alpha is associated with Cu2+, Zn2+-superoxide dismutase in the liver

Administration of bezafibrate in rats significantly reduced the levels of plasma thiobarbituric acid-reactive substances (TBARS) in comparison with those obtained in rats fed a soy or lard chow. Moreover, an elevation of in vitro conjugated diene production and linoleic acid levels in the high-density lipoproteins and low-density lipoproteins induced by a soy or lard chow, was reduced by bezafibrate administration. In addition, the liver Cu2+, Zn2+-superoxide dismutase (SOD) gene expression showed a significant positive correlation with the liver peroxisome proliferator-activated receptor alpha (PPARalpha) mRNA level (R=0.769, p<0.0001). This unique characteristic of bezafibrate, which possesses both a hypolipidemic effect and antioxidant activity, may be beneficial in preventing vascular complications in hyperlipidemia.

Effect of lipophilic ions on the intramembrane charge movement and intracellular Ca2+ release in fetal mouse skeletal muscle cells

The effects of lipophilic ions on the intramembrane charge movement and intracellular calcium transient were studied using freshly dissociated skeletal muscle cells from mice fetuses. The lipophilic cations Rhodamine 6G and tetraphenylphosphonium (TPP) immobilized part of the intramembrane charge movement in a dose-dependent manner, and inhibited both calcium transient and contraction evoked by membrane depolarization. In contrast, the lipophilic anion 1-anilinonaphthalene-8-sulfonic acid (ANS) had no effect on intramembrane charge movement. We suggest that the lipophilic cations block the voltage-sensing mechanism for the excitation-contraction (E-C) coupling mechanism.

Evidence for association between the class I subset of the insulin gene minisatellite (IDDM2 locus) and IDDM in the Japanese population

Although the shortest (class I) minisatellite (i.e., variable number of tandem repeats [VNTR]) alleles in the 5' region of the insulin gene are positively associated with IDDM in Caucasians, the majority of Japanese are homozygous for class I alleles. Here, we determined the exact length, in number of repeat units (RUs), of class I alleles in Japanese subjects. The distribution of class I alleles in Japanese was trimodal, with peaks located at 32/33, 41, and 44 RUs. The shortest component (i.e., 1S [25-38 RUs]) alleles were significantly increased in the IDDM group compared with the control group (54 vs. 46%; P = 0.040). The 1S/1S genotype was significantly increased in the IDDM patients (34 vs. 20%; P = 0.005; relative risk 2.1). Furthermore, the transmission disequilibrium test of Japanese families with 1S/1M or 1S/1L heterozygous parents confirmed the association of 1S alleles; 17 alleles of 1S and 6 alleles of 1M (39-41 RUs) or 1L (42-44 RUs) were transmitted to affected offspring (P = 0.022). In addition, we found tight linkage of 1S with allele 9 of the tyrosine hydroxylase gene microsatellite and allele (-) of the IGF-II gene Apa I polymorphism, but neither 9 nor (-) alleles were significantly associated with IDDM. The present study suggests that a class I subset may have a role in IDDM susceptibility in Japan. It was revealed that the difference between 1S alleles and 1M or 1L alleles is almost consistently characterized by a sequence variation generated by deletion of two copies of an ACAGGGGTCC CGGGG repeat element, implying that sequence variation of class I alleles may influence disease susceptibility.

The peroxisome proliferator-activated receptor alpha (PPAR alpha) regulates the plasma thiobarbituric acid-reactive substance (TBARS) level

We investigated whether liver expression of the peroxisome proliferator-activated receptor alpha (PPAR alpha) gene is related to the plasma thiobarbituric acid-reactive substance (TBARS) level, as well as to plasma cholesterol (TC) level and plasma triglyceride (TG) level in rats fed a high fat chow containing a variety of fatty acids. Only the plasma TBARS level showed a significant negative correlation with the liver PPAR alpha mRNA level (TC, R = 0.001, p = 0.9967; TG, R = 0.248, p = 0.1276; TBARS, R = 0.439, p = 0.0046). Although further studies are needed to clarify whether the increase of the liver PPAR alpha mRNA level confers a reduction in plasma TBARS levels, it is likely that PPAR alpha activity plays a regulatory role in the pathogenesis of hyperlipidemia and atherosclerosis.

A conditionally immortalized cell line from murine proximal tubule

We have developed a conditionally immortalized murine cell line with proximal tubule characteristics (tsMPT) and a background suitable for genetic manipulations. tsMPT was derived from the F1 progeny of crosses between: [1] a transgenic mouse harboring a gamma-interferon (IFN-gamma)-inducible, temperature sensitive SV40 large T antigen gene (tsA58) and [2] mice of the 129/SvEv strain, the background from which most embryonic stem (ES) cells are derived. Under permissive conditions (33 degrees C and in the presence of IFN-gamma), tsMPT cells grow rapidly as monolayers with a doubling time of 23 hours; the large T antigen can be detected by immunocytochemistry and by Western blotting. When transferred to non-permissive conditions (39 degrees C, without IFN-gamma), the cells undergo differentiation coinciding with the disappearance of the large T antigen. By electron microscopy, tsMPT cells are polarized and show microvilli at their apical surface. tsMPT cells express brush border enzymes gamma-glutamyl transpeptidase and carbonic anhydrase IV. They possess Na(+)-dependent transport systems for Pi, D-glucose and L-proline as well as an amiloride-insensitive Na(+)-H+ exchanger. Intracellular cAMP generation is stimulated by parathyroid hormone but not by arginine vasopressin. Angiotensinogen mRNA and protein are present in tsMPT with markedly higher levels at non-permissive conditions. tsMPT cells should be a useful model for investigation of the functional features of the proximal tubule epithelium in relation to cellular differentiation.

Troglitazone has a scavenging effect on reactive oxygen species

Troglitazone (CS-045), a newly developed antidiabetic thiazolidinedione that enhances insulin sensitivity, is similar in structure to several antioxidants, including alpha-tocopherol and probucol. The in vitro antioxidant activity of troglitazone has been demonstrated in alloxan-induced hyperlipoperoxidemic and hyperlipidemic mice. In this study, we found that troglitazone had a scavenging effect on reactive oxygen produced by xanthine-xanthine oxidase and generated by stimulated neutrophils and tends to be the radical form. Our results suggest that troglitazone is an antioxidant similar to alpha-tocopherol. However, under the same conditions, pioglitazone, another thiazolidinedione drug, did not have a scavenging effect. The antioxidant action of troglitazone, which is attributable to the similarity of its molecular structure to that of alpha-tocopherol, may be of benefit in preventing diabetic vascular complications, in addition to having hypoglycemic and hypolipidemic effects.

Acarbose controls postprandial hyperproinsulinemia in non-insulin dependent diabetes mellitus

We investigated how fasting or postprandial insulin levels were altered by treatment with acarbose or sulfonylureas. Plasma glucose and serum insulin, C-peptide, and proinsulin levels were measured before as well as 1 and 2 h after breakfast in 23 patients with non-insulin-dependent diabetes mellitus and 17 patients with impaired glucose tolerance. In the diabetic patients, 12 weeks of acarbose therapy decreased the postprandial levels of glucose (1 h: -60.0%; 2 h: -67.6%), insulin (1 h: -67.5%; 2 h: -72.2%) and proinsulin (1 h: -55.2%; 2 h: -46.7%), and proinsulin (1 h: -20.9%; 2 h: -57.5%). In contrast, sulfonylurea treatment increased postprandial insulin and proinsulin levels. Since increased in the serum insulin or proinsulin levels are associated with a higher risk of cardiovascular disease, the present findings suggest that the acarbose-induced reduction of the postprandial serum insulin or proinsulin responses to food intake might be useful for preventing vascular complications in patients with diabetes.