Amino acid limitation negatively regulates insulin-like growth factor-II mRNA levels and E-domain peptide secretion at a post-transcriptional step in BRL-3A rat liver cells

Brain Signaling of Indispensable Amino Acid Deficiency

Our health requires continual protein synthesis for maintaining and repairing tissues. For protein synthesis to function, all the essential (indispensable) amino acids (IAAs) must be available in the diet, along with those AAs that the cells can synthesize (the dispensable amino acids). Here we review studies that have shown the location of the detector for IAA deficiency in the brain, specifically for recognition of IAA deficient diets (IAAD diets) in the anterior piriform cortex (APC), with subsequent responses in downstream brain areas. The APC is highly excitable, which makes is uniquely suited to serve as an alarm for reductions in IAAs. With a balanced diet, these neurons are kept from over-excitation by GABAergic inhibitory neurons. Because several transporters and receptors on the GABAergic neurons have rapid turnover times, they rely on intact protein synthesis to function. When an IAA is missing, its unique tRNA cannot be charged. This activates the enzyme General Control Nonderepressible 2 (GCN2) that is important in the initiation phase of protein synthesis. Without the inhibitory control supplied by GABAergic neurons, excitation in the circuitry is free to signal an urgent alarm. Studies in rodents have shown rapid recognition of IAA deficiency by quick rejection of the IAAD diet.

An Endeavor to Find Starter Feed Alternatives and Techniques for Zebrafish First-Feeding Larvae: The Effects on Viability, Morphometric Traits, Digestive Enzymes, and Expression of Growth-Related Genes

Low and variable growth and survival rates (SR) of 6-10 days postfertilization zebrafish larvae are a problem. This problem seems to be linked to starter feed characteristics. This study is an attempt to find alternatives to address these requests. For this, larvae were fed fresh and lyophilized microalgae (Chlorella, Scenedesmus, and Haematococcus), egg yolk (YOLK), lyophilized Artemia nauplii (LAN), and a combination of them. The lowest SR was observed in algae-fed larvae. All died on day 11 showing an emaciated appearance, similar to starved larvae. The highest SR was observed in YOLK- and LAN-fed larvae, which also showed an elongated anterior part of the body. Negative correlations of SR with vegfaa (vascular endothelial growth factor) and morphometric traits with igf2a (insulin-like growth factor) were also found and supported by changes at the molecular level. The presence of algae in the digestive tract of the larvae and the observation of fecal droppings indicate that the algae have an appropriate size and are palatable. The increase in the digestive enzyme activity shows the larval effort to digest the algae. The fact that the algae-fed larvae died even before the larvae were kept in starvation indicates the dramatic amount of energy that the larvae spent in microalgae digestion. Although both YOLK- and LAN-fed larvae had the highest SR, LAN group started to feed on Artemia nauplii sooner. This can be linked to the delayed growth in YOLK-fed larvae and an accelerated growth in the case of LAN-fed group. LAN is an expensive feed with negative effects on water quality, whereas YOLK is a cheap and nutritionally balanced feed with fine granular texture that contributes to a larval SR similar to LAN without affecting water quality. In conclusion, microalgae cannot be considered a suitable starter food for zebrafish, whereas LAN and YOLK can be considered good starter feeds.

Imprinted gene expression in the rat embryo-fetal axis is altered in response to periconceptional maternal low protein diet

In our previous study, we have shown that maternal low protein diet (LPD, 9% casein vs 18% casein control) fed exclusively during the rat preimplantation period (0-4.25 day postcoitum) induced low birth weight, altered postnatal growth and hypertension in a gender-specific manner. In this study, we investigated the effect of maternal LPD restricted only to the preimplantation period (switched diet) or provided throughout gestation on fetal growth and imprinted gene expression in blastocyst and fetal stages of development. Male, but not female, blastocysts collected from LPD dams displayed a significant reduction (30%) in H19 mRNA level. A significant reduction in H19 (9.4%) and Igf2 (10.9%) mRNA was also observed in male, but not in female, fetal liver at day 20 postcoitum in response to maternal LPD restricted to the preimplantation period. No effect on the blastocyst expression of Igf2R was observed in relation to maternal diet. The reduction in H19 mRNA expression did not correlate with an observed alteration in DNA methylation at the H19 differentially methylated region in fetal liver. In contrast, maternal LPD throughout 20 days of gestation did not affect male or female H19 and Igf2 imprinted gene expression in fetal liver. Neither LPD nor switched diet treatments affected H19 and Igf2 imprinted gene expression in day 20 placenta. Our findings demonstrate that one contributor to the alteration in postnatal growth induced by periconceptional maternal LPD may derive from a gender-specific programming of imprinted gene expression originating within the preimplantation embryo itself.

Novel activities of pro-IGF-I E peptides: regulation of morphological differentiation and anchorage-independent growth in human neuroblastoma cells

Insulin-like growth factor-I (IGF-I) is translated as a pre-pro-peptide that is posttranslationally processed to its mature form by proteolytic removal of the signal peptide and the E-domain peptide. Contrary to the mature human (h) IGF-I, the recombinant rtEa4 -peptide significantly reduced the anchorage-independent cell growth in human neuroblastoma cells (SK-N-F1), shown by colony formation assay in vitro. Significant inhibition of colony formation is also observed in SK-N-F1 cells stably transfected with a bicistronic expression construct encoding a secretory form of the rtEa4 peptide. Furthermore, treatment with the recombinant rtEa4 peptide, but not the mature hIGF-I, resulted in morphological differentiation of SK-N-F1 cells characterized by long neurite outgrowth. Similar morphological differentiation is also observed in SK-N-F1 cell clones stably transfected with the rtEa4 peptide expression construct. A spectrum of biological activities similar to those of rtEa4 peptide is also observed in the synthetic hEb peptide, but not-the hEa peptide. Results of further characterization reveal that neurites induced by rtEa4 or hEb peptide contain neuronal-specific MAP-2, Tau, and neurofilament (NF-160), accompanied by an increased expression of the neuronal marker gene neuropeptide tyrosine (NPY). Furthermore, effects of signal transduction inhibitors are indicative of the involvement of MAP-kinase PI-3-kinase cascades. The activation of ERK-1/-2 is markedly increased in response to rtEa-4 or hEb peptide stimulation, further indicating the involvement of MAPK signaling cascade. These unique biological activities exhibited by the rtEa4 or hEb peptide suggest that E peptide of the pro-IGF-I may play distinct roles in regulating cell growth and differentiation in neuroblastoma cells.

Negative and positive regulation of IGF-II mRNA expression in cultured rat cells by chicken serum

We have investigated the possibility that some serum factors might negatively regulate the expression of the insulin-like growth factor-II (IGF-II) gene in 18-54, SF cells. Northern blot analyses indicated that there were three major transcripts (3.8 kb, 1.8 kb, and 1.2 kb) of the IGF-II gene in these cells. We found that incubation of 18-54, SF cells in medium containing very high concentrations (50-100%) of chicken serum greatly inhibited the steady-state level of all three IGF-II mRNA species. In addition, we also found that incubation of 18-54, SF cells in medium containing lower concentrations (10-50%) of chicken serum induced a 3.5 kb IGF-II mRNA. The inhibitory effect of high concentrations of chicken serum on IGF-II mRNA expression was not due to a cytotoxic effect of the serum, because these cells were maintained in 100% chicken serum for up to two weeks without loss of cell viability. The inhibitory effect of chicken serum on IGF-II mRNA was reversible after withdrawal of the serum. Nuclear run-on assays suggested that this negative regulation of IGF-II mRNA in 18-54, SF cells by chicken serum was not the result of transcriptional inhibition. Treatment of 18-54, SF cells that had been previously incubated in 100% chicken serum for 24 h with actinomycin D resulted in a partial restoration of the expression of the 3.8 kb and 1.2 kb IGF-II mRNA in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequestration and secretion of insulin-like growth factor-I by bovine aortic endothelial cells

Endothelial cells elaborate growth promoting activities in culture medium that support limited smooth muscle cell and fibroblast growth in vitro in the absence of serum. We investigated whether insulin-like growth factor-I (IGF-I) was synthesized and secreted by bovine aortic endothelial cells in vitro. Subconfluent endothelial cell cultures in serum-free medium secreted severalfold higher IGF-I levels than confluent cultures by acid-sizing chromatography and IGF-I radioimmunoassay. The IGF-I secretory level was not sustained during a second serum-free incubation. In contrast, secretion of IGF binding proteins persisted and was maintained at constant levels throughout the same observation periods. Analysis of poly(A+)RNA by northern blots revealed hybridization of an IGF-I cDNA to a 7.5- to 7.0-kb transcript and superinduction of the 7.5-7.0-kb mRNA by the translational inhibitor, cyclohexamide. However, no endogenously labeled IGF-I was detected in conditioned media after incubation of cultures with [35S]cysteine or [3H]leucine. When cultures were incubated in the presence of serum supplemented with IGF-I, subconfluent cultures sequestered and released more IGF-I than confluent cultures. We concluded that the majority of IGF-I secreted in vitro was sequestered from serum.

Short- and long-term effects of insulin on tyrosine aminotransferase gene expression

In the present study the relationship between changes in tyrosine aminotransferase (TAT) enzyme activity, cytoplasmic mRNA levels, and gene transcription in response to both short- and long-term exposure to insulin was investigated. Insulin acutely inhibited transcription of the TAT gene by 50% in serum-deprived rat H4 hepatoma cells. Following this initial 50% decrease in transcription, there was a 2.5-fold induction in TAT activity that could not be accounted for by a concomitant increase in TAT mRNA levels. Insulin had no effect on the half-life of TAT mRNA. Insulin exposure for short periods of time also inhibited the glucocorticoid- and cAMP-induced transcription of the TAT gene. Like insulin, protein synthesis inhibitors acutely inhibited basal and glucocorticoid-induced TAT transcription. TAT activity gradually returned toward basal levels after 8 h of insulin treatment. A second insulin-induced increase in TAT activity (3.5-fold above basal levels) was observed by 24 h of insulin treatment. This second phase of insulin-induced TAT activity was associated with elevated levels of TAT transcription and TAT mRNA levels, and therefore, unlike the earlier stimulation, could be accounted for by changes in gene expression. Thus, the insulin-mediated regulation of the TAT gene in H4 cells is complex. Different transcriptional and post-transcriptional mechanisms are likely to be involved in the biphasic responses to insulin.

Regulation of insulin-like-growth-factor-II gene expression in rat liver cells

The rat insulin-like-growth-factor-(IGF)-II gene is expressed at high levels during embryonic and fetal life and at low levels in adult animals. To study the regulation of IGF-II gene expression, we analyzed the synthesis and localization of the IGF-II transcripts in cultured rat liver cells either expressing (BRL3A cells) or not expressing (BRL30E and FAO cells) the IGF-II mRNA. The IGF-II gene is transcribed at a similar rate in expressing and non-expressing cells, whereas its nuclear and cytoplasmic RNA levels are diversely distributed in the cells. IGF-II RNA is more abundant in the cytoplasmic than in the nuclear RNA fraction of BRL3A cells and is present in the nucleus but not in the cytoplasm of the FAO cells. However, both precursor and mature IGF-II nuclear RNA levels are reduced in FAO cells. Our data indicate that the IGF-II gene expression is regulated by mechanisms affecting the subcellular distribution and the abundance of the transcripts.

Effects of streptozotocin-induced diabetes mellitus on growth and hepatic insulin-like growth factor I gene expression in the rat

Poorly controlled diabetes mellitus in humans and animals is often accompanied by impaired growth. We undertook this study in young rats to determine whether the reduction in growth rate associated with streptozotocin (STZ)-induced diabetes might be related to changes in both serum insulin-like growth factor I (IGF-I) and IGF-II levels, and, if so, whether these changes reflect alterations in serum growth hormone (GH) and in hepatic IGF-I and IGF-II gene expression. Serum rat GH (rGH) levels were variable during the first 4 days after STZ administration, but during the subsequent 5- to 11-day period the mean (+/- SEM) levels in insulin-treated (DI) (21.4 +/- 4.9 ng/mL) and untreated (D) (8.5 +/- 1.5 ng/ml) diabetic rats were significantly (P less than .001) lower than in controls (C) (117.8 +/- 22.9 ng/mL). Multiple transcripts of IGF-I (7.0, 4.0, 1.9, 1.0 kb), but barely detectable amounts of IGF-II mRNA, were found in the livers of normal and diabetic rats by Northern blot analysis. Using dot blot analysis, we have shown that the abundance of total hepatic IGF-I mRNA in untreated, growth-retarded diabetic animals decreases rapidly over a period of 3 days after STZ administration. Both serum IGF-I and IGF-II levels are also diminished during this interval in these markedly hyperglycemic rats. Insulin treatment for 3 to 4 days, started either immediately (6 hours) or within 3 days after administering STZ, blunts diabetes-induced impairment of growth and restores mean hepatic IGF-I mRNA abundance to control levels, but does not normalize serum IGF-I and IGF-II concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)