Thyroid hormone increases glyceraldehyde 3-phosphate dehydrogenase gene expression in rat liver

Livers from hypophysectomized rats had low levels of glyceraldehyde 3-phosphate dehydrogenase mRNA. Administration of L-triiodothyronine increased these levels over 20-fold. The peak response was seen 72 h after hormone administration. A half-maximal response was obtained with 5 micrograms of T3 per 100 g of body weight. Thus the expression of hepatic glyceraldehyde 3-phosphate dehydrogenase appears to be regulated by thyroid hormone.     

Lithium administration affects gene expression of thyroid hormone receptors in rat brain.

Even though lithium has received wide attention in the treatment of manic depressive illness, the mechanisms underlying its mood stabilizing effects are not understood. Lithium is known to interact with the thyroid axis and causes hypothyroidism in a subgroup of patients, which compromises its mood stabilizing effects. Since lithium was recently reported to alter thyroid hormone metabolism in the rat brain, the present study investigated whether these effects were mediated through regulation of thyroid hormone receptor (THR) gene expression. Adult male euthyroid rats were either given a diet containing 0.25% lithium or one without lithium for 14 days. Rats were sacrificed in the evening and RNA was isolated from different brain regions to quantitate the isoform specific mRNAs of THRs. Following 14 days of lithium treatment, THR alpha1 mRNA levels were increased in the cortex and decreased in hypothalamus; THR alpha2 mRNA levels were increased in the cortex and THR beta mRNA levels were decreased in the hypothalamus. No significant difference in the expression of these THR isoforms was observed in the hippocampus or cerebellum. Thus, chronic lithium treatment appeared to regulate THR gene expression in a subtype and region specific manner in the rat brain. It remains to be determined whether the observed effects of lithium on THR gene expression are related to its therapeutic efficacy in the treatment of bipolar disorder.     

Thyroid hormone regulates alpha and alpha + isoforms of Na,K-ATPase during development in neonatal rat brain

The brain contains two molecular forms of Na,K-ATPase designated alpha found in non-neuronal cells and neuronal soma and alpha + found in axolemma. Previously we have shown that the abundance of both forms (determined by immunoblots) as well as Na,K-ATPase activity increases 10-fold between 4 days before and 20 days after birth (Schmitt, C. A., and McDonough, A. A. (1986) J. Biol. Chem. 261, 10439-10444). Hypothyroidism in neonates blunts these increases. Neonatal, but not adult brain Na,K-ATPase is thyroid hormone (triiodothyronine, T3) responsive. This study defines the period during which brain Na,K-ATPase responds to T3. The start of the critical period was defined by comparing Na,K-ATPase activity and alpha and alpha + abundance in hypothyroid and euthyroid neonates (birth to 30 days of age). For all parameters, euthyroid was significantly higher by 15 days of age. The end of the critical period was defined by dosing hypothyroid neonates with T3 daily (0.1 micrograms/g body weight) beginning at increasing days of age, and sacrificing all at 30 days then assaying enzyme activity and abundance. Those starting T3 treatment on or before day 19 were restored to euthyroid levels of Na,K-ATPase activity and abundance, while those starting T3 treatment on or after day 22 remained at hypothyroid levels of enzyme activity and abundance. We conclude that brain Na,K-ATPase alpha and alpha + isoforms are sensitive to T3 by as late as 15 days of age and that the period of thyroid hormone responsiveness is over by 22 days.     

Regulation of protein disulfide isomerase gene expression in brain and liver during rat development

A 4-fold increase in protein disulfide isomerase (PDI) mRNA is observed in brain of 10 days-old rats and in liver of 20 days-old foetuses when compared with 20 days-old (brain) and 18 days-old (liver) foetuses respectively. During further postnatal development, the mRNA for PDI decreases in both organs to the initial values present in foetuses and remains practically unchanged in brain till the adult. By contrast in liver by 35-40 days after birth, and coincident with sexual maturation, there is a 2.5-fold increase in PDI mRNA that is maintained by 55 days (adult). These results clearly show that protein disulfide isomerase gene expression is differentially regulated in liver and brain during rat development.     

Differential expression of GABAA receptor alpha-subunits in rat brain during development.

Unique cytoplasmic loop regions of the alpha 1, alpha 2, alpha 3, and alpha 5 subunits of the GABAA receptor have been expressed in E. coli and used to generate polyclonal antisera specific for these subunits. The antibodies identify proteins by SDS-polyacrylamide gel electrophoresis and western blotting of molecular size 51 kDa, 53 kDa, 59 kDa and 55 kDa, respectively, which show differential patterns of expression during development. Whereas the alpha 2 and alpha 3 subunits are present at early stages, the expression of alpha 1 and alpha 3 subunits is low at birth and increases with age. This differential expression could be correlated with previous studies examining the developmental expression of BZ1 and BZ2 benzodiazepine binding sites.     

Thyroid hormone receptors in brain and liver during ageing

The binding properties--binding capacity (MBC) and affinity (Ka)--of T3 nuclear receptors were analyzed in cortex, cerebellum and liver of rats aged 3, 6, 12 and 24 months. A slight but not significant decrease of Ka was observed in different tissues of normal rats. In hypothyroid animals the Ka in cortex at 24 months was significantly lower than at 3 months. During ageing the MBC of brain receptors decreased whereas hepatic receptors were not altered. Hypothyroidism did not further affect the MBC of the receptors. The data indicate that during ageing the T3 nuclear receptors behave differently in brain and liver. The difference in MBC suggests selectivity in organ sensitivity to thyroid hormones.     

Thyroid hormone metabolism and cardiac gene expression after acute myocardial infarction in the rat

In a rat model of acute myocardial infarction (MI) produced by coronary artery ligation, thyroid hormone metabolism was altered with significant reductions (54%) in serum triiodo-L-thyronine (T(3)), the cellular active hormone metabolite. T(3) has profound effects on the heart; therefore, rats were treated with T(3) after acute MI for 2 or 3 wk, at either replacement or elevated doses, to determine whether cardiac function and gene expression could be normalized. Acute MI resulted in a 50% (P < 0.001) decrease in percent ejection fraction (%EF) with a 32-35% increase (P < 0.01) in compensatory left ventricle (LV) hypertrophy. Treatment of the MI animals with either replacement or elevated doses of T(3) significantly increased %EF to 64 and 73% of control, respectively. Expression levels of several T(3)-responsive genes were altered in the hypertrophied LV after MI, including significant decreases in alpha-myosin heavy chain (MHC), sarcoplasmic reticulum calcium-activated ATPase (SERCA2), and Kv1.5 mRNA, whereas beta-MHC and phospholamban (PLB) mRNA were significantly increased. Normalization of serum T(3) did not restore expression of all T(3)-regulated genes, indicating altered T(3) responsiveness in the postinfarcted myocardium. Although beta-MHC and Kv1.5 mRNA content was returned to control levels, alpha-MHC and SERCA2 were unresponsive to T(3) at replacement doses, and only at higher doses of T(3) was alpha-MHC mRNA returned to control values. The present study showed that acute MI in the rat was associated with a fall in serum T(3) levels, LV dysfunction, and altered expression of T(3)-responsive genes and that T(3) treatment significantly improved cardiac function, with normalization of some, but not all, of the changes in gene expression.     

Protein malnutrition up-regulates growth hormone receptor expression in rat splenic B lymphocytes

The reciprocal interaction between the endocrine and immune systems has been the subject of active research during the last decade, and an important body of evidence has accumulated supporting the role of the GH/IGF axis in immune function. More recently, the GH/IGF axis has been postulated as playing an important role in the modulation of stress conditions, such as catabolic stages, aging-related disorders, immunodeficient aids patients and malnutrition. Whether these effects are exerted through endocrine, autocrine or paracrine mechanisms remains to be determined for different immune cell types and tissues. The aim of the current study was to define which specific subsets of lymphocytes are the primary targets for GH action. In addition, the regulatory role of stress induced by protein restriction was investigated with respect to the relative distribution of GH receptor positive lymphoid cells. Normal growing rats were fed isocaloric diets with variable protein content (0, 4, 8, 12 and 20%) for a period of 14 days. The lymphoid cells were then separated from spleen, lymph nodes and peripheral blood lymphocytes. Flow cytometry analysis measured the binding characteristics of Fluos-rrGH to lymphocytes together with specific PE-labelled mAbs defining CD4+ and CD8+ T cells and B lymphocytes. The pattern of expression of the GH receptor differed among the lymphoid tissues and cell subsets. Spleen was the most responsive organ to protein deprivation with highest GH receptor expression in B lymphocytes, followed by CD4+ T cells. As the protein intake was decreased from 20% to 0%, the percentage of GHR positive cells increased from 12% to 52% in splenic B lymphocytes and from 8% to 17% in CD4+ T cells. In contrast, only 10%-13% of lymphocytes in lymph nodes and 2%-4% in circulation, showed binding sites to GH associated with protein deprivation. In conclusion, the increase in GH receptors on lymphocytes under catabolic stress induced by protein malnutrition gives support to the hypothesis of a modulatory role of the GH/IGF axis in preserving the homeostasis of immune tissues.     

Thyroid hormone effect on gene expression of the adenine nucleotide translocase in different rat tissues

The ADP/ATP transport across the mitochondrial membrane is achieved by the adenine nucleotide translocase (ANT), an integral inner mitochondrial membrane protein. As deduced from experiments in rat liver in vivo and in isolated rat liver mitochondria this ADP/ATP transport is accelerated by thyroid hormone application, thus explaining, at least to a considerable extent, the thyroid hormone mediated increase in mitochondrial metabolic activity. The present study investigates the effect of T3 on rat liver, heart, and kidney ANT gene expression. As shown by Northern blot analysis, a cDNA for beef heart ANT-mRNA showed cross-hybridization with the ANT-mRNA from rat heart, liver, and kidney. Hypo- and hyperthyroid rats showed no differences in size nor in amounts of heart, liver, and kidney ANT-mRNA. Measurement of heart ANT-protein level revealed no major differences among the various thyroid states. Thus, the long-term action of thyroid hormones on increasing the carrier-mediated ADP/ATP translocation cannot be ascribed to an effect of T3 on ANT gene expression. The mechanism by which T3 activates this transporter system remains to be identified but some possibilities are suggested.     

Thyroid hormone differentially regulates cellular development in neonatal rat heart and kidney.

The role of thyroid hormone in the control of cardiac and renal cell development was examined in neonatal rats made hyperthyroid by administration of triiodothyronine (T3, 0.1 mg/kg s.c. on postnatal days 1-5) or hypothyroid by administration of propylthiouracil (PTU, 20 mg/kg s.c. given to dams on gestational day 17 through postnatal day 5 and to pups on postnatal days 1-5). Indices of total cell number (total DNA per tissue), cell packing density (DNA per g tissue), and relative cell size (protein/DNA ratio) were evaluated from birth through young adulthood. PTU administration led to primary shortfalls in cell number that were of similar magnitude in both tissues, but persisted somewhat longer in the kidney than in the heart. Deficits in cell packing density and cell size in the hypothyroid animals were secondary to the effect on cell number, displaying smaller magnitudes of effect and a lag in appearance and disappearance of the deficits compared to that for total DNA; indeed, the phase in which tissues were restoring their cell numbers was accompanied by increased cell packing density, reflecting a more rapid restitution of cell numbers than tissue weight or cell size. In contrast to the relatively similar effects of PTU on developing cardiac and renal cells, the effects of T3 were selective for the heart. Although T3 caused general growth impairment, it evoked marked cardiac overgrowth that was accompanied by a striking increase in cell number and a small increase in cell size. The cardiac hyperplasia is unique to the developing animal, as post-replicative heart cells in adult animals show only hypertrophy in response to thyroid hormone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Suboptimal energy balance selectively up-regulates muscle GLUT gene expression but reduces insulin-dependent glucose uptake during postnatal development.

The major facilitative glucose transporters in muscle, GLUT1 (insulin-independent) and GLUT4 (insulin-dependent), are essential for normal growth and metabolism, but factors controlling their expression during postnatal development are poorly understood. We have therefore determined the role of energy status in regulating muscle GLUT gene expression and function in young, growing pigs on a high (H) or low (L) food intake (H =2L) at 35 degrees C or 26 degrees C. RNase protection assays revealed selective up-regulation of GLUT1 and GLUT4 by mild undernutrition 20-24 h after feeding: mRNA levels were elevated in longissimus dorsi (P<0.001) and rhomboideus (P<0.05), but not in diaphragm or cardiac muscles. Assessment of 2-deoxy-glucose uptake in a small isolated muscle, flexor carpi radialis, showed that the 26L group, which had suboptimal energy balance and the greatest GLUT4 expression, had the highest insulin-independent glucose uptake but the lowest insulin-dependent increment: 20% compared with 70% in the other groups. These novel findings are directly relevant to an understanding of mechanisms underlying the development of insulin resistance and demonstrate 1) muscle-specific up-regulation of GLUT gene expression by postnatal undernutrition that is not related simply to myofiber type, but to whole-body function; and 2) that the degree of GLUT up-regulation and the subcellular distribution and function of GLUT proteins are dependent on energy status.     

Tissue-specific and differential expression of prothymosin alpha gene during rat development.

We have analyzed the RNA expression of prothymosin alpha (ProT alpha) gene during rat development in several tissues and compared it to that of two proteins related to cell proliferation: proliferating cell nuclear antigen (PCNA)/cyclin and histone H3 (H3). The expression of ProT alpha gene was found to be regulated in a developmental and tissue-specific manner. The mRNA levels of ProT alpha followed a similar time-course in liver, brain, kidney, and testis, being highly increased in the early periods of postnatal development. However, in thymus ProT alpha mRNA showed only moderate changes throughout development. Our findings suggest that ProT alpha participates in developmental processes like cell proliferation and/or differentiation.