Effects of growth hormone on cognitive function

Whether growth hormone deficiency (GHD) and/or treatment in childhood and adolescence influences cognitive outcome in children with GHD or girls with Turner syndrome (TS) is controversial. Previous studies also suggest that quality of life (QoL) is reduced in adults with GHD, particularly in the areas of social isolation and fatigue. Baseline QoL scores were significantly lower in patients with GHD than in the general population of the same age, gender, and nationality. Unfortunately, few data are available describing QoL in children with GHD. TS is a genetic disorder characterized by short stature, gonadal dysgenesis, and a particular neurocognitive profile of normally developed language abilities (particularly verbal intelligence quotients) and impaired visual-spatial and/or visual-perceptual abilities. This study evaluated the effects of GH treatment on neurocognitive function in girls with TS who were enrolled in a long-term, double-blind, placebo-controlled trial of the effects of GH treatment on final adult height. Treatment duration ranged from 1 to 7 years. The major result of this study was the absence of GH treatment effects on cognitive function in girls with TS. GHD and/or treatment in childhood and adulthood influences cognitive and/or QoL outcomes in some but not all studies. This study did not support a role for GH in influencing the characteristic nonverbal neurocognitive deficits associated with TS. However, evaluation of QoL should be a part of the routine clinical management of patients with GHD or TS.     

hnRNP A2, a potential ssDNA/RNA molecular adapter at the telomere

The heterogeneous nuclear ribonucleoprotein (hnRNP) A2 is a multi-tasking protein that acts in the cytoplasm and nucleus. We have explored the possibility that this protein is associated with telomeres and participates in their maintenance. Rat brain hnRNP A2 was shown to have two nucleic acid binding sites. In the presence of heparin one site binds single-stranded oligodeoxyribonucleotides irrespective of sequence but not the corresponding oligoribonucleotides. Both the hnRNP A2-binding cis-acting element for the cytoplasmic RNA trafficking element, A2RE, and the ssDNA telomere repeat match a consensus sequence for binding to a second sequence-specific site identified by mutational analysis. hnRNP A2 protected the telomeric repeat sequence, but not the complementary sequence, against DNase digestion: the glycine-rich domain was found to be necessary, but not sufficient, for protection. The N-terminal RRM (RNA recognition motif) and tandem RRMs of hnRNP A2 also bind the single-stranded, template-containing segment of telomerase RNA. hnRNP A2 colocalizes with telomeric chromatin in the subset of PML bodies that are a hallmark of ALT cells, reinforcing the evidence for hnRNPs having a role in telomere maintenance. Our results support a model in which hnRNP A2 acts as a molecular adapter between single-stranded telomeric repeats, or telomerase RNA, and another segment of ssDNA.     

Vertebrate DNA damage tolerance requires the C-terminus but not BRCT or transferase domains of REV1

REV1 is central to the DNA damage response of eukaryotes through an as yet poorly understood role in translesion synthesis. REV1 is a member of the Y-type DNA polymerase family and is capable of in vitro deoxycytidyl transferase activity opposite a range of damaged bases. However, non-catalytic roles for REV1 have been suggested by the Saccharomyces cerevisiae rev1-1 mutant, which carries a point mutation in the N-terminal BRCT domain, and the recently demonstrated ability of the mammalian protein to interact with each of the other translesion polymerases via its extreme C-terminus. Here, we show that a region adjacent to this polymerase interacting domain mediates an interaction with PCNA. These C-terminal domains of REV1 are necessary, although not sufficient, for effective tolerance of DNA damage in the avian cell line DT40, while the BRCT domain and transferase activity are not directly required. Together these data provide strong support for REV1 playing an important non-catalytic role in coordinating translesion synthesis. Further, unlike in budding yeast, rad18 is not epistatic to rev1 for DNA damage tolerance suggesting that REV1 and RAD18 play largely independent roles in the control of vertebrate translesion synthesis.     

Thermoregulatory responses to lipopolysaccharide in the mouse: dependence on the dose and ambient temperature

Most published studies of thermoregulatory responses of mice to LPS involved a stressful injection of LPS, were run at a poorly controlled and often subneutral ambient temperature (T(a)), and paid little attention to the dependence of the response on the LPS dose. These pitfalls have been overcome in the present study. Male C57BL/6 mice implanted with jugular vein catheters were kept in an environmental chamber at a tightly controlled T(a). The relationship between the T(a)s used and the thermoneutral zone of the mice was verified by measuring tail skin temperature, either by infrared thermography or thermocouple thermometry. Escherichia coli LPS in a wide dose range (10(0)-10(4) microg/kg) was administered through an extension of the jugular catheter from outside the chamber. The responses observed were dose dependent. At a neutral T(a), low (just suprathreshold) doses of LPS (10(0)-10(1) microg/kg) caused a monophasic fever. To a slightly higher dose (10(1.5) microg/kg), the mice responded with a biphasic fever. To even higher doses (10(1.75)-10(4) microg/kg), they responded with a polyphasic fever, of which three distinct phases were identified. The dose dependence and dynamics of LPS fever in the mouse appeared to be remarkably similar to those seen in the rat. However, the thermoregulatory response of mice to LPS in a subthermoneutral environment is remarkably different from that of rats. Although very high doses of LPS (10(4) microg/kg) did cause a late (latency, approximately 3 h) hypothermic response in mice, the typical early (latency, 10-30 min) hypothermic response seen in rats did not occur. The present investigation identifies experimental conditions to study LPS-induced mono-, bi-, and polyphasic fevers and late hypothermia in mice and provides detailed characteristics of these responses.     

Modeling a hydropic recipient twin in twin-twin transfusion syndrome

We developed a mathematical model of twin-twin transfusion syndrome (TTTS) that includes a hydropic recipient twin, adding interstitial and intracellular fluid compartments, fetal congestive cardiac failure, and the dynamics of renin-angiotensin system (RAS) mediators to our previous TTTS model. Ten differential equations for each twin, coupled by the net fetofetal transfusion of blood and blood components, i.e., colloids, osmoles, and RAS mediators, describe the development of fetal arterial and venous blood volumes, blood osmolality and colloid osmotic pressure (COP), interstitial fluid volume and COP, intracellular fluid volume, amniotic fluid volume and osmolality, and RAS mediator concentration. We included varying placental anastomoses, placental sharing, and amnionicity. The 20 differential equations were solved numerically from 0 to 40 wk with a 0.6-s time step. Consistent with clinical experience, model predictions are as follows. Unidirectional arteriovenous anastomoses and arteriovenous anastomoses inadequately compensated by oppositely directed anastomoses cause severe TTTS that includes a hydropic recipient. Adequately compensated arteriovenous anastomoses simulated TTTS without hydrops. The probability that oppositely directed anastomoses prevent onset of a hydropic recipient after TTTS onset, i.e., the largest interval between onset of TTTS and onset of hydrops in the recipient, was best for a venovenous anastomosis, closely followed by an arterioarterial and finally an oppositely directed arteriovenous anastomosis. Hydropic recipients have decreased amniotic fluid volume. Unequal placental sharing and amnionicity modify hydrops onset. In conclusion, our model simulates a sequence of events that results in a hydropic recipient twin in severe TTTS. The model may allow an assessment of the efficacy of current therapeutic interventions for TTTS cases that include a hydropic recipient twin.     

Protective effect of prenatal water restriction on offspring cardiovascular homeostasis in response to hemorrhage

We determined the cardiovascular and AVP responses of prenatally dehydrated (PreDehy) neonates to intravascular hemorrhage. Ewes with singleton fetuses were subjected to water restriction from 110 days of gestation to full term to achieve hypernatremia of 8-10 meq/l. Water and food were provided ad libitum to control ewes. After delivery, water and food were provided ad libitum to ewes from both groups, and newborns were allowed to nurse ad libitum. At 15 +/- 2 days of age, PreDehy and control lambs were prepared with bladder and femoral catheters and studied at 25 +/- 2 days of age. After a 2-h basal period, lambs were hemorrhaged to 30% of blood volume over 1 h (0.5% of blood volume/min) and monitored 1 h after hemorrhage. Neonatal arterial blood pressure was measured, and blood samples were collected. Basal plasma sodium levels, plasma osmolality, hematocrit, and mean arterial pressure were increased in PreDehy lambs compared with controls. Both groups had similar basal AVP levels and heart rate. In response to hemorrhage, all parameters remained significantly elevated in PreDehy lambs. Blood pressure decreased less in PreDehy lambs than in controls. The hemorrhage-AVP threshold (percent blood volume withdrawal at which plasma AVP values significantly increased) was markedly elevated (20 vs. 15%) and peak hemorrhage-induced AVP plasma levels were lower (5.6 +/- 1.5 vs. 10.1 +/- 1.5 pg/ml, P < 0.01) in PreDehy lambs than in controls. Thus offspring of dehydrated ewes demonstrate enhanced AVP secretory responses to hypotension. Despite potential long-term adverse effects of systemic hypertension, these results suggest a protective effect of prenatal water restriction on offspring cardiovascular homeostasis during blood volume reduction.     

Effect of branched-chain fatty acid on lipid dynamics in mice lacking liver fatty acid binding protein gene

Although a role for liver fatty acid protein (L-FABP) in the metabolism of branched-chain fatty acids has been suggested based on data obtained with cultured cells, the physiological significance of this observation remains to be demonstrated. To address this issue, the lipid phenotype and metabolism of phytanic acid, a branched-chain fatty acid, were determined in L-FABP gene-ablated mice fed a diet with and without 1% phytol (a metabolic precursor to phytanic acid). In response to dietary phytol, L-FABP gene ablation exhibited a gender-dependent lipid phenotype. Livers of phytol-fed female L-FABP–/– mice had significantly more fatty lipid droplets than male L-FABP–/– mice, whereas in phytol-fed wild-type L-FABP+/+ mice differences between males and females were not significant. Thus L-FABP gene ablation exacerbated the accumulation of lipid droplets in phytol-fed female, but not male, mice. These results were reflected in the lipid profile, where hepatic levels of triacylglycerides in phytol-fed female L-FABP–/– mice were significantly higher than in male L-FABP–/– mice. Furthermore, livers of phytol-fed female L-FABP–/– mice exhibited more necrosis than their male counterparts, consistent with the accumulation of higher levels of phytol metabolites (phytanic acid, pristanic acid) in liver and serum, in addition to increased hepatic levels of sterol carrier protein (SCP)-x, the only known peroxisomal enzyme specifically required for branched-chain fatty acid oxidation. In summary, L-FABP gene ablation exerted a significant role, especially in female mice, in branched-chain fatty acid metabolism. These effects were only partially compensated by concomitant upregulation of SCP-x in response to L-FABP gene ablation and dietary phytol. gene targeting; phytanic acid     

Suppression of glial glutamine release to the extracellular fluid studied in vivo by NMR and microdialysis in hyperammonemic rat brain

Release of glial glutamine (GLN) to the extracellular fluid (ECF), mainly mediated by the bidirectional system N transporter SN1, was studied in vivo in hyperammonemic rat brain, using (15)N-nuclear magnetic resonance (NMR) to monitor intracellular [5-(15)N]GLN and microdialysis/gradient (1)H-(15)N heteronuclear single-quantum correlation NMR to analyse extracellular [5-(15)N]GLN. GLN(ECF) was elevated to 2.4 +/- 0.2 mm after 4.5 h of intravenous ammonium acetate infusion. The [GLN(i)]/[GLN(ECF)] ratio (i = intracellular) was 9.6 +/- 0.9, compared with 17-20 in normal brain. GLN(ECF) then decreased substantially at t = 4.9 +/- 0.1 h. Comparison of the time-courses of intra- and extra-cellular [5-(15)N]GLN strongly suggested that the observed decrease reflects partial suppression of glial GLN release to ECF. Suppression also followed elevation of GLN(ECF) to 1.9 mM, resulting in a [GLN](i)/[GLN(ECF)] ratio of 8.4, upon perfusion of alpha-(methylamino)isobutyrate which inhibits neuronal uptake of GLN(ECF) mediated by sodium-coupled amino acid transporter (SAT). The results provide first evidence for bidirectional operation of SN1 in vivo, and clarify the effect of transmembrane GLN gradient on glial GLN release at physiological Na(+) gradient. Implications of the results for SN1 as an additional regulatory site in the glutamine/glutamate cycle and utility of this approach for examining the role of GLN in an experimental model of fulminant hepatic failure are discussed.