Focal brain injury increases activin betaA mRNA expression in hippocampal neurons

The Effect of Lutein on Eye and Extra-Eye Health

Lutein is a carotenoid with reported anti-inflammatory properties. A large body of evidence shows that lutein has several beneficial effects, especially on eye health. In particular, lutein is known to improve or even prevent age-related macular disease which is the leading cause of blindness and vision impairment. Furthermore, many studies have reported that lutein may also have positive effects in different clinical conditions, thus ameliorating cognitive function, decreasing the risk of cancer, and improving measures of cardiovascular health. At present, the available data have been obtained from both observational studies investigating lutein intake with food, and a few intervention trials assessing the efficacy of lutein supplementation. In general, sustained lutein consumption, either through diet or supplementation, may contribute to reducing the burden of several chronic diseases. However, there are also conflicting data concerning lutein efficacy in inducing favorable effects on human health and there are no univocal data concerning the most appropriate dosage for daily lutein supplementation. Therefore, based on the most recent findings, this review will focus on lutein properties, dietary sources, usual intake, efficacy in human health, and toxicity.

Lutein levels in arterial cord blood correlate with neuroprotein activin A in healthy preterm and term newborns: A trophic role for lutein?

BACKGROUND

Lutein (LT) is a naturally occurring xanthophyll carotenoid most predominant in the central nervous system (CNS), but its neurotrophic role is still debated. We therefore investigated whether cord blood concentrations correlated with a well-established neurobiomarker, namely activin A.

METHODS

We conducted a prospective study on the distribution of LT and activin A in arterial cord blood of healthy preterm (n=50) and term (n=82) newborns according to weeks of gestational age (wGA) and gender.

RESULTS

LT and activin A showed a pattern of concentration characterized by higher levels (P<0.01, for all) at 33-36 wGA followed by a progressive decrease (P<0.01, for all) from 37 onwards with a dip at term. Both LT and activin A were gender-dependent with significantly (P<0.01, for all) higher levels in all recruited females and after sub-grouping for preterm and term births. LT (R=0.33; P<0.001) correlated with wGA at sampling. There were significant positive correlations between lutein and activin A in male (R=0.93; P<0.001) and female (R=0.89; P<0.001) groups.

CONCLUSIONS

The present data showing a correlation between LT and activin A support the notion of a neurotrophic role gender-dependent for LT and open the way to further investigations correlating LT with well-established biochemical markers of CNS development/damage.

Activin A prevents neuron-like PC12 cell apoptosis after oxygen-glucose deprivation

In this study, PC12 cells were induced to differentiate into neuron-like cells using nerve growth factor, and were subjected to oxygen-glucose deprivation. Cells were treated with 0, 10, 20, 30, 50, 100 ng/mL exogenous Activin A. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide assay and Hoechst 33324 staining showed that the survival percentage of PC12 cells significantly decreased and the rate of apoptosis significantly increased after oxygen-glucose deprivation. Exogenous Activin A significantly increased the survival percentage of PC12 cells in a dose-dependent manner. Reverse transcription-PCR results revealed a significant increase in Activin receptor IIA, Smad3 and Smad4 mRNA levels, which are key sites in the Activin A/Smads signaling pathway, in neuron-like cells subjected to oxygen-glucose deprivation, while mRNA expression of the apoptosis-regulation gene caspase-3 decreased. Our experimental findings indicate that exogenous Activin A plays an anti-apoptotic role and protects neurons by means of activating the Activin A/Smads signaling pathway.

Acute modulation of synaptic plasticity of pyramidal neurons by activin in adult hippocampus

Activin A is known as a neuroprotective factor produced upon acute excitotoxic injury of the hippocampus (in pathological states). We attempt to reveal the role of activin as a neuromodulator in the adult male hippocampus under physiological conditions (in healthy states), which remains largely unknown. We showed endogenous/basal expression of activin in the hippocampal neurons. Localization of activin receptors in dendritic spines (=postsynapses) was demonstrated by immunoelectron microscopy. The incubation of hippocampal acute slices with activin A (10 ng/mL, 0.4 nM) for 2 h altered the density and morphology of spines in CA1 pyramidal neurons. The total spine density increased by 1.2-fold upon activin treatments. Activin selectively increased the density of large-head spines, without affecting middle-head and small-head spines. Blocking Erk/MAPK, PKA, or PKC prevented the activin-induced spinogenesis by reducing the density of large-head spines, independent of Smad-induced gene transcription which usually takes more than several hours. Incubation of acute slices with activin for 2 h induced the moderate early long-term potentiation (moderate LTP) upon weak theta burst stimuli. This moderate LTP induction was blocked by follistatin, MAPK inhibitor (PD98059) and inhibitor of NR2B subunit of NMDA receptors (Ro25-6981). It should be noted that the weak theta burst stimuli alone cannot induce moderate LTP. These results suggest that MAPK-induced phosphorylation of NMDA receptors (including NR2B) may play an important role for activin-induced moderate LTP. Taken together, the current results reveal interesting physiological roles of endogenous activin as a rapid synaptic modulator in the adult hippocampus.

Elevated Activin A urine levels are predictors of intraventricular haemorrhage in preterm newborns

AIM

Intraventricular haemorrhage (IVH) is the most common variety of cerebral haemorrhage and cause of neurological disabilities in preterm newborns. We evaluated the usefulness of urine Activin A concentrations for the early detection of perinatal IVH.

METHODS

We conducted a case-control study on 100 preterm newborns (20 with IVH and 80 without IVH) in whom urine Activin A was measured at five predetermined time-points in the first 72 h after birth. IVH diagnosis and the extension of the lesion were performed by ultrasound scanning within the first 72 h and at 1 week after birth, respectively.

RESULTS

Urine Activin A in infants who developed IVH was significantly higher than in controls at all monitoring time-points (p < 0.01 for all), increasing progressively from first urination to 24 h when it reached the highest peak (p < 0.001). At a cut-off 0.08 ng/L, at the first void, Activin A sensitivity and specificity were 68.7% (CI: 41.3-89%) and 84.5% (CI: 75-91.5%).

CONCLUSION

Activin A measurements in urine soon after birth can constitute a promising tool for identifying preterm infants at risk of IVH.

Age-dependent brain gene expression and copy number anomalies in autism suggest distinct pathological processes at young versus mature ages

Autism is a highly heritable neurodevelopmental disorder, yet the genetic underpinnings of the disorder are largely unknown. Aberrant brain overgrowth is a well-replicated observation in the autism literature; but association, linkage, and expression studies have not identified genetic factors that explain this trajectory. Few studies have had sufficient statistical power to investigate whole-genome gene expression and genotypic variation in the autistic brain, especially in regions that display the greatest growth abnormality. Previous functional genomic studies have identified possible alterations in transcript levels of genes related to neurodevelopment and immune function. Thus, there is a need for genetic studies involving key brain regions to replicate these findings and solidify the role of particular functional pathways in autism pathogenesis. We therefore sought to identify abnormal brain gene expression patterns via whole-genome analysis of mRNA levels and copy number variations (CNVs) in autistic and control postmortem brain samples. We focused on prefrontal cortex tissue where excess neuron numbers and cortical overgrowth are pronounced in the majority of autism cases. We found evidence for dysregulation in pathways governing cell number, cortical patterning, and differentiation in young autistic prefrontal cortex. In contrast, adult autistic prefrontal cortex showed dysregulation of signaling and repair pathways. Genes regulating cell cycle also exhibited autism-specific CNVs in DNA derived from prefrontal cortex, and these genes were significantly associated with autism in genome-wide association study datasets. Our results suggest that CNVs and age-dependent gene expression changes in autism may reflect distinct pathological processes in the developing versus the mature autistic prefrontal cortex. Our results raise the hypothesis that genetic dysregulation in the developing brain leads to abnormal regional patterning, excess prefrontal neurons, cortical overgrowth, and neural dysfunction in autism.

Autism is a disorder characterized by aberrant social, communication, and restricted and repetitive behaviors. It develops clinically in the first years of life. Toddlers and children with autism often exhibit early brain enlargement and excess neuron numbers in the prefrontal cortex. Adults with autism generally do not display enlargement but instead may have a smaller brain size. Thus, we investigated DNA and mRNA patterns in prefrontal cortex from young versus adult postmortem individuals with autism to identify age-related gene expression differences as well as possible genetic correlates of abnormal brain enlargement, excess neuron numbers, and abnormal functioning in this disorder. We found abnormalities in genetic pathways governing cell number, neurodevelopment, and cortical lateralization in autism. We also found that the key pathways associated with autism are different between younger and older autistic individuals. These findings suggest that dysregulated gene pathways in the early stages of neurodevelopment could lead to later behavioral and cognitive deficits associated with autism.

Activin signaling as an emerging target for therapeutic interventions

After the initial discovery of activins as important regulators of reproduction, novel and diverse roles have been unraveled for them. Activins are expressed in various tissues and have a broad range of activities including the regulation of gonadal function, hormonal homeostasis, growth and differentiation of musculoskeletal tissues, regulation of growth and metastasis of cancer cells, proliferation and differentiation of embryonic stem cells, and even higher brain functions. Activins signal through a combination of type I and II transmembrane serine/threonine kinase receptors. Activin receptors are shared by multiple transforming growth factor-β (TGF-β) ligands such as myostatin, growth and differentiation factor-11 and nodal. Thus, although the activity of each ligand is distinct, they are also redundant, both physiologically and pathologically in vivo. Activin receptors activated by ligands phosphorylate the receptor-regulated Smads for TGF-β, Smad2 and 3. The Smad proteins then undergo multimerization with the co-mediator Smad4, and translocate into the nucleus to regulate the transcription of target genes in cooperation with nuclear cofactors. Signaling through receptors and Smads is controlled by multiple mechanisms including phosphorylation and other posttranslational modifications such as sumoylation, which affect potein localization, stability and transcriptional activity. Non-Smad signaling also plays an important role in activin signaling. Extracellularly, follistatin and related proteins bind to activins and related TGF-β ligands, and control the signaling and availability of ligands.

The functions of activins through activin receptors are pleiotrophic, cell type-specific and contextual, and they are involved in the etiology and pathogenesis of a variety of diseases. Accordingly, activin signaling may be a target for therapeutic interventions. In this review, we summarize the current knowledge on activin signaling and discuss the potential roles of this pathway as a molecular target of therapy for metabolic diseases, musculoskeletal disorders, cancers and neural damages.

Bone morphogenetic proteins 4, 6, and 7 are up-regulated in mouse spinal cord during experimental autoimmune encephalomyelitis

Although spontaneous remyelination occurs in multiple sclerosis (MS), the extent of myelin repair is often inadequate to restore normal function. Oligodendrocyte precursors remaining in nonremyelinating MS plaques may be restricted by an inhibitory signal. Bone morphogenetic proteins (BMPs) have been implicated as repressors of oligodendrocyte development and inducers of astrogliogenesis. We hypothesized that BMPs are up-regulated in MS lesions and play a role in demyelination and astrogliosis. We examined expression of BMPs in an animal model of MS, chronic experimental autoimmune encephalomyelitis (EAE) induced by the myelin oligodendrocyte glycoprotein (MOG) peptide in C57BL/6 mice. By 14 days postimmunization, compared to those of control mice, the lumbar spinal cords of MOG-peptide EAE mice demonstrated prominent astrogliosis, infiltration of inflammatory cells, and disrupted expression of myelin proteins. Quantitative RT-PCR showed that expression of BMP4, BMP6, and BMP7 mRNA increased 2- to 4-fold in the lumbar spinal cords of animals with symptomatic EAE versus in vehicle-treated and untreated controls on days 14, 21, and 42 postimmunization. BMP2 mRNA expression was not altered. BMP4 mRNA was much more abundant in the spinal cords of all animals than was mRNA encoding BMP2, BMP6, and BMP7. Immunoblot analysis confirmed the increased expression of BMP4 in the EAE animals. Immunohistochemistry revealed increased BMP4 immunoreactivity in areas of inflammation in MOG-peptide EAE animals. BMP4 labeling was mostly limited to macrophages but was sometimes associated with astrocytes and oligodendrocytes. These results indicate that members of the BMP family are differentially expressed in adult spinal cord and are up-regulated during EAE. (c) 2007 Wiley-Liss, Inc.

The role of repulsive guidance molecules in the embryonic and adult vertebrate central nervous system

During the development of the nervous system, outgrowing axons often have to travel long distances to reach their target neurons. In this process, outgrowing neurites tipped with motile growth cones rely on guidance cues present in their local environment. These cues are detected by specific receptors expressed on growth cones and neurites and influence the trajectory of the growing fibres. Neurite growth, guidance, target innervation and synapse formation and maturation are the processes that occur predominantly but not exclusively during embryonic or early post-natal development in vertebrates. As a result, a functional neural network is established, which is usually remarkably stable. However, the stability of the neural network in higher vertebrates comes at an expensive price, i.e. the loss of any significant ability to regenerate injured or damaged neuronal connections in their central nervous system (CNS). Most importantly, neurite growth inhibitors prevent any regenerative growth of injured nerve fibres. Some of these inhibitors are associated with CNS myelin, others are found at the lesion site and in the scar tissue. Traumatic injuries in brain and spinal cord of mammals induce upregulation of embryonic inhibitory or repulsive guidance cues and their receptors on the neurites. An example for embryonic repulsive directional cues re-expressed at lesion sites in both the rat and human CNS is provided with repulsive guidance molecules, a new family of directional guidance cues.

Neogenin and repulsive guidance molecule signaling in the central nervous system

The repulsive guidance molecule (RGM) is a membrane-bound protein that was originally identified as an axon guidance molecule in the visual system. Functional studies have revealed that it has roles in axon guidance and laminar patterning in Xenopus and chick embryos, and in controlling cephalic neural tube closure in mouse embryos. The recent identification of neogenin as a receptor for RGM has provided evidence of the diverse functions of this ligand-receptor pair. Re-expression of RGM is observed after injury in the adult human and rat central nervous systems. Inhibition of RGM enhances growth of injured axons and promotes functional recovery after spinal cord injury in rats. Thus, re-expression of embryonic repulsive cues in adult tissues contributes to failure of axon regeneration in the central nervous system.

Activin A In Brain Injury

Activin A is a growth factor composed of two betaA subunits belonging to the transforming growth factor beta (TGF-beta) superfamily of dimeric proteins. The biological activity of activin A is mediated by two different types of receptors, the type I (ARI and ARIB) and the type II receptors (ARII and ARIIB), and by two activin-binding proteins, follistatin and follistatin-related gene. These factors bind to activin A and thereby inhibit its biological effects. Activin A, its receptors, and binding proteins are widely distributed throughout the brain. Studies employing models of acute brain injury strongly implicate enhanced activin A expression as a common response to acute neuronal damage of various origins. Hypoxic/ischemic injury, mechanical irritation, and chemical damage of brain evoke a strong upregulation of activin A. Subsequent experimental studies have shown that activin A has a beneficial role to neuronal recovery and that, by activating different pathways, activin A has robust neuroprotective activities. Because activin A induction occurs early after brain injury, its measurement may provide a potential biochemical index of the presence, location, and extent of brain injury. This approach may also facilitate the diagnosis of subclinical lesions at stages when monitoring procedures are unable to detect brain lesion and furthermore establish a prognosis.

Activin A Release into Cerebrospinal Fluid in a Subset of Patients with Severe Traumatic Brain Injury

Activin A is a member of the transforming growth factor-beta superfamily and has been demonstrated to be elevated during inflammation and to have neuroprotective properties following neural insults. In this study, we examined whether traumatic brain injury (TBI) induced a response in activin A or in the concentrations of its binding protein, follistatin. Thirty-nine patients with severe TBI had daily, matched cerebrospinal fluid (CSF) and serum samples collected post-TBI and these were assayed for activin A and follistatin using specific immunoassays. Concentrations of both molecules were assessed relative to a variety of clinical parameters, such as the Glasgow Coma Score, computer tomography classification of TBI, measurement of injury markers, cell metabolism and membrane breakdown products. In about half of the patients, there was a notable increase in CSF activin A concentrations in the first few days post-TBI. There were only minor perturbations in either serum activin or in either CSF or serum follistatin concentrations. The CSF activin A response was not related to any of the common TBI indices, but was strongly correlated with two common markers of brain damage, neuronal specific enolase and S100-beta. Further, activin A levels were also associated with indices of metabolism, such as lactate and pyruvate, excitotoxicity (glutamate) and membrane lipid breakdown products such as glycerol. In one of the two patients who developed a CSF infection, activin A concentrations in CSF became markedly elevated. Thus, some TBI patients have an early release of activin A into the CSF that may result from activation of inflammatory and/or neuroprotective pathways.

Activin A concentrations in human cerebrospinal fluid are age-dependent and elevated in meningitis

OBJECTIVE

Activin A, and its binding protein, follistatin (FS), are expressed in the central nervous system (CNS). We have previously shown elevated concentrations of FS in the cerebrospinal fluid (CSF) of patients with meningitis and increased concentrations of activin A in the CSF of rabbits with bacterial meningitis.

METHODS

We measured CSF and serum concentrations of activin A and FS in normal subjects and in patients with various neurological diseases using previously validated immunoassays specific for activin A or FS.

RESULTS

In healthy persons, serum concentrations of both activin A and FS were age-dependent. In CSF, concentrations of activin A ranged from 0.03 to 0.33 ng/ml and were strongly correlated with age in both sexes, whereas FS CSF concentrations were below the assay detection limit in most of the patients. Activin A concentrations in CSF of patients with various neurological diseases, including meningitis, chronic inflammatory CNS diseases, neurodegenerative diseases, tumors in the CNS, cerebral ischemia, intracerebral/subarachnoid hemorrhages, subdural hemorrhages and epileptic seizures, were compared with age- and sex-matched control patients. The comparisons revealed significantly elevated concentrations of activin A in patients with meningitis (P=0.017). Serum concentrations of activin A or FS were not affected by any of the neurological diseases examined.

CONCLUSIONS

Our results show for the first time that in normal subjects concentrations of activin A in CSF are correlated with age, and furthermore, that activin A CSF concentrations are elevated in patients with meningitis. The latter underlines a role for activin A in acute inflammatory processes within the CNS.

Transgenic mice expressing dominant-negative activin receptor IB in forebrain neurons reveal novel functions of activin at glutamatergic synapses

The transforming growth factor beta family member activin is an important regulator of development and tissue repair. It is strongly up-regulated after acute injury to the adult brain, and application of exogenous activin protects neurons in several lesion models. To explore the role of endogenous activin in the normal and acutely damaged brain, we generated transgenic mice expressing a dominant-negative activin receptor IB (dnActRIB) mutant in forebrain neurons. The functionality of the transgene was verified in vivo. Hippocampal neurons from dnActRIB mice were significantly more vulnerable to intracerebroventricular injection of the excitotoxin kainic acid than those from control littermates, indicating a crucial role of endogenous activin in the rescue of neurons from excitotoxic insult. Because dnActRIB is only expressed in neurons, but not in glial cells, activin affords protection at least in part through a direct action on endangered neurons. Unexpectedly, the transgenic mice also revealed a prominent novel role of activin in glutamatergic neurotransmission in the intact adult brain. Electrophysiologic examination of excitatory synapses onto CA1 pyramidal cells in hippocampal slices of dnActRIB mice showed a reduced NMDA current response, which was associated with impaired long term potentiation. This is the first demonstration that activin receptor signaling is essential to optimize the performance of neuronal circuits in the mature brain under physiological conditions.

Increased Plasma Concentrations of Activin A Predict Intraventricular Hemorrhage in Preterm Newborns

Background: Intraventricular hemorrhage (IVH) is a major cause of neurologic disabilities in preterm newborns. We evaluated the use of plasma activin A concentrations to predict the development of perinatal IVH.

Methods: We measured nucleated erythrocyte (NRBC) counts, plasma activin A, hypoxanthine (Hyp), and xanthine (Xan) in arterial blood samples obtained from 53 preterm infants during the first hour after birth. Cerebral ultrasound was performed within 48 h of birth and repeated at 5- or 6-day intervals until the age of 4 weeks.

Results: Grade I or II IVH was detected during the first 10 days of life in 11 of 53 patients (21%). Activin A, Hyp, and Xan concentrations and NRBC counts were higher in preterm newborns who subsequently developed IVH than in those who did not (P &lt;0.0001, except P = 0.019 for Xan). Neonatal activin A was correlated (P &lt;0.0001) with Hyp (r = 0.95), Xan (r = 0.90), and NRBC count (r = 0.90) in newborns without later IVH and in those who developed IVH (Hyp, r = 0.89, P = 0.0002; Xan, r = 0.95, P &lt;0.0001; NRBC count, r = 0.90, P = 0.0002). At a cutoff of 0.8 μg/L activin A, the sensitivity and specificity were 100% [11 of 11; 95% confidence interval (CI), 71%–100%] and 93% (39 of 42; 95% CI, 81%–98%), and positive and negative predictive values were 79% (95% CI, 61%–100%) and 0% (95% CI, 0%–2%), respectively. The area under the ROC curve was 0.98.

Conclusions: Activin A concentrations at birth are increased in preterm newborns who later develop IVH and may be useful for early identification of infants with hypoxic-ischemic brain insults who are at high risk for IVH.

Stroke injury in rats causes an increase in activin A gene expression which is unaffected by oestradiol treatment

Activins are members of the transforming growth factor-beta superfamily that exert neurotrophic and neuroprotective effects on various neuronal populations. To determine the possible function of activin in stroke injury, we assessed which components of the activin signalling pathway were modulated in response to middle cerebral artery occlusion (MCAO). Furthermore, because oestradiol replacement protects against MCAO-induced cell death, we explored whether oestradiol replacement influences activin gene expression. Female Sprague-Dawley rats underwent permanent MCAO and the expression of activins and their corresponding receptors was determined by semiquantitative reverse transcriptase-polymerase chain reaction at 24 h after onset of ischaemia. We observed up-regulation of activin betaA and activin type I receptor A mRNA in response to injury. Dual-label immunocytochemistry followed by confocal z-stack analysis showed that the activin A expressing cells comprised neurones. Next, we monitored the time course of activin betaA mRNA expression in oestradiol- or vehicle-treated rats at 4, 8, 16 and 24 h after MCAO via in situ hybridisation. Starting at 4 h after injury, activin betaA mRNA was up-regulated in cortical and striatal areas in the ipsilateral hemisphere. Activin betaA mRNA levels in the cortex increased dramatically with time and were highest at 24 h after the insult, and oestradiol replacement did not influence this increase.

Activin: an important regulator of wound repair, fibrosis, and neuroprotection

We recently identified the gene encoding the activin betaA chain as a novel injury-regulated gene. We showed that activin over-expression in the skin of transgenic mice enhances the speed of wound healing but also the scarring response. By contrast, inhibition of activin action by over-expression of the activin antagonist follistatin caused a severe delay in wound repair, but the quality of the healed wound was improved. In a search for activin-regulated genes in keratinocytes we identified the Mad1 transcription factor as a direct target of activin in these cells. Since Mad1 inhibits proliferation and induces differentiation of various cell types, our results suggest that activin regulates these processes in keratinocytes via induction of mad1. In addition to its role in the skin, we recently identified activin as a novel neuroprotective factor in vivo. Together with results from other laboratories, these findings suggest that activin is an important player in inflammation, repair and cytoprotection in various organs.

Emerging roles for bone morphogenetic proteins in central nervous system glial biology

Bone morphogenetic proteins, members of the TGFbeta superfamily have been implicated in a variety of roles in the developing and mature nervous system. These divergent functions are a reflection of the closely defined spatial and temporal expression of BMPs in the CNS, and the potential interactions of the BMP signaling pathway with the STAT and MAP kinase pathways. In this review we discuss the roles of BMPs in early patterning of the CNS, determination of neural cell fate, and regulation of oligodendrocyte maturation during CNS development. Additional functions for members of the TGFbeta superfamily in CNS injury responses are emerging suggesting these molecules represent useful targets for manipulating neural responses to CNS insults.

Fibroblast growth factors and neuroprotection

Several members of the FGF family, in particular FGF2, are intimately involved in neuronal protection and repair after ischemic, metabolic or traumatic brain injury. Expression of Fgf2 mRNA and protein is strongly upregulated after neuronal damage, with glial cells as the predominant source. Given its survival-promoting effects on cultured neurons, exogenous FGF2 was tested in several animal models of stroke and excitotoxic damage, in which it consistently proved protective against neuronal loss. FGF2 affords neuroprotection by interfering with a number of signaling pathways, including expression and gating of NMDA receptors, maintenance of Ca2+ homeostasis and regulation of ROS detoxifying enzymes. FGF2 prevents apoptosis by strengthening anti-apoptotic pathways and promotes neurogenesis in adult hippocampus after injury. The protective action of FGF2 has been linked to its augmenting effect on the lesion-induced upregulation of activin A, a member of the TGF-beta superfamily. Despite the well-documented benefits of FGF2 in animal models of stroke, there is currently no clinical development in stroke, after a phase II/III trial with FGF2 in acute stroke patients was discontinued because of an unfavorable risk-to-benefit ratio. As the molecular targets of FGF2 are going to be unraveled over the next years, new therapeutic strategies will hopefully emerge that enable us to influence the various protective mechanisms of FGF2 in a more specific fashion.

Increased activin levels in cerebrospinal fluid of rabbits with bacterial meningitis are associated with activation of microglia

Activin, a member of the transforming growth factor superfamily, is upregulated in a number of inflammatory episodes such as septicemia and rheumatoid arthritis. In the CNS, activin has been predominantly assessed in terms of a neuroprotective role. In this report we characterized the activin response in the CNS in a rabbit model of meningitis. In normal animals, cerebrospinal fluid (CSF) activin levels were higher than those in serum, indicating an intracranial secretion of this cytokine. Following intracisternal inoculation with Streptococcus pneumoniae, activin in CSF was unchanged for the first 12 h and then rose progressively; levels were increased approximately 15-fold within 24 h. Activin levels were correlated positively with CSF protein content and with the number of apoptotic neurons in the dentate gyrus. No apparent correlation was observed between CSF activin concentrations and bacterial titer, lactate concentrations or leukocyte density. Using immunohistochemistry, activin staining was localized to epithelial cells of the choroid plexus, cortical neurons and the CA3 region of the hippocampus, with similar staining intensities in both normal and meningitic brains. However, in meningitic brains there was also strong staining in activated microglia and infiltrating macrophages. Taken together, these results demonstrate that activin forms part of the CNS response to immune challenge and may be an important mediator to modulate inflammatory processes in the brain.

The roles of activin in cytoprotection and tissue repair

Activin is a member of the transforming growth factor beta family of growth and differentiation factors. Initially discovered as a protein that stimulates release of follicle-stimulating hormone, it is now well accepted as an important regulator of cell growth and differentiation. Most interestingly, a series of previous studies have revealed novel roles of activin in inflammation and repair. Our own results have provided evidence for an important function of activin in cutaneous wound repair as well as in neuroprotection, and these data will be summarized and discussed in this chapter.

DNA microarray analysis of the contused spinal cord: effect of NMDA receptor inhibition

Spinal cord injury (SCI)-induced neurodegeneration leads to irreversible and devastating motor and sensory dysfunction. Post-traumatic outcomes are determined by events occurring during the first 24 hours after SCI. An increase in extracellular glutamate concentration to neurotoxic levels is one of the earliest events after SCI. We used Affymetrix DNA oligonucleotide microarrays (with 1,322 DNA probes) analysis to measure gene expression in order to test the hypothesis that SCI-induced N-methyl-D-aspartate (NMDA) receptor activation triggers significant postinjury transcriptional changes. Here we report that SCI, 1 hour after trauma, induced change in mRNA levels of 165 genes and expression sequence tags (ESTs). SCI affected mRNA levels of those genes that regulate predominantly transcription factors, inflammation, cell survival, and membrane excitability. We also report that NMDA receptor inhibition (with -(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine hydrogen maleate [MK-801]) reversed the effect of SCI on about 50% of the SCI-affected mRNAs. Especially interesting is the finding that NMDA receptor activation participates in the up-regulation of inflammatory factors. Therefore, SCI-induced NMDA receptor activation is one of the dominant, early signals after trauma that leads to changes in mRNA levels of a number of genes relevant to recovery processes. The majority of MK-801 effects on the SCI-induced mRNA changes reported here are novel. Additionally, we found that the MK-801 treatment also changed the mRNA levels of 168 genes and ESTs that had not been affected by SCI alone, and that some of their gene products could have harmful effects on SCI outcome.

The roles of activins in repair processes of the skin and the brain

A recent study from our laboratory demonstrated a strong upregulation of activin expression during cutaneous wound healing. To further analyze the role of activin A in skin morphogenesis and wound repair, we generated transgenic mice that overexpress activin A under the control of the keratin 14 promoter. The latter targets expression of transgenes to the basal, proliferating layer of the epidermis. Hetero- as well as homozygous transgenic animals were viable and fertile. However, they were smaller than non-transgenic littermates and they had smaller ears and shorter tails. Histological analysis of their skin revealed dermal hyperthickening, mainly due to the replacement of fatty tissue by connective tissue, and an increase in suprabasal, partially differentiated epidermal layers. After cutaneous injury, a strong enhancement of granulation tissue formation was observed. Furthermore, the extent of re-epithelialization was increased in some of the wounds. These data demonstrate that activin A is a potent stimulator of the wound healing process. Using an in vivo model of local brain injury, we found that activin A also plays a significant role in the early cellular response to neuronal damage. Expression of activin mRNA and protein is markedly upregulated within a few hours of injury. If applied exogenously, recombinant activin A is capable of rescuing neurons from acute cell death. Studying the interaction between bFGF, a well-established neuroprotective agent, which is currently being tested in stroke patients, and activin A, we arrived at the unexpected conclusion that it is the strong induction of activin A by bFGF which endows the latter with its beneficial actions in patients. These findings suggest that the development of substances directly targeting activin expression or receptor binding should offer new possibilities in the acute treatment of stroke and brain trauma.

Induction of activin A is essential for the neuroprotective action of basic fibroblast growth factor in vivo

Exogenous application of neurotrophic growth factors has emerged as a new and particularly promising approach not only to promote functional recovery after acute brain injury but also to protect neurons against the immediate effect of the injury. Among the various growth factors and cytokines studied so far, the neuroprotective and neurotrophic profile of basic fibroblast growth factor (bFGF) is the best documented. Using an animal model of acute excitotoxic brain injury, we report here that the neuroprotective action of bFGF, which is now being tested in stroke patients, depends on the induction of activin A, a member of the transforming growth factor-beta superfamily. Our evidence for this previously unknown mechanism of action of bFGF is that bFGF strongly enhanced lesion-associated induction of activin A; in the presence of the activin-neutralizing protein follistatin, bFGF was no longer capable of rescuing neurons from excitotoxic death; and recombinant activin A exerted a neuroprotective effect by itself. Our data indicate that the development of substances influencing activin expression or receptor binding should offer new ways to fight neuronal loss in ischemic and traumatic brain injury.

Expression of the activin axis and neuronal rescue effects of recombinant activin A following hypoxic-ischemic brain injury in the infant rat

Neurotrophic factors are induced in the brain in response to injury and may restrict the extent of neuronal loss and facilitate recovery. We have previously reported a strong neuronal induction of activin betaA subunit mRNA expression after a hypoxic-ischemic (HI) injury in the rat brain. Here, we further extended our studies to examine a role for the activin inhibitory binding protein, follistatin after injury and also to determine the potential of activin as a neuronal rescue agent. Ribonuclease protection assay (RPA) was used to quantify the time course of the mRNA expression of activin betaA subunit and follistatin, following a 60-min HI brain injury. Activin betaA subunit mRNA level increased in the contralateral hemisphere 5 h after injury and returned to normal at 10 h post injury. In contrast, follistatin mRNA levels decreased in the same hemisphere at 5 and 10 h after injury. The effect of intracerebroventrically (i. c.v.) administered recombinant human activin A or its antagonist, inhibin A, on neuronal death after a 15-min HI brain injury was determined for a number of brain regions. One microgram activin A (n=23) reduced the neuronal loss in the hippocampal CA1/2 region, dorsolateral striatum but not in the parietal cortex. In contrast, 1 microg of inhibin A (n=18) did not have a significant effect on the extent of neuronal loss in any of the affected regions. This pattern of neuroprotection was consistent with the distribution of immunoreactivity for the activin receptor type II subunit. These results demonstrate that activin A, but not its functional antagonist inhibin A, can enhance the survival of injured hippocampal and striatal neurons. Since follistatin is thought to exert a neutralising effect on activin A activity, the down-regulation of follistatin expression post injury may be allowing activin A to become more accessible to neurons after injury. Overall, these results suggest a role of the activin axis in modulating the survival of specific populations of injured neurons.

Administration of recombinant human Activin-A has powerful neurotrophic effects on select striatal phenotypes in the quinolinic acid lesion model of Huntington's disease

Huntington disease is characterized by the selective loss of striatal neurons, particularly of medium-sized spiny glutamate decarboxylase67 staining/GABAergic projection neurons which co-contain the calcium binding protein calbindin. Lesioning of the adult rat striatum by intrastriatal injection of the N-methyl-D-aspartate receptor agonist quinolinic acid (100 nmol) results in a pattern of striatal neuropathology seven days later that resembles that seen in the Huntington brain. Using this animal model of human Huntington's disease we investigated the effect of daily intrastriatal infusion of the nerve cell survival molecule ActivinA (single bolus dose of 0.73 microg daily for seven days) on the quinolinic acid-induced degeneration of various striatal neuronal phenotypes. By seven days, unilateral intrastriatal infusion of quinolinic acid produced a partial but significant loss (P < 0.01) in the number of striatal neurons immunoreactive for glutamate decarboxylase (to 51.0+/-5.8% of unlesioned levels), calbindin (to 58.7+/-5.1%), choline acetyltransferase (to 68.6+/-6.1%), NADPH-diaphorase (to 47.4+/-5.4%), parvalbumin (to 58.8+/-4.1%) and calretinin (to 60.6+/-8.6%) in adult rats that were administered intrastriatal phosphate-buffered saline for seven days following quinolinic acid. In contrast, in rats that received intrastriatal recombinant human ActivinA once daily for seven days following quinolinic acid, phenotypic degeneration was significantly attenuated in several populations of striatal neurons. Treatment with ActivinA had the most potent protective effect on the striatal cholinergic interneuron population almost completely preventing the lesion induced decline in choline acetyltransferase expression (to 95.1+/-5.8% of unlesioned levels, P < 0.01). ActivinA also conferred a significant protective effect on parvalbumin (to 87.5+/-7.7%, P < 0.01) and NADPH-diaphorase (to 77.5+/-7.5%, P < 0.01) interneuron populations but failed to prevent the phenotypic degeneration of calretinin neurons (to 56.6+/-5.5%). Glutamate decarboxylase67 and calbindin-staining nerve cells represent largely overlapping populations and both identify striatal GABAergic projection neurons. We found that ActivinA significantly attenuated the loss in the numbers of neurons staining for calbindin (to 79.7+/-6.6%, P < 0.05) but not glutamate decarboxylase67 (to 61.1+/-5.9%) at seven days following quinolinic acid lesioning. Taken together these results suggest that exogenous administration of ActivinA can rescue both striatal interneurons (labelled with choline acetyltransferase, parvalbumin, NADPH-diaphorase) and striatal projection neurons (labelled by calbindin) from excitotoxic lesioning with quinolinic acid. Longer-term studies will be required to determine whether these surviving calbindin-expressing projection neurons recover their ability to express the glutamate decarboxylase67/GABAergic phenotype. These results therefore suggest that treatment with ActivinA may help to prevent the degeneration of vulnerable striatal neuronal populations in Huntington's disease.

Activity and injury-dependent expression of inducible transcription factors, growth factors and apoptosis-related genes within the central nervous system

This review primarily discusses work that has been performed in our laboratories and that of our direct collaborators and therefore does not represent an exhaustive review of the current literature. Our aim is to further discuss the role that gene expression plays in neuronal plasticity and pathology. In the first part of this review we examine activity-dependent changes in the expression of inducible transcription factors (ITFs) and neurotrophins with long-term potentiation (LTP) and kindling. This work has identified particular ITFs (Krox-20 and Krox-24) and neurotrophin systems (particularly the brain-derived neurotrophic factor (BDNF)/tyrosine receptor kinase-B, Trk-B system) that may be involved in stabilizing long-lasting LTP (i.e. LTP3). We also show that changes in the expression of other ITFs (Fos, Jun-D and Krox-20) and the BDNF/trkB neurotrophin system may play a central role in the development of hippocampal kindling, an animal model of human temporal lobe epilepsy. In the next part of this review we examine changes in gene expression after neuronal injuries (ischemia, prolonged seizure activity and focal brain injury) and after nerve transection (axotomy). We identify apoptosis-related genes (p53, c-Jun, Bax) whose delayed expression selectively increases in degenerating neurons, further suggesting that some forms of neuronal death may involve apoptosis. Moreover, since overexpression of the tumour-suppressor gene p53 induces apoptosis in a wide variety of dividing cell types we speculate that it may perform the same function in post-mitotic neurons following brain injuries. Additionally, we show that neuronal injury is associated with rapid, transient, activity-dependent expression of neurotrophins (BDNF and activinA) in neurons, contrasting with a delayed and more persistent injury-induced expression of certain growth factors (IGF-1 and TGFbeta) in glia. In this section we also describe results linking ITFs and neurotrophic factor expression. Firstly, we show that while BDNF and trkB are induced as immediate-early genes following injury, the injury-induced expression of activinA and trkC may be regulated by ITFs. We also discuss whether loss of retrograde transport of neurotrophic factors such as nerve growth factor following nerve transection triggers the selective and prolonged expression of c-Jun in axotomized neurons and whether c-Jun is responsible for regeneration or degeneration of these axotomized neurons. In the last section we further examine the role that gene expression may play in memory formation, epileptogenesis and neuronal degeneration, lastly speculating whether the expression of various growth factors after brain injury represents an endogenous neuroprotective response of the brain to injury. Here we discuss our results which show that pharmacological enhancement of this response with exogenous application of IGF-1 or TGF-beta reduces neuronal loss after brain injury.