Triple knock-out of CNTF, LIF, and CT-1 defines cooperative and distinct roles of these neurotrophic factors for motoneuron maintenance and function

Efficacy of Human Recombinant Growth Hormone in Females of a Non-Obese Hyperglycemic Mouse Model after Birth with Low Birth Weight

We examined whether the administration of growth hormone (GH) improves insulin resistance in females of a non-obese hyperglycemic mouse model after birth with low birth weight (LBW), given that GH is known to increase muscle mass. The intrauterine Ischemia group underwent uterine artery occlusion for 15 min on day 16.5 of gestation. At 4 weeks of age, female mice in the Ischemia group were divided into the GH-treated (Ischemia-GH) and non-GH-treated (Ischemia) groups. At 8 weeks of age, the glucose metabolism, muscle pathology, and metabolome of liver were assessed. The insulin resistance index improved in the Ischemia-GH group compared with the Ischemia group (p = 0.034). The percentage of type 1 muscle fibers was higher in the Ischemia-GH group than the Ischemia group (p < 0.001); the muscle fiber type was altered by GH. In the liver, oxidative stress factors were reduced, and ATP production was increased in the Ischemia-GH group compared to the Ischemia group (p = 0.014), indicating the improved mitochondrial function of liver. GH administration is effective in improving insulin resistance by increasing the content of type 1 muscle fibers and improving mitochondrial function of liver in our non-obese hyperglycemic mouse model after birth with LBW.

The Cell Autonomous and Non-Cell Autonomous Aspects of Neuronal Vulnerability and Resilience in Amyotrophic Lateral Sclerosis

Simple Summary

Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by a progressive paralysis due to the loss of particular neurons in our nervous system called motor neurons, that exert voluntary control of all our skeletal muscles. It is not entirely understood why motor neurons are particularly vulnerable in ALS, neither is it completely clear why certain groups of motor neurons, including those that regulate eye movement, are rather resilient to this disease. However, both vulnerability and resilience to ALS likely reflect cell intrinsic properties of different motor neuron subpopulations as well as non-cell autonomous events regulated by surrounding cell types. In this review we dissect the particular properties of different motor neuron types and their responses to disease that may underlie their respective vulnerabilities and resilience. Disease progression in ALS involves multiple cell types that are closely connected to motor neurons and we here also discuss their contributions to the differential vulnerability of motor neurons.

Abstract

Amyotrophic lateral sclerosis (ALS) is defined by the loss of upper motor neurons (MNs) that project from the cerebral cortex to the brain stem and spinal cord and of lower MNs in the brain stem and spinal cord which innervate skeletal muscles, leading to spasticity, muscle atrophy, and paralysis. ALS involves several disease stages, and multiple cell types show dysfunction and play important roles during distinct phases of disease initiation and progression, subsequently leading to selective MN loss. Why MNs are particularly vulnerable in this lethal disease is still not entirely clear. Neither is it fully understood why certain MNs are more resilient to degeneration in ALS than others. Brain stem MNs of cranial nerves III, IV, and VI, which innervate our eye muscles, are highly resistant and persist until the end-stage of the disease, enabling paralyzed patients to communicate through ocular tracking devices. MNs of the Onuf’s nucleus in the sacral spinal cord, that innervate sphincter muscles and control urogenital functions, are also spared throughout the disease. There is also a differential vulnerability among MNs that are intermingled throughout the spinal cord, that directly relate to their physiological properties. Here, fast-twitch fatigable (FF) MNs, which innervate type IIb muscle fibers, are affected early, before onset of clinical symptoms, while slow-twitch (S) MNs, that innervate type I muscle fibers, remain longer throughout the disease progression. The resilience of particular MN subpopulations has been attributed to intrinsic determinants and multiple studies have demonstrated their unique gene regulation and protein content in health and in response to disease. Identified factors within resilient MNs have been utilized to protect more vulnerable cells. Selective vulnerability may also, in part, be driven by non-cell autonomous processes and the unique surroundings and constantly changing environment close to particular MN groups. In this article, we review in detail the cell intrinsic properties of resilient and vulnerable MN groups, as well as multiple additional cell types involved in disease initiation and progression and explain how these may contribute to the selective MN resilience and vulnerability in ALS.

A cholinergic neuroskeletal interface promotes bone formation during postnatal growth and exercise

The autonomic nervous system is a master regulator of homeostatic processes and stress responses. Sympathetic noradrenergic nerve fibers decrease bone mass, but the role of cholinergic signaling in bone has remained largely unknown. Here, we describe that early postnatally, a subset of sympathetic nerve fibers undergoes an interleukin-6 (IL-6)-induced cholinergic switch upon contacting the bone. A neurotrophic dependency mediated through GDNF-family receptor-α2 (GFRα2) and its ligand, neurturin (NRTN), is established between sympathetic cholinergic fibers and bone-embedded osteocytes, which require cholinergic innervation for their survival and connectivity. Bone-lining osteoprogenitors amplify and propagate cholinergic signals in the bone marrow (BM). Moderate exercise augments trabecular bone partly through an IL-6-dependent expansion of sympathetic cholinergic nerve fibers. Consequently, loss of cholinergic skeletal innervation reduces osteocyte survival and function, causing osteopenia and impaired skeletal adaptation to moderate exercise. These results uncover a cholinergic neuro-osteocyte interface that regulates skeletogenesis and skeletal turnover through bone-anabolic effects.

CNTF-STAT3-IL-6 Axis Mediates Neuroinflammatory Cascade across Schwann Cell-Neuron-Microglia

Neuroinflammation is a crucial mechanism in many neurological disorders. Injury to the peripheral sensory nerves leads to a neuroinflammatory response in the somatosensory pathway, from dorsal root ganglia (DRG) to the spinal cord, contributing to neuropathic pain. How the immune reaction is initiated peripherally and propagated to the spinal cord remains less clear. Here, we find that ciliary neurotrophic factor (CNTF), highly expressed in Schwann cells, mediates neuroinflammatory response through the activating signal transducer and activator of transcription 3 (STAT3) and inducing interleukin 6 (IL-6) in sensory neurons. Cntf deficiency attenuates neuroinflammation in DRG and the spinal cord with alleviated pain post-injury. Recombinant CNTF applied to the sensory nerves recapitulates neuroinflammation in the DRG and spinal cord, with consequent pain development. We delineate the CNTF-STAT3-IL-6 axis in mediating the onset and progression of the inflammatory cascade from the periphery to the spinal cord with therapeutic implications for neuropathic pain.

LCM-seq reveals unique transcriptional adaptation mechanisms of resistant neurons and identifies protective pathways in spinal muscular atrophy

Somatic motor neurons are selectively vulnerable in spinal muscular atrophy (SMA), which is caused by a deficiency of the ubiquitously expressed survival of motor neuron protein. However, some motor neuron groups, including oculomotor and trochlear (ocular), which innervate eye muscles, are for unknown reasons spared. To reveal mechanisms of vulnerability and resistance in SMA, we investigate the transcriptional dynamics in discrete neuronal populations using laser capture microdissection coupled with RNA sequencing (LCM-seq). Using gene correlation network analysis, we reveal a TRP53-mediated stress response that is intrinsic to all somatic motor neurons independent of their vulnerability, but absent in relatively resistant red nucleus and visceral motor neurons. However, the temporal and spatial expression analysis across neuron types shows that the majority of SMA-induced modulations are cell type-specific. Using Gene Ontology and protein network analyses, we show that ocular motor neurons present unique disease-adaptation mechanisms that could explain their resilience. Specifically, ocular motor neurons up-regulate (1) Syt1, Syt5, and Cplx2, which modulate neurotransmitter release; (2) the neuronal survival factors Gdf15, Chl1, and Lif; (3) Aldh4, that protects cells from oxidative stress; and (4) the caspase inhibitor Pak4. Finally, we show that GDF15 can rescue vulnerable human spinal motor neurons from degeneration. This confirms that adaptation mechanisms identified in resilient neurons can be used to reduce susceptibility of vulnerable neurons. In conclusion, this in-depth longitudinal transcriptomics analysis in SMA reveals novel cell type-specific changes that, alone and combined, present compelling targets, including Gdf15, for future gene therapy studies aimed toward preserving vulnerable motor neurons.

Nerve cells developmental processes and the dynamic role of cytokine signaling

The stunning diversity of neurons and glial cells makes possible the higher functions of the central nervous system (CNS), allowing the organism to sense, interpret and respond appropriately to the external environment. This cellular diversity derives from a single primary progenitor cell type initiating lineage leading to the formation of both differentiated neurons and glial cells. The processes governing the differentiation of the progenitor pool of cells into mature nerve cells will be here briefly reviewed. They involve morphological transformations, specialized modes of cell division, migration, and controlled cell death, and are regulated through cell-cell interactions and cues provided by the extracellular matrix, as well as by humoral factors from the cerebrospinal fluid and the blood system. In this respect, a quite large body of studies have been focused on cytokines, proteins representing the main signaling network that coordinates immune defense and the maintenance of homeostasis. At the same time, they are deeply involved in CNS development as regulatory factors. This dual role in the nervous system appears of particular relevance for CNS pathology, since cytokine dysregulation (occurring as a consequence of maternal infection, exposure to environmental factors or prenatal hypoxia) can profoundly impact on neurodevelopment and likely influence the response of the adult tissue during neuroinflammatory events.

Novel combinatorial screening identifies neurotrophic factors for selective classes of motor neurons

Numerous neurotrophic factors promote the survival of developing motor neurons but their combinatorial actions remain poorly understood; to address this, we here screened 66 combinations of 12 neurotrophic factors on pure, highly viable, and standardized embryonic mouse motor neurons isolated by a unique FACS technique. We demonstrate potent, strictly additive, survival effects of hepatocyte growth factor (HGF), ciliary neurotrophic factor (CNTF), and Artemin through specific activation of their receptor complexes in distinct subsets of lumbar motor neurons: HGF supports hindlimb motor neurons through c-Met; CNTF supports subsets of axial motor neurons through CNTFRα; and Artemin acts as the first survival factor for parasympathetic preganglionic motor neurons through GFRα3/Syndecan-3 activation. These data show that neurotrophic factors can selectively promote the survival of distinct classes of embryonic motor neurons. Similar studies on postnatal motor neurons may provide a conceptual framework for the combined therapeutic use of neurotrophic factors in degenerative motor neuron diseases such as amyotrophic lateral sclerosis, spinal muscular atrophy, and spinobulbar muscular atrophy.

Low-Dose Pulsatile Interleukin-6 As a Treatment Option for Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) remains one of the most common and serious complications of diabetes. Currently, pharmacological agents are limited to treating the pain associated with DPN, and do not address the underlying pathological mechanisms driving nerve damage, thus leaving a significant unmet medical need. Interestingly, research conducted using exercise as a treatment for DPN has revealed interleukin-6 (IL-6) signaling to be associated with many positive benefits such as enhanced blood flow and lipid metabolism, decreased chronic inflammation, and peripheral nerve fiber regeneration. IL-6, once known solely as a pro-inflammatory cytokine, is now understood to signal as a multifunctional cytokine, capable of eliciting both pro- and anti-inflammatory responses in a context-dependent fashion. IL-6 released from muscle in response to exercise signals as a myokine and as such has a unique kinetic profile, whereby levels are transiently elevated up to 100-fold and return to baseline levels within 4 h. Importantly, this kinetic profile is in stark contrast to long-term IL-6 elevation that is associated with pro-inflammatory states. Given exercise induces IL-6 myokine signaling, and exercise has been shown to elicit numerous beneficial effects for the treatment of DPN, a causal link has been suggested. Here, we discuss both the clinical and preclinical literature related to the application of IL-6 as a treatment strategy for DPN. In addition, we discuss how IL-6 may directly modulate Schwann and nerve cells to explore a mechanistic understanding of how this treatment elicits a neuroprotective and/or regenerative response. Collectively, studies suggest that IL-6, when administered in a low-dose pulsatile strategy to mimic the body's natural response to exercise, may prove to be an effective treatment for the protection and/or restoration of peripheral nerve function in DPN. This review highlights the studies supporting this assertion and provides rationale for continued investigation of IL-6 for the treatment of DPN.

Astroglial Cells in Development, Regeneration, and Repair

Three main cellular components have been described in the CNS: neurons, astrocytes, and oligodendrocytes. In the past 10 years, lineage studies first based on retroviruses in the embryonic CNS and then by genetic fate mapping in both the prenatal and postnatal CNS have proposed that astroglial cells can be progenitors for neurons and oligodendrocytes. Hence, the population of astroglial cells is increasingly recognized as heterogeneous and diverse, encompassing cell types performing widely different roles in development and plasticity. Astroglial cells populating the neurogenic niches increase their proliferation after perinatal injury and in young mice can differentiate into neurons and oligodendrocytes that migrate to the cerebral cortex, replacing the cells that are lost. Although much remains to be learned about this process, it appears that the up-regulation of the Fibroblast growth factor receptor is critical for mediating the injury-induced increase in cell division and perhaps for the neuronal differentiation of astroglial cells. NEUROSCIENTIST 13(2):173—185, 2007.

Activation of transcription factors STAT1 and STAT5 in the mouse median eminence after systemic ciliary neurotrophic factor administration

Exogenously administered ciliary neurotrophic factor (CNTF) causes weight loss in obese rodents and humans through leptin-like activation of the Jak-STAT3 signaling pathway in hypothalamic arcuate neurons. Here we report for the first time that 40min after acute systemic treatment, rat recombinant CNTF (intraperitoneal injection of 0.3mg/kg of body weight) induced nuclear translocation of the tyrosine-phosphorylated forms of STAT1 and STAT5 in the mouse median eminence and other circumventricular organs, including the vascular organ of the lamina terminalis and the subfornical organ. In the tuberal hypothalamus of treated mice, specific nuclear immunostaining for phospo-STAT1 and phospho-STAT5 was detected in ependymal cells bordering the third ventricle floor and lateral recesses, and in median eminence cells. Co-localization studies documented STAT1 and STAT5 activation in median eminence β-tanycytes and underlying radial glia-like cells. A few astrocytes in the arcuate nucleus responded to CNTF by STAT5 activation. The vast majority of median eminence tanycytes and radial glia-like cells showing phospho-STAT1 and phospho-STAT5 immunoreactivity were also positive for phospho-STAT3. In contrast, STAT3 was the sole STAT isoform activated by CNTF in arcuate nucleus and median eminence neurons. Finally, immunohistochemical evaluation of STAT activation 20, 40, 80, and 120min from the injection demonstrated that cell activation was accompanied by c-Fos expression. Collectively, our findings show that CNTF activates STAT3, STAT1, and STAT5 in vivo. The distinctive activation pattern of these STAT isoforms in the median eminence may disclose novel targets and pathways through which CNTF regulates food intake.

Role of leukemia inhibitory factor in the nervous system and its pathology

Leukemia inhibitory factor (LIF) is a multifunction cytokine that has various effects on different tissues and cell types in rodents and humans; however, its insufficiency has a relatively mild impact. This could explain why only some aspects of LIF activity are in the limelight, whereas other aspects are not well known. In this review, the LIF structure, signaling pathway, and primary roles in the development and function of an organism are reviewed, and the effects of LIF on stem cell growth and differentiation, which are important for its use in cell culturing, are described. The focus is on the roles of LIF in central nervous system development and on the modulation of its physiological functions as well as the involvement of LIF in the pathogenesis of brain diseases and injuries. Finally, LIF and its signaling pathway are discussed as potential targets of therapeutic interventions to influence both negative phenomena and regenerative processes following brain injury.

Effects of resistance training on muscle strength, endurance, and motor unit according to ciliary neurotrophic factor polymorphism in male college students

Changes in muscle mass and strength across the adult age span are variable and related to the ciliary neurotrophic factor (CNTF) genotype. In particular, a single CNTF haplotype (1357 G→A) is important for neuronal and muscular developments and may be associated with muscle strength response to resistance training. We examined whether CNTF genotype differentially influences the effect of resistance training on neuromuscular improvement in male college students. Resistance training of the upper extremities comprised 3 sets at 75%-85% intensity per 1 repetition maximum, 3 times a week, for a total of 8 weeks. We measured isokinetic muscle function of the elbow joint with regard to strength (60°/s) and endurance (180°/s) by using an isokinetic dynamometer. The biceps brachii (BB) and brachioradialis muscles were studied using surface electromyography with spike-triggered averaging to assess surface-detected motor unit potential (SMUP) area. After resistance training, the SMUP of the BB increased significantly at 60°/s (p < 0.05), but no difference in the CNTF genotype was observed. The SMUP of the BB at 180°/s increased significantly in the GG/AA genotype group compared with that in the GA genotype group (p < 0.05). The average power of the elbow flexor at 180°/s increased significantly after resistance training (p < 0.05), but again, no difference in the CNTF genotype was observed. Thus, improvements in muscle strength and endurance may have resulted directly from resistance training rather than from genetic factors related to nerves in muscle tissue. Key PointsResistance training improves muscle strength and endurance in young men.This improvement in muscular strength and endurance is irrespective of CNTF genotypes.

The contribution of leukemia inhibitory factor (LIF) for embryo implantation differs among strains of mice

Despite of the claim that maternal leukemia inhibitory factor (LIF) - a member of interleukin 6 (IL6) family of cytokines - plays indispensable roles for murine embryo implantation, these roles remain undefined in humans because the potency of LIF on implantation appears to vary among individuals. Here, we showed that the contribution of LIF for murine implantation was dependent on the strains of mice (ICR, C57BL/6J (B6), ddY, BALB/c, DBA/2Cr and MF1 strains). Inhibition of LIF during the implantation period caused severe disruption of embryo implantation in B6 and MF1 strains. Implantation was partly disrupted in other strains, but some embryos were implanted successfully. We speculated that other IL6 family members compensate for LIF actions on implantation in ICR, ddY, BALB/c, and DBA/2Cr strains. Indeed, the expression level of Ctf1 was upregulated by blockage of LIF function. CT-1 (encoded by Ctf1) treatment induced successful implantation without LIF in delayed implantation mice (ICR and B6) via phosphorylation of the signal transducer and activator of transcription 3 (STAT3) in the uterine luminal epithelium. Simultaneous inhibition of LIF and CT-1 did not block implantation completely in ICR mice, indicating that embryo implantation in this strain was robustly protected by LIF, CT-1 and other potential STAT3 activators. The present study might provide an explanation for the individual variation in the potency of LIF for embryo implantation in humans.

Motoneuron disease

Amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) represent the two major forms of motoneuron disease. In both forms of disease, spinal and bulbar motoneurons become dysfunctional and degenerate. In ALS, cortical motoneurons are also affected, which contributes to the clinical phenotype. The gene defects for most familial forms of ALS and SMA have been discovered and they point to a broad spectrum of disease mechanisms, including defects in RNA processing, pathological protein aggregation, altered apoptotic signaling, and disturbed energy metabolism. Despite the fact that lack of neurotrophic factors or their corresponding receptors are not found as genetic cause of motoneuron disease, signaling pathways initiated by neurotrophic factors for motoneuron survival, axon growth, presynaptic development, and synaptic function are disturbed in ALS and SMA. Better understanding of how neurotrophic factors and downstream signaling pathways interfere with these disease mechanisms could help to develop new therapies for motoneuron disease and other neurodegenerative disorders.

Opposite effects of a high-fat diet and calorie restriction on ciliary neurotrophic factor signaling in the mouse hypothalamus

In the mouse hypothalamus, ciliary neurotrophic factor (CNTF) is mainly expressed by ependymal cells and tanycytes of the ependymal layer covering the third ventricle. Since exogenously administered CNTF causes reduced food intake and weight loss, we tested whether endogenous CNTF might be involved in energy balance regulation. We thus evaluated CNTF production and responsiveness in the hypothalamus of mice fed a high-fat diet (HFD), of ob/ob obese mice, and of mice fed a calorie restriction (CR) regimen. RT-PCR showed that CNTF mRNA increased significantly in HFD mice and decreased significantly in CR animals. Western blotting confirmed that CNTF expression was higher in HFD mice and reduced in CR mice, but high interindividual variability blunted the significance of these differences. By immunohistochemistry, hypothalamic tuberal and mammillary region tanycytes stained strongly for CNTF in HFD mice, whereas CR mice exhibited markedly reduced staining. RT-PCR and Western blotting disclosed that changes in CNTF expression were paralleled by changes in the expression of its specific receptor, CNTF receptor α (CNTFRα). Injection of recombinant CNTF and detection of phospho-signal transducer and activator of transcription 3 (P-STAT3) showed that CNTF responsiveness by the ependymal layer, mainly by tanycytes, was higher in HFD than CR mice. In addition, in HFD mice CNTF administration induced distinctive STAT3 signaling in a large neuron population located in the dorsomedial and ventromedial nuclei, perifornical area and mammillary body. The hypothalamic expression of CNTF and CNTFRα did not change in the hyperphagic, leptin-deficient ob/ob obese mice; accordingly, P-STAT3 immunoreactivity in CNTF-treated ob/ob mice was confined to ependymal layer and arcuate neurons. Collectively, these data suggest that hypothalamic CNTF is involved in controlling the energy balance and that CNTF signaling plays a role in HFD obese mice at specific sites.

Mechanisms for axon maintenance and plasticity in motoneurons: alterations in motoneuron disease

In motoneuron disease and other neurodegenerative disorders, the loss of synapses and axon branches occurs early but is compensated by sprouting of neighboring axon terminals. Defective local axonal signaling for maintenance and dynamics of the axonal microtubule and actin cytoskeleton plays a central role in this context. The molecular mechanisms that lead to defective cytoskeleton architecture in two mouse models of motoneuron disease are summarized and discussed in this manuscript. In the progressive motor neuropathy (pmn) mouse model of motoneuron disease that is caused by a mutation in the tubulin-specific chaperone E gene, death of motoneuron cell bodies appears as a consequence of axonal degeneration. Treatment with bcl-2 overexpression or with glial-derived neurotrophic factor prevents loss of motoneuron cell bodies but does not influence the course of disease. In contrast, treatment with ciliary neurotrophic factor (CNTF) significantly delays disease onset and prolongs survival of pmn mice. This difference is due to the activation of Stat-3 via the CNTF receptor complex in axons of pmn mutant motoneurons. Most of the activated Stat-3 protein is not transported to the nucleus to activate transcription, but interacts locally in axons with stathmin, a protein that destabilizes microtubules. This interaction plays a major role in CNTF signaling for microtubule dynamics in axons. In Smn-deficient mice, a model of spinal muscular atrophy, defects in axonal translocation of β-actin mRNA and possibly other mRNA species have been observed. Moreover, the regulation of local protein synthesis in response to signals from neurotrophic factors and extracellular matrix proteins is altered in motoneurons from this model of motoneuron disease. These findings indicate that local signals are important for maintenance and plasticity of axonal branches and neuromuscular endplates, and that disturbances in these signaling mechanisms could contribute to the pathophysiology of motoneuron diseases.

Neurotrophic molecules in the treatment of neurodegenerative disease with focus on the retina: status and perspectives

Neurotrophic factors are operationally defined as molecules that promote the survival and differentiation of neurons. Chemically, they belong to divergent classes of molecules but most of the classic neurotrophic factors are proteins. Together with stem cells, viral vectors and genetically engineered cells, they constitute important tools in neuroprotective and regenerative neurobiology. Protein neurotrophic molecules signal through receptors located on the cell membrane. Their downstream signaling exploits pathways that are often common to chemically different factors and frequently target a relatively restricted set of transcription factors, RNA interference and diverse molecular machinery involved in the life vs. death decisions of neurons. Application of neurotrophic factors with the aim of curing or, at least, improving the outcome of neurodegenerative diseases requires (1) profound knowledge of the complex molecular pathology of the disease, (2) the development of animal models as closely as possible resembling the human disease, (3) the identification of target cells to be addressed, (4) intense efforts in chemical engineering to ensure the stability of molecules or to design carriers and small analogs with the ability to cross the blood-brain barrier and (5) scrutinity with regard to possible side effects. Last, but not least, engineering efforts to optimize administration, e.g., by designing the right canulae and infusion devices, are important for the successful translation of preclinical advances into clinical benefit. This article presents selected examples of neurotrophic factors that are currently being tested in animal models or developed for transfer to the clinic, with a major focus on factors with the potential of becoming applicable in various forms of retinal degeneration.

Role of inflammation and cytokines in peripheral nerve regeneration

This chapter provides a review of immune reactions involved in classic as well as alternative methods of peripheral nerve regeneration, and mainly with a view to understanding their beneficial effects. Axonal degeneration distal to nerve damage triggers a cascade of inflammatory events alongside injured nerve fibers known as Wallerian degeneration (WD). The early inflammatory reactions of WD comprise the complement system, arachidonic acid metabolites, and inflammatory mediators that are related to myelin fragmentation and activation of Schwann cells. Fine-tuned upregulation of the cytokine/chemokine network by Schwann cells activates resident and hematogenous macrophages to complete the clearance of axonal and myelin debris and stimulate regrowth of axonal sprouts. In addition to local effects, immune reactions of neuronal bodies and glial cells are also implicated in the survival and conditioning of neurons to regenerate severed nerves. Understanding of the cellular and molecular interactions between the immune system and peripheral nerve injury opens new possibilities for targeting inflammatory mediators to improve functional reinnervation.

What can we learn about stroke from retinal ischemia models?

Retinal ischemia is a very useful model to study the impact of various cell death pathways, such as apoptosis and necrosis, in the ischemic retina. However, it is important to note that the retina is formed as an outpouching of the diencephalon and is part of the central nervous system. As such, the cell death pathways initiated in response to ischemic damage in the retina reflect those found in other areas of the central nervous system undergoing similar trauma. The retina is also more accessible than other areas of the central nervous system, thus making it a simpler model to work with and study. By utilizing the retinal model, we can greatly increase our knowledge of the cell death processes initiated by ischemia which lead to degeneration in the central nervous system. This paper examines work that has been done so far to characterize various aspects of cell death in the retinal ischemia model, such as various pathways which are activated, and the role neurotrophic factors, and discusses how these are relevant to the treatment of ischemic damage in both the retina and the greater central nervous system.

An anti-inflammatory role for leukemia inhibitory factor receptor signaling in regenerating skeletal muscle

Skeletal muscle regeneration in pathology and following injury requires the coordinated actions of inflammatory cells and myogenic cells to remove damaged tissue and rebuild syncytial muscle cells, respectively. Following contusion injury to muscle, the cytokine leukemia inhibitor factor (LIF) is up-regulated and knockout of Lif negatively impacts on morphometric parameters of muscle regeneration. Although it was speculated that LIF regulates muscle regeneration through direct effects on myogenic cells, the inflammatory effects of LIF have not been examined in regenerating skeletal muscle. Therefore, the expression and function of LIF was examined using the antagonist MH35-BD during specific inflammatory and myogenic stages of notexin-induced muscle regeneration in mice. LIF protein and mRNA were up-regulated in two distinct phases following intramuscular injection of notexin into tibialis anterior muscles. The first phase of LIF up-regulation coincided with the increased expression of pro-inflammatory cytokines; the second phase coincided with myogenic differentiation and formation of new myotubes. Administration of the LIF receptor antagonist MH35-BD during the second phase of LIF up-regulation had no significant effects on transcript expression of genes required for myogenic differentiation or associated with inflammation; there were no significant differences in morphometric parameters of the regenerating muscle. Conversely, when MH35-BD was administered during the acute inflammatory phase, increased gene transcripts for the pro-inflammatory cytokines Tnf (Tumor necrosis factor), Il1b (Interleukin-1β) and Il6 (Interleukin-6) alongside an increase in the number of Ly6G positive neutrophils infiltrating the muscle were observed. This was followed by a reduction in Myog (Myogenin) mRNA, which is required for myogenic differentiation, and the subsequent number of myotubes formed was significantly decreased in MH35-BD-treated groups compared to sham. Thus, antagonism of the LIF receptor during the inflammatory phase of skeletal muscle regeneration appeared to induce an inflammatory response that inhibited subsequent myotube formation. We propose that the predominant role of LIF in skeletal muscle regeneration appears to be in regulating the inflammatory response rather than directly effecting myogenic cells.

LIF-dependent signaling: new pieces in the Lego

LIF, a member of the IL6 family of cytokine, displays pleiotropic effects on various cell types and organs. Its critical role in stem cell models (e.g.: murine ES, human mesenchymal cells) and its essential non redundant function during the implantation process of embryos, in eutherian mammals, put this cytokine at the core of many studies aiming to understand its mechanisms of action, which could benefit to medical applications. In addition, its conservation upon evolution raised the challenging question concerning the function of LIF in species in which there is no implantation. We present the recent knowledge about the established and potential functions of LIF in different stem cell models, (embryonic, hematopoietic, mesenchymal, muscle, neural stem cells and iPSC). We will also discuss EVO-DEVO aspects of this multifaceted cytokine.

Role of neurotrophins in the development and function of neural circuits that regulate energy homeostasis

Members of the neurotrophin family, including nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4/5, and other neurotrophic growth factors such as ciliary neurotrophic factor and artemin, regulate peripheral and central nervous system development and function. A subset of the neurotrophin-dependent pathways in the hypothalamus, brainstem, and spinal cord, and those that project via the sympathetic nervous system to peripheral metabolic tissues including brown and white adipose tissue, muscle and liver, regulate feeding, energy storage, and energy expenditure. We briefly review the role that neurotrophic growth factors play in energy balance, as regulators of neuronal survival and differentiation, neurogenesis, and circuit formation and function, and as inducers of critical gene products that control energy homeostasis.

Genetic deletion of trkB.T1 increases neuromuscular function

Neurotrophin-dependent activation of the tyrosine kinase receptor trkB.FL modulates neuromuscular synapse maintenance and function; however, it is unclear what role the alternative splice variant, truncated trkB (trkB.T1), may have in the peripheral neuromuscular axis. We examined this question in trkB.T1 null mice and demonstrate that in vivo neuromuscular performance and nerve-evoked muscle tension are significantly increased. In vitro assays indicated that the gain-in-function in trkB.T1(-/-) animals resulted specifically from an increased muscle contractility, and increased electrically evoked calcium release. In the trkB.T1 null muscle, we identified an increase in Akt activation in resting muscle as well as a significant increase in trkB.FL and Akt activation in response to contractile activity. On the basis of these findings, we conclude that the trkB signaling pathway might represent a novel target for intervention across diseases characterized by deficits in neuromuscular function.

Mice null for calsequestrin 1 exhibit deficits in functional performance and sarcoplasmic reticulum calcium handling

In skeletal muscle, the release of calcium (Ca²⁺) by ryanodine sensitive sarcoplasmic reticulum (SR) Ca²⁺ release channels (i.e., ryanodine receptors; RyR1s) is the primary determinant of contractile filament activation. Much attention has been focused on calsequestrin (CASQ1) and its role in SR Ca²⁺ buffering as well as its potential for modulating RyR1, the L-type Ca²⁺ channel (dihydropyridine receptor, DHPR) and other sarcolemmal channels through sensing luminal [Ca²⁺]. The genetic ablation of CASQ1 expression results in significant alterations in SR Ca²⁺ content and SR Ca²⁺ release especially during prolonged activation. While these findings predict a significant loss-of-function phenotype in vivo, little information on functional status of CASQ1 null mice is available. We examined fast muscle in vivo and in vitro and identified significant deficits in functional performance that indicate an inability to sustain contractile activation. In single CASQ1 null skeletal myofibers we demonstrate a decrease in voltage dependent RyR Ca²⁺ release with single action potentials and a collapse of the Ca²⁺ release with repetitive trains. Under voltage clamp, SR Ca²⁺ release flux and total SR Ca²⁺ release are significantly reduced in CASQ1 null myofibers. The decrease in peak Ca²⁺ release flux appears to be solely due to elimination of the slowly decaying component of SR Ca²⁺ release, whereas the rapidly decaying component of SR Ca²⁺ release is not altered in either amplitude or time course in CASQ1 null fibers. Finally, intra-SR [Ca²⁺] during ligand and voltage activation of RyR1 revealed a significant decrease in the SR[Ca²⁺]_free in intact CASQ1 null fibers and a increase in the release and uptake kinetics consistent with a depletion of intra-SR Ca²⁺ buffering capacity. Taken together we have revealed that the genetic ablation of CASQ1 expression results in significant functional deficits consistent with a decrease in the slowly decaying component of SR Ca²⁺ release.

Alterations in the expression of leukemia inhibitory factor following exercise: comparisons between wild-type and mdx muscles

BACKGROUND

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine, belonging to the interleukin-6 family of cytokines, that has been suggested to have positive effects on myogenesis following injury and to minimise dystrophic pathology in mdx mice. Previous reports have suggested that Lif mRNA is up-regulated in the limb and diaphragm muscles of mdx mice, in human cases of dystrophy and acutely following exercise. This study examined expression of Lif mRNA in the quadriceps muscles of mdx and wild-type mice that were either sedentary or allowed to exercise voluntarily for two weeks.

RESULTS

Exercise caused a decrease in Lif mRNA expression in wild-type muscle, but this was not the case in mdx muscle. Lif mRNA levels in sedentary mdx mice were similar to those in exercised wild type muscles, and in mdx mice there was no further decrease in levels following exercise. Similar down-regulation of Lif mRNA was observed in the tibialis anterior and diaphragm muscles of mdx mice at three and six weeks of age respectively, compared with wild-type controls. Transcripts for the LIF receptor (Lifr) were also down-regulated in these mdx muscles, suggesting LIF activity may be minimised in dystrophic muscle. However fluorescent immunohistochemical labeling of LIF did not correlate with transcript expression data, as LIF immunoreactivity could not be detected in wild-type muscle, where mRNA expression was high, but was present in dystrophic muscle where mRNA expression was low. This study also described the translocation of membrane proteins, including LIFR, to the nuclei of syncytial muscle cells during differentiation and fusion. In addition this study demonstrates that survival of donor myoblasts injected into dystrophic muscle was enhanced by co-administration of recombinant LIF.

CONCLUSIONS

This study provides new evidence to support a role for LIF in normal muscle biology in response to exercise. Although expression levels of Lif transcript in mdx muscles were not consistent with previous studies, the detection of LIF protein in mdx muscle but not wild-type muscle supports a role for LIF in dystrophy. This study also provides evidence of the differential localisation of the LIFR, and the potential for anti-inflammatory actions of LIF that promote survival of transplanted myoblasts in dystrophic muscle.*corresponding author: Jason White, Muscular Dystrophy Research Group, Murdoch Childrens Research Institute; email: jasondw@unimelb.edu.au.

Motor neuron trophic factors: therapeutic use in ALS?

The modest effects of neurotrophic factor (NTF) treatment on lifespan in both animal models and clinical studies of Amyotropic Lateral Sclerosis (ALS) may result from any one or combination of the four following explanations: 1.) NTFs block cell death in some physiological contexts but not in ALS; 2.) NTFs do not rescue motoneurons (MNs) from death in any physiological context; 3.) NTFs block cell death in ALS but to no avail; and 4.) NTFs are physiologically effective but limited by pharmacokinetic constraints. The object of this review is to critically evaluate the role of both NTFs and the intracellular cell death pathway itself in regulating the survival of spinal and cranial (lower) MNs during development, after injury and in response to disease. Because the role of molecules mediating MN survival has been most clearly resolved by the in vivo analysis of genetically engineered mice, this review will focus on studies of such mice expressing reporter, null or other mutant alleles of NTFs, NTF receptors, cell death or ALS-associated genes.

The canonical nuclear factor-κB pathway regulates cell survival in a developmental model of spinal cord motoneurons

In vivo and in vitro motoneuron survival depends on the support of neurotrophic factors. These factors activate signaling pathways related to cell survival or inactivate proteins involved in neuronal death. In the present work, we analyzed the involvement of the nuclear factor-κB (NF-κB) pathway in mediating mouse spinal cord motoneuron survival promoted by neurotrophic factors. This pathway comprises ubiquitously expressed transcription factors that could be activated by two different routes: the canonical pathway, associated with IKKα/IKKβ kinase phosphorylation and nuclear translocation RelA (p65)/p50 transcription factors; and the noncanonical pathway, related to IKKα kinase homodimer phosphorylation and RelB/p52 transcription factor activation. In our system, we show that neurotrophic factors treatment induced IKKα and IKKβ phosphorylation and RelA nuclear translocation, suggesting NF-κB pathway activation. Protein levels of different members of the canonical or noncanonical pathways were reduced in a primary culture of isolated embryonic motoneurons using an interference RNA approach. Even in the presence of neurotrophic factors, selective reduction of IKKα, IKKβ, or RelA proteins induced cell death. In contrast, RelB protein reduction did not have a negative effect on motoneuron survival. Together these results demonstrated that the canonical NF-κB pathway mediates motoneuron survival induced by neurotrophic factors, and the noncanonical pathway is not related to this survival effect. Canonical NF-κB blockade induced an increase of Bim protein level and apoptotic cell death. Bcl-x(L) overexpression or Bax reduction counteracted this apoptotic effect. Finally, RelA knockdown causes changes of CREB and Smn protein levels.

Cardiotrophin-1 in cardiovascular regulation

Cardiotrophin (CT)-1 was discovered by coupling expression cloning with an embryonic stem cell-based model of cardiogenesis. Comparison of similarity in amino acid sequence and conformational structure indicates that CT-1 is a member of the interleukin (IL)-6 type cytokine family that shares the transmembrane signaling protein, glycoprotein (gp) 130 as a receptor. These cytokines mediate overlapping pleiotropic actions on a variety of cell types including cardiac myocytes, hepatocytes, megakaryocytes, osteoclasts, and neuronal cells. CT-lmediates its hypertrophic and cytoprotective properties through the Janus kinase/signal transducers and activators of transcription (JAK/STAT), mitogen-activated protein (MAP) kinase, phosphatidylinositol (PI) 3 kinase, and nuclear factor kappa B (NFkappaB) pathways. CT-1 gene and protein are distributed not only in the heart, but also in the pulmonary, renal, gastrointestinal, cerebral, and muscular tissues. CT-1 could also be synthesized and secreted from vascular endothelial cells and adipocytes. CT-1 has hypertrophic actions on the cardiac myocytes, skeletal muscle cells, and smooth muscle cells as well as cytoprotective actions on the cardiac myocytes, neuronal cells, and hepatocytes. CT-1 is circulating in the body, and its plasma concentration is increased in various cardiovascular and renal diseases such as hypertension, congestive heart failure, myocardial infarction, valvular heart disease, metabolic syndrome, and chronic kidney disease. Treatment with CT-1 is beneficial in experimental animal models of cardiovascular diseases. CT-1 specifically protects the cardiac myocytes from ischemic damage when CT-1 is given not only prior to the ischemia, but also given at the time of reoxygenation. Current evidence suggests that CT-1 plays an important role in the regulation of the cardiovascular system.

Motor neuron diversity in development and disease

Although often considered as a group, spinal motor neurons are highly diverse in terms of their morphology, connectivity, and functional properties and differ significantly in their response to disease. Recent studies of motor neuron diversity have clarified developmental mechanisms and provided novel insights into neurodegeneration in amyotrophic lateral sclerosis (ALS). Motor neurons of different classes and subtypes--fast/slow, alpha/gamma--are grouped together into motor pools, each of which innervates a single skeletal muscle. Distinct mechanisms regulate their development. For example, glial cell line-derived neurotrophic factor (GDNF) has effects that are pool-specific on motor neuron connectivity, column-specific on axonal growth, and subtype-specific on survival. In multiple degenerative contexts including ALS, spinal muscular atrophy (SMA), and aging, fast-fatigable (FF) motor units degenerate early, whereas motor neurons innervating slow muscles and those involved in eye movement and pelvic sphincter control are strikingly preserved. Extrinsic and intrinsic mechanisms that confer resistance represent promising therapeutic targets in these currently incurable diseases.

Fibroblast growth factor signaling in the developing neuroendocrine hypothalamus

Fibroblast growth factor (FGF) signaling is pivotal to the formation of numerous central regions. Increasing evidence suggests FGF signaling also directs the development of the neuroendocrine hypothalamus, a collection of neuroendocrine neurons originating primarily within the nose and the ventricular zone of the diencephalon. This review outlines evidence for a role of FGF signaling in the prenatal and postnatal development of several hypothalamic neuroendocrine systems. The emphasis is placed on the nasally derived gonadotropin-releasing hormone neurons, which depend on neurotrophic cues from FGF signaling throughout the neurons' lifetime. Although less is known about neuroendocrine neurons derived from the diencephalon, recent studies suggest they also exhibit variable levels of dependence on FGF signaling. Overall, FGF signaling provides a broad spectrum of cues that ranges from genesis, cell survival/death, migration, morphological changes, to hormone synthesis in the neuroendocrine hypothalamus. Abnormal FGF signaling will deleteriously impact multiple hypothalamic neuroendocrine systems, resulting in the disruption of diverse physiological functions.

Neuroimmune pharmacology from a neuroscience perspective

The focus of this commentary is to describe how neuroscience, immunology, and pharmacology intersect and how interdisciplinary research involving these areas has expanded knowledge in the area of neuroscience, in particular. Examples are presented to illustrate that the brain can react to the peripheral immune system and possesses immune function and that resident immune molecules play a role in normal brain physiology. In addition, evidence is presented that the brain immune system plays an important role in mediating neurodegenerative diseases, the aging process, and neurodevelopment and synaptic plasticity. The identification of these mechanisms has been facilitated by pharmacological studies and has opened new possibilities for pharmacotherapeutic approaches to the treatment of brain disorders. The emerging field of neuroimmune pharmacology exemplifies this interdisciplinary approach and has facilitated the study of basic cellular and molecular events and disease states and opens avenues for novel therapies.

Role of fibroblast growth factor signaling in gonadotropin-releasing hormone neuronal system development

There is growing evidence demonstrating that fibroblast growth factor (FGF) signaling is important for the development of the gonadotropin-releasing hormone (GnRH) neuronal system. In humans, loss-of-function mutations in FGF receptor 1 (Fgfr1) and Fgf8 lead to hypogonadotropic hypogonadism (HH) with or without anosmia. Insights into how FGF signaling deficiency disrupts the GnRH system in humans are beginning to emerge from studies using transgenic mouse models. In this review, we summarize GnRH system defects in several lines of FGF signaling-deficient mice. We showed that FGF signaling is critically required for olfactory placode induction, differentiation, and GnRH neuronal fate specification and postnatal maintenance. Extrapolating from these transgenic mouse data, we suggest that idiopathic HH in patients harboring loss-of-function Fgfr1 and/or Fgf8 mutations is not merely a result of defective GnRH neuronal migration, but also insults accumulated in the GnRH system during fate specification and postnatal development.

Ciliary neurotrophic factor enhances nicotinic synaptic transmission in sympathetic neurons

Nicotinic acetylcholine receptors mediate fast synaptic transmission in both central and peripheral nervous systems. These receptors play important roles in various physiological functions and are involved in different neurological diseases. A disruption in nicotinic receptor-mediated synaptic transmission due to the loss of nAChRs was detected in the brains of patients with Parkinson's disease and Alzheimer's disease. Although ciliary neurotrophic factor (CNTF) has been reported to promote the cholinergic properties by increasing the production and storage of acetylcholine, it is still unclear whether CNTF can enhance nicotinic synaptic neurotransmission. In this study, we found that CNTF dramatically enhanced the frequency and amplitude of nicotinic excitatory post-synaptic currents in rat superior cervical ganglion neurons maintained in a medium supplemented with nerve growth factor. Moreover, the number of neurons displaying nicotinic synaptic currents was also significantly increased by CNTF. These results suggest that CNTF could enhance nicotinic synaptic transmission via both presynaptic and postsynaptic mechanisms. The findings of this study reinforce the rationale for the usage of combinations of different neurotrophic factors for the therapy of neurodegenerative diseases.

Intramyocardial fibroblast myocyte communication

Cardiac fibroblasts are emerging as key components of normal cardiac function, as well as the response to stressors and injury. These most numerous cells of the heart interact with myocytes via paracrine mechanisms, alterations in extracellular matrix homeostasis, and direct cell-cell interactions. It is possible that they are a contributor to the inability of adult myocytes to proliferate and may influence cardiac progenitor biology. Furthering our understanding of how cardiac fibroblasts and myocytes interact may provide an avenue to novel treatments for heart failure prevention. This review discusses the most recent concepts in cardiac fibroblast-myocyte communication and areas of potential future research.

MCP-1/CCL2 modifies axon properties in a PMP22-overexpressing mouse model for Charcot-Marie-tooth 1A neuropathy

Charcot-Marie-Tooth 1A (CMT1A) neuropathy, the most common inherited peripheral neuropathy, is primarily caused by a gene duplication for the peripheral myelin protein-22 (PMP22). In an accordant mouse model, we investigated the role of monocyte chemoattractant protein-1 (MCP-1/CCL2) as a regulator of nerve macrophages and neural damage including axonopathy and demyelination. By generating PMP22tg mice with reduced levels or lack of MCP-1/CCL2, we found that MCP-1/CCL2 is involved in the increase of macrophages in mutant nerves. PMP22tg mice with wild-type levels of MCP-1/CCL2 showed strong macrophage increase in the diseased nerves, whereas either 50% reduction or total absence of MCP-1/CCL2 led to a moderate or a strong reduction of nerve macrophages, respectively. Interestingly, MCP-1/CCL2 expression level and macrophage numbers were correlated with features indicative of axon damage, such as maldistribution of K+ channels, reduced compound muscle action potentials, and muscle weakness. Demyelinating features, however, were most highly reduced when MCP-1/CCL2 was diminished by 50%, whereas complete lack of MCP-1/CCL2 showed an intermediate demyelinating phenotype. We also identified the MEK1/2-ERK1/2-pathway as being involved in MCP-1/CCL2 expression in the Schwann cells of the CMT1A model. Our data show that, in a CMT1A model, MCP-1/CCL2 activates nerve macrophages, mediates both axon damage and demyelination, and may thus be a promising target for therapeutic approaches.

Ciliary neurotrophic factor-induced sprouting preserves motor function in a mouse model of mild spinal muscular atrophy

Proximal spinal muscular atrophy (SMA) is caused by homozygous loss or mutation of the SMN1 gene on human chromosome 5. Depending on the levels of SMN protein produced from a second SMN gene (SMN2), different forms of the disease are distinguished. In patients with milder forms of the disease, type III or type IV SMA that normally reach adulthood, enlargement of motor units is regularly observed. However, the underlying mechanisms are not understood. Smn(+/-) mice, a mouse model of type III/IV SMA, reveal progressive loss of motor neurons and denervation of motor endplates starting at 4 weeks of age. Loss of spinal motor neurons between 1 month and 12 months reaches 40%, whereas muscle strength is not reduced. In these animals, amplitude of single motor unit action potentials in the gastrocnemic muscle is increased more than 2-fold. Confocal analysis reveals pronounced sprouting of innervating motor axons. As ciliary neurotrophic factor (CNTF) is highly expressed in Schwann cells, we investigated its role for a compensatory sprouting response and maintenance of muscle strength in this mouse model. Genetic ablation of CNTF results in reduced sprouting and decline of muscle strength in Smn(+/-) mice. These findings indicate that CNTF is necessary for a sprouting response and thus enhances the size of motor units in skeletal muscles of Smn(+/-) mice. This compensatory mechanism could guide the way to new therapies for this motor neuron disease.

Neuroprotective and axon growth-promoting effects following inflammatory stimulation on mature retinal ganglion cells in mice depend on ciliary neurotrophic factor and leukemia inhibitory factor

After optic nerve injury retinal ganglion cells (RGCs) normally fail to regenerate axons in the optic nerve and undergo apoptosis. However, lens injury (LI) or intravitreal application of zymosan switch RGCs into an active regenerative state, enabling these neurons to survive axotomy and to regenerate axons into the injured optic nerve. Several factors have been proposed to mediate the beneficial effects of LI. Here, we investigated the contribution of glial-derived ciliary neurotrophic factor (CNTF) to LI-mediated regeneration and neuroprotection using wild-type and CNTF-deficient mice. In wild-type mice, CNTF expression was strongly upregulated in retinal astrocytes, the JAK/STAT3 pathway was activated in RGCs, and RGCs were transformed into an active regenerative state after LI. Interestingly, retinal LIF expression was correlated with CNTF expression after LI. In CNTF-deficient mice, the neuroprotective and axon growth-promoting effects of LI were significantly reduced compared with wild-type animals, despite an observed compensatory upregulation of LIF expression in CNTF-deficient mice. The positive effects of LI and also zymosan were completely abolished in CNTF/LIF double knock-out mice, whereas LI-induced glial and macrophage activation was not compromised. In culture CNTF and LIF markedly stimulated neurite outgrowth of mature RGCs. These data confirm a key role for CNTF in directly mediating the neuroprotective and axon regenerative effects of inflammatory stimulation in the eye and identify LIF as an additional contributing factor.

Cytokines and CNS development

Cytokines are pleotrophic proteins that coordinate the host response to infection as well as mediate normal, ongoing signaling between cells of nonimmune tissues, including the nervous system. As a consequence of this dual role, cytokines induced in response to maternal infection or prenatal hypoxia can profoundly impact fetal neurodevelopment. The neurodevelopmental roles of individual cytokine signaling pathways are being elucidated through gain- and loss-of-function studies in cell culture and model organisms. We review this work with a particular emphasis on studies where cytokines, their receptors, or components of their signaling pathways have been altered in vivo. The extensive and diverse requirements for properly regulated cytokine signaling during normal nervous system development revealed by these studies sets the foundation for ongoing and future work aimed at understanding how cytokines induced normally and pathologically during critical stages of fetal development alter nervous system function and behavior later in life.

Neurotrophic modulation of motor neuron development

Neurotrophic factors (NTFs) are a pleiotropic group of secreted growth factors that regulate multiple aspects of neuronal development, including the regressive event of cell death. Skeletal muscleinnervating lower motoneurons (MNs) of the brain stem and spinal cord comprise one population of central neurons in which programmed cell death (PCD) during embryogenesis has been actively investigated, as much for reasons of technical facility as clinical relevance. The precise identity of NTF-dependent MNs has remained unclear, with most studies simply reporting losses or gains across the entire spinal cord or individual brain-stem nuclei. However, MNs are grouped into highly heterogenous populations based on transcriptional identity, target innervation, and physiological function. Therefore, recent work has focused on the effects of NTF overexpression or deletion on the survival of these MN subpopulations. Together with the recent progress attained in the generation of conditional mutant mice, in which the function of an NTF or its receptor can be eliminated specifically in MNs, these recent studies have begun to define the differential trophic requirements for MN subpopulations during PCD. The intent of this review is to summarize these recent findings and to discuss their significance with respect to neurotrophic theory.

Expression of the regeneration-associated protein SPRR1A in primary sensory neurons and spinal cord of the adult mouse following peripheral and central injury

Small proline-rich repeat protein 1A (SPRR1A) is expressed in dorsal root ganglion (DRG) neurons following peripheral nerve injury but it is not known whether SPRR1A is differentially expressed following injury to peripheral versus central DRG projections and a detailed characterization of expression in sensory neuron subpopulations and spinal cord has not been performed. Here we use immunocytochemical techniques to characterize SPRR1A expression following sciatic nerve, dorsal root, and dorsal column injury in adult mice. SPRR1A was not detected in naïve spinal cord, DRG, or peripheral nerves and there was minimal expression following injury to the centrally projecting branches of DRG neurons. However, following peripheral (sciatic) nerve injury, intense SPRR1A immunoreactivity was observed in the dorsal horn and motoneurons of the spinal cord, in L4/5 DRG neurons, and in the injured nerve. A time-course study comparing expression following sciatic nerve crush and transection revealed maximum SPRR1A levels at day 7 in both models. However, while SPRR1A was downregulated to baseline by 30 days postlesion following crush injury, it remained elevated 30 days after transection. Cell-size and double-labeling studies revealed that SPRR1A was expressed by DRG cells of all sizes and colocalized with classical markers of DRG subpopulations and their primary afferent terminals. High coexpression of SPRR1A with activating transcription factor-3 and growth-associated protein-43 was observed, indicating that it is expressed by injured and regenerating neurons. This study supports the hypothesis that SPRR1A is a regeneration-associated gene and that SPRR1A provides a valuable marker to assess the regenerative potential of injured neurons.

Deletion of the mouse RegIIIbeta (Reg2) gene disrupts ciliary neurotrophic factor signaling and delays myelination of mouse cranial motor neurons

A large number of cytokines and growth factors support the development and subsequent maintenance of postnatal motor neurons. RegIIIbeta, also known as Reg2 in rat and HIP/PAP1 in humans, is a member of a family of growth factors found in many areas of the body and previously shown to play an important role in both the development and regeneration of subsets of motor neurons. It has been suggested that RegIIIbeta expressed by motor neurons is both an obligatory intermediate in the downstream signaling of the leukemia inhibitory factor/ciliary neurotrophic factor (CNTF) family of cytokines, maintaining the integrity of motor neurons during development, as well as a powerful influence on Schwann cell growth during regeneration of the peripheral nerve. Here we report that in mice with a deletion of the RegIIIbeta gene, motor neuron survival was unaffected up to 28 weeks after birth. However, there was no CNTF-mediated rescue of neonatal facial motor neurons after axotomy in KO animals when compared with wild-type. In mice, RegIIIbeta positive motor neurons are concentrated in cranial motor nuclei that are involved in the patterning of swallowing and suckling. We found that suckling was impaired in RegIIIbeta KO mice and correlated this with a significant delay in myelination of the hypoglossal nerve. In summary, we propose that RegIIIbeta has an important role to play in the developmental fine-tuning of neonatal motor behaviors mediating the response to peripherally derived cytokines and growth factors and regulating the myelination of motor axons.

Transregulation of leukemia inhibitory [corrected] factor receptor expression and function by growth factors in neuroblastoma cells

The cytokines that signal through the leukemia inhibitory factor (LIF) receptor are members of the neuropoietic cytokine family and have varied and numerous roles in the nervous system. In this report, we have determined the effects of growth factor stimulation on LIF receptor (LIFR) expression and signal transduction in the human neuroblastoma cell line NBFL. We show here that stimulation of NBFL cells with either epidermal growth factor or fibroblast growth factor decreases the level of LIFR in an extracellular signal-regulated kinase (Erk)1/2-dependent manner and that this down-regulation is due to an increase in the apparent rate of lysosomal LIFR degradation. Growth factor-induced decreases in LIFR level inhibit both LIF-stimulated phosphorylation of signal transducers and activators of transcription 3 and LIFR-mediated gene induction. We also show that Ser1044 of LIFR, which we have previously shown to be phosphorylated by Erk1/2, is required for the inhibitory effects of growth factors. Neurons are exposed to varying combinations and concentrations of growth factors and cytokines that influence their growth, development, differentiation, and repair in vivo. These findings demonstrate that LIFR expression and signaling in neuroblastoma cells can be regulated by growth factors that are potent activators of the mitogen-activated protein kinase pathway, and thus illustrate a fundamental mechanism that underlies crosstalk between receptor tyrosine kinase and neuropoietic cytokine signaling pathways.

The neurotrophic effects of glial cell line-derived neurotrophic factor on spinal motoneurons are restricted to fusimotor subtypes

Glial cell line-derived neurotrophic factor (GDNF) regulates multiple aspects of spinal motoneuron (MN) development, including gene expression, target selection, survival, and synapse elimination, and mice lacking either GDNF or its receptors GDNF family receptor alpha1 (GFRalpha1) and Ret exhibit a 25% reduction of lumbar MNs at postnatal day 0 (P0). Whether this loss reflects a generic trophic role for GDNF and thus a reduction of all MN subpopulations, or a more restricted role affecting only specific MN subpopulations, such as those innervating individual muscles, remains unclear. We therefore examined MN number and innervation in mice in which Ret, GFRalpha1, or GDNF was deleted and replaced by reporter alleles. Whereas nearly all hindlimb muscles exhibited normal gross innervation, intrafusal muscle spindles displayed a significant loss of innervation in most but not all muscles at P0. Furthermore, we observed a dramatic and restricted loss of small myelinated axons in the lumbar ventral roots of adult mice in which the function of either Ret or GFRalpha1 was inactivated in MNs early in development. Finally, we demonstrated that the period during which spindle-innervating MNs require GDNF for survival is restricted to early neonatal development, because mice in which the function of Ret or GFRalpha1 was inactivated after P5 failed to exhibit denervation of muscle spindles or MN loss. Therefore, although GDNF influences several aspects of MN development, the survival-promoting effects of GDNF during programmed cell death are mostly confined to spindle-innervating MNs.

The neuropoietic cytokine family in development, plasticity, disease and injury

Neuropoietic cytokines are well known for their role in the control of neuronal, glial and immune responses to injury or disease. Since this discovery, it has emerged that several of these proteins are also involved in nervous system development, in particular in the regulation of neurogenesis and stem cell fate. Recent data indicate that these proteins have yet more functions, as key modulators of synaptic plasticity and of various behaviours. In addition, neuropoietic cytokines might be a factor in the aetiology of psychiatric disorders.

Neuroprotection against neurodegenerative diseases: development of a novel hybrid neuroprotective peptide Colivelin

Neuronal death is directly implicated in the pathogenesis of neurodegenerative diseases (NDDs). NDDs cannot be cured because the mechanisms underlying neuronal death are too complicated to be therapeutically suppressed. Neuroprotective factors, such as neurotrophins, certain growth factors, neurotrophic cytokines, and short neuroprotective peptides, support neuronal survival in both physiological and pathological conditions, suggesting that these factors may be good drug candidates for NDDs. We recently generated a novel neuroprotective peptide named Colivelin by attaching activity-dependent neurotrophic factor (ADNF) to the N-terminus of a potent Humanin derivative, AGA-(C8R)HNG17. HN was originally identified from an Alzheimer's disease (AD) brain as an endogenous neuroprotective peptide that suppresses ADrelevant toxicity. Colivelin protects neurons from death relevant to NDDs by activating two independent prosurvival signals: an ADNF-mediated Ca2+/calmodulin-dependent protein kinase IV pathway and an HN-mediated STAT3 pathway. The neuroprotective effect of Colivelin provides novel insights into therapy for NDDs.

Interleukin-6 family cytokine M17 induces differentiation and nitric oxide response of goldfish (Carassius auratus L.) macrophages

Cytokines belonging to the interleukin-6 (IL-6) family function in many biological processes and display a high degree of redundancy within the family. Although a number of mRNA transcripts from teleost fish that resemble IL-6 family cytokines have been identified none have been functionally characterized to confirm their identity. We report on the identification and functional characterization of goldfish M17, a molecule possessing sequence and mRNA expression patterns similar to the mammalian and avian ciliary neurotrophic factor and mammalian leukemia inhibitory factor. Goldfish M17 was found to induce the production of nitric oxide in goldfish macrophages and stimulate the proliferation of macrophage progenitor cells when added in combination with cell-conditioned medium. Moreover, goldfish M17 was found to facilitate the differentiation of sorted monocytes into macrophages at biologically relevant concentrations.