Functional and molecular evidence of myelin- and neuroprotection by thyroid hormone administration in experimental allergic encephalomyelitis.

AIMS: Recent data in mouse and rat demyelination models indicate that administration of thyroid hormone (TH) has a positive effect on the demyelination/remyelination balance. As axonal pathology has been recognized as an early neuropathological event in multiple sclerosis, and remyelination is considered a pre-eminent neuroprotective strategy, in this study we investigated whether TH administration improves nerve impulse propagation and protects axons. METHODS: We followed up the somatosensory evoked potentials (SEPs) in triiodothyronine (T3)-treated and untreated experimental allergic encephalomyelitis (EAE) Dark-Agouti female rats during the electrical stimulation of the tail nerve. T3 treatment started on the 10th day post immunization (DPI) and a pulse administration was continued until the end of the study (33 DPI). SEPs were recorded at baseline (8 DPI) and the day after each hormone/ vehicle administration. RESULTS: T3 treatment was associated with better outcome of clinical and neurophysiological parameters. SEPs latencies of the two groups behaved differently, being briefer and closer to control values (=faster impulse propagation) in T3-treated animals. The effect was evident on 24 DPI. In the same groups of animals, we also investigated axonal proteins, showing that T3 administration normalizes neurofilament immunoreactivity in the fasciculus gracilis and tau hyperphosphorylation in the lumbar spinal cord of EAE animals. No sign of plasma hyperthyroidism was found; moreover, the dysregulation of TH nuclear receptor expression observed in the spinal cord of EAE animals was corrected by T3 treatment. CONCLUSIONS: T3 supplementation results in myelin sheath protection, nerve conduction preservation and axon protection in this animal model of multiple sclerosis.

Triiodothyronine administration ameliorates the demyelination/remyelination ratio in a non-human primate model of multiple sclerosis by correcting tissue hypothyroidism.

Remyelination failure is a key landmark in chronic progression of multiple sclerosis (MS), the most diffuse demyelinating disease in human, but the reasons for this are still unknown. It has been shown that thyroid hormone administration in the rodent models of acute and chronic demyelinating diseases improved their clinical course, pathology and remyelination. In the present study, we translated this therapeutic attempt to experimental allergic encephalomyelitis (EAE) in the non-human primate Callithrix Jacchus (marmoset). We report that short protocols of triiodothyronine treatment shifts the demyelination/remyelination balance toward remyelination, as assessed by morphology, immunohistochemistry and molecular biology, and improves the clinical course of the disease. We also found that severely ill animals display hypothyroidism and severe alteration of deiodinase and thyroid hormone receptor mRNAs expression in the spinal cord, which was completely corrected by thyroid hormone treatment. We therefore suggest that thyroid hormone treatment improves myelin sheath morphology in marmoset EAE, by correcting the dysfunction of thyroid hormone cellular effectors.

A single prenatal exposure to the endocrine disruptor 2,3,7,8-tetrachlorodibenzo-p-dioxin alters developmental myelination and remyelination potential in the rat brain.

Polychlorinated dibenzo-dioxins, furans and dioxin-like polychlorinated biphenyls are ubiquitous in foodstuffs of animal origin and accumulate in the fatty tissues of animals and humans. The most toxic congener is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a lipophilic endocrine-disrupting molecule that accumulates in adipose tissue, placenta and milk. polychlorinated biphenyls and TCDD are known to interfere with thyroid hormone metabolism and signaling in the developing brain. As thyroid hormone is critical in the myelination process during development, we investigated the effect of a single dose of TCDD prenatal exposure (gestational day 18) on the myelination process. A semi-quantitative analysis of oligodendrocyte markers at different stages of maturation was performed in the offspring's medulla oblongata, cerebellum, diencephalon and telenchephalon at different postnatal days (2/3, 14, 30 and 135). The most significant alterations observed were: (i) cerebellum and medulla oblongata: altered expression of oligodendroglial lineage and platelet-derived growth factor alpha receptor, myelin basic protein (MBP) mRNAs (P2/3, P135) and MBP protein (P135); (ii) diencephalon: increase in platelet- derived growth factor alpha receptor mRNA level (P2/3); (iii) telenchephalon: decrease in MBP mRNA expression. The oligodendroglial generation capability of adult neural stem/precursor cells obtained ex vivo from TCDD and vehicle-treated dams was then explored. TCDD impairs neurosphere proliferation and retards CNPase-positive cell generation from adult neurospheres.

Skin homeostasis during inflammation: a role for nerve growth factor.

The skin is a neuroendocrine immune organ in which many different molecules operate in autocrine-paracrine manner to guarantee tissue homeostatsis in physiological and pathophysiological conditions. In this paper we examined NGF and p75 receptor expression in the skin, during CFA induced inflammation, in a time-course study. We also examined cutaneus innervation and proliferation, by means of immunohistochemistry and quantitative image analysis, RT-PCR and Western blot. Spontaneous and evoked pain-behavior was also measured in experimental rats. The main results can be summarized as follows: 1). a peripheral sensory neuropathy develops in this condition, as indicated by thermal hyperalgesia, thus leading to a sensory denervation of the hind-paw skin as indicated by disappearance of CGRP and PGP9.5-IR fibers; 2). NGF and p75 expression (mRNA and protein) increases in the skin (keratinocytes) in the acute phase of CFA inflammation; 3). at this stage, a higher proliferative activity is observed in the skin, as defined by the expression of cell cycle-associated protein Ki67; 4). in the long-lasting chronic phase there is a further up-regulation of NFG and p75 expression in the skin; 5). trkA mRNA expression inversely correlates with p75 and NGF mRNA expression. These results suggest that CFA chronic inflammation evolves from inflammation to a small fibers sensory neuropathy and NGF seems to play a role in both events.

Changes in brain cholinergic markers and spatial learning in old galanin-overexpressing mice.

The cholinergic forebrain system is involved in learning and memory, and its age-dependent decline correlates with a decrease in cognitive performance. Since the neuropeptide galanin participates in cholinergic neuron regulation, we have studied 19- to 23-month-old male mice overexpressing galanin under the platelet-derived growth factor B promoter (GalOE) and wild-type (WT) littermates by monitoring behavioral, neurochemical and morphological/histochemical parameters. In the Morris water maze test, old transgenic animals showed a significant impairment in escape latency in the hidden platform test compared to age-matched WT animals. The morphological/histochemical studies revealed that cholinergic neurons in the basal forebrain display a slight, age- but not genotype-related, alteration in choline acetyltransferase- (ChAT) immunoreactivity. The neurochemical studies showed an age-related decline in ChAT activity in the cerebral cortex of all mice, whereas in the hippocampal formation this effect was seen in GalOE but not WT animals. Expression of BDNF mRNA in the hippocampal formation, as evaluated by RT-PCR, was reduced in old animals; no age- or genotype-induced variations in NGF mRNA expression were observed. These data suggest that galanin overexpression further accentuates the age-related decline of the cholinergic system activity in male mice, resulting in impairment of water maze performance in old animals.

Endogenous stem and precursor cells for demyelinating diseases: an alternative for transplantation?

Remyelination can be very effective in human. However, this process ultimately fails in multiple sclerosis (MS). In this paper, we discuss the possibility of stimulating endogenous oligodendrocyte precursors to participate in remyelination in experimental models (rat and primate Callithrix jacchus) of MS through thyroid hormone (TH) administration. TH is in fact known to be a key signal in brain development, oligodendrocyte development and myelin protein gene expression regulation.

p75(NTR)-immunoreactivity in the subventricular zone of adult male rats: expression by cycling cells.

While the study of in vitro regulation of neural stem cell lineage from both embryonic and adult neurospheres is greatly advanced, much less is known about factors acting in situ for neural stem cell lineage in adult brain. We reported that neurotrophin low affinity receptor p75(NTR) is present in the subventricular zone (SVZ) in adult male rats. We then characterized co-distribution of markers associated with precursor cells (nestin and PSA-NCAM) with growth factor receptors (p75(NTR), trkA, EGFr) and proliferation-associated antigens (Ki67 and BrDU-uptake) in adult male rat by immunocytochemistry and confocal laser scan microscopy. Distribution of p75(NTR)-immunoreactivity (IR) was investigated using different mono- and polyclonal antisera. p75(NTR-) is not co-distributed with glial fibrillary acid protein. It was found to be co-distributed with a small number of nestin-IR cells, whereas no coexistence with PSA-NCAM-IR was observed. Conversely, p75(NTR)-IR was present in numerous dividing cells (Ki-67-positive) and co-distributed with EGFr. In order to verify the possible association between p75(NTR) and cell death, we investigated co-distribution of p75(NTR)-IR with nuclear condensation images as visualized by Hoechst 33258 staining. While few images indicating nuclear condensation were observed in the SVZ, no coexistence with p75(NTR) was found. TrkA- and trkB-IR was not found in the SVZ. We also investigated p75(NTR) immunostaining on post-natal day 1 and day 16, because of the dramatic reduction of proliferating cells in SVZ over this time-interval. p75(NTR)-IR was not increased in the early post-natal phase. Thus, p75(NTR) seems to be associated with cell cycle regulation in SVZ in adult rat brain.