Distal transcriptional activators of the myelin basic protein gene in oligodendrocytes and Schwann cells

Myelin is a multilamellar sheath that wraps the axons in the Central Nervous System (CNS) and in the Peripheral Nervous System (PNS). It is required for normal development, axonal health and to facilitate impulse conduction. MBP, one of the major myelin proteins, is synthesised by both oligodendrocytes (OL) in CNS and Schwann cells (SC) in PNS. Its synthesis is regulated primarily at the transcriptional level. MBP transcription is activated as a part of a program of coordinate myelin gene expression during development, overlapping but specific in OL as compared to SC. The nuclear proteins that bind to the MBP promoter are largely unidentified. In vitro and in vivo studies show that activation of the MBP proximal promoter requires different DNA binding sites and proteins in OL as compared to SC. Recently, transgenic mice studies identified a SC enhancer (SCE) located 9.0Kb upstream of the transcriptional start site of MBP. In this work, we compared MBP transcription mechanisms in OL and SC. Transient transfection analyses, in primary cultures of OL and SC, confirm the importance of SCE, and suggest that SCE is an activator in both cell types, but it is an enhancer only in SC. Biochemical analyses show that there are regions differentially protected by SC and OL nuclear extracts that can account for differential function. Analysis of internal deletions and transversion mutations of SCE suggests that multiple cis-acting elements cooperate to produce activation. Analyses of stably transfected SC show that chromatin upregulates SCE activation at least three fold. Co-culture of these stably transfected SC and dorsal root ganglia neurons reveal that axons markedly activate SCE, by at least two orders of magnitude. These results describe a model in which to analyse SCE biochemistry and function and identify trans-acting signals from axons that regulate MBP transcription in SC

The Complex Work of Proteases and Secretases in Wallerian Degeneration: Beyond Neuregulin-1

After damage, axons in the peripheral nervous system (PNS) regenerate and regrow following a process termed Wallerian degeneration, but the regenerative process is often incomplete and usually the system does not reach full recovery. Key steps to the creation of a permissive environment for axonal regrowth are the trans-differentiation of Schwann cells and the remodeling of the extracellular matrix (ECM). In this review article, we will discuss how proteases and secretases promote effective regeneration and remyelination. We will detail how they control neuregulin-1 (NRG-1) activity at the post-translational level, as the concerted action of alpha, beta and gamma secretases cooperates to balance activating and inhibitory signals necessary for physiological myelination and remyelination. In addition, we will discuss the role of other proteases in nerve repair, among which A Disintegrin And Metalloproteinases (ADAMs) and gamma-secretases substrates. Moreover, we will present how matrix metalloproteinases (MMPs) and proteases of the blood coagulation cascade participate in forming newly synthetized myelin and in regulating axonal regeneration. Overall, we will highlight how a deeper comprehension of secretases and proteases mechanism of action in Wallerian degeneration might be useful to develop new therapies with the potential of readily and efficiently improve the regenerative process

BACE1 Processing of NRG1 Type III Produces a Myelin-Inducing Signal but Is Not Essential for the Stimulation of Myelination

Myelin sheath thickness is precisely adjusted to axon caliber, and in the peripheral nervous system, neuregulin 1 (NRG1) type III is a key regulator of this process. It has been proposed that the protease BACE1 activates NRG1 dependent myelination. Here, we characterize the predicted product of BACE1-mediated NRG1 type III processing in transgenic mice. Neuronal overexpression of a NRG1 type III-variant, designed to mimic prior cleavage in the juxtamembrane stalk region, induces hypermyelination in vivo and is sufficient to restore myelination of NRG1 type III-deficient neurons. This observation implies that the NRG1 cytoplasmic domain is dispensable and that processed NRG1 type III is sufficient for all steps of myelination. Surprisingly, transgenic neuronal overexpression of full-length NRG1 type III promotes hypermyelination also in BACE1 null mutant mice. Moreover, NRG1 processing is impaired but not abolished in BACE1 null mutants. Thus, BACE1 is not essential for the activation of NRG1 type III to promote myelination. Taken together, these findings suggest that multiple neuronal proteases collectively regulate NRG1 processing. © 2011 Wiley Periodicals, Inc

Dysregulated copper transport in multiple sclerosis may cause demyelination via astrocytes

Demyelination is a key pathogenic feature of multiple sclerosis (MS). Here, we evaluated the astrocyte contribution to myelin loss and focused on the neurotrophin receptor TrkB, whose up-regulation on the astrocyte finely demarcated chronic demyelinated areas in MS and was paralleled by neurotrophin loss. Mice lacking astrocyte TrkB were resistant to demyelination induced by autoimmune or toxic insults, demonstrating that TrkB signaling in astrocytes fostered oligodendrocyte damage. In vitro and ex vivo approaches highlighted that astrocyte TrkB supported scar formation and glia proliferation even in the absence of neurotrophin binding, indicating TrkB transactivation in response to inflammatory or toxic mediators. Notably, our neuropathological studies demonstrated copper dysregulation in MS and model lesions and TrkB-dependent expression of copper transporter (CTR1) on glia cells during neuroinflammation. In vitro experiments evidenced that TrkB was critical for the generation of glial intracellular calcium flux and CTR1 up-regulation induced by stimuli distinct from neurotrophins. These events led to copper uptake and release by the astrocyte, and in turn resulted in oligodendrocyte loss. Collectively, these data demonstrate a pathogenic demyelination mechanism via the astrocyte release of copper and open up the possibility of restoring copper homeostasis in the white matter as a therapeutic target in MS

Nerves and Pancreatic Cancer: New Insights into A Dangerous Relationship

Perineural invasion (PNI) is defined as the presence of neoplastic cells along nerves and/or within the different layers of nervous fibers: epineural, perineural and endoneural spaces. In pancreatic cancer—particularly in pancreatic ductal adenocarcinoma (PDAC)—PNI has a prevalence between 70 and 100%, surpassing any other solid tumor. PNI has been detected in the early stages of pancreatic cancer and has been associated with pain, increased tumor recurrence and diminished overall survival. Such an early, invasive and recurrent phenomenon is probably crucial for tumor growth and metastasis. PNI is a still not a uniformly characterized event; usually it is described only dichotomously (“present” or “absent”). Recently, a more detailed scoring system for PNI has been proposed, though not specific for pancreatic cancer. Previous studies have implicated several molecules and pathways in PNI, among which are secreted neurotrophins, chemokines and inflammatory cells. However, the mechanisms underlying PNI are poorly understood and several aspects are actively being investigated. In this review, we will discuss the main molecules and signaling pathways implicated in PNI and their roles in the PDAC

Niacin‐mediated Tace activation ameliorates CMT neuropathies with focal hypermyelination

Abstract Charcot–Marie–Tooth (CMT) neuropathies are highly heterogeneous disorders caused by mutations in more than 70 genes, with no available treatment. Thus, it is difficult to envisage a single suitable treatment for all pathogenetic mechanisms. Axonal Neuregulin 1 (Nrg1) type III drives Schwann cell myelination and determines myelin thickness by ErbB2/B3‐PI3K–Akt signaling pathway activation. Nrg1 type III is inhibited by the α‐secretase Tace, which negatively regulates PNS myelination. We hypothesized that modulation of Nrg1 levels and/or secretase activity may constitute a unifying treatment strategy for CMT neuropathies with focal hypermyelination as it could restore normal levels of myelination. Here we show that in vivo delivery of Niaspan, a FDA‐approved drug known to enhance TACE activity, efficiently rescues myelination in the Mtmr2−/− mouse, a model of CMT4B1 with myelin outfoldings, and in the Pmp22+/− mouse, which reproduces HNPP (hereditary neuropathy with liability to pressure palsies) with tomacula. Importantly, we also found that Niaspan reduces hypermyelination of Vim (vimentin)−/− mice, characterized by increased Nrg1 type III and Akt activation, thus corroborating the hypothesis that Niaspan treatment downregulates Nrg1 type III signaling

Neural stem cells derived from iPSCs represent a safe and effective source for stem cell therapy in experimental autoimmune encephalomyelitis

Neural stem cell (NSCs) transplantation is a promising therapy for Multiple Sclerosis (MS). The clinical translation of such approach is limited by the lack of expandable autologous precursors. Induced pluripotent stem cells (iPSCs) may overcome this limitation. In our work we investigated whether the transplantation of NSCs derived from iPSCs (NS iPSCs) could represent a safe and effective therapeutic strategy in a mouse model of MS, namely experimental autoimmune encephalomyelitis (EAE). Methods: NS iPSCs were derived from iPSCs obtained by lentiviral reprogramming of mouse fibroblasts. EAE was induced in C57/BL6 mice by subcutaneous immunization with myelin oligodendrocyte glycoprotein (MOG)35-55. At 25 days post immunization (dpi), EAE mice were intrathecally transplanted with GFP-labelled NS iPSCs. Neuropathology was assessed at 40 and 80 dpi while the influence of NS iPSCs on remyelination was further evaluated in vitro on primary oligodendrocyte precursor cell (OPC) cultures. Results: Upon transplantation in EAE mice, NS iPSCs did not induce any tumour formation and significantly reduced clinical severity, demyelination, axonal loss and neuroinflammation when compared to shamtreatment. Since transplanted NS iPSCs remained undifferentiated in close contact with perivascular inflammatory infiltrates, we investigated whether the inflammatory environment could induce NS iPSCs to promote endogenous repair mechanisms. Indeed we observed that, in vitro, the conditioned medium of NS iPSCs – challenged with inflammatory cytokines (IFNγ and TNFα) – markedly increased survival and differentiation of OPC primary cultures. This effect was not dependent on IFNγ or TNFα, as these cytokines alone were not able to sustain OPC survival. Conclusions: Our work provides the first evidence of the safety and efficacy of NS iPSCs in EAE. We showed that transplanted NS iPSCs exert their therapeutic bystander effect by persisting undifferentiated near the perivascular infiltrate. In vitro experiments suggest that the inflammatory environment could induce NS iPSC to secrete a variety of molecules that might promote endogenous remyelination