Differential hormonal regulation of L-glycerol 3-phosphate dehydrogenase in rat brain and skeletal muscle

Effect of hibernation, thyroid hormones and dexamethasone on cytosolic and mitochondrial glycerol-3-phosphate dehydrogenase from jerboa (Jaculus orientalis)

Tissue distribution of the cytosolic and mitochondrial glycerol-3-phosphate dehydrogenase (cGPDH and mGPDH) activities in jerboa (Jaculus orientalis), a hibernator, shows the highest level of enzyme activity in skeletal muscle and brown adipose tissue, respectively. The effect of hibernation on cGPDH indicates an increase of activity in all tissues examined. In contrast, hibernation decreases mGPDH activity in all tissues, except skeletal muscle. The effect of thyroid hormones on GPDH activity was tissue specific: in kidneys, cGPDH activity doubled in euthermic jerboas treated with T4. In contrast, 6-n-propyl-2-thiouracil treatment provokes an increase of enzyme activity in brown adipose tissue, liver and brain. T4 treatment leads to a 2.7-fold increase in liver mGPDH activity. 6-n-propyl-2-thiouracil treatment decreases mGPDH activity in the skeletal muscle whereas the opposite effect was observed in brain. Dexamethasone stimulates cGPDH in all tissues examined, except skeletal muscle and kidneys. In the case of mGPDH activity, this increase was observed only for brown adipose tissue and brain. Our results suggest that hibernation, thyroid hormones and dexamethasone probably play a role in the regulation of cGPDH and mGPDH activities in jerboa. Our findings confirm that these enzymes are involved in metabolic adaptation to thermal stress in Jaculus orientalis.

Oligodendrocytes as glucocorticoids target cells: functional analysis of the glycerol phosphate dehydrogenase gene

Previous research has established that the development and function of oligodendrocytes are influenced by glucocorticoids. The enzyme glycerol phosphate dehydrogenase (E.C.1.1.1.8) has been used as a model to study glucocorticoid regulation of gene expression in oligodendrocytes and the C6 glial cell line. In the rat brain this enzyme is exclusively localized to oligodendrocytes. The sequence of the 5' flanking region for the rat gene encoding Glycerol Phosphate Dehydrogenase (GPDH; EC 1.1.1.8) was determined. 4 kb of sequence from the 5' flanking region, exon 1, and part of intron 1 of the rat GPDH gene was compared to the corresponding mouse sequence. Dotplot matrix comparison revealed that the rat sequence is more than 80% similar to the mouse sequence, but differs from the mouse sequence in two regions: the rat sequence is devoid of 200 bp of B1 repeat sequence that is present in the mouse, and the rat sequence has an excess 700 bp of B2 repeat sequence inserted between -0.7 kb and -1. 4 kb that is absent in the mouse. To determine the regulatory activity of the rat GPDH 5' flanking region, various portions of the rat GPDH 5' flanking region were placed in luciferase reporter constructs and tested for transcriptional activity. Transient transfection of reporter constructs into the C6 glial cell line revealed that the distal end of the 5' flanking region was glucocorticoid-inducible. A 385 bp Glucocorticoid Response Unit (GRU) was identified whose glucocorticoid induction was enhanced by dibutyryl-cAMP and reduced by phorbol esters. Sequence analysis of the GRU revealed the presence of four consensus GRE sequences and other putative consensus elements. Results here suggest that the 5' flanking region of the GPDH gene mediates the ligand-inducible regulation of GPDH, and that multiple signaling pathways converge at the 5' regulatory sequence to modulate GPDH gene expression in oligodendrocytes.

Characterization of a glucocorticoid-sensitive hippocampal protein

Increased synthesis of a rat hippocampal protein with an apparent molecular weight (Mr) of 35,000 Da occurs in response to elevation of serum corticosterone levels. Subcellular fractionation has localized this protein in the cytosol. Two-dimensional gel electrophoresis indicated that this protein has an isoelectric point (IEP) of 6.6. A similar protein in liver has a slightly higher Mr and an IEP of 6.8. Increased synthesis of one additional hippocampal protein with an Mr of 46,000 Da and an IEP of 6.2 and of two other liver proteins, one with an Mr of 53,000 Da and an IEP of 6.2 and the other with an Mr of 45,000 Da and a range of IEPs from 8.7 to 7.8, was also seen after injection of corticosterone into rats. One possible identity of the 35,000 Da protein is glycerol 3-phosphate dehydrogenase (GPDH), based upon the reported Mr and IEP of this enzyme. The 35,000 Da hippocampal protein co-eluted from a gel filtration column with GPDH activity. No alteration of hippocampal GPDH activity was seen in intact rats 4 or 24 h after injection of either corticosterone or the type II receptor-specific agonist RU 28362. However, daily administration of corticosterone to rats beginning 10 days after adrenalectomy returned hippocampal GPDH activity to normal values after 2-3 days. In contrast, synthesis of the 35,000 Da protein was maximally increased 4 h after a single injection of steroid and not elevated at later times.

Developmental expression of neural cell type-specific mRNA markers in the myelin-deficient mutant rat brain: inhibition of oligodendrocyte differentiation

We have studied gene expression of neuroglial cell markers in the myelin-deficient (md) rat brain during postnatal development. Northern blots and slot blots of poly(A)+ RNA from developing brain were sequentially probed with cDNAs specific for the oligodendrocyte markers glycerol phosphate dehydrogenase (GPDH), myelin basic protein (MBP), and proteolipid protein (PLP), for the neuronal marker glutamic acid decarboxylase (GAD), and for the astrocyte markers glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS). GPDH mRNA levels were also examined in two peripheral tissues, liver, and skeletal muscle (hindlimb). Despite a lack of CNS myelin in the md mutant, transcripts of all oligodendroglial markers were detectable except the 1.6-kb PLP message. Brain GPDH mRNA levels were initially equivalent in md and unaffected littermates at postnatal day 15 (PI5), but the mutants failed to display the normal developmental increase in gene expression. By P25, GPDH mRNA expression in md rat brain was approximately 20% of control levels. GPDH mRNA expression in peripheral tissues was less affected than in brain and was lower in md mutants only at the later developmental ages. Expressions of GAD, GFAP, and GS mRNAs in developing md rat brain were not altered. The mRNA levels of the two myelin markers, MBP and PLP, were severely impaired in md rat brain during the entire myelinating period and represented less than 10% of control mRNA levels at P25. The most important observation was that the large PLP transcript (3.2 kb) was slightly shorter in size in md rat brain as compared to normals.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoid stimulation of metabolism and glycerol-3-phosphate dehydrogenase activity in cultured heart cells

The direct effects of the glucocorticoids hydrocortisone and corticosterone on myocardial metabolism were studied in cultured heart cells by assessing several parameters previously unreported. Hormone and growth factor concentrations were carefully controlled by using a serum-free medium, which also allowed maintenance of cells in the absence of glucocorticoids. Heart cell beating rate, glucose uptake rate, and CO2 evolution from radioactively labeled glucose were increased by the addition of 0.03 microM corticosterone to the medium of cells maintained in culture for 11 days. There were no further changes in these parameters as steroid concentration was increased to 14.43 microM. The activity of NAD-linked sn-glycerol-3-phosphate dehydrogenase (EC 1.1.1.8) was increased by both corticosteroids and was dose dependent between 0.06 and 1.44 microM corticosterone. The difference between glycerol-3-phosphate dehydrogenase activity in cells maintained with hydrocortisone as compared to cells maintained without hydrocortisone increased with days in culture. The protein and DNA contents of dishes maintained with corticosteroid were depressed, demonstrating an inhibitory effect on cellular replication. Glucocorticoids have numerous direct effects on cardiac cell metabolism, and the nature of these effects suggests that secondary responses of the cell to chronic exposure are significant.

Glycerol phosphate dehydrogenase in developing retina of normal and mutant mice

The specific activity of glycerol phosphate dehydrogenase (GPDH; E.C. 1.1.1.8) was determined in the retinas of C57BL/6J mice from 2 to 45 days after birth. Comparisons were made with age-matched mice congenic to C57BL/6J and homozygous for the autosomal recessive mutations for retinal degeneration (rd) and light ear (le). The total activity of GPDH in the developing retina was similar in each strain throughout development. However, following the loss of photoreceptor cells in the rdle mice, the specific activity of GPDH increased to approximately twice the level of that in the controls. These data suggest that GPDH is absent from the photoreceptor cells and that its expression in the remaining retinal cells is unaffected by the loss of the photoreceptor cells. Retinal GPDH does not exhibit the eight-to ten-fold increase seen during development of the brain, but instead remains essentially constant during this time period, and in adult animals the specific activity of GPDH in the retina is about 20-fold less than it is in the brain. Neither mouse retinal GPDH nor brain GPDH is affected by adrenalectomy, suggesting that they are not regulated by glucocorticoids. The major form of GPDH in the retina is distinct from the major form in mouse brain since immunotitration experiments demonstrated that 70-80% of retinal GPDH does not react with anti-GPDH IgG, whereas the reverse was true for the brain enzyme.

Adrenalectomy of rats results in hypomyelination of the central nervous system

The effect of adrenalectomy on CNS myelin accumulation was investigated to determine whether glucocorticoids play a role in regulating myelination. When 14-day-old rats were adrenalectomized and sacrificed 7-8 days later, the amount of bulk-isolated myelin in whole brain, as expressed per gram wet weight of brain or per milligram DNA-phosphate, was reduced to about 75% that of sham-operated controls. Both brain weight and DNA content were unchanged by adrenalectomy. Examination of individual brain regions also revealed decreased amounts of myelin in adrenalectomized animals. Brain glycerol 3-phosphate dehydrogenase specific activity was reduced in adrenalectomized animals to 40-60% that of controls, and serum corticosterone levels were less than 0.6% of control levels. The amount of cerebral myelin in animals adrenalectomized on day 21 and sacrificed 9 days later was not significantly reduced. This suggests a possible role of glucocorticoids during the early period of rapid myelination.

Unique modification of human heart glycerol 3-phosphate dehydrogenase by blue agarose

The major form of glycerol phosphate dehydrogenase in human heart (GPDH-1) is a minor form (less than 15%) in brain and other tissues and is extremely labile. After GPDH-1 was eluted from an agarose column to which Cibacron blue F3GA had been covalently linked, (a) it was no longer labile (t 1/2 at 40 degrees C changed from 1.6 min to greater than 180 min); (b) it could now be stained for activity on native gels following electro-phoresis; and (c) it now migrated with the bromphenol blue dye front. The results suggest that this stabilized form of GPDH-1 is due to the covalent binding of charged ligands from the column and that this technique may be useful for studying the molecular structure and/or the active site of GPHD-1 and possibly of other enzymes which bind to blue agarose.

Mouse sn-glycerol-3-phosphate dehydrogenase: molecular cloning and genetic mapping of a cDNA sequence

The isozymes of glycerol-3-phosphate dehydrogenase (GPDH; sn-glycerol-3-phosphate:NAD+2-oxidoreductase, EC 1.1.1.8) in tissues of the mouse are coded for by two structural genes, Gdc-1 and Gdc-2, located on chromosomes 15 and 9, respectively. In order to investigate the expression of these genes, we isolated a GPDH cDNA clone from a mRNA preparation isolated from brown adipose tissue. The GPDH cDNA clone was identified by colony hybridization and hybrid selection of a mRNA that was translated in vitro to produce immunoprecipitable GPDH protein. In blot analysis, the GPDH cDNA hybridized to a single mRNA species that migrated at the position of 23S ribosomal RNA. This GPDH cDNA clone was mapped to the Gdc-1 locus by identification of a restriction enzyme polymorphism present in genomic DNA isolated from Gdc-1 congeneic lines of mice.

Glycerol phosphate dehydrogenase in developing chick retina and brain

The development of cytoplasmic glycerol phosphate dehydrogenase (GPDH) activity in chick neural retina is compared with that in brain. GPDH converts dihydroxyacetone phosphate to glycerol 3-phosphate, an intermediate in phospholipid synthesis. The enzyme is known to be under corticosteroid control in rat brain and spinal cord (but not muscle or liver) and in primary oligodendrocyte cultures. It has not been previously studied in the eye. In chick brain the GDPH specific activity rises fivefold from the early embryo to the adult, with nearly all the increase occurring between embryonic day 14 and hatching. This time course correlates well with the known maturation of chick adrenal cortex (which produces corticosteroids). On the other hand, in chick retina the GPDH specific activity remains at a low basal level throughout development. Furthermore, adult rat and beef retinas show much lower enzyme activity than do the corresponding brain tissues. GPDH can be induced precociously by hydrocortisone in embryonic chick brain from days 12 through 16, both in the intact embryo and in tissue culture; however, GPDH is not at all inducible in chick retina. The developmental increase in chick brain GPDH can be correlated qualitatively with myelin formation, as shown by luxol fast blue staining, whereas no myelin is seen in retina at any age. Our results are consistent with recent immunocytochemical studies demonstrating that GPDH in rat brain is associated with myelin-producing oligodendroglial cells, absent in retina. In comparison, another glial enzyme, glutamine synthetase (GS), known to be inducible in both chick brain and retina, is localized in brain astrocytes and retinal Müller cells.

Immunocytochemical localization of glycerol-3-phosphate dehydrogenase in rat oligodendrocytes

In this study, two indirect immunoperoxidase staining procedures were used to investigate the cellular localization of rat brain glycerol-3-phospate dehydrogenase (EC 1.1.1.8;GPDH). At the light and electron microscopic level, we found that the use of monospecific rabbit antibodies to GPDH consistently resulted in the specific staining of only one glial cell population. GPDH-positive cells in perineuronal, interfascicular and perivascular positions were identified as oligodendrocytes by classical morphological criteria. The specificity of GPDH antigen-antibody reaction was determined by qualitative and quantitative immunochemical methods and by imunocytochemical controls for immunologic and methodologic sources of nonspecific reaction product. The illustrative data from this study serve to qualitatively define GPDH as a biochemical marker for oligodendrocytes in rat central nervous tissue. In view of the fact that the synthesis of rat brain GPDH is specifically regulated by glucocorticoids, the positive results obtained in this study further warrant the interpretation that rat oligodendrocytes are target cells for glucocorticoids.