Saturable entry of ciliary neurotrophic factor into brain

Melatonin in Synaptic Impairments of Alzheimer's Disease

Alzheimer's disease (AD) underlies dementia for millions of people worldwide with no effective treatment. The dementia of AD is thought stem from the impairments of the synapses because of their critical roles in cognition. Melatonin is a neurohormone mainly released by the pineal gland in a circadian manner and it regulates brain functions in various manners. It is reported that both the melatonin deficit and synaptic impairments are present in the very early stage of AD and strongly contribute to the progress of AD. In the mammalian brains, the effects of melatonin are mainly relayed by two of its receptors, melatonin receptor type 1a (MT1) and 1b (MT2). To have a clear idea on the roles of melatonin in synaptic impairments of AD, this review discussed the actions of melatonin and its receptors in the stabilization of synapses, modulation of long-term potentiation, as well as their contributions in the transmissions of glutamatergic, GABAergic and dopaminergic synapses, which are the three main types of synapses relevant to the synaptic strength. The synaptic protective roles of melatonin in AD treatment were also summarized. Regarding its protective roles against amyloid-β neurotoxicity, tau hyperphosphorylation, oxygenation, inflammation as well as synaptic dysfunctions, melatonin may be an ideal therapeutic agent against AD at early stage.

Neuroimmune Axes of the Blood-Brain Barriers and Blood-Brain Interfaces: Bases for Physiological Regulation, Disease States, and Pharmacological Interventions

Central nervous system (CNS) barriers predominantly mediate the immune-privileged status of the brain, and are also important regulators of neuroimmune communication. It is increasingly appreciated that communication between the brain and immune system contributes to physiologic processes, adaptive responses, and disease states. In this review, we discuss the highly specialized features of brain barriers that regulate neuroimmune communication in health and disease. In section I, we discuss the concept of immune privilege, provide working definitions of brain barriers, and outline the historical work that contributed to the understanding of CNS barrier functions. In section II, we discuss the unique anatomic, cellular, and molecular characteristics of the vascular blood-brain barrier (BBB), blood-cerebrospinal fluid barrier, and tanycytic barriers that confer their functions as neuroimmune interfaces. In section III, we consider BBB-mediated neuroimmune functions and interactions categorized as five neuroimmune axes: disruption, responses to immune stimuli, uptake and transport of immunoactive substances, immune cell trafficking, and secretions of immunoactive substances. In section IV, we discuss neuroimmune functions of CNS barriers in physiologic and disease states, as well as pharmacological interventions for CNS diseases. Throughout this review, we highlight many recent advances that have contributed to the modern understanding of CNS barriers and their interface functions.

Biological hypotheses and biomarkers of bipolar disorder

The most common mood disorders are major depressive disorders and bipolar disorders (BD). The pathophysiology of BD is complex, multifactorial, and not fully understood. Creation of new hypotheses in the field gives impetus for studies and for finding new biomarkers for BD. Conversely, new biomarkers facilitate not only diagnosis of a disorder and monitoring of biological effects of treatment, but also formulation of new hypotheses about the causes and pathophysiology of the BD. BD is characterized by multiple associations between disturbed brain development, neuroplasticity, and chronobiology, caused by: genetic and environmental factors; defects in apoptotic, immune-inflammatory, neurotransmitter, neurotrophin, and calcium-signaling pathways; oxidative and nitrosative stress; cellular bioenergetics; and membrane or vesicular transport. Current biological hypotheses of BD are summarized, including related pathophysiological processes and key biomarkers, which have been associated with changes in genetics, systems of neurotransmitter and neurotrophic factors, neuroinflammation, autoimmunity, cytokines, stress axis activity, chronobiology, oxidative stress, and mitochondrial dysfunctions. Here we also discuss the therapeutic hypotheses and mechanisms of the switch between depressive and manic state.

Central Interleukin-1β Suppresses the Nocturnal Secretion of Melatonin

In vertebrates, numerous processes occur in a rhythmic manner. The hormonal signal reliably reflecting the environmental light conditions is melatonin. Nocturnal melatonin secretion patterns could be disturbed in pathophysiological states, including inflammation, Alzheimer's disease, and depression. All of these states share common elements in their aetiology, including the overexpression of interleukin- (IL-) 1β in the central nervous system. Therefore, the present study was designed to determine the effect of the central injection of exogenous IL-1β on melatonin release and on the expression of the enzymes of the melatonin biosynthetic pathway in the pineal gland of ewe. It was found that intracerebroventricular injections of IL-1β (50 µg/animal) suppressed (P < 0.05) nocturnal melatonin secretion in sheep regardless of the photoperiod. This may have resulted from decreased (P < 0.05) synthesis of the melatonin intermediate serotonin, which may have resulted, at least partially, from a reduced expression of tryptophan hydroxylase. IL-1β also inhibited (P < 0.05) the expression of the melatonin rhythm enzyme arylalkylamine-N-acetyltransferase and hydroxyindole-O-methyltransferase. However, the ability of IL-1β to affect the expression of these enzymes was dependent upon the photoperiod. Our study may shed new light on the role of central IL-1β in the aetiology of disruptions in melatonin secretion.

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.

Inhibition of acetylcholinesterase activity by rivastigmine decreases lipopolysaccharide-induced IL-1β expression in the hypothalamus of ewes

The present study was designed to determine the effect of subcutaneous rivastigmine treatment on IL-1β expression and IL-1 type I receptor (IL-1R1) gene expression in the hypothalamic structures (preoptic area [POA], anterior hypothalamus [AHA], and medial basal hypothalamus [MBH]) of ewes after lipopolysaccharide (LPS) treatment. Endotoxin treatment increased (P ≤ 0.01) both IL-1β and IL-1R1 gene expression in the POA, AHA, and MBH compared with the control group, whereas concomitant rivastigmine and LPS injection abolished this stimulatory effect. It was also found that LPS elevated (P ≤ 0.01) IL-1β concentration in the hypothalamus (71.0 ± 2.3 pg/mg) compared with controls (16.1 ± 3.6 pg/mg). The simultaneous injection of LPS and rivastigmine did not increase IL-1β concentration in the hypothalamus (24.6 ± 13.0 pg/mg). This central change in IL-1β synthesis seems to be an effect of acetylcholinesterase (AChE) inhibition by rivastigmine, which decreases (P ≤ 0.01) the activity of this enzyme from 78.5 ± 15.0 μmol · min(-1) · g(-1) of total protein in the control and 68.8 ± 9.8 μmol · min(-1) · g(-1) of total protein in LPS-treated animals to 45.2 ± 5.6 μmol · min(-1) · g(-1) of total protein in the rivastigmine and LPS-treated group. Our study showed that rivastigmine could effectively reverse the stimulatory effect of immune stress induced by LPS injection on IL-1β synthesis through a decrease in AChE activity in the hypothalamic area of sheep. Our results also proved that the cholinergic anti-inflammatory pathway could directly modulate the central response to endotoxin.

Cytokine signaling modulates blood-brain barrier function

The blood-brain barrier (BBB) provides a vast interface for cytokines to affect CNS function. The BBB is a target for therapeutic intervention. It is essential, therefore, to understand how cytokines interact with each other at the level of the BBB and how secondary signals modulate CNS functions beyond the BBB. The interactions between cytokines and lipids, however, have not been fully addressed at the level of the BBB. Here, we summarize current understanding of the localization of cytokine receptors and transporters in specific membrane microdomains, particularly lipid rafts, on the luminal (apical) surface of the microvascular endothelial cells composing the BBB. We then illustrate the clinical context of cytokine effects on the BBB by neuroendocrine regulation and amplification of inflammatory signals. Two unusual aspects discussed are signaling crosstalk by different classes of cytokines and genetic regulation of drug efflux transporters. We also introduce a novel area of focus on how cytokines may act through nuclear hormone receptors to modulate efflux transporters and other targets. A specific example discussed is the ATP-binding cassette transporter-1 (ABCA-1) that regulates lipid metabolism. Overall, cytokine signaling at the level of the BBB is a crucial feature of the dynamic regulation that can rapidly change BBB function and affect brain health and disease.

Concepts for biologically active peptides

Here we review a unique aspect of CNS research on biologically active peptides that started against a background of prevalent dogmas but ended by exerting considerable influence on the field. During the course of refuting some doctrines, we introduced several concepts that were unconventional and paradigm-shifting at the time. We showed that (1) hypothalamic peptides can act 'up' on the brain as well as 'down' on the pituitary, (2) peripheral peptides can affect the brain, (3) peptides can cross the blood-brain barrier, (4) the actions of peptides can persist longer than their half-lives in blood, (5) perinatal administration of peptides can exert actions persisting into adulthood, (6) a single peptide can have more than one action, (7) dose-response relationships of peptides need not be linear, (8) the brain produces antiopiate as well as opiate peptides, (9) there is a selective high affinity endogenous peptide ligand for the mu-opiate receptor, (10) a peptide's name does not restrict its effects, and (11) astrocytes assume an active role in response to metabolic disturbance and hyperleptinemia. The evolving questions in our laboratories reflect the diligent effort of the neuropeptide community to identify the roles of peptides in the CNS. The next decade is expected to see greater progress in the following areas: (a) interactions of peptides with other molecules in the CNS; (b) peptide involvement in cell-cell interactions; and (c) peptides in neuropsychiatric, autoimmune, and neurodegenerative diseases. The development of peptidomics and gene silencing approaches will expedite the formation of many new concepts in a new era.

Pharmacological treatment of obesity in children and adolescents: present and future

The prevalence of overweight and obesity is increasing in children and adolescents worldwide raising the question on the approach to this condition because of the potential morbidity, mortality, and economic tolls. Dietetic and behavioral treatments alone have only limited success; consequently, discussion on strategies for treating childhood and adolescent obesity has been promoted. Considering that our knowledge on the physiological systems regulating food intake and body weight is considerably increased, many studies have underlined the scientific and clinical relevance of potential treatments based on management of peripheral or central neuropeptides signals by drugs. In this paper, we analyze the data on the currently approved obesity pharmacological treatment suggesting the new potential drugs.

Neurotrophic growth factors for the treatment of amyotrophic lateral sclerosis: where do we stand?

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that results in progressive loss of motoneurons, motor weakness and death within 3–5 years after disease onset. Therapeutic options remain limited despite substantial number of approaches that have been tested clinically. Many neurotrophic growth factors are known to promote the survival of neurons and foster regeneration in the central nervous system. Various neurotrophic factors have been investigated pre-clinically and clinically for the treatment of ALS. Although pre-clinical data appeared promising, no neurotrophic factors succeeded yet in a clinical phase III trial. In this review we discuss the rationale behind those factors, possible reasons for clinical failures, and argue for a renewal of hope in this powerful class of drugs for the treatment of ALS.

Ciliary neurotrophic factor infused intracerebroventricularly shows reduced catabolic effects when linked to the TAT protein transduction domain

Ciliary neurotrophic factor (CNTF) regulates the differentiation and survival of a wide spectrum of developing and adult neurons, including motor neuron loss after injury. We recently described a cell-penetrant recombinant human CNTF (rhCNTF) molecule, formed by fusion with the human immunodeficiency virus-1 transactivator of transcription (TAT) protein transduction domain (TAT-CNTF) that, upon subcutaneous administration, retains full neurotrophic activity without cytokine-like side-effects. Although the CNTF receptor is present in hypothalamic nuclei, which are involved in the control of energy, rhCNTF but not TAT-CNTF stimulates signal transducers and activators of transcription 3 phosphorylation in the rat hypothalamus after subcutaneous administration. This could be due limited TAT-CNTF distribution in the hypothalamus and/or altered intracellular signaling by the fusion protein. To explore these possibilities, we examined the effect of intracerebroventricular administration of TAT-CNTF in male adult rats. TAT-CNTF-induced weight loss, although the effect was smaller than that seen with either rhCNTF or leptin (which exerts CNTF-like effects via its receptor). In contrast to rhCNTF and leptin, TAT-CNTF neither induced morphological changes in adipose tissues nor increased uncoupling protein 1 expression in brown adipose tissue, a characteristic feature of rhCNTF and leptin. Acute intracerebroventricular administration of TAT-CNTF induced a less robust phosphorylation of signal transducers and activators of transcription 3 in the hypothalamus, compared with rhCNTF. The data show that fusion of a protein transduction domain may change rhCNTF CNS distribution, while further strengthening the utility of cell-penetrating peptide technology to neurotrophic factor biology beyond the neuroscience field.

Effects of systemic administration of ciliary neurotrophic factor on Bax and Bcl-2 proteins in the lumbar spinal cord of neonatal rats after sciatic nerve transection

Ciliary neurotrophic factor (CNTF) is a cytokine that plays a neuroprotective role in relation to axotomized motoneurons. We determined the effect of daily subcutaneous doses of CNTF (1.2 microg/g for 5 days; N = 13) or PBS (N = 13) on the levels of mRNA for Bcl-2 and Bax, as well as the expression and inter-association of Bcl-2 and Bax proteins, and the survival of motoneurons in the spinal cord lumbar enlargement of 2-day-old Wistar rats after sciatic nerve transection. Five days after transection, the effects were evaluated on histological and molecular levels using Nissl staining, immunoprecipitation, Western blot analysis, and reverse transcriptase-polymerase chain reaction. The motoneuron survival ratio, defined as the ratio between the number of motoneurons counted on the lesioned side vs those on the unlesioned side, was calculated. This ratio was 0.77 +/- 0.02 for CNTF-treated rats vs 0.53 +/- 0.02 for the PBS-treated controls (P < 0.001). Treatment with CNTF modified the level of mRNA, with the expression of Bax RNA decreasing 18% (with a consequent decrease in the level of Bax protein), while the expression of Bcl-2 RNA was increased 87%, although the level of Bcl-2 protein was unchanged. The amount of Bcl-2/Bax heterodimer increased 91% over that found in the PBS-treated controls. These data show, for the first time, that the neuroprotective effect of CNTF on neonatal rat axotomized motoneurons is associated with a reduction in free Bax, due to the inhibition of Bax expression, as well as increased Bcl-2/Bax heterodimerization. Thus, the neuroprotective action of the CNTF on axotomized motoneurons can be related to the inhibition of this apoptotic pathway.

A putative physiological role of hypothalamic CNTF in the control of energy homeostasis

Administration of CNTF durably reduces food intake and body weight in obese humans and rodent models. However, the involvement of endogenous CNTF in the central regulation of energy homeostasis needs to be elucidated. Here, we demonstrate that CNTF and its receptor are expressed in the arcuate nucleus, a key hypothalamic region controlling food intake, and that CNTF levels are inversely correlated to body weight in rats fed a high-sucrose diet. Thus endogenous CNTF may act, in some individuals, as a protective factor against weight gain during hypercaloric diet and could account for individual differences in the susceptibility to obesity.

Endocytosis at the blood–brain barrier: From basic understanding to drug delivery strategies

The blood-brain barrier (BBB) protects the central nervous system (CNS) from potentially harmful xenobiotics and endogenous molecules. Anatomically, it comprises the brain microvasculature whose functionality is nevertheless influenced by associated astrocyte, pericyte and neuronal cells. The highly restrictive paracellular pathway within brain microvasculature restricts significant CNS penetration to only those drugs whose physicochemical properties afford ready penetration into hydrophobic cell membranes or are capable of exploiting endogenous active transport processes such as solute carriers or endocytosis pathways. Endocytosis at the BBB is an essential pathway by which the brain obtains its nutrients and affords communication with the periphery. The development of strategies to exploit these endocytic pathways for the purposes of drug delivery to the CNS is still an immature field although some impressive results have been documented with the targeting of particular receptors. This current article initially provides an overview of general endocytosis processes and pathways showing evidence of their functional existence within the BBB. Subsequent sections provide, in an entity-specific manner, comprehensive reviews on BBB transport investigations of endocytosis involving: transferrin and the targeting of the transferrin receptor; hormones; cytokines; cell penetrating peptides; microorganisms and toxins, and nanoparticles aimed at more effectively delivering drugs to the CNS.

Cytokine transport across the injured blood-spinal cord barrier

Spinal cord injury (SCI) induces dynamic changes of the blood-spinal cord barrier and even the more distant blood-brain barrier. Besides an immediate increase of paracellular permeability resulting from the direct impact of the injury, the transport systems for selective cytokines undergo regulatory changes. Since many of the transported molecules play essential roles in neuroregeneration, we propose that this altered peripheral tissue / CNS interaction benefits remodeling of the spinal cord and functional recovery after SCI. This review examines the transport of cytokines and neurotrophic factors into the spinal cord, emphasizing the upregulation of two cytokines--tumor necrosis factor alpha (TNF) and leukemia inhibitory factor (LIF)--during the course of SCI. The increased transport of TNF and LIF after SCI remains saturable and does not coincide with generalized BBB disruption, highlighting a pivotal regulatory role for the blood-spinal cord barrier.

TNF reduces LIF endocytosis despite increasing NFkappaB-mediated gp130 expression

To examine how the proinflammatory cytokine tumor necrosis factor alpha (TNF) modulates the response of cerebral microvessels to other cytokines, we used rat cerebral microvessel endothelial RBE4 cells to simulate the in vitro blood-brain barrier (BBB). The gp130 receptor, which is shared by the interleukin (IL)-6 family of cytokines, showed specific upregulation by TNF. TNF treatment (5 ng/ml for 30 min to 24 h) increased gp130 at both the levels of transcription and protein expression. The stability of gp130 protein was mediated by NFkappaB activity, as the inhibitors quinazoline and MG132 not only blocked the increase induced by 6 h of TNF treatment, but also reduced its basal level of expression. By contrast, the lysosomal inhibitor chloroquine and the extracellular regulated kinase inhibitor U0126 showed no effect. Despite the increase of gp130, TNF caused a significant reduction in the cell binding and endocytosis of leukemia inhibitory factor (LIF), another proinflammatory cytokine that binds to the gp130 co-receptor and its unique gp190 receptor. This is consistent with our previous findings that TNF reduces gp190 expression and Stat3 activation. Thus, TNF stimulation results in decreased responsiveness of RBE4 cells to LIF, indicating complex regulatory interactions of cytokines at the BBB.

Continued administration of ciliary neurotrophic factor protects mice from inflammatory pathology in experimental autoimmune encephalomyelitis

Multiple sclerosis is an inflammatory disease of the central nervous system that leads to loss of myelin and oligodendrocytes and damage to axons. We show that daily administration (days 8 to 24) of murine ciliary neurotrophic factor (CNTF), a neurotrophic factor that has been described as a survival and differentiation factor for neurons and oligodendrocytes, significantly ameliorates the clinical course of a mouse model of multiple sclerosis. In the acute phase of experimental autoimmune encephalomyelitis induced by myelin oligodendrocyte glycoprotein peptide 35-55, treatment with CNTF did not change the peripheral immune response but did reduce the number of perivascular infiltrates and T cells and the level of diffuse microglial activation in spinal cord. Blood brain barrier permeability was significantly reduced in CNTF-treated animals. Beneficial effects of CNTF did not persist after it was withdrawn. After cessation of CNTF treatment, inflammation and symptoms returned to control levels. However, slight but significantly higher numbers of oligodendrocytes, NG2-positive cells, axons, and neurons were observed in mice that had been treated with high concentrations of CNTF. Our results show that CNTF inhibits inflammation in the spinal cord, resulting in amelioration of the clinical course of experimental autoimmune encephalomyelitis during time of treatment.

Neuregulin-1-β1 enters brain and spinal cord by receptor-mediated transport

Proteins of the neuregulin (NRG) family play important regulatory roles in neuronal survival and synaptic activity. NRG-1-beta1 has particular potential as a therapeutic agent because it enhances myelination of neurites in spinal cord explants. In this study, we determined the permeation of NRG-1-beta1 across the blood-brain and blood-spinal cord barriers (BBB and BSCB respectively). Intact radioactively labeled NRG-1-beta1 had a saturable and relatively rapid influx rate from blood to the CNS in mice. Capillary depletion studies showed that NRG-1-beta1 entered the parenchyma of the brain and spinal cord rather than being trapped in the capillaries that compose the BBB. The possible mechanism of receptor-mediated transport was shown by the ability of antibodies to erbB3 and erbB4 receptors to inhibit the influx. Lipophilicity, less important for such saturable transport mechanisms, was measured by the octanol : buffer partition coefficient and found to be low. The results indicate that NRG-1-beta1 enters spinal cord and brain by a saturable receptor-mediated mechanism, which provides the opportunity for possible therapeutic manipulation at the BBB level.

Brain repair and neuroprotection by serum insulin-like growth factor I

The existence of protective mechanisms in the adult brain is gradually being recognized as an important aspect of brain function. For many years, self-repair processes in the post-embryonic brain were considered of minor consequence or nonexistent. This notion dominated the study of neurotrophism. Thus, although the possibility that neurotrophic factors participate in brain function in adult life was prudently maintained, the majority of the studies on the role of trophic factors in the brain were focused on developmental aspects. With the recent recognition that the adult brain keeps a capacity for cell renewal, although limited, a new interest in the regenerative properties of brain tissue has emerged. New findings on the role of insulin-like growth factor I (IGF-I), a potent neurotrophic peptide present at high levels in serum, may illustrate this current trend. Circulating IGF-I is an important determinant of proper brain function in the adult. Its pleiotropic effects range from classical trophic actions on neurons such as housekeeping or anti-apoptotic/ pro-survival effects to modulation of brain-barrier permeability, neuronal excitability, or new neuron formation. More recent findings indicate that IGF-I participates in physiologically relevant neuroprotective mechanisms such as those triggered by physical exercise. The increasing number of neurotrophic features displayed by serum IGF-I reinforces the view of a physiological neuroprotective network formed by IGF-I, and possibly other still uncharacterized signals. Future studies with IGF-I, and hopefully other neurotrophic factors, will surely reveal and teach us how to potentiate the self-reparative properties of the adult brain.

The regulation and activation of ciliary neurotrophic factor signaling proteins in adipocytes

Ciliary neurotrophic factor (CNTF) is primarily known for its roles as a lesion factor released by the ruptured glial cells that prevent neuronal degeneration. However, CNTF has also been shown to cause weight loss in a variety of rodent models of obesity/type II diabetes, whereas a modified form also causes weight loss in humans. CNTF administration can correct or improve hyperinsulinemia, hyperphagia, and hyperlipidemia associated with these models of obesity. In order to investigate the effects of CNTF on fat cells, we examined the expression of CNTF receptor complex proteins (LIFR, gp130, and CNTFRalpha) during adipocyte differentiation and the effects of CNTF on STAT, Akt, and MAPK activation. We also examined the ability of CNTF to regulate the expression of adipocyte transcription factors and other adipogenic proteins. Our studies clearly demonstrate that the expression of two of the three CNTF receptor complex components, CNTFRalpha and LIFR, decreases during adipocyte differentiation. In contrast, gp130 expression is relatively unaffected by differentiation. In addition, preadipocytes are more sensitive to CNTF treatment than adipocytes, as judged by both STAT 3 and Akt activation. Despite decreased levels of CNTFRalpha expression in fully differentiated 3T3-L1 adipocytes, CNTF treatment of these cells resulted in a time-dependent activation of STAT 3. Chronic treatment of adipocytes resulted in a substantial decrease in fatty-acid synthase and a notable decline in SREBP-1 levels but had no effect on the expression of peroxisome proliferator-activated receptor gamma, acrp30, adipocyte-expressed STAT proteins, or C/EBPalpha. However, CNTF resulted in a significant increase in IRS-1 expression. CNTFRalpha receptor expression was substantially induced in the fat pads of four rodent models of obesity/type II diabetes as compared with lean littermates. Moreover, we demonstrated that CNTF can activate STAT 3 in adipose tissue and skeletal muscle in vivo. In summary, CNTF affects adipocyte gene expression, and the specific receptor for this cytokine is induced in rodent models of obesity/type II diabetes.

Long-term control of food intake and body weight by hydrodynamics-based delivery of plasmid DNA encoding leptin or CNTF

BACKGROUND

Obesity contributes to many common diseases, including cardiovascular and metabolic disorders such as diabetes, hypertension, and stroke. Leptin and ciliary neurotrophic factor (CNTF), two members of the cytokine family, play important roles in controlling food intake and body weight in rodents. Here, we used the hydrodynamics-based gene delivery technique to introduce leptin and CNTF expression plasmids, pCAGGS-leptin and pCAGGS-CNTF, into mice and to assess whether they could induce high expression of leptin or CNTF and reduce food intake and body weight in the mice.

METHODS

Plasmid DNA (50 microg) in lactated Ringer's solution (0.1 ml/g body weight) was rapidly injected into the tail vein of 4-week-old male MCH-ICR mice.

RESULTS

After a single injection, serum leptin peaked (at 32.0 +/- 3.1 ng/ml) 2 days after the injection, and serum CNTF peaked (at 22.0 +/- 0.8 microg/ml) 1 day after the injection. The high expression of either leptin or CNTF was sustained and dramatically reduced food intake (CNTF and leptin group vs. control group; 2.3 +/- 0.5 and 3.1 +/- 0.5 g/day vs. 4.8 +/- 0.6 g/day; p < 0.001) and body weight (3 weeks after the injection; CNTF and leptin group vs. control group; -19.5% and +3.3% vs. +33.3-47.5%; p < 0.001) in the mice, suggesting potent in vivo activities for these exogenously expressed proteins.

CONCLUSIONS

These results suggest that hydrodynamics-based gene delivery could have broad applications in the study of appetite regulation and metabolism.

Null mutation in human ciliary neurotrophic factor gene confers higher body mass index in males

Ciliary neurotrophic factor (CNTF) administration reduces weight in leptin-resistant mice via the signalling pathway normally activated by leptin. A G>A null mutation in the CNTF gene results in complete absence of protein. We hypothesised that absence of CNTF could lead to diminished initiation of anorectic pathways, with consequent increase in body mass. In 575 Caucasian men aged 59-73 years, the A/A genotype (frequency 1.9%) was associated with a 10 kg increase in weight (P=0.03, 2 df) and 3 kg/m(2) greater BMI (P=0.02, 2 df). There was no effect in women. The CNTF G>A null mutation therefore confers a moderate effect on obesity in males of A/A genotype, who represent 1% of the general population.

Astrocytic alterations in interleukin-6/Soluble interleukin-6 receptor alpha double-transgenic mice

Interleukin-6 (IL-6), a major cytokine with diverse effects on cells mainly of the immune and hematopoietic systems, has been linked to several neurological disorders such as acquired immune deficiency syndrome dementia, multiple sclerosis, and Alzheimer's disease. Central nervous system (CNS)-specific expression of IL-6 caused neurodegeneration, massive gliosis, and vascular proliferation in transgenic mice. However, the effects of systemically circulating IL-6 and its receptor IL-6Ralpha on the CNS are unknown. IL-6Ralpha is the specific component of the IL-6 receptor system and hence an important co-factor of IL-6. IL-6Ralpha is bioactive in a membrane-bound and in a soluble (s) form. We investigated the effects of systemically elevated levels of either human IL-6 or human sIL-6Ralpha or both on the CNS of transgenic mice. Although IL-6 and sIL-6Ralpha single transgenic mice were free of neurological disease, IL-6/sIL-6Ralpha double-transgenic mice showed neurological signs, such as tremor, gait abnormalities, and paresis. However, these mice also frequently showed prominent general weakness probably because of the systemic effects of IL-6/IL-6Ralpha such as liver damage and plasmacytomas. IL-6/sIL-6Ralpha transgenic mice exhibited massive reactive gliosis. Lack of signs of neuronal breakdown versus ample astrogliosis suggested that astrocytes were selectively affected in these mice. There was neither vascular proliferation nor inflammatory infiltration. Ultrastructural analysis revealed blood-brain barrier (BBB) changes manifested by hydropic astrocytic end-feet. However, albumin immunohistochemistry did not reveal major BBB leakage. Our results indicate that increased and constitutive systemic expression of IL-6 together with its soluble receptor sIL-6Ralpha is less harmful to the brain than to other organs. The BBB remains primarily intact. IL-6/IL-6Ralpha, however, might be directly responsible for the selective activation of astrocytes.

Saturable entry of leukemia inhibitory factor from blood to the central nervous system

Leukemia inhibitory factor (LIF) is a neurotrophic cytokine now under clinical investigation for its effects on the CNS. We studied its passage across the blood-brain barrier (BBB) from blood to brain and spinal cord. Although a large amount of LIF was reversibly associated with the cerebral vasculature, intact LIF did reach brain parenchyma. Multiple-time regression analysis showed ready access of LIF to the CNS at a rate much faster than that of the vascular marker albumin. Excess LIF inhibited the entry of 125I-LIF after administration i.v. or by in-situ perfusion in blood-free buffer. Efflux of LIF from brain to blood was slower than reabsorption by CSF bulk flow, indicating that LIF tended to be retained in the brain. Although ciliary neurotrophic factor (CNTF) and LIF bind to the same receptor complex, CNTF did not cross-inhibit the entry of LIF into the CNS. A monoclonal antibody to LIF, however, abolished the entry of LIF. Our results show that peripherally administered LIF readily enters the brain and spinal cord by a saturable transport system across the BBB that may have biological implications.

Peptides crossing the blood-brain barrier: some unusual observations

An interactive blood-brain barrier (BBB) helps regulate the passage of peptides from the periphery to the CNS and from the CNS to the periphery. Many peptides cross the BBB by simple diffusion, mainly explained by their lipophilicity and other physicochemical properties. Other peptides cross by saturable transport systems. The systems that transport peptides into or out of the CNS can be highly specific, transporting MIF-1 but not Tyr-MIF-1, PACAP38 but not PACAP27, IL-1 but not IL-2, and leptin but not the smaller ingestive peptides NPY, orexin A, orexin B, CART (55-102[Met(O)(67)]), MCH, or AgRP(83-132). Although the peptides EGF and TGF-alpha bind to the same receptor, only EGF enters by a rapid saturable transport system, suggesting that receptors and transporters can represent different proteins. Even the polypeptide NGF enters faster than its much smaller subunit beta-NGF. The saturable transport of some compounds can be upregulated, like TNF-alpha in EAE (an animal model of multiple sclerosis) and after spinal cord injury, emphasizing the regulatory role of the BBB. As has been shown for CRH, saturable transport from brain to blood can exert effects in the periphery. Thus, the BBB plays a dynamic role in the communication of peptides between the periphery and the CNS.