Prominent expression of the selenoprotein thioredoxin reductase in the medullary rays of the rat kidney and thioredoxin reductase mRNA variants differing at the 5' untranslated region.

The mammalian selenoprotein thioredoxin reductase is a central enzyme in protection against oxidative damage or the redox control of cell function. Previously a neuroblastoma-cell-derived 2193 bp cDNA for rat thioredoxin reductase 1 (TrxR1) was characterized [Zhong, Arnér, Ljung, Aslund and Holmgren (1998) J. Biol. Chem. 273, 8581-8591]. Here, the major rat TrxR1 mRNA was determined as 3.5 kb by Northern blotting. A corresponding full-length 3360 bp liver-derived cDNA was cloned and sequenced, being extended in the 3' untranslated region (3' UTR) compared with the previous clone. Among tissues examined, lowest TrxR1 mRNA levels were found in spleen and testis and highest in liver and kidney. High expression in kidney was unexpected and in situ hybridization of adult rat kidney was performed. This revealed a highly structured expression pattern with the mRNA being prominently synthesized in the proximal tubules of the medullary rays. Analysing rat kidney cDNA, a 5' UTR domain of TrxR1 was found that was different from that in liver- or neuroblastoma-derived cDNA clones. The kidney-derived 5' UTR mRNA domain was instead highly similar to kidney-derived cDNA variants of murine apolipoprotein E. By sequence determination of the rat genomic sequence upstream of the open reading frame for TrxR1, an exon was encountered that encoded a third alternative 5' UTR domain that could also be expressed, as confirmed by its presence in a mouse skin TrxR1 cDNA clone. It can therefore be concluded that TrxR1 mRNA is expressed in at least three different variants that differ at their 5' UTRs.

IGF-1 influences olfactory bulb maturation. Evidence from anti-IGF-1 antibody treatment of developing grafts in oculo.

Recent studies have indicated that both insulin-like growth factor-1 (IGF-1) and IGF-1 receptor mRNA are abundant in developing and adult olfactory bulbs, and that IGF-1 receptor mRNA is abundant in the prenatal cerebral cortex. To examine the potential role of IGF-1 in development of a central nervous system region rich in IGF-1 and its receptor (the olfactory bulb), as compared to one in which IGF-1 is less abundant (the cerebral cortex), tissue pieces of these two central nervous system areas from E15-E17 rat fetuses were transplanted into the anterior chamber of the eye of adult host rats. The transplants were treated with either a total of 300 ng truncated IGF-1, two different IGF-1 polyclonal antisera, two different non-immune sera, a total of 15 micrograms IGF binding protein-1, or vehicle alone. Treatments were administered by preincubation just prior to grafting and by 5 microliters injections into the anterior chamber on days 5, 10 and 15 postgrafting. Olfactory bulb grafts treated with either of the two IGF-1 antisera grew significantly larger than grafts receiving any other treatment. No enhancement of graft size was seen in E16-E17 parietal cortex grafts after IGF-1 antibody treatment. Immunohistochemical studies revealed no difference between the treatments with regard to glial fibrillary acidic protein-, tyrosine hydroxylase- or neurofilament-immunoreactivity within the olfactory bulb grafts. Since, in the olfactory bulb the presumed reduction of endogenous IGF-1 achieved by antibody treatment caused enhanced growth, we suggest that the presence of appropriate endogenous levels of IGF-1 in this area induces maturation. This mechanism is not operative in all brain areas since it was not seen in cortex cerebri grafts. Thus, endogenous IGF-1 appears to influence brain development in a regionally specific manner.

Localization of cellular retinoid-binding proteins suggests specific roles for retinoids in the adult central nervous system.

Retinoic acid, the active metabolite of retinoids (vitamin A compounds), is thought to act as a gene regulator via ligand-activated transcription factors. In order to investigate possible roles of retinoids and retinoid-controlled gene expression in brain function, we have used immunohistochemistry to localize the possible presence of two intracellular retinoid-binding proteins, cellular retinol-binding protein type I and cellular retinoic acid-binding protein type I, in the adult rat central nervous system. We find a widespread, yet distinct, presence of these two binding proteins in the brain and spinal cord. Most of the immunoreactivity is neuronal, including cell somata, as well as dendritic and axonal processes and axon terminals. Cellular retinol-binding protein type I-immunoreactivity is also found in the walls of cerebral blood vessels, the meninges, the choroid plexus, certain ependymal cells, tanocytes and certain other glial elements. The cellular retinol-binding protein type I- and cellular retinoic acid-binding protein type I-immunoreactivity patterns appear to be almost exclusively non-overlapping. Very strong cellular retinol-binding protein type I-immunoreactivity is found in the dendritic layers of the hippocampal formation and dentate gyrus. Cellular retinol-binding protein type I-immunoreactivity is also present in layer 5 cortical pyramidal neurons and neurons in the glomerular layer of the olfactory bulb. Many other areas, e.g. hypothalamic nuclei and amygdala areas, contain networks of varicose cellular retinol-binding protein type I-immunoreactive nerve fibers. The medial amygdaloid nucleus contains strongly cellular retinol-binding protein type I-positive neurons. Cellular retinoic acid-binding protein type I-immunoreactivity is more restricted in the adult brain. Strong cellular retinoic acid-binding protein type I-immunoreactivity is, however, found in a population of medium-sized neurons scattered throughout the striatum, in neurons in the glomerular layer of the olfactory bulb, the olfactory nerve and in a group of nerve cells close to the third ventricle in hypothalamus. The remarkably selective patterns of cellular retinol-binding protein type I- and cellular retinoic acid-binding protein type I-immunoreactivity discovered in the adult rat brain suggest that retinoids have important roles as regulators of gene expression in normal brain function. The high levels of cellular retinol-binding protein type I-immunoreactivity found in hippocampus suggest that one such role might relate to brain plasticity.

Brain-derived neurotrophic factor and trkB receptor mRNAs in grafts of cortex cerebri.

Trophic factors are expressed by neurons throughout several areas of the CNS. We studied the mRNA expression of a member of the neurotrophin family, brain-derived neurotrophic factor (BDNF), and of the two receptor transcripts, full-length trkB and truncated trkB in single intraocular cortex cerebri grafts and in double cortex cerebri grafts. All single as well as double intraocular cortex grafts grew well, reaching a maximal size 4 weeks postgrafting. BDNF mRNA was moderately expressed in neurons in all intraocular grafts and significantly increased compared to that in adult rat cortex. Truncated trkB mRNA was strongly expressed in neurons and glia, while full-length trkB mRNA was moderately expressed only in neurons in the intraocular cortical grafts. The expression of the two trkB transcripts in the grafted cortex did not differ from that of adult rat cortex. No difference in the expression of mRNAs for full-length or truncated trkB was found between single grafts grown for 4 or 8 weeks or between single and double grafts. Similarly, no difference in expression of BDNF mRNA in single grafts grown for 4 or 8 weeks was detected. However, BDNF mRNA levels were significantly lower in grafts which were placed in close contact with previously grafted cortex in the eye chamber. Moreover, contact with a second graft led to downregulation of BDNF mRNA in the first graft.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of platelet-derived growth factor isoforms on dopamine neurons in vivo: -BB supports cell survival, -AA enhances fiber formation.

Trophic effects of platelet-derived growth factor -AA and -BB on developing (embryonic day 14) ventral mesencephalon were studied using the in vivo model of intraocular transplantation to sympathetically denervated host eyes. This model enabled studies of survival and growth of grafted brain tissue, dopaminergic fiber outgrowth from the grafts onto the host iris as well as morphological effects of platelet-derived growth factor on grafted tissue using markers for tyrosine hydroxylase and glial fibrillary acid protein. Growth of grafts was followed by repeated observations directly through the cornea of the host using a stereomicroscope. This revealed that there was no apparent effect on volume increase of mesencephalic grafts after treatments with either platelet-derived growth factor-AA (100 ng/ml buffer), platelet-derived growth factor-BB (100 ng/ml buffer) or vehicle solution (high salt buffer) alone. Growth factor treatments were administered immediately prior to grafting by incubating the grafts in the appropriate factor as well as on days 5, 10 and 15 postgrafting by administration of 5-microliters intraocular injections of similar solutions as used for incubation. Platelet-derived growth factor-AA significantly enhanced dopaminergic fiber outgrowth from mesencephalic grafts when compared to both platelet-derived growth factor-BB and controls, without an accompanying rise in the number of tyrosine hydroxylase-positive neurons. In contrast, a significantly greater number of tyrosine hydroxylase-positive neurons was seen in grafts treated with platelet-derived growth factor-BB but without an accompanying increase in outgrowth of dopamine-containing fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibroblast growth factors enhance dopamine fiber formation from nigral grafts.

Members of the fibroblast growth factor (FGF) family have earlier been shown to exert potent trophic effects on cells of both the central and peripheral nervous system. The presence of FGF-1 and -2 (FGF-1, acidic FGF; FGF-2, basic FGF) has recently been demonstrated in the dopaminergic cells of substantia nigra in rat and FGF-2 has been shown to be able to increase survival and promote neurite outgrowth of cultured mesencephalic neurons. In the presence study, we have investigated possible trophic effects of FGF-1 and FGF-2 on developing rat ventral mesencephalon of different fetal stages by utilizing the in vivo method of intraocular transplantation to sympathetically denervated hosts. Survival and growth of developing grafts after growth factor treatment was followed in oculo. The Falck-Hillarp technique was used for evaluation of catecholaminergic fiber outgrowth into the host iris in whole-mount preparations. FGF-2 significantly increased the volume of the mesencephalic grafts when compared to grafts treated with the vehicle alone. The mean volume of FGF-1-treated grafts was larger than that of control grafts, but this difference was not statistically significant. FGF-1 significantly increased the area of outgrowth of dopaminergic fibers into the host iris without a corresponding increase in the number of dopaminergic neurons, as evaluated by TH immunohistochemistry. FGF-2 had no effect on dopaminergic fiber outgrowth on grafted E14 ventral mesencephalon but it did have a significant effect on fiber outgrowth from E15 and E16 grafts. Moreover, the FGF-2 treated E16 grafts contained a larger number of dopaminergic neurons as compared to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of platelet-derived growth factors on fetal hippocampal and cortical grafts: evidence from intraocular transplantation in rats.

Effects of platelet-derived growth factor-AA (PDGF-AA) and platelet-derived growth factor-BB (PDGF-BB) on developing parietal cortex (E16) and hippocampal (E18-E19) grafts were studied using the in vivo method of intraocular transplantation. Survival and growth of grafts in the anterior eye chamber of adult host rats under the influence of regular treatments with 0.5 ng (in a 100 ng/ml concentration) PDGF-AA or PDGF-BB was followed and compared to those receiving vehicle solution alone (0.5 mg HSA/ml Hanks). Both PDGF-AA and PDGF-BB increased the volume of transplanted cortical grafts. PDGF-BB also exerted trophic effects on grafted hippocampal tissue whereas PDGF-AA seemed to inhibit hippocampal growth. Histological and immunohistochemical studies revealed an increase in the density of astroglial elements in PDGF-AA- and PDGF-BB-treated cortical grafts whereas the PDGF-AA- and PDGF-BB-treated hippocampal grafts maintained a cytoarchitecture closely resembling that of control grafts. These findings support in vitro experiments showing that developing glial cells are stimulated by PDGFs and we further propose regional differences of action of PDGFs in the developing central nervous system.

Acidic and basic fibroblast growth factors augment growth of fetal brain tissue grafts.

The fibroblast growth factor family of peptides (FGF's) are biological regulators which have a diverse array of activities. Among the biological responses reported are inductive effects during early embryogenesis, mitogenic activity on a variety of mesenchymally derived tissues, potent angiogenic activity and neurotrophic activity for both the peripheral and central nervous system. In vitro studies have been performed showing that the FGF's play a regulatory role in the survival and growth of neurons from several regions of the developing rat brain. By using the in vivo model of intraocular transplantation and repeated injections into the anterior chamber, we have been able to observe and follow the survival and growth of small, defined areas of central nervous system (CNS) under the influence of acidic (a) FGF or basic (b) FGF. Acidic FGF significantly enhanced growth of transplanted parietal cortex, embryonic day 17-20 [E17-20], hippocampus [E20] but not spinal cord [E14] when compared to the bovine serum albumin (BSA) vehicle alone. Parietal cortex grafts increased approximately 200% and the hippocampus grafts 100% when stimulated with aFGF. Basic FGF greatly enhanced the growth of intraocularly transplanted parietal cortex (E17-18), hippocampus (E16-17), and spinal cord (E14) by approximately 400%, 100% and 50% respectively when compared to the vehicle alone, and was thus significantly more potent than aFGF at the same concentration. Effects on all areas were seen using concentrations of aFGF down to 25 micrograms/ml and bFGF as low as 2.5 micrograms/ml. Histochemical and immunohistochemical studies carried out on cryostat sectioned grafts suggested either no change or normalization of markers for vascularization, glial and neuronal populations.(ABSTRACT TRUNCATED AT 250 WORDS)

Truncated IGF-1 exerts trophic effects on fetal brain tissue grafts.

Truncated IGF-1 (tIGF-1), a form of IGF-1 identified in the human brain, has been suggested, from in vitro experiments, to exert neurotrophic effects on developing fetal brain tissue. We studied the effects of tIGF-1 and IGF-1 on small defined areas of the developing central nervous system by using the in vivo model of intraocular transplantation which allows for direct observations of graft survival and growth. Truncated IGF-1 was found to significantly enhance the growth of fetal spinal cord (Embryonic Day (E) 14) and parietal cortex (E16-17) grafts transplanted to the anterior chamber of the eye of adult rats. tIGF-1 increased the volume of cerebral cortex grafts by approximately 100% and of E14 spinal cord grafts by approximately 50%. E18 spinal cord grafts and hippocampal grafts were not stimulated by tIGF-1 as compared to controls given HSA. Effects in cortex were seen with tIGF-1 using concentrations down to at least 10 ng/microliters. Interestingly, intact IGF-1 had no effect on cortical grafts. These findings show for the first time, using an in vivo system, that tIGF-1 is a potent stimulator of growth of grafted fetal cortex cerebri and spinal cord and suggest a possible role for endogenous tIGF-1 in cortical and spinal cord development.