Evidence for decreased copper associated with demyelination in the corpus callosum of cuprizone-treated mice

Demyelination within the central nervous system (CNS) is a significant feature of debilitating neurological diseases such as multiple sclerosis and administering the copper-selective chelatorcuprizone to mice is widely used to model demyelination in vivo. Conspicuous demyelination within the corpus callosum is generally attributed to cuprizone's ability to restrict copper availability in this vulnerable brain region. However, the small number of studies that have assessed copper in brain tissue from cuprizone-treated mice have produced seemingly conflicting outcomes, leaving the role of CNS copper availability in demyelination unresolved. Herein we describe our assessment of copper concentrations in brain samples from mice treated with cuprizone for 40 d. Importantly, we applied an inductively coupled plasma mass spectrometry methodology that enabled assessment of copper partitioned into soluble and insoluble fractions within distinct brain regions, including the corpus callosum. Our results show that cuprizone-induced demyelination in the corpus callosum was associated with decreased soluble copper in this brain region. Insoluble copper in the corpus callosum was unaffected, as were pools of soluble and insoluble copper in other brain regions. Treatment with the blood-brain barrier permeant copper compound CuII(atsm) increased brain copper levels and this was most pronounced in the soluble fraction of the corpus callosum. This effect was associated with significant mitigation of cuprizone-induced demyelination. These results provide support for the involvement of decreased CNS copper availability in demyelination in the cuprizone model. Relevance to human demyelinating disease is discussed.

Early microglial response, myelin deterioration and lethality in mice deficient for very long chain ceramide synthesis in oligodendrocytes

The sphingolipids galactosylceramide (GalCer), sulfatide (ST) and sphingomyelin (SM) are essential for myelin stability and function. GalCer and ST are synthesized mostly from C22-C24 ceramides, generated by Ceramide Synthase 2 (CerS2). To clarify the requirement for C22-C24 sphingolipid synthesis in myelin biosynthesis and stability, we generated mice lacking CerS2 specifically in myelinating cells (CerS2ΔO/ΔO ). At 6 weeks of age, normal-appearing myelin had formed in CerS2ΔO/ΔO mice, however there was a reduction in myelin thickness and the percentage of myelinated axons. Pronounced loss of C22-C24 sphingolipids in myelin of CerS2ΔO/ΔO mice was compensated by greatly increased levels of C18 sphingolipids. A distinct microglial population expressing high levels of activation and phagocytic markers such as CD64, CD11c, MHC class II, and CD68 was apparent at 6 weeks of age in CerS2ΔO/ΔO mice, and had increased by 10 weeks. Increased staining for denatured myelin basic protein was also apparent in 6-week-old CerS2ΔO/ΔO mice. By 16 weeks, CerS2ΔO/ΔO mice showed pronounced myelin atrophy, motor deficits, and axon beading, a hallmark of axon stress. 90% of CerS2ΔO/ΔO mice died between 16 and 26 weeks of age. This study highlights the importance of sphingolipid acyl chain length for the structural integrity of myelin, demonstrating how a modest reduction in lipid chain length causes exposure of a denatured myelin protein epitope and expansion of phagocytic microglia, followed by axon pathology, myelin degeneration, and motor deficits. Understanding the molecular trigger for microglial activation should aid the development of therapeutics for demyelinating and neurodegenerative diseases.

Remodelling of myelinated axons and oligodendrocyte differentiation is stimulated by environmental enrichment in the young adult brain

Oligodendrocyte production and myelination continues lifelong in the central nervous system (CNS), and all stages of this process can be adaptively regulated by neuronal activity. While artificial exogenous stimulation of neuronal circuits greatly enhances oligodendrocyte progenitor cell (OPC) production and increases myelination during development, the extent to which physiological stimuli replicates this is unclear, particularly in the adult CNS when the rate of new myelin addition slows. Here, we used environmental enrichment (EE) to physiologically stimulate neuronal activity for 6 weeks in 9-week-old C57BL/six male and female mice and found no increase in compact myelin in the corpus callosum or somatosensory cortex. Instead, we observed a global increase in callosal axon diameter with thicker myelin sheaths, elongated paranodes and shortened nodes of Ranvier. These findings indicate that EE induced the dynamic structural remodelling of myelinated axons. Additionally, we observed a global increase in the differentiation of OPCs and pre-myelinating oligodendroglia in the corpus callosum and somatosensory cortex. Our findings of structural remodelling of myelinated axons in response to physiological neural stimuli during young adulthood provide important insights in understanding experience-dependent myelin plasticity throughout the lifespan and provide a platform to investigate axon-myelin interactions in a physiologically relevant context.

Acute treatment with TrkB agonist LM22A-4 confers neuroprotection and preserves myelin integrity in a mouse model of pediatric traumatic brain injury

Young children have a high risk of sustaining a traumatic brain injury (TBI), which can have debilitating life-long consequences. Importantly, the young brain shows particular vulnerability to injury, likely attributed to ongoing maturation of the myelinating nervous system at the time of insult. Here, we examined the effect of acute treatment with the partial tropomyosin receptor kinase B (TrkB) agonist, LM22A-4, on pathological and neurobehavioral outcomes after pediatric TBI, with the hypothesis that targeting TrkB would minimize tissue damage and support functional recovery. We focused on myelinated tracts-the corpus callosum and external capsules-based on recent evidence that TrkB activation potentiates oligodendrocyte remyelination. Male mice at postnatal day 21 received an experimental TBI or sham surgery. Acutely post-injury, extensive cell death, a robust glial response and disruption of compact myelin were evident in the injured brain. TBI or sham mice then received intranasal saline vehicle or LM22A-4 for 14 days. Behavior testing was performed from 4 weeks post-injury, and brains were collected at 5 weeks for histology. TBI mice showed hyperactivity, reduced anxiety-like behavior, and social memory impairments. LM22A-4 ameliorated the abnormal anxiolytic phenotype but had no effect on social memory deficits. Use of spectral confocal reflectance microscopy detected persistent myelin fragmentation in the external capsule of TBI mice at 5 weeks post-injury, which was accompanied by regionally distinct deficits in oligodendrocyte progenitor cells and post-mitotic oligodendrocytes, as well as chronic reactive gliosis and atrophy of the corpus callosum and injured external capsule. LM22A-4 treatment ameliorated myelin deficits in the perilesional external capsule, as well as tissue volume loss and the extent of reactive gliosis. However, there was no effect of this TrkB agonist on oligodendroglial populations detected at 5 weeks post-injury. Collectively, our results demonstrate that targeting TrkB immediately after TBI during early life confers neuroprotection and preserves myelin integrity, and this was associated with some improved neurobehavioral outcomes as the pediatric injured brain matures.

Partial deletion of p75NTR in large-diameter DRG neurons exerts no influence upon the survival of peripheral sensory neurons in vivo

The p75 neurotrophin receptor (p75NTR ) is required for maintaining peripheral sensory neuron survival and function; however, the underlying cellular mechanism remains unclear. The general view is that expression of p75NTR by the neuron itself is required for maintaining sensory neuron survival and myelination in the peripheral nervous system (PNS). Adopting a neuronal-specific conditional knockout strategy, we demonstrate the partial depletion of p75NTR in neurons exerts little influence upon maintaining sensory neuron survival and peripheral nerve myelination in health and after demyelinating neuropathy. Our data show that the density and total number of dorsal root ganglion (DRG) neurons in 2-month-old mice is not affected following the deletion of p75NTR in large-diameter myelinating neurons, as assessed by stereology. Adopting experimental autoimmune neuritis induced in adult male mice, an animal model of demyelinating peripheral neuropathy, we identify that deleting p75NTR in myelinating neurons exerts no influence upon the disease progression, the total number of DRG neurons, and the extent of myelin damage in the sciatic nerve, indicating that the expression of neuronal p75NTR is not essential for maintaining peripheral neuron survival and myelination after a demyelinating insult in vivo. Together, results of this study suggest that the survival and myelination of peripheral sensory neurons is independent of p75NTR expressed by a subtype of neurons in vivo. Thus, our findings provide new insights into the mechanism underpinning p75NTR -mediated neuronal survival in the PNS.

Schwann cell p75 neurotrophin receptor modulates small fiber degeneration in diabetic neuropathy

Diabetic neuropathy has an incidence as high as 50% of diabetic patients and is characterized by damage to neurons, Schwann cells and blood vessels within the peripheral nervous system. The low-affinity neurotrophin receptor p75 (p75^NTR ), particularly expressed by the Schwann cells in the peripheral nerve, has previously been reported to play a role in developmental myelination and cell survival/death. Increased levels of p75^NTR , in the endoneurium and plasma from diabetic patients and rodent models of disease, have been observed, proposing that this receptor might be involved in the pathogenesis of diabetic neuropathy. Therefore, in this study, we addressed this hypothesis by utilizing a mouse model of selective nerve growth factor receptor (Ngfr) deletion in Schwann cells (SC-p75^NTR -KO). Electron microscopy of sciatic nerves from mice with high fat diet induced obesity demonstrated how loss of Schwann cell-p75^NTR aggravated axonal atrophy and loss of C-fibers. RNA sequencing disclosed several pre-clinical signaling alterations in the diabetic peripheral nerves, dependent on Schwann cell p75^NTR signaling, specially related with lysosome, phagosome, and immune pathways. Morphological and biochemical analyses identified abundant lysosomes and autophagosomes in the C-fiber axoplasm of the diabetic SC-p75^NTR -KO nerves, which together with increased Cathepsin B protein levels corroborates gene upregulation from the phagolysosomal pathways. Altogether, this study demonstrates that Schwann cell p75^NTR deficiency amplifies diabetic neuropathy disease by triggering overactivation of immune-related pathways and increased lysosomal stress.

Imaging and Quantification of Myelin Integrity After Injury With Spectral Confocal Reflectance Microscopy

Developing a high-throughput approach to quantify the extent of myelin integrity in preclinical models of demyelinating diseases will enhance our capacity to identify novel therapies for myelin repair. In light of the technical limitations of electron microscopy and immunohistochemical analyses of myelination, we have utilized a novel imaging technique, spectral confocal reflectance (SCoRe) microscopy. SCoRe takes advantage of the optically reflective properties of compact myelin, allowing the integrity of compact myelin to be quantified over the course of the cuprizone-induced model of central demyelination. We applied SCoRe imaging on fixed frozen brain sections. SCoRe analysis of control mice identified an increase in corpus callosum myelination during the period of cuprizone administration and recovery, suggesting that the normal developmental processes of myelination are ongoing at this time. Importantly, analysis of mice subjected to cuprizone identified a significant reduction in compact myelin in both rostral and caudal corpus callosum compared to age-matched control mice. SCoRe microscopy also allowed the visualization and quantification of the amount of myelin debris in demyelinating lesions. Combining SCoRe imaging with immunohistochemistry, we quantified the amount of myelin debris within IBA-1+ microglia and found that 11% of myelin debris colocalized in microglia irrespective of the callosal regions, with the vast majority of debris outside of microglia. In summary, we have demonstrated that SCoRe microscopy is an effective and powerful tool to perform both quantitative and qualitative analyses of compact myelin integrity in health or after injury in vivo, demonstrating its future application in high-throughput assessments and screening of the therapeutic efficacy of myelin repair therapies in preclinical animal models of demyelinating diseases.

TrkB Agonist LM22A-4 Increases Oligodendroglial Populations During Myelin Repair in the Corpus Callosum

The neurotrophin, brain-derived neurotrophic factor (BDNF) promotes central nervous system (CNS) myelination during development and after injury. This is achieved via activation of oligodendrocyte-expressed tropomyosin-related kinase (Trk) B receptors. However, while administration of BDNF has shown beneficial effects, BDNF itself has a poor pharmacokinetic profile. Here, we compare two TrkB-targeted BDNF-mimetics, the structural-mimetic, tricyclic dimeric peptide-6 (TDP6) and the non-peptide small molecule TrkB agonist LM22A-4 in a cuprizone model of central demyelination in female mice. Both mimetics promoted remyelination, increasing myelin sheath thickness and oligodendrocyte densities after 1-week recovery. Importantly, LM22A-4 exerts these effects in an oligodendroglial TrkB-dependent manner. However, analysis of TrkB signaling by LM22A-4 suggests rather than direct activation of TrkB, LM22A-4 exerts its effects via indirect transactivation of Trk receptors. Overall, these studies support the therapeutic strategy to selectively targeting TrkB activation to promote remyelination in the brain.

Peripheral Nerve Regeneration Is Independent From Schwann Cell p75NTR Expression

Schwann cell reprogramming and differentiation are crucial prerequisites for neuronal regeneration and re-myelination to occur following injury to peripheral nerves. The neurotrophin receptor p75^NTR has been identified as a positive modulator for Schwann cell myelination during development and implicated in promoting nerve regeneration after injury. However, most studies base this conclusion on results obtained from complete p75^NTR knockout mouse models and cannot dissect the specific role of p75^NTR expressed by Schwann cells. In this present study, a conditional knockout model selectively deleting p75^NTR expression in Schwann cells was generated, where p75^NTR expression is replaced with that of an mCherry reporter. Silencing of Schwann cell p75^NTR expression was confirmed in the sciatic nerve in vivo and in vitro, without altering axonal expression of p75^NTR. No difference in sciatic nerve myelination during development or following sciatic nerve crush injury was observed, as determined by quantification of both myelinated and unmyelinated nerve fiber densities, myelinated axonal diameter and myelin thickness. However, the absence of Schwann cell p75^NTR reduced motor nerve conduction velocity after crush injury. Our data indicate that the absence of Schwann cell p75^NTR expression in vivo is not critical for axonal regrowth or remyelination following sciatic nerve crush injury, but does play a key role in functional recovery. Overall, this represents the first step in redefining the role of p75^NTR in the peripheral nervous system, suggesting that the Schwann cell-axon unit functions as a syncytium, with the previous published involvement of p75^NTR in remyelination most likely depending on axonal/neuronal p75^NTR and/or mutual glial-axonal interactions.

Brain-Derived Neurotrophic Factor in Central Nervous System Myelination: A New Mechanism to Promote Myelin Plasticity and Repair

Brain-derived neurotrophic factor (BDNF) plays vitally important roles in neural development and plasticity in both health and disease. Recent studies using mutant mice to selectively manipulate BDNF signalling in desired cell types, in combination with animal models of demyelinating disease, have demonstrated that BDNF not only potentiates normal central nervous system myelination in development but enhances recovery after myelin injury. However, the precise mechanisms by which BDNF enhances myelination in development and repair are unclear. Here, we review some of the recent progress made in understanding the influence BDNF exerts upon the myelinating process during development and after injury, and discuss the cellular and molecular mechanisms underlying its effects. In doing so, we raise new questions for future research.

Ubiquitin Regulation of Trk Receptor Trafficking and Degradation

The regulation of Trk receptors is critical for orchestrating multiple signalling pathways required for developing and maintaining neuronal networks. Activation of Trk receptors results in signalling, internalisation and subsequent degradation of the protein. Although ubiquitination of TrkA by Nedd4-2 has been identified as an important degradation pathway, much less is known about the pathways regulating the degradation of TrkB and TrkC. Critical to the interaction between TrkA and Nedd4-2 is a PPxY motif present within TrkA but absent in TrkB and TrkC. Given the absence of this interaction motif, it remains to be determined how TrkB and TrkC are ubiquitinated. Here we report that the adaptor protein Ndfip1 can interact with all three Trk receptors and show for TrkB the recruitment of Nedd4-2 through PPxY motifs present in Ndfip1. Ndfip1 mediates the ubiquitination of TrkB, resulting in receptor trafficking predominantly on Rab7 containing late endosomes, highlighting a pathway for TrkB degradation at the lysosome. In vitro, overexpression of Ndfip1 increased TrkB ubiquitination and decreased viability of BDNF-dependent primary neurons. In vivo, conditional genetic deletion of Ndfip1 increased TrkB in the brain and resulted in enlargement of the granular cell layer of the dentate gyrus.

Tropomyosin-Related Kinase B (TrkB) Regulates Neurite Outgrowth via a Novel Interaction with Suppressor of Cytokine Signalling 2 (SOCS2)

Brain-derived neurotrophic factor (BDNF) is highly expressed in the hippocampus, where it can initiate signalling pathways leading to neurite outgrowth, neuron survival, spine maturation and increased synapse strength. Although suppressor of cytokine signalling 2 (SOCS2) is primarily known to negatively regulate cytokine signalling, it is also highly expressed in the hippocampus and exerts neuron-specific functions in the brain, effecting the length and architecture of neurons. However, little is known about the role of SOCS2 in the hippocampus. In this study, we hypothesised that SOCS2 may have a regulatory role in BDNF-dependent neurite growth and hippocampal neuronal function. Here our data demonstrate that SOCS2 interacts with the kinase domain of the BDNF receptor TrkB. Germline overexpression of SOCS2 results in a BDNF-dependent increase in hippocampal neurite outgrowth, whereas deletion of SOCS2 results in shorter neurite outgrowth. Expression of SOCS2 also results in increased ubiquitination of the juxtamembrane region of TrkB, and alters the trafficking of TrkB into recycling endosomes. Collectively, our data suggest a novel role for SOCS2 in interacting with and regulating the trafficking of TrkB, leading to increased neurite outgrowth in hippocampus neurons.

BDNF haploinsufficiency exerts a transient and regionally different influence upon oligodendroglial lineage cells during postnatal development

Brain-Derived Neurotrophic Factor (BDNF) plays important roles in promoting myelination in the developing central nervous system (CNS), however the influence it exerts on oligodendrocyte development in vivo remains unclear. As BDNF knockout mice die in the perinatal period, we undertook a systematic developmental analysis of oligodendroglial lineage cells within multiple CNS regions of BDNF heterozygous (HET) mice. Our data identify that BDNF heterozygosity results in transient reductions in oligodendroglial lineage cell density and progression that are largely restricted to the optic nerve, whereas the corpus callosum, cerebral cortex, basal forebrain and spinal cord white matter tracts are unaffected. In the first two postnatal weeks, BDNF HET mice exhibit reductions in the density of oligodendroglial lineage cells, oligodendrocyte precursor cells (OPCs) and postmitotic oligodendrocytes selectively in the optic nerve, but not in the brain or spinal cord white matter tracts. However, this normalizes later in development. The overall proportion of OPCs and mature oligodendrocytes remains unchanged from P9 to P30 in all CNS regions. This study identifies that BDNF exerts transient effects on oligodendroglial lineage cells selectively in the optic nerve during postnatal development. Taken together, this provides compelling evidence that BDNF haploinsufficiency exerts modest effects upon oligodendroglial cell density and lineage progression in vivo, suggesting its major role is restricted to promoting oligodendrocyte myelination.

Myelin Protein Zero180-199 Peptide Induced Experimental Autoimmune Neuritis in C57BL/6 Mice

Mouse models of peripheral demyelinating neuropathy play an important role in enabling the study of disease pathogenesis. Further, induction in transgenic mice allows for the precise interrogation of disease mechanisms, as well as the analysis of the efficacy and mechanisms of potential new therapies. Here we describe a method to successfully induce experimental autoimmune neuritis (EAN) using myelin protein zero (P0)_180-199 peptide in combination with Freund's complete adjuvant and pertussis toxin in the C57BL/6 mouse strain. We also outline a sensitive paradigm of accurately assessing the extent of functional deficits occurring in murine EAN.

A Simple Approach to Induce Experimental Autoimmune Neuritis in C57BL/6 Mice for Functional and Neuropathological Assessments

Experimental autoimmune neuritis (EAN) is a well-appreciated experimental model of autoimmune peripheral demyelinating diseases. EAN disease is induced by immunizing mice with neurogenic peptides to direct an inflammatory attack toward components of the peripheral nervous system (PNS). Recent advances have enabled the induction of EAN in the relatively resistant C57BL/6 mouse line using myelin protein zero (P0)106-125 or P0180-199 peptides delivered in adjuvant combined with the injection of pertussis toxin. The ability to induce EAN in the C57BL/6 strain allows for the use of the numerous genetic tools that exist on this mouse background, and thus allows the sophisticated study of disease pathogenesis and interrogation of the mechanistic action of novel therapeutics in combination with transgenic approaches. In this study, we demonstrate a simple approach to successfully induce EAN using the P0180-199 peptide in C57BL/6 mice. We also outline a protocol for the assessment of functional deficits that occur in this model, accompanied by an array of neuropathological features. Thus, this model is a powerful experimental model to study the pathogenesis of human peripheral demyelinating neuropathies, and to determine the efficacy of potential therapies that aim to promote myelin repair and protect against nerve damage in autoimmune neuritis.

A Brain-Derived Neurotrophic Factor-Based p75NTR Peptide Mimetic Ameliorates Experimental Autoimmune Neuritis Induced Axonal Pathology and Demyelination

Axonal damage and demyelination are major determinants of disability in patients with peripheral demyelinating neuropathies. The neurotrophin family of growth factors are essential for the normal development and myelination of the peripheral nervous system (PNS), and as such are potential therapeutic candidates for ameliorating axonal and myelin damage. In particular, BDNF promotes peripheral nerve myelination via p75 neurotrophin receptor (p75NTR) receptors. Here, we investigated the therapeutic efficacy of a small structural mimetic of the region of BDNF that binds to p75NTR (cyclo-dPAKKR) in experimental autoimmune neuritis (EAN), an established animal model of peripheral demyelinating neuropathy. Examination of rodents induced with EAN revealed that p75NTR is abundantly expressed in affected peripheral nerves. We found that systemic administration of cyclo-dPAKKR ameliorates EAN disease severity and accelerates recovery. Animals treated with cyclo-dPAKKR displayed significantly better motor performance compared to control animals. Histological assessment revealed that cyclo-dPAKKR administration limits the extent of inflammatory demyelination and axonal damage, and protects against the disruption of nodal architecture in affected peripheral nerves. In contrast, a structural control peptide of cyclo-dPAKKR exerted no influence. Moreover, all the beneficial effects of cyclo-dPAKKR in EAN are abrogated in p75NTR heterozygous mice, strongly suggesting a p75NTR-dependent effect. Taken together, our data demonstrate that cyclo-dPAKKR ameliorates functional and pathological defects of EAN in a p75NTR-dependant manner, suggesting that p75NTR is a therapeutic target to consider for future treatment of peripheral demyelinating diseases and targeting of p75NTR is a strategy worthy of further investigation.

A Functional and Neuropathological Testing Paradigm Reveals New Disability-Based Parameters and Histological Features for P0180-190-Induced Experimental Autoimmune Neuritis in C57BL/6 Mice

We assessed novel disability-based parameters and neuropathological features of the P0180-190 peptide-induced model of experimental autoimmune neuritis (EAN) in C57BL/6 mice. We show that functional assessments such as running capacity provide a more sensitive method for detecting alterations in disease severity than a classical clinical scoring paradigm. We performed detailed ultrastructural analysis and show for the first time that tomaculous neuropathy is a neuropathological feature of this disease model. In addition, we demonstrate that ultrastructural assessments of myelin pathology are sufficiently sensitive to detect significant differences in both mean G-ratio and mean axon diameter between mice with EAN induced with different doses of pertussis toxin. In summary, we have established a comprehensive assessment paradigm for discriminating variations in disease severity and the extent of myelin pathology in this model. Our findings indicate that this model is a powerful tool to study the pathogenesis of human peripheral demyelinating neuropathies and that this assessment paradigm could be used to determine the efficacy of potential therapies that aim to promote myelin repair and protect against nerve damage in autoimmune neuritides.

Bone Morphogenetic Protein 4 Signalling in Neural Stem and Progenitor Cells during Development and after Injury

Substantial progress has been made in identifying the extracellular signalling pathways that regulate neural stem and precursor cell biology in the central nervous system (CNS). The bone morphogenetic proteins (BMPs), in particular BMP4, are key players regulating neuronal and glial cell development from neural precursor cells in the embryonic, postnatal, and injured CNS. Here we review recent studies on BMP4 signalling in the generation of neurons, astrocytes, and oligodendroglial cells in the CNS. We also discuss putative mechanisms that BMP4 may utilise to influence glial cell development following CNS injury and highlight some questions for further research.

Fyn is an intermediate kinase that BDNF utilizes to promote oligodendrocyte myelination

Fyn, a member of the Src family of nonreceptor tyrosine kinases, promotes central nervous system myelination during development; however the mechanisms mediating this effect remain unknown. Here we show that Fyn phosphorylation is modulated by BDNF in vivo. Concordant with this, we find that BDNF stimulates Fyn phosphorylation in myelinating cocultures, an effect dependent on oligodendroglial expression of TrkB. Importantly, PP2, a pharmacological inhibitor of Src family kinases, not only abrogated the promyelinating influence of BDNF in vitro, but also attenuated BDNF-induced phosphorylation of Erk1/2 in oligodendrocytes. Over-expression of Fyn in oligodendrocytes significantly promotes phosphorylation of Erk1/2, and promotes myelination to the extent that exogenous BDNF exerts no additive effect in vitro. In contrast, expression of a kinase-dead mutant of Fyn in oligodendrocytes significantly inhibited BDNF-induced activation of Erk1/2 and abrogated the promyelinating effect of BDNF. Analysis of white matter tracts in vivo revealed that phosphorylated Fyn primarily colocalized with mature oligodendrocytes, and was rarely observed in oligodendrocyte progenitor cells, a profile that closely parallels the detection of phosphorylated Erk1/2 in the developing central nervous system. Taken together, these data identify that Fyn kinase exerts a key role in mediating the promyelinating influence of BDNF. Here we identify a pathway in which BDNF activation of oligodendroglial TrkB receptors stimulates the phosphorylation of Fyn, a necessary step required to potentiate the phosphorylation of Erk1/2, which in turn regulates oligodendrocyte myelination.

The roles of extracellular related-kinases 1 and 2 signaling in CNS myelination

Substantial progress has been made in identifying the intracellular signaling pathways that regulate central nervous system myelination. Recently, the mitogen activated protein kinase pathway, in particular the extracellular signal-related kinase 1 (Erk1) and Erk2, have been identified as critically important in mediating the effects of several growth factors that regulate oligodendroglial development and myelination. Here we will review the recent studies that identify the key role that Erk1/2 signaling plays in regulating oligodendroglial development, myelination and remyelination, discuss the potential mechanisms that Erk1/2 may utilize to influence myelination, and highlight some questions for further research. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Production and use of lentivirus to selectively transduce primary oligodendrocyte precursor cells for in vitro myelination assays

Myelination is a complex process that involves both neurons and the myelin forming glial cells, oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS). We use an in vitro myelination assay, an established model for studying CNS myelination in vitro. To do this, oligodendrocyte precursor cells (OPCs) are added to the purified primary rodent dorsal root ganglion (DRG) neurons to form myelinating co-cultures. In order to specifically interrogate the roles that particular proteins expressed by oligodendrocytes exert upon myelination we have developed protocols that selectively transduce OPCs using the lentivirus overexpressing wild type, constitutively active or dominant negative proteins before being seeded onto the DRG neurons. This allows us to specifically interrogate the roles of these oligodendroglial proteins in regulating myelination. The protocols can also be applied in the study of other cell types, thus providing an approach that allows selective manipulation of proteins expressed by a desired cell type, such as oligodendrocytes for the targeted study of signaling and compensation mechanisms. In conclusion, combining the in vitro myelination assay with lentiviral infected OPCs provides a strategic tool for the analysis of molecular mechanisms involved in myelination.

A novel role of suppressor of cytokine signaling-2 in the regulation of TrkA neurotrophin receptor biology

Suppressor of cytokine signaling-2 (SOCS2) is a regulator of intracellular responses to growth factors and cytokines. Cultured dorsal root ganglia neurons from neonatal mice with increased or decreased SOCS2 expression were examined for altered responsiveness to nerve growth factor (NGF). In the presence of NGF, SOCS2 over-expression increased neurite length and complexity, whereas loss of SOCS2 reduced neurite outgrowth. Neither loss nor gain of SOCS2 expression altered the relative survival of these cells, suggesting that SOCS2 can discriminate between the differentiation and survival responses to NGF. Interaction studies in 293T cells revealed that SOCS2 immunoprecipitates with TrkA and a juxtamembrane motif of TrkA was required for this interaction. SOCS2 also immunoprecipitated with endogenous TrkA in PC12 Tet-On cells. Over-expression of SOCS2 in PC12 Tet-On cells increased total and surface TrkA expression. In contrast, dorsal root ganglion neurons which over-expressed SOCS2 did not exhibit significant changes in total levels but an increase in surface TrkA was noted. SOCS2-induced neurite outgrowth in PC12 Tet-On cells correlated with increased and prolonged activation of pAKT and pErk1/2 and required an intact SOCS2 SH2 domain and SOCS box domain. This study highlights a novel role for SOCS2 in the regulation of TrkA signaling and biology.

Genome-wide association study of shared components of reading disability and language impairment

Written and verbal languages are neurobehavioral traits vital to the development of communication skills. Unfortunately, disorders involving these traits-specifically reading disability (RD) and language impairment (LI)-are common and prevent affected individuals from developing adequate communication skills, leaving them at risk for adverse academic, socioeconomic and psychiatric outcomes. Both RD and LI are complex traits that frequently co-occur, leading us to hypothesize that these disorders share genetic etiologies. To test this, we performed a genome-wide association study on individuals affected with both RD and LI in the Avon Longitudinal Study of Parents and Children. The strongest associations were seen with markers in ZNF385D (OR = 1.81, P = 5.45 × 10(-7) ) and COL4A2 (OR = 1.71, P = 7.59 × 10(-7) ). Markers within NDST4 showed the strongest associations with LI individually (OR = 1.827, P = 1.40 × 10(-7) ). We replicated association of ZNF385D using receptive vocabulary measures in the Pediatric Imaging Neurocognitive Genetics study (P = 0.00245). We then used diffusion tensor imaging fiber tract volume data on 16 fiber tracts to examine the implications of replicated markers. ZNF385D was a predictor of overall fiber tract volumes in both hemispheres, as well as global brain volume. Here, we present evidence for ZNF385D as a candidate gene for RD and LI. The implication of transcription factor ZNF385D in RD and LI underscores the importance of transcriptional regulation in the development of higher order neurocognitive traits. Further study is necessary to discern target genes of ZNF385D and how it functions within neural development of fluent language.

A small peptide mimetic of brain-derived neurotrophic factor promotes peripheral myelination

The expression of the neurotrophins and their receptors is essential for peripheral nervous system development and myelination. We have previously demonstrated that brain-derived neurotrophic factor (BDNF) exerts contrasting influences upon Schwann cell myelination in vitro - promoting myelination via neuronally expressed p75NTR, but inhibiting myelination via neuronally expressed TrkB. We have generated a small peptide called cyclo-dPAKKR that structurally mimics the region of BDNF that binds p75NTR. Here, we have investigated whether utilizing cyclo-dPAKKR to selectively target p75NTR is an approach that could exert a unified promyelinating response. Like BDNF, cyclo-dPAKKR promoted myelination of nerve growth factor-dependent neurons in vitro, an effect dependent on the neuronal expression of p75NTR. Importantly, cyclo-dPAKKR also significantly promoted the myelination of tropomyosin-related kinase receptor B-expressing neurons in vitro, whereas BDNF exerted a significant inhibitory effect. This indicated that while BDNF exerted a contrasting influence upon the myelination of distinct subsets of dorsal root ganglion (DRG) neurons in vitro, cyclo-dPAKKR uniformly promoted their myelination. Local injection of cyclo-dPAKKR adjacent to the developing sciatic nerve in vivo significantly enhanced myelin protein expression and significantly increased the number of myelinated axons. These results demonstrate that cyclo-dPAKKR promotes peripheral myelination in vitro and in vivo, suggesting it is a strategy worthy of further investigation for the treatment of peripheral demyelinating diseases.

Common genetic variation near the connexin-43 gene is associated with resting heart rate in African Americans: a genome-wide association study of 13,372 participants

BACKGROUND

Genome-wide association studies have identified several genetic loci associated with variation in resting heart rate in European and Asian populations. No study has evaluated genetic variants associated with heart rate in African Americans.

OBJECTIVE

To identify novel genetic variants associated with resting heart rate in African Americans.

METHODS

Ten cohort studies participating in the Candidate-gene Association Resource and Continental Origins and Genetic Epidemiology Network consortia performed genome-wide genotyping of single nucleotide polymorphisms (SNPs) and imputed 2,954,965 SNPs using HapMap YRI and CEU panels in 13,372 participants of African ancestry. Each study measured the RR interval (ms) from 10-second resting 12-lead electrocardiograms and estimated RR-SNP associations using covariate-adjusted linear regression. Random-effects meta-analysis was used to combine cohort-specific measures of association and identify genome-wide significant loci (P≤2.5×10(-8)).

RESULTS

Fourteen SNPs on chromosome 6q22 exceeded the genome-wide significance threshold. The most significant association was for rs9320841 (+13 ms per minor allele; P = 4.98×10(-15)). This SNP was approximately 350 kb downstream of GJA1, a locus previously identified as harboring SNPs associated with heart rate in Europeans. Adjustment for rs9320841 also attenuated the association between the remaining 13 SNPs in this region and heart rate. In addition, SNPs in MYH6, which have been identified in European genome-wide association study, were associated with similar changes in the resting heart rate as this population of African Americans.

CONCLUSIONS

An intergenic region downstream of GJA1 (the gene encoding connexin 43, the major protein of the human myocardial gap junction) and an intragenic region within MYH6 are associated with variation in resting heart rate in African Americans as well as in populations of European and Asian origin.

Gas6 increases myelination by oligodendrocytes and its deficiency delays recovery following cuprizone-induced demyelination

Multiple sclerosis (MS) is a complex demyelinating disease of the central nervous system. Current research has shown that at least in some cases, the primary insult in MS could be directed at the oligodendrocyte, and that the earliest immune responses are primarily via innate immune cells. We have identified a family of receptor protein tyrosine kinases, known as the TAM receptors (Tyro3, Axl and Mertk), as potentially important in regulating both the oligodendrocyte and immune responses. We have previously shown that Gas6, a ligand for the TAM receptors, can affect the severity of demyelination in mice, with a loss of signalling via Gas6 leading to decreased oligodendrocyte survival and increased microglial activation during cuprizone-induced demyelination. We hypothesised TAM receptor signalling would also influence the extent of recovery in mice following demyelination. A significant effect of the absence of Gas6 was detected upon remyelination, with a lower level of myelination after 4 weeks of recovery in comparison with wild-type mice. The delay in remyelination was accompanied by a reduction in oligodendrocyte numbers. To understand the molecular mechanisms that drive the observed effects, we also examined the effect of exogenous Gas6 in in vitro myelination assays. We found that Gas6 significantly increased myelination in a dose-dependent manner, suggesting that TAM receptor signalling could be directly involved in myelination by oligodendrocytes. The reduced rate of remyelination in the absence of Gas6 could thus result from a lack of Gas6 at a critical time during myelin production after injury. These findings establish Gas6 as an important regulator of both CNS demyelination and remyelination.

Brain-derived neurotrophic factor promotes central nervous system myelination via a direct effect upon oligodendrocytes

The extracellular factors that are responsible for inducing myelination in the central nervous system (CNS) remain elusive. We investigated whether brain-derived neurotrophic factor (BDNF) is implicated, by first confirming that BDNF heterozygous mice exhibit delayed CNS myelination during early postnatal development. We next established that the influence of BDNF upon myelination was direct, by acting on oligodendrocytes, using co-cultures of dorsal root ganglia neurons and oligodendrocyte precursor cells. Importantly, we found that BDNF retains its capacity to enhance myelination of neurons or by oligodendrocytes derived from p75NTR knockout mice, indicating the expression of p75NTR is not necessary for BDNF-induced myelination. Conversely, we observed that phosphorylation of TrkB correlated with myelination, and that inhibiting TrkB signalling also inhibited the promyelinating effect of BDNF, suggesting that BDNF enhances CNS myelination via activating oligodendroglial TrkB-FL receptors. Together, our data reveal a previously unknown role for BDNF in potentiating the normal development of CNS myelination, via signalling within oligodendrocytes.

The role of neurotrophins in the regulation of myelin development

Neurotrophins comprise a family of growth factors that are expressed in a variety of cell types, and which exert influences on a large range of cellular activities that are important for development and the maintenance of the nervous system, as well as in neurodegenerative and psychiatric disorders. More recently, neurotrophins have been implicated in influencing the dynamic and complex signals that occur between neurons and glial cells, including Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system that regulate myelination. Here we review the recent studies that identify neurotrophins as important regulators of both peripheral and central myelination, highlight some of the many questions that remain to be answered, and identify possibilities for further research.

Design of a conformationally defined and proteolytically stable circular mimetic of brain-derived neurotrophic factor

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family of neurotrophic factors. BDNF has long been recognized to have potential for the treatment of a variety of human neurodegenerative diseases. However, clinical trials with recombinant BDNF have yet to yield success, leading to the suggestion that alternative means of harnessing BDNF actions for therapeutic use may be required. Here we describe an approach to create low molecular weight peptides that, like BDNF, promote neuronal survival. The peptides were designed to mimic a cationic tripeptide sequence in loop 4 of BDNF shown in previous studies to contribute to the binding of BDNF to the common neurotrophin receptor p75NTR. The best of these peptides, the cyclic pentapeptide 2 (cyclo(-D-Pro-Ala-Lys-Arg-)), despite being of low molecular weight (Mr 580), was found to be an effective promoter of the survival of embryonic chick dorsal root ganglion sensory neurons in vitro (maximal survival, 68 +/- 3% of neurons supported by BDNF). Pentapeptide 2 did not affect the phosphorylation of either TrkB (the receptor tyrosine kinase for BDNF) or the downstream signaling molecule MAPK, indicating that its mechanism of neuronal survival action is independent of TrkB. NMR studies reveal that pentapeptide 2 adopts a well defined backbone conformation in solution. Furthermore, pentapeptide 2 was found to be effectively resistant to proteolysis when incubated in a solution of rat plasma in vitro. These properties of pentapeptide 2 (low molecular weight, appropriate pharmacological actions, a well defined solution conformation, and proteolytic stability) render it worthy of further investigation, either as a template for the further design of neuronal survival promoting agents or as a lead compound with therapeutic potential in its own right.

Neurotrophin receptor homolog-2 regulates nerve growth factor signaling

The neurotrophin receptor homolog (NRH2) is closely related to the p75 neurotrophin receptor (p75NTR); however, its function and role in neurotrophin signaling are unclear. NRH2 does not bind to nerve growth factor (NGF), however, is able to form a receptor complex with tropomyosin-related kinase receptor A (TrkA) and to generate high-affinity NGF binding sites. Despite this, the mechanisms underpinning the interaction between NRH2 and TrkA remain unknown. Here, we identify that the intracellular domain of NRH2 is required to form an association with TrkA. Our data suggest extensive intracellular interaction between NRH2 and TrkA, as either the juxtamembrane or death domain regions of NRH2 are sufficient for interaction with TrkA. In addition, we demonstrate that TrkA signaling is dramatically influenced by the co-expression of NRH2. Importantly, NRH2 did not influence all downstream TrkA signaling pathways, but rather exerted a specific effect, enhancing src homology 2 domain-containing transforming protein (Shc) activation. Moreover, downstream of Shc, the co-expression of NRH2 resulted in TrkA specifically modulating mitogen-activated protein kinase pathway activation, but not the phosphatidylinositol 3-kinase/Akt pathway. These results indicate that NRH2 utilizes intracellular mechanisms to not only regulate NGF binding to TrkA, but also specifically modulate TrkA receptor signaling, thus adding further layers of complexity and specificity to neurotrophin signaling.

Holes a plenty: oral health status a major issue for newly arrived refugees in Australia

BACKGROUND

Dental health needs of newly arrived refugees are much greater than for the wider Australian community. This paper identifies the disparities and highlights major dental health issues for Australia's growing and constantly changing refugee population.

METHODS

Using available data and the decayed, missing and filled teeth (DMFT) index as a measure of oral health, the reported oral health status of refugee groups in Australia was compared with that of the general population, Indigenous Australians, recipients of public dental services, special needs groups in Australia and other refugee groups outside Australia.

RESULTS

The reported oral health status of Australian refugees compared poorly with the comparison groups. Of particular concern was the number of reported untreated decayed teeth (D). This ranged from a mean of 2.0 to 5.2 compared with 0.6 to 1.4 for the general Australian population. Refugee groups also reported fewer filled teeth (1.0 to 5.8) compared with the general population (4.1 to 9.3). Similar results were found when reported D, M and F teeth for refugees were compared to Indigenous Australians, public dental service recipients, immigrants and special needs groups in Australia.

CONCLUSIONS

Dental health of refugees, particularly untreated decay, compared poorly to that of Indigenous Australians, and special needs populations in Australia who all have known worse dental health than the general population. There is an urgent need for the inclusion of this at risk population among targeted dental services. In addition, sources of health related data must clearly identify refugees to enable appropriate comparisons with other population groups. Recommendations for refugees are made regarding on-arrival dental assessment and treatment, and community based oral health programmes.

Effect of p75 neurotrophin receptor antagonist on disease progression in transgenic amyotrophic lateral sclerosis mice

Neurotrophin level imbalances and altered p75 neurotrophin receptor (p75(NTR)) expression are implicated in spinal motor neuron degeneration in human and mouse models of amyotrophic lateral sclerosis (ALS). Recently, elevated reactive astrocyte-derived nerve growth factor (NGF) was linked to p75(NTR)-expressing motor neuron death in adult transgenic ALS mice. To test the role of NGF-dependent p75(NTR)-mediated signalling in ALS, we examined the effects of a cyclic decapeptide antagonist of p75(NTR) ligand binding by using neurotrophin-stimulated cell death assays and transgenic ALS mice. Murine motor neuron-like (NSC-34) cell cultures expressed full-length and truncated p75(NTR), tyrosine receptor kinase B (TrkB), and the novel neurotrophin receptor homolog-2 (NHR2) but were TrkA deficient. Accordingly, treatment of cells with NGF induced dose-dependent cell death, which was significantly blocked by the cyclic decapeptide p75(NTR) antagonist. Application of brain-derived neurotrophic factor, neurotrophin-3, or neurotrophin-4 to cultures increased cell proliferation, and such trophic effects were abolished by pretreatment with the tyrosine kinase inhibitor K-252a. Systemic administration of a modified cyclic decapeptide p75(NTR) antagonist conjugated to the TAT4 cell permeabilization sequence to presymptomatic transgenic SOD1(G93A) mice affected neither disease onset nor disease progression, as determined by hindlimb locomotor, grip strength, and survival analyses. These studies suggest that disrupting NGF-p75(NTR) interactions by using this approach is insufficient to alter the disease course in transgenic ALS mice. Thus, alternate ligand-independent pathways of p75(NTR) activation or additional NGF receptor targets may contribute to motor neuron degeneration in ALS mice.

A novel p75 neurotrophin receptor-related protein, NRH2, regulates nerve growth factor binding to the TrkA receptor

Nerve growth factor (NGF) functions as a ligand for two receptors, the TrkA tyrosine kinase receptor and the p75 neurotrophin receptor (p75NTR). The Ig-like domains of Trk receptors and the cysteine-rich repeats of p75NTR are involved in binding to the neurotrophins. Recently, a closely related gene to p75NTR called neurotrophin receptor homolog-2 (NRH2) was identified; however, the function of NRH2 and its relevance to neurotrophin signaling are unclear. NRH2 contains a similar transmembrane and intracellular domain as p75NTR but lacks the characteristic cysteine-rich repeats in the extracellular domain. Here we show that NRH2 is expressed in several neuronal populations that also express p75NTR and Trk receptors. NRH2 does not bind to NGF; however, coimmunoprecipitation experiments demonstrate that NRH2 is capable of interacting with TrkA receptors. Coexpression of NRH2 with TrkA receptors resulted in the formation of high-affinity binding sites for NGF. These results indicate that a transmembrane protein related to p75NTR is capable of modulating Trk receptor binding properties.

Low-affinity neurotrophin receptor with targeted mutation of exon 3 is capable of mediating the death of axotomized neurons

1. In vivo studies have shown that the low-affinity 75 kDa neurotrophin receptor (p75NTR) is involved in axotomy-induced cell death of sensory and motor neurons. To further examine the importance of p75NTR in mediating neuronal death in vivo, we examined the effect of axotomy in the p75NTR-knockout mouse, which has a disrupted ligand-binding domain. 2. The extent of sensory and motor neuron loss in the p75NTR-knockout mouse following axotomy was not significantly different to that in wild-type mice. This suggests that disruption of the ligand-binding domain is insufficient to block the cell death process in axotomized neurons. 3. Immunohistochemical studies showed that axotomized neurons continue to express this mutant receptor with its intracellular death-signalling moiety intact. 4. Treatment with antisense oligonucleotides targeted against p75NTR resulted in significant reduction in the loss of axotomized neurons in the knockout mouse. 5. These data suggest that the intracellular domain of p75NTR is essential for death-signalling and that p75NTR can signal apoptosis, despite a disrupted ligand-binding domain.

Constitutive expression of the low-affinity neurotrophin receptor and changes during axotomy-induced death of sensory neurones in the neonatal rat dorsal root ganglion

Sensory neurones in the dorsal root ganglion (DRG) of the neonatal rat express the 75-kDa low-affinity neurotrophin receptor (p75NTR) and these neurones degenerate rapidly after axotomy. p75NTR belongs to the tumour necrosis factor superfamily, several members of which have a role in cell death and it is constitutively expressed within a subpopulation of DRG neurones. p75NTR has been implicated in mediating the degeneration of these neurones after axotomy. In this study, we characterize the expression of p75NTR in sensory neurones of the newborn rat DRG using immunohistochemistry. Furthermore, we investigate the change in constitutive expression pattern of p75NTR in these neurones following axotomy. In the C7 and C8 DRG of the newborn rat, p75NTR is expressed in approximately 70% of DRG neurones. Those expressing p75NTR can be classified into subpopulations with moderate or intense p75NTR expression, each present in approximately equal proportions. Whilst p75NTR expression is observed in neurones throughout the entire neuronal diameter range, a correlation exists between neuronal diameter and p75NTR expression intensity. We also found that the most vulnerable population following axotomy were those sensory neurones which constitutively express the highest levels of p75NTR, i.e. the large-diameter neurones.

A potential role for the p75 low-affinity neurotrophin receptor in spinal motor neuron degeneration in murine and human amyotrophic lateral sclerosis

INTRODUCTION

The p75 neurotrophin receptor has been recognized as a death-signalling molecule under certain circumstances. Its role in motor neuron degeneration in amyotrophic lateral sclerosis (ALS) was analysed in SOD1-G93A transgenic mice and in spinal cords from human amyotrophic lateral sclerosis.

METHOD

The precise loss of motor neurons in SOD1-G93A transgenic mice from birth to adulthood was established using the unbiased fractionator/optical dissector neuronal counting technique.

RESULTS

This study showed an early trend in the loss of lumbar motor neurons in SOD1-G93A mice, beginning at birth and progressing to a massive 80% reduction by 4 months of age, when the disease is severe. This study also found that the p75 neurotrophin receptor was expressed in lumbar motor neurons in symptomatic SOD1-G93A mice and in motor neurons in the cervical spinal cords of patients with ALS.

CONCLUSIONS

The murine and human ALS data suggest that the p75 neurotrophin receptor may play a death-signalling role in the pathogenesis of motor neuron degeneration. The precise mechanism by which this receptor drives the apoptotic process, both in murine SOD1-G93A motor neuron degeneration and in human amyotrophic lateral sclerosis, remains to be determined.

High-Resolution X-ray Imaging of a Globular Cluster Core: Compact Binaries in 47Tuc

We have obtained high-resolution (approximately 1") deep x-ray images of the globular cluster 47Tucanae (NGC 104) with the Chandra X-ray Observatory to study the population of compact binaries in the high stellar density core. A 70-kilosecond exposure of the cluster reveals a centrally concentrated population of faint (Lx approximately 10(30-33) ergs per second) x-ray sources, with at least 108 located within the central 2' x 2.5' and greater, similar half with Lx approximately 10(30.5) ergs per second. All 15 millisecond pulsars (MSPs) recently located precisely by radio observations are identified, though 2 are unresolved by Chandra. The x-ray spectral and temporal characteristics, as well as initial optical identifications with the Hubble Space Telescope, suggest that greater, similar50 percent are MSPs, about 30 percent are accreting white dwarfs, about 15 percent are main-sequence binaries in flare outbursts, and only two to three are quiescent low-mass x-ray binaries containing neutron stars, the conventional progenitors of MSPs. An upper limit of about 470 times the mass of the sun is derived for the mass of an accreting central black hole in the cluster. These observations provide the first x-ray "color-magnitude" diagram for a globular cluster and census of its compact object and binary population.

Effects of dietary restriction on appendicular bone in the SENCAR mouse

Peptide hormones, cytokines, and growth factors regulate cellular metabolism by stimulating second messenger signal transduction cascades in target tissues. A mutation in the regulatory domain of protein kinase C (PKC) in SENCAR (sensitive to carcinogenesis) mice renders them extremely sensitive to diacylglycerol and phorbol esters, resulting in rapid growth, high free radical generation, carcinogenesis, and metabolic bone disease. Dietary restriction (DR) normalizes PKC and ameliorates adverse downstream effects, including carcinogenesis, in SENCAR mice. We hypothesized that DR sufficient to ameliorate carcinogenesis would prevent or delay the early onset of metabolic bone disease in SENCAR mice. Male mice were assigned to 1 of 4 feeding groups from 10 to 16 weeks of age (the critical period when metabolic bone disease develops): ad libitum (AL)-fed; AL antioxidant (0.07% thioproline)-fed; 40% DR; or 40% DR antioxidant-fed. Femoral bone mass was determined gravimetrically. Tibial total, cortical, and trabecular bone mineral density (BMD) were determined by quantitative computed tomography. Body weight, femoral bone mass, and tibial cortical BMD were lower in DR than in AL mice. However, tibial total and trabecular BMD were higher in DR than in AL mice. Serum calcitonin, the hormone that inhibits the osteoclastic bone resorption that is most notable in trabecular bone, was 2-fold higher in DR than in AL-fed mice. Dietary thioproline had no major effects. Thus, DR sufficient to ameliorate carcinogenesis in SENCAR mice did not prevent early-onset metabolic bone disease, but it had a beneficial effect on tibial trabecular BMD that occurred at the apparent expense of cortical BMD. DR in SENCAR mice was also associated with elevated serum calcitonin, which may inhibit osteoclastic resorption and account for trabecular bone conservation in this model. In conclusion, PKC or the downstream metabolic processes regulated by it appear to play previously unrecognized roles in the regulation of tibial trabecular BMD and serum calcitonin in SENCAR mice.

Systemic administration of antisense p75(NTR) oligodeoxynucleotides rescues axotomised spinal motor neurons

The 75 kD low-affinity neurotrophin receptor (p75(NTR)) is expressed in developing and axotomised spinal motor neurons. There is now convincing evidence that p75(NTR) can, under some circumstances, become cytotoxic and promote neuronal cell death. We report here that a single application of antisense p75(NTR) oligodeoxynucleotides to the proximal nerve stumps of neonatal rats significantly reduces the loss of axotomised motor neurons compared to controls treated with nonsense oligodeoxynucleotides or phosphate-buffered saline. Our investigations also show that daily systemic intraperitoneal injections of antisense p75(NTR) oligodeoxynucleotides for 14 days significantly reduce the loss of axotomised motor neurons compared to controls. Furthermore, we found that systemic delivery over a similar period continues to be effective following axotomy when intraperitoneal injections were 1) administered after a delay of 24 hr, 2) limited to the first 7 days, or 3) administered every third day. In addition, p75(NTR) protein levels were reduced in spinal motor neurons following treatment with antisense p75(NTR) oligodeoxynucleotides. There were also no obvious side effects associated with antisense p75(NTR) oligodeoxynucleotide treatments as determined by behavioural observations and postnatal weight gain. Our findings indicate that antisense-based strategies could be a novel approach for the prevention of motor neuron degeneration associated with injuries or disease.

Expression of leukemia inhibitory factor receptor mRNA in sensory dorsal root ganglion and spinal motor neurons of the neonatal rat

Previous studies have shown that the application of leukemia inhibitory factor to the proximal nerve stump prevents the degeneration of axotomized sensory neurons in the dorsal root ganglion and motor neurons in the spinal cord of newborn rats. This study investigated the expression of leukemia inhibitory factor receptor mRNA in these neurons using in situ hybridization. Leukemia inhibitory factor receptor mRNA was detected both in sensory neurons within the dorsal root ganglion and motor neurons of the cervical spinal cord. Twenty-four hours after axotomy these neurons continue to express leukemia inhibitory factor receptor mRNA. This pattern of leukemia inhibitory factor receptor expression provides a mechanism by which endogenous and exogenous leukemia inhibitory factor could act on injured sensory and motor neurons.

Role of neurotrophin receptor p75NTR in mediating neuronal cell death following injury

1. The neurotrophin receptor p75NTR has been shown to mediate neuronal cell death after nerve injury. 2. Down-regulation of p75NTR by antisense oligonucleotides is able to inhibit both sensory and motor neuron death and this treatment is more effective than treatment with growth factors. 3. p75NTR induces cell death by a unique death signalling pathway involving transcription factors (nuclear factor kappa B and c-jun), Bcl-2 family members and caspases.

A Chandra High-Resolution X-ray Image of Centaurus A

We present first results from a Chandra X-Ray Observatory observation of the radio galaxy Centaurus A with the High-Resolution Camera. All previously reported major sources of X-ray emission including the bright nucleus, the jet, individual point sources, and diffuse emission are resolved or detected. The spatial resolution of this observation is better than 1&arcsec; in the center of the field of view and allows us to resolve X-ray features of this galaxy not previously seen. In particular, we resolve individual knots of emission in the inner jet and diffuse emission between the knots. All of the knots are diffuse at the 1&arcsec; level, and several exhibit complex spatial structure. We find the nucleus to be extended by a few tenths of an arcsecond. Our image also suggests the presence of an X-ray counterjet. Weak X-ray emission from the southwest radio lobe is also seen, and we detect 63 pointlike galactic sources (probably X-ray binaries and supernova remnants) above a luminosity limit of approximately 1.7x1037 ergs s-1.

First Light Measurements of Capella with the Low-Energy Transmission Grating Spectrometer aboard the Chandra X-Ray Observatory

We present the first X-ray spectrum obtained by the Low-Energy Transmission Grating Spectrometer (LETGS) aboard the Chandra X-Ray Observatory. The spectrum is of Capella and covers a wavelength range of 5-175 Å (2.5-0.07 keV). The measured wavelength resolution, which is in good agreement with ground calibration, is Deltalambda approximately 0.06 Å (FWHM). Although in-flight calibration of the LETGS is in progress, the high spectral resolution and unique wavelength coverage of the LETGS are well demonstrated by the results from Capella, a coronal source rich in spectral emission lines. While the primary purpose of this Letter is to demonstrate the spectroscopic potential of the LETGS, we also briefly present some preliminary astrophysical results. We discuss plasma parameters derived from line ratios in narrow spectral bands, such as the electron density diagnostics of the He-like triplets of carbon, nitrogen, and oxygen, as well as resonance scattering of the strong Fe xvii line at 15.014 Å.

Differential loss of spinal sensory but not motor neurons in the p75NTR knockout mouse

Sensory neurons in the dorsal root ganglia (DRG) and motor neurons in the spinal cord express the 75 kDa low-affinity neurotrophin receptor (p75NTR) during prenatal development. The p75NTR gene knockout mouse provides a unique opportunity to assess the role of p75NTR during this period. Quantitative analysis of the p75NTR knockout mouse revealed a significant developmental loss of sensory neurons. In the cervico-thoracic ganglia approximately 75% of the neurons are lost, while in the lumbar ganglia the loss is approximately 50%. In contrast, motor neurons were not lost in either the cervical or lumbar spinal cord. These data suggest that p75NTR is essential for the prenatal survival of a significant number of sensory, but not motor neurons.

The ubiquitin-proteasome system and cellular proliferation and regulation in osteoblastic cells

The 26S proteasome is the macromolecular assembly that mediates ATP- and ubiquitin-dependent extralysosomal intracellular protein degradation in eukaryotes. However, its contribution to the regulation of osteoblast proliferation and hormonal regulation remains poorly defined. Treating osteoblasts with MG-132 or lactacystin (membrane-permeable proteasome inhibitors) attenuates proliferation. Three proteasome activities (peptidylglutamyl-peptide bond hydrolase-, chymotrypsin-, and trypsin-like) were detected in osteoblasts. Catabolic doses of PTH stim-ulated these activities, and cotreatment with PTH and MG-132 blocked stimulation. The proteasome alpha- and beta-subunits, polyubiquitins, and large ubiquitin-protein conjugates were detected by Western blotting. A 90-min treatment with 10 nM PTH had no effect on the amount of proteasome alpha or beta subunit protein, but increased the relative amount of large ubiquitin-protein conjugates by 200%. MG-132 inhibited deubiquitination of large ubiquitin-protein conjugates. The protein kinase A inhibitor SQ22536 blocked much of the PTH-induced stimulation of MCP activities, while dibutyryl cAMP stimulated it, suggesting that protein kinase A-dependent phosphorylation is important in PTH stimulation of proteasome activities. In conclusion, the ubiquitin-proteasome system is essential for osteoblast proliferation under control and PTH-treated conditions. PTH mediates its metabolic effects on the osteoblast, in part, by enhancing ubiquitinylation of protein substrates and stimulating three major proteasome activities by a cAMP-dependent mechanism.