Myelin Protein Gene Expression Research Articles

Transcription factor 7-like 2 (TCF7l2) regulates CNS myelination separating from its role in upstream oligodendrocyte differentiation.

Oligodendrocyte progenitor cells (OPCs) differentiation into oligodendrocytes (OLs) and subsequent myelination are two closely coordinated yet differentially regulated steps for myelin formation and repair in the CNS. Previously thought as an inhibitory factor by activating Wnt/beta-catenin signaling, we and others have demonstrated that the Transcription factor 7-like 2 (TCF7l2) promotes OL differentiation independent of Wnt/beta-catenin signaling activation. However, it remains elusive if TCF7l2 directly controls CNS myelination separating from its role in upstream oligodendrocyte differentiation. This is partially because of the lack of genetic animal models that could tease out CNS myelination from upstream OL differentiation. Here, we report that constitutively depleting TCF7l2 transiently inhibited oligodendrocyte differentiation during early postnatal development, but it impaired CNS myelination in the long term in adult mice. Using time-conditional and developmental-stage-specific genetic approaches, we further showed that depleting TCF7l2 in already differentiated OLs did not impact myelin protein gene expression nor oligodendroglial populations, instead, it perturbed CNS myelination in the adult. Therefore, our data convincingly demonstrate the crucial role of TCF7l2 in regulating CNS myelination independent of its role in upstream oligodendrocyte differentiation.

N-Acetylaspartate Drives Oligodendroglial Differentiation via Histone Deacetylase Activation.

An unmet clinical goal in demyelinating pathologies is to restore the myelin sheath prior to neural degeneration. N-acetylaspartate (NAA) is an acetylated derivative form of aspartate, abundant in the healthy brain but severely reduced during traumatic brain injury and in patients with neurodegenerative pathologies. How extracellular NAA variations impact the remyelination process and, thereby, the ability of oligodendrocytes to remyelinate axons remains unexplored. Here, we evaluated the remyelination properties of the oligodendroglial (OL) mouse cell line Oli-neuM under different concentrations of NAA using a combination of biochemical, qPCR, immunofluorescence assays, and in vitro engagement tests, at NAA doses compatible with those observed in healthy brains and during brain injury. We observed that oligodendroglia cells respond to decreasing levels of NAA by stimulating differentiation and promoting gene expression of myelin proteins in a temporally regulated manner. Low doses of NAA potently stimulate Oli-neuM to engage with synthetic axons. Furthermore, we show a concentration-dependent expression of specific histone deacetylases essential for MBP gene expression under NAA or Clobetasol treatment. These data are consistent with the idea that oligodendrocytes respond to lowering the NAA concentration by activating the remyelination process via deacetylase activation.

Developmental Changes in Oligodendrocyte Genesis, Myelination, and Associated Behavioral Dysfunction in a Rat Model of Intra-generational Protein Malnutrition.

Impairments in oligodendrocyte development and resultant myelination deficits appear as a common denominator to all neurological diseases. An optimal in utero environment is obligatory for normal fetal brain development and later life brain functioning. Late embryonic and early postnatal brains from F1 rat born to protein malnourished mothers were studied through a combination of immunocytochemical and quantitative PCR assay for analyzing the relative expression of platelet-derived growth factor receptor-α (PDGFRα), myelin-associated glycoprotein (MAG), proteolipid protein (PLP), and myelin oligodendrocyte glycoprotein (MOG) to determine oligodendrocyte genesis, differentiation, maturation, and myelination. Myelin integrity and corpus callosum caliber was assessed by Luxol fast blue (LFB) staining, whereas grip strength test and open field activity monitoring for behavioral evaluation in F1 rats. We demonstrate that intra-generational protein deprivation results in drastically low PDGFRα+ oligodendrocyte precursor (OPC) population and significantly reduced expression of myelin protein genes resulting in poor pre-myelinating and mature myelinating oligodendrocyte number, hypo-myelination, and misaligned myelinated fibers. LFB staining and MOG immunolabeling precisely revealed long-term changes in corpus callosum (CC) caliber and demyelination lesions in LP brain supporting the behavioral and cognitive changes at early adolescence and adulthood following maternal protein malnutrition (PMN). Thus, intra-generational PMN negatively affects the oligodendrocyte development and maturation resulting in myelination impairments and associated with behavioral deficits typically mimicking clinical hallmarks of neuropsychiatric disorders. Our results further strengthen and augment the hypothesis "Impaired gliogenesis is a big hit for neuropsychiatric phenotype."

Charcot-Marie-Tooth type 1A drug therapies: role of adenylyl cyclase activity and G-protein coupled receptors in disease pathomechanism

Charcot‑Marie‑Tooth type 1A (CMT1A) is a dysmyelinating disease of the peripheral nervous system that results in a slow progressive weakening and wasting of the distal muscles of the upper and lower limbs. Despite extensive research and clinical trials there is still no treatment for CMT1A that results in complete neurological improvement. Recent studies investigating various pharmacological modulators of adenylyl cyclase activity, including ascorbic acid and ligands of G protein‑coupled receptors (GPCRs), provide hope for future treatments of this type of hereditary motor and sensory neuropathy. A review of mechanisms of action of several compounds tested for CMT1A in pre‑clinical and clinical studies ascorbic acid, onapristone, PXT3003 (baclofen, naltrexone, and sorbitol), and ADX71441, very clearly indicates an important role for adenylyl cyclase activity and GPCRs in the pathomechanism of the disease. Metabotropic γ‑aminobutyric acid receptors (GABABR), subtype mu (μ) opioid receptors (MOR), and muscarinic acetylcholine receptors (mACh) appear to be particularly significant in both pathogenesis and treatment, and their activation may exert a similar and synergistic effect on the physiology of Schwann cells as well as neurons. These receptors participate in proliferation and differentiation of Schwann cells and influence excitatory transmission in neurons. We also hypothesize that onapristone might act through a non‑classical mechanism via membrane progesterone receptor (mPR) and cAMP signaling. This review endeavors to outline a pathway leading inversely from therapy to an indispensable role for adenylyl cyclase activity and GPCRs in the modulation of dosage sensitive peripheral myelin protein (PMP22) gene expression.

The control of reactive oxygen species production by SHP-1 in oligodendrocytes.

We have previously described reduced myelination and corresponding myelin basic protein (MBP) expression in the central nervous system of Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) deficient motheaten (me/me) mice compared with normal littermate controls. Deficiency in myelin and MBP expression in both brains and spinal cords of motheaten mice correlated with reduced MBP mRNA expression levels in vivo and in purified oligodendrocytes in vitro. Therefore, SHP-1 activity seems to be a critical regulator of oligodendrocyte gene expression and function. Consistent with this role, this study demonstrates that oligodendrocytes of motheaten mice and SHP-1-depleted N20.1 cells produce higher levels of reactive oxygen species (ROS) and exhibit corresponding markers of increased oxidative stress. In agreement with these findings, we demonstrate that increased production of ROS coincides with ROS-induced signaling pathways known to affect myelin gene expression in oligodendrocytes. Antioxidant treatment of SHP-1-deficient oligodendrocytes reversed the pathological changes in these cells, with increased myelin protein gene expression and decreased expression of nuclear factor (erythroid-2)-related factor 2 (Nrf2) responsive gene, heme oxygenase-1 (HO-1). Furthermore, we demonstrate that SHP-1 is expressed in human white matter oligodendrocytes, and there is a subset of multiple sclerosis subjects that demonstrate a deficiency of SHP-1 in normal-appearing white matter. These studies reveal critical pathways controlled by SHP-1 in oligodendrocytes that relate to susceptibility of SHP-1-deficient mice to both developmental defects in myelination and to inflammatory demyelinating diseases.

Neurotoxocarosis alters myelin protein gene transcription and expression.

Neurotoxocarosis is an infection of the central nervous system caused by migrating larvae of the common dog and cat roundworms (Toxocara canis and Toxocara cati), which are zoonotic agents. As these parasites are prevalent worldwide and neuropathological and molecular investigations on neurotoxocarosis are scare, this study aims to characterise nerve fibre demyelination associated with neurotoxocarosis on a molecular level. Transcription of eight myelin-associated genes (Cnp, Mag, Mbp, Mog, Mrf-1, Nogo-A, Plp1, Olig2) was determined in the mouse model during six time points of the chronic phase of infection using qRT-PCR. Expression of selected proteins was analysed by Western blotting or immunohistochemistry. Additionally, demyelination and neuronal damage were investigated histologically. Significant differences (p ≤ 0.05) between transcription rates of T. canis-infected and uninfected control mice were detected for all analysed genes while T. cati affected five of eight investigated genes. Interestingly, 2', 3 ´-cyclic nucleotide 3'-phosphodiesterase (Cnp) and myelin oligodendrocyte glycoprotein (Mog) were upregulated in both T. canis- and T. cati-infected mice preceding demyelination. Later, CNPase expression was additionally enhanced. As expected, myelin basic protein (Mbp) was downregulated in cerebra and cerebella of T. canis-infected mice when severe demyelination was present 120days post infectionem (dpi). The transcriptional pattern observed in the present study appears to reflect direct traumatic and hypoxic effects of larval migration as well as secondary processes including host immune reactions, demyelination and attempts to remyelinate damaged areas.

Sex-dimorphic effects of dehydroepiandrosterone in diabetic neuropathy

Our recent observations have demonstrated that gonadectomy in female, but not in male diabetic animals, exert protection in the peripheral nervous system and that these effects were associated with an increase in the levels of dehydroepiandrosterone (DHEA) in the female sciatic nerve [Pesaresi M, Giatti S, Cavaletti G, Abbiati F, Calabrese D, Bianchi R, Caruso D, Garcia-Segura LM, Melcangi RC (2011) Exp Neurol 228:215–221]. That is interesting because the neuroprotective effects of this neuroactive steroid have so far only been analyzed in male diabetic animals. Using the experimental model of streptozotocin-induced diabetic neuropathy, we have here compared the effect of DHEA treatment in male and in female animals. Data obtained indicate that DHEA treatment is able to counteract the decrease in nerve conduction velocity (NCV) induced by diabetes in both sexes. However, it was only in females that this neuroactive steroid was able to reestablish NCV to control levels. In addition, it was only in females that DHEA exerted neuroprotective actions on functional (i.e., thermal sensitivity) or molecular parameters, such as gene expression of myelin proteins. Sex-depending neuroprotective effects of DHEA were also confirmed by the finding that it was only in females that this neuroactive steroid fully restored the intra-epidermal nerve fiber density, which was decreased by diabetes. Interestingly, the metabolic fate of DHEA is also different in males and females. Thus, analysis of the neuroactive steroid levels after the treatment with DHEA indicates that in the sciatic nerve of male diabetic animals 17α-estradiol levels decrease in association with an increase of its isomer 17β-estradiol and with a decrease in the levels of α-androstane-3α, 17β-diol. These changes were not observed in the sciatic nerve of females. Altogether, these results suggest that DHEA could be considered as a candidate for a sex-specific therapy based on neuroactive steroids.

Docetaxel‐induced peripheral neuropathy: protective effects of dihydroprogesterone and progesterone in an experimental model

Peripheral neurotoxicity is a frequent complication limiting docetaxel chemotherapy in patients with cancer. We developed an experimental model that closely mimics the course of neuropathy in patients, aiming to investigate both the mechanisms of neurotoxicity at biochemical, functional and morphological levels and the potential neuroprotective role of neuroactive steroids. We demonstrated that treatment with dihydroprogesterone (DHP) or progesterone (P) counteracts docetaxel-induced neuropathy, preventing nerve conduction and thermal threshold changes, and degeneration of skin nerves in the foodpad. Neuroactive steroids also counteract the changes in gene expression of several myelin proteins and calcitonin gene-related peptide induced by docetaxel in sciatic nerve and lumbar spinal cord, respectively. Most nerve abnormalities observed during the treatment with docetaxel spontaneously recovered after drug withdrawal, similarly to what occurs in patients. However, results of midterm follow-up experiments indicated that animals cotreated with DHP or P have a faster recovery of the neuropathy compared with docetaxel-treated rats. Our study confirmed that neuroactive steroids exert a protective effect on peripheral nerves at different levels, suggesting that they might represent a new therapeutic frontier for patients with chemotherapy-induced neuropathy.

Abnormal Indices of Cell Cycle Activity in Schizophrenia and their Potential Association with Oligodendrocytes

The goal of this study was to determine what signaling pathways may elicit myelin-specific gene expression deficits in schizophrenia (SZ). Microarray analyses indicated that genes associated with canonical cell cycle pathways were significantly affected in the anterior cingulate gyrus (ACG), the region exhibiting the most profound myelin-specific gene expression changes, in persons with SZ (N=16) as compared with controls (N=19). Detected gene expression changes of key regulators of G1/S phase transition and genes central to oligodendrocyte differentiation were validated using qPCR in the ACG in an independent cohort (Ns=45/34). The relative abundance of phosphorylated retinoblastoma protein (pRb) was increased in the white matter underlying the ACG in SZ subjects (Ns=12). The upregulation of cyclin D1 gene expression and the downregulation of p57(Kip2), accompanied by increased cyclin D/CDK4-dependent phosphorylation of pRb, acting as a checkpoint for G1/S phase transition, suggest abnormal cell cycle re-entry in postmitotic oligodendrocytes in SZ. Furthermore, gene expression profiling of brain samples from myelin mutant animal models, quaking and myelin-associated glycoprotein (MAG) null mice, showed that cell cycle gene expression changes were not a necessary consequence of the reduced gene expression of structural myelin proteins, such as MAG. While, quaking, a known modulator of cell cycle activity during oligodendrocyte differentiation impairs the expression of multiple myelin genes, including those that are affected in SZ. These data suggest that the normal patterns of cell cycle gene and protein expression are disrupted in SZ and that this disruption may contribute to the oligodendroglial deficits observed in SZ.

T2-weighted μMRI and Evoked Potential of the Visual System Measurements During the Development of Hypomyelinated Transgenic Mice

Our objective was to follow the course of a dysmyelinating disease followed by partial recovery in transgenic mice using non-invasive high-resolution (117 x 117 x 70 microm) magnetic resonance (microMRI) and evoked potential of the visual system (VEP) techniques. We used JOE (for J37 golli overexpressing) transgenic mice engineered to overexpress golli J37, a product of the Golli-mbp gene complex, specifically in oligodendrocytes. Individual JOE transgenics and their unaffected siblings were followed from 21 until 75-days-old using non-invasive in vivo VEPs and 3D T2-weighted microMRI on an 11.7 T scanner, performing what we believe is the first longitudinal study of its kind. The microMRI data indicated clear, global hypomyelination during the period of peak myelination (21-42 days), which was partially corrected at later ages (>60 days) in the JOE mice compared to controls. These microMRI data correlated well with [Campagnoni AT (1995) "Molecular biology of myelination". In: Ransom B, Kettenmann H (eds) Neuroglia--a Treatise. Oxford University Press, London, pp 555-570] myelin staining, [Campagnoni AT, Macklin WB (1988) Cellular and molecular aspects of myelin protein gene-expression. Mol Neurobiol 2:41-89] a transient intention tremor during the peak period of myelination, which abated at later ages, and [Lees MB, Brostoff SW (1984) Proteins in myelin. In: Morell (ed) Myelin. Plenum Press, New York and London, pp 197-224] VEPs which all indicated a significant delay of CNS myelin development and persistent hypomyelination in JOE mice. Overall these non-invasive techniques are capable of spatially resolving the increase in myelination in the normally developing and developmentally delayed mouse brain.

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.

Sex‐dimorphic effects of progesterone and its reduced metabolites on gene expression of myelin proteins by rat Schwann cells

Data obtained in our and other laboratories have indicated that progesterone (P) and its derivatives, dihydroprogesterone (DHP) and tetrahydroprogesterone (THP), stimulate the expression of two myelin proteins of the peripheral nervous system (PNS) [i.e., glycoprotein zero (P0) and peripheral myelin protein 22 (PMP22)]. We have now considered the effects of P and its derivatives on these and other myelin proteins [i.e., myelin-associated glycoprotein (MAG) and myelin and lymphocyte protein (MAL)] in sex-specific cultures of rat Schwann cells. Gene expression of myelin proteins was assessed by RNase protection assay. Treatment with P or DHP induced a stimulatory effect on P0 mRNA levels in male but not in female Schwann cells. In contrast, treatment with THP increased gene expression of P0 exclusively in female Schwann cells. A similar sex-difference was also evident for other myelin proteins. Indeed, PMP22 expression was stimulated by treatment with P in male cultures, whereas THP induced an increase of mRNA levels in female cultures. Moreover, MAG was stimulated by THP treatment in male cultures only, whereas MAL expression was unaffected by neuroactive steroid treatment in both male and female cultures. In conclusion, the present observations indicate that the effects of neuroactive steroids on myelin proteins are sexually dimorphic. This finding might represent an important background for sex-specific therapies of acquired and inherited peripheral neuropathies.

Sexually dimorphic effect of progesterone and its reduced metabolites on the gene expression of myelin proteins in rat Schwann cells

Sexually dimorphic effect of progesterone and its reduced metabolites on the gene expression of myelin proteins in rat Schwann cells

Steroid Effects on the Gene Expression of Peripheral Myelin Proteins

The present article summarizes recent observations obtained in our laboratory which clearly indicate that sex steroids exert relevant effects on the peripheral nervous system. In particular, the following important points have emerged: (1) Steroids exert stimulatory actions on the synthesis of the proteins proper of the peripheral myelin (e.g., glycoprotein Po and peripheral myelin protein 22) in vivo and on the Schwann cells in culture; (2) in many cases the actions of hormonal steroids are not due to their native molecular forms but rather to their metabolites (e.g., dihydroprogesterone and tetrahydroprogesterone in the case of progesterone; dihydrotestosterone and 5α-androstane–3α,17β-diol in the case of testosterone); (3) the mechanism of action of the various steroidal molecules may involve both classical (progesterone and androgen receptors) and nonclassical steroid receptors (GABAA receptor); and finally, (4) the stimulatory action of steroid hormones on the proteins of the peripheral myelin might have clinical significance in cases in which the rebuilding of myelin is needed (e.g., aging, peripheral injury, demyelinating diseases, and diabetic neuropathy).

Interferon-γ Protects against Cuprizone-Induced Demyelination

Evidence suggests that interferon-γ (IFN-γ), a proinflammatory cytokine secreted by activated T lymphocytes, contributes a deleterious effect to immune-mediated demyelinating disorders such as multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). Nevertheless, mouse strains that are normally resistant to EAE induction become susceptible when the gene encoding either IFN-γ or its receptor is mutated, demonstrating that the role that this cytokine plays in demyelinating disorders is complex. We have examined the effect of IFN-γ in a chemically induced model of CNS demyelination. Mice that receive through their diet the copper chelator cuprizone display extensive demyelination of the corpus callosum. Remarkably, transgenic mice that ectopically express low levels of IFN-γ in the CNS did not display evidence of demyelination when treated with cuprizone, nor did they shows signs of oligodendroglial death, astrogliosis, or microgliosis, which are typically seen in treated animals. Myelin protein gene expression was, however, dramatically reduced in both the treated control and the transgenic animals, indicating that demyelination is not an obligatory consequence of a large diminution of myelin protein synthesis. Interestingly, the CNS of the IFN-γ-expressing mice contained elevated levels of insulin-like growth factor I, which has been demonstrated to have a protective effect against the demyelinating action of cuprizone.

The re-expression of the homeodomain transcription factor Gtx during remyelination of experimentally induced demyelinating lesions in young and old rat brain

Since myelination and remyelination both involve investing an axon with a myelin sheath, a plausible hypothesis is that the two processes involve the expression of similar transcription factors. In this study we have addressed this hypothesis by comparing the expression of messenger RNA of Gtx, a homeodomain transcription factor expressed within oligodendrocytes during myelination, with the expression of messenger RNAs of the major myelin proteins, myelin basic protein and proteolipid protein during remyelination of experimentally induced demyelination in the adult rat brain. We have found a close temporal and spatial association between the expression patterns of the three messenger RNA species during remyelination. By comparing the expression patterns in rapidly remyelinating lesions in young adult rats with slowly remyelinating lesions in old adult rats, we have shown that Gtx messenger RNA expression follows the reappearance of myelin basic protein and proteolipid protein messenger RNAs regardless of the rate of remyelination. This observation demonstrates a clear association between the expression of Gtx messenger RNA and myelin repair. We have also shown that there is a decrease in constitutive levels of expression of myelin basic protein, proteolipid protein and Gtx messenger RNA in old adults compared with young adults. Taken together, our results indicate that Gtx, which has multiple binding sites in the promoter regions of both myelin basic protein and proteolipid protein genes, may have a similar role in the regulation of myelin protein gene expression during remyelination as has been proposed in myelination.

Trembler as a Mouse Model of CMT1A?

The Trembler mouse suffers from a dominantly inherited autosomal mutation that results in an abnormal myelination of the peripheral nervous system. Biochemical studies have shown that dysmyelination is the primary event, demyelination being a late-occurring process. The expression of myelin protein genes has been studied. The steady-state levels for PMP22 mRNA represent 10 and 5% of normal values in the nerves of heterozygous and homozygous Trembler, respectively. This is due to a reduced expression of the specific transcript driven by the promoter 1 of the PMP22 gene. Collective results indicate that Trembler dysmyelination is not necessarily the consequence of a large accumulation of the mutated PMP22 protein. Moreover, it appears that the situation in the Trembler is different from that encountered in most CMT1A patients, where an increased PMP22 gene dosage is responsible for the disease. Therefore, the Trembler mutant is perhaps not an ideal model for this human neuropathy.

Insulin-Like Growth Factor I Protects Oligodendrocytes from Tumor Necrosis Factor- -Induced Injury

Tumor necrosis factor-α (TNF-α) has been causally implicated in several demyelinating disorders, including multiple sclerosis. Because insulin-like growth factor I (IGF-I) is a potent stimulator of myelination, we investigated whether it can protect oligodendrocytes and myelination from TNF-α-induced damage using mouse glial cultures as a model. Compared with controls, TNF-α decreased oligodendrocyte number by approximately 40% and doubled the number of apoptotic oligodendrocytes and their precursors. Addition of Boc-aspartyl(Ome)-fluoromethyl ketone (BAF), an inhibitor of interleukin-1β converting enzyme (ICE)/caspase proteases, blocked TNF-α-induced reductions in oligodendrocytes, indicating that the TNF-α-induced reduction in oligodendrocytes is, at least in part, due to apoptosis, and that ICE/caspases are one of TNF-α action mediators. Simultaneous addition of IGF-I to TNF-α-treated cultures negated these TNF-α effects nearly completely. Furthermore, IGF-I promoted oligodendrocyte precursor proliferation and/or differentiation in TNF-α-treated cultures. To analyze TNF-α and IGF-I actions on oligodendrocyte function, we measured the abundance of messenger RNAs (mRNAs) for two major myelin-specific proteins, myelin basic protein (MBP) and proteolipid protein (PLP). While TNF-α decreased MBP and PLP mRNA abundance by 5- to 6-fold, IGF-I abrogated TNF-α-induced reductions in a dose- and time-dependent manner. The changes in MBP and PLP mRNA abundance could not be completely explained by the changes in oligodendrocyte number, indicating that myelin protein gene expression is regulated by both TNF-α and IGF-I. These data support the hypothesis that TNF-α can mediate oligodendrocyte and myelin damage, and indicate that IGF-I protects oligodendrocytes from TNF-α insults by blocking TNF-α-induced apoptosis, and by promoting oligodendrocyte and precursor proliferation/differentiation and myelin protein gene expression.

Insulin-like growth factor I protects oligodendrocytes from tumor necrosis factor-alpha-induced injury.

Tumor necrosis factor-alpha (TNF-alpha) has been causally implicated in several demyelinating disorders, including multiple sclerosis. Because insulin-like growth factor I (IGF-I) is a potent stimulator of myelination, we investigated whether it can protect oligodendrocytes and myelination from TNF-alpha-induced damage using mouse glial cultures as a model. Compared with controls, TNF-alpha decreased oligodendrocyte number by approximately 40% and doubled the number of apoptotic oligodendrocytes and their precursors. Addition of Boc-aspartyl(Ome)-fluoromethyl ketone (BAF), an inhibitor of interleukin-1beta converting enzyme (ICE)/caspase proteases, blocked TNF-alpha-induced reductions in oligodendrocytes, indicating that the TNF-alpha-induced reduction in oligodendrocytes is, at least in part, due to apoptosis, and that ICE/caspases are one of TNF-alpha action mediators. Simultaneous addition of IGF-I to TNF-alpha-treated cultures negated these TNF-alpha effects nearly completely. Furthermore, IGF-I promoted oligodendrocyte precursor proliferation and/or differentiation in TNF-alpha-treated cultures. To analyze TNF-alpha and IGF-I actions on oligodendrocyte function, we measured the abundance of messenger RNAs (mRNAs) for two major myelin-specific proteins, myelin basic protein (MBP) and proteolipid protein (PLP). While TNF-alpha decreased MBP and PLP mRNA abundance by 5- to 6-fold, IGF-I abrogated TNF-alpha-induced reductions in a dose- and time-dependent manner. The changes in MBP and PLP mRNA abundance could not be completely explained by the changes in oligodendrocyte number, indicating that myelin protein gene expression is regulated by both TNF-alpha and IGF-I. These data support the hypothesis that TNF-alpha can mediate oligodendrocyte and myelin damage, and indicate that IGF-I protects oligodendrocytes from TNF-alpha insults by blocking TNF-alpha-induced apoptosis, and by promoting oligodendrocyte and precursor proliferation/differentiation and myelin protein gene expression.

The expression of myelin protein mRNAs during remyelination of lysolecithin‐induced demyelination

To gain insights into the mechanisms of myelin repair in the CNS and to establish the extent to which this process resembles myelination in development we have examined the patterns of expression of transcripts of the major myelin proteins, myelin basic protein (MBP) and proteolipid protein (PLP) during remyelination of lysolecithin-induced demyelination in the adult rat spinal cord. Injection of 1 microliter 1% lysolecithin into the dorsal funiculus caused a dramatic decrease in levels of MBP exon 1 and MBP exon 2-containing transcripts and PLP/DM20 transcripts. Between 10 and 21 days post-lesion induction there was a gradual increase in levels of expression of all transcripts, which had returned to levels associated with normally myelinated spinal cord white matter at 21 days. These increases in levels of expression corresponded to the appearance of remyelinated axons, detected on toluidine blue-stained resin sections. Foci of high levels of expression occurred in regions of the lesion in which new myelin sheath formation was occurring, although the level of expression throughout the lesion never exceeded levels associated with myelin sheath maintenance in normal white matter due to the asynchronous pattern of remyelination. The changes in levels of expression of MBP exon 2 closely followed those of MBP exon 1. Our results indicate that (i) myelin protein gene expression associated with myelinogenesis during remyelination follows a similar pattern to that of myelinogenesis during development and that (ii) in rat models of demyelination changes of expression of MBP exon 1 and exon 2-containing transcripts are of equal value, an observation relevant to quantifying the effects of putative remyelination-enhancing strategies using the lysolecithin model.