The dipeptidyl peptidase-4 inhibitor vildagliptin has the capacity to repair β-cell dysfunction and insulin resistance

The aim of the present study was to determine whether the dipeptidyl peptidase (DPP)-4 inhibitor could repair pancreatic β-cell dysfunction and insulin resistance. Ten subjects with type 2 diabetes who had never received DPP-4 inhibitor treatment were enrolled in the study. Just before and 3 months after twice-daily administration of vildagliptin (50 mg tablets), insulin secretion and insulin sensitivity were estimated using 2-compartment model analysis of C-peptide kinetics and insulin-modified minimal model parameters, respectively. The first-phase insulin secretion (CS1) was determined as the sum of the C-peptide secretion rate (CSR) from 0 to 5 min (normal range 6.8-18.5 ng/ml/min). The whole-body insulin sensitivity index (SI) was calculated using a minimal model software program (normal range 2.6-7.6×10(-4)/min/μU/ml). After vildagliptin treatment, reductions in mean (± SE) HbA1c were noted (43.28±1.53 vs. 40.98±1.77 mmol/mol; p=0.019). Vildagliptin treatment increased the area under the curve for the C peptide reactivity (CPR) (AUCCPR; 26.66±5.15 vs. 33.02±6.12 ng/ml · 20 min; p=0.003) and CS1 (0.80±0.20 vs. 1.35±0.38 ng/ml/min; p=0.037) in response to an intravenous glucose load. -Vildagliptin treatment significantly increased SI (0.46±0.27 vs. 1.21±0.48×10(-4)/min/μU/ml; p=0.037). The long-term administration of vildagliptin improved CS1 and Si suggesting that this drug has the capacity to repair impairments in pancreatic β-cell function and insulin resistance in type 2 diabetes.

Functional characterization of rhesus embryonic stem cell-derived serotonin neurons

Optimal function of the serotonin system is essential for mental health and its role in psychopathologies is undisputed. Enhancing the ability to study primate serotonin neurons in culture would facilitate understanding of intracellular signaling pathways that mediate the action of drugs and other epigenetic or developmental factors impacting human mental health. We were the first group to report differentiation of the non-human primate rhesus monkey embryonic stem cell (ESC) line 366.4 into cultures of serotonin neurons. In this study, we optimized yield and obtained functional characteristics of the derived serotonin neurons. Sequential treatments of ESC 366.4 during expansion stage with fibroblast growth factor 4 and sonic hedgehog markedly increased the yield of serotonin neurons. These serotonin neurons propagated action potentials and expressed GABA receptors. Also, for the first time we demonstrate that these ESC-derived serotonin neurons exhibit functional high-affinity transporter sites, as well as high-affinity 5HT(1A) binding sites, which are essential targets of common psychoactive drugs. Finally, to test the generality of this method, we utilized another rhesus ESC line, ORMES-22, which efficiently differentiated into serotonin neurons. Together, these findings demonstrate the feasibility of our protocol to direct different primate ESC lines to serotonin neurons with physiological characteristics, which makes them a useful in vitro model system.

Protective actions of ovarian hormones in the serotonin system of macaques

The serotonin neurons of the dorsal and medial raphe nuclei project to all areas of the forebrain and play a key role in mood disorders. Hence, any loss or degeneration of serotonin neurons could have profound ramifications. In a monkey model of surgical menopause with hormone replacement and no neural injury, E and P decreased gene expression in the dorsal raphe nucleus of c-jun n-terminal kinase (JNK1) and kynurenine mono-oxygenase (KMO) that promote cell death. In concert, E and P increased gene expression of superoxide dismutase (SOD1), VEGF, and caspase inhibitory proteins that promote cellular resilience in the dorsal raphe nucleus. Subsequently, we showed that ovarian steroids inhibit pivotal genes in the caspase-dependent and caspase-independent pathways in laser-captured serotonin neurons including apoptosis activating factor (Apaf1), apoptosis-inducing factor (AIF) and second mitochondria-derived activator of caspases (Smac/Diablo). SOD1 was also increased specifically in laser-captured serotonin neurons. Examination of protein expression in the dorsal raphe block revealed that JNK1, phosphoJNK1, AIF and the translocation of AIF from the mitochondria to the nucleus decreased with hormone therapy, whereas pivotal execution proteins in the caspase pathway were unchanged. In addition, cyclins A, B, D1 and E were inhibited, which would prevent re-entry into the cell cycle and catastrophic death. These data indicated that in the absence of gross injury to the midbrain, ovarian steroids inhibit the caspase-independent pathway and cell cycle initiation in serotonin neurons. To determine if these molecular actions prevented cellular vulnerability or death, we examined DNA fragmentation in the dorsal raphe nucleus with the TUNEL assay (terminal deoxynucleotidyl transferase nick end labeling). Ovarian steroids significantly decreased the number of TUNEL-positive cells in the dorsal raphe. Moreover, TUNEL staining prominently colocalized with TPH immunostaining, a marker for serotonin neurons. In summary, ovarian steroids increase the cellular resilience of serotonin neurons and may prevent serotonin neuron death in women facing decades of life after menopause. The survival of serotonin neurons would support cognition and mental health.

Expression profile of differentiating serotonin neurons derived from rhesus embryonic stem cells and comparison to adult serotonin neurons

The rhesus monkey embryonic stem cell line 366.4 differentiates into serotonin neurons. We examined the genetic cascade during differentiation and compared ESC-derived serotonin neurons to adult monkey serotonin neurons. RNA was extracted from ESC colonies, embryoid bodies (EBs), neurospheres in selection (N1) and proliferation stages (N2), differentiated serotonin neurons (N3) and from laser captured (LC) serotonin neurons of spayed female macaques treated with placebo, estrogen (E), progesterone (P) or E+P. The RNA was labeled and hybridized to Rhesus Monkey Affymetrix Gene Chips (n=1 per stage and 2 per animal treatment). Gene expression was examined with GeneSifter software. 545 genes that were related to developmental processes showed a threefold or greater change between stages. TGFb, Wnt, VEGF and Hedgehog signaling pathways showed the highest percent of probe set changes during differentiation. Genes in the categories (a) homeobox binding and transcription factors, (b) growth factors and receptors, (c) brain and neural specific factors and (d) serotonin specific factors are reported. Pivotal genes were confirmed with quantitative RT-PCR. In the serotonin developmental cascade, FGFR2 was robustly expressed at each stage. GATA3 was robustly expressed in EBs. Sonic hedgehog (Shh), PTCH (Shh-R) and Fev1 transcription factor expression coincided with the induction of serotonin specific marker genes during N1-selection. A majority of the examined genes were expressed in adult serotonin neurons. However, in the ESC-derived neurons, there was significant over-representation of probe sets related to cell cycle, axon guidance & dorso-ventral axis formation. This analysis suggests that the 366.4 cell line possesses cues for serotonin differentiation at early stages of differentiation, but that ESC-derived serotonin neurons are still immature.

Unique responses of midbrain CART neurons in macaques to ovarian steroids

CART (cocaine and amphetamine regulated transcript) is a neuropeptide involved in the control of several physiological processes, such as response to psychostimulants, food intake, depressive diseases and neuroprotection. It is robustly expressed in the brain, mainly in regions that control emotional and stress responses and it is regulated by estrogen in the hypothalamus. There is a distinct population of CART neurons located in the vicinity of the Edinger-Westphal nucleus of the midbrain that also colocalize urocortin-1. The aims of this study were 1) to determine the distribution of CART immunoreactive neurons in the monkey midbrain, 2) to examine the effects of estrogen (E) and progesterone (P) on midbrain CART mRNA and peptide expression and 3) to determine whether midbrain CART neurons contain steroid receptors. Adult female rhesus monkeys (Macaca mulatta) were spayed and either treated with placebo (OVX), estrogen alone (E), progesterone alone (P) or E+P. Animals were prepared (a) for RNA extraction followed by microarray analysis and quantitative (q) RT-PCR (n=3/group); (b) for immunohistochemical analysis of CART and CART+tryptophan hydroxylase (TPH), CART+estrogen receptors (ER) or CART+progesterone receptors (n=5/group) and (c) for Western blots (n=3/group). Both E- and E+P-administration decreased CART gene expression on the microarray and with qRT-PCR. Stereological analysis of CART immunostaining at five levels of the Edinger-Westphal nucleus indicated little effect of E or E+P administration on the area of CART immunostaining. However, P administration increased CART-immunopositive area in comparison to the OVX control group with Student's t-test, but not with ANOVA. CART 55-102 detection on Western blot was unchanged by hormone administration. ERbeta and PR were detected in CART neurons and CART fibers appeared to innervate TPH-positive serotonin neurons in the dorsal raphe. In summary, E decreased CART mRNA, but this effect did not translate to the protein level. Moreover, P administration alone had a variable effect on CART mRNA, but it caused an increase in CART immunostaining. Together, the data suggest that CART neurons in the midbrain have a unique steroid response, which may be mediated by nuclear receptors, neuroactive steroids or interneurons.

Neuroprotective actions of ovarian hormones without insult in the raphe region of rhesus macaques

Using a nonhuman primate model of surgical menopause, our laboratory has shown that ovarian hormone treatment (HT) improves 5-HT neural function in the dorsal raphe nucleus (DRN). We further hypothesize that HT may increase 5-HT neuronal resilience. Recent data from microarray analysis indicated that HT regulates gene expression in pathways that lead to apoptosis. In this study, we questioned whether HT alters protein expression in caspase-dependent and independent pathways. Ovariectomized monkeys received Silastic implants containing placebo (empty), estrogen (E) or E+ progesterone (P). A small block of the midbrain containing the DRN was dissected and subjected to subcellular fractionation, yielding cytosolic, nuclear and mitochondrial fractions (n=4/group). The pro-apoptotic protein, c-jun n-terminal kinase (JNK1) and its phosphorylation were decreased by E+P treatment in the cytosolic fraction. Downstream of JNK are proteins in the caspase-dependent and -independent pathways. First, in the caspase-dependent pathway, cytoplasmic and mitochondrial fractions were immunoblotted for Bcl-2 family members, cytochrome c, Apaf1 and XIAP. However, the expression of these proteins did not differ among treatments. Pro-caspase 3 was decreased by E+P, but there was no evidence of active caspase in any group. Then, we examined the involvement of a protein in the caspase-independent pathway, called apoptosis-inducing factor (AIF). AIF mRNA (n=3/group) and AIF mitochondrial protein tended to decrease with hormone treatment. However, AIF protein in the nuclear fraction in E+P treated monkeys was significantly reduced. This indicates that HT is reducing the translocation of AIF from mitochondria to nucleus, thus inhibiting AIF-mediated apoptosis. AIF was immunocytochemically localized to large 5-HT-like neurons of the dorsal raphe. These data suggest that in the absence of global trauma or ischemia, HT may act through the caspase-independent pathway to promote neuroprotection in the 5-HT system.

Thr199phosphorylation targets nucleophosmin to nuclear speckles and represses pre-mRNA processing

Nucleophosmin (NPM) is a multifunctional phosphoprotein, being involved in ribosome assembly, pre-ribosomal RNA processing, DNA duplication, nucleocytoplasmic protein trafficking, and centrosome duplication. NPM is phosphorylated by several kinases, including nuclear kinase II, casein kinase 2, Polo-like kinase 1 and cyclin-dependent kinases (CDK1 and 2), and these phosphorylations modulate the activity and function of NPM. We have previously identified Thr(199) as the major phosphorylation site of NPM mediated by CDK2/cyclin E (and A), and this phosphorylation is involved in the regulation of centrosome duplication. In this study, we further examined the effect of CDK2-mediated phosphorylation of NPM by using the antibody that specifically recognizes NPM phosphorylated on Thr(199). We found that the phospho-Thr(199) NPM localized to dynamic sub-nuclear structures known as nuclear speckles, which are believed to be the sites of storage and/or assembly of pre-mRNA splicing factors. Phosphorylation on Thr(199) by CDK2/cyclin E (and A) targets NPM to nuclear speckles, and enhances the RNA-binding activity of NPM. Moreover, phospho-Thr(199) NPM, but not unphosphorylated NPM, effectively represses pre-mRNA splicing. These findings indicate the involvement of NPM in the regulation of pre-mRNA processing, and its activity is controlled by CDK2-mediated phosphorylation on Thr(199).

Characterization of centrosomal association of nucleophosmin/B23 linked to Crm1 activity

Nucleophosmin (NPM)/B23 is a multifunctional protein, involving in a wide variety of basic cellular processes, including ribosome assembly, DNA duplication, nucleocytoplasmic trafficking, and centrosome duplication. It has previously been shown that NPM/B23 localizes to centrosomes, and dissociate from centrosomes upon phosphorylation by Cdk2/cyclin E. However, detail characterization of centrosomal association of NPM/B23 has been hampered by the lack of appropriate antibodies that efficiently detects centrosomally localized NPM/B23, as well as by apparent loss of natural behavior of NPM/B23 when tagged with fluorescent proteins. Here, by the use of newly generated anti-NPM/B23 antibody, we conducted a careful analysis of centrosomal localization of NPM/B23. We found that NPM/B23 localizes between the paired centrioles of unduplicated centrosomes, suggesting the role of NPM/B23 in the centriole pairing. Upon initiation of centrosome duplication, some NPM/B23 proteins remain at mother centrioles of the parental centriole pairs. We further found that inhibition of Crm1 nuclear export receptor results in both accumulation of cyclin E at centrosomes and efficient dissociation of NPM/B23 from centrosomes.

Inactivation of E2F3 results in centrosome amplification

The E2F family of transcription factors is critical for the control of cell cycle progression. We now show that the specific inactivation of E2F3 in mouse embryo fibroblasts (MEFs) results in a disruption of the centrosome duplication cycle. Loss of E2F3, but not E2F1, E2F2, E2F4, or E2F5 results in unregulated cyclin E-dependent kinase activity, defects in nucleophosmin B association with centrosomes, and premature centriole separation and duplication. Consequently, this defect leads to centrosome amplification, mitotic spindle defects, and aneuploidy. Our findings implicate the E2F3 transcription factor as an important link that orchestrates DNA and centrosome duplication cycles, ensuring the faithful transmission of genetic material to daughter cells.

A patient with subcutaneous-insulin resistance treated by insulin lispro plus heparin

Severe resistance to subcutaneous insulin but sensitivity to intravenous insulin persisted for 11 years in a 23-year-old diabetic woman. Several therapeutic trials revealed that (1) intravenous regular insulin improved her metabolic control; (2) continuous subcutaneous infusion (CSII) treatment with regular insulin or insulin lispro caused hyperglycemic period with hypoinsulinemia and hypoglycemic period with hyperinsulinemia alternately; (3) adding heparin to insulin lispro in CSII resulted in dramatic increase of serum insulin level and improvement of glycemic control; and (4) regular insulin plus heparin in CSII could not increase serum insulin level and thus the glycemic values was not improved. From these results, the patient followed the insulin lispro plus heparin protocol and obtained a better glycemic control without any adverse events. Effectiveness of this therapy may lead us to further understanding of pathophysiology of this syndrome.

Difference in the centrosome duplication regulatory activity among p53 'hot spot' mutants: potential role of Ser 315 phosphorylation-dependent centrosome binding of p53

The p53 tumor suppressor protein regulates centrosome duplication through multiple pathways, and p21(Waf1/Cip1) (Waf1), a major target of p53's transactivation function, has been shown to be one of the effectors. However, it had been unclear whether the p53's Waf1-independent centrosome duplication regulatory pathways require its transactivation function. In human cancers, specific residues of p53 are mutated at a high frequency. These 'hot spot' mutations abrogate p53's transactivation function. If p53 regulates centrosome duplication in a transactivation-independent manner, different 'hot spot' mutants may regulate centrosome duplication differently. To test this, we examined the effect of two 'hot spot' mutants (R175H and R249S) for their centrosome duplication regulatory activities. We found that R175H lost the ability to regulate centrosome duplication, while R249S partially retained it. Moreover, R249S associates with both unduplicated and duplicated centrosomes similar to wild-type p53, while R175H only associates with duplicated, but not unduplicated centrosomes. Since cyclin-dependent kinase 2 (CDK2) triggers initiation of centrosome duplication, and p53 is phosphorylated on Ser 315 by CDK2, we examined the p53 mutants with a replacement of Ser 315 to Ala (A) and Asp (D), both of which retain the transactivation function. We found that S315D retained a complete centrosome duplication activity, while S315A only partially retained it. Moreover, S315D associates with both unduplicated and duplicated centrosomes, while S315A associates with only duplicated, but not unduplicated centrosomes. Thus, p53 controls the centrosome duplication cycle both in transactivation-dependent and transactivation-independent manners, and the ability to bind to unduplicated centrosomes, which is controlled by phosphorylation on Ser 315, may be important for the overall p53-mediated regulation of centrosome duplication.

Class switch recombination signals induce lymphocyte-derived Spo11 expression and Spo11 antisense oligonucleotide inhibits class switching

Recently, we showed that mouse Spo11 is induced in normal mu(+) B cells by class switch recombination (CSR) stimuli, by RT-PCR using primers based on the reported cDNA sequence of testis-derived Spo11 (test-Spo11) cDNA. In the present study, we first determined the cDNA sequence of lymphocyte-derived Spo11 (lym-Spo11). The 5' upstream portion had an as yet unreported sequence but the remaining part from exons 2 to 12 and the subsequent 3'UTR was completely identical to that of test-Spo11. RT-PCR analysis indicated that lymphocytes express lym-Spo11 but not test-Spo11. Second, we showed that lym-Spo11 is strongly induced (above eightfold) in the IgA CSR system of LPS-stimulated mu(+)B cells in the presence of all-trans retinoic acid and IL-4. Finally, we examined whether lym-Spo11 antisense S-oligonucleotide (AS) can inhibit CSR reactions in three in vitro CSR systems, IgA,IgG1, and IgE. Lym-Spo11 AS or the sense oligonucleotide was added to the cultures at the start, and total RNA was extracted after 4 days. IgA, IgG1, and IgE mRNAs (J(H)C(H)) and mature germline C(H) transcripts (I(H)C(H)) were quantitatively assayed by RT-PCR. AS inhibited J(H)C(H) expression dose-dependently. In all three systems, the maximum inhibition by 20 microM AS was in the range of 60 to 90%. Interestingly, I(H)C(H) was also inhibited by AS to a similar extent as J(H)C(H). These results suggested that lym-Spo11 plays an important role in the initiation step of CSR.

Pathophysiologic phenotypes of Japanese subjects with varying degrees of glucose tolerance: using the combination of C-peptide secretion rate and minimal model analysis

We tried to characterize the clinical features associated with glucose metabolism in the development of diabetes. Study subjects were glucose-tolerant subjects without a family history of diabetes (normal glucose tolerance [NGT]1 group, n = 15) and with a first-degree diabetes relative (NGT2, n = 9), 12 subjects with impaired glucose tolerance (IGT), and 13 subjects with type 2 diabetes mellitus (DM). The first phase C-peptide secretion (CS1), insulin sensitivity (Si), and glucose effectiveness (Sg) were assessed by the combination of C-peptide 2-compartment model and minimal model analyses. Using these parameters, each group was characterized: CS1 was decreased in NGT2 and IGT compared with NGT1 and further decreased in DM; Si was not different among NGT1, NGT2, and IGT, whereas Si was decreased in DM; CS1 x Si value was decreased in NGT2 compared with NGT1 and decreased in IGT, DM, progressively; Sg was decreased in IGT and DM compared with NGT1 and NGT2. CS1 x Si and Sg values could segregate each group distinctively, although it had a large variety of phenotypes. CS1 x Si value and Sg are assumed to represent the contributions of insulin-dependent and independent mechanisms to glucose tolerance, respectively, and thus, both mechanisms should play an important role in the characterization of pathophysiologic phenotypes of the subjects with various degrees of glucose tolerance.

Specific phosphorylation of nucleophosmin on Thr(199) by cyclin-dependent kinase 2-cyclin E and its role in centrosome duplication

The kinase activity of cyclin-dependent kinase 2 (CDK2)-cyclin E is required for centrosomes to initiate duplication. We have recently found that nucleophosmin (NPM/B23), a phosphoprotein primarily found in nucleolus, associates with unduplicated centrosomes and is a direct substrate of CDK2-cyclin E in centrosome duplication. Upon phosphorylation by CDK2-cyclin E, NPM/B23 dissociates from centrosomes, which is a prerequisite step for centrosomes to initiate duplication. Here, we identified that threonine 199 (Thr(199)) of NPM/B23 is the major phosphorylation target site of CDK2-cyclin E in vitro, and the same site is phosphorylated in vivo. NPM/T199A, a nonphosphorylatable NPM/B23 substitution mutant (Thr(199) --> Ala) acts as dominant negative when expressed in cells, resulting in specific inhibition of centrosome duplication. As expected, NPM/T199A remains associated with the centrosomes. These observations provide direct evidence that the CDK2-cyclin E-mediated phosphorylation on Thr(199) determines association and dissociation of NPM/B23 to the centrosomes, which is a critical control for the centrosome to initiate duplication.

Direct regulation of the centrosome duplication cycle by the p53-p21Waf1/Cip1 pathway

The function of the centrosomes to direct mitotic spindles is critical for accurate chromosome transmission to daughter cells. Since each daughter cell inherits one centrosome, each centrosome must duplicate prior to the next mitosis, and do so only once. Thus, there are control mechanism(s) that ensure the coordinated progression of centrosome duplication and other cell cycle events (i.e. DNA synthesis), and limit centrosome duplication to once per cell cycle. Deregulation of the centrosome duplication cycle results in abnormal amplification of centrosomes, leading to aberrant mitoses and increased chromosome transmission errors. This has been found to be the case for cells lacking functional p53 tumor suppressor protein. However, it had remained to be determined whether the deregulation of the centrosome duplication cycle is the direct or indirect effect of loss/mutational inactivation of p53. Here, we found that the normal centrosome duplication cycle is almost completely restored in p53(-/-) cells by re-introduction of wild-type p53 at a physiologically relevant level, demonstrating that p53 is directly involved in the regulation of centrosome duplication. Since cyclin dependent kinase 2 (CDK2)/cyclin E triggers DNA synthesis as well as centrosome duplication, we tested whether Waf1, a CDK inhibitor and a major target of p53's transactivation function, is an effector of p53-mediated regulation of centrosome duplication. We found that induced expression of Waf1 in p53(-/-) cells only partially restored the centrosome duplication control, suggesting that Waf1 comprises one of the multiple effector pathways of the p53-mediated regulation of the centrosome duplication cycle.

Nucleophosmin/B23 is a target of CDK2/cyclin E in centrosome duplication

In animal cells, duplication of centrosomes and DNA is coordinated. Since CDK2/cyclin E triggers initiation of both events, activation of CDK2/cyclin E is thought to link these two events. We identified nucleophosmin (NPM/B23) as a substrate of CDK2/cyclin E in centrosome duplication. NPM/B23 associates specifically with unduplicated centrosomes, and NPM/B23 dissociates from centrosomes by CDK2/cyclin E-mediated phosphorylation. An anti-NPM/B23 antibody, which blocks this phosphorylation, suppresses the initiation of centrosome duplication in vivo. Moreover, expression of a nonphosphorylatable mutant NPM/ B23 in cells effectively blocks centrosome duplication. Thus, NPM/B23 is a target of CDK2/cyclin E in the initiation of centrosome duplication.

Mutations in the hepatocyte nuclear factor-4alpha gene in Japanese with non-insulin-dependent diabetes: a nucleotide substitution in the polypyrimidine tract of intron 1b

Mutations of the hepatocyte nuclear factor 4 alpha (HNF-4alpha) gene have been demonstrated in maturity-onset diabetes of the young (MODY) 1 families. To investigate the possibility that the HNF-4alpha gene contributes to the onset of non-insulin-dependent diabetes mellitus (NIDDM) in Japanese patients, we screened all exons and flanking introns of this gene for mutations in 100 patients with NIDDM diagnosed after 25 years of age. We identified two missense mutations: M49V in exon 1c and T1301 in exon 4; and two nucleotide substitutions in introns: cytosine to thymidine at -5 nt in intron 1b and adenine to thymidine at -21 nt in intron 5. We screened an additional 220 diabetic subjects for the polymorphism in intron 1b. The c/t substitution in intron 1b was associated with NIDDM. This substitution in the polypyrimidine tract, an important cis-acting element directing intron removal, is likely to influence pre-mRNA splicing of this gene. T1301 in exon 4 was observed in only two diabetic subjects. This mutation could influence the conformation of this peptide, resulting in changes in ligand binding domain function. M49V in exon 1c was found in both diabetic and non-diabetic subjects; isoforms HNF-4alpha 4, 5, and 6 with this mutation may impair glucose metabolism in tissue. In contrast to the primary cause of nonsense and missense mutations of the HNF-4alpha gene in MODY1, the nucleotide substitution in intron 1b may partially contribute to development of NIDDM in combination with other genetic and environmental factors.

Mouse homolog of Saccharomyces cerevisiae spo11 is induced in normal mu(+)B-cells by stimuli that cause germline C(H) transcription and subsequent class switch recombination

The first step of Ig heavy chain class switch recombination (CSR) is considered to be DNA double strand break (DSB) formation in the two switch (S) regions (S(mu) and downstream S(H)), although the underlying mechanism is unknown. Recently, it has been demonstrated that at least Spo11, a homolog of the novel type II topoisomerase (topo VI) that catalyzes DSB formation, is involved in the initiation of meiotic recombination of Saccaromyces cerevisiae. In the present study, we examined whether the mouse homolog of Spo11 is induced in normal mouse mu(+)B-cells by stimuli that cause an early step of CSR, germline C(H) transcription, and subsequent CSR. Two CSR systems were used: IgA CSR induced by all-trans retinoic acid, IL-5, and LPS, and IgG1 CSR induced by IL-4 and LPS. Germline transcript and mouse Spo11 expression were analyzed by RT-PCR. In both systems, first germline transcripts were clearly detected on day 2 and then Spo11 was detected on day 3, increasing thereafter with time. The time course of changes in Spo11 expression coincided with that of CSR. Spo11 seems to be induced by CSR-inducing stimuli, regardless of the direction of CSR. These results suggested that mouse Spo11 might participate in the initiation step of CSR.

Tumor necrosis factor alpha signaling pathway and apoptosis in pancreatic beta cells

Cytokines induce apoptosis in pancreatic beta cells, but the exact mechanisms and sequence of events are not clear. Here, we investigate a role for tumor necrosis factor alpha (TNF-alpha) in the apoptosis of beta cells. Using the ribonuclease (RNase) protection assay and the reverse transcriptase-polymerase chain reaction (RT-PCR) method, we confirmed that TNF receptor 1 (TNFR1), TNFR1-associated death domain protein (TRADD), Fas receptor-associated intracellular protein with death domain (FADD), and FADD-like interleukin-1beta-converting enzyme (FLICE) were expressed in the pancreatic beta cell line, MIN6 cells. Fluorescent microscopic examination using Hoechst 33342 dye (Sigma, St Louis, MO) demonstrated that TNF-alpha induced time- and dose-dependent apoptotic nuclear changes in these beta cells. In situ end-labeling (ISEL) DNA analysis revealed that 10 nmol/L TNF-alpha generated new 3'-OH DNA strand breaks. Moreover, qualitative assessment of the induced DNA damage on agarose gels showed that 10 nmol/L TNF-alpha produced characteristic apoptotic patterns of DNA fragments formed by internucleosomal hydrolysis of static chromatin. In addition, C2-ceramides and natural ceramides dispersed in a solvent mixture of ethanol and dodecane induced characteristic features of apoptosis in MIN6 cells, mimicking TNF-induced DNA damage. We also determined endosomal ceramide production after TNF-alpha (10 nmol/L) treatment in MIN6 cells using the diacylglycerol kinase assay. These results suggest that TNF-alpha can cause apoptosis in pancreatic beta cells through TNFR1-linked apoptotic factors, TRADD, FADD, and FLICE, and TNF-induced ceramide production may be involved in the pathways.

Questionnaire survey and prevalence of intestinal helminthic infections in Barru, Sulawesi, Indonesia

A questionnaire survey with parasitological study was carried out on the inhabitants of 4 villages in Barru district, Sulawesi, Indonesia from 1994 to 1995. The questionnaire dealt with life style and sanitary conditions. In 482 houses in the 4 villages, interviews for the items of the questionnaire were conducted with the owner, housekeeper and children of the same family. In Pancana and Lalolang, 37.7% and 50% respectively of man inhabitants surveyed were fishermen, while in Lompo Riaja and Pattappa, 38.6% and 65.5% respectively were farmers. The highest proportion of official workers was 33.7% in Lompo Riaja. Educational level was low; 88.4% in Pancana, 90.4% in Lalolang, 62.1% in Lompo Riaja and 91.2% in Pattappa had elementary or below elementary school education. In Lompo Riaja, 30.8% of the inhabitants graduated from senior high school or university. The percentage of families having their own latrine was 30.3% in Pancana, 13.2% in Lalolang, 31.9% in Pattapa and 60% in Lompo Riaja. The people without latrines usually defecated in rice fields, seaside or riverside. A total of 654 fecal samples was examined by the modified Kato-Katz thick smear method. Five nematode species, Ascaris lumbricoides, Trichuris trichiura, Necator americanus, Strongyloides stercoralis and unidentified Rhabditoids of free-living nature were detected. Cestode, Hymenolepis nana infection was confirmed. All the hookworms examined by the modified Harada-Mori culture technic were Necator americanus. Trichuris infection was most common, followed by hookworm and Ascaris infections, both in young (aged 4-14) and older (aged over 15) age groups. The prevalence of hookworm infection was significantly higher in males than in females of older age. Among the older age group, the prevalence of Trichuris infection was significantly lower in Lompo Riaja, while hookworm infection was the highest in Pattappa. Among all the inhabitants examined for parasite infection, 17.4% had 3 kinds of nematode, Ascaris, Trichuris and hookworm. However, egg counts revealed that most of the inhabitants with Trichuris or hookworm had light infections. The inhabitants with higher education background had significantly lower infection rates of Ascaris and Trichuris. The prevalence of hookworm infection was not significantly different between the inhabitants owning latrine and without it, but the prevalence of Ascaris and Trichuris, differed significantly.

The regulatory effects of all-trans-retinoic acid on isotype switching: retinoic acid induces IgA switch rearrangement in cooperation with IL-5 and inhibits IgG1 switching

All-trans-retinoic acid (RA) can induce germline Calpha transcription in LPS-stimulated murine mu(+)B-cells by a TGF-beta-independent mechanism. In the present study, we examined whether RA can further drive the IgA switching process to Smu-Salpha switch rearrangement by DC-PCR. RA alone could not induce switch rearrangement but required the cooperation of IL-5. RA has another effect on isotype switching; RA strongly inhibits IL-4-dependent IgG1 and IgE production. To analyze the mechanism of IgG1 inhibition, we tested whether RA can inhibit IL-4-dependent Smu-Sgamma1 switch rearrangement. IL-4 by itself could induce Smu-Sgamma1 switch rearrangement in LPS-stimulated mu(+)B-cells. Addition of RA inhibited this reaction. RA also showed an inhibitory effect on the preceding step, i.e., Igamma1Cgamma1 transcription. Therefore, RA inhibition of Smu-Sgamma1 switch rearrangement was regulated at the level of germline Cgamma1 transcription. We further analyzed the amounts of both Igamma1Cgamma1 and IalphaCalpha expressed in LPS-stimulated B-cells exposed to mixtures of the two switch inducers, RA and IL-4, at various concentrations and found that the two transcripts were regulated antagonistically. These results indicated that RA can regulate isotype switching at the level of germline transcription and directs switching to IgA with the help of IL-5 and inhibits IgG1 switching.

A missense mutation in the CD38 gene, a novel factor for insulin secretion: association with Type II diabetes mellitus in Japanese subjects and evidence of abnormal function when expressed in vitro

Cyclic adenosine 5'diphosphate-ribose (cADPR) is thought to have a second messenger role in insulin secretion through mobilisation of Ca2+. As human lymphocyte antigen CD38 has both ADP-ribosyl cyclase and cADPR hydrolase activity, it may be important in glucose-induced insulin secretion in islets. Thirty one randomly selected Japanese patients with Type II diabetes mellitus who had first-degree and/or second-degree relative(s) with Type II diabetes mellitus were screened for mutations of this gene using single-stranded conformation polymorphism. Two variant patterns in exon 3 and exon 4 of the CD38 gene were identified. The variant in exon 3 resulted in an amino acid substitution from Arg140 (CGG) to Trp (TGG). The Arg140Trp mutation was observed in 4 of 31 patients, and allele frequencies were significantly different in patients and the control subjects (p = 0.004). One patient with this mutation has two missense mutations on beta cell/liver glucose transporter (GLUT2) gene; her mother, who has impaired glucose tolerance, also has this mutation on the CD38 gene and one missense mutation on the GLUT2 gene. Enzyme activity studies using COS-7 cells expressing the Arg140Trp mutation showed a reduction in ADP-ribosyl cyclase and cADPR hydrolase activity of around 50%. The Arg140Trp mutation on CD38 thus appears to contribute to the development of Type II diabetes mellitus via the impairment of glucose-induced insulin secretion in the presence of other genetic defects.

Molecular cloning of rat Pax4: identification of four isoforms in rat insulinoma cells

Molecular cloning of rat Pax4 cDNA from a rat insulinoma cell line, RINm5F, library by PCR-based cloning strategy revealed four isoforms of the protein. Analysis of tissue distribution using Northern blotting and RT-PCR showed specific expression of Pax4 mRNA in pancreatic islets and RIN cells. RT-PCR confirmed that the mRNAs of four isoforms are expressed in RIN cells. These Pax4 variants may regulate the transcriptional activity of Pax4 during the development of pancreatic islets.

Identification of gestationally regulated genes in rat myometrium by use of messenger ribonucleic acid differential display

OBJECTIVE

We hypothesized that the proteins contributing to myometrial changes during gestation could be identified indirectly by analyzing the changing pattern of messenger ribonucleic acid expression in the myometrium during pregnancy.

STUDY DESIGN

Ribonucleic acid was extracted from myometrium of timed pregnant Sprague-Dawley rats on days 12, 16, 20, 21, and 22 of pregnancy and on day 1 post partum. The technique of messenger ribonucleic acid differential display, a simple and sensitive polymerase chain reaction-based method for rapidly identifying messenger ribonucleic acids whose levels increase or decrease, was performed with the nine different anchoring primers (oligodeoxythymidine11 VN: V = G, A, or C; N = G, A, or C) in combination with 24 different 10-base oligonucleotides of random sequence. The polymerase chain reaction products were separated by electrophoresis on a 5% polyacrylamide sequencing gel, and those whose levels changed were then cloned, sequenced, and compared with those in the GenBank database to determine whether they corresponded to a known sequence in the database or were novel. Semiquantitative reverse transcriptase-polymerase chain reaction was used to confirm differential expression of selected products.

RESULTS

Messenger ribonucleic acid differential display revealed > 500 polymerase chain reaction products that were differentially expressed during gestation, 179 of which were cloned and sequenced. Of these, 157 were from messenger ribonucleic acids whose levels increased during gestation, and 22 were from transcripts that decreased. Eighty-seven (49%) were related to sequences in the GenBank database, of which 62 (35%) were from messenger ribonucleic acids encoding known proteins and 25 (14%) corresponded to known expressed sequence tags. The technique of semiquantitative reverse transcriptase-polymerase chain reaction confirmed the increased expression of messenger ribonucleic acids encoding beta-tropomyosin, type II phosphatidyl inositol-4-phosphate 5-kinase, and a novel myometrial messenger ribonucleic acid named RPU0901AC.

CONCLUSION

Messenger ribonucleic acid differential display is a simple and sensitive method for rapidly identifying myometrial messenger ribonucleic acids that are differentially regulated during pregnancy. The identification of these differentially expressed messenger ribonucleic acids may lead to a better understanding of the molecular basis of normal and abnormal parturition.

Retinoic acid induces the expression of germ-line C alpha transcript mainly by a TGF-beta-independent mechanism

The effects of retinoic acid (RA) on expression of germ-line transcripts, I alpha C alpha and I gamma 1C gamma 1, and of IgA and IgG1 mRNAs by murine surface IgM-positive B-cells were examined by reverse transcriptase-polymerase chain reaction (RT-PCR). LPS-stimulated B-cells were cultured for 2-3 days in the presence of IL-4 and IL-5 with or without RA. Total RNA was extracted from the cells, and RT-PCR specific for the germ-line transcripts was carried out. RA strongly induced mature germ-line C alpha transcript (I alpha C alpha) at concentrations between 10 and 100 nM. On the other hand, RA completely inhibited IL-4-induced I gamma 1C gamma 1 expression. Significant induction of I alpha C alpha was observed even at a low RA concentration (0.2 nM) in the presence of LPS (1.5-5 micrograms/ml) and without cytokines, and three- to fourfold stimulation of I alpha C alpha induction was seen at 5 nM. I alpha C alpha expression induced by RA (10 nM) and LPS (1.5 micrograms/ml) was not significantly affected by addition of anti-TGF-beta 1 and anti-TGF-beta 2 neutralizing antibodies, although that induced by TGF-beta 1 or TGF-beta 2 was completely inhibited by these antibodies. These results suggest that the major induction pathway of I alpha C alpha was not mediated by active TGF-beta and that RA at physiological concentrations may be involved in IgA isotype switching in vivo in a TGF-beta-independent manner.

Changes in endothelial nitric oxide synthase mRNA during vasospasm after subarachnoid hemorrhage in monkeys

OBJECTIVE

We attempt to determine whether changes in messenger ribonucleic acid (mRNA) for nitric oxide synthase (NOS) and soluble guanylate cyclase, enzymes that mediate endothelium-dependent vasodilation in cerebral arteries, occur after subarachnoid hemorrhage (SAH) in monkeys.

METHODS

Baseline cerebral angiograms were obtained, and right-sided SAH was induced by microsurgically placing autologous blood clot against the right anterior circle of Willis in seven monkeys. Seven days later, angiographic studies were repeated and the animals were killed. Right (vasospastic) and left (control) middle cerebral arteries and underlying cortex were removed. The competitive reverse transcriptase polymerase chain reaction was used to quantify mRNA for soluble guanylate cyclase and two isoforms of constitutive NOS in these tissues.

RESULTS

Comparison of angiograms at baseline and after 7 days showed a 41 +/- 7% (mean +/- standard error of the mean, P < 0.05, Wilcoxon test) decrease in diameter of the right middle cerebral artery. After the animals were killed, comparison of right and left middle cerebral arteries showed a 56 +/- 11% decrease (P < 0.005, paired t test) in endothelial NOS mRNA. There was a 142 +/- 39% (P < 0.05) increase in right cortex endothelial NOS mRNA compared to the left cortex. There were no significant differences between right and left sides in mRNAs for soluble guanylate cyclase or brain NOS.

CONCLUSION

Decreased endothelial NOS mRNA in cerebral arteries 7 days after SAH may be caused by endothelial cell damage and could contribute to vasospasm after SAH. Increased endothelial NOS in brain tissue may reflect a compensatory vasodilator mechanism of the brain against the cerebral ischemia associated with vasospasm and SAH.

Islet amyloid polypeptide/amylin contents in pancreas change with increasing age in genetically obese and diabetic mice

To search for a possible relationship between islet amyloid polypeptide (IAPP)/amylin and the pathophysiology of non-insulin-dependent (type 2) diabetes mellitus (NIDDM), we examined the changes in IAPP contents in the pancreata of genetically obese and diabetic mice (C57BL/6J ob/ob and C57BL/KsJ db/db mice). In the male ob/ob mice, IAPP and insulin contents began to increase at 16 weeks and continued to increase. In the male db/db mice, IAPP content began to increase at 8 weeks of age and insulin content at 4 weeks. Both contents continued to increase until 16 weeks, but drastically decreased at 24 weeks. Immunohistochemical studies using anti-IAPP8-17 antibody showed the increase of islet cell mass and the heterogeneous immunoreactivity for IAPP in islet cells in the ob/ob mice at 24 weeks of age. In the db/db mice at the same age, the immunoreactivity was heterogeneous and weak in many islet cells. These results suggest that genetic factors that are important in the manifestation of NIDDM influence the capacity of beta-cells to synthesize and secrete IAPP, and that IAPP synthesis and secretion change in the course of the disease.

Increased expression of endothelin B receptor mRNA following subarachnoid hemorrhage in monkeys

These studies tested the hypothesis that the cerebral vasospasm that follows subarachnoid hemorrhage (SAH) is due to alterations in endothelin (ET) and ET receptor expression. Eight monkeys underwent cerebral angiography and induction of SAH. Angiography was repeated 7 days later to confirm the presence of cerebral vasospasm, and animals were killed. RNA was isolated from right (vasospastic) and left (control) side middle cerebral arteries and surrounding cerebral cortex. The levels of prepro (PP) ET-1 (ppET-1) and ppET-3 and ETA and ETB receptor MRNAs were determined using a quantitative reverse transcriptase polymerase chain reaction-based assay. ET-1 peptide was also measured in CSF at baseline and after 7 days. Specific agonist binding to ETA and ETB receptors in both middle cerebral arteries and in surrounding brain cortex was measured in three animals by autoradiographic binding assays. Levels of ETB receptor mRNA were 3.4 +/- 2.2-fold higher in the right than in the left cerebral arteries (p < 0.01). There were no significant differences in the levels of ppET-1, ppET-3, or ETA receptor mRNA in cerebral arteries. ET-1 peptide was not elevated in CSF. Levels of ETA and ETB receptor mRNAs were 2.6 +/ 1.1- and 2.1 +/ 1.3-fold higher, respectively, in the right than in the left cerebral cortex, while the level of ppET-3 mRNA was 2.1 +/- 1.0-fold lower. There were no differences in ppET-1 mRNA levels between right and left cerebral cortex. Binding to ETA and ETB receptors in cerebral arteries and cortex did not differ significantly between right and left sides. These results do not support the hypothesis that overexpression of ET-1 is principal cause of vasospasm, but rather they suggest that SAH causes complex changes in the ET system that together are responsible for the cellular response to SAH.

Retinoids as Ig isotype-switch modulators. The role of retinoids in directing isotype switching to IgA and IgG1 (IgE) in association with IL-4 and IL-5

The role of retinoids was analyzed in directing isotype switching to IgA and IgG1 (IgE) by LPS-stimulated murine mu(+)B-cells in the presence of two Th2-type cytokines, IL-4 and IL-5. All trans retinoic acid (RA) enhanced the production of IgA at high concentrations (10-100 nM) in the presence of IL-5. Addition of IL-4 to the system modulated the IgA response in a dose-dependent manner. Namely, IL-4 inhibited the response at concentrations higher than 250 u/ml, but showed slight enhancement at lower concentrations (130 u/ml). IL-4 alone, which is considered to be an IgE isotype-switch inducer, strongly enhanced the IgG1 and IgE responses. Addition of IL-5 to the system showed a synergistic effect which could be attenuated by addition of low concentrations of RA (about 1 nM). Thus, the presence of switch modulators such as IL-4 and IL-5, their concentration ratios, and concentrations of retinoids are crucial factors in initiating and directing isotype switching to IgA and IgG1 (IgE).

Binding of botulinum type B neurotoxin to Chinese hamster ovary cells transfected with rat synaptotagmin II cDNA

We have previously identified synaptotagmin, a synaptic vesicle membrane protein from rat brain, as a binding protein for Clostridium botulinum type B neurotoxin. In this report, rat synaptotagmin II was expressed by transfection in Chinese hamster ovary cells and interaction with the neurotoxin was studied. In stable transfectants, the NH(2)-terminal region of synaptotagmin was exposed to the extracellular medium. Synaptotagmin-expressing cells were shown to possess an extremely low binding activity for the radiodinated toxin. However, toxin-binding was markedly increased to cells which had been treated with gangliosides G T1b or G D1a. In synapses, the intravesicular NH(2)-terminus of synaptotagmin becomes exposed at the cell surface after following exocytosis. These findings suggest that the NH(2)-terminal domain of synaptotagmin II forms the binding site for type B neurotoxin by associating with specific gangliosides in presynaptic plasma membranes.

Rat inwardly rectifying potassium channel Kir6.2: cloning electrophysiological characterization, and decreased expression in pancreatic islets of male Zucker diabetic fatty rats

The ATP-sensitive potassium channel of insulin-secreting pancreatic beta-cells is a complex of Kir6.2, a member of the inwardly rectifying potassium channel superfamily, and the sulfonylurea receptor. We have isolated cDNA clones encoding rat Kir6.2. Co-expression of rat Kir6.2 and sulfonylurea receptor in human embryonic kidney cells generated a potassium current with the properties of the beta-cell ATP-sensitive potassium channel. A quantitative reverse transcriptase-polymerase chain reaction assay indicated that Kir6.2 and sulfonylurea receptor mRNAs were abundantly expressed in rat islets and that expression of Kir6.2 mRNA was reduced by >70% in islets from Zucker diabetic fatty male rats, whereas there was no significant change in sulfonylurea receptor mRNA levels. Thus, decreased expression of Kir6.2 could contribute to the beta-cell dysfunction which characterizes diabetes mellitus in this animal model.

The high-affinity binding of Clostridium botulinum type B neurotoxin to synaptotagmin II associated with gangliosides GT1b/GD1a

125I-labeled botulinum type B neurotoxin was shown to bind specifically to recombinant rat synaptotagmins I and II. Binding required reconstitution of the recombinant proteins with gangliosides GT1b/GD1a. Scatchard plot analyses revealed a single class of binding site with dissociation constants of 0.23 and 2.3 nM for synaptotagmin II and synaptotagmin I, respectively, values very similar to those of the high- (0.4 nM) and low-affinity (4.1 nM) binding sites in synaptosomes. The high-affinity binding of neurotoxin to synaptosomes was specifically inhibited by a monoclonal antibody recognizing with the amino-terminal region of synaptotagmin II. These results suggest that this region of synaptotagmin II participates in the formation of the high-affinity toxin binding site by associating with specific gangliosides.

Differential effects of overexpressed glucokinase and hexokinase I in isolated islets. Evidence for functional segregation of the high and low Km enzymes

Glucose-stimulated insulin secretion is believed to require metabolism of the sugar via a high Km pathway in which glucokinase (hexokinase IV) is rate-limiting. In this study, we have used recombinant adenoviruses to overexpress the liver and islet isoforms of glucokinase as well as low Km hexokinase I in isolated rat islets of Langerhans. Glucose phosphorylating activity increased by up to 20-fold in extracts from islets treated with adenoviruses containing the cDNAs encoding either tissue isoform of glucokinase, but such cells exhibited no increase in 2- or 5-[3H]glucose usage, lactate production, glycogen content, or glucose oxidation. Furthermore, glucokinase overexpression enhanced insulin secretion in response to stimulatory glucose or glucose plus arginine by only 36-53% relative to control islets. In contrast to the minimal effects of overexpressed glucokinases, overexpression of hexokinase I caused a 2.5-4-fold enhancement in all metabolic parameters except glycogen content when measured at a basal glucose concentration (3 mM). Based on measurement of glucose phosphorylation in intact cells, overexpressed glucokinase is clearly active in a non-islet cell line (CV-1) but not within islet cells. That this result cannot be ascribed to the levels of glucokinase regulatory protein in islets is shown by direct measurement of its activity and mRNA. These data provide evidence for functional partitioning of glucokinase and hexokinase and suggest that overexpressed glucokinase must interact with factors found in limiting concentration in the islet cell in order to become activated and engage in productive metabolic signaling.

NIDDM is associated with loss of pancreatic beta-cell L-type Ca2+ channel activity

Development of non-insulin-dependent diabetes mellitus (NIDDM) is associated with defects in glucose-stimulated insulin secretion. We have investigated Zucker diabetic fatty rats (ZDF), an animal model of NIDDM, and found that, compared with control islets, the expression of mRNA encoding C- and D-isoforms of alpha 1-subunits of beta-cell L-type voltage-dependent Ca2+ channels (VDCC) was significantly reduced in islets isolated from ZDF rats. This correlated with a substantial reduction of L-type Ca2+ currents (ICa) in ZDF beta-cells. Intracellular Ca2+ concentration responses in ZDF islets after glucose, KCI, or BAY K 8644 stimulation were markedly attenuated, whereas responses evoked by carbachol were unimpaired, consistent with a specific decrease in ICa in the diabetic islets. This reduction was accompanied by loss of pulsatile insulin secretion from ZDF islets treated with oscillatory increases of external glucose concentration. Our findings suggest that the attenuation of ICa in diabetic islets may contribute to the abnormal glucose-dependent insulin secretory responses associated with NIDDM and indicate that this defect is caused by decreased expression of genes encoding beta-cell VDCC alpha 1-subunits.

Evolution of beta-cell dysfunction in the male Zucker diabetic fatty rat

The molecular basis for the beta-cell dysfunction that characterizes non-insulin-dependent diabetes mellitus (NIDDM) is unknown. The Zucker diabetic fatty (ZDF) male rat is a rodent model of NIDDM with a predictable progression from the prediabetic to the diabetic state. We are using this model to study beta-cell function during the development of diabetes with the goal of identifying genes that play a key role in regulating insulin secretion and, thus, may be potential targets for therapeutic intervention aimed at preserving or improving beta-cell function. As a first step, we have characterized morphology, insulin secretion, and pattern of gene expression in islets from prediabetic and diabetic ZDF rats. The development of diabetes was associated with changes in islet morphology, and the islets of diabetic animals were markedly hypertrophic with multiple irregular projections into the surrounding exocrine pancreas. In addition, there were multiple defects in the normal pattern of insulin secretion. The islets of prediabetic ZDF rats secreted significantly more insulin at each glucose concentration tested and showed a leftward shift in the dose-response curve relating glucose concentration and insulin secretion. Islets of prediabetic animals also demonstrated defects in the normal oscillatory pattern of insulin secretion, indicating the presence of impairment of the normal feedback control between glucose and insulin secretion. The islets from diabetic animals showed further impairment in the ability to respond to a glucose stimulus. Changes in gene expression were also evident in islets from prediabetic and diabetic ZDF rats compared with age-matched control animals. In prediabetic animals, there was no change in insulin mRNA levels. However, there was a significant 30-70% reduction in the levels of a large number of other islet mRNAs including glucokinase, mitochondrial glycerol-3-phosphate dehydrogenase, voltage-dependent Ca2+ and K+ channels, Ca(2+)-ATPase, and transcription factor Islet-1 mRNAs. In addition, there was a 40-50% increase in the levels of glucose-6-phosphatase and 12-lipoxygenase mRNAs. There were further changes in gene expression in the islets from diabetic ZDF rats, including a decrease in insulin mRNA levels that was associated with reduced islet insulin levels. Our results indicate that multiple defects in beta-cell function can be detected in islets of prediabetic animals well before the development of hyperglycemia and suggest that changes in the normal pattern of gene expression contribute to the development of beta-cell dysfunction.

Endogenous cytokine expression profiles in retinoic acid-induced IgA production by LPS-stimulated murine splenocytes

All-trans-retinoic acid (RA) enhances IgA production by LPS-stimulated murine splenocytes. After stimulation by RA and LPS, or by LPS alone, total RNA was extracted from cultured cells on Days 1 to 4, and the kinetics of expression of various cytokine mRNAs were analyzed by the RT-PCR method. RA induced the expression of IL-5 and TGF-beta 2 mRNAs in the LPS-stimulated cells. In addition, the expression of IL-6 and IL-2 mRNAs was more intensive in RA-stimulated cells than in unstimulated cells. TGF-beta 1 and TGF-beta 3 mRNAs were constitutively expressed in both culture groups. RA enhanced IgA production by LPS-stimulated spleen cells but not that by LPS-stimulated mu(+) naive splenic B-cells. For RA-induced IgA production, the B-cells required T-cells or the culture supernatant from RA-stimulated T-cells. Furthermore, exogenous IL-5 replaced the T-cell requirement, at least in part, in RA-induced IgA production by LPS-stimulated B-cells. This reaction was partially inhibited by anti-TGF-beta-neutralizing antibodies. These findings suggest that RA induces IgA production by (IL-5 + LPS)-stimulated B-cells in TGF-beta-independent and TGF-beta-dependent manners.

Magnesium supplementation reduces development of diabetes in a rat model of spontaneous NIDDM

We examined the effects of a magnesium-supplemented (Mg-S) diet in the male obese Zucker diabetic fatty rat, a model of non-insulin-dependent diabetes mellitus (NIDDM). Obese rats were maintained on either a control (0.20% Mg) or magnesium-supplemented (Mg-S; 1% Mg) diet for 6 wk beginning at 6 wk of age. The rats maintained on the Mg-S diet had markedly lower fasting and fed-state blood glucose concentrations and an improved glucose disposal. By 12 wk of age, all of the eight animals on the control diet became diabetic, whereas diabetes developed in only one of eight animals on the Mg-S diet. Insulin and C-peptide concentrations, in addition to pancreatic GLUT-2 and insulin mRNA expression, were higher in the male obese Mg-S rats than in their control-fed counterparts. A subgroup of rats on the control diet with established diabetes was switched to a Mg-S diet for an additional 4 wk. The Mg-S diet did not reverse diabetes once already established. These data indicate that an increased dietary Mg intake in male obese rats prevents deterioration of glucose tolerance, thus delaying the development of spontaneous NIDDM.

A long-term follow-up study in direct cerebral aneurysm surgery

A long-term follow-up study covering between one and twenty-two years after surgery was carried out on 177 patients with direct operations for cerebral aneurysms. Rebleeding was detected in five out of 18 patients with incomplete operations; one patient within 6 months and four patients within 5 to 8 years after surgery. The rebleeding rate of incompletely operated patients in the first decade was similar to that of untreated patients with ruptured aneurysms. This suggests that wrapping, coating and incomplete clipping procedures provide some protection against rebleeding in the first 6 months but little in the period extending beyond 5 years after surgery. Showing two types of newly-formed aneurysms after complete surgery and enlarged residual aneurysms after incomplete surgery, the possibility of rebleeding from these aneurysms is discussed in the present report.

Cloning of rat KATP-2 channel and decreased expression in pancreatic islets of male Zucker diabetic fatty rats

ATP-regulated potassium channels play a key role in regulating insulin secretion. We have isolated cDNA clones from a RINm5F insulinoma cell cDNA library that encode a protein, KATP-2, whose sequence shows 72% identity with the rat heart potassium channel KATP. RNA blotting showed that KATP-2 mRNA was present at high levels in brain and undetectable in heart, spleen, lung, liver, skeletal muscle, kidney and testis. A quantitative RT-PCR assay indicated that there were 1.85 +/- 0.32 x 10(5) molecules of KATP-2 mRNA per microgram of total RNA in pancreatic islets from nondiabetic rats. The levels of KATP-2 mRNA were reduced by 34% in islets from diabetic Zucker diabetic fatty male rats, a model of non-insulin dependent diabetes mellitus, compared to their lean nondiabetic littermates (p < 0.05), suggesting that decreased expression of KATP-2 may contribute to beta-cell dysfunction in this animal model.

Cloning of rat and mouse P2Y purinoceptors

The cellular responses to ATP are mediated by specific high-affinity receptors designated as P2 purinoceptors, five subclasses of which have been defined pharmacologically-P2X, P2Y, P2U, P2T, and P2Z. A cDNA clone encoding a rat P2Y purinoceptor was isolated from an insulinoma cDNA library. The 373-amino acid rat P2Y purinoceptor sequence has 85.7% and 37.8% identity with chicken P2Y and rat P2U purinoceptors, respectively. The sequence of the mouse P2Y purinoceptor was also determined and there was 97.1% amino acid identity with the corresponding rat sequence. RNA blotting studies showed that rat P2Y purinoceptor mRNA was expressed at variable levels in many tissues including heart, brain, spleen, lung, liver, skeletal muscle and kidney, although it was not detected in testis. The cloned rat P2Y purinoceptor was expressed in Xenopus laevis oocytes and possessed the properties expected for this receptor subtype.

Retinoids inhibit IL-4-dependent IgE and IgG1 production by LPS-stimulated murine splenic B cells

The effects of retinoids (all-trans-retinoic acid (RA) and vitamin A) and hydrocortisone (HC) on the IL-4-dependent IgE and IgG1 response by mouse whole spleen cells and splenic B cells were studied. Whole spleen cells were cultured for 8 days in the presence of LPS and IL-4 and the supernatants were assayed for IgG1 and IgE. The levels of the two classes were enhanced about twofold by the addition of HC at 10 nM. The addition of retinoids to the above culture system within 1 day from the start strongly inhibited both IgG1 and IgE responses. The concentration inhibiting both of the reactions by 50% was about 3-10 nM for RA and 300 nM-1 microM for vitamin A. In the case of splenic B cells, HC also showed an enhancing effect on the IgG1 and IgE production at extremely low concentrations (20 pM-2 nM), but at higher concentrations (above 10 nM) it was inhibitory. IL-4-dependent IgG1 and IgE production of LPS-stimulated splenic B cells was also inhibited by retinoids. The concentration giving 50% inhibition was 0.2 nM for RA and 150 nM for vitamin A. Exogenous TGF-beta 1 also inhibited the IL-4-dependent IgG1 and IgE production by splenic B cells and the inhibition was reverted in the presence of the specific neutralizing antibody to TGF-beta 1. However, the inhibition by 1 nM RA could not be abolished by the excess antibodies to TGF-beta 1 and TGF-beta 2.

Formation of islet amyloid fibrils in beta-secretory granules of transgenic mice expressing human islet amyloid polypeptide/amylin

To investigate the relationship between human islet amyloid polypeptide (IAPP)/amylin expression and islet amyloid deposits in the pathogenesis of human non-insulin-dependent diabetes mellitus (NIDDM), we developed transgenic mice using a human IAPP cDNA connected to an insulin promoter. Ribonucleic acid blotting and immunohistochemistry revealed the expression of the transgene in the pancreatic beta cells. Immunogold electron microscopy showed that beta-secretory granules contained the human C-terminal flanking peptide of the IAPP precursor. Reverse-phase HPLC demonstrated human and mouse IAPP amide in the pancreas. Electron microscopy showed the accumulation of fibril-like material in a considerable number of beta-secretory granules. These results suggest that in transgenic mice, the human IAPP precursor is expressed in beta cells and becomes normally sorted into beta-secretory granules in which normal conversion to mature human IAPP takes place. The human IAPP molecules, because of their amyloidogenesis, aggregate into amyloid fibrils in secretory granules. Glucose tolerance was normal at 7 months old and islet amyloid was not observed. A longer time may be required for islet amyloid deposits and hyperglycemia to develop in mice. Our working hypothesis is that in human NIDDM, IAPP aggregates into amyloid fibrils in beta-secretory granules, and that the fibrils are released into the extracellular space and islet amyloid deposits become substantial with time.

Modulation of ATP-sensitive K+ channels by internal acidification in insulin-secreting cells

The effect of intracellular acidification (low pHi) on open probability of the ATP-sensitive K+ (KATP) channel was examined in insulin-secretion cells using an inside-out configuration of the patch-clamp technique. In an insulin-secreting cell line beta-TC3, KATP single-channel currents (IKATP) were readily recorded in the absence of internal ATP. ATP (50 microM and 0.5 mM) dramatically decreased the channel activity. A step decrease of intracellular pH (pHi) from 7.4 to 6.7 or 6.3 in the presence of ATP gradually increased the channel activity. In addition, low pHi in the presence of ATP could partially restore channel activity lost in a process called "rundown." Kinetic analysis revealed a change in channel gating at low pHi with ATP. The bursting durations of IKATP at pHi 6.3 in the presence of ATP were significantly longer than those at pHi 7.4 in the absence of ATP. These results suggest that the increased channel activity at low pHi might have resulted from a mechanism involving an alteration of channel conformation. We also observed an inhibitory effect of low pHi on channel activity. However, the inhibitory effect was much more apparent at pHi 5.7 and was only partially reversible. The activation effect of low pHi on IKATP in the presence of ATP was also observed in acutely isolated rat islet cells and in another insulin-secretion cell line RINm5F, although the effect was weaker and was variable among experiments. We conclude that, as in frog skeletal muscle and cardiac muscle, an increase in channel activity at low pHi is one of the mechanisms underlying proton modulation of IKATP in insulin-secreting cells.

Retinoic acid and steroid hormones regulate IgA production by LPS-stimulated murine spleen cells

We examined the regulatory effects of steroid hormones (beta-estradiol and glucocorticoids) on in vitro IgA production. Addition of retinoic acid (RA, 100-500 nM) to the LPS-stimulated spleen cell culture enhanced IgA production (8-22-fold). Simultaneous addition of beta-estradiol, but not testosterone, enhanced the effect of RA synergistically (a further 2-4-fold). In contrast, glucocorticoids inhibited the reaction. The concentration inhibiting IgA production by 50% was 1 nM, 6 nM and 10 nM for dexamethasone, prednisolone and hydrocortisone, respectively. None of the hormones tested alone affected IgA production by LPS-stimulated spleen cells. Hydrocortisone enhanced the IgG1 production by LPS-stimulated spleen cells. This effect was completely abolished by simultaneous addition of RA. These findings indicate that RA can direct the class-switching to IgA in LPS-stimulated spleen cells, and that beta-estradiol and glucocorticoids have positive and negative regulatory effects, respectively, on the IgA production.