Anxiolytic-like behavior in rats is induced by the neonatal intracranial injection of apotransferrin

Combination therapy of apo-transferrin and thyroid hormones enhances remyelination

The current study presents two different approaches with a view to elucidating the interaction between thyroid hormones (TH) and apo-transferrin (aTf) and their role in myelination and remyelination. First, in vitro assays were conducted to determine the single and combined effects of aTf and triiodothyronine (T3) on oligodendroglial cell lineage proliferation and oligodendrocyte (OLG) maturation in primary cultures. Results revealed higher proliferation rates upon single aTf treatment but Control values upon T3 and aTf + T3 treatments. In addition, both aTf and T3 accelerated OLG maturation, with the greatest effects being exerted by combined aTf + T3 administration in terms of both myelin basic protein (MBP) expression and morphological complexity. Second, in vivo assays were carried out to establish single and combined effects of aTf and T3, as well as TH receptor (THR) inhibitor I-850, on remyelination following a CPZ-induced demyelination protocol. Results showed an increase in myelin deposition and the number of mature remyelinating OLG upon single treatments, but a synergic effect upon combined aTf + T3 treatment which was prevented by THR inhibition. It may be thus concluded that combined treatment yielded the most beneficial effects on OLG maturation parameters in vitro and remyelinating capacity in vivo when compared to single treatments. These findings may help explore the development of new target molecules in the treatment of demyelinating diseases.

Prenatal stress-induced programming of genome-wide promoter DNA methylation in 5-HTT-deficient mice

The serotonin transporter gene (5-HTT/SLC6A4)-linked polymorphic region has been suggested to have a modulatory role in mediating effects of early-life stress exposure on psychopathology rendering carriers of the low-expression short (s)-variant more vulnerable to environmental adversity in later life. The underlying molecular mechanisms of this gene-by-environment interaction are not well understood, but epigenetic regulation including differential DNA methylation has been postulated to have a critical role. Recently, we used a maternal restraint stress paradigm of prenatal stress (PS) in 5-HTT-deficient mice and showed that the effects on behavior and gene expression were particularly marked in the hippocampus of female 5-Htt+/- offspring. Here, we examined to which extent these effects are mediated by differential methylation of DNA. For this purpose, we performed a genome-wide hippocampal DNA methylation screening using methylated-DNA immunoprecipitation (MeDIP) on Affymetrix GeneChip Mouse Promoter 1.0 R arrays. Using hippocampal DNA from the same mice as assessed before enabled us to correlate gene-specific DNA methylation, mRNA expression and behavior. We found that 5-Htt genotype, PS and their interaction differentially affected the DNA methylation signature of numerous genes, a subset of which showed overlap with the expression profiles of the corresponding transcripts. For example, a differentially methylated region in the gene encoding myelin basic protein (Mbp) was associated with its expression in a 5-Htt-, PS- and 5-Htt × PS-dependent manner. Subsequent fine-mapping of this Mbp locus linked the methylation status of two specific CpG sites to Mbp expression and anxiety-related behavior. In conclusion, hippocampal DNA methylation patterns and expression profiles of female prenatally stressed 5-Htt+/- mice suggest that distinct molecular mechanisms, some of which are promoter methylation-dependent, contribute to the behavioral effects of the 5-Htt genotype, PS exposure and their interaction.

Effects of early weaning on anxiety and prefrontal cortical and hippocampal myelination in male and female Wistar rats

We investigated developmental changes in myelin formation in the prefrontal cortex and the hippocampus, and behavioral effects of early weaning in Wistar rats. Early-weaned rats showed decreased numbers of open-arm entries in an elevated plus-maze in both sexes at 4 weeks old; this effect persisted in males, but ceased in females after this age. Expression of myelin basic protein (MBP) showed both age-dependent increases and sex differences; 4-week-old males exhibited higher MBP levels in the hippocampus, whereas 7-week-old males showed lower MBP levels in the prefrontal cortex compared to females of the same age. There was a tendency for group differences from weaning for the 21.5-kDa isoform in the prefrontal cortex. Although these results suggest that male rats are more vulnerable than females to early-weaning effects on anxiety-related behaviors, further detailed analysis is needed to clarify the functional relationship between myelination and anxiety-related behaviors.

Differential gene expression during development in two oligodendroglial cell lines overexpressing transferrin: a cDNA array analysis

In the central nervous system, transferrin (Tf) is produced by oligodendroglial cells (OLGcs) and is essential for their development. Recently, using the complete cDNA of the human Tf gene, we obtained clones overexpressing Tf in two OLGc lines, N19 and N20.1, which represent different stages of differentiation. We showed that the overexpression of this glycoprotein promotes the maturation and myelinogenic capacity of both cell lines. In this work, using cDNA array technology, we examined changes induced by Tf in 1,176 genes. We found 41 genes differentially expressed in both cell lines, all of them involved in OLGc development. In the less mature cells (N19) overexpressing Tf, there was a significant increase in key enzymes of neurosteroid metabolism, such as cholesterol side chain cleavage cytochrome P450, 3beta-hydroxysteroid dehydrogenase and 5alpha-reductase type 1. In the more mature cell line (N20.1), Tf overexpression produced an induction of several mRNAs of the GABA(A) receptor subunits, of thyroid hormone receptors and of proteins involved in axon-glia interactions such as F3/contactin. In addition, in both cell lines, Tf overexpression induced an increase in the expression of different isoforms of transforming growth factor beta receptors and in several genes related to mitochondrial function and to complex lipid metabolism, crucial steps in myelin synthesis. Differentiation produced by Tf in both cell lines seems to occur by modulation of different genes depending on the maturational stage of the cells. Our findings provide new insights into the molecular basis of OLGc differentiation and on the role played by Tf in this process.

Deprivation of mother-pup interaction by early weaning alters myelin formation in male, but not female, ICR mice

We previously reported that early-weaned Balb/c mice develop a persistent increase in anxiety as well as aggression, and we suggested that deprivation of mother-pup interaction from postnatal days 15 to 21 might account for this phenomenon. In the present study, we investigated developmental changes in myelin formation and behavioral effects of early weaning in male and female ICR mice. Early weaning was associated with decreased numbers of open-arm entries in an elevated plus-maze for both male and female mice at 3 weeks of age (W3); this effect was persistently observed in males, but ceased after W3 in females. Compared to the brains of normally weaned mice, the brains of the early-weaned males at W8 and of the females at W5 were of lesser mass. Western blotting with whole-brain homogenates identified four isoforms of myelin basic protein (MBP; 21.5, 18.5, 17.0, and 14.0 kDa). Expression of these MBPs increased gradually in normally weaned mice. In contrast, in the early-weaned male mice, but not the early-weaned female mice, it increased robustly at W3 and then declined at W5, as compared to the normally weaned mice. These results suggest that early weaning influences not only anxiety-related behavior but also myelin formation in the brain during the developmental period, particularly between 3 and 5 weeks of age, and male mice are more vulnerable than females to early-weaning effects on behavior and myelin formation.

Effects of early weaning on anxiety and autonomic responses to stress in rats

Environmental stimuli affect various aspects of the early physical and behavioral development in rats. One of the most important events in the early stage of life is weaning, and we recently reported that precocious weaning augments anxiety and aggressiveness in rats and mice. In the present study, we investigated the autonomic responses to stress in two groups of rats: the early-weaned group (weaned at 16 days of age), and the normally weaned group (weaned at 30 days) as a control. First, the early and normally weaned rats were subjected to an elevated plus-maze test to assess their anxiety levels. It was confirmed that early-weaned male rats, but not the females, showed a lower frequency of entry into and shorter duration of stay in the open arms of the maze compared to the normally weaned rats. Subsequently, the two groups were either placed in a novel clean cage or exposed to an unfamiliar conspecific, and their heart rates and core body temperatures were monitored to evaluate their autonomic stress responses. There was an exacerbation of autonomic responses, such as stress-induced hyperthermia and tachycardia, and an alternation of behavioral responses, including increased sniffing, and decreased grooming and resting. These effects of early weaning were significant only in males. In contrast, when rats encountered an unfamiliar individual, no significant differences were observed between the two groups in either sex. This suggests that stimuli emanating from an unfamiliar intruder were too intense to detect the augmentation of stress responses in the early-weaned rat. The results of the present study demonstrate that precocious weaning augments, not only behavioral but also autonomic responses, to stressful conditions with sexually dimorphic patterns, i.e. more profoundly in males than in females.

Mechanisms and regulation of transferrin and iron transport in a model blood-brain barrier system

For peripheral iron to reach the brain, it must transverse the blood-brain barrier. In order for the brain to obtain iron, transferrin receptors are present in the vascular endothelial cell to facilitate movement of transferrin bound iron into the brain parenchyma. However, a number of significant voids exist in our knowledge about transport of iron into the brain. These gaps in our knowledge are significant not only because iron is an essential neurotrophic factor but also because the system for delivery of iron into the brain is being viewed as an opportunity to circumvent the blood-brain barrier for delivery of neurotoxins to tumors or trophic factors in neurodegenerative diseases. In this study, we have used fluorescein-transferrin-59Fe in a bovine retinal endothelial cell culture system to determine the mechanism of transferrin-iron transport and to test the hypothesis that the iron status of the endothelial cells would influence iron transport. Our results indicated that iron is transported across endothelial cells both bound to and not bound to transferrin. The ratio of non-transferrin-bound iron to transferrin-bound iron transported is dependent upon the iron status of the cells. Blocking acidification of endosomes led to a significant decrease in transport of non-transferrin-bound iron but not transferrin-bound iron. Blocking pinocytosis had no effect on either transferrin or iron transcytosis. These results indicate that there is both transferrin-mediated and non-transferrin-mediated transcytosis of iron and that the process is influenced by the iron status of the cells. These data have considerable implications for common neurodegenerative diseases that are associated with excess brain iron accumulation and the numerous neurological complications associated with brain iron deficiency.

Morphological changes of myelin sheaths in rats intracranially injected with apotransferrin

Previous findings from our laboratories indicate that the intracranial injection of apotransferrin (aTf) in neonatal rats produces an accelerated oligodendrocyte maturation and an enhanced production and deposition of myelin membranes in the brain. To evaluate the anatomical distribution and the morphological characteristics of the myelin in these rats, we analyzed the optic nerves, cerebellum, and selected areas of brain sections from aTf-treated and control rats by both light and electron microscopy. Microscopic identification of myelin using a specific staining procedure, showed that in aTf-injected rats, in coincidence with previous biochemical studies, there was an increased deposition of myelin in selected areas of the nervous system. Qualitative and quantitative analysis of electron micrographs from areas showing increased myelinaton, such as the optic nerves and the corpus callosum, showed that among other changes, the intracranial treatment with aTf produces ultrastructural evidences of myelin decompaction, consisting of an enlargement in the distance between adjacent major dense lines, a decreased density of the intraperiod line, and an increased electron density of the major dense line, accompanied by a significant increase in its width. The intracranial administration of aTf induces an increased deposition of myelin by oligodeudroglial cells (OLGc), and these myelin membranes, in spite of the changes in composition and in morphology, appear to function normally. Apotransferrin can be considered as a differentiation factor that could be used to stimulate remyelination in cases in which myelin has been destroyed by various pathological processes.