Protective role of selenium-enriched supplement on spinal cord injury through the up-regulation of CNTF and CNTF-Ralpha

OBJECTIVE

Spinal cord injury (SCI), as one of the common serious spine disorders, often leads to severe neurological dysfunction and even permanent disability, which will cause heavy economical burden for family and society. Currently, selenium-enriched products have an obvious role in the protection and recovery of SCI; however, its protective mechanism is still unclear.

MATERIALS AND METHODS

In order to explore the protective effect of selenium-enriched supplement (SES) on SCI, the adult rats were randomly divided into sham operation control (SC) group, ischemia-reperfusion model (IM) group and SES pretreatment (ST) group to investigate the change of ciliary neurotrophic factor (CNTF) and its receptor-alpha (CNTF-Ralpha) during SCI in the presence of SES. The rats in IM and ST groups were subjected to the blockage of their abdominal aorta to establish the model of SCI; but the rats in SC group were subjected to sham operation without the blockage of abdominal aorta. The rats in ST group were fed with foods containing SES at the dose of equivalent 5 mg/L selenium in water before blocking their abdominal aorta. After 7 days, the rats were sacrificed to observe the structure of nerve cells through HE staining and the expression of CNTF and CNTF-Ralpha by Western blot, immunohistochemical, and RT-PCR methods, respectively.

RESULTS

Both protein and mRNA of CNTF and CNTF-Ralpha were positively expressed in rats from SC group. The mRNA expression levels of CNTF and CNTF-Ralpha in ST group were much higher than SCI model group.

CONCLUSIONS

SES can execute a protective role in SCI through up-regulating the expression of CNTF and CNTF-Ralpha.

High level soluble expression, purification, and characterization of human ciliary neuronotrophic factor in Escherichia coli by single protein production system

Ciliary neurotrophic factor (CNTF) is characterized as a neuropoietic cytokine for a broad spectrum of neurons, leading to its evaluation in humans suffering from neurodegenerative diseases. Due to its wide range of biological applications, high yield production of soluble biologically active recombinant human CNTF (rhCNTF) in heterologous expression system is demanded. Many attempts had been undertaken to product rhCNTF in Escherichia coli (E. coli), however, the expression level of rhCNTF was low and most of which formed insoluble inclusion bodies. In this study, we described a new and efficient method to express rhCNTF. The human CNTF gene was codon optimized and then expressed by the single protein production (SPP) expression system in E. coli. The results showed that rhCNTF was expressed as a soluble biologically active protein, and upon purification, the final yield was about 250 mg/L in shake flask with a specific neuroprotective activity in Aβ-induced SH-SY5Y cell injury model. Our study might open up a new strategy for large-scale production of functional rhCNTF for clinical applications as well as basic research.

[Bone marrow stromal cells transfected with ciliary neurotrophic factor gene ameliorates the symptoms and inflammation in C57BL/6 mice with experimental allergic encephalomyelitis]

OBJECTIVE

To investigate the anti-inflammatory effect of bone marrow stromal cells (MSCs) transfected with recombinant adenovirus-mediated ciliary neurotrophic factor (CNTF) gene in C57BL/6 mice with experimental allergic encephalomyelitis (EAE).

METHODS

An adenovirus vector containing CNTF gene Ad-CNTF-IRES-GFP was constructed and transfected in the MSCs (MSC-CNTF). After examination of CNTF expression, the transfected cells were transplanted in C57BL/6 mice with MOG 35-55-induced EAE, which were monitored for the changes in the symptoms scores. The levels of tumor necrosis factor-alpha (TNF-alpha), inteferon-gamma (IFN-gamma), interleukin-12P35 (IL-12P35), and IL-10 in the peripheral blood of the mice were detected, and the number of MSC-CNTF cells in the spleen and spinal cord was counted. CD3+ T cell infiltration and TNF-alpha and IFN-gamma expressions in the lesions were also observed after the cell transplantation.

RESULTS

CNTF gene transfection resulted in significantly increased CNTF expression in the MSCs. The mice receiving MSC-CNTF transplantation exhibited significantly improved symptoms with shortened disease course and lessened disease severity. The cell transplantation also resulted in significantly decreased peripheral blood TNF-alpha levels, ameliorated CD3+T cell infiltrations and lowered TNF-alpha expression in the lesions, while the levels of IFN-gamma underwent no significant changes.

CONCLUSION

Transplantation of CNTF gene-transfected MSCs results in decreased peripheral blood TNF-alpha and IFN-gamma levels and reduced inflammatory cells, CD3-positive cells and TNF-alpha expression in the lesion of EAE, therefore providing better effect than MSCs in relieving the symptoms of EAE in mice.

NT-501: an ophthalmic implant of polymer-encapsulated ciliary neurotrophic factor-producing cells

Neurotech Pharmaceuticals Inc is developing NT-501, an implantable polymeric device containing a genetically modified cell line that secretes ciliary neurotrophic factor, for the potential treatment of retinitis pigmentosa (RP) and age-related macular degeneration (AMD). Phase III clinical trials for RP and a phase II clinical trial for dry AMD are ongoing. A phase I clinical trial showed that NT-501 treatment was well tolerated with variable, but positive improvements in visual acuity.

Impaired hypoglossal nerve regeneration in mutant mice lacking complex gangliosides: down-regulation of neurotrophic factors and receptors as possible mechanisms

Gangliosides, sialic acid-containing glycosphingolipids, have been considered to play roles as neurotrophic factors. Exogenous gangliosides added to the culture medium of neuronal cells or injected in artificially injured sites of nerve tissues actually showed neurotrophic factor-like effects such as neurite extension and alleviation of nerve tissue deterioration. In this study, neuroregeneration in the mutant mice lacking complex gangliosides was examined. To determine whether the nervous system maintains regenerative activity in the long-term absence of complex gangliosides, we analyzed hypoglossal nerve regeneration after axotomy in the mutant mice of GM2/GD2 synthase. These mice exhibited marked impairment of regenerative activity both in the number of surviving neurons and in the number of peroxidase-positive neurons. Moreover, reduced levels of gene expression of neurotrophic factors and their receptors including CNTF, p75 NTR, TrkB, and others in hypoglossal neurons were observed in real-time reverse transcription-polymerase chain reaction combined with laser capture microdissection, suggesting that these molecules are, at least partly, involved in the regeneration of lesioned nerves and that their expression levels are precisely controlled in the presence of intact expression of complex gangliosides.

Effects of electro-acupuncture on CNTF expression in spared dorsal root ganglion and the associated spinal lamina II and nucleus dorsalis following adjacent dorsal root ganglionectomies in cats

It is well known that plasticity occurs in deafferented spinal cord, and that electro-acupuncture (EA) could promote functional restoration. The underlying mechanism is, however, unknown. Ciliary neurotrophic factor (CNTF) plays a crucial role in neurite outgrowth and neuronal survival both in vivo and in vitro, and its expression might explain some of the mechanism. In this study, we investigated the effects of EA on CNTF expression in the spared L(6) dorsal root ganglion (DRG), and spinal lamina II at spinal segments L(3) and L(6) as well as nucleus dorsalis (ND) of L(3) spinal segment following removal of L(1)-L(5) and L(7)-S(2) (DRG) in the cat. After ganglionectomies, the total and small-to-medium-sized numbers of immunoreactive neurons decreased at 3 dpo, and returned to the sham-operated level as early as 7 dpo. After EA, immunoreactive neurons in L(6) DRG noticeably increased at 7 dpo, compared with the non-acupunctured group. Notable increase in the large neurons was seen at 14 dpo, while their numbers in L(3) and L(6) spinal cord segments significantly declined at 3 dpo. Those in L(3) segment did not reach the sham-operated level until 14 dpo, but their numbers in L(6) segment returned to the sham-operated level as early as 7 dpo. CNTF immunopositive neurons in the ND of L(3) segment returned to the sham-operated level at 14 dpo. After EA, their number significantly increased as early as 7 dpo in lamina II of L(6) segment, and as late as 14 dpo in ND of L(3) segment. Western blot analysis showed CNTF changes corresponding to those shown in immunohistochemical staining. It is concluded that CNTF expression was involved in the EA promoted plastic changes in L(6) DRG and the associated deafferented spinal lamina and ND.

JAK-STAT signaling pathway mediates astrogliosis in brains of scrapie-infected mice

Scrapie is characterized histologically, in part, by astrogliosis in brain and spinal cord. However, the mechanisms of astrogliosis in brain injury occurring during prion infection are not well understood. In this study, we investigated the expression levels and cellular localization of Janus kinase (JAK) -signal transducers and activators of transcription (STAT) signaling molecules and growth factors such as leukemia inhibitory factor (LIF) and ciliary neurotropic factor (CNTF) by western blot analysis and immunohistochemistry. We found that expression levels of LIF and CNTF were increased in scrapie-infected brains and phosphorylated (p)-JAK2, p-STAT1 (Ser727 and Tyr701), p-STAT3 (Tyr705), and glial fibrillary acidic protein were expressed strongly in scrapie-infected brains. Moreover, we found that p-STAT1 and p-STAT3 were found mainly in the nucleus in scrapie-infected brains. Immunohistochemically, p-STAT1 was colocalized with LIF and CNTF and p-JAK2 in many reactive astrocytes in scrapie-infected brains. In contrast, immunostaining for p-STAT3 was found in comparatively few astrocytes in limited regions; p-STAT3 staining merged with p-JAK2 in hippocampus sections of scrapie-infected brains. Taken together, our results suggest that activation of JAK2-STAT1 signaling pathway occurred in reactive astrocytes in hippocampus of scrapie-infected brains.

Effect of ammonia on ciliary neurotrophic factor mRNA and protein expression and its upstream signalling pathway in cultured rat astroglial cells: possible implication of c-fos, Sp1 and p38MAPK

Ciliary neurotrophic factor (CNTF) may be implicated in the pathogenetic mechanisms of hepatic encephalopathy. We tested this hypothesis by treating confluent primary cultures of rat astroglial cells with ammonium chloride for various periods and analysing the effect of ammonia on the signalling pathway that regulates CNTF mRNA and protein expression. Ammonia treatment induced a dose- and time-dependent reduction in CNTF mRNA and protein expression. Surface-enhanced laser desorption/ionization-time-of-flight mass spectrometry analysis of CNTF in the culture medium demonstrated that ammonia also induced a significant decrease in CNTF release. In addition, ammonia affected Sp1 and c-fos, transcription factors that regulate CNTF mRNA and protein expression, which showed partial dephosphorylation and significantly lower mRNA and protein levels. Total content of p38MAPK (for which Sp1 and c-fos are substrates) was unaffected by ammonia, although the diphosphorylated (active) form was significantly reduced after ammonia exposure.

Impaired wound healing after cerebral hypoxia-ischemia in the diabetic mouse

Impaired peripheral wound healing is a hallmark of diabetics pathology and has been attributed to compromised macrophage activation. Stroke is another component of diabetic pathology, with increased tissue infarction and worsened recovery although the mechanisms remain unresolved. In this study, we investigated whether a compromised glial/macrophage response might contribute to cerebral hypoxic-ischemic (H/I) brain damage in diabetic (db/db), relative to their normoglycemic db/+ mice. Hypoxia-ischemia was induced in 8-week-old male db/db and db/+ mice by the ligation of right common carotid artery followed by systemic hypoxia (8% O2: 92% N2) for 17 mins. Mice were killed at specific intervals of reperfusion/recovery and the brains analyzed by in situ hybridization or total RNA isolation. In situ hybridization using bfl-1 (microglia) and glial fibrillary acidic protein (GFAP) (astrocytes) revealed expression of both bfl-1 and GFAP in the ipsilateral hemisphere at 4 h in the db/+ mice, which was delayed and minimal in the db/db mice. RNase protection assays showed a robust increase in expression of the proinflammatory cytokines tumor necrosis factor-alpha (TNFalpha), interleukin-1 IL-1alpha, and IL-1beta mRNA in the db/+ mice at 6 to 8 h of reperfusion peaking at 8 to 12 h; in db/db mice expression was markedly delayed and diminished. Real-time-polymerase chain reaction (RT-PCR) confirmed the reduced and delayed expression TNFalpha, IL-1alpha, IL-1beta, and the growth factors insulin-like growth factor-1 and ciliary neurotrophic factor in the db/db mice; enzyme-linked immunosorbent assays confirmed the reduced and delayed translation of IL-1beta protein. These findings suggest that a compromised inflammatory response may underlie the greater infarct associated with diabetic db/db mice compared with their nondiabetic littermates following a hypoxic/ischemic insult.

Ciliary neurotrophic factor (CNTF) for human retinal degeneration: phase I trial of CNTF delivered by encapsulated cell intraocular implants

Neurotrophic factors are agents with a promising ability to retard progression of neurodegenerative diseases and are effective in slowing photoreceptor degeneration in animal models of retinitis pigmentosa. Here we report a human clinical trial of a neurotrophic factor for retinal neurodegeneration. In this Phase I safety trial, human ciliary neurotrophic factor (CNTF) was delivered by cells transfected with the human CNTF gene and sequestered within capsules that were surgically implanted into the vitreous of the eye. The outer membrane of the encapsulated cell implant is semipermeable to allow CNTF to reach the retina. Ten participants received CNTF implants in one eye. When the implants were removed after 6 months, they contained viable cells with minimal cell loss and gave CNTF output at levels previously shown to be therapeutic for retinal degeneration in rcd1 dogs. Although the trial was not powered to form a judgment as to clinical efficacy, of seven eyes for which visual acuity could be tracked by conventional reading charts, three eyes reached and maintained improved acuities of 10-15 letters, equivalent to two- to three-line improvement on standard Snellen acuity charts. A surgically related choroidal detachment in one eye resulted in a transient acuity decrease that resolved with conservative management. This Phase I trial indicated that CNTF is safe for the human retina even with severely compromised photoreceptors. The approach to delivering therapeutic proteins to degenerating retinas using encapsulated cell implants may have application beyond disease caused by genetic mutations.

Enhanced Neurotrophin Synthesis and Molecular Differentiation in Non-Transformed Human Retinal Progenitor Cells Cultured in a Rotating Bioreactor

One approach to the treatment of retinal diseases, such as retinitis pigmentosa, is to replace diseased or degenerating cells with healthy cells. Even if all of the problems associated with tissue transplant were to be resolved, the availability of tissue would remain an ongoing problem. We have previously shown that transformed human retinal cells can be grown in a NASA-developed horizontally rotating culture vessel (bioreactor) to form three-dimensional-like structures with the expression of several retinal specific proteins. In this study, we have investigated growth of non-transformed human retinal progenitors (retinal stem cells) in a rotating bioreactor. This rotating culture vessel promotes cell-cell interaction between similar and dissimilar cells. We cultured retinal progenitors (Ret 1-4) alone or as a co-culture with human retinal pigment epithelial cells (RPE, D407) in this system to determine if 3D structures can be generated from non-transformed progenitors. Our second goal was to determine if the formation of 3D structures correlates with the upregulation of neurotrophins, basic fibroblast growth factor (bFGF), transforming growth factor alpha (TGFalpha), ciliary neurotrophic factor (CNTF), and brain-delivered neurotrophic factor (BDNF). These factors have been implicated in progenitor cell proliferation, commitment, differentiation, and survival. We also investigated the expression of the following retinal specific proteins in this system: neuron specific enolase (NSE); tyrosine hydroxylase (TH); D(2)D(3), D(4) receptors; protein kinase-C alpha (PKCalpha), and calbindin. The 3D structures generated were characterized by phase and scanning transmission electron microscopy. Retinal progenitors, cultured alone or as a co-culture in the rotating bioreactor, formed 3D structures with some degree of differentiation, accompanied by the upregulation of bFGF, CNTF, and TGFalpha. Brain-derived neurotrophic factor, which is expressed in vivo in RPE (D407), was not expressed in monolayer cultures of RPE but expressed in the rotating bioreactor-cultured RPE and retinal progenitors (Ret 1-4). Upregulation of neurotrophins was noted in all rotating bioreactor-cultured cells. Also, upregulation of D(4) receptor, calbindin, and PKCalpha was noted in the rotating bioreactor-cultured cells. We conclude that non-transformed retinal progenitors can be grown in the rotating bioreactor to form 3D structures with some degree of differentiation. We relied on molecular and biochemical analysis to characterize differentiation in cells grown in the rotating bioreactor.

Differential expression of suppressors of cytokine signaling-1 and -3 and related cytokines in central nervous system during remitting versus non-remitting forms of experimental autoimmune encephalomyelitis

SJL mice exhibit a relapsing-remitting course of experimental autoimmune encephalomyelitis (EAE), whereas C57BL/6 (B6) mice display a more chronic course without complete remissions. Suppressor of cytokine signaling (SOCS)-1 and SOCS-3 are members of a family of inducible intracellular proteins that negatively regulate cytokine signaling in cells of hematopoietic origin and may influence the Th1 to Th2 balance. SOCS-1 and SOCS-3 are induced by cytokines that are known to be up-regulated during EAE, including IFN-gamma (IFN-g) and IL-6, respectively. To test the hypothesis that the level of induction of SOCS-1 and SOCS-3 correlates with the course of EAE, mRNA levels were compared in spinal cords of SJL and B6 mice during discrete stages of disease. SOCS-1 and SOCS-3 were elevated throughout active disease in both strains. At peak EAE, SOCS-1 was higher and SOCS-3 was lower in B6 cords compared with SJL cords. This correlated with greater expression of the Th1 cytokine, IFN-g, and less of the Th2 cytokine, IL-10, in B6 cords relative to SJL cords during onset and peak disease. SOCS-3 inducers in the IL-6 family were expressed differentially between the strains. IL-6 and leukemia inhibitory factor were higher at onset in B6 cords whereas ciliary neurotrophic factor was increased in SJL cords during peak disease. Expression of fibroblast growth factor-2, which may be involved in remyelination, was higher in SJL cords at peak. Comparison of these models suggests that cytokine autoregulatory mechanisms involving SOCS may play a role in determining the course of EAE.

Protection of Photoreceptor Cells from Phototoxicity by Transplanted Retinal Pigment Epithelial Cells Expressing Different Neurotrophic Factors

Transplantation of cells or tissues and the intravitreal injection of neurotrophic factors are two methods that have been used to treat retinal diseases. The purpose of this study was to examine the effects of combining both methods: the transplantation of retinal pigment epithelial (RPE) cells expressing different neurotrophic factors. The neutrophic factors were Axokine, brain derived-neurotrophic factor (BDNF), and basic fibroblast growth factor (bFGF). The enhanced green fluorescence protein (eGFP) gene was used as a reporter gene. These genes were transduced into RPE cells by lipofection, selected by antibiotics, and transplanted into the subretinal space of 108 rats. The rats were examined at 1 week and 3 months after the transplantation to determine whether the transduced cells were present, were expressing the protein, and were able to protect photoreceptors against phototoxicity. The survival of the transplanted cells was monitored by the presence of eGFP. The degree of protection was determined by the thickness of the outer nuclear layer. Our results showed that the degree of photoreceptor protection was different for the different types of neurotrophic factors at 1 week. After 3 months, the number of surviving transplanted cell was markedly reduced, and protection was observed only with the BDNF-transduced RPE cells. A significant degree of rescue was also observed by BDNF-transduced RPE cells in the nontransplanted area of the retina at both the early and late times. Lymphocytic infiltration was not detected in the vitreous, retina, and choroid at any time. We conclude that the transplantation of BDNF-transduced RPE cells can reduce the photoreceptor damage induced by phototoxicity in the transplanted area and weakly in the nontransplanted area.

Ciliary neurotrophic factor is expressed in the magnocellular neurosecretory system of the rat in vivo: evidence for injury- and activity-induced upregulation

Although ciliary neurotrophic factor (CNTF) has been shown to promote the survival of magnocellular neurons when applied exogenously to explants of the paraventricular and supraoptic nuclei (SON) in vitro, little is known regarding its expression or regulation in the adult magnocellular neurosecretory system (MNS) following injury in vivo. Therefore, we utilized in situ hybridization and immunocytochemical analysis in conjunction with quantitative optical densitometric analysis to identify the cellular source of CNTF and examine the temporal pattern of its expression, following unilateral transection of the hypothalamo-neurohypophysial tract in the adult rat. In intact rats, CNTF immunoreactivity (CNTF-ir) was predominantly localized within identified astrocytes within the ventral glial limitans subjacent to the SON. Quantitative optical densitometric analysis of CNTF-ir levels in the axotomized SON demonstrated that the proportional area of CNTF-ir was significantly elevated between 3 and 30 days following injury. A significant but more limited increase was also observed in the non-injured contralateral SON. In situ hybridization confirmed the expression and upregulation of CNTF in the axotomized SON. These results demonstrate the expression of CNTF in the adult rodent MNS in vivo and provide evidence that levels of CNTF are upregulated in response to both direct injury, and heightened metabolic activity, within the lesioned and sprouting SON, respectively.

[Construction of superagonist mutein of human CNTF and its expression in Pichia pastoris]

Human ciliary neurotrophic factor (hCNTF) and its derivatives are promising therapeutics for obesity associated with diabetes. To reduce its side effects and increase its efficacy, superagonist mutein of human CNTF was constructed by the introduction of S165D/Q166H mutation into AX15(R13K), which is a mutein of naturally occurring hCNTF, with improved biological activity, stability, solubility and KEX2 resistance. In vitro TF-1 cell survival assay and in vivo antiobesity tests showed DH-AX(R13K) was about 5 fold more potent than AX15(R13K). It was further demonstrated that the antiobesity effect of DH-AX15(R13K) was more durable than that of AX15(R13K). The more durable effects of DH-AX15(R13K) is ascribed to its higher specific activity, but not to its prolonged half-life. The superagonist mutein of human CNTF would have an improved side effect profile and thus have superior therapeutic potential.

[Expression of CNTF and PDGF in spared dorsal root ganglion after partial dorsal root rhizotomy]

OBJECTIVE

To investigate the expression of ciliary neurotrophic factor (CNTF) and platelet derived growth factor (PDGF) in spared dorsal root ganglion (DRG) after partial dorsal root rhizotomy.

METHODS

Twenty adult cats were divided into four groups. Five cats were kept intact in the control group. Fifteen cats were subjected to bilateral root rhizotomy, and on the 3rd day, 7th day and 14th day after operation, they were sacrificed as subjects in the three experiment groups respectively (n=5 per group) and their DRGs (L6) were taken. Immunochemical ABC method was used to detect the distribution of CNTF and PDGF-immunoreactivity neurons in those DRGs. The quantitative analysis was conducted to get the numbers of CNTF, PDGF-positive total, large, and medium-small sized neurons in each group.

RESULTS

CNTF, PDGF-immunoreactants were distributed in large and medium-small sized neurons. The numbers of total and medium-small sized CNTF positive neurons were noted to be decreased on the 3rd day after operation (P<0.05), and no difference 7th and 14th days was seen when compared with control (P>0.05), but the large positive neurons showed no difference. The total and medium-small sized PDGF positive neurons were found decreased apparently on the 3rd day and 7th day, but there was no difference on the 14th day as compared with normal level. Large positive neurons displayed no change at every time.

CONCLUSION

Partial dorsal root rhizotomy exerts different influence on the expression of CNTF and PDGF for different neurons in spared DRG.

Expression of ciliary neurotrophic factor (CNTF), CNTF receptor alpha (CNTFR-alpha) following experimental intracerebral hemorrhage in rats

Ciliary neurotrophic factor (CNTF) is known as a neuro-survival factor in the developing and developed CNS, as well as in the CNS following injury. However, little is known about the expression of CNTF or that of its receptor (CNTFR-alpha) in cases of intracerebral hemorrhage (ICH). We investigated the temporal and spatial profiles of CNTF and CNTFR-alpha expression using a collagenase-induced ICH rat model. CNTF expression was up-regulated from the day following ICH induction and reached a peak level at 5 to 14 days, with increased expression observed in brain tissue surrounding the hematoma lesion and white matter structures in association with astroglial proliferation. Further, CNTFR-alpha was transiently expressed in the cerebral cortex surrounding the hematoma, with a peak at 5 days. Administration of exogenous CNTF into the lesion following initiation of ICH resulted in a prolonged expression of CNTFR-alpha on cortical neurons neighboring the hematoma. Our findings suggest differential regulation of CNTF and CNTFR-alpha, and the possibility of a therapeutic strategy using CNTF administration for ICH.

Ciliary neurotrophic factor protects retinal ganglion cells from axotomy-induced apoptosis via modulation of retinal gliain vivo

Adenoviral-mediated transfer of ciliary neurotrophic factor (CNTF) to the retina rescued retinal ganglion cells (RGCs) from axotomy-induced apoptosis, presumably via activation of the high affinity CNTF receptor alpha (CNTFRalpha) expressed on RGCs. CNTF can also activate astrocytes, via its low affinity leukemia inhibitory receptor beta expressed on mature astrocytes, suggesting that CNTF may also protect injured neurons indirectly by modulating glia. Adenoviral-mediated overexpression of CNTF in normal and axotomized rat retinas was examined to determine if it could increase the expression of several glial markers previously demonstrated to have a neuroprotective function in the injured brain and retina. Using Western blotting, the expression of glial fibrillary acid protein (GFAP), glutamate/aspartate transporter-1 (GLAST-1), glutamine synthetase (GS), and connexin 43 (Cx43) was examined 7 days after intravitreal injections of Ad.CNTF or control Ad.LacZ. Compared to controls, intravitreal injection of Ad.CNTF led to significant changes in the expression of CNTFRalpha, pSTAT(3), GFAP, GLAST, GS, and Cx43 in normal and axotomized retinas. Taken together, these results suggest that the neuroprotective effects of CNTF may result from a shift of retinal glia cells to a more neuroprotective phenotype. Moreover, the modulation of astrocytes may buffer high concentrations of glutamate that have been shown to contribute to the death of RGCs after optic nerve transection.

[Construction of protease resistant mutein of human CNTF and its expression in Pichia pastoris]

AX15 is a mutein of naturally occurring human ciliary neurophic factor (hCNTF), with improved biological activity, stability and solubility. AX15 is susceptible to protease degradation when expressed in Pichia pastoris. Amino acid sequencing revealed the degradation was occurred behind position 12 and 13 amino acid residues, which constitute a dibasic site, RR. Based on the substrate specificity of KEX2, a KEX2 resistant mutein of AX15-AX15 (R13K) was constructed, in which RR was replaced by RK. It was demonstrated that the stability of AX15 (R13K) improved significantly, as no degradation was detected even after 120 hours of induction. AX15 (R13K) was purified to homogeneity by ultrafiltration and gel filtration. TF-1 cell survival bioassay showed AX15 (R13K) had equivalent specific activity to AX15. The protease resistant mutein of AX15 may have greater in vivo stability and thus have superior therapeutic potential.

Long-term lentiviral-mediated expression of ciliary neurotrophic factor in the striatum of Huntington's disease transgenic mice

Ciliary neurotrophic factor (CNTF) has been shown to prevent behavioral deficits and striatal degeneration in neurotoxic models of Huntington's disease (HD), but its effect in a genetic model has not been evaluated. Lentiviral vectors expressing the human CNTF or LacZ reporter gene were therefore injected in the striatum of wild-type (WT) and transgenic mice expressing full-length huntingtin with 72 CAG repeats (YAC72). Behavioral analysis showed increased locomotor activity in 5- to 6-month-old YAC72-LacZ mice compared to WT-LacZ animals. Interestingly, CNTF expression reduced the activity levels of YAC72 mice compared to control animals. In both WT and YAC72 mice, CNTF expression was demonstrated in striatal punches, up to a year after lentiviral injection. Stereological analysis revealed that the number of LacZ and DARPP-32-positive neurons were decreased in YAC72-LacZ mice compared to WT-LacZ animals. Assessment of the benefit of CNTF expression in the YAC72 mice was, however, complicated by a down-regulation of DARPP-32 and to a lesser extent of NeuN in all mice treated with CNTF. The expression of the neuronal marker NADPH-d was unaffected by CNTF, but expression of the astrocytic marker glial fibrillary acidic protein (GFAP) was increased. Finally, a reduction of the number of striatal dark cells was observed in YAC mice treated with CNTF compared to LacZ. These data indicate that sustained striatal expression of CNTF can be achieved with lentiviruses. Further studies are, however, needed to investigate the intracellular signaling pathways mediating the long-term effects of CNTF expression on dopamine signaling, glial cell activation and how these changes may affect HD pathology.

Ciliary neurotrophic factor inhibits differentiation of photoreceptor-like cells in rat pineal glands in vitro

Ciliary neurotrophic factor (CNTF) is a unique member of the interleukin-6 (IL-6) family, whose receptor subunit for ligand binding is exclusively expressed in the nervous system and muscle. The role of CNTF in mammalian development remains unknown. We recently reported the specific expression of CNTF in the pineal gland and eyes. To further examine the expression pattern and role of CNTF in development, we prepared a polyclonal antibody against rat CNTF, performed western blotting with this antibody, and confirmed a strong and specific expression of the CNTF protein in pineal glands and a moderate expression in the eyes among the various tissues examined in newborn rats. In pineal organ cultures of newborn rats, exogenously added recombinant rat CNTF potently inhibited the differentiation of photoreceptor-like cells in a dose-dependent manner, while CNTF did not influence the survival of pineal cells. Among several cell growth factors known to have a similar effect in retinal cultures examined, strong inhibitory effects were seen only with CNTF and the leukemia inhibitory factor (LIF), both of which belong to the IL-6 cytokine family. This inhibitory effect was the strongest during three to 6 days of culture when CNTF was added to these cultures. These results suggest that CNTF plays an inhibitory role in the development of photoreceptor-like cells in early postnatal rat pineal glands.

Adenoviral gene transfer of GDNF, BDNF and TGF beta 2, but not CNTF, cardiotrophin-1 or IGF1, protects injured adult motoneurons after facial nerve avulsion

We examined neuroprotective effects of recombinant adenoviral vectors encoding glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), cardiotrophin-1 (CT1), insulin-like growth factor-1 (IGF1), and transforming growth factor-beta2 (TGFbeta2) on lesioned adult rat facial motoneurons. The right facial nerves of adult Fischer 344 male rats were avulsed and removed from the stylomastoid foramen, and adenoviral vectors were injected into the facial canal. Animals avulsed and treated with adenovirus encoding GDNF, BDNF, CNTF, CT1, IGF1 and TGFbeta2 showed intense immunolabeling for these factors in lesioned facial motoneurons, respectively, indicating adenoviral induction of the neurotrophic factors in these neurons. The treatment with adenovirus encoding GDNF, BDNF, or TGFbeta2 after avulsion significantly prevented the loss of lesioned facial motoneurons, improved choline acetyltransferase immunoreactivity and prevented the induction of nitric oxide synthase activity in these neurons. The treatment with adenovirus encoding CNTF, CT1 or IGF1, however, failed to protect these neurons after avulsion. These results indicate that the gene transfer of GDNF and BDNF and TGFbeta2 but not CNTF, CT1 or IGF1 may prevent the degeneration of motoneurons in adult humans with motoneuron injury and motor neuron diseases.

Retinoic acid downregulates the expression of ciliary neurotrophic factor in rat Schwann cells

Neuropoietic cytokines, which serve as mediators in neuroglial interactions, are differentially regulated after peripheral nerve injury. In Schwann cells, the expression of ciliary neurotrophic factor (CNTF) decreases. Pursuing the hypothesis that retinoic acid (RA) serves as a regulator of lesion-induced cytokine signaling we found that all RA receptors and retinoid X receptors are expressed in Schwann cell primary cultures. Using quantitative reverse transcription-polymerase chain reaction, we have investigated the effect of RA on the expression of CNTF in these cells. After treatment with 10 nM all-trans RA for 22 h the concentration of CNTF mRNA was reduced to 63% of the control level, reminiscent of the regulation after nerve injury in vivo. In addition to CNTF, the mRNAs of leukemia inhibitory factor, interleukin-6, ciliary neurotrophic factor receptor component alpha and gp130 were detected in the Schwann cells.

[Expression of CNTFs in facial motoneurons during facial nerve regeneration in rats and their association with TGF-beta and rhBMP-2]

OBJECTIVE

The aim of this study was to observe the expression of ciliary neurotrophic factors (CNTFs) in the facial motor neurons in rats during facial nerve regeneration.

METHODS

The expression amount of CNTFs in eight groups was determined with immunohistochemical staining and image analysis.

RESULTS

The expression of CNTFs increased during the process of nerve regeneration, and reached the maximum one-week and one-month after nerve injury respectively. After one month, the intensity of CNTFs reduced gradually. The expression of recombinant human bone morphogenetic protein-2 (rhBMP-2) did not show distinct difference comparing with the control, but beta transforming growth factors (TGF-beta) benefited the expression of CNTFs during nerve regeneration.

CONCLUSION

The endogenous CNTFs promotes the axon outgrow during regeneration, and TGF-beta promotes the expression of CNTFs to rescue motoneuron during facial nerve regeneration.

[The expression of ciliary neurotrophic factor in facial nucleus after long-term facial denervation]

OBJECTIVE

To explore the expression and distribution of Ciliary neurotrophic factor (CNTF) mRNA and its protein in the facial motoneuron in order to clarify its functional state after long-term facial denervation.

METHOD

The facial nerves on the right sides were cut in dogs. Brain stems were removed and sectioned, and sections were separately used for histochemistry, immunohistochemistry and in situ hybridization of CNTF. The facial motoneurons were identified by Nissl staining. The count and intense of positive reactive motoneurons were measured by computer image processing system.

RESULT

Transection of the facial nerve led to a very marked reduce in the count and intense of CNTF mRNA positive reactive motoneurons, and reached the minimal levels at week 3. CNTF immunoreactivity increased rapidly and reached the maximal levels at also week 3. At week 4, a significant increase in CNTF mRNA expression and decrease in CNTF immunoreactivity were observed. At week 6, both CNTF mRNA and its protein expression were significantly less than those of unlesioned contralateral sides. Although a little difference between at week 12 and at 32 was observed, the motoneurons were generally stable in the expression level of CNTF mRNA and its protein, and in the size and count after 12 weeks, with 78%, 84.4%, 80.9% and 83.7% respectively as compared with the unlesioned contralateral facial motoneurons.

CONCLUSION

The results indicated that although degenerating changes occurred in the facial motoneurons after long-term facial denervation, the ciliary neurotrophic factors activity of the lesioned motoneurons was still maintained at a certain level.

Microglia-Müller glia cell interactions control neurotrophic factor production during light-induced retinal degeneration

Activation of microglia commonly occurs in response to a wide variety of pathological stimuli including trauma, axotomy, ischemia, and degeneration in the CNS. In the retina, prolonged or high-intensity exposure to visible light leads to photoreceptor cell apoptosis. In such a light-reared retina, we found that activated microglia invade the degenerating photoreceptor layer and alter expression of neurotrophic factors such as nerve growth factor (NGF), ciliary neurotrophic factor (CNTF), and glial cell line-derived neurotrophic factor (GDNF). Because these neurotrophic factors modulate secondary trophic factor expression in Müller glial cells, microglia-Müller glia cell interaction may contribute to protection of photoreceptors or increase photoreceptor apoptosis. In the present study, we demonstrate the possibility that such functional glia-glia interactions constitute the key mechanism by which microglia-derived NGF, brain-derived neurotrophic factor (BDNF), and CNTF indirectly influence photoreceptor survival, although the receptors for these neurotrophic factors are absent from photoreceptors, by modulating basic fibroblast growth factor (bFGF) and GDNF production and release from Müller glia. These observations suggest that microglia regulate the microglia-Müller glia-photoreceptor network that serves as a trophic factor-controlling system during retinal degeneration.

Ciliary neurotrophic factor (CNTF) in combination with its soluble receptor (CNTFRalpha) increases connexin43 expression and suppresses growth of C6 glioma cells

The loss of gap junctional intercellular communication has been proposedas playing a major role in the process of carcinogenesis. Most neoplastic cells, including C6 gliomas, express less connexins and have fewer gap junctions, reduced gap junctional intercellular communication, and increased growth rates compared with their nonneoplastic counterparts. The purpose of this study was to determine whether ciliary neurotrophic factor (CNTF) can be used to increase endogenous connexin43 levels, increase intercellular coupling, and retard the growth rate of C6 glioma cells. C6 cells were grown in serum-reduced medium (1% serum) and exposed to the following agents: vehicle (PBS), CNTF (20 ng/ml), CNTF soluble receptor (CNTFRalpha; 200 ng/ml), or Complex (CNTF + CNTFRalpha). Reverse transcription-PCR analysis indicated that C6 cells express CNTF mRNA but not CNTFRalpha mRNA. When cells were exposed to the above agents, only Complex caused an up-regulation of connexin43 protein (based on immunocytochemical and immunoblot analysis). Furthermore, Complex increased gap junctional coupling in C6 cells as noted by the passage of the gap junction permeable dye calcein. Finally, it was demonstrated that Complex-treatment reduces the growth rate of C6 cells compared with all of the other agents tested. Taken together, this study has demonstrated that CNTF in combination with its soluble receptor can increase connexin43 expression, increase gap junctional coupling, and reduce the in vitro proliferation of C6 glioma cells.

Secretion of IL-6, IL-11 and LIF by human cardiomyocytes in primary culture

Interleukin (IL)-6-type cytokines are multifunctional proteins involved in cardiac hypertrophy and myocardial protection. Recent studies, performed on animal models, report the production of these cytokines by heart. The aim of this study was to analyse the capacity of myocytes and fibroblasts isolated from human atrium to secrete IL-6, leukaemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), IL-11, oncostatin M (OSM), ciliary neurotrophic factor (CNTF) and the soluble receptor subunits sIL-6R and sgp130 during primary culture. We detected LIF, IL-11, sgp130 and a large amount of IL-6, but not OSM, CT-1, CNTF nor IL-6R in these culture supernatants. Both cardiomyocytes and fibroblasts are able to spontaneously produce IL-6. The increase of IL-6 production all along the culture period appears to be the consequence of fibroblast proliferation and gp130 stimulation. This is the first demonstration that human cardiac cells are able to secrete IL-6, but also LIF and IL-11 in vitro. These cytokines could be involved in an autocrine and/or a paracrine networks regulating myocardial cyto-protection, hypertrophy and fibrosis.

CNTF is specifically expressed in developing rat pineal gland and eyes

Ciliary neurotrophic factor (CNTF) attracts considerable attention because it supports survival and differentiation of various types of neurons and glial cells in vitro. Although CNTF functions as a moderate neurotrophic factor in mature motor neurons, its role in embryonic development remains unknown. Here, we found a specific CNTF expression in the rat pineal gland and eyes during embryonic development. In vitro, neonatal rat pineal extract including CNTF supported the survival of neonatal sympathetic neurons, which innervate pineal glands immediately after birth.

Levobetaxolol-induced Up-regulation of retinal bFGF and CNTF mRNAs and preservation of retinal function against a photic-induced retinopathy

Betaxolol (racemic), a beta-adrenoceptor antagonist that is used to lower intraocular pressure in the treatment of glaucoma, has been shown to protect inner retina cells from various insults. To determine if such protection could be afforded to retinal photoreceptors and retinal pigment epithelial cells (RPE), levobetaxolol (S-betaxolol) was evaluated in a photic-induced retinopathy model. Rats were dosed (IP) with vehicle or levobetaxolol (10 and 20 mg kg(-1)) 48, 24 and 0 hr prior to exposure for 6 hr to fluorescent blue light. The electroretinogram (ERG) and retinal morphology were assessed after a 3 week recovery period. Evaluation of the ERG demonstrated significant protection of retinal function in levobetaxolol (20 mg kg(-1))-dosed rats compared to vehicle-dosed rats. Similarly, the RPE and outer nuclear layer were significantly thicker in levobetaxolol (20 mg kg(-1))-dosed rats compared to vehicle-dosed rats. To elucidate potential mechanism(s) of the neuroprotective activity of levobetaxolol, bFGF and CNTF mRNA levels in normal rat retinas were evaluated 12 hr after a single i.p. injection. Northern blot analysis of levobetaxolol treated retinas demonstrated a 10-fold up-regulation of bFGF and a two-fold up-regulation of CNTF mRNA levels, trophic factors that have been shown to inhibit retinal degeneration in a number of species. These studies suggest that levobetaxolol can be used as a novel neuroprotective agent to ameliorate retinopathy.

The regrowth of axons within tissue defects in the CNS is promoted by implanted hydrogel matrices that contain BDNF and CNTF producing fibroblasts

In this study we demonstrate the potential for combining biocompatible polymers with genetically engineered cells to elicit axon regrowth across tissue defects in the injured CNS. Eighteen- to 21-day-old rats received implants of poly N-(2-hydroxypropyl)-methacrylamide (HPMA) hydrogels containing RGD peptide sequences that had been infiltrated with control (untransfected) fibroblasts (n = 8), fibroblasts engineered to express brain-derived neurotrophic factor (BDNF) (n = 5), ciliary neurotrophic factor (CNTF) (n = 5), or a mixture of BDNF and CNTF expressing fibroblasts (n = 11). Fibroblasts were prelabeled with Hoechst 33342. Cell/polymer constructs were inserted into cavities made in the left optic tract, between thalamus and superior colliculus. After 4-8 weeks, retinal projections were analyzed by injecting right eyes with cholera toxin (B-subunit). Rats were perfused 24 h later and sections were immunoreacted to visualize retinal axons, other axons (RT97 antibody), host astrocytes and macrophages, donor fibroblasts, and extracellular matrix molecules. The volume fraction (VF) of each gel that was occupied by RT97(+) axons was quantified. RT-PCR confirmed expression of the transgenes prior to, and 5 weeks after, transplantation. Compared to control rats (mean VF = 0.02 +/- 0.01% SEM) there was increased ingrowth of RT97(+) axons into implants in CNTF (mean VF = 0.33 +/- 0.19%) and BDNF (mean VF = 0.62 +/-0.19%) groups. Axon growth into hydrogels in the mixed BDNF/CNTF group (mean VF = 3.58 +/- 0.92%) was significantly greater (P < 0.05) than in the BDNF or CNTF fibroblast groups. Retinal axons exhibited a complex branching pattern within gels containing BDNF or BDNF/CNTF fibroblasts; however, they regrew the greatest distances within implants containing both BDNF and CNTF expressing cells.

IL-6 up-regulates CNTF mRNA expression and enhances neurite regeneration

Interleukin-6 (IL-6) is a neurotrophic cytokine, however, its direct effect on nerve regeneration has not been well characterized. We therefore examined the effect of IL-6 on neurite regeneration using the rat dorsal root ganglion. IL-6 significantly enhanced neurite regeneration from transected nerve terminals. We also examined the mRNA expression of IL-6 family cytokines and their receptors during the regeneration. The mRNA expressions of IL-6, IL-6 receptor, leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF) receptor alpha, and LIF receptor beta showed no significant differences by the addition of IL-6. In contrast, IL-6 enhanced the mRNA expression of gp130 and CNTF. In addition, CNTF significantly increased neurite regeneration when added exogenously. Our data suggest that IL-6 enhanced regeneration via up-regulating CNTF expression.

Inhibition of Ras extracellular-signal-regulated kinase (ERK) mediated signaling promotes ciliary neurotrophic factor (CNTF) expression in Schwann cells

Ciliary neurotrophic factor (CNTF) can prevent injury-induced motor neuron death. However, it is also evident that expression of CNTF in Schwann cells is suppressed during nerve regeneration. In this report, we have addressed the mechanism underlying the down-regulation of CNTF expression in injured nerves using a mouse Schwann cell line IMS32 and mouse sciatic nerve. In IMS32 cells, activation of the Ras extracellular-signal-regulated kinase (ERK) pathway by adenoviral vector-mediated expression of dominant active MEK1 did not alter a basal level of CNTF expression, whereas inhibition of the Ras-ERK pathway by using adenoviral vectors resulted in a marked increase in CNTF expression. This inverse relation between before and after axotomy was also observed in mouse sciatic nerve. In the axotomized sciatic nerve, the phosphorylated ERK was markedly increased; in contrast, the expression of CNTF was markedly decreased. These findings suggest that an inactive state of ERK is crucial for the CNTF expression in Schwann cells, and that activation of ERK following nerve injury critically influences the expression of CNTF. This might well explain why CNTF is highly expressed in quiescent Schwann cells in the peripheral nervous system, and also why CNTF is not abundant in axotomized nerves or cultured Schwann cells in which the proliferation signal is obviously active.

Induction of astrocyte differentiation by endothelial cells

Here we have investigated the mechanisms that control astrocyte differentiation within the developing rat optic nerve. Astrocytes are normally generated by astrocyte precursor cells within the embryonic optic nerve. We show that there is a close temporal and spatial correlation between endothelial and astrocyte differentiation. We tested the potential role of endothelial cells in inducing astrocyte differentiation by developing an immunopanning method to highly purify endothelial cells from developing optic nerves. We show that the purified endothelial cells, but not other embryonic optic nerve cell types, strongly induce the differentiation of purified astrocyte precursor cells into astrocytes in vitro. Leukemia inhibitory factor (LIF) and LIF receptors have been implicated previously in astrocyte differentiation in vivo. We show that purified endothelial cells express LIF mRNA and that their ability to induce astrocyte differentiation is prevented by a neutralizing anti-LIF, but not anti-ciliary neurotrophic factor, antiserum. These findings demonstrate a role for endothelial cells in inducing astrocyte differentiation. The induction of astrocyte differentiation by endothelial cells makes sense phylogenetically, anatomically, and functionally, because astrocytes evolved concurrently with brain vasculature and ensheathe capillaries throughout the brain. The ability to purify and culture astrocytes and endothelial cells should provide an excellent model system for future studies of blood-brain barrier development.

Intravitreal adenoviral gene transfer evokes an immune response in the retina that is directed against the heterologous lacZ transgene product but does not limit transgene expression

Recombinant E1-deleted adenoviral vectors (DeltaE1-Ad) are promising tools for in vivo gene transfer into the mammalian CNS including the retina. However, the duration of transgene expression is limited, and this limitation has partly been attributed to an immune response directed against vector-derived proteins. Here, we employed immunocytochemistry to assess the immune response to intravitreously injected DeltaE1-Ad encoding the lacZ gene or various neurotrophins (NTs). beta-Galactosidase was expressed by retinal cells for up to 4 weeks. Following intravitreal inoculation of AdCMV-lacZ, microglial and T cells were detected with a panel of antibodies in the retinal cell layers after 2 days (D2). The inflammatory response reached a maximum between D7 and D14. In contrast, no immune response was seen following injection of Ad encoding NTs. Yet, like with Ad-CMV-lacZ, their expression was also limited to approximately 4 weeks. Thus, beta-galactosidase seems to trigger a host immune response following intravitreal adenoviral lacZ gene transfer, but immune responses are not the cause of limited NT transgene expression from the CMV promoter in the inner retina.

Up-regulated CNTF plays a protective role for retrograde degeneration in the axotomized rat retina

Using reverse transcription-polymerase chain reaction and in situ hybridization, we investigated the expression and cellular localization of ciliary neurotrophic factor receptor alpha (CNTFRalpha) in the rat retina following optic nerve transection (ONT). Following ONT, a signal for CNTFRalpha mRNA appeared in a layer-specific and time-dependent manner. In the ganglion cell layer, the signal showed a peak value 1 day after ONT, and then gradually decreased. In the inner nuclear layer the signal reached a peak value at 14 days of about 500% of control level, but then decreased at 4 weeks. Our findings suggest that CNTF might play a protective role for the retrograde degeneration of retinal cells induced by ganglion cell death in the rat retina following ONT.

Central nervous system-initiated inflammation and neurotrophism in trauma: IL-1 beta is required for the production of ciliary neurotrophic factor

Injury to the CNS results in the production and accumulation of inflammatory cytokines within this tissue. The origin and role of inflammation within the CNS remains controversial. In this paper we demonstrate that an acute trauma to the mouse brain results in the rapid elevation of IL-1beta. This increase is detectable by 15 min after injury and significantly precedes the influx of leukocytes that occurs hours after. To confirm that IL-1beta up-regulation is initiated by cells within the CNS, in situ hybridization for cytokine transcript was combined with cell type immunohistochemistry. The results reveal parenchymal microglia to be the sole source of IL-1beta at 3 h postinjury. A role for CNS-initiated inflammation was addressed by examining the expression of the neurotrophic factor, ciliary neurotrophic factor (CNTF). Analysis of their temporal relationship suggests the up-regulation of CNTF by IL-1beta, which was confirmed through three lines of evidence. First, the application of IL-1 receptor antagonist into the lesion site attenuated the up-regulation of CNTF. Second, the examination of corticectomized animals genetically deficient for IL-1beta found no CNTF up-regulation. Third, the lack of CNTF elevation in IL-1beta null mice was rescued through exogenous application of IL-1beta into the lesion site. These findings provide the first evidence of the requirement for IL-1beta in the production of CNTF following CNS trauma, and suggest that inflammation can have a beneficial impact on the regenerative capacity of the CNS.

The ciliary neurotrophic factor and its receptor, CNTFR alpha

Ciliary neurotrophic factor (CNTF) is expressed in glial cells within the central and peripheral nervous systems. CNTF stimulates gene expression, cell survival or differentiation in a variety of neuronal cell types such as sensory, sympathetic, ciliary and motor neurons. In addition, effects of CNTF on oligodendrocytes as well as denervated and intact skeletal muscle have been documented. CNTF itself lacks a classical signal peptide sequence of a secreted protein, but is thought to convey its cytoprotective effects after release from adult glial cells by some mechanism induced by injury. Interestingly, mice that are homozygous for an inactivated CNTF gene develop normally and initially thrive. Only later in adulthood do they exhibit a mild loss of motor neurons with resulting muscle weakness, leading to the suggestion that CNTF is not essential for neural development, but instead acts in response to injury or other stresses. The CNTF receptor complex is most closely related to, and shares subunits with the receptor complexes for interleukin-6 and leukemia inhibitory factor. The specificity conferring alpha subunit of the CNTF complex (CNTFR alpha), is extremely well conserved across species, and has a distribution localized predominantly to the nervous system and skeletal muscle. CNTFR alpha lacks a conventional transmembrane domain and is thought to be anchored to the cell membrane by a glycosyl-phosphatidylinositol linkage. Mice lacking CNTFR alpha die perinatally, perhaps indicating the existence of a second developmentally important CNTF-like ligand. Signal transduction by CNTF requires that it bind first to CNTFR alpha, permitting the recruitment of gp130 and LIFR beta, forming a tripartite receptor complex. CNTF-induced heterodimerization of the beta receptor subunits leads to tyrosine phosphorylation (through constitutively associated JAKs), and the activated receptor provides docking sites for SH2-containing signaling molecules, such as STAT proteins. Activated STATs dimerize and translocate to the nucleus to bind specific DNA sequences, resulting in enhanced transcription of responsive genes. The neuroprotective effects of CNTF have been demonstrated in a number of in vitro cell models as well as in vivo in mutant mouse strains which exhibit motor neuron degeneration. Intracerebral administration of CNTF and CNTF analogs has also been shown to protect striatal output neurons in rodent and primate models of Huntington's disease. Treatment of humans and animals with CNTF is also known to induce weight loss characterized by a preferential loss of body fat. When administered systemically, CNTF activates downstream signaling molecules such as STAT-3 in areas of the hypothalamus which regulate food intake. In addition to its neuronal actions, CNTF and analogs have been shown to act on non-neuronal cells such as glia, hepatocytes, skeletal muscle, embryonic stem cells and bone marrow stromal cells.